Succession of picophytoplankton during the spring bloom 2012 in Disko Bay (West Greenland)—an unexpectedly low abundance of green algae

Picoplankton are an ecologically important component of pelagic Arctic marine ecosystems that may be heavily impacted by climate change. In order to assess potential impacts of a changing environment on this group, it is necessary to develop a better understanding of their population dynamics and seasonal distribution. This study, carried out in Disko Bay, West Greenland, during spring 2012, demonstrates that fuco-algae (e.g. chrysophytes, cryptophytes, diatoms and pelagophytes) dominated the picophytoplankton during the spring bloom with minor contributions from haptophytes. In the post-bloom phase, fuco-algae were replaced by haptophytes. In contrast to total chlorophyll a, which varied dramatically over the study period, the picoplanktonic chlorophyll a remained relatively stable despite the variability in picophytoplankton community composition. Based on mostly molecular studies, a general picture has emerged from the literature that mamiellophytes (a group within the green algae) dominate Arctic picophytoplankton. Here, however, green algae were found to contribute with only about 10 % of the picoplanktonic chlorophyll a. We suggest here that differences in cell size may offer a plausible explanation for the contrast between results obtained from molecular studies and those obtained from pigment- and microscopybased studies.