For scientists to solve the mysteries of the ocean, they need to start with questions like “how do fish float?” Duke University biology professor Sönke Johnsen joins host Krys Boyd to discuss the wonders of vertical migration, why sharks must keep swimming to stay alive, and the clues offered to biologists that help piece together the questions of aquatic life evolution. His book is “Into the Great Wide Ocean: Life in the Least Known Habitat on Earth.”
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Transcript
Krys Boyd [00:00:00] 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 moved to different depths. How did their bodies handle the change in pressure from Kera in Dallas, this is Think. I’m Krys Boyd. Human divers have to learn how conditions ten feet below the surface differ from conditions 20 or 50 or 100ft 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 managed to avoid sinking or rising to 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. Sönke Johnsen 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.” Sönke welcome to Think.
Sönke Johnsen [00:01:11] Well, thank you. I’m glad to be here.
Krys Boyd [00:01:12] So you grew up visiting the Outer Banks of North Carolina with your family on 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 post-doc training in marine biology that you had thought very much about how different coastal waters are from the rest of the ocean.
Sönke Johnsen [00:01:32] Yes. Yes, that’s very true. I just I, like many people, had an idea that the ocean was the ocean we see from land. You know, we see the beach, we see the CO2 in 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 see 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 world.
Krys Boyd [00:02:02] Yeah. You make us aware of the fact that as land animals, we are in many ways missing out on the real life of most of the planet, right? We inhabit a world that is mostly covered by water, but we’re on the small part that is covered by land.
Sönke Johnsen [00:02:16] Yeah, exactly. And it’s not just, you know, I mean, I remember from all the way back in third grade, they would always tell us that the oceans were about three quarters of the surface of the planet. But the oceans are also so much deeper than our life on land. I mean, our life on land is maybe a few hundred meters deep. If you go from, you know, the animals living underground, you know, to the birds and such flying above and the tallest trees and so on. But the ocean is on average two miles deep, you know, about 10,000ft. And so about 99% of the earth’s livable space is actually in the water. So we’re sort of at heart a water planet.
Krys Boyd [00:02:56] In your work, you mostly focus on the pelagic portion of the ocean. What does that term mean?
Sönke Johnsen [00:03:02] So pelagic is pretty much everything that’s not the bottom. A great deal of deep sea biology research is focused on the bottom for a number of reasons. I mean, one, it can be easier to sample things there and study things there. But the pelagic is everything, basically ranging from the very surface. You know, there are animals that live right underneath the surface all the way down to the bottom, but not including the bottom. So it’s the animals that have to, in one way or another, sort of float in that space. They have to not sink. They have to not rise too much. They have to deal with, you know, gravity and pressure and light and just the utter vastness and featureless ness of that environment, which to us seems completely alien in any number of ways, but really is the fundamental nature of our planet.
Krys Boyd [00:03:51] There’s still a lot we want to know, in part because it’s not so easy to be down there and observe. Your first extended trip on a research vessel was, shall we call it rough. I’m curious. Yeah. Yeah. Tell us a little bit about that.
Sönke Johnsen [00:04:05] Yeah, I mean, so it was rough. We left from Fort Pierce, Florida, on a boat called the Edwin Link, which was a converted mud boat. You know, the idea that research cruises are somehow like pleasure cruises is just not true. They’re much, much rougher boats. It’s better to think of them as like a loading dock or a factory floor that, you know, can move around rather than is like a mountain, like any sort of a pleasure thing. And yeah, my very first cruise, we were traveling up to the north to an area off the coast of Maine, which meant about four days in the middle of the Gulfstream. The Gulfstream is, you know, as people often talk about, it’s warm and provides warmth, you know, to Europe and so on. But it’s also very wavy and has a very high current. And when that wavyness and current meets bad weather, it becomes pretty startling. And so the waves were pretty regularly between about 12 and 18ft, which meant the boat was hurdling in all directions. It wasn’t a huge boat. It was only about 170ft long, which means that it was really tossed left and right and up and center. And I’d never dealt with seasickness of that kind before in my life. So it was sort of a trial by fire. And I was trying very hard, not well, not to throw up because I was also not used to the smells. I wasn’t used to the water flying everywhere. I wasn’t used to the fact that a 12 foot wave could just smash into me from the side if I stood outside and so on. So, you know, as my post-doc advisor, they called it really was a trial by fire in water.
Krys Boyd [00:05:42] I had not fully appreciated the extent to which falling overboard a ship out at sea, any kind of ship is nearly always fatal, even for people who are expert swimmers. Even if the water is not so cold that it freezes you. Why is it so hard to locate a person bobbing in the ocean?
Sönke Johnsen [00:06:01] One of them is that we’re what we call neutrally buoyant. And I mean, you realize that when you go into a pool and you just try to float. Most of us just barely float and we only float when we breathe in and then we sink a little bit when we breathe out. And so when you’re in the water, unless you’re kicking your feet very hard, your head’s just above water. And the waves, even in the nicest ocean, are usually at least 4 to 6ft high with a lot of little white caps and so on. And so once somebody is more than about 50 or so feet away from the boat, they’re, you know, sort of wet. Dark head is very hard to see. And the bigger problem is that the ships are I mean, they’re not huge, but they’re big enough that they’re very slow to turn around. And these boats only go about 11 miles an hour and they have a turning radius that’s enormous. And so if you fall overboard, the amount of time it will take for them to turn the boat around and come back to you is assuming they can find you is about 20 minutes or so for a medium sized boat, which means that they probably won’t find you unless you have something that makes you a lot more visible. So my main advisor again early on in that first cruise said, Imagine that you’re walking on a 3000 foot cliff except a cliff that could, you know, pitch you off the edge of it at any moment, and that you shouldn’t think that just because the water is only five feet away, if you drop that, this is a survivable accident.
Krys Boyd [00:07:34] So rule number one, do do not find fall overboard.
Sönke Johnsen [00:07:37] And if you do fall overboard, never do it when the boat is moving. And especially if it’s at night.
Krys Boyd [00:07:43] Your training as a diver caused you to think a lot about the forces of buoyancy and gravity? First of all, why do human beings ever drown when floating is a relatively simple thing for most of us to do? I mean, you mentioned the fact that, you know, we’re neutrally buoyant, but but most of us in a swimming pool could float for hours on it.
Sönke Johnsen [00:08:06] Yeah. Yeah. And I mean, with a little bit of training, one could float in the ocean for quite a while until one got tired. You just have to. Not panic is a big part of it. Because the problem is, is if you panic and you inhale even a little bit of water, that causes sort of a nasty feedback loop where you become heavier and heavier and then go down. And so with a little training, you can’t float. The problem is it’s exhausting because the ocean, like I said, the waves are always about 4 to 6ft and sometimes considerably larger. And trying to float while you’re continually being smashed on the side by different waves and being yanked upside up and down is difficult. And this is assuming the water is warm, which very often it’s not in that first cruise. Like I said, we’re off the coast of Maine. And if you went into the water, you had maybe 20 minutes to half an hour of useful movement in your limbs before they got too cold to use. And when we’re not in the summer, I mean, that can be on the order of a couple of minutes. And at that point, if you don’t move your body, you will sink. And on top of that, if you are in warm water and it is nice and still and so on and they don’t find you, that’s probably the worst thing that can happen because at that point, oceanic sharks will eventually show up and eat you. You know, the majority of people that have ever been eaten by sharks have been eaten by sharks, far from land, typically from shipwrecks, from things like torpedo boats and things of that sort in the various wars. They get knocked into the water and in tropical water you can, if it’s calm, last a long time, but then eventually the predators will show up and eat you. So you probably better I mean, best case is that you freeze to death, fall unconscious and drown. Second best as you become exhausted, go down and drown. And then the worse is that you get eaten. So none of the options are great.
Krys Boyd [00:10:03] They’re not great. And thank you for this work that you do. When you and your colleagues are diving. You rely on technology known as a buoyant buoyancy control device, which does what it says. But pelagic animals do this with their bodies. And it’s so easy as humans not to think about how miraculous it is that sea creatures don’t just sink, they generally remain at whatever depth suits them. One way some of them manage this is by having evolved very, very light bodies.
Sönke Johnsen [00:10:33] Yeah, there are a number of different tricks and it is miraculous. I mean, many times when we show up and we find an animal, it looks like it’s just sort of nailed to the sky because it is a featureless world down there and it’s beautifully blue and they’re just stuck there like not going up, not going down or anything without any effort. And they do have different tricks. I mean, one of which is to become as light as possible, but it’s very hard for them to become lighter than water or even the same as water. I mean, tissue always weighs a little bit more than water except for fat tissue, which is a little bit lighter. And so some of these animals can balance out the little bit of themselves that’s heavier than water with fat that’s lighter. Some balance it out with a tiny little pocket of air, which can work but can be tricky to use. And some do really clever things where they actually change how heavy the water in their body is. Sea water is full of a lot of different chemicals. Some of those chemicals are heavier than water and some are pretty light. So, for example, sulfate is heavy as a heavy molecule and ammonia is a light one. And so they will take seawater into their bodies and pump out the sulfates and pump in the ammonia. So there’s sort of like a big water float. It doesn’t have a lot of buoyancy, but it’s enough. Once you’ve already made your body very light.
Krys Boyd [00:11:50] Other animals just go wide. They spread themselves thin to stay at the correct depth or even on the surface.
Sönke Johnsen [00:11:57] Yeah, you can do that too. Especially a slow yourself falling. You can basically be like a skydiver. So, you know, if a skydiver wants to slow him or self down dropping, you know, they’ll spread out their arms and legs and a number of the plankton in different animals will do that. They’ll have long spikes or long limb like attachments that they can spread out. And that increases how challenging it is for like gravity to pull them down. It increases something we call their drag. So they go through the water more slowly, but it won’t let them just float. It just slows down how quickly they fall.
Krys Boyd [00:12:33] What about pelagic animals that prefer a particular depth below the surface? What are some of the ways they can take in air to fill something like a swim bladder?
Sönke Johnsen [00:12:42] Yes, a swim bladder. Sort of the classic way to do it. There are animals like various jellyfish, like animals that just have a little bubble. But the swim bladders are pretty highly developed. You find them pretty much in fish and they do a couple of different tricks. So the ones that are close enough to the surface to periodically go up to the surface, they will just go up in the air. And you’ll see this in. Like some of the fish that you might have in your own fish tank at home. You see them gulping at the surface and you might think, you know, they’re suffocating. Mostly what they’re doing is helping inflate their little swim bladders. The ones that can’t get to the surface, like a lot of the deep sea animals, they actually fill their swim bladders with air that’s dissolved in their bloodstream. So, you know, they normally are getting, you know, oxygen from gills and then some of that oxygen is peeled off from the bloodstream via a sort of a fancy little gland called the reed meraviglia, which means like the miraculous reed, which is a really cute name. And that will help dump air into these swim bladders. And they can do it at enormous depths. It’s like more or less like you’re inflating a balloon with the Empire State Building, standing on top of it.
Krys Boyd [00:13:57] Sönke before human divers can be certified, they have to learn about the effects of water pressure on the body. Like if you descend, is it 30ft? That’s like doubling the atmospheric pressure one experiences on land.
Sönke Johnsen [00:14:11] Yeah, pretty much. For every 30ft you go down, it’s another atmosphere and it doesn’t take much. I mean, so if you had a snorkel that was only 3 or 4ft long, you wouldn’t be able to use it because the pressure on your lungs would be so much greater than the air pressure of the air above the water that you’re trying to breathe, that you don’t have the musculature to actually breathe in. So doubling the pressure is enormous and, you know, going, you know, 30ft after 30ft after 30ft after that, it becomes prohibitive.
Krys Boyd [00:14:46] So what do you have to do to accommodate that when you go deep below the surface?
Sönke Johnsen [00:14:52] So as a scuba diver, we swim around with a tank of compressed air that’s compressed to an extremely high pressure. And then we have these regulators that I still think of as totally magic, and they somehow know exactly what depth they’re at and they provide air at exactly the pressure of that depth. And so if you’re 30ft down, they provide air at two atmospheres instead of one. And that allows us to breathe in and out without having to work our lungs terribly hard. It does feel a little different when you go deeper. I mean, it’s almost like the air somehow feels thicker or harder to move around, but the pressure difference isn’t there, and so we’re capable of doing it.
Krys Boyd [00:15:33] So I’m glad that you have this equipment. But of course, huge numbers of animals engage in daily migrations from one ocean depth to another. Sometimes it’s thousands of feet per day. How did they adjust to pressure differences as they ascend and descend in the ocean?
Sönke Johnsen [00:15:50] It’s really interesting because, you know, for us, it’s it’s brutal. You know, as we learn as scuba divers, there are so many terrible things that will happen to you as you breathe air of hired air pressure. And, you know, the actual pressure on your body is typically not a problem because we’re mostly made of water. So being in depth is like water squeezing water. If you had water in your lungs and in a couple of other places like your middle ear and other places that have a little bit of air in them, you can go down to the sea floor and not really be squeezed. But the problem then is, you know, how do you breathe and so on. And so the animals that are made completely of water, they get their oxygen in through gills, which doesn’t require that there be any air in any cavity or anything. And so things like all these different sort of weird critters like I show in the book, they they do just fine doing that. The ones that have the problems are the ones that need to breathe like us, the animals that need to breathe air in like air form. You know, we are actually like, somehow sucking in like a big volume of air. And that’s mostly the marine mammals and a few of the things like, you know, marine turtles and things of that sort. And they do the weirdest thing, which I had to be one of the bigger surprises when I first started graduate school and was learning about these things is right before they dive, they don’t inhale. I mean, like we do like if we go on a deep dive for fun to show off how long we could stay underwater. You know, we breathe in as much as we can, and they breathe out. They breathe out incredibly hard to completely or as close to completely empty their lungs. And so when they’re at depth, they’re pretending like they’re all the other animals that just breathe with gills. There’s no more oxygen left in their lungs. And so they don’t have any high pressure to worry about squeezing, you know, the air cavities of their body. And they’re not breathing high pressure air, which is what causes most of the the challenges of being at depth. But of course, then they don’t have any air. And so they have clever tricks and various ways to hide air inside their body and dissolve form. They dissolve an awful lot of it in their muscles. They dissolve a lot of it in their bloodstream. If you look at whale meat, for example, which most people don’t, but you may have seen pictures. The meat’s incredibly dark. It’s not red like, you know, like beef or something like that. It’s almost purplish black. And that’s because it’s got tissues in it that are incredibly good at absorbing oxygen. And so they more or less pretend like they’re a fish once they get underwater and, you know, just not having any air inside them. And so if you don’t have air inside, you can go almost as deep as you want and not worry about it. But if you do, problems start to mount within the first 5 to 10ft.
Krys Boyd [00:18:44] Do we know how they become aware of that they need to resurface and get some more air?
Sönke Johnsen [00:18:51] Wow, that’s a good question, because they they seem to be doing a lot better than we imagine they can. So people have been putting tags on whales for a long time and looking at their diving behavior. And we know that if you exercise for a long time and this is hard exercise to swim all the way down, go hunting and come back up. We know that if you do that, you build up lactic acid in your tissues. That’s what happens. Like people who run, you know, lots of 100m sprints. They start to feel that pain in their legs. And that’s partially the lactic acid building up. And these animals should be building it up like crazy because they’re working very hard without any new oxygen coming in. And somehow they get around that and people have an entirely figured out, you know, how they’re doing it. They seem to just have remarkable abilities. And one of the clues seems to be that they have a really advanced version of what we call the dive reflex, which is when you go underwater, especially if you’re young and really especially if you’re a baby, your body completely changes almost into water mode and you only send oxygen to your heart and to your brain, and that makes it last a lot longer. That’s why young children were often, you know, found drowned and then can be revived because their body has saved what, little oxygen and put it into their brains and into their heart. And they seem to have a really incredible ability to do that. But how they can do that and still supply enough oxygen to their muscles to catch things down there like a sperm whale going after a giant squid. It’s a really good question and we really don’t know how they know when to come up except I mean, I always imagine it’s like what we do is, you know, we just suddenly get the urge and we realize we’re running out of air. But they do manage to do an absolutely extraordinary feat.
Krys Boyd [00:20:45] Some animals don’t have to come up for air, but they do have to keep moving to avoid sinking. And you divided into two categories. There are the fliers and the frantic strugglers. Sharks are fliers, right?
Sönke Johnsen [00:20:58] Yeah. You can really think of the underwater world, the pelagic part of the underwater world as just another sky. It’s a sky of thicker air. Many of the animals, like many of the fish and the sharks and so on, aren’t really swimming through water so much as they’re flying through it. They’re able to generate lift using the fins on the sides. So they’re not so different from like little cessna airplanes, but they have to keep moving to do it. And so that’s one trick. And then the other is really it does look like frantic, struggling. There’s one poor animal. It’s a snail with a very unusual name. It’s called Limousin. And this snail has these little sort of wings that used to be its feet in some distant evolutionary past, and then a large boulder like shell attached to it, at least large for the size of the feet. And it just flaps those little wings like crazy to keep up. It just it really looks kind of sad, actually. And then periodically they give up and they sink like a stone while they’re giving up. And then they’ll just start flapping, you know, to move their way back up. And it just seems like a really harsh existence. When I was a kid, we used to have to tread water for half an hour for like a swim test or something like that. And this, I imagine doing that was just somebody tied like a 25 pound bag of kitty litter to my feet and, you know, just how awful that would be. And that’s what I imagine these animals feel like. It does look very frantic.
Krys Boyd [00:22:29] Like Sisyphus, right? Pushing the Rock Hill all day long.
Sönke Johnsen [00:22:32] And it really is like Sisyphus that you just and yeah they’re only and it’s a whole life of that it’s a whole life of you know like paddle, paddle, paddle to go up, up, up. And then the rock pulls you back down and then paddle out about all, you know, back up in the rock pulls, you down until like some predator shows up and eats you. And that is a funny thing about biology is sort of getting yourself into the mind of different lives and what that would be like. And I suppose our lives look really odd to them.
Krys Boyd [00:22:57] Maybe they look at us and think, capitalism, I would not want to have to deal with that.
Sönke Johnsen [00:23:01] Exactly right. Or wow, they sure look at screens a lot, right? Or something like that. I mean. I mean, sometimes I like to imagine, like the animals looking at us from the outside. Like we look at them psycho.
Krys Boyd [00:23:11] What do we know about why so many animals engage in these daily vertical migrations? What would be the benefits of that?
Sönke Johnsen [00:23:18] It’s a good question. The long standing idea has been that they’re doing it to hide. So what they do is they’re typically deep during the day. And, you know, when you’re deep during the day or night, it’s pretty dark. And typically they come up at night to shallower water. And when you’re in shallower water, one, everybody’s sort of crushed together because all the different depths are sort of pushed up against the surface. And so it’s easier to find food to eat and so on. And it’s dark because, you know, you’ve come up at night. So that’s always been the main idea, is that they’re doing it, that it’s not so much. They’re coming up at night is that they’re going down during the day. It’s like during the day they want to be down in the dark as sort of a like a little refuge to hide from all the predators. People do argue about it a lot. I mean, we know that for some animals, they’re mostly just trying to avoid a sunburn. But that’s mostly when people have looked at animals that are lakes and so on that they’ll go deep to avoid getting too much U.V. light. Some seem to be following other animals up in other algae up. And so, you know, if other things are going up to the surface at night, then they’ll go up there to munch on them. And it’s a bit of a, you know, a chicken egg problem. You know, who’s chasing who. But the usual idea is that they’re just going up to eat, going down to hide.
Krys Boyd [00:24:33] But if they don’t have air cavities in their bodies or gas cavities, water pressure is not a factor at all for them.
Sönke Johnsen [00:24:39] Not substantially, no. I mean, if they go I mean, our usual rule of thumb is if we collect an animal at 3000ft or less depth, we can put it in an aquarium in our home. And as long as we keep the water cold and we feed it, it’s just fine. I remember once one of the labs I was at the next door lab. They had deep sea, sea urchins and they were collected from about 3000ft down. And they love carrots. And so you just see all these animals in this dark room, you know, munching on carrots as if, you know, they’re on the deep sea floor, but they’re just sitting in these little aquarium. So for the most part, yeah, the going up and down does not affect pressure much. The ones it does very much so are the ones with swim bladders because it’s hard to deflate a swim bladder as fast as you might go up, or especially as fast as something might pull you up. So if you’re caught by some animal recon patrol or something like that and you’re pulled to shallower water, then the swim bladder will get bigger and bigger until it explodes. But the animals without swim bladders, they can go up and down fairly easily and not worry about the pressure, even though the pressure is enormous. It just builds and builds and builds.
Krys Boyd [00:25:48] If these animals that do vertical migrations, those migrations mostly happen in predictable daily cycles. It would make sense that they’re responding to light from the sky that tells them it’s time to go down to avoid, you know, being burned by solar radiation. But when they’re deep under water and maybe can’t perceive any light from above, how do they know it’s time to rise?
Sönke Johnsen [00:26:11] You know, that’s been a head scratcher among oceanographers for quite a while. We do know that many animals have circadian clocks all the way back from when there’ve been experiments where somebody would put themselves in a cave. I think it was actually Mammoth Cave and noticed that he still lived on a 25 hour cycle, which is really close to our 24 hour cycle. A lot of these in-built cycles, they get calibrated every day or two by the sun going up or down. And so animals do have like a reasonable amount of ability to tell time. So there is that, you know, the ones down there can say, well, I’ve been down about long enough time to go out. It’s this is a bit of a mystery, though, because, I mean, think about it. You know, it’s so dark. How do you know that sunset is occurred when it’s already dark and it’s the upward migration that tends to be the one that’s the tightest. I was just thinking, well, you know, maybe they’re, you know, going sloppily and they don’t have a good timing of it, but they do start to go crazy right around sunset. And so somehow they know that even though it’s too dark for them usually to tell that there was a sunset, the going back down at night is much more spread out. It’s almost like they go up to eat and then it’s sort of like a crazy all you can eat buffet. They go up the hill like crazy and different people get fall at different times and then head back down for the day. And that can happen, you know, all through the wee hours of the morning. But the going up is all at once. And I mean, the best anyone can guess is that, you know, they have a timer built in the really deep ones. The ones that are shallow can pick up the sudden drop in illumination. You know, they can pick up the fact that the sun’s actually going down. But the ones that are really deep and some of them really are, it’s just going from pitch black to pitch black.
Krys Boyd [00:27:52] Speaking of being well below the area where light exists, different animals have evolved like a fascinating array of eyes to make this possible. What are the tradeoffs of developing eyes big and powerful enough to perceive surroundings in very low light?
Sönke Johnsen [00:28:08] Well, the first one, which sounds like a really trivial one, but most of these animals are pushing the limit on it is You’ve only got so much head. You know, as your eyes get bigger and bigger and they eventually meet in the middle. So if you look at, let’s say, the skeleton of an owl or of a lot of deep sea fish, they basically run out of room to put out to put their eyes. And you need to leave enough room for a brain and so on. So that’s one problem. The other is that eyes are really their energy hogs. Of all the tissue in your body, your retina uses more energy for its size than anything else. It’s just an incredible energy hog. And so if you make your eyes bigger, more or less, you need to eat more to be able to use them in the. You know, a second difficulty. The third difficulty is sometimes having really big eyes makes you really visible. We often, without knowing it, you know, spot animals. Let’s say if you’re on a scuba, you know, and you’re looking at a coral reef or something, you’re trying to find fish. Usually you find their eyes first. There’s just something about, you know, animals looking at each other that, you know, we really focus in on our eyes and they can be hard to distinguish. And so it can be tricky if you have an enormous eye to not let that I give you away. So there are some real costs to just making eyes bigger and bigger and bigger.
Krys Boyd [00:29:24] Some animals compensate for low light with bioluminescence, including a kind of what, integrated flashlight system for some.
Sönke Johnsen [00:29:31] Exactly. I mean, so that, you know, is one of the great solutions of the open ocean, which something like 80 to 90% of the animals down there do, which is that they make their own light. And it’s not even that expensive to make light. And you don’t even need that much because it’s already so dark. And so any little bit of light is an advantage. And many of them will have light organs, which we call photo fours wrapped around their eyes. So they’ll be just above the eye, just below the eye. And they have filters and shutters and mirrors and so on, pretty much acting almost like cameras in reverse. They’re really sophisticated and they will shoot out a beam of light in front of them that they can use to find things. Most of these beams are blue. A few of them have red beams that are very useful for finding red animals, which are pretty common in the deep sea. So, yeah, you you’re basically once you get deep enough, you’re in a world surrounded by animals that are trying to find you with flashlights. It’s sort of like if somebody puts you in a giant arena at night and turned out all the lights and gave everybody, you know, a flashlight and a sword and they’re all like, you know, trying to be the one that comes out at the end. It’s, you know, the deep sea is a I mean, it’s a challenging environment and a spooky one.
Krys Boyd [00:30:49] Sankar Why is it that we see things crystal clear if we are wearing good goggles but we find things blurry if we just open our eyes directly underwater?
Sönke Johnsen [00:30:59] Yes. So, I mean, this pretty much comes down to the fact that, I mean, when you’re younger, they often, you know, tell you, you know, your eye has a lens in it and it operates like a camera lens. And that’s how you focus light to see. But the lens actually does very little. Mostly what the lens does is it changes shape to let you see things close up, which is the thing that fails as you get older like me, and it becomes harder and harder to see things close up. Pretty much the real lens that’s doing at least three quarters of the work is the cornea sitting out, you know, the front of your eye. It’s curved and it acts like a lens because the inside of it is a fluid and the outside of it is just the air. And so that difference in the properties, you know, affect the way that, you know, a lens can work if you have a big difference, you know, in the outside world, in the inside of the lens, then it can be a pretty strong lens. And that does most of the focusing for you. But when you go underwater, the cornea is now just this pretty much like a thin window of tissue between a watery outside world and a watery inside of your eye. And so it no longer has any strong focusing power. And the only focusing power you have in your eye that’s left is your lens, which isn’t nearly good enough. I mean, as everybody knows, you go under water and you open your eyes and your vision is extremely blurry.
Krys Boyd [00:32:24] So it’s probably not blurry for animals that live underwater. What are some of the ways that their eyes are set up to avoid this problem?
Sönke Johnsen [00:32:34] Yeah, they do one main trick, which is they don’t bother with the cornea. So if they have a cornea, which weirdly enough, they don’t all have some, their eyes are just kind of open to the environment, but their cornea will be flat. It won’t do anything. It won’t focus any light. And all the light instead is focused by a lens. And unlike our lens, that looks a lot like an M&M. You know, like a little like saucer or something like that. The lenses of animals in the ocean are balls, which makes them really strong and allows them to focus light really well. There are lenses are also a lot denser when you get to the inside of these lenses. It’s like a little rock. And ours is more like a little gummy bear or something like that. And so they’re able to do all the focusing just with the lens itself. And they don’t have to worry about the fact that their cornea is not doing anything. It’s tricky to make a lens that’s a ball and actually have it focus well. But they’ve evolved like some really clever sort of bio evolutionary engineering to make a lens that has just the right structure so that even though it’s a ball, it ends up creating a really clear image.
Krys Boyd [00:33:44] So on the one hand, the oceans are teeming with life, but that life is actually still spread out pretty far because as you mentioned, you know, there’s lots of depth to navigate and of course, a huge amount of area. What are the challenges of finding things to eat when anything you might want to eat not only might be far away, but keeps moving.
Sönke Johnsen [00:34:04] It’s a real challenge. I mean, what makes it worse is that everything in the ocean moves. I mean, you know, unlike on land where I mean, let’s say, you know, you want to go to a McDonald’s, you pretty much guarantee that the McDonald’s is, you know, always going to be in the same spot. Like, in my case, I know there’s a McDonald’s about 100 yards to my right. But in the ocean, everything is being moved around by the currents. And so you can’t even count on the fact that you know where things are. And things are, for the most part, really spread out. There are regions that are dense with life. Areas around the North and South Pole tend to be really dense with life. Certain fishing areas are really, really full of life and so on. But the tropical oceans, which are a really major part of the ocean, are pretty empty. And so it’s an enormous challenge and it’s a three dimensional challenge. I mean, you know, you can’t just like like we do run around in all directions and on a two dimensional earth surface and, you know, trying to find the things we want to find, we’d have to worry about going up or down by miles to find things. So it is very much not an easy problem and there’s just nothing there. No signposts. You know, there’s nothing you know, there’s no tree, there’s no mountain, You know, there’s no, you know, billboard. There’s just absolutely nothing to tell you where you are. I mean, it’s sort of like wherever you are, there you are.
Krys Boyd [00:35:25] Okay, So it’s hard to find things to eat. It’s also hard to find people to mate with. Right. People of your own kind if you don’t happen to travel in a school of some kind.
Sönke Johnsen [00:35:37] Yeah, that’s even worse because, you know, the number of species that, you know, you can successfully mate with is much, much smaller than the number that you could like, let’s say, enjoy eating. So, you know, you might chanced upon all sorts of different things eventually to eat. But the chance of finding an animal of your own species is really low. We know that some just sort of give up and they just release all of their reproductive cells, you know, their gametes into the water, you know, that release their sperm and their eggs in the water by sometimes by the billions or trillions. And in many cases, they’ll float up to the surface. And there’s some just some crazy number of these things all floating around. Try to find each other by the right species, like they’ve sort of passed on the problem to the to the gametes. It’s like, you know, I can’t find a mate, but maybe you can. So a lot of them do that, but a number of them do need to find each other. And we have videos of them having found each other and mating and so on. Like my sort of the thing that keeps me up at night is there’s a beautiful, transparent octopus that always swims to the water. It doesn’t go to the bottom. It just looks like a swimming chandelier. And we have videos of the mating. They need to be together. They wrap their arms around each other. It is very cute. And we have absolutely no idea how they managed to find each other because many of these animals are quite rare. The ocean is enormous and a lot of them are already heavily adapted to be invisible. You know, they’re trying so hard not to become someone’s, you know, dinner or lunch that it can be very hard to, you know, find a date, as it were.
Krys Boyd [00:37:17] What about animals that go to a specific place and mass to spawn? Like, how do you know who who gives the memo to be somewhere in the Sargasso Sea or on the coast of, you know, Florida or something? How do these animals know where to go?
Sönke Johnsen [00:37:31] My God. I mean, they do have some have navigational abilities. I mean, some of the best we know about are sea turtles. Sea turtles will actually use properties of the earth’s magnetic field to not only know where north is, but where they are in the ocean. It’s like a really crude GPS system. If you can sort of figure out how strong the magnetic field is and what direction it’s pointing and so on, you can get a decent sense of where you are. And so we know some are doing that. We know some are probably just being pushed around by currents and just end up in a certain place because that’s where everybody ends up. It is probably the greatest mystery of the ocean is figuring out how animals have any idea where they are inside it because there’s just almost no information, which is why people focus heavily on the magnetic field, because at least it is there. We know that there’s a lot going out there in the world, and so much of it is just completely mysterious to us.
Krys Boyd [00:38:29] So we know it’s hard to find things to eat, but it happens every day. What are some of the tricks animals use to avoid being spotted by other animals?
Sönke Johnsen [00:38:40] Pretty much every trick they can think of because unlike, you know, in our world, where if a predator shows up, we have a fair number of options. I mean, I’m thinking about this moment now. You know, if somebody let a cougar loose inside this building. There are any number of rooms I could run into and shut the door or I could duck under a table behind a chair. You know, I could, you know, if I was a fancier sort of animal, I could pretend to be a chair or something like that. But in the open ocean, there’s just nothing you can do. All you can do is either swim away, usually more slowly than your predator, which means they’re going to get you. You might have a poison that you can use, but not many of them have that. Or you can pretend that you don’t exist by looking like water, which is a challenge. And they do it in a couple of different ways. Some are transparent. That’s not uncommon. You see a lot of animals, like I talked about with that octopus that are just clear as glass. I mean, you can read a book through them. A number of animals hide themselves with mirrors, all those silvery fish you see, if you ever go, you know, to a harbor and see them, bring in the catch. Or if you just open a sardine can that so those silvery sides actually turn out to be extremely good camouflage in the ocean because in the ocean they just reflect more ocean and so they end up being good camouflage. Some worry a lot about their silhouettes because other animals swim below them and look up and to see if, you know, they make a silhouette. And so they have lots of little light organs on their bellies that light up to exactly match the light coming down even as quickly as clouds passing overhead and so on. And so they can hide themselves that way and be as if, like, you know, a 747 had a pile of lights, you know, underneath it. You could just turn it on and make itself disappear against the sky. So they use, you know, any number of tricks. Some use different coloration. Ones that are really, really deep will often be extremely black so that the animals with the flashlights can’t get any light reflected off of them. But pretty much anything that can be tried has been tried by those animals because it’s a fairly desperate situation.
Krys Boyd [00:40:48] Otherwise it would seem to me sanker that animals that generate their own light are just putting out a sign that says, Here I am, please eat me. But bioluminescence sometimes can function. What is a way to throw predators off people?
Sönke Johnsen [00:41:04] You know, when we say very often, you know, 80 to 90% of, you know, life in the ocean is bioluminescent. And people imagine that if you go down, it’s like this beautiful light show. And in fact, you see nothing if you go down in a submersible, which, you know, I have and some other people have. And you set the submersible so that it doesn’t move around and bother anyone. You know, you make it neutrally buoyant. You won’t see any light at all. I mean, you can sit there in the dark for half an hour and there’s just not a flash. And so they really don’t want to give themselves away. I mean, the flashlight fish are out there using their flashlights, but they’re probably turning them on and off pretty quickly. Some animals are down there using lures, and those are on Most of the time, though, they’re often pretty dim. But the rest are using bioluminescence, usually in a defensive way. So like if somebody attacks you, one defensive use is to put out a huge amount of light so that they’re startled or temporarily blinded. It’s not any different from shining a flashlight in somebody’s face If they attack you at night and then you run away. And a lot of times you only need to run away a few feet and then, you know, you’re sort of gone again. So they’ll do that or they’ll actually release body parts that are bioluminescent and then the animal will chase after the body parts and not them. Wow. And, you know, the main part of the. Yeah, that’s called a sacrificial tag. Some animals like we’ll just vomit. I mean, it’s not really vomit. My friend Steve Animal yelled at me for saying it’s vomit, but they’ll have two different glands on each side of their mouth that makes the chemicals for bioluminescence in the water. And so they create this incredibly brilliant cloud of swirling light in front of them, and then they can jump away from behind it. And either, you know, the animal will be so enamored of, you know, this blast of light and focus on that, or they’ll be so startled and disturbed by it that they’ll run away. The final trick, which is one that we as deep sea biologists argue about a lot, is that they might be putting out light to sort of label the attacker. So a number of animals have bioluminescent mucus. It’s almost like the purple paint, you know, explosives they put on like banknotes. You know, the robbers, you know. Yeah. The dye packs and boom, they go off and then you’re labeled. Except in this case, you know, it’s not a purple Dye says, blasting light. And the idea is, you know, if you pester me, you’re going to get covered with this bioluminescent mucus or I’ll just start flashing like crazy. And then somebody’s much worse than both of us is going to show up. And they’ll prefer you because you’re bigger and tastier than, you know, poor little old me. And then, you know, you again run off a few feet away and, you know, sort of watched. And that’s been known as the burglar alarm hypothesis for a long time. You know, you’re using the light to bring in an even higher level predator to take care of the animal that’s bothering you.
Krys Boyd [00:43:47] You tell us at the outset of this book that it’s not a work specifically about conservation, but I wonder how you think learning about ocean life forms might affect our interest in preserving them?
Sönke Johnsen [00:43:59] Well, I mean, in my view, we save what we love and we love what we see. And for people to feel something about, you know, let’s say a set of animals or a habitat or anything, really, they have to know about it. They have to know it’s there. They have to appreciate it. I often call that, you know, the flipper principle. Everybody became much more enamored of dolphins and worried about dolphins being caught in nets and, you know, even changing the name of what, you know, we used to call a dolphin, but it’s now called my my. You still say, you know, love dolphin for dinner. And, you know, we don’t do that anymore. And a lot of that, I think, came out of the Flipper show, you know, gave people this appreciation of dolphins. And so I’d say it’s sort of an indirect book about conservation in that it’s trying to get people to appreciate a world that they will probably never visit. You know, we go to the coast. We go to coral reefs, you know, sometimes to dive. But very, very few people are hundreds of miles away from land and jump into the water and see what’s actually there. And so my goal in writing this and the goal of other people who are enamored of this world is to show this world. I mean, in some ways it’s not so different than, you know, the Hubble Space Telescope showing us what’s out there in space, except we don’t have to worry about, you know, conservation of supernova or gaseous nebula because they’re safe from us. But in the case of the oceans, we very much have to worry about that.
Krys Boyd [00:45:27] Sönke Johnsen 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.” Sönke, this has been so interesting. Thank you for the conversation.
Sönke Johnsen [00:45:39] Of course. Thanks so much for talking to me.
Krys Boyd [00:45:41] Think is distributed by PRX, the public radio exchange. You can find us on Facebook and Instagram and wherever you get your podcasts. If you want to find our website. It’s think.kera.org. Again, I’m Krys Boyd. Thanks for listening. Have a great day.
