Population Genetic Structure, Abundance, and Health Status of Two Dominant BenthicSpecies in the Saba Bank National Park, Caribbean Netherlands: <i>Montastraea cavernosa</i> and <i>Xestospongia muta</i>

Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attainedinternational conservation status due to the rich diversity of species that reside on the bank.In order to assess the role of Saba Bank as a potential reservoir of diversity for the surroundingreefs, we examined the population genetic structure, abundance and health status oftwo prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongiamuta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) onSaba Bank and around Saba Island, and compared with published data across the widerCaribbean. Our data indicate that there is genetic connectivity between populations onSaba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean,ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populationsof M. cavernosa (p = 0.055) and X. muta (p = 0.0010) was comparable to those in otherregions in the western Atlantic. Densities and health status were determined along 11 transectsof 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa(0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind.m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations.No disease or bleaching was present in any of the specimens of the coral M. cavernosa,however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth(48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta(83.5%) showed signs of presumed bleaching. The combined results of apparent gene flowamong populations on Saba Bank and surrounding reefs, the high abundance and uniquegenetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish genetic diversity or as a storehouseof diversity that can be utilized if needed for restoration practices