The Giants Lurking In The Deep Sea

The bathypelagic zone of the ocean is 1,000 to 4,000 meters below the surface. Sometimes it's called the midnight zone, because it's too deep for sunlight to reach. Most animals here are much smaller than their shallow-water counterparts. But occasionally, researchers find the rare deep sea giant: giant isopods, giant squids, colossal squids, sea spiders. While these giants sound like the subjects of some people's nightmares, deep sea biologist Craig McClain https://craigmcclain.com/ dreams about them. And today on the show, he helps unravel the mystery and research behind these creatures. SIGN UP https://www.npr.org/newsletter/sea-camp?utm_source=feeddescription FOR OUR SEA CAMP NEWSLETTER! WE WORKED SO HARD ON IT! Interested in more ocean mysteries? Let us know at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

  This message comes from Doppel. Social engineering attacks come in disguise, but Doppel sees through them. The Agentic platform shuts down threats, turns employees into first-line defenders, and more. Learn more at D-O-P-P-E-L dot com.

• 0:16Regina Barber?

  Before we start, I want to encourage you to sign up for our Sea Camp newsletter, where we go deeper with all the cool science we learn each week. There's extra research, animals, and even fun games. Sign up at npr.org/c camp.

• 0:29Speaker 02

  You're listening to Short Wave from NPR.

• 0:35Regina Barber?

  Hey, Short Wavers. Regina Barber here with another installment of Sea Camp, our special summer series all about the ocean and the depths within it. And this week, we're diving into the Ba'athi Pelagic Zone, which is 1,000 to 4,000 meters below the surface, also called the midnight zone because it's too deep for sunlight to reach.

• 0:56Speaker 00

  This is the first zone we get to from the surface that has no light.

• 0:59Regina Barber?

  That's Noel Bolin, Short Wave's go-to marine biologist at the National Oceanic and Atmospheric Administration. And she says sometimes this is where we hit the bottom.

• 1:09Speaker 00

  If we take all of the oceans around the world, 4,000 meters is the average depth.

• 1:14Regina Barber?

  Joining me for this journey to the midnight zone is producer Hannah Chin, who's going to tell us about the giants of the deep.

• 1:21Speaker 02

  Yeah, Gina.

• 1:22Regina Barber?

  I'm so excited.

• 1:23Speaker 02

  And just to start, these giants are famous, not only because, well, the deep ocean is a very dark and very hostile place, but because most animals get smaller, not larger, in these conditions.

• 1:36Speaker 03

  Overwhelmingly, most deep-sea animals are much smaller than their shallow-water counterparts. In fact, deep-sea miniaturization is by far the more normal thing, and gigantism is a very rare thing that occurs in the deep ocean.

• 1:51Speaker 02

  So this is Craig McLean. He's a professor at the University of Louisiana-Lafayette and a deep sea biologist.

• 1:57Speaker 03

  Examples of deep sea gigantism, of course, include like the giant isopod, giant squids, colossal squids. The other good example are what we call pyknegonids, which are sea spiders. Typically in shallow water, they're like the size of a quarter. But in the deep ocean, they can get up to the size of a dinner plate.

• 2:16Regina Barber?

  Oh, my gosh. That's so scary. Giant spiders. I do like the name pyknegonids, though.

• 2:21Speaker 02

  Craig loves them. He told me, for as long as he can remember, he's been fascinated by giant things.

• 2:28Speaker 03

  My entire life, even as a kid, like been really, really fascinated by like roadside attractions. The world's largest ball of yarn, the world's largest rocking chair. And in fact, if you go to like my Instagram or my like Blue Sky accounts, you'll find this whole hashtag called Craig with big things. And it's just like pictures of me over and over and over again with giant versions of things, like the world's largest fire hydrant, et cetera, et cetera.

• 2:51Speaker 02

  Now, this is what Craig specializes in. The bulk of his work on deep sea organisms really focuses on these organisms' body size. So he studies everything from small animals to big animals to really big animals. He told me it's really fascinating because these creatures are so rare. They're so hard to find and they're so mysterious.

• 3:12Speaker 03

  We really don't know why deep sea gigantism occurs. And then there's a bunch of like running ideas, but in actuality, we don't know.

• 3:21Regina Barber?

  So today on the show, how scientists are trying to unravel the mystery of deep sea size.

• 3:28Regina Barber?

  What makes the giant sea spider so giant and the colossal squid so colossal?

• 3:35Speaker 02

  What do biologists think? How do they even study those theories? And what would it take to know for sure?

• 3:41Regina Barber?

  You're listening to Short Wave, the science podcast from NPR.

• 4:00Speaker 04

  Stay tuned for the following announcements and messages from our sponsors.

• 4:04Speaker 00

  This message comes from ProLon with their five-day fasting mimicking diet, a clinically-developed nutrition program with the goal of promoting fat loss while protecting lean body mass. Learn more at prolonlife.com/NPR.

• 4:17Speaker 04

  This message comes from 80,000 Hours. You want your work to pay the bills. You'd also like it to do some good. How do you find a career that does both? 80,000 Hours is a nonprofit with 15 years of research into fulfilling careers that make a difference. Their research, job board, and one-on-one advice are all free. Start with their career guide, free when you sign up for their newsletter at 80000hours.org/NPR.

• 4:44Speaker 00

  This message comes from Subaru. Discover the 2027 Subaru Crosstrek Hybrid. With up to 630 miles per tank, this Subaru Crosstrek Hybrid delivers up to 50% better city MPG, along with increased horsepower, with standard symmetrical all-wheel drive and 8.7 inches of ground clearance. Equipped with a standard 11.6-inch multimedia navigation system touchscreen, it keeps your trip on track. Their most fuel-efficient, lowest-emission Subaru Crosstrek. Adventure on the edge.

• 5:15Regina Barber?

  OK, producer Hannah Chen, we're here to investigate the mystery of the deep-sea giants. Like, where are we even going to start?

• 5:22Speaker 02

  So there are multiple theories, and I promise we'll get to all of them. But the first one starts on land with one of your favorite things, Gina. Can you guess what it is?

• 5:31Regina Barber?

  Uh, robots? Food? Batman? Movies?

• 5:36Speaker 02

  Movies, yes. Movies. And the early days of Hollywood.

• 5:39Regina Barber?

  Ooh.

• 5:40Speaker 02

  In the heyday of Western silent movies.

• 5:43Speaker 03

  Hollywood was filming a lot of Westerns out in the Channel Islands because they had this rough landscape. And so to have like a more authentic filming environment, they introduced Bison out to the Channel Islands.

• 5:54Regina Barber?

  What?

• 5:55Speaker 02

  So these movie crews bring in Bison. They film on Catalina Island, which is one of the Channel Islands. It's off the coast of Southern California, so real close to Hollywood.

• 6:03Regina Barber?

  Yeah.

• 6:03Speaker 02

  And then when they're done filming... They just kind of leave the bison there.

• 6:08Regina Barber?

  Wait, so what happens to the bison?

• 6:10Speaker 02

  So bison aren't native to Catalina Island, right?

• 6:13Regina Barber?

  No, they are not.

• 6:14Speaker 02

  But they do OK. They don't die out. Instead, they form a herd. Over the years, they've become this tourist attraction. And they all get notably smaller.

• 6:24Regina Barber?

  What? They get smaller?

• 6:25Speaker 02

  Yeah. And Gina, it isn't just them. Craig told me this type of thing is very common.

• 6:31Speaker 03

  The body size of animals on islands is wonky, for lack of a better term. Like, it's really, it's like, very noticeably off. And the tendency is, is that animals that are small on the mainland, on islands, get bigger. And things that are big on the mainland get smaller on islands.

• 6:47Regina Barber?

  Wow. I love this. I love that it's true, but why would this pattern exist?

• 6:52Speaker 02

  Well, a lot of it has to do with lack of food.

• 6:55Regina Barber?

  OK.

• 6:55Speaker 02

  Like, obviously, some islands are tropical, but a lot of them are not particularly green or lush environments. They're not built to sustain a lot of life. So if you're a small animal on the mainland, you might evolve to be bigger because it'll help you roam the entire island and really make the most of the territory that's available to you.

• 7:15Speaker 03

  And then, conversely, like, if you're a very big animal on the mainland and, you know, you colonize an island, then there's this pressure for you to become smaller because the island can't meet all your food needs.

• 7:25Regina Barber?

  OK, this does make a lot of sense, but this is happening on land. This is the story you're telling me. And maybe you're going to tell me this is happening in the ocean, too?

• 7:34Speaker 02

  Yes.

• 7:35Regina Barber?

  OK.

• 7:35Speaker 02

  So Craig published a whole paper on this. He plotted a bunch of data on body size and ocean depth. And he and his colleague started to notice this pattern that looked really similar to what was happening on the island. Basically, in the deep sea, smaller animals were getting bigger, and bigger ones were getting smaller.

• 7:55Speaker 03

  And so we hypothesized at this time that the reason why we see these patterns on islands and in the deep sea is because they're constrained by the same thing, which is lower food availability.

• 8:04Speaker 02

  And this would make sense, right? Because there's no plant life in the deep sea. There's very little prey availability. All of these animals are like scavengers. So they have to be big enough to travel far enough to scavenge for food.

• 8:16Regina Barber?

  Right, because they're like reliant on the food that's produced on the surface. Like whether it's plankton or even like giant whales. Like that stuff is dying and then falling to the ocean floor.

• 8:27Speaker 02

  Yeah, exactly.

• 8:27Regina Barber?

  Okay.

• 8:28Speaker 02

  And we should say there are hydrothermal vents and methane seeps, which produce a lot of nutrients and kind of foster their own thriving ecosystems.

• 8:36Regina Barber?

  These are my favorite.

• 8:37Speaker 02

  I know, and they may be the focus of an upcoming Sea Camp episode. But Gina, those are like the equivalent of oases in the desert. They're relatively few and far between.

• 8:47Regina Barber?

  Got it. So is this island theory like the best explanation of why some animals in the ocean are bigger and some are smaller? It feels like this might not account for all the animals we're talking about here.

• 8:58Speaker 02

  Yeah, that's a good point. And there are other theories. One is called Bergman's Rule. It's the idea that size increases when temperature decreases.

• 9:06Regina Barber?

  Okay, so that would mean like animals are getting bigger when it's cold.

• 9:09Speaker 02

  Yes, because colder temperatures slow metabolism and other life processes. They allow animals to live longer and thus become bigger.

• 9:19Speaker 03

  Colder temperatures sort of slow growth rates, increase lifespans. We know that that is true. We have lots of data to show that that happens in the deep sea and it's temperature related.

• 9:32Speaker 03

  But the issue with that is that once you reach about like 600 meters or so in depth, the oceans are largely about four degrees Celsius. So temperature doesn't change after that. But in most groups, size continues to change after that.

• 9:51Regina Barber?

  So there's like a lower limit to the temperature of the ocean. But we continue to see like the size variation even after like reaching that lower limit.

• 9:59Speaker 02

  Yeah, that's what he's saying.

• 10:00Regina Barber?

  OK.

• 10:01Speaker 02

  And there's also another theory. It's called the oxygen temperature hypothesis. It combines the fact that low temperatures slow metabolism with the fact that colder water can hold more oxygen, right?

• 10:11Regina Barber?

  Oh, OK.

• 10:12Speaker 02

  And it suggests that because there's more oxygen available, those animals have a larger maximum size than they would in warmer and less oxygen-rich waters.

• 10:22Regina Barber?

  Huh.

• 10:22Speaker 02

  Again, that's still being studied. Scientists have different ideas about how it works, depending on who you talk to, and we don't understand it completely. So just another theory.

• 10:32Regina Barber?

  So which of these theories is kind of like winning this race? Like, what's the solution to this like deep-sea gigantism mystery?

• 10:39Speaker 02

  Craig says, we don't know yet, right? It could be one of these theories. It could be a combination of them. Like, the giant isopod might be giant for a different evolutionary reason than the colossal squid or the sea spider.

• 10:51Regina Barber?

  Right.

• 10:51Speaker 02

  And the reality is also that we may never know for sure, because our knowledge of these animals is still so limited.

• 10:58Speaker 03

  We can kind of come up with stories or sort of what we call post hoc explanations to explain things, but actually testing those may just not be possible.

• 11:10Speaker 02

  So that said, one key thing that scientists are trying to do is collect more data. So this summer, Craig and several of his colleagues launched the Marine Organismal Body Size Database. It's an online compilation of body size data for over 85,000 marine species, as tiny as a sea slug or as huge as a whale shark. And their goal is eventually to have information about size ranges for all the half million animals we know of in the ocean.

• 11:36Regina Barber?

  Wow. That's really cool.

• 11:39Speaker 02

  You're right.

• 11:39Regina Barber?

  OK, Han, I do have one lingering question, though.

• 11:42Speaker 02

  Yeah.

• 11:42Regina Barber?

  Like, you mentioned that temperatures could have something to do with like why animals have the body sizes they do, but I'm wondering, like, what does that mean? In a changing climate because the deep sea ocean is probably like slowly going to get warmer.

• 11:55Speaker 02

  Yes, it is. So I talked to Camilo Mora about this. He's a researcher in the Department of Geography and Environment at the University of Hawaii. And he's also part of a team of scientists that published research almost 10 years ago, indicating that, yes, the deep sea would be impacted significantly by climate change.

• 12:13Speaker 05

  Unfortunately, the deepest part of the oceans are probably going to be affected, if not as much, probably even higher than what we have seen in the upper surface.

• 12:23Speaker 02

  And their projections indicate that the bathypalagic zone's temperature could increase by 1 degree Celsius or 2.5 degrees Fahrenheit before the end of the century. Even though that doesn't necessarily sound like a lot, Camilo said it could have really disastrous impacts.

• 12:39Speaker 05

  The species that are living on the deepest part of the ocean, they are used to stability. The temperature changes are very small. They might not even have seasons as strong as you see then on the upper part of the ocean. So these species have lived and adapted to survive in environments that are not used to change.

• 12:58Speaker 05

  So when you change the conditions for just a tiny bit, that could be enough for you to wipe out a lot of species down there.

• 13:07Speaker 02

  And again, Gina, this is still an active area of debate. Some scientists have suggested that these deep sea animals will adjust. They'll become smaller again. They'll adapt in reverse to these shifting conditions. But others don't think that'll happen. Climate change is just happening too quickly for animals to keep up. And Craig says that as the oceans warm up, they're also going to produce less carbon.

• 13:32Speaker 03

  And so that means that the deep sea is actually going to get less food. And so for a system that is already very food limited, they may be at the edge of what they can actually survive at.

• 13:43Speaker 02

  Which is why both Camilo and Craig told me it's really important to study these deep sea animals now because they're already so rare. And if climate change continues at its current rate, they're going to become even rarer.

• 13:56Regina Barber?

  Or if it's possible to slow climate change and buy these like giant sea creatures more time, maybe, you know, scientists will be able to study them. That would be great, too.

• 14:07Speaker 02

  That would be wonderful.

• 14:08Regina Barber?

  Thanks for bringing us this reporting hand.

• 14:10Speaker 02

  No problem, Gina. Thank you for having me.

• 14:16Regina Barber?

  This episode was produced by Hannah Chin and Rachel Carlson. It was edited by Brody McCoy and our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Jimmy Keeley was the audio engineer.

• 14:26Speaker 02

  Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Hannah Chin.

• 14:32Regina Barber?

  And I'm Regina Barber. Thank you for listening to Short Wave from NPR.

• 14:50Speaker 00

  Stay tuned for the following announcements and messages from our sponsors.