Comparative study of the trophic structure of soft-bottom assemblages in the Bay of Blanes (Western Mediterranean Sea)

This study describes the trophic structure and dynamics of the soft-bottom macroinfauna inhabiting shallow sublittoral zones off the Bay of Blanes. The area is influenced by the inputs of the Tordera River, the activity of Blanes Harbor, and the effluent of domestic sewage. Five assemblages were studied from March 1992 to March 1993. Biomass data have been used for the analysis. Coarse sand sediments with low organic matter content were dominated by filter feeders and carnivores. The mixed group (filter and surface-deposit feeders) was the dominant one in fine sand sediments at the opening of the harbor. Subsurface-deposit feeders became more abundant in silty-sand sediments with the highest percentage of organic matter Water depth, granulometry and organic matter content were correlated to the observed spatial distribution. Rainfall, chlorophyll-a concentration in the water column, and organic matter content in the sediment were used to explain the seasonal variability. Annual dominance of trophic soups among sampled sites showed higher differences than the seasonal variability within sites. Comparisons of the trophic structure among stations were carried out using a trophic group importance index. The use of the traditional trophic indexes was discussed.