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

Abstract

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.

Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower‐density coral skeletons

“…Dead coral fragments colonized by multi‐phyletic assemblages were collected by SCUBA at two sites in the Upper Florida Keys: Cheeca Rocks and Little Conch (depth: 3–5 m) on October 27, 2022. Cheeca Rocks (24.8966 N, 80.6169 W) is a patch reef off Islamorada characterized by regionally high coral cover (~25%) (Webb et al., 2023). The rubble samples were collected from dense rubble beds composed of branching Porites spp.…”

“…However, intensifying degradation and loss of habitat due to combined anthropogenic stressors have exacerbated erosion, threatening the delicate balance between constructive and erosional forces on contemporary reefs (Molina‐Hernández et al., 2020; Perry et al., 2013). Today, many reefs exhibit diminished growth potential following transitions in community compositions and, going forward, may not be able to keep pace with rising sea levels (Kuffner et al., 2019; Perry et al., 2018; Webb et al., 2023; Yates et al., 2017). Numerous factors contribute to this precarious situation, and they range in scale from acute local or regional stressors to chronic global issues (Wolff et al., 2018).…”

Sequential Treatment Application Robot (STAR) for high-replication marine experimentation

“…The STAR system is also relevant to ocean acidification research, where sensitivity analysis is particularly important for predicting ecosystem persistence [14] and nonlinear responses are not uncommon [15] . Rather than exposing 48 organisms to high and low-CO 2 treatments, the same number of organisms could be subjected to 48 different CO 2 conditions, just by applying different ratios of high and low-CO 2 water to each beaker with the peristaltic pumps.…”

Coral restoration for coastal resilience: Integrating ecology, hydrodynamics, and engineering at multiple scales

“…Severe loss of coral cover has already compromised the carbonate budgets of coral reefs, and many reefs are bioeroding rather than accreting (Morris et al, 2022; Perry et al, 2013). Future ocean acidification and reduced aragonite saturation state conditions may compromise the calcification of living coral (Pandolfi et al, 2011), and the expectation of reef accretion through restoration may not be realistic everywhere (Toth et al, 2022; Webb et al, 2023). Restorations may therefore require gray or hybrid elements to provide wave attenuation (e.g., engineered structures) to meet restoration goals in the timeframe needed (Figure 2).…”