Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession

The ability of phytoplankton species to initiate photo-protective mechanisms and the rates by which they do so have been suggested to be partly responsible for species succession. To examine whether this is also true in the case of diatom spring blooms preceding Phaeocystis globosa, cultures of P. globosa and Thalassiosira sp. were investigated under controlled laboratory conditions for differences in their xanthophyll cycling rates and abilities. It was found that P. globosa exhibited active and rapid xanthophyll cycling when cultures photoacclimated to 10, 50 and 100 μmol quanta m−2 s−1, were shifted to 150 and 250 μmol quanta m−2 s−1. The early spring diatom Thalassiosira only exhibited xanthophyll cycling when acclimated to 10 μmol quanta m−2 s−1. P. globosa always exhibited faster xanthophyll cycling rates than Thalassiosira, giving P. globosa a possible competitive edge over Thalassiosira sp. It was also found that the magnitude of xanthophyll cycling correlates with the intensity of light changes during the one-hour xanthophyll cycling experiments, and thus may be regarded as related to photoacclimation.