SPATIAL STRUCTURE AND SEASONALITY OF DECAPOD CRUSTACEAN POPULATIONS ON THE NORTHWESTERN MEDITERRANEAN SLOPE

Two trawl surveys designed for geostatistical analysis were made in sp ring and fall 1991 on Nephrops norvegicus fishing grounds off Barcelon a, Spain. High-resolution geostatistical techniques-a new tool for ana lyzing species assemblages-were used to map and assess species abundan ces. Of the 43 decapod crustacean species collected, the spatial struc tures of the nine most abundant were analyzed and mapped by kriging. T he maps of abundance drawn by kriging showed that the populations with in the depth range of a species were not spread uniformly but were seg regated in areas of high density. The locations of high concentration patches were generally mutually exclusive between pairs of species. Th e depth-related zonation of the mega-faunal assemblage studied was com plemented by a strong alongshore spatial heterogeneity. The spatial st ructure revealed by the geostatistical analysis, namely local dominanc e by one or a few species and a spatial pattern of high-density patche s, made it difficult to predict the relative species composition at a given place, thus challenging the concept of a community of ecological ly interacting decapod crustaceans over the continental slope. Local f actors, such as canyon-mediated hydrographic processes and sediment re suspension, helped account for the horizontal heterogeneity in the spa tial distribution of decapod crustaceans.