Role of Algal Community Stability in Harmful Algal Blooms in River-Connected Lakes.

Harmful algal blooms (HABs) in freshwater produce toxins that pose a threat to public health and aquatic ecosystems. Although algal communities have been studied globally to understand the characteristics of HABs, the occurrence of toxic cyanobacteria in freshwater ecosystems is rarely understood. Unlike abiotic factors, the effects of biotic factors (e.g., interaction, dominance, and variability) on the occurrence of toxic cyanobacteria were overlooked due to the intricate interaction of microorganisms under different environmental conditions. To address this problem, a comprehensive ecological concept stability, which encompasses variations in species or communities due to changing biological interactions or environmental fluctuations, was applied in this study. The algal communities in six river-connected lakes in the North Han River, South Korea, were classified into high and low stability groups. The algal species belonging to diatoms and green algae groups played a major role in the interaction within the algal community in highly stable lakes, but the frequency of Microcystis led the interaction within the algal community at the center of the network in low-stability lakes. These results indicate that the interaction within the cluster is easily changed by Microcystis, where the abundance explosively increases in lakes with low algal community stability. Water quality is more strongly associated with the occurrence of toxic cyanobacteria (Microcystis and Dolichospermum). In low-stability lakes, more diverse water quality indicators are correlated with the development of toxic algae than in high-stability lakes. This paper is the first report on the importance of algal community stability in freshwater in the occurrence of toxic cyanobacteria and offers a new perspective on Microcystis monitoring and management.