Using biotic indices to estimate macrobenthic community perturbations in the Bay of Brest

Shallow-water macrofaunal communities have been studied in the Bay of Brest in order to estimate the impact of the main sources of urban, industrial, harbour and agricultural perturbations. Sampling stations were located on the shallow muddy grounds, between 0 and 5 m depth and in the estuaries. The analytic method of evaluation was based on the recognition of ecological groups of different sensitivity to organic matter overload. Their relative abundances allowed identification of stages of perturbation including eutrophication. The heavily polluted areas were easily identified in the northern basin, along Brest city and its harbour complex. With respect to the latter, opposite situations were shown for the northern and southern basins (the northern being eutrophicated). The double statistical analysis revealed that the first factor structuring the communities was anthropogenic perturbations, the second was the edaphic factor.