ULTRAPHYTOPLANKTON IN THE EASTERN MEDITERRANEAN-SEA - TOWARDS DERIVING PHYTOPLANKTON BIOMASS FROM FLOW CYTOMETRIC MEASUREMENTS OF ABUNDANCE, FLUORESCENCE AND LIGHT SCATTER

Prochlorophytes, cyanobacteria and eukaryotic ultraphytoplankton from the southern Levantine Basin of the eastern Mediterranean Sea were analyzed by flow cytometry to obtain measurements of cell abundance, relative cellular fluorescence and relative cellular light scatter. Assuming that fluorescence is a proxy for chlorophyll and that light scatter is a proxy for cellular carbon, phytoplankton biomass can be expressed as the sum (over all cell groups) of adaptive cellular characteristics (i.e. chorophyll and carbon) weighted by cell abundance. On this basis, much of the carbon appeared attributable to eukaryotic ultraphytoplankton, but chlorophyll was more evenly partitioned such that the contributions from prochlorophytes and cyanobacteria were also significant. The subsurface chlorophyll maximum coincided with the maximum in total fluorescence but not with the maximum abundance of cells nor with the presumed maximum in the carbon biomass of ultraphytoplankton.