Influence of the Kuroshio Current on the benthic communities in the southern seas of Korea

• Seasonal variability in temperature, salinity, dissolved oxygen, grain size, and organic carbon strongly influenced benthic habitats from 2015 to 2024. • Polychaetes were the dominant macrobenthic group, with several species acting as reliable seasonal indicators of environmental change. • Bottom water temperature showed significant positive associations with species richness, density, and diversity across seasons. • Benthic community structure reflected both Kuroshio-driven hydrographic variability and local sedimentary characteristics. The Kuroshio Current, a major western boundary current in the North Pacific, intrudes into the southern seas of Korea through the Tsushima Warm Current (TWC) and exerts strong influence on benthic ecosystems. From 2015 to 2024, we assessed seasonal variability in hydrography, sediments, and benthic macrofauna. Summer conditions featured warmer surface waters (27.8 °C), lower dissolved oxygen, and more organic-rich, coarse sediments. Benthic communities showed clear seasonality, with all community metrics highest in spring, lowest in winter, and intermediate in summer and autumn. Sediments were mainly sandy silt and silty sand, dominated by polychaetes, with higher species density and biomass observed in summer and autumn. Bottom temperature was modestly related to richness and density, while biomass declined with surface warming. These patterns closely resemble observations from other Kuroshio-affected regions, including seasonal oxygen depletion and organic enrichment on the East China Sea shelf, enhanced nutrient flux and benthic shifts off Taiwan, and polychaete-dominated assemblages in southern Japan. The convergence of these features across Kuroshio-influenced margins provides evidence that the benthic ecosystems of Korea are directly shaped by the hydrographic and biogeochemical forcing of the Kuroshio system.