Echinoderm assemblages of Mauritanian slope

Abstract

The echinoderm fauna of North-eastern Atlantic is one of the best known worldwide. However, despite a great number of published works on Atlantic echinoderms, this group remains poorly know in Northwest African waters, where the available information basically comes from the old oceanographic expeditions carried out from the late 19th- to mid-20th centuries (Challenger, Prince Albert I of Monaco, Travailleur et Talisman, Michael Sars, Valdivia, Atlantide ). During the four multidisciplinary Maurit surveys, carried out annually from 2007 to 2010 onboard R/V Vizconde de Eza in Mauritanian EEZ, between Cape Blanc (21° N) and the Senegalese border (16° N), a total of 342 trawling stations were sampled between 79 and 1867 m depth. Most of stations were located in soft bottoms and were accomplished with a commercial trawl and a beam-trawl. Only 26 stations were deployed in hard bottoms, namely canyons borders, the giant cold-water coral reef and a seamount, using a rock dredge. This paper deals with the echinoderms obtained in these surveys and compares soft-bottoms and hard bottom assemblages. Echinoderms were collected in 271 stations (79.2%) of which 252 (93.0%) were located in soft bottoms and only 19 (7.0%) in hard substrata. Global diversity reaches 100 species identified in both soft and hard substrata, including 29 Holothuroidea, 28 Asteroidea, 27 Ophiuroidea, 13 Echinoidea and 3 Crinoidea. Eighty-two species were collected on soft bottoms, 25 were collected on hard substrata, but only six were reported in both. Ophiuroidea and Asteroidea were the most diverse echinoderms found on soft bottoms, versus Holothuroidea and Ophiuroidea in hard bottoms. Nevertheless, numerically the soft bottoms assemblages were clearly dominated by deposit-feeder Holothuroidea, while the dominance in hard bottoms is mostly suspension-feeder Holothuroidea (Dendrochirotida) and Ophiuroidea.