Hydrozoans from Mauritanian deep-waters

Abstract

During the four Maurit surveys carried out annually from 2007 to 2010, 342 trawl stations were sampled off the Mauritanian coast between 80 and 2000-m depth. Hydroids were captured at 174 stations, totalling 6169 colonies belonging to 63 species and 19 families. Most of the species were Leptothecata and only seven belonged to Anthoathecata. Thirty-two of the 63 species are new records for Mauritania. Plumulariidae showed the highest species richness (8 species), followed by Sertulariidae and Campanulariidae (7 species), Lafoeidae, Haleciidae and Aglopheniidae (6 species). The most abundant were Sertulariidae, followed by Aglaopheniidae, Plumulariidae, Campanulariidae, Halopterididae and Haleciidae. The ability of hydroids to colonize Mauritanian soft bottoms was driven by hydrorhizal modifications for anchoring the colony to the sediment and by epizoism on 11 invertebrate groups. Families whose species developed both strategies and those which were typically epibionts on hydroids were the most frequent and abundant. Most of the species were eurybathic (58 species), with four species recorded only in the coastal realm, 18 exclusively in the deep benthic realm and 41 in both realms. Therefore, overall hydroid diversity was highest in the deep benthic realm. Biogeographical components included two main groups: species with a wide distribution (59%) and species of Atlantic distribution (41%); our results also emphasize the similarity between the Mauritanian hydroid fauna and the Atlantic-Mediterranean region. Only one species, Hydractinia multitentaculata (Millard 1975), has West African distribution. No endemic species were reported.