Heavy rainfall shifts microbial control from nutrient-temperature to precipitation dependence in subtropical coastal waters

Abstract

Extreme rainfall events are becoming more frequent under climate change, yet their short-term impacts on microbial community dynamics in coastal ecosystems remain poorly understood. This study investigated how rainfall modulates the effects of environmental conditions on microbial communities at a subtropical Pacific coastal station, based on two high-frequency (daily) time series totaling nearly 200 days. The abundances of viruses, bacteria, Synechococcus spp., nanoflagellates, ciliates, and diatoms were analyzed in relation to fluctuations in hydrology and nutrients. Heavy rainfall significantly reduced salinity and stimulated nutrient enrichment, resulting in distinct microbial responses that were substantially different from those observed on non-heavy rainfall days. At low precipitation (<39 mm day(-1)), temperature and nutrient concentrations (phosphate, PO4; nitrate, NO3) primarily governed the growth of bacteria and Synechococcus spp., whereas under intense rainfall (>39 mm day(-1)), salinity became the dominant environmental driver. Viral abundance increased following storm-induced nutrient pulses, indicating an enhanced infection potential during ecosystem recovery after storm disturbance. These findings demonstrate that rainfall-induced hydrological variability exerts rapid and cascading effects on microbial food webs, with implications for coastal biogeochemical cycling and ecosystem stability under a changing climate.