RESUMO
We examined the genotypic diversity of the large population of Heliopora coerulea, discovered recently in Ooura Bay, northern Okinawa Main Island Japan, together with another large population in Shiraho Reef, also in southwest Japan, using 9 polymorphic microsatellite markers. From each population, 40 samples were systematically collected along 2 transect lines with 4-m intervals. Surprisingly, all 40 samples from Ooura Bay were mono-genotypic, implying that the huge coral structure (30 m×80 m) originated from a single larva. Conversely, the 40 samples collected from the Shiraho Reef site all had different genotypes; measurements of genetic diversity, H(E) and H(O), were 0.075-0.975 and 0.064-0.655, respectively. At least four factors are considered to make such a huge H. coerulea population with a single genotype in Ooura Bay, (1) origin of single larva or fragment (2) a genetic bottleneck, (3) post settlement selection, and (4) frequent asexual propagation.