New innovations attempting to rescue coral reefs

As Hurricane Fiona left a swath of destruction across the Caribbean and North Atlantic this past week, it was a reminder of the devastating power of coastal storms. Scientists are predicting more intense weather because of climate change, but they’re also warning that one of the best existing sources of protection from waves and floods is dying off. By serving as natural buffers, coral reefs prevent billions of dollars in damage to the U.S. each year, according to the U.S. Geological Survey. The state of Florida, which has been hit by 18 hurricanes over the last 40 years, has one of the largest barrier reefs in the world. But nearly 90% of the living coral in the Florida Keys has disappeared during that time. The situation’s so serious that marine biologists have stepped up their efforts to find innovative ways to try to rescue the reefs. And that’s what our story tonight is about. It involves strange underwater farms, the U.S. Department of Defense, and more than we ever thought we’d need to know about the sex lives of coral.

We left Miami behind us and headed two miles off the coast with marine biologists Andrew Baker and Diego Lirman. They’re old friends and colleagues, professors at the University of Miami, who’ve seen first-hand how the reefs have changed.

Andrew Baker: The whole of the Caribbean– is seeing a lot of coral loss and– and die-off as a result of climate change, but also water quality and– pollution. But, you know, Florida Keys probably leads the way in terms of the sheer amount of coral that’s been lost.

And that’s why, in this spot in the ocean, the University of Miami has built something you’d normally visit on land to buy a tree or a rose bush – a nursery.

Diego Lirman: This is our coral nursery. This is where we– just like you do on land. You grow your corals, you prune them, and then you put them somewhere else on– on a natural reef.

Diego Lirman and Andrew Baker

The water was murky and the current strong as we went to take a look. A nurse shark checked us out, but quickly lost interest. Corals are often confused with rocks, or plants, but they’re actually colonies of tiny animals called polyps, whose calcium carbonate skeletons build the reefs and protect the shores. After a short swim, we came upon an area with 40 of these tree-like structures.

Hanging from them, like Christmas ornaments, are pieces of living coral that have been pruned from healthy colonies all over Florida. They’re positioned close to the surface so they get lots of sunlight and nutrients and occasionally cleaned of macro-algae that can damage them. Andrew Baker explained…

Andrew Baker: The great advantage of these nurseries is they allow us to grow lots of coral tissue very quickly.  They grow faster in these trees than they do on the reefs.


Many of the corals growing here are important and threatened Florida species, like Staghorn and Elkhorn. Every diver knows you’re not supposed to touch coral, so it was odd to be handed a clipper and told to start cutting off pieces. We brought the staghorn coral I cut to an area nearby called Rainbow Reef that Professor Lirman and his team began re-planting two-and-a-half years ago. 

Correspondent Anderson Cooper with the coral he cut

He showed me how to use a special kind of cement to attach the newly cut pieces to the reef. With the current, it’s a lot harder than it sounds. But even more difficult is making sure these corals don’t get killed off by the same forces that destroyed their predecessors – water pollution, disease, and a phenomenon called “bleaching,” in which coral can lose their color and die because of rising ocean temperatures caused by climate change. 

Re-planting the coral

Andrew Baker: We need to make sure that the corals that we put out are not just gonna be the next set of victims for the next bleaching episode, or the next stressor that comes along. 

Anderson Cooper: In a sense, it sounds like you’re trying to accelerate the process of natural selection, try to find the corals which are hardier, which can survive in higher temperatures.

Andrew Baker: That’s exactly right.

To do that, Professor Baker and scientists from the Shedd Aquarium in Chicago are using a technique that allows them to determine the future survivability of coral in a few hours, on a boat anchored above the nursery. When we arrived, researchers were putting samples of Elkhorn coral just brought to the surface into these converted party coolers containing increasingly warm water to see which varieties would do best in higher temperatures. Ross Cunning is a research biologist with the Shedd Aquarium.

Ross Cunning: So just like all of us are different genetic individuals, and all of us humans vary in traits like height, all of these different genetic strains of Elkhorn coral will vary naturally in heat tolerance.

Anderson Cooper: So just because it’s all Elkhorn coral, it doesn’t mean it’s all the same genetically.

Ross Cunning: Right. And that’s exactly what we wanna get at is the fine scale individual variation among different Elkhorn corals. Then we can use those corals to optimize restoration programs by planting more of them on the reef.

Ross Cunning

Scientists are also trying to breed the most heat and disease-resistant coral together. It’s called selective breeding. Liv Williamson is a biologist at the University of Miami. Her lab is filled with vats of frozen coral sperm. 

Anderson Cooper: So this is coral sperm? 

Liv Williamson: This is coral sperm that has been kept at these really, really low temperatures now for a year or more.

Her work is similar to that of domestic animal breeders. She and her team mix the sperm with carefully chosen coral eggs, to create offspring that’ll be more likely to survive outbreaks of disease and rising ocean temperatures.

Anderson Cooper: I never thought I would ask this question. But h– how do coral have sex? (LAUGH)

Liv Williamson: So the idea is that all of the different colonies on a reef. They’re all using cues from the environment to make sure that they release their eggs and sperm all at once so that they’re able to mix with the spawn of other colonies.

The sex life of coral is nothing to write home about. Most spawn only once or twice a year after a full moon. So scientists have to be ready to capture the sperm and eggs at the exact right moment.

  Liv Williamson

Liv Williamson: We use very fine mesh nets with a jar at the top. And they slowly float their way up into the jar. And all we have to do is cap off the jar and take it with us. It literally looks like being in a snow globe under water. It’s amazing. It’s totally incredible to be able to see it.

This is where Williamson raises what she calls “the coral babies” she’s bred. The blue light mimics sunlight filtering through the water, helping them grow.

Liv Williamson: This particular brain coral baby that you’re holding right now is actually the offspring of a– coral colony here in Miami that we think is resistant to disease… 

Anderson Cooper: So you know the history of these polyps.

Liv Williamson: Yeah, in many cases I collected them as eggs or sperm. Or I put them together to fertilize them– have been there really since– since birth, if you will.

Anderson Cooper: Do you feel, like, warm and cuddly toward coral?

Liv Williamson: I really do. (LAUGH)

Anderson Cooper: Because, I mean, it’s not something that…

Liv Williamson: They don’t seem too warm and cuddly.

Liv Williamson: I show coral baby pictures to people. And they usually don’t want to see them. But– (LAUGHTER)

Cooper and Williamson

Today, they’re growing slowly on small ceramic plates. But they may someday be growing in underwater nurseries and re-populating reefs.

Anderson Cooper: And so this one’s– how old?

Liv Williamson: Al– almost a year old. Corals in general grow really slowly. But that’s part of the problem with their conservation is that while we’re losing these big, old colonies on the reef, some of those are thousands or hundreds of years old. They’ve taken so long to grow. Replacing them isn’t easy.

But with less coral serving as a natural buffer, many communities need more protection right away from increasingly powerful storms that have been battering their shores.

One way researchers hope to restore coral and provide more immediate protection along the coast is to create hybrid reefs. This is a small-scale prototype. The honey-combed structures on the bottom would be made of concrete and are designed to absorb wave energy immediately. The corals on top would provide more and more protection as they grow.

A prototype hybrid reef

Inside this simulator at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science, Professor Brian Haus and his team can create the equivalent of a category five hurricane with winds up to 155 miles per hour.

The simulator can test how well different structures and types of coral absorb wave energy and prevent damage on land.

The University of Miami is developing this hybrid reef for DARPA, which is the Pentagon’s research agency. The Defense Department is looking for ways to protect its many military bases near the coast, like Tyndall Air Force Base in Florida which got destroyed by Hurricane Michael in 2018, causing nearly $5 billion in damage. DARPA plans to give the University of Miami up to $20 million to build a hybrid reef off the coast of Florida within the next five years.

Brian Haus

Anderson Cooper: What role does coral play in that, as opposed to just a man-made honeycomb structure?

Brian Haus: Depending on the types of waves and things, you can have anywhere as high as 60% of additional dissipation of wave energy by having corals on top of the structure. They add friction to the surface.

Anderson Cooper: I mean, this isn’t just a man-made structure that is static. because of the coral, it would actually expand. It would continue to grow?

Brian Haus: that’s one of the real exciting things about this. It’s essentially self-healing. And I– if it gets impacted by a storm, it can grow back.

Professors Baker and Lirman will provide the coral on DARPA’s hybrid reef, with specific goals in mind.

Anderson Cooper: They have very ambitious goals for you.

Andrew Baker: They do and I think that reflects the– the scale of the problem, to be honest. We know that, for example, coral reefs are going to be facing increasing warming temperatures. So, here’s a project that’s asking us to try to achieve what corals are gonna face in 20 to 30 years within just a five-year timeframe, and then actually go well beyond that. 

Anderson Cooper: So, they’re saying within five years that they want you to be able to find coral that can resist a two-degree centigrade rise in temperatures in the ocean?

Andrew Baker: That’s right. two or even three degrees centigrade warmer temperatures.

Anderson Cooper: Were you surprised that DARPA was interested in your work?

Andrew Baker: We were surprised in the sense that it was the Department of Defense that was the first agency to come forward and say, “Hey, you guys, as a community, why don’t you think big?


DARPA also recently awarded contracts to Rutgers University to create a hybrid reef that’ll use oysters rather than coral… and to the University of Hawaii which is developing a different configuration of coral and other materials. And DARPA’s not the only government agency taking action. The National Oceanic and Atmospheric Administration is using nursery-grown coral to restore seven iconic reefs in the Florida Keys National Marine Sanctuary.

There are many potential obstacles to restoring coral reefs – as Diego Lirman and his team learned after Hurricane Irma hit Florida in 2017.

Diego Lirman: It was a major setback. We– we lost 90% of all of the corals that we had been growing for a decade.

Anderson Cooper: Wow.

Diego Lirman: It was a huge loss. But we also rebuilt very quickly.

There’s not much anyone can do about a major hurricane. But perhaps the biggest criticism of restoring reefs or creating hybrid ones is that it’s not possible to do this on the scale that’s needed.

Anderson Cooper: There are some people who think this is like spitting into the ocean, that this is not gonna be enough to counteract climate change.

Andrew Baker: We get that all the time. But if we don’t address this challenge in terms of maintaining coral resilience in the meantime while we deal with some of these larger societal problems, we won’t have any coral reefs left by the time we get this other problem under control.

Anderson Cooper: Without a meaningful reduction of carbon gasses to address climate change, will you be able to rescue the reefs?

Diego Lirman: Absolutely not. the mantra is, “We are buying time.” 

Anderson Cooper: The intergovernmental panel on climate change predicts that with a– two degrees Celsius– increase in warming, 99% of the world’s coral reefs could be irreversibly lost in the next 30 years. I mean, that’s a pretty dire assessment.

Andrew Baker: That’s right. So, coral reefs are on their way to becoming probably the first global ecosystem — that we’ll lose as a result of climate change. So, you know, we– we have no time to lose.

Produced by Andy Court. Associate producers, Evie Salomon and Annabelle Hanflig. Edited by Sean Kelly.
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