Winter biomasses of the benthic fauna in the Bay of Brest were estimated to model carbon fluxes through the benthic food web. Total biomass (9.59 g C m(-2)) is dominated by macrofaunal suspension feeders (53%) and carnivores (25%). Macrofaunal deposit feeders and herbivores, meiofauna, bacteria and demersal fishes accounted for 22% of total biomass. Most of the biomass was found on coarse coralline algae bottoms, in relation to environmental and biotic factors. Mean macrofaunal biomass is significantly higher in the Bay of Brest than in many other temperate coastal ecosystems. The proliferation of suspension feeders in the Bay would correspond to the first perturbation level of the ecosystem, due to organic enrichment. Suspension feeders would prevent eutrophication by controlling phytoplankton biomass.