Phytoplankton photosynthesis and carbon-specific growth: light-saturated rates in a nutrient-rich environment

Light-saturated photosynthesis from short term (2 h) and daily (24 h) measurements were correlated in phytoplankton of two size fractions, net plankton dominated by diatoms and nanoplankton dominated by chlorophytes. Diurnal variations in short term photosynthesis were characterized by a midday maximum and tended to be a greater amplitude in net plankton than in nanoplankton populations. Nanoplankton photosynthesis varied on a seasonal scale while net plankton photosynthesis varied on a daily scale-a phenomenon which appeared to be reflected in the relationship between short term photosynthesis and growth. The latter, calculated from daily photosynthesis, increased exponentially with temperature and was more closely coupled to short term photosynthesis in nanoplankton than in net plankton populations. These differences seem to be related to the way in which the two size fractions are distributed in time and space as a consequence of interactions between physical process and time-dependent growth