2026 Volume 73 Issue 1 Pages 1-13
Growing evidence highlights the diverse biogeochemical processes that stimulate biological productivity in the oligotrophic Kuroshio. Although biological productivity stimulated by upwelling nutrients has been proposed by experimental approaches and intensive oceanographic observations, subsequent increases in zooplankton standing stocks and productivity have not been observed in the downstream Kuroshio. Here, we report geographical variations in standing stocks, productivity, and taxonomic composition of zooplankton communities in the Kuroshio based on oceanographic observations. Less saline water in the surface layers extended toward the Kuroshio Current, corresponding to high nutrient and chlorophyll a concentrations. Zooplankton standing stocks and taxonomic compositions exhibited significant differences between the coastal and Kuroshio waters, but no clear pattern was observed from the upstream to the downstream Kuroshio. Based on multivariate analysis, copepod species compositions were segregated between the coastal and Kuroshio waters, but some coastal species appeared abundantly in the Kuroshio waters. Significant positive correlations were found between nutrients, chlorophyll a concentrations, and zooplankton standing stocks, and the mixed ratio of less saline waters. We suggest that the geographical distribution patterns of zooplankton standing stocks and community structure along the Kuroshio current are affected by the advection of coastal communities in less saline waters than by locally stimulated biological productivity.
