Colorful coral reef found near the surface of the ocean is common, but to find it at greater depths is rare. Colorful coral reef found near the surface of the ocean is common, but to find it at greater depths is rare. Colorful coral reef found near the surface of the ocean is common, but to find it at greater depths is rare. (Photo: Volodymyr Goinyk/Shutterstock)

The surprising reason some corals glow in the dark

A new study sheds light on those beautiful fluorescent creatures way down in the depths of the ocean.

Deep in the ocean, corals are glowing in the dark. And scientists think they've just figured out why.

Researchers from the United Kingdom and Israel have been observing these stunning yet endangered organisms. They've previously discovered that corals – specifically the ones that dwell in shallow waters – use fluorescent proteins to catch harmful UV rays and give themselves a fighting chance against some pretty insurmountable odds. (Coral around the world are dying off in record numbers due to higher ocean temperatures.)

But why do deep water corals glow in the dark? They're not in danger of being sunburned like their shallow-water cousins. As it turns out, it is a survival mechanism – but for an entirely different reason. In deep water, corals light up not to deflect sunlight, but to absorb it – or what little of it there is.

To conduct their research, the scientists analyzed how well different colors spread through the corals' dense layers, called zooxanthellae. They found that corals survive in deep water by making a special type of fluorescent protein that captures blue light and re-emits it as orange-red light, which has the potential to penetrate deeper into the coral's tissue and promote photosynthesis.

TIME hotspotCoral reefs are some of the most beautiful natural occurrences in the world, but underneath all those colors lies some real danger. (Photo: This Is My Earth)

This is good news and bad news. On the one hand, knowing that these corals have a survival mechanism is promising. However, knowing that the shallow-water habitats are becoming so hostile for corals is forcing scientists to think about moving them to safer environments. If deep water is also threatened by the same circumstances afflicting shallow areas, that rehoming technique may need tweaking.

Climate change is posing a serious threat to the ecosystem of the Great Barrier Reef.Clownfish swim through the coral on Australia's Great Barrier Reef. Climate change is posing a serious threat to the reef's ecosystem. (Photo: WILLIAM WEST/AFP/Getty Images)

"Deep water habitats are discussed as potential refuges for corals from the increasingly degraded shallow water reefs," said Professor Jörg Wiedenmann, head of the Coral Reef Laboratory at the University of Southampton, who worked with scientists from the Interuniversity Institute for Marine Sciences of Eilat and the University of Haifa in Israel. "Our work shows that the 'deep blue sea' may not be the welcoming sanctuary our endangered coral reefs can retreat to without consequence."

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