Effects of a blue mussel Mytilus edulis bed on vertical distribution and composition of the pelagic food web

The impact of a mussel bed on the neighbouring pelagic food web is investigated by a comparative study of the vertical distribution of plankton above a mussel bed with that above a bare sandy bottom. The use of conventional water bottles did not reflect the near-bed dynamics. However, use of a high-resolution water sampler in the bottom 1 m of the water column above the sea floor revealed statistically significant differences. The results document for the first time in situ grazing on all major components of the pelagic food web. The vertical distributions of phytoplankton, bacteria, protozoa, meroplankton and copepods were statistically significantly different above the mussel and sand beds. The mussel bed recycled nutrients back to the water column as waste products. The present investigation stresses the need for a more diverse view of the trophic role of suspension-feeding bivalves in shallow coastal ecosystems.