**2. Research methods**

## **2.1 Study site**

*Invertebrates - Ecophysiology and Management*

in the rocky intertidal zone.

composed of six 1 m2

processes primarily competition for space. The so called competitive dominance is manifested through the use of space. Community organization depends on consumer-prey interaction, physical disturbances as factors and competition for space [6]. Gastropods are the largest and the most diverse faunal group in *Phylum Mollusca*. The gastropods are known to have a wide range of distribution. They can live in a variety of habitats and are adapted to varying environmental conditions as affected by daily fluctuating tidal patterns and duration of exposure to sunlit which determine diurnal temperatures. These one-shelled marine invertebrates considered as economically important are the major inhabitants of the intertidal marine ecosystem. Marine gastropod species are varied and abundant as an important source of food for higher consumers and contribute to coastal food chains [7, 8]. Mollusks in the rocky shore are highly important in maintaining dynamics in the shore and ecological balance in beaches in addition to their key role in the trophic chains and nutrient recirculation [9]. Further, gastropods have important role in structuring the intertidal assemblages and regulating the intertidal communities since they can respond to variation in microhabitats in a vertical gradient and change their behavior in response to environmental occurrences [10]. Gastropod assemblage is influenced by the characteristic substrate which the majority of the shores are rocks. Characteristically, gastropods show variation in sizes, color and other phenotypic diversity [11]. Gastropods are motile however they are comparatively slow in locomotion which prevents them from moving into and out of the intertidal zone over a relatively short period of tidal range [12]. Hence these molluscan descendants have low migration potential which determines habitat stability

Studies on gastropod assemblage and diversity were conducted in various intertidal habitats of the marine ecosystem. A biodiversity study of gastropod in the intertidal zone of fine sand and coral reef was conducted in January 2017 in Sombu Beach, Wakatobi, Indonesia using quadrant plot method. Ten transects along the beach were established composed of four plots. There were 40 plots used as sources of data for analysis. The diversity of gastropod community was determined using Shannon-Wiener index [H′], evenness index (E) and dominance index (D). Results showed 13 species of gastropods which belong to three genera since the variety of substrate is low which has an impact on food resource and habitat of the identified gastropods [13]. A baseline study was conducted between November 2016 and February 2017 on marine gastropods diversity and distribution in two intertidal rocky shores of Terengganu, Peninsular Malaysia. The intertidal area was categorized and divided into three zones: upper, middle and lower. A 40 m length transect

quadrats was laid at random perpendicular to shore. Results

revealed a total of five subclasses of gastropods which belong to nine families and 28 species from upper to lower intertidal zones. Diversity indices based on the results of Shannon-Wiener index (H) and Pielou's evenness index (J') were compared with reference to the identified zones [14]. In another study, a spatial distribution of macroinvertebrates on intertidal rocky shores was conducted in Gorgona Island, Colombia of the Tropical Eastern Pacific. Qualitative data were determined using rapid ecological assessments while quadrat method for quantitative data. Species richness, abundance and diversity were determined using Shannon-Wiener H′ and Pielou J' for evenness. Results of the study revealed 121 species of macroinvertebrates. Mollusks were the most abundant in terms of species and individual count. Researchers concluded that environmental stressor, heterogeneity and stability are limiting factors on the spatial distribution of macroinvertebrates species in this particular area of intertidal rocky shores [15]. A biodiversity study of gastropoda was conducted in the coastal waters of Ambon Island, Indonesia to determine the correlation between the physico-chemical factors and the diversity of coastal waters

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The study area is located in the northeastern part of Dry Dock Beach commonly known as Asry Beach in Hidd, Muharraq having geographic coordinates of 26.1957°N and 50.6623°E. The total area of the intertidal zone is 206.30 m stretch where people usually perform beach activities during low tide. Part of the area is a 73.05 m stretch which composed the rocky intertidal biota (**Figure 1**). Both macrofauna and macroflora assemblages abound in the area in spite of the various human activities and other natural environmental occurrences.

## **2.2 Sampling, identification and field collection**

This particular research was undertaken from January 2016 to January 2018 in a small parcel of the rocky environment of Dry Dock Beach commonly called Asry Beach in Muharraq, Kingdom of Bahrain. Sampling was done every month during the low tide between 7:00 and 1:00 pm. Belt transect method [12–14] was utilized for the quantitative assessment of gastropods in the rocky shore. A-50 m belt transect made of 0.45 mm clear nylon beading wire and 12 mm corrugated round steel bar post was established parallel to the elevated rocky shoreline during the low tide. The transect line was divided into 25 1 m2 quadratic plots [13, 14] made of size 18 twisted nylon cord Bead Smith Super-Lon (S-Lon) on both sides for a total of 50 quadrates. The area where the transect line was laid represented the rocky intertidal ecosystem of the 73.05 m stretch. Random sampling [14] was conducted

**Figure 1.** *Part of the 73.05 m stretch of the rocky shore during low tide (*↔*).*

simultaneously for a total 25 sampled plots. Both live gastropod species and empty shells within the sampled quadrates including those in rock crevices were identified *in situ*. Aerial temperature was taken at the same time every sampling month using non-mercury thermometer.

Unidentified gastropod species and shells were photo-documented and collected. Specimens were placed in labeled transparent plastic bags. While in the field, the collected samples of live specimen were stored in an ice bucket to prevent desiccation. Collected samples were brought in the BioLab for identification to the lowest possible taxonomic level based on morphological characteristics using references in gastropods taxonomic identification [18–20]. The species names were also verified in a database [14] for marine species of gastropods [21]. Using taxonomic classification, identified gastropods were categorized into three hierarchy or categories namely: (1) *family*, (2) *genus*, and (3) *species*. Some live specimens in their natural habitat were photo-documented using Nikon D7000 camera. Collected specimens and shells were measured end-to-end from the longest point of axis for the length using Vernier caliper with ±0.01 mm accuracy and likewise photographed in the laboratory.

#### **2.3 Data analysis**

#### *2.3.1 Determination of species diversity*

Diversity of gastropod species was calculated using Shannon-Wiener Index (H′) with the formula: [13–15].

$$H^{'} = -\sum\_{i=1}^{4} p\_i \log \mathbf{p}\_i \tag{1}$$

where H′ = value of Shannon-Wiener diversity index; *Pi* = proportion of the ith species; loge = natural logarithm of *pi*; s = number of species in the community or species richness.

Using Shannon-Wiener diversity index (H′), species of gastropod in the assemblage is classified based on the following category: low (H′ < 2); moderate (2 < H′ < 4); and high (H′ > 4).

Species evenness index was determined using Pielou's evenness index with the formula:

$$\mathbf{J}^{'} = \mathbf{H}^{'} / \mathbf{H}^{'} \,\mathrm{m} \mathbf{a} \,\mathrm{x} \tag{2}$$

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**Figure 2.**

*Assemblage of Gastropods in the Rocky Intertidal Zone of Asry Beach, Kingdom...*

where H′ = Shannon-Wiener diversity index; Hmax = natural logarithm of species

Species ranges from zero to one; zero means no evenness and one means com-

One-way analysis of variance (ANOVA) was used to find out significant differences in the total species assemblage. Correlation analysis using Pearson correlation coefficient *r* determined if the aerial temperature significantly affected the total

The characteristic substrate of the study site in Asry Beach is shown in **Figure 2**. It is an obligate, slightly elevated rocky platform which is often exposed to alternating tide sequences resulting to its periodic submergence and emergence. As part of the public beach, however people prefer the sandy part and spend their leisure time in water for swimming. Hence this area remains undisturbed which promotes massive growth of algae that provides nutrients and venue for ecological and intra-inter-specific interactions [5] among the faunal community of organisms. Based on observation and results of the study on the entire intertidal ecosystem [17] human factor is considerably not a limiting factor for the gastropod assemblage to be abundant in the area. This is in contrast to some research findings that human activities may intensify the exploitation of gastropod species for commercial purposes [11, 14]. Hence the rocky platform of the intertidal zone in this particular area serves as the habitation of the many life forms

A total of 16 families composed of 25 genera and 31 species were identified in the rocky shore of Asry Beach from January 2016 to January 2018. The taxonomic

*Cut view of the sampling site showing the rocky habitat (A) during low tide with massive algal growth (B).*

*DOI: http://dx.doi.org/10.5772/intechopen.87772*

annual species assemblage of gastropods.

enduring the harsh environmental condition [1].

**3.2 Sampling, identification and field collection**

richness.

plete evenness.

**3.1 Study site**

*2.3.2 Statistical analysis*

**3. Results and discussion**

*Assemblage of Gastropods in the Rocky Intertidal Zone of Asry Beach, Kingdom... DOI: http://dx.doi.org/10.5772/intechopen.87772*

where H′ = Shannon-Wiener diversity index; Hmax = natural logarithm of species richness.

Species ranges from zero to one; zero means no evenness and one means complete evenness.

## *2.3.2 Statistical analysis*

*Invertebrates - Ecophysiology and Management*

non-mercury thermometer.

*Part of the 73.05 m stretch of the rocky shore during low tide (*↔*).*

**Figure 1.**

**2.3 Data analysis**

species richness.

with the formula: [13–15].

(2 < H′ < 4); and high (H′ > 4).

*J*

*2.3.1 Determination of species diversity*

*H*′

simultaneously for a total 25 sampled plots. Both live gastropod species and empty shells within the sampled quadrates including those in rock crevices were identified *in situ*. Aerial temperature was taken at the same time every sampling month using

caliper with ±0.01 mm accuracy and likewise photographed in the laboratory.

Diversity of gastropod species was calculated using Shannon-Wiener Index (H′)

where H′ = value of Shannon-Wiener diversity index; *Pi* = proportion of the ith species; loge = natural logarithm of *pi*; s = number of species in the community or

Species evenness index was determined using Pielou's evenness index with the

*p*<sup>i</sup> log pi (1)

*max* (2)

= −∑ *i*= *s*

Using Shannon-Wiener diversity index (H′), species of gastropod in the assemblage is classified based on the following category: low (H′ < 2); moderate

> ′ = *H*′ /*H*′

Unidentified gastropod species and shells were photo-documented and collected. Specimens were placed in labeled transparent plastic bags. While in the field, the collected samples of live specimen were stored in an ice bucket to prevent desiccation. Collected samples were brought in the BioLab for identification to the lowest possible taxonomic level based on morphological characteristics using references in gastropods taxonomic identification [18–20]. The species names were also verified in a database [14] for marine species of gastropods [21]. Using taxonomic classification, identified gastropods were categorized into three hierarchy or categories namely: (1) *family*, (2) *genus*, and (3) *species*. Some live specimens in their natural habitat were photo-documented using Nikon D7000 camera. Collected specimens and shells were measured end-to-end from the longest point of axis for the length using Vernier

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formula:

One-way analysis of variance (ANOVA) was used to find out significant differences in the total species assemblage. Correlation analysis using Pearson correlation coefficient *r* determined if the aerial temperature significantly affected the total annual species assemblage of gastropods.
