Composition and significance of picophytoplankton in Antarctic waters

Filter fractionated picophytoplankton from Antarctic coastal waters (summer 2001) represented only 7-33% of total phytoplankton, even though total stocks were low (average Chl a = 0.32 mu g l(-1), range = 0.13-1.03 mu g l(-1)). Though all cells passed a 2 mu m filter, electron microscopy revealed most cells were over 2 mu m, principally Parmales, Phaeocystis sp., and small diatoms. CHEMTAX analysis of HPLC pigment data suggested type 8 haptophytes (e.g. Phaeocystis sp. plus Parmales and pelagophytes) contributed 7-58% of picoplanktonic chlorophyll a, type 6 haptophytes (e.g. coccolithophorids) 18-59%, diatoms 0-18% (mostly type 2 diatoms, e.g. Pseudonitzschia sp., 0-15%), prasinophytes 0-17%, with cell fragments of cryptophytes 0-40%, and dinoflagellates 0-11%. Only stocks of type 8 haptophytes and prasinophytes differed significantly due to successional changes. Zeaxanthin concentrations exceeded estimates from previous cyanobacterial counts and may derive from non-photosynthetic bacteria.