Population genetic structure of the deep-sea precious red coral Hemicorallium laauense along the Hawaiian Ridge

The deep-sea precious red coral Hemicorallium laauense has long been overharvested in the North Pacific for the jewelry and curio trades. An understanding of the population structure and connectivity of these octocorals has been limited due to the difficulty of sampling and taxonomic challenges within the Family Coralliidae. We report on population genetics of 270 H. laauense individuals from 16 populations throughout the Main Hawaiian Islands (MHI) and the Northwestern Hawaiian Islands (NWHI) using nine microsatellite loci. Observed heterozygosity (0.69-0.85) was generally lower than expected heterozygosity (0.71-0.85) except for the population at Twin Banks. Moderate F-IS values (0.01-0.20) were present in nearly half of the populations. Global G'(ST) (0.166) and pairwise values were moderate to high ( - 0.003 to 0.489). G'(ST) values also show moderate genetic structuring among populations within seamounts (0.12-0.22) for populations separated by as little as 3 km. DAPC indicated separation of the MHI from the NWHI, but two NWHI sites fall into the MHI clusters and samples from Ka'ena Point (an MHI site) appear to form their own cluster. Membership assignments showed moderate admixture between some locations, while three locations showed almost no admixture. Within-seamount admixture was surprisingly limited for populations on the same seamount. A pattern of isolation by distance, with exchange primarily among adjacent seamounts, was supported by MIGRATE results but not by Mantel tests. These results suggest a mixed pattern of connectivity, with some distant locations well connected and others more isolated. The inconsistent connectivity of these corals is likely amplified by their patchy distributions.