Soft bottom macrobenthic communities of North Biscay revisited: Long-term evolution under fisheries-climate forcing

Thirty-five years after the first description of the benthic community and sediments of the North Bay of Biscay continental shelf (80–200 m depth in the “Grande Vasière” region) by Glémarec (personal communication), the sampling stations were revisited to provide a new reference on the status of the macrozoobenthic communities to help our understanding and management of fisheries that are highly developed in this area. Results showed that large modifications occurred in the communities and sediments of the central part of the “Grande Vasière”, while these modifications remained moderate in the surroundings on the outer continental shelf. Revisited, macrobenthic communities differed greatly from those recorded in the 1960s, and were less numerous and more homogeneous. The dominant species which characterized the communities and sub-communities had also changed. The main factor that can explain these differences is the granulometry of the sediments which has shown large changes: a strong decrease in the mud fraction and increase in the fine sand fraction. These sedimentary changes should be linked with human activities: increase in bottom trawling effort that induces the resuspension of fine mud particles and the homogenization of sediments over large areas, and decrease in terrigenous particulate fluxes due to anthropic activities on the shoreline and in coastal waters. Effects of global climatic change on the observed evolution remain low, even if some species common in the south of the Bay of Biscay in the 1960s but rare or absent in the north, had increased in density and spread to the north. Trawling activities are probably the main force driving benthic community evolution in the North Bay of Biscay both through direct action on the fauna (inhibition and facilitation processes) and indirect action by modifying sediment characteristics.