Succession of Aphanizomenon flos-aquae and Microcystis aeruginosa in direct co-culture experiments at different temperatures and biomasses

Cyanobacterial blooms have become a serious global environmental issue due to their potential risk for releasing detrimental secondary metabolites into aquatic ecosystems, posing a great threat to water quality management for public health authorities. Aphanizomenon , a common filamentous cyanobacterial genus belonging to Nostocales, is under particular concern because its several members are able to form harmful blooms. Furthermore, succession of bloom between A. flos-aquae and Microcystis occurs in many natural lakes. To evaluate the competitiveness of A. flos-aquae vs. M. aeruginosa , two sets of experiments at different ratios of biomass at 15 °C and 25 °C were conducted. Results show that at 15 °C, the two species were able to coexist, and A. flos-aquae showed a specific higher growth rate, and its growth was promoted by the presence of M. aeruginosa . At 25 °C, the growth of A. flos-aquae was inhibited by the biomass of M. aeruginosa , and M. aeruginosa suppressed A. flos-aquae in competition. Additionally, the vegetative cell size of A. flos-aquae was significantly influenced by the co-culture with M. aeruginosa , whereas the filament length of A. flos-aquae was not significantly affected. This study confirms that temperature is the dominating factor on the succession of A. flos-aquae and M. aeruginosa of a different biomass.