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This summer, environmental reporter Benji Jones went on a diving trip to the Florida Keys. And that's where he met Captain Slate. I've been driving dive boats here since 1978, and I can't tell you how many millions of trips I've run out here. I'm sure 100,000. Millions sounds like a lot. But that's what I've been doing my whole life.
Back in the 70s and 80s, there were sprawling expanses of coral throughout the Florida Keys. It was just, you could snorkel on it and you couldn't see the end of the coral. I mean, you had to anchor off and swim toward it. There was no open spots in between the growths of coral to throw you a hook without tearing it up. Decades ago, there was this really vibrant ecosystem that supports not only so many marine animals,
but also coastal communities that really depend on reefs for protection from storms. I mean, a coral reef is literally a seawall. It's just a wall underwater, and that can prevent big waves from hitting the coastline. And also having a vibrant reef like it was was a major driver of tourism in the area because people come to snorkel and dive and fish. I mean, you couldn't put your fin down on the statue reef because you'd hit a piece of coral, and that's all gone.
Florida's coral reefs have had a long history of damage and destruction. From storms and pollution, from disease and global warming. And they are not in good shape. Nearly 90% of Florida's corals have been lost. Our tourists come and they don't know how it was. They think that's it. But it's not how it was. And we sure don't waste time telling them about it because they'll only get sad.
Coral reefs in general are among the most threatened ecosystems on the planet. But what makes these reefs in Florida extra important is that until recently, they were a source of hope. Organizations like the Coral Restoration Foundation have spent over a decade meticulously tending to thousands and thousands of pieces of coral and then planting them onto the reef.
So in 2022, we watched people from the Coral Restoration Foundation actually planting coral on this reef like you might plant trees in a forest. And I mean, these were like underwater gardens. The Elkhorn coral were this gorgeous, like golden orange color. Really, they did look like just
antlers growing out of the sea floor and they were sprawling meters wide. It was really, it was really beautiful. It just looked like what you expect like a reef in photographs to look like. Like it looked like the postcards you see in the Florida Keys and the souvenir shops. So when we were there in 2022, it was just cool to see what successful restoration looks like. To see like a forest that had been regrown. This reef had come back to life.
Benji left Florida last year feeling pretty good. There are so few stories of hope in the environmental world, and this was one of them. This was the cutting edge of restoration, and it was happening in real time, and we could see the results of that. So it seemed like there was, I'm not going to say positive future, because we know that climate change is just such a threat, but there was a solution. That's what it felt like. But then this summer, in 2023, Benji heard some alarming news reports. ♪
The Florida Keys baking in weeks of record heat. And it's not just the air. The water is sweltering too. Starting in around July, early July, there was a major marine heat wave that hit Florida and much of the Caribbean, and it pushed temperatures to unprecedented heights. Soaring ocean temperatures. Obliterating records. Unprecedented water temperatures.
Some surface buoys in the water were registering over 100 degrees Fahrenheit. So just like literally it is as hot as a hot tub. This marine heat wave started way earlier than heat waves of the past. Not only that, it lasted longer and got much, much hotter. With water this hot, this long, and this early, the coral can die fast.
Benji was worried about the beautifully restored underwater gardens of coral he had seen just a year ago. And so he headed back out to the Florida reefs with Captain Slate and the Coral Restoration Foundation. We wanted to come back to this reef after a summer of extreme heat to understand how it had changed. I'm Meredith Hodnot, and this week on Unexplainable, does this coral have a future?
So we visited a reef called Pickles Reef, which was about half an hour, I want to say, from Key Largo. It was a really beautiful afternoon. It was hot, really, really hot. But the water was this clear blue you could see straight down to the bottom when we got near the dive site. And that's really when we started to see the problem.
You could see these large patches of white. I leap off the boat.
And pretty quickly, once my head was under the water, I just looked around and sure enough, yeah, there were fields of bleached staghorn coral that looked like white tree branches just sunk to the floor. I mean, it looked like we were cruising over like a boneyard. I mean, that's how grim it felt and really what it looked like because of all that white color.
So bleaching in the simplest terms is when coral turns white and starves to death. In each coral, you have a partnership. You have the coral polyp and inside that polyp you have
algae and the algae gives coral not only its color but food in the form of sugar in exchange for nutrients like nitrogen and also a place to live and photosynthesize. So every coral you see is actually a pair of organisms. You have the algae and you have the coral polyp and together they make this thriving, vibrant coral colony. And what heat does is that it causes that relationship between the coral and the algae to break down
So as the algae leaves the coral, coral starts to starve to death and it also turns white. It turns white because algae give it its color. And so bleaching, scientists call it coral bleaching because they look white. Just this really white, white, this stark white color. And so it was pretty bleak. I mean, I don't think we saw any coral in that part of the reef that wasn't bleached or dead.
I was like, is my mask leaking or am I crying? I know, it's so sad. Much worse than I thought it was going to be. I think part of what made this sad is diving with people who have spent a lot of their careers on these reefs. Roxanne, the dive administrator for Coral Restoration Foundation, she's been working at this spot for years. I've been working in the coral fields.
feels like my whole life. We visited this reef specifically because the Coral Restoration Foundation has planted more than 40,000 bits of coral onto Pickles Reef and that's a lot of pieces of coral so it's a major site of their restoration work. Thousands of people have come to help return corals to this reef.
So most, if not all of these corals were planted by them over the last decade. And most, nearly all were bleached that we saw. And talking to Roxanne after she came out of the water, after seeing all this bleaching was really, really emotional. What was that dive like for you? Heartbreaking. Heartbreaking. She said, it's heartbreaking. I've never seen bleaching quite on this scale. The worst I saw was in 2015.
And this has surpassed that in an indescribable way. The extent of bleaching is far more than I've ever seen. And yeah, I mean, it was devastating. It was so hard to see not only so much of this ecosystem
like on its last legs, but to know that all of this work to restore this reef is now kind of burned up already, to see that work just evaporate. Seeing all of this in the shape that it is right now is really hard. I think at one point her voice cracked a little bit, like she was brought to tears by seeing this. And I think that that's a sentiment that's echoed by so many people who have devoted their lives to trying to protect these reefs.
These marine heat waves that are causing wide-scale bleaching all around the world in the Great Barrier Reef, in the Caribbean, Florida Keys, all of it. That's a big problem. It underscores a need to rethink the way that organizations do restoration or at least reestablish
amp them up in a way or at a pace that has not been done before. I think that there are scientists out there saying, look, if we're seeing years of work burned up in a few weeks, we need to do this differently.
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I live on this reef a long, long way from here. So Benji Jones has been riding the roller coaster of restoration and devastation on Florida's coral reefs. Years of work, thousands and thousands of corals planted, a reef brought back to life. And yet so much of it was wiped away with this summer's super early, super long, super intense marine heat wave.
So, what is the future of coral restoration? How much can we do with science to make coral stronger? Florida needs coral that's more heat resistant, that can stand up better to the intense marine heat waves we're seeing today because of climate change.
And so scientists are breeding special corals in the lab. They know that thermal tolerance is rooted in genetics, and so selectively breeding corals to be more tolerant can actually help our reefs be more resilient. But breeding corals isn't easy work. And a lot of the science behind coral spawning, which is how these animals reproduce, is still unknown.
Coral spawning is truly like one of the coolest things. So they do this only once a year in the middle of the night during hurricane season, a set number of days after the full moon. So like it's literally a magical phenomenon and it's only lasts a few minutes. So to see spawning, it's like really difficult because you have to time it exactly right. You have to know where to be. And then
And this is all assuming that the coral is healthy enough to actually spawn, which means that it's not bleached. It's of a certain size and so forth. So like it is really, it happens yearly if the coral is healthy, but it's still even so very, very difficult to see. And so Benji wanted to try and see this mysterious process for himself. So we timed our trip to coincide with coral spawning.
And the odds were not in our favor to actually see this happening because we knew that it was going to be really, really unlikely. And we also knew it was going to be hard because we were going to be doing a bunch of night diving. And like, frankly...
It's scary. The ocean is scary. Scary in the dark. It's scary in the dark. And like, you have to know what you're doing. And I'm not that comfortable in the water in the daytime, let alone at night. And so it was scary. And then we got to the reef and started suiting up.
Hannah Cook, a marine scientist, placed glow sticks on the heads of coral that were large enough and healthy enough to spawn, which was really fun because we're like, ooh, underwater rave, glow sticks. Exactly. It was like the opposite of that vibe, but like, yes, in general to that.
And like, it is exhilarating to be on the reef at night. We saw moray eels. We saw a big stingray. There were like groups of squids swimming overhead. The water was, it was like magical because when you move your hands around, it would like pop in color because of bioluminescence. It was like literally a light show. Internally, I'm like panicking. Externally, it is literally a rave and absolutely gorgeous. So we had six healthy coral heads with glow sticks on it.
We're all waiting for something to happen. Nothing's happening. And, like, I started to get disappointed because it just seemed, like, almost impossible to see this happening. I mean, the researchers were basically like... This is not the night, yeah. Do not hold your breath. Like, do not hold your breath. Mm-hmm. Then...
Hannah starts waving her flashlight around and we swim over to her and she and another biologist who was with us that night, Celia, were pointing frantically at a big blob-like head of brown coral. It was called lobe star coral. And sure enough, you can see these little pearl couscous
sperm and egg packets in the mouth of every, or not every, but maybe most of the polyps in this colony of coral. And then like a few minutes in, we just start to see across the coral head, these little balls just start puffing out of the coral like an underwater salt shaker. Like that's like literally what it looks like. And it just kind of like
Section by section, you start to see these little balls released in an instant, float for a second, and then kind of like wave back and forth before floating away. And it was just so cool. I mean, to see something that I had read about and heard about and been told that we wouldn't see it, like that was very cool to see that. But also just to know that like each of those balls was like...
the potential future of, I don't know, maybe healthy coral on this reef because that coral was fine. That coral was doing great. So maybe something in its genetics were like giving it a leg up and maybe it will give that advantage to the little babies that will come from all those little puffballs. Oh shit, I wasn't recording. All right, let's go. What do we see? Oh my God!
Coral spawning! Is it recording now? We saw coral spawning and I'm so excited because there's actually a new species that hadn't seen before. Oh my gosh, I was so excited.
I have no idea what's going on. I'm just like, someone's pulling me over to see something. And it was a really healthy coral. It was the whole entire coral was healthy, full color, no paling, no bleaching, no partial mortality. It was a beautiful colony and just really an amazing thing to see. So if this is such a tricky and mysterious process...
How are scientists trying to get corals to spawn in the lab? So scientists are trying to get corals to spawn in a tank, in a fish tank, in a lab. And you can do that by basically, you have these advanced, really advanced fish tanks that you can basically make
mimic the conditions of the ocean. So imagine like a large 100 gallon fish tank, like you might see at an aquarium, where you can control everything from like the light, the time of day the light rises, the nutrition in the water. And so scientists like literally are trying to like build the natural ocean indoors.
So kind of like the moon is imitating hurricane season for this. And if all goes to plan, the coral are totally duped and they think they're in the ocean. And they're like, okay, moon is out. It's warm. It feels like August. Let's spawn. Let's do this. Let's do this. The mood is right. I mean, literally, it is like mood lighting, like moon mood lighting. But so then going from that to selective breeding,
Basically, you know who your parents are. You've tested certain parents to know that they're, I don't know, more tolerant to heat, whatever. You get those parents to spawn. You collect that spawn in a tank and then you mix that spawn together and you test those babies to see how much they inherited from their parents in terms of their ability to withstand heat. That's awesome. So what are the limits to these breeding programs? Scale is one of them. It's really hard to do this professionally.
with like, I mean, when you're talking about restoration, you need to
produce like thousands of corals. And it's really important that the corals are not only tolerant, but also diverse, because if you have a disease that comes through and all of your corals are very specific variety of a thermally tolerant, like a strong coral, then you might lose a lot of them or all of them if they're all the same genetically. And so you don't want it to be like a monoculture. Exactly. Exactly. You don't want a monoculture farm of even like well adapted corals because adaptation is not just about
tolerating one threat. It's about being able to tolerate many, many threats. And so we're talking about developing lots of different
like strong varieties of coral individuals for every species, like that is really hard to do. Scientists only know how to do this like selective breeding approach as far as I know with a handful of different species. This is not something that is like guaranteed across all different types of coral. So I think just scaling this up to the level that's needed to restore these reefs just because they've lost so much of their coral over the last few decades is
is going to be really, really difficult. So that's part of it. But then there's also this fundamental biological limit that coral has. You can only bake in a certain amount of heat tolerance by tweaking their genetics through breeding, through selective breeding. So it's not clear what that threshold is, but I don't think that
I don't think scientists are going to be able to get more than a few degrees. It's just, there's going to be limits to coral biology. So is that enough? Is this selective reading enough to cope with, like, how fast the ocean is warming? No. I mean, no, it's not. Like, it will certainly help. I mean, it'd be great to be able to dive on a reef like the one in the Keys that we just did and see, I don't know, only half of the corals bleached. Not all of them, but I think that, like...
We're staring down a world where marine heat waves that bring water temperatures several degrees higher than average are more common. I mean, 100 degrees Fahrenheit or 95 degrees Fahrenheit in the Florida Keys is like...
more than 10 degrees above the threshold of bleaching for the corals in that region. So just not going to cut it. Yeah. And I don't think scientists are going to be able to increase the kind of thermal tolerance of corals by more than a few or several degrees Fahrenheit through selective breeding. And
Yeah, I just, I don't think that's enough. Right. So what can be accomplished here? Time. I mean, breeding corals is going to buy time. That is, I think, the main message, which is just warming is happening and we know it's going to get worse. How long can we help coral reefs hold on while everybody else tries to figure out how to
make climate change go away. Like, I think the scientists that I spoke to are like, look, this is our job. Our job is doing the biology side of things, but policymakers have their job. Those are different. So yeah, I in no way think that coral restoration and selective breeding is futile, is not worth pursuing. I just think that it has a very clear limit in terms of how it could actually help coral reefs.
So this is like the heart of what we don't know here is just like, once we buy this time, can we act fast enough? Can we like use this time in order to, you know, have an ocean in which these corals could flourish again?
Yeah. And I think even in a world where we reduce emissions dramatically, which I don't know, I'm trying to stay hopeful that that will happen. But even in that world, still scientists are going to need to do selective breeding. They're still going to need to do a lot of planting of coral on the reef because like if we really wanted to bring coral reefs back to what
they were previously in previous decades, it requires both restoration, advanced restoration and reducing emissions dramatically. And I think there's just a big question of whether both of those things are going to come together and happen. Right. So yes, to your point, like the heart of uncertainty is just, will this be enough?
Benji Jones is an environmental reporter at Vox. You can find his great coverage of Florida's coral reefs at Vox.com, along with eerily beautiful photos by photojournalist Jennifer Adler.
This episode was produced by Meredith Hodnot, who also manages our show. Brian Resnick edited the piece with help from Noam Hassenfeld and me, Bird Pinkerton. Noam wrote the music. Christian Ayala did the mixing and the sound design with an ear from Rob Byers. Serena Solon checked the facts. And Manding Nguyen found a new home floating out at sea.
Special thanks to Captain Spencer Slate, Roxanne Boonstra, Hannah Cook, Celia Lido, the Coral Restoration Foundation, the Mote Marine Laboratory and Aquarium, and the Pulitzer Center, who supported Benji's reporting. This podcast and all of Vox is free in part because of gifts from our readers and listeners. You can go to vox.com slash give to give today. And please say you're giving because you love Unexplainable.
Also, please leave us a review or write us an email with your thoughts or questions. We are at unexplainable at Vox.com. And we really, really love hearing from all of you. Unexplainable is part of the Vox Media Podcast Network. And we'll be back next week.
