Coral under threat again. The world is currently experiencing, for the second time in ten years, a massive episode of coral bleaching due to record ocean temperatures, the American Oceanic and Atmospheric Observing Agency (NOAA) warned on Monday.
This decline threatens the survival of coral reefs around the world, including the Great Barrier Reef near Australia. “As the oceans continue to warm, coral bleaching is becoming more frequent and severe,” said Derek Manzello, coordinator of NOAA's Coral Reef Observatory.
“Clear proof of the harmful effects of climate change”
Linked to the increase in water temperature, this process which results in discoloration can lead to the death of these living organisms in the event of prolonged or severe exposure to thermal stress. But the phenomenon can be reversible: affected corals can survive if temperatures drop and other stress factors, such as overfishing or pollution, are reduced.
The current bleaching episode is the fourth recorded by NOAA since 1985. The previous ones were observed in 1998, 2010 and 2016. “The scale and severity of mass coral bleaching are clear evidence of the harmful effects of climate change at the moment,” said Pepe Clarke, of the environmental NGO WWF.
NOAA estimates that the planet has already lost 30 to 50% of its coral reefs and that these could, without major changes, completely disappear by the end of the century. The temperature of the oceans, which play a key role in regulating the global climate, reached a new absolute record in March, with an average of 21.07°C measured on the surface, excluding areas near the poles, according to the European Copernicus Observatory. .
Coral colonies are made up of tiny creatures called polyps, which secrete a limestone exoskeleton. Heat waves kill animals either simply by excess heat, or by ejecting from their bodies the algae that provide them with nutrients: this is coral bleaching. “From February 2023 to April 2024, significant coral bleaching was observed in the northern and southern hemispheres of each major ocean basin,” said Derek Manzello of NOAA.
Several regions of the world affected
Such phenomena have been observed since the beginning of 2023 in Florida (southern United States), in the Caribbean, in Brazil and even in the eastern tropical Pacific. The Red Sea and the South Pacific are also heavily affected, as is the Great Barrier Reef off the coast of Australia.
This coral reef, the largest in the world and the only one visible from space, is undergoing a process of “mass bleaching”, Australian authorities announced in early March. “We know that the greatest threat to the world's coral reefs is climate change. The Great Barrier Reef is no exception,” Australian Environment Minister Tanya Plibersek declared at the time.
The consequences of such phenomena are multiple: they affect ocean ecosystems, but also human populations, impacting their food security and local economies, particularly tourism. According to the WWF, around 850 million people around the world depend on coral reefs for their food, their jobs and even for the protection of coastlines. They also play an important role in marine ecosystems, with more than a quarter of marine species having taken up residence there.
Coral reefs thus constitute “a visual and contemporary example of what is at stake with each fraction of a degree of warming”, underlines Pepe Clarke of the WWF. NOAA, however, said it had made “significant advances” in developing techniques to combat coral bleaching. These include “moving coral nurseries to deeper, cooler waters” or installing shade to protect corals from the sun's rays in other areas.