Hydrozoan diversity from Western Sahara and Atlantic coast of Morocco

Abstract

The hydroid fauna from the Atlantic coast of Morocco is currently the best known in Northwest Africa. This knowledge is due to the work of Patriti (1970), based on the study of hydroid collections of the Institut Scientifique Chérifien de Rabat, that also includes previous available records from the literature. Other relevant contributions were the report of Ramil and Vervoort (1992) on deep–water hydroids from the Ibero–Moroccan gulf and those of Medel and Vervoort (1998, 2000), Ansín Agís et al. (2001) and Vervoort (2006) based on the material collected by the Dutch CANCAP Expeditions. The aim of this work is the study of the benthic hydroids collected along the Western Sahara and the Atlantic coast of Morocco during two ecosystemic surveys carried out on board of the R/V Dr. Fridtjof Nansen, in the framework of the FAO project “Canary Current Large Marine Ecosystem” (CCLME). The sampling program was performed following latitudinal transects perpendicular to the depth isobaths and spaced 20 nautical miles apart. The samples were collected with a commercial otter trawl at four bathymetric strata: 20‐50 m, 50‐100 m, 100‐200 m and 200-500 m depth. Occasional trawls were also conducted to 800-100 m depth. The sampling period was November-December in 2011 and June-July in 2012. Hydroids were sorted on board from the total catch and directly preserved in 70% ethanol for further studies at the laboratory. A total of 3498 colonies were collected in both surveys, 2781 in Western Sahara and only 716 in Moroccan coast, despite the similar number of stations sampled in each region: 78 in Sahara and 67 in Morocco. Hydroid diversity was also higher in Saharan coast, where 56 species belonging to 16 different families were identified, versus 40 species included in 10 families reported from Moroccan waters. In the Western Sahara, Aglaopheniidae (54%) was the most abundant family, followed by Sertulariidae (17%) and Plumulariidae (15%); eleven species, Aglaophenia parvula, Nemertesia perrieri, Sertularella gayi gayi, Sertularella cylindritheca, Streptocaulus dollfusi, Nemertesia ramosa, Sertularella mediterranea, Obelia dichotoma, Lytocarpia myriophyllum, Halecium liouvillei and Campanularia hincksii account for more than 50 colonies each one. The same families were also the most representatives in Morocco, but in this case with a shared dominance: Plumulariidae (27%), Aglaopheniidae (26%) and Sertulariidae (22%); only three species, N. perrieri, A. parvula and S. gayi gayi account for more than 50 colonies. The permanent upwelling conditions in this region (Pelegri & Benazzouz, 2015) and the high primary production during the whole year (Pastor et al. 2008) drives the highest hydroid diversity and abundance in Saharan waters. Nevertheless, and despite the differences in species richness and mainly in abundance, the hydroid fauna of Western Sahara and the Atlantic coast of Morocco is very similar, showing the same zoogeographical structure and a strong affinity with the Atlantic-Mediterranean fauna. In addition, the most representative families as well as the most abundant species (A. parvula, N. perrieri, S. gayi gayi) are also the same.