All language subtitles for Blue.Planet.Revisited.S01E02.720p.iP.WEBRip.x264-GalaxyTV

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.

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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."

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