Biodiversity and biogeographic relationships of the polychaete fauna in French Atlantic and Mediterranean waters

A survey of the literature, including the recent systematic reviews, reveals that 934 polychaete species have been recorded in French Atlantic (including the English Channel) and Mediterranean marine waters, including 818 species living on the continental shelf and 116 species that are strictly bathyal. These 934 species belong to 71 families, among which the Syllidae is the most diverse (97 species), followed by the Serpulidae (69 species), Spionidae and Phyllodocidae, each with more than 40 species. Forty-four families have fewer than 10 species recorded in each. The total number of species is spread over 11 continental shelf areas as well as the Atlantic and Mediterranean bathyal depths. In terms of species diversity, the richest areas are the Mediterranean coasts of Provence-Côte d’Azur (507 species) and Languedoc-Roussillon (483 species), the western part of the English Channel (402 species), and the southern part of the Bay of Biscay (343 species). The lowest numbers of species were recorded in the eastern English Channel, due to an impoverishment of all the fauna in this part of the Channel. Other areas—for example, the Iroise Sea, the coast of Corsica and Mediterranean bathyal depths—also show low numbers, but this may only reflect the fact that insufficient information about these areas is available. A similarity analysis of 13 areas distinguishes four distinct faunal groups, each specific to one of four general locations: (1) the bathyal Atlantic and Mediterranean zones, including the coast of Corsica, (2) the two Mediterranean coastal areas (Provence-Côte d’Azur and Languedoc-Roussillon), (3) the four zones of the Atlantic continental shelf, and (4) the English Channel. The combined species can be separated into 17 different biogeographic groups.