Safeguarding Florida's Coral Reefs: The Urgency of Assisted Gene Flow for Elkhorn Coral Conservation
The devastating 2023 heatwave is the latest in a series of disasters that has decimated the Florida population of elkhorn coral (Acropora palmata) to a critically low level, pushing this species to a precarious tipping point. Precautionary management currently forbids outplanting of corals from outside Florida. This precaution is intended to prevent the introduction of novel genes that could cause outbreeding depression and to preserve local adaptive variation in the Florida population. However, the multi-decadal decline of Florida’s elkhorn corals indicates a lack of adaptation to the shifting environmental conditions on Florida reefs. The potential risks of outbreeding depression associated with introducing new genetic variants from outside sources pale in comparison to the continuous demographic decline through successive heat waves, and the threat of inbreeding depression. Operational risks of Assisted Gene Flow (AGF) can be managed by introducing non-Florida alleles via outplanting of the existing lab-based juveniles rather than adults sourced from the wild. Further, the extent to which new genetic material is introduced should be proportional to Florida’s founder population. NOAA’s Florida Genetic Management Plan (F3P) can guide the introduction of non-Florida alleles versus the introduction of sexually produced offspring from the limited floridian parental stock. We conclude that assisted gene flow via lab-based crossing of Florida’s elkhorn with elkhorn from elsewhere in the Caribbean is a strategy with manageable risks and mission-critical benefits. AGF should be implemented urgently to introduce new genetic variants, thereby increasing the elkhorn coral’s genetic diversity, and enhancing the resilience of these populations to future stress. Without such intervention, coupled with the high probability of additional 2023-scale heatwaves, the grim prospect of completely losing all elkhorn corals from Florida’s reefs within this decade becomes increasingly probable.
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