Possible mechanisms underlying copepod grazing responses to levels of toxicity in red tide dinoflagellates

Abstract A previous study indicated that rates of ingestion exhibited by adult female copepods of Acartia hudsonica (Pinhey) and Pseudocalanus spp. were lowered by increasing levels of toxicity in clonal cultures of the bloom-causing dinoflagellate Protogonyaulax tamarensis (Taylor). In the present study, three types of laboratory grazing experiments were performed to determine which of two contending hypotheses —behavioural rejection or physiological incapacitation - could explain the observed relationship best. The experimental results consistently supported the postulated mechanism of physiological incapacitation, and not the mechanism of behavioural rejection, as the reason for the lowered rates of ingestion on the more toxic dinoflagellate clones.

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