Why dull, brown corals light up like Christmas when you shine blue light on them

By ROB WAUGH

A giant clam which appears a dull brown under natural light, fluoresces bright red in the blue light of Louise Murray's torch. The creatures also respond to ultraviolet - like the sun's rays - but blue torches produce a clear, visible result

Louise Murray has spent a decade photographing corals - most of which appear dull and brown to the naked eye.
But when the photographer shines a blue torch on them, 'It's like the difference between walking down Oxford Street at midnight in June, and walking down when all the Christmas lights are on.'
'It blows you away completely the first time.' Murray works with scientists who believe the weird effect could be a sort of 'sunscreen' to help protect the animals from being bleached.

Goniopora corals: Some scientists believe that the fantastic colours of the pigments form a kind of sunscreen from the string ultraviolet rays in shallow water

Hard coral polyps feeding at night fluoresce brilliant orange and green - an effect that only shows up in the blue light of a torch

The wildlife photographer uses a powerful blue light to stimulate photosensitive pigments in the marine life, which then emit fluorescent colours. The creatures also respond to UV light - but Murray gets better results using blue. She wears a yellow mask while diving to see the colours more clearly.
Louise explains: 'Almost all these photographs were shot after dark as the sunlight masks the colours.'

'The stronger the light the better the results, I have to filter my camera and eyes with a yellow mask so the true colours are revealed.'
'The pigments are photo-pigments, they respond to being flooded with blue light by emitting
their own colours - both the coral animals and the plant.'
Scientists suspect that it's a defence against being bleached by the sun.

Both undersea plants AND animals glow under the blue light - Murray uses blue because it's easier to capture clear pictures, although the animals also glow under ultraviolet

Her latest collection was captured while diving in the dark waters of Tondoba Bay in the Red Sea of Egypt.
Louise first started capturing the fluorescent colours of marine wildlife over a decade ago.
She said: "I love doing it, the colours still blow me away, and scientists are still trying to come up with an explanation for their purpose.
"On land peacocks use fluorescent pigments to make themselves more colourful and sexy to the opposite sex, which could be part of the story for some of these fish.'

source: dailymail