Abstract
Population outbreaks of the coral‐eating starfish, Acanthaster planci , are hypothesized to spread to many localities in the Indo‐Pacific Ocean through dispersal of planktonic larvae. To elucidate the gene flow of A. planci across the Indo‐Pacific in relation to ocean currents and to test the larval dispersal hypothesis, the genetic structure among 23 samples over the Indo‐Pacific was analysed using seven highly polymorphic microsatellite loci. The F ‐statistics and genetic admixture analysis detected genetically distinct groups in accordance with ocean current systems, that is, the Southeast African group (Kenya and Mayotte), the Northwestern Pacific group (the Philippines and Japan), Palau, the North Central Pacific group (Majuro and Pohnpei), the Great Barrier Reef, Fiji, and French Polynesia, with a large genetic break between the Indian and Pacific Oceans. A pattern of significant isolation by distance was observed among all samples ( P = 0.001, r = 0.88, n = 253, Mantel test), indicating restricted gene flow among the samples in accordance with geographical distances. The data also indicated strong gene flow within the Southeast African, Northwestern Pacific, and Great Barrier Reef groups. These results suggest that the western boundary currents have strong influence on gene flow of this species and may trigger secondary outbreaks.