Ecophysiological characteristics of red, green, and brown strains of the Baltic picocyanobacterium Synechococcus sp. – a laboratory study

The bloom of picocyanobacteria (PCY), accompanied by a drastic ecological crisis is a new phenomenon in Europe, which requires careful investigation. Therefore, this work examined the response of Synechococcus sp. physiology to different environmental conditions. Three strains of Synechococcus sp. (red BA-120, green BA-124 and brown BA-132) were cultivated in a laboratory under previously determined environmental conditions. These conditions were as follows: temperature (T) from 10 by 5 to 25 °C, salinity from 3 by 5 to 18 and Photosynthetically Active Radiation (PAR) from 10 by 90 to 280 μmol photons m −2  s −1 , which gave 64 combinations of synthetic, though real environmental conditions. Scenarios reflecting all possible combinations were applied in the laboratory experiments. Results pointed to differences in growth rates between strains. However, there was also a similar pattern for BA-124 and BA-132, which showed the highest concentrations of picocyanobacteria cells at higher T and PAR. This was also found to be true for BA-120, but only to a certain degree as the growth rates started to decrease above 190 μmol photons m −2  s −1 PAR. Pigmentation, chlorophyll a (Chl a ), fluorescence and rate of photosynthesis presented both similarities and differences between the strains. In this context, more consistent features were observed for brown and red strains when compared to the green. In this paper are defined the ecophysiological responses of PCY.