Genetic connectivity of the scleractinian coral Goniastrea aspera around the Okinawa Islands

Genetic variation and gene flow in the scleractinian coral Goniastrea aspera (Verrill), found around the north–south Okinawa Islands, were studied using allozyme and starch gel electrophoresis. The relative contribution of sexual and asexual reproduction to recruitment was determined. Analysis of multilocus genotypes of samples, collected at least 3 m apart, identified a high number of unique genotypes (N_G) relative to the number of individuals sampled (N) (mean N_G: N=0.97±0.03 SD]), and also highly observed genotypic diversity (G_O) relative to expected genotypic diversity under Hardy–Weinberg equilibrium (G_E) (mean G_O: G_E=0.95±0.06 SD]). These results suggest that the collected G. aspera propagated predominantly by sexual reproduction in Okinawan populations. The UPGMA grouping of five populations in the Okinawa, based on Neis unbiased genetic distance, showed two clusters that were south and north Okinawa populations. AMOVA analyses that incorporated the data of populations from the Kerama and the Ishigaki Islands detected significant F_SC values among the populations within groups in analyses distinguishing north–south Okinawa, Okinawa–Kerama, and Okinawa–Kerama–Ishigaki. Significant F_CT values were neither detected between north–south Okinawa nor between the Okinawa–Kerama groups. The local-recruits hypothesis, which assumes that a substantial proportion of recruits is produced locally, appears to be applicable to coral populations in the Ryukyu Archipelago. On the other hand, detection of nonsignificant F_CT values indicated the presence of genetic connectivity between north–south Okinawa and Kerama–Okinawa groups.