Scientists have found that some fishes absorb up to 99.956 percent of the light that hits them. The deep-sea menagerie just got a whole lot weirder.
BOBBING ALONG ON the research vessel Western Flyer just outside California’s Monterey Bay, marine biologist Karen Osborn and her colleagues were hauling deep-sea fish to the surface for cataloging and a photo shoot. Osborn got her hands on a fangtooth, a self-explanatory creature with a mouth full of nasty, big, pointy teeth, attached to a stout, teardrop-shaped body. Using her custom-built system of strobe lights and a camera mounted above a tank, she could capture the rare specimen for science.
Yet when she put the fangtooth in front of the camera, it turned into a living black hole—the outline was there, but not the fine details, as if the fish was devouring light. “I was trying to take pictures of it, and I was just getting these silhouettes,” Osborn says. “They were terrible.”
This wasn’t her first photo shoot with a deep-sea fish, so it couldn’t be operator error. But wait a second, Osborn figured. “I had tried to take pictures of deep-sea fish before and got nothing but these really horrible pictures, where you can't see any detail,” she says. “How is it that I can shine two strobe lights at them and all that light just disappears?”
It disappears because the fangtooth, along with 15 other species that Osborn and her colleagues have found so far, camouflage themselves with “ultra-black” skin, the deep-sea version of Vantablack, the famous human-made material that absorbs almost all the light you shine at it. These fish have evolved a different and devilishly clever way of going ultra-black with incredible efficiency: One species the researchers found absorbs 99.956 percent of the light that hits it, making it nearly as black as Vantablack.
“We had no idea there were any fishes at all that were ultra-black,” says Duke University biologist Alexander Davis, lead author on a new paper in Current Biology describing the findings. “As far as we knew, the only vertebrates that were ultra-black were these birds-of-paradise and a couple other bird species. It was the first case we have of something this black really being used as camouflage as well.” You might be wondering why, if the sun’s photons don’t penetrate past 200 meters deep, these fish would need to camouflage themselves with some of the blackest black in the animal kingdom. The reality is that the ocean’s depths are actually aglow with light, in the form of bioluminescence produced by critters clear across the tree of life, from bacteria to fish to squid. (The researchers collected specimens down to 2,000 meters deep.)
This light show serves a wide array of purposes. Some species, accustomed to becoming lunch, spew a cloud of luminescent goo that confuses their hunters—or even sticks to the hunters' bodies, marking them for their own predators. Other deep-sea fish throw off luminescent beams from their faces—searchlights that help them find food. Perhaps most famously, the anglerfish uses a glowing lure to draw prey into its toothy maw. And in the total darkness, the males and females of some species must light up like billboards to find each other.
“Imagine yourself in a bunker with no light whatsoever, and you have to find your mate. You hope you have a flashlight, right?” asks Scripps Institution of Oceanography’s Dimitri Deheyn, who studies bioluminescence but wasn’t involved in the new study. “Light is exploding there, but it's biological light. And most of the time it is mainly blue light, because it’s what propagates the farthest in these waters.”
There’s a problem, though: All this light attracts attention, both for prey and predators. If the prey can see an anglerfish’s face lit up by its dangling lure, the jig is up. Same thing if your face has headlights that help you spot your food. “Obviously, you don't want your prey to see that light casting all over your face,” says Davis. “So if your head is now ultra-black, none of that light goes back to the prey, and you’re more likely to get within range.”
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