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 ana lyzed by flow cytometry to obtain measurements of cell abundance, rela tive cellular fluorescence and relative cellular light scatter. Assumi ng that fluorescence is a proxy for chlorophyll and that light scatter is a proxy for cellular carbon, phytoplankton biomass can be expresse d as the sum (over all cell groups) of adaptive cellular characteristi cs (i.e. chorophyll and carbon) weighted by cell abundance. On this ba sis, much of the carbon appeared attributable to eukaryotic ultraphyto plankton, but chlorophyll was more evenly partitioned such that the co ntributions from prochlorophytes and cyanobacteria were also significa nt. The subsurface chlorophyll maximum coincided with the maximum in t otal fluorescence but not with the maximum abundance of cells nor with the presumed maximum in the carbon biomass of ultraphytoplankton.