Repeated ex situ Spawning in Two Highly Disease Susceptible Corals in the Family Meandrinidae

Abstract

Members of the family Meandrinidae are highly susceptible to stony coral tissue loss disease, resulting in population reductions up to 88% in both Dendrogyra cylindrus and Meandrina meandrites along the Florida Reef Tract. Reductions in abundance on this scale leave these species susceptible to limitations in sexual reproduction and natural recovery without intervention. In response to the ongoing outbreak of the disease across the Caribbean, a variety of genetic rescue projects have been implemented to bring disease susceptible species into ex situ culture and preserve living genetic diversity. In this study, corals being held in a long-term ex situ genetic bank were maintained using artificial lighting and temperature cues programmed to mimic natural cycles in Key Largo, FL, United States. Synchronized broadcast spawning events in both species were documented in aquaria over two annual spawning cycles in 2019 and 2020. Timing of gamete release relative to the perceived date and sunset was highly synchronized with wild observations. Up to 21 unique D. cylindrus genotypes collected from reef locations spanning over 230 km contributed gametes to the larval pool. The majority of these parental colonies are no longer alive in the wild. Repeatable and predictable ex situ spawning events such as these will become an essential tool for managed breeding and assisted fertilization in species suffering from severe population declines. These annual events have the potential to produce thousands of genetically diverse offspring for restoration efforts and offer future hope for the long-term survival of these threatened species.

Kinship and genetic variation in aquarium-spawnedAcropora hyacinthuscorals

“…The development of standard husbandry protocols for grow-out may also help optimize genetic diversity of broodstock by maximizing survivorship, and therefore minimizing bottlenecks, at each life stage. This may include species-specific protocols for settlement, symbiont inoculations, feeding regimes, and cleaning/grazing regimens (Levenstein et al, 2021; O’Neil et al, 2021; Rahnke et al, 2022).…”

“…Recent advances in long-distance transport of corals, as well as improvements in system design to mimic seasonal water temperature fluctuations, solar irradiance, lunar cycles, and diel cycles ex situ, have allowed predictable coral spawning ex situ to become possible (Craggs et al, 2017(Craggs et al, , 2018O'Neil et al, 2021). Public aquariums are an ideal setting for coral spawning and breeding pilot programs, as they have the infrastructure, resources, and technical expertise in the form of personnel who know how to keep corals alive and healthy.…”

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

“…Juveniles from those efforts are alive and growing today. Subsequently, rescued D. cylindrus colonies held at the Florida Aquarium's Center for Conservation were the first Caribbean corals to be acclimated to artificially mimicked abiotic cues in order to control coordinated and synchronous spawning (O'Neil et al, 2021). Ex situ reproduction events also provide opportunities to refine cryopreservation techniques, promoting long-term genetic banking and future assisted reproduction of the species.…”

Horizon scan of rapidly advancing coral restoration approaches for 21st century reef management

“…Many challenges still remain to rear offspring from brooders [ 89 , 90 ]. Growing records of coral reproduction timing in nature [ 91 ] now enable practitioners to better target spawning events, whilst improved knowledge of reproduction cues has led to innovative land-based systems to induce multiple spawning events ex situ [ 92 ], allowing limitations of natural timings to be overcome. A critical focus of larval-based methods is to maximise larval production, survival and resilience.…”