Mysteries of the deep: How some sharks glow green in the dark

WASHINGTON: It may not sound like the best way to go incognito, but some species of shark that lurk on the ocean floor glow a bright green hue visible to others of their kind.
Scientists said on Thursday they had identified the molecules responsible for the marine predators’ biofluorescence, and that it might perform other functions too like fighting microbial infection. The research was published in the journal iScience and pinpoints a previously unknown family of small-molecule metabolites.
“It’s very different from all the other forms of marine biofluorescence” such as the processes seen in jellyfish and corals, David Gruber, a professor at City University of New York and co-author of the study said.
“This is a small molecule rather than a protein, and it shows that in the blue ocean, animals are independently evolving this ability to absorb blue light and transform it into other colours.” The paper focused on two species, the swell shark and chain catshark, that Gruber studied during scuba dive trips in Scripps Canyon, off the coast of San Diego. These are altogether more bashful characters than the great whites or tiger sharks that you might see on TV’s “Shark Week.”
“They’re like a metre long, they lay at the bottom, they’re quite shy and they’re not good swimmers,” said Gruber.
What’s more, they dwell at depths of 30 metres or more, where only light at the blue end of the spectrum penetrates — if you were bitten there and started bleeding, it would come out looking inky black.
Gruber and his colleague Jason Crawford at Yale University noticed that the sharks’ skin had two tones, light and dark, and after extracting chemicals discovered a fluorescent molecule only present in the light skin that helps the sharks intake blue light and emit green. — AFP