TESTING THE VALIDITY OF THE SYNTHESIS RATIO OF PROTEIN TO LOW-MOLECULAR-WEIGHT METABOLITES AS AN ESTIMATION OF PHYTOPLANKTON GROWTH IN THE FIELD

Cholorophyll a, primary production and the patterns of C-14 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.