Connectivity of Coral Reefs Along the Kuroshio Current Calls for Transboundary Conservation Strategies.

Environmental conservation becomes more effective when ecological connectivity between patchy habitats is maintained. The coral reef ecosystems of the Yaeyama and Miyako Islands (YAE) in Japan are highly biodiverse and culturally significant but have deteriorated over recent decades. Although coral larvae are expected to be supplied to YAE via the Kuroshio Current from regions outside Japan, previous population genetic and biophysical studies have focused exclusively on connectivity among Japanese coral populations. In this study, we conducted biophysical modelling of 30 years of larval dispersal across the Northwest Pacific using Lagrangian particle tracking, aiming to identify major sources of coral larvae to YAE. The model showed that 86% of virtual larvae reaching YAE represented self-recruitment. Of the externally sourced virtual larvae, ~70% came from the Philippines, ~20% from Taiwan and only a few percent from Japan. The Kuroshio Current acted as a corridor facilitating dispersal from the northeast Philippines and eastern Taiwan, while simultaneously serving as a barrier to retrograde or transverse dispersal from northern Taiwan and Japan. These findings suggest that most externally supplied larvae to YAE originate from regions outside Japan, upstream of the Kuroshio Current. This study highlights that transboundary collaboration is crucial to understanding and maintaining connectivity between coral reef ecosystems along ocean currents.