Rapid coral mortality and tissue disintegration in heat-stressed corals attracted wider attention following observations on Australia’s Great Barrier Reef during the 2014–2017 global bleaching event and during the 2023 heatwaves in the Caribbean and eastern tropical Pacific. But what was happening inside the corals remained unclear.

To understand how and why corals may die before bleaching, a KAUST-led team examined whether extreme heat could leave them short of oxygen.

In laboratory experiments, the researchers used microsensors to measure oxygen in the thin layer of water directly next to the tissues of corals exposed to acute heat stress. Oxygen levels fell rapidly immediately before the tissue began to disintegrate. Experiments involving corals from the Red Sea and Australia showed that rapid mortality and tissue disintegration were not limited to one species or region.

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