Ingestion and assimilation of carbon from cellulolytic bacteria and heterotrophic flagellates by the mussels Geukensia demissa and Mytilus edulis (Bivalvia, Mollusca)

Abstract

We 14C-labeled cellulolytic bacteria and 3 species of bacterivorous nanoflagellates and fed these cultured organisms to 2 species of intertidal mussels, Geukensia demissa and Mytilus edulis, using a pulse-chase experimental design under controlled laboratory conditions. Ingestion and assimilation of C from these microheterotrophs by mussels were calculated from measured rates of defecation, respiration, excretion, and tissue incorporation. The proportion of available C ingested by G. demissa did not differ significantly among bacteria (39%), heterotrophic flagellates (58%), or the unicellular algae Isochrysis galbana (66%), which was used as a reference diet. In contrast, M. edulis ingested a significantly lower proportion (19%) of the small bacteria (<1 μm in diameter) than the larger (3 to 5 μm diameter) heterotrophic flagellates (58%). The efficiency with which G. demissa assimilated C from I. galbana (77%) was significantly greater than that from either bacteria (42%) or heterotrophic flagellates (44%). M. edulis assimilated bacterial C with significantly lower efficiency (21%) than C from heterotrophic flagellates (62%). These results indicate that heterotrophic flagellates can contribute to the C requirements of both G. demissa and M. edulis; however, only G demissa is capable of assimilating a considerable amount of C from bacteria.