Mesoscale geographical patterns in the distribution of pandalid shrimps Plesionika spp. in the Western Mediterranean

Six bottom-trawl cruises, undertaken in spring 1994 to 1999 along the Spanish Mediterranean coastline, sampled pandalid shrimps from 30 to 800 m depth. Data analysis yielded a description of the distribution patterns of the 4 most common species (Plesionika heterocarpus, P. martia, R gighohi, P. edwardsi) over an area of 45 331 km(2). We analysed abundance of juveniles and adults by partial correspondence analysis (pCCA) in order to determine the effect on distribution of depth (as an overall estimate of temperature, salinity, turbidity and other variables), time (among-survey variability) and space (geographical location). The main null hypothesis we explicitly evaluated is that species composition remains constant along the Spanish Mediterranean coastline after controlling for depth and time. A significant (8.2 %) effect of geographical location was found. Hauls located in the central zone of the sampling cruises (Valencia: Ibiza Channel) showed an intermediate relative abundance of all species. By contrast, the samples from northern and southern zones showed a large relative abundance of P. martia and R heterocarpus, respectively. This pattern may be related to environmental specificity of the hydrodynamic conditions in the Ibiza Channel, dynamic topography characteristics linked to the canyons in the North Catalan zone, and surface production inputs, as found in the North Alboran zone (southern zone), where the main species (P. heterocarpus) exhibited the shallowest bathymetric distribution. Although discrimination between depth preferences of juveniles and adults (with adults being located deeper) is already known on a local scale, our results extend this pattern to the entire Spanish Mediterranean coastline and across all the species studied.