Chemically-mediated rejection of dinoflagellate prey by the copepods Calanus pacificus and Paracalanus parvus: mechanism, occurrence and significance

Thirteen species of dinoflagellates, ranging in size from 16 to 48 pm, were tested for particle rejection behavior in the copepods Calanuspacificusand Paracalanusparvus. Five dinoflagellates were rejected as food: Gonyaulax tamarensis (429). G. tamarensis (Ipswich), Ptychodiscus brev~s, Scrippsiella trochoidea and Protoceratium reticulatum. The response of copepods to P. reticulatum was examined in detail. Starved copepods could not b e induced to feed on this species; C. pacificus maintained in bloom concentrations ceased reproduction and had high mortality. Both the cells themselves and filtrate from the cell culture suppressed feeding on normally edible dinoflagellates.