Original subtitles

Coral reefs...

..home to an astonishing diversity of life

that's vital to the health of our seas.

Lying off the coast of eastern Australia, the Great Barrier Reef

is the world's largest expanse of coral reefs.

But this extraordinary place and all the life that it supports

is under threat like never before.

Some experts predict we could lose it all in just 30 years.

To find out what's being done to save one of the earth's greatest

natural wonders, we've based ourselves on Heron Island

at the southern tip of the Great Barrier Reef.

This is one of the last healthy areas and a hub

for pioneering research.

By working with leading scientists, we've come here to discover

the magnificent life found within this fragile kingdom

of our blue planet.

WHALE SONG ECHOES

Positioned off the coast of Queensland, the Great Barrier Reef

is a network of habitats where open ocean meets coral gardens

and island paradises.

These provide food and shelter for over 9,000 species.

At 1,400 miles long,

it also protects the Australian mainland by bearing the brunt

of powerful storms.

Each year, millions of people come from far and wide to see and study

this natural wonder -

the largest living structure on the planet.

The minute you look beneath the surface,

you are hit between the eyes

with so much colour and so many animals.

This underwater metropolis is made up of billions of tiny organisms

called polyps, organised together to form a single megastructure.

Each polyp is growing a skeleton, and the one beside it, and the one

beside it again, until you've got hundreds, thousands, even millions

of coral animals

building these incredibly beautiful structures.

These coral cities take centuries to grow

and it's taken the Great Barrier Reef

around 500,000 years to evolve.

But today, its existence is under threat as the changing

climate warms our seas.

From our base on Heron Island, 50 miles off the Queensland coast,

we can unearth its many riches...

..teaming up with the scientists who are working to both understand

and protect it.

Professor Peter Harrison is a global expert in coral reefs,

having spent the last 40 years studying their inner workings.

Heron Island provides the perfect base for him to examine corals...

..but to see how the whole reef functions, he needs to take

to the air.

The first time I flew over the reef was in the 1990s,

and for the first time I actually got a sense of the scale

of the whole reef.

Extraordinary beauty at large scale.

This is a spectacular, interconnected ecosystem.

When looking at a reef system from the air, we start to gain a much

better understanding of how the system functions,

all the different zones.

The scalloped reef edge where you see all the dynamic forces, the wave

actions coming in, the wash moving through, all the new nutrients

coming into the reef system.

And then you move into the shallow reef flat areas where certain types

of corals are specialised in coping with these extreme environments.

My favourite part of the reef is actually the lagoon where you get

all of these complex reef systems forming a patchwork layer.

It's like a mosaic system.

The incredible colours that are coming from the reefs,

just this azure blue and turquoise colours.

And every time I see those, it does something to me personally.

It makes the hairs on the back of my neck stand up.

I just react to that colour.

And, for me, it's kind of like a spiritual home

for the marine world.

There's no other systems on our planet, anything like this.

It's just a spectacular environment, so visually beautiful,

so ecologically complex and so amazingly fragile.

I wish everyone on the planet could come and see a healthy,

functioning reef system, and hopefully in the future

there will still be enough so that people can enjoy them.

Back on the ground below,

summer is in full swing and Heron Island is at its busiest.

It's only 800 metres long, but the dense forest canopy offers

prime real estate for those looking to nest.

From December to March each year, the wildlife here is booming.

There's no better time to meet the residents of this tropical oasis.

Every inch of the forest is occupied with over 100,000 birds working

tirelessly to raise their young.

The white sandy beaches that encircle the island are home

to a busy green sea turtle nursery.

Heron Island is at the centre of a reef

over 100 times larger than the island itself, which is full

of charismatic creatures.

An extraordinary number of fish

and 18 species of rays and sharks

call these waters home.

But it's the towering corals that provide food and shelter

for such an abundance of life.

Each day, this magical place springs to life,

as every animal within this underwater wonderland

has a role to play.

Damselfish stand guard over their coral gardens.

And this bubble-tip anemone provides a safe home for clownfish.

Whilst larger reef residents patrol for food.

One of the busiest parts of the reef is the cleaning station.

Marine creatures will pass through here whenever they need some

attention from a cleaner fish.

A green sea turtle arrives to take

a well-earned rest from its travels.

By raising its head and stretching out its flippers, this turtle shows

it's ready for a once-over.

Its shell is so sensitive it can feel every nibble.

Every animal here helps to keep the reef and its residents

clean and healthy.

With such an abundance of marine life, Heron Reef

is relatively pristine.

But sadly, this place is the exception to the rule.

As across the globe, coral reefs are struggling.

Coral reefs are an essential part of our life support system.

Unfortunately, over the past 30 years, we've lost a lot of corals

and it's been a combination of problems -

pollution, overfishing

and, of course, nowadays we have the threat

of major climate change.

Director of The Global Change Institute,

Professor Ove Hoegh-Guldberg, is a world expert

on climate change and coral reefs.

Climate change impacts coral reefs in a number of ways.

As we are adding carbon dioxide to the atmosphere

that then drives the temperature up,

and it doesn't matter whether you're on land

or in the upper layers of the ocean,

that's enough to cause problems with coral reefs.

If we see coral reefs die and other parts of the ocean die,

we will start to threaten our very own existence.

Ove first came to Heron Island when he was 18 years old, and now,

along with the team at the research station, is leading the way

in understanding what the future holds for all life found

on coral reefs.

We've been coming to Heron Island for three or four decades now,

and because it's near pristine, we really have a unique opportunity,

together with the facilities that the university provides, to get

at some really important questions.

Run by the University of Queensland, Heron Island Research Station

carries out ground-breaking work using the latest technologies

to explore the inner workings of reefs.

The ability to have access to advanced laboratory tools,

cameras and so on,

it's really generating enormous amounts of interest and research

and so on.

This work equips organisations and governments with the information

they need to protect coral reefs.

Scientists here study everything the island has to offer,

from the colourful corals that are the foundations of all life

here to the feathered families that arrive each year to breed.

And, as December dawns, one of the reef's most charismatic

residents comes to shore to nest, offering researchers an unrivalled

chance to get a closer look at these ancient mariners.

Green sea turtles have been monitored on Heron Island for almost

50 years.

For turtle biologist Janine Ferguson and her team,

it's like old friends coming home.

I love it. Been involved with the turtles here since

about 1987, but I'm not sure what it is about sea turtles

that grabs a lot of people's attention and they just do fall

in love with them.

During the nesting season, as night begins to fall,

females patrol the beaches, looking for a spot to lay their eggs.

They haul themselves up and out of the water, a herculean effort.

What she is looking for is a position that's high enough

above the high-water mark

so that her eggs are in a safe place

and will not get inundated with any water from high tides

or a tidal surge from a cyclone.

The turtle digs a hole around 60 centimetres deep.

She's using her front flippers to actually get rid of that sand,

the more drier sand,

and she'll also use her rear flippers as well, to flick the sand

backwards away from where she actually wants to dig

that egg chamber.

They spend a lot of time up there, getting rid of that

soft sand from around them.

The bone structure within their rear flippers is very similar

to our hand.

She can actually cup it and bring it up and out of the egg chamber

and then reach in with her other flipper and bring out another

flipper full of sand and put it beside her.

It's in sort of a bowl shape.

And she needs to get that specific shape so that she can actually

then put her eggs into that, what we call the egg chamber.

It can take up to five hours of hard work for her to lay over 100 eggs.

She is more committed to putting those eggs into the ground.

So she's a lot more accepting of us being around her.

She's actually filling in her egg chamber and she's just using

her rear flippers again just to cover those eggs

up into a nice little secure area.

Once she's finished laying her eggs, Janine can move

in to attach an ID tag.

The project itself has been going since 1974, and most of our females

during that period of time should be tagged.

So if we don't have a tag on this girl, it probably means

that this is her first laying season.

Since Janine and her team started monitoring Heron's turtles

their numbers have more than doubled.

A great sign that this population is doing well.

But the impact rising temperatures will have on this species

is not well understood.

So this long-term monitoring work is more important than ever.

This turtle mother's task is over.

She heads back towards the water.

There are plenty of opportunities on the reef around Heron Island

for hungry turtles to replenish their food stores.

They gather around an old shipwreck, feasting on a treat brought

in by a high tide.

Small, jelly-like creatures called salps, a type of plankton,

are carried here by the current,

and they make for a nutritious meal on the move.

But these magnificent turtles also help the reef in return, in ways

we're only beginning to comprehend.

Green turtles can often be found perusing the underwater gardens,

which neighbour coral reefs.

These are filled with the ocean's

only flowering plants, seagrass.

Seagrass meadows can store ten times

as much carbon dioxide as the same area of rainforest,

and regular mowing keeps them in good condition.

Consuming up to four kilos of seagrass a day, a turtle

will graze the same patch for several months before moving on.

But like any terrestrial prairie,

seagrass meadows also attract herds of giant grazers.

Dugongs...

..one of the largest herbivores in the ocean.

There are more dugongs in Australia than any other place on Earth.

A distant relative of the elephant, they can reach three metres

in length and weigh half a tonne.

And they eat almost nothing but seagrass.

These regular grazers play an essential role, spreading seagrass

seeds far and wide.

And importantly for coral reefs, seagrass meadows provide safe

nursery grounds for young fish.

Fish that are still too small to cope with the hustle and bustle

of reef life

but who will one day grow up to join this extravagant world.

Fish found on the reef are reliant on the healthy appetites

of dugongs and turtles.

It's these interconnected relationships that underpin

the foundations of the Great Barrier Reef.

And perhaps the most important one of all involves the corals

themselves as they harness up to 90% of their energy from microscopic

algae living within their cells.

Only with this help can they build such impressive reefs.

It's a relationship that's vital to everything that calls

this natural wonder home.

But in recent years, it's come under increasing pressure

as our planet faces a climate crisis.

Our seas are warming.

And a rise in temperature of just two degrees for a month

can be enough to cause the coral polyps to eject their algae.

When this happens, the corals fade, losing both their colour

and their main food supply.

If high temperatures are sustained, corals bleached in this way

are likely to die.

Since 2016, half of the Great Barrier Reef's shallow water

corals have perished due to bleaching.

If we don't change our habits with regards to CO2 emissions,

I do not believe it's possible that coral reefs will be here

in the future.

On Heron Island, Professor Sophie Dove

is in a race against time,

trying to predict what the future may look like for coral reefs.

By creating miniature reefs in a set of tanks,

she can find out how corals might react to future climate conditions.

The aim is to reproduce a structure that looks a little bit at least

what we have out there on the reef slope

so that we can then examine

what increases in temperature and acidification

do to the mini reefs.

We put them and we weigh them underwater.

We do a lot of 3D scanning now and so they give us volumetric change

and also the change over the surface area of the coral.

And those are fundamental to understanding

whether it is possible to generate corals that can grow and survive

the type of environments that we're going to have in the future.

Sophie's experiments have shown that if temperatures continue to rise

at their current rate, we will lose our coral reefs

in just 30 years.

They literally disintegrate.

They start off as these lovely 3-D tiered structures

and they collapse in to this 2-D scuzz of cyanobacteria.

The situation is desperate.

But scientists are doing their best to bide coral reefs more time.

And the way that corals reproduce is providing a much-needed

glimmer of hope.

Coral expert Professor Peter Harrison

has travelled to the northern Great Barrier Reef

with a ground-breaking idea that could offer reefs a lifeline.

Coral IVF.

Collecting eggs and sperm from corals

that have survived mass bleaching

and transferring them to recolonise dead reefs.

For this to work, he's searching for live coral

that's healthy enough to spawn.

But these corals release eggs and sperm

on just a few nights each year,

so there is no margin for error.

There's good coral cover, really good diversity,

lots of survivors from the recent bleaching events.

We need to capture these eggs and sperm now

before the next bleaching event

because we can't be absolutely sure that these corals will survive

the coming bleaching.

With a site identified,

the team can deploy the 65-metre spawn catcher,

a giant ring of floats that will corral

the released eggs and sperm

into a fine net where it can be collected.

But as night falls, the weather turns.

It's always a bit of a worry when the wind blows up,

and particularly as the wind is coming from the wrong direction.

We're having to use a more exposed site.

The window of opportunity is shrinking fast.

And because artificial light affects the spawning,

the team prepare to work in virtual darkness.

It's a race against time.

Our dive teams are in the water

and now our job is to start looking for surface slicks

as they start to develop before the wind picks up,

because if we can get even a little bit of it

in these spawn catcher nets,

then we're looking good over the next few days.

As long as we can stay on the water...

CLAP OF THUNDER

..because that was a big lightning strike.

Small boats are one of the most dangerous places to be

in a lightning storm.

Peter and the team might be battling the weather on the surface,

but their timing is perfect.

Beneath them, the coral is putting on a dazzling display.

Millions of individual corals are releasing their eggs and sperm

at exactly the same time.

This extraordinary natural phenomenon

is happening right on cue.

For more than 1,000 kilometres over the Great Barrier Reef,

you'll see synchronous spawning of many of these same species.

The team work deep into the night to collect as much as possible.

By the time they're finished, it's 3:30 in the morning.

Overnight, the spawn is transported 21 miles north to Vlasoff Reef.

Just 18 months ago, Vlasoff was full of life and colour.

But today, it's a dead, white expanse.

Peter's team have built floating pools above this reef

where the microscopic larvae will mature.

In time, they will be released to form new colonies

on the dead skeleton below.

In just three years, the new corals should be ready to breed.

It's a complex operation.

We've got a lot of healthy embryos in the cultures

and it looks like we're going to be successful in at least getting

through the second stage of rearing the larvae.

We've still got a way to go

but, so far, I'm really happy and increasingly confident

that we will get a good result.

Peter's ground-breaking coral IVF

is able to speed up the growth and recovery of damaged coral reefs.

But the health of these reefs is not only influenced by life

beneath the waves.

Recent research has shown that life on land is more connected to coral

reefs than we ever thought possible.

On Heron Island, the birds are busy looking after their young.

It's now January, and in burrows below the forest's trees

13,000 wedge-tailed shearwaters are incubating their eggs.

During the day,

it's hard to know they're here as they keep below ground.

But by using burrow cameras, Abbie Taylor and the team

at Heron Island Research Station can get a unique insight

into their lives.

The shearwaters have travelled all the way from Micronesia,

nearly 4,000 miles away, to nest here.

This shearwater mum, called Winona, got off to a rather bad start.

Winona is a little bit of a special story to us.

She was a bird that was rescued out of a skip bin,

that was placed in a nest, just to give her a little bit of a rest,

and she happened to lay an egg in the first 24 hours

of being in the nest.

So we knew exactly when her egg was laid, which was great,

because we could predict when it was going to hatch.

Over a month has passed and her chick, named Willie, is almost

ready to hatch.

Winona, we're predicting, is a first-time mum.

And she got a little bit scared when the egg started to vibrate

when it was hatching and actually kicked it across the nest.

And so it was pretty cool to see.

It actually hit the back wall

and you could hear Willie squawking inside the egg.

SQUEAKING

Being a shearwater parent is challenging.

Growing chicks need a regular supply of food.

So each morning, well before sunrise,

they leave in search of the next meal.

But here, in the dense forest, there is little room to fly.

By walking along the forest's well-trodden footpath,

they make their way towards the beach where there's easy access

to the open ocean.

They line up in clearings as if taxiing for takeoff...

..and, with a good run-up, head out to sea.

These expert foragers will spend the entire day fishing at sea.

One of the parents fishes close by to provide a regular supply

of food for the chick.

While the other will spend two weeks on the wing travelling up to 600

miles to stock up on food for itself.

The adults only return under cover of darkness.

After a bumpy landing, they'll quickly head

into their burrows to provide their chicks with a meal

of fish and squid.

Every couple of weeks, the parents will meet to swap shifts,

using their haunting calls to find each other.

When both parents come in, they are, um, I guess, super...

'romantic' is a terrible word,

but they are really affectionate towards each other and there is lots

of nuzzling and preening of both parents and then the chick as well.

So they will sit in a little kind of family huddle

and, yeah, preen each other, which is very cute.

Their reunion is brief, as the next morning both parents

will go their separate ways to fish.

It's these foraging trips that are the key

to helping coral reefs.

Every time they return to the island from their long-distance hunting

trips, sea birds bring back essential nutrients in their

droppings, or guano, which flow into the surrounding waters.

These nutrients result in greater numbers of fish

and healthier coral reefs...

..helping these precious ecosystems to thrive.

Across our seas, ocean commuters carry nutrients

for thousands of miles.

And few more so than migrating whales,

who spend their lives traversing the big blue.

Humpback whales make their way

from Antarctica to the Great Barrier Reef each year.

They've travelled all the way here to breed.

And these warm tropical waters provide a safe place

for their calves to grow and fatten up before returning to cooler seas.

But during the breeding season, some of the greatest migrations

on the Great Barrier Reef are carried out by an animal

just centimetres in size.

Loggerhead turtle hatchlings from the Great Barrier Reef travel

down the East Australian Current, past New Zealand, and all the way

across the Pacific to Chile and Peru, a distance

of over 8,000 miles.

They won't arrive back until they're around 16 years of age.

As adults, marine turtles will then establish home ranges

travelling between feeding and nesting areas.

Each year, in the northern Great Barrier Reef, tens of

thousands of turtles gather near their natal breeding grounds.

They spread out as far as the eye can see.

And each turtle will carry little hitchhikers, parasites

and barnacles, on their bodies, transporting them from open ocean

to coral reefs -

increasing the biodiversity of our blue planet.

But as our influence on the ocean increases, these migrations are also

exposing marine turtles to great dangers.

It's thought 52% of sea turtles worldwide

have ingested plastic debris.

And over 1,000 die each year due to entanglement.

Across the world, marine turtle populations are struggling.

But there are people trying to help.

In the northern Great Barrier Reef,

the Cairns Turtle Rehabilitation Centre, run by Jennie Gilbert, works

to get sick and injured turtles back into the wild.

One of the current residents is this female,

who was hit by a boat after ingesting some fishing line.

It's not only done enormous amounts of damage to her shell,

but we're going to have to amputate that back flipper

because the propeller went through and she's got nerve damage.

It's completely overwhelming, isn't it?

Just... She is a case study in what we are doing to our oceans.

Whether through entanglement or ingestion, plastics are clearly

having a major impact on turtle populations.

So this rescue and rehabilitation effort is more essential

than ever before.

At Cairns Aquarium is a very special green sea turtle called Midori.

She was brought in two and a half years ago with tumours and plastics

blocking her bowels.

But now she's testament to the team's hard work and dedication.

Isn't she beautiful?

She looks in great shape, Jennie. She really does.

She's in such good shape, she needs to go.

Before Midori is released

she needs a thorough checkup to make sure she's fit enough.

For this, Jennie and the team have access to state-of-the-art

medical equipment at the local hospital.

A CT scan will reveal if she's free from tumours

and plastic.

So, Jennie, what are your thoughts looking at the scan?

I can't see any obvious tumours.

And also, we haven't picked up any plastic.

So no tumours, no plastic.

Is she ready to go? She's healthy and she's right to go.

This magnificent turtle has the all clear.

The next task is to fit Midori with a GPS tracker so the team

can monitor her after her release.

As much as we're aware that their carpuses

are incredibly sensitive.

Apparently, this beautiful female is re-assured

if we just scratch it a little bit and pat it.

So that's the job I've got right now,

just to try and calm her down a little bit before we attach the tag.

And...it's quite the privilege.

This is nontoxic, right? Nontoxic, yes.

So what kind of data is this going to give you

about Midori once she's out in the wild?

A tracker that size is amazing.

It gives us a top time, a bottom time, dive time, dive depth,

water temperature, distance and salinity.

All in there. All in that little thing? Yes.

You know, the most important thing about releasing a turtle

is that we want a health profile.

So we want to know that this turtle is diving and staying down there

and feeding, rather than doing short and shallow dives.

With the tracker fitted, Midori is transported to a reef 15 miles

off the coast.

She's to be released from this permanent platform

at the reef's edge.

This enables us to get in the water with her and make sure she's stable

and happy before we let her go.

After two and a half years of rehabilitation,

this is a crucial moment.

OK. Ready. Step forward. Stepping forward.

Here we go. She's ready to go.

She's going this way. We're heading her that way. Go, go, go, go.

Yeah!

LAUGHTER

How are you feeling? Fantastic. What a great release.

She was amazing. So amazing. So amazing.

You know, that's two and a half years in captivity

and she's just gone...straight out.

With every turtle successfully released back into the wild,

the future of our coral reefs looks a little bit brighter.

But wildlife here needs to be ready for every eventuality.

In the waters around Heron Island, reef residents have adapted

in extraordinary ways...

..to this ever-changing landscape.

Twice a day, Heron Reef undergoes a dramatic transformation...

..as the tide turns and gallons of water drain away.

As the water finally recedes, this epaulette shark

is left high and dry.

No shark can breathe in air.

But this fish out of water has a trick.

By shutting down parts of its brain

it can cope without oxygen for an hour.

And, if necessary, it switches to survival strategy number two.

This is a shark that can walk.

As it searches for a refuge of water,

it uses its fins as legs...

..until it reaches the sea.

The epaulette shark is supremely adapted to life in the shallows.

But in deeper waters, other weird and wonderful species

have evolved their own unique strategies for survival.

A Spanish dancer.

This otherworldly creature is in fact a swimming sea slug.

It spends most of its life on the sea floor,

but by using flamenco-style movements,

it glides through the water from one patch

of reef to another to escape any threats.

And its bright colours warns predators that it would make

an unsavoury meal.

On the seabed below, a tuskfish is presented with a problem.

It spends each day foraging for clams, but these shells

are difficult to open.

Ingeniously, the tusk fish has a few tools under its belt.

Its protruding teeth make excellent clamps

and this mooring could provide the perfect workbench.

It doesn't seem to be working.

He takes a break for a mouth clean courtesy of a wrasse

before starting round two.

Will this brick prove to be more useful?

Not this time.

But it's clear that there is far more to these ocean

creatures than first meets the eye.

And this is never more apparent than at dawn, when coral reefs

are filled with a chorus of sounds.

ECHOES, CLICKS AND WHISTLES FROM MARINE LIFE

These underwater cities are alive with conversation.

On Heron Reef, one of the most talkative residents

is the Barrier Reef clownfish.

CLOWNFISH GRUNTS AND CLICKS

This family have a convenient home within the tentacles

of a bubble-tip anemone.

The tentacles can kill, but by continuously rubbing

against them, the clownfish can remain immune to their sting.

Here they can shelter from danger and, in return, they help to keep

the anemone clean.

As with all clownfish, there is only one female present in this group

and she rules over the rest.

She's the largest amongst them and uses her size to chase

off any intruders.

The whole family communicates by popping and clicking, which helps

to maintain ranks amongst the group

and, when accompanied by some twitching, re-affirms a pair's bond.

The noise of a coral reef is a key indication that the community

is in good shape.

In fact, the louder the community, the more inviting

it is to newcomers.

Deciphering this underwater language could be the secret

to helping coral reefs.

This little clownfish is no bigger than a button.

But the time has come for it to find its place in the big city.

At this stage in life, it may not be the best swimmer, but its hearing

is so sensitive it can detect the presence of a reef over 100

metres away.

Exactly what sounds attract

these tiny reef fish to a new home has so far evaded scientists.

But on the outer edge of Heron Reef, Dr Steve Simpson and fellow

biologist Tim Gordon are hoping to collect young reef fish to learn

more about their acoustic world.

It's here that juvenile reef fish will first arrive after spending

several weeks at sea.

They're swimming back towards coral reef environments.

They're trying to find a place to make home.

So if we take one of those fish, we can catch them in light traps.

The baby reef fish will make their final approach in the dark

to avoid predators and will be attracted to the bright lights

of the trap.

The next day, any fish that have been drawn in are ready

for the team to retrieve.

Right. So we've got a fish. Yes! Which is great.

This is a peacock damselfish. That's large for the fish

when they arrive on the reef.

With this school of reef fish,

they can begin their research.

In the middle of the night, Steve and Tim set up a long plastic tube

in shallow waters with speakers rigged at each end.

OK. One of the fish is then transferred into the tube

while speakers play different reef sounds.

After a few moments to orientate itself, the fish clearly heads

towards one of the speakers.

By repeating this hundreds of times,

the team can record which sounds are the most attractive

to young reef fish.

They really are attracted by that sound of snapping shrimp -

the higher-frequency sounds that you could hear,

those crackling sounds.

And we think that that's because snapping shrimp live

in the kind of rubbly areas on the edges of reefs,

as do the baby fish.

So we think snapping shrimp is a really good way of them finding

the best possible place to live.

The amazing thing, if we then play other sounds, then the larger fish

start to show an interest.

So we think that they can use snapping shrimp to find a good place

to set up home.

Once they're ready to graduate into the big fish community,

they then start listening out for other fish.

By carrying out these experiments,

Steve can create a library of recorded sounds which could help

to recolonize reefs.

A bleached reef is a ghostly, silent place with very few fish around.

But by playing the right sounds, fish could soon come back to a

damaged reef,

and an abundance of fish can lead to the growth of new coral.

When you set up a restoration project, you often quickly get

overgrown by algae, which means that the reef quite quickly dies.

But the fish are really important as herbivores for keeping that away.

We've got to keep these reefs alive.

We've actually got to be throwing them lifelines to give them every

opportunity as one of the greatest wonders on the Earth.

Each new discovery about coral reefs is crucial.

So much life depends on them.

On Heron Island, summer is drawing to a close.

It's now March and the island's fluffy chicks have ventured

from their nests, exploring the world around them.

Up in the trees,

this year's noddy tern chicks have lost most of their down to make

room for their flight feathers.

Flapping like this may not get them very far yet...

..but this is essential practice

to strengthen growing flight muscles.

And it won't be long until they take to the skies.

On the ground, shearwater chicks are getting their first glimpse

of sunlight.

Many of their parents have now started their long journeys

back to their wintering grounds, leaving the young chicks to teach

themselves how to fly and find their own way across the equator.

We're predicting that we've got a few more weeks

for the shearwaters to leave.

It will be a little bit sad.

You get so used to them being around and the constant noise throughout

the night-time. And the adults will slowly go now.

And then when the chicks go, they go in one big wave.

So you'll just wake up one night and there'll just be no sound.

So it's kind of eerie getting used to that sound

and then just having nothing.

Over the next few weeks, most of the island's birds will embark

on huge migrations across the globe.

But it's not just the bird life that's departing the island.

As the dawn light starts to warm the sand,

new life stirs.

It's time for Heron's turtle hatchlings to embark on the greatest

journey of their lives.

These hatchlings are emerging from the sand

after two months in the dark.

Having never seen water or their mother, instinct drives them

towards the sea.

But danger is all around.

This youngster will need luck on its side to make

it past the swathes of gulls picking off its siblings.

It's a race against all the odds.

This year, 43,000 turtle hatchlings have left Heron Island's beaches

to head off into the open ocean.

And unbelievably, only about 43 of these will make it to adulthood.

The odds are stacked against them, but we need to give them

the best chance possible.

We are releasing seven green sea turtle hatchlings into the sea.

Thanks to Janine's hard work, seven individuals are getting a new chance

at life out into this very precious reef because of the work that's

taking place here.

The contribution of scientists here is vital.

The Great Barrier Reef needs these turtles, as well

as its breeding birds and all other reef residents to thrive.

All species here are connected.

And when these relationships are strained, life falters.

The Great Barrier Reef is essential to life on Earth, but it's facing

some of its toughest challenges yet.

And we risk losing coral reefs before we've even discovered

just how important they are.

This spectacular light show of glowing colours and striking

patterns is only visible to the naked eye

once the sun has set.

The fluorescence is produced by proteins within the corals

that are able to alter the wavelength of light.

Little is known about exactly how they do this, but it's thought

that the process provides the corals with protection

from the harsh rays of the sun, whilst allowing enough light

to reach the algae within their cells that provide

them with food.

It's one of the ingenious mechanisms of coral reefs that have enabled

them to survive for hundreds of millions of years.

Scientists are working tirelessly, searching for novel and innovative

ways to preserve the future of this natural wonder.

It's now down to us to give reefs and our planet that relies

on them a helping hand.

There is no denying that this awe-inspiring kingdom

really is worth saving.

When I think about the idea that we could easily have a world

without a coral-dominated Great Barrier Reef.

I mean, to me, the fact that we can talk about that spurs me on to keep

wanting to say, "No, we still have time and we could still turn

"this thing around and still have these beautiful and diverse

"ecosystems to wonder and be in awe of."