**Abstract**

The macrofaunal components find its habitat in all areas of the marine ecosystem. Specifically, gastropods are considered the most common inhabitants of the intertidal zone with wide range of distribution in the rocky intertidal biota. A 3-year study on gastropod assemblage in Asry Beach, Kingdom of Bahrain was conducted from 2016 to 2018 which determines diversity and evenness of the rocky intertidal species. Taxonomic identification showed 31 species which belong to 25 genera and 16 families. The total annual population of gastropod assemblage does not vary significantly at *p* < 0.05 using analysis of variance (ANOVA). Shannon-Wiener species diversity index (H′) revealed high species diversity (H′ = 4.19) in the *Family Muricidae*; moderate (H′ = 2.04–3.29) among the species of the *Family Pyramidellidae*, *Cerithiidae*, *Oliveliidae*, *Calliostomatidae*, *Turbinidae*, *Trochidae*, *Buccinidae*, *Velutinidae* and *Margeliidae*; and low (H′ = 1.04–1.11) among the species of the *Family Batillariidae*, *Borsoniidae*, *Cerethiopsidae*, *Epitoniidae*, *Volutidae* and *Columbellidae*. Pielou's evenness index show that most of the species have complete evenness (J' = 1.0–3.81). The varying annual mean temperature exert no effect on the total assemblage of gastropods (r = −0.0231). Tolerant species include *C. selectum*, *L. attenuatum* and *Turbonilla* sp. 1. The rocky intertidal pool is typically diverse although exposed to varying environmental occurrences.

**Keywords:** gastropod assemblage, rocky intertidal, tolerant species, Shannon-Wiener index, Pielou's evenness index

## **1. Introduction**

The marine ecosystem is ecologically rich in terms of community of organisms which comprise the wide coastal area extending to a vast oceanic environment. The intertidal habitat had been the focus of many studies for ecological interactions which has an impact on diverse assemblage of macroflora and macrofauna. The rocky shore as an intertidal area is found at the shoreline between low and high tides and predominantly composed of solid rocks. Macrofaunal community tends to survive despite fluctuating daily diurnal tidal patterns and intense temperature [1]. This zone is considered highly productive with varying levels of biodiversity and dynamic due to diversity of both macrofauna and macroflora [2–4]. The wet rocky shore promotes enormous algal growth which serves as the feeding ground for the many macrofaunal community, specifically the gastropods thus promoting more diversity [5]. The rocky intertidal as a community is influenced by competitive

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*Invertebrates - Ecophysiology and Management*

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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 in the rocky intertidal zone.

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 composed of six 1 m2 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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**2. Research methods**

**2.1 Study site**

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

gastropods. The physical and chemical factors included temperature, salinity, pH and dissolved oxygen (DO). Results showed a total of 65 species in the two established research stations which belong to 48 genera, 19 families and 7 orders. The station-to station averages of the physico-chemical parameters were also determined. Results further show a very high diversity in both stations. Correlation analysis revealed a significant positive correlation between the physical and chemical factors (temperature, salinity, pH and DO) and the diversity of gastropods in

The Kingdom of Bahrain is endowed with a marine biota as habitat of all life forms. A number of public beach is found in Bahrain however Dry Dock Beach or commonly called Asry Beach in Hidd, Muharraq is of great interest. The beach as it is known to the people is part of the dry dock shipyard in the area. As a public beach, the area is often threatened by unaccountable wastes which may also affect the macrocomponents of the marine ecosystem. Hence continuous monitoring of the macroinvertebrates specifically the gastropods in the intertidal ecosystem is being undertaken since 2011 [17]. The intertidal ecosystem in Asry Beach is predominantly rocky and sandy. The shoreline is characteristically wide during ebb tide while very narrow during the spring tide. The rocky substrate extreme variation in temperature may exert drastic effect on the gastropod community. Hence, this study was conducted to determine the current status of the assemblage of gastropod population in the rocky intertidal zone of Asry Beach from January 2106 to January 2018. Specifically to identify and classify taxonomically the species of gastropod assemblage from the sampled quadrates; find out significant differences in the annual species assemblage of gastropods; calculate diversity using Shannon-Wiener (H′) diversity index; find out species evenness using Pielou's evenness index; and relate the effect of the aerial temperature on the total species assemblage of gastropods.

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

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

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

quadratic plots [13, 14] made of

activities and other natural environmental occurrences.

**2.2 Sampling, identification and field collection**

low tide. The transect line was divided into 25 1 m2

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

the coastal waters of Ambon Island, Indonesia [16].

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

gastropods. The physical and chemical factors included temperature, salinity, pH and dissolved oxygen (DO). Results showed a total of 65 species in the two established research stations which belong to 48 genera, 19 families and 7 orders. The station-to station averages of the physico-chemical parameters were also determined. Results further show a very high diversity in both stations. Correlation analysis revealed a significant positive correlation between the physical and chemical factors (temperature, salinity, pH and DO) and the diversity of gastropods in the coastal waters of Ambon Island, Indonesia [16].

The Kingdom of Bahrain is endowed with a marine biota as habitat of all life forms. A number of public beach is found in Bahrain however Dry Dock Beach or commonly called Asry Beach in Hidd, Muharraq is of great interest. The beach as it is known to the people is part of the dry dock shipyard in the area. As a public beach, the area is often threatened by unaccountable wastes which may also affect the macrocomponents of the marine ecosystem. Hence continuous monitoring of the macroinvertebrates specifically the gastropods in the intertidal ecosystem is being undertaken since 2011 [17]. The intertidal ecosystem in Asry Beach is predominantly rocky and sandy. The shoreline is characteristically wide during ebb tide while very narrow during the spring tide. The rocky substrate extreme variation in temperature may exert drastic effect on the gastropod community. Hence, this study was conducted to determine the current status of the assemblage of gastropod population in the rocky intertidal zone of Asry Beach from January 2106 to January 2018. Specifically to identify and classify taxonomically the species of gastropod assemblage from the sampled quadrates; find out significant differences in the annual species assemblage of gastropods; calculate diversity using Shannon-Wiener (H′) diversity index; find out species evenness using Pielou's evenness index; and relate the effect of the aerial temperature on the total species assemblage of gastropods.
