The ecophysiology of Phaeocystis globosa:A review

A straightforward ecophysiological characterization of Phaeocystis globosa is hampered by its complex polymorphic life cycle in which flagellates and colonial cells express different physiological and morphological properties. There is also increasing evidence that, besides the existence of different species, the most widespread species Phaeocystis globosa (Scherffel) has to be subdivided into at least five different ecotypes which again differ in their ecophysiological properties. Most research has been performed on the P. globosa ecotype North European (English Channel/North Sea isolates). From the available literature it must be concluded that flagellate cells are better competitors for light and phosphate than colonial cells, due to their superior uptake characteristics. To a limited extent this phenomenon is compensated in colonial cells by their ability to continue growth and cell division in the dark at the same rate as in the light, at the expense of extracellular colonial mucus. In contrast with other algal species, colonial cells of P. globosa are better competitors for nitrogen than for phosphorus.Flagellates transform into vegetative cells and form colonies in environments with irradiance levels of about 50 mu E . m(-2). s(-1) or more and an optimum phosphate concentration of 1 mu M. A solid substrate and the presence of calcium are prerequisites for colony formation. In environments where phosphorus is limiting no new colonies are formed. There is some evidence that nitrate stimulates colony formation, whereas high ammonium values (above 1 mu M) tend to suppress colony formation. Massive blooms of P. globosa colonies can be attributed to a combination of environmental conditions that induce colony formation and smaller grazing losses of colonial cells than of flagellates, rather than to superior ecophysiological characteristics of colonial cells.