Saving the Last Unicorns: The Genetic Rescue of Florida’s Pillar Corals

Abstract

As stony coral tissue loss disease (SCTLD) swept through the Florida Reef Tract, one of the most severely impacted species was the iconic pillar coral, Dendrogyra cylindrus. As the species’ population experienced a precipitous decline, a collaborative rescue project collected colony fragments for safekeeping at onshore and offshore nursery facilities. Between 2015 and 2019, a total of 574 fragments representing 128 genotypes were collected. These are currently dispersed among five facilities where they continue to provide opportunities to (1) refine best husbandry practices for D. cylindrus, (2) develop treatment options for SCTLD that have been adapted for use on other species, (3) maximize growth and fragmentation to provide the live tissue needed for eventual restoration, and (4) provide a source of parent colonies for assisted sexual reproduction and new genetic diversity. With the wild pillar coral population in Florida at the end of 2020 at less than 6% of its known 2014 population and continuing to decline, the rescued ex situ colonies represent the entirety of the restoration potential for this species in Florida.

Stony coral tissue loss disease: a review of emergence, impacts, etiology, diagnostics, and intervention

“…Cryopreserved and thawed sperm of the highly susceptible species, Diploria labyrinthiformis, was successful at fertilizing newly collected eggs (Grosso-Becerra et al, 2021) and could be used as a method to increase the species' genetic diversity on SCTLD impacted reefs. In response to SCTLD outbreaks, efforts have included collection and cryopreservation of coral gametes as well as collection and maintenance of susceptible coral fragments that are gene-banked and potentially spawned ex situ (Hagedorn et al, 2012;Novak et al, 2020;Grosso-Becerra et al, 2021;Neely et al, 2021b;O'Neil et al, 2021). The D. cylindrus coral population in Florida was driven to functional extinction by SCTLD outbreaks (Neely et al, 2021a).…”

“…As a result, maintaining genetic diversity of the few remaining D. cylindrus was prioritized. From 2015-2019, 574 fragments representing 128 genotypes were collected from D. cylindrus colonies and then held in in situ or ex situ nurseries across five facilities in Florida and South Carolina (Neely et al, 2021b). Other rescue efforts were also prioritized in order to maximize tissue area and retain a diverse parental source for future use in sexual reproduction and restoration (Neely et al, 2021b).…”

Differences in the progression rate of SCTLD in Pseudodiploria strigosa are related to colony size and morphology

“…SCTLD lesions spread rapidly across an infected individual and can kill large colonies within weeks. In heavily affected reef areas, highly susceptible species can be virtually extirpated (Estrada-Saldıvar et al, 2021;Neely et al, 2021).…”