♪ M. Sanjayan: When you think about all the habitat types on Earth that are sensitive to climate change, obviously, ice comes to mind.

But the other thing that comes to mind is coral reefs.

Healthy reefs are vital for marine wildlife.

Over a million species depend on them to survive, from the tiniest fish to flocks of seabirds and gigantic manta rays.

Around the world, 500 million people rely on reefs for food and to protect coastlines from storms and rising sea levels.

They're also crucial for humanity as a whole.

Coral reefs are the cornerstones of a well-functioning ocean ecosystem.

They create habitat for seagrass beds and mangroves, which in turn absorb carbon and store it, helping to stabilize the climate.

But the future of coral reefs is hanging in the balance.

♪ They are really sensitive to lots of things-- seawater rise, seawater temperature, acidification of the oceans, pollution-- and that's why they are really one of the most endangered habitats on Earth.

We are at a tipping point.

♪ Half of all coral reefs have already been lost or severely damaged.

And experts predict that without action, nearly all reefs could die off in the next few decades.

♪ Now groundbreaking scientific collaborations are offering a beacon of hope, if they work.

♪ For the past two years, this ambitious project has been following the pioneering work of scientists and conservationists at key places around the world.

But this year, I'm focusing on a habitat that's facing the most urgent threat--coral reefs.

♪ I'm taking a special in-depth look at the crucial efforts to save coral and innovative techniques that could bring reefs back to life.

Man: Reefs around the world are literally collapsing 'cause they don't have enough corals on them.

♪ Woman: Everything we do today has to focus on saving what we have and rebuilding what we've lost.

♪ Sanjayan, voice-over: My search for practical, scalable solutions has brought me here to the Maldives because this is the epicenter of climate change, coral reefs, and practical science.

♪ ♪ Coral reefs are extraordinarily sensitive to temperature.

They can live and thrive in a narrow band of temperature, and when temperatures spike, you often get bleaching.

♪ Under stress, corals bleach.

The tiny coral animals eject the symbiotic algae living within them and lose their magnificent color.

♪ And when that happens, it makes them more susceptible to death and disease.

And so, you get too much bleaching, and coral reefs ultimately disintegrate, and the recovery is extraordinarily slow.

♪ More than 90% of the heat from greenhouse gases and emissions from fossil fuels is absorbed by our oceans.

Seawater temperatures were the hottest ever recorded in 2023.

♪ As bleaching events become more frequent, there's a race against time to find ways to help damaged reefs recover.

♪ Lying 450 miles southwest of Sri Lanka in the Indian Ocean, the Maldives are a chain of nearly 1,200 islands clustered in circular formations called atolls.

♪ As the flattest country on Earth, much of it just 3 or 4 feet above the waves, healthy reefs provide vital protection for the half a million people who live here, as well as income from tourism and fishing.

But the clock is ticking on this ecological time bomb.

♪ The last big bleaching event in 2016 damaged 73% of the coral here, and it struggled to recover.

♪ I'm here to meet top marine biologists from opposite sides of the globe who are coming together for an ambitious rescue project that's never been tried before.

If successful, it could be the key to restoring coral reefs, not just in the Maldives but around the world.

Man: That's beautiful.

I mean, I'm really happy... Sanjayan, voice-over: Peter Harrison has spent decades studying how corals reproduce and has invented a technique to maximize their success.

Basically, fertility treatment for corals, a bit like IVF.

Science underpins everything we do.

Understanding how corals spawn, how the embryos develop, what they need, how we settle them.

And doing it at scale.

And doing it at scale.

But in terms of making it a production system on the reef, it goes into a completely different world, and that's what I've been exploring for some time now.

♪ Sanjayan, voice-over: Steve Simpson is an expert in underwater acoustics.

Last year, we saw Steve discover that microscopic coral larvae respond to fish vocalizations and, crucially, they're triggered to sync, settle, and grow.

Look at that.

I mean, that one's falling out of space.

It looks like a meteorite, doesn't it?

Sanjayan, voice-over: These two eminent scientists are collaborating for the first time by combining Peter's coral fertility treatment to produce millions of baby coral with Steve's acoustic expertise to lure them to settle on the damaged reefs here on Laamu Atoll.

♪ Sanjayan: This is your first time meeting with Peter and the rest of the team.

It feels like we're almost kind of tunneling from opposite ends of the same problem, and this is our chance to meet in the middle.

Yes.

I love science that's always on the edge of two different disciplines.

When it comes together, it's kind of magical.

♪ Sanjayan, voice-over: Steve and Peter are working with local scientists from the Maldives Underwater Initiative, who predict that in the next few nights, just after the March full moon, there should be a mass coral spawning event.

Coral spawn under the cover of darkness, releasing billions of eggs and sperm into the ocean that the team will collect.

They plan to turn the waters around Laamu Atoll into a giant coral IVF lab.

♪ But first, the team needs to find out if the coral is actually ready to spawn.

Peter L. Harrison: Today's dive is really about going out and checking as many corals as possible.

So, we'll look to see whether we can see colored eggs and sperm developing.

So, let's go diving and see what we can find.

♪ Sanjayan: Really amazing seeing this reef.

♪ Just a couple of days after the full moon now, and if the coral are gonna spawn, now would be the time.

The problem in the Maldives is that they don't all spawn at the same time.

OK.

I think he might have spotted one.

It's only a small bit, but it's still quite strange for me to see someone break coral because as a diver, you are just taught never touch coral.

It's not ready to spawn.

OK. Sanjayan, voice-over: Once it's put back, that fragment of coral will repair itself and regrow.

Sanjayan: This reef that we're on is in pretty decent shape, although you can see that it needs restoration.

It was bleached out by warming, and it hasn't really fully recovered.

So, it's an ideal place for Peter and the team to really set up long-term experiments on coral restoration.

♪ Sanjayan, voice-over: Coral are incredible creatures, related to jellyfish.

Just like jellyfish, they have tentacles with powerful stinging cells that they use to catch prey, like plankton or small fish.

♪ Most are colonial.

The structure we see is made up of thousands of tiny genetically identical animals called polyps, all living together.

♪ Oh, yes.

So the inside has these tiny pink or red dots.

Those are just globules of eggs and sperm in a little packet.

So, if we're lucky, we come back to this coral tonight, we should see active coral spawning.

♪ Sanjayan, voice-over: We'll have to wait until after dark to see if the coral really will spawn.

♪ The project in the Maldives aims to help coral reproduce more effectively.

But what about areas where there's barely any coral left?

♪ Florida has the third largest barrier reef in the world, a 360-mile-long living storm break, home to hundreds of species of fish, dolphins, and sharks.

♪ But now its survival is on a knife edge.

In fact, its future relies on a state-of-the-art facility 20 miles inland.

♪ Woman: Over the last 50 years, we've lost over 98% of our living coral, meaning we only have 2% left.

So, we are truly at the brink of functional extinction.

♪ Sanjayan, voice-over: This high-tech warehouse is like a Noah's Ark for Florida's coral, a last-ditch attempt to prevent them going extinct.

If every coral dies throughout Florida's coral reef, we have the building blocks here within the ark to rebuild that reef from the ground up.

♪ Sanjayan, voice-over: Erinn and the team feed and nurture thousands of coral fragments... ♪ all part of a huge groundbreaking project to resuscitate Florida's reefs.

The coral reef is so important that there's a collaborative effort to restore 3 million square feet of the reef over the next 20 years.

It's gonna take $100 million to do it and at least a million corals.

♪ Sanjayan, voice-over: Breeding a million corals is no small feat.

And the team want to future-proof Florida's reef by only breeding corals that are tough enough to survive warmer oceans.

We don't want any random corals to be the parents.

We want them to be the super heroes.

So, what we do is expose a lot of our corals to high water temperatures, temperatures that aren't just high today, but what we expect to be really high in 100 years from now.

Sanjayan, voice-over: And sea temperatures are already reaching record highs.

In the summer of 2023, waters around Florida hit over 100 degrees Fahrenheit.

Muller: If we can future-proof them, the corals that we put out on the reef today could be around for thousands of years to come.

♪ Sanjayan, voice-over: Back in the Maldives, Steve wants to create the perfect soundtrack to attract coral larvae to set up home on a degraded reef.

Jess Hodge, a marine ecologist researching coral restoration at Laamu, has spent the last few months identifying prime spots to record the sound of marine wildlife on a pristine reef at the peak spawning season.

♪ Just from the audio recorders, you can hear the health of this reef.

When you hear it compared to some of our other sites, when you have that comparison side by side, you can really hear the difference and you can hear how healthy it is.

It's really exciting.

Sanjayan: The coral larvae are attracted to these sounds, right?

We know that from lab work.

We first discovered it with an experiment where a group of collaborators took my speakers, took a bunch of coral larvae, played the sounds, and to my amazement-- I thought they were crazy-- these tiny coral larvae started moving towards the speaker.

You didn't think that would happen?

No, I just thought these--these-- I mean, they don't have ears.

They haven't got ears, they haven't got a central nervous system, they haven't got a brain.

Yeah.

And yet somehow, they were able to move towards sound.

I mean, it's almost like magic.

It's crazy.

And the whole idea here is to try and see what can encourage them to come back to a reef.

That's right.

Yeah.

So, our plan here, really, is to try and understand what sounds in the Maldives, in Laamu Atoll, the local corals can hear, are attracted by, and then when we go to some of these degraded sites, can we actually accelerate recovery of those sites using sound?

♪ Sanjayan, voice-over: Jess has identified a pristine reef called Hassan's Haa as a good spot to record.

And she's had audio recorders underwater for a week.

While she's collecting them and deploying new ones, I want to see what a healthy reef should look like.

♪ This reef is only 8 miles away from the damaged one we're trying to restore, and yet it was largely unaffected by the bleaching event.

♪ That's a good size range.

And it's nice to see these big-- this big fish also use this reef.

We've seen a few sharks.

It's a clear sign that this reef is really healthy.

Look at the size of this guy!

♪ Sanjayan, voice-over: Ultimately, all the marine life here, from large predators to tiny fish, rely on the coral.

Sanjayan: Here in the Maldives, there are over 260 different reef-building corals.

And you can see the diversity of that living system here.

Lots of life, lots of color, and lots of living coral.

This 3-dimensional structure, this skyscraper under the ocean.

A healthy reef, like a healthy city, makes lots of sound.

♪ Sanjayan, voice-over: The hope is that the soundtrack from here can help to regenerate nearby reefs that were devastated by bleaching.

♪ Warming seas are just one challenge that corals face.

In Florida, there's another threat... an underwater pandemic that's having a devastating effect.

♪ Muller: Stony coral tissue loss disease has been around since 2014.

It's the largest and most deadly coral disease that has ever been recorded.

Sanjayan, voice-over: This disease can spread frighteningly fast, potentially 100 meters a day, leaving thousands of dead and dying coral in its wake.

Muller: When I was diving at one of my favorite reef sites that just has these huge, several-hundred-year-old brain corals, corals that have been around here since Columbus landed, and when I went down, I could just see that half of them were just bright white from stony coral tissue loss disease.

Seeing that kind of loss and devastation just really was heartbreaking, and I literally cried underwater.

Sanjayan, voice-over: Stony coral tissue loss disease has spread to 20 different countries, prompting scientists from completely different disciplines to collaborate on developing a treatment.

♪ So, my background is in chemical engineering and formulation science, and Erinn is an expert in coral ecology, but we're able to sort of work together and use each other's expertise to create something that has never been done before.

Muller: What we're doing here is we're creating a medicine to treat stony coral tissue loss disease.

This one in particular utilizes amoxicillin.

Curtis: The bright color is not only beautiful, it actually acts as a marker, so, it indicates how much of the amoxicillin still remains in the treatment.

So, if you go down there and you can see that it's turned white, then you know that all of the amoxicillin has been administered to the coral.

♪ Muller: The good news is, is that we have a way to treat stony coral tissue loss disease, but it relies on an antibiotic.

And there are risks, like creating antibiotic-resistant bacteria.

Sanjayan, voice-over: If the disease becomes resistant to the current treatments, it could become unstoppable.

To try to stay one step ahead, today, Erinn is testing out some new medicines that don't rely on antibiotics.

Muller: On this side, we're gonna be going underwater and looking for sick corals and apply a paste right onto where the coral is looking sick.

♪ Every time we go down underwater and see a sick coral and can save it from dying is a success in my eyes.

But I know that in a decade from now, we're gonna be a much better place than we are in today.

♪ Sanjayan, voice-over: Back in the Maldives, it's time to analyze Jess' sound recordings from the healthy reef.

[Recording: crackling sounds] Sanjayan: Wow.

I mean, there's a lot of information there, isn't there?

Right?

It is.

I mean, that's hundreds of animals, possibly thousands of animals, all overlapping each other.

But what I'm listening for with this is particular acoustic events that I can go and try and investigate, OK?

So, you can probably even see it in this spectrogram.

Yeah.

So, this is just a visual representation of all the sounds.

Simpson: That's right.

Sanjayan: And I can see this spike.

You can see this event, right?

So, what we hear in the soundscape quite often is individual pops-- [Imitates popping] sort of sounds, OK?

And then here we get to a point in the recording... [Recording playing] Simpson: OK. Did you hear those two?

So, there's a double-- [boop-boop] and then a [grr].

Exactly.

Play that again.

[Recording: two percussive taps, then rapid percussive sounds] Yeah, like a double tap.

[Da-da], and then a [brr], OK?

Now, this is all synced with the 360 camera.

You go back to the video to that exact same moment and see who's doing that.

Exactly.

Exactly.

So, these humbug damselfish.

[Recording playing] Simpson: And so, these are the sounds that I want to now go and play to our baby corals, because these are the sounds that corals would be listening out for to choose the best place to go and make their home.

[Recording playing] Sanjayan, voice-over: Steve now has what he needs for his part of this groundbreaking experiment.

♪ But without Peter's coral larvae, this venture will fail.

♪ Now is the moment of truth.

Will the corals we checked earlier actually spawn or not?

♪ Peter and the team use special nets to catch as much spawn as possible before it drifts away on the current.

♪ You can see how this ingenious device works.

It just allows the spawn to come up, and it catches it in sort of a mosquito net, really, and just traps everything up there because that spawn just wants to rise to the top of the surface.

There.

Yes, there.

That's it.

Oh, that's one of them.

Just going up to the surface.

Little, little globules of fat, eggs, and sperm in a bundle together.

That's where this entire reef comes from, that beginning.

♪ There's all these guys coming out now.

You can really see it now just kicking off.

Oh, hundreds.

Hundreds and hundreds.

♪ It is just great.

Science in action.

To see it in front of me, to go today, find this coral, know that it might be breeding tonight and then come back here, just amazing.

♪ Absolutely amazing.

♪ Good job, Peter.

That's superb.

Thank you.

Honestly, thank you.

This is once in a lifetime.

♪ How cool was that?

Look at this.

Look at this.

Oh, egg and sperm bundles.

There's gotta be thousands of larvae we can try and rear from these.

That was way better than even what I expected.

So, thank you.

You're very welcome.

I'm so glad you're here on such a magic night, 'cause this is really important for the reef.

This is when the reef gets reborn.

Yeah.

Oh, look at that.

Whoo-hoo!

Oh, such a good sight.

[Chuckles] You know, I can smell them.

Yes, you can, and that's the smell of coral spawn.

So, I know when corals are spawning by the smell.

It's so fantastic... they smell.

And I bet you that's how fish figure it out, too.

Yeah, absolutely.

Yeah.

I mean, it really smells like, um, like uni, you know, like sea urchin eggs.

If you have sushi, you have uni.

Yeah.

Because I was smelling something, but I didn't want to ask.

I was like, is that that or is that you?

Yeah, it's me.

Well, we're all gonna stink of coral spawn after tonight, but it's a good smell to have.

[Chuckles] Sanjayan, voice-over: The future of the reef could be determined by this bucket full of smelly spawn.

By putting all the collected eggs and sperm in one container, there's a much greater chance of reproduction than in the wild.

♪ So, by doing this technique, we can maximize fertilization and we can also increase genetic diversity.

Yeah.

Thank you, sir.

Really appreciate it.

Really appreciate it.

That was good fun.

♪ Sanjayan, voice-over: Whilst the project in the Maldives is designed to maximize coral spawning success, the team in Florida are growing coral in the lab in a much more radical way--cloning.

♪ Corals can reproduce sexually just like humans do, where sperm and egg combine to create a zygote, and then eventually, you get a baby coral.

Or a colony on the reef can actually fragment or break into multiple different pieces, and each of those pieces can become an independent colony that's a clone of the original.

Sanjayan, voice-over: It's like taking a cutting from a plant to create a new one.

But Jason and the team supercharge and speed up this process by breaking the coral up into tiny pieces.

Spadaro: It's very much like your skin.

Your skin is growing constantly but very slow.

But if you damage it, it jumps into high growth phase, right, to heal that wound.

So, when we're cutting these corals into small fragments and it jumps into that healing growth phase where it grows 40 to 60 times faster than a natural fragment.

♪ Sanjayan, voice-over: It might sound brutal, but encouraging coral to grow as fast as possible is vital in the race against time to restore Florida's reef.

Once the coral fragments reach a certain size, they're ready to be acclimatized back in the ocean and grow even bigger.

Spadaro: Underwater here is one of our offshore coral nurseries.

It's about an acre in size.

It holds 400 coral trees.

Each one of those coral trees can hold between 100 and 160 fragments of coral.

Sanjayan, voice-over: Many of these corals have been bred to resist warmer and more acidic waters, and they are destined to fill a hole on Florida's reef.

And because they're clones, these coral fragments will join forces.

Spadaro: If you plant them close enough to each other, they'll grow and fuse instead of fight 'cause they'll recognize that they're the same critter.

And within a few years, you actually have all of those fragments grow, touch, fuse, and become a large reproductive colony that would have taken a natural recruit somewhere on the order of 25 or 50 years.

Sanjayan, voice-over: Not only does fragmentation produce thousands of corals, it also means they grow to reproductive size up to 10 times faster than normal, accelerating the rebuilding of the reef.

But each coral still needs to be planted by hand, time-consuming and labor-intensive work.

So far, the team has planted over 216,000 corals, but Jason is aiming for 50% coral coverage, which will need about two million corals.

To meet this ambitious target, the process is going to have to expand exponentially.

Spadaro: There are folks looking at automation and robotics that go into the production and outplanting so that we can scale this to the point where globally, we're moving from tens to hundreds of thousands of corals a year to billions of corals per year being put back out on the reef and surviving.

♪ Sanjayan, voice-over: Back in the Maldives, our next step is to create a safe place for the developing embryos to grow for a few days before being put out onto the damaged Olhuveli reef.

We set up inflatable pools to act like coral nurseries made from netting that has holes small enough to keep the spawn in but large enough for water to flow through.

Harrison: So, what we need to do now is transfer the embryos we've got in those cultures, which are going well.

Corals are really sensitive.

Their eggs and sperm react really badly to changes in the environment.

So, we need to protect them as much as possible during this critical early, high floating stage at the surface of the water.

So, what we're gonna do now is inflate these pools that we've developed, and then we're gonna pop a net inside the pool, and then we're gonna tow these over and anchor them nearby, and then we're gonna transfer those embryos across into the pool and hope we don't get torrential rain in 12 hours.

A bit of trial and error, but it mostly works well from the beginning.

[Indistinct conversations] [Drill running] ♪ Sanjayan: What I love about being here in coral-- frankly, coral science--is that it's so cutting-edge.

It's so new in some ways, that everything you're seeing, you're seeing for the first time kind of ever, and every step has such massive chance of failure.

Like, if it rains, it's done.

If this pool doesn't blow up, we're done.

Sanjayan, voice-over: In another world first, this coral nursery is going to hear a soundtrack.

Steve is going to play the sounds of a healthy reef to the baby coral that he will later use to attract them back to the degraded reef... Simpson: And then convince them to go down and settle into these places where they've got a great chance of survival, but they'd never find it.

-In the lab, you've shown this.

-Yeah.

So, this is basically trying to replicate it, but with a very large chamber in the open ocean...

This is an industrial scale.

This is taking it up to the scale that we need it to be to be able to really restore coral reefs.

That's what I love.

Like, it's innovation every step of the way.

It's science, it's engineering, it's natural history, and it's conservation and restoration at a grand scale.

It's that hive mind, isn't it?

Absolutely.

Exactly what you need to solve, like, things like climate change, right?

It's never gonna be solved by one thing or one discipline.

It's gotta be cross-disciplinary, and I think that is what is so cool about this.

♪ Harrison: OK. Whoo-hoo!

Sanjayan: I don't know how that did it.

Harrison: Down, down, down, down, down.

Put 'em down.

You're good?

Hodge: OK, now what?

Sanjayan: Now what?

Harrison: OK, and then we're going to-- Simpson: Go down from here?

Harrison: Take it across and pop it in the middle there.

Well done.

[Cheering and applause] Fantastic.

♪ Sanjayan, voice-over: The reef restoration will be an ongoing process.

Peter is going to leave the nursery pool here and train the local team how to use it for future spawning events.

♪ [Indistinct conversations] ♪ Harrison: Give it a little push.

Whoo-hoo!

Simpson: Very nicely done.

OK, divers, ready to rock?

♪ Sanjayan: Now one more critical step, which is, How do you get this spawn, which is in giant buckets here, into the contraption?

One slip and it goes over in the ocean and experiment's done for at least a month, if not more.

Steady, steady, steady, steady, steady, steady, steady.

OK. Ready?

Careful.

♪ Yep.

Ready?

Keep it even, keep it even, keep it even.

That's right.

And now gently pour it in.

♪ Whoo-hoo!

Babies!

Hodge: Babies.

[Cheering and applause] ♪ Well done.

♪ Sanjayan, voice-over: We have seen how Florida's reef have been devastated by a coral disease.

But it's facing another problem.

It's been overrun by algae.

Oh, that's just gut-wrenching every time.

Devastating.

♪ Sanjayan, voice-over: A healthy reef depends on a delicate balance of interactions between algae, coral, and other animals.

When one vital piece of the jigsaw is missing, the result can be disastrous.

In 2022, a critically important species of sea urchin that grazed seaweeds and algae was killed off by a deadly parasite, leaving the reef in serious trouble.

Spadaro: When we don't have enough herbivores on the reef, eating the algae as it's growing, it can get out of hand.

It can get overgrown, and it can absolutely smother corals or even engage in kind of chemical warfare with corals and cause disease and--and other things that really are a problem.

Algae also cover up the space that little baby corals need to settle and make it so that they can't find a place to settle and become a new coral colony.

So, essentially, there are no babies on reefs with too much algae.

Sanjayan, voice-over: With more than 98% of the urchin population wiped out, Jason and a team of researchers are hoping that another grazing animal can step up and take over the urchin's role.

Spadaro: This is the Caribbean king crab.

This is a very large male.

They're phenomenal herbivores.

They eat algae and they eat algae that other stuff won't, more algae than most of the urchins in the region as well.

Sanjayan, voice-over: So, could these crabs be the answer?

Spadaro: In field tests, we increased the density of these crabs by about a millionfold, from one per square kilometer to one per square meter on these small test reefs.

And over the course of one year, they grazed the algae down by about 85%.

So, we're very confident that these are-- these are excellent candidates for grazing on coral reefs.

Sanjayan, voice-over: But the number of crabs needed to make a real impact is mind-boggling.

Just to meet the needs for 7 of the reefs that we're working on, we're going to need to produce 2.8 million crabs.

Sanjayan, voice-over: To create such an enormous army of algae eaters, Jason has set up a huge crab breeding facility.

♪ Spadaro: Here's a little baby right here.

You can see him on my finger now.

♪ This little guy could be the size of that larger male in 8 to 10 months from now.

♪ They're fast-growing and ready to go out onto the reef very quickly.

♪ So, they're just a dream to work with.

Sanjayan, voice-over: Today, Jason is diving to check on his expectant mothers.

♪ Spadaro: The color of the egg kind of tells us what developmental stage the eggs are in, and these dark red eggs, they're about halfway through.

So, she's probably a week and a half in or a week and a half out from-- from hatching.

Sanjayan, voice-over: By carefully nurturing the mums and babies, Jason and the team aim to produce 250,000 juvenile crabs a year to release onto Florida's reef and increase the population density by a millionfold.

♪ It might seem like a crazy strategy, but Jason believes the risks are low.

Spadaro: First, they're a native species.

They naturally occur throughout the entire region.

And all we're doing is increasing their density to fill this functional void on the reef.

Sanjayan, voice-over: By closely monitoring the crabs and their effects on the reef, Jason can detect any adverse effects, but ultimately, more crabs mean more food for their predators, like groupers, snappers, and octopus.

♪ When coral reefs are under threat, all the marine creatures that rely on them are vulnerable, too.

♪ Hawksbill turtles have swum in our oceans for over 100 million years but are now critically endangered.

♪ In the Maldives, a team of researchers is dedicated to monitoring and protecting these beautiful turtles, whose lives are completely intertwined with the health of the reef.

♪ Man: Hawksbills feed primarily on sea sponges, and so, the reefs provide a lot of area for sea sponges to grow.

So, without the hawksbills, a lot of these sea sponges that are regularly fed on would tend to grow over some of the corals.

They compete with corals for space on the reef, and sometimes they might outcompete corals and end up actually taking over entire reef systems.

♪ Sanjayan, voice-over: Turtles are vital for the coral to thrive.

And the reverse is also true.

Without the reef, the turtles have no food.

The team keeps a close eye on the population here.

Woman: We take photo IDs from both sides of their faces 'cause the scales on their face, they're different from one turtle to the other.

Kind of like a human fingerprint.

So you kind of monitor them using that photo ID?

Yes, yeah.

And you can individually map a turtle.

And what does the population look like here?

So, we've been doing this photo ID study for just over 4 years now, and we've documented about 830-plus turtles.

Just over 500 are hawksbills, and just over 300 are green turtles.

Sanjayan, voice-over: Today, I'm joining Sarah and Julian on their survey to photograph the turtles visiting this reef and see if any new faces show up.

♪ Sanjayan: This reef has loads of turtles, particularly hawksbill turtles.

And, you know, for a critically endangered species, I saw, I think, at least 3 down there.

Sarah Ibrahim: So, these are the pictures we took today.

Oh, wow.

That's a great shot.

You're right.

You can really see the pattern.

Ibrahim: The pattern.

So, who is it?

Sanjayan, voice-over: These distinctive scale patterns allow the team to identify individuals.

Ibrahim: Found it.

Sanjayan: You did?

This one.

Look at the-- Wow.

Yeah, I can buy that.

Ibrahim: Yeah.

Yeah, and then that's that, that's that.

That's that.

Yeah.

So, what's that one called?

Does it have a name or just a number?

Yeah.

Bandit.

Sanjayan, voice-over: Bandit is just one of hundreds of hawksbills on the team's database.

By keeping track of individual turtles, they can monitor any changes in the population and their movements across the globe.

The long-term hope is that other projects around the world will start using photo ID so that, let's say if we see one of the hawksbills foraging here in the Maldives and someone takes a picture of a nesting hawksbill in, let's say, Madagascar or even Sri Lanka, then we can instantly match the turtles.

To a global database where every hawksbill is essentially identified and you have that full tracking capability, so, if it shows up on the other side of the world, you know it's from here.

Exactly.

And then we can start to build that map so that we can also better protect their foraging and nesting sites.

♪ Sanjayan, voice-over: The hawksbill population here depends on a healthy reef for their survival.

♪ Anything that can help damaged coral on Laamu Atoll recover can only bolster their numbers.

♪ Coral reefs protect the Maldives from storm damage and erosion.

But it's not just island nations who are struggling with rising sea levels and extreme weather events.

♪ In 2018, Hurricane Michael hit Florida's coastline and powered straight through Tyndall Air Force Base, causing $5 billion in damage.

Now the Department of Defense is turning to coral to protect the U.S. military.

♪ It's funding scientists at the University of Miami to create artificial reefs.

♪ Man: This is the only facility in the world that's able to generate Category 5 hurricane force winds, which is 150 miles an hour and higher.

And at that point, really, the damage is catastrophic.

♪ Sanjayan, voice-over: This huge 75-feet-long tank allows Andrew and his team to design reefs that can reduce storm damage.

Baker: If you look upstream of the two reef lines, you can see that there's a lot of turbulence and stormy conditions.

But as you move over the first reef line, and especially over the second, you've got much calmer conditions.

Sanjayan, voice-over: Andrew is hoping to create a hybrid reef, a concrete structure designed to dissipate dangerous waves covered with a living coral layer.

But rather than traditional methods of farming coral, he has a more high-tech option... ♪ printing live coral larvae onto a substrate with everything it needs to grow.

Baker: What we're trying to do is to make sure that every single one of those baby corals has the best chance of surviving, and the way we're doing that is to give each one of them a sort of a life support system that has all of the ingredients that they need in it for survival.

♪ Sanjayan, voice-over: This droplet of gel contains a single coral larva plus beneficial bacteria and probiotics... and, most importantly, the vital microscopic algae that it needs to take into its body to provide energy.

Baker: We need to give them those tiny algae and, ideally, give them exactly the right kinds of algae that will help them survive in a warmer climate.

♪ This is brand-new.

We've never tried this before.

I mean, in theory, it should work, but there's often a big gap between in theory and practice.

Sanjayan, voice-over: Within a few years, a machine like this could be pumping out thousands of coral life capsules every hour that could create a ready-made living reef.

Baker: And that's really where the key to the restoration of coral reefs is going to be in the future is scaling up, making it cheap, making it fast, and making it easy.

♪ Sanjayan, voice-over: It might seem like science fiction, but producing living reefs on an industrial scale could soon be science fact.

♪ Engineered to protect coastline from the power of the sea and covered with coral, these hybrid reefs could provide home for wildlife and protect our homes.

Baker: Healthy coral reefs that already exist around Miami and Fort Lauderdale protect those communities to the extent of about $675 million a year in avoided damages.

And that's just on a regular year, not a year that we have a particularly powerful storm.

And so, these nature-based approaches are really beginning to be appreciated for the hard dollar value to protecting coastlines and protecting the bottom line.

We have so much to lose and, therefore, so much to gain by getting it right.

♪ Sanjayan, voice-over: It's clear that coral reefs have huge benefits for both people and nature, but globally, they're in urgent need of help.

♪ Back in the Maldives, we're ready for the final stage of this new IVF process that has the potential to bring dying reefs back to life.

Over the last few days, the coral larvae have developed in their safety net, and now they're ready to be released onto the damaged reef, where they will hopefully settle and grow.

Each tiny larva is precious, so, the team have a special remotely-operated vehicle to deliver them to exactly the right spot.

♪ Woman: This is Floaty Boat.

She's been designed to help automate the larval restoration work that we've been working on.

Once we've reared the coral spawn into their larval stage and they're ready to settle, we pour it into this bladder here.

It holds 100 liters.

And then we have a larval-friendly pump here.

It draws in the concentrated larvae, and then it pushes the larvae out without damaging the larvae.

There's a camera that classifies the substrate in real time, whether or not it's suitable for larvae to land and grow on.

♪ Sanjayan, voice-over: At first, Peter and the team must carefully retrieve the larvae from their nursery.

♪ Harrison: That's looking good, folks.

Really good.

Lifting.

Look at that.

See, this is how it works.

Love it.

Perfect.

Oh, what a team.

OK, you're watching this, guys?

[Splash] [All cheering] OK, we'll have one bucket to rinse this out, please, then we'll wash the last of the larvae down.

Man: That's pretty good.

Harrison: So, what we're gonna do now is distribute the larvae.

♪ Steve will put down these underwater speakers in the center of each block, and then what we're going to do is distribute 16 tiles around a 5-by-5-meter plot.

Sanjayan, voice-over: These tiles will help the team track the progress of the experiment.

Over time, the researchers can monitor them to assess the numbers-- survival and growth rate-- of the newly settled coral larvae.

♪ So, it's just straight up here, Steve.

♪ Sanjayan, voice-over: Floaty Boat delivers the last of her cargo.

Mou: It looks pretty all right.

Harrison: That looks all right.

I reckon you could keep going that way.

Mou: All right.

Harrison: Yeah.

♪ Sanjayan, voice-over: After months of planning and a huge amount of work, the success of this experiment and the future of this reef now lies with these tiny, microscopic larvae.

♪ Harrison: Well, that was great.

-Amazing.

-Yeah.

Simpson: So, we got a waiting game first, and then we got a counting game.

Yeah, we've got some hours of work to look at under a microscope.

♪ Sanjayan, voice-over: Peter and Steve have spent their lives trying to come up with ways of saving coral reefs, probably the most threatened habitat when it comes to climate change.

This is a habitat that I am not confident that my daughter will get to see when she's my age.

But what blows me away is there is hope right there.

There is hope in that lab.

♪ What do you expect your kids will be able to see when they're your age?

I think there's a whole range of possibilities.

I think they could see, really, the very last coral reefs hanging on for survival.

They might even watch the last coral reef in their lifetime disappear.

But I don't believe that it has to be the way that it happens.

Harrison: We must be optimistic.

We all feel ecological grief every time we read about, you know, another bleaching event or more loss of these fantastic natural ecosystems.

Yeah.

But the point is we can't give up.

You've gotta become more determined and you've gotta channel what was grief and then frustration about the inaction on these issues into something positive.

Yeah, great.

♪ Sanjayan, voice-over: The early results of this groundbreaking experiment are promising.

But Steve and Peter can't afford to wait for the final numbers.

♪ They're so confident that this process will work that they're already planning to use these new techniques on the Great Barrier Reef in Australia.

♪ The problems that coral reefs face can seem insurmountable.

But around the globe, the scientific community are working together and working fast to come up with novel and surprising techniques to give coral a lifeline, and the project here in the Maldives gives me real hope.

What I was seeing was a solution to climate change and its impacts on these reefs at scale that could never have come up from any one branch.

And putting those two branches of science together to intuit a nature-based solution that gets a helping push from humans to really accelerate it at scale, at the scale of an atoll, at the scale of an entire reef, then you really have a solution that can save the planet, that can save coral reefs.

♪ ♪ ♪ "Changing Planet: Season Three" is available on Amazon Prime video ♪ ♪