Macrofaunal variability in the continental shelf and canyons in the southeastern Bay of Biscay

Abstract

Located in the southeastern Bay of Biscay, the eastern Cantabrian Sea is characterized by the presence of the Capbreton Canyon and a highly diverse and complex geomorphology. The sedimentary seafloor is dominant and biota inhabiting it has been widely studied. The objective of the present research is to contribute to the knowledge of the spatial variability in the composition of the soft-bottom macrofaunal communities in a transitional zone from the continental shelf to the tributary valleys of the Capbreton Canyon. A total of 72 grab samples was studied in the southeastern Cantabrian Sea covering a range of depths of 97-1476 m. A decrease of density and species, and an increase of `phylogenetic' diversity within depth were observed. In the continental shelf greater variability in species assemblages was noticed, according to greater variability in sedimentary characteristics. However, no clear relationship was found between the sedimentary characteristics and the macrofaunal structural indexes (species, Shannon (H'), `phylogenetic' diversity). The most remarkable depth-related change in macrofauna happened at the depth of ca. 200-400 m, coinciding with a change in sediment characteristics, mainly organic matter content and mean grain size. Because the percentage of unidentified taxa at species level increased with depth, patterns in relation to depth should be considered with caution. The present research provides valuable information to gain knowledge in the communities living in the area for conservation and management purposes. (C) 2021 The Author(s). Published by Elsevier B.V.