Ecological transition of mollusc governing vertical zonation of Morawala rocky shore Negombo, Sri Lanka, over the past few decades.

Ecological transition of mollusc governing vertical zonation of Morawala rocky shore Negombo, Sri Lanka, over the past few decades. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 4 March 2025 V1 Latest version Share on Ecological transition of mollusc governing vertical zonation of Morawala rocky shore Negombo, Sri Lanka, over the past few decades. Authors : A.A.D.N. Thathsarani 0009-0001-8483-6440 , R.S. Rajakaruna , and U.A. Jayawardena 0000-0001-9613-4385 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174106999.93648468/v1 366 views 190 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Aim: The research on the ecology of the rocky coast is now qualitative, quantitative and experimental. The Sri Lankan rocky shore (RS) ecology has not yet been studied extensively in terms of its species diversity to express its truest response to environmental episodes. The present narrative review attempts to reflect the transition of the molluscan diversity of Morawala RS concerning its vertical zonation relative to the Former Repository by Arudpragasam (1984) in his book chapter Ecology of Rocky Shores and Estuaries in Sri Lanka Location: A 500 m stretch of Morawala RS, Negombo, Sri Lanka has been systematically observed for its mollusc diversity and abundance from May 2022 to February 2023 during the lowest low tide time. Methods: The ecological survey was conducted using stratified random quadrate sampling techniques. Shannon Weiner’s diversity index was used to calculate the molluscan species diversity. The present data was then compared with the information in Arudpragasam (1984). Results: 15 different molluscan species representing grazers, gastropods and filter feeders have been identified. The diversity indices for the mid-tide (MT) and low-tide (LT) zones were high during the Northeast (NE) monsoon. However, the high-tide (HT) diversity index was high during the Southwest (SW) monsoon. There was no significant seasonal variation (p>0.05) in the molluscan diversity between the locations within the season and between the two different monsoon seasons. But, molluscan species density was high during the Northeast monsoon season. Conclusion: It was evident similar species richness has been recorded in the present survey similar to the reported species in Ardupragasam (1984). The mollusc species abundance is high in the Northeast monsoon season since the organisms can withstand the dynamics on RS during this period. To predict spatial and temporal variations of the sentinel molluscs in tropical RSs, continuing investigations and observational research are highly warranted. Narrative review Ecological transition of mollusc governing vertical zonation of Morawala rocky shore Negombo, Sri Lanka, over the past few decades. A.A.D.N. Thathsarani 1 , R.S. Rajakaruna 2 , U.A. Jayawardena 3 * 1,3 Department of Zoology, Faculty of Natural Sciences, The Open University of Nawala, Sri Lanka. 2 Department of Zoology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka. *Corresponding author email: [email protected] Abstract Aim: The research on the ecology of the rocky coast is now qualitative, quantitative and experimental. The Sri Lankan rocky shore (RS) ecology has not yet been studied extensively in terms of its species diversity to express its truest response to environmental episodes. The present narrative review attempts to reflect the transition of the molluscan diversity of Morawala RS concerning its vertical zonation relative to the Former Repository by Arudpragasam (1984) in his book chapter Ecology of Rocky Shores and Estuaries in Sri Lanka Location: A 500 m stretch of Morawala RS, Negombo, Sri Lanka has been systematically observed for its mollusc diversity and abundance from May 2022 to February 2023 during the lowest low tide time. Methods: The ecological survey was conducted using stratified random quadrate sampling techniques. Shannon Weiner’s diversity index was used to calculate the molluscan species diversity. The present data was then compared with the information in Arudpragasam (1984). Results: 15 different molluscan species representing grazers, gastropods and filter feeders have been identified. The diversity indices for the mid-tide (MT) and low-tide (LT) zones were high during the Northeast (NE) monsoon. However, the high-tide (HT) diversity index was high during the Southwest (SW) monsoon. There was no significant seasonal variation (p>0.05) in the molluscan diversity between the locations within the season and between the two different monsoon seasons. But, molluscan species density was high during the Northeast monsoon season. Conclusion: It was evident similar species richness has been recorded in the present survey similar to the reported species in Ardupragasam (1984). The mollusc species abundance is high in the Northeast monsoon season since the organisms can withstand the dynamics on RS during this period. To predict spatial and temporal variations of the sentinel molluscs in tropical RSs, continuing investigations and observational research are highly warranted. Keywords : Diversity, Mollusc, Negombo, Rocky shore, Sri Lanka , Zonation Introduction Marine environments are the world’s biggest natural resources where humans shall conquer in the blue economic concepts towards a sustainable future. It is always essential to get familiar with the two terms, coastal and marine environments before diving deep into their biotic component evidence and ecological concepts (Bracken and Williams, 2013). Coastal environments are the areas where the land masses meet the seas, the transition zone which connects the terrestrial and marine environments. It includes intertidal environments such as tidal wetlands, estuaries, lagoons, bays, shallow near-shore waters, mangrove swamps and intertidal rocky shores, sea grass beds, salt marshes and sandy shores. Marine environments can be defined as a combination of physical (wave action, direct exposure to sunlight, high daytime temperatures, and high wind currents), chemical (high salinity, pH levels, high conductivity), geological and biological (organisms such as planktons, algae, marine invertebrates and vertebrates) components which interact and determine the productivity and quality of marine ecosystems. This includes the Open Ocean, the deep sea ocean and the coastal marine ecosystems (coastal environment) (Hayden et al., 1984). Thus, coastal environments could be considered as a subset of marine environments. The intertidal zone is one such crucial coastal and marine environment because of its productivity, high diversity and ability to reflect the effect of pollutant stress through different responses and alterations in the biotic and abiotic components. The term intertidal zone refers to the area in between the lowest low tide and highest high tide during a lunar day. The RS and sandy shore ecosystems are the most spectacular, dynamic and highly diversified regions in the intertidal zone. Rocky shores all around the world could be identified as natural marine laboratories and repositories for their higher biodiversity recorded compared to sandy shores (Arudpragassam, 1984). The temperate and tropical RS environments are being researched mainly for conservative requirements and to identify the local species populations that are tolerant to the specific local environmental changes over time. The tropical waters are warmer than the waters of the temperate regions (Helmuth et al., 2006). This specific difference may have caused major differences in tropical ocean waters such as higher species diversity, higher species richness, changes in the surface water currents etc. Thus affecting the species clusters of the beach protective natural barriers to the rocky ecosystems. These effects including the vertical zonation diversity of the Sri Lankan reefs, its classification, and the dominant species of the Sri Lankan RS have been tremendously well explained together in the book chapter by Arudpragasam (1984). The present narrative review mainly highlights the present state of the Morawala RS (category one RS type in Sri Lanka) its species richness and the abundance of the dominant RS species compared to the book chapter written by the author Arudpragasam in the book Ecology and Biogeography of Sri Lanka by the editor Fernando (2012). Of them, the major concern will be on the molluscan diversity of the Morawala RS. Since, molluscs are considered the sentinels of the local environmental changes especially on the ecosystem health over time (Berheth, 2012). Human activities in coastal areas may threaten biological communities and lead to the loss of biodiversity (Deepananda and Macusi, 2013). Therefore, it is a requirement to assess the biodiversity status of the RS around the country since the communities reserved there will recite us a giant story beyond what we see. Sri Lanka is an island in the Indian Ocean being a tropical country must pay more attention to conserving the coastal wild invertebrate inhabitants of the RSs since these organisms provide the feeding ground for many migratory birds and in turn to the local human communities in their day to day living. Rocky shores ecology on the Western coast of Sri Lanka The chapter, ecology of rocky shores by K.D. Arudpragassam (1984), in the book Ecology and Biogeography in Sri Lanka, describes well the basic ecology of the RSs in Sri Lanka. The present review mainly discusses the ecological transition of one of the Western coast RSs in Sri Lanka. The seven months of data and information we gathered by sampling and surveying the Negombo Morawala reef from May 2022 to February 2023 over the major monsoon seasons, we will be able to address how have been the present status of the once fascinating reef biology and its ecosystem biotic components have been deviated comparative to the knowledge gathered by Arudpragassam (1984) in his book chapter. Since the chapter encounters the topography and the species composition in the RS; it also serves as a primary repository to compare the diversity of the species, the horizontal and vertical RS zonation and the parameters of the abiotic components in the different RS types, with the recent research data. According to Cooray (1967), the island of Sri Lanka has a coastline of about 1,760 km, by then which is mostly low-lying and geologically polygenetic. The continental shelf extends for a distance which varies from 9-45 km at an average depth of 36 fathoms. Sri Lankan shelf tends to narrow around the southern part of the island widens to the north and merges with the Indian Continental Shelf. Most of the inland freshwater lotic water bodies empty into the open ocean at the coastlines. Except on the northern coastline, the mouths of many rivers indent the coastline and form estuaries or estuarine lagoons. In considering the ecology of RS, even though it is a temperate or a tropical RS, it is a pertinent requirement to have a sound knowledge of how the tidal fluctuations in relation to daytime temperatures are happening at the specific site. The lowest low tide time will be the best time to observe the entire RS when surveying the reef for its species composition. With the tidal increment, it will be challenging to observe the organisms since the RS starts to inundate gradually with the seawater. The tides are of mixed variety. As described by the author, semidiurnal tides are dominant during and around the spring tides but a gradual transition takes place to diurnal tides during and around neap tides. The highest tides of the year are around 0.88 m and the range is about 0.70 m at its maximum (Arudpragasam, 1984). In considering the ecology of RS, it is important to have information about times of low tides in relation to daytime temperatures. The highest daytime temperatures are usually experienced around 2.00 pm. As described by Arudpragassam (1984), the low tide time is observed in between 7.00 and 11.00 am from January to September and between 7.30 and 9.00 pm from October to December which we could rely on even for today. Therefore, the rocky shores on the west coast are not fully exposed during the hottest periods of the year. Moreover, it is roughly high water or wave action could be observed along the west coast between Mannar Island and Galle. The general pattern of currents on the west coast is southerly during the northeast monsoon and northerly during the southwest monsoon. Generally, RS is made up of granitic gneiss, sandstone, coral debris or a combination of these. Proceeding northwards from Colombo to the headland off Negombo, sandstone reef fringes are prominent. They are compressed and bound together. Seaward aspects, massed tubes of sabellariid worms, themselves made up of sand and shell fragments cemented together, are often seen. The same pattern is still observed along the Morawala, RS, Negombo. Throughout the major monsoon seasons, these sabellariid worms have been constantly attached to the rock surfaces providing an extra substratum for many marine gastropods (Arudpragasam, 1984). Rocky shore zonation The wisdom on RS zonation in Sri Lanka had been envisioned and progressed very first by Atapattu (1968) and Arudpragasam (1970). Both the authors have described that the zonation of the RS is not solely based on a single point aspect but from a holistic niche of the indicator species (invertebrates and algae) who could withstand the extreme environmental conditions falling on the RS. The recognition of zone is not principally constructed on the tidal levels. As mentioned above, the tidal level is only a single abiotic factor that is running and breaking along the reef. The RS zonation based on the indicator organisms had been a matter of arguments and discussions. As stated by Arudpragassam (1984) in his chapter, the ecologists and environmentalists such as Stephenson and Stephenson 1952, Guiler 1953, Lewis 1962, 1964, and Southward 1958 contributed to the paradigm to get explained. The archetype had been detailed by Lewis (1962), who pointed out that, while tidal and other changes in the sea level are primarily responsible for the appearance of zones, the complete physical environment is a balance of many additional forces. Since it is not feasible to measure the entire physical environment, the zonation according to one factor the tides, had been inappropriate. He emphasized that there would be no alternative but to rely on the dominant zone-forming organisms. Rocky shores are termed as the world’s natural marine laboratories. Since it harvests many organisms by providing ample amounts of microhabitats for them to live in. Creeks, crevices, rock surfaces, rock pools and canopy-forming algae are a few of the major microhabitats established in the RS. Atapattu (1968), in the course of a study of the molluscan fauna of littoral rocks around the island, has defined a categorization for the island RS based on the universal categorization of the RS proposed by Stephenson and Stephenson (1949). The Sri Lankan RS has been divided into three groups in terms of zonation, indicator organisms and molluscan fauna. These are: Group I shores of the west, southwest and south and exposed shores of the east; Group II sheltered shores of the east coast and Group III shores of the north coast. The zones recognised are the littoral fringe, the eulittoral and the sublittoral. On Group I shores the eulittoral tends to be demarcated into three subzones; an upper, a mid and a lower eulittoral zone with a more or less clearly defined belt of oysters. Comparative analysis of the Morawala rocky shore molluscan diversity and its molluscan species abundance. The referred book chapter by key author Arudpragassam, has documented the major molluscan groups that have dominated the RS based on the research findings of the era. Morawala RS, Negombo Sri Lanka belongs to category I type reefs as described by Atapattu (1968). According to the results that are been discussed throughout this article relative to the new research information of the reviewing authors it is evident that the Morawala RS is still governed and dominated by the molluscan species. Since molluscs have been considered the indicator species of the RS environments, they could be used as sentinels, to test the local environmental changes of the respective site due to countless marine microcontaminants. Table 1 refers to the major vertical zonation of the Morawala rocky shore with the major molluscan species which complies with Atapattu (1968) classification as per Arudpragasam (1984). Table 1: Major vertical zonation of category I shore and its dominant molluscan species as stated in Arudpragassam (1984), in the book ecology and Biogeography in Sri Lanka. Littoral Littorina undulata, Nodilittorina pyramidalis, Littorina undulate, Nodillitorina pyramidalis, Nodilittorina granularis Eulittoral Upper Mid Lower Cellana radiate, N. granularis, Barnacles Oysters Saccrostrea sp. and Crassotrea cucullata sp. (Forming oyster belt), N. granularis, Clypidina notate, Perna sp., and Brachidontes variabilis Limpets, Anachis Terpsichore, Trochus radiatus. Thais alveolata, Drupa granulata. N. granularis Sub littoral - Not available The eulittoral sub zonation indicates a mid eulittoral zone which is governed by the oyster belt, the lower eulittoral is a zone where they have observed a discrete patches of macro sea weeds growths, including-species of Laurencia , Gracilaria , Caulerpa , Chaetomorpha , Gelidium , Viva , and Jania . Most of these algae form a canopy for the fauna to adhere to and act as a protective shield for the major molluscan groups to withstand the wave action without being detached which is pounding against the RS. The molluscs inhabiting this area are the serpulid Potatoleios crosslandi , Cellana radiata and other groups of molluscs. The other groups of molluscs have not been mentioned in his book chapter therefore it is challenging us to compare the diversity of all the molluscan species that we have encountered thus far. According to Arudpragasam (1970), N. granularis had reached its greatest density on the RS. The upper eulittoral is a subzone of mainly the littorines and the barnacles. Of the littorines, N. granularis and a few specimens of N. pyramidalis had been widely spread and high in abundance. According to the information comprehended in the chapter, they could identify and document 18 major molluscan species. But the Mytilus sp. had not been identified up to the species level. When comparing the type 1 sandstone and granite RSs, sandstone appears not to favour the settlement of many barnacles and in turn, encourages littorines. Therefore, a clear belt of barnacles above the oysters may not develop on such shores (Arudpragasam, 1984). Moreover, in a horizontal sandstone platform, the oysters tend to scatter to a greater degree than on a sloping rock surface. Further, the lower eulittoral and especially the upper sublittoral on sandstone tend to be populated by sea urchins which form individual burrows on the surface (Arudpragasam, 1984). According to our systematic observation over a consecutive period the following observations could be reported comparatively to the ground information given by Arudpragasam (1984) and Arudpragasam (1970). A similar trend which had been observed years ago is still observed in the Morawala rocky shore, Negombo, Sri Lanka in terms of scattered oysters, and the densely populated sea urchins in the eulittoral lower and the sublittoral areas. To date, locating a littoral fringe is hard, and demarcating it as a part of the RS is still challenging. Since the granitic rocks that were placed as a littoral fringe are mostly human-mediated adjustment. However, from time to time, according to the recreational activities that are been carried around and in the Morawala, RS ecosystem, has exhibited often changes to the granitic rocky boundary which is located before the sandy shore which is immediately before the horizontal sandstone rocky platform. One of our physical parameter results is also in compliance with Arudpragasam (1984), we found the highest temperature ranges from 33\RL–֠ C–34 values around 2.00 pm. The most important finding during our survey which has been carried out at Morawala reef is that during the northeastern monsoon seasons in the consecutive years 2022 and 2023 the starting daytime temperatures were from 32 \RL–֠C to 33 \RL–֠C in the morning hours and remained static throughout the entire sampling duration per day for about 7 to 8 hours. The molluscan shell diversity is very much important when studying the RS environments. Since, they are dominating the RSs, assessing their diversity, abundance, species richness and distribution along the RS environment is an indeed criterion. We may consider it as a prerequisite for an eco-toxicological survey which will be carried along a particular RS since these species mostly act as sentinels rather than bioindicators for both acute and chronic environmental stresses. Since this biodiversity survey was carried out after the catastrophic X-press pearl ship wreck, this article will be very useful to assess and to evaluate the real situation of the Morawala RS in terms of biodiversity. However, this will be a comparative analysis and narrative documentation concerning the insight disclosed by Arudpragasam (1984). Even though the diversity indices have not been published in his chapter, more or less a clear idea could be provided in our results as a support for the evidence provided in the initial articles. Figure 1 depicts the overall Molluscan diversity and their abundance in the vertical zonation of Morawala RS Negombo during SW and the NE monsoon seasons From May 2022 to February 2023. Over the course of surveyed duration, it was calculated that the Shannon-Weiner index for the RS during SW monsoon was 0.98 for HTZ, 1.16 for MTZ, 0.53 for LTZ and during NE monsoon the counts were 0.59 for HTZ, 1.18 for MTZ and 0.79 for the LTZ. Also, it was evident that the HTZ diversity index was high during SW monsoon season but the MTZ and the LTZ diversity indices were high during NE monsoon seasons. According to our field observations, we may state that the mere reason behind this trend during the NE monsoon period could be the less wave action experienced by the Morawala RS compared to the SW monsoon season. Both the LTZ and the MTZ algal diversity and their abundance were also high during NE monsoon season, Therefore, the molluscan might get enough shade, much food availability and the seaweed canopy to attach to the substratum without being washed away against the crashing less severe waves. Figure 1: Comparison of the Shannon Weiner Diversity indices (H) for different vertical zones of the Morawala rocky shore during SW and NE monsoon seasons from May 2022 to February 2023. (a), the location-wise Shannon Weiner Diversity indices for vertical zonation of the Morawala rocky shore over 500 m stretch of rocky shore extending parallel to the shoreline. (LF-Littoral fringe, HTZ-High tide zone, MTZ- Mid tide zone and LTZ- Low tide zone). (b), the Shannon Weiner Diversity indices for the respective zonation for the entire study site from May 2022 to February 2023 based on the surveyed pooled data. During the survey period, we could identify 14 different molluscan species across the 500 m stretch of Morawala RS. Of the 14 different molluscan species, the following species dominated the MTZ and the area between the lower eulittoral mid zone and the sublittoral areas. They are Saccostrea sp., Crassostrea sp., Brachiodontes sp. and Nodilittorina quadricincta . These species were in habitat throughout the study period. Apart from these Morula granularis, Nodilitoorina pyramidalis, Thais bufo, Cyprea sp, Perna perna and Mytilus edulis appeared seasonally but not in a greater abundance relative to the former mentioned species. More or less similar species richness has been observed in the present study as documented in the Arudpragasam (1984). But, it is interesting to record that there is a difference in the species’ nomenclature then and now. Until it is clarified further, it is very perplexing to state that the species that we have encountered today with a different name would be the same that appeared in another name in earlier classifications. These knowledge gaps must be filled to recognize the disparities in taxonomy related to mollusc species. Since the species richness, densities and abundance values had not been given in Arudpragasam (1984), the possibility of stating the decrement or increment in the dominant molluscan species abundance and the density in the Morawala RS is still blindly ended since, a timely species diversity assessment based scientific research article has not yet been published targeting the Morawala RS, Negombo, Sri Lanka and also including the other RSs in the western coast of Sri Lanka. Also, these parameter values had not been mentioned quantitatively in the selected scientific communication of Arudpragasam for which the narrative documentation is unwinding. The present studies’ results will be able to fill the paucity in the particular research arena based on the percentage occurrence and the species density of dominant mollusc species in the HTZ and the MTZ of the Morawala RS. The result of the present study will be able to nurture the missing pieces in the Arudpragasam (1984), since the results will be able to confront the transition of the diversity parameters of the major mollusc species in the Morawala RS. According to Figure 1 and Figure 2, the Shannon-Weiner index for the RS during SW monsoon was 0.98 for HTZ, 1.16 for MTZ, 0.53 for LTZ and during NE monsoon the counts were 0.59 for HTZ, 1.18 for MTZ and 0.79 for the LTZ. Nodilittorina quadricincta (mean density = 457.4 m -2 , % occurrence = 63.56%) was identified as the dominant species at the HTZ during both seasons. Saccrostrea sp. (mean density = 176 m -2 , % occurrence = 16.96%), Crassostrea sp. (mean density = 7.2 m -2 , % occurrence = 1.78%), Brachiodontes sp. (mean density = 124.2 m -2 , % occurrence = 12.31%) and Nodilittorina quadricincta (mean density = 229.4 m -2 , % occurrence = 34.67%) dominated the MTZ at both vertical and horizontal zonation. A seasonally varied, nearly significant, high % occurrence for Crassostrea sp. was observed (p=0.078, one-way ANOVA). With the onset of NE monsoon, a less mean density of the Brachiodontes sp. (106.4 m -2 ) was also observed. The limpets such as Cellana rota , Clypidina notata dominated the LF and the horizontal surfaces of the LTZ at locations where a very few number of microhabitats were observed. The mean percentage occurrence and the species densities of the dominant molluscan species were insignificantly high during NE monsoon season. Further, surveying over time is indeed to affirm the seasonality of the species over the RS vertical zonation. Figure 2, represents the relative percentage occurrence and the species density of the molluscan species along the vertical zonation of the Morawala RS over the major monsoon seasons starting from May 2022 up to February 2023. Also, Figure 3 provides a plate for the major mollusc species encountered during the sampling period. Figure 2: The percentage occurrence and the species densities of the dominant mollusc species over the vertical zonation of Morawala RS Negombo, Sri Lanka, from May 2022 to February 2023. (a) The overall percentage occurrence of Nodilittorina quadricincta in the HTZ of the RS during South West and North East monsoon seasons. (b) The species density of N. quadricincta in the HTZ during South West and North East monsoon seasons, (c) The overall percentage occurrence of dominant molluscs species in the MTZ of the RS during South West and North East monsoon seasons, (d) Species densities of the dominant mollusc species in the MTZ of the RS during South West and North East monsoon seasons. Results are compared as Mean ± SEM (One Way ANOVA test, (p>0.05). Figure 3. Interior, exterior and lateral views of dominant Rocky shore molluscan species of Morawala rocky shore Negombo, Sri Lanka during May 2022 to February 2023.a) Thais bufo , b) Littorina sp., c) Trochus radiates , d) Perna perna, Brachiodontes sp., e) Pinetada margaritifera (juvenile stages), f) Cyprea arabicia and Cyprea feline listeri g) Clypidina notata , h) Cellana rota , i) Patelloidia striata , j) Morula granulata , k) Saccostrea cucullata , l) Crassostrea sp . , m) Nodilittorina quadricincta , n) Littoraria undulata sp. were among the major molluscan species recorded within the randomly placed quadrate samples along the vertical zonation of the Morawala rocky shore Negombo Sri Lanka during the lowest low tide time of the day. Species were identified with referred to the key of shells of the Sri Lanka sea shore (by Malik Fernando, published by ministry of environment Sri Lanka (2010)) and Annotated Checklist of Indian Marine Molluscs (Dey, A. (2010). Conclusions and recommendations Molluscan species richness is 15 out of 25 species of macroinvertebrates and affirms the Morawala RS is dominated by the molluscans. The trend observed in the 19’s has not been changed and still, the molluscs govern the RS. The diversity indices for the MT and LT zones were high during the NE monsoon. However, the HT diversity index was high during the SW monsoon. However, there was no significant seasonal variation (p>0.05) in the molluscan diversity between the locations within the season and between the two different monsoon seasons. Relative to the book chapter written by Arudpragsam (1984), it is still challenging to put forward a strong conclusion about whether the mollusc’s diversity index, percentage occurrence and species density parameters are high or low compared to our research findings. The research will endorse a positive outcome towards the marine ecosystem health in aspects of diversity and abundance of molluscan inhabitants in the RS of the Western and the Southwestern coast of Sri Lanka. Since the present study addresses the decade missing research information; the findings may address the missing pieces of the Sri Lankan database of the biodiversity of RS molluscans on the western coast of the country. Moreover, with the recent X-Press Pearl shipwreck, local scholars will get an opportunity to compare the data with both the published and unpublished disclosed data based on the marine shell diversity around the island. Thus, it will open up the doors for new ventures in research, related to the in-situ conservation of RS inhabitants to protect and to take necessary conservation approaches to establish the resilience of the ecosystem. Also, this would be a timely needed approach in supporting and narrating Arudpragasam (1984) findings, as the author is well known for his pioneering service towards identification and establishing the categorization of the Sri Lankan RS faunal (molluscan) vertical zonation. Based on the present research data it is very proactive to further survey the entire RS for a biodiversity assessment to launch conservative measures to protect this natural faunal laboratory the Morawala RS in Negombo, Sri Lanka. Data availability statement All the data used in compiling the review based on the research team’s results are available in the supplementary files attached herewith the manuscript. 6. References Arudpragasam, K. D. (1970). Zonation on two shores on the west coast of Ceylon. Journal of the Marine Biological Association of India, 12, 1-14. Arudpragasam, K. D. (1984). Ecology of rocky shores and estuaries of Sri Lanka. In Ecology and Biogeography in Sri Lanka (pp. 283-296). Dordrecht: Springer Netherlands. Atapattu, D. H. (1968). Studies on molluscan fauna of rocks of Ceylon. Ph. D. thesis. Berthet, B. (2012). Sentinel species. Ecological biomarkers: indicators of ecotoxicological effects, 155. Bracken, M. E., and Williams, S. L. (2013). Realistic changes in seaweed biodiversity affect multiple ecosystem functions on a rocky shore. Ecology, 94(9), 1944-1954. Cooray, P. G. (1967). An introduction to the geology of Ceylon (Vol. 31, No. 1). National Museums of Ceylon. Deepananda, K. H. M. A., and Macusi, E. D. (2013). Human disturbance in a tropical rocky shore reduces species diversity. The Philippine Scientist, 50, 39-58 Dey, A. (2010). Annotated Checklist of Indian Marine Molluscs: Cephalopoda, Bivalvia and Scaphopoda (No. 320). Zoological Survey of India. Fernando, C. H. (Ed.). (2012). Ecology and biogeography in Sri Lanka (Vol. 57). Springer Science & Business Media. Hayden, B. P., Ray, G. C., and Dolan, R. (1984). Classification of coastal and marine environments. Environmental Conservation, 11(3), 199-207. Lewis, J. R. (1964). The ecology of rocky shores. Southward, A. J. (1958). The zonation of plants and animals on rocky sea shores. Biological Reviews, 33(2), 137-177. Stephenson, T. A., and Stephenson, A. (1949). The universal features of zonation between tide-marks on rocky coasts. The Journal of Ecology, 289-305. Stephenson, T. A., and Stephenson, A. (1952). Life between tide-marks in North America: II. Northern Florida and the Carolinas. The Journal of Ecology, 1-49. Information & Authors Information Version history V1 Version 1 04 March 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords diversity mollusc negombo rocky shore sri lanka zonation Authors Affiliations A.A.D.N. Thathsarani 0009-0001-8483-6440 Open University of Sri Lanka View all articles by this author R.S. Rajakaruna University of Peradeniya Faculty of Science View all articles by this author U.A. Jayawardena 0000-0001-9613-4385 [email protected] Open University of Sri Lanka View all articles by this author Metrics & Citations Metrics Article Usage 366 views 190 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation A.A.D.N. Thathsarani, R.S. Rajakaruna, U.A. Jayawardena. Ecological transition of mollusc governing vertical zonation of Morawala rocky shore Negombo, Sri Lanka, over the past few decades.. Authorea . 04 March 2025. DOI: https://doi.org/10.22541/au.174106999.93648468/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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