In the depths of the Red Sea, a magical world exists.

It's a world where corals light up the dark. They harvest light, providing an underwater rainbow of beautiful colours.

These fluorescent corals were already known to exist in shallow waters, but deeper down, new glowing coral reefs have been discovered.

Found at depths of 50-100 metres, these colours had not previously been observed in shallower water of the same reef.

Some of these corals even change from their natural green colour to a red hue when exposed to ultraviolet light.

What's more, the fluorescence of these deeper corals were orange and red.

Living at these depths only makes them glow more brightly as they absorb the scarce light available.

“These fluorescent pigments are actually proteins," explains Jörg Wiedenmann, of the University of Southampton’s Coral Reef Laboratory in the UK.

“When they are illuminated with blue or ultraviolet light, they give back light of longer wavelengths, such as reds or greens."

He and colleagues have published new insights into these glowing reefs in the journal Plos One.

The colour pigments of the corals in shallow water protect them from light stress or too much exposure.

They serve as a sort of sunscreen for the coral, to protect the "symbiotic algae" which lives inside their tissue.

These algae are symbiotic because corals and algae have a harmonious relationship. The algae produces sugar that fuels the coral. The coral in turn produces rich nitrogen and phosphorous waste, which acts as fertiliser for the algae.

That fluorescent corals were discovered in darker depths, where light barely reaches, is puzzling to the researchers.

"At 50 metres or greater you would not expect the corals to suffer from too much light. They actually struggle to get enough for the photosynthesising algae," says Wiedenmann.

It is believed that their fluorescence may help them absorb more light, needed for the algae to survive.  

Their fluorescent glow could even make them useful tools for biomedical research. They can be used to highlight living cells.

By implanting the fluorescent proteins into living cells they can be used to visualise cellular processes in action, or track the activity of genes of interest.

"The fact that we now have a whole area of pigment from a completely different environment makes us hope there might be some new properties among them," adds Wiedenmann.

"They have evolved for different biological functions in a different light environment."

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