While it has been suggested that advections of coastal waters stimulate plankton standing stocks and productivity in the oligotrophic Kuroshio, there is still limited information. Here, we explore the source and process of coastal waters advected to the Kuroshio using particle-tracking experiments with a high-resolution coastal ocean model. Advections of coastal waters to the Kuroshio were stimulated by encountering frequent disturbances such as meandering and eddy near the Kuroshio front. The source of coastal waters advected to the Kuroshio were the largest from southern Kyushu throughout the year and from the East China Sea during winter to spring. Zooplankton biomass fluxes across the Kuroshio front were equivalent to 2 to 44% of those across the Kuroshio path. The estimated fluxes across the Kuroshio front were comparable to zooplankton biomass increase by their growth rates reported in the Kuroshio. These results suggest that the coastal zooplankton community advected to the Kuroshio supports food requirements for the fish community in the Kuroshio.

To examine the population dynamics, and particularly the reproductive ecology, of asari (Manila) clams in Sanbanze, Tokyo Bay, we monitored in detail the biweekly temporal variations in spatial density of clams through their growth stages from larva to spawner in 2001–2005, and the long-term bimonthly variation in overall density in the benthic clams in 1988–2014. In the four autumn cohorts in 2001–2004, there was a high density of the dominant cohort in 2002. The distribution in growth stages from larva to spawner indicated an abundance of spawner clams due to migrated larvae. Long-term variation of juvenile density in spring (June) did not correlate significantly with that of spawners in the previous autumn (October) (spawner–juvenile relation), although the density of spawners in autumn correlated with that of juveniles in the previous spring (juvenile–spawner relation). Particularly, the abundant 2002 autumn cohort, driven by a small spawner cohort in 2001, could generate extremely poor numbers in the 2003 cohort despite its high abundance. Non-significant correlations between the densities of spawner and offspring juvenile could be attributed to reported reproductive characteristics of the asari clam. Specifically, plasticity in gametogenesis, i.e., unsynchronized development of gametes within a gonad and among individuals along with frequent resorption of fully developed gametes, may play an important role in the fluctuation of the abundance of released eggs. Moreover, variability in the strength and frequency of key stimulants for clam spawning (temperature, physical disturbance, and other factors) could cause additional fluctuation. Successful spawning of the previous generation may be one of the determinant factors for the abundance of spawner stock in Sanbanze.