Variation in photosynthetic rates among individual cells of a marine dinoflagellate

Abstract

Rates of photosynthesis for individual cells from a field population of the dinoflagellate Ceratium tripos were measured by incubating them in situ with NaH super(14)CO sub(3) then assaying them, 1 cell per scintillation vial. The mean rate per cell was a maximum of 0.51 to 0.71 ng C cell super(-1) h super(-1) (estimated doubling time 5.9 to 4.2 d) at the surface and an order of magnitude less at greater depths or on cloudy days. For each of 4 sampling dates the estimate of carbon specific growth obtained for C. tripos using this single cell assay was correlated significantly with the estimate obtained for the entire phytoplankton community using conventional filter techniques. The authors used cultures of the related Ceratium longipes to prove the single cell assay against a direct measurement (absolute increase in carbon per cell) and obtained agreement within 5%. Individual cells from the same water samples differed in their absolute rates of tracer uptake, a previously unknown dimension of population structure in phytoplankton. Factors that may contribute to this variation are discussed.