Benthic foraminiferal distribution in the Mediterranean Sea

Recent benthic foraminiferal distribution patterns in the Mediterranean Sea are investigated in relation to water depth, substrate characteristics and food availability. Patterns of presence/absence abundances, and foraminife ral diversities differ between the main eastern and western Mediterranean b asins. The small basins in the Sicily Strait show the closest affinity with the western basin. The primary result of the present study is that no high resolution Mediterranean-wide bathymetric zonation can be determined becau se the modern benthic distribution patterns appear to be governed by intera ctions between water depth, substrate. and food supply. We can, however, de fine a broad subdivision between "shallow-water" and "deep-water" assemblag es, which can be traced throughout the Mediterranean Sea. The deepwater (>1 000 m) assemblage is characterized by low diversity and consists of Glomosp ira charoides, Gyroidinoides circularis/orbicularis, Gyroidinoides altiform is, Anomalinoides minimus, Robertinoides translucens and Biloculinella/Numm oloculina spp, The shallow-water assemblage has higher diversities and cons ists of Cassidulina crassa, Cassidulina laevigata/carinata, and Bulimina ma rginata. Decreasing primary productivity values from west to east result in a simila r decrease in organic flu to the sea floor and, therefore, in lower food av ailability to the benthic fauna. This trend might explain why species with low food demands, such as Gyroidinoides circularis/orbicularis and Glomospi ra charoides are more abundant in the eastern Mediterranean. Deep infaunal species such as Globobulimina spp,, Chilostomella spp,, and Brizalina alata seem to prefer high amounts of sedimentary organic carbon and thrive on se diments with low carbonate concentrations. This results in a distribution m ore or less restricted to areas with highest primary productivity values. M axima of this group are consequently found in the Alboran Sea, off Algeria, and in the northern Aegean Sea.