Phycotoxin accumulation in zooplankton feeding on Alexandrium fundyense -: vector or sink?

Zooplankton can consume toxic Alexandrium spp. dinoflagellates in the Gulf of Maine and retain paralytic shellfish poisoning (PSP) toxins, potentially acting as toxin vectors. We performed experiments to determine toxin budgets for common species of copepods (Acartia hudsonica, Eurytemora herdmani, Centropages hamatus) feeding on toxic Alexandrium fundyense, offered as monocultures or in mixtures of algal prey, by comparing calculated toxin ingestion rates and toxin content of copepod body tissue and fecal pellets. When fed monocultures, both copepod tissue and fecal pellet fractions accounted for less than or equal to 5% each of the calculated ingested toxin, and thus by difference greater than or equal to 90% was lost as a dissolved fraction into the seawater medium. The presence of alternative food did not significantly alter the efficiency of toxin retention. Sloppy feeding or regurgitation are probable mechanisms for release of toxin to sea water. Experiments using varying concentrations of A. fundyense and alternativenon-toxic species did not show significant effects of cell concentration on toxin retention efficiency. Total toxin retained and efficiency of retention varied among copepod species. Toxin profiles (% molar composition) of dinoflagellates, copepod tissues and fecal pellets differed slightly, suggesting some metabolic transformation. Because of their low retention efficiency, copepod grazers can effectively disperse PSP toxins produced by Alexandrium spp. into the environment, where they are much less likely to be harmful-zooplankton act as a sink for PSP toxins. Nevertheless, sufficient toxin body burdens are attained to contribute to propagation of PSP toxins to other trophic levels.