Spatial structure and seasonality of decapod crustacean populations on the northwestern Mediterranean slope

Abstract

Two trawl surveys designed for geostatistical analysis were made in spring and fall 1991 on Nephrops norvegicus fishing grounds off Barcelona, Spain. High-resolution geostatistical techniques - a new tool for analyzing species assemblages - were used to map and assess species abundances. Of the 43 decapod crustacean species collected, the spatial structures of the nine most abundant were analyzed and mapped by kriging. The maps of abundance drawn by kriging showed that the populations within the depth range of a species were not spread uniformly but were segregated in areas of high density. The locations of high concentration patches were generally mutually exclusive between pairs of species. The depth-related zonation of the megafaunal assemblage studied was complemented by a strong alongshore spatial heterogeneity. The spatial structure revealed by the geostatistical analysis, namely local dominance by one or a few species and a spatial pattern of high-density patches, made it difficult to predict the relative species composition at a given place, thus challenging the concept of a community of ecologically interacting decapod crustaceans over the continental slope. Local factors, such as canyon-mediated hydrographic processes and sediment resuspension, helped account for the horizontal heterogeneity in the spatial distribution of decapod crustaceans