PICOCYANOBACTERIA IN THE BANDA SEA DURING 2 DIFFERENT MONSOONS

The relative abundance of red-pigmented picocyanobacteria, a recently recognized component of ocean primary productivity, was examined in the Banda Sea during August 1984 (cruise 1, southeast monsoon, upwelling) and February/March 1985 (cruise 2, northwest monsoon, downwelling). These small-sized (<1 μm) species are rich in the red pigment phycoerythrin (PE) and belong to the Synechococcus-type species that was studied in continuous culture. The cell concentrations were assessed by using the characteristic PE-absorbance peak at 545 nm in the in vivo absorption spectra as tracer and epifluorescence microscopy. Picocyanobacteria were found in relatively high concentrations (104-105 cells·cm-3) at 75% and 96% of the Banda Sea stations of cruise 1 and 2, respectively. The cell-numbers were higher during the first cruise, but their relative importance (as part of the total phytoplankton-biomass) was higher during the second cruise. The species showed a preference for deeper layers where light intensities were low. Their low surface abundance seemed to show a diurnal pattern (i.e. decreasing during the course of the day), correlated with surface irradiance. The occurrence of such a diurnal pattern is discussed in relation with results of light shift experiments with continuous cultures of Synechococcus. © 1990.