Coral comes back from the dead after climate warming

Coral reef
iStock/ultramarinfoto

Researchers, from the University of Barcelona, have discovered that some types of coral can regenerate and even ‘come back from the dead’ after climate warming events.

Scientists have discovered strategy, researchers report for the first time. Coral polyps shrink inward, partially abandoning their skeleton during periods of warming-induced stress, only to revitalise their dead colonies years later.

‘Rejuvenescence’ and similar strategies may provide a narrow window of opportunity for corals to cope with warming caused by climate change. Previous studies have documented this phenomenon in fossil corals, but scientists had never observed it in living ones. Diego Kersting et al. monitored 243 Mediterranean scleractinian (Cladocora caespitosa) coral colonies for 16 years, examining them after the summer months, when deadly warming events occur, and recording the damage with photographs and sketches.

Researchers, from the University of Barcelona, Spain, identified surviving polyps by closely inspecting dead colony areas and inspecting extreme close-up photographs. As described in fossil corals, the researchers report that each polyp’s metabolic activity would have reduced during periods of warming-induced stress, causing it to shrink drastically, partially retreating from inner skeletal structures and forming a new calyx (protective cup within which the polyp sits).

It does this while staying connected to some of the old skeletal structures, fossil data have shown. In this new study, the researchers found up to three new calices inside the original, shedding light on the origin and causes of similar skeletal structures described in fossil corals. No signs of life were detected in the first years after mortality events, but Kersting and colleagues eventually observed recoveries in 38% of the warming-impacted colonies, with polyps growing to their original size and budding over dead neighbours. After a decade, near-full recoveries were observed in 13% of colonies, perhaps explaining why the process remained undiscovered for a long period of time.

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