These sharks are shining green - now we know why

There are more brilliant animals in the world's oceans than you might think. A study that looked at the coast off California found that around 76% of all marine animals there - jellyfish, corals, starfish and fish - shine by themselves.

It is called bioluminescence and is the most common kind of light created by animals in our ocean depths.

A slightly more unusual variant is the one these cat sharks have and it is called biofluorescence. The sharks do not shine by themselves. They get their green light either by the blue light of the sea or by lighting them with flashlights.

- Researching biofluorescence in the seas is like a detective novel that is constantly changing with new clues that emerge as research progresses, says biologist David Gruber at City University of New York.

He and his research colleagues have previously discovered a large number of new species of brilliant marine animals. And now they have found what it is that makes these cat sharks fluoresce.

It is because of a small previously completely unknown molecule. A so-called metabolite that, among other things, seems to help them withstand microbial infections.

- The study is interesting because of this molecule they found. In the past, the GFP protein has always been talked about when it comes to fluorescence, says marine biologist Jenny Lindström at the University of Gothenburg.

The discovery of the luminescent protein GFP was awarded the Nobel Prize in chemistry in 2008. The green light of the protein is used extensively in biochemistry today to follow processes inside cells and reveal diseases.

Perhaps this newly discovered molecule could also be used in this way in the future.

The study was published in iScience.