Original subtitles

Coral reefs have captured the human imagination

for as long as we have ventured beneath the waves.

Towering, romantic, strong, resilient,

but very ornate and, and delicate at the same time.

There really is nothing else like it.

Beyond their beauty and brilliance,

coral reefs support a quarter of all marine life

and are crucial for ocean health

and human survival.

But now these precious creatures

are in crisis,

as ocean heat waves are bleaching corals

of all color and life.

By the end of this century, coral reefs could be lost.

Can we help them?

Can we accelerate natural selection?

Can we accelerate adaptive rates?

On tropical reefs around the globe,

scientists are fighting a desperate race against time.

Unlocking the secrets of millions of years

of coral evolution

and trying to speed it up.

If we are going to save coral reefs,

we have to start intervening.

Their ideas are new and experimental.

And for the first time, their daring research

will be put to the test.

I think science and scientists

are being asked to solve problems.

Honestly, we don't know

whether it's going to work.

The risk of doing nothing is the risk of

risking every reef on the planet.

"Reef Rescue," right now on "NOVA."

I will often describe it as my cathedral.

If you could imagine a cathedral

with all of the stained-glass windows,

all of that color is splashed across the landscape,

with the fish darting in and out.

It's the place I go where I feel awed

by the complexity of the architecture around me.

Coral reefs have been compared

to tropical rainforests, and what I mean by that is

the diversity of the species and how they're packed in together,

how they create this kaleidoscope

of color and function.

When I go underwater,

each coral head is like its own little city.

When you get to a massive spur and groove system,

it's like downtown Atlanta,

super busy, bustling,

characters everywhere, different sounds,

clicking and popping and bubbling.

And it reminds you

that we are all one piece of a community, or ecosystem.

Corals appeared 500 million years ago.

They may look like rocks, but corals are in fact animals.

Each tiny coral creature

is called a polyp.

The polyp is essentially a mouth with tentacles

used to trap floating food,

but most corals also have another source of nourishment.

Inside the cells of the animal,

there is a tiny plant cell and they, as all plants do,

are able to use the energy of the sun, capture it,

to combine carbon dioxide and water

into a small food molecule and oxygen.

These microscopic plant-like organisms are algae.

The algae feed the coral animal,

and the coral gives the algae a home.

It's a dynamic symbiotic relationship.

So much so that the algae are called symbionts.

Reefs begin when coral polyps

secrete a thin layer of calcium carbonate

to create a skeleton.

Hundreds and hundreds of identical coral polyps

create a colony.

And over thousands of years of growth,

coral colonies build the reef.

So animal, vegetable, mineral.

That is what a coral is.

Christmas Island is an atoll

in the Pacific Ocean made entirely of coral.

Julia Baum is a Canadian marine biologist.

For more than a decade,

she's studied the reef's unique ecosystem

and the threats it faces.

It always feels great to be back.

It's a bit of a mix of emotions;

there's, there's so much invested in every single trip.

Always a little bit of excitement

about an adventure that's about to begin,

and also maybe a little apprehension

just to make sure,

is everything going to go okay?

Hey!

Hi!

I think that it's actually, I know it sounds crazy...

And then I think that...

but I think it's actually you're gonna,

you're gonna drop there.

And that's...

It's Julia's first day out on the reef this year.

Oh, did you...

The team dives down to take stock of the coral.

When I first started doing research on the ocean,

I had been so focused on sharks and fish,

and at some point,

I think I kind of looked down and saw the coral and realized,

"Hey, the coral are the whole foundation

of this ecosystem."

And if we're worried about this ecosystem,

we really have to be worried about the coral themselves.

We have hundreds of corals

tagged all around the island,

and we take tiny tissue samples from them.

We can take the photos

to identify individual coral colonies themselves

and get a sense of who's there in the community.

A brain coral is one of

the main types of corals that we've been working with.

There's also branching corals and flat corals,

so lots of different shapes,

and those are important because they provide

different types of habitat for fishes.

Each year, Julia and her team meticulously tag,

sample, and photograph 40 plots of coral,

building a timeline of how the reefs are changing.

During the 2015 and 2016 El Niño,

water temperatures here

increased by four degrees Fahrenheit.

The heat set itself down on this island

and just got a chokehold on it,

and it just kept going and going for ten straight months.

And what we saw was a complete ecological meltdown.

By the time we came back

in March 2016, almost everything was dead.

It was like a graveyard.

It's just hard to believe that a whole island can die

in less than a year.

How'd it go? Okay?

Tough, a lot of stuff going on there.

I want to look at both of those dive slates

and compare the corals,

photo for all of them,

tissue for all of them, and growth for some of them.

Yeah. Okay.

It's pretty devastating, being down there,

because I just remember that being my favorite site,

and it just feels, like, how did this happen?

And even though, obviously,

intellectually I know exactly what happened,

but emotionally it still feels like...

it's just really, um... it's a pretty sad remnant

of what it was.

It's gone, really.

Tropical reefs around the globe were severely impacted

by the deadly ocean heatwave.

And scientists have been mobilizing...

led by the Hawaii Institute of Marine Biology...

a research station perched on an island

surrounded by coral reef.

Guiding this enormous effort

is visionary scientist Ruth Gates.

You have a couple of options:

you move, you adapt, or you die.

Obviously corals are dying, they can't move,

so their only option is to adapt.

Corals have a natural ability

to adapt to changes in their environment

and have done so for millions of years.

But now,

the oceans are heating up too fast.

So, can we help them?

Can we accelerate natural selection?

Can we accelerate adaptive rates?

Ruth is a revolutionary thinker

in a new area of coral science.

It's called assisted evolution.

It is our responsibility to take our science

and activate things that can make a difference,

try to solve the problem

instead of just describe that it exists.

And to take a closer look at the problems corals are facing,

researchers use a powerful laser microscope

to generate images of living corals.

Fluorescence highlights the algae partners in red.

This is a most beautiful coral.

It's completely healthy, it's showing,

it's extending its polyps away from the skeleton.

Kind of out there, waving.

It's just dynamic and beautiful.

Each polyp looks like it's got a different personality

and it's blowing me a kiss.

It's this one that's blowing me a kiss.

But what happens to the symbiotic algae

when waters warm?

This is actually a partially bleached coral.

It's starting to lose its symbionts.

You can see there's a lot more black space

in between the corals.

When heat stresses the corals,

they expel their algae.

These dots of red are the plant cells

that the animal has essentially spat out.

They're no longer serving the animal.

It's no longer moving anywhere near as dynamically.

It's kind of gone very quiet.

Without the algae,

corals lose their color.

And this is coral bleaching.

Alannah Vellacott is a diver

and coral restoration specialist

who understands this problem firsthand.

They can always use a bit of fanning.

Oh, sorry, buddy.

I keep knocking you.

Alannah works at Coral Vita,

a coral farm in the Bahamas that grows corals

to revitalize dying reefs.

Currently, 80 percent of corals

are dead in the Caribbean.

That is especially sad and especially troubling

because we cannot afford to lose our coral reefs.

Reefs are highly diverse ecosystems.

Fish shelter, find food, and rear their young

in their many nooks and crannies.

Fewer reefs means fewer fish,

but it's not just the marine ecosystem that's at risk.

People depend on reefs for food and income.

Bahamians are very intimately

tied to our waters, because it is our livelihood.

Whether you work in a hotel,

whether you're a dive operator,

whether you're a fisherman,

whether you just enjoy having a conch snack

at the end of the day,

we all depend on these coral reefs.

If the world continues

to go in the direction that it's going in,

ignoring what our reefs are trying to tell us,

it very well is the end of our livelihoods

here in the Bahamas.

Bahamas and beyond,

some three billion people

rely on fish as a source of protein,

and the overall economic value of reefs

is estimated at tens of billions of dollars annually.

Almost 90 percent of the corals

surrounding Christmas Island bleached,

and Julia wonders if the reef

and the biodiverse habitat it provides

could be lost.

Okay, so I have 2015 loaded. Mm-hmm.

This is just five months before

the heat stress started to hit.

So, the reef is looking really healthy.

So then let's load the 2017 on top of that

and take a look at that one overlaid.

Kind of shows how much the structure is breaking down.

Just... all the height is eroding.

Devoid of living corals,

the reef is crumbling and falling apart.

Oh, God, this is horrible.

Can a damaged reef regenerate?

Each year, Julia's team anchors

new clay tiles to the reef and retrieves tiles

from previous years.

Normally, baby corals will settle on these,

and the team will document any signs of new growth.

It feels like a waiting game to see...

is this gonna turn the corner and recover,

or is it gonna decline and die?

I still need the white light to look at it though.

We have a baby coral from one of the degraded sites.

We hoped for it, but we didn't really expect it.

So, yeah, that's exciting.

This first evidence of new life

is a tentative sign of regeneration.

But how could this happen?

After bleaching,

researchers feared the reef was lost.

In the midst of all this devastation,

we found a glimmer of hope.

Julia discovered life among the ruins...

baby corals struggling to rebuild.

This meant some of the parent corals withstood the heat.

The corals here had been

sitting in essentially a hot water bath for ten months,

so they had been stressed out

more than any coral on the planet,

and yet, here they were, looking perfectly healthy.

Here, while water temperatures remained high,

a small percentage of the corals recovered,

making these the only corals ever observed

to have been exposed to such extreme temperatures

for so long and survive.

So, to me, this was almost like a miracle.

What is it that's so special, that's so unique

about these corals that healed themselves

while they were still under stress.

What is it about them?

Why do some corals survive when others perish?

What is the secret of these super corals?

And what can we learn from these survivors to help save the rest?

Traffic, traffic.

Greg Asner's Airborne Observatory

is a custom-designed plane

equipped to create a picture of how reefs are changing.

How many passes through here?

We're going to do...

five more.

Using a spectrometer

and LiDAR lasers,

Greg can analyze the corals from above,

measure their chemistry, and create a 3D image.

This region here, in the pinks, that's the live coral.

These corals are all a mix of dead and live.

The system gives us a very unique view of coral reefs,

an understanding of where the live coral is located.

That's really critical, especially nowadays

where we're looking for surviving corals

in literally... in a sea of a lot of dead coral.

Yeah, we're over the big island now.

Like many other reefs,

they've gone through a lot of change.

The burning of fossil fuels

has increased the concentration

of atmospheric carbon dioxide,

raising the Earth's overall average temperature.

You raise the total temperature of the planet

and you've changed literally the fundamental heat flow

over the earth's surface.

You're causing heat waves in the oceans.

You're causing droughts on land.

You're causing a rebalancing of the entire thermal portfolio

or profile of the earth's system,

and that's the thing that we're dealing with as biologists.

These changes may have deadly consequences.

So Greg is taking his airborne research one step further...

teaming up with Ruth Gates

to find corals that are resistant to bleaching.

We're going to be getting in the water

to look at the corals that we flew over yesterday.

And this is key for linking the aircraft data

to what's going on in the coral itself.

That's how we make the connection.

Underwater, Greg will use a small spectrometer

specifically designed for diving.

Tools in hand, Ruth and Greg set out to find

the specific corals identified by the airborne observatory

as survivors of heat stress.

They need to confirm that the data from the plane

reflects the reality on the reef.

By monitoring the reef over several years,

Ruth has already identified

corals that have resisted bleaching.

And sure enough,

Greg's spectral data from the air

matches Ruth's observations underwater,

bringing them one step closer

to identifying super corals

at a scale and speed previously unimaginable.

So, the dark brown coral

in the bucket right now,

we affectionately term "super corals,"

and we call them that because

they are unaffected by the conditions or the stress

that is causing other corals

immediately adjacent to them to pale and whiten

and show signs of very severe stress.

So once we can understand what is different

between the super corals and the weak corals,

our goal is to develop or breed more super corals

that we can use to restore damaged reefs.

Now Ruth's team prepares

to breed the super corals

that have survived bleaching events.

Corals here are spawning tonight

and researchers will act as matchmakers.

If we've got

a really good performer

over here and over here,

let's not leave it to chance

that their eggs and sperm would meet.

Let's bring them together and make sure they do.

So that's accelerating a natural process,

really having a slight human intervention

to make sure we breed the best moving forward.

As night falls,

Ruth's team prepares

for one of the most phenomenal events in all of nature.

Each coral species spawns at a very specific moment,

timed with seasonal temperatures and the moon.

Corals can sense the moon,

and they will release their eggs and sperm

within five minutes

of a particular phase of the moon,

it's an astonishing thing.

Once spawning begins,

it won't last long.

Researchers use red lights,

so they won't disturb the corals' ability

to sense lunar cues.

Then move it across...

The team must work quickly

to collect the precious sperm and eggs.

An entire year's work is on the line.

Corals are fixed in place, so they release

gamete bundles containing their egg and sperm

into the water column.

These buoyant bundles rise towards the surface,

creating an underwater blizzard where fertilization begins.

The gametes from selected coral

are caught in the nets.

Lids secured,

researchers head back to the boat.

Yeah, we have everything!

The team combines the coral gametes

according to a predetermined plan,

breeding them for their strengths.

Time will tell if

tonight's efforts were successful,

but past years of collecting, breeding, and observation

have already paid off,

as lab-reared “super corals ” can tolerate

warmer temperatures.

How do we move the needle

and scale to many different places?

Because the corals that do well in Hawaii

don't all live, say,

in the Great Barrier Reef.

In Australia, hopes are high

that assisted evolution could help save

one of the seven natural wonders

of the world.

The Great Barrier Reef has been hit hard by

successive ocean heat waves,

resulting in severely bleached coral

along its entire 1,400-mile length.

Researchers here are taking the next big step,

moving assisted evolution out of the lab

and into the ocean.

And there is no better place

to prepare super corals for this journey

than in the state-of-the-art

National Sea Simulator.

Here, Ruth Gates' long-time collaborator,

ecological geneticist Madeleine van Oppen,

is soon to embark on a groundbreaking trial.

Ruth and I met,

I think maybe 2005.

I think the idea was already starting to happen

that we should use the knowledge

that we had gained over the past decades

on how corals adapt and acclimatize,

to actually harness those mechanisms

to help corals evolve further.

Researchers here can set the temperature and acidity levels

of individual aquariums to match those predicted

for the ocean in the years ahead.

And Madeleine is creating a new kind of super coral:

a hybrid.

A hybrid is a cross between two entirely different species.

Hybridization does happen in nature,

in corals and also in other plants and animals,

but it doesn't happen frequently.

When it does, hybrids have proven to be more resilient.

This is a hybrid coral that we've actually

created in the lab in 2015,

and actually we put it through seven months of exposure

to future ocean conditions,

so warmer and more acidified oceans,

and it survived those conditions.

Now that Madeleine has achieved success

with lab-reared hybrids, she needs to find out

if newborn hybrids can grow and survive in real ocean waters.

To create these new hybrids,

Madeleine needs eggs from one species

and sperm from another.

There is no better time to gather these ingredients

than when corals spawn.

So, this cup is full of the bundles of eggs and sperm

that are collected outside which I will now pour over this mesh.

And the mesh is of a size that the sperm will go through,

and the eggs will stay on top.

With egg and sperm from two selected

coral species separated,

Madeleine can now bring these together to create the hybrid.

Even though we have a fabulous sea simulator,

it still is an aquarium

and it's not exactly the natural environment,

so we need to test those results,

validate those results in the field.

For the first time ever, these babies are headed

to the Great Barrier Reef.

The biggest challenge is the really high mortality

we tend to see in the field.

These lab-reared babies have never experienced

real ocean waters before,

and the transition could be deadly.

We might get a cyclone that all of a sudden

pulls down the water, or we might get

a lot of cloud formation during summer

that will reduce the amount of light.

The baby corals grow on tiles

and are transported on trays

to a designated site alongside the reef.

We really need to have these

field results before the regulators will allow us

to actually implement these interventions

in reef restoration.

After three months, scientists from Madeleine's lab

oversee the infant hybrids' first checkup.

So, right now we're cleaning the tiles,

which we just brought up from the ocean,

so that they'll be ready for the photographer

to get a clean shot of.

I'm just going through each tile,

trying to find the babies,

which are still quite small, they're kind of,

adolescents, I guess you could say now,

about six months old,

and so we just find them, and then I circle them,

we take a photo, and that allows us to look at survival,

and then it also allows us to measure growth.

There are more than a thousand tiles

with different genetic combinations.

It will take over a week to examine and photograph

every one individually.

So we've just taken all these photos outside,

so now we're going to start analyzing them,

and the first thing we do

is just look at alive or dead.

Yeah, so no...

No pencil marks on this one.

Maybe try the next one?

I don't see anything on that one,

some dead ones, yeah, long dead.

Yeah.

A lot of dead guys.

Early observations are concerning.

Many of the baby hybrids did not survive the journey

from lab to sea.

But hope is not lost.

There are more tiles to examine

in the week ahead.

Climate change has affected the Great Barrier Reef

quite dramatically in recent years.

We lost half of the coral present.

As soon as populations start to lose genetic diversity,

the capacity to adapt further and respond

to environmental change also diminishes.

It can become a downward spiral very, very quickly.

Let's think about how we actually react

instead of just watching our system die before our eyes

and then asking ourselves 20 years from now,

"God, I really wish I'd done something."

During the filming of this documentary,

Ruth Gates is diagnosed with brain cancer.

Like the coral reef she loves, her life hangs in the balance.

Laetitia Hedouin is a scientist who studied under Ruth Gates.

On the island of Mo'orea in French Polynesia,

Laetitia is "conditioning"

or "training" corals to survive ocean heat waves.

Her recent graduates are growing in this coral nursery.

Laetitia aims to train large quantities of corals

to make them more resilient.

So her work begins in the crucial first hours

of a coral's life.

Laetitia will expose these coral embryos

to increasing amounts of heat stress.

Like young athletes on a treadmill,

they will be conditioned to become "super."

The goal is to increase their

thermal tolerance by subjecting them to an exercise regime

similar to what they may experience

in an ocean heat wave.

The embryos have grown quickly into tiny larvae.

This is the only time in a coral's life

that it will ever swim.

Once settled, the coral polyp begins to grow.

Soon it should be moved to the coral nursery

in Mo'orea's lagoon.

But now, Laetitia finds trouble brewing on the reef.

An impending ocean heatwave threatens the reef,

and her research.

As the summer heat intensifies,

so do warnings from the Intergovernmental Panel

on Climate Change.

About 1900 to present, that basically represents

a degree Celsius of warming.

With one and a half degrees,

70 to 90 percent of coral reefs are lost,

but at two it's virtually all of them.

It's very clear that half a degree matters.

I think this report is alarming,

it should make us act.

IPCC and other reports now coming out

are just getting to the level where they're saying,

"Look, this is happening faster and, and more extreme

than we thought."

The urgency of this cannot be overstated.

The changes are real, the changes are rapid,

and they can be quite extreme.

And if we lose reefs, there will be dramatic consequences.

Coral reefs provide safe harbor for our coastlines.

They buffer waves, helping to prevent erosion,

property damage, and loss of life.

So, if you look out just in front of the horizon,

there's a line there, a line of, of,

of waves, a line of foam,

and that is the reef crest, and that

is our first line of defense

when it comes to storms and hurricanes.

When natural ecosystems that protect coastlines

are in poor condition,

people are vulnerable.

When Hurricane Dorian hit,

it was the worst tropical cyclone on record

to reach the Bahamas.

The damage was catastrophic.

So, September last year, the islands of Abaco

and Grand Bahama were absolutely devastated by Hurricane Dorian.

Sixty percent of Grand Bahama was underwater,

and thousands and thousands of people lost their homes.

Hundreds of people are still missing today.

My childhood home where my dad lives was completely destroyed.

For the first time I experienced what it was like

to be a climate change refugee.

And as much as we'd like to think

of climate change refugees as people of the future,

the future is today.

It's happening right now.

And what happened in the Bahamas

could happen to coastal communities anywhere.

Billions of people live within 60 miles of a coastline.

The east coast of Florida is lined with coral reefs

that have protected people here for thousands of years.

But now, these reefs are crumbling.

The Sustain Laboratory at the University of Miami

is one of the few places in the world designed

to measure the impacts of a Category 5 hurricane.

Here, Andrew Baker and his team

are working to quantify how corals

mitigate the impacts of extreme storms.

Is there any wind going on this?

Now there is, now there is, yeah.

That's pretty good, it's breaking right on the coral.

Because of climate change, we're seeing rising seas,

we're seeing more powerful storms,

we're seeing storm surge

and other kinds of flooding impacts.

Coral reefs have been shown to reduce wave energy

in some cases by 94, 95 percent.

Without reefs to protect its shoreline,

storm surges could devastate Miami.

How do we make coral reefs

more climate ready, more climate tolerant,

more thermally tolerant,

and how do we protect our coastlines

from the damaging effects of storms?

So, what we're trying to do is not only use coral reefs

to build natural breakwaters, but make the very corals

that we're using to build those reefs

themselves more thermally tolerant.

Andrew and his team are trying to make reefs

more climate-ready by helping corals switch their algae

to ones that can take the heat.

The researchers use a technique called "controlled bleaching,"

attaching the corals to a raft,

then raising them up toward the surface

where they'll receive more sunlight.

After a few hot days under clear skies,

the coral stress, eject their algae, and bleach.

And without the nourishment the algae provide,

the corals will soon die.

But Andrew has a plan to save them from this fate...

This partnership between the coral and its algae

dates back over a hundred million years.

We have different types of corals,

but we also have many different types of algae,

and in fact they can sometimes switch from one type of alga

to another, and that's exactly what we think

we're seeing under climate change.

And some of these algae

are more tolerant to heat.

If corals are able to flexibly associate

with different types of algae,

perhaps they could switch to these more heat tolerant ones

and that might help them survive.

Heat-tolerant algae are less likely

to be expelled by the coral,

and the coral won't bleach.

If the corals bleached on the raft recover

with heat-tolerant algae, they may survive the next

ocean heat wave.

And this could be a big step forward

for assisted evolution.

This is a test... we're hoping

that this is going to be something that

proves successful, that is easily scalable,

cost effective, and we can roll it out and apply it

to the restoration efforts that are going on

all over the place.

Today, Andrew's team

plants the corals that bleached on the raft out on the reef.

Standard corals act as a control group.

We're hoping that the corals that we've bleached

on these rafts are going to recover with

different symbionts that we hope

are more thermally tolerant

and that help these corals resist bleaching in the future.

The corals may now have the ability to survive bleaching,

and the next ocean heat wave.

But what about the one after that?

If climate change is still ongoing past 2100,

then nothing we're doing is going to help solve that.

Ultimately, we have to get

carbon emissions under control

and try to prevent this runaway warming event.

And in the midst of this planetary crisis,

coral scientists receive devastating news.

At age 56, Ruth Gates, pioneer of assisted evolution, dies.

Yeah, it's difficult to talk about it, but, um...

I just, it's so hard to believe that she's gone, right?

Ruth was a very inspiring person.

She was always smiling

and laughing, and... and so I think, um...

yeah, sorry.

She always find a good word

and, and the time to be here when you need it.

I think that I, I've never laughed so much, um,

doing science than I have with Ruth Gates.

It was, we had a great time,

and to lose her,

it's like a huge piece of the, of the science machine,

but also the leadership machine just disappeared.

What she did do was instill so much spirit

and motivation to keep going.

We wanted to really send out the message

that assisted evolution is an important approach to explore,

and Ruth, of course,

played a very big role in sending that message out

across the world and I think we have succeeded.

We've been able to convince the community

that this is important.

When Madeleine van Oppen's team first checked

the experimental hybrids, the results were discouraging.

But they didn't give up.

There it is.

I knew it was on here, I saw it.

Tiny young corals are alive on the tiles,

signs that these heartier hybrids are surviving

life outside the lab,

a first for the team.

Well, we still have to take a good look at the data,

but we're seeing corals popping up here and there.

Is Grant gonna take it down?

They're gonna take them back out onto the reef,

and we'll be keeping those guys out there for another

few months until we check up on them again in October.

Back at the sea simulator,

researchers share their documentation with Madeleine.

I see some kind of...

Yes, it looks like there's some structure still there,

rather than the whole, isn't it?

And it's smooth texture.

That is clean.

That one is quite pale, isn't it?

Yeah.

I saw a lot of variability in color.

When we first bred coral recruits in the sea simulator

five years ago, everything died between Christmas and New Year.

We had a huge effort, and then the year after we had

a little bit longer survival, and so we learned as we went.

These are the baby steps that we have made,

but small steps in the right direction.

It gives me hope and I just pray that it's gonna be enough.

Assisted evolution is now a growing movement

around the globe.

Scientists are finding successful solutions

that might give corals the chance they need

to make it through the coming decades.

Coral Vita is expanding its farming operations

beyond the Bahamas, aiming to provide

resilient corals to reef rescue operations worldwide.

We can make choices to help our environment,

to help our coral reefs, to bring them back to life.

We are growing corals to be more resilient to the effects

that climate change is having on our oceans.

Super corals tested and planted by the Gates Coral Lab

are now being used to restore the protective reef around Oahu.

Andrew Baker's corals bleached and recovered,

but did not switch to the heat-tolerant algae.

However, back in the lab,

different species have successfully made the swap

and are now being planted on reefs off Miami to see

if these corals remain resilient in warming ocean waters.

Julia Baum discovered that

the corals that survived the mass bleaching

on Christmas Island did so because

they switched to a heat-tolerant algae naturally.

Tragically,

the reefs around the island of Mo'orea

experienced a massive ocean heat wave.

Fifty percent of the corals raised in the nursery perished.

But those that made it proved

their resilience and Laetitia Hedouin is optimistic

that she will learn from the survivors.

We need to know more, so we can harness that knowledge.

I mean, what could be better than that?

Being a part of a solution that will help the world.