Genetic variation and clonal structure in the scleractinian coral Pocillopora damicornis in the Ryukyu Archipelago, southern Japan

Samples of the scleractinian coral Pocillopora a damicornis were collected from six sites located around four islands in the Ryukyu Archipelago, south ern Japan, and subjected to allozyme electrophoresis. Seven polymorphic loc i were examined for their allelic patterns. The ratio of observed to expect ed genotypic diversity (0.30 < G(o):G(e) < 0.64), the ratio of the observed number of genotypes to the number of individuals (0.47 < N-g:N-i < 0.75), and deviations from Hardy-Weinberg equilibrium indicated that asexual repro duction plays a major role in the maintenance of established populations. H owever, populations were not completely dominated by a single or a few clon es, and most clones were represented by only a few individual samples. The high frequency of typhoons in the region suggests that, in P. damicornis, f ragmentation caused through occasional exposure to powerful waves is a majo r mode of asexual reproduction, but asexual production of planulae may also be contributing to the maintenance of populations. A significant genetic d ifferentiation (F-ST) was found between the six populations examined (0.027 < F-ST < 0.092, average F-ST = 0.056). The moderate gene flow is discussed according to characteristics of the larval stage of the species, and to ci rculation patterns in the region.