Variation in Genotypic Diversity of the Threatened Pillar Coral, Dendrogyra cylindrus, and its Algal Symbiont in Florida, Curacao, and the US Virgin Islands

The threatened pillar coral, Dendrogyra cylindrus , is the only species in its genus, and thus its extinction would mean the extinction of a genus. Comprehensive surveys of Caribbean reefs over the past 30 years failed to find any pillar coral recruits, mobilizing efforts for active management of this unique species. Prior to nursery rearing and outplanting of fragments, the population genetics of the host and its specific symbiotic algal species ( Symbiodinium ‘dendrogyrum’ ) must be evaluated. Eleven microsatellite markers were developed de novo for D. cylindrus and nine existing microsatellites markers were applied to S. ‘dendrogyrum’ . Coral colonies from sites along the Florida Reef Tract, Curacao, and the US Virgin Islands were genotyped using these markers. Results indicate that D. cylindrus is highly clonal in Florida, with dense patches containing just one host genotype. Host populations in Curacao, however, appear to be more diverse and were highly differentiated from Florida populations. The genotypic diversity of S. ‘dendrogyrum’ is lower than its host, with identical clones often occupying multiple reefs. While D. cylindrus is known as a gonochoric broadcast spawner, observations revealed that pillars of identical genotype released gametes of the opposite sex, indicating that D. cylindrus might be a hermaphrodite capable of geitonogamy. The low genotypic diversity of host and symbiont and apparent strong host population differentiation in D. cylindrus make it imperative that diverse genotypes are incorporated into local restoration efforts throughout the Caribbean.