A baseline for the genetic conservation of tropical seagrasses in the western North Pacific under the influence of the Kuroshio Current: the case of Syringodium isoetifolium

Recently, seagrasses have been declining along coastlines worldwide. We genetically analyzed 1058 ramets of Syringodium isoetifolium collected from 21 populations in the Philippines and 9 in the Ryukyu Islands using nine microsatellite markers, to provide a baseline of genetic information on seagrasses in the western North Pacific region under the influence of the Kuroshio Current, and aid in their genetic conservation. We detected 421 genotypes and the average clonal richness (R) was relatively low (R = 0.38), suggesting that S. isoetifolium populations were formed mainly through asexual reproduction. The index of genetic differentiation among populations for S. isoetifolium was high (\(D_{ST}^{\prime }\) = 0.238 and \(G_{ST}^{\prime }\) = 0.337), and most pairwise F ST values were significantly greater than zero, suggesting that gene flow among populations is rare. Clear genetic structure in S. isoetifolium populations were detected, indicating four genetically-similar bioregions, that is, the Ryukyu, northwest Philippines, northeast Philippines, and central Philippines populations. This genetic structure indicated that the Kuroshio strongly affects the formation of S. isoetifolium populations and should be factored into conservation efforts for S. isoetifolium.