MEPS 341:191-203 (2007)  -  doi:10.3354/meps341191

Spatial pattern in species richness of demersal fish assemblages on the continental shelf of the northern Mediterranean Sea: a multiscale analysis

Jean-Claude Gaertner1,*, Jacques A. Bertrand2, Giulio Relini3, Costas Papaconstantinou4, Nabila Mazouni5, Luis Gil de Sola6, Jean-Pierre Durbec1, Stjepan Jukic-Peladic7, Arnauld Souplet8

1Centre d’Océanologie de Marseille, LMGEM, UMR CNRS 6117, Rue de la batterie des Lions, 13007 Marseille, France
2IFREMER, Laboratoire Ecologie Halieutique, BP 21105, 44311 Nantes Cedex 03, France
3Universita di Genova, Via Baldi 5, 16126 Genoa, Italy
4NCMR, Aghios Kosmas Hellinikion, 16644 Athens, Greece
5Cépralmar, 20 rue de la République, 34000 Montpellier, France
6Centro Oceanográphico de Málaga (IEO), Puerto pesquero s/n, 29640 Fuengirola (Malaga), Spain
7Institut Za Oceanografiju i Ribarstvo, PO Box 500, 21000 Split, Croatia
8IFREMER, Laboratoire Ressources Halieutiques, BP 171, 34203 Sète, France

ABSTRACT: The species richness pattern of groundfish species in the entire northern Mediterranean Sea was examined at 3 spatial scales: region, large biogeographical zone and basin. We analysed 1914 trawl hauls collected using a single sampling design in the trawlable areas of the continental shelves between the Strait of Gibraltar and the Strait of Dardanelles (from 36.3 to 45.7°N and 5.3°W to 28°E). Spatial pattern in species diversity was assessed using complementary methods (Chao2 estimates of total species richness, mean species richness and beta diversity). No matter which scale was used, the expected longitudinally decreasing trend in species richness, which has been widely described in previous studies, did not appear when comparing estimates of total species richness per unit of area. Only the mean species richness pattern showed a moderate eastwards decrease at the largest spatial scale, but the trend progressively disappeared as the scale of analysis was reduced. In contrast to what is usually expected, our results suggest that Atlantic inflow does not play a key role in the present spatial pattern of fish species richness within the northern Mediterranean Sea. Furthermore, we show that the Aegean Sea can no longer be considered the least species-diverse zone in the northern Mediterranean Sea. Our results provide the first description of a quantitative ‘reference state’, with which the temporal changes in species richness patterns throughout the entire northern Mediterranean Sea can be compared in the future.

KEY WORDS: Species richness · Beta diversity · Groundfishes · Mediterranean Sea · Large scale · Lessepsian

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