Benthic foraminifera from the Southeastern Mediterranean shelf: Dead assemblages and living-dead comparisons recording consequences of Nile River damming

Abstract

This study explores the role of the Nile River damming in shaping the recent benthic ecology in the southeastern Levantine (SL) Basin, the saltiest, hottest and the most oligotrophic basin within the Mediterranean Sea. The spatial distribution and diversity patterns of dead benthic foraminiferal (BF) faunas from the SL shelf were analyzed at 59 stations (40–100 water depths) sampled in August 2011 off the Israeli coast. Distinct dead BF assemblages were determined using multivariate statistical analyses, reflecting ecological preferences and their association with different environmental settings. The dead BF assemblages investigated in the current study were significantly different from the living BF assemblages explored in a previous study at the same stations. Ongoing human activity may explain these discrepancies, especially in the middle shelf, where continuous grain size coarsening, increase in carbonate content and decrease in TOC have occurred since the construction of the Aswan High Dam across the Nile River. These changes comprise (I) modest but clear changes in the lateral distribution of the biotopes, including continuous southward retreat of the southern middle shelf Nilotic biotope, and appearance of more fragmented, small biotopes due to the reduced impact of the Nile littoral cell; (II) dissimilarities in assemblage composition with higher numbers of opportunistic species occurring in the dead assemblages and increasing densities of sensitive taxa in the living assemblages.