The past, present, and future of coral reef growth in the Florida Keys

The potential for coral reef restoration to mitigate coastal flooding as sea levels rise

The ability of reefs to protect coastlines from storm-driven flooding hinges on their capacity to keep pace with sea-level rise. Here, we show how and whether coral restoration could achieve the often-cited goal of reversing the impacts of coral-reef degradation to preserve this essential function. We combined coral-growth measurements and carbonate-budget assessments of reef-accretion potential at Buck Island Reef, U.S. Virgin Islands, with hydrodynamic modeling to quantify future coastal flooding under various coral-restoration, sea-level rise, and storm scenarios. Our results provide guidance on how restoration of Acropora palmata, if successful, could mitigate the most extreme impacts of coastal flooding by reversing projected trajectories of reef erosion and allowing reefs to keep pace with the ~0.5 m of sea-level rise expected by 2100 with moderate carbon-emissions reductions. This highlights the potential long-term benefits of pursuing coral-reef restoration alongside climate-change mitigation to support the persistence of essential coral-reef ecosystem services.

Restoration and coral adaptation delay, but do not prevent, climate-driven reef framework erosion of an inshore site in the Florida Keys

For reef framework to persist, calcium carbonate production by corals and other calcifiers needs to outpace loss due to physical, chemical, and biological erosion. This balance is both delicate and dynamic and is currently threatened by the effects of ocean warming and acidification. Although the protection and recovery of ecosystem functions are at the center of most restoration and conservation programs, decision makers are limited by the lack of predictive tools to forecast habitat persistence under different emission scenarios. To address this, we developed a modelling approach, based on carbonate budgets, that ties species-specific responses to site-specific global change using the latest generation of climate models projections (CMIP6). We applied this model to Cheeca Rocks, an outlier in the Florida Keys in terms of high coral cover, and explored the outcomes of restoration targets scheduled in the coming 20 years at this site by the Mission: Iconic Reefs restoration initiative. Additionally, we examined the potential effects of coral thermal adaptation by increasing the bleaching threshold by 0.25, 0.5, 1 and 2˚C. Regardless of coral adaptative capacity or restoration, net carbonate production at Cheeca Rocks declines heavily once the threshold for the onset of annual severe bleaching is reached. The switch from net accretion to net erosion, however, is significantly delayed by mitigation and adaptation. The maintenance of framework accretion until 2100 and beyond is possible under a decreased emission scenario coupled with thermal adaptation above 0.5˚C. Although restoration initiatives increase reef accretion estimates, Cheeca Rocks will only be able to keep pace with future sea-level rise in a world where anthropogenic CO₂ emissions are reduced. Present results, however, attest to the potential of restoration interventions combined with increases in coral thermal tolerance to delay the onset of mass bleaching mortalities, possibly in time for a low-carbon economy to be implemented and complementary mitigation measures to become effective.