Effects of surface seawater temperature and oxygen availability on molluscan taxonomic diversity in Cyprus

Abstract

The Mediterranean Sea, a semi-enclosed basin, hosts a rich marine biodiversity, with most of the region's native species being of temperate origin. Climate change poses a significant threat, with sea surface temperatures increasing at a rate 20% faster than the global average. Projections suggest further warming by 2100, exacerbating ocean acidification and threatening calcifying organisms. Moreover, local anthropogenic stressors have worsened in recent decades, compounded by an ever-increasing population density. Lessepsian species pose additional ecological threats by altering native biodiversity patterns. To better understand these dynamics, this paper examines the impacts on mollusks by utilizing living and death assemblages. It compares two locations along the southern coast of Cyprus, Akrotiri and Cape Greco, which have sea surface temperature differences of up to 3°C in the summer. Additionally, it compares two habitats, rocky substrates and Posidonia oceanica meadows, to gain insight into the effects of local oxygen availability. Results reveal a live-dead match, suggesting a relatively healthy ecosystem compared to other areas in the Eastern Mediterranean. However, radiocarbon dating results indicate young death assemblages at all location/habitat subsets, rendering them insufficient to capture all anthropogenic impacts. Akrotiri appears to be a refugium for endemic species due to its higher relative species richness compared to Cape Greco. The most drastic live-dead mismatch in species richness was at Cape Greco’s Posidonia meadow, highlighting that the benefits of oxygen super-saturation are not infinite, and many endemic species may have already been pushed beyond their thermal tolerance limits. Finally, non-indigenous species abundance increased at all four sample subsets, but their ecological ramifications likely differ. In conclusion, this study highlights the need for the extension of conservation efforts in the Mediterranean, especially for key habitats like Posidonia oceanica meadows and rocky substrates.