Life in the clear
Muse Science Magazine for Kids|January 2021
THE SECRET TO BEING (ALMOST) INVISIBLE
Diane A. Kelly

In the open ocean, there’s nowhere to hide. There are no rocks to slip under, no kelp to duck behind—nothing but clear water all around. “Every direction you look looks pretty much the same—it’s this ridiculous unearthly blue,” says Sönke Johnsen, a marine biologist and professor at Duke University. If you went swimming out here in the clear blue, you’d stick out like a billboard. Everything with eyes could see you coming. Being visible isn’t safe for creatures that live here; it’s too easy to be spotted by both potential prey and potential predators. So many of them have adopted a remarkable form of camouflage: they’re transparent.

I See Right Through You

Transparent animals let light pass through their bodies the same way it passes through a window. An amazing variety of open-ocean animals can do this: bowl-shaped jellyfish, comb jellies as long as a person, small shrimp-like arthropods, big-eyed squid, tiny larval fish, and snails that look like Christmas ornaments.

These animals typically live between the surface of the ocean and a depth of about 3,300 feet (1,000 m)— as far as most light can reach. Most of them are extremely delicate and can be damaged by a simple touch. Johnsen says these animals drift through life alone: “They never touch anything unless they’re eating it, or unless something is eating them.”

And they are as clear as glass. How does an animal become see-through? It’s trickier than you might think.

The objects around you are visible because they interact with light. Light typically travels in a straight line. But some materials slow and scatter light, bouncing it away from its original path. Others absorb light, stopping it dead in its tracks. Both scattering and absorption make an object look different from the stuff around it, so you can see it easily.

But a transparent object doesn’t interact with light, at least not very much. Light can pass through it without bending or stopping. That means a transparent object doesn’t look very different from the surrounding air or water. You don’t see it—you see the things behind it.

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