Biodiversity of benthic molluscs in Kaakkaithivu coastal waters, Jaffna estuary, Sri Lanka

Benthic mollusc diversity in the northern Jaffna estuary, particularly the coastal waters of Kaakkaithivu, was investigated from July 2018 to January 2019. A total of 266 individuals representing six families and eight species were collected from three sampling sites. The assemblage comprised five gastropods and three bivalves: Terebralia palustris, Cerithidea cingulata, Murex virgineus, Volegalea sp., Morula margariticola, Cardita bicolor, Donax sp., and Dosinia lincta. Shannon–Wiener diversity was highest at Site 1 (1.2303), followed by Site 3 (0.8709) and Site 2 (0.5632). T. palustris (41.00%) and C. cingulata (36.47%) were the most abundant species. The distribution of C. cingulata differed significantly among selected sites (p < 0.05), reflecting differences in site condition and environmental stress. The low diversity and evenness values indicate that the Kaakkaithivu coastal ecosystem is under considerable environmental pressure, particularly at Sites 2 and 3. These baseline data are relevant to ecological assessment, estuarine management, habitat restoration, and control of anthropogenic activities in the Jaffna estuary.