Composition of ultraphytoplankton in the central North Atlantic

In the central North Atlantic Ocean, the ultraphytoplankton averaged over depth and season comprises 78% Prochlorococcus spp., 12% Synechococcus spp. and 10% eukaryotic algae by nurnbers. However, on the basis of light scatter (a substitute for carbon biomass), the average percentages are 11, 2 and 87 % respectively. On the basis of red fluorescence (a substitute for chlorophyll biomass), the average percentages are 28, 11 and 61 % respectively. On the basis of primary productivity, the average percentages are 19, 13 and 68% respectively. Thus, eukaryotic algae dominate the biomass and productivity of ultraphytoplankton.