STATIS-CoA: A methodological solution to assess the spatio-temporal organization of species assemblages. Application to the demersal assemblages of the French Mediterranean Sea

Abstract

The organizational patterns of demersal assemblages (fish, crustaceans and cephalopods) in the Gulf of Lions were investigated on the basis of a set of six bottom trawl surveys performed between 1994 and 1999 (MEDITS programme). The use of a recent multitable method (STATIS-CoA) provided a detailed representation of the stable and variable parts of the spatial organization of demersal assemblages during the studied period. We showed that demersal assemblages of the Gulf of Lions were organized along a coast-open sea gradient. At the scale of the Gulf, we showed that this gradient can be split into three areas: 1) the coastal region and the continental shelf (10 to 200 m depth), 2) the upper slope (200 to 500 m) and 3) the deeper slope (500 to 800 m). Associated to this bathymetric structuring we found a species-richness gradient which decreases from the coast to the upper slope. Our analysis showed that this spatial organization pattern was highly persistent during the course of the study. However, some species caught in the slope area exhibited a strong variability of their spatial distribution mainly during the 1999 survey. From a methodological point of view, STATIS-CoA offers a rigorous theoretical framework for the simultaneous analysis of a three-dimensional set of data. Applied in the field of fisheries ecology, this method (1) constitutes a relevant way to analyse the spatial organization of species assemblages and its pattern of changes, and (2) could be of particular interest to treat the MEDITS data both at a local and at the North Mediterranean Sea scales.