Monsoon-driven short-term temporal changes and geomorphological controls on bacterial community dynamics in Korean coastal lagoons

In this study, we investigated monsoon-driven short-term temporal changes in bacterial community composition in two contrasting coastal lagoons in Korea: Gyeongpoho (permanently open) and Hyangho (intermittently open). Using a metabarcoding approach with 16S rRNA gene sequencing, we analyzed the bacterial diversity in these lagoons in relation to environmental variables before and after the monsoon season. Gyeongpoho exhibited greater variability in bacterial composition owing to the continuous seawater exchange, whereas Hyangho freshwater dominance resulted in a more stable microbial community. Salinity fluctuations driven by freshwater inflow significantly influenced microbial diversity, with distinct temporal shifts observed in the dominant bacterial taxa, including Proteobacteria, Bacteroidetes, Acidobacteria, and Chloroflexi. The prevalence of heterotrophic bacteria may be related to their roles in organic matter degradation and nutrient cycling, which are essential for maintaining ecosystem functions. The correlations between bacterial communities and environmental parameters, as revealed by self-organizing map (SOM) and canonical correspondence analysis (CCA) analyses, emphasize the sensitivity of microbial assemblages to hydrological changes. Geomorphological characteristics and hydrological dynamics play important roles in shaping bacterial assemblages. These findings provide crucial insights into the ecological implications of lagoon hydrodynamics and microbial diversity in assessing ecosystem responses to environmental disturbances and climate variability.