Abstract
Grazing by the copepod Centropages hamatus upon various combinations of toxic Alexandrium tamarense and non-toxic A. tamarense and Scrippsiella trochoidea revealed that rates of grazing and egg production, and egg hatching success were influenced by the relative proportions of the different dinoflagellate diets. These relations were variable, in that there was selection either for, or against ingestion of toxic dinoflagellates, depending upon relative proportions. Egg production rates and egg hatching success progressively declined with decreasing proportions of non-toxic S. trochoidea and increasing proportions of toxic A. tamarense. However, with diets of nontoxic A. tamarense, natural sea water and filtered sea water, egg production and hatching success were lower than on diets of either non-toxic S. trochoidea or toxic A. tamarense. Copepods ingested all diets with almost no mortality and accumulated toxins from toxic diets. These results support previous studies showing that zooplankton grazing and fecundity is influenced by food quality, but that responses of grazers to toxic phytoplankters are varied, inconsistent, and often surprising.