The Reef That Built Itself Back: Coral Recovery After Bleaching

0:00 About 1,000 miles south of Hawaii, there's this reef of coral so remote that almost nobody lives there. In 2023, the water around it heated up so much and stayed hot for so long, more than half a year, the reef essentially bleached. And the man who monitors it described feeling the suffering in his own body. And what he found when he went back is the most hopeful thing I'd ever read about a coral all year. Now, there's a tiny ring of coral in the North Pacific, and for more than six months the water stays really, really hot, almost too hot. And some of the brightest most vibrant corals on the reef turn completely white, so they bleach. And the scientist who monitors that reef later said he honestly didn't know if it'd ever come back.

0:42 When he went back three years later, he put his face in the water and he found it was covered with baby corals. Now, today I'm going to show you why this happened, because the reason has a lot to do with you. Welcome back to the How to Protect the Ocean podcast. I'm your host, Andrew Lewin, a marine biologist and science communicator, here to talk to you about marine science, marine news, and marine conservation or ocean conservation, however you wanna say it. Because it's, really important that we get to know more about what's happening with the ocean. I covered this story a little while ago on our YouTube channel. But I wanted to cover it a little bit here 'cause I wanted to share the good news, because there's hope for coral, and I think that's really important when people have hope for coral. Now, yesterday we talked about marine protected areas as nature reserves of the sea, and why most people couldn't name one.

1:25 If you listened to it, I gave you a bit of an exercise to find out, like, what the marine protected area nearest you is and what was in it and all that kind of stuff. But today it's all about what those reserves actually do when things go wrong, And especially when coral bleaching and we have, like, heat waves and stuff. And now let's, be honest like, the feeling around corals first, Every time you see a headline about coral bleaching, there's a little voice inside you that says, " Well, that's it for reefs," like, "They're done. We're never really gonna see it." Chasing Coral was probably one of the most depressing documentaries I've ever seen on Netflix and just in general. And it made people, like, emotional after, and it didn't really give people hope for what the corals can do.

2:06 All right? And of course the numbers don't help. Like, living coral around the world has dropped about 10% since 1980, and mostly from repeated bleaching. And right now, with a strong El Niño pushing ocean temperatures up, and of course we had an El Niño not too long ago as well. This round of bleaching could end up being among the worst ever recorded. So if you quietly give up on coral, I get it. I understand where you're taking this. I get it. But I've had those days too. Like, it's not something that we should keep close. We should realize that these corals are tough. They've been around for millions of years. And I've been studying the ocean my whole career. I want you to give me the next 15 minutes just to be able to tell you about this interesting story that we're gonna talk about.

2:47 Because this tells us that corals can be really resilient, especially when left by themselves and on their own. I think it's really important. So let's talk about what coral bleaching is, Coral is an animal. It shares its body with tiny algae that lives inside the tissues, kinda like roommates if you think about it, those roommates make food from sunlight, and they hand most of that food over to the coral so they can build the skeleton. And that's where the corals get most of their energy, and it's where their colors come from a lot of the times. So when the water gets too hot for too long, that relationship breaks down, and the coral just kicks the algae out of the coral skeleton. Without them, you see straight through the tissue, and you see the white skeleton behind that.

3:29 That white skeleton is always there, but the tissue hides the white skeleton because it's got the color, and it's, like, the fleshy. And that's bleaching, when that color disappears from the fleshy coral. Now, a bleached coral it's starving. It's not dead, but it's starving. it still has a chance. So if the water cools down in time, the algae can move back in, probably different algae, it's not the same algae, and the coral can recover. If the heat lasts too long, the coral dies, and something, like, else moves in that takes place, whether it's algae or something like that, we don't know. Like, a different type of algae, like a hairy algae that goes along the outside. Something like seaweed or something like that. It will kill the fleshy material for sure, and it'll prevent it from growing back. So the real question is what decides which way a reef goes after that heat breaks?

4:13 Because there's a bit of a transition after that. Now, to answer that, we need to go to a place where nothing has been taken away. So about 1,000 miles south of Hawaii, middle of the Pacific, there's an atoll called the Palmyra. And Palmyra is a ring of tiny islands built by coral itself. So sitting on top of an old volcano that wore away under the sea a very, very long time ago. During World War II, the US military built a runway and a few buildings on there just to kinda have this home, because as they needed these islands to make land in these islands for positioning. Now, after that, most people just left it alone. No towns, no permanent residences. Today, it's a US National Wildlife, Refuge, and with a small research station on it, and a few dozen people working there at any one point in time.

4:55 Well, now when you get in the water, it's like a city at lunch hour, schools of fish moving between coral the size of cars, like massive, massive coral. A grouper parked on the coral head with, like, a tiny cleaner fish that picks parasites off its skin, basically like a spa appointment, like you get these cleaning stations is what we call them. And then, of course, an octopus watching from the crack, just kinda hiding out of the way, and black tip reef sharks cruising around the edges. Now, Joe Pawlik is a senior reef strategy lead at The Nature Conservancy, and he monitors the reefs. And he describes corals so packed together that they're growing on top of one another, fighting over space, that happens a lot when you have a healthy reef. On most reefs around the world, that's a memory. We don't see that anymore. But on Palmyra, it's a normal Tuesday Then, of course, 2023 arrived, and a marine heatwave rolled over Palmyra and stayed for more than half a year.

5:43 Pawlik watched some of the most vibrant corals of the reef turn completely white. He later described it as devastating. He goes, "The kind of thing you feel in your body." And he admitted he didn't know if the reef would ever come back. it's tough when you see it bleach for so long, and then you wonder like, "Is this ever gonna recover? We have no idea." There's no control over it at that point. Three years later, he goes back to Palmyra. He's back in the water, and some of the damage is still there. He still sees it. Some reefs recovered faster than others. But around the scarred corals, there are hundreds of little bumps that look like tiny cauliflowers. He called it an absolute sea of baby, tiny baby corals. Those babies became the corals that survived. Research shows corals that make it through a bleaching often can handle heat better, and that tolerance can be passed down to the next generation.

6:29 So the reef that came back may be tougher than the one that was bleached. Now, I should put a caveat in here. It's pretty much natural selection. There are certain types of algae that can handle the heat a little better, so if they repopulate within the coral, that can have a higher heat tolerance. They won't leave as quickly as others. It doesn't necessarily mean that all different types of corals are going to survive. There could be some that are more prone to attracting the sp-specific algae, like Zoantella is what they call it. But it still shows that they're a little bit tougher when it comes to this type of bleaching. But the question is, it's not just the corals. Why did Palmyra get a second chance when so many reefs don't? And it comes down to the crew of three. And the crew of three is kind of interesting.

7:11 You have the cleaners, the parrotfish. All over Palmyra, parrotfish graze the reef all day, scraping off algae off the corals. After bleaching, that job becomes life or death. Seaweed grows faster in warm water, and it's always looking for open real estate. So if it takes over dead or, bleached patches on corals, it's very hard for the corals to ever get a chance to grow back. And parrotfish keep that space clear of that algae because that's what they do. They eat algae. They're herbivores Now, of course, there's always the landing pad of the actual coral, You need coral colonies to be able to come back if that flesh kinda goes away. So you have this crustose coralline algae. It's a specific type of algae, and it's one of my favorite things. It's a bubblegum pink crust that grows over the rock and dead coral.

7:54 So it's not the same algae as what you would think of, like the hairy algae that would grow over top and prevent other corals from growing. But it's on the corals team, this one. Baby corals floating in the water column go looking for somewhere to settle, and many of them prefer to land right on top of this pink crust. And it holds space for them until, like, the conditions are right for those corals to move back in. Now, of course, then you got, like, the bosses, You got the sharks. And Palmyra has one of the highest densities of predators ever recorded by scientists. And that matters for the corals in a bit of a roundabout way. Sharks eat the mid-sized predatory fish, and those mid-sized fish eat the grazers, like the parrotfish. So with plenty of sharks around, the mid-sized predators stay in check, and the parrotfish and other grazers like, they stay around, they stay abundant.

8:35 Pull out the sharks, and the whole cleaning crew shrinks, and that, can be difficult. And that's what is the difference in terms of why Palmyra survives so well. It's an intact food web. That's what it looks like. You have predators, you have grazers, and you have the coralline algae that kind of sits there to hold that space open because the algae can't grow on top of it. And it's rare. You don't see it a lot. Around the world, sharks and rays have declined by 71% since 1970, mostly from overfishing Now, you might be thinking like, "Sure, that works in the middle of nowhere with no people, but what about places where people live and fish every day?" And for that, we have to go to the southern tip of Africa one of the oldest marine protected areas on the continent. On South Africa's southern coast, there's a stretch of rocky shoreline called Siksikama.

9:19 I think I'm pronouncing that properly. It's been protected for decades and the oldest marine protected area in Africa, and fishing has been banned there for a long, long time. Now living on those rocky reefs is a fish called the red roman. It's a bright red sea bream, and it's, it's a homebody. It likes to stay around. That red roman tend to stay in the same small patch of the reef their entire lives. That makes them perfect for an experiment because red roman born inside a marine protected area is likely to live its whole life inside that marine protected area. So researchers at Rhodes University wanted to know whether the protected waters handle extreme conditions differently from the fish in fished waters. So they fitted these red romans with small acoustic tags that record how much the fish moves, which is a good proxy for how active and healthy it is.

10:04 Now, they tagged one population that's fished and one population that's not inside the marine protected area. Then nature ran the test for them. First there was an intense upwelling when cold water surges upward towards the coast, then the marine cold spell. When the temperature crashed, the fish population slowed down, so the fish became a little sluggish because it was too cold. The protected population they kept moving. Now the research explanation is really important here. Fishing tends to take certain kinds of fish, and it may be removing the individuals that are the best at handling temperature extremes, so the bold, active ones. So inside a protected area, those tough individuals stay in the population and keep breeding. It's not even just, like, the tough species, it's the tough individuals from that specific species.

10:48 So climate change means more extremes in both directions, so hotter heat waves and sharper cold snaps depending on where you are. And the researchers concluded that the networks of marine protected areas can help build the fish populations that are ready for those conditions. So we got two stories here, a coral reef in the Pacific and a reef in South Africa pointing to the same type of idea. When you leave the ecosystem whole, that means no fishing, no bothersome, it keeps its best tools for bouncing back Now, I wanna be straight with you here because you deserve the entire picture, the full picture. Protected areas allow restoration by time and resilience, so that's great. On their own, they can't save reefs just like from unlimited warming.

11:28 that eventually will take a toll. The UN's climate panel estimates that at 1.5 degrees of warming, somewhere between 70% of coral reefs could be lost. Based on current national pledges, the world is heading towards roughly 2.6 degrees by the end of the century. So researchers at Rhodes have made the same point over and over again. If climate change overwhelms its ecosystem's resilience, cutting carbon emissions is the primary fix. It's not restoration of corals. That can help. It can give it a little bit of time, but that heating and that climate change, that's just what's gonna be the big downfall. Cutting emissions turns down the heat. keeps the survivors in the game, so there's something left over to recover when it does. And we need both.

12:09 So we need both, One of them is something you can push for in your own region this year. And, like, the lessons of Palmyra are already traveling, which is great. Woods Hole Oceanographic Institution, Stanford University, and the Nature Conservancy built a framework called Super Reefs, and it looks at water conditions, currents, and coral genetics to find the reefs most likely to survive a hotter future, then focuses on protection and restoration in those areas. Now, they're working with local partners in places like Maui and Belize, which is kinda cool to see. And in Florida, Mote Marine Laboratory has started releasing hatchery-raised Caribbean king crabs onto reefs because those king crabs eat seaweed. And in Puerto Rico, restoration teams are bringing back sea urchins for the same type of job, to eat the algae, and they're rebuilding the cleaning crew that Palmyra never lost.

12:55 So it's all different types of species, but it has the same function. You have your grazers. You have the coralline algae that you can find in a lot of places around the world, and then you have your predators, which will be different and unique in every situation. So here's the one thing I want you to take home from this, Because every, episode we try to have a CTA, like a call to action. So the next time a marine protected area consultation opens up in your region, like submit one comment of support. You wanna support that. You wanna show the government, "Hey, this is something that I really wanna have in my area." These consultations happen more often than people realize, so check them out at different places, and they're usually open to anyone. In Canada, Fisheries Oceans Canada post them online. And in the US, look at NOAA or your state agencies. Most countries have something similar.

13:36 Like, they all have, like, on their government website. Now, your comment doesn't have to be long. It can be two sentences. It could be, " I support protecting this area because intact ecosystems recover faster from heat waves. Please give science-based protections full weight," and that's enough, officials count those comments. And as we talked about yesterday, the other side always shows up, the people who don't want the marine protected areas. And if you wanna just take what I just said and post it into a comment period, I'm gonna put this in the show notes so you can get access to it and just copy and paste it into your next comment. And if you want help finding an open consultation near you, like, message me. You can hit me up as a Spotify comments, or if you are listening to your favorite podcast app and you don't have access to comments, then all you have to do is just look in the show notes and, you'll have, access to my socials there, and you can just DM me, I love to hear from you guys.

14:24 Now, I want you, like, as you know this, as you now learn this, I want you to picture that reef in Palmyra, Three years after it turned white, the floor is covered with little baby corals, each one the child of a survivor and tougher than before. And parrotfish are cleaning spaces for more to be able to colonize on it, and pink crusts are holding that door open to make sure algae doesn't grow on top, and sharks are keeping the whole system in balance to make sure that it just stays as is, and it grows back those corals. And Joe Pollock put it this way, pretty much more or less: "We're nowhere near ready to write the obituary on coral reefs. They're not gone. And when the ecosystem is whole, it starts to fight back. And our job is to keep more of them whole so that they can fight."

15:06 now tomorrow we're talking about the people side of all of this. Those parrotfish and red roman, someone somewhere fishes them to feed their family. So why telling people fishing is bad backfires and what works better is what we're gonna be talking about tomorrow. So I want you to hit that follow button so you don't miss it and you can catch it. And this has been another wonderful episode, I think wonderful episode. We got to talk a lot about coral reefs in a positive way. but I am your host, Andrew Lewin, and you've been listening to the How to Protect the Ocean podcast. I want you to have a great day. We'll talk to you tomorrow morning, and happy conservation.