Typhoon‐Induced Vertical Mixing Rapidly Reshapes Bacterioplankton Communities Across Ocean Depths

Abstract Typhoon‐induced vertical mixing of stratified water columns can profoundly impact ocean ecosystems. Such mixing processes are expected to replenish nutrients throughout the water column, thereby stimulating the growth of certain bacterial taxa and altering bacterioplankton communities. Furthermore, it may redistribute bacterioplankton functional potential across depths, reshaping community diversity and composition. However, the effects of typhoons on bacterioplankton communities throughout the water column in open‐ocean environments remain poorly understood, largely due to the scarcity of immediate in situ field observations. To address this gap, we conducted in situ sampling of environmental and microbial variables across three to four water layers at eight stations before (3–5 days) and after (2–5 days) Typhoon Maria passed through the southern East China Sea, and analyzed them with high‐throughput sequencing. Following the typhoon, we observed significant increases in nutrient concentrations, chlorophyll‐ a levels, primary production, bacterial production, and bacterial respiration, along with a marked decrease in water temperature. The community shifted considerably between pre‐ and post‐typhoon conditions. This community restructuring was characterized by an enrichment of copiotrophic taxa (e.g. , Alteromonadaceae ) and a decline in oligotrophic lineages (e.g. , SAR11 ), revealing a potential mechanism through which storms enhance microbially mediated biogeochemical cycling. Additionally, the typhoon increased community similarity across depths (i.e., reduced vertical β‐diversity), particularly between distantly separated layers. By elucidating how typhoon‐induced mixing reshapes bacterioplankton communities, our findings contribute to improving predictions of ecosystem responses to the increasing frequency and intensity of storms under climate change.