Is Prymnesium patelliferum toxic for copepods? Grazing, egg production, and egestion of the calanoid copepod Eurytemora affinis in mixtures of "good" and "bad" food

The potentially toxic, bloom-forming prymnesiophyte Prymnesium patelliferum was offered to the copepod Eurytemora affinis as a sole food and in mixtures with the green alga Brachiomonas submarina and the chrysophyte Pseudopedinella elastica. Filtration, ingestion, egg and faecal pellet production, and mortality were measured. In addition, videofilm was used to check the condition of copepods and possible changes in feeding behaviour due to different food species. With both B. submarina and P. elastica as a sole food, filtration, ingestion, egg production, and egestion were generally high and mortality low. In contrast, when fed with P. patelliferum, egg production and egestion were low. Mortality of copepods fed high concentrations of P. patelliferum was high, but copepods fed low concentrations survived generally well, both in single-species experiments and in mixtures. However, there were no significant differences in ingestion rates between algae species or concentrations. Thus, differences in ingestion of P. patelliferum could not explain the lower mortality in lower concentrations. We conclude that lethal effects were connected to toxic cell exudates, and thus independent on ingestion. When P. patelliferum was mixed with other species (1:1), egg production was equally high (P. elastica), or even higher (B. submarina), than with P. elastica and B. submarina alone. We conclude that even though P. patelliferum is harmful for copepods if offered as a sole food species, it can add to nutritional quality of other species in mixtures. In the experiments this may have been due to P. patelliferum containing specific nutritionally important components lacking from green algae, such as polyunsaturated fatty acids.