Tracing red-pigmented marine cyanobacteria using in vivo absorption maxima

The relative abundance of small coccoid cyanobacteria in the Banda Sea (Indonesia) was examined during the first cruise of the “Pelagic Systems” Theme 3 of the Snellius II expedition in August 1984. The survey study embraced 34 stations that were located 50 miles apart. The peak-height of the distinct maximum at 545 nm in the in vivo absorption spectra of continuous cultures of Synechococcus WH7803 (DC2) appeared to be an excellent marker for fast tracing of small red-pigmented Synechococcus-type cyanobacteria. These picocyanobacteria were found at 75% of the Banda Sea Stations, ranging from 10⁴ to 10⁵ cells ml⁻¹ and with a preference for the deeper layers where light intensities were low. Their low surface abundance seemed to show a diurnal pattern (i.e., decreased during the course of the day), correlating with surface irradiance. These observations suggest that red-pigmented picocyanobacteria are well adapted to grow and photosynthesis at relatively low irradiances. This is consistent with laboratory results.