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

Studies carried our in four submarine canyons in the northwestern Mediterra nean Sea have resulted ill the discovery of a new fauna composed chiefly of hydromedusae, This finding has led us to postulate the existence of a sing ular planktonic community in these canyons that is probably maintained by t he flux and deposit of organic material from the continental shelf. The spe cific composition and abundance of the populations differ from canyon to ca nyon and seem to be related to vertical fluxes, topography, and both the hy drographic and ecological features of each canyon, This hydromedusan fauna is characterized by meroplanktonic species that appear to live out their en tire life cycles inside the canyons. Those cycles seem to be linked to seas onal production processes related to factors such as canyon topography, sed imentation, and circulation of water masses within the canyons, The present study indicates that submarine canyons could be a new key habitat to an un derstanding of the biodiversity of coastal and shelf zones. The origin of t he deep-water Mediterranean fauna is reviewed, and the hypothesis of a Teth ys origin for some of the deep-water hydromedusae endemic to the Mediterran ean is entertained. (C) 2000 Elsevier Science Ltd. All rights reserved.