**Introduction**

**Chapter 1**

**Provisional chapter**

**Introductory Chapter: Mangrove Ecosystem Research**

**Introductory Chapter: Mangrove Ecosystem Research** 

Mangroves are trees and shrubs grow in intertidal zone or brackish water of tropical and subtropical coastal areas between 5°N and 5°S latitude spanning over 118 countries. Mangroves grow in harsh environmental conditions such as high saline conditions and are therefore also called halophytes. They can grow in extreme environment due to their morphological and physiological adaptations, including complex root and salt filtration abilities to cope with inundation of salt water and wave action. Mangroves are well adapted to grow in anoxic conditions as they experience regular inundation and saturated soil conditions. There are around 70 known species of mangroves around the globe, out of which 11 are threatened species and are listed in IUCN Red List [1]. Mangrove species have its own ecosystem services; therefore, mangrove loss can impact surrounding coastal ecosystem and associated ecosystems. Mangrove ecosystem has several faunal species because they create characteristics and productive habitat for them. The biodiversity of fauna in mangrove ecosystem is high due to

Mangrove forests provide many ecosystem services that include provisioning, regulating, culture, and supporting services. Mangrove forests provide several provisioning services such as food, timber, fuelwood, etc., which provides economic benefits and security to local coastal communities [2]. It was recognized better after 2004 Asian tsunami wave attenuation became one of the regulating services [3]. Mangroves blue carbon storage and sequestration capability are important regulatory services since 2011 because of global climate change mitigation [4]. Mangroves also play an important role in enhancing coastal water quality by stabilizing fine sediment and by absorbing pollutants (like heavy metals) [5]. Mangrove forests also provide a slew of cultural services such as tourism and education as well as cultural heritage and

Though mangroves provide many important ecosystem services, they are one of the most threatened ecosystems in the world [8]. Mangrove forests are being deforested and degraded due to extensive aquaculture pond creation, agriculture, urban development, palm oil

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.80962

**Trends - Where has the Focus been So Far**

**Trends - Where has the Focus been So Far**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

the availability of food resources and their detritus food cycle.

esthetic values to local communities as well as visiting tourists [6, 7].

http://dx.doi.org/10.5772/intechopen.80962

Sahadev Sharma

Sahadev Sharma

#### **Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far**

DOI: 10.5772/intechopen.80962

#### Sahadev Sharma Sahadev Sharma

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.80962

Mangroves are trees and shrubs grow in intertidal zone or brackish water of tropical and subtropical coastal areas between 5°N and 5°S latitude spanning over 118 countries. Mangroves grow in harsh environmental conditions such as high saline conditions and are therefore also called halophytes. They can grow in extreme environment due to their morphological and physiological adaptations, including complex root and salt filtration abilities to cope with inundation of salt water and wave action. Mangroves are well adapted to grow in anoxic conditions as they experience regular inundation and saturated soil conditions. There are around 70 known species of mangroves around the globe, out of which 11 are threatened species and are listed in IUCN Red List [1]. Mangrove species have its own ecosystem services; therefore, mangrove loss can impact surrounding coastal ecosystem and associated ecosystems. Mangrove ecosystem has several faunal species because they create characteristics and productive habitat for them. The biodiversity of fauna in mangrove ecosystem is high due to the availability of food resources and their detritus food cycle.

Mangrove forests provide many ecosystem services that include provisioning, regulating, culture, and supporting services. Mangrove forests provide several provisioning services such as food, timber, fuelwood, etc., which provides economic benefits and security to local coastal communities [2]. It was recognized better after 2004 Asian tsunami wave attenuation became one of the regulating services [3]. Mangroves blue carbon storage and sequestration capability are important regulatory services since 2011 because of global climate change mitigation [4]. Mangroves also play an important role in enhancing coastal water quality by stabilizing fine sediment and by absorbing pollutants (like heavy metals) [5]. Mangrove forests also provide a slew of cultural services such as tourism and education as well as cultural heritage and esthetic values to local communities as well as visiting tourists [6, 7].

Though mangroves provide many important ecosystem services, they are one of the most threatened ecosystems in the world [8]. Mangrove forests are being deforested and degraded due to extensive aquaculture pond creation, agriculture, urban development, palm oil

production, and conversions to other land use types [9]. Anthropogenic factors are big threats to mangroves; however, they are also threatened due to climate change impacts such as sea level rise, rising temperature, and increasing storm intensities [10]. These threats are causing variations in river run-off and fresh water inputs which result in species loss and productivity, that eventually will alter aquatic food webs in coastal setting.

Therefore, many researchers, scientists, academicians, stakeholders, and policy makers are involved to maintain the remaining mangrove forest area cover globally. Many government and nongovernment organizations are involved in increasing mangrove area cover such as the IUCN (https://www.iucn.org/news/forests/201707/mangroves-make-great-conservationallies) and the International Timber Trade Organization (ITTO) (http://www.itto.int/files/ user/pdf/E-BROCHURE-Bali%20Call%20to%20Action.pdf) have identified effective mangrove restoration as a key priority.

Past study reassessed ecological role and services of mangrove forest, where authors mainly discussed carbon dynamics, nursery role, shoreline protection, and land building capacity of mangroves [11]. Consequently, this chapter contains information pertaining to mangrove carbon research—how it has evolved over time and also their role in mitigating climate change. In this chapter, important research topics are discussed to enhance our understanding of the global mangrove research covering topics such as climate change, blue carbon, deforestation and degradation, fauna and flora losses, etc. As one might think, all these topics are interrelated and a clear overlap is visible in search engine results. This provides a clear indication of mangrove carbon research trend in the recent years.

### **1. Methodology**

The Web of Science® online database was used to access the mangrove forests research published between years 1980 and 2017. We searched various topics using specific keywords: (1) mangrove, (2) mangrove climate change, (3) mangrove carbon, (4) mangrove blue carbon, (5) mangrove biomass, (6) mangrove litter, (7) mangrove productivity, (8) mangrove deforestation and degradation, (9) mangrove remote sensing, (10) mangrove fauna, (11) mangrove invertebrate, (12) mangrove Polychaeta, (13) mangrove bird, and (14) mangrove mammals.

> Mangrove research has increased exponentially from 1980 to 2017, although year 2016 and 2017 shows a bit lower publication record as per the curve fitting (**Figure 2**). Year 2015 shows higher publication than year 2016, yet they might not be statistically significantly different.

> Mangrove climate change search showed total 1053 publication records. Mangrove climate change research exponentially increased since year 1991 (**Figure 3**). Climate change or global warming is directly related to carbon cycle [12]. Therefore, mangrove carbon keyword was searched and a total of 1927 records were found, which was higher than climate change records. That means researchers were involved in mangrove carbon research than ecological,

biological, environmental, and physiological aspects of mangrove research.

**Figure 2.** Number of publication records for keyword "mangrove" from 1980 to 2017.

**Figure 1.** Number of publication belongs to different research field with in mangrove forest.

Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far

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5

### **2. Result and discussions**

A total of 14,741 records on keyword "mangrove" were found in the Web of Science. **Figure 1** shows different fields of research within mangrove ecosystem. Approximately, 50% research was done in the field of marine freshwater biology, environmental sciences, and ecology. About 50% of mangrove research fields are broad and comprised many particular research fields such as climate change, productivity, water quality, pollution, physiology, ecology, carbon dynamics, etc.

Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far http://dx.doi.org/10.5772/intechopen.80962 5

**Figure 1.** Number of publication belongs to different research field with in mangrove forest.

production, and conversions to other land use types [9]. Anthropogenic factors are big threats to mangroves; however, they are also threatened due to climate change impacts such as sea level rise, rising temperature, and increasing storm intensities [10]. These threats are causing variations in river run-off and fresh water inputs which result in species loss and productiv-

Therefore, many researchers, scientists, academicians, stakeholders, and policy makers are involved to maintain the remaining mangrove forest area cover globally. Many government and nongovernment organizations are involved in increasing mangrove area cover such as the IUCN (https://www.iucn.org/news/forests/201707/mangroves-make-great-conservationallies) and the International Timber Trade Organization (ITTO) (http://www.itto.int/files/ user/pdf/E-BROCHURE-Bali%20Call%20to%20Action.pdf) have identified effective man-

Past study reassessed ecological role and services of mangrove forest, where authors mainly discussed carbon dynamics, nursery role, shoreline protection, and land building capacity of mangroves [11]. Consequently, this chapter contains information pertaining to mangrove carbon research—how it has evolved over time and also their role in mitigating climate change. In this chapter, important research topics are discussed to enhance our understanding of the global mangrove research covering topics such as climate change, blue carbon, deforestation and degradation, fauna and flora losses, etc. As one might think, all these topics are interrelated and a clear overlap is visible in search engine results. This provides a clear indication

The Web of Science® online database was used to access the mangrove forests research published between years 1980 and 2017. We searched various topics using specific keywords: (1) mangrove, (2) mangrove climate change, (3) mangrove carbon, (4) mangrove blue carbon, (5) mangrove biomass, (6) mangrove litter, (7) mangrove productivity, (8) mangrove deforestation and degradation, (9) mangrove remote sensing, (10) mangrove fauna, (11) mangrove invertebrate, (12) mangrove Polychaeta, (13) mangrove bird, and (14) mangrove mammals.

A total of 14,741 records on keyword "mangrove" were found in the Web of Science. **Figure 1** shows different fields of research within mangrove ecosystem. Approximately, 50% research was done in the field of marine freshwater biology, environmental sciences, and ecology. About 50% of mangrove research fields are broad and comprised many particular research fields such as climate change, productivity, water quality, pollution, physiology, ecology,

ity, that eventually will alter aquatic food webs in coastal setting.

of mangrove carbon research trend in the recent years.

grove restoration as a key priority.

4 Mangrove Ecosystem Ecology and Function

**1. Methodology**

**2. Result and discussions**

carbon dynamics, etc.

**Figure 2.** Number of publication records for keyword "mangrove" from 1980 to 2017.

Mangrove research has increased exponentially from 1980 to 2017, although year 2016 and 2017 shows a bit lower publication record as per the curve fitting (**Figure 2**). Year 2015 shows higher publication than year 2016, yet they might not be statistically significantly different.

Mangrove climate change search showed total 1053 publication records. Mangrove climate change research exponentially increased since year 1991 (**Figure 3**). Climate change or global warming is directly related to carbon cycle [12]. Therefore, mangrove carbon keyword was searched and a total of 1927 records were found, which was higher than climate change records. That means researchers were involved in mangrove carbon research than ecological, biological, environmental, and physiological aspects of mangrove research.

models [19–21]. A total of 1180 publications were identified using mangrove biomass keyword. Mangrove biomass research showed an exponential increase in the number of publication (**Figure 5**), although after year 2008, it seems biomass research has decreased. This decrease might be due to that researchers started to convert biomass into carbon for estimating total ecosystem carbon stocks. Measurement of litter fall is an important component of mangrove forest productivity [22–24]. Litter is also an indicator of episodic climate event such as storm [25], phenology [25–28], coastal productivity [29], detritus food cycle [30], etc. Measurement of litter quantity is a traditionally accepted method for measuring mangrove forest productivity. Mangrove litter research publication showed linear increment rather than

Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far

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Mangrove productivity estimation includes both biomass increment and litter fall production. Mangrove litter and productivity show same exponential rate of publication from year 1981 to 2006 (**Figure 5**), while after year 2006, the number of publications on mangrove productivity still shows an exponential growth (**Figure 5**). These mangrove productivity publications could be from different fields such as marine, phytoplankton, coastal, produc-

Mangrove deforestation and degradation lead to the loss of carbon that has been stored in the mangrove ecosystems. Keyword mangrove deforestation and degradation show a total of 59 publications from 1996 to 2017. **Figure 6** showed exponential trend but data are fluctuating over years. Earlier studies in the field of deforestation were done to study species loss, area cover loss, loss of ecosystem services, etc., while year 2016 and 2017 showed higher number of publications as compared to earlier years possibly due to climate change research and carbon

It is sometimes difficult to work inside mangrove forest due to accessibility, high number of mosquitoes, difficult to walk due to muddy condition, etc. **Figure 5** describes mangrove litter publication that showed weak exponential growth, because for litter studies, researchers need to go every month to field collect litter to understand seasonal trend and production of litter fall [28]. Many researchers started to use technology-based research such as using remote sensing [31], drone [32], camera, and different kind of sensors, eddy covariance system [33],

**Figure 5.** Number of publication records for keywords "mangrove biomass," "mangrove litter," and "mangrove

an exponential increment (**Figure 5**).

loss due to deforestation (**Figure 6**).

productivity" from 1981 to 2017.

tivity, etc.

**Figure 3.** Number of publication records for key words "mangrove climate change" and "mangrove carbon" from 1980 to 2017.

**Figure 4.** Number of publication records for keywords "mangrove climate change" and "mangrove blue carbon" from 2011 to 2017. Since Nature Geoscience publication [4] and blue carbon term (2009) [13].

Carbon stored in coastal and marine living organism such as mangrove forests, salt marshes, seagrass meadows, and intertidal flats is called "blue carbon," as termed by UNEP in 2009 [13]. The keyword mangrove blue carbon was searched, and a total of 124 records were found on Web of Science. Since 2011, publications on mangrove blue carbon have increased exponentially in terms of mitigating climate change (**Figure 4**). Mangrove climate change research showed very high number of publication after year 2011 (**Figure 3**), while mangrove carbon research showed lower publication as per the exponential graph (**Figure 3**). Mangrove carbon research got a boost since 2011 after a paper was published in the Nature Geoscience Journal [4] and after blue carbon term was coined/introduced [13] (**Figure 4**). **Figure 4** shows exponential increase in publication in the field of mangrove climate change research since year 2011. From **Figure 3**, it is clear that mangrove carbon research was primarily conducted in the field of climate change after year 2011.

Biomass is a measure of carbon stored in mangrove vegetation. Researchers have been measuring mangrove carbon indirectly through biomass [14–18] that is estimated using allometric models [19–21]. A total of 1180 publications were identified using mangrove biomass keyword. Mangrove biomass research showed an exponential increase in the number of publication (**Figure 5**), although after year 2008, it seems biomass research has decreased. This decrease might be due to that researchers started to convert biomass into carbon for estimating total ecosystem carbon stocks. Measurement of litter fall is an important component of mangrove forest productivity [22–24]. Litter is also an indicator of episodic climate event such as storm [25], phenology [25–28], coastal productivity [29], detritus food cycle [30], etc. Measurement of litter quantity is a traditionally accepted method for measuring mangrove forest productivity. Mangrove litter research publication showed linear increment rather than an exponential increment (**Figure 5**).

Mangrove productivity estimation includes both biomass increment and litter fall production. Mangrove litter and productivity show same exponential rate of publication from year 1981 to 2006 (**Figure 5**), while after year 2006, the number of publications on mangrove productivity still shows an exponential growth (**Figure 5**). These mangrove productivity publications could be from different fields such as marine, phytoplankton, coastal, productivity, etc.

Mangrove deforestation and degradation lead to the loss of carbon that has been stored in the mangrove ecosystems. Keyword mangrove deforestation and degradation show a total of 59 publications from 1996 to 2017. **Figure 6** showed exponential trend but data are fluctuating over years. Earlier studies in the field of deforestation were done to study species loss, area cover loss, loss of ecosystem services, etc., while year 2016 and 2017 showed higher number of publications as compared to earlier years possibly due to climate change research and carbon loss due to deforestation (**Figure 6**).

It is sometimes difficult to work inside mangrove forest due to accessibility, high number of mosquitoes, difficult to walk due to muddy condition, etc. **Figure 5** describes mangrove litter publication that showed weak exponential growth, because for litter studies, researchers need to go every month to field collect litter to understand seasonal trend and production of litter fall [28]. Many researchers started to use technology-based research such as using remote sensing [31], drone [32], camera, and different kind of sensors, eddy covariance system [33],

Carbon stored in coastal and marine living organism such as mangrove forests, salt marshes, seagrass meadows, and intertidal flats is called "blue carbon," as termed by UNEP in 2009 [13]. The keyword mangrove blue carbon was searched, and a total of 124 records were found on Web of Science. Since 2011, publications on mangrove blue carbon have increased exponentially in terms of mitigating climate change (**Figure 4**). Mangrove climate change research showed very high number of publication after year 2011 (**Figure 3**), while mangrove carbon research showed lower publication as per the exponential graph (**Figure 3**). Mangrove carbon research got a boost since 2011 after a paper was published in the Nature Geoscience Journal [4] and after blue carbon term was coined/introduced [13] (**Figure 4**). **Figure 4** shows exponential increase in publication in the field of mangrove climate change research since year 2011. From **Figure 3**, it is clear that mangrove carbon research was primarily conducted in the

**Figure 4.** Number of publication records for keywords "mangrove climate change" and "mangrove blue carbon" from

2011 to 2017. Since Nature Geoscience publication [4] and blue carbon term (2009) [13].

**Figure 3.** Number of publication records for key words "mangrove climate change" and "mangrove carbon" from 1980

Biomass is a measure of carbon stored in mangrove vegetation. Researchers have been measuring mangrove carbon indirectly through biomass [14–18] that is estimated using allometric

field of climate change after year 2011.

to 2017.

6 Mangrove Ecosystem Ecology and Function

**Figure 5.** Number of publication records for keywords "mangrove biomass," "mangrove litter," and "mangrove productivity" from 1981 to 2017.

**Figure 6.** Number of publication records for keywords "mangrove deforestation and degradation" from 1996 to 2017.

**Figure 7.** Number of publication records for keyword "mangrove remote sensing" from 1989 to 2017.

etc. Remote sensing is very useful technology to estimate mangrove forest deforestation rate and area cover [34, 35]. Therefore, search was performed for keyword "mangrove remote sensing." Mangrove remote sensing research publications have increased exponentially over time, although it shows some interesting trends (**Figure 7**). Both mangrove remote sensing and deforestation and degradation figures show higher number of publication after year 2015 that means researchers are using remote sensing technology to estimate several parameters such as biomass, carbon stock, leaf area index, area cover, deforestation rate, etc. from mangrove forest.

the studies have been conducted on mangrove birds and invertebrates (**Figure 9**) and show exponential increment of publication. Invertebrates, macrofauna (mainly crabs), are an important component of mangrove ecosystem and called ecosystem engineers due to their habit of digging burrows. These invertebrates feed on leaf litter, detritus, plankton, etc. and play a key role in litter breakdown and decomposition of detritus material. Birds are important component in deciding wetland site under Ramsar convention. Most of the mangrove forests are under Ramsar sites. Therefore, mangrove bird research is important in terms of conservation and protection of mangrove forest. On the other hand, mangrove polycheats and mammals show lower and fluctuating publication rate, consequently weak exponential

**Figure 9.** Number of publication records for keywords "mangrove invertebrate," "mangrove polycheat," "mangrove

Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far

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9

**Figure 8.** Number of publication records for keyword "mangrove fauna" from 1984 to 2017.

Past studies have showed that literature review could provide important research outputs. In mangroves research, many studies in different fields have been done through literature

increment (**Figure 9**).

bird," and "mangrove mammal" from 1981 to 2017.

reviews [36–40].

Overall mangrove fauna research has been increasing every year (**Figure 8**). Several fauna found in and surrounding mangrove forest area such as fish, crabs, birds, large and small mammals, reptiles, amphibians, etc. These organisms play an important part in ecological function and coastal food web. Search results from Web of Science show that majority of Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far http://dx.doi.org/10.5772/intechopen.80962 9

**Figure 8.** Number of publication records for keyword "mangrove fauna" from 1984 to 2017.

etc. Remote sensing is very useful technology to estimate mangrove forest deforestation rate and area cover [34, 35]. Therefore, search was performed for keyword "mangrove remote sensing." Mangrove remote sensing research publications have increased exponentially over time, although it shows some interesting trends (**Figure 7**). Both mangrove remote sensing and deforestation and degradation figures show higher number of publication after year 2015 that means researchers are using remote sensing technology to estimate several parameters such as biomass, carbon stock, leaf area index, area cover, deforestation rate, etc. from man-

**Figure 7.** Number of publication records for keyword "mangrove remote sensing" from 1989 to 2017.

**Figure 6.** Number of publication records for keywords "mangrove deforestation and degradation" from 1996 to 2017.

Overall mangrove fauna research has been increasing every year (**Figure 8**). Several fauna found in and surrounding mangrove forest area such as fish, crabs, birds, large and small mammals, reptiles, amphibians, etc. These organisms play an important part in ecological function and coastal food web. Search results from Web of Science show that majority of

grove forest.

8 Mangrove Ecosystem Ecology and Function

**Figure 9.** Number of publication records for keywords "mangrove invertebrate," "mangrove polycheat," "mangrove bird," and "mangrove mammal" from 1981 to 2017.

the studies have been conducted on mangrove birds and invertebrates (**Figure 9**) and show exponential increment of publication. Invertebrates, macrofauna (mainly crabs), are an important component of mangrove ecosystem and called ecosystem engineers due to their habit of digging burrows. These invertebrates feed on leaf litter, detritus, plankton, etc. and play a key role in litter breakdown and decomposition of detritus material. Birds are important component in deciding wetland site under Ramsar convention. Most of the mangrove forests are under Ramsar sites. Therefore, mangrove bird research is important in terms of conservation and protection of mangrove forest. On the other hand, mangrove polycheats and mammals show lower and fluctuating publication rate, consequently weak exponential increment (**Figure 9**).

Past studies have showed that literature review could provide important research outputs. In mangroves research, many studies in different fields have been done through literature reviews [36–40].

### **3. Conclusion**

Mangrove research has increased over time around the world in all kind of research areas. From results, it is confirmed that mangrove research is increasing exponentially around the globe. Also number of mangrove researcher is also increasing in the world. There was a time when very few researchers were involved in mangrove forest-related research. The Web of Science search engine can be helpful in quick identification of key research area as well as evolving trends. Also other search engines such as Scopus, Google Scholar, CiteSeer, BioOne, etc., should be taken into account for finer search results.

[5] Analuddin K, Sharma S, Septiana A, Sahidin I, Rianse U, Nadaoka K. Heavy metal bioaccumulation in mangrove ecosystem at the coral triangle ecoregion, Southeast Sulawesi,

Introductory Chapter: Mangrove Ecosystem Research Trends - Where has the Focus been So Far

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11

[6] James GK, Adegoke JO, Osagie S, Ekechukwu S, Nwilo P, Akinyede J. Social valuation of mangroves in the Niger Delta region of Nigeria. International Journal of Biodiversity

[7] Thiagarajah J, Wong SK, Richards DR, Friess DA. Historical and contemporary cultural ecosystem service values in the rapidly urbanizing city state of Singapore. Ambio.

[8] Valiela I, Bowen JL, York JK. Mangrove forests: One of the World's threatened major tropical environments: At least 35% of the area of mangrove forests has been lost in the past two decades, losses that exceed those for tropical rain forests and coral reefs, two

[9] Richards DR, Friess DA. Rates and drivers of mangrove deforestation in Southeast Asia, 2000-2012. Proceedings of the National Academy of Sciences. 2016;**113**:344-349 [10] Ward RD, Friess DA, Day RH, MacKenzie RA. Impacts of climate change on mangrove ecosystems: A region by region overview. Ecosystem Health and Sustainability.

[11] Lee SY, Primavera JH, Dahdouh-Guebas F, McKee K, Bosire JO, Cannicci S, et al. Ecological role and services of tropical mangrove ecosystems: A reassessment. Global

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[14] Clough B, Scott K. Allometric relationships for estimating above-ground biomass in six

[15] Hoque A, Sharma S, Hagihara A. Above and belowground carbon acquisition of mangrove Kandelia obovata trees in Manko wetland, Okinawa, Japan. International Journal

[16] Kangkuso A, Jamili J, Septiana A, Raya R, Sahidin I, Rianse U, et al. Allometric models and aboveground biomass of Lumnitzera racemosa Willd. forest in Rawa Aopa Watumohai National Park, Southeast Sulawesi, Indonesia. Forest Science and Technology.

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Mindanao Island, Philippines. Hydrobiologia. 2017;**803**(1):359-371

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### **Acknowledgements**

The author would like to acknowledge the Institute of Ocean and Earth Sciences, University of Malaya for all support. The author also would like to thank Dr. Rupesh Kumar Bhomia for reviewing the manuscript and for his valuable comments.

### **Author details**

Sahadev Sharma

Address all correspondence to: ssharma@hawaii.edu

Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia

### **References**


[5] Analuddin K, Sharma S, Septiana A, Sahidin I, Rianse U, Nadaoka K. Heavy metal bioaccumulation in mangrove ecosystem at the coral triangle ecoregion, Southeast Sulawesi, Indonesia. Marine Pollution Bulletin. 2017;**125**:472-480

**3. Conclusion**

10 Mangrove Ecosystem Ecology and Function

**Acknowledgements**

**Author details**

Sahadev Sharma

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2010;**5**:e10095

Mangrove research has increased over time around the world in all kind of research areas. From results, it is confirmed that mangrove research is increasing exponentially around the globe. Also number of mangrove researcher is also increasing in the world. There was a time when very few researchers were involved in mangrove forest-related research. The Web of Science search engine can be helpful in quick identification of key research area as well as evolving trends. Also other search engines such as Scopus, Google Scholar, CiteSeer, BioOne,

The author would like to acknowledge the Institute of Ocean and Earth Sciences, University of Malaya for all support. The author also would like to thank Dr. Rupesh Kumar Bhomia for

Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia

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eddy covariance. Biogeosciences.

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peninsular Malaysia. Forest Ecology and Management. 2018;**411**:35-45

subtropical mangrove forest equipped with CO2

and Biogeography. 2011;**20**:154-159

tion exercises. PLoS One. 2014;**9**:e107706

Biogeography. 2016;**25**:729-738

**37**:317-332

2013;**10**:2145-2158. https://doi.org/10.5194/bg-10-2145-2013


[32] Otero V, Van De Kerchove R, Satyanarayana B, Martínez-Espinosa C, Fisol MAB, Ibrahim MRB, et al. Managing mangrove forests from the sky: Forest inventory using field data and unmanned aerial vehicle (UAV) imagery in the Matang mangrove Forest reserve, peninsular Malaysia. Forest Ecology and Management. 2018;**411**:35-45

[18] Woodroffe CD. Studies of a mangrove basin, Tuff Crater, New Zealand: I. Mangrove biomass and production of detritus. Estuarine, Coastal and Shelf Science. 1985;**20**(3):265-280

[19] Deshar R, Sharma S, Mouctar K, Wu M, Hoque A, Hagihara A. Self-thinning exponents for partial organs in overcrowded mangrove Bruguiera gymnorrhiza stands on Okinawa

[20] Kangkuso A, Sharma S, Jamili J, Septiana A, Sahidin I, Rianse U, et al. Trends in allometric models and aboveground biomass of family Rhizophoraceae mangroves in the Coral Triangle ecoregion, Southeast Sulawesi, Indonesia. Journal of Sustainable Forestry.

[21] Komiyama A, Ong JE, Poungparn S. Allometry, biomass, and productivity of mangrove

[22] Kamruzzaman M, Osawa A, Deshar R, Sharma S, Mouctar K. Species composition, biomass, and net primary productivity of mangrove forest in Okukubi River, Okinawa

[23] Lugo AE, Snedaker SC. The ecology of mangroves. Annual review of ecology and sys-

[24] POLL D. Litter production in mangrove forests of southern Florida and Puerto Rico. Paper presented at the Proceedings of the international symposium on biology and man-

[25] Sharma S, Hoque AR, Analuddin K, Hagihara A. Litterfall dynamics in an overcrowded mangrove *Kandelia obovata* (S., L.) Yong stand over five years. Estuarine, Coastal and

[26] Kamruzzaman M, Sharma S, Hagihara A. Vegetative and reproductive phenology of the

[27] Kamruzzaman M, Sharma S, Kamara M, Hagihara A. Phenological traits of the mangrove Rhizophora stylosa Griff. at the northern limit of its biogeographical distribution.

[28] Kamruzzaman M, Sharma S, Kamara M, Hagihara A. Vegetative and reproductive phenology of the mangrove Bruguiera gymnorrhiza (L.) Lam. on Okinawa Island, Japan.

[29] Twilley RR. Coupling of mangroves to the productivity of estuarine and coastal waters, coastal-offshore ecosystem interactions. Heidelberg, Germany: Springer; 1988:155-180

[30] Flores-Verdugo FJ, Day JW Jr, Briseño-Dueñas R. Structure, litter fall, decomposition, and detritus dynamics of mangroves in a Mexican coastal lagoon with an ephemeral

[31] Sharma S, Bahuguna A, Chaudhary N, Nayak S, Chavan S, Pandey C. Status and monitoring the health of coral reef using Multi-temporal remote sensing—A case study of Pirotan Coral Reef Island, Marine National Park, Gulf of Kachchh, Gujarat, India. In:

Proceedings of 11th International Coral Reef Symposium; 2008. pp. 647-651

mangrove Kandelia obovata. Plant Species Biology. 2013;**28**(2):118-129

Wetlands ecology and management. 2013a;**21**(4):277-288

inlet. Marine Ecology Progress Series. 1987;**35**:83-90

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tematics. 1974;**5**(1):39-64

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Trees. 2013b;**27**(3):619-628


**Section 2**

**Mangrove Ecology, Structure and Function**

**Mangrove Ecology, Structure and Function**

**Chapter 2**

**Provisional chapter**

**Mangrove Species Distribution and Composition,**

**Mangrove Species Distribution and Composition,** 

DOI: 10.5772/intechopen.79028

**Adaptive Strategies and Ecosystem Services in the**

**Adaptive Strategies and Ecosystem Services in the** 

Mangroves of the Niger River Delta grade into several plant communities from land to sea. This mangrove is a biodiversity hot spot, and one of the richest in ecosystem services in the world, but due to lack of data it is often not mentioned in many global mangrove studies. Inland areas are sandy and mostly inhabited by button wood mangroves (*Conocarpus erectus*) and grass species while seaward areas are mostly inhabited by red (*Rhizophora racemosa*), black (*Laguncularia racemosa*) and white (*Avicennia germinans*) mangroves species. Anthropogenic activities such as oil and gas exploration, deforestation, dredging, urbanization and invasive nypa palms had changed the soil type from swampy to sandy mud soil. Muddy soil supports nypa palms while sandy soil supports different grass species, core mangrove soil supports red mangroves (*R. racemosa*), which are the most dominant

swampy soils. They possess long root system (i.e. 10 m) that originates from the tree stem to the ground, to provide extra support. The red mangrove trees are economically most viable as the main source of fire wood for cooking, medicinal herbs and dyes for clothes.

Mangroves are one of the world's most productive ecosystems. This is because they enrich coastal waters and serve as supermarket of the sea. They are globally distributed and occupy

**Keywords:** adaptation, deforestation, ecosystem services, west African mangroves

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

) of 52.02. The red mangroves are adapted to the

**Niger River Delta, Nigeria**

**Niger River Delta, Nigeria**

http://dx.doi.org/10.5772/intechopen.79028

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

of all species, with importance value (I<sup>v</sup>

**1.1. Global mangrove species distribution and composition**

Aroloye O. Numbere

Aroloye O. Numbere

**Abstract**

**1. Introduction**

#### **Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services in the Niger River Delta, Nigeria Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services in the Niger River Delta, Nigeria**

DOI: 10.5772/intechopen.79028

Aroloye O. Numbere Aroloye O. Numbere

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79028

#### **Abstract**

Mangroves of the Niger River Delta grade into several plant communities from land to sea. This mangrove is a biodiversity hot spot, and one of the richest in ecosystem services in the world, but due to lack of data it is often not mentioned in many global mangrove studies. Inland areas are sandy and mostly inhabited by button wood mangroves (*Conocarpus erectus*) and grass species while seaward areas are mostly inhabited by red (*Rhizophora racemosa*), black (*Laguncularia racemosa*) and white (*Avicennia germinans*) mangroves species. Anthropogenic activities such as oil and gas exploration, deforestation, dredging, urbanization and invasive nypa palms had changed the soil type from swampy to sandy mud soil. Muddy soil supports nypa palms while sandy soil supports different grass species, core mangrove soil supports red mangroves (*R. racemosa*), which are the most dominant of all species, with importance value (I<sup>v</sup> ) of 52.02. The red mangroves are adapted to the swampy soils. They possess long root system (i.e. 10 m) that originates from the tree stem to the ground, to provide extra support. The red mangrove trees are economically most viable as the main source of fire wood for cooking, medicinal herbs and dyes for clothes.

**Keywords:** adaptation, deforestation, ecosystem services, west African mangroves

### **1. Introduction**

#### **1.1. Global mangrove species distribution and composition**

Mangroves are one of the world's most productive ecosystems. This is because they enrich coastal waters and serve as supermarket of the sea. They are globally distributed and occupy

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

more than 150,000 km<sup>2</sup> , occur in over 123 countries and are made up of more than 73 species and/ or hybrids [1–3]. Mangroves are divided into the Indo-West Pacific (IWP) and the Atlantic East Pacific (AEP) groups [4, 5]. They originated from a hot environment [6] and their distribution is influenced by meteorological events [7] such as temperature [8] and precipitation [9]. These climatic parameters influence their distribution to different habitat [10]. Although, tolerance to warm conditions dictates their distribution, they sometimes drift to temperate regions where intense cold weather threatens their survival [11]. Global warming causes mangroves to spread beyond their latitudinal limit [12]. Mangroves are largely restricted to latitudes between 30° north and 30° south. Northern extensions of this limit occur in Japan (31° 22′N°) and Bermuda (32° 20′N); southern extensions are in New Zealand (38°03′S), Australia (38° 45′S) and on the east coast of South Africa (32°59′S) [2]; while there are robust mangrove population on the western coast of Africa with mangroves in Nigeria as one of the most dominant.

chewing the leaves. The fire wood is also useful in bakery, where larger wood stumps are

Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services…

http://dx.doi.org/10.5772/intechopen.79028

19

The wood is burnt completely in kiln to form charcoal that is used for outdoor cooking. Charcoal industry is a lucrative business embarked upon by many people in the Niger Delta. The charcoals is measured, put in bags and sold in the market. It is used by a large number of people for outdoor cooking especially during occasions and festivities. It is also used by road

The mangrove stems are cut to make stakes. They are also used for construction and building of scaffold. The wood is sawed into different sizes and used as ply wood for building houses. The wood is tough and can be used as roofing boards for houses. However, the use of mangrove for building is restricted because of its high combustibility. Other examples of industrial building materials derived from mangrove include: thatches, bamboo, poles, boats and wooden bridges in local communities. The wood is also used as support pillars and reinforcements for locally built houses and bridges across small rivers or canals. Poles from mangrove are used to con-

The red mangrove propagule is succulent and rich in nutrients and is eaten by crabs (*Goniopsis pelii*). In the Niger Delta people feed on products of animals and insects that live in mangrove forest such as honey combs built by bees in thick mangrove forest. The following organisms are also found in the mangrove forest: mammals, birds, reptiles, insects, roots, stem, flower, honey resins, gum, silk, fabrics, rope, animal oil, and cosmetics. The mangrove forest serves as source of water from streams and lakes. The red mangrove sepal has an enclosure that contains a sweet tasting liquid that is sucked. The tree bark is cut into small bits and used as spices for cooking. The sweet smelling aroma is also used in the manufacture of creams and

Tree barks and roots are mixed with other components to produce medicinal herbs that are used to treat some ailments. The bark is chopped into small pieces and put in locally made alcohol to dissolve; lemon is added and left for some time after which it is consumed as medicinal herb for curing several ailments. The mangrove tree bark is boiled with other herbs

The mangrove swamps serve as natural fish ponds. The site is dug and surrounded by soil like an embankment with a passageway. During high tides water carrying fishes flows into

side food vendors to roast food items such as plantain, corn, bean balls, pan cakes etc.

nect electric wires, which supplies electricity from one part of the town to another.

perfumes; and also bathing soaps that are produced locally.

placed underneath large ovens for baking bread.

*1.2.2. Charcoal manufacture*

*1.2.3. Building*

*1.2.4. Food*

*1.2.5. Medicinal herbs*

and used to treat malaria.

*1.2.6. Fishery*

Tropical conditions are the best for mangroves, but excessive heat cause rapid evaporation leading to increase in salinity [13], which triggers the succession of salt tolerant mangrove species (e.g. *Avicennia germinans*) over less salt-tolerant species (e.g*. Rhizophora* species) [14]. Increase in temperature affects water body [15]. Temperature greater than 35°C affects root structure, seedling establishment and photosynthetic activity in mangroves [16]. Unrestricted increase in temperature can lead to the migration of species into subtropical salt marsh areas [17] and Arctic pole [18]. Precipitation regulates nutrient up-take and affects productivity [19] and survivability [20] of mangroves. Moderately warm and wet equatorial areas with high rainfall have rich supply of mangrove populations [21]. However, increase in sea level [22] can drown fringe mangroves [13]. In the same vein, global cooling and warming [23, 24] can lead to range shifts and the extinction of organisms [25, 26]. Mangrove propagules are dispersed by tidal currents, but land barriers prevent their free movement [4] leading to a discontinuous distribution. This discontinuity causes intra-specific, morphologic and genetic variation in Rhizophora species [27], which is one of the most dominant mangrove species in the world.

#### **1.2. Ecosystem services of Niger Delta mangroves**

The mangrove trees conserve water resources and serve as wind breaks in many communities. Specifically, in the Niger Delta, there are several uses of mangroves by the indigenous people, these include; fire wood, building materials, medicinal products, food baskets and fishing tools etc.

#### *1.2.1. Cooking*

Fire wood is a major means of cooking and heating. The firewood is got mostly from the red mangrove tree stems (i.e. Rhizophora species). The trees are first cut into 0.6 m stumps and thereafter chopped into smaller pieces of wood and sold. Fire wood is the preferred cooking method in most rural areas in Nigeria. This is because the wood retains heat for long. Pieces of the wood numbering about 3–5 are gathered and placed under metal tripod stands, and lighted to cook food. The wood ash that comes out after the burning of the wood is used as soil enhancer and disease destroyer in farms when it is spread on the soil surface or on the leaves of crops. It prevents biting and chewing insect pest (grasshoppers and locust) from chewing the leaves. The fire wood is also useful in bakery, where larger wood stumps are placed underneath large ovens for baking bread.

#### *1.2.2. Charcoal manufacture*

The wood is burnt completely in kiln to form charcoal that is used for outdoor cooking. Charcoal industry is a lucrative business embarked upon by many people in the Niger Delta. The charcoals is measured, put in bags and sold in the market. It is used by a large number of people for outdoor cooking especially during occasions and festivities. It is also used by road side food vendors to roast food items such as plantain, corn, bean balls, pan cakes etc.

#### *1.2.3. Building*

more than 150,000 km<sup>2</sup>

18 Mangrove Ecosystem Ecology and Function

in the world.

fishing tools etc.

*1.2.1. Cooking*

, occur in over 123 countries and are made up of more than 73 species and/

or hybrids [1–3]. Mangroves are divided into the Indo-West Pacific (IWP) and the Atlantic East Pacific (AEP) groups [4, 5]. They originated from a hot environment [6] and their distribution is influenced by meteorological events [7] such as temperature [8] and precipitation [9]. These climatic parameters influence their distribution to different habitat [10]. Although, tolerance to warm conditions dictates their distribution, they sometimes drift to temperate regions where intense cold weather threatens their survival [11]. Global warming causes mangroves to spread beyond their latitudinal limit [12]. Mangroves are largely restricted to latitudes between 30° north and 30° south. Northern extensions of this limit occur in Japan (31° 22′N°) and Bermuda (32° 20′N); southern extensions are in New Zealand (38°03′S), Australia (38° 45′S) and on the east coast of South Africa (32°59′S) [2]; while there are robust mangrove population on the western

Tropical conditions are the best for mangroves, but excessive heat cause rapid evaporation leading to increase in salinity [13], which triggers the succession of salt tolerant mangrove species (e.g. *Avicennia germinans*) over less salt-tolerant species (e.g*. Rhizophora* species) [14]. Increase in temperature affects water body [15]. Temperature greater than 35°C affects root structure, seedling establishment and photosynthetic activity in mangroves [16]. Unrestricted increase in temperature can lead to the migration of species into subtropical salt marsh areas [17] and Arctic pole [18]. Precipitation regulates nutrient up-take and affects productivity [19] and survivability [20] of mangroves. Moderately warm and wet equatorial areas with high rainfall have rich supply of mangrove populations [21]. However, increase in sea level [22] can drown fringe mangroves [13]. In the same vein, global cooling and warming [23, 24] can lead to range shifts and the extinction of organisms [25, 26]. Mangrove propagules are dispersed by tidal currents, but land barriers prevent their free movement [4] leading to a discontinuous distribution. This discontinuity causes intra-specific, morphologic and genetic variation in Rhizophora species [27], which is one of the most dominant mangrove species

The mangrove trees conserve water resources and serve as wind breaks in many communities. Specifically, in the Niger Delta, there are several uses of mangroves by the indigenous people, these include; fire wood, building materials, medicinal products, food baskets and

Fire wood is a major means of cooking and heating. The firewood is got mostly from the red mangrove tree stems (i.e. Rhizophora species). The trees are first cut into 0.6 m stumps and thereafter chopped into smaller pieces of wood and sold. Fire wood is the preferred cooking method in most rural areas in Nigeria. This is because the wood retains heat for long. Pieces of the wood numbering about 3–5 are gathered and placed under metal tripod stands, and lighted to cook food. The wood ash that comes out after the burning of the wood is used as soil enhancer and disease destroyer in farms when it is spread on the soil surface or on the leaves of crops. It prevents biting and chewing insect pest (grasshoppers and locust) from

coast of Africa with mangroves in Nigeria as one of the most dominant.

**1.2. Ecosystem services of Niger Delta mangroves**

The mangrove stems are cut to make stakes. They are also used for construction and building of scaffold. The wood is sawed into different sizes and used as ply wood for building houses. The wood is tough and can be used as roofing boards for houses. However, the use of mangrove for building is restricted because of its high combustibility. Other examples of industrial building materials derived from mangrove include: thatches, bamboo, poles, boats and wooden bridges in local communities. The wood is also used as support pillars and reinforcements for locally built houses and bridges across small rivers or canals. Poles from mangrove are used to connect electric wires, which supplies electricity from one part of the town to another.

#### *1.2.4. Food*

The red mangrove propagule is succulent and rich in nutrients and is eaten by crabs (*Goniopsis pelii*). In the Niger Delta people feed on products of animals and insects that live in mangrove forest such as honey combs built by bees in thick mangrove forest. The following organisms are also found in the mangrove forest: mammals, birds, reptiles, insects, roots, stem, flower, honey resins, gum, silk, fabrics, rope, animal oil, and cosmetics. The mangrove forest serves as source of water from streams and lakes. The red mangrove sepal has an enclosure that contains a sweet tasting liquid that is sucked. The tree bark is cut into small bits and used as spices for cooking. The sweet smelling aroma is also used in the manufacture of creams and perfumes; and also bathing soaps that are produced locally.

#### *1.2.5. Medicinal herbs*

Tree barks and roots are mixed with other components to produce medicinal herbs that are used to treat some ailments. The bark is chopped into small pieces and put in locally made alcohol to dissolve; lemon is added and left for some time after which it is consumed as medicinal herb for curing several ailments. The mangrove tree bark is boiled with other herbs and used to treat malaria.

#### *1.2.6. Fishery*

The mangrove swamps serve as natural fish ponds. The site is dug and surrounded by soil like an embankment with a passageway. During high tides water carrying fishes flows into the ponds, during ebb tide the water leaves and the fishes get trapped and remain in the embankment. The advantage of this fish pond is that there is a natural exchange of water from the sea, without the use of tap water. The need for external water supply is minimized because of the adjoining water body that supplies constant water to the pond.

of boot camps for seismic workers within the forest, etc. leading to the truncation of wildlife activities [31]. Similarly, the use of explosives such as dynamites during exploration for crude oil also led to the death of organisms and the destruction of the forest. Indiscriminate sand dredging is high in the area and had led to the disappearance of many coastal communities because of their conversion from aquatic to a terrestrial environment for the purpose of land expansion to establish residential and industrial quarters. The mangrove forest once destroyed takes up to 15 years or more to re-vegetate as compared to the rain forest that takes 5 years to re-grow. This shows that all aspects of oil exploration are inimical to the mangroves right from the pre-exploratory, exploratory and post exploratory stages. This is because each stage of oil and gas exploration involves hydrocarbon pollution and physical destruction of the mangrove forest. Pollution impacts flora and fauna, for instance oils from spillages clog the roots of mangroves causing outright death through the suffocation of the lenticels, leaf yellowing and defoliation [31, 32]. Pollution has effect on mollusk, crustaceans, echinoderms, polychaetes, cnidarians, oysters, scallops, periwinkles and different species of fishes that inhabit the mangrove forest. Similarly, the immobility of benthic organisms predisposes them to death from pollution. Different species of crabs such as *Callinectes* 

Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services…

http://dx.doi.org/10.5772/intechopen.79028

21

*pallidus*, *Uca tangeri*, *Ostrea tulipa* and *Goniopsis pelii* are also affected by pollutants.

overwhelm them.

**1.4. Mangrove species composition in the Niger Delta**

Urbanization is also a major threat to the mangroves, this is because population explosion in Nigeria, which is the most populous country in Africa, had led to the migration of a large number of people numbering over 20 million [33] into coastal regions of the Niger Delta to establish houses. Industrialization of wetland areas leads to the urbanization of rural areas that were formerly a habitat for mangroves. Increase in anthropogenic activities around mangrove forest had resulted to the invasion by opportunistic nypa palms (*Nypa fruticans*) and other alien species. The nypa palms were intentionally introduced in 1906 for the purpose of fighting coastal erosion [34]. The palms were originally not a threat to the mangroves, but within the last 30 years due to unabated anthropogenic activities they have become a major threat to mangroves after hydrocarbon pollution [35]. They have currently displaced 5% of the entire mangrove forest in the last 20 years [35] caused mainly by oil and gas exploration, urbanization and deforestation [36], which had opened up the forest to further exploitation. Despite the impacts of the aforementioned factors, mangroves are still resilient to environmental perturbations [37] and have robust growth in the Niger Delta. However, the current threat to mangroves that can lead to their extinction is the interaction of all the factors. It is found that mangroves can survive hydrocarbon pollution by adapting to the contaminated environment through the activities of increased soil fertility via hydrocarbon utilizing bacteria. They can also survive some forms of selective deforestation aimed at harvesting firewood for human use. They can also survive invasion by nypa palm propagules as long as their soil quality is not reduced as a result of the actions of solid and liquid waste. But they would hardly survive when all the aforementioned factors combine and

There are several species of mangroves in the Niger Delta, but the most dominant ones are the red (*Rhizophora racemosa*), black (*Laguncularia racemosa*) and white (*Avicennia germinans*) mangroves [38]. Button wood mangroves (*Conocarpus erectus*) are also prominent but less studied and is not too common around core mangrove forest. They are mostly found in

#### *1.2.7. Forest products*

This includes timber and non-timber products. The timber products are used by the furniture and building industry. Several furniture products are derived from trees cut from the rain forest. Non-timber products include medicinal herbs and pharmaceutical products used locally to treat certain ailments.

#### *1.2.8. Recreation and tourist attraction*

Mangrove forests are relaxation points for many citizens who visit the area on site seeing trips. The mangrove forest has a sweet smelling aroma that is therapeutic when one spends time in it. The sea breeze that blows and serenades the trees is a soothing balm that calms a restless nerve. Scientific research is also carried out in the area to identify numerous species found within the forest. The mangrove forest of the Niger Delta contains numerous unidentified species. The forest is a living laboratory that requires further scientific work to identify and classify the species.

#### *1.2.9. Spiritual purpose*

The mangrove forest serves as sites for libation and ancestral activities by natives who visit the area to derive some spiritual powers. Big trees are usually not cut, but allowed to grow and serves as points for libation by people that practices African traditional religion. The mangrove forest also serves as hiding place for natives during local wars.

#### *1.2.10. Production of dyes*

The tree bark when boiled produces dye used by the clothing industry. The red mangrove tree bark is boiled in hot water to bring out dyes made of red to brown coloration. This is then used to dye fishing net, which help to disguise and attract fishes for higher catch by fishermen.

The mangrove forest is also a region rich in crude oil and gas, which has made Nigeria the largest producer of crude oil in Africa and the sixth largest in the world [28].

#### **1.3. Threats to Niger Delta mangroves**

The major threats to mangroves in the Niger Delta are oil and gas exploration, deforestation, dredging, urbanization and Invasive Nypa palm species. Oil exploration began when the first oil well was struck in Oloibiri in the Niger Delta in 1956. Since the striking of this oil well thousands of other oil wells had been drilled resulting to millions of crude oil spillages [28]. The oil spillages had lead to the constant pollution of the mangrove forest leading to the death of numerous mangrove stands [29, 30]. Additionally, the exploratory process involves different stages such as deforestation activities aimed at creating a right of way passage (ROW) for oil pipelines, building of boot camps for seismic workers within the forest, etc. leading to the truncation of wildlife activities [31]. Similarly, the use of explosives such as dynamites during exploration for crude oil also led to the death of organisms and the destruction of the forest. Indiscriminate sand dredging is high in the area and had led to the disappearance of many coastal communities because of their conversion from aquatic to a terrestrial environment for the purpose of land expansion to establish residential and industrial quarters. The mangrove forest once destroyed takes up to 15 years or more to re-vegetate as compared to the rain forest that takes 5 years to re-grow. This shows that all aspects of oil exploration are inimical to the mangroves right from the pre-exploratory, exploratory and post exploratory stages. This is because each stage of oil and gas exploration involves hydrocarbon pollution and physical destruction of the mangrove forest. Pollution impacts flora and fauna, for instance oils from spillages clog the roots of mangroves causing outright death through the suffocation of the lenticels, leaf yellowing and defoliation [31, 32]. Pollution has effect on mollusk, crustaceans, echinoderms, polychaetes, cnidarians, oysters, scallops, periwinkles and different species of fishes that inhabit the mangrove forest. Similarly, the immobility of benthic organisms predisposes them to death from pollution. Different species of crabs such as *Callinectes pallidus*, *Uca tangeri*, *Ostrea tulipa* and *Goniopsis pelii* are also affected by pollutants.

the ponds, during ebb tide the water leaves and the fishes get trapped and remain in the embankment. The advantage of this fish pond is that there is a natural exchange of water from the sea, without the use of tap water. The need for external water supply is minimized

This includes timber and non-timber products. The timber products are used by the furniture and building industry. Several furniture products are derived from trees cut from the rain forest. Non-timber products include medicinal herbs and pharmaceutical products used locally

Mangrove forests are relaxation points for many citizens who visit the area on site seeing trips. The mangrove forest has a sweet smelling aroma that is therapeutic when one spends time in it. The sea breeze that blows and serenades the trees is a soothing balm that calms a restless nerve. Scientific research is also carried out in the area to identify numerous species found within the forest. The mangrove forest of the Niger Delta contains numerous unidentified species. The forest is a living laboratory that requires further scientific work to identify and classify the species.

The mangrove forest serves as sites for libation and ancestral activities by natives who visit the area to derive some spiritual powers. Big trees are usually not cut, but allowed to grow and serves as points for libation by people that practices African traditional religion. The

The tree bark when boiled produces dye used by the clothing industry. The red mangrove tree bark is boiled in hot water to bring out dyes made of red to brown coloration. This is then used to dye fishing net, which help to disguise and attract fishes for higher catch by fishermen. The mangrove forest is also a region rich in crude oil and gas, which has made Nigeria the

The major threats to mangroves in the Niger Delta are oil and gas exploration, deforestation, dredging, urbanization and Invasive Nypa palm species. Oil exploration began when the first oil well was struck in Oloibiri in the Niger Delta in 1956. Since the striking of this oil well thousands of other oil wells had been drilled resulting to millions of crude oil spillages [28]. The oil spillages had lead to the constant pollution of the mangrove forest leading to the death of numerous mangrove stands [29, 30]. Additionally, the exploratory process involves different stages such as deforestation activities aimed at creating a right of way passage (ROW) for oil pipelines, building

mangrove forest also serves as hiding place for natives during local wars.

largest producer of crude oil in Africa and the sixth largest in the world [28].

because of the adjoining water body that supplies constant water to the pond.

*1.2.7. Forest products*

20 Mangrove Ecosystem Ecology and Function

to treat certain ailments.

*1.2.9. Spiritual purpose*

*1.2.10. Production of dyes*

**1.3. Threats to Niger Delta mangroves**

*1.2.8. Recreation and tourist attraction*

Urbanization is also a major threat to the mangroves, this is because population explosion in Nigeria, which is the most populous country in Africa, had led to the migration of a large number of people numbering over 20 million [33] into coastal regions of the Niger Delta to establish houses. Industrialization of wetland areas leads to the urbanization of rural areas that were formerly a habitat for mangroves. Increase in anthropogenic activities around mangrove forest had resulted to the invasion by opportunistic nypa palms (*Nypa fruticans*) and other alien species. The nypa palms were intentionally introduced in 1906 for the purpose of fighting coastal erosion [34]. The palms were originally not a threat to the mangroves, but within the last 30 years due to unabated anthropogenic activities they have become a major threat to mangroves after hydrocarbon pollution [35]. They have currently displaced 5% of the entire mangrove forest in the last 20 years [35] caused mainly by oil and gas exploration, urbanization and deforestation [36], which had opened up the forest to further exploitation. Despite the impacts of the aforementioned factors, mangroves are still resilient to environmental perturbations [37] and have robust growth in the Niger Delta. However, the current threat to mangroves that can lead to their extinction is the interaction of all the factors. It is found that mangroves can survive hydrocarbon pollution by adapting to the contaminated environment through the activities of increased soil fertility via hydrocarbon utilizing bacteria. They can also survive some forms of selective deforestation aimed at harvesting firewood for human use. They can also survive invasion by nypa palm propagules as long as their soil quality is not reduced as a result of the actions of solid and liquid waste. But they would hardly survive when all the aforementioned factors combine and overwhelm them.

#### **1.4. Mangrove species composition in the Niger Delta**

There are several species of mangroves in the Niger Delta, but the most dominant ones are the red (*Rhizophora racemosa*), black (*Laguncularia racemosa*) and white (*Avicennia germinans*) mangroves [38]. Button wood mangroves (*Conocarpus erectus*) are also prominent but less studied and is not too common around core mangrove forest. They are mostly found in inland areas that have sandy soil. They have green leaves and hairy round seeds (**Figure 1c**). The mangroves are mainly fringe forests [39]. This is because they are found at the fringes of the coastlines facing the river. Oil palm trees (*Elaeis guineensis*), mangrove fern (*Acrostichum aureum*) and grass species such as vines, sedges etc. (**Figure 1I**) are found around sandy or disturbed parts of the forest in inland locations. A major factor for their distribution pattern is the nature of the soil, which is less fertile and less saline. Non-mangrove species perform better in soils with low salinity unlike mangrove soil that thrives in highly saline environment [7, 40]. Human activities such as sand filling, reclamation and dredging (**Figure 2**) change the soil from muddy to sandy soil leading to the intrusion of non-mangrove species in mangrove forest.

The white mangroves (*Avicennia germinans*) on the other hand, are the next most dominant after the button wood in sandy areas. The red mangroves are the closest to the seashore whereas the black and white mangroves are more adapted to disturbed soils. They are often found on the edges of shorelines where waste are deposited. In contrast, the red mangroves are mostly found in undisturbed pure swampy soils than mixed or contaminated soils. This is because presence in soils contaminated by waste impairs the growth of red mangroves. An example of a disturbed soil is the sand filled mangrove forest in Buguma, Niger Delta, Nigeria. This area was sand filled in 1984, and since then no mangrove had ever grown on it. Rather the dominant species found

are a variety of non-mangrove species in both the seaward and landward areas. The landward area has sandy soil that has large percentage growth of grass species such as corn vine (*Dalbergia ecastaphyllum*), coco plum (*Chrysobalanus icaco*) etc. Because of the proliferation of anthropogenic activities around mangrove forest some grass species had taken over the area. Examples of other species present include carpet grass (*Axonopus compressus*), elephant grass (*Pennisetum purpureum*), guinea grass (*Panicmum maximum*), goose grass (*Eleusine indica*) and goat weed (*Ageratum conyzoides*). A major observation during field work is that mangroves when cut never grow back rather the area from where they are cut is over taken by weeds [28] which forms gradients around the wetland soil. Oil and gas exploration also affect species composition in mangrove forests [35]. For example, industrial activities had led to a permanent change in soil and species composition, which accelerates the proliferation of weeds and other alien species. The weed when they grow becomes the hiding place for foreign insects and rodent pest, which later invade the mangroves.

**Figure 2.** Dredged and sand filled mangrove forest in Buguma, Niger Delta, Nigeria. There are still some mangroves that can be seen at the foreground. On the left of the picture is the fence of a secondary school. No mangrove tree has ever grown in this area since the sand filling in 1984. The area is now occupied by weeds and other alien plant species.

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Combinations of biotic and abiotic factors had made the mangroves one of the most unique, but less studied systems in the world. The problem of data gap in Africa is often cited in many literatures with little done to correct this trend. This work therefore, brings to fore the distribution and composition of mangroves and non-mangroves species in two locations in the Niger Delta to enable scientist in other regions of the world to have a better understating of the largest mangrove forest in Africa. The emphasis of mangrove study in the past has been the effect of pollution on mangrove forest, but no mention was made of species composition and distribution. This is the reason why this study is embarked upon to help bridge the data

1. To determine the distribution, composition and structural characteristics of mangroves

**2.** To evaluate the adaptive strategies of mangroves vis-a-vis their significance to the

gap. This study thus intends to achieve the following objectives;

**1.5. Data gaps**

*1.5.1. Objectives*

environment.

**Figure 1.** Different mangrove and non-mangrove species found in mangrove swamps affected by anthropogenic activities (dredging and sand filling). (a) Nypa palm (*Nypa fruticans*), (b) black mangroves (*Laguncularia racemosa*), (c) button wood (*Conocarpus erectus*) (d) herb (e) red mangrove (*Rhizophora racemosa*) (f) mangrove associated fern, (g) white mangrove (*Avicennia germinans*), (h) *Heritiera littoralis* (I) mangrove fern (*Acrostichum aureum).*

Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services… http://dx.doi.org/10.5772/intechopen.79028 23

**Figure 2.** Dredged and sand filled mangrove forest in Buguma, Niger Delta, Nigeria. There are still some mangroves that can be seen at the foreground. On the left of the picture is the fence of a secondary school. No mangrove tree has ever grown in this area since the sand filling in 1984. The area is now occupied by weeds and other alien plant species.

are a variety of non-mangrove species in both the seaward and landward areas. The landward area has sandy soil that has large percentage growth of grass species such as corn vine (*Dalbergia ecastaphyllum*), coco plum (*Chrysobalanus icaco*) etc. Because of the proliferation of anthropogenic activities around mangrove forest some grass species had taken over the area. Examples of other species present include carpet grass (*Axonopus compressus*), elephant grass (*Pennisetum purpureum*), guinea grass (*Panicmum maximum*), goose grass (*Eleusine indica*) and goat weed (*Ageratum conyzoides*). A major observation during field work is that mangroves when cut never grow back rather the area from where they are cut is over taken by weeds [28] which forms gradients around the wetland soil. Oil and gas exploration also affect species composition in mangrove forests [35]. For example, industrial activities had led to a permanent change in soil and species composition, which accelerates the proliferation of weeds and other alien species. The weed when they grow becomes the hiding place for foreign insects and rodent pest, which later invade the mangroves.

#### **1.5. Data gaps**

inland areas that have sandy soil. They have green leaves and hairy round seeds (**Figure 1c**). The mangroves are mainly fringe forests [39]. This is because they are found at the fringes of the coastlines facing the river. Oil palm trees (*Elaeis guineensis*), mangrove fern (*Acrostichum aureum*) and grass species such as vines, sedges etc. (**Figure 1I**) are found around sandy or disturbed parts of the forest in inland locations. A major factor for their distribution pattern is the nature of the soil, which is less fertile and less saline. Non-mangrove species perform better in soils with low salinity unlike mangrove soil that thrives in highly saline environment [7, 40]. Human activities such as sand filling, reclamation and dredging (**Figure 2**) change the soil from muddy to sandy soil leading to the intrusion of non-mangrove species in mangrove

The white mangroves (*Avicennia germinans*) on the other hand, are the next most dominant after the button wood in sandy areas. The red mangroves are the closest to the seashore whereas the black and white mangroves are more adapted to disturbed soils. They are often found on the edges of shorelines where waste are deposited. In contrast, the red mangroves are mostly found in undisturbed pure swampy soils than mixed or contaminated soils. This is because presence in soils contaminated by waste impairs the growth of red mangroves. An example of a disturbed soil is the sand filled mangrove forest in Buguma, Niger Delta, Nigeria. This area was sand filled in 1984, and since then no mangrove had ever grown on it. Rather the dominant species found

**Figure 1.** Different mangrove and non-mangrove species found in mangrove swamps affected by anthropogenic activities (dredging and sand filling). (a) Nypa palm (*Nypa fruticans*), (b) black mangroves (*Laguncularia racemosa*), (c) button wood (*Conocarpus erectus*) (d) herb (e) red mangrove (*Rhizophora racemosa*) (f) mangrove associated fern, (g)

white mangrove (*Avicennia germinans*), (h) *Heritiera littoralis* (I) mangrove fern (*Acrostichum aureum).*

forest.

22 Mangrove Ecosystem Ecology and Function

Combinations of biotic and abiotic factors had made the mangroves one of the most unique, but less studied systems in the world. The problem of data gap in Africa is often cited in many literatures with little done to correct this trend. This work therefore, brings to fore the distribution and composition of mangroves and non-mangroves species in two locations in the Niger Delta to enable scientist in other regions of the world to have a better understating of the largest mangrove forest in Africa. The emphasis of mangrove study in the past has been the effect of pollution on mangrove forest, but no mention was made of species composition and distribution. This is the reason why this study is embarked upon to help bridge the data gap. This study thus intends to achieve the following objectives;

#### *1.5.1. Objectives*


### **2. Materials and methods**

#### **2.1. Study area**

The Niger Delta region is situated in the southern part of Nigeria and bordered to the south by the Atlantic Ocean and to the East by Cameroon. It occupies a surface area of about 112,110 km<sup>2</sup> . It represents about 12% of Nigeria's total surface area and it is predicted that by the year 2020 its population would have exceeded 45 million inhabitants, which is almost two third of the entire population of Nigeria (i.e. 200 million). The region is made up of nine of Nigeria's constituent states (i.e. 37) (**Table 1**):

known as the "August break". During the dry season harmattan winds also called the North East Trade winds blow particles of dust from the Sahara Desert to the coastal maritime regions in the Niger Delta. The monthly temperature ranges between 26 and 30°C. Temperatures are generally high in the region and fairly constant throughout the year. Average monthly maximum and minimum temperatures vary from 28 to 33°C and 21 to 23°C, respectively. The warmest months are February, March and early April in most parts of the Niger Delta Region. The coolest months are June through to September during the peak of rainfall during the wet season. The soil is swampy and grades from red to brown as a result of iron deposition [38]. The soil compaction ranges from 0.25–0.75 tonnes/cm, while the pH ranges from 5.0–7.0.

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A study on species distribution was conducted between seaward and landward sites in Buguma. Along a 20 m transect running across the middle of the plot, eight equally spaced points were identified and soil samples collected and species composition and diversity indices estimated from seaward to landward locations. The soil samples were collected with a hand held augur (Germany) and placed in a black cellophane bag. Leaf samples were collected at each point and placed in an ice cooler, and sent to the laboratory for physico-chemical

Floristic diversity, which is the percentage occurrence of mangrove species present around the

in the Niger Delta. The dbh for trees with small girth were measured with a vernier caliper at an accuracy of 0.01 cm while the stems of larger girth were measured with tapes (Forestry suppliers Inc., Jackson, MS). The tree heights were randomly measured within the plot with EC II Haglof

The stand basal area, which is the summation of all individual basal areas per unit ground

The importance value is a quantitative parameter used to show the significance of each species within a stand, and it includes the summation of relative density, relative frequency and

The allometric method was used to estimate the plot AGB, since biomass was an indicator of the productivity of a mangrove stand [45, 46]. This method is used for estimating tree weight from field verifiable structural indices such as diameter at breast height (dbh) and tree height (h) [46]. The amount of standing biomass in mangrove forest is a function of the systems productivity

The importance value (IV) of the mangroves was calculated using the equations of [43]:

area, was calculated as described by [43]. The area of the main plot, 400 m2

sub-plots within a 20 × 20 m plot in Buguma and Okrika

(i.e. 5 × 5 m) were used as the conversion factor of 1 hectare

(i.e. 20 × 20 m), and

analysis. The different plant communities were identified by a plant taxonomist.

**2.3. Sample collection**

*2.3.1. Species occurrence and stand structure*

forests, was determined within a 5 × 5 m2

clinometers at an accuracy of 0.1 m.

*2.3.2. Stand structural characteristics*

the area of the sub-plots, 25 m2

*2.3.3. Above ground biomass (AGB)*

relative dominance.

[44]. The outcome of this calculation is in [45].


**Table 1.** Land area and population of people in different states of the Niger Delta, Nigeria.

The Niger Delta region makes up 4% of Nigerian population. There is an annual growth rate of 3.5% The population of youths below 30 years (62%) far exceed that of adults of 30–69 years (36%) and older adults above 70 years (2%). The life expectancy is about 50 years. There is resurgence in population of people migrating into the mangrove forest areas to seek for habitation in the last 20 years. The consequence of this situation is the clearing of more mangrove forests.

#### **2.2. Climatic conditions**

Mangroves in the Niger River Delta, Nigeria are the largest in Africa, and the third largest in the world. It is estimated to cover between 5000 and 8500 km<sup>3</sup> [42]. It has a tropical monsoon climate and rainfall occurs almost all throughout the year, except November, December and January. Mean annual rainfall ranges from over 4000 mm in the coastal towns, and decreases inland to 3000 mm in the mid-delta area; and slightly less than 2400 mm in the northern parts of the region. In the north western portions including Edo and Ondo States, annual rainfall ranges from 1500 to 2000 mm, respectively. The two seasons that prevail in the Niger Delta are the wet (February–October) and the dry (November–January) seasons with a break in August, known as the "August break". During the dry season harmattan winds also called the North East Trade winds blow particles of dust from the Sahara Desert to the coastal maritime regions in the Niger Delta. The monthly temperature ranges between 26 and 30°C. Temperatures are generally high in the region and fairly constant throughout the year. Average monthly maximum and minimum temperatures vary from 28 to 33°C and 21 to 23°C, respectively. The warmest months are February, March and early April in most parts of the Niger Delta Region. The coolest months are June through to September during the peak of rainfall during the wet season. The soil is swampy and grades from red to brown as a result of iron deposition [38]. The soil compaction ranges from 0.25–0.75 tonnes/cm, while the pH ranges from 5.0–7.0.

#### **2.3. Sample collection**

**2. Materials and methods**

24 Mangrove Ecosystem Ecology and Function

Nigeria's constituent states (i.e. 37) (**Table 1**):

**States Land area (km2**

The Niger Delta region is situated in the southern part of Nigeria and bordered to the south by the Atlantic Ocean and to the East by Cameroon. It occupies a surface area of about

the year 2020 its population would have exceeded 45 million inhabitants, which is almost two third of the entire population of Nigeria (i.e. 200 million). The region is made up of nine of

Abia 4877 5,106,000 Umuahia Akwa Ibom 6806 5,285,000 Uyo Bayelsa 1107 2,703,000 Yenagoa Cross River 21,930 4,325,000 Calabar Delta 17,163 5,681,000 Asaba Edo 19,698 4,871,000 Benin Imo 5165 5,283,000 Owerri Ondo 15,086 4,782,000 Akure

Rivers 10,378 7,679,000 Port Harcourt

**Table 1.** Land area and population of people in different states of the Niger Delta, Nigeria.

Total 112,110 45,715,000

The Niger Delta region makes up 4% of Nigerian population. There is an annual growth rate of 3.5% The population of youths below 30 years (62%) far exceed that of adults of 30–69 years (36%) and older adults above 70 years (2%). The life expectancy is about 50 years. There is resurgence in population of people migrating into the mangrove forest areas to seek for habitation in the last 20 years. The consequence of this situation is the clearing of more mangrove

Mangroves in the Niger River Delta, Nigeria are the largest in Africa, and the third largest in

climate and rainfall occurs almost all throughout the year, except November, December and January. Mean annual rainfall ranges from over 4000 mm in the coastal towns, and decreases inland to 3000 mm in the mid-delta area; and slightly less than 2400 mm in the northern parts of the region. In the north western portions including Edo and Ondo States, annual rainfall ranges from 1500 to 2000 mm, respectively. The two seasons that prevail in the Niger Delta are the wet (February–October) and the dry (November–January) seasons with a break in August,

[42]. It has a tropical monsoon

the world. It is estimated to cover between 5000 and 8500 km<sup>3</sup>

. It represents about 12% of Nigeria's total surface area and it is predicted that by

**) Population City capital**

**2.1. Study area**

112,110 km<sup>2</sup>

forests.

**2.2. Climatic conditions**

Source: Adjusted from [41].

A study on species distribution was conducted between seaward and landward sites in Buguma. Along a 20 m transect running across the middle of the plot, eight equally spaced points were identified and soil samples collected and species composition and diversity indices estimated from seaward to landward locations. The soil samples were collected with a hand held augur (Germany) and placed in a black cellophane bag. Leaf samples were collected at each point and placed in an ice cooler, and sent to the laboratory for physico-chemical analysis. The different plant communities were identified by a plant taxonomist.

#### *2.3.1. Species occurrence and stand structure*

Floristic diversity, which is the percentage occurrence of mangrove species present around the forests, was determined within a 5 × 5 m2 sub-plots within a 20 × 20 m plot in Buguma and Okrika in the Niger Delta. The dbh for trees with small girth were measured with a vernier caliper at an accuracy of 0.01 cm while the stems of larger girth were measured with tapes (Forestry suppliers Inc., Jackson, MS). The tree heights were randomly measured within the plot with EC II Haglof clinometers at an accuracy of 0.1 m.

#### *2.3.2. Stand structural characteristics*

The stand basal area, which is the summation of all individual basal areas per unit ground area, was calculated as described by [43]. The area of the main plot, 400 m2 (i.e. 20 × 20 m), and the area of the sub-plots, 25 m2 (i.e. 5 × 5 m) were used as the conversion factor of 1 hectare [44]. The outcome of this calculation is in [45].

The importance value (IV) of the mangroves was calculated using the equations of [43]:

The importance value is a quantitative parameter used to show the significance of each species within a stand, and it includes the summation of relative density, relative frequency and relative dominance.

#### *2.3.3. Above ground biomass (AGB)*

The allometric method was used to estimate the plot AGB, since biomass was an indicator of the productivity of a mangrove stand [45, 46]. This method is used for estimating tree weight from field verifiable structural indices such as diameter at breast height (dbh) and tree height (h) [46]. The amount of standing biomass in mangrove forest is a function of the systems productivity [45]. The development of site and species specific allometric relationship is best done using harvesting method [47]. But this method was not used because of its negative effect on the environment. The above ground biomass was therefore, calculated following the equations developed by [48] and presented in 4 studies of [45].

Erlenmeyer flask, and mechanical shaker was used to shake the mixture for 30 min. The suspension was later emptied into a funnel containing Whatman No. 40 Paper to obtain a clear filtrate. The solution was stored and phosphorus was determined using Calorimetric Method [53].

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A portion of 0.25 g of air dried sediment samples were weighed into a Teflon inset of a microwave digestion vessel and 2 ml concentrated (90%) nitric acid (Sigma-Aldrich, Dorset, UK) were added. The metals were extracted using a microwave accelerated reaction system (MARS Xpress, CEM Corporation, Matthews, North Carolina) at 1500 W power (100%), ramped to 175°C in 5.5 min, held for 4.5 min, and allowed to cool down for 1 h. The cool digest solution was filtered through the Whatman 42 filter paper and made up to 100 ml in a volumetric flask

For the water samples, 2 ml concentrated (90%) nitric acid (Sigma-Aldrich) was added to 0.2 ml water and the volume was made up to 10 ml with de-ionized water (X 5 dilution). Metal concentrations were analyzed by inductively coupled plasma mass spectrometry (ICP MS:

All chemicals and reagents used were of analytical grade and of highest purity possible. Analytical blanks were prepared with each batch of the digestion set and analyzed (one blank for every set of six samples) in the same way as the samples. The analytical methodologies were confirmed using certified reference materials for sandy clay (CRM 049-050, Sigma-Aldrich RTC, Salisbury).

Most locations in the Niger Delta have similar mangroves species composition. Some mangrove species found include: *Rhizophora harrisonii* and *Laguncularia racemosa*. The three most commonly found mangrove species are: *Rhizophora racemosa*, *Rhizophora mangle*, and *Avicennia germinans*. Species diversity indices indicates that among the mangroves *Rhizophora racemosa* had the highest abundance and species diversity (**Table 2**) while for the palm species, the nypa palm dominated (**Table 3**) and for the grass species, *Dalbergia ecastophylum* had the highest

Species distribution from seaward to landward areas indicates that core mangrove species were found in the seaward side, whereas the non-mangrove species were found in the land-

There was gradation of heavy metal concentration along the established 20 m transect. It shows that the concentration of metals from landward to seaward directions remained

**3.3. Heavy metal and nutrient concentrations distribution along a transect**

unchanged while Zinc (Zn) concentration along transect fluctuate.

*2.4.4. Metal analysis*

by adding de-ionized water.

**3. Results**

diversity (**Table 4**).

ward direction.

**3.2. Species distribution**

model X7, Thermo Electron, Winsford-Cheshire, UK).

**3.1. Species composition and diversity indices**

This equation is the Model 1 (diameter-height-wood density) mangrove biomass regression model. The wood specific density (*ρ*) for African mangroves from the Global Density Database was used in the calculation [49–51]. A total of five dominant mangrove species were taxonomically identified in the study locations and their wood specific densities (*ρ*) recorded as follows: *R. racemosa* (0.96 g cm−3), *R. mangle* (0.98 g cm−3), *A. germinans* (0.90 g cm−3), *R. harrisonii* (0.86 g cm−3) and *L. racemosa* (0.61 g cm−3). These specific densities were put into the Model 1 mangrove regression model to calculate the plot AGB.

#### **2.4. Soil sample analysis**

A comprehensive physicochemical analysis of soils collected from Buguma and Okrika was done at the laboratory where standard methods were observed to analyze the parameters.

#### *2.4.1. Soil organic carbon (Walkley-Black method)*

A representative soil sample was collected and grinded into fine particles, such that it can pass through 0.5mm sieve and air dried. Soil samples were weighed in duplicates of 75 g and transferred to 250 ml Erlenmeyer flask. 10 ml of K<sup>2</sup> Cr<sup>2</sup> O7 solution was accurately pipetted and dispensed into each of the flasks and swirled gently to disperse the soil. 20 ml of concentrate H<sup>2</sup> SO<sup>4</sup> was added rapidly and directing the stream into the suspension. The soil and the reagents were mixed by swirling the flask gently for 1 min. The beaker was rotated again and the flask was allowed to stand on a sheet of asbestos for about 30 min, thereafter, 100 ml of distilled water was added. Then, 3–4 drops of indicator were added and titrated with 0.5 ml of ferrous sulphate solution. As the end point is approached, a greenish caste was observed which later changed to dark green. Thereafter, ferrous sulphate was added, drop by drop until the color changed sharply from blue to red (maroon color) in reflected light against a white background. The blank titration was prepared in the same manner using the above mentioned steps but without soil to standardize the dichromate.

The result was obtained using the formula of [52].

The result was obtained using the formula of [52].

$$\% \text{Organic Carbon in soil} = \frac{\text{Blank Titan Value-Sample Time Value}}{\text{Weight of Air-dried Sol (g)}} \tag{1}$$

#### *2.4.2. Soil pH and conductivity*

pH meter was used to check the acidity and alkalinity of the soil in situ. Conductivity was measured in field using conductivity meter.

The KH<sup>2</sup> PO4 Extraction Method was used to analyze sulphate content of the soil.

#### *2.4.3. Sulphate and phosphorus analysis*

The KH<sup>2</sup> PO4 Extraction Method was used to analyze sulphate content of the soil. 2 g of soil with one tea spoon of carbon black and 40 ml of extracting solution were added into 125 ml of Erlenmeyer flask, and mechanical shaker was used to shake the mixture for 30 min. The suspension was later emptied into a funnel containing Whatman No. 40 Paper to obtain a clear filtrate. The solution was stored and phosphorus was determined using Calorimetric Method [53].

#### *2.4.4. Metal analysis*

[45]. The development of site and species specific allometric relationship is best done using harvesting method [47]. But this method was not used because of its negative effect on the environment. The above ground biomass was therefore, calculated following the equations developed

This equation is the Model 1 (diameter-height-wood density) mangrove biomass regression model. The wood specific density (*ρ*) for African mangroves from the Global Density Database was used in the calculation [49–51]. A total of five dominant mangrove species were taxonomically identified in the study locations and their wood specific densities (*ρ*) recorded as follows: *R. racemosa* (0.96 g cm−3), *R. mangle* (0.98 g cm−3), *A. germinans* (0.90 g cm−3), *R. harrisonii* (0.86 g cm−3) and *L. racemosa* (0.61 g cm−3). These specific densities

A comprehensive physicochemical analysis of soils collected from Buguma and Okrika was done at the laboratory where standard methods were observed to analyze the parameters.

A representative soil sample was collected and grinded into fine particles, such that it can pass through 0.5mm sieve and air dried. Soil samples were weighed in duplicates of 75 g and transferred

idly and directing the stream into the suspension. The soil and the reagents were mixed by swirling the flask gently for 1 min. The beaker was rotated again and the flask was allowed to stand on a sheet of asbestos for about 30 min, thereafter, 100 ml of distilled water was added. Then, 3–4 drops of indicator were added and titrated with 0.5 ml of ferrous sulphate solution. As the end point is approached, a greenish caste was observed which later changed to dark green. Thereafter, ferrous sulphate was added, drop by drop until the color changed sharply from blue to red (maroon color) in reflected light against a white background. The blank titration was prepared in the same manner

%Organic Carbon in Soil <sup>=</sup> Blank Titre Value‐Sample Titre Value \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Weight of Air‐dried Soil (g) (1)

pH meter was used to check the acidity and alkalinity of the soil in situ. Conductivity was

Extraction Method was used to analyze sulphate content of the soil.

with one tea spoon of carbon black and 40 ml of extracting solution were added into 125 ml of

Extraction Method was used to analyze sulphate content of the soil. 2 g of soil

solution was accurately pipetted and dispensed into

SO<sup>4</sup>

was added rap-

were put into the Model 1 mangrove regression model to calculate the plot AGB.

Cr<sup>2</sup> O7

using the above mentioned steps but without soil to standardize the dichromate.

each of the flasks and swirled gently to disperse the soil. 20 ml of concentrate H<sup>2</sup>

by [48] and presented in 4 studies of [45].

26 Mangrove Ecosystem Ecology and Function

*2.4.1. Soil organic carbon (Walkley-Black method)*

The result was obtained using the formula of [52].

measured in field using conductivity meter.

*2.4.3. Sulphate and phosphorus analysis*

*2.4.2. Soil pH and conductivity*

The KH<sup>2</sup>

The KH<sup>2</sup>

PO4

PO4

to 250 ml Erlenmeyer flask. 10 ml of K<sup>2</sup>

**2.4. Soil sample analysis**

A portion of 0.25 g of air dried sediment samples were weighed into a Teflon inset of a microwave digestion vessel and 2 ml concentrated (90%) nitric acid (Sigma-Aldrich, Dorset, UK) were added. The metals were extracted using a microwave accelerated reaction system (MARS Xpress, CEM Corporation, Matthews, North Carolina) at 1500 W power (100%), ramped to 175°C in 5.5 min, held for 4.5 min, and allowed to cool down for 1 h. The cool digest solution was filtered through the Whatman 42 filter paper and made up to 100 ml in a volumetric flask by adding de-ionized water.

For the water samples, 2 ml concentrated (90%) nitric acid (Sigma-Aldrich) was added to 0.2 ml water and the volume was made up to 10 ml with de-ionized water (X 5 dilution). Metal concentrations were analyzed by inductively coupled plasma mass spectrometry (ICP MS: model X7, Thermo Electron, Winsford-Cheshire, UK).

All chemicals and reagents used were of analytical grade and of highest purity possible. Analytical blanks were prepared with each batch of the digestion set and analyzed (one blank for every set of six samples) in the same way as the samples. The analytical methodologies were confirmed using certified reference materials for sandy clay (CRM 049-050, Sigma-Aldrich RTC, Salisbury).

### **3. Results**

### **3.1. Species composition and diversity indices**

Most locations in the Niger Delta have similar mangroves species composition. Some mangrove species found include: *Rhizophora harrisonii* and *Laguncularia racemosa*. The three most commonly found mangrove species are: *Rhizophora racemosa*, *Rhizophora mangle*, and *Avicennia germinans*. Species diversity indices indicates that among the mangroves *Rhizophora racemosa* had the highest abundance and species diversity (**Table 2**) while for the palm species, the nypa palm dominated (**Table 3**) and for the grass species, *Dalbergia ecastophylum* had the highest diversity (**Table 4**).

#### **3.2. Species distribution**

Species distribution from seaward to landward areas indicates that core mangrove species were found in the seaward side, whereas the non-mangrove species were found in the landward direction.

#### **3.3. Heavy metal and nutrient concentrations distribution along a transect**

There was gradation of heavy metal concentration along the established 20 m transect. It shows that the concentration of metals from landward to seaward directions remained unchanged while Zinc (Zn) concentration along transect fluctuate.


**Table 2.** Shannon wiener diversity indices (H) of major mangrove species in the Niger Delta, Nigeria.


**Table 3.** Diversity indices (H) of palm species commonly found around most mangrove forest in the Niger Delta, Nigeria.


**Table 4.** Shannon wiener diversity indices (H) of weed species commonly found around mangrove forest in the Niger Delta, Nigeria.

Nutrient contents varied along the 20 m transect from seaward to landward directions. There was an increase in sulphate (SO<sup>4</sup> ) and potassium (K) content while there was a decrease in Calcium (Ca), Magnesium (Mg), Manganese (Mn) and Phosphorous (P) contents.

**Study** 

**Conductivity** 

**pH**

**TOC** 

**P (mg/**

**SO42− (mg/**

**Cd (mg/**

**Pb (mg/**

**Zn (mg/**

**Cu (mg/**

**Mn (mg/**

**Ca (mg/**

**K (mg/**

**Mg (mg/kg)**

**(%)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**location**

OK1 OK2 OK3 Mean

SD SE **Table 5.**

2989.04

0.15 0.49

0.02

11.2 Soil physico-chemical characteristics of different mangrove forest in Okrika, Niger Delta, Nigeria. OK refers to Okrika.

0.02

2.07

1.05

0.42

1.28

3.52

96.18

111.64

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29

5177.17

0.26 0.86

0.03

19.40

0.03

3.58

1.82

0.73

2.22

6.09

166.58

193.37

3945.33

6.10 2.34

0.06

37.67

0.02

2.07

2.91

0.42

2.22

38.47

142.69

295.47

9920

5.97 3.315

0.09

60

0.001

0.001

2.6

0.001

4.71

36.95

334.8

513.2

783

6.4

1.716

0.03

28

0.001

0.001

1.26

0.001

0.44

45.17

38.31

143.73

1133

5.94 1.989

0.07

25

0.06

6.21

4.86

1.26

1.52

33.28

54.95

229.48

**μs/cm**


Nutrient contents varied along the 20 m transect from seaward to landward directions. There

**Table 4.** Shannon wiener diversity indices (H) of weed species commonly found around mangrove forest in the Niger

Calcium (Ca), Magnesium (Mg), Manganese (Mn) and Phosphorous (P) contents.

**Scientific name Common name Abundance Proportion (Pi) Ln (Pi**

**Scientific name Common name Abundance Proportion (Pi**

**Table 2.** Shannon wiener diversity indices (H) of major mangrove species in the Niger Delta, Nigeria.

**Scientific name Common name Abundance Proportion (Pi**

28 Mangrove Ecosystem Ecology and Function

*Nypa fruticans* Nypa palm 5 0.83 −0.186 −0.154 *Elaeis guineensis* Date palm 1 0.17 −1.772 0.366 Total 6 H 0.52

*Rhizophora mangle* Red 5 0.21 −1.561 −0.328 *Rhizophora racemosa* Red 8 0.33 −1.109 −0.366 *Rhizophora harrisonii* Red 2 0.08 −2.526 −0.202 *Avicennia germinans* White 6 0.25 −1.386 −0.347 *Laguncularia racemosa* Black 3 0.13 −2.040 −0.265 Total 24 H 1.508

**Table 3.** Diversity indices (H) of palm species commonly found around most mangrove forest in the Niger Delta, Nigeria.

*Dalbergia ecastophylum* Corn vine 6 0.24 −1.427 −0.343 *Chrysobala musicaco* Coco plum 4 0.16 −1.833 −0.293 *Paspalum* Silt grass 2 0.08 −2.526 −0.202 *Scleria verrucosa* Bush knife 1 0.04 −3.219 −0.129 *Combretum racemosum* Christmas tree 3 0.12 −2.120 −0.254 *Osbeckia tubulosa* Melastomataceae 1 0.04 −3.219 −0.129 *Mariscus longibracteatus* Sedge 1 0.04 −3.219 −0.129 *Acrostichum aureum* Aquatic fern 1 0.04 −3.219 −0.129 *Scleria naumanniana* Bush knife 1 0.04 −3.219 −0.129 *Lycopodium cernuum* Fern 1 0.04 −3.219 −0.129 *Alchornea laxiflora* Christmas bush 1 0.04 −3.219 −0.129 *Syzygium guineense* Myrtaceae 3 0.12 −2.120 −0.254 Total 25 H 2.249

) and potassium (K) content while there was a decrease in

**) P i**

**) P i**

 **Ln(Pi )**

**) Ln (Pi**

**) Ln (Pi**

**) Pi**

 **Ln(Pi )**

 **Ln(Pi )**

was an increase in sulphate (SO<sup>4</sup>

Delta, Nigeria.

**Table 5.** Soil physico-chemical characteristics of different mangrove forest in Okrika, Niger Delta, Nigeria. OK refers to Okrika.


**Table 6.** Soil physico-chemical characteristics of different mangrove forest in Buguma, Niger Delta, Nigeria. BG refers to Buguma. A detailed physico-chemical analysis of the study locations is presented in **Tables 5** and **6**.

Mangrove Species Distribution and Composition, Adaptive Strategies and Ecosystem Services…

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Stem diameter of the mangrove trees ranged from 0.01 to 16 cm. *Avicennia germinans* had the largest diameter among species. Tree height ranged from 0.02 to 6.71 m. The average diameter

*Rhizophora racemosa* was the most dominant species in all locations. This is in line with the

*racemosa* (i.e. 52.02) was the highest for all locations. It is similar to the value derived by [54] in south-eastern Nigeria (i.e. 55.6). The next most dominant species of mangroves are *R.* 

The dominance of the red mangroves (i.e. *Rhizophoraceae* family) is because they grow best in core mangrove soil. They are mostly old growth forest that had been growing for the past 20–30 years without disturbance. They have large diameter and grow beyond 6 m in height. The trees grow in groups and are self-sustaining and support each other. Because of the large sizes of the stem they are often used for firewood and charcoal. Constant destruction of the mangroves by humans had, however, made them to regenerate and grow afresh, making them have less significant wood for charcoals production. Clear cutting lead to renewed sprouting of fresh mangroves, which unifies regeneration [55]. Hydrocarbon pollution and selective deforestation lead to uneven growth. Nevertheless, the growth in height and stem diameter is greater in younger mangrove forest than in older mangrove forest [56]. The forest is also cut to create room for building residential and

Baseline data on biomass will help to recognize importance of mangroves in Nigeria. Biomass differences among mangrove forests are indicator of healthy and unhealthy forest. Mangrove forest in unprotected areas seems to show unhealthy condition or fragmentation and degradation due to illegal logging and aquaculture [57, 58]. Thus, management effort of rehabilitating degraded forest must be done to improve carbon sequestration and produc-

Four kinds of soils found in mangrove forest in the Niger Delta include: are mud, chikoko-wet, chikoko-dry and sandy soils. Muddy soils is fine to the touch, light brown in color, wet, and mixed with litter. It can be molded into shapes because of its high plasticity and low porosity. This soil allows the growth of few weeds, and few mangrove species. The chikoko-wet is dark brown in color, rough to the touch, forms a semi mold, and often wet and has medium plasticity and low porosity. This soil is the best for the growth of red, black and white mangroves. The chikoko-dry is coffee-brown in color, rough to the touch, has particulate matter and forms no mold. It contains litter material, and has low plasticity and medium porosity. This soil does not support the growth of many plant species because of its dryness. The sandy soil is whitish to dark brown in color, rough to the touch, forms no mold, and has low plasticity, but high

) of *R.* 

31

outcome of previous studies done in the Niger Delta [40]. The importance value (I<sup>v</sup>

and average tree height for most locations are not significantly different from each other.

**3.4. Stand structure and above ground biomass**

*mangle* followed by *A. germinans* [45].

tivity in unprotected mangroves forest.

**4. Discussion**

industrial quarters.

A detailed physico-chemical analysis of the study locations is presented in **Tables 5** and **6**.

#### **3.4. Stand structure and above ground biomass**

Stem diameter of the mangrove trees ranged from 0.01 to 16 cm. *Avicennia germinans* had the largest diameter among species. Tree height ranged from 0.02 to 6.71 m. The average diameter and average tree height for most locations are not significantly different from each other.

### **4. Discussion**

**Study** 

**Conductivity** 

**pH**

**TOC** 

**P (mg/**

**SO42− (mg/**

**Cd (mg/**

**Pb (mg/**

**Zn (mg/**

**Cu (mg/**

**Mn (mg/**

**Ca (mg/**

**K (mg/**

**Mg (mg/kg)**

**(%)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**kg)**

**location**

BG1 BG2 BG3 Mean

SD SE **Table 6.**

6344.43

0.09 0.52

0.04

74.51 Soil physico-chemical characteristics of different mangrove forest in Buguma, Niger Delta, Nigeria. BG refers to Buguma.

0.40

7.07

25.99

11.21

17.75

289.91

87.57

23.59

10988.9

0.16 0.91

0.07

129.05

0.69

12.25

45.01

19.43

30.74

502.13

151.68

40.86

6591.33

6.65 2.96

0.16

91.00

0.76

13.99

60.30

19.38

39.72

862.65

232.77

749.15

19,280

6.58 3.939

0.24

240

0.001

0.001

8.4

0.001

4.77

282.85

407.4

794.61

30 Mangrove Ecosystem Ecology and Function

186

6.83 2.145

0.1

15

0.93

22.82

88.55

38.85

62.55

1156

157.05

715.49

308

6.53 2.808

0.15

18

1.34

19.14

83.97

19.28

51.84

1149.1

133.85

737.35

**μs/cm**

*Rhizophora racemosa* was the most dominant species in all locations. This is in line with the outcome of previous studies done in the Niger Delta [40]. The importance value (I<sup>v</sup> ) of *R. racemosa* (i.e. 52.02) was the highest for all locations. It is similar to the value derived by [54] in south-eastern Nigeria (i.e. 55.6). The next most dominant species of mangroves are *R. mangle* followed by *A. germinans* [45].

The dominance of the red mangroves (i.e. *Rhizophoraceae* family) is because they grow best in core mangrove soil. They are mostly old growth forest that had been growing for the past 20–30 years without disturbance. They have large diameter and grow beyond 6 m in height. The trees grow in groups and are self-sustaining and support each other. Because of the large sizes of the stem they are often used for firewood and charcoal. Constant destruction of the mangroves by humans had, however, made them to regenerate and grow afresh, making them have less significant wood for charcoals production. Clear cutting lead to renewed sprouting of fresh mangroves, which unifies regeneration [55]. Hydrocarbon pollution and selective deforestation lead to uneven growth. Nevertheless, the growth in height and stem diameter is greater in younger mangrove forest than in older mangrove forest [56]. The forest is also cut to create room for building residential and industrial quarters.

Baseline data on biomass will help to recognize importance of mangroves in Nigeria. Biomass differences among mangrove forests are indicator of healthy and unhealthy forest. Mangrove forest in unprotected areas seems to show unhealthy condition or fragmentation and degradation due to illegal logging and aquaculture [57, 58]. Thus, management effort of rehabilitating degraded forest must be done to improve carbon sequestration and productivity in unprotected mangroves forest.

Four kinds of soils found in mangrove forest in the Niger Delta include: are mud, chikoko-wet, chikoko-dry and sandy soils. Muddy soils is fine to the touch, light brown in color, wet, and mixed with litter. It can be molded into shapes because of its high plasticity and low porosity. This soil allows the growth of few weeds, and few mangrove species. The chikoko-wet is dark brown in color, rough to the touch, forms a semi mold, and often wet and has medium plasticity and low porosity. This soil is the best for the growth of red, black and white mangroves. The chikoko-dry is coffee-brown in color, rough to the touch, has particulate matter and forms no mold. It contains litter material, and has low plasticity and medium porosity. This soil does not support the growth of many plant species because of its dryness. The sandy soil is whitish to dark brown in color, rough to the touch, forms no mold, and has low plasticity, but high porosity. This soil strictly allows only grasses and other weed species grow on it. They are often found in dredged or sand filled areas.

The red mangroves (e.g*. Rhizophora mangle*) are viviparous and have spear-like propagules that germinate while still attached to the tree. This is an adaptation for quick deployment and growth especially when they fall on swampy soils. The base of the propagule contains root cells, which begin to grow immediately it touches the soil or water. However, if the propagules fall on hard surface it lies horizontal, but if it falls in water it would be carried away by tidal currents. The seeds, nevertheless survive being swept away by water current because of its buoyancy, as compared to the nypa palm seeds that are round and are partially submerged

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The torpedo shape of the mangrove propagule enables it to float upright i.e. bottom down and

Rootlets of the white mangrove trees protrude from oxygen-depleted soils like spikes to take in oxygen. This is a way of boosting their survival in a difficult and marshy environment. This characteristic is most often exhibited by the black and white mangroves, but not the red mangroves. This is because white and black mangroves are mostly found in disturbed environments, such as dump sites and sand filled areas. The stems of the red mangroves are elastic and are adapted to wear and tear. The stems and roots form a network that prevents the free movement of animals and humans within the forest. They also restrict the movement

The leaves of the red mangroves (*Rhizophora germinans*) are leathery and succulent and have some xerophytic [62] and schlerophyllic attributes. The epidermis has thick outer walls which enables them to withstand both dry and wet conditions. During the dry season from October to January, the leaves do not fall, and do not undergo rapid transpiration and evaporation, thus preventing desiccation. The mangroves rather look robust, fresh and evergreen in both dry and wet seasons. High litter fall usually occur in the dry season unlike in other areas where the rate of litter fall was higher in wet season. Studies had shown that seasonal changes and hydrocarbon pollution are the two major causes of litter fall and litter accumulation in the Niger Delta, Nigeria. The highest rate of litter fall was recorded in the dry season, between November and March. This is because of reproductive activity (i.e. fruiting and flowering) and harmattan winds that occur mainly during the dry season. The litter enriches the soil and supplies the raw materials needed for decomposition [63]. This leads to the constant enrichment of the soil, which makes the mangrove forest rich in

The mangrove soil is red in color and has life-saving gas that breathes life into the entire mangrove ecosystem. The soil has numerous fiber-like materials that hold and reinforce the soil against water erosion and tide. The combination of nutrients and red soil water with fibrous materials is what has made the mangrove a biodiversity hot spot. Therefore, if these qualities are destroyed as a result of human activities the red mangrove population will decline leading to succession [14] and entry of foreign species [64]. The surface of an undisturbed mangrove soil is slimy and facilitates the movement of creeping and swimming organisms such as mud skippers during low or ebb tides. The slimy and soft nature of the top soil also acts as a defensive mechanism to prevent the free movement of man and

heads up when submerged in water. This allows easy soil implantation and growth.

of humans and machinery during exploratory activities.

when carried by tidal currents.

biodiversity.

Mangroves have low growth in muddy soil because the soil suffocate their lenticels, which may lead to death. The case is, however, different for the weeds, which have better growth in muddy soil. A species composition study done in a sand filled area indicates that in a 20 m transect starting from the seaward to the landward direction; there was a significant difference in the number of species found. Similarly, there was a significant difference in soil physico-chemistry at eight points along the transect. The result indicates that the sandier the soil the more the number of weeds, while the swampier the soil the more the population of red mangrove trees (**Table 2**).

The breathing root system of mangrove is built for survival in anaerobic soils. That is why the mangroves thrive in areas where other species fail that soil types influence mangrove growth. For instance, results from a fieldwork I embarked on indicates that total organic content (TOC) was higher in farm (1.99 ± 0.01%) and Nypa palm (1.87 ± 0.01%) soils than in mangrove soils (1.01–1.48%). Similarly, soil types influence the height of mangrove and nypa palm seedlings (P < 0.001), but did not influence diameter of seedlings (P > 0.05). Mangrove propagules grew best in farm soils. This shows that mangrove distribution is strongly influenced by soil types. Therefore, the more the soil type changes as a result of anthropogenic activities the more it harbors foreign species, which are non-mangroves. In addition, tidal fluctuation and soil moisture content affects the amount of organic matter in sediments [59].

Changes in heavy metals and nutrients can also influence the distribution of mangroves and other plant species in a wet land area. In a study carried out in dredged and sand filled site in Buguma Niger Delta, Nigeria, the result indicates that apart from zinc, which fluctuated, other heavy metals did not vary significantly along a 20 m transect from sandy to mangrove soil (P > 0.05). Mangroves play environmental role by acting as a biofilter of heavy metals [60]. Lastly, maintaining high diversity of mangroves is crucial to ensure the health and productivity of coastal zones [60].

#### **4.1. Adaptive strategies of mangroves**

There are several adaptive features in mangroves [61] including some that are peculiar to the Niger Delta, Nigeria. The mangrove develops long root system that can easily be mistaken for a tree branch. They grow up to 3 m in height, and grow out from tree branches to the ground. This helps to provide extra support for the trees. The adventitious roots do not only grow from the base, but grow from the top of the trees to the ground. The giant roots support and provide extra surface area for atmospheric respiration during high tides when the ground roots are submerged in water. The branches hardly submerge during high tide or flooding because of the nature of the root system, which grow above the water level. The red mangrove trees are more dominant and more adapted to core mangrove soils. The red mangrove propagules have limited growth in sandy or mixed soils. They are mostly adapted to wet chikoko soil, which is slightly muddy.

The red mangroves (e.g*. Rhizophora mangle*) are viviparous and have spear-like propagules that germinate while still attached to the tree. This is an adaptation for quick deployment and growth especially when they fall on swampy soils. The base of the propagule contains root cells, which begin to grow immediately it touches the soil or water. However, if the propagules fall on hard surface it lies horizontal, but if it falls in water it would be carried away by tidal currents. The seeds, nevertheless survive being swept away by water current because of its buoyancy, as compared to the nypa palm seeds that are round and are partially submerged when carried by tidal currents.

porosity. This soil strictly allows only grasses and other weed species grow on it. They are often

Mangroves have low growth in muddy soil because the soil suffocate their lenticels, which may lead to death. The case is, however, different for the weeds, which have better growth in muddy soil. A species composition study done in a sand filled area indicates that in a 20 m transect starting from the seaward to the landward direction; there was a significant difference in the number of species found. Similarly, there was a significant difference in soil physico-chemistry at eight points along the transect. The result indicates that the sandier the soil the more the number of weeds, while the swampier the soil the more the population of

The breathing root system of mangrove is built for survival in anaerobic soils. That is why the mangroves thrive in areas where other species fail that soil types influence mangrove growth. For instance, results from a fieldwork I embarked on indicates that total organic content (TOC) was higher in farm (1.99 ± 0.01%) and Nypa palm (1.87 ± 0.01%) soils than in mangrove soils (1.01–1.48%). Similarly, soil types influence the height of mangrove and nypa palm seedlings (P < 0.001), but did not influence diameter of seedlings (P > 0.05). Mangrove propagules grew best in farm soils. This shows that mangrove distribution is strongly influenced by soil types. Therefore, the more the soil type changes as a result of anthropogenic activities the more it harbors foreign species, which are non-mangroves. In addition, tidal fluctuation and soil moisture content affects the amount of organic matter in

Changes in heavy metals and nutrients can also influence the distribution of mangroves and other plant species in a wet land area. In a study carried out in dredged and sand filled site in Buguma Niger Delta, Nigeria, the result indicates that apart from zinc, which fluctuated, other heavy metals did not vary significantly along a 20 m transect from sandy to mangrove soil (P > 0.05). Mangroves play environmental role by acting as a biofilter of heavy metals [60]. Lastly, maintaining high diversity of mangroves is crucial to ensure the health and productiv-

There are several adaptive features in mangroves [61] including some that are peculiar to the Niger Delta, Nigeria. The mangrove develops long root system that can easily be mistaken for a tree branch. They grow up to 3 m in height, and grow out from tree branches to the ground. This helps to provide extra support for the trees. The adventitious roots do not only grow from the base, but grow from the top of the trees to the ground. The giant roots support and provide extra surface area for atmospheric respiration during high tides when the ground roots are submerged in water. The branches hardly submerge during high tide or flooding because of the nature of the root system, which grow above the water level. The red mangrove trees are more dominant and more adapted to core mangrove soils. The red mangrove propagules have limited growth in sandy or mixed soils. They are mostly adapted to wet chikoko soil, which is

found in dredged or sand filled areas.

32 Mangrove Ecosystem Ecology and Function

red mangrove trees (**Table 2**).

sediments [59].

ity of coastal zones [60].

slightly muddy.

**4.1. Adaptive strategies of mangroves**

The torpedo shape of the mangrove propagule enables it to float upright i.e. bottom down and heads up when submerged in water. This allows easy soil implantation and growth.

Rootlets of the white mangrove trees protrude from oxygen-depleted soils like spikes to take in oxygen. This is a way of boosting their survival in a difficult and marshy environment. This characteristic is most often exhibited by the black and white mangroves, but not the red mangroves. This is because white and black mangroves are mostly found in disturbed environments, such as dump sites and sand filled areas. The stems of the red mangroves are elastic and are adapted to wear and tear. The stems and roots form a network that prevents the free movement of animals and humans within the forest. They also restrict the movement of humans and machinery during exploratory activities.

The leaves of the red mangroves (*Rhizophora germinans*) are leathery and succulent and have some xerophytic [62] and schlerophyllic attributes. The epidermis has thick outer walls which enables them to withstand both dry and wet conditions. During the dry season from October to January, the leaves do not fall, and do not undergo rapid transpiration and evaporation, thus preventing desiccation. The mangroves rather look robust, fresh and evergreen in both dry and wet seasons. High litter fall usually occur in the dry season unlike in other areas where the rate of litter fall was higher in wet season. Studies had shown that seasonal changes and hydrocarbon pollution are the two major causes of litter fall and litter accumulation in the Niger Delta, Nigeria. The highest rate of litter fall was recorded in the dry season, between November and March. This is because of reproductive activity (i.e. fruiting and flowering) and harmattan winds that occur mainly during the dry season. The litter enriches the soil and supplies the raw materials needed for decomposition [63]. This leads to the constant enrichment of the soil, which makes the mangrove forest rich in biodiversity.

The mangrove soil is red in color and has life-saving gas that breathes life into the entire mangrove ecosystem. The soil has numerous fiber-like materials that hold and reinforce the soil against water erosion and tide. The combination of nutrients and red soil water with fibrous materials is what has made the mangrove a biodiversity hot spot. Therefore, if these qualities are destroyed as a result of human activities the red mangrove population will decline leading to succession [14] and entry of foreign species [64]. The surface of an undisturbed mangrove soil is slimy and facilitates the movement of creeping and swimming organisms such as mud skippers during low or ebb tides. The slimy and soft nature of the top soil also acts as a defensive mechanism to prevent the free movement of man and animals on the forest floor. The soil has some holes, which serve as air pockets and safe sanctuaries for threatened organisms (e.g. crabs, mudskippers).

to the proliferation of hydrocarbon utilizing bacteria, which detoxifies the soil and increase the soil fertility leading to a positive feedback such as increase in nutrient turnover. This leads to the rapid growth of mangroves in highly polluted soils. This study is supported by other studies which revealed that the rate of herbivory of crabs and insects on mangrove leave was higher on trees growing in highly polluted soils than in trees growing in lowly

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Mangrove of the Niger Delta, Nigeria is one of the most productive systems in terms of biodiversity, and ecosystem services in the world, but because of lack of data it is often not mentioned in many literatures. This chapter has brought to light the distribution of different species of mangroves between landward and seaward areas and the effect of soil physicochemistry on mangrove species distribution. *Rhizophora* species i.e. red mangroves are the most dominant species and is often found in the seaward areas whereas the white mangroves and the button wood mangroves are found in the landward locations. The positions of the different species of mangroves in the coastal areas had given them the ability to adapt to their difficult environment. The red mangrove of the Niger Delta has one of the longest above ground root systems, which it uses for support and respiration. The stem is also used for fire wood and charcoal production. The mangrove despite its usefulness to man and the environment has faced a lot of anthropogenic disturbances, which if not curtailed will lead to the final

Department of Animal and Environmental Biology, University of Port Harcourt, Nigeria

[1] Bunt JS. Introduction. In: Tropical Mangrove Ecosystem. Washington D.C.: American

[2] Spalding M. The global distribution and status of mangrove ecosystems. Proceedings of the International News Letter of Coastal Management-Inter-Coastal Network, Special

[3] Spalding M, Kainuma M, Collins L. World Atlas of Mangroves. Routledge: Earthscan;

[4] Duke NC. Morphological variation in the mangrove genus *AvicenniainAustralasia*: Systematic and ecological considerations. Australian Systematic Botany. 1990;**3**:221-239

polluted soils.

**5. Conclusion**

extinction of the mangroves.

Address all correspondence to: aroloyen@yahoo.com

Geophysical Union; 1992. pp. 1-6

Edition 1; 1997. pp. 20-21

**Author details**

**References**

2010

Aroloye O. Numbere

A symbiotic relationship does exist between the red mangrove trees and black ants. Large number of black ants are always found on the leaves, branches and stems of trees, which serve as a source of food for the ants while the ants in turn provide protection for the tree against intruders. Termites also build huge termitarium on the tree trunks, which further provides extra security for the plants by warding off intruders and predators. The ants are entomophagous because they feed on other insects along their path. The ants also attack humans that climb to exploit the trees.

The stems of the mangrove trees are very rigid and could withstand severe external impact or fracture during wind storm. It is also extremely difficult to cut down the trees with a machete. The trees are often cut with chain saw or brought down with bulldozers. The mangroves grow in groups, which gives them extra protection from wind storms. The closeness of the trees to each other also leads to the accumulation of large amount of ground litter materials that decompose to drive the nutrient cycle of the forest [14].

Tree climbing skill is exhibited by red mangrove crabs (*Goniopsis pelii*) to hide from ground predators and evade capture. The crabs eat mangrove leaves thereby contributing to litter fall, which help to enrich the mangrove soil.

The mangrove forest is rich in biodiversity and has organism such as monkeys, guinea fowl, periwinkle, mudskipper, crabs (*Goniopsis pelii*), birds (i.e. cranes) and insects [3]. The whole mangrove system is built to withstand stressful conditions. For example, its roots are natural air pumps that suck in oxygen from the atmosphere. The roots are also one of the largest above ground root systems possessed by any plant in the world. The roots provide extra support for growth in soft soil. The mangrove seeds are highly buoyant, which enables them to float, travel and colonize vast areas without drowning. The tenacity of their stems make their wood to be suitable for the production of charcoal and fire wood for cooking in most African communities. The wood have high combustibility and high fire retention capability. The mangrove forest serves as home for many rural dwellers, who build their houses right inside the forest because it provides protection from flood, tsunami or hurricanes.

In addition to plant and animal resources the Niger Delta mangrove forest is rich in crude oil. Most oil and gas exploration activities do occur within the mangrove forest. These exploratory activities have decimated the mangroves in many locations, which may lead to extinction if this trend is not stopped [4, 5]. Over the years the mangroves had survived many environmental disturbances such as hydrocarbon pollution, deforestation, urbanization, and invasive species by adapting to very difficult conditions.

Mangroves are adapted to hydrocarbon pollution: This is because series of studies and field observations have shown that mangroves growing in highly polluted plots had better structural characteristics, above ground biomass and species composition than mangrove trees growing in lowly polluted soil [45, 54]. It has been difficult to provide answers to the cause of this trend, but of recent it was discovered that the robust growth of mangroves in highly polluted plots is as a result of decomposition and nutrient cycling from excess defoliations as a result of oil and gas exploration. The reason is that oil spill leads to increase in litter fall, which covers the soil surface, and decomposes to enrich the soil. This condition leads to the proliferation of hydrocarbon utilizing bacteria, which detoxifies the soil and increase the soil fertility leading to a positive feedback such as increase in nutrient turnover. This leads to the rapid growth of mangroves in highly polluted soils. This study is supported by other studies which revealed that the rate of herbivory of crabs and insects on mangrove leave was higher on trees growing in highly polluted soils than in trees growing in lowly polluted soils.

### **5. Conclusion**

animals on the forest floor. The soil has some holes, which serve as air pockets and safe

A symbiotic relationship does exist between the red mangrove trees and black ants. Large number of black ants are always found on the leaves, branches and stems of trees, which serve as a source of food for the ants while the ants in turn provide protection for the tree against intruders. Termites also build huge termitarium on the tree trunks, which further provides extra security for the plants by warding off intruders and predators. The ants are entomophagous because they feed on other insects along their path. The ants also attack humans that

The stems of the mangrove trees are very rigid and could withstand severe external impact or fracture during wind storm. It is also extremely difficult to cut down the trees with a machete. The trees are often cut with chain saw or brought down with bulldozers. The mangroves grow in groups, which gives them extra protection from wind storms. The closeness of the trees to each other also leads to the accumulation of large amount of ground litter materials

Tree climbing skill is exhibited by red mangrove crabs (*Goniopsis pelii*) to hide from ground predators and evade capture. The crabs eat mangrove leaves thereby contributing to litter fall,

The mangrove forest is rich in biodiversity and has organism such as monkeys, guinea fowl, periwinkle, mudskipper, crabs (*Goniopsis pelii*), birds (i.e. cranes) and insects [3]. The whole mangrove system is built to withstand stressful conditions. For example, its roots are natural air pumps that suck in oxygen from the atmosphere. The roots are also one of the largest above ground root systems possessed by any plant in the world. The roots provide extra support for growth in soft soil. The mangrove seeds are highly buoyant, which enables them to float, travel and colonize vast areas without drowning. The tenacity of their stems make their wood to be suitable for the production of charcoal and fire wood for cooking in most African communities. The wood have high combustibility and high fire retention capability. The mangrove forest serves as home for many rural dwellers, who build their houses right

inside the forest because it provides protection from flood, tsunami or hurricanes.

In addition to plant and animal resources the Niger Delta mangrove forest is rich in crude oil. Most oil and gas exploration activities do occur within the mangrove forest. These exploratory activities have decimated the mangroves in many locations, which may lead to extinction if this trend is not stopped [4, 5]. Over the years the mangroves had survived many environmental disturbances such as hydrocarbon pollution, deforestation, urbanization, and invasive species

Mangroves are adapted to hydrocarbon pollution: This is because series of studies and field observations have shown that mangroves growing in highly polluted plots had better structural characteristics, above ground biomass and species composition than mangrove trees growing in lowly polluted soil [45, 54]. It has been difficult to provide answers to the cause of this trend, but of recent it was discovered that the robust growth of mangroves in highly polluted plots is as a result of decomposition and nutrient cycling from excess defoliations as a result of oil and gas exploration. The reason is that oil spill leads to increase in litter fall, which covers the soil surface, and decomposes to enrich the soil. This condition leads

sanctuaries for threatened organisms (e.g. crabs, mudskippers).

that decompose to drive the nutrient cycle of the forest [14].

which help to enrich the mangrove soil.

by adapting to very difficult conditions.

climb to exploit the trees.

34 Mangrove Ecosystem Ecology and Function

Mangrove of the Niger Delta, Nigeria is one of the most productive systems in terms of biodiversity, and ecosystem services in the world, but because of lack of data it is often not mentioned in many literatures. This chapter has brought to light the distribution of different species of mangroves between landward and seaward areas and the effect of soil physicochemistry on mangrove species distribution. *Rhizophora* species i.e. red mangroves are the most dominant species and is often found in the seaward areas whereas the white mangroves and the button wood mangroves are found in the landward locations. The positions of the different species of mangroves in the coastal areas had given them the ability to adapt to their difficult environment. The red mangrove of the Niger Delta has one of the longest above ground root systems, which it uses for support and respiration. The stem is also used for fire wood and charcoal production. The mangrove despite its usefulness to man and the environment has faced a lot of anthropogenic disturbances, which if not curtailed will lead to the final extinction of the mangroves.

### **Author details**

Aroloye O. Numbere

Address all correspondence to: aroloyen@yahoo.com

Department of Animal and Environmental Biology, University of Port Harcourt, Nigeria

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**Chapter 3**

Provisional chapter

**The Comparison of Vascular Epiphytes Diversity**

**Related to their Occurrence in Natural and Artificial**

The Comparison of Vascular Epiphytes Diversity Related

DOI: 10.5772/intechopen.79133

The eastern Nicaraguan coasts bordered by mangrove forests are often negatively affected by catastrophic events. One of the most destructive was hurricane Joan in 1988, which damaged as much as 80% of the forests. Though neotropical mangrove woodlands are not famous for their high species richness, vascular epiphytes occurring in the mangrove canopies are characterized by high biodiversity. The research presented in this study was focused on vascular epiphytes found in a private Nicaraguan reservation Greenfields. The main aim of the work presented here was to compare two parts of same-age mangrove area surrounding a water channel that runs through the forest stands in the reservation. The biodiversity observed in the initial natural part of the water channel was compared with the biodiversity observed in the artificial part at the end of the channel. In total, there were identified 13 epiphyte species belonging to 5 families on both banks. The Shannon-Wiener index amounts to 1.63 and Simpson index equates to 0.7. In natural channel, there was Shannon-Wiener index of 1.77 and Simpson index 0.75 and for the artificial part it was 0.82 and 0.46. The most common vascular epiphyte species was Tillandsia bulbosa belonging to Bromeliaceae family; there were exactly recorded 141 occurrences of this specie which amounts to more than a half of all the

Keywords: mangrove flora, vascular epiphytes, species diversity, red mangroves,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

to their Occurrence in Natural and Artificial Mangrove

**Mangrove Channels, Greenfields, Eastern Coast of**

Channels, Greenfields, Eastern Coast of Nicaragua

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

individual epiphytes examined in the research.

Greenfields, Nicaragua, hurricane Joan

http://dx.doi.org/10.5772/intechopen.79133

**Nicaragua**

Kupec Anna

Kupec Anna

Abstract

Provisional chapter

**The Comparison of Vascular Epiphytes Diversity Related to their Occurrence in Natural and Artificial Mangrove Channels, Greenfields, Eastern Coast of Nicaragua** The Comparison of Vascular Epiphytes Diversity Related to their Occurrence in Natural and Artificial Mangrove Channels, Greenfields, Eastern Coast of Nicaragua

DOI: 10.5772/intechopen.79133

#### Kupec Anna Kupec Anna

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79133

#### Abstract

The eastern Nicaraguan coasts bordered by mangrove forests are often negatively affected by catastrophic events. One of the most destructive was hurricane Joan in 1988, which damaged as much as 80% of the forests. Though neotropical mangrove woodlands are not famous for their high species richness, vascular epiphytes occurring in the mangrove canopies are characterized by high biodiversity. The research presented in this study was focused on vascular epiphytes found in a private Nicaraguan reservation Greenfields. The main aim of the work presented here was to compare two parts of same-age mangrove area surrounding a water channel that runs through the forest stands in the reservation. The biodiversity observed in the initial natural part of the water channel was compared with the biodiversity observed in the artificial part at the end of the channel. In total, there were identified 13 epiphyte species belonging to 5 families on both banks. The Shannon-Wiener index amounts to 1.63 and Simpson index equates to 0.7. In natural channel, there was Shannon-Wiener index of 1.77 and Simpson index 0.75 and for the artificial part it was 0.82 and 0.46. The most common vascular epiphyte species was Tillandsia bulbosa belonging to Bromeliaceae family; there were exactly recorded 141 occurrences of this specie which amounts to more than a half of all the individual epiphytes examined in the research.

Keywords: mangrove flora, vascular epiphytes, species diversity, red mangroves, Greenfields, Nicaragua, hurricane Joan

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

### 1. Introduction

Mangroves are notable amphibious ecosystems with narrow habitat specificity. They are adapted to coping with harsh conditions in coastal brackish water. Owing to their ability to persist in extreme environmental conditions such as salinity, anoxic soil conditions or tidal inundation, mangroves form a very important transition between terrestrial and aquatic ecosystems.

intolerant of salt; thus, one encounters only a limited range of species in the black mangal, while the range is relatively high in the canopy, and in areas transitional to adjacent terrestrial communities where the epiphytes are more characteristics. On the other hand, in Ref. [12], Benzing and Davidson wrote that halophytism has not been reported so far in epiphytes, but a certain level of salt tolerance has. This observation is further proved by Griffiths' note [13] with an example of Tillandsia paucifolia growing on Rhizophora mangle in South Florida which contained quantities of sodium up to several percent of shoot dry weight. Species of vascular plants associated with mangroves whether as climbers or true epiphytes are the same as those that occur in adjacent terrestrial communities. They are unable to tolerate high salt levels and therefore do not penetrate deeply into the mangrove habitat. There are, however, some apparent exceptions. Some bromeliads, for instance, have succulent leaves and seem to accumulate salt within their tissues. This suggests that they have evolved a degree of salt tolerance parallel to the mangrove trees on which they grow [14]. Benzing and Davidson [12] made a special study of the effects of salt on some epiphytic bromeliads that can occur in Mangroves in South Florida: despite the statement that they can be "dense" on mangroves, it is suggested that Rhizophora mangle supports few or no epiphytes because of an axenic bark response, even though seedlings of Tillandsia pauciflora can be experimentally germinated on its bark if well-

The Comparison of Vascular Epiphytes Diversity Related to their Occurrence in Natural and Artificial Mangrove…

http://dx.doi.org/10.5772/intechopen.79133

43

More than half (about 55%) of the epiphytes live in Americas (New World), in part because neither Bromeliaceae nor Cactaceae ranges beyond this region except all terrestrials. The responsibility for this asymmetry lies with the heavily epiphytic pantropical families (e.g., Araceae, Gesneriaceae, and Orchidaceae), a majority of which experienced their robust arboreal radiations

Atwood [16] estimated that 73% of all species of Orchidaceae family are epiphytic; however, considering the relative numbers of epiphytic to terrestrial species validly described since 1986, that percentage has risen. Some species are temporarily submerged during periodic flooding. Although there are no truly marine orchids, some species of Brassavola, Myrmecophila, Dendrobium, and other genera are epiphytic on mangroves in estuaries; many others have

Epiphytes and epizoites generally have an adverse effect on the mangroves on which they grow because they block lenticels and impede gas exchange [20]. Mangrove forests occupy about 15 million hectares of tropical and subtropical coastline worldwide. Although they amount to only 1% of the total area of tropical forests, mangroves are highly productive ecosystems rich in biodiversity consisting of a wide variety of plant species that provide important

Within the mangrove environment, most plant species are relatively widely dispersed. However, major differences in the environmental connections also occur, particularly in relation to water, salt, nutrients and light, and it seems clear that the sharp boundaries between areas

It seems no known epiphyte species are exclusive to mangroves. Most bromeliads extend over large altitudinal ranges, nevertheless bromeliads are characteristic epiphytes of mangroves in

adapted to salt spray and soil salinity in established coastal dunes [17–19].

dominated by different species are often the direct result of competition [22].

watered.

in Neotropic woodlands [15].

habitats for a wealth of fauna and flora [21].

The effect of tropical cyclones and mangrove roles in the process of tidal inundation is essential for the proper functioning of the mangrove ecosystems. Periodic destruction of Caribbean mangrove forests by cyclonic storms is proposed as one explanation for their characteristically low structural complexity as well as the lack of typical climax components in the vegetation [1]. Hurricane Joan toppled or snapped in southeastern Nicaragua 80% of the trees and completely destroyed 500,000 hectares (1,200,000 acres) of canopy [2]. Meteorological data are not available for the Greenfields but data from Bluefields 25 km away from there show records of sustained wind speeds of more than 200 km h<sup>1</sup> . Rainfall totalled more than 400 mm for the period between October 21 and 23, 1988 [3]. Therefore, Greefields was attacked seriously, and the mangrove vegetation was completely changed. One of the after effects of the hurricane attack was the start of mangrove regeneration which occurred naturally with only minor artificial intervention. However, the human interventions to the natural succession of the ecosystems were as a minor, at the same time, the end part of the water channel was constructed as a prolongation of the natural one. This meant in fact the most significant human influence on the new ecosystem development in relation to the hurricane Joan affects in the area of Greenfields.

Mangrove habitats have relatively low levels of species richness compared to other tropical habitats such as, for example, tropical rain forests [4]. In the American tropics, only 10 species of mangroves have been recognized [5]. In general, floristic diversity equates directly to structural diversity and function of mangroves. The same factors which limit species presence and growth also affect the functions and benefits of particular mangrove stands such as shoreline stabilization, primary production, and habitat for a range of dependent organisms [6]. Regardless of what is the level of species diversity, mangroves are characterized by many specific life strategies and adaptations. Mangrove uniqueness is derived from their pneumatophore arthropod assemblages together with aerial roots which are responsible for the root fixation mostly in estuarine water exposed in anaerobic sediments.

Epiphytes, as for trees, are generally distributed mostly on branches and trunks; however, minor occurrence was also noticed on the aerial roots. The bulk of the epiphytic biomass in the Pacific and many other areas is on branches and although studies of epiphytes on main trunks can be informative, and trunks are not necessarily representative of branches [7]. Vascular epiphytes are a conspicuous part of tropical rainforest canopies, representing a large fraction of plant biodiversity [8] and forest nutrient capital [9].

Many epiphytes also grow on mangrove trees: these include an assortment of creepers, orchids, ferns, and other plants, many of which cannot tolerate salt and therefore grow only high in the mangrove canopy [10]. In Ref. [11], there was mentioned that most vascular epiphytes are intolerant of salt; thus, one encounters only a limited range of species in the black mangal, while the range is relatively high in the canopy, and in areas transitional to adjacent terrestrial communities where the epiphytes are more characteristics. On the other hand, in Ref. [12], Benzing and Davidson wrote that halophytism has not been reported so far in epiphytes, but a certain level of salt tolerance has. This observation is further proved by Griffiths' note [13] with an example of Tillandsia paucifolia growing on Rhizophora mangle in South Florida which contained quantities of sodium up to several percent of shoot dry weight. Species of vascular plants associated with mangroves whether as climbers or true epiphytes are the same as those that occur in adjacent terrestrial communities. They are unable to tolerate high salt levels and therefore do not penetrate deeply into the mangrove habitat. There are, however, some apparent exceptions. Some bromeliads, for instance, have succulent leaves and seem to accumulate salt within their tissues. This suggests that they have evolved a degree of salt tolerance parallel to the mangrove trees on which they grow [14]. Benzing and Davidson [12] made a special study of the effects of salt on some epiphytic bromeliads that can occur in Mangroves in South Florida: despite the statement that they can be "dense" on mangroves, it is suggested that Rhizophora mangle supports few or no epiphytes because of an axenic bark response, even though seedlings of Tillandsia pauciflora can be experimentally germinated on its bark if wellwatered.

1. Introduction

42 Mangrove Ecosystem Ecology and Function

Greenfields.

of sustained wind speeds of more than 200 km h<sup>1</sup>

Mangroves are notable amphibious ecosystems with narrow habitat specificity. They are adapted to coping with harsh conditions in coastal brackish water. Owing to their ability to persist in extreme environmental conditions such as salinity, anoxic soil conditions or tidal inundation, mangroves form a very important transition between terrestrial and aquatic ecosystems. The effect of tropical cyclones and mangrove roles in the process of tidal inundation is essential for the proper functioning of the mangrove ecosystems. Periodic destruction of Caribbean mangrove forests by cyclonic storms is proposed as one explanation for their characteristically low structural complexity as well as the lack of typical climax components in the vegetation [1]. Hurricane Joan toppled or snapped in southeastern Nicaragua 80% of the trees and completely destroyed 500,000 hectares (1,200,000 acres) of canopy [2]. Meteorological data are not available for the Greenfields but data from Bluefields 25 km away from there show records

period between October 21 and 23, 1988 [3]. Therefore, Greefields was attacked seriously, and the mangrove vegetation was completely changed. One of the after effects of the hurricane attack was the start of mangrove regeneration which occurred naturally with only minor artificial intervention. However, the human interventions to the natural succession of the ecosystems were as a minor, at the same time, the end part of the water channel was constructed as a prolongation of the natural one. This meant in fact the most significant human influence on the new ecosystem development in relation to the hurricane Joan affects in the area of

Mangrove habitats have relatively low levels of species richness compared to other tropical habitats such as, for example, tropical rain forests [4]. In the American tropics, only 10 species of mangroves have been recognized [5]. In general, floristic diversity equates directly to structural diversity and function of mangroves. The same factors which limit species presence and growth also affect the functions and benefits of particular mangrove stands such as shoreline stabilization, primary production, and habitat for a range of dependent organisms [6]. Regardless of what is the level of species diversity, mangroves are characterized by many specific life strategies and adaptations. Mangrove uniqueness is derived from their pneumatophore arthropod assemblages together with aerial roots which are responsible for the root

Epiphytes, as for trees, are generally distributed mostly on branches and trunks; however, minor occurrence was also noticed on the aerial roots. The bulk of the epiphytic biomass in the Pacific and many other areas is on branches and although studies of epiphytes on main trunks can be informative, and trunks are not necessarily representative of branches [7]. Vascular epiphytes are a conspicuous part of tropical rainforest canopies, representing a large fraction

Many epiphytes also grow on mangrove trees: these include an assortment of creepers, orchids, ferns, and other plants, many of which cannot tolerate salt and therefore grow only high in the mangrove canopy [10]. In Ref. [11], there was mentioned that most vascular epiphytes are

fixation mostly in estuarine water exposed in anaerobic sediments.

of plant biodiversity [8] and forest nutrient capital [9].

. Rainfall totalled more than 400 mm for the

More than half (about 55%) of the epiphytes live in Americas (New World), in part because neither Bromeliaceae nor Cactaceae ranges beyond this region except all terrestrials. The responsibility for this asymmetry lies with the heavily epiphytic pantropical families (e.g., Araceae, Gesneriaceae, and Orchidaceae), a majority of which experienced their robust arboreal radiations in Neotropic woodlands [15].

Atwood [16] estimated that 73% of all species of Orchidaceae family are epiphytic; however, considering the relative numbers of epiphytic to terrestrial species validly described since 1986, that percentage has risen. Some species are temporarily submerged during periodic flooding. Although there are no truly marine orchids, some species of Brassavola, Myrmecophila, Dendrobium, and other genera are epiphytic on mangroves in estuaries; many others have adapted to salt spray and soil salinity in established coastal dunes [17–19].

Epiphytes and epizoites generally have an adverse effect on the mangroves on which they grow because they block lenticels and impede gas exchange [20]. Mangrove forests occupy about 15 million hectares of tropical and subtropical coastline worldwide. Although they amount to only 1% of the total area of tropical forests, mangroves are highly productive ecosystems rich in biodiversity consisting of a wide variety of plant species that provide important habitats for a wealth of fauna and flora [21].

Within the mangrove environment, most plant species are relatively widely dispersed. However, major differences in the environmental connections also occur, particularly in relation to water, salt, nutrients and light, and it seems clear that the sharp boundaries between areas dominated by different species are often the direct result of competition [22].

It seems no known epiphyte species are exclusive to mangroves. Most bromeliads extend over large altitudinal ranges, nevertheless bromeliads are characteristic epiphytes of mangroves in tropical and subtropical regions of Central and South America [22]. Common mangrove epiphytes include Aechmea bracteata and some species of genera Tillandsia [23].

The entire forest stands including the mangrove forests in the east coast were destroyed by hurricane Joan in 1988. Although this event may thus appear catastrophic at the first sight, it in fact, triggered a system of regenerative mechanisms leading to necessary succession. Existing water channels surrounded by mangrove ecosystems were reserved and afterwards were established new artificial ones. The artificial channels were excavated in the original mangrove area and in fact opened the previous mangrove stands. Occurring secondary mangrove forests originated from previous mangrove stands was starting their redevelopment by the regeneration after the hurricane attack in 1988. Now they are dominated by red mangroves with prevailing Rhizophora mangle in species composition, as was also found in the present study. All the surveyed trees were determined as Rhizophora mangle. All mangroves are as was mentioned secondary forest stands, and current forest age is approximately of 30 years.

The Comparison of Vascular Epiphytes Diversity Related to their Occurrence in Natural and Artificial Mangrove…

The research took place during a period from May 2015 to July 2015 and was conducted on the banks of a 2-km long mangrove channel in which first part (1200 m) is of natural origin, while the subsequent part (800 m) is artificial, as it was constructed shortly after the hurricane attack. The age of the mangrove stand was considered to be approximately the same (roughly 30 years), considering the concurrent natural regeneration after the hurricane attack and visual homogeneity of the forest stand (homogeneous DBH, mean value 12 cm and tree height, mean value 5.5 m). There was no undergrowth layer under the canopy. Considering that the forest stands on the banks of these two parts are in almost the same age, grow in similar environmental conditions, and the same habitat, it was concluded that the two channel parts could be compared to each other. The density of the forest stand was visually approximated (for mean

The average height of the mangrove forest stand was 5–6 m in total and spread over 22 ha. Due to the high density of the forest stand, the research was carried out according to the following design. A channel leading through the mangrove stand was divided into 20 sectors, each 100 m long. Two edge trees situated directly within the channel bank at the end of each sector were marked and surveyed: one tree on the right side of the channel and one tree on the left side. These trees were determined into the species and epiphytes occurring there were determined as well. Each mangrove tree was surveyed in an appropriate way. In the case of epiphyte occurrence on higher sprays, it was necessary to climb the tree for the purpose of determining the epiphyte species. Additionally, canoes were used in the process of determining the epiphyte species on the lower branches. This two-tree design was chosen due to the enormous number of epiphyte individuals that can be found in the majority of mangroves.

There were two parameters recorded and evaluated in the research: occurrence of epiphytic individuals and vascular epiphytes' diversity. The recorded values were matched with the channel sector where they had been collected, and therefore the parameters were studied at

The diversity was analyzed using of two types of diversity indexes—Simpson index [26] and

) and was recognized as similar as well as the

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45

2.2. Methods

approximately 30 mangrove stems per 100 m2

the background of the particular part's origin.

Shannon-Wiener index [27].

distance between adjacent trees.

There is a significant deficiency of information focused on the epiphytes diversity in mangrove forest. One of few studies focused on the assessment of the plant diversity was carried out in Malaysia, but in general, this assessment targets to the quantitative study of the mangrove vegetation primarily [24]. Another study has been done in more similar conditions in Brazil focusing on the diversity and distribution of epiphytic bromeliads in mangroves. This study aimed to assess the diversity of epiphytic bromeliads in a subtropical mangrove, evaluating their distribution and relationship with their host trees [25].

Presented study aimed to characterize and analyze vascular epiphytes species occurring in mangroves and their comparison on the example of Greenfields, East Nicaragua. The research was centered around a hypothesis which suggests that there is more significant level of species richness in natural mangrove channels in comparison with channel constructed artificially. To verify this thought, an observation was held which focused on the measurement of species diversity.

### 2. Materials and methods

#### 2.1. Study site and plant survey

The study area is located in Nicaragua, South Caribbean Coast Autonomous Region approximately 2 km south of Kukra Hill town, 12�13<sup>0</sup> N, 83�44<sup>0</sup> W. The research area is a part of a private forest reservation owned by Gaudens Pfranger, which was established to support nature conservation and protection of endangered species. The area is connected to the sea by meandering water channel leading through the mangrove stands. These coastal ecosystems border an adjacent terrestrial biome—a tropical rain forest stand (see Figure 1).

Figure 1. Location of study area and map of the channel (Greenfields, Nicaragua).

The entire forest stands including the mangrove forests in the east coast were destroyed by hurricane Joan in 1988. Although this event may thus appear catastrophic at the first sight, it in fact, triggered a system of regenerative mechanisms leading to necessary succession. Existing water channels surrounded by mangrove ecosystems were reserved and afterwards were established new artificial ones. The artificial channels were excavated in the original mangrove area and in fact opened the previous mangrove stands. Occurring secondary mangrove forests originated from previous mangrove stands was starting their redevelopment by the regeneration after the hurricane attack in 1988. Now they are dominated by red mangroves with prevailing Rhizophora mangle in species composition, as was also found in the present study. All the surveyed trees were determined as Rhizophora mangle. All mangroves are as was mentioned secondary forest stands, and current forest age is approximately of 30 years.

#### 2.2. Methods

tropical and subtropical regions of Central and South America [22]. Common mangrove

There is a significant deficiency of information focused on the epiphytes diversity in mangrove forest. One of few studies focused on the assessment of the plant diversity was carried out in Malaysia, but in general, this assessment targets to the quantitative study of the mangrove vegetation primarily [24]. Another study has been done in more similar conditions in Brazil focusing on the diversity and distribution of epiphytic bromeliads in mangroves. This study aimed to assess the diversity of epiphytic bromeliads in a subtropical mangrove, evaluating

Presented study aimed to characterize and analyze vascular epiphytes species occurring in mangroves and their comparison on the example of Greenfields, East Nicaragua. The research was centered around a hypothesis which suggests that there is more significant level of species richness in natural mangrove channels in comparison with channel constructed artificially. To verify this thought, an observation was held which focused on the measurement of species

The study area is located in Nicaragua, South Caribbean Coast Autonomous Region approximately 2 km south of Kukra Hill town, 12�13<sup>0</sup> N, 83�44<sup>0</sup> W. The research area is a part of a private forest reservation owned by Gaudens Pfranger, which was established to support nature conservation and protection of endangered species. The area is connected to the sea by meandering water channel leading through the mangrove stands. These coastal ecosystems

border an adjacent terrestrial biome—a tropical rain forest stand (see Figure 1).

Figure 1. Location of study area and map of the channel (Greenfields, Nicaragua).

epiphytes include Aechmea bracteata and some species of genera Tillandsia [23].

their distribution and relationship with their host trees [25].

diversity.

2. Materials and methods

44 Mangrove Ecosystem Ecology and Function

2.1. Study site and plant survey

The research took place during a period from May 2015 to July 2015 and was conducted on the banks of a 2-km long mangrove channel in which first part (1200 m) is of natural origin, while the subsequent part (800 m) is artificial, as it was constructed shortly after the hurricane attack. The age of the mangrove stand was considered to be approximately the same (roughly 30 years), considering the concurrent natural regeneration after the hurricane attack and visual homogeneity of the forest stand (homogeneous DBH, mean value 12 cm and tree height, mean value 5.5 m). There was no undergrowth layer under the canopy. Considering that the forest stands on the banks of these two parts are in almost the same age, grow in similar environmental conditions, and the same habitat, it was concluded that the two channel parts could be compared to each other. The density of the forest stand was visually approximated (for mean approximately 30 mangrove stems per 100 m2 ) and was recognized as similar as well as the distance between adjacent trees.

The average height of the mangrove forest stand was 5–6 m in total and spread over 22 ha. Due to the high density of the forest stand, the research was carried out according to the following design. A channel leading through the mangrove stand was divided into 20 sectors, each 100 m long. Two edge trees situated directly within the channel bank at the end of each sector were marked and surveyed: one tree on the right side of the channel and one tree on the left side. These trees were determined into the species and epiphytes occurring there were determined as well. Each mangrove tree was surveyed in an appropriate way. In the case of epiphyte occurrence on higher sprays, it was necessary to climb the tree for the purpose of determining the epiphyte species. Additionally, canoes were used in the process of determining the epiphyte species on the lower branches. This two-tree design was chosen due to the enormous number of epiphyte individuals that can be found in the majority of mangroves.

There were two parameters recorded and evaluated in the research: occurrence of epiphytic individuals and vascular epiphytes' diversity. The recorded values were matched with the channel sector where they had been collected, and therefore the parameters were studied at the background of the particular part's origin.

The diversity was analyzed using of two types of diversity indexes—Simpson index [26] and Shannon-Wiener index [27].

### 3. Results and discussion

Fourty trees were examined in the mangrove channel which was divided into twenty transect, each one hundred meters long. All these tree individuals were determined as Rhizophora mangle, which in agrees with conclusions of the available sources stating that more than 40% of the stand on the Nicaraguan Atlantic coasts is formed by red mangrove [28].

Consequently, there were two trees chosen at the end of each 100 m sector, that is, 20 trees on the right bank and 20 on the left bank in total, and the number of epiphytes found on these trees was recorded. Through this method, there were 273 vascular epiphytes found in total. The distribution of the vascular epiphyte individuals is presented in Table 1. As was mentioned above, epiphytes prefer habitats on branches rather than on trunks or aerial roots. In agreement with this observation, all the recorded vascular epiphytes occurred on the branches, while no vascular epiphytes were found on the mangroves' stems, which is in agreement with conclusions of Pike's study [7].

Furthermore, it was also observed that there were differences in epiphyte distribution depending on the origin of the channel. The data obtained in the first 1200 m long part of the mangrove channel show a significantly asymmetric distribution of vascular epiphytes (presented in Table 2) in comparison to the shorter (800 m) artificial part of the channel (presented in Table 3). An

amount of 73% of all vascular epiphytes were found in the natural channel. However, this is a quit high value, it would be unwise to base any conclusion on this number, as it is necessary to take into consideration the asymmetry between lengths of the natural and the artificial parts of the channel. Therefore, the comparison of biodiversity was based on the following indexes in

Segment of the channel (km) 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Right bank (no. of epiphytic individuals) 6 0 0 0 0 0 35 Left bank (no. of epiphytic individuals) 8 1 0 0006

Segment of the channel (km) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Right bank (no. of epiphytic individuals) 0 8 2 6 0 1 1 9 23 0 7 32 Left bank (no. of epiphytic individuals) 0 6 7 17 5 18 1 4 7 1 5 39

The Comparison of Vascular Epiphytes Diversity Related to their Occurrence in Natural and Artificial Mangrove…

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As the research also focused on epiphyte species diversity, the observed epiphytes were determined into species and families and were evaluated according to their localization within the channel parts. There were 13 epiphytic species and 5 families found in the whole mangrove channel (Table 1). The most abundant occurrence was observed for Tillandsia bulbosa, Bromeliaceae —exactly 141 individuals—which is a number representing more than a half of all the epiphytes that were found here, more precisely 52% (see Table 1). The survey led to the discovery that the vast majority of occurrences belong to family Bromeliaceae. Seven species belonging into Bromeliaceae family were observed in the mangroves, namely, Tillandsia bulbosa Hook., Tillandsia caput-medusae E. Morren, Catopsis berteroniana (Schult. & Schult. f.) Mez, Oncidium sp., Vriesea sp., Tillandsia utriculata L., Peperomia sp., Tillandsia anceps G. Lodd., Aechmea bracteata (Sw.) Griseb., Anthurium trinerve Miq., Encyclia alata (Bateman) Schltr., Brassavola sp., and Polypodium fraxinifolium Jacq (Table 1). Orchidaceae was detected as the family with the second most abundant occurrence and was represented by genera Oncidium, Brassavola, and Encyclia alata (Bateman) Schltr. Epiphytes belongs to family Orchidaceae were not found in artificial mangrove channel with the exception of one individual Encyclia alata (Bateman) Schltr. (Table 1). All the plant species

order to prevent the difference in length from influencing the results.

Table 2. Distribution of vascular epiphyte in the natural part of the channel.

Table 3. Distribution of vascular epiphyte in the natural part of the channel.

The natural mangrove channel

The artificial mangrove channel

were determined according to the taxonomy used in Flora de Nicaragua [29].

berteroniana (Schult. & Schult. f.), Mez, Vriesea sp., and Encyclia alata (Bateman) Schltr.

To the comparison of two parts of the mangrove channel in consideration of their origin was to detect essential difference between natural and artificial channel. The species distribution as well as the frequency of occurrence was lower in the artificial channel. There were only four vascular epiphytes species determined in the artificial channel: Tillandsia bulbosa Hook., Catopsis


Table 1. The distribution of the vascular epiphyte individuals.


Table 2. Distribution of vascular epiphyte in the natural part of the channel.

3. Results and discussion

46 Mangrove Ecosystem Ecology and Function

conclusions of Pike's study [7].

3 Catopsis berteroniana (Schult. & Schult. f.) Mez

No. Species Family No. of

Table 1. The distribution of the vascular epiphyte individuals.

Fourty trees were examined in the mangrove channel which was divided into twenty transect, each one hundred meters long. All these tree individuals were determined as Rhizophora mangle, which in agrees with conclusions of the available sources stating that more than 40% of the stand

Consequently, there were two trees chosen at the end of each 100 m sector, that is, 20 trees on the right bank and 20 on the left bank in total, and the number of epiphytes found on these trees was recorded. Through this method, there were 273 vascular epiphytes found in total. The distribution of the vascular epiphyte individuals is presented in Table 1. As was mentioned above, epiphytes prefer habitats on branches rather than on trunks or aerial roots. In agreement with this observation, all the recorded vascular epiphytes occurred on the branches, while no vascular epiphytes were found on the mangroves' stems, which is in agreement with

Furthermore, it was also observed that there were differences in epiphyte distribution depending on the origin of the channel. The data obtained in the first 1200 m long part of the mangrove channel show a significantly asymmetric distribution of vascular epiphytes (presented in Table 2) in comparison to the shorter (800 m) artificial part of the channel (presented in Table 3). An

1 Tillandsia bulbosa Hook. Bromeliaceae 141 39 51 36 15 2 Tillandsia caput- medusacae E. Morren Bromeliaceae 28 18 10 - -

 Oncidium sp. Orchidaceae 19 9 10 - - Vriesea sp. Bromeliaceae 16 4 8 2 2 Tillandsia utriculata L. Bromeliaceae 11 10 1 - - Peperomia sp. Piperaceae 8 62 - - Tillandsia anceps G. Lodd. Bromeliaceae 8 35 - - Aechmea bracteata (Sw.) Griseb. Bromeliaceae 7 43 - - Anthurium trinerve Miq. Araceae 4 22 - - Encyclia alata (Bateman) Schltr. Orchidaceae 3 2- 1- Brassavola sp. Orchidaceae 1 -1 -- Polypodium fraxinifolium Jacq. Polypodiaceae 1 -1 --

individuals

Natural water channel

> Right side

Left side

Bromeliaceae 26 - 8 15 3

Artificial water channel

> Right side

Left side

on the Nicaraguan Atlantic coasts is formed by red mangrove [28].


Table 3. Distribution of vascular epiphyte in the natural part of the channel.

amount of 73% of all vascular epiphytes were found in the natural channel. However, this is a quit high value, it would be unwise to base any conclusion on this number, as it is necessary to take into consideration the asymmetry between lengths of the natural and the artificial parts of the channel. Therefore, the comparison of biodiversity was based on the following indexes in order to prevent the difference in length from influencing the results.

As the research also focused on epiphyte species diversity, the observed epiphytes were determined into species and families and were evaluated according to their localization within the channel parts. There were 13 epiphytic species and 5 families found in the whole mangrove channel (Table 1). The most abundant occurrence was observed for Tillandsia bulbosa, Bromeliaceae —exactly 141 individuals—which is a number representing more than a half of all the epiphytes that were found here, more precisely 52% (see Table 1). The survey led to the discovery that the vast majority of occurrences belong to family Bromeliaceae. Seven species belonging into Bromeliaceae family were observed in the mangroves, namely, Tillandsia bulbosa Hook., Tillandsia caput-medusae E. Morren, Catopsis berteroniana (Schult. & Schult. f.) Mez, Oncidium sp., Vriesea sp., Tillandsia utriculata L., Peperomia sp., Tillandsia anceps G. Lodd., Aechmea bracteata (Sw.) Griseb., Anthurium trinerve Miq., Encyclia alata (Bateman) Schltr., Brassavola sp., and Polypodium fraxinifolium Jacq (Table 1). Orchidaceae was detected as the family with the second most abundant occurrence and was represented by genera Oncidium, Brassavola, and Encyclia alata (Bateman) Schltr. Epiphytes belongs to family Orchidaceae were not found in artificial mangrove channel with the exception of one individual Encyclia alata (Bateman) Schltr. (Table 1). All the plant species were determined according to the taxonomy used in Flora de Nicaragua [29].

To the comparison of two parts of the mangrove channel in consideration of their origin was to detect essential difference between natural and artificial channel. The species distribution as well as the frequency of occurrence was lower in the artificial channel. There were only four vascular epiphytes species determined in the artificial channel: Tillandsia bulbosa Hook., Catopsis berteroniana (Schult. & Schult. f.), Mez, Vriesea sp., and Encyclia alata (Bateman) Schltr.


• Even after 30 years of developing the new epiphytic communities in mangrove forests surrounding the artificial part of the channel the diversity is not on the level of the natural one there; however, the abiotic determining abiotic conditions (esp. light conditions) are

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• After 30 years of development, the current status of new epiphytic communities located in the mangroves of artificially constructed water channel are on the level of approximately 50% (60% as for Simpson index and 46% as for Shannon-Wiener index) of the fully developed mature epiphytic communities of the mangroves located by the natural one. This fact can be highlighted as an important in the consequences of generally accepted

• The differences in the epiphytes distribution are mainly determined by the light conditions on the "stand walls" (i.e., vertical edges) which are in case of natural channel long time opened contrary to the case of artificial channel opened only for 30 years. The main result which authors want to point out is that even after this period the new epiphyte community (in artificial channel) still does not reach the diversity level of original natural

Mendel University in Brno, Faculty of Forestry and Wood Technology, Department of Forest

[1] Roth LC. Hurricanes and mangrove regeneration: Effects of hurricane Joan, October 1988, on the vegetation of Isla del Venado, Bluefields, Nicaragua. Biotropica. 1992;24(3):375-384.

[2] Yih K, Boucher DH, Vandermeer JH, Zamora N. Recovery of the rain forest of southeastern Nicaragua after destruction by hurricane Joan. Biotropica. 1991;23(2):106-113. DOI:

[3] INETER (Instituto Nicaraguense de Estudios Territoriales). Ciclones tropicales y sus efectos en Nicaragua. In: Domínguez GC, López RF, editors. El Ojo Maldito. Managua, Nicaragua:

[4] Ricklefs RE, Latham RE. Global patterns of diversity in mangrove floras. In: Ricklefs RE, Schutler D, editors. Species Diversity in Ecological Communities: Historical and Geo-

graphical Perspectives. Chicago: University of Chicago Press; 1993. pp. 215-229

opinion of fast forest community development in tropic areas.

seemed the same.

one (natural channel).

DOI: 10.2307/2388607

10.2307/2388295

Address all correspondence to: annajashari@seznam.cz

Editorial Nueva Nicaragua; 1988. pp. 193-214

Botany, Dendrology and Geobiocoenology, Czech Republic

Author details

Kupec Anna

References

Table 4. Comparison of biodiversity indexes results.

For the comparison of the two channel parts, there were two types of indexes used to determine the biodiversity—Simpson and Shannon-Wiener indexes (see Table 4). Diversity indices provide more information about community composition than simply species richness.

Based on the collected data, it was found that the values of Simpson and Shannon-Wiener indexes differ depending on the origin of the mangrove channel where the data were collected. The results showed that the epiphytes were abundant on the surveyed mangrove trees in both of natural and artificial channels. The Shannon-Wiener index equals to 0.7 and Simpson index equates to 1.63 (Table 4).

In the natural channel, the Shannon-Wiener index was 1.77 and Simpson index 0.75, while for the artificial part, it was 0.82 and 0.46 (Table 4). Comparing Simpson index 0.75 for the natural channel and 0.46 for the artificial channel could indicate higher value of evenness of natural mangrove channel (1 is a maximum value—being complete evenness). In case of Shannon-Wiener index, the relative abundances of different species were also taken into account. There should be noticed as well as in the first index higher value in the case of natural channel 1.77 a 0.82. Considerably small value of Shannon-Wiener index could point out the small amount of species, H decreases dramatically as the number of species decreases.

All researched epiphytes were present on the mangrove branches. This fact can be caused by the high level of tidal inundation in a narrow water channel, which does not allow to colonize the basal part of trees or also by the effortless colonization of horizontal parts of mangroves.

### 4. Conclusion

Based on the results presented above, the following statements can be summarized:


### Author details

Kupec Anna

For the comparison of the two channel parts, there were two types of indexes used to determine the biodiversity—Simpson and Shannon-Wiener indexes (see Table 4). Diversity indices provide more information about community composition than simply species richness.

Mangrove channel total (2 km) 0.7 1.63 Natural channel (1.2 km) 0.75 1.77 Artificial channel (0.8 km) 0.46 0.82

Simpson index Shannon-Wiener index

Based on the collected data, it was found that the values of Simpson and Shannon-Wiener indexes differ depending on the origin of the mangrove channel where the data were collected. The results showed that the epiphytes were abundant on the surveyed mangrove trees in both of natural and artificial channels. The Shannon-Wiener index equals to 0.7 and Simpson index

In the natural channel, the Shannon-Wiener index was 1.77 and Simpson index 0.75, while for the artificial part, it was 0.82 and 0.46 (Table 4). Comparing Simpson index 0.75 for the natural channel and 0.46 for the artificial channel could indicate higher value of evenness of natural mangrove channel (1 is a maximum value—being complete evenness). In case of Shannon-Wiener index, the relative abundances of different species were also taken into account. There should be noticed as well as in the first index higher value in the case of natural channel 1.77 a 0.82. Considerably small value of Shannon-Wiener index could point out the small amount of

All researched epiphytes were present on the mangrove branches. This fact can be caused by the high level of tidal inundation in a narrow water channel, which does not allow to colonize the basal part of trees or also by the effortless colonization of horizontal parts of

Based on the results presented above, the following statements can be summarized:

• The diversity of epiphytic communities within the study area is taking into account the results of used indexes relatively high where the diversity of epiphytes located in the natural part of the channel is approximately two times higher than in case of artificial one as was expected definitely. This is very important finding especially when the mangrove ecosystems are generally known as the ecosystems with relatively low species richness [4].

• The epiphytic communities located in the natural channel mangrove forests served (and probably still serves) as a refugium for the new developing epiphytic communities in the artificial part (no epiphytic species different than those which originated in the natural

species, H decreases dramatically as the number of species decreases.

equates to 1.63 (Table 4).

Table 4. Comparison of biodiversity indexes results.

48 Mangrove Ecosystem Ecology and Function

mangroves.

4. Conclusion

part was found there).

Address all correspondence to: annajashari@seznam.cz

Mendel University in Brno, Faculty of Forestry and Wood Technology, Department of Forest Botany, Dendrology and Geobiocoenology, Czech Republic

### References


[5] Sánchez-Páez H, Álvarez-León R, Guevara-Mancera O, Zamora-Guzmán O, Rodríguez-Cruz H, Bravo-Pazmino H. Diagnóstico y zonificatión preliminar de los manglares del Pacífico Colombiano. In Castillo-Cárdenas MF, Toro-Perea N, editors. Low genetic diversity within Carribean patches of Pelliciera rhizophorae, a Neotropical mangrove species with reduced distribution. Aquatic Botany. 2012;96(1):48-51. DOI: 10.1016/j.aquabot.2011.09.011 [18] Linder HP, Kurzweil H. Orchids of Southern Africa. In: Stern WL, editor. Anatomy of the Monocotyledons Volume X: Orchidaceae. 2014. DOI: 10.1093/acprof:osobl/9780199689071.

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[19] Hágsater E, Soto-Arenas MA, Salazar GA, Jiménez-Machorro R, López MA, Dressler RL. Orchids of Mexico. In: Stern WL, editor. Anatomy of the Monocotyledons Volume X:

[20] Farnsworth EJ, Ellison AM, Gong WK. Elevated CO2 alters anatomy, physiology, growth, and reproduction of red mangrove (Rhizophora mangle L.). Oecologia. 1996;108(4):599-609.

[22] Saenger P. Mangrove Ecology, Silviculture and Conservation. Kluwer Academic Publ; 2002 [23] Olmstead I, Gómez-Juárez M. Distribution and conservation of epiphytes on the Yucatán

[24] Ashton EC, Macintosh DJ. Preliminary assessment of the plant diversity and community ecology of the Sematan Mangrove Forest, Sarawak, Malaysia. Forest Ecology and Man-

[25] Sousa MM, Colpo KD. Diversity and distribution of epiphytic bromeliads in a Brazilian subtropical mangrove. Anais Da Academia Brasileira De Ciencias. 2017;89(2):1085-1093.

[27] Shannon CE. A mathematical theory of communication. The Bell System Technical Journal.

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oso/9780198716549.003.0001


**Chapter 4**

**Provisional chapter**

**Cameroon Mangrove Forest Ecosystem: Ecological and**

**Cameroon Mangrove Forest Ecosystem: Ecological and** 

This study examined the ecological effects of local scale mangrove exploitation through surveys, empirical field experiments, modeling and questionnaires. The ecosystem "health" was assessed by parameterising a mass-balance model (ECOPATH with ECOSIM). The results suggest that forest exploitation affects mangrove forest structure and two-third of the canopy gaps were caused by human activities. Regeneration was affected, and more seedlings were recorded in canopy gaps compared to closed canopy areas. A total of 1358 crabs were collected to assess it population structure, 770 females (56.7%) and 588 males (43.3%), belonging to 13 species. The family Sesarmidae contains 5 species (38.5%), while Grapsidae 2 species (30.8%), Ocypodidae 1 species (15.4%) and to each of the families Portunidae and Gecarcinidae (7.7% each). *Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the two dominant species, constituting 44.1 and 21.9%, respectively, of the total sampled crabs. Propagules predation was a major source of mortality for mangrove. An average of 65.9% of the propagules was predated and most were found to be non-viable. The Ecopath analysis suggests that the Cameroon mangrove ecosystem is relatively healthy and moderately mature. This analysis allowed a reasonable model representation of the Cameroon mangrove system, as the model viability was determined

**Keywords:** crabs, West Africa, anthropogenic pressure, canopy gaps, propoagule

Mangrove forests are one of the unique features of intertidal zones throughout tropical and subtropical regions of the world and cover an area of approximately 15 million hectares

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.79021

**Environmental Dimensions**

**Environmental Dimensions**

http://dx.doi.org/10.5772/intechopen.79021

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

by using the sensitive analysis function.

recruitment, ecopath model

**1. Introduction**

Ngomba Longonje Simon

Ngomba Longonje Simon

**Abstract**

#### **Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions**

DOI: 10.5772/intechopen.79021

Ngomba Longonje Simon Ngomba Longonje Simon

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79021

#### **Abstract**

This study examined the ecological effects of local scale mangrove exploitation through surveys, empirical field experiments, modeling and questionnaires. The ecosystem "health" was assessed by parameterising a mass-balance model (ECOPATH with ECOSIM). The results suggest that forest exploitation affects mangrove forest structure and two-third of the canopy gaps were caused by human activities. Regeneration was affected, and more seedlings were recorded in canopy gaps compared to closed canopy areas. A total of 1358 crabs were collected to assess it population structure, 770 females (56.7%) and 588 males (43.3%), belonging to 13 species. The family Sesarmidae contains 5 species (38.5%), while Grapsidae 2 species (30.8%), Ocypodidae 1 species (15.4%) and to each of the families Portunidae and Gecarcinidae (7.7% each). *Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the two dominant species, constituting 44.1 and 21.9%, respectively, of the total sampled crabs. Propagules predation was a major source of mortality for mangrove. An average of 65.9% of the propagules was predated and most were found to be non-viable. The Ecopath analysis suggests that the Cameroon mangrove ecosystem is relatively healthy and moderately mature. This analysis allowed a reasonable model representation of the Cameroon mangrove system, as the model viability was determined by using the sensitive analysis function.

**Keywords:** crabs, West Africa, anthropogenic pressure, canopy gaps, propoagule recruitment, ecopath model

### **1. Introduction**

Mangrove forests are one of the unique features of intertidal zones throughout tropical and subtropical regions of the world and cover an area of approximately 15 million hectares

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

worldwide [1]. In recent years, these ecosystems have been extensively studied. The basic botany of mangrove has been described by Tomlinson [2]. An overview of mangrove ecology, distribution and biology has been described in [3–5].

but they are among the most exploited ecosystems [7]. Frequent, but low intensity, smallscale anthropogenic disturbance, such as firewood extraction, may strongly affect forest structure

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

http://dx.doi.org/10.5772/intechopen.79021

55

Mangrove crabs are probably the most prominent and significant biotic components of mangrove ecosystems in terms of species richness and their ecological engineering role [10–12]. Their distribution is influenced by biotic and abiotic factors, such as water salinity, temperature, food availability and preference, sediment properties, vegetation type, interspecific competition and predation [13, 14]. The most common crabs in mangroves are either Fiddler crabs (Family Ocypodidae, genus *Uca*) or Sesarmid crabs (Family Grapsidae, subfamily

The ecological role of crabs in terms of the functioning of the mangrove ecosystem is thought to be significant [16]. Energy assimilated by crabs plays a significant role in nutrient recycling [17], crabs aerate the soil by burrowing [18], increase nutrient content by burying organic matter, decrease toxic sulphide and ammonium concentrations within the sediment [19], reduce pore water salinity by flushing water through burrows [20] and create a microhabitat for other fauna [21]. Despite the vital role played by crabs in the mangrove ecosystem, data on crabs in

Several species of mangrove macrofauna are known to consume plant materials, including crabs [22–24]. Among these, crabs are thought to be major consumers and to be a key source

Ecosystem health is a concept that sets new goals for environmental management, and its definition and assessment methods are still being perfected [26]. According to Costanza [27], ecosystem health represents a desired endpoint of environmental management. The advances in this concept are evident from the fact that it is now recognised that a reflexive relationship exists between human systems and natural ecosystems in that the health of one is dependent on the health of the other [28]. According to Rapport et al. [29], healthy ecosystems must not only be ecologically sound, but must also be economically viable and able to sustain healthy

There are different approaches for assessing ecosystem health, and one is ecological modelling, used as a tool to describe complex system-level metrics related to health. Specifically, I use the mass balance model Ecopath [30]. This model represents trophic networks that connect species (functional groups) in a system, and the magnitude of flows of materials and higher-level indices within the different functional groups can be calculated from the

The research framework in which the present study fits involves a number of separate sections, each of which constitutes a piece of the entire study. The discussion links all of these sections, specifically, the objectives are to assess: (a) the mangrove use and structural effects of locallevel cutting of Cameroon mangrove forests, (b) the distribution, diversity and abundance

complex network, which can in turn be related to ecosystem health.

and species composition in tropical forests [8, 9].

some areas remain patchy in Cameroon.

**1.1. Research framework and objectives**

of leaf and seedling mortality in mangroves [25].

Sesarmidae) [15].

human communities.

Cameroon mangrove forests are found east and west of Mount Cameroon with smaller formations dispersed along the estuaries of the other rivers. The main stands of trees are the Rio-del-Rey and the Cameroon Estuary, respectively (**Figure 1**). The latter covers an estimated surface area of about 75,000 ha (approximately 50 km of coastline), while the former covers an estimated surface area of 175,000 ha (approximately 60 km of coastline from the River Sanaga to the Bimbia estuary).

The floristic composition of Cameroon mangrove is characteristic of the Atlantic mangroves of West Africa. It is dominated by *Rhizophora* and comprises mostly three species, *R. mangle*, *R. harrisonii* and *R. racemosa* [3]. The pioneer species *Rhizophora racemosa* constitute 90–95% of the mangrove area [6]. Other mangrove species include *Avicennia germinans*, which occurs on the higher elevation fibrous clay or sandier soils, *Laguncularia racemosa* and *Conocarpus erectus*, *Acrostichum aureum*, *Pandanus candelabrum* and the introduced *Nypa fruticans* [3, 6].

Human activities in coastal areas such as physical alteration of the habitat, over-exploitation of the resources and pollution cause significant pressure on the environment. These pressures have increased steadily as the human population increases. Coastal areas, including mangroves, are characterised by high productivity creating important nurseries for offshore fish,

**Figure 1.** The Cameroon coastline showing mangrove forest locations (Adapted from UNEP –WCMC, 2005).

but they are among the most exploited ecosystems [7]. Frequent, but low intensity, smallscale anthropogenic disturbance, such as firewood extraction, may strongly affect forest structure and species composition in tropical forests [8, 9].

Mangrove crabs are probably the most prominent and significant biotic components of mangrove ecosystems in terms of species richness and their ecological engineering role [10–12]. Their distribution is influenced by biotic and abiotic factors, such as water salinity, temperature, food availability and preference, sediment properties, vegetation type, interspecific competition and predation [13, 14]. The most common crabs in mangroves are either Fiddler crabs (Family Ocypodidae, genus *Uca*) or Sesarmid crabs (Family Grapsidae, subfamily Sesarmidae) [15].

The ecological role of crabs in terms of the functioning of the mangrove ecosystem is thought to be significant [16]. Energy assimilated by crabs plays a significant role in nutrient recycling [17], crabs aerate the soil by burrowing [18], increase nutrient content by burying organic matter, decrease toxic sulphide and ammonium concentrations within the sediment [19], reduce pore water salinity by flushing water through burrows [20] and create a microhabitat for other fauna [21]. Despite the vital role played by crabs in the mangrove ecosystem, data on crabs in some areas remain patchy in Cameroon.

Several species of mangrove macrofauna are known to consume plant materials, including crabs [22–24]. Among these, crabs are thought to be major consumers and to be a key source of leaf and seedling mortality in mangroves [25].

Ecosystem health is a concept that sets new goals for environmental management, and its definition and assessment methods are still being perfected [26]. According to Costanza [27], ecosystem health represents a desired endpoint of environmental management. The advances in this concept are evident from the fact that it is now recognised that a reflexive relationship exists between human systems and natural ecosystems in that the health of one is dependent on the health of the other [28]. According to Rapport et al. [29], healthy ecosystems must not only be ecologically sound, but must also be economically viable and able to sustain healthy human communities.

There are different approaches for assessing ecosystem health, and one is ecological modelling, used as a tool to describe complex system-level metrics related to health. Specifically, I use the mass balance model Ecopath [30]. This model represents trophic networks that connect species (functional groups) in a system, and the magnitude of flows of materials and higher-level indices within the different functional groups can be calculated from the complex network, which can in turn be related to ecosystem health.

#### **1.1. Research framework and objectives**

worldwide [1]. In recent years, these ecosystems have been extensively studied. The basic botany of mangrove has been described by Tomlinson [2]. An overview of mangrove ecology,

Cameroon mangrove forests are found east and west of Mount Cameroon with smaller formations dispersed along the estuaries of the other rivers. The main stands of trees are the Rio-del-Rey and the Cameroon Estuary, respectively (**Figure 1**). The latter covers an estimated surface area of about 75,000 ha (approximately 50 km of coastline), while the former covers an estimated surface area of 175,000 ha (approximately 60 km of coastline from the River Sanaga

The floristic composition of Cameroon mangrove is characteristic of the Atlantic mangroves of West Africa. It is dominated by *Rhizophora* and comprises mostly three species, *R. mangle*, *R. harrisonii* and *R. racemosa* [3]. The pioneer species *Rhizophora racemosa* constitute 90–95% of the mangrove area [6]. Other mangrove species include *Avicennia germinans*, which occurs on the higher elevation fibrous clay or sandier soils, *Laguncularia racemosa* and *Conocarpus erectus*, *Acrostichum aureum*, *Pandanus candelabrum* and the introduced *Nypa* 

Human activities in coastal areas such as physical alteration of the habitat, over-exploitation of the resources and pollution cause significant pressure on the environment. These pressures have increased steadily as the human population increases. Coastal areas, including mangroves, are characterised by high productivity creating important nurseries for offshore fish,

**Figure 1.** The Cameroon coastline showing mangrove forest locations (Adapted from UNEP –WCMC, 2005).

distribution and biology has been described in [3–5].

to the Bimbia estuary).

54 Mangrove Ecosystem Ecology and Function

*fruticans* [3, 6].

The research framework in which the present study fits involves a number of separate sections, each of which constitutes a piece of the entire study. The discussion links all of these sections, specifically, the objectives are to assess: (a) the mangrove use and structural effects of locallevel cutting of Cameroon mangrove forests, (b) the distribution, diversity and abundance of mangrove crabs in Cameroon mangroves, (c) the ecological effect of mangrove crab herbivore feeding preferences in Cameroon mangrove forests, (d) to examine mangrove community function in terms of trophic linkages, in which a mass-balance model (ECOPATH with ECOSIM) is parameterised and explored.

The approach of administering the questionnaires was made flexible enough to accommodate questions and answers, with the aim of making the process more interactive, friendly and to obtain as much information as possible. Interviews were conducted in English, French and the local dialect, but the filling out the answers to the questions was done in English. The information gathered allowed an evaluation of the uses of the mangrove vegetation and ecosystem, an assessment of the mangrove area and the socio-economic profile of local

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

http://dx.doi.org/10.5772/intechopen.79021

57

Direct observation alone was carried out where a group refused to answer some questions or tried to give deliberately false answers based on my personal judgement and the opinion of

To assess the distribution, diversity and abundance of mangrove crabs, data were collected at low tide when crabs are more active. Data on crab species present were recorded using 10 × 42 binoculars. Subsequently, crab species were collected by hand for 15–30 min. On approaching the crabs, it immediately retreated to their burrows or took refuge. To offset any bias in favour of collecting slow-moving species, more time and effort was allocated to catching the larger, faster-moving crabs. This may introduce another bias, but previous experience has shown that this gives a more representative overall assessment of species composition [31]. A 1-m2 quadrat was placed randomly and excavated to a depth of 30 cm and all crabs collected. This excavation method is thought to offer a more reliable estimate of crab density [32]. The crabs were sedated in iced water for a few minutes, washed and stored in 70% alcohol, later identified, weighed (wet weight) and carapace width measured. All the specimens collected were stored carefully to ensure that no appendages were lost due to stress, and identified with the aid of field keys [33–35]. To assess the ecological considerations of mangrove crab herbivore feeding preferences, the level of damage to and preference for mangrove leaves and propagules was studied. Propagule predation was studied by tethered propagules independently with a 50-cm length of nylon twine, the other end of which was tied to a piece of wood on the forest floor. The propagules were spaced far enough apart so that the tethers could not get tangled. The length of each propagule was measured, and propagules individually tagged. The propagules were checked from a distance using binoculars over a 6-h period, after which they were checked once a day for 1 week. All observations were carried out during low tide

Predation status was recorded following [22]: (1) when the epicotyl was eaten (2) when 50% of the hypocotyl was lost (3) when the propagule was pulled into the burrow of crab. Each propagule was classified as viable (capable of growth, i.e. ≤50% of propagule eaten), nonviable (incapable of growth, i.e. >50% of propagule eaten) and missing (when lost). Signs of

Leaf predation for all the three mangrove species in Cameroon (*Laguncularia*, *Avicennia* and *Rhizophora*). Fresh and senescent leaves were gathered, fresh leaves by harvesting from trees, whilst senescent leaves (yellow and easily abscised) were either picked from the forest floor or harvested from the tree. Ten replicate leaves (fresh and senescent) of each species were tethered with a nylon string 50 cm in length with the other end tied to approximately

communities.

the local interpreter.

when the crabs are very active.

snail predation were also recorded.

### **2. Methodology**

To assess mangrove, use and structural effects of local–level cutting of Cameroon mangrove forests data of forest characteristics were collected. I employed the quadrat/census plot method [12].

To assess the floristic composition and stand structure, data were collected on tree species composition, diameter at breast height (dbh), tree height, seedlings, canopy cover, gaps, gap size, stumps and snag (dead stems). In each plot, every tree was numbered, marked and measured (>1.0 m tall) and seedlings (<1.0 m) recorded [13]. The diameter at breast height (dbh) of each tree stem was measured at 1.3 m or above the highest prop root, following [12]. Tree height was measured using marked bamboo poles and clinometers. Evidence of human cutting was also recorded. Data for local uses were collected in villages in the study area, selection of the study site was on the basis of their accessibility, cooperation and background knowledge of village communities utilising mangrove forest. They are assumed representative of the larger mangrove community.

Data were collected by focus group discussion. Five group meetings were carried out per village, first with the chief and the village councillors, followed by three separate meetings with elderly fishermen and one meeting with the elderly women. Data collection was through indepth interviews and systematic filling out of questionnaires and direct observation of everyday life during village visits. Answering of the questions was done through participatory rapid appraisal method (PRA). The participants were allowed to discuss among themselves and every person's opinion was relevant, until they reached a consensus. In some circumstances, they were given 20 stones to distribute them into categories, to reflect their views.

The questionnaire was mainly structured, with a few semi-structured questions. Elderly residents with a long residency history were chosen in order to explore perceptions of mangrove forest status. More males were interviewed because of the gender bias that exists in the division of labour in this region. Men alone are involved in fishing and harvesting wood, while women assist in wood transportation as well as fish smoking.

Increased participation and some degree of reliability of the interviewee to provide information was enhanced as follows:


The approach of administering the questionnaires was made flexible enough to accommodate questions and answers, with the aim of making the process more interactive, friendly and to obtain as much information as possible. Interviews were conducted in English, French and the local dialect, but the filling out the answers to the questions was done in English. The information gathered allowed an evaluation of the uses of the mangrove vegetation and ecosystem, an assessment of the mangrove area and the socio-economic profile of local communities.

of mangrove crabs in Cameroon mangroves, (c) the ecological effect of mangrove crab herbivore feeding preferences in Cameroon mangrove forests, (d) to examine mangrove community function in terms of trophic linkages, in which a mass-balance model (ECOPATH with

To assess mangrove, use and structural effects of local–level cutting of Cameroon mangrove forests data of forest characteristics were collected. I employed the quadrat/census plot

To assess the floristic composition and stand structure, data were collected on tree species composition, diameter at breast height (dbh), tree height, seedlings, canopy cover, gaps, gap size, stumps and snag (dead stems). In each plot, every tree was numbered, marked and measured (>1.0 m tall) and seedlings (<1.0 m) recorded [13]. The diameter at breast height (dbh) of each tree stem was measured at 1.3 m or above the highest prop root, following [12]. Tree height was measured using marked bamboo poles and clinometers. Evidence of human cutting was also recorded. Data for local uses were collected in villages in the study area, selection of the study site was on the basis of their accessibility, cooperation and background knowledge of village communities utilising mangrove forest. They are assumed representa-

Data were collected by focus group discussion. Five group meetings were carried out per village, first with the chief and the village councillors, followed by three separate meetings with elderly fishermen and one meeting with the elderly women. Data collection was through indepth interviews and systematic filling out of questionnaires and direct observation of everyday life during village visits. Answering of the questions was done through participatory rapid appraisal method (PRA). The participants were allowed to discuss among themselves and every person's opinion was relevant, until they reached a consensus. In some circumstances, they were given 20 stones to distribute them into categories, to reflect their views.

The questionnaire was mainly structured, with a few semi-structured questions. Elderly residents with a long residency history were chosen in order to explore perceptions of mangrove forest status. More males were interviewed because of the gender bias that exists in the division of labour in this region. Men alone are involved in fishing and harvesting wood, while

Increased participation and some degree of reliability of the interviewee to provide informa-

women assist in wood transportation as well as fish smoking.

**1.** Contact with the chief of each village before starting data collection; **2.** High degree of socialisation with the interviewee during sampling;

ECOSIM) is parameterised and explored.

56 Mangrove Ecosystem Ecology and Function

tive of the larger mangrove community.

tion was enhanced as follows:

**3.** The use of a field guard (interpreter).

**2. Methodology**

method [12].

Direct observation alone was carried out where a group refused to answer some questions or tried to give deliberately false answers based on my personal judgement and the opinion of the local interpreter.

To assess the distribution, diversity and abundance of mangrove crabs, data were collected at low tide when crabs are more active. Data on crab species present were recorded using 10 × 42 binoculars. Subsequently, crab species were collected by hand for 15–30 min. On approaching the crabs, it immediately retreated to their burrows or took refuge. To offset any bias in favour of collecting slow-moving species, more time and effort was allocated to catching the larger, faster-moving crabs. This may introduce another bias, but previous experience has shown that this gives a more representative overall assessment of species composition [31]. A 1-m2 quadrat was placed randomly and excavated to a depth of 30 cm and all crabs collected. This excavation method is thought to offer a more reliable estimate of crab density [32]. The crabs were sedated in iced water for a few minutes, washed and stored in 70% alcohol, later identified, weighed (wet weight) and carapace width measured. All the specimens collected were stored carefully to ensure that no appendages were lost due to stress, and identified with the aid of field keys [33–35]. To assess the ecological considerations of mangrove crab herbivore feeding preferences, the level of damage to and preference for mangrove leaves and propagules was studied. Propagule predation was studied by tethered propagules independently with a 50-cm length of nylon twine, the other end of which was tied to a piece of wood on the forest floor. The propagules were spaced far enough apart so that the tethers could not get tangled. The length of each propagule was measured, and propagules individually tagged. The propagules were checked from a distance using binoculars over a 6-h period, after which they were checked once a day for 1 week. All observations were carried out during low tide when the crabs are very active.

Predation status was recorded following [22]: (1) when the epicotyl was eaten (2) when 50% of the hypocotyl was lost (3) when the propagule was pulled into the burrow of crab. Each propagule was classified as viable (capable of growth, i.e. ≤50% of propagule eaten), nonviable (incapable of growth, i.e. >50% of propagule eaten) and missing (when lost). Signs of snail predation were also recorded.

Leaf predation for all the three mangrove species in Cameroon (*Laguncularia*, *Avicennia* and *Rhizophora*). Fresh and senescent leaves were gathered, fresh leaves by harvesting from trees, whilst senescent leaves (yellow and easily abscised) were either picked from the forest floor or harvested from the tree. Ten replicate leaves (fresh and senescent) of each species were tethered with a nylon string 50 cm in length with the other end tied to approximately 5 m of string and tagged. The leaves were tied randomly and far apart to avoid tangling. The leaf surface was measured by tracing around the edge on graph paper. Leaves were checked after 24 h, damage recorded, and it was noted whether the leaves were found on the surface or in a crab burrow. Leaves that were in a burrow were removed by gently pulling on the attached string.

primary producer and make the link with fishing pressure. The functional group benthos was

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59

The input parameters for each group were: the biomass (B), the production/biomass ratio (P/B), the consumption/biomass ratio (Q/B) and ecotrophic efficiency (EE). Input parameters were estimated from the field or extracted from the literature, either from studies done within a similar mangrove ecosystem (in Central Atlantic region) or on the West Africa continental shelf. The diet matrix was constructed by designating the percentage of each prey that occurs in each predator's diet. Diets were derived mostly from the scientific literature, except for crab's groups

3. Zooplankton Neritic copepods, bivalve larvae, ostracods, mysids, nauplii, fish eggs and others

21. Shorebirds Finfoot (*Podica senegalensis*), Avocet (*Recutrvirostra avosetta*), White-footed plover

(*Gypohierax angolensis*), Harrier hawk (*Polyboriodes typhus*)

22. Birds of prey Black kite (*Milvus migrans*), Fish eagle (*Haliaeetus vocifer*), Palm nut vulture

sandpiper (*Actitis hypoleucos*).

23. Insectivorous birds Grey flycatcher (*Musicapa cassini*), Pied crow (*Corvus albus*)

**Table 1.** Descriptions of some functional groups of the mangrove ecosystem in Cameroon.

(*Charadrius marginatus*), Common Green shank (*Tringa nebularia*), Common

included because of its contribution to the diets of other groups.

1. Mangrove *Rhizophora* spp., *Avicennia* spp., *Laguncularia racemosa*

4. Shrimps *Peneaus* spp., *Parapenaeopsis atlantica*, *Penaeus notiali*

7. Other crabs *Scylla serrata*, *Cardisoma carnifex* and others

9. *Pseudotolithus* spp. *P. senegalensis*, *P. typus* and *P. elongates*

14. *Arius* spp. *A. heudelotii* and *A. parkii*

18. *Lutjanus* spp. *L. goreensis* and *L. dentatus*

20. *Caranx* spp. *C. senegallus*, *C. hippo* and *C. senegalensis*

26. Detritus Organic matters and associated like bacteria

2. Phytoplankton Diatoms, dinoflagellates and others

5. Mangrove crabs Sesarmid species 6. Fiddler crabs *Uca* species

8. *Ilisha africana*

10. *Pentanemus quinquarius* 11. *Sardinella maderensis* 12. *Brachydeuterus auritus* 13. *Dreprane africana*

15. *Pomadasys jubelini* 16. *Galeoides decadactyl* 17. *Raja miraletus*

19. *Mugil curema*

24. Benthos 25. Insects

Additional data on leaf predation were gathered from crabs predating within the canopy. Crabs were seen residing on tree trunks, branches and the prop roots. They were observed climbing mangrove trees, usually early in the morning to feed on leaves and by midday they all moved back down, moving up the tree again early in the evening and down again by late evening. An average of 5 crabs was found on a single tree. Young trees (1.5–2 m tall, dbh 2.3–5 cm) of each species (*Laguncularia*, *Avicennia* and *Rhizophora*) were observed from a close distance for about 5 hours and crab feeding activities and presence of crab damage recorded. The percentage of the leaves with damage was used to calculate the damaged leaves per plant, and these values were averaged for each species within the sample area.

To evaluate ecosystem structure, its function and organisation, I applied the Ecopath with Ecosim model (www.ecopath.org) to the Cameroon mangrove estuarine system. Selected ecosystem indicators that could be used to monitor ecosystem status or health were analysed using a set of ecosystem goal functions, representative of Odum's attributes of ecosystem maturity [36]. The attributes represent three different aspects of ecosystem development: (1) complexity in community structure, (2) community energetics and, (3) overall community homeostasis.

The steps and governing principles of the general approach of Ecopath and Ecosim have been described in detail in [30, 37], and can be accessed at http://www.ecopath.org. The detail modelling approach (Ecopath with Ecosim) can be accessed at [35, 36, 38, 39].

For this study, the selection of functional groups to represent the Cameroon mangrove food web was a product of a collaborative process. A number of stakeholders and experts (including myself) participated in the discussion to produce functional groups based on the following criteria:


In the final iteration, based on these criteria, 26 functional groups were selected for this model (**Table 1**): 13 fishes, 3 kinds of birds (11 species), groupings of 3 crabs, mangroves, phytoplankton, zooplankton, detritus, benthos, shrimps and insects. All the species within a functional group have ecological similarities, defined by similarities in diet, production and consumption rates, life history, and habitat associations, but also sometimes on value-driven criteria, such as commercial status or importance for subsistence users. Because of the nature of the Cameroon mangrove forest, where mangrove wood products are used extensively as source of energy to smoke fish, it is important therefore to consider the mangrove forest as a primary producer and make the link with fishing pressure. The functional group benthos was included because of its contribution to the diets of other groups.

5 m of string and tagged. The leaves were tied randomly and far apart to avoid tangling. The leaf surface was measured by tracing around the edge on graph paper. Leaves were checked after 24 h, damage recorded, and it was noted whether the leaves were found on the surface or in a crab burrow. Leaves that were in a burrow were removed by gently pulling on the

Additional data on leaf predation were gathered from crabs predating within the canopy. Crabs were seen residing on tree trunks, branches and the prop roots. They were observed climbing mangrove trees, usually early in the morning to feed on leaves and by midday they all moved back down, moving up the tree again early in the evening and down again by late evening. An average of 5 crabs was found on a single tree. Young trees (1.5–2 m tall, dbh 2.3–5 cm) of each species (*Laguncularia*, *Avicennia* and *Rhizophora*) were observed from a close distance for about 5 hours and crab feeding activities and presence of crab damage recorded. The percentage of the leaves with damage was used to calculate the damaged leaves per plant,

To evaluate ecosystem structure, its function and organisation, I applied the Ecopath with Ecosim model (www.ecopath.org) to the Cameroon mangrove estuarine system. Selected ecosystem indicators that could be used to monitor ecosystem status or health were analysed using a set of ecosystem goal functions, representative of Odum's attributes of ecosystem maturity [36]. The attributes represent three different aspects of ecosystem development: (1) complexity in community structure, (2) community energetics and, (3) overall community

The steps and governing principles of the general approach of Ecopath and Ecosim have been described in detail in [30, 37], and can be accessed at http://www.ecopath.org. The detail

For this study, the selection of functional groups to represent the Cameroon mangrove food web was a product of a collaborative process. A number of stakeholders and experts (including myself) participated in the discussion to produce functional groups based on the follow-

• There must be some relevant data for those species (although not necessarily for the

In the final iteration, based on these criteria, 26 functional groups were selected for this model (**Table 1**): 13 fishes, 3 kinds of birds (11 species), groupings of 3 crabs, mangroves, phytoplankton, zooplankton, detritus, benthos, shrimps and insects. All the species within a functional group have ecological similarities, defined by similarities in diet, production and consumption rates, life history, and habitat associations, but also sometimes on value-driven criteria, such as commercial status or importance for subsistence users. Because of the nature of the Cameroon mangrove forest, where mangrove wood products are used extensively as source of energy to smoke fish, it is important therefore to consider the mangrove forest as a

modelling approach (Ecopath with Ecosim) can be accessed at [35, 36, 38, 39].

• The species must be representative and abundant

Cameroon mangrove forest).

• The species must be relevant to the overall aims of the study

and these values were averaged for each species within the sample area.

attached string.

58 Mangrove Ecosystem Ecology and Function

homeostasis.

ing criteria:

The input parameters for each group were: the biomass (B), the production/biomass ratio (P/B), the consumption/biomass ratio (Q/B) and ecotrophic efficiency (EE). Input parameters were estimated from the field or extracted from the literature, either from studies done within a similar mangrove ecosystem (in Central Atlantic region) or on the West Africa continental shelf. The diet matrix was constructed by designating the percentage of each prey that occurs in each predator's diet. Diets were derived mostly from the scientific literature, except for crab's groups


**Table 1.** Descriptions of some functional groups of the mangrove ecosystem in Cameroon.


**Prey**

> 23

24 25 26 **Table 2.**

Diet composition.

Detritus

Insects

Benthos

Insectivorous birds

**Predator**

**3** —

—

—

0.2 0.4 0.2 0.1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

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—

—

—

—

0.1 0.3

—

—

0.2 0.3

—

—

0.2

—

—

—

0.2

—

—

—

—

0.1 0.4

—

—

—

0.2

—

—

—

—

—

—

—

—

—

—

0.05 0.9

—

—

0.1 0.1 0.2

—

0.1 0.1 0.4

—

0.1 0.4 0.3 0.1

—

—

—

—

—

—

—

—

—

—

—

0.4 0.05 0.3

—

0.4 0.9

—

—

—

—

—

—

—

—

—

—

—

—

—

**4**

**5**

**6**

**7**

**8**

**9**

**10**

**16 17**

**18**

**23**

**24 25**


**Prey**

> 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Birds of prey

Shorebirds

*Caranx* spp.

*Mugil curema*

*Lutjanus* spp.

*Raja Miraletus*

*Galeoides decadactylus*

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

*Pomadasys jubelini*

*Arius* spp.

*Dreprane africana*

*Brachydeuterus auritus*

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

0.05

—

0.1

—

—

—

—

0.1

—

—

—

—

—

—

—

—

—

0.05

—

—

—

—

—

—

0.1

—

—

—

—

0.1

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

0.1

—

—

—

—

0.1

—

—

—

*Sardinella maderensis*

*Pentanemus quinquarius*

—

—

—

—

—

—

—

0.2 0.1

—

—

—

—

—

—

0.1

0.05

—

—

—

0.1

—

—

—

—

—

—

—

—

—

—

—

—

0.05

—

0.1

—

—

—

—

0.1

—

—

—

*Pseudotolithus* spp.

*Ilisha africana*

Other crabs

Fiddler crabs (*Uca*)

—

—

—

—

—

—

0.05

—

—

0.05

—

—

—

—

—

—

0.1

—

—

—

—

0.1

—

—

—

—

—

0.05

—

—

0.3 0.05

—

—

—

—

—

—

0.1

0.05

—

—

—

0.1

—

—

—

—

—

—

—

—

—

—

—

—

—

0.1

—

0.1 0.05 0.1

—

—

0.1

—

—

—

—

—

—

—

—

—

—

—

—

—

—

0.1

—

0.1 0.05 0.1

—

—

—

—

—

—

—

Mangrove crabs (Sesarmidae)

—

—

—

—

—

—

—

—

—

—

—

0.1

—

0.1 0.05 0.1

—

—

—

—

—

—

—

Shrimps

Zooplankton

Phytoplankton

Mangrove

**Predator**

**3** —

0.8 0.1 0.1

—

—

—

—

0.05

—

—

—

—

—

—

—

—

—

0.1 0.05 0.2

—

—

—

—

0.05

—

—

0.4

—

0.05

—

0.3 0.4 0.1

0.2 0.4 0.3 0.2 0.6

—

—

0.3

—

—

0.4 0.2 0.3 0.2

—

—

0.2 0.05 0.1

—

0.6

—

—

0.05

—

—

60 Mangrove Ecosystem Ecology and Function

—

—

0.8

—

—

—

—

—

0.5

—

0.6 0.5

0.9

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

0.9 0.1

**4**

**5**

**6**

**7**

**8**

**9**

**10**

**16 17**

**18**

**23**

**24 25**

> **Table 2.** Diet composition.

where stomach content analysis was carried out. The degree of confidence, that the parameters are appropriate for the Cameroon is expressed through the data pedigree coding option.

Diet information for crabs was obtained directly from stomach content analysis Literature data were used for all other functional groups (**Table 2**).

#### **2.1. Balancing the model**

After entering all the basic inputs into the Ecopath model, the first step is to check if the outputs are sensible, in other words, whether the biomasses of all groups can be supported by their consumption rates and the productivities of their prey. Detailed on how to balance the model can be accessed at [36, 37] in the Ecopath manual. Once the model was balanced, various ecosystem attributes were evaluated, these attributes include those given in [36, 40], allowing inferences to be drawn about the health of the ecosystem.

regeneration. Significantly more seedlings were observed in canopy gaps compared to closed canopy areas (T = 3.5, P = 0.008). *Rhizophora* seedlings were more abundant in canopy gap than in closed canopy areas (T = 2.4, P = 0.04), whilst *Avicennia* and *Laguncularia* were

) 27.4

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

) 72.3

) 3.1

Human cause (%) 66.3 Non-human cause (%) 33.6

**Average**

63

http://dx.doi.org/10.5772/intechopen.79021

The size-frequency distributions of all mangrove species are represented in **Figure 2**. All three-species showed a higher concentration of stems in small size classes (<25 cm). Compared to *Rhizophora*, *Avicennia* is completely absent from size classes greater than 95 cm,

All mangrove species are used by the villagers for different purposes. The principal uses are sources for fuelwood and poles for construction (**Figure 3**) and the most preferred species are Rhizophora species (*Rhizophora racemosa*, *Rhizophora harrisonii*) and *Avicennia germinans*. They are preferred because of their slow burning properties, resilience and availability. One of the most interesting properties of mangrove wood is that it burns well when fresh, so the process of drying the wood is not necessary. This property contributes to make it a favourable choice of fuel wood. All the tree parts (branches, stem and roots) are used as fuelwood, mostly for fish

Poles for construction are used mostly for building houses, bridges, fences and fish smoking barns (**Table 6**). The preferred species for construction is *Avicennia germinans*; because of it

A total of 1358 crabs were collected over the study period, 770 females (56.7%) and 588 males (43.3%) (**Table 7**) belonging to 13 species. Of the 13 species, 5 belonged to the family Sesarmidae (38.5%), 4 species to the family Grapsidae (30.8%), 2 species to the family Ocypodidae (15.4%) and 1 species to each of the families Portunidae and Gecarcinidae (7.7% each). *Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the two-dominant species, constituting 44.1 and 21.9% respectively of the total sampled crabs. *Uca tangeri* dominated the mudflat in

resilience property and mostly tree stem of different sizes are used.

zone four, whilst *Goniopsis pelii* dominated zone one (disturbed young forest).

**3.5. Distribution, diversity and abundance of mangrove crabs**

not (**Table 5**).

smoking.

*3.3.1. Forest species composition*

Canopy gap density (n/100 m2

Canopy density (n/100 m2

**Table 4.** Canopy gaps.

Gap size (m2

**3.4. Local uses of mangrove wood**

and *Laguncularia* from classes more than >25 cm.

### **3. Results**

#### **3.1. Mangrove use and structural effects of local-level cutting**

A total of 3167 individual trees, 423 stumps and 103 snags were recorded. *Rhizophora* (Red mangrove) was the dominant species (83.6%) followed by *Avicennia* (Black mangrove) at 9.1% and *Laguncularia* (White mangrove) at (7.1%).

#### **3.2. Cameroon mangrove forest structure**

Mangrove forests differed structurally, due to a combination of anthropogenic and natural factors. The mean tree density and seedling density, the mean diameter at breast height (dbh) and basal areas are presented in (**Table 3**).

#### **3.3. Canopy gaps**

A total of 257 gaps were recorded during the study. Human influence was responsible for most of the gaps created (**Table 4**). An average gap size of 3.1 m2 was recorded. The average gap density of 27.4 was recorded overall. The relationship between seedlings and canopy was examined as an alternative way to estimate the effect of exploiting forest on mangrove


**Table 3.** Summary of selected ecological characteristics with mean values and standard deviation (in parentheses).


**Table 4.** Canopy gaps.

where stomach content analysis was carried out. The degree of confidence, that the parameters are appropriate for the Cameroon is expressed through the data pedigree coding option.

Diet information for crabs was obtained directly from stomach content analysis Literature

After entering all the basic inputs into the Ecopath model, the first step is to check if the outputs are sensible, in other words, whether the biomasses of all groups can be supported by their consumption rates and the productivities of their prey. Detailed on how to balance the model can be accessed at [36, 37] in the Ecopath manual. Once the model was balanced, various ecosystem attributes were evaluated, these attributes include those given in [36, 40],

A total of 3167 individual trees, 423 stumps and 103 snags were recorded. *Rhizophora* (Red mangrove) was the dominant species (83.6%) followed by *Avicennia* (Black mangrove) at 9.1%

Mangrove forests differed structurally, due to a combination of anthropogenic and natural factors. The mean tree density and seedling density, the mean diameter at breast height (dbh)

A total of 257 gaps were recorded during the study. Human influence was responsible for

gap density of 27.4 was recorded overall. The relationship between seedlings and canopy was examined as an alternative way to estimate the effect of exploiting forest on mangrove

) 16.0 (20.2)

/ha) 60.1 (29.8)

) 23.5(40.1)

) 0.32 (0.3)

**Table 3.** Summary of selected ecological characteristics with mean values and standard deviation (in parentheses).

**Characteristics Average**

Diameter at breast height (dbh) of stem (cm) 23.8 (19.7)

was recorded. The average

data were used for all other functional groups (**Table 2**).

allowing inferences to be drawn about the health of the ecosystem.

**3.1. Mangrove use and structural effects of local-level cutting**

most of the gaps created (**Table 4**). An average gap size of 3.1 m2

and *Laguncularia* (White mangrove) at (7.1%).

**3.2. Cameroon mangrove forest structure**

and basal areas are presented in (**Table 3**).

**2.1. Balancing the model**

62 Mangrove Ecosystem Ecology and Function

**3. Results**

**3.3. Canopy gaps**

Tree density (n/100 m2

Stem basal area (m2

Seedling density (n/100 m2

Gap size (m2

regeneration. Significantly more seedlings were observed in canopy gaps compared to closed canopy areas (T = 3.5, P = 0.008). *Rhizophora* seedlings were more abundant in canopy gap than in closed canopy areas (T = 2.4, P = 0.04), whilst *Avicennia* and *Laguncularia* were not (**Table 5**).

#### *3.3.1. Forest species composition*

The size-frequency distributions of all mangrove species are represented in **Figure 2**. All three-species showed a higher concentration of stems in small size classes (<25 cm). Compared to *Rhizophora*, *Avicennia* is completely absent from size classes greater than 95 cm, and *Laguncularia* from classes more than >25 cm.

#### **3.4. Local uses of mangrove wood**

All mangrove species are used by the villagers for different purposes. The principal uses are sources for fuelwood and poles for construction (**Figure 3**) and the most preferred species are Rhizophora species (*Rhizophora racemosa*, *Rhizophora harrisonii*) and *Avicennia germinans*. They are preferred because of their slow burning properties, resilience and availability. One of the most interesting properties of mangrove wood is that it burns well when fresh, so the process of drying the wood is not necessary. This property contributes to make it a favourable choice of fuel wood. All the tree parts (branches, stem and roots) are used as fuelwood, mostly for fish smoking.

Poles for construction are used mostly for building houses, bridges, fences and fish smoking barns (**Table 6**). The preferred species for construction is *Avicennia germinans*; because of it resilience property and mostly tree stem of different sizes are used.

#### **3.5. Distribution, diversity and abundance of mangrove crabs**

A total of 1358 crabs were collected over the study period, 770 females (56.7%) and 588 males (43.3%) (**Table 7**) belonging to 13 species. Of the 13 species, 5 belonged to the family Sesarmidae (38.5%), 4 species to the family Grapsidae (30.8%), 2 species to the family Ocypodidae (15.4%) and 1 species to each of the families Portunidae and Gecarcinidae (7.7% each). *Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the two-dominant species, constituting 44.1 and 21.9% respectively of the total sampled crabs. *Uca tangeri* dominated the mudflat in zone four, whilst *Goniopsis pelii* dominated zone one (disturbed young forest).


**Table 5.** Seedling abundance of different mangrove species in open and closed canopies.

**Figure 2.** Size-frequency distribution of (dbh) of *Rhizophora*, *Avicennia* and *Laguncularia* species.

and *Sesarma* species (KS = 1.59, P = 0.013). All three of the most abundant species were better described by a bimodal rather than a unimodal distribution (**Figure 4a–c**). *Goniopsis pelii* shows a bimodal distribution with highest modal size ranging from 2 to 2.25 cm carapace width and a probable second mode at 6 cm, 2–2.3 cm carapace width for *Sesarma* species and *Uca tangeri* shows a bimodal distribution with highest modal sizes ranging from 1.5 to 1.75, 2

Furniture, fencing poles, firewood, construction poles, canoe anchors, poles for building bridges and fish smoking barns, paddles, fishing traps, roof

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65

poles, fencing poles, resting bed, canoe anchors, fishing traps, and paddles

supports, axe handles and resting beds *Rhizophora* Red matanda Firewood, poles for building bridges and fish smoking barns, construction

Firewood, poles for fences and furniture

*Sesarma* (*Perisesarma*) *huzardi* 28 17 45 *Sesarma* (*Chiromantes*) *elegans* 21 9 30 *Sesarma* (*Perisesarma*) *alberti* 17 8 25 *Sesarmine* species 27 22 49

Grapsus grapsus 49 60 109 Pachygrapsus transversus 7 21 28 Pachygrapsus spp. 8 4 12

*Uca tangeri* 322 212 534 Total 770 588 1358

**Family Species Female Male Total** Portunidae *Portunus validus* (*Neptunus alidus*) 2 2 4 Sesarmidae *Metagrapsus curvatus* 24 20 44

Gecarcinidae *Cardisoma* species 39 28 67 Grapsidae *Goniopsis pelii* (*G. cruentata*) 171 167 338

Ocypodidae *Ocypode africana* 50 20 70

*Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the most abundant crabs associated with Cameroon mangroves. Estimating their biomass is essential in order to evaluate their importance to the system. Carapace width and wet weight were therefore determined

**3.6. Relationship between carapace width and wet weight for** *Uca tangeri*

for *Uca tangeri* and *Goniopsis pelii*. The relationships are as follows:

to 2.3, and 2 to 2.25 cm carapace width.

**Table 7.** Number of crabs collected.

**Tree Local names Uses**

matanda

matanda

**Table 6.** Local uses of mangrove trees in the sampled villages.

*Avicennia* Black

*Laguncularia racemosa* White

**(Ocypodidae) and** *Goniopsis pelii* **(Grapsidae)**

**Figure 3.** Different uses of mangrove wood as revealed by local users.

The size range for *Uca tangeri* was 0.1–5.5 cm, *Goniopsis pelii* 0.2–7.8 cm and *Sesarma* species 0.2–5.6 cm carapace width (CW) (**Figure 4a**–**c**). The size frequency distribution differed from normality, for *Goniopsis pelii* (KS = 2.902, P = 0001), *Uca tangeri* (KS = 2.56, P = 0.0001),


**Table 6.** Local uses of mangrove trees in the sampled villages.


**Table 7.** Number of crabs collected.

The size range for *Uca tangeri* was 0.1–5.5 cm, *Goniopsis pelii* 0.2–7.8 cm and *Sesarma* species 0.2–5.6 cm carapace width (CW) (**Figure 4a**–**c**). The size frequency distribution differed from normality, for *Goniopsis pelii* (KS = 2.902, P = 0001), *Uca tangeri* (KS = 2.56, P = 0.0001),

**Species Canopy gap Closed canopy t-values P-values** Rhizophora 863 375 2.4 0.04 *Laguncularia* 220 59 1.2 0.25 *Avicennia* 161 93 1.2 0.16 Total 1244 527 3.5 0.01

**Table 5.** Seedling abundance of different mangrove species in open and closed canopies.

64 Mangrove Ecosystem Ecology and Function

**Figure 2.** Size-frequency distribution of (dbh) of *Rhizophora*, *Avicennia* and *Laguncularia* species.

**Figure 3.** Different uses of mangrove wood as revealed by local users.

and *Sesarma* species (KS = 1.59, P = 0.013). All three of the most abundant species were better described by a bimodal rather than a unimodal distribution (**Figure 4a–c**). *Goniopsis pelii* shows a bimodal distribution with highest modal size ranging from 2 to 2.25 cm carapace width and a probable second mode at 6 cm, 2–2.3 cm carapace width for *Sesarma* species and *Uca tangeri* shows a bimodal distribution with highest modal sizes ranging from 1.5 to 1.75, 2 to 2.3, and 2 to 2.25 cm carapace width.

#### **3.6. Relationship between carapace width and wet weight for** *Uca tangeri* **(Ocypodidae) and** *Goniopsis pelii* **(Grapsidae)**

*Uca tangeri* (Ocypodidae) and *Goniopsis pelii* (Grapsidae) were the most abundant crabs associated with Cameroon mangroves. Estimating their biomass is essential in order to evaluate their importance to the system. Carapace width and wet weight were therefore determined for *Uca tangeri* and *Goniopsis pelii*. The relationships are as follows:

*Goniopsis pelii* WW biomass = 1.2588 (CW) 1.9095 (R2 = 0.58) and *Uca tangeri* WW biomass = 1.1209(CW) 2.0917 (R2 = 0.6619) (**Figure 5**).

#### **3.7. Ecological effect of mangrove crab herbivore feeding preferences**

Propagule predation by crabs occurred in all of the mangrove species ranging from 61.6 to 69.1% (**Table 8**). The effect of crab predation on propagules did not differ among mangrove species. The majority of propagules were found to be non-viable after predation and some were lost by being washed away by high tide (**Figure 6**). There was a significant difference between the number of non-viable and viable propagule (T = 2.13, df = 4, P = 0.002) with majority being non-viable. Some propagules were predated by gastropods, but the extent of this was minimal.

The percentage of leaves consumed by crabs varied among mangrove species (**Figure 6a**). *Rhizophora* species was the most consumed and *Avicennia* was the least, although this was not significant between species (ANOVA, F = 2.3, P = 0.24). Senescent leaves were preferred more than fresh leaves for all species (**Figure 7a**), and there was a significant difference in the percentage consumed of fresh and senescent leaves (T = 4.3, df = 2, P = 0.02). The majority of leaves

were taken into burrows (**Figure 7b** and **Table 9**), and they had been substantially grazed when recovered from those burrows. There was no leaf breakage during removal from the burrows.

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The structure and network analysis parameter estimates for the model are shown in **Table 10**. These parameters include trophic estimates, biomass estimates, production/biomass estimates, consumption/biomass estimates, production/consumption ratios, gross efficiency estimates and omnivory index estimates. The Cameroon mangrove food web (as depicted here) consists of 3 trophic levels and 17 sublevels, which range from 1.0 to 3.74. The trophic level (TL) is an important index because it identifies an organism's food preferences. The highest values correspond to insectivorous birds, followed by the fish *Pentanemus quinquarius* and *Pseudotolithus* spp., whilst the lowest values correspond to the primary producer; mangrove, phytoplankton and detritus.

**3.8. Mangrove community function in terms of trophic linkages**

**Figure 5.** Relationship between carapace width and weight for (a) *Uca tangeri* (b) *Goniopsis pelii*.

**Species Average (%)**

*Rhizophora racemosa* 69.8 *Rhizophora mangle* 66.3 *Rhizophora harrisonii* 61.6

**Table 8.** Summary of the percentage of propagules predated by crabs.

**Figure 4.** (a) Size (carapace width) frequency distribution of *Goniopsis pelii*, all zones combined. (b) Size (carapace width) frequency distribution of *Uca tangeri*, all zones combined. (c) Size (carapace width) frequency distribution of *Sesarma* species, all zones combined.

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions http://dx.doi.org/10.5772/intechopen.79021 67

**Figure 5.** Relationship between carapace width and weight for (a) *Uca tangeri* (b) *Goniopsis pelii*.


**Table 8.** Summary of the percentage of propagules predated by crabs.

*Goniopsis pelii* WW biomass = 1.2588 (CW) 1.9095 (R2 = 0.58) and *Uca tangeri* WW bio-

Propagule predation by crabs occurred in all of the mangrove species ranging from 61.6 to 69.1% (**Table 8**). The effect of crab predation on propagules did not differ among mangrove species. The majority of propagules were found to be non-viable after predation and some were lost by being washed away by high tide (**Figure 6**). There was a significant difference between the number of non-viable and viable propagule (T = 2.13, df = 4, P = 0.002) with majority being non-viable. Some propagules were predated by gastropods, but the extent of

The percentage of leaves consumed by crabs varied among mangrove species (**Figure 6a**). *Rhizophora* species was the most consumed and *Avicennia* was the least, although this was not significant between species (ANOVA, F = 2.3, P = 0.24). Senescent leaves were preferred more than fresh leaves for all species (**Figure 7a**), and there was a significant difference in the percentage consumed of fresh and senescent leaves (T = 4.3, df = 2, P = 0.02). The majority of leaves

**Figure 4.** (a) Size (carapace width) frequency distribution of *Goniopsis pelii*, all zones combined. (b) Size (carapace width) frequency distribution of *Uca tangeri*, all zones combined. (c) Size (carapace width) frequency distribution of *Sesarma*

**3.7. Ecological effect of mangrove crab herbivore feeding preferences**

mass = 1.1209(CW) 2.0917 (R2 = 0.6619) (**Figure 5**).

66 Mangrove Ecosystem Ecology and Function

this was minimal.

species, all zones combined.

were taken into burrows (**Figure 7b** and **Table 9**), and they had been substantially grazed when recovered from those burrows. There was no leaf breakage during removal from the burrows.

#### **3.8. Mangrove community function in terms of trophic linkages**

The structure and network analysis parameter estimates for the model are shown in **Table 10**. These parameters include trophic estimates, biomass estimates, production/biomass estimates, consumption/biomass estimates, production/consumption ratios, gross efficiency estimates and omnivory index estimates. The Cameroon mangrove food web (as depicted here) consists of 3 trophic levels and 17 sublevels, which range from 1.0 to 3.74. The trophic level (TL) is an important index because it identifies an organism's food preferences. The highest values correspond to insectivorous birds, followed by the fish *Pentanemus quinquarius* and *Pseudotolithus* spp., whilst the lowest values correspond to the primary producer; mangrove, phytoplankton and detritus.

**Habitat TL Area (km2 )**

5 Mangrove crabs (*Sesarmidae*)

10 *Pentanemus quinquarius*

11 *Sardinella maderensis*

16 *Galeoides decadactylus*

**TL**: trophic level; **B**: biomass (t/km2

*auritus*

12 *Brachydeuterus* 

**Biomass (t/km2**

1 Mangrove **1.00** 1.000 60.870 15.000 — **0.564 — —** 2 Phytoplankton **1.00** 1.000 34.400 180.000 — **0.712 0.313 —** 3 Zooplankton **2.00** 1.000 27.130 15.000 160.000 **0.129 0.280 —** 4 Shrimps **2.50** 1.000 0.417 5.380 19.200 0.950 **0.161 0.250**

6 Fiddler crabs (*Uca*) **2.41** 1.000 1.300 5.500 95.000 **0.319 0.091 0.452** 7 Other crabs **2.00** 1.000 2.500 2.000 22.000 **0.456 0.550 —** 8 *Ilisha africana* **2.50** 1.000 1.993 3.006 55.000 0.950 **0.101 0.250** 9 *Pseudotolithus* spp. **3.22** 1.000 1.780 0.648 6.400 0.950 **0.179 0.159**

13 *Dreprane africana* **2.70** 1.000 1.396 0.820 8.100 **0.134 0.187 0.210** 14 *Arius* spp. **2.65** 1.000 2.570 1.140 6.100 **0.440 0.187 0.303** 15 *Pomadasys jubelini* **2.80** 1.000 0.289 0.731 7.700 **0.760 0.095 0.160**

17 *Raja Miraletus* **3.33** 1.000 1.645 0.560 6.900 **0.008 0.081 0.146** 18 *Lutjanus* spp. **3.14** 1.000 2.017 0.770 4.300 **0.010 0.179 0.102** 19 *Mugil curema* **2.00** 1.000 1.858 1.367 21.800 **0.350 0.063 —** 20 *Caranx* spp. **2.80** 1.000 0.415 0.655 24.300 **0.083 0.027 0.160** 21 Shorebirds **3.00** 1.000 0.021 0.160 65.000 **0.000 0.002 —** 22 Insectivorous birds **3.74** 1.000 0.150 0.100 10.000 **0.000 0.010 0.167** 23 Birds of prey **3.03** 1.000 0.022 12.000 60.000 **0.000 0.200 0.012** 24 Benthos **2.00** 1.000 12.000 15.000 80.000 **0.571 0.188 —** 25 Insects **2.00** 1.000 20.600 12.000 30.000 **0.054 0.400 —** 26 Detritus **1.00** 1.000 10,000,000 — — **0.308 — 0.274**

ecotrophic efficiency; **P/Q** annual production/consumption ratio; **OI**: omnivory index

**Table 10.** Basic input and model estimated output **(bold)** of the Cameroon mangrove estuary.

**2.10** 1.000 2.400 2.250 14.000 **0.422 0.058 0.090**

**3.29** 1.000 0.294 1.775 9.900 0.950 **0.030 0.151**

**2.40** 1.000 1.015 1.260 42.200 0.950 **0.016 0.290**

**2.50** 1.000 1.615 1.026 63.000 **0.780 0.101 0.250**

**2.99** 1.000 0.869 0.828 9.700 **0.223 0.085 0.284**

); **P/B**: annual production/biomass ratio; **Q/B**: annual consumption/biomass ratio; **EE**:

**) P/B Q/B EE P/Q OI**

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69

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

**Figure 6.** Number of propagules per plot killed by crabs, lost or still viable after predation.

**Figure 7.** (a) Percentage of leaf material consumed by crabs for each mangrove species. LF = Laguncularia fresh, LS = Laguncularia senescent, AF = Avicennia fresh, AS = Avicennia senescent, RF = Rhizophora fresh, RS = Rhizophora senescent. (b) Number of leaves taken down crab burrows.


**Table 9.** Total number of leaves taken down crab burrows for each species and leaf status.

Summary statistics and basic flows and indices are shown in **Table 11**. The complexity in community structure is measured by the omnivory index (OI) [38]. The OI value for this study is 0.143 which is quite low when compared with Vega-Cendejas and Arreguín-Sánchez


**TL**: trophic level; **B**: biomass (t/km2 ); **P/B**: annual production/biomass ratio; **Q/B**: annual consumption/biomass ratio; **EE**: ecotrophic efficiency; **P/Q** annual production/consumption ratio; **OI**: omnivory index

**Table 10.** Basic input and model estimated output **(bold)** of the Cameroon mangrove estuary.

Summary statistics and basic flows and indices are shown in **Table 11**. The complexity in community structure is measured by the omnivory index (OI) [38]. The OI value for this study is 0.143 which is quite low when compared with Vega-Cendejas and Arreguín-Sánchez

**Figure 7.** (a) Percentage of leaf material consumed by crabs for each mangrove species. LF = Laguncularia fresh, LS = Laguncularia senescent, AF = Avicennia fresh, AS = Avicennia senescent, RF = Rhizophora fresh, RS = Rhizophora

**Figure 6.** Number of propagules per plot killed by crabs, lost or still viable after predation.

**Species Leaf status n Number taken down burrows**

Senescent 10 5

Senescent 10 5

Senescent 10 7

**Table 9.** Total number of leaves taken down crab burrows for each species and leaf status.

senescent. (b) Number of leaves taken down crab burrows.

68 Mangrove Ecosystem Ecology and Function

*Laguncularia* Fresh 10 7

*Avicennia* Fresh 10 6

*Rhizophora* Fresh 10 8

Total 60 38


According to Christensen et al. [42], food web structure changes from linear to web like as the system mature. Hence, CI is correlated with maturity [42]. The Cameroon mangrove CI is 0.174 which is close to the value 0.191 reported by Villanueva et al. [43] for Ebere lagoon in Ivory Coast and lower than 0.3 reported by Vega-Cendejas and Arreguín-Sánchez [41] for

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

The total system throughput (T) is the size of the entire system in terms of flow [42, 44]. A high T value means the system is capable of growth, suggesting the system is full of energy

compared to 3049 reported for Golfo de Nicoya (Costa Rica), 6240 reported for Ebere logoon

Total system primary production and total respiration ratio (PP/R) shows the balance between production and consumption. When the PP/R ratio is close to 1, this indicates a mature ecosystem [40, 43]. When the PP/R ratio is greater than 1, production exceeds respiration and indicates the system is in an earlier development stages. When PP/R is less than 1, this indicates the system is accumulating a lot of organic matter. The Cameroon mangrove PP/R value

The transfer efficiency for the Cameroon mangrove system is 6.4%, which is low compared to 9.8% reported for Yacatan Peninsula (Mexico) and 14.9% reported for Golfo de Nicoya (Costa Rica) [41, 45], meaning that the system is relative inefficient to recover after disturbance. The model estimate of primary production/biomass of 38.6 compared to 23.9 reported by Walters et al. [45] for Craeté mangrove estuary (Brazil), the system was reported to be relatively mature, hence this indicates that the Cameroon system is mature and may therefore

Flow indicators related to "overall community homeostasis", which describes the size and the degree of organisation with which the material is being processed within the system, is within the range of most mangrove or estuary ecosystems. These are closely linked to ecosystem efficiency, maturity and development [44]. These indicators include ascendancy (9929.25) and

Energy use and matter recycling in the system are important processes in ecosystem functioning [40] and are measured as Finn's cycling index (FCI) and Finn's mean pathway. The model estimated value for FCI is 2 which are relatively low compared to 5.5 for Golfo de Nicoya (Costa Rica) and Finn's mean pathway of 1.717 estimated by the model is also relatively low compared to 3.4 and 4.4 reported for Craeté mangrove estuary (Brazil) and Yacatan Peninsula

Few studies have examined the ecological impacts of small-scale exploitation of mangrove with the aim of assessing ecological and environmental dimensions. Small-scale cutting of mangrove in the Caribbean reduces the abundance of large trees, but greatly increase the density of smaller trees [47]. Cutting of mangroves in the Philippines resulted in stunted and shrubby tree growth [46], but other studies have shown otherwise. For instance, Nurkin [48]

·year, relatively high

71

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and resilience. The Cameroon mangrove system T value is 18,615 t/km2

is 1.865, low when compared with other values from tropical ecosystems.

(Mexico). This indicates that the Cameroon system is immature.

(Ivory Coast) and 10,558 reported for Craeté mangrove estuary (Brazil) [45, 46].

Yucantan Peninsula in Mexico.

be relatively stable.

**4. Discussion**

relative ascendancy (0.250).

**Table 11.** Summary statistics and basic flows and indices.

[41] who estimated OI of 2 for the Yucantan Peninsula in Mexico. The low OI value may be due to some groups being highly specialised and environmental conditions might alter the availability of prey.

#### *3.8.1. Community energetics*

Attributes of ecosystem maturity and stability include connectivity index (CI), total system throughput (T), system total primary production/total respiration ratio (PP/R), primary production/biomass ratio (PP/B), and biomass over throughput (B/T). The connective index (CI) is the number of actual links to the number of possible links for a given food web [38]. According to Christensen et al. [42], food web structure changes from linear to web like as the system mature. Hence, CI is correlated with maturity [42]. The Cameroon mangrove CI is 0.174 which is close to the value 0.191 reported by Villanueva et al. [43] for Ebere lagoon in Ivory Coast and lower than 0.3 reported by Vega-Cendejas and Arreguín-Sánchez [41] for Yucantan Peninsula in Mexico.

The total system throughput (T) is the size of the entire system in terms of flow [42, 44]. A high T value means the system is capable of growth, suggesting the system is full of energy and resilience. The Cameroon mangrove system T value is 18,615 t/km2 ·year, relatively high compared to 3049 reported for Golfo de Nicoya (Costa Rica), 6240 reported for Ebere logoon (Ivory Coast) and 10,558 reported for Craeté mangrove estuary (Brazil) [45, 46].

Total system primary production and total respiration ratio (PP/R) shows the balance between production and consumption. When the PP/R ratio is close to 1, this indicates a mature ecosystem [40, 43]. When the PP/R ratio is greater than 1, production exceeds respiration and indicates the system is in an earlier development stages. When PP/R is less than 1, this indicates the system is accumulating a lot of organic matter. The Cameroon mangrove PP/R value is 1.865, low when compared with other values from tropical ecosystems.

The transfer efficiency for the Cameroon mangrove system is 6.4%, which is low compared to 9.8% reported for Yacatan Peninsula (Mexico) and 14.9% reported for Golfo de Nicoya (Costa Rica) [41, 45], meaning that the system is relative inefficient to recover after disturbance. The model estimate of primary production/biomass of 38.6 compared to 23.9 reported by Walters et al. [45] for Craeté mangrove estuary (Brazil), the system was reported to be relatively mature, hence this indicates that the Cameroon system is mature and may therefore be relatively stable.

Flow indicators related to "overall community homeostasis", which describes the size and the degree of organisation with which the material is being processed within the system, is within the range of most mangrove or estuary ecosystems. These are closely linked to ecosystem efficiency, maturity and development [44]. These indicators include ascendancy (9929.25) and relative ascendancy (0.250).

Energy use and matter recycling in the system are important processes in ecosystem functioning [40] and are measured as Finn's cycling index (FCI) and Finn's mean pathway. The model estimated value for FCI is 2 which are relatively low compared to 5.5 for Golfo de Nicoya (Costa Rica) and Finn's mean pathway of 1.717 estimated by the model is also relatively low compared to 3.4 and 4.4 reported for Craeté mangrove estuary (Brazil) and Yacatan Peninsula (Mexico). This indicates that the Cameroon system is immature.

### **4. Discussion**

[41] who estimated OI of 2 for the Yucantan Peninsula in Mexico. The low OI value may be due to some groups being highly specialised and environmental conditions might alter the

**Parameter Value Unit** Sum of all consumption 6723.632 t/km2

70 Mangrove Ecosystem Ecology and Function

Sum of all exports 3305.708 t/km2

Sum of all respiratory flows 3810.424 t/km2

Sum of all flows to detritus 4775.025 t/km2

Total system throughput 18,615 t/km2

Sum of all production 893 t/km2

Total net primary production 7105.1 t/km2

Total primary production/total respiration 1.865 t/km2

Net system production 3294.4 t/km2

Total primary production/total biomass 38.6 t/km2

Total biomass/throughput 0.01 t/km2

Total biomass (excluding detritus) 184.2 t/km2

Connectance index 0.3 t/km2

System omnivory index 0.143 t/km2

Zooplankton 2050.348 t/km2

Phytoplankton 1785.893 t/km2

Mangrove 397.640 t/km2

Insect 357.515 t/km2

Ascendancy (flow bits) 9929.2 Relative ascendancy 0.25 Overhead (flow bits) 19117.1 Overhead (%) 48 Capacity (flow bits) 39661.3 Transfer efficiencies 6.3 Finn's cycling index (FCI %) 2 Finn's mean path length 1.717

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

·year

Attributes of ecosystem maturity and stability include connectivity index (CI), total system throughput (T), system total primary production/total respiration ratio (PP/R), primary production/biomass ratio (PP/B), and biomass over throughput (B/T). The connective index (CI) is the number of actual links to the number of possible links for a given food web [38].

availability of prey.

Flow to detritus

*3.8.1. Community energetics*

**Table 11.** Summary statistics and basic flows and indices.

Few studies have examined the ecological impacts of small-scale exploitation of mangrove with the aim of assessing ecological and environmental dimensions. Small-scale cutting of mangrove in the Caribbean reduces the abundance of large trees, but greatly increase the density of smaller trees [47]. Cutting of mangroves in the Philippines resulted in stunted and shrubby tree growth [46], but other studies have shown otherwise. For instance, Nurkin [48] suggests that small-scale mangrove exploitation has an insignificant effect on mangrove forest structure. In the present study, the impact of small-scale mangrove wood exploitation created large forest gaps.

The mangrove forest habitat is unique and rich in crab species. Thirty-nine crab species have been recorded in West and Central Africa mangroves [55]. In this study 13 species were identified belonging to two dominant groups, grapsid and fiddler crabs. All the species in the present study are found in mangroves elsewhere in the Central African region and common genera such as *Uca* and *Sesarma* tend to occur in mangrove habitats worldwide. The distinctness of the Central African mangrove fauna lies in the relative importance of particular families. For example, four to six species of *Uca* are found in all other mangrove regions, but only one species, the widespread *Uca tangeri*, has been reported in Central African mangroves [56]. Environmental factors such as vegetation, substratum, salinity and tidal exposure have been reported to influence the distribution of mangrove crabs [14, 57], with vegetation playing an important role. Environmental conditions were not formally measured in the present study, but the distribution of crab species did differ in the study area. The size frequency distribution of the major species in this study seems bimodal, skewed to the right. Similar distributions have been reported from Mozambique [58] and South American mangrove areas [27]. This

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distribution suggests that the crab populations recorded here have good recruitment.

for the large number of leaves dragged into burrows (as well as avoiding predation).

The ecopath model analysis allowed a reasonable model representation of a Cameroon mangrove system. Model viability was determined by using the sensitive analysis function i.e. pedigree index [42]. The sensitivity analysis suggests that parameterisation of groups within the model is most sensitive to decreases in biomass estimates and that the impact of changes in the parameters of one group on another is influenced by the trophic dependency of the impacting group on the impacted group. The impacts of an increase in biomass in one group

and win more intra-specific fights [60].

According to Mantelatto et al. [59], sexual dimorphism is a result of females being smaller having reduced somatic growth compared to males, because they devote more energy to gonad development. Also larger male crabs are more successful in copulating with females,

Grapsid and sesarmid crabs are clearly predators of mangrove propagules. *Sesarma* and *Metapograpsus* spp. have been reported predating *Rhizophoraceae* and *Avicennia* propagules [22, 62]. In the present study, 66.7% of the propagules were predated leaving 50% non-viable. This high predation pressure could affect natural restoration of mangrove forest in Cameroon. Seedling establishment (i.e. type of planting strategy, horizontal or vertical) may also influence predation rate. In the present study, horizontally planted propagules were predated more heavily. This might be because the crabs face difficulties handling vertical propagule due to their size and weight. Although seedling establishment type and tides might influence recruitment, selectivity of crabs might also alter natural restoration of mangrove seedlings in a species-specific way [10]. In the present study, propagule predation did not differ significantly between crab species, but the dominant species foraging on plant material was *Goniopsis pelii.* In the present study, the average percentage of the leaves consumed was high (71.3%), and similarly high leaf consumption rates have been reported in Australia [23, 61]. The "swept" appearance of the forest floor observed during this study might be as a result of a combination of tidal inundation and high crab activity in the region, and any addition of leaves for crabs (as done here) will be consumed rapidly. Removal of leaves by tide action may be the reason

Not surprisingly, the canopy gaps created by trees cut were relatively small, the largest gap size measured for this study was 72.2 m2 , but the mean gap size was much smaller at 0.32 m2 , relatively small when compared to findings from other mangrove studies. For example, Ewel et al. [49] recorded a mean gap size of 158 m2 for mangrove in Kosrae Micronesia, though the author deliberately ignored gap sizes less than 10 m2 . Smith et al. [19] observed gap sizes of mature mangrove forest in Australia of 40–120 m2 , but it is possible that he overlooked gaps of less than 10 m2 . By contrast, Walter [7] found a smaller mean gap size on 2.6 m2 for Philippines mangroves and studies of other forest types have shown that such small canopy gaps have an important effect on the forest structure [50, 51].

Exploitation of mangrove wood product was not completely species selective in this study, but *Rhizophora* was the preferred species for fuelwood and for poles for construction. There is evidence that wood exploitation might have changed *Rhizophora* stem size distribution.

Mangroves are thought to recover quickly after disturbance [47], but the evidence is mixed. Thus, Ewel et al. [49] found no differences in gap regeneration as a result of selective logging in Kosrae. Clarke and Kerrigan [25] found that canopy gap had a strong influence on the abundance of mangrove seedlings, and the most sensitive species was *Rhizophora*, which shows a significant difference in gap regeneration. Smith [52] observed significant recruitment of *Rhizophora* species in gaps [53]. According to Feller and Mckee [50] gap size does not influence *Rhizophora* regeneration.

According to Smith [52] mangrove seedlings regenerate quickly in large numbers in the canopy opening. In the present study, the relatively low seedling density coupled with the small canopy size might suggest that the Cameroon mangrove canopy is relatively closed. This is supported by large canopy density and may imply that the Cameroon mangrove forest structure is relatively healthy.

This study suggests that mangrove resources play an important role in the economic and social life of most local communities within the mangrove area, resulting to significant level of dependency of the local communities on the mangrove resources. The framework of dependence include: pole for building houses, fuelwood for smoking fish, timber building of band, resting beds, bridges, anchor for canoe, pole for fish trap and fences. Among the fabric of uses, the most significant use was fuelwood for fish smoking. The use of mangrove wood as fuelwood mostly for charcoal and cooking has also been reported in Kenya, Vietnam and Malaysia as well [54]. The peculiarity in this study is that fuelwood is used predominantly used for smoking fish and this process is an important economic activity in the area.

In the present study, local mangrove wood exploitation is an important form of ecological disturbance and a potential threat to forest health. Although forest alteration is not dramatic, impacts on species composition and regeneration are apparent. Whilst dramatic changes in mangrove forest species composition and ecosystem health have been seen in many places, due to anthropogenic influences, hence, small-scale exploitation like that seen here, might contribute significantly to long-term environmental problems if not properly managed.

The mangrove forest habitat is unique and rich in crab species. Thirty-nine crab species have been recorded in West and Central Africa mangroves [55]. In this study 13 species were identified belonging to two dominant groups, grapsid and fiddler crabs. All the species in the present study are found in mangroves elsewhere in the Central African region and common genera such as *Uca* and *Sesarma* tend to occur in mangrove habitats worldwide. The distinctness of the Central African mangrove fauna lies in the relative importance of particular families. For example, four to six species of *Uca* are found in all other mangrove regions, but only one species, the widespread *Uca tangeri*, has been reported in Central African mangroves [56].

suggests that small-scale mangrove exploitation has an insignificant effect on mangrove forest structure. In the present study, the impact of small-scale mangrove wood exploitation created

Not surprisingly, the canopy gaps created by trees cut were relatively small, the largest gap

relatively small when compared to findings from other mangrove studies. For example, Ewel

. By contrast, Walter [7] found a smaller mean gap size on 2.6 m2

mangroves and studies of other forest types have shown that such small canopy gaps have an

Exploitation of mangrove wood product was not completely species selective in this study, but *Rhizophora* was the preferred species for fuelwood and for poles for construction. There is evidence that wood exploitation might have changed *Rhizophora* stem size distribution.

Mangroves are thought to recover quickly after disturbance [47], but the evidence is mixed. Thus, Ewel et al. [49] found no differences in gap regeneration as a result of selective logging in Kosrae. Clarke and Kerrigan [25] found that canopy gap had a strong influence on the abundance of mangrove seedlings, and the most sensitive species was *Rhizophora*, which shows a significant difference in gap regeneration. Smith [52] observed significant recruitment of *Rhizophora* species in gaps [53]. According to Feller and Mckee [50] gap size does not

According to Smith [52] mangrove seedlings regenerate quickly in large numbers in the canopy opening. In the present study, the relatively low seedling density coupled with the small canopy size might suggest that the Cameroon mangrove canopy is relatively closed. This is supported by large canopy density and may imply that the Cameroon mangrove forest

This study suggests that mangrove resources play an important role in the economic and social life of most local communities within the mangrove area, resulting to significant level of dependency of the local communities on the mangrove resources. The framework of dependence include: pole for building houses, fuelwood for smoking fish, timber building of band, resting beds, bridges, anchor for canoe, pole for fish trap and fences. Among the fabric of uses, the most significant use was fuelwood for fish smoking. The use of mangrove wood as fuelwood mostly for charcoal and cooking has also been reported in Kenya, Vietnam and Malaysia as well [54]. The peculiarity in this study is that fuelwood is used predominantly

used for smoking fish and this process is an important economic activity in the area.

In the present study, local mangrove wood exploitation is an important form of ecological disturbance and a potential threat to forest health. Although forest alteration is not dramatic, impacts on species composition and regeneration are apparent. Whilst dramatic changes in mangrove forest species composition and ecosystem health have been seen in many places, due to anthropogenic influences, hence, small-scale exploitation like that seen here, might contribute significantly to long-term environmental problems if not properly managed.

, but the mean gap size was much smaller at 0.32 m2

for mangrove in Kosrae Micronesia, though the

. Smith et al. [19] observed gap sizes of

, but it is possible that he overlooked gaps of

,

for Philippines

large forest gaps.

72 Mangrove Ecosystem Ecology and Function

less than 10 m2

size measured for this study was 72.2 m2

et al. [49] recorded a mean gap size of 158 m2

author deliberately ignored gap sizes less than 10 m2

mature mangrove forest in Australia of 40–120 m2

important effect on the forest structure [50, 51].

influence *Rhizophora* regeneration.

structure is relatively healthy.

Environmental factors such as vegetation, substratum, salinity and tidal exposure have been reported to influence the distribution of mangrove crabs [14, 57], with vegetation playing an important role. Environmental conditions were not formally measured in the present study, but the distribution of crab species did differ in the study area. The size frequency distribution of the major species in this study seems bimodal, skewed to the right. Similar distributions have been reported from Mozambique [58] and South American mangrove areas [27]. This distribution suggests that the crab populations recorded here have good recruitment.

According to Mantelatto et al. [59], sexual dimorphism is a result of females being smaller having reduced somatic growth compared to males, because they devote more energy to gonad development. Also larger male crabs are more successful in copulating with females, and win more intra-specific fights [60].

Grapsid and sesarmid crabs are clearly predators of mangrove propagules. *Sesarma* and *Metapograpsus* spp. have been reported predating *Rhizophoraceae* and *Avicennia* propagules [22, 62]. In the present study, 66.7% of the propagules were predated leaving 50% non-viable. This high predation pressure could affect natural restoration of mangrove forest in Cameroon.

Seedling establishment (i.e. type of planting strategy, horizontal or vertical) may also influence predation rate. In the present study, horizontally planted propagules were predated more heavily. This might be because the crabs face difficulties handling vertical propagule due to their size and weight. Although seedling establishment type and tides might influence recruitment, selectivity of crabs might also alter natural restoration of mangrove seedlings in a species-specific way [10]. In the present study, propagule predation did not differ significantly between crab species, but the dominant species foraging on plant material was *Goniopsis pelii.*

In the present study, the average percentage of the leaves consumed was high (71.3%), and similarly high leaf consumption rates have been reported in Australia [23, 61]. The "swept" appearance of the forest floor observed during this study might be as a result of a combination of tidal inundation and high crab activity in the region, and any addition of leaves for crabs (as done here) will be consumed rapidly. Removal of leaves by tide action may be the reason for the large number of leaves dragged into burrows (as well as avoiding predation).

The ecopath model analysis allowed a reasonable model representation of a Cameroon mangrove system. Model viability was determined by using the sensitive analysis function i.e. pedigree index [42]. The sensitivity analysis suggests that parameterisation of groups within the model is most sensitive to decreases in biomass estimates and that the impact of changes in the parameters of one group on another is influenced by the trophic dependency of the impacting group on the impacted group. The impacts of an increase in biomass in one group on other groups within the systems can be shown using a mixed trophic impact plot. This can be used to get an overall indication of the sensitivities and responses to reduced biomass in one group on another and dependent upon them.

**Author details**

**References**

1986

Ngomba Longonje Simon

Address all correspondence to: nlongonje@yahoo.com

Society for Mangrove Ecosystem; 1997

in Marine Biology. 2001;**40**:81-251

Tropical Ecology. 1992;**8**:129-152

Freshwater Research. 1998;**49**:335-343

Crustaceana. 1980;**39**:157-183

(H. Milne Edwards). Hydrobiologia. 2001;**449**:201-212

East Africa. Wetlands Ecology and Management. 2002;**10**:203-213

roon. Marine Geology. 2004;**208**:315-330

Ecology and Management. 2005;**206**:331-348

Department of Environmental Science, Faculty of Science, University of Buea, Cameroon

Cameroon Mangrove Forest Ecosystem: Ecological and Environmental Dimensions

http://dx.doi.org/10.5772/intechopen.79021

75

[1] FAO (Food and Agricultural Organisation). Report on the mangrove area extent and changes worldwide were launched at Ramsar COP9; Kampala, Uganda; 2005

[2] Tomlinson PB. The Botany of Mangroves. Cambridge, UK: Cambridge University Press;

[3] Spalding M, Blasco F, Field C. World Mangrove Atlas. Okinawa, Japan: The International

[5] Kathiresan K, Bingham BL. Biology of mangroves and mangrove ecosystem. Advances

[6] Van Campo E, Bengo MD. Mangrove palynology in recent marine sediments off Came-

[7] Walter BB. Ecological effect of small scale-cutting of Philippine mangrove forests. Forest

[8] Smiet AC. Forest ecology on Java: Human impact and vegetation on Montane Forest.

[9] Kappelle M, Geuze T, Leal ME, Cleef AM. Successional age and forest in a Costa Rican

[10] Lee SY. Ecological role of grapsid crabs in mangrove ecosystems: A review. Marine and

[11] Skov MW, Hartnoll RG. Comparative suitability of binocular observation, burrow counting and excavation for the quantification of the mangrove fiddler crab *Uca annulipes*

[12] Hartnoll RG, Cannicci S, Emmerson WD, Fratini S, Macia A, Mgaya Y, Porri F, Ruwa RK, Shunnula JP, Skov MW, Vannini M. Geographic trends in mangrove crab abundance in

[13] Frith DW, Brunenmeister S. Ecological and population studies of fiddler crabs (Ocypodidae, genus *Uca*) on a mangrove shore at Phuket Island, Western Peninsular Thailand.

upper montane Quercus forest. Journal of Tropical Ecology. 1996;**12**:681-698

[4] Hogarth JP. The Biology of Mangroves. Oxford, UK: Oxford University Press; 1999

The viability value of 0.52 estimated by the model is an indication that the model was tightly fitted, as the simulation values have remarkably little difference from the original input. The balanced model parameter estimates indicate a mixture of a mature and immature system. The mature indices include: total system throughput (T) that is the sum of all flows (consumption, respiration, export and flow into detritus) is 18,615 t/km2 ·year, appears to be high when compared to other values from tropical coastal system. The system primary production/respiration (PP/R) ratio estimated by the model is 1.87 indicating that the system is relatively developed [38].The high ascendancy value of 9929.2 and relative ascendancy of 0.250 indicate that the system is mature. However, the relative ascendancy of 0.250 reported by Vega-Cendejas and Arreguín-Sánchez [41] for Yucatan Peninsula (Mexico) was considered high by the author. The total system biomass value is 184.193 t/km2 ·year which appears high fits well within the range of other tropical systems [38].

The model results show that more than 98.6% of the flows to detritus is from TL 1 and 2, these levels playing a significant role in supporting the energy utilised by higher TL groups, and indicate a detritus-based food web and bottom-top control system, which is typical of a mature system.

System energy and matter recycling is an important process in ecosystem functioning [40], and the model low estimate of Finn's cycling index (FCI) and Finn's mean pathway of 1.983 and 1.717, respectively, is indicative of an immature system.

### **5. Conclusion**

In the present study, has shown that local mangrove wood exploitation is an important form of ecological disturbance and a potential threat to forest health. Although forest alteration is not dramatic, impacts on species composition and regeneration are apparent. Whilst dramatic changes in mangrove forest species composition and ecosystem health have been seen in many places, due to anthropogenic influences, hence, small-scale exploitation like that seen here, might contribute significantly to long-term environmental problems if not properly managed. Furthermore, it revealed that Cameroon grapsid and sesarmid crabs consumed large amounts of mangrove plant material, both leaves and propagules, and this may have significant ecological consequences for ecosystem structure and function.

The above system parameters provide a mixed picture of the maturity stage of the Cameroon mangrove ecosystem. Some indicate the system is immature and others that it is mature. It could be concluded that the overall health of the system is sustainable.

Nevertheless, to establish a truly holistic, ecosystem-based approach to the management of the Cameroon mangrove forest, social and economic indicators need to be included and local users, the beneficiaries of the services delivered by the forest, need be included at all stages in the management process and this process need more research.

### **Author details**

on other groups within the systems can be shown using a mixed trophic impact plot. This can be used to get an overall indication of the sensitivities and responses to reduced biomass in

The viability value of 0.52 estimated by the model is an indication that the model was tightly fitted, as the simulation values have remarkably little difference from the original input. The balanced model parameter estimates indicate a mixture of a mature and immature system. The mature indices include: total system throughput (T) that is the sum of all flows (con-

when compared to other values from tropical coastal system. The system primary production/respiration (PP/R) ratio estimated by the model is 1.87 indicating that the system is relatively developed [38].The high ascendancy value of 9929.2 and relative ascendancy of 0.250 indicate that the system is mature. However, the relative ascendancy of 0.250 reported by Vega-Cendejas and Arreguín-Sánchez [41] for Yucatan Peninsula (Mexico) was considered

The model results show that more than 98.6% of the flows to detritus is from TL 1 and 2, these levels playing a significant role in supporting the energy utilised by higher TL groups, and indicate a detritus-based food web and bottom-top control system, which is typical of a

System energy and matter recycling is an important process in ecosystem functioning [40], and the model low estimate of Finn's cycling index (FCI) and Finn's mean pathway of 1.983

In the present study, has shown that local mangrove wood exploitation is an important form of ecological disturbance and a potential threat to forest health. Although forest alteration is not dramatic, impacts on species composition and regeneration are apparent. Whilst dramatic changes in mangrove forest species composition and ecosystem health have been seen in many places, due to anthropogenic influences, hence, small-scale exploitation like that seen here, might contribute significantly to long-term environmental problems if not properly managed. Furthermore, it revealed that Cameroon grapsid and sesarmid crabs consumed large amounts of mangrove plant material, both leaves and propagules, and this may have significant ecological consequences for ecosystem struc-

The above system parameters provide a mixed picture of the maturity stage of the Cameroon mangrove ecosystem. Some indicate the system is immature and others that it is mature. It

Nevertheless, to establish a truly holistic, ecosystem-based approach to the management of the Cameroon mangrove forest, social and economic indicators need to be included and local users, the beneficiaries of the services delivered by the forest, need be included at all stages in

could be concluded that the overall health of the system is sustainable.

the management process and this process need more research.

·year, appears to be high

·year which appears high

one group on another and dependent upon them.

74 Mangrove Ecosystem Ecology and Function

sumption, respiration, export and flow into detritus) is 18,615 t/km2

high by the author. The total system biomass value is 184.193 t/km2

fits well within the range of other tropical systems [38].

and 1.717, respectively, is indicative of an immature system.

mature system.

**5. Conclusion**

ture and function.

Ngomba Longonje Simon

Address all correspondence to: nlongonje@yahoo.com

Department of Environmental Science, Faculty of Science, University of Buea, Cameroon

### **References**


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**Chapter 5**

Provisional chapter

**Salt Compartmentation and Antioxidant Defense in**

Salt Compartmentation and Antioxidant Defense in

**under Salt Stress**

under Salt Stress

Abstract

Cunfu Lu and Shaoliang Chen

Cunfu Lu and Shaoliang Chen

http://dx.doi.org/10.5772/intechopen.75583

enzymes, X-ray microanalysis

Niya Li, Xiaoyang Zhou, Ruigang Wang, Jinke Li,

Niya Li, Xiaoyang Zhou, Ruigang Wang, Jinke Li,

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

**Roots and Leaves of Two Non-Salt Secretor Mangroves**

DOI: 10.5772/intechopen.75583

The effects of increasing NaCl (100–400 mM) on cellular salt distribution, antioxidant enzymes, and the relevance to reactive oxygen species (ROS) homeostasis were investigated in 1-year-old seedlings of two non-salt secretor mangroves, Kandelia obovata and Bruguiera gymnorhiza. K. obovata accumulated less Na<sup>+</sup> and Cl in root cells and leaf compartments under 400 mM NaCl compared to B. gymnorhiza. However, B. gymnorhiza leaves are notable for preferential accumulation of salt ions in epidermal vacuoles relative to mesophyll vacuoles. Both mangroves upregulated antioxidant enzymes in ASC-GSH cycle to scavenge the salt-elicited ROS in roots and leaves but with different patterns. K. obovata rapidly initiated antioxidant defense to reduce ROS at an early stage of salt stress, whereas B. gymnorhiza maintained a high capacity to detoxify ROS at high saline. Collectively, our results suggest that salinized plants of the two mangroves maintained ROS homeostasis through (i) ROS scavenging by antioxidant enzymes and (ii) limiting ROS production by protective salt compartmentation. In the latter case, an efficient salt exclusion is favorable for K. obovata to reduce the formation of ROS in roots and leaves, while the effective vacuolar salt compartmentation benefited B. gymnorhiza leaves to avoid

Keywords: Bruguiera gymnorhiza, Kandelia obovata, reactive oxygen species, antioxidant

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

excessive ROS production in a longer term of increasing salinity.

Roots and Leaves of Two Non-Salt Secretor Mangroves

#### **Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under Salt Stress** Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under Salt Stress

DOI: 10.5772/intechopen.75583

Niya Li, Xiaoyang Zhou, Ruigang Wang, Jinke Li, Cunfu Lu and Shaoliang Chen Niya Li, Xiaoyang Zhou, Ruigang Wang, Jinke Li, Cunfu Lu and Shaoliang Chen

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75583

#### Abstract

The effects of increasing NaCl (100–400 mM) on cellular salt distribution, antioxidant enzymes, and the relevance to reactive oxygen species (ROS) homeostasis were investigated in 1-year-old seedlings of two non-salt secretor mangroves, Kandelia obovata and Bruguiera gymnorhiza. K. obovata accumulated less Na<sup>+</sup> and Cl in root cells and leaf compartments under 400 mM NaCl compared to B. gymnorhiza. However, B. gymnorhiza leaves are notable for preferential accumulation of salt ions in epidermal vacuoles relative to mesophyll vacuoles. Both mangroves upregulated antioxidant enzymes in ASC-GSH cycle to scavenge the salt-elicited ROS in roots and leaves but with different patterns. K. obovata rapidly initiated antioxidant defense to reduce ROS at an early stage of salt stress, whereas B. gymnorhiza maintained a high capacity to detoxify ROS at high saline. Collectively, our results suggest that salinized plants of the two mangroves maintained ROS homeostasis through (i) ROS scavenging by antioxidant enzymes and (ii) limiting ROS production by protective salt compartmentation. In the latter case, an efficient salt exclusion is favorable for K. obovata to reduce the formation of ROS in roots and leaves, while the effective vacuolar salt compartmentation benefited B. gymnorhiza leaves to avoid excessive ROS production in a longer term of increasing salinity.

Keywords: Bruguiera gymnorhiza, Kandelia obovata, reactive oxygen species, antioxidant enzymes, X-ray microanalysis

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 1. Introduction

Mangrove plants form a dominant ecosystem in tropical and subtropical coastlines [1]. Bruguiera gymnorhiza is widely distributed in tropical and subtropical area, from the southeastern coast of Africa through Asia to Australia and the southwestern Pacific [2]. Kandelia obovata is distributed mostly in the transition regions from tropical to subtropical coastlines of southern China, Taiwan, and the southern islands of Japan [3]. Climatic factors affecting the vegetative and reproductive phenology of B. gymnorhiza and K. obovata growing in subtropical regions were assessed in recent years. Temperature, day length, and rainfall are suggested to be the important external controlling factors of leaf initiation in B. gymnorhiza [4]. Leaf litterfall of the subtropical mangrove K. obovata was correlated to monthly day length and maximum wind speed [5]. Flowering of K. obovata was influenced by monthly sunshine hour and monthly mean air temperature [6]. While in B. gymnorhiza, flowering phenophase was linked with rainfall and relative humidity [4]. B. gymnorhiza and K. obovata are two major mangrove species along southern China coastlines. B. gymnorhiza is a frontline species and mostly occurs in high-saline zones compared with K. obovata, which grows in low-saline creeks in mangrove areas [7].

partition Cl into leaf sheaths relative to blades [39]. The preferential accumulation of Cl in the sheath would lessen the effect of salinity on photosynthetic processes in the leaf blade. Furthermore, X-ray microanalysis of various cell types in leaf sheaths and blades revealed that Cl was preferentially accumulated in epidermal vacuoles, relative to mesophyll vacuoles in salt-tolerant barley and sorghum [39, 40]. The high Cl concentration in the leaf blade mesophyll cells of a barley cultivar (cv. Clipper) suggests that the lower salt resistance of this cultivar is directly related to the degree of Cl exclusion by these cells [40]. Thus, it can be inferred that compartmentalizing salt ions in cell layers of leaf blade would reduce the perturbation of salt on photosynthetic processes in photosynthetically active mesophyll, especially the electron transport processes in chloroplasts. As a result, ROS is less produced [26, 27]. Although salt increased H2O2 in K. candel leaves, the ROS-induced necrotic lesions were not seen during the period of stress [16]. In addition to ROS scavenging by both enzymatic and nonenzymatic antioxidants, it is possible that mangrove plants could attenuate oxidative stress by a reasonable salt compartmentation in cells. However, this needs further investigations, e.g.,

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

Under salt stress, the antioxidant defense system serves to remove reactive oxygen species

42]. H2O2 is further detoxified through a reaction catalyzed by an ascorbate-specific peroxidase (APX), glutathione peroxidase (GPX), and catalase (CAT). APX utilizes ascorbate (AsA) as its specific electron donor to reduce H2O2 to water with the concomitant generation of monodehydroascorbate (MDAsA), a univalent oxidant of AsA [43]. CAT, an enzyme that splits hydrogen peroxide to yield oxygen and water, is an important part of the antioxidant defense [44]. GPX efficiently catalyzes the reduction of hydrogen peroxide and organic hydroperoxides by glutathione [45, 46]. In addition to these antioxidant enzymes that can directly scavenge toxic oxygen species, glutathione reductase (GR), which regenerates glutathione (GSH) that has been oxidized during ROS scavenging, is also implicated in redox homeostasis control [47]. The contribution of antioxidant defense to salt tolerance has been confirmed in crop species [32, 33, 48, 49] and woody plants, e.g., poplars [25–27] and mangroves [8, 10, 50, 51]. Takemura et al. detected an increased activity of SOD and CAT in B. gymnorhiza at high salt [50]. Parida et al. found that the elevation of antioxidant enzymes, APX and guaiacol peroxidase, was able to scavenge salt-induced H2O2 in B. parviflora [51]. Therefore, the capacity for regulating ROS homeostasis serves as one important component for salt tolerance in man-

Analyses of isoforms of antioxidant enzymes showed species differences in antioxidant defense system against salt treatment. Plants generally have three SOD isozymes: Cu/Zn-SOD in the cytosol and chloroplasts, Mn-SOD in mitochondria, and Fe-SOD in chloroplasts [52]. Activity of CuZn-SOD I and CuZn-SOD II, the two dominant SOD proteins in poplar leaves, was not detectable in P. popularis (salt-sensitive) after 16 days of salt stress, while there were no marked inhibitory effects of NaCl on the two SOD isoenzymes in P. euphratica (salt-resistant) during the observation period [26]. Furthermore, genetic differences were found in the timing of APX and CAT response to increasing salinity. Salt treatments increased activity of CAT and APX isoenzymes in the two poplar species, but their activity increased earlier in P. euphratica than in P. popularis [27]. In mangrove, a certain number of SOD isoenzymes (Mn-SOD, Fe-SOD),

• and H2O2) in the chloroplast, mitochondria, and cytosol. Superoxide dismutases

• and the reaction product [41,

http://dx.doi.org/10.5772/intechopen.75583

83

by X-ray microanalysis, to clarify.

(SODs) are considered to be the first defense line against O2

(e.g., O2

groves.

The most striking feature of mangroves is the capacity to withstand high salinity concentrations [8–11]. In general, secretor and non-salt secretor mangroves both exhibited a high capacity to maintain Na+ homeostasis under sodium chloride (NaCl) stress [7, 12–15]. Root flux recordings showed that B. gymnorhiza, K. candel (or K. obovata, non-salt secretors), Aegiceras corniculatum, and Avicennia marina (secretors) retained an obvious Na+ exclusion under NaCl treatment [7, 13–16]. Hydrogen peroxide (H2O2), nitric oxide (NO), and calcium (Ca2+) mediated Na<sup>+</sup> /H<sup>+</sup> antiport across the PM, thus contributing to control ionic homeostasis in the two non-salt secretor mangrove species [7]. Recently, multiple signaling networks of extracellular ATP (eATP), H2O2, Ca2+, and NO in the mediation of root ion fluxes were established in saltstressed K. obovata and A. corniculatum [15]. Salt exclusion by roots is the most important salttolerant mechanism in woody plants [17–22] and herbaceous species [23–24]. Although mangrove roots could effectively exclude salt ions under NaCl stress, Na+ and Cl taken up by roots would eventually transport to shoots via the transpiration stream during a long-term salt exposure [16, 20–22]. Jing et al. found that Na+ extrusion capacity in K. candel roots declined with the prolonged duration of salt exposure [16]. As a result, large amount of Na<sup>+</sup> accumulated in roots was transported to shoots [12, 16]. Excessive Na+ accumulation in leaves leads to oxidative stress by the production of reactive oxygen species (ROS) in trees [25–27]. Similarly, salt-induced oxidative stress has been widely shown in herbaceous species [28–35]. In mitochondria and chloroplasts, superoxide anions (O2 ) are generated as a by-product of electron transfer to O2 via photosynthetic and respiratory electron transport chain [36, 37]. The active O2 leads to subsequent formation of H2O2 and hydroxyl radicals (OH•) through chemical and enzymatic reactions [36, 37]. Salt induced an oxidative stress in chloroplast and mitochondria of pea leaves [28–30, 34]. In poplars, great buildup of Na+ and Cl in chloroplasts may directly cause ion toxicity and induce the subsequent oxidative stress [26, 38]. X-ray microanalysis results showed that the inability for the restriction of Na+ entry into the chloroplasts leads to an uncontrolled oxidation in Populus popularis [26, 38]. Salt-resistant plants may maintain ROS homeostasis through limiting ROS production by a protective salt partitioning. Evidence presented elsewhere suggests that NaCl-stressed sorghum plants preferentially

partition Cl into leaf sheaths relative to blades [39]. The preferential accumulation of Cl in the sheath would lessen the effect of salinity on photosynthetic processes in the leaf blade. Furthermore, X-ray microanalysis of various cell types in leaf sheaths and blades revealed that Cl was preferentially accumulated in epidermal vacuoles, relative to mesophyll vacuoles in salt-tolerant barley and sorghum [39, 40]. The high Cl concentration in the leaf blade mesophyll cells of a barley cultivar (cv. Clipper) suggests that the lower salt resistance of this cultivar is directly related to the degree of Cl exclusion by these cells [40]. Thus, it can be inferred that compartmentalizing salt ions in cell layers of leaf blade would reduce the perturbation of salt on photosynthetic processes in photosynthetically active mesophyll, especially the electron transport processes in chloroplasts. As a result, ROS is less produced [26, 27]. Although salt increased H2O2 in K. candel leaves, the ROS-induced necrotic lesions were not seen during the period of stress [16]. In addition to ROS scavenging by both enzymatic and nonenzymatic antioxidants, it is possible that mangrove plants could attenuate oxidative stress by a reasonable salt compartmentation in cells. However, this needs further investigations, e.g., by X-ray microanalysis, to clarify.

1. Introduction

82 Mangrove Ecosystem Ecology and Function

ated Na<sup>+</sup>

O2

Mangrove plants form a dominant ecosystem in tropical and subtropical coastlines [1]. Bruguiera gymnorhiza is widely distributed in tropical and subtropical area, from the southeastern coast of Africa through Asia to Australia and the southwestern Pacific [2]. Kandelia obovata is distributed mostly in the transition regions from tropical to subtropical coastlines of southern China, Taiwan, and the southern islands of Japan [3]. Climatic factors affecting the vegetative and reproductive phenology of B. gymnorhiza and K. obovata growing in subtropical regions were assessed in recent years. Temperature, day length, and rainfall are suggested to be the important external controlling factors of leaf initiation in B. gymnorhiza [4]. Leaf litterfall of the subtropical mangrove K. obovata was correlated to monthly day length and maximum wind speed [5]. Flowering of K. obovata was influenced by monthly sunshine hour and monthly mean air temperature [6]. While in B. gymnorhiza, flowering phenophase was linked with rainfall and relative humidity [4]. B. gymnorhiza and K. obovata are two major mangrove species along southern China coastlines. B. gymnorhiza is a frontline species and mostly occurs in high-saline zones compared with

The most striking feature of mangroves is the capacity to withstand high salinity concentrations [8–11]. In general, secretor and non-salt secretor mangroves both exhibited a high capacity to maintain Na+ homeostasis under sodium chloride (NaCl) stress [7, 12–15]. Root flux recordings showed that B. gymnorhiza, K. candel (or K. obovata, non-salt secretors), Aegiceras corniculatum, and Avicennia marina (secretors) retained an obvious Na+ exclusion under NaCl treatment [7, 13–16]. Hydrogen peroxide (H2O2), nitric oxide (NO), and calcium (Ca2+) medi-

non-salt secretor mangrove species [7]. Recently, multiple signaling networks of extracellular ATP (eATP), H2O2, Ca2+, and NO in the mediation of root ion fluxes were established in saltstressed K. obovata and A. corniculatum [15]. Salt exclusion by roots is the most important salttolerant mechanism in woody plants [17–22] and herbaceous species [23–24]. Although mangrove roots could effectively exclude salt ions under NaCl stress, Na+ and Cl taken up by roots would eventually transport to shoots via the transpiration stream during a long-term salt exposure [16, 20–22]. Jing et al. found that Na+ extrusion capacity in K. candel roots declined with the prolonged duration of salt exposure [16]. As a result, large amount of Na<sup>+</sup> accumulated in roots was transported to shoots [12, 16]. Excessive Na+ accumulation in leaves leads to oxidative stress by the production of reactive oxygen species (ROS) in trees [25–27]. Similarly, salt-induced oxidative stress has been widely shown in herbaceous species [28–35]. In mito-

transfer to O2 via photosynthetic and respiratory electron transport chain [36, 37]. The active

 leads to subsequent formation of H2O2 and hydroxyl radicals (OH•) through chemical and enzymatic reactions [36, 37]. Salt induced an oxidative stress in chloroplast and mitochondria of pea leaves [28–30, 34]. In poplars, great buildup of Na+ and Cl in chloroplasts may directly cause ion toxicity and induce the subsequent oxidative stress [26, 38]. X-ray microanalysis results showed that the inability for the restriction of Na+ entry into the chloroplasts leads to an uncontrolled oxidation in Populus popularis [26, 38]. Salt-resistant plants may maintain ROS homeostasis through limiting ROS production by a protective salt partitioning. Evidence presented elsewhere suggests that NaCl-stressed sorghum plants preferentially

/H<sup>+</sup> antiport across the PM, thus contributing to control ionic homeostasis in the two

) are generated as a by-product of electron

K. obovata, which grows in low-saline creeks in mangrove areas [7].

chondria and chloroplasts, superoxide anions (O2

Under salt stress, the antioxidant defense system serves to remove reactive oxygen species (e.g., O2 • and H2O2) in the chloroplast, mitochondria, and cytosol. Superoxide dismutases (SODs) are considered to be the first defense line against O2 • and the reaction product [41, 42]. H2O2 is further detoxified through a reaction catalyzed by an ascorbate-specific peroxidase (APX), glutathione peroxidase (GPX), and catalase (CAT). APX utilizes ascorbate (AsA) as its specific electron donor to reduce H2O2 to water with the concomitant generation of monodehydroascorbate (MDAsA), a univalent oxidant of AsA [43]. CAT, an enzyme that splits hydrogen peroxide to yield oxygen and water, is an important part of the antioxidant defense [44]. GPX efficiently catalyzes the reduction of hydrogen peroxide and organic hydroperoxides by glutathione [45, 46]. In addition to these antioxidant enzymes that can directly scavenge toxic oxygen species, glutathione reductase (GR), which regenerates glutathione (GSH) that has been oxidized during ROS scavenging, is also implicated in redox homeostasis control [47]. The contribution of antioxidant defense to salt tolerance has been confirmed in crop species [32, 33, 48, 49] and woody plants, e.g., poplars [25–27] and mangroves [8, 10, 50, 51]. Takemura et al. detected an increased activity of SOD and CAT in B. gymnorhiza at high salt [50]. Parida et al. found that the elevation of antioxidant enzymes, APX and guaiacol peroxidase, was able to scavenge salt-induced H2O2 in B. parviflora [51]. Therefore, the capacity for regulating ROS homeostasis serves as one important component for salt tolerance in mangroves.

Analyses of isoforms of antioxidant enzymes showed species differences in antioxidant defense system against salt treatment. Plants generally have three SOD isozymes: Cu/Zn-SOD in the cytosol and chloroplasts, Mn-SOD in mitochondria, and Fe-SOD in chloroplasts [52]. Activity of CuZn-SOD I and CuZn-SOD II, the two dominant SOD proteins in poplar leaves, was not detectable in P. popularis (salt-sensitive) after 16 days of salt stress, while there were no marked inhibitory effects of NaCl on the two SOD isoenzymes in P. euphratica (salt-resistant) during the observation period [26]. Furthermore, genetic differences were found in the timing of APX and CAT response to increasing salinity. Salt treatments increased activity of CAT and APX isoenzymes in the two poplar species, but their activity increased earlier in P. euphratica than in P. popularis [27]. In mangrove, a certain number of SOD isoenzymes (Mn-SOD, Fe-SOD), guaiacol peroxidase isoenzymes, and GR isoenzymes were preferentially elevated by NaCl in B. parviflora [51]. The induction of antioxidant enzymes might be the result of salt-induced gene transcription. Northern blot analysis revealed that the transcript level of cytosolic Cu/Zn-SOD was increased after a few days of NaCl treatment [50]. Similarly, NaCl was shown to increase KcCSD expression in K. candel leaves [16]. Proteomic analysis of K. candel leaves revealed that SOD abundance increased in response to high NaCl at 450–600 mM [53]. Furthermore, overexpression of copper/zinc superoxide dismutase from mangrove K. candel in tobacco enhances salinity tolerance by the reduction of reactive oxygen species in chloroplast [16].

time. At the final harvest time, roots and upper mature leaves were sampled from control and

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

• production rate was typically higher in roots than in leaves in control plants of the

absent in the two mangroves when NaCl concentration was below 300 mM (Table 1). The same

Increasing NaCl stress did not significantly elevate root H2O2 levels in either species; rather, a significant reduction of H2O2 was observed in B. gymnorhiza when NaCl saline ranged from 100 to 300 mM (Table 1). An abrupt rise of H2O2 occurred in K. obovata leaves when plants were subjected to 400 mM NaCl, although H2O2 remained less than controls at low salt (100– 200 mM, Table 1). However, salinized B. gymnorhiza maintained a H2O2 level similar to control

salinity (400 mM NaCl) in the two mangrove species, although root and leaf ROS levels were usually downregulated after exposure to a lower salinity (100–200 mM NaCl), e.g., O2

and H2O2 in B. gymnorhiza roots and H2O2 in K. obovata leaves (Table 1). Similarly, NaClinduced increase of H2O2 was observed in leaves of B. parviflora [51] and K. candel [16] under hydroponic conditions. In this study, the moderate ROS increment induced by 400 mM NaCl caused no oxidative burst in both species, suggesting that stressed plants of K. obovata and B. gymnorhiza maintained ROS homeostasis throughout the duration of salt exposure. Our data showed that salt compartmentation and antioxidant enzymes contributed to ROS homeostasis

In this study, SEM-EDX analysis was performed on cross sections of B. gymnorhiza and K. obovata roots. Na+ and Cl were detectable in root cells of no-salt controls (Table 2). Under salt conditions, Na+ and Cl levels significantly increased in the tested structures, i.e., epidermis, exodermis, cortex, endodermis, and stelar parenchyma (Table 2). The long-term salt treatment with increasing NaCl saline (100–400 mM, 15 d) significantly increased the content

In leaf cells of control plants, TEM-EDX data showed an evident Na+ and Cl in epidermis, mesophyll, and xylem vessels (leaf vascular bundle), but B. gymnorhiza exhibited 28–195% higher Na+ than K. obovata in all measured cell compartments, such as xylem vessel, epidermal wall and vacuole, mesophyll wall and vacuole, and chloroplast (Table 3). NaCl (400 mM) treatment markedly increased Na+ and Cl concentrations in the apoplastic space and vacuoles

) and 0.5–5.1 fold (Cl), although Na<sup>+</sup> and Cl levels were typically

• production and/or H2O2 levels in roots and leaves were enhanced by high

and 83% in K. obovata and B. gymnorhiza, respectively, but the salt-induced rise of O2

• production rate by 82

http://dx.doi.org/10.5772/intechopen.75583

• was only observed in

• was

85

stressed plants and used for X-ray microanalysis.

B. gymnorhiza leaves at 400 mM NaCl (Table 1).

• and H2O2 levels in roots and leaves

two species (Table 1). High salinity (400 mM NaCl) increased root O2

trend was observed in leaves, but the NaCl-induced increase of O2

leaves despite of a NaCl increase, from 100 to 400 mM (Table 1).

in both species but with different patterns under NaCl stress (see below).

higher in B. gymnorhiza than in K. obovata in all measured structures (Table 2).

2.3. Salt compartmentation and ROS production

2.3.1. Salt compartmentation within root and leaf cells

of salt ions by 0.6–9.6 (Na+

2.2. O2

In general O2

O2

We have previously shown species differences between secretor and non-salt secretor mangroves in root salt exclusion and leaf gas exchange response to salt treatment [7, 12, 15]. The object of this study is to investigate the effect of NaCl on the pattern of cellular salt compartmentation, variations in antioxidant enzymes, and their contributions to ROS (in particular, O2 •� and H2O2) homeostasis maintenance in non-salt secretor mangroves.

### 2. Salt compartmentation and antioxidant defense

#### 2.1. Plant materials and salt treatment

K. obovata hypocotyls developed from fruits turned into mature propagules, which began to drop in March and continued dropping until May [6]. Mature and developing propagules of B. gymnorhiza were found throughout the year, but the abundance of mature propagules was highest in summer and lowest in winter [4]. In early March, 200 of propagules of K. obovata and B. gymnorhiza were obtained from Dongzhai Harbor in Hainan Province of China (latitude 19�51<sup>0</sup> N and longitude 110�24<sup>0</sup> E). Propagules were collected from the surface of soil or seawater during the ebb tide. Single hypocotyls were planted in individual pots (15 cm in diameter and 18 cm in height) containing sand and placed in a greenhouse at Beijing Forestry University, Beijing, China (latitude 39�56<sup>0</sup> N and longitude 116�20<sup>0</sup> E). The pots were fertilized with 1000 ml half strength Hoagland nutrient solution every 14 d. Seedlings were raised from March to August under nonsaline conditions. The relative humidity was maintained at 60– 70%, and photosynthetically active radiation (PAR) varied from 400 to 1200 μmol m�<sup>2</sup> s �1 . Salt treatment was carried out when the fourth pair of leaves came out from the apex of the growing shoots (mid-August) [12].

NaCl concentration started from 100 mM and increased stepwise by 100 mM [12], reaching 400 mM and remained at this salinity until the terminal of experiment. Increasing NaCl saline was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM), respectively. Control plants were kept well watered with no addition of NaCl. PAR was 400– 1200 μmol m�<sup>2</sup> s �1 , and air temperature was 20–35�C over the duration of experiment. On day 2, day 5, day 9, and day 14, leaves and roots were sampled for ROS (O2 •� and H2O2) determination and total activity measurements of antioxidant enzymes, i.e., superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR). For SOD and CAT isoenzyme analyses, leaves and roots were sampled at day 3, day 6, day 10, and day 15. Three replicated plants per treatment were harvested at each sampling time. At the final harvest time, roots and upper mature leaves were sampled from control and stressed plants and used for X-ray microanalysis.

#### 2.2. O2 • and H2O2 levels in roots and leaves

guaiacol peroxidase isoenzymes, and GR isoenzymes were preferentially elevated by NaCl in B. parviflora [51]. The induction of antioxidant enzymes might be the result of salt-induced gene transcription. Northern blot analysis revealed that the transcript level of cytosolic Cu/Zn-SOD was increased after a few days of NaCl treatment [50]. Similarly, NaCl was shown to increase KcCSD expression in K. candel leaves [16]. Proteomic analysis of K. candel leaves revealed that SOD abundance increased in response to high NaCl at 450–600 mM [53]. Furthermore, overexpression of copper/zinc superoxide dismutase from mangrove K. candel in tobacco enhances salinity tolerance by the reduction of reactive oxygen species in chloroplast [16].

We have previously shown species differences between secretor and non-salt secretor mangroves in root salt exclusion and leaf gas exchange response to salt treatment [7, 12, 15]. The object of this study is to investigate the effect of NaCl on the pattern of cellular salt compartmentation, variations in antioxidant enzymes, and their contributions to ROS (in particular,

K. obovata hypocotyls developed from fruits turned into mature propagules, which began to drop in March and continued dropping until May [6]. Mature and developing propagules of B. gymnorhiza were found throughout the year, but the abundance of mature propagules was highest in summer and lowest in winter [4]. In early March, 200 of propagules of K. obovata and B. gymnorhiza were obtained from Dongzhai Harbor in Hainan Province of China (latitude

ter during the ebb tide. Single hypocotyls were planted in individual pots (15 cm in diameter and 18 cm in height) containing sand and placed in a greenhouse at Beijing Forestry Univer-

N and longitude 116�20<sup>0</sup>

1000 ml half strength Hoagland nutrient solution every 14 d. Seedlings were raised from March to August under nonsaline conditions. The relative humidity was maintained at 60– 70%, and photosynthetically active radiation (PAR) varied from 400 to 1200 μmol m�<sup>2</sup> s

treatment was carried out when the fourth pair of leaves came out from the apex of the

NaCl concentration started from 100 mM and increased stepwise by 100 mM [12], reaching 400 mM and remained at this salinity until the terminal of experiment. Increasing NaCl saline was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM), respectively. Control plants were kept well watered with no addition of NaCl. PAR was 400–

determination and total activity measurements of antioxidant enzymes, i.e., superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR). For SOD and CAT isoenzyme analyses, leaves and roots were sampled at day 3, day 6, day 10, and day 15. Three replicated plants per treatment were harvested at each sampling

2, day 5, day 9, and day 14, leaves and roots were sampled for ROS (O2

, and air temperature was 20–35�C over the duration of experiment. On day

E). Propagules were collected from the surface of soil or seawa-

E). The pots were fertilized with

�1 . Salt

•� and H2O2)

•� and H2O2) homeostasis maintenance in non-salt secretor mangroves.

2. Salt compartmentation and antioxidant defense

2.1. Plant materials and salt treatment

84 Mangrove Ecosystem Ecology and Function

N and longitude 110�24<sup>0</sup>

sity, Beijing, China (latitude 39�56<sup>0</sup>

growing shoots (mid-August) [12].

�1

1200 μmol m�<sup>2</sup> s

O2

19�51<sup>0</sup>

O2 • production rate was typically higher in roots than in leaves in control plants of the two species (Table 1). High salinity (400 mM NaCl) increased root O2 • production rate by 82 and 83% in K. obovata and B. gymnorhiza, respectively, but the salt-induced rise of O2 • was absent in the two mangroves when NaCl concentration was below 300 mM (Table 1). The same trend was observed in leaves, but the NaCl-induced increase of O2 • was only observed in B. gymnorhiza leaves at 400 mM NaCl (Table 1).

Increasing NaCl stress did not significantly elevate root H2O2 levels in either species; rather, a significant reduction of H2O2 was observed in B. gymnorhiza when NaCl saline ranged from 100 to 300 mM (Table 1). An abrupt rise of H2O2 occurred in K. obovata leaves when plants were subjected to 400 mM NaCl, although H2O2 remained less than controls at low salt (100– 200 mM, Table 1). However, salinized B. gymnorhiza maintained a H2O2 level similar to control leaves despite of a NaCl increase, from 100 to 400 mM (Table 1).

In general O2 • production and/or H2O2 levels in roots and leaves were enhanced by high salinity (400 mM NaCl) in the two mangrove species, although root and leaf ROS levels were usually downregulated after exposure to a lower salinity (100–200 mM NaCl), e.g., O2 and H2O2 in B. gymnorhiza roots and H2O2 in K. obovata leaves (Table 1). Similarly, NaClinduced increase of H2O2 was observed in leaves of B. parviflora [51] and K. candel [16] under hydroponic conditions. In this study, the moderate ROS increment induced by 400 mM NaCl caused no oxidative burst in both species, suggesting that stressed plants of K. obovata and B. gymnorhiza maintained ROS homeostasis throughout the duration of salt exposure. Our data showed that salt compartmentation and antioxidant enzymes contributed to ROS homeostasis in both species but with different patterns under NaCl stress (see below).

#### 2.3. Salt compartmentation and ROS production

#### 2.3.1. Salt compartmentation within root and leaf cells

In this study, SEM-EDX analysis was performed on cross sections of B. gymnorhiza and K. obovata roots. Na+ and Cl were detectable in root cells of no-salt controls (Table 2). Under salt conditions, Na+ and Cl levels significantly increased in the tested structures, i.e., epidermis, exodermis, cortex, endodermis, and stelar parenchyma (Table 2). The long-term salt treatment with increasing NaCl saline (100–400 mM, 15 d) significantly increased the content of salt ions by 0.6–9.6 (Na+ ) and 0.5–5.1 fold (Cl), although Na<sup>+</sup> and Cl levels were typically higher in B. gymnorhiza than in K. obovata in all measured structures (Table 2).

In leaf cells of control plants, TEM-EDX data showed an evident Na+ and Cl in epidermis, mesophyll, and xylem vessels (leaf vascular bundle), but B. gymnorhiza exhibited 28–195% higher Na+ than K. obovata in all measured cell compartments, such as xylem vessel, epidermal wall and vacuole, mesophyll wall and vacuole, and chloroplast (Table 3). NaCl (400 mM) treatment markedly increased Na+ and Cl concentrations in the apoplastic space and vacuoles


buffer [50 mM potassium phosphate, pH 7.0, 1.0 mM EDTA, 1% (w/v) PVP] and then centrifuged at 10,000 g for 20 min at 4C. A 1.0 ml of extract was mixed with same volume of 50 mM sodium phosphate buffer (pH 7.8) and 10 mM hydroxylammonium chloride. The mixture was kept at 25C (water bath) for 20 min and then centrifuged at 1500 g for 10 min. Then, 1.0 ml of the mixture was mixed with same volume of 17 mM sulfanilic acid and 7.0 mM 1-naphthylamine. After incubation at 25C for 20 min, 3.0 ml ethyl ether was introduced to the mixture, shaken to uniform, and centrifuged at 1500 g for 5 min. Absorbance of the water phase at 530 nm was then recorded. For blank controls, the same amount of 50 mM sodium phosphate buffer (pH 7.8) was added into the reaction system instead of the enzyme extract. Measurement of H O2 2 content was performed according to Patterson et al. [55], Liu et al. [56], and Wang et al. [27] with modifications. In brief, leaf and root tissues (ca. 0.5 g) were ground to a fine powder in liquid N2 and then homogenized in 3.0 ml precooled acetone. The homogenate was centrifuged at 10,000 g for 20 min at 4C. A 1.0 ml supernatant, 2.5 ml extractant (CCl4:CHCl3 = 3:1, v/v), and 2.5 ml redistilled water was mixed and centrifuged at 5000 g for 5 min at 4C. Then, 2.0 ml water phases in the

concentration.

 catalase (by high

 were introduced

 to both series [57]. The

 at 508 nm was recorded, and

 reagent, 1.0 ml of 0.2 mM Ti(IV)-PAR,

temperature

 for 20 min. Finally, the absorbance

 with room

 For the blank control, catalase

temperature)

 was added into

supernatant

was introduced the H O2 2 extract. Then, 1.0 ml of 0.2 M sodium phosphate buffer (pH 7.8) and colorimetric

color was developed

 at 45C for 20 min and then allowed to equilibrate

 to a

concentration

 of 3.0 U ml1 and then kept at 30C for 10 min. Same amount of solution with inactivated

 were divided into two aliquots of 1.0 ml. One was taken as blank control and the other was used to examine H O2 2

concentration of H O2 2 was given based on the established standard curve. Each value (SE) is the mean of three plants, and values in the same column followed by different letters are significantly different (<sup>P</sup> < 0.05) between control and NaCltreatment.

Table 1. Effects of NaCl on H O2 2 (nmol g1 fw) levels and O2• production rates (nmol min1 mg1 pro) in leaves and roots of K. obovata and B. gymnorhiza.

of the two species but with the exception of Cl

SE) is the mean of three plants, and 5

stressed B. gymnorhiza as compared to K. obovata

<sup>+</sup> and Cl

Table 2. Salt distribution in root cells of K. obovata and B. gymnorhiza

Noteworthy, B. gymnorhiza preferentially accumulated 73

<sup>+</sup> and Cl

2.3.2. Salt compartmentation and ROS production in roots and leaves

<sup>+</sup> and Cl

Epidermis Control 2.98

Exodermis Control 1.05

Cortex Control 0.70

Endodermis Control 1.39

Stelar parenchyma Control 1.56

–400 mM). Cellular Na

fractions of Na

treatment (100

(K + , Na +

Each value (

treatment.

the Na

significantly increase Na

, Ca2+, Mg2+, and Cl

<sup>+</sup> and Cl

vacuolar fractions of Na

regardless of treatments (Table 3).

X-ray microanalysis data show that Na

plants in the two mangroves (Tables 2 and

in K. obovata

.

concentrations were higher in the vacuole than in the chloroplast (Table 3).

concentrations in the chloroplast of two mangroves (Table 3).

–94% higher Na

in stressed K. obovata remained the same as that of chloro-

in the xylem vessel, cell wall, and vacuole were 30

Vacuolar compartmentation in mesophyll was clearly seen in stressed B. gymnorhiza, in which

Compartment Treatment K. obovata B. gymnorhiza

<sup>+</sup> Cl

0.30b 5.35

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

2.19a 32.8

0.23b 12.1

1.24a 23.6

0.34b 7.71

1.36a 43.7

0.97b 10.2

0.96a 49.3

0.58b 6.96

1.12a 38.6

roots with tips were washed free of soil particles and rapidly frozen in liquid nitrogen, vacuum freeze-dried at

K. obovata and B. gymnorhiza roots were sampled from control and stressed plants after 15 days of increasing NaCl

in a high vacuum sputter coater and analyzed with a Hitachi S-3400 N scanning electron microscope equipped with an energy-dispersive X-ray detector (EX-250, Horiba Ltd. Kyoto, Japan). Probe measurements of samples were taken with a broad electron beam covering the whole cells that were randomly selected in the epidermis, exodermis, cortex, endodermis, and stele. Na<sup>+</sup> and Cl levels were expressed as a percentage of the total atomic number for all the major elements

Na

1.26b 10.3

3.94a 16.0

2.12b 7.76

4.72a 23.9

1.05b 12.6

2.65a 26.3

0.37b 15.8

1.64a 31.0

1.33b 17.1

2.51a 35.3

contents were measured by SEM-EDX according to Sun et al. [58]. Briefly,

–12 measurements (for each compartment) were taken from each root.

<sup>+</sup> Cl

4.46b 24.3

http://dx.doi.org/10.5772/intechopen.75583

3.82a 44.9

1.78b 27.2

3.33a 51.4

3.54b 34.2

3.32a 51.2

4.90b 35.9

5.82a 57.3

2.19b 24.8

7.89a 48.2

C) for 24 h. Freeze-dried roots were gold coated

1.76b

87

1.96a

4.46b

2.14a

1.42b

3.50a

3.08b

5.14a

2.46b

4.51a

100 C for

Na

NaCl 7.36

NaCl 11.1

NaCl 5.39

NaCl 4.84

NaCl 5.80

24 h, and then slowly allowed to equilibrate to room temperature (ca. 22

<sup>+</sup> and Cl

) detected from the cell samples.

Values in the same column followed by different letters are significantly different (

of epidermal cells as compared to mesophyll vacuoles (Table 3). In contrast to B. gymnorhiza

plast, and vacuolar Na<sup>+</sup> and Cl in epidermis was similar to that in mesophyll vacuole

propagules were collected from the surface of soil or seawater in coastal habitats of mangrove

<sup>+</sup> and Cl

(Table 3). In comparison, the

P < 0.05) between control and NaCl

<sup>+</sup> and Cl

(Table 3). However, NaCl stress did not

were evident in root and leaf cells of control

3), presumably originated from hypocotyls as

–196% higher in

in vacuoles

,

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under… http://dx.doi.org/10.5772/intechopen.75583 87


K. obovata and B. gymnorhiza roots were sampled from control and stressed plants after 15 days of increasing NaCl treatment (100–400 mM). Cellular Na<sup>+</sup> and Cl contents were measured by SEM-EDX according to Sun et al. [58]. Briefly, roots with tips were washed free of soil particles and rapidly frozen in liquid nitrogen, vacuum freeze-dried at 100 C for 24 h, and then slowly allowed to equilibrate to room temperature (ca. 22C) for 24 h. Freeze-dried roots were gold coated in a high vacuum sputter coater and analyzed with a Hitachi S-3400 N scanning electron microscope equipped with an energy-dispersive X-ray detector (EX-250, Horiba Ltd. Kyoto, Japan). Probe measurements of samples were taken with a broad electron beam covering the whole cells that were randomly selected in the epidermis, exodermis, cortex, endodermis, and stele. Na<sup>+</sup> and Cl levels were expressed as a percentage of the total atomic number for all the major elements (K<sup>+</sup> , Na<sup>+</sup> , Ca2+, Mg2+, and Cl) detected from the cell samples.

Each value (SE) is the mean of three plants, and 5–12 measurements (for each compartment) were taken from each root. Values in the same column followed by different letters are significantly different (P < 0.05) between control and NaCl treatment.

Table 2. Salt distribution in root cells of K. obovata and B. gymnorhiza.

of the two species but with the exception of Cl in K. obovata (Table 3). In comparison, the fractions of Na+ and Cl in the xylem vessel, cell wall, and vacuole were 30–196% higher in stressed B. gymnorhiza as compared to K. obovata (Table 3). However, NaCl stress did not significantly increase Na+ and Cl concentrations in the chloroplast of two mangroves (Table 3).

Vacuolar compartmentation in mesophyll was clearly seen in stressed B. gymnorhiza, in which the Na<sup>+</sup> and Cl concentrations were higher in the vacuole than in the chloroplast (Table 3). Noteworthy, B. gymnorhiza preferentially accumulated 73–94% higher Na+ and Cl in vacuoles of epidermal cells as compared to mesophyll vacuoles (Table 3). In contrast to B. gymnorhiza, vacuolar fractions of Na+ and Cl in stressed K. obovata remained the same as that of chloroplast, and vacuolar Na<sup>+</sup> and Cl in epidermis was similar to that in mesophyll vacuole regardless of treatments (Table 3).

#### 2.3.2. Salt compartmentation and ROS production in roots and leaves

Treatment

K. obovata

Leaf

H

Control NaCl (100 mM)

Control NaCl (200 mM)

Control NaCl (300 mM)

Control NaCl (400 mM)

O2

buffer [50 mM potassium phosphate, volume of 50 mM sodium phosphate buffer (pH 7.8) and 10 mM

at 1500 g for 10 min. Then, 1.0 ml of the mixture was mixed with same volume of 17 mM sulfanilic acid and 7.0 mM

3.0 ml ethyl ether was introduced

blank controls, the same amount of 50 mM sodium phosphate buffer (pH 7.8) was added into the reaction system instead of the enzyme extract.

Measurement

were ground to a fine powder in liquid N2 and then

supernatant,

supernatant

was introduced

the H color was developed

concentration

Each value (

treatment.

Table 1. Effects of NaCl on H

O2 2 (nmol g1 fw) levels and O2

•

production

 rates (nmol min1 mg1 pro) in leaves and roots of K. obovata and B. gymnorhiza.

 of H SE) is the mean of three plants, and values in the same column followed by different letters are

O2 2 was given based on the established

 at 45C for 20 min and then allowed to equilibrate

O2 2 extract. Then, 1.0 ml of 0.2 M sodium phosphate buffer (pH 7.8) and colorimetric

 to a

concentration

 of 3.0 U ml1 and then kept at 30C for 10 min. Same amount of solution with inactivated

 were divided into two aliquots of 1.0 ml. One was taken as blank control and the other was used to examine H

 2.5 ml extractant

(CCl4:CHCl3 = 3:1, v/v), and 2.5 ml redistilled water was mixed and centrifuged

 of H

O2 2 content was performed according to Patterson et al. [55], Liu et al. [56], and Wang et al. [27] with

homogenized

 in 3.0 ml precooled acetone. The

 to the mixture, shaken to uniform, and centrifuged

production

 rate was measured as described by Wang and Luo [54] and Wang et al. [27]. Briefly, leaf and root tissues (ca. 0.5 g) were

 pH 7.0, 1.0 mM EDTA, 1% (w/v) PVP] and then centrifuged

•

 41.38

 8.97a

 1.76

 0.31a

 11.62

 3.09a

 3.08

 0.46a

 22.90

 at 10,000 g for 20 min at 4C. A 1.0 ml of extract was mixed with same

hydroxylammonium

 chloride. The mixture was kept at 25C (water bath) for 20 min and then centrifuged

 at 1500 g for 5 min. Absorbance

1-naphthylamine.

 of the water phase at 530 nm was then recorded. For

modifications.

homogenate

 was centrifuged

 at 5000 g for 5 min at 4C. Then, 2.0 ml water phases in the

O2 2

 catalase (by high

 were introduced

 to both series [57]. The

 at 508 nm was recorded, and

 reagent, 1.0 ml of 0.2 mM Ti(IV)-PAR,

temperature

 for 20 min. Finally, the absorbance

significantly

 different (<sup>P</sup> < 0.05) between control and NaCl

 with room

> standard curve.

concentration.

 For the blank control, catalase

temperature)

 was added into

 at 10,000 g for 20 min at 4C. A 1.0 ml

 In brief, leaf and root tissues (ca. 0.5 g)

 After incubation at 25C for 20 min,

 3.40a

 1.08

 0.13a

 16.07

 3.31a homogenized

 in a 3-ml ice-cold

 4.85

 0.52a

 11.47 11.60

 5.80b

 1.76

 0.41a

 8.05

 1.08a

 1.69

 0.06b

 19.12

 1.18a

 0.71

 0.09b

 10.39

 2.15a

 2.65

 0.09b

 5.10a

 0.84

 0.12a

 13.93

 2.34a

 1.78

 0.13a

 23.13

 1.10a

 0.69

 0.29a

 4.66

 0.35b

 1.89

 0.52a

 1.50 10.97

 1.23a

 0.67

 0.09a

 13.10

 2.07a

 1.54

 0.09a

 15.93

 4.50a

 0.48

 0.07a

 26.44

 4.98a

 1.81

 0.60a

 0.05b

 1.26

 0.04a

 3.20

 1.02a

 4.34

 1.25a

 9.01

 4.52a

 0.69

 0.28a

 4.79

 1.57b

 2.68

 0.02a

 2.37 16.48

 4.10a

 1.11

 0.07a

 4.95

 1.86a

 4.03

 1.35a

 3.33

 1.12a

 0.50

 0.29a

 31.43

 4.79a

 3.63

 0.58a

 0.60b

 1.35

 0.11a

 7.76

 2.56a

 6.26

 0.99a

 11.53

 4.96a

 0.47

 0.08a

 1.43

 1.91b

 2.35

 0.22a

17.63

 6.00a

 1.16

 0.12a

 10.04

 1.98a

 5.77

 1.00a

 5.93

 0.91a

 0.61

 0.07a

 17.50

 0.17a

 3.44

 0.56a

86 Mangrove Ecosystem Ecology and Function

O2 2

O2

H

O2 2

O2

H

O2 2

O2

H

O2 2

O2

•

•

•

•

Root

B. gymnorhiza

Leaf

Root

X-ray microanalysis data show that Na<sup>+</sup> and Cl were evident in root and leaf cells of control plants in the two mangroves (Tables 2 and 3), presumably originated from hypocotyls as propagules were collected from the surface of soil or seawater in coastal habitats of mangrove


B. gymnorhiza are notable for (1) vacuolar compartmentation in mesophyll cells and (2) preferential accumulation of Na+ and Cl in epidermal vacuoles, relative to mesophyll vacuoles (Table 3). The ability to extrude Na+ from root cells of K. obovata likely results from an active Na+

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

vacuoles likely depends on active transport of salt ions across the tonoplast. Salinity may increase the activity of vacuole H+ pumps, thus making a contribution to the compartmentation

the elevated concentrations of Na+ and Cl in swelling vacuoles were correlated with the salt-

suggest that the two mangrove plants may maintain ROS homeostasis through limiting ROS production by a protective cellular salt compartmentation, in addition to scavenging ROS by

a. Salt exclusion and ROS production in K. obovata: NaCl treatment increased Na<sup>+</sup> in the leaf apoplast and vacuole of epidermis and mesophyll, but did not elevate Cl in K. obovata (Table 3). Moreover, the absolute values of Na+ and Cl in these measured compartments were lower in K. obovata than in B. gymnorhiza under 400 mM NaCl (Table 3). Result suggests that K. obovata plants had a higher capacity for NaCl exclusion, presumably due to the salt uptake and transport restrictions in roots (Table 2) [7, 12, 15]. Effective salt exclusion is a benefit for K. obovata to reduce ROS production. We have shown that the

oxidative burst in leaf cells of a salt-sensitive poplar, P. simonii (P. pyramidalis Salix

dria of pea cultivars [28, 29]. Accordingly, we hypothesize that the B. gymnorhiza limits ROS production by preferential accumulation of Na+ and Cl in epidermal vacuoles, as

Under no-salt control conditions, total activity of measured antioxidant enzymes roots and leaves, SOD, APX, CAT, and GR, varied markedly during the observation period (Tables 4

b. Vacuolar salt compartmentation and ROS production in B. gymnorhiza: B. gymnorhiza leaves exhibited a more pronounced salt accumulation than K. obovata (Table 3), resulting from a higher root-to-shoot salt transport [12]. Noteworthy, B. gymnorhiza preferentially accumulated Na<sup>+</sup> and Cl in epidermal vacuoles, instead of mesophyll vacuoles (Table 3). Similar findings were observed in leaf sheaths and blades of sorghum and barley in which Cl was preferentially accumulated in most cell layers, particularly the adaxial epidermal cells [39, 40]. The evident Cl exclusion from photosynthetically active mesophyll would lessen the effect of salinity on photosynthetic processes, especially the electron transport in chloroplasts in the mesophyll. Moreover, fractions of Na<sup>+</sup> and Cl remained higher in mesophyll vacuole than in the cytoplasm (Table 3), which may inhibit the enhancement

antioxidant enzymes in a longer term of increasing salinity (see below). In brief:

inability to exclude NaCl favored the formation of O2

matsudana) (P. popularis cv. '35–44') [26, 27, 38].

NaCl was found to favor the formation of O2

well as vacuolar compartmentation in mesophyll cells.

2.4. Antioxidant enzymes contributed to ROS homeostasis

2.4.1. Activity of antioxidant enzymes in roots and leaves

of NaCl on the formation of O2

antiport driven by H+ pumping activity of PM H+

of toxic ions into the vacuoles via Na+

induced activation of tonoplast H+

/H+

89


http://dx.doi.org/10.5772/intechopen.75583

• and H2O2, which causes an

/H+ antiporter systems [62–64]. Mimura et al. found that


• and H2O2 in the cytosol, chloroplasts, and mitochondria.

• and H2O2 in chloroplasts and mitochon-

K. obovata and B. gymnorhiza leaves were sampled from control and stressed plants after 15 days of increasing NaCl treatment (100–400 mM). Standard procedures required for sample preparation and X-ray microanalysis were followed as described in Fritz [59, 60]. In brief, leaf segments, 2–3 mm long and 1–2 mm wide, were cut with a razor blade along the smaller veins adjacent to the central vein and immediately placed into aluminum sample holders and rapidly frozen in a 3:1 mixture of propane:isopentane at the temperature of liquid nitrogen. Samples were vacuum freeze-dried at 60C for 72 h and then slowly allowed to equilibrate to room temperature (ca. 22C) over a period of 24 h. Then, samples were stored over silica gel until infiltration in plastic. Freeze-dried leaf samples were transferred into vacuum-pressure chambers and infiltrated in ether at 27C overnight before infiltrating with plastic. The plastic used was a 1:1 mixture of styrene (Merck Schuchardt) and butyl methacrylate (Sigma-Aldrich) containing 1% benzoyl peroxide stabilized with 50% phthalate. Infiltration with plastic was carried out in the following steps: 1:1 ether:plastic for 24 h, 1:3 ether:plastic for 24 h, and finally 100% plastic for 24 h. Following infiltration, samples were transferred into gelatin capsules and polymerized at 60C for 12 h, then transferred into 35C oven, and polymerized for at least 7 days. After polymerization, agar samples were cut into 1-μm-thick sections using dry glass knife with an ultramicrotome (Ultracut E, Reichert-Jung, Vienna, Austria). The slices were mounted in copper grids (mesh 50), coated with carbon, and stored over silica gel until analysis.

Leaf sections were analyzed in a Phillips EM 420 electron transmission microscope (Eindhoven, the Netherlands) with the energy dispersive system EDAX DX-4 (EDAX International, Mahwah, NJ 07430, USA). The operating parameters were as follows: accelerating voltage was 120 kV; take-off angle was 25; and the time for collecting X-rays was 60 live seconds. Probe measurements were made on xylem vessels in the bundle, spongy, and palisade mesophyll, adaxial, and abaxial epidermis. The following structures were examined: cell wall, vacuole, and chloroplast (mesophyll), and magnification was at 6350. Probe measurements of cell walls were taken with a long and narrow electron beam, and measurements of vacuole and chloroplasts were taken with a broad electron beam covering the target structures. For each section, 10–20 measurements were taken from each compartment. The X-ray spectra were processed with EDAX DX-4 software after manual fitting of the background. Concentrations of Na<sup>+</sup> and Cl were determined by analytical calibration standard of NaCl that established according to Fritz and Jentschke [61].

Values in the same column followed by different letters are significantly different (P < 0.05) between control and NaCl treatment.

Table 3. Salt compartmentation within leaf cell compartments of K. obovata and B. gymnorhiza.

forest. Mangrove propagules absorbed salt ions when they contacted seawater [7, 12]. Na+ and Cl increased in cell compartments of roots and leaves (Tables 2 and 3). This indicates that the salt ions taken up by roots transported to shoots under NaCl stress [12, 16, 22]. Our data show that there were marked differences in the pattern of salt compartmentation in the two mangroves. K. obovata exhibited a high capacity to exclude NaCl from root and leaf cells, whereas B. gymnorhiza are notable for (1) vacuolar compartmentation in mesophyll cells and (2) preferential accumulation of Na+ and Cl in epidermal vacuoles, relative to mesophyll vacuoles (Table 3). The ability to extrude Na+ from root cells of K. obovata likely results from an active Na+ /H+ antiport driven by H+ pumping activity of PM H+ -ATPase [7, 15]. Salt compartmentation in vacuoles likely depends on active transport of salt ions across the tonoplast. Salinity may increase the activity of vacuole H+ pumps, thus making a contribution to the compartmentation of toxic ions into the vacuoles via Na+ /H+ antiporter systems [62–64]. Mimura et al. found that the elevated concentrations of Na+ and Cl in swelling vacuoles were correlated with the saltinduced activation of tonoplast H+ -ATPase in suspension-cultured cells of B. sexangula [65]. We suggest that the two mangrove plants may maintain ROS homeostasis through limiting ROS production by a protective cellular salt compartmentation, in addition to scavenging ROS by antioxidant enzymes in a longer term of increasing salinity (see below). In brief:


#### 2.4. Antioxidant enzymes contributed to ROS homeostasis

#### 2.4.1. Activity of antioxidant enzymes in roots and leaves

forest. Mangrove propagules absorbed salt ions when they contacted seawater [7, 12]. Na+ and Cl increased in cell compartments of roots and leaves (Tables 2 and 3). This indicates that the salt ions taken up by roots transported to shoots under NaCl stress [12, 16, 22]. Our data show that there were marked differences in the pattern of salt compartmentation in the two mangroves. K. obovata exhibited a high capacity to exclude NaCl from root and leaf cells, whereas

Table 3. Salt compartmentation within leaf cell compartments of K. obovata and B. gymnorhiza.

Values in the same column followed by different letters are significantly different (P < 0.05) between control and NaCl

Compartment Treatment K. obovata B. gymnorhiza

88 Mangrove Ecosystem Ecology and Function

Xylem vessels (leaf vascular bundle) Control 131 102b 633 48a 309 22b 576 101b

Epidermal wall (abaxial and adaxial) Control 266 96b 725 181a 403 22b 812 101b

Mesophyll wall (palisade and spongy) Control 228 35b 669 224a 420 46b 545 67b

Epidermal vacuole (abaxial and adaxial) Control 75 71b 495 282a 221 42b 646 23b

Mesophyll vacuole (palisade and spongy) Control 86 14b 510 123a 123 16b 531 33b

Chloroplast (palisade and spongy) Control 103 18a 532 129a 182 69a 640 89a

(mesh 50), coated with carbon, and stored over silica gel until analysis.

NaCl that established according to Fritz and Jentschke [61].

treatment.

K. obovata and B. gymnorhiza leaves were sampled from control and stressed plants after 15 days of increasing NaCl treatment (100–400 mM). Standard procedures required for sample preparation and X-ray microanalysis were followed as described in Fritz [59, 60]. In brief, leaf segments, 2–3 mm long and 1–2 mm wide, were cut with a razor blade along the smaller veins adjacent to the central vein and immediately placed into aluminum sample holders and rapidly frozen in a 3:1 mixture of propane:isopentane at the temperature of liquid nitrogen. Samples were vacuum freeze-dried at 60C for 72 h and then slowly allowed to equilibrate to room temperature (ca. 22C) over a period of 24 h. Then, samples were stored over silica gel until infiltration in plastic. Freeze-dried leaf samples were transferred into vacuum-pressure chambers and infiltrated in ether at 27C overnight before infiltrating with plastic. The plastic used was a 1:1 mixture of styrene (Merck Schuchardt) and butyl methacrylate (Sigma-Aldrich) containing 1% benzoyl peroxide stabilized with 50% phthalate. Infiltration with plastic was carried out in the following steps: 1:1 ether:plastic for 24 h, 1:3 ether:plastic for 24 h, and finally 100% plastic for 24 h. Following infiltration, samples were transferred into gelatin capsules and polymerized at 60C for 12 h, then transferred into 35C oven, and polymerized for at least 7 days. After polymerization, agar samples were cut into 1-μm-thick sections using dry glass knife with an ultramicrotome (Ultracut E, Reichert-Jung, Vienna, Austria). The slices were mounted in copper grids

Leaf sections were analyzed in a Phillips EM 420 electron transmission microscope (Eindhoven, the Netherlands) with the energy dispersive system EDAX DX-4 (EDAX International, Mahwah, NJ 07430, USA). The operating parameters were as follows: accelerating voltage was 120 kV; take-off angle was 25; and the time for collecting X-rays was 60 live seconds. Probe measurements were made on xylem vessels in the bundle, spongy, and palisade mesophyll, adaxial, and abaxial epidermis. The following structures were examined: cell wall, vacuole, and chloroplast (mesophyll), and magnification was at 6350. Probe measurements of cell walls were taken with a long and narrow electron beam, and measurements of vacuole and chloroplasts were taken with a broad electron beam covering the target structures. For each section, 10–20 measurements were taken from each compartment. The X-ray spectra were processed with EDAX DX-4 software after manual fitting of the background. Concentrations of Na<sup>+</sup> and Cl were determined by analytical calibration standard of

Na<sup>+</sup> Cl Na<sup>+</sup> Cl

NaCl 246 4a 636 101a 729 119a 1069 254a

NaCl 377 110a 945 71a 840 119a 1305 254a

NaCl 336 27a 926 170a 904 287a 1445 418a

NaCl 183 133a 558 285a 509 125a 1148 121a

NaCl 134 31a 634 31a 263 6a 664 3a

NaCl 141 15a 681 45a 145 57a 494 101a

Under no-salt control conditions, total activity of measured antioxidant enzymes roots and leaves, SOD, APX, CAT, and GR, varied markedly during the observation period (Tables 4 and 5). This was presumably resulted from genetic difference of seedlings and variations in light intensity and air temperature. In our study, natural PAR was 400–1200 μmol m<sup>2</sup> s<sup>1</sup> , and air temperature was 20–35C over the duration of experiment. In general, activities of antioxidant enzymes in roots and leaves were not reduced upon increasing saline (with a few exceptions) but upregulated in both species (Tables 4 and 5). Noteworthy, there were species differences in antioxidant defense to increasing salinity. Activity of each component in the measured antioxidant defense system, SOD, APX, CAT, and GR, drastically increased in K. obovata roots at 300 mM NaCl, while the same trend was observed in B. gymnorhiza roots at 400 mM (Table 4). Furthermore, B. gymnorhiza leaves showed a higher increase of SOD, APX, and CAT at 400 mM NaCl as compared to K. obovata (Table 5). SOD of K. obovata was upregulated after salt exposure, but the response is quite variable in roots and leaves. Root SOD activity was increased by 100 and 300 mM NaCl, while leaf activity was increased by 200 and 400 mM (Tables 4 and 5). SOD activity in roots and leaves of B. gymnorhiza did not increase after exposure to 100–300 mM NaCl (Tables 4 and 5). The variable response of antioxidant enzymes to salt treatment was also seen in GR. It exhibited a marked elevation in B. gymnorhiza leaves at 100 mM NaCl, whereas the steady increase of GR in K. obovata was observed at a salt concentration of 300 mM (root) and 400 mM (leaf) (Tables 4 and 5).

SOD isoenzymes and CAT isoenzymes in roots and leaves were analyzed by native PAGE. In root extracts, three dominant SOD isoenzymes were detected in K. obovata roots, whereas there were two SOD isoforms in B. gymnorhiza (Figure 1A and B). KCN and H2O2 inhibited the activity of these isoenzymes in the two species, indicating they were CuZn-SOD isoforms (Figure 1A and B). NaCl did not restrict activity of all SOD isoforms in K. obovata roots during the period of salt treatment (Figure 1C), but a marked elevation of CuZn-SODs was observed in B. gymnorhiza at 300–400 mM NaCl (Figure 1D).

Three dominant SOD isoenzymes were detected in control leaves of both species but with different patterns (Figure 2A and B). KCN and H2O2 inhibited activity of two SOD isoenzymes in both genotypes, indicating that these were CuZn-SOD isoforms (Figure 2A and B). Another SOD isoform was defined as Mn-SOD since it was resistant to both inhibitors (Figure 2A and B). Activity of SOD isoenzymes in K. obovata leaves was increased by a lower salt, e.g., Mn-SOD at 100 and 200 mM NaCl and Cu/Zn-SOD1 and Cu/Zn-SOD2 at 200 NaCl mM (Figure 2C). B. gymnorhiza upregulated both Mn-SOD and Cu/Zn-SODs at a higher salt, 300–400 mM NaCl (Figure 2D).

Native PAGE of root extract showed three CAT isoenzymes in K. obovata and two in B. gymnorhiza (Figure 3). Increasing NaCl, from 100 to 400 mM, did not restrict activity of all CAT isoforms in both species, although activity of CAT isoforms in control roots fluctuated over the observation period (Figure 3). Compared with K. obovata, B. gymnorhiza exhibited typically a higher activity of CAT1 and CAT2 regardless of treatments (Figure 3).

Three and four CAT isoenzymes were identified in K. obovata and B. gymnorhiza leaves, respectively (Figure 4). Salt markedly enhanced the activity of CAT2 in K. obovata at 200 mM; however, the enhancement of NaCl on CAT2, CAT3, and CAT4 in B. gymnorhiza was observed at 300–400 mM NaCl (Figure 4).

Treatment

K. obovata

SOD

> Control

NaCl (100 mM)

Control NaCl (200 mM)

Control NaCl (300 mM)

Control NaCl (400 mM) K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. NaCl saline was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Roots of

control and salinized plants were harvested at day 2, day 5, day 9, and day 14, respectively.

ground in cold mortars using liquid nitrogen and

centrifuged

measurement,

serum albumin as standard. Total SOD activity was assayed as described in Giannopolits methionine (130 mM), 0.3 ml nitroblue tetrazolium salt (750 μM), 0.3 ml Na2EDTA (100 μM), 30 μ<sup>l</sup> enzyme extract, and 0.3 ml riboflavin (20 μM). The cocktail was mixed and then illuminated

by cool white fluorescent lamps (30 μmol m2 s

extract. The increase in absorbance at 560 nm, due to the formation of formazan, was recorded. SOD activity was calculated as Aenzyme Acontrol. One unit of SOD is defined as the amount of

enzyme that causes a 50% inhibition of the

Total CAT activity was determined

(3.0 ml) contained 50 mM potassium phosphate (pH 7.0) and 2% H

used to calculate the activity. One unit is defined as the amount of catalase decomposing 50 mM sodium phosphate buffer (30 μl, pH 7.0) was added into the reaction system instead of the enzyme extract.

Total APX activity was assayed as described in Mishra et al. [68]. The reaction mixture (3.0 ml) contained 50 mM potassium phosphate (pH 7.0), 15 mM ascorbic acid, and 30 mM H

μ<sup>l</sup> enzyme extract. The reaction at 25C was initiated by the addition of H

2.8 mM1 cm1) for 2 min. One unit of APX is defined as the amount of enzyme required to consume 1.0 μmol of ascorbate per min. Correction was done for the low,

of ASC by H

Total GR activity was determined at 25C by measuring the rate of NADPH oxidation [47]. The reaction mixture (3.0 ml) contained 50 mM potassium phosphate (pH 7.8), 2.0 mM Na2EDTA, 0.15 mM NADPH, 0.5 mM oxidized glutathione (GSSG), and 50 μ<sup>l</sup> of enzyme extract. NADPH was added to start the reaction, and the decrease in absorbance at 340 nm (extinction coefficient

6.2 mM1 cm1) was recorded as soon as the reaction began. Corrections were made for the background the amount of enzyme that oxidizes 1.0 μmol of NADPH per min. For blank controls, a 50 μ<sup>l</sup> potassium phosphate buffer (50 mM, pH 7.8) was added into the reaction system instead of the

enzyme extract.

Each value (SE) is the mean of three plants, and values in the same column followed by different letters are significantly Table 4. Effects of increasing NaCl on activity of SOD, CAT, APX, and GR in roots of K. obovata and B. gymnorhiza.

O2 2 [69]. In blank controls, a 30 μ<sup>l</sup> potassium phosphate buffer (50 mM, pH 7.0) was added into the reaction system instead of the enzyme extract.

 1.0 mM ascorbic acid (ASC) was added into the enzyme extraction buffer [27]. Protein

 at 10,000 g for 20 min at 4C and used for the assays of superoxide dismutase (SOD), catalase (CAT), and glutathione

 244.4 64.1a

 54.6 18.6a

 77.8 4.5a

 26.1 0.5a

 Three replicated plants per treatment were harvested at each sampling time. Roots (ca. 0.5 g) were

 reductase (GR). For ascorbate peroxidase (APX)

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

concentration

 in the supernatant was determined according to Bradford [66] using bovine

homogenized

 in a 3.0-ml ice-cold extraction buffer [50 mM potassium phosphate, pH 7.0, 1.0 mM EDTA, 1%(w/v) PVP]. The extracts were

 and Ries [67] with

1) for 6 min. For blank controls, a 30 μ<sup>l</sup> potassium phosphate buffer (50 mM, pH 7.8) was added into the reaction system instead of the enzyme

aforementioned

spectrophotometrically

 reaction in comparison with a blank sample.

 by measuring the rate of H

O2 2. Immediately,

O2 2

 after the addition of 30 μ<sup>l</sup> enzyme extract, the initial linear rate of decrease in absorbance at 240 nm was

 1.0 μmol of hydrogen peroxide per minute at pH 7.0 at 25C. In blank controls, the same amount of

O2 2. APX activity was immediately

 measured by recording the decrease in absorbance at 290 nm (extinction coefficient

 absorbance at 340 nm, without the addition of NADPH. One unit of GR is defined as

 different (<sup>P</sup> < 0.05) between control and NaCl treatment.

91

O2 2 and 30

nonenzymatic

 oxidation

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consumption

 (extinction coefficient 39.4 mM1 cm1) at 240 nm for 3 min [44]. The reaction mixture

modifications.

 The reaction mixture contained 1.8 ml potassium phosphate (50 mM, pH 7.8), 0.3 ml L-

 377.4 32.9a 193.8 88.8a

 35.1 6.3a

 62.2 5.7a

 17.9 3.6a

 60.71 8.0a

 343.7 96.4a

 49.4 11.4a

 112.2 61.2a

148.4 1.7b

 28.9 6.2b

 119.8 16.4b

 17.4 6.0b

 151.9 27.2a

 181.4 15.4a

 77.6 12.2a

 406.4 21.5a 108.0 20.2a

 152.9 21.4a

 249.7 46.5a

 49.9 8.0a

 136.2 11.1a

 272.3 22.2a

 15.7 3.3a

246.9 25.0b

 138.1 21.2a

 270.0 22.3a

 33.7 15.2a

CAT

APX

GR

B. gymnorhiza

SOD 133.3 9.0a 125.2 7.3a 149.0 31.3a 148.6 17.9a

98.4 17.4a 121.8 28.1a 132.6 11.8b 232.4 19.5a

 132.6 1.7a

 361.6 80.7a

 59.8 15.0a

 109.0 16.3a

 218.1 55.6b

 23.7 2.3b

 27.8 1.2a

 178.1 47.7a

 29.8 6.5a

 46.7 10.1a

 26.4 1.8a

 120.8 27.7a

 30.0 9.4a

 369.4 94.6a

 30.4 13.8a

 43.3 2.9a

 377.1 34.1a

 19.1 5.6a

 45.1 19.0a

 144.1 18.6a

 20.7 3.1a

 27.8 4.8a

 130.2 7.8a

 12.9 2.9a

CAT

APX

GR


and 5). This was presumably resulted from genetic difference of seedlings and variations in light intensity and air temperature. In our study, natural PAR was 400–1200 μmol m<sup>2</sup> s

and air temperature was 20–35C over the duration of experiment. In general, activities of antioxidant enzymes in roots and leaves were not reduced upon increasing saline (with a few exceptions) but upregulated in both species (Tables 4 and 5). Noteworthy, there were species differences in antioxidant defense to increasing salinity. Activity of each component in the measured antioxidant defense system, SOD, APX, CAT, and GR, drastically increased in K. obovata roots at 300 mM NaCl, while the same trend was observed in B. gymnorhiza roots at 400 mM (Table 4). Furthermore, B. gymnorhiza leaves showed a higher increase of SOD, APX, and CAT at 400 mM NaCl as compared to K. obovata (Table 5). SOD of K. obovata was upregulated after salt exposure, but the response is quite variable in roots and leaves. Root SOD activity was increased by 100 and 300 mM NaCl, while leaf activity was increased by 200 and 400 mM (Tables 4 and 5). SOD activity in roots and leaves of B. gymnorhiza did not increase after exposure to 100–300 mM NaCl (Tables 4 and 5). The variable response of antioxidant enzymes to salt treatment was also seen in GR. It exhibited a marked elevation in B. gymnorhiza leaves at 100 mM NaCl, whereas the steady increase of GR in K. obovata was observed at a salt concentration of 300 mM (root) and 400 mM (leaf)

SOD isoenzymes and CAT isoenzymes in roots and leaves were analyzed by native PAGE. In root extracts, three dominant SOD isoenzymes were detected in K. obovata roots, whereas there were two SOD isoforms in B. gymnorhiza (Figure 1A and B). KCN and H2O2 inhibited the activity of these isoenzymes in the two species, indicating they were CuZn-SOD isoforms (Figure 1A and B). NaCl did not restrict activity of all SOD isoforms in K. obovata roots during the period of salt treatment (Figure 1C), but a marked elevation of CuZn-SODs was observed

Three dominant SOD isoenzymes were detected in control leaves of both species but with different patterns (Figure 2A and B). KCN and H2O2 inhibited activity of two SOD isoenzymes in both genotypes, indicating that these were CuZn-SOD isoforms (Figure 2A and B). Another SOD isoform was defined as Mn-SOD since it was resistant to both inhibitors (Figure 2A and B). Activity of SOD isoenzymes in K. obovata leaves was increased by a lower salt, e.g., Mn-SOD at 100 and 200 mM NaCl and Cu/Zn-SOD1 and Cu/Zn-SOD2 at 200 NaCl mM (Figure 2C). B. gymnorhiza upregulated both Mn-SOD and Cu/Zn-SODs at a higher salt, 300–400 mM NaCl

Native PAGE of root extract showed three CAT isoenzymes in K. obovata and two in B. gymnorhiza (Figure 3). Increasing NaCl, from 100 to 400 mM, did not restrict activity of all CAT isoforms in both species, although activity of CAT isoforms in control roots fluctuated over the observation period (Figure 3). Compared with K. obovata, B. gymnorhiza exhibited

Three and four CAT isoenzymes were identified in K. obovata and B. gymnorhiza leaves, respectively (Figure 4). Salt markedly enhanced the activity of CAT2 in K. obovata at 200 mM; however, the enhancement of NaCl on CAT2, CAT3, and CAT4 in B. gymnorhiza was observed

typically a higher activity of CAT1 and CAT2 regardless of treatments (Figure 3).

(Tables 4 and 5).

90 Mangrove Ecosystem Ecology and Function

(Figure 2D).

at 300–400 mM NaCl (Figure 4).

in B. gymnorhiza at 300–400 mM NaCl (Figure 1D).

1 , glutathioneμ<sup>l</sup>enzyme6.2 mM1 cm1) was recorded as soon as the reaction began. Corrections were made for the background absorbance at 340 nm, without the addition of NADPH. One unit of GR is defined as the amount of enzyme that oxidizes 1.0 μmol of NADPH per min. For blank controls, a 50 μ<sup>l</sup> potassium phosphate buffer (50 mM, pH 7.8) was added into the reaction system instead of the enzyme extract.

0.15 mM NADPH, 0.5 mM oxidized

 (GSSG), and 50

 of

 extract. NADPH was added to start the reaction, and the decrease in absorbance at 340 nm (extinction coefficient

Each value (SE) is the mean of three plants, and values in the same column followed by different letters are significantly different (<sup>P</sup> < 0.05) between control and NaCl treatment.

Table 4. Effects of increasing NaCl on activity of SOD, CAT, APX, and GR in roots of K. obovata and B. gymnorhiza.


K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. NaCl saline was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Roots of control and salinized plants were harvested at day 2, day 5, day 9, and day 14, respectively. Three replicated plants per treatment were harvested at each sampling time. Leaf tissues (ca. 0.5 g) were ground in cold mortars using liquid nitrogen and homogenized in a 3.0-ml ice-cold extraction buffer [50 mM potassium phosphate, pH 7.0, 1.0 mM EDTA, 1%(w/v) PVP]. The extracts were centrifuged at 10,000 g for 20 min at 4C and used for the assays of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR). For ascorbate peroxidase (APX) measurement, 1.0 mM ascorbic acid (ASC) was added into the enzyme extraction buffer [27]. Protein concentration in the supernatant was determined according to Bradford [66] using bovine serum albumin as standard. Methodologies for total activity of SOD, CAT, APX, and GR are shown in Table 4 legend.

Each value ( SE) is the mean of three plants, and values in the same column followed by different letters are significantly different (<sup>P</sup> < 0.05) between control and NaCltreatment.

Table 5. Effects of increasing NaCl on activity of SOD, CAT, APX, and GR in leaves of K. obovata and B. gymnorhiza.

Figure 1. Identification of root SOD isoenzymes and effect of increasing NaCl on SOD isoforms in roots of K. obovata and B. gymnorhiza. (A and B) Identification of root SOD isoenzymes. Different isoforms of SOD in K. obovata and B. gymnorhiza were determined by incubating the gels with 5 mM H2O2 to inhibit both Cu/Zn-SOD and Fe-SOD or with 5 mM KCN to inhibit only Cu/ZnSOD [70]. Meanwhile, Mn-SOD activity was obtained since it is resistant to both inhibitors, H2O2 and KCN. (C and D) NaCl effects on SOD isoforms. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Roots of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. Electrophoretic separation for CAT and SOD was performed at 4C using the Laemmli (1970) buffer systems [71]. Prior to loading onto the gels, crude protein extracts were mixed with 10% glycerol (v/v) and 0.25% bromophenol blue. Separating gel (10%) and stacking gel (3.9%) were used for native PAGE of SOD isoenzymes. SOD isoenzymes were visualized by the activity staining [72]. In each track 20 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. The gels were run at a constant current, 35 mA at 4C for no longer than 6 h. Immediately, after electrophoretic separation, gels were incubated in staining buffer (50 mM potassium phosphate buffer, pH 7.8, 0.1 mM EDTA, 28 mM TEMED, 0.003 mM riboflavin, and 0.25 mM NBT) for 30 min in the dark at room temperature. Thereafter, gels were exposed to two fluorescent tubes (20 W each) until the SOD bands became visible (SOD bands appeared as light bands on a blue background).

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Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under… http://dx.doi.org/10.5772/intechopen.75583 93

Figure 1. Identification of root SOD isoenzymes and effect of increasing NaCl on SOD isoforms in roots of K. obovata and B. gymnorhiza. (A and B) Identification of root SOD isoenzymes. Different isoforms of SOD in K. obovata and B. gymnorhiza were determined by incubating the gels with 5 mM H2O2 to inhibit both Cu/Zn-SOD and Fe-SOD or with 5 mM KCN to inhibit only Cu/ZnSOD [70]. Meanwhile, Mn-SOD activity was obtained since it is resistant to both inhibitors, H2O2 and KCN. (C and D) NaCl effects on SOD isoforms. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Roots of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. Electrophoretic separation for CAT and SOD was performed at 4C using the Laemmli (1970) buffer systems [71]. Prior to loading onto the gels, crude protein extracts were mixed with 10% glycerol (v/v) and 0.25% bromophenol blue. Separating gel (10%) and stacking gel (3.9%) were used for native PAGE of SOD isoenzymes. SOD isoenzymes were visualized by the activity staining [72]. In each track 20 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. The gels were run at a constant current, 35 mA at 4C for no longer than 6 h. Immediately, after electrophoretic separation, gels were incubated in staining buffer (50 mM potassium phosphate buffer, pH 7.8, 0.1 mM EDTA, 28 mM TEMED, 0.003 mM riboflavin, and 0.25 mM NBT) for 30 min in the dark at room temperature. Thereafter, gels were exposed to two fluorescent tubes (20 W each) until the SOD bands became visible (SOD bands appeared as light bands on a blue background).

Treatment

K. obovata

SOD

> Control

NaCl (100 mM)

Control NaCl (200 mM)

Control NaCl (300 mM)

Control NaCl (400 mM)

K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. NaCl saline was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10

(400 mM). Roots of control and salinized plants were harvested at day 2, day 5, day 9, and day 14, respectively.

sampling time. Leaf tissues (ca. 0.5 g) were ground in cold mortars using liquid nitrogen and

phosphate,

catalase (CAT), and glutathione

[27]. Protein

CAT, APX, and GR are shown in Table 4 legend.

Each value (

treatment.

Table 5. Effects of increasing NaCl on activity of SOD, CAT, APX, and GR in leaves of K. obovata and B. gymnorhiza.

SE) is the mean of three plants, and values in the same column followed by different letters are

concentration

 in the supernatant

 was determined

 according to Bradford [66] using bovine serum albumin as standard.

 reductase (GR). For ascorbate peroxidase

 pH 7.0, 1.0 mM EDTA, 1%(w/v) PVP]. The extracts were centrifuged

 74.8

 4.2a

 356.6

 15.1a

 129.8

 2.5a

 36.8

 4.1a

59.7

 8.6a

 Three replicated plants per treatment were harvested at each

homogenized

 at 10,000 g for 20 min at 4C and used for the assays of superoxide

 (APX)

measurement,

 1.0 mM ascorbic acid (ASC) was added into the enzyme extraction buffer

 in a 3.0-ml ice-cold extraction buffer [50 mM

potassium

 dismutase (SOD),

Methodologies

significantly

 different (<sup>P</sup> < 0.05) between control and NaCl

 for total activity of SOD,

 250.7

 29.6a

 213.9

 16.3a

 7.4

 2.1a

 64.4 52.2

 13.9b

 331.3

 4.0a

 111.9

 6.4a

 19.9

 1.2b

30.6

 9.4b

 75.9

 5.1b

 116.1

 15.7b

 9.5

 1.4a

 10.9a

 150.5

 29.1a

 47.3

 4.7b

 16.0

 1.0a

46.4

 6.6a

 125.2

 2.1a

 60.4

 11.7b

 12.9

 3.3a

 83.8 66.2

 8.6a

 135.6

 21.8a

 83.6

 6.4a

 22.1

 6.4a

32.0

 4.9a

 118.0

 1.4a

 130.5

 12.4a

 18.9

 3.3a

 5.0a

 205.7

 22.8a

 90.7

 16.5a

 32.0

 2.6a

42.2

 7.9a

 89.1

 9.9a

 179.0

 10.1a

 9.7

 1.6b

 67.5 61.2

 5.9b

 223.9

 3.3a

 102.9

 1.9a

 25.8

 3.4a

52.2

 4.2a

 88.7

 8.2a

 181.2

 19.5a

 22.5

 0.2a

92 Mangrove Ecosystem Ecology and Function

 17.6a

 138.9

 7.5a

 76.4

 5.4a

 20.0

 3.1a

32.6

 4.5a

 37.5

 9.0a

 64.9

 7.5a

 10.4

 1.5a

49.1

 8.6a

 107.4

 6.5b

 62.0

 2.2a

 16.5

 3.1a

38.1

 3.0a

 69.3

 24.7a

 58.7

 1.1a

 5.8

 0.6b

CAT

APX

GR

SOD

CAT

APX

GR

B. gymnorhiza

Figure 2. Identification of leaf SOD isoenzymes and effect of increasing NaCl on SOD isoforms in leaves of K. obovata and B. gymnorhiza. (A and B) Identification of leaf SOD isoenzymes. (C and D) NaCl effects on SOD isoforms. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Leaves of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. In each track 40 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. Electrophoretic separation for SOD isoforms is shown in Figure 1 legend.

2.4.2. Salt-elicited antioxidant enzymes contributed to ROS homeostasis

negative bands, representing CAT enzymes, appeared on the blue background of the gel.

Salt-elicited antioxidant enzymes contributed to ROS homeostasis in the two mangroves but with different patterns. Salinized K. obovata exhibited an early and rapid antioxidative defense as compared to B. gymnorhiza. After exposure to 100–200 mM NaCl, total SOD activity in K. obovata leaves marked increased coincident with the increase of Cu/Zn-SOD1, Cu/Zn-

Figure 3. Effect of increasing NaCl on CAT isoforms in roots of K. obovata and B. gymnorhiza. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Roots of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. Stacking gel (3.9%) and separating gel (7.5%) containing 0.5% soluble starch were used for native PAGE of CAT isoforms. In each track 20 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. The activity staining procedure for catalase was followed as per Thorup et al. [73] with modifications. Immediately, after electrophoresis as described above, the gel was incubated in a solution containing 18 mM sodium thiosulphate and 679 mM H2O2 for 30 s at room temperature (25C). The gel was then rinsed with distilled water and incubated in 90 mM potassium iodide solution acidified with 0.5% glacial acetic acid. Finally,

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Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under… http://dx.doi.org/10.5772/intechopen.75583 95

Figure 3. Effect of increasing NaCl on CAT isoforms in roots of K. obovata and B. gymnorhiza. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Roots of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. Stacking gel (3.9%) and separating gel (7.5%) containing 0.5% soluble starch were used for native PAGE of CAT isoforms. In each track 20 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. The activity staining procedure for catalase was followed as per Thorup et al. [73] with modifications. Immediately, after electrophoresis as described above, the gel was incubated in a solution containing 18 mM sodium thiosulphate and 679 mM H2O2 for 30 s at room temperature (25C). The gel was then rinsed with distilled water and incubated in 90 mM potassium iodide solution acidified with 0.5% glacial acetic acid. Finally, negative bands, representing CAT enzymes, appeared on the blue background of the gel.

#### 2.4.2. Salt-elicited antioxidant enzymes contributed to ROS homeostasis

Figure 2. Identification of leaf SOD isoenzymes and effect of increasing NaCl on SOD isoforms in leaves of K. obovata and B. gymnorhiza. (A and B) Identification of leaf SOD isoenzymes. (C and D) NaCl effects on SOD isoforms. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Leaves of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. In each track 40 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. Electrophoretic separation for SOD isoforms is shown in Figure 1

legend.

94 Mangrove Ecosystem Ecology and Function

Salt-elicited antioxidant enzymes contributed to ROS homeostasis in the two mangroves but with different patterns. Salinized K. obovata exhibited an early and rapid antioxidative defense as compared to B. gymnorhiza. After exposure to 100–200 mM NaCl, total SOD activity in K. obovata leaves marked increased coincident with the increase of Cu/Zn-SOD1, Cu/Zn-

we found that a salt-resistant Populus species, P. euphratica, was able to enhance active oxygen detoxification by increasing antioxidant enzymes at an early stage of salt stress, thus preventing an oxidative burst [26]. Protein abundance of SOD in K. obovata leaves might increase under a high level of NaCl [53]. Furthermore, Jing et al. showed that NaCl increased KcCSD transcription in K. candel leaves [16]. Thus, it could be inferred that K. obovata would upregulate the gene expression of antioxidant enzymes to deal with a long-term saline stress. Salt-induced elevation of antioxidant enzymes in B. gymnorhiza was usually found at high salinity. SOD, APX, and CAT in roots and leaves of B. gymnorhiza were all upregulated by 400 mM NaCl (Tables 4 and 5). Native PAGE analyses showed that the elevation of leaf SOD in salinized B. gymnorhiza resulted from the increase of all detected SOD isoforms, Mn-SOD, Cu/Zn-SOD1, and Cu/Zn-SOD2 (Table 5 and Figure 2), whereas the rise of SOD activity in roots was mainly the result of Cu/Zn-SODs (Table 4 and Figure 1). A similar trend was found in salt-stressed B. parviflora in which a significant enhancement of SOD was observed in leaves, mainly due to an increase in Mn-SOD and Fe-SOD2 [51]. NaCl-induced activity of CAT in B. gymnorhiza leaves was due to the increase of CAT2, CAT3, and CAT4 (Table 5 and Figure 4). Noteworthy, both K. obovata and B. gymnorhiza maintained evident activity of each CAT isoform in root tissues at 400 mM NaCl (Figure 3), showing a constant and stable capacity to

Salt Compartmentation and Antioxidant Defense in Roots and Leaves of Two Non-Salt Secretor Mangroves under…

whereas there was no corresponding changes in H2O2 when K. obovata and B. gymnorhiza were

We conclude that both K. obovata and B. gymnorhiza maintained ROS homeostasis as external

i. K. obovata restricted the increase of salt influx, which is necessary to avoid abrupt increase of ROS. Moreover, K. obovata was sensitive to lower salt stress and rapidly initiated antioxidant defense to scavenge active oxygen species by, at least in part, components of

ii. B. gymnorhiza maintained higher capacity to detoxify ROS at high salinity; furthermore, the effective vacuolar salt compartmentation in mesophyll cells and the preferential accumulation of Na<sup>+</sup> and Cl in epidermal vacuoles may benefit B. gymnorhiza plants to reduce ROS production in the mesophyll. Together with antioxidant mechanisms, both enzymatic and nonenzymatic, the critical balance between ROS production and ROS detoxification is remained under salt stress. To elucidate the mechanism underlying the vacuolar compartmentation, critical ion channels and transporters in the vacuolar mem-

proton pumps, which accelerate the salt exclusion across the plasma membrane, need to

• increased by 82–83%,

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97

/H<sup>+</sup> antiport system and

control H2O2 levels. This may partly explain the finding that root O2

NaCl saline increased from 100 to 400 mM but via different pathways:

the ASC-GSH cycle, e.g., SOD, APX, CAT, and GR. The Na+

branes need to be identified in future investigations.

subjected to 400 mM NaCl (Table 1).

be further investigated.

3. Conclusions

Figure 4. Effect of increasing NaCl on CAT isoforms in leaves of K. obovata and B. gymnorhiza. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Leaves of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. In each track 40 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. Electrophoretic separation for CAT isoforms is shown in Figure 3 legend.

SOD2, and Mn-SOD (Table 5, Figure 2), even though Fe-SOD was not detected as that reported in other mangroves [51]. CAT in K. obovata leaves resembles the trend of SOD, and the increased activity was presumably due to the rise of CAT2 (Table 5, Figure 4). This is inconsistent with a previous report conducted on B. parviflora in which NaCl induced a decrease of CAT activity [51]. In the present study, the coincident increase of CAT with SOD in K. obovata reveals an elevated capacity to detoxify both O2 • and H2O2 that is caused by NaCl, which is required for rapid removal of ROS and thus avoids oxidative damage. Likewise, we found that a salt-resistant Populus species, P. euphratica, was able to enhance active oxygen detoxification by increasing antioxidant enzymes at an early stage of salt stress, thus preventing an oxidative burst [26]. Protein abundance of SOD in K. obovata leaves might increase under a high level of NaCl [53]. Furthermore, Jing et al. showed that NaCl increased KcCSD transcription in K. candel leaves [16]. Thus, it could be inferred that K. obovata would upregulate the gene expression of antioxidant enzymes to deal with a long-term saline stress.

Salt-induced elevation of antioxidant enzymes in B. gymnorhiza was usually found at high salinity. SOD, APX, and CAT in roots and leaves of B. gymnorhiza were all upregulated by 400 mM NaCl (Tables 4 and 5). Native PAGE analyses showed that the elevation of leaf SOD in salinized B. gymnorhiza resulted from the increase of all detected SOD isoforms, Mn-SOD, Cu/Zn-SOD1, and Cu/Zn-SOD2 (Table 5 and Figure 2), whereas the rise of SOD activity in roots was mainly the result of Cu/Zn-SODs (Table 4 and Figure 1). A similar trend was found in salt-stressed B. parviflora in which a significant enhancement of SOD was observed in leaves, mainly due to an increase in Mn-SOD and Fe-SOD2 [51]. NaCl-induced activity of CAT in B. gymnorhiza leaves was due to the increase of CAT2, CAT3, and CAT4 (Table 5 and Figure 4).

Noteworthy, both K. obovata and B. gymnorhiza maintained evident activity of each CAT isoform in root tissues at 400 mM NaCl (Figure 3), showing a constant and stable capacity to control H2O2 levels. This may partly explain the finding that root O2 • increased by 82–83%, whereas there was no corresponding changes in H2O2 when K. obovata and B. gymnorhiza were subjected to 400 mM NaCl (Table 1).

### 3. Conclusions

SOD2, and Mn-SOD (Table 5, Figure 2), even though Fe-SOD was not detected as that reported in other mangroves [51]. CAT in K. obovata leaves resembles the trend of SOD, and the increased activity was presumably due to the rise of CAT2 (Table 5, Figure 4). This is inconsistent with a previous report conducted on B. parviflora in which NaCl induced a decrease of CAT activity [51]. In the present study, the coincident increase of CAT with SOD

Figure 4. Effect of increasing NaCl on CAT isoforms in leaves of K. obovata and B. gymnorhiza. K. obovata and B. gymnorhiza plants were subjected to increasing NaCl treatment. Increasing NaCl was applied at day 1 (100 mM), day 3 (200 mM), day 6 (300 mM), and day 10 (400 mM). Control plants were kept well watered with no addition of NaCl. Leaves of control and salinized plants were harvested at day 3, day 6, day 10, and day 15, respectively. Three replicated plants per treatment were harvested at each sampling time. The three replicates were extracted independently and ran on three different gels, a representative one of which is shown in the figure. In each track 40 μg of soluble protein was applied to native polyacrylamide gel electrophoresis at 4C. Electrophoretic separation for CAT isoforms is shown in Figure 3

NaCl, which is required for rapid removal of ROS and thus avoids oxidative damage. Likewise,

• and H2O2 that is caused by

in K. obovata reveals an elevated capacity to detoxify both O2

legend.

96 Mangrove Ecosystem Ecology and Function

We conclude that both K. obovata and B. gymnorhiza maintained ROS homeostasis as external NaCl saline increased from 100 to 400 mM but via different pathways:


### Acknowledgements

The research was supported jointly by the National Natural Science Foundation of China (grant nos. 31770643, 31570587, and 31160150), Beijing Natural Science Foundation (grant no. 6182030), the Research Project of the Chinese Ministry of Education (grant no. 113013A), the Program of Introducing Talents of Discipline to Universities (111 Project, grant no. B13007), and the Natural Science Foundation of Hainan Province (grant no. 30408). Ms. Huijuan Zhu, Ms. Yunxia Zhang, Mr. Yong Shi, and Mr. Jie Shao all from Beijing Forestry University are greatly acknowledged for their assistance in electrophoresis and activity measurements of antioxidant enzymes. We thank Ms. Hui Zhang (Beijing Forestry University) for her contribution to the SEM-EDAX analysis.

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### Conflict of interest

The authors declare that there is no conflict of interest.

### Author details

Niya Li1,2, Xiaoyang Zhou1 , Ruigang Wang1,3, Jinke Li1 , Cunfu Lu1 and Shaoliang Chen<sup>1</sup> \*

\*Address all correspondence to: lschen@bjfu.edu.cn

1 Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, College of Biological Sciences and Technology, Beijing Forestry University, Beijing, PR China

2 Department of Biology, Hainan Normal University, Haikou, PR China

3 Center for Research in Ecotoxicology and Environmental Remediation, Agro-environmental Protection Institute, Ministry of Agriculture, Tianjin, PR China

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Acknowledgements

98 Mangrove Ecosystem Ecology and Function

tion to the SEM-EDAX analysis.

The authors declare that there is no conflict of interest.

\*Address all correspondence to: lschen@bjfu.edu.cn

, Ruigang Wang1,3, Jinke Li1

Biological Sciences and Technology, Beijing Forestry University, Beijing, PR China

2 Department of Biology, Hainan Normal University, Haikou, PR China

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**Section 4**

**Mangrove Faunal Ecology**

