Unexpected high molluscan diversity in a submarine cave in the Eastern Mediterranean

Marine caves are abundant throughout the Mediterranean Sea, but most studies have focused on those occurring in its western part so far. However, the few studies covering the Eastern Mediterranean showed that its caves are characterized by high diversity. We here describe the molluscan assemblage of the Kakoskali submarine cave in northwestern Cyprus, a shallow water cave characterized by the occurrence of large biostalactites. To avoid any destructive sampling in such a delicate environment, we used death assemblages from cave sediments (that can faithfully represent the composition of nearby living assemblages) sampled across a gradient from the inner chamber to nearby Posidonia patches outside the cave. Inside the cave, we found 217 species, 38% of the molluscan fauna currently known from Cyprus; sampling saturation was 0.99 and the estimated diversity at perfect coverage was 258 (+ 17%) species. One species has never been reported from Cyprus previously (Austronucula perminima) and another one is a first record for the entire Eastern Mediterranean (Hyalogyra zibrowii). We also report an unidentified Pyramidellidae which has eluded all identification efforts. In the cave, we found only five (2%) non-indigenous species represented by 50 individuals (1%). The Posidonia patches outside the cave hosted 143 species with a coverage of 0.98 and an estimated 180 (+ 26%) species at perfect coverage. The high diversity here recorded highlights the important role played by caves as biodiversity reservoirs. Additionally, this diversity is higher than the one described from Western Mediterranean caves inspected with comparable methods, contributing to questioning the magnitude of the west to east decreasing diversity gradient in the Mediterranean Sea.