Population differentiation across small distances in a coral reef-associated vermetid (Ceraesignum maximum) in Palau

Despite being one of the world’s leading countries in coral reef conservation and management, very little data exist for coral reef-associated species in the island nation of Palau, hampering managers’ ability to more effectively protect coral reef ecosystems.Here we examine populations of the vermetid Ceraesignum maximum, a common species on coral reefs, with short or absent pelagic larval stage, in order to elucidate patterns of gene flow within Palauan reefs. We collected specimens (n = 582) from 20 sites across Palau. Cytochrome oxidase subunit I analyses show private haplotypes at all sites examined, with a clear separation between outer and inner reef locations, and a unique population within isolated Nikko Bay. Oceanographic isolation between the waters of Nikko Bay, inner and outer reefs may contribute to our observed genetic differentiation. Our results indicate past demographic expansion of C. maximum across the region and also indicate that multiple sites of both inner and outer reef locations would need to be protected to conserve this species’ genetic diversity, including unique Nikko Bay. These results demonstrate the utility of C. maximum as a good species to investigate gene flow across small scales (< 10 km) as seen in Palau.