Genetic diversity of farmed and wild populations of the reef-building coral, Acropora tenuis

Transplantation of nursery-farmed corals is a primary management tool for restoration of degraded coral reefs. However, there have been concerns about the potential loss of genetic diversity in nurseries due to asexual propagation methods used to prepare transplants. Two coral nurseries at Maeganeku and Onna, Okinawa Island, Japan, furnish source material for regional restoration activities. Using 13 microsatellite markers, this study compared the genetic diversity of 132 Acropora tenuis colonies from these nurseries with that of 298 wild colonies from 15 sites across the Nansei Islands. Even though no clonal colonies were detected at wild sites, we estimated clonal richness of farmed corals to be 0.523 (Maeganeku) and 0.579 (Onna). Genotypic diversity is high in the nursery populations, 0.894 (Maeganeku) and 0.937 (Onna), but lower than in the natural populations (1.000). However, expected heterozygosity did not differ significantly between locations, including the coral nurseries (one-way analysis of variance, p > 0.05). Inbreeding coefficients of nursery populations (Onna, -0.019 to Maeganeku, 0.097) fell within the range of estimates from wild populations (Sesoko, -0.058 to Maeda, 0.278). Furthermore, based on Structure analysis, farmed A. tenuis comprises the same genetic population that occupies the surrounding natural area. Thus, given no additional statistically significant increase of clonal colonies within nurseries, using farmed coral assemblages for reef restoration may be preferable to transplanting and damaging wild assemblages. Coral gametes of farmed colonies may also be used to produce coral larvae for transplantation of sexually propagated corals.