By Thomás Banha
Reef-building corals in the South Atlantic have long been considered resilient to bleaching, a phenomenon in which corals turn stark white in response to a stressor and are at risk of dying. However, their limits were tested in 2024 as ocean temperatures reached record temperatures. The unprecedented outcome raised pressing questions: Can even these resistant species withstand the challenges posed by global warming?
In 2020, I published my first article for Reefbites (you can read it here), where I discussed research highlighting the South Atlantic as a potential refuge for reef-building corals to global warming. Over the following years, new studies both supported and challenged this notion. In subtropical Brazil, researchers found evidence that corals were thriving in the years following a massive heatwave in 2019. Yet, in Abrolhos – the main reef system in Brazil – the picture was far more troubling.
Figure 1: Bleached colonies of the Brazilian-endemic brain coral Mussismilia hispida at the Alcatrazes Archipelago, São Paulo, subtropical Brazil. This bleaching event resulted from the extreme heatwave in the region in 2019 (see Banha et al. 2020, for further details). Photo credit: Marcelo Kitahara.
Another study reported high mortality in key reef-building species, including the Brazilian-endemic, critically endangered brain coral Mussismilia braziliensis. Nearby Abrolhos, corals are also struggling with recurrent thermal stress events, reaching the point where no recovery can be seen even after three years of a major 2019 bleaching event. This context increased concern and raised questions if the corals here may have reached a tipping point.
Last year broke the record as the warmest year ever recorded since the Industrial Revolution, culminating in the Fourth Global Coral Bleaching Event. This event spread to many parts of the ocean, affecting more than 50 countries, and eventually reached the South Atlantic, posing a challenge to reef-builders.
Brazil experienced mass coral bleaching and mortality on an unprecedented scale, devastating shallow reef communities and even impacting the deeper mesophotic reefs in the northeast of the country. This marked the worst bleaching event ever recorded in the region’s history.
But amidst the devastation, there were glimmers of hope. In some parts of Brazil, including the coast of São Paulo, corals remained largely unaffected by bleaching. 2024 was the hottest year ever recorded, and some affirmed that it would be the coldest of the rest of our lives. The good news is that the average daily sea surface temperature in 2025 is currently lower than those from 2024. The bad news is that it remains higher than any other year pre-2024.
Figure 2: Daily sea surface temperature estimates between 1981 and 2025.
We must continue to monitor these ecosystems, advocate for reductions in greenhouse gas emissions, and fight for more funding to conserve reef ecosystems. Ultimately, if corals find themselves on the ropes once more, let us hope they have the resilience to rise again – and keep fighting.
REFERENCES
Abdala V (2024) Coral bleaching spreading in Northeast Brazil. Available at: agenciabrasil.ebc.com.br/en/geral/noticia/2024-03/coral-bleaching-spreading-northeast-brazil
Banha T (2020) South Atlantic corals are tough. Available at: reefbites.com/2020/07/13/south-atlantic-corals-are-tough/
Banha TNS et al. (2020) Low coral mortality during the most intense bleaching event ever recorded in subtropical Southwestern Atlantic reefs. Coral Reefs 39:515–521.
Cardoso FC et al. (2024). Nowhere to hide: massive corals’ mortality after cumulative heat stress in a putative climate change refugium. Coral Reefs.
Copernicus (2024) The 2024 Annual Climate Summary. Global Climate Highlights 2024. Available at: climate.copernicus.eu/global-climate-highlights-2024
Corazza BM et al. (2024) No coral recovery three years after a major bleaching event in reefs in the Southwestern Atlantic refugium. Mar Biol 171:114
Mies M et al. (2020) South Atlantic coral reefs are major global warming refugia and less susceptible to bleaching. Front Mar Sci 7:514.
Reimer JD et al. (2024) The Fourth Global Coral Bleaching Event: Where do we go from here? Coral Reefs 43:1121–1125.
Roos NC et al. (2024) Scleractinian Corals at Their Subtropical Southwestern Atlantic Limit: Post‐2019 Mass Bleaching Event Analysis. Aquat Conserv: Mar Freshw Ecosyst 34(12): e70031.
Spring J, Benassatto L (2024) Brazil braces for worst coral bleaching ever. Available at: reuters.com/business/environment/brazil-braces-worst-coral-bleaching-ever-2024-04-17/
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