Chlorophyll (alpha) -normalized photosynthetic parameters, e.g. the photosynthetic efficiency ((alpha) B), and the maximum photosynthetic rate (PBm), for natural phytoplankton communities exhibit extreme ranges of variation. Part of this variation is related to the species composition of the communities, another part has methodological causes, and a large part has physiological causes, i.e. manifestations of adaptational responses to variations in environmental factors. To exemplify species differences in Chl(alpha) -normalized photosynthetic parameters, the high parameter values for prymnesiophytes in contrast to diatoms are discussed. These are primarily due to the lower chlorophyll (alpha) :carbon (Chl(alpha) :C) ratios in prymnesiophytes and therefore do not indicate that prymnesiophytes are superior to diatoms in the harvesting of light.