Living benthic foraminifera of southeastern Mediterranean ultra-oligotrophic shelf habitats: Implications for ecological studies

The Levantine Basin, the saltiest, hottest and the most ultra-oligotrophic basin in the Mediterranean Sea, continues to be affected by recent anthropogenic changes. That includes the long-term influence of the opening of the Suez Canal and the enhanced oligotrophy in this region due to the damming of the Nile River. This study explores the spatial distribution and diversity patterns of living benthic foraminifera in this impacted SE Levantine shelf, between 40 and 100 water depths at 59 sites, sampled in August 2011 off the Israeli coast. Multivariate statistical analyses resulted in the identification of four distinct benthic foraminiferal assemblages, reflecting their ecological preferences distributed within four coherent biotopes with different environmental settings. Two biotopes were identified along the 40 m depth interval: 1. the middle and the southern shelf in which Deuterammina rotaliformis accompanied by Eggerelloides scaber predominate, and their abundance is positively related to Chl-a concentrations and negatively related to total organic carbon (TOC) and fine-grained sediment contents, and 2. the northern middle sandier carbonate rich shelf in which Lessepsian taxa and others calcareous foraminifera such as Quinqueloculina schlumbergeri and Ammonia tepida dominate the assemblage. The other two biotopes that occur between 60 m and 100 m water depths consist of high concentrations of fine-grained sediments, relatively rich with TOC. Hanzawaia rhodiensis, Asterigerinata mamilla and Rosalina spp. reveal a positive relationship with the carbonate-rich sediments of the northern outer shelf biotope. Lagenammina sp, Reophax scorpiurus, Glomospira charoides, Valvulineria bradyana, and Bolivina striatula exhibit a more positive relationship with higher clayey-silty organic rich sediment of the central-southern outer-shelf biotope. A comparison between the living assemblages investigated in the current study and during a previous study in the late 90s, at the same sites, indicates a prominent foraminiferal response to the ongoing human activity in this region. That includes (I) the expansion of some Lessepsian species into ~40 m water depths habitats indicating the availability of suitable bottom water conditions for these species attributed to the increase in ultra-oligotrophy at this water depth. (II) the very recent introduction (either by shipping/aquaculture) of Deuterammina rotaliformis to the Israeli coast, sometime between the late 90s and 2011and its becoming the most dominant species in the southern middle shelf, a region most affected by the ongoing consequences of the damming of the Nile.