Growth, toxicity and oxidative stress of a cultured cyanobacterium (Dolichospermum sp.) under different CO₂/pH and temperature conditions

Summary Cyanobacteria blooms are a worldwide nuisance in fresh, brackish and marine waters. Changing environmental conditions due to upwelling, changed mixing conditions or climate change are likely to influence cyanobacteria growth and toxicity. In this study, the response of the toxic cyanobacterium D olichospermum sp. to lowered pH (−0.4 units by adding CO 2 ) and elevated temperature (+4° C ) in an experimental set‐up was examined. Growth rate, microcystin concentration and oxidative stress were measured. The growth rate and intracellular toxin concentration increased significantly as a response to temperature. When D olichospermum was exposed to the combination of elevated temperature and high CO 2 /low pH , lipid peroxidation increased and antioxidant levels decreased. Microcystin concentrations were significantly correlated with growth rates. Our results show, although oxidative stress increases when exposed to a combination of high CO 2 /low pH and high temperature, that growth and toxicity increase at high temperature, suggesting that the cyanobacterium in general seems to be fairly tolerant to changes in pH and temperature. Further progress in identifying biological responses and predicting climate change consequences in estuaries experiencing cyanobacteria blooms requires a better understanding of the interplay between stressors such as pH and temperature.