Temperature effects on growth, colony development and carbon partitioning in three Phaeocystis species

Phaeocystis is an ecologically important marine phytoplankton genus that is globally distributed. We examined the effects of temperature on the 3 most common species: P. globosa, P. antarctica, and P. pouchetii, which grew at 16-32, 0-6, and 4-8 degrees C, respectively. P. pouchetii did not form colonies; P. globosa formed colonies at 16, 20, and 24 degrees C, and P. antarctica colonies were observed at all temperatures. More cells were partitioned into the colonial form at lower temperatures than at higher temperatures for P. globosa and P. antarctica. P. globosa colony size decreased with temperature, whereas P. antarctica colony size showed no distinct response to temperature. Numbers of cells per unit of colony surface area of P. globosa and P. antarctica were lowest at temperatures where highest growth rates and colonial abundances were observed; more organic carbon was partitioned into solitary cell biomass at higher temperatures, whereas the carbon concentration of colonies was not affected by temperature. Maximum quantum yield of P. antarctica and P. globosa exhibited subtle responses to temperature, whereas that of P. pouchetii was relatively invariant within the growth temperature range. Future changes in sea surface temperature may dramatically alter the ecology and biogeochemical cycles of systems dominated by Phaeocystis spp. and result in further degradation, via oxygen depletion and altered food web structure.