COPEPOD GRAZING ON A PHYTOPLANKTON COMMUNITY CONTAINING THE TOXIC DINOFLAGELLATE DINOPHYSIS-ACUMINATA

Copepod grazing on the toxic dinoflagellate Dinophysis acuminata from the west coast of France (La Rochelle) was studied with a concentrated (40-70 mu m) phytoplankton assemblage dominated by Leptocylindrus danicus, D. acuminata, Ceratium fusus and Ceratium fuca. Copepod nauplii were also present. Three to five copepods/copepodites (Acartia clausi, Isias clavipes and Centropages typicus) were incubated together with the phytoplankton. Dinophysis acuminata was grazed upon by all copepod species. However, to some extent, I. clavipes and C. typicus avoided it as food. Dinophysis acuminata cells represented for them only 5-10% of total ingested carbon during the first 24 h, and almost all individuals survived and thrived well. In contrast, A. clausi did not avoid D. acuminata, which represented 30% of ingested carbon in 1 day. Acartia clausi then had a lower survival than the two other copepod species. However, the survival of A. clausi was high in control incubations, where a plankton community without D. acuminata was used as food. It is concluded that the okadaic acid of D. acuminata is potentially toxic to some grazers, and/or might function as an allelopathic grazer repellent.