Reduction in the toxicity of the dinoflagellate Gymnodinium catenatum when fed on by the heterotrophic dinoflagellate Polykrikos kofoidii

Abstract

To investigate the ability of the heterotrophic dinoflagellate Polykrikos kofoidii to reduce the toxicity pro- duced by the dinoflagellate Gymnodinium catenatum (toxic- ity = 2.0 to 3.9 Mouse Units (MU)/10 5 G. catenatum cells), we used the mouse bioassay to measure the toxicity retained in a population of P. kofoidii, originally fed G. catenatum for 2 d (ingestion rate = 5.6 cells grazer -1 d -1 ) and then starved. As a control, we measured the toxicity retained in a population of P. kofoidii originally fed a non-toxic strain of Scrippsiella tro- choidea. The toxicity retained in a population of P. kofoidii at Hour 0 (P. kofoidii starved for 0 to 48 h after being fed) was 17.3 MU/10 5