Dramatic effect of extreme rainfall event and storm on microbial community dynamics in a subtropical coastal region

Extreme weather events, such as heavy rainfall and typhoons, are becoming more frequent due to climate change and can significantly impact coastal microbial communities. This study examines the short-term alterations in microbial food webs-viruses, bacteria, picophytoplankton, nanoflagellates, ciliates, and diatom-following Typhoon Krathon in Taiwan's coastal waters in October 2024. Daily in situ sampling revealed a significant post-typhoon increased in viral, nanoflagellate, and Synechococcus spp. abundance. Furthermore, viral, Synechococcus spp., and nanoflagellate abundance increased by approximately 4.2 to 12.8-fold, 33.3 to 160 fold, and 0.5 to 9.4 fold in response to these weather events, compared to periods pre-typhoon, respectively. Modified dilution experiments showed that, before the typhoon, nanoflagellate grazing was the major cause of bacterial mortality, while viral lysis was the main cause of Synechococcus spp. mortality. Post-typhoon, there was a notable shift, with nanoflagellate grazing increasing mortality rates of bacteria and Synechococcus spp., suggesting that grazing became the dominant top-down control mechanism after the disturbance. Our findings suggest that extreme weather events shift microbial mortality dynamics, increasing the role of grazing in controlling microbial populations, with potential implications for carbon cycling in coastal ecosystems.