Epibenthic communities of trawlable grounds of the Cantabrian Sea

Epibenthic communities of the Cantabrian shelf were sampled in October 2000 and October 2001 using a 3.5 m beam trawl. The surveys were undertaken following a pattern of stratified sampling in four transects perpendicular to the coastline and included three depth strata (30-100, 101-200, 201-400 m). The total number of species collected was 241, belonging to 9 taxa, of which the best represented were molluscs and crustaceans. Longitudinal differences in ecological indices were detected in relation to biogeographical and hydrographic patterns. Three main assemblage groups were identified using cluster analysis. The effect of environmental variables (depth, near-bottom temperature and salinity, sediment morphology, Atlantic influence) on assemblages was also identified by canonical ordination, showing a pattern of two gradients: depth/water temperature and sediment characteristics. Assemblages identified by both methods were spatially coherent. The hermit crab Diogenes pugilator typifies the poor fine sands of the inner shelf; fishes (Arnoglossus laterna, Callyonimus maculatus, Pomatochistus sp.) and a hermit crab, Anapagurus laevis, characterise the assemblage of inner and middle shelf sediments with higher organic content, and the echinoderm Ophiura affinis, the fish Lepidorhombus boscii and Crangonidae Crustacea typify the deeper community of medium and fine sediments with intermediate levels of organic content.