Figure 5
Cytometric differentiation of picophytoplankton populations. These different subpopulations were identified according to their differences in side scatter and both red and orange fluorescence; Synechococcus emit a strong orange fluorescence whereas Prochlorococcus emit only red fluorescence when excited by blue light [35]. In addition, Synechococcus cells are significantly larger than Prochlorococcus cells (ca. 1-0.6 μm in diameter respectively) [4]. Pico-eukaryotes were identified by their larger size (SSC) and higher red fluorescence. Scatter plot of orange versus red fluorescence (A) and side scatter versus red fluorescence (B) observed on Station S2 (i;e. Salinity = 2.44%), showing: (i) 2 populations of pico-cyanobacteria, one exhibiting fluorescence and side-scatter characteristics of Prochlorococcus sp. (referred as Prochlorococcus-like) and the second exhibiting fluorescence and side-scatter characteristics of Synechococcus (referred as Synechococcus-like) and (ii) 2 populations of pico-eukaryotes (P-Eu1 and P-Eu2).