Relative grazing impact of microzooplankton and mesozooplankton on a bloom of the toxic dinoflagellate Alexandrium minutum

Abstract

Grazing can be a substantial loss factor for harm- ful algal blooms (HABs) and a possible cause of their termina- tion. There is, however, a considerable gap in our knowledge of the relative grazing impact of the different components of the planktonic community on a red tide. In this study, we examine the importance of grazing control on a naturally occurring bloom of the toxic dinoflagellate Alexandrium minu- tum. We estimated the grazing impact of microzooplankton (by the dilution method) and copepods (by 24 h incubations with cultured populations of Acartia grani and Oithona davisae) on a bloom of A. minutum. Grazing by microzooplankton (0.84 d -1 ) was equal to and even exceeded A. minutum growth rates (0.79 d -1