INTERSPECIFIC DIFFERENCES IN THE PHOTOSYNTHETIC CARBON METABOLISM OF MARINE-PHYTOPLANKTON

Six species of marine phytoplankton of different sizes and taxonomic categories were grown in microcosms under identical experimental conditions; the species cultured were: Pavlova lutheri (Prymnesiophyceae), Dunaliella tertiolecta (Chlorophyceae), Phaeodactylum tricornutum (Baciollariophyceae), Eutreptiella sp. (Euglenophyceae), Alexandrium tamarense (Dinophyceae), and Phaeocystis pouchetii (Prymnesiophyceae). The photosynthetic carbon metabolism of these phytoplankton was studied throughout the exponential and lag phases of growth after nutrient depletion. The relative incorporation of carbon into protein was positively correlated with phytoplankton growth, while carbon assimilation into low molecular weight metabolites (LMWM) and storage products, i.e., lipid and polysaccharides, generally increased under nutrient-limiting conditions. Clear taxon-specific differences were observed in the proportions of carbon incorporated into cell constituents. A significant linear relationship was consistently found between the relative synthesis of protein to LMWM, and both the production normalised to chlorophyll (P:B) and the phytoplankton growth rate. However, ANCOVA revealed significant, interspecific differences in these relationships.