Deep-sea benthic foraminifera in an area around the Cassidaigne Canyon (NW Mediterranean) affected by bauxite discharges

Abstract

During an environmental survey, living (stained) benthic foraminiferal faunas were investigated at 14 stations within the Cassidaigne Canyon (NW Mediterranean Sea) and the surrounding area. For many decades, industrial bauxite residues (namely red mud) have drained into this canyon via a submarine pipe. Stations investigated in this paper are located between water depths of 288 and 2,432 m from the shelf break to the deeper basin and at a distance ranging between ~5 and ~70 km from the pipe outlet. At almost every site, surface sediment is characterized by red mud deposits and their geochemical imprints. Our ecological observations show that foraminiferal standing stocks and simple diversity (S) decrease across the margin in response to the decreasing food input to the seafloor with increasing water depth. The foraminiferal composition echoes the overall meso-oligotrophic patterns of our study area. The contribution of opportunistic and stress-tolerant species, commonly identified as recolonizers of freshly disturbed areas, is minor at the 14 stations. This clearly shows that red mud dispersal in the Cassidaigne Canyon and the surrounding area has no major ecological impact on foraminiferal diversity.