(Inside Science) -- There are just a handful of land animals that can create their own light -- the most well-known are fireflies. But down in the deep sea, where natural light is limited, some creatures have to make their own light.
It’s estimated that about 75 percent of deep-sea creatures are bioluminescent, meaning they can create light by mixing two chemicals within their bodies, making themselves glow. The light tends to be green or blue -- colors that travel far in sea water. And in the dark of the deep ocean, glowing can help creatures attract mates, lure prey or confuse predators.
Marine biologist Dimitri Deheyn has spent years studying how marine animals use light, focusing, in particular, on a shark species that glows.
“The catshark is a shark that lives in great depths in the ocean where there is usually no light. They have a chemical in their skin that makes them glow. We wanted to know -- can the sharks see their own fluorescence, or at least the fluorescence of their mates? We found that those sharks have this yellow filter in front of their eyes, meaning that they don’t see blue, but they see mainly green. And the green is indeed the color of the fluorescence from the skin of that particular species. At a certain time of the year, though, they come back to shallow waters where they like to hang out and to find their mates,” said Deheyn, at the Scripps Institution of Oceanography.
When the sharks are ready to mate, they glow to attract members of the opposite sex.
“This glow can actually be detected, so that as they mate, you can pinpoint and find where your mates are and more easily reproduce. So that particular shark, the catshark or the swell sharks, have evolved to use fluorescence as maybe a tool for visual ecology,” said Deheyn.
Researchers are still figuring out what sharks and other sea creatures are seeing and saying to each other with their glowing features.
“We are developing now new tools to understand how important is vision. What does a shark or a shrimp or any other fish -- what do they actually see? And by learning these fundamental questions, we can probably understand much better how our ocean is working, and how all those animals that make the ocean what it is can actually thrive and make a sustainable environment,” concluded Deheyn.