The soft bottom polychaete community of an area in front of Barcelona (NW Mediterranean) was monitored during the years 1990 and 1991 (7 cruises), detecting two pollution gradients. The first is in a northeast-southwest alongshore direction. With increasing distance from the pollution
source, sediment size and species richness increase while percentages of organic matter, total density and biomass of polychaetes, and density of Capitella capitata, decrease. The second gradient is bathymetric, with organic matter and biotic variables increasing and sediment size decreasing
with distance offshore. Results obtained with redundancy and principal component analyses allowed us to discuss the more or less "pollution indicator" character of some polychaete species and to determine the spatial distribution of species assemblages along the pollution gradient. Between
the "polluted bottoms", in the deeper northern zone and the "altered" bottoms mainly in the south, there is a "fluctuating" zone with the highest variability in species composition. The contribution of the sampling sites to spatial and interannual variability was assessed using anova on the
factor scores from the PCA. The most polluted zone showed the highest interannual variability.
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