The worldwide colony-forming haptophytephytoplankton Phaeocystis spp. are key organismsin trophic and biogeochemical processes in theocean. Many organisms from protists to Wsh ingestcells and/or colonies of Phaeocystis. Reports on speciWcmortality of Phaeocystis in natural plankton ormixed prey due to grazing by zooplankton, especiallyprotozooplankton, are still limited. Reported feedingrates vary widely for both crustaceans and protistsfeeding on even the same Phaeocystis types and sizes.Quantitative analysis of available data showed that:(1) laboratory-derived crustacean grazing rates onmonocultures of Phaeocystis may have been overestimatedcompared to feeding in natural planktoncommunities, and should be treated with caution;(2) formation of colonies by P. globosa appeared toreduce predation by small copepods (e.g., Acartia,Pseudocalanus, Temora and Centropages), whereaslarge copepods (e.g., Calanus spp.) were able to feedon colonies of Phaeocystis pouchetii; (3) physiologicaldiVerences between diVerent growth states, species,strains, cell types, and laboratory culture versusnatural assemblages may explain most of the variationsin reported feeding rates; (4) chemical signalingbetween predator and prey may be a major factor controllinggrazing on Phaeocystis; (5) it is unclear towhat extent diVerent zooplankton, especially protozooplankton,feed on the diVerent life forms of Phaeocystisin situ. To better understand the mechanismscontrolling zooplankton grazing in situ, future studies should aim at quantifying speciWc feeding rates ondiVerent Phaeocystis species, strains, cell types, preysizes and growth states, and account for chemical signalingbetween the predator and prey. Recently developedmolecular tools are promising approaches toachieve this goal in the future.
