THE TAXONOMIC IDENTITY OF THE COSMOPOLITAN PRYMNESIOPHYTE PHAEOCYSTIS- A MORPHOLOGICAL AND ECOPHYSIOLOGICAL APPROACH

Phaeocystis species diversity has been reviewed by comparing the morph ological and physiological characteristics of Phaeocystis cells and co lonies of different geographical origin. These analyses gave evidence for four Phaeocystis species: P. globosa, P. scrobiculata, P. poucheti i and one undefined antarctic species, distinguishing themselves by co lony and single cell morphology and temperature tolerance. Typical col onial shape constitutes the most apparent morphological characteristic s distinguishing P. pouchetii from P. globosa. Differences between col onies referable to pouchetii and globosa can be confirmed on the basis of variation in temperature and light requirements, as well as morpho logical descriptions of palmelloid stages, e.g. colony shape and size, organisation of the cells inside the colonies. The most striking feat ures of the motile single cell are the thread-like appendages, which a re much longer than the cell itself, the organic scales covering the c ells, varying in shape and size, the haptonema and the flagella. On th is basis, previous Phaeocystis records were analysed and the geographi cal distribution of the genus reported. There was no evidence for stra in specific elemental composition or photosynthesis or growth performa nce of cells and colonies. This indicates that more elaborate molecula r and biochemical analyses are required to identify different species. Possible opportunities available through modern chemical and molecula r biological advances are described.