Patterns in molluscan death assemblages along the Israeli Mediterranean continental shelf

Abstract

The Mediterranean coast of Israel can be divided into two distinct provinces (south to north): the Nilotic, which up to the construction of the Aswan Dam received most of its quartz-rich sediments from the Nile, and the Levantine, which receives most of its sediments from local, carbonate-rich sources. These differences in sediment composition should have a strong effect on the faunal composition. We studied the very abundant molluscan fauna, a major biogenic component of the shallow Mediterranean sediments and suggest that variations in assemblages are associated with different substrates. We examined the dead molluscan component of sediment samples collected at 40 m water depth at five stations along the Israeli Mediterranean coast to determine the variations in biodiversity trends. The use of shelly death assemblages that accumulate on the seafloor averages out short-term, environmental fluctuations such as seasonality and reproduction, and presents a more complete “modern” picture than would be attained based on single live censuses alone. More than 2000 specimens yielded 114 species, with the bivalve Corbula gibba being the most abundant. Samples originating from the Levantine Province show greater species richness and a higher portion of epifaunal species compared to samples from the Nilotic Province. Specifically, 30 bivalves and 20 gastropods were only found in the Levantine samples, while only six bivalves and three gastropods were only found in the Nilotic samples. Our results point to a spatial biodiversity pattern along the Israeli coast, in which the Levantine Province is richer in species, feeding strategies and life habits than the Nilotic Province. The data collected can be used as a baseline for future ecological studies in the area, as they shed light on the under-studied molluscan benthos of the intermediate continental shelf of the Israeli Mediterranean.