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

Phaeocystis species diversity has been reviewed by comparing the morphological and physiological characteristics of Phaeocystis cells and colonies of different geographical origin. These analyses gave evidence for four Phaeocystis species: P. globosa, P. scrobiculata, P. pouchetii and one undefined antarctic species, distinguishing themselves by colony and single cell morphology and temperature tolerance. Typical colonial shape constitutes the most apparent morphological characteristics distinguishing P. pouchetii from P. globosa. Differences between colonies referable to pouchetii and globosa can be confirmed on the basis of variation in temperature and light requirements, as well as morphological descriptions of palmelloid stages, e.g. colony shape and size, organisation of the cells inside the colonies. The most striking features of the motile single cell are the thread-like appendages, which are much longer than the cell itself, the organic scales covering the cells, varying in shape and size, the haptonema and the flagella. On this basis, previous Phaeocystis records were analysed and the geographical distribution of the genus reported. There was no evidence for strain specific elemental composition or photosynthesis or growth performance of cells and colonies. This indicates that more elaborate molecular and biochemical analyses are required to identify different species. Possible opportunities available through modern chemical and molecular biological advances are described.