Tidal Zonation Shapes Microbial Communities and Sediment Properties in a UNESCO World Heritage Site (Gomso Bay, Korea)

This study investigates the effect of intertidal zonation on sediment characteristics, organic matter content, and microbial community distribution in Gomso Bay, Republic of Korea—an ecologically significant estuarine system and part of the UNESCO-designated Getbol, Korean Tidal Flats. It was hypothesized that physicochemical properties and microbial communities differ significantly among the inner, middle, and outer tidal zones due to variations in tidal exposure, sediment texture, and organic matter accumulation. Sediment samples were collected from nine sites across these zones and analyzed for total organic carbon (TOC), acid volatile sulfide (AVS), and trace metals (As, Cd, Cr, Cu, Hg, Li, Ni, Pb, Zn), along with sediment texture. Microbial community structure was examined using 16S rRNA gene amplicon sequencing to evaluate the influence of zonation on microbial diversity and composition. Results revealed distinct spatial variations along the intertidal gradient. Inner tidal zones with finer sediments showed higher TOC, AVS, and metal concentrations, whereas outer zones with coarser sediments exhibited lower values. Microbial composition also varied, with aerobic microorganisms dominating the high tidal flats and anaerobic taxa prevailing in the low tidal flats. Heterotrophic and autotrophic bacteria were more abundant in the outer zone, while chemolithotrophs predominated in the inner zone. Redundancy and Pearson’s correlation analyses further indicated significant relationships between sediment texture, TOC, AVS, heavy metals, and microbial diversity. Overall, the findings confirm that tidal zonation drives distinct sedimentary and microbial patterns, highlighting the ecological complexity of intertidal ecosystems.