Simulated connectivity of crown-of-thorns starfish around Ashizuri-Uwakai National Park (western Japan) based on a high-resolution hydrodynamic modeling

Outbreaks of crown-of-thorns starfish (COTS) pose a major threat to coral reefs in the Ashizuri-Uwakai National Park, Japan, which is partially affected by the Kuroshio Current. The purpose of this study was to identify the upstream areas of the Kuroshio significantly contributing to the supply of larvae to this area, where the larvae are most likely to reach within the Ashizuri-Uwakai area (inter-connectivity), and to clarify the connectivity within the park (intra-connectivity). Using a hydrodynamic model based on a 12-year dataset with a high spatial resolution (ca. 2 km), this study evaluated the transport and dispersion processes into and within the region, although the proportion of particles reaching the Ashizuri-Uwakai area the major sources were Tanegashima and Yakushima islands and the east coast of Kyushu. Grid cells with a high supply from these source areas were identified within Ashizuri-Uwakai and quantitatively shown to have high sink strength in the southwestern and cape areas. We were also able to show where particles released within Ashizuri-Uwakai tend to accumulate. Since locations with high sink strength generally coincided with diving sites and areas where conservation activities have been conducted, strengthening conservation activities in these locations can be considered to be effective in controlling outbreaks of COTS.