REPRESSION OF COPEPOD FEEDING AND FECUNDITY BY THE TOXIC HAPTOPHYTE PRYMNESIUM-PATELLIFERUM

Late copepodids and adults of Acartia clausi GIESBRECHT showed no mort ality when kept in a very dense culture (10(9) cells 1(-1)) of a toxic strain of the haptophyte Prymnesium patelliferum GREEN, HIBBERD & PIE NNAR, for 48 h at 26-28 PSU. However, the haptophyte had strong negati ve effects on copepod egestion and reproduction rates, both when the h aptophyte was offered as the only food, and when offered in mixtures w ith Rhodomonas baltica KARSTEN sensu ZIMMERMANN, an alga known to be i ngested and support reproduction in Acartia. The rates were depressed already at concentrations of 0.1-0.3 10(6) cells 1(-1) of P. patellife rum, and decreased further with increasing concentration of the haptop hyte. At typical bloom concentrations (greater than or equal to 4 . 10 (6) cells 1(-1)) of P. patelliferum, the rates were no greater than th ose of starved copepods. These results demonstrates that zooplankton f eeding and reproduction in coastal waters may be constrained by presen ce of toxic haptophytes, also when these algae occur in moderate conce ntrations and mortality is not registered.