Growth Responses in the Marine Picocyanobacteria Synechococcus: A Multi Stressor Approach

Marine Synechococcus are among the most abundant photosynthetic organisms on Earth, and are often exposed to large fluctuations in temperature and CO₂ concentrations. These two key photosynthetic stressors co-vary to different extents in different parts of the ocean, and are expected to change in the coming decades due to ocean acidification and changing circulation patterns. To understand the effects of future global change on marine picocyanobacteria, we cultured the Synechococcus strain WH 8109 (previously isolated from northwestern Atlantic Ocean slope water) under three different temperature (22 °C, 24 °C and 26 °C) and CO₂ levels (400 ppm, 600 ppm and 800 ppm) simultaneously. We maintained a constant light intensity of 20 µE m^-2 s^-1 during the experiments. We also monitored the changes in medium pH during the experimental period. The highest specific growth rate of 0.61 d^-1 was observed at 24 °C and 800 ppm CO₂ concentration. Also, higher specific growth rates were obtained at 26 °C as compared to 22 °C under the three different CO₂ levels tested. Thus, Synechococcus WH8109 showed good growth response at high temperature and CO₂ levels, which suggests their potential advantage in the future ocean.