Seasonal Changes in Molluscan Diversity, Density and Biomass (Gastropoda and Bivalvia) in Pomorie Lake (Black Sea, Bulgaria)

The seasonal variations in molluscan diversity, density and biomass (Gastropoda and Bivalvia) in Pomorie Lake (Black Sea), were examined. The research was conducted over an eight-month period (April–November 2022), covering six distinct sampling sites. A total of 12 molluscan species were identified. The average molluscan density was 26,746 ind/m². The dominant species in terms of density throughout all seasons and sites was Ecrobia maritima, demonstrating extreme seasonal variability. Other abundant species included Mytilaster lineatus, Bittium reticulatum and Cerastoderma glaucum, which exhibited distinct seasonal density peaks. Densities of M. lineatus, Pusillina lineolata and C. glaucum peaked in spring, while B. reticulatum had maximum abundance in summer. Cerastoderma glaucum was the dominant species in terms of biomass (43% of total biomass), followed by M. lineatus (40%). The study highlighted the influence of environmental parameters (salinity, temperature, substrate composition and anthropogenic impacts) on the molluscan community structure. The observed fluctuations suggest that the ecosystem of the Pomorie Lake is undergoing shifts due to hydrological and climatic changes. The findings contribute to the long-term monitoring of the biodiversity in this protected wetland and offer insights into the ecological dynamics of hypersaline lagoons.