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Corals creating own sunscreen for protection against rising sea temperatures, scientists say | UK News

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Some corals are creating a ‘sunscreen’ to protect their skeletons from rising sea temperatures, according to a new study.

Many have algae embedded in their cells which helps both to thrive.

A rise of even 1C can cause problems for that balance, causing the algae to be lost.

Major bleaching has affected the coral reefs of the Society Islands in French Polynesia
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Bleaching has affected swathes of coral reefs

This leaves the coral’s limestone skeleton exposed to sunlight which often leads to the coral dying. This is called coral bleaching.

Coral bleaches when water temperatures reach 30-31C (86-87.8F). It ejects the symbiotic algae inside its tissues that provide it with much of its food.

If the warm water persists for more than a few weeks the coral dies.

Scientists from the University of Southampton’s coral reef laboratory have published a report in the journal, Current Biology, that states they observed some corals produce a ‘sunscreen’ in the form of a colourful display during mild or short warming incidents.

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The team believe the bright neon colours that are emitted encourage the algae to return in what they call an “optical feedback loop”.



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Professor Jorg Wiedenmann explained: “Our research shows colourful bleaching involves a self-regulating mechanism, a so-called optical feedback loop, which involves both partners of the symbiosis [the coral and the algae].

“In healthy corals, much of the sunlight is taken up by the photosynthetic pigments of the algal symbionts.

“When corals lose their symbionts [the algae], the excess light travels back and forth inside the animal tissue, reflected by the white coral skeleton.

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“However, if the coral cells can still carry out at least some of their normal functions, despite the environmental stress that caused bleaching, the increased internal light levels will boost the production of colourful, photoprotective pigments.

“The resulting sunscreen layer will subsequently promote the return of the symbionts.”

Dr Cecilia D’Angelo, lecturer of molecular coral biology at the university, added: “Unfortunately, recent episodes of global bleaching caused by unusually warm water have resulted in high coral mortality, leaving the world’s coral reefs struggling for survival.”

Earlier this month, scientists announced they had found a way to make coral resistant to the impact of increasingly warm waters by growing new strains of microalgae and exposed them to warmer temperatures for four years.

The scientists then injected coral larvae with one strain each and exposed them to 31C (88F) heat for a week and found three of the 10 strains protected the coral from bleaching.

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