Feeding and survival rates of the copepods Euterpina acutifrons Dana and Acartia grani Sars on the dinoflagellates Alexandrium minutum Balech and Gyrodinium corsicum Paulmier and the Chryptophyta Rhodomonas baltica Karsten

Here we studied the feeding performances and survival rates of the copepods Euterpina acutifrons and Acartia grani exposed to cultures of the toxic dinoflagellates Alexandrium minutum and Gyrodinium corsicum and the nontoxic Chryptophyta Rhodomonas baltica. The presence of hemolysins in G. corsicum was also analysed. For both copepod species, high ingestion rates on A. minutum and lower but similar rates on G. corsicum and R. baltica were found. After 120 h, only the E. acutifrons that grazed on G. corsicum or R. baltica showed 100% survival, whereas survival of the copepods that grazed on A. minutum was significantly lower. A. grani was more sensitive to the dinoflagellates, and at 120 h showed survival rates of 70% on G. corsicum and 60% on A. minutum. These results support the hypothesis that the feeding interactions between copepods and toxic dinoflagellates are highly species-specific. Long-term observations indicated that E. acutifrons can graze on G. corsicum without impairing their feeding or growth performances. Both copepod species consumed A. minutum in the short-term, but their long-term impact on this and other toxic marine dinoflagellates would be limited by the toxic effects of these flagellates. We did not find any evidence of haemolytic activity in extracts of G. corsicum. Toxins other than haemolysins may be responsible for the deleterious effects observed on A. grani. (C) 2002 Elsevier Science B.V. All rights reserved.