Ultraphytoplankton photoacclimation through flow cytometry and pigment analysis of mediterranean coastal waters
B. Bautista and F. Jiménez Gómez

Prochlorophytes, cyanobacteria and eukaryotic ultraplankton from coastal waters of the western Mediterranean Sea were analyzed by flow cytometry to obtain measurements of cell abundance, relative fluorescence per cell (related to cellular pigment content) and relative light scatter per cell (related to cellular size). Cyanobacteria were the dominant group followed by small eukaryotic cells and prochlorophytes. The depth distribution of these ultraplanktonic components in the euphotic layer showed a decrease in the cell abundance with depth in parallel to the decrease of irradiance. Relative cellular light scatter showed similar distributions at the different depths, indicating no variation in the cell size. However, relative cellular fluorescence showed a clear increase with depth, both in red (chlorophyll a) and orange (phycoerythrin) fluorescence, suggesting photoacclimation. This was confirmed by the increase in cellular chlorophyll a concentration with depth, as derived from fractionated chlorophyll a analysis. The total fluorescence (F), calculated from the integration of the flow cytometric ineasurements of cellular fluorescence weighed by the cell abundance for each group, was significatively correlated with the fractionated chlorophyll a measurements, suggesting F as a useful means to characterize the group composition of bulk chlorophyll a, and therefore both as rough estimators of ultraphytoplankton biomass.

Keywords: Ultraphytoplankton, photoacclimation, flow cytometry, chlorophyll a, Mediterranean, cyanobacteria, prochlorophytes.
Contents of this volume Sci. Mar. 60(Suppl.1) : 233-241 Back PDF
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