Stochastic processes driving cyanobacterial temporal succession in response to typhoons in a coastal reservoir.

Typhoons associated with heavy rainfall events, potentially triggering harmful algal blooms (cyanoHABs) dominated by cyanobacteria in coastal reservoirs. These blooms deteriorate water quality and produce toxins, posing a threat to aquatic ecosystems. However, the ecological mechanisms driving cyanobacteria communities in response to typhoons remain unclear. To address this gap, we investigated a coastal reservoir with high-frequency sampling during two typhoon seasons. We employed comprehensive statistical methods under neutral and evolutionary theories to analyze environmental dynamics and cyanobacterial genus succession. Our findings revealed a significant increase in nutrient loads following typhoons, with concentrations of total nitrogen (TN), total phosphorus (TP), and ammonia-nitrogen (NH-N) rising from 0.4 mg/L to 1.0 mg/L, 0.02 mg/L to 0.63 mg/L, and 0.03 mg/L to 0.26 mg/L, respectively. These changes coincided with fluctuations in other physicochemical parameters under changing hydrometeorological conditions. Despite significant environmental disturbances, the cyanobacterial community exhibited a remarkable recovery within 15-25 days following the typhoons. This recovery progressed through four distinct successional phases, with a notable shift in community composition from Raphidiopsis and Pseudoanabaena to Aphanocapsa, subsequently replaced by Raphidiopsis and Microcystis, before reverting to the pre-typhoon community structure. During the entire successional phase, the availability of TN and the TN/TP ratio played a dominant role, as indicated by PLS-PM analysis (total effects = -0.6; p < 0.05). Pre-typhoon, environmental factors primarily influenced community structure (54 %) based on modified stochasticity ratio. However, following the typhoons, stochastic fluctuations took precedence (71 %-91 %). The rapid recovery of cyanobacterial communities and the shift in driving mechanisms from deterministic to stochastic processes underscore the complex ecological responses to typhoon events. This study provides essential insights for biodiversity preservation and ecosystem restoration, emphasizing the need to consider both stochastic and deterministic processes in ecological management strategies.