10:56am

Thu April 7, 2011
Animals

Under The Sea, Sex Is Slimy Business

Originally published on Wed May 23, 2012 12:01 pm

Never threaten a hagfish. And if you do, watch out.

"When it's threatened or in danger or gets injured, it produces — very quickly — huge amounts of slime," says Ellen Prager, a marine scientist and educator. "In fact, they found that in just a few minutes, it can fill up seven buckets full of gooey, slimy gunk."

The hagfish isn't the only underwater inhabitant with unusual tactics for survival. In Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter, Prager describes some of the craziest underwater activities that help ocean creatures stay alive, fight predators, find food and reproduce.

Consider The Lobster

There are more than 100 species of lobsters in the ocean, but the one Americans are probably most familiar with is the Maine lobster, a wide-clawed nocturnal creature with a propensity for urinating on potential mates.

"The male lobsters use [urine] aggressively, but the female lobsters shoot it as a Love Potion No. 9," says Prager. "She shoots when she comes up to a den that might have a male in it. She actually seduces him with her pee and instead of clobbering her over the head with his claw, he says, 'Come in, come in' and gets all touchy-feely."

But before the female and male lobsters mate, the female sheds her shell.

"For the female lobster's private parts to become available, she has to molt," says Prager. "And then she becomes acceptable to the male."

Dominant males are routinely seduced into one-off sexual encounters while female lobsters are generally more choosy, says Prager. Females can store a male's sperm for up to three years, using it to fertilize several batches of eggs.

Coral Reefs: The More, The Merrier

Prager has a unique view of marine life because she used to be the chief scientist at an underwater research lab in the Florida Keys. The lab, which sits underneath 60 feet of water, allows scientists to spend hours underwater studying the ocean without worrying about decompression.

The warm and relatively shallow water provided a fertile ground for reef-building corals. The organism, which looks like rock, is considered an animal, plant and mineral. It also provides food and shelter for other marine life and can develop into some of the biggest biologic structures on the planet, says Prager. And just how do they build those structures?

Most coral reefs are what scientists refer to as "broadcasters." That means they release either eggs or sperm into the water, where they float to the surface, mix and become fertilized.

"So if you're a coral and you want to mix your eggs with the sperm of another coral of your species, [you must] release [them] at the same time," says Prager. "So coral reefs spawn synchronously throughout the world. All those corals release their eggs and sperm at the same time."

Prager says she's witnessed the synchronized release of eggs and sperm while on night dives.

"It looks like an undersea snowstorm," she says. "The eggs look like little tiny pink balls and they all start floating up. And coral spawn is yummy fish food so worms and other things come to feed on it. It really [makes you think about] how active the ocean is."

Like the hagfish, corals also emit a mucuslike slime — dubbed "coral snot" — when disturbed.

"I will tell you from experience that if you disturb corals through something like drilling, [they] start to exude huge quantities of slime," she says. "You come up just covered in the stuff."

Ellen Prager has written several books about underwater life, including Chasing Science at Sea: Racing Hurricanes, Stalking Sharks and Living Undersea with Ocean Experts and Volcano: Iceland's Inferno and Earth's Most Active Volcanoes. She has worked at the Sea Education Association in Woods Hole, Mass., the University of Miami's Rosenstiel School of Marine and Atmospheric Science, and the National Undersea Research Center in the Bahamas. Prager has a Ph.D. from Louisiana State University and was chairwoman of the Ocean Research and Resources Advisory Panel for the U.S. government.


Interview Highlights

On the volcanic sexual activity of sea sponges

"A lot of the sponges release their sperm into the water. Other sponges will basically suck in that sperm and fertilize their egg. It looks like smoke coming out of the sponges and you look at it and go, 'What the heck is going on?' and they're broadcasting sponge sperm."

On the transgendered parrotfish

"If you have a harem of parrotfish — a group of female parrotfish, let's say — and it has one dominant male. Something happens to the dominant male and it dies. Amazingly, within several weeks, one of those females can change to a male. And, in fact, some of them change to what we call supermales — [and] become big and extremely colorful and aggressive. They then become the dominant male of the other female parrotfish in the harem. I like to say, 'It's not only transgender. It's transgender on-call.' "

On the well-endowed conch

"Turns out that in the conch, they call the penis its verge. The verge has been the thing of limericks and poems. The biologists know all about this. Not only is it exceptionally long, but because the queen conch is this really big snail, the male sidles up to a female on the seafloor and he has to get his verge outside of his shell and around and underneath the female shell. So that's why it's so long. But there's a little problem: When it's outside of his shell, crabs and eels are all too happy to take advantage of his vulnerabilities. Yum, yum, yum. Well, poor conch. But turns out, he loses one [and] he just grows another. He can regenerate his penis."

On why scientists are interested in kissing anglerfish

"The females are small, soft and they swim around trying to catch food. The males are dwarfs and their entire goal in life is to find a female. They swim around looking for the females. When they find them, I call it the 'never-ending kiss.' They bite into them and their lips get fused to the female and they end up living as a parasite on the female providing sperm. Scientists are really interesting in the immune system of anglerfish because the female's body doesn't reject the male."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

TERRY GROSS, host:

This is FRESH AIR. I'm Terry Gross.

If humans were mating the way that some sea creatures do, it would be considered mighty kinky. My guest, Ellen Prager, says she didn't realize the extent of the strange sex going on in the oceans until she started researching her new book. It's called "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter."

And as we'll hear, the odd creatures she writes about, creatures most of us never heard of, are beneficial to humans in ways most of us don't realize. Prager has spent short intervals living underwater. She's the former chief scientist at the world's only undersea research station, Aquarius Reef Base, in the Florida Keys.

Dr. Ellen Prager, welcome to FRESH AIR. The title of your book is "Sex, Drugs, and Sea Slime." Sex, okay. I figured, you know, all species have to reproduce. Drugs, we're getting some drugs now from ocean creatures. Sea slime. Why did you want to...

(Soundbite of laughter)

GROSS: Why did you want to emphasize sea slime?

Dr. ELLEN PRAGER (Author): Well, the truth is, the original title for this book was something like "Weird and Wild Under the Sea and Why These Creatures Matter." But as I started doing my research, I discovered some themes that were quite intriguing, not just there's reproduction going on in the ocean, but there's a lot of strange sex strategies going on in the ocean.

And as you mentioned, not only are we searching for new drugs through marine organisms, but also there's a huge number and diverse kinds of animals that are being used as models in biomedical research. And the other thing is, I could not believe, even though I knew a lot, how many organisms are either made up of slime or use slime. And so it was kind of startling.

GROSS: Let's take an example of the hagfish, a lovely name.

Dr. PRAGER: Oh, fantastic.

(Soundbite of laughter)

GROSS: Describe the hagfish and how it uses slime.

Dr. PRAGER: Well, the hagfish, when it's threatened or in danger or gets injured, it produces, very quickly, huge amounts of slime. In fact, they found that in just a few minutes it can fill up seven buckets full of gooey, slimy gunk.

GROSS: And what's the point of it?

Dr. PRAGER: Well, imagine if something comes to attack you, and you can, you know, throw globs of slime at it. It might go away. So it's basically either used as a decoy or to scare off creatures.

But there's a little problem with the hagfish. It can get trapped in its own slime. So it's had to evolve ways to prevent a very unpleasant death, which is, you know, death by goo.

So it actually will sneeze its own slime out its nose, or amazingly it will wrap its tail around its body and slide it up. They kind of look like eels. It will slide it up just to de-slime itself.

GROSS: Do most of the fish that create slime use the slime as a defense mechanism?

Dr. PRAGER: Some do. Others use it in a really wide variety of ways. Some use it to sort of slicken their path and travels. Some use it for protection. One really cool example is that in the tropics, some species of parrotfish will sleep at night in the reef and they will spin a cocoon of mucus as sort of a protective blanket so that things can't smell them or detect that they're there sleeping.

There's a really amazing sort of swimming snail that creates a parachute, almost, of or a bubble of mucus, and that's what uses sort of like a net to capture food particles, and then it slurps it in to eat. So there's really a wide variety of uses of slime in the sea.

GROSS: Let's get to sex. I have to say, I was so surprised hearing about lobster sex.

(Soundbite of laughter)

GROSS: You have to describe it. It's really interesting.

Dr. PRAGER: Well, it turns out lobsters have super-soaker blasters in their head that they basically use to shoot pee. The male lobsters use it aggressively. They sort of get pissed off when they fight. But the female lobsters shoot it as a - like a Love Potion Number 9.

And she shoots - when she comes up to a den that might have a male in it, she actually sort of soaks it, seduces him with her pee, and instead of clobbering her over the head with his claw, he says: Come in, come in, and gets all touchy-feely.

GROSS: But then the female lobster actually molts before sex. She sheds her shell.

Dr. PRAGER: Well, all crustaceans molt. They molt basically to get bigger. That's how they grow, because their shells are rigid, and so if they want to get bigger, they can't just grow linearly. They actually have to shed their shell and grow another one.

For the female lobster's private parts to become, shall we say, available, she has to molt. So she has to get rid of her shell. And then she becomes, you know, acceptable to the male.

GROSS: Well, she's pretty vulnerable without a shell.

Dr. PRAGER: She is, and in fact she will stay in a male's lair for several days just recuperating from that molt because she's very vulnerable and she can't really feed or hunt without, you know, hard shells and hard walking legs or feeding parts.

GROSS: If you're just joining us, my guest is Dr. Ellen Prager. She's the former chief scientist at the world's only undersea research station, the Aquarius Reef Base in the Florida Keys, and she's the author of the new book "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter."

So one of the chapters in your book is about coral reefs, which are amazing ecosystems that illustrate all the themes in your book, the sex, drugs and sea slime.

And you had a unique view of coral reefs when you worked as the chief scientist at the underwater research lab, the Aquarius Reef, based in the Florida Keys. Would you describe the lab and where it was?

Dr. PRAGER: Well, the lab is actually the world's only operating undersea research station. And it sits in about 60 feet of water, just about four miles offshore of Key Largo in the Florida Keys. And it's a place where scientists can go and live for one to two weeks to study coral reefs.

We also, surprisingly, get astronauts coming to live there because it's the closest thing to living in space, is living underwater. And the Navy also trains divers.

But the real advantage here is that when you're diving from the surface, you only have a couple hours at the most underwater to do your research. If you're diving to 60 feet, you might have an hour at a time and maybe one or two hours a day.

But if you live underwater, you actually have six to nine hours a day diving to do your work. And then you have to...

GROSS: Why is that?

Dr. PRAGER: Well, because of decompression issues. You just stay down. You don't worry about decompression until the end of a mission. So let's say you stay down for two weeks. You don't worry about decompression. The 60 feet or 50 feet where the habitat, sort of the living space is, becomes your surface.

And so until you're ready to come all the way back up, you don't have to worry about decompression, which you do at the end, and you have to go through 17 hours.

GROSS: Would you describe what the lab looked like and what your view of the coral reef and the rest of the ocean was?

Dr. PRAGER: It kind of looks like a cylindrical, extended underwater mobile home. It's kind of a big cylinder that sits on legs that sit down in the sand, and it's pretty tight. It houses six people at a time, but they're close, not a lot of privacy.

You've got sort of a big main area that has a lot of controls for life support and communications. But you have a little kitchenette and a table. I mean, there's a bunk room.

And outside it has very - fairly large view ports, and one of the really special things about living underwater is you feel like you're part of the coral reef. You don't feel like you're just a temporary visitor.

So one of my favorite times is when the coral reef goes from night to day. And so you get to watch the water go from black to royal blue and shafts of sunlight flickering. And the fish that are nocturnal, you get to see them coming back to the habitat, where they may spend their days, and it's kind of like shift workers changing on the reef.

So you get to see things that you typically don't see if you're just spending, you know, an hour diving from the surface.

GROSS: So enough sunlight penetrates down to 60 feet so that you can actually see during the daytime?

Dr. PRAGER: Oh, definitely. It's quite light. But I will tell you, there is weather underwater just like there is above on the surface. Cloudy days are darker. Windy days, when there's waves, you can feel the pressure change as the waves go by you.

So you know, some days are better than others. Some day - you also have changes in visibility. But it is plenty light at 60 feet, even down to 100 feet.

GROSS: Now, why are coral reefs so important as ecosystems?

Dr. PRAGER: Well, coral reefs provide sort of the habitat for an amazing diversity of life, from small microbes to the fish to the worms to the algae. It's like if you were to look at a city, it would be the condos of a metropolis.

And within that then you get food for those creatures. You get protection -very, very important. And so you have one of the richest places for life in the sea.

GROSS: So let's skip ahead to, literally, the sexy stuff.

(Soundbite of laughter)

GROSS: Let's talk more about the reef. You describe coral reefs as having group sex. What does that mean?

Dr. PRAGER: There's an awful lot of this going on under the ocean. But for corals, some corals, the majority, in fact, are what we call broadcasters. They release eggs and sperm into the water, they float to the surface, they mix and get fertilized.

Well, if you're a coral, and you want to mix your eggs with the sperm of another coral of your species, guess what? They'd better be released at the same time. Otherwise that's not going to happen. So coral reefs release, or they spawn, synchronously throughout the world at different times, depending on where you are, but all those corals release their eggs and sperm at the same time.

And it's kind of a mystery. We don't really know how they all know to do that. You know, there's no enticing mating dance or, you know, enticing language going on. We think it has something to do with the season, the temperature. It's usually around a full moon.

There may be chemical cues. You know, maybe one starts releasing and there may be chemical cues for the other. It's a very interesting process.

GROSS: So what does it look like?

Dr. PRAGER: You know, it's kind of like an undersea snow storm, because the eggs look like little tiny, often pink balls, and they all start floating up. And then the other thing that happens is that coral spawn is yummy fish food. So worms and other things come to feed on it. So you also can get a sort of feeding frenzy in the water at the time.

GROSS: So you know, the title of your new book is "Sex, Drugs and Sea Slime." We talked a little bit about group sex on a coral reef. Let's get to the sea slime. What's one of the creatures on the reef that use slime, that secrete slime?

Dr. PRAGER: Well, interestingly enough, corals are also friends of the slime. They actually have a coating of mucus over their top surface, that when particulate matter and things land on it, they just exude more, and it sloughs off particles so that they don't get smothered.

There's also research that suggests bacteria in that mucus or slime is a very important mechanism for protecting the coral from disease. Some corals use their slime to capture particles that they may eat.

And I will tell you from experience that if you disturb corals through something like drilling - one time we were taking a coral when I worked for the U.S. Geological Survey, and we were drilling coral cores, and the corals start to exude huge quantities of slime. And you come up just covered in the stuff. And we like to call it sort of - because it comes out kind of - you see it sort of stringing off the corals. We like to call it coral snot.

(Soundbite of laughter)

Dr. PRAGER: It's really disgusting.

GROSS: And is the purpose of that to try to keep you away?

Dr. PRAGER: That's right. It's a protective response to disturbance.

GROSS: And corals have other ways of protecting themselves. You describe these, like, tentacles that corals have.

Dr. PRAGER: They do. They have - actually have a couple ways of protecting themselves that most people don't know. It's really interesting.

You know, on the reef, space is very limited. And they have to protect themselves from things growing over them or, you know, growing next to them and trying to attach to them.

So they can do two things. They have these filaments that they extend from their stomachs, actually, and they attack the invaders with digestive enzymes from their stomach, and they eat away at the invaders, which is really kind of strange. And some corals are pretty aggressive with what we call the mesenterial filaments.

Corals also have extremely long tentacles, more than their sort of regular tentacles that we call sweeper tentacles, and they kind of go out at night and protect the perimeter, you know, sort of act like guards at night so nothing can try to overgrow them or come too close.

GROSS: My guest, if you're just joining us, is Dr. Ellen Prager. Her new book is called "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter." We're going to take a short break here, and then we're going to talk some more. This is FRESH AIR.

(Soundbite of music)

GROSS: If you're just joining us, my guest is Ellen Prager, author of "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter."

We're going to be talking about the mating habits of these odd creatures. So parents, if you haven't yet told your children about the birds and the bees, they may not be ready to hear what the ocean's oddest creatures are up to.

Now, there's a lot of unusual creatures living on coral reefs, including sponges, and you say sponges are stunning to look at.

Dr. PRAGER: Sponges are some of the most beautiful creatures on the reef. They come in the most amazing shades of color.

There's this one sponge called a - it's a vase(ph) sponge, and it almost looks crystalline, kind of a bluish purple, it has very delicate ridges, and sometimes if the sunlight hits it, it almost seems iridescent, really spectacular.

There may be bright red sponges, yellow sponges, purples sponges. The colors are just amazing.

GROSS: And what do the sponges do? Do they move?

Dr. PRAGER: Well, they look like they're just sort of sitting there, but it turns our sponges are very active organisms. They pump water through holes in their body. Essentially, it pulls the water in through the holes, and then they take out oxygen and food particles. They filter it, and then they release the seawater back into the ocean.

And they're continually pumping. And I will tell you, some researchers that I know discovered that a very large barrel sponge, they can actually pump as much as the volume in an Olympic-size swimming pool in one day.

GROSS: Wow, and what function does that have within the ecosystem of the coral reef?

Dr. PRAGER: That's a great question. We don't really know. And that's actually - there's one group of researchers from the University of North Carolina, Chapel Hill - that's exactly what they're studying because if these sponges can pump so much, they must have an impact on the chemistry of the water on the coral reef, and that's one of the things we're trying to understand right now, as coral reefs change around the world.

In the Florida Keys, it appears that we may be seeing more sponges growing on the reefs, rather than corals. And so obviously that's going to change the chemistry of the water. So that's a really big question right now.

GROSS: Now, you say sponges are stunning, but sometimes they erupt like volcanoes.

Dr. PRAGER: Remember how I said the corals were broadcasters? A lot of the sponges are broadcasters too, in that they will release their sperm into the water and other sponges will basically suck in that sperm and fertilize their eggs.

So it looks like smoke coming out of the sponges, and you kind of look and you go: What the heck is going on? They're broadcasting sponge sperm.

GROSS: So you talked about how colorful sponges were. Do the colors serve a function?

Dr. PRAGER: You know, I'm not sure. The very bright coloration in many things underwater we think is a warning sign to other animals not to eat them. So the sponges often have spicules of silica in them, and some of them can secrete acid. And so they're not - for many organisms, they're not something that they want to eat.

They also - because they don't move, their defense is chemical, and it's also why sponges are one of the most important animals in drug development, in looking for new drugs, because they're attached to the sea floor.

They don't have sharp teeth. They can't run away. They can't swim. So the only way they can defend themselves against predators is mainly chemicals. And so scientists have been looking at sponges to see if those chemicals can be used as pharmaceuticals.

And I will tell you that there are anti-cancer drugs in development, some already on the market, that are derived from research on marine sponges.

GROSS: One of the unusual creatures living on coral reefs is the parrotfish, which you describe as transgendered. What makes the parrotfish transgendered?

Dr. PRAGER: Again, this is just - you know, amazing things going on down there. So if you have a harem of parrotfish - so let's say you have a group of female parrotfish, and it has one dominant male, something happens to the dominant male, it dies.

Amazingly, within several weeks one of those females can change to a male. And in fact, some of them change to what we call super males, become big and extremely colorful and aggressive. And so they then become the dominant male of the other female parrotfish in the harem. So I like to say: It's not only transgender, it's transgender on call.

(Soundbite of laughter)

GROSS: What's the difference between the male and the female parrotfish?

Dr. PRAGER: Well, we think that change happens by hormones. I should say one other interesting thing is once you go from female to male, it's irreversible, you can't go back. But we think hormone drives that change. And obviously as a male you develop different body parts, and you can produce sperm, whereas obviously the females can produce eggs.

GROSS: One of the things I took away from your book is how creative sea creatures are in reproducing, I mean how creatively designed they are.

Dr. PRAGER: They are. And I have to tell you, one of my favorite stories from the book comes from Al Stoner(ph), who is a conch biologist, kind of serious guy.

But I sent him an email. I said: Hey, you know, Al, you got any really great stories about queen conch? Which I knew he'd been studying for years. And he sends me back an email that says: There's a real advantage to studying the reproductive biology of an organism that is big, slow, mates for hours on end, and has a penis half its total body length. I couldn't believe it.

(Soundbite of laughter)

Dr. PRAGER: So I started doing a little bit of research, and it turns out in the conch they call the penis its verge. The verge has been the thing of limericks and poems. The biologists know all about this.

And not only is it exceptionally long, but because the queen conch is this really big snail - you know, most people have seen their shells - the male sidles up to a female on the sea floor and he has to get his verge outside of his shell and around and under the female, so that's why it's so long.

But there's a little problem: When it's outside of his shell, crabs and eels are all too happy to take advantage of his vulnerabilities. Yum, yum, yum. Well, poor conch. But turns out he loses one, he just grows another.

GROSS: Wow, talk about adaptability.

Dr. PRAGER: Exactly. So talk about really strange things. I was fascinated. It was amazing.

GROSS: Ellen Prager will be back in the second half of the show. Her new book is called "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter." I'm Terry Gross, and this is FRESH AIR.

(Soundbite of music)

GROSS: This is FRESH AIR. I'm Terry Gross, back with Ellen Prager, the former chief scientist at the world's only undersea research station, Aquarius Reef Base, in the Florida Keys. She's the author of the new book "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter."

We have a slideshow of some of these odd creatures on our website, freshair.npr.org, so you might want to take a look as you listen.

So, you know, we've talked about - your book is called "Sex, Drugs, and Sea Slime." We've talked about sex and sea slime with sea creatures. Let's talk about drugs. And you say, for instance, that the coral reefs are being considered now like the rain forest of drugs. You know, a lot of the drugs that we use or the things that drugs are based on come from ingredients in the rain forest ecosystem, and now that's true of coral reefs, too. Give me some examples.

Dr. PRAGER: Well, I think one of my favorite examples is an organism that is found in places other than reefs, but mainly in coral reefs, and it's called the cone snail. The cone snail is an amazing - it's just an amazing creature. They, you know, are just like snails. They are slow moving on the bottom, but they have evolved amazing weaponry. They actually have harpoon-like teeth that are on a tether, and they have venoms. And not only do different species have different venoms, one individual cone snail can switch its venom between strikes. And here's the slow-moving snail, some of them eat fish. So they have to have very strong venoms.

Turns out that scientists think the cone snail, more than any other animal in nature, has potential for pharmaceuticals. And, in fact, there's a new drug, non-opiate painkiller on the market called Prialt that comes from the cone snail. And the beauty of this is people who are allergic or get addicted to opiate-derived painkillers can now use this Prialt, which comes from the common snail.

GROSS: So this is on the market already?

Dr. PRAGER: It is on the market already.

GROSS: And what kind of pain is it used for?

Dr. PRAGER: The same kinds of things that morphine would be used for.

GROSS: Hm.

Dr. PRAGER: And they're also looking at it - other uses or other venoms, as well as Prialt - to combat inflammation associated with other diseases, a wide range of applications in medicine.

GROSS: Is it mostly the venoms that are being used for medicine?

Dr. PRAGER: In terms of the cone snail, yes. Because, you know, they are very selective. They're diverse, and they can target specific cells processes. And so that's of great interest to scientists and people who are looking for new drugs to fight things like cancer and inflammation and diseases. But I will tell you that only a few of the venoms from the cone snail have been studied in any detail, and so people think that there's just huge potential for these one organisms.

The other one is the sponges. The sponges have already produced several drugs that are on the market. Many are now in development. And, in fact, AZT, which is used in HIV, was developed based on compounds found in the marine sponges.

GROSS: You know, it wouldn't have been very long ago that we would've thought of sea sponges as, well, they're odd and they're beautiful, but they're maybe not of any use to us. And now you're mentioning these drugs that are coming from them, and they actually have life-saving value to us now.

Dr. PRAGER: I mean, even the most bizarre creatures, and I give you - this one is really crazy. So, in the deep sea, there's something called an anglerfish -a deep sea anglerfish. And the females, you know, they're kind of small, soft and they swim around, trying to catch food. The males are dwarfs, and they're tiny little males, and their whole goal in life is to find a female. They swim around looking for the females. When they find them - I call it the never ending kiss. They bite into them, and their lips get fused to the female, and they end up sort of living as a parasite on the female just providing sperm.

Well, it turns out scientists are really interested in the immune system of the anglerfish, because how come the females body doesn't reject the male?

GROSS: Hm.

Dr. PRAGER: So even the strangest thing. Even the hagfish are a lovely, slimy, eel-like hagfish. Because they feed on sort of the dead and dying of the sea, they get exposed to a lot of bacteria and microbes, but it doesn't impact them. So scientists are studying - not only studying their immune system, but they've found several antimicrobial compounds in the hagfish that might be of use to humans.

GROSS: One of the ocean creatures you write about is krill. And krill are becoming - formally obscure krill are becoming superstars of the ocean now. They're being used in food supplements and as protein additives. So let's start with: What are krill doing in your book about ocean oddities?

Dr. PRAGER: Well, one of the first chapters I call sort of the invisible crowd, the smaller creatures of the sea that we don't necessarily see with our own naked eye, but are incredibly important to the ocean and the creatures that live there.

And krill, you know, we can actually see them with the naked eye, but they're really part of the plankton and incredibly important sort of packed with protein, not just for the creatures of the sea. A lot of things survive based on krill in the oceans. But now, as you said, people are recognizing that this is a really potentially important source of protein and other compounds that can not only help human health, but they're putting in face creams. They're, you know, new - the new, like, supplements that, you know, you're going to live longer because you're eating krill - really interesting both in terms of the ocean ecosystem, but also for the relevance to society.

GROSS: And why are they such a seemingly recent discovery? Why is it now that they're becoming so popular as protein additives and as food supplements?

Dr. PRAGER: Well, I think it's a - as we progress through our - I hate to say exploitation of the ocean, krill are very healthy source of protein. They have omega-3 oils. They have a lot of things that we see as being healthy for people, and there's a lot of it.

And as we look for populations that we can use for sustenance and to feed world populations, there's a lot of krill out there. And so it's becoming an important fishery on the planet, a commercial fishery. And, you know, I just want to say that while I recognize the importance of krill and all fish as potential source of food for people, they also have to - it's a fishery that has to be managed. We can't just take as much as we want out of the sea, of krill or anything else. And so it is going to be a very big fishery, and we have to watch how we do it.

GROSS: Well, Alan Prager, thank you so much for talking with us.

Dr. PRAGER: Well, thank you.

GROSS: Ellen Prager is the author of "Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter." You can see a slideshow of some of these odd creatures and read a chapter from Prager's book on our website, freshair.npr.org.

Coming up, reinterpreting music from 1920's Harlem and Chicago: We talk with Brian Carpenter, the leader of Ghost Train Orchestra.

This is FRESH AIR. Transcript provided by NPR, Copyright NPR.