A MARTÍNEZ, HOST:
Florida's coral reefs are suffering from hot ocean temperatures again. The past three years have been the worst on record. To try and save the reefs, scientists are starting to breed coral that can handle heat better, and they're crossing international boundaries to do it. Lauren Sommer from NPR's climate desk reports from the Florida Keys.
LAUREN SOMMER, BYLINE: If you want to know what Florida's coral reefs used to look like, ask Ken Nedimyer. He's been diving there for more than 50 years. He says there used to be fields of coral.
KEN NEDIMYER: Just incredible. I mean, you could look left and right and forward, and you couldn't see anything but that.
SOMMER: There were corals with huge branching arms.
NEDIMYER: These great big branches would go out, you know, six feet from the base, and all interlaced into each other. And you go there now, and there's absolutely none at all. It's completely gone.
SOMMER: Florida's coral reefs have been hit with a lot. Water quality problems, damage from boats and people. More than 90% of living coral in the Florida Keys has been lost. So there's been a big push to restore the reefs, which Nedimyer does with the nonprofit Reef Renewal USA. They grow coral and plant it in the ocean. But the biggest threat now is heat, like in 2023, when the water temperature soared.
NEDIMYER: The middle Keys got to 94 out on the reef, you know, top to bottom. I mean, 94, that's, like, crazy.
SOMMER: That causes coral to bleach, turning them a bone white color.
NEDIMYER: It looked like there was a snowstorm, just white coral everywhere, and two weeks later, you go out there, and they were all gray and dead. And it was, like, so hard to see this, you know, 20 years of hard work gone in one week.
SOMMER: It was a glimpse of the future, Nedimyer says. The ocean will keep getting hotter as the climate continues to warm. So Florida is changing the playbook.
(SOUNDBITE OF WATER SPLASHING)
NEDIMYER: So this is called Orbicella faveolata. That's the scientific name for it.
SOMMER: Nedimyer's group is focusing more on the corals that survived the 2023 heat wave, like brain and star corals. He's cutting one on a tile saw.
(SOUNDBITE OF TABLE SAW WHIRRING)
SOMMER: Each small piece will grow into a new coral.
NEDIMYER: Like a plant, yeah.
SOMMER: These survivor corals are being used to restore Florida's reefs now. But with climate change, scientists say Florida may need coral that are even tougher. So they're trying to breed them at the University of Miami.
ANDREW BAKER: This is the Honduran tank.
SOMMER: The tanks of coral in Andrew Baker's lab are like an international coral summit. In one tank, there are Florida corals. In another, are the same species, but from Honduras.
BAKER: It's these guys, the brain corals, that we are hoping will spawn tonight.
SOMMER: Baker's lab is using these coral parents to make babies, which they call Flonduran (ph). Half Floridian, half Honduran. Get it? The babies from last year's spawning are already growing.
BAKER: So you can see they're about an inch by an inch, that kind of size.
SOMMER: Their Honduran parents came from a reef that already sees really hot temperatures.
BAKER: So the idea would be to try to bring some of the genes from this really heat-tolerant population in Honduras and introduce them to the Florida population through breeding.
SOMMER: It's about speeding up evolution to try to keep up with climate change. Some of these Flonduran babies were put onto a reef off Miami this summer. It's the first time internationally bred corals have been allowed in the ocean in the U.S., Baker says.
BAKER: So far, so good. They're all doing great. But we're under heat stress, so we actually are very interested to see what happens in this pretty severe bleaching event.
SOMMER: Baker says there are no guarantees that these crossbred corals can handle a hotter future. But there's a huge amount at stake for Florida, both in protecting marine life and people.
BAKER: Coral reefs off our coastline are responsible for preventing on average about $400 million of coastal flooding damage every year. So they are incredibly valuable. And if we lose those ecosystems and the structures that they build, we're going to be vulnerable to all of those flooding impacts.
SOMMER: It's why Baker says the only choice for him is not to give up, despite how much has been lost on Florida's reefs.
Lauren Sommer, NPR News.
(SOUNDBITE OF SIGNAL HILL'S "WILD WERE THE WAVES") Transcript provided by NPR, Copyright NPR.
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