Deterrent effect of Gymnodinium catenatum Graham PSP-toxins on grazing performance of marine copepods

Abstract: The present study aimed to determine the effects of different concentrations of the toxic dinoflagellate Gymnodinium catenatum on the feeding performance, survival rates, and PSP toxin profiles of Euterpina acutifrons Dana and Acartia grani Sars. Each of the three different experiments was conducted in order to determine the feeding rates of adult female copepod species. Feeding experiments were performed in four 75-ml vessels each containing five copepods and different concentrations of cells (C1=2.68×102, C2=5.36×102 cellsml−1). Initial and final cell concentrations were estimated using a Coulter counter, while the carbon and nitrogen content were determined using a CHN analyzer. High-performance liquid chromatography was used to determine the composition of the PSP toxins, and estimate their concentrations in the tissue of the copepods. In experiment 1, significantly higher (p <0.05) ingestion rates were recorded for A. grani when feeding on the second concentration of cells (C2). Filtration rates were also significantly higher (p <0.05) for C2. A similar pattern was recorded for ingestion rates in E. acutifrons. By contrast, filtration rates were apparently higher for the lower concentration (C1). In experiment 2, A. grani ingestion rates were significantly higher (p <0.05) for the higher concentration (C2) in all three time phases. However, filtration rates for C2 were significantly higher (p <0.05) at 12 and 18h. E. acutifrons also presented significantly higher ingestion rates (p <0.05) for C2 at 12 and 18h. Filtration rates were significantly higher (p <0.05) for C2 only in the 12-h phase. In experiment 3, both copepods presented significantly lower (p <0.05) ingestion and filtration rates following exposure to G. catenatum for 24h. Carbamoyl toxins in the chromatograms were dominated by GTX1 and STX, followed by GTX2 and GTX3. Total cell toxicity was 2.58 and 2.34pgSTXeqcell−1 for cells harvested at the beginning and the end of the experiments, respectively. Total toxicity in the tissues of E. acutifrons and A. grani was 11.51 and 7.56(gSTXeqg−1, respectively. Survival rates in A. grani and E. acutifrons fed on C2 were 0% after 168 and 192h, respectively. Overall, the present study indicates that the copepods E. acutifrons and A. grani can not only ingest G. catenatum toxic cells, but also transfer their PSP toxins to other trophic levels. However, G. catenatum PSP toxins were shown to have had a deterrent and negative time-dependent effect on the feeding and survival rates, respectively, of E. acutifrons and A. grani. [Copyright &y& Elsevier]