Spatial and Environmental Factors Affecting the Distribution of the Main Decapod Crustacean Prey Species in the NW Mediterranean

Abstract

The decapod crustaceans Alpheus glaber, Calocaris macandreae, Processa canaliculata and Solenocera membranacea are some of the most common prey items for both fish and other decapod crustaceans in the muddy bottom communities of the lower continental shelf and upper slope in the western Mediterranean Sea. Despite their high densities and key ecological role, these species are often neglected in scientific studies due to their relatively small size and the associated difficulties in adequately sampling them, so little information is available on their biological and ecological characteristics. We studied the spatial distribution of these four main crustacean prey species in an area off the Ebro Delta (W Mediterranean), using non-linear geostatistics. We performed log-normal kriging, considering depth as a covariate in the spatial model (universal kriging with external trend). All semivariograms were fitted to a spherical model, but with different relationships to depth. All species were more abundant in a sub-area characterised by a gentler slope and the presence of submarine canyons. The spatial correlation between densities of all species and sediment variables were analysed. All species except Solenocera membranacea were negatively correlated with sorting coefficient (IGSD), showing a preference for well sorted, homogeneous sediments corresponding to low energy areas. Further, Calocaris macandreae higher densities were associated with areas of coarser grain size (Φ) and Processa canaliculata density was negatively correlated with carbonate content of the sediment (CO3).