Changes in the structure of fish communities of the Cantabrian Sea shelf are analysed using information from bottom trawl surveys carried out every autumn during the period 1990-1999. The trend of ecological indices (species richness and diversity) has been less stable in shallowest strata during the decade. The effect of environmental variables on the fish communities is explained by interset correlation of canonical axis of canonical correspondence analysis (CCA) with the abiotic variables considered (depth, near-bottom temperature, near-bottom salinity, longitude and geographic stratum) to determine the assemblages of fishes each year. Interannual variations in the communities structure are analysed using multitable methods. In contrast to adjacent areas, the narrowest surface of the Cantabrian Sea shelf produces strong environmental gradients over a short distance. Depth is the most influential and stable factor determining the assemblages observed. The coastal, outer shelf and shelf-break communities are the strongest sources of variation, both intra-annual and interannual. Using time-series of indices of the main hydrographic driving agents, Navidad current and upwelling, we try to discover the causes of the instability of spatial structure of assemblages not explained by the abiotic variables considered in the analyses.

No