Grazing impacts of the heterotrophic dinoflagellate Polykrikos kofoidii on a bloom of Gymnodinium catenatum

Abstract

In 1998, a red tide of the paralytic shellfish poisoning (PSP)-producing dinoflagellate Gymnodinium catenaturn Graham occurred in Yatsushiro Sea, western Japan. The dramatic decline of dominant G. catenatum cells occurred during the field and laboratory assessments, accompanied with growth of the heterotrophic dinoflagellate Polyknkos kofoidii Chatton. Microscopic observations on both field and laboratory cultured bloom water revealed that >50% of P. kofoidii predated on the natural population of G. catenaturn, and 1 to 8 G. catenatum cells were found in food vacuoles of P. kofoidii pseudocolonies. Our results suggest that predation by P. kofoidii contributes to the cessation of a G. catenatum bloom.