High genetic differentiation and moderate genetic diversity of the degenerative branching coral Pocillopora verrucosa in the tropical South China Sea.

Global warming is causing rapid degradation of coral reefs, among which branching corals are degrading the fastest. An assessment of coral genetic diversity and adaptive potential provides a basis for coral reef protection. In this study, we selected the branching coral Pocillopora verrucosa, a widely distributed species in the tropical South China Sea (SCS), to carry out population genetic studies. To analyze the genetic diversity and structure of 319 P. verrucosa samples from 10 populations in 4 SCS regions, twelve pairs of microsatellite primers and two nuclear markers, ITS and β-tub, were selected. Microsatellite marker results showed moderate genetic diversity for P. verrucosa in the SCS, but relatively low diversity in Dazhou Island and Yongxing Island. The haplotype network showed that P. verrucosa in the SCS was derived from two ancestors, which may be linked to geographical isolation in the Pleistocene glacial period. AMOVA (ΦST = 0.3375) and FST pairwise analysis results based on β-tub showed that the populations were highly differentiated, with most FST values (21/45) > 0.25. Yongxing and Qilianyu Islands populations were significantly different from those in the Xisha area. Mantel test results showed that genetic differentiation among P. verrucosa populations was significantly and positively correlated with both mean sea surface temperature (SST) and SST variance, and was not correlated with distance, chlorophyll-a, or turbidity. The reproductive mode of brooding planulae was an important factor contributing to high genetic differentiation among populations. The moderate genetic diversity of SCS P. verrucosa indicates that this population has a certain genetic potential in the context of global changes, but the high genetic differentiation between populations increases the risk of local degradation or extinction. This study provides a theoretical basis for the protection and restoration of SCS coral reefs.