Starr, M. Department of Fisheries and Oceans Canada, StarrM@dfo-mpo.gc.ca
Runge, J. Department of Fisheries and Oceans Canada, RungeJ@dfo-mpo.gc.ca
St-Amand, L. Department of Fisheries and Oceans Canada,
ARE DIATOMS TOXIC OR JUST NUTRITIONALLY INSUFFICIENT FOR SUCCESSFUL COPEPOD REPRODUCTION?
The importance of diatoms as a high-quality food source for copepod reproduction has recently been questioned. Studies have suggested that diatoms can be toxic to copepods by preventing their eggs from hatching or by causing fatal deformities in early naupliar stages. While there is now strong evidence that many diatom species are by themselves an insufficient food source for sustained successful copepod reproduction, the hypothesis that they are toxic remains to be properly tested. In laboratory experiments, we have offered to the calanoid copepod, Calanus finmarchicus, three different ratios (25:75; 50:50; 75:25 of a constant, total carbon concentration) of a mixture of the diatom Thalassiosira nordenskioldii, a suspected toxic species, and a known, non-deleterious species, Skeletonema costatum. As a control, we fed T. nordenskioldii at concentrations varying between 1500 and 6000 cells per ml. Ingestion rate, egg production and egg viability were measured. Our results show that Thalassiosira alone significantly reduces the hatching success of Calanus eggs; hatching success was inversely proportional to the female ingestion rate. In all mixture experiments, Calanus grazed on both Thalassiosira and Skeletenoma, however, egg viability was not higher than expected from the proportion of Thalassiosira in the maternal diet. These new data are consistent with the hypothesis that certain common diatoms contain toxic agents that block copepod embryogenesis.
Day: Wednesday, Feb. 3
Location: Sweeney Center