Oceans are hitting record heat levels. Could 'super corals' cope? Coral reefs face a dire future as oceans get hotter. Scientists are breeding corals that can handle heat better, in the hope they can survive long enough for humans to rein in climate change.

Scientists are breeding 'super corals.' Can they withstand climate change?

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STEVE INSKEEP, HOST:

Corals on Australia's Great Barrier Reef are going through a mass bleaching event. The ocean gets so hot the corals turn white. It's happening more often as the climate grows hotter. So scientists have started breeding super corals that can take the heat. Lauren Sommer from NPR's climate desk went to Australia to see them.

(SOUNDBITE OF FOOTSTEPS)

LAUREN SOMMER, BYLINE: One week a year, just after the full moon, Annika Lamb goes into work late at night.

ANNIKA LAMB: You're not really sure what's going to happen. There's a lot of magic. There's a lot of unknown.

SOMMER: She goes into a room full of massive tanks and puts on a headlamp with a red light.

LAMB: We don't want to be distressing the corals or confusing the corals. So our corals need darkness to be able to get signaled to spawn.

SOMMER: Lamb is waiting for corals to get in the mood. She works at the Australian Institute of Marine Science on the east coast of Australia. They figured out how to keep these sensitive animals alive at their lab.

LAMB: What you're seeing in the tank is just a little section of a much larger colony. Exactly.

SOMMER: They kind of look like little - I don't know, trees. What do they look like?

LAMB: Yeah. They have this really beautiful kind of branching structure.

SOMMER: This species of coral is one of the main builders of the Great Barrier Reef - an ecosystem that's so big it can be seen from space. They only make baby corals once per year, when, all together, on one night only, they release their genetic material, which fills the water like confetti.

LAMB: And then we're here ready to collect those eggs and those sperm.

SOMMER: Because the corals in these tanks are special. They've been put through tests and each one has a number, kind of like athletes after a race.

LAMB: So then the bold number on the end, that's their ranking. Yeah.

SOMMER: So that guy's the worst.

LAMB: Yes. Straight up. Yep (laughter).

SOMMER: But the best ones - those are the corals that can handle extreme heat, because heat can be deadly to coral. It causes them to lose the algae that live in their tissue, which is why they turn white. Those algae are important. They're basically the roommates that get the groceries. So without them, corals can starve. And as the climate gets hotter, that bleaching is happening more often.

LAMB: We're seeing rapid changes. We're seeing increased frequency of summer heat waves. And this is alarming, because we know that those disturbances cause mass mortality events out there on the reef.

SOMMER: The mass bleaching going on now is the fifth time it's happened on the Great Barrier Reef since 2016. Reefs can recover from these events, but not if they drag on for weeks or happen back-to-back, which is why Lamb is focused on these corals that can handle heat better. And she mixes them.

(SOUNDBITE OF WATER TRICKLING)

SOMMER: The results are in another set of tanks - a kind of coral nursery.

LAMB: So these are now about day three post-fertilization.

SOMMER: Three-day-old babies.

LAMB: Three-day-old coral babies.

SOMMER: At this age, corals are tiny, and they can swim. It's how they find a new spot to settle down. Lamb has tanks of them all with different parents. She's trying to breed a super coral - one that could survive climate change better. Corals have some ability to adapt to more heat, but climate change is happening too fast for them to keep up. So the idea is to help them out by assisting evolution.

LAMB: When we're talking about assisted evolution, we're trying to take those natural processes and speed them up.

SOMMER: But evolution is tricky. Lamb could breed only the very best corals at handling heat, but that might sacrifice other abilities they need, like resisting disease or handling cold temperatures. You need a coral that's good at everything to survive. So these corals are being put out on the Great Barrier Reef to see how they do. The hope is to create corals that can be used to restore reefs as conditions keep getting worse.

DAVID WACHENFELD: I think this is a defining moment in the history of the Great Barrier Reef. But honestly, it's a defining moment in the history of coral reefs all around the world.

SOMMER: David Wachenfeld is research program director at the Australian Institute of Marine Science.

(SOUNDBITE OF WATER SPLASHING)

SOMMER: We're standing on the coastline where the Great Barrier Reef extends miles offshore. Recently, they've seen impacts here they've never seen before, like in 2016.

WACHENFELD: The water got so hot so quickly. The coral just died. It did not bleach. So bleaching is a stress response. The coral did not have time to have a stress response. It just died.

SOMMER: The long-term outlook for reefs is not good. If humans keep burning fossil fuels at the same pace, 99% of coral reefs will likely die off by the end of the century. That could impact a quarter of all marine life on Earth that depends on reefs and the humans that need those reefs, too.

WACHENFELD: Hundreds of millions of people throughout the tropics of the world depend upon coral reefs for food, for economy and for coastal protection.

SOMMER: That's why his colleagues have started breeding super corals. But, he cautions, they are only a temporary solution. It's about buying time for coral reefs - helping them hang on long enough for humans to get climate change under control.

WACHENFELD: There are certainly very plausible future scenarios where, with the best science in the world, we won't be able to protect the Great Barrier Reef.

SOMMER: It's a heavy reality to face coming to work every day. Wachenfeld says he tries to stay positive.

WACHENFELD: We can develop the tools for tomorrow that give reefs and the people that depend upon them the best fighting chance possible. And that's what gets me out of bed every morning.

SOMMER: But not everyone agrees it's the right thing to focus on.

TERRY HUGHES: We're not going to solve this problem by breeding corals in an aquarium.

SOMMER: Terry Hughes is a coral scientist at James Cook University in Australia. He says the Great Barrier Reef is more than a thousand miles long, which means you'd need to grow massive amounts of corals to make even a small difference. And the risk to the rest of the ecosystem also needs to be considered, he says.

HUGHES: We have a long history on this planet of introduced invasive species that have been absolute ecological disasters. So we need new laws to regulate these novel interventions.

SOMMER: Hughes also thinks there's a risk in concentrating too much on these kinds of projects.

HUGHES: They send the subliminal message that the clever scientist can fix this, when in reality, the only way we're going to fix it is by reducing greenhouse gas emissions.

SOMMER: He says the most crucial thing for coral reefs is getting off fossil fuels and switching to renewable energy.

HUGHES: It's in our hands as a global society to determine the trajectory of the world's coral reefs and where it ends up. There's still time to reduce greenhouse gas emissions very sharply.

SOMMER: But, he says, that time is running out fast.

Lauren Sommer, NPR News.

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