The Purple Urchins Don't Die : Short Wave NPR climate correspondent Lauren Sommer explains how scientists are getting creative to deal with the hordes of urchins overtaking kelp forests in the Pacific Ocean — and why this kind of drastic ecological change may become more common as the climate gets hotter.

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The Purple Urchins Don't Die

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The Purple Urchins Don't Die

The Purple Urchins Don't Die

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript


You're listening to SHORT WAVE from NPR.

Hey, everybody. Maddie Sofia here with NPR climate correspondent Lauren Sommer. Hey, Lauren.

LAUREN SOMMER, BYLINE: Hey. OK, Maddie, today I want you to picture diving in the Pacific Ocean.

SOFIA: OK, I like where this is headed.

SOMMER: OK, you look down, but instead of seeing rocks and seaweed and stuff, you see purple.

SOFIA: Purple.

SOMMER: Yeah, hundreds of round, spiky purple things.

MORGAN MURPHY-CANNELLA: It looks like someone rolled out a purple carpet over the sea floor as far as you could see.

SOMMER: They're purple sea urchins. Morgan Murphy-Cannella is a diver, and she's seen an explosion of them off the Northern California coast.

SOFIA: OK. What's going on?

SOMMER: These urchins have taken over what used to be kelp forests. You know, that's the seaweed that grows 30- to 60-feet tall. So it creates this really lush underwater forest. Urchins eat kelp but normally not enough to really hurt the whole kelp population. But there have been some big ecological shifts that have led to the urchin explosion. And now there are so many urchins, the kelp forests are disappearing.


SOFIA: So does that mean that the urchins are going to go away?

SOMMER: Actually, no. I mean, you might predict a major urchin die-off because there isn't a lot of food left.

SOFIA: Right.

SOMMER: But that hasn't happened. Morgan says they can endure that.

MURPHY-CANNELLA: They're kind of like zombies. You know, they can last for a long time without eating, and they just live. They're, yeah, a very bizarre animal. I have to respect them, though.

SOMMER: So now the big question is, is there anything that can be done? You know, has the scale tipped too far, or can the kelp forests be brought back?


SOFIA: So today on the show, how scientists are getting creative to deal with urchin hordes in the Pacific Ocean and why this kind of drastic ecological change may become more common as the climate gets hotter. You're listening to SHORT WAVE, the daily science podcast from NPR.


SOFIA: So, Lauren, you've described, basically, a horror movie for seaweed.


SOFIA: There's a mass of slow-moving urchins coming to devour the kelp off the coast of California. How did this all start?

SOMMER: So it started in 2014 with the Blob.

SOFIA: Oh, come on, Lauren. The Blob? What is this?


SOMMER: The Blob, yeah. It was this huge patch of abnormally warm water off the west coast. It grew and grew, and it raised water temperatures far above normal, which is bad for the kelp off the Northern California coast, which is a species called bull kelp. You know, it grows incredibly fast, and it likes cool water with lots of nutrients. And that warm water was low in nutrients, and that lasted for several years.

SOFIA: OK, got it.

SOMMER: So, I mean, that was kind of the first hit. And the second hit was the purple urchins. Their numbers really exploded because their main predator on California's north coast has disappeared. It's this really large sea star called the sunflower sea star.

SOFIA: Sea star - that's the same thing we call starfish, right?

SOMMER: Yeah, totally the same thing. But a lot of marine biologists are trying to move away from starfish because, you know, it's not really a fish. So sea star is kind of the preferred term these days.

SOFIA: OK, marine biologists, we see you see. Sea star it is. We can change. We can change.

SOMMER: OK, so the sea star - the sunflower sea star - it's pretty amazing. It's got more than 20 arms, and it's a couple feet across. And it's really good at eating urchins. But on the west coast, sea stars have been hit by a disease known as sea star wasting disease.

SOFIA: I've heard of this, Lauren, actually. It basically, like, turns them into goo.

SOMMER: Yeah, yeah, like, attacks their bodies. And a lot of divers I spoke to said it's been years and years since they've seen a sunflower sea star on the west coast. So without a predator to keep them in check, the purple urchins exploded. I mean, normally they're kind of tucked in nooks and crannies. But as competition for food increased, they got increasingly bold. That's what Meredith McPherson described to me. She's a diver and a graduate student at UC Santa Cruz.

MEREDITH MCPHERSON: Sometimes, we see dozens of them crawling up the stem of the kelp and kind of taking it down from there.

SOMMER: And then when the kelp really spores, you know, to grow the next generation of plants, urchins are just there waiting to gobble those up, too. So the kelp forest isn't growing back. And Meredith and her colleagues actually measured that. They used satellite imagery and found that across a big swath of Northern California, 95% of the kelp forest has disappeared since 2014.

MCPHERSON: We were expecting something like that, but it doesn't really make it any easier to digest in terms of the actual loss of the coastal ecosystem.

SOFIA: Yeah, those are tough data. And that's got to be a problem - right? - for a lot of other species, too, who also live in the forest.

SOMMER: Yeah, because it's a really key ecosystem. It's kind of like a redwood forest is on land, you know, with animals that are specially adapted to just live there. Now it's turned into an urchin barren, as it's known - right? - with these urchins that can survive even without much food to eat. And it really shows how change can be extremely drastic in an ecosystem. You know, it's kind of like dominoes.

SOFIA: Right. OK, so first, there's the blob, the warm water blob, then sea star disease, and then the rise of this urchin mob. Feels like, Lauren, like, this is linked to something bigger. Like, is this a climate change thing?

SOMMER: Yes. You knew I was going there, right?

SOFIA: Yeah, I knew you were.

SOMMER: There's definitely a link that scientists think is there because marine heat waves are expected to get more intense and more frequent with climate change. And then they also think that sea stars are just more susceptible to disease in warmer water. So you can think of climate change as just, like, the added stressor here. It's something that can cause these abrupt changes to happen. And it's happening more and more in different ecosystems.

SOFIA: So is there anything that can be done here, Lauren? Like, do scientists think this urchin boom will slow down on its own? Or...

SOMMER: They're definitely keeping an eye out for that because when you get these really dense populations, there's a chance that, you know, there's a disease or something else that's going to sweep through more easily. But in the meantime, people are trying to give the kelp forest a chance. And there are three strategies.

SOFIA: OK, lay them on me.

SOMMER: OK, number one, get rid of urchins. Near Fort Bragg, Calif., there's a group called Reef Check California, and they're citizen scientist divers. They're focusing on trying to bring back one particular patch of kelp. It's a spot that's near some healthy kelp. So they think if they can get rid of the urchins, then maybe the kelp might have a chance to grow back.

SOFIA: Got it. So remove the urchins. Are they, like, trying to catch them all?

SOMMER: I mean, basically, yes. There's a group of divers. They go down there, and they grab all they can. Morgan Murphy-Cannella, who we heard from at the beginning, is coordinating those dives.

MURPHY-CANNELLA: It's crazy to see them work, you know, when it's really thick of urchin. They're just, like, shoveling them, just, like, going at it. And they can really get a lot. It's pretty amazing to see them work.

SOMMER: Some of them actually wear these big wire rakes on their hands to grab them because, you know, they're pretty sharp animals...

SOFIA: Right.

SOMMER: ...With all those spines. And they scoop them up, put them in big baskets. And then, eventually, they're taken to a composting facility. And last year, they brought in more than 20,000 pounds of urchins.

SOFIA: Wow. I mean, that sounds like, honestly, a lot of pounds, Lauren. But, I mean, do they think that they can actually stop the urchin onslaught? Like, it feels like kind of a short term solution to, like, a bigger systemic problem.

SOMMER: Yeah. I asked Morgan that.

MURPHY-CANNELLA: You know, I think that we can do this. It's going to have to be a long-term project. But I think we can create these oasis zones where we can see kelp grow back.

SOMMER: I mean, they're concentrating on a small area and trying to maintain it, she says. So this will be the second year of her doing it to see if they can kind of give kelp that chance. And that brings us to urchin strategy number two.


SOMMER: That is a sea otter, a baby sea otter, actually, at the Monterey Bay Aquarium.

SOFIA: OK. I am familiar with these cute but merciless killers.

SOMMER: Otters are excellent urchin predators. In fact, the ones that eat a lot of urchins - their teeth actually turn kind of purple. Around Monterey, you know, in central California, the kelp forests are doing a lot better, in part because otters are eating urchins and keeping their numbers in check.

SOFIA: OK, so the idea might be, like, recruit the otters, get them in there, take out some urchins.

SOMMER: Yeah, but there still aren't many sea otters in California. They were once hunted almost to extinction for their fur. They're only around today because a small population managed to survive. And the Monterey Bay Aquarium and others - they've been working to bring them back.

SOFIA: Got you.

SOMMER: There's been talk of reintroducing them in northern California, but that's tricky. You know, the otters probably can't get established there on their own because of all the white sharks.

SOFIA: Dang, OK. I didn't expect sharks to come in here, Lauren, but I should have.

SOMMER: Yeah, there's been some biting, unfortunately.

SOFIA: (Laughter).

SOMMER: But, you know, another big question is just how much the otters might help in Northern California at all because it turns out they really don't like the urchins in places where the kelp has already disappeared. You know, they eat the ones in the kelp forests, which are yummier, basically. You know, those urchins have a higher nutritional value because they have plenty of food. And the otters don't tend to eat the ones in the urchin barrens.

SOFIA: Got it. You know, honestly, this is not the first time I've been disappointed in a sea otter, Lauren, you know?


SOFIA: (Laughter).

SOMMER: Anyway, otters are not the only things that eat sea urchins. Like, have you, Maddie, eaten one?

SOFIA: Oh, yeah. Wait. I have. Like, uni is the gonads of urchins, right?


SOFIA: Like, when you go to a sushi restaurant and you eat uni.

SOMMER: Yeah. I mean, humans - that's strategy number three, because we are predators, too.

SOFIA: If you can't beat them, eat them. Classic human strategy.

SOMMER: Exactly. I mean, if it was on the West Coast, you probably didn't eat a purple urchin. You ate another species, most likely. But I met someone who's trying to change that.

STEPHANIE MUTZ: Hi. What's your order number?


SOMMER: I caught up with Stephanie Mutz on a street in San Francisco, which is where she set up her seafood pop-up. She runs Sea Stephanie Fish, based in Santa Barbara, where she's an urchin diver.

MUTZ: So this is as big as they get, pretty much. These guys can get a bit bigger.

SOMMER: She was bagging up purple urchins for her customers out of her van because, you know, as a diver, Stephanie has seen purple urchins boom.

MUTZ: It's frustrating to - essentially, to see all these and watching them eat all the kelp. It's frustrating as heck.

SOMMER: So she and her partners decided to market them. And that's not easy - right? - because even otters don't even like those urchins. They usually have very little uni inside. So what they do is they catch the purple urchins in the wild. They bring them to a shellfish farm on land, and then they fatten them up. And people are into it. I mean, for this San Francisco pop-up, she sold 300 urchins in six minutes online.

MUTZ: The word has gotten out about the nuisance of the purple urchin. So it's, like, I'm doing really great for the environment. I'm going to eat these guys.

SOFIA: I mean, yeah, I guess so, if people are buying urchins out of a van on a street corner, Lauren.

SOMMER: Yeah. And, you know, and she's not alone. There are other urchin ranchers that are trying to get these projects going. It's not necessarily going to fix everything, but I think people are trying whatever they can to give kelp kind of a leg up in the hope that maybe conditions are going to get better in the future. Hopefully, every little bit helps. I mean, for this story, I ate purple urchins, and they were delicious.


SOFIA: OK, Lauren. Thank you for reporting and for eating your part. We appreciate you.

SOMMER: Thanks, Maddie.


SOFIA: This episode was produced by Rebecca Ramirez, edited by Geoff Brumfiel and fact checked by Rasha Aridi. The audio engineer for this episode was Josh Newell. Special thanks to Lauren's computer fan, which has now become a sentient being in her recording closet. I'm Maddie Sofia. Thanks for listening to SHORT WAVE.

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