Testing The Validity of the Synthesis Ratio of Protein to Low Molecular Weight Metabolites as an Estimation of Phytoplankton Growth in the Field

Abstract

Cholorophyll a, primary production and the patterns of 14C assimilation into the major end-products of photosynthesis were determined for phytoplankton in the coastal waters off Plymouth, in order to study their physiological ecology during spring conditions. At the end of the study period, a diatom bloom occurred after the development of a slight thermocline. Throughout the pre-bloom period, the majority of the label was found in storage products, and phytoplankton growth was not nutrient-limited. During the development of the bloom, however, an increase in protein synthesis was found, which is interpreted as a result of an active phytoplankton growth. Both synthesis ratios for protein to storage products, i.e. lipid and polysaccharide, (P/L+S) and protein to low molecular weight metabolites (P/M), summarize the variations in the physiological state of phytoplankton during this study. Comparison of the P/M synthesis ratio and different estimations of phytoplankton growth rate shows the usefulness of this index for characterising natural populations.