Effects of the red tide dinoflagellate, Karenia brevis, on grazing and fecundity in the copepod Acartia tonsa

Among studies of copepod grazers fed harmful algae, decreased grazing and fecundity are the most common results. The causes of decreased grazing (physiological incapacitation, behavioral avoidance or lack of stimulation) and decreased fecundity (toxic versus nutritional effect) vary among studies. This study used a series of controlled laboratory experiments to investigate the cause of decreased grazing and fecundity in the copepod Acartia tonsa fed sole and mixed diets of the harmful alga, Karenia brevis. Copepods fed K. brevis mixed with the nutritionally viable dinoflagellate Peridinium foliaceum had higher ingestion rates and offspring production than copepods fed a sole diet of K. brevis (even when K. brevis was virtually nontoxic). Copepods fed mixtures did not discriminate between P. foliaceum and K. brevis while feeding. The results of this study suggest that K. brevis is not toxic to A. tonsa but lacks some chemical component responsible for stimulating a grazing response in A. tonsa as well as the nutritional requirements for normal offspring production.