Their feathers are darkly pigmented to begin with, but also make use of tiny tree-like structures that bounce light around, absorbing more photons. Consider the ultra-black birds-of-paradise. These fish have evolved a fascinating kind of hybrid approach to ultra-blackness. Because if they don't, they're going to starve." Other quirks of their morphology also betray this desperation: Species like the anglerfish have enormous mouths and bellies, all the better to consume whatever they stumble upon in the darkness. And the reason I think is because there's so little prey that they have to be very efficient, to the point of being able to catch almost 100 per cent of whatever they come in contact with. "If they weren't so ultra-black, they would still be relatively invisible. "Ultra-black seems like an extreme– why would they spend so much energy and evolutionary time in making that?" asks Luiz Rocha, curator of fishes at the California Academy of Sciences, who wasn't involved in this research. But in the vastness of the deep, prey is relatively scarce, so predators are under much more pressure to score a meal. A coral reef teems with masses of fish, giving predators plenty of choices on the menu. You also don't want to be swimming around with an empty belly. “Once it comes in, it bounces around between all of those little balls and doesn't come back out.” “It's kind of like a gumball machine, where all of the gumballs inside are the right size and shape to trap light within the machine,” adds Davis. “And so what they've done is create this super-efficient, very-little-material system where they can basically build a light trap with just the pigment particles and nothing else.” “But what isn't absorbed side-scatters into the layer, and it's absorbed by the neighbouring pigments that are all packed right up close to it,” says Osborn. When you shine a light on a fangtooth or its peers, the melanosomes absorb most of the photons right away. Tons of melanin alone, though, couldn’t make these fish rival the darkness of Vantablack. The skin of these fishes is positively packed with a layer of organelles called melanosomes, themselves loaded with melanin. So how do these 16 species of ultra-black fish camouflage themselves so well? It’s all about melanin, the same stuff that gives us humans our skin coloration. “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.”Ī specimen of the ultra-black fish species Anoplogaster cornuta Karen Osborn/Smithsonian “Obviously, you don't want your prey to be seeing that light casting all over your face,” says Davis. Same thing if your face has headlights that help you spot your food. If the prey can see an anglerfish’s face lit up by its dangling lure, the jig is up. There’s a problem, though: All this light attracts attention, both for prey and predators. And most of the time it is mainly blue light, because it’s what propagates the farthest in these waters.” “Light is exploding there, but it's biological light. 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. “Imagine yourself in a bunker with no light whatsoever, and you have to find your mate. And in the total darkness, the males and females of some species must light up like billboards to find each other to mate. Perhaps most famously, the anglerfish uses a glowing lure to draw prey into its toothy maw. Other species of deep-sea fish throw off beams of bioluminescent light from their faces – searchlights that help them find food. Some creatures, accustomed to becoming lunch, spew a cloud of bioluminescent goo that confuses their hunters, or even sticks to their bodies, marking the hunters for their own predators. This light show serves a wide array of purposes. (The researchers collected specimens down to 2,000 meters deep.) 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. 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.
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