A multidisciplinary approach to the understanding of hydromedusan populations inhabiting Mediterranean submarine canyons

Studies carried out in four submarine canyons in the northwestern Mediterranean Sea have resulted in the discovery of a new fauna composed chiefly of hydromedusae. This finding has led us to postulate the existence of a singular planktonic community in these canyons that is probably maintained by the flux and deposit of organic material from the continental shelf. The specific composition and abundance of the populations differ from canyon to canyon and seem to be related to vertical fluxes, topography, and both the hydrographic and ecological features of each canyon. This hydromedusan fauna is characterized by meroplanktonic species that appear to live out their entire life cycles inside the canyons. Those cycles seem to be linked to seasonal production processes related to factors such as canyon topography, sedimentation, and circulation of water masses within the canyons. The present study indicates that submarine canyons could be a new key habitat to an understanding of the biodiversity of coastal and shelf zones. The origin of the deep-water Mediterranean fauna is reviewed, and the hypothesis of a Tethys origin for some of the deep-water hydromedusae endemic to the Mediterranean is entertained.