Phytoplankton were enumerated using a FACSCalibur flow cytometer (Becton Dickinson) and populations characterized as previously described (Johnson et al., 2010). Briefly, cells were excited with a 488 nm laser (15 mW Ar) and inelastic forward (<15°) scatter, inelastic side (90°) scatter (SSC), green (530 ± 30 nm) fluorescence, orange fluorescence (585 ± 42 nm), and red fluorescence (> 670 nm) emissions were measured. Populations were deemed ‘phytoplankton’ if they contained red-fluorescence, i.e. had a chlorophyll signal and were subsequently assigned to specific taxa (i.e. Prochlorococcus, Synechococcus or Pico-photosynthetic eukaryotes) based on previous classification schemes (Johnson et al., 2010).
References:
Johnson, Z.I., Shyam, R., Ritchie, A.E., Lin, Y., Mioni, C., Lance, V.P. et al. (2010) The effects of iron- and light-limitation on phytoplankton communities of deep chlorophyll maxima of the Western Pacific Ocean. Journal of Marine Research 68: 1-26. doi: 10.1357/002224010793721433