Light-induced toxic properties of the marine alga Phaeocystis pouchetii towards cod larvae

The marine alga Phaeocystis pouchetii, which is common worldwide, has generally been regarded as a harmless representative of the prymnesiophytes. However, deterrent properties of Phaeocystis towards zooplankton and fish, and a possible toxic effect of Phaeocystis on fish larvae induced by high irradiance, have been reported. Accordingly, we exposed cod larvae to cultures of Phaeocystis, and manipulated the rearing water and irradiance to investigate the possible toxic properties. The experiments revealed that Phaeocystis produces chemical compounds which are lethal to cod larvae, and the production of these toxins appears to be dependent on the level of irradiance. The toxins seem to be released into the water, as demonstrated by the toxic effects of filtered seawater during Phaeocystis blooms. The production of harmful chemical substances by Phaeocystis during hatching and the initial growth of fish larvae may have consequences for the annual variation in the classes of marine fish in natural ecosystems. (C) 1998 Elsevier Science B.V.