The trophic linkage between zooplankton and benthic suspension feeders: direct evidence from analyses of bivalve faecal pellets

Using radiotracer (C-14) and microscopic observation, we demonstrated that mussels (Mytilus edulis and Perna viridis) could be predators of mesozooplankton (rotifer Brachionus plicatilis). At radio-labelled rotifer densities of 0.1, 0.2, 0.5, 1.0 individual ml(-1), faecal pellets of mussels showed different degrees of radio signals and most of the faecal pellets were expelled 4 h after pulse feeding on rotifers. The maximum gut retention time (GRT) of C-14-labelled rotifers in the digestive diverticula did not o show any significant difference between the two mussel species or the different densities of rotifers, and the averaged GRT was 43.4 +/- 3.06 h (mean +/- SE). At a rotifer density of 4.5 individual ml(-1), rotifer lorica pieces and rotifer bodies without eggs were found in faeces of M. edulis, while in the pseudofaeces, only complete rotifer bodies were found.