Environmental factors drive megabenthic faunal distributions patterns on the East and West wall of Whittard Canyon

Submarine canyons are regarded as major conduits for organic matter transport from the continental shelf to the food limited deep-sea. In addition, canyons are characterised by heterogeneous topography, which interacts with the hydrography, generating distinctive currents and a large variety of suitable habitats numerous benthic and sessile species. Together, these variables allow for high biomass and species diversity and therefore canyons have been characterised as hotspots for fauna. During two cruises with RV Pelagia the easternmost branch of the Whittard Canyon system (NE Atlantic) was visited. Our main aim was to study megabenthic faunal abundance and diversity on the east and west wall of the branch. Since both canyon walls have different characteristics it was hypothesized that faunal communities and densities will differ. To study habitat and megabenthic faunal variability video transects were made and environmental variables, like temperature and oxygen were measured. Substrate changed rapidly along canyon transects with distance and depth but also between the canyon walls. The eastern wall consisted mostly of soft sediment and cliffs while the western wall was characterised by soft sediment. Also distinct faunal patterns were observed with depth and between canyon walls. The eastern wall showed a higher overall abundance and diversity in contrast to the western wall. Sea pens were the most abundant fauna until 1000m depth where hard and soft coral abundance increased in the east, while corals were almost absent on the western wall at comparable depths. Filter feeders were dominant in both the eastern and western wall, however the eastern wall had twofold the percentage of predators and deposit feeders. Faunal distribution patterns can be explained by the morphological and substrate differences on the walls as well as particle density and near-bed hydrodynamics.