Environmental parameters constraint on distribution of benthic foraminifera in the Strait of Bonifacio (Mediterranean Sea)

The Strait of Bonifacio is located between the Isles of Sardinia and Corsica (Mediterranean Sea), its maximum depth is about 100 m. The Strait is the exchange zone between the waters of the Tyrrhenian and Ligurian-Provençal basins and is strongly affected by high current action. Benthic foraminifera were identified in 31 samples collected during an oceanographic cruise (“Bocche 2003” - P.I.C Interreg III Project) that provided new geomorphological and sedimentological data on the western continental shelf of the Strait of Bonifacio. Several biotic parameters were calculated (species diversity, density, Fisher α index, Shannon-Weaver index, and Dominance) and multivariate analyses (Cluster Analysis, Principal Component Analysis and Canonical Correspondence Analysis) were performed to identify foraminiferal assemblages in the context of environmental parameters. Strong current, bathymetry, grain-size, organic matter and food availability are the main factors exerting control on the spatial distribution of benthic foraminifera in the Strait of Bonifacio. Three groups of assemblages were differentiated according to several sampling sites, which varied mainly due to degrees of energy. The first group included the shallowest station, close to the islands of Corsica and Sardinia, while the two other were typical of high-energy environments and were localized in the central area of the Strait. Cluster C concerns those located at a central position, while cluster B includes those in a more lateral position at the deepest part of the Strait. Elphidium crispum, Eponides concameratus and Textularia agglutinans appeared to be the more adapted species in this high-hydrodynamic system. The dominance of the epibenthic foraminifera (e.g. Lobatula lobatula and Planorbulina mediterranensis), permanently attached to sea grasses (Posidonia oceanic) and algae has been related to both the greater current velocities in the sampled area. The occurrences of Miliolinella subrotunda, Neoconorbina nitida, Quinqueloculina stelligera, Rosalina globularis, R. vilardeboana and Sigmoilinita costata appear to be closely related to the abundance of organic carbon and higher C/N ratios. The distribution of S. sagittula appear closely linked with bathymetry. Interaction between multiproxy ecological factors (oxygen, food, toxic substances, biological interactions, transport, light penetration, turbidity, etc.) characterize peculiar microenvironments in the sediment-water interface, allowing different species to occupy different niches within a relatively small area. A detailed understanding of environmental parameters that influence benthic foraminifera distribution in natural systems is a necessary prerequisite for the use of foraminifera as useful tools for ecological and environmental interpretations.