Last year while checking out coral reefs and sharks in the Solomon Islands, marine biologist David Gruber stumbled upon something bizarre: a "glowing" sea turtle.Turns out it wasn't a nuclear experiment gone awry, but rather one of hundreds of fluorescent marine species that Gruber has discovered in recent years.It's not as if we didn't know that many of these species existed, but rather just that we didn't know they were fluorescent because the characteristic isn't visible to the naked human eye.
Sometimes confused with bioluminescence, fluorescence is when an animal absorbs light and then emits it at a lower energy level, causing the light to be a different color. In order to capture the turtle emitting glowing light, Gruber and his team used blue lights and a camera with yellow filters capable of capturing the turtle's luminosity.While taking pictures of luminescent fish can make for some awesome shots, scientists generally have no idea why so many species exhibit the characteristic.Some studies show that fish may use it to signal one another or for camouflage, but no one knows for sure. The fact that so many different species evolved to have the characteristic indicate that it must be used for something, but it's still a mystery. Gruber and his team think that they now might have uncovered some answers.In a new video from National Geographic, Gruber shows off a "shark-eye" camera that he built in order to simulate the ways in which two luminescent sharks, swell sharks, and chain catsharks see each other in the depths of the ocean. In their model, the researchers found that when the sharks swim deeper into the dark ocean, the fluorescence of other sharks' does seem to stand out. This indicates that maybe the trait helps them find one another.As The Atlantic reported though, not all scientists are convinced by Gruber's findings. Two other researchers, Nathan Hart, a biologist at Macquarie University in New South Wales and Christine Bedore, of Georgia South University, both doubted whether the study really uncovered the mystery behind bioluminescence. Gruber stressed that these findings are only the first step, and that there's still a lot to be learned. For now, we just don't know for sure why so much of the ocean is glowing.