Lots of people have observed that fish don't know they're in the water.

The substance in which they live their entire lives is just what surrounds them, like we live on land and are just surrounded by air.

But because we know aquatic animals live in the ocean, we can overlook big and frankly profound questions about

their existence. Like when they move to different depths, how do their bodies handle the change

in pressure? From KERA in Dallas, this is Think. I'm Chris Boyd.

Human divers have to learn how conditions 10 feet below the surface differ from conditions 20 or 50 or 100 feet below,

and they have to return slowly enough to let their bodies adjust.

But some animals in the ocean migrate hundreds of meters up and down every single day.

Others thrive at very specific depths and manage to avoid sinking or rising too far from that ideal.

And as my guest will tell us, evolution has yielded some wild adaptations that allow these

creatures to thrive in exactly the right places. Sunka Johnson is professor of biology at Duke University. His new book

is called Into the Great Wide Ocean, Life in the Least Known Habitat on Earth. Sunca, welcome to think.

Oh, well, thank you. I'm glad to be here. So you grew up visiting the Outer Banks of North Carolina

with your family on like summer vacation,

and that sparked this kind of reverence for the ocean for you. But you write that it wasn't until you were preparing for your postdoc training in marine biology that you had thought

very much about how different coastal waters are from the rest of the ocean. Yes, yes, that's very true.

I just, like many people, I had an idea that the ocean of the ocean. Yes, yes, that's very true. I just, like many people, I had an idea that

the ocean was the ocean we see from land. You know, we see the beach, we see the sea oats or the

rocks, or if we're in the west coast, we see all the, you know, the driftwood and so on. And we

sort of imagine that's the ocean. That's what it smells like. That's, you know, how it

looks. And it really wasn't until I actually went to sea that I realized I'd only been looking at

the outside of the ocean and that when I was actually inside it, it was just a completely different

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