Population genetic structures of newly recruited and adult populations of pocilloporid corals in southwestern Shikoku, Japan

In this era of global warming, southwestern Shikoku is a strong candidate as a refugium for tropical reef corals in the Pacific. In this study, we documented patterns of species composition among pocilloporid recruits, the dominant coral family being recruited to southern Shikoku, and we evaluated genetic population relationships between recruits and adults at four sites, using seven nuclear microsatellite markers. Pocilloporid recruits in the area comprised two genera and three species, including the most heavily recruited species, Pocillopora damicornis, and the minor P. acuta. This is the first observation of the latter species in this area. In P. damicornis, clonality differed among the four sites and clonal recruits were observed at two sites. However, proportions of clones were relatively low. Strong genetic differentiation among the four sites was observed in populations of P. damicornis, although three genetic clusters were shared among these sites. In addition, compositions of these three clusters were similar between recruits and adults at each site. This indicates that populations of P. damicornis in southwestern Shikoku are maintained primarily by sexual reproduction and that larvae derived from sexual reproduction are supplied mainly from their natal habitats at all sites. As local population persistence and self-recruitment are important to maintain populations of this species in southwestern Shikoku, conservation efforts should be directed at protecting extant local populations.