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Fascinating and fragile corals



Last spring, corals around the world were experiencing a massive bleaching event, the fourth since 1985, with previous events dating back to 1998, 2010 and 2016. Bleaching is a sign that the coral has expelled the microalgae it usually hosts in response to thermal stress. Without microalgae, corals bleach and their nutrition is compromised. These episodes, due to the rise in seawater temperature, can therefore lead to the decline of these splendid marine animals.

The magazine Science Advances offers them its cover of the June 28 issue with a magnificent photo taken in Micronesia. Devoid of a title, this cover calls for wonder but also for awareness.Coral reefs feed more than a billion people”, recalls the specialist weekly. “But unprecedented heat waves are devastating for these crucial ecosystems.

In the current context of global warming, it is important to be able to identify the most exposed reefs and those that could better resist bleaching. This is what Camille Mellin, from the University of Adelaide, in Australia, and other researchers, signatories of a scientific article published inside the magazine.

They show that “by 2080 (there is expected to be) a shift in the onset of coral bleaching from late summer to spring in most coral reef regions“, they write. As a result, there will be a “overlap of coral bleaching with key stages of the coral life cycle, including spawning”, which could lead to irreversible damage to coral populations.

But researchers have also highlighted the existence of “potential climate refuges”, that is to say, areas where, thanks to sea currents in particular, the corals will be much less subject to thermal stress.

There remains one unknown, which could offer a less dire future for coral reefs: their ability to adapt to warm, even very hot, water.

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