Original subtitles

Coral reefs cover just 1% of the ocean floor

and yet they're home to a quarter of all marine life.

This is totally overwhelming.

A complete sensory overload.

It's extraordinary.

Reefs feed us and keep us safe,

shielding coastlines from storm surges and rising sea levels.

But the corals that live in warm, clear waters

face a multitude of challenges that threaten their very existence.

Half of all reefs are already dead or damaged, and without action,

we could lose most of what's left in the next 20 to 30 years.

Scientists all over the world are racing to try

and find creative solutions.

Just about anything they can do to give corals a helping hand.

In this, the third series of Our Changing Planet,

where we look at precious ecosystems,

and the people trying to save them.

We're focusing on the habitat

that's facing the most urgent threat - our coral reefs.

I'm taking a look at high-tech, creative and imaginative solutions

to the coral crisis that are being developed on dry land here in the UK

and also in the US.

On their own, none of these projects can save our reefs,

but the hope is that together they'll deliver a crucial

lifeline and a much-needed conservation success story.

I'm back in the Maldives, where a pioneering team of scientists

is attempting to regrow a damaged reef by helping it

to reproduce more effectively.

It's going to be exhilarating. Seat-of-our-pants kind of science.

Nice work!

It's a ground-breaking, astonishing idea

to combine a fertility treatment for corals with, incredibly,

a soundtrack of fish vocalisations to bring life back to this reef.

It's a world-first so no-one knows if we can pull it off.

If it works, it's going to be a global game-changer.

The Maldives is the flattest country on Earth,

much of it just 90 centimetres above the waves.

These reefs act as a living shield,

protecting half a million people that live here from the sea.

They're also home to a dazzling number of animals.

There may be as many as a million different species that rely

on coral reefs to survive.

They have a baffling array of different forms - tables,

vases, branching stag horns, great massifs like this -

some of which could be 2,000 years old.

Despite that, they are now in serious trouble.

We've lost approximately 50% of corals in my lifetime.

Corals are living creatures, sensitive to rising temperatures.

When the sea is too warm for long periods, the corals get stressed

and eject the microscopic algae living within them.

These normally act like solar panels,

providing most of the coral's energy.

Without them, the corals turn white and starve.

It's known as bleaching.

This reef was hit really hard in the 2016 bleaching event.

73% of corals died.

But there were survivors, which must have some natural resilience

to increased temperature

that they're likely to pass on to their offspring.

That could be the key to long-term recovery here, but there are

so few of them that they might struggle to do it naturally.

OK, we need to bring some back.

So, to save this reef, scientists are converging on the Maldives

to help these surviving corals breed more successfully.

Corals start life as tiny floating larvae

that settle on solid surfaces,

replicate themselves,

and build hard external skeletons.

The structure we see is a colony of thousands

of genetically identical animals all living together.

But one of the drawbacks is once you've settled, you can't move.

So, how do you go about breeding?

Well, that is one of the most exciting spectacles in nature.

On just a few nights a year,

triggered by a full moon,

corals release millions of eggs and sperm into the water

in a process called spawning,

where they fertilise and become larval corals

looking for a place to settle.

It's this miraculous spawning process that has become

the life's work of one of the world's leading coral scientists.

The real challenge we face is we need to produce a lot more larvae

than are currently being naturally produced.

Professor Peter Harrison is a coral expert who has spent 40 years

studying Australia's Great Barrier Reef.

He pioneered a revolutionary technique known as coral IVF.

Peter collects spawn from the wild,

artificially fertilises it,

grows the larvae in specially designed protective pools,

and then, when they're ready, he releases them back onto the reef.

We target the release of those larvae onto degraded parts

of the reef to kick-start the recovery.

Back to me. Down, down, down, down.

The first stage in the process is to collect as much spawn as possible.

Corals here only spawn a few times a year, so we can't afford to miss it.

This multi-national team are straight in the water,

carefully checking each surviving coral for colourful eggs,

a sign that spawning is close.

Once replaced, the fragments will repair themselves and regrow.

Time is tight, so we work long into the night.

Below the waves, it's an unearthly scene.

Some corals contain a fluorescent protein that glows

in our UV torchlight.

I feel like I've been transported into a scene

from a 1970s Star Trek movie.

Everything looks so surreal,

transformed into a whole different world of colour

I've never seen before.

Utterly dazzling.

Beautiful as it is, we're not here to take in the view -

there's work to be done.

This is kind of the magic part of what's being called coral IVF.

The team have identified, during the daytime,

colonies of corals that are ready to spawn,

and they're tagged.

Once they're ready, they'll release their sexual cells and they're

pretty much cast adrift and at the mercy of the elements and predators.

The damage to this reef means there are too few reproductive

adult corals spread across a very large area, so when they spawn,

there's little chance of the eggs meeting sperm and fertilising.

But we have a way of increasing our odds -

using this cone,

a gamete trap which almost functions

like a coral condom.

The bundles of egg and sperm will be released up

into the pot on the top...

..and that is going to be the raw material

that helps us do the experiments

that could be a massive part of the potential future of these reefs.

In the wild, out of a million larvae,

maybe one will make it to adulthood.

On the Great Barrier Reef, Peter's coral IVF has made

larval survival up to 100 times more likely.

And one advantage of the coral we're working on here

is that any offspring that do survive could grow

an impressive ten centimetres a year

and be sexually mature in just three.

Now the traps are in place,

we could be waiting for days before the coral spawns.

You never know what they're going to do.

These branching corals that we are expecting to see spawn here,

they are quite variable in their timings, and in some cases,

they wait until seven or eight nights after the full moon.

They're amongst the simplest animals on our planet

but they're very complex and they keep us guessing.

Suddenly, on our first night,

there's a buzz of excitement.

Word is that one of the colonies has started spawning.

Didn't expect it to spawn tonight,

but you can't predict corals, apparently.

I'd come here expecting to be waiting for days, maybe even weeks,

for this extraordinary spectacle to take place,

and right now one of the most special and important events

in the whole natural world,

and certainly in our seas,

is happening beneath us right now.

It might be unexpectedly early but we're ready for it -

the coral condoms are in place

and the nursery pools are ready to receive and protect the harvest.

But mixed with excitement is trepidation.

Spawning in the Maldives is different

to that on the Great Barrier Reef where Peter usually works.

We don't know if these corals will spawn together,

or in great enough quantities for the experiment to continue.

It's happening!

Across this brutalised reef,

the surviving adult corals are in full reproductive flow.

Hundreds of thousands, maybe millions of eggs and sperm,

are rising upwards.

The cells are full of fat so they float, and this is key.

If the cells drifted at different levels in the sea

they might not bump into each other and fertilise.

Because they all rise to the surface, mixing is much more likely.

So, already the gamete traps are working their magic.

Inside, you can see the precious sexual cells gathering at the top.

The potential future of this reef.

There are so few of each type of adult corals here,

that it's possible that none of the spawn would fertilise naturally.

There's so much riding on the success of Peter's IVF attempt.

Every stage completed feels like an obstacle overcome.

Well done. Congratulations. What an amazing job!

Spawn is being collected all across the reef tonight.

Mm, beautiful.

Eggs and sperm from the same colony

don't normally self-fertilise.

What we need to do is mix all the eggs and sperm from as many colonies

as possible to get as much genetic diversity amongst the larvae.

On the damaged reef, less than 5% of the spawn will be fertilised,

but in the containers, the fertilisation rate exceeds 95%.

Cheers all around.

THEY CHEER

Well done, team.

It's been a long but successful night.

As the sun rises,

the now fertilised spawn is very cautiously transferred

into protective pools

where it will spend a few critical days developing.

But it's not all good news.

There's not as much spawn as we'd hoped for -

only enough to fill one of the nursery pools.

A stark reminder of how hard these reefs have been hit.

Even the spawn that we have managed to collect is in danger.

A storm is approaching the island.

THUNDER RUMBLES

The spawn is floating on the sea surface,

and a downpour of fresh water can kill it

before life has even had a chance.

If that happens, the rescue project will be abandoned

and we'll all be going home early.

It's going to be a sleepless night.

When you're doing coral conservation work on the open sea,

you've little control over the elements.

And for something as precious and specialised as coral spawning,

it would be really useful to be able to manage at least

some of the conditions to maximise the chances of success.

And that's exactly what scientists are doing here in South London.

Inside this unassuming warehouse is a ground-breaking research facility

exploring novel ways to culture corals on land,

that could then be planted out in the ocean.

The scientists here were the first in the world to work out

how to trigger coral spawning in captivity by mimicking

some of the natural conditions they need.

We have been trying to get corals to breed and to grow quicker,

survive better, and really impart some of that knowledge

on the rest of the world, really.

In the wild, mass spawning is a highly coordinated event...

..with the corals relying on environmental signals

like moonlight and temperature.

When all the cues are just right,

the ocean is filled with masses of released eggs and sperm.

How on earth do you begin to do that in a laboratory situation?

All of these types of things can be done in aquariums.

We managed to get corals to spawn in about eight months

after putting all this in place.

We knew 100% we were onto something.

Jamie and the team have developed a ready-to-use

coral spawning system that can be shipped around the world

and can be controlled from a mobile phone.

Oh, it looks beautiful in here.

So, this is a spawning system. OK.

The reason why we're standing in something that looks like

a photography blackout studio,

which means we can walk in and out of here

and block any external light.

Then we can slide these across and we can completely enclose

the corals, because we don't want to be coming in and out of here

and putting light all over them

and ruining that cue that they need to release their eggs and sperm.

OK. And when it comes to moonlight, how did you find out how you could

replicate that moonlight here, how strong it had to be?

We know that full moon is about 0.1 lux.

It's a really small amount of light.

One lux is the amount of light

you can detect from a single candle a metre away,

so 0.1 lux is actually very faint.

I have a light meter

and I went round waving it around in my garden at full moon.

You didn't? I did.

And then trying to get the amount of light from an LED to match

that intensity of light, but also the colour of the moon as well.

Once Jamie had control of the timing and quality of the light,

he could manipulate the corals into spawning more often,

essentially speeding up coral reproduction.

And now the lab is growing a whole raft of healthy young corals,

at different stages of development in a series of nursery tanks.

What are your ambitions for this system going forward?

You imagine you go to a farm now, vast greenhouses producing

millions of plants to go into people's gardens.

You know, this has the same potential to do that,

but to go onto reefs.

We want to see this on colossal scale,

producing millions of corals a year.

It won't be able to rebuild the reefs

the way they were 50 years ago.

It will buy time until we can sort out the bigger issues

that are facing our planet.

And it's working.

70 spawning systems have already been shipped

to coral restoration projects all around the world,

with new, healthy corals being planted out onto reefs in the wild.

STEVE: After a stormy night in the Maldives,

it's a peaceful but tense morning.

Our precious cargo is contained

within those floating pontoons out there.

At this stage, they're incredibly susceptible to any changes

in the environment, and last night, we had torrential rain.

Peter designed these nursery pools.

They allow the fertilised spawn

to develop into larvae in natural conditions,

but the fine mesh prevents them being swept away or eaten.

The team are taking samples to check for signs of life.

To get a decent sample size, we need to stir it up.

Ah, this is amazing. It's like stirring

the most expensive witch's cauldron in history. Exactly, yeah.

Right now, to the untrained eye, these larvae are almost invisible,

but Peter and his team know what they're looking for.

There's one.

There's over 600,000 in here and you've got one!

Yeah. So some of those... THEY LAUGH

We try again.

Come on up, my lovelies.

Oh, yeah. Beautiful.

Ah, that's more like it!

That's where they all are.

So, basically, my stirring wasn't good enough!

Yeah, sorry. You didn't stir the pot enough.

You gave me one job!

One job. Oh, no!

There's literally many hundreds there,

probably a few thousand.

I was seriously worried that we might just have had too much rain.

Exactly. I mean, that's the whole thing.

Every stage of this process,

like life for a coral naturally,

is full of risk.

Because they're so tiny, it's hard to think of the larvae as creatures,

but these are baby animals.

Thankfully, the majority of the larvae have survived,

which means we're still on track.

LIZ: Life for a developing coral is filled with jeopardy.

If it's not warming seas or intense storms,

it's explosions of algal blooms.

Not the vital microscopic algae that live inside the coral's tissues

but larger species of algae that can smother and kill the coral.

I am back at the coral spawning lab in London, where Jamie

and the team have developed an ingenious system for breeding

and growing thousands of corals in captivity.

But this conservation breakthrough is under threat from algae.

On a healthy reef, algae are normally kept in check by herbivores

like turtles and crabs but here in the lab, with no grazing animals,

the algae can quickly grow out of control,

swamping the growing coral and killing as much as 95% of it.

Now, Professor Michael Sweet has developed an ingenious solution

that's entirely natural.

Don't get spiked.

Well, don't spike me!

This is an adult urchin, it's called a tuxedo urchin,

largely because of the sort of shiny blue, blue black colouration

in between those spines.

There are around 950 species of sea urchins in our oceans.

Related to starfish, they move across the seafloor

on tubular feet that they also use to attach themselves to rocks.

So, why harness the power of sea urchins

when it came to your problem with the algae?

So, urchins are, are common-or-garden,

they're found all over the place, really,

and they're massive herbivores.

So they're really interesting,

and as all are herbivores, they have a very big stomach

for the size of the animal, so they can actually eat quite a lot.

And what they like to eat is algae.

In the wild, urchins make light work of any algae they come across.

But that voracious appetite can sometimes be a problem

if another species gets in their way.

If we put these guys in the tanks,

they'll bulldoze over our baby corals.

They're not targeting the corals, they're doing it inadvertently.

As they're feeding? Exactly, yeah.

The answer was to think small, matching the size of the urchins

to the coral, with the two species growing in size, together.

And it all comes down to perfect timing.

We know where the corals are going to be spawning and then we need

to target that same spawn date for our urchins.

But that's another huge challenge. How do you time it?

With urchins it's actually relatively simple

and we can hopefully show you how that works now.

We're going to give them a little spa treatment in a nice warm bath.

A spa treatment? Exactly. Very scientific, Mike.

As long as I don't have to give them a massage!

Moving the urchins to warmer water

triggers the release of their eggs and sperm,

just like corals in response to environmental cues like moonlight.

This guy looks quite happy.

In the sense that he's ready? He's waving his arms around, so...

How do you define a happy urchin, ready to spawn?

I mean, for goodness' sake.

A male spawns first,

releasing its sperm in plumes

from openings called gonopores.

There's a beautiful slow-moving cloud emanating from the top.

And then a female releases a cloud of eggs,

wafting them through the water.

Got the eggs coming in the female now. Oh, look at the eggs! Yeah.

Oh, this is... This is amazing.

This is just so amazing.

It's just a beautiful thing that's happening in a tiny little tank

in an industrial estate in London.

Once the corals and urchins have developed for several weeks,

it's time to introduce them to each other.

So these little babies are about two months old.

This is the Holy Grail. This is exactly what we want.

Actually, on these plugs are baby coral, so little corals which have

just settled and now the urchins are doing their job,

cleaning up those little bits of algae

and making sure our corals can survive.

The babies will grow together, and by eight months old,

the corals will be robust enough to survive the bigger urchins.

By adding baby urchins to their coral nurseries, Mike and the team

have increased the number of corals surviving by more than 40%.

It's a smart solution,

inspired by what sea urchins do naturally in the wild.

But on the east coast of the US, there's a problem.

The importance of sea urchins for coral survival has sadly been

all too evident off the coast of Florida recently.

In 2022, a disease wiped out huge numbers of urchins,

and in their absence,

algae smothered miles of coral on an already endangered reef.

Scientists at Mote Marine Laboratory in Florida

monitor the complex interactions on the reefs here,

looking for ways to restore the balance.

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 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.

The parasitic disease that killed 98% of Florida's sea urchins

currently has no cure, so Jason is looking for another native

species to rescue the reefs from the overgrowing algae.

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.

Jason believes that these crabs could be the answer.

In field tests, we increase the density of these crabs

by about a millionfold from one per square kilometre

to one per square metre on these small test reefs

and over the course of one year,

they graze the algae down by about 85%.

So, we're very confident that these are excellent candidates

for grazing on coral reefs.

But the number of crabs needed to make a real difference

is mind-boggling.

Just to meet the needs for seven of the reefs that we're working on,

we're going to need to produce 2.8 million crabs.

To create the army he needs, Jason has set up an enormous crab nursery.

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 eight to ten months from now.

They're just a dream to work with.

Once the shells measure three centimetres across,

the crabs are reef-ready.

From hatching to release takes less than five months.

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 reefs,

increasing the population density a millionfold.

It might seem like a crazy strategy,

but Jason believes the risks are low.

First, they're a native species that naturally occur throughout

the entire region, and all we're doing is

increasing their density to fill this functional void on the reefs.

The team will monitor the reef for any potential adverse effects,

but, ultimately, more crabs means more food for predators,

which can lead to more marine life and in turn, a healthier coral reef.

It could just be a solution to this urgent problem.

STEVE: In the Maldives, Peter has used his coral IVF method

to produce half a million coral larvae.

The first stage is complete.

Peter's work has already helped damaged reefs come back

to life elsewhere, and the process has enormous global potential,

but there's always been one factor standing in his way.

We know that when we release tens of millions of larvae from these

pools, they disperse over the reef, some of them get eaten by fish,

some of them drift off the reef and are never seen again.

The weak spot in the process is maximising the settlement

of those larvae on the target reef areas

that we're really interested in restoring.

Now, for the first time ever, Peter is collaborating

with a scientist who thinks he may have a solution.

I've been fascinated by how corals find a reef

and choose where they're going to make their home.

Professor Steve Simpson is a bio acoustics expert

from Bristol University in the UK.

In the last series, I was with Steve and his team when they made

the breakthrough discovery that tiny larval coral,

with no ears and no brain,

are attracted to the sounds of a healthy reef.

Hang on, hold the phone!

You're talking about teeny tiny floating larvae hearing a reef?

Absolutely.

In fact, the team discovered that it's the sounds of the fish

that are the trigger for coral to sink to the bottom and set up home.

Look at that.

It looks like a meteorite.

Fish song is what encourages coral to build a reef.

Boof! THEY LAUGH

Steve's audacious plan is to use recordings of fish to lure

the millions of larvae produced by Peter's fertility treatment,

to set up home and resuscitate this stricken reef.

What we need to do now is work out what sorts of reef song

is most likely to start attracting larvae.

And if we can do that, that could be incredibly important.

I mean, it feels almost like a bit of a Live Aid for the coral reef.

So, you're Bob Geldof, what does that make you?

Midge Ure, I guess! Obviously, yeah!

The whole idea of a meeting of minds is incredibly exciting,

but, I mean, it sounds to me like all this stuff should take decades

to figure out with experiments. We've got, like, a week.

We are going to have to work at an absolute rate of knots.

It's going to be exhilarating, seat-of-our-pants kind of science.

There's no time to lose.

Our first challenge is how to record the sound of a healthy reef,

so we're travelling to a reef called Hassan Haa,

that we know is full of life.

Last year we tested a rudimentary prototype of giant swimming ears

for just this moment,

and Steve thinks he's finally cracked the design.

You remember how sometimes it was

just kind of hanging a bit loose in the water?

We've now got it basically modelled on a underwater paper aeroplane.

So, we've got this huge tail at the end.

I'm hoping that, underwater, this is going to glide silently.

There's only one way to find out.

Time for the maiden voyage!

As we glide over the reef,

four giant ears pick up every groan, shriek and whistle.

RAPID CLICKING

I'm retreating to a safe distance

so as not to disturb the crucial recordings.

It's the most incredible thought,

that these fish around me right now have their own songs.

Wow! Look at this!

Clownfish have an amazing attitude.

They will protect their anemone home with their life, if needs be.

And the sounds they make

while they're doing it are just extraordinary.

WATERY GURGLE Did you hear that?

Did you hear that as it came towards me? Unbelievable!

It just did it right then.

How's about that? I have never heard that before.

But in all likelihood,

that's probably just cos I haven't been listening properly.

WATERY GRUMBLING

That is the first time I've been given a telling off by a fish!

When we get back to the boat,

we're both thrilled by what we've seen and heard.

It's super, super exciting

and seeing the amount of life down there and the amount of diversity...

I know. Well, what a reef to take it to, eh?

The first time it ever gets to record a reef

and it's a reef like that. Beautiful.

Soon there are hundreds of hours of data to crunch...

..and now the pressure's on.

By the time the larvae are mature enough to start looking

for somewhere to settle down,

Steve needs to have selected the best sounds to attract them.

But he's discovering that the recordings vary enormously.

So, here we've got midnight.

RAPID RATTLING Can you hear those?

"Do-do do-doo. Do-do do-doo."

WATERY GROAN

And then that groan. "Grrrrr."

So we've got a lot of fish activity here.

These are all nocturnal predators, and they really use sound

as a way of keeping the hunting pack together.

They're like a bunch of wolves out on the reef,

and they're howling to each other when they find potential food.

CRACKLING

Throughout the day, different animals dominate the recordings.

One that I have to say I'm most excited about hearing is

the dawn chorus. Right, OK. So, the dawn chorus.

This is where you've got the emergence of all the daytime fish.

CRACKLES

So, you've got this, "Bup-bup-bup, bup-bup-bup,"

that's the kind of clownfish sounds that you tend to find.

"Brrrp. Bup-bup."

Very obvious, just these differences in the soundscapes.

Begging the question,

do coral respond differently to different recordings?

Steve had planned to run multiple experiments

with large numbers of larvae, but because the damaged reef

has produced far less spawn then expected,

Steve has to limit his experiments.

So, he's forced to test a hunch that busy is best.

Steve thinks the recordings from the vibrant and varied healthy reef

could be the most effective.

What we're hoping, I guess,

is that those teeny tiny corals can tell the difference. Mm. Yeah.

We're going to put them into the choice chambers,

play these different sounds from one end or the other,

and then look to see the directional movement of our coral larvae.

I'm nervous, I've got to tell you. I'm very nervous!

And in the lab, things go to plan.

Steve thinks he's cracked it.

The larvae actively move towards the sound of the busiest locations.

But now we have to test it again, under natural conditions.

And that's no mean feat.

This has never been done before.

It's one of those moments where science is actually happening,

and to get in there and watch is really quite an honour.

OK, so this is the moment of truth.

We have our cylinder suspended in the water.

The speaker underneath it with the sounds coming up,

and Peter has in his fingers,

just a few of those precious larvae to enter into the system.

OK, we've got one.

So you can see one of the larvae inside, quite clearly.

So now we're going to switch on the sounds of a healthy reef.

CRACKLING Oh, I can feel it and I can hear it.

I really can't quite believe we're doing this.

That one there has definitely dropped.

Yeah.

What about that one, Peter? You think that's dropping as well?

It went from here to here.

It went corkscrewing down.

It can see a home!

And they're all down to the bottom.

Six of them.

So best-case scenario was for these larvae to start to

make their way down towards the sounds of the healthy reef,

which are coming from below.

And it very much seems that that is what's happening.

You happy? Good news!

That is absolutely fantastic.

And now that we know that in principle this can work,

the next stage has to be release enormous amounts of these

larvae and try and create something big and something special.

How exciting is that?

Nice work!

Natural reef restoration takes time, but some of the options being

explored could help to speed things up.

Coral reefs are not exclusive to warm tropical

waters like those found in the Maldives.

Here in the UK, cold waters harbour incredible reefs too,

and they're just as important and precious.

A coral reef is built from the hard calcium carbonate

skeletons of stony corals.

But a reef can also be made up of other marine species.

Mussels and oysters tightly packed together and attached to old

shells, rocks and sandy material also create solid reef structures,

providing homes for a variety of species, including soft corals.

The UK has around 60 species of soft coral,

and as their name suggests, they don't grow a hard exoskeleton.

Most develop fleshy and flexible tissues like tentacles.

But just like their stony coral cousins,

their larvae need a stable surface to grow on.

Around the world, reef structures have been

destroyed by activities like dredging and trawler fishing.

The resulting marine wastelands are no good for corals to settle on.

On an industrial estate in Cornwall, a band of resourceful school friends

decided to come up with a novel solution to bring back their reefs.

So this is how we started.

Our first-ever mixer was 120 quid off eBay.

This is...this is literally how you did your first one?

So we literally went on to eBay, bought a mixer for 120 quid,

and now it's gone from making a couple, to thousands a day.

Tom Birbeck and his team are producing the building blocks

of artificial reefs.

The cubes are made from 98% recycled materials.

They're carbon-neutral, and once lowered into place,

they start working immediately, dispersing wave energy and providing

solid structures for soft corals and other creatures to settle on.

Carefully designed nooks and grooves on the cube's surface

will attract all sorts of marine life,

each needing their own very specific home.

Tell me a little bit about how this all started for you.

So I started off spear fishing with my dad at sort of ten, 11.

Erm, always used to catch fish. Thought it was great.

Then about 15, 16, you'd barely catch any fish. You know,

nothing, literally barren.

The actual rocky reef area that had been destroyed, that won't regrow.

So we looked at trying to build something ourselves and between us,

we've sort of carved out the product that we think we can use.

The team are already manufacturing the blocks on a large scale,

but because they can be produced using simple tools

and materials, they're perfect for restoration projects everywhere.

Why have I got a tiny little... What's this about?

And you've got the big shovel. This is really sexist!

Do you want to... Do you want to... It's really sexist. I'm just saying!

No, I'll hang on to it cos it's less work, but...

OK, we're pouring. We're pouring. Right, OK.

What we're really lucky to have in the southwest is

an abundance of waste material like this, from the clay pits.

Only about 11% of what they actually dig is clay. The rest is this. OK.

So all that is basically a waste by-product

and we've got millions of tonnes of this sat around.

All around the UK, the demand for artificial reefs is

growing, in an effort to recover our coastal biodiversity

and to protect our shores and infrastructure from erosion.

It's early morning in Torbay, and we are taking reef cubes

out into the bay to help restore the reef.

Getting these 500kg cubes to the bottom of the sea is

a team effort.

I've never operated a crane. I just want to make that clear.

So you'll be looking at Tom in the wheelhouse.

Tom will give you the thumbs up

when he's happy for you to lower it away. When he's happy,

make sure Sam's happy... Gosh, so much to think about.

..and when Sam's happy, push the lever.

What if I'm not happy?

OK, do it.

All right, let's go down for a minute.

Down on the wire. Down a bit.

Whoa. Stop? Stop.

The cable lowers the block to about 15 metres.

Happy? Yeah.

Right, we'll put it...put it away

and then we can do the last bit down...

It's on the bottom, but is it where we wanted it to be?

We're launching a robotic camera sub to check on the final

position of the cube.

There she is!

How long before life starts to make this their new home?

So the fish have already arrived on site,

so by the evening, you'd expect crustaceans to move in.

In less than 24 hours, crustaceans will move in? Yeah.

That's extraordinary.

So this is the before?

This is the before, let's go now and look at the after.

Ones that have been down a couple of years.

By providing these ready-made reef structures,

the team are bringing the bay back to life.

Me and James did the surveys pre-installation and it was just a

barren seabed, cos it's sort of been decimated by industrial fishing.

But now we've actually created a reef here and so far,

we've identified over 160 species.

You're jok... 160 species?

Yeah, 160 species.

The reef cubes not only provide a home for wildlife, like lobsters

and velvet swimming crabs,

they're also being used to protect offshore wind farms.

They could replace the millions of tonnes of carbon-intensive

granite and concrete currently used to protect the turbine

structures and cables on the seafloor.

Look at you, you cannot take your eyes off the screen.

As a biologist, is this just unbelievable to you? It's amazing.

I came up towards the end of last year and I was saying,

it's the best UK dive I've ever done, you know? Aw.

I've probably got about just under 3,000 dives.

Thanks to the team's ingenuity,

marine life here is bouncing back remarkably quickly,

and the bay will be better protected from increasing weather extremes.

The need to protect our coasts from intensifying storm surges has

become so urgent that in Florida,

the Department of Defense is now funding a new generation of

artificial reefs, built to withstand even the mightiest of hurricanes.

Florida's 360-mile barrier reef system has lost

a staggering 98% of its coral cover,

and with it, its ability to act as a crucial storm break.

In 2018, Hurricane Michael hit Florida's coastline

and powered straight through Tyndall Air Force Base,

causing $5 billion worth of damage.

A healthy reef can absorb 97% of a wave's energy.

With Florida's coastal infrastructure now

so exposed to the full force of storms,

a team at the University of Miami has been tasked with engineering

rapid response reefs, for use by the American military around the world.

So this is the only facility in the world that's able to generate

category five hurricane force winds, which is 150mph

and higher, and at that point, really, the damage is catastrophic.

This 23-metre long tank allows Andrew

and the team to test how man-made reefs can reduce storm damage.

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.

Like reef cubes,

the design has an artificial base to dissipate wave energy.

But here, the innovation is a living top layer of larval corals,

each bio-printed into a sealed capsule.

What we are 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.

The capsules are made out of seaweed gel,

each containing a single coral larva that was cultured

in a spawning system provided by Jamie and the team in London.

It also contains beneficial bacteria, probiotics,

and millions of heat-tolerant micro-algae.

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.

After the first critical few weeks, the capsule will dissolve

and the coral will continue to grow naturally.

A machine like this could produce thousands of coral-containing

capsules every hour.

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.

Those themes of accessibility

and scalability are what make the project in the Maldives so exciting.

The big day dawns,

when we release the IVF larvae onto the damaged reef, and use

Steve's soundtrack to trick it into settling where it's needed most.

Inside this bag are those hundreds of thousands of larvae

that are the result of everyone's hard work, and this next

couple of hours is the crucial bit,

to find out if this is going to work.

It's worth remembering that in almost eight years, this reef

has struggled to recover naturally from the last bleaching event.

This is a mammoth task and starts with some old-fashioned muscle.

What we're planning to do now is to gently pull up the larval pool,

let all the sea water drain out of the fine mesh at the side

and retain the larvae.

Very slowly.

It's taken almost an hour to get to this stage.

It's physically hard and no-one wants to be the one

responsible for dropping the net and releasing all that precious cargo.

Perfect.

The smell is quite extraordinary.

Like Billingsgate Fish Market.

THEY CHEER

OK, we'll have one bucket.

Good work. Go, team! Woo!

The larvae are safely onboard, and very much alive!

Yay!

This brown sediment in the bottom of these black tubs

doesn't look like anything, but it's frighteningly important

and the result of so much hard graft.

It's not surprising everyone's celebrating like it's

New Year's Eve.

In the wild, most, if not all, of these larvae would already be dead

but because of the intervention, almost all have survived.

We've already massively cheated the odds.

Rather than a smattering of larvae lost in a massive ocean, we now

have over half a million ready to be deployed in specific sites.

The corals are getting to a point where they need to settle,

and if they settle in the tubs, they'll die.

So we're in a race against time.

We are now. So we want to get these larvae onto the reef.

A mistake at this stage could be fatal to the larvae,

and the project.

We are so close.

This is the grand moment.

The hours of sweat and graft is coming to fruition right now.

We'll be giving those coral larvae the acoustic

experience of being on one of the healthiest reefs in the atoll.

So as those larvae are seeking homes, they're

moving around the reef trying to work out where to settle,

they're going to think that they're on an absolute belter of a reef.

The speakers are put in place, where they'll play

continuously for 12 hours.

There's one critical process left.

We need to drop the larvae into precisely the right places

and for that we need an AI remotely operated vehicle, or ROV.

So, Serena, this remarkable bit of technology

is very much your baby, right? Absolutely.

This is Bree. That's her name.

Bree is loaded up with larvae.

She's far more accurate and efficient at delivery than

we humans can be.

She's trained to identify the types of places where coral larvae

will survive best and artificial intelligence allows her to

learn as she goes.

What is it that the camera and the

AI is going to actually be looking for?

So it's looking for nice, like, rocky, solid substrates,

and it turns off when it sees algae on the substrate because

if the coral lands there, they will just eventually die.

It's a very fine estate agent looking for the very best

of neighbourhoods. Exactly.

The ROV can cover huge areas of reef,

targeting the perfect spots and never wasting larvae.

Well, this is such a complex operation,

so many moving parts, and trying to communicate

when half of you are under water is just about impossible,

but it looks like somehow it's all coming together.

Ah, that was brilliant.

Did you see how all the fish...

Did you see how all the fish just gathered

round as soon as the sound system turned up?

So they know it's a party. Yeah.

At last, all of Peter's larvae is out in the ocean,

hopefully spiralling downwards towards Steve's fish songs.

Well, guys, that was a chaotic few hours.

Proper science in action, wasn't it? Yeah. Yeah.

I can't believe we've actually pulled off that plan for the day.

I think we're really onto something.

Peter and Steve are jubilant.

We know Peter's coral IVF works, and he and the team have

successfully reared and released over half a million larvae here.

We know Steve's acoustic method works.

He's controlled larval settlement in lab experiments,

and now we've seen it work in the ocean under real conditions.

The results we're hoping for - new corals growing on the reef -

won't be visible for many months, but as a result of this

extraordinary experience, Peter and Steve are confident

that their hybrid method could be the key to boost reef recovery,

not just here, but on damaged reefs around the world.

This new technique couldn't have come at a better time.

We're running out of corals on the planet.

They're not replacing themselves naturally fast enough.

They don't have time to recover before the next major

bleaching event or the next major storm event.

I think in the short-term, this is such a crucial part of the

challenge, that we find all of these interventions that allow us,

as soon as we've got a problem,

to get in and try to repair some of the damage.

Peter and Steve are taking their ground-breaking, scalable

and speedy restoration method, and they're running as fast

and as far as they can with it.

THEY CHEER

In eight months, Australia's Great Barrier Reef will spawn.

Peter and Steve and the coral rescue team will be there,

ready and waiting.

In the meantime, we've got to be tackling climate change.

This is buying us time.

It's kind of firefighting while we try

and work out how we get to that much more harmonious relationship

with the planet, which I hope will be in this century.

I really do.

Without this collaborative rescue effort,

the areas of this reef that have lain dead and crumbling

for the last eight years may have remained silent and still.

Now there could be thousands of new corals growing on that reef.

We know that corals attract fish and, in turn,

fish will call more corals in.

Now, nature takes over.

We've witnessed what becomes possible

when we share expertise and work together for a common goal.

We'll be back in years to come,

to check on the progress of this reef...

..and the ongoing work of these extraordinary scientists.