NOVA

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