Structure and composition of molluscs (bivalves and gastropods) in the mangrove ecosystem of Pacitan District, East Java, Indonesia

Abstract

Abstract.  Wiraatmaja MF, Hasanah R, Dwirani NM, Pratiwi AS, Riani FE, Hasnaningtyas S, Nugroho GD, Setyawan AD. 2022. Structure and composition molluscs (bivalves and gastropods) in the mangrove ecosystem of Pacitan District, East Java, Indonesia. Intl J Bonorowo Wetlands 12: 1-11. The mangrove ecosystem is a habitat for several species of molluscs. Therefore, mollusc's existence has an important role in the sustainability of the mangrove ecosystem. This research was conducted to determine the structure and composition of molluscs (gastropods and bivalves) in the mangrove ecosystem of Pacitan, East Java, Indonesia. The mollusc sampling was carried out at three mangrove ecosystems: Teleng Ria, Grindulu, and Siwil. Each sampling research location made a plot of 10 x 10 m. Then, the collected individual and mollusk species were analyzed using the Shanon-Weiner biodiversity index, species density, Margalef species richness index, evenness index, and Simpson dominance index. The molluscs found were 25 species, consisting of 17 gastropod species with 13 families. The gastropod families with the most species are Littorinidae (3), Ellobidae (2), and Potamididae (2). Meanwhile, there are eight species of bivalves consisting of five families. Then, Mytilidae (2), Ostreidae (2), and Veneridae (2) are the families with the most number of species in bivalves. The total molluscs obtained had a density of 36.9 individuals/100 m². The mollusc biodiversity index was 2.14 (medium), mollusc species richness reached 4.1 (medium), the evenness of species in this research reached 0.66 (quite even), and the species dominance index was recorded at 0.34 (low), which means that there are no dominant species in the research location. Then, each research location has a different species and density species of molluscs. That is caused by differences in the type of substrate (such as sandy, muddy, or rocky) and abiotic factors found in the research location (such as temperature, pH, and salinity).