Abstract
Global climate change is a major threat to reefs by increasing the frequency and severity of coral bleaching events over time, reducing coral cover and diversity. Ocean warming may cause shifts in coral communities by increasing temperatures above coral’s upper thermal limits in tropical regions, and by making extratropical regions (marginal reefs) more suitable and potential refugia. We used Bayesian models to project coral occurrence, cover and bleaching probabilities in Southwestern Atlantic and predicted how these probabilities will change under a high-emission scenario (RCP8.5). By overlapping these projections, we categorized areas that combine high probabilities of coral occurrence, cover and bleaching as vulnerability-hotspots. Current coral occurrence and cover probabilities were higher in the tropics (1°S–20°S) but both will decrease and shift to new suitable extratropical reefs (20°S–27°S; tropicalization) with ocean warming. Over 90% of the area present low and mild vulnerability, while the vulnerability-hotspots represent ~ 3% under current and future scenarios, but include the most biodiverse reef complex in South Atlantic (13°S–18°S; Abrolhos Bank). As bleaching probabilities increase with warming, the least vulnerable areas that could act as potential refugia are predicted to reduce by 50%. Predicting potential refugia and highly vulnerable areas can inform conservation actions to face climate change.
Highlights
Coral reefs are threatened by increasing ocean temperatures and extreme heating events related to humaninduced global climate c hange[1,2,3]
Coral occurrence showed the greatest changes of probability from current to future scenarios in comparison to coral cover and bleaching probabilities (Fig. 1b,c; Table S1)
Coral occurrence and mean coral cover probabilities increased poleward with warming, only coral occurrence decreased between 1°S and 20°S of latitude, while there was almost no change for coral cover (Fig. 1)
Summary
Coral reefs are threatened by increasing ocean temperatures and extreme heating events related to humaninduced global climate c hange[1,2,3]. The survival of coral species in a warmer future will likely depend on their ability to disperse to thermal refuges, where temperatures remain tolerable or become more suitable (e.g. extratropical, deeper reefs, marginal r eefs[20]). Extratropical reefs can be considered marginal and potentially act as refugia since it experiences less intense thermal stress events[23] and annual severe coral bleaching events are expected to start years later in comparison to tropical reefs[7]. Corals in mesophotic reefs can experience less bleaching due to lower light availability and milder temperatures[24, 25] Identifying potential refugia, such as marginal and mesophotic reefs, is critical to understand coral resilience under future scenarios. Identifying the most vulnerable areas to coral bleaching could inform actions to minimize local impacts and reduce threats from global s tressors[35, 36]
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