Preingestive selection of different microalgal mixtures in Crassostrea gigas and Mytilus edulis, analysed by flow cytometry

The potential impact of selective grazing by filter-feeding bivalves was studied on the relative composition of both planktonic and benthic algae that are commonly suspended in coastal areas, Different feeding behaviour was observed in the oyster Crassostrea gigas and the mussel Mytilus edulis. C, gigas preferentially filtered and rejected (as pseudofaeces prior to ingestion) diatom species relative to flagellates. These differences appear to depend upon differences in algal shape and flexibility. Findings also suggest that ratios of rejection to filtration for flagellate species were influenced by the planktonic or benthic origin of the other available algal species. Future studies of trophic flux and resource utilisation should therefore consider the extent to which different filter-feeding species may preferentially filter and/or ingest separate algal species that are simultaneously available in the surrounding seston. (C) 1997 Elsevier Science B.V.