Deciphering the response mechanism of microorganisms to green tide outbreaks: Diversity, assembly processes, and co-occurrence patterns.

Green tide, a widespread coastal water environmental issue, significantly impacts the ecology of nearshore microorganisms. Despite extensive research on green tides, the dynamics of microbial communities and their assembly mechanisms throughout the development of these events are still not well understood. To elucidate these responses and underlying mechanisms, we conducted a comprehensive study examining the diversity, composition, and ecological dynamics of prokaryotic and microeukaryotic communities at various phases of green tide events by integrating high-throughput sequencing. The results revealed that deterministic processes predominated prokaryotic community assembly during green tide events, transitioning to stochastic processes in the post-bloom phase, while the assembly of microeukaryotic communities was consistently driven by deterministic processes at all phases. Co-occurrence network analysis indicated that green tide outbreaks reduced the connectivity and modularity of microbial networks, thereby weakening their overall stability. Functional predictions suggest that green tides may influence methane oxidation and inhibit nitrogen fixation, while simultaneously enhancing nitrification and denitrification processes. These changes could potentially alter the carbon and nitrogen cycles in coastal ecosystems. Additionally, we observed an increase in the abundance of the dddL gene, which may promote the production of dimethyl sulfide (DMS) and thus impact the atmospheric sulfur cycle. Furthermore, the outbreaks of green tides appear to facilitate phosphorus synthesis and iron oxidation. Overall, this study provides a foundational microbial dataset and novel insights into the dynamics of microbial networks during green tide events. These findings offer a better understanding of the microbial community's response to green tides and their potential impacts on biogeochemical cycles in coastal ecosystems.