A first insight into the megabenthos of Mauritanian Canyons

Resumo

The composition of megabenthic communities from the Northern Mauritanian canyons was studied using data and material obtained during the four Maurit surveys, accomplished in November-December of 2007-2010. Cartography of the canyons was carried out using a multibeam echosounder and a high resolution seismic system (TOPAS). Oceanographic data were obtained in 29 vertical CTD profiles located in four transects along the canyons. The megabenthos survey was limited to canyon edges and included 11 stations sampled with a rock dredge. Twenty nine canyons and other minor channels, grouped in four large complex systems, were located in the Arguin Province. The canyons, with very steep walls, can reach down to 700 m depth and extend over 8-70 km in length along the slope. The water mass influencing the canyons correspond to the South Atlantic Central Water (SACW). The megabenthos species richness was estimated to be over 206 species, distributed among 29 high?range taxa. Hydroids, sponges, decapods, bivalves, polychaetes and prosobranchs showed the highest species richness, oscillating from 29 to 15 species. In terms of feeding strategies, suspension-feeders dominated the species richness (63%), abundance (75%) and also biomass (94%). While ophiuroids composed the largest proportion of total abundances (23%), demosponges dominated the biomass (80%). Multivariate analysis identified two megabenthic assemblages mainly segregated by its trophic strategy. The first cluster was defined by strong dominance of suspension?feeders and higher values of diversity indexes, and included four stations where living corals were collected. The second cluster was dominated by scavengers, carnivorous and detritivorous species, with much lower diversity.