All language subtitles for BBC.Great.Barrier.Reef.with.David.Attenborough.3of3.Survival.1080p.HDTV.x264.AAC.MVGroup.org.eng

In this series,

I have travelled the length and
breadth of the Great Barrier Reef...

..and used the latest techniques
to watch its wildlife.

But the reef has
one more story to tell.

The residents of this marine paradise

have seen their habitat change
rapidly within the last few decades.

And time is running out for them.

The Barrier Reef is facing
one of the most serious challenges

to its continued existence -

the effect of human beings.

But there is hope.

This time, our research vessel,
the Alucia,

will be taking me to meet
teams of scientists

who are developing new ways
to try and save it.

And I'll be going to
its deepest parts,

where new discoveries are being made

that might hold clues
to its survival.

Nobody has ever dived
as deep as this before

on the Great Barrier Reef.

This is one of the greatest and most
important ecosystems on the planet -

and what happens here affects us all.

So, what does the future hold
for this complex wonder?

I'm travelling along
Australia's north east coast

to look at one of the greatest

and most splendid natural treasures
that the world possesses -

a chain of tropical islands
and coral reefs

that lies between the coast
and the open ocean.

I will never forget
the first time I came here.

YOUNGER DAVID: 'And what
a world this was -

'beneath me lay an endless
landscape of coral,

'of every conceivable
colour and shape.'

It was unimaginable then to think
that we might ever lose the reef.

But now, I've returned, and
I can see that the reef is changing.

In the last 30 years, almost
half the coral has disappeared.

The greatest concern now is that
we might lose the reef altogether.

Parts of the Great Barrier Reef
still remain a mystery.

Its immense size and remote depths

make it extremely
difficult to explore.

But today, exciting new technology
has made it possible

to survey the entire reef
from top to bottom.

And that is revealing
extraordinary things

about the way in which the reef
itself has evolved over time.

By looking into the reef's past,

we may discover something
about its future.

So, I'm meeting marine geologist
Dr Robin Beaman.

'He is on board the Alucia

'and shows me some of his
remarkable discoveries.'

This is a depth model of
the Great Barrier Reef -

of the entire
Great Barrier Reef.

And there's a whole lot
of different tools we use,

the main one being
multibeam echosounders,

so it gives you
a scan of the seafloor

and we can actually map great
areas of the continental shelf.

This white part is land?

That's right.

So, everything that's coloured
rainbow colours is under water.

'By combining computer modelling
and deep sea surveying,

'Beaman has discovered new evidence

'that the reef has already
experienced great changes.'

As a scientist -
as geological scientists -

we're trying to understand
how the Great Barrier Reef

has responded to changes in the past

and there are clues there as to what
the Great Barrier Reef has done,

so if I zoom back,
you can see, geologically,

it's gone through some
dramatic changes.

Beaman's scans showed
traces of an ancient reef

that thrived over the last
half million years

and is now hidden along the edge
of this great drop-off.

This earlier reef existed
long before the one we know today.

It lay up to 70 metres deep

and stretched nearly unbroken
for more than 500 miles.

It's been described as
the world's largest fossil.

This is what the older
Great Barrier Reef looked like.

And we call these "drowned reefs" -

they're drowned in the sense that
the water over them is so deep

that the reef no longer grows.

These ancient reefs were drowned
by dramatic climate changes

that caused sea levels to rise.

This last happened less
than 14,000 years ago.

So, water released from
the melting icecaps

is going to start flooding
across here, is it? That's right.

The sea level was high enough
to actually inundate

and cover these old limestone hills

and created the Great Barrier Reef
that we know today.

So, the changes that
we're seeing going on now

are nothing new, in terms of change.

I mean, the Barrier Reef
has always been changing.

We do find it's quite robust.

It has actually reformed,

despite these catastrophic changes
that have occurred.

It's been exposed and flooded
at least four times that we know of.

To us, it's astounding.

This new insight into
the ancient history of the reef

shows that, given enough time,
it can regenerate.

It seems that if seawater
is clear and warm,

simple organisms will
eventually evolve

that can build limestone
homes to protect themselves

from the waves and their enemies.

But most of these events started long
before human beings appeared on Earth

and took many thousands
of years to complete.

We now know the reef has
dwindled and recovered

many times in its long history,

but it also has to withstand
a major change every 24 hours,

as the tide retreats and comes back.

At low tide, the water
drains away very quickly,

leaving the topmost community
of creatures dangerously exposed.

Some are washed out with the tide.

Others swim to safety.

But the coral polyps can't move.

Temperatures on
the surface of the reef

can now reach a scorching
30 degrees centigrade.

The exposed corals
could easily dry out

and be damaged by intense
ultraviolet rays.

But corals have ways
of protecting themselves.

When exposed to air, they produce
huge amounts of mucus,

which keeps them wet
and acts like a sunscreen.

This remarkable slime actually
increases its UV resistance,

becoming stronger
if the temperatures soar.

So, the coral manages to survive for
the few hours that it's out of water.

But there's one fish that manages to
turn this exposure to its advantage.

The epaulette shark remains on the
reef even when the tide goes out.

Of course, with so little water,

it doesn't get as much oxygen
as it requires normally,

but it deals with that possibility
by shutting off a part of its brain

and so, reducing its oxygen demands.

As the retreating tide exposes
the topmost branches of the corals,

the shark remains in the little pools
between them for as long as it can.

And then, it sets off
to try and find food -

shrimps, crabs and small worms
that live on the reef.

And it does that by exploiting
another talent it has.

It can, in effect, walk.

It may be slow-going, but the
little shark manages to make its way

between the rocky pools to look for
prey that may be imprisoned in them.

It has the run of the place,

until the tide returns once more
to flood the reeftop.

So, the inhabitants of the reef,
each in its own way,

deal with the daily hazards
brought by exposure.

But there is one catastrophe
that can strike each year

against which there is no defence.

From November onwards,

warm, moisture-laden winds
from the northwest

sweep down across these tropic seas

and it's then that cyclones form.

They are, in fact, the biggest
killers of the reef's corals.

But that doesn't mean that the
corals are permanently destroyed.

Their resilience once more
comes apparent.

And there's an extraordinary
example of that

in the most unlikely of places.

This is the wreck
of the SS Yongala.

It was sunk by a cyclone in 1911.

It lies 30 metres below the surface
on a barren, sandy plain...

..miles away from
any natural coral reefs.

By the time it was discovered,
decades later,

it had become an artificial reef...

..and had been colonised by
an extraordinary variety of life.

It was an oasis
in the featureless ocean.

But in the century since it sank,

the wreck has been hit
repeatedly by more cyclones.

The waters here are not deep

so the turbulence created by
a cyclone can reach the sea floor.

THUNDERCLAP

Cyclones travelling
towards the coast

can rip up hundreds
of miles of coral.

Captain Trevor Jackson, who has been
diving on this wreck for decades,

saw the devastating effects caused
in 2011 by a category five cyclone.

Cyclone Yahtzee, a massive system,

crossed the coast
just north of here.

The cyclone was so large,

it generated waves that exposed
the top of the Yongala.

THUNDERCLAP

There was a lifting action...

..and in the process,

this scoured the top of the reef
of all marine life.

What was once a thriving ecosystem
was now an almost bare skeleton.

But amazingly,
the reef on the Yongala

began to repair itself within months.

Green algae appeared on the wreck.

Barnacles followed,
allowing corals to get a grip.

And soon, a new community
had established itself.

One of the things that makes
the Yongala so unique

is the way it rejuvenates itself
after a major weather event.

In the course of the last
four or five years,

about 80% of the reef has re-grown.

The story of the Yongala shows that
a coral reef can, remarkably,

recover from natural disaster.

And such recovery can be
surprisingly quick

when a reef is healthy
and in balance.

Most of the reef's inhabitants
depend on one another for survival.

But it is the coral that is
the foundation of the reef

and it plays a crucial role
in many of the relationships.

This is the crown-of-thorns starfish.

For it, coral is food

and it will eat relentlessly
if not kept in check.

But to other creatures,
like the guard crab,

coral is home.

The crab is prepared
to defend its patch

from the carnivorous starfish
at all costs.

The crown-of-thorns, however,

is much larger than most
other starfish on the reef,

so the tiny crab is forced to
take a more stealthy approach.

Hidden within the coral,
it waits for its moment to attack.

The starfish has left itself
dangerously exposed,

but the crab is cautious.

When it can, the crab
uses its powerful pincers

to snip at the starfish's
spines and tube-like feet...

..before retreating back
into the safety of the coral.

The crab has won this battle.

But recently, something has changed

and the balance has been upset.

The number of crown-of-thorns
has increased dramatically

and they've become
a big problem on the reef.

To find out more,

the Alucia is taking me to a research
station in the far north of the reef.

It's situated on Lizard Island, where
we can observe this problem up close.

Lizard is surrounded by some of
the most spectacular reefs

on the entire barrier.

But they are under attack
from the coral-eating starfish.

And at the island's research station,

they've been studying why we might be
seeing more of them than we used to.

They have an extraordinary ability

to suddenly increase vastly
in numbers, like a plague.

There have been three such plagues
since the 1960s

and, unfortunately,

it seems as though we're in
the middle, now, of a fourth.

You might think that these plagues
are just another natural disaster

that the reef has had to
withstand, like cyclones.

There are reasons to
suppose that, in fact,

the plagues have been
affected by human activity -

either through an accumulation of
run-off of fertilisers from the land

that creates more food
for the young starfish,

or because we have overfished

and so destroyed
the natural balance of the reef.

The starfish outbreaks
have been responsible

for over 40% of the coral
loss of the last 30 years.

It's just one of the huge changes
here witnessed by Dr Charlie Veron.

In 1972, Charlie was appointed

the reef's first full-time
coral scientist.

He's gone on to become
a world authority on coral

and has identified a third
of the world's known species.

He was one of the first scientists to
spend time in this underwater world

and that was due to
a particular piece of technology.

What we knew about corals
at the beginning of the scuba era

was just almost nothing.

So, scuba gear must have
changed things radically.

It changed everything.

When you went down
the face of a coral reef,

you could see how corals fed,
how they fought each other,

how they reproduced and still,

we're only just scratching
the surface.

Think of all the things that happen
in a rainforest,

how much we know about it.

We haven't got a thousandth
part of that information
on the coral reef yet.

'But since Charlie's
first discoveries,

'the reef has altered dramatically.'

I've been going back to the
same spots 10, 20, 30, 40 years ago

and every time I go back,

I'm sickened by some of
the changes I've seen.

Sometimes, I go back,
I know it's the same spot

and I can barely recognise it.

Some species have been wiped out
in the shallows now.

It's already happened.

What Charlie had witnessed were
the effects of mankind upon the reef.

When I myself first visited the
Queensland coast almost 60 years ago,

it was very different.

Since then, like many
coastlines around the world,

there has been a massive
increase in population

and an explosion of industry.

By 1975, the reef had been declared
a National Marine Park.

It was the biggest one
of its kind in the world.

But then, a new threat
began to be recognised -

not only to the reef,
but to the world's oceans -

climate change.

THUNDERCLAPS

There is more carbon dioxide
in our atmosphere now

than there has been in 800,000 years.

Industrialised nations
have been burning fossil fuels

at an alarming rate.

Global warming is slowly
heating up our planet

and threatens to cause
huge problems for us all.

Around 30% of the carbon dioxide
we produce is absorbed by the ocean.

As a result, we're seeing
an increase in the temperature

and acidity of our seas.

Both are killing
the inhabitants of the reef.

But how quickly is it being damaged?

To find out, I'm heading to meet
Professor Ove Hoegh-Guldberg

He's studying the effects
of climate change on coral.

Ove is based on Heron Island,

near the southern end
of the Great Barrier.

Heron is a low, sandy island,
50 miles out from the mainland,

right on the reef itself...

..so its research station
is very well-placed.

Here, Ove is carrying out
an experiment

to see how the reef is going to cope.

At the research station here,

the experiment we're running is
really climate change sped up.

Because it's often hard for people
to really get their heads around

when you talk about
global change over decades

and what might happen
to coral reefs.

We have, essentially,
in these experiments, sped things up

so that you can literally,
over a year,

see the impacts of what might be
occurring over the next hundred.

Each of these tanks contains
a miniature coral reef

with the same species of coral.

But each is being subjected to

slightly different conditions
of temperature and acidity -

the two factors that are most likely
to alter with climate change.

Using these tanks, scientists
have shown that increasing acidity

restricts hard corals from building
their limestone skeletons.

And a rise in temperature -

a single degree centigrade
warmer than normal -

can cause corals
to become so stressed

that they eject
the photosynthesising algae

that enable them to grow
and give some colour.

So they bleach,
turning ghostly white.

If you go back in time,

you can see the big swings between
ice ages and the warm periods

where the Great Barrier Reef
disappears and regrows

and that's happened numerous times.

So, we've always had changes,

but we're talking about changes
over 10,000 years, in those cases.

But we're now seeing is
the equivalent in a few decades.

And that, of course, is stretching
life's capacity to keep up.

Organisms, ecosystems are falling
behind as the world changes,

faster than it has in this
enormous amount of time.

It's been shown here that a rise
of just two degrees centigrade

will turn a healthy reef
into a decimated one.

And such a rise will almost
certainly happen in these seas

if we continue to do
what we are doing.

As Ove's tests suggest,

this man-made problem
has reached the point

where it needs a man-made solution.

I'm returning to mainland Australia

to meet the scientists who are
approaching this problem

in a radically new way.

The Australian Institute of
Marine Science, AIMS,

is based in northeast Queensland,
right on the coast.

Here, pioneering research is pushing
the boundaries of coral science.

Over three million litres
of filtered seawater

are pumped through
these tanks every day.

So, it's possible for scientists
to study the minute

and often very complex changes
that can affect coral's health.

So, here, they're also
conducting research

to see whether it
might not be possible

to devise techniques of restoring
damaged reefs back to health.

In these tanks, they can simulate
the exact conditions of the reef.

They've been so successful
that remarkably,

the corals respond to the same
astronomic and seasonal rhythms

as those out in the ocean.

And that is proving useful for
one particular experiment.

Corals are usually able to adapt
to changing circumstances,

given enough time.

And that is partly due to
the way they reproduce.

After the first full moon in October,

the great synchronised
coral spawning event begins.

It's a wonderful,
annual rejuvenation.

Hundreds of species release
sperm and eggs into the ocean.

Just as pollen from plants is
blown far and wide by the wind,

so coral spawn is swept away
by the ocean currents.

And at the same time,
under the same moonlight,

the corals will spawn here
in the laboratory tanks.

Using red light, so as
not to disturb the process,

scientists wait for
the moment of release.

And when it finally happens,

they move fast to collect
the sperm and the eggs.

It's their one chance to get
all the samples they need

for a year's worth of research.

But what exactly are they
planning to do with them?

Here, Dr Madeleine van Oppen has
been selectively breeding them,

using much the same techniques that
we've used to produce crops on land

that are resistant
to drought and disease.

It's the first time that
selective breeding

has been used in marine conservation.

They release their
sperm and eggs in bundles

and those bundles float
to the surface of the tank.

We then agitate that to separate
the eggs from the sperm.

And we use that to set up

our specific in vitro
processes, basically.

In the ocean, there is the potential

for different species of coral
to breed with each other.

So, here, scientists wonder

if you might be able to
produce a new kind of coral

that proves more successful in
the changing waters of the reef.

The problem that corals
are facing now is that

the change of the environment
is extremely fast -

much faster than ever recorded -

so we need to help them
a little bit in the lab.

We need to speed up those
natural processes of evolution.

Van Oppen's aim is to use selective
breeding to produce strains of coral

that are able to withstand the
worst effects of climate change...

..and to use them to bring life back
to worst-affected part of the reef.

Maybe in five years or so,

we will be allowed
to place those corals

onto a real reef, a disturbed reef -

and test it and these
selectively-bred corals

will be able to restore
that reef faster.

And you have to realise, this is
really a last resort option.

We wouldn't want to do that if
the reef is able to restore itself.

But is there a chance that the reef,
damaged by our activities,

could restore itself
without our help?

Well, we now think that
there may be clues

in the reef's most distant
and mysterious regions.

There are still parts of
the Great Barrier Reef

that are virtually unexplored.

But today, we have got remarkable
new underwater vessels,

like this submersible,
that can take us to places

where no unprotected human being
could possibly go.

What they will find down there,
nobody knows.

But I'm lucky enough
to be one of those

who's about to go down to find out.

At the outer edge of the reef,

the continental shelf plunges down
over 2,000 metres to the seafloor.

The Alucia has brought us
over the edge of the drop-off,

90 miles out into the Coral Sea...

..out to Osprey Reef.

Here at Osprey, this sheer
vertical drop of the seafloor

enables us to see corals
at a variety of depths.

Between 100 and 150 metres down,

daylight is reduced to a glimmer.

This is the mesophotic zone.

Here, a mysterious community
of corals is thriving,

despite the damage being done
to the reef above.

The Great Barrier Reef,
it's a marvel beyond marvels.

It's a million species living
in this symbiotic tangle,

half of which we don't know.

I mean, when you get
to mesophotic depths,

we know very few of
the species down there.

It literally is one of the
last frontiers of biology,

to understand this system.

Scientists are now beginning
to wonder if these corals

might have the potential to restore
the damaged parts of the reef.

RADIO: '..Down about 100 metres...'

Our state-of-the-art submersible

is going to take me to see
these deep corals for myself

and even bring back a sample.

Nadir in position.

Are we clear to vent?

You are clear to vent,
clear to vent.

Roger. Venting now.

We are descending
into the twilight zone.

As we drop down the face of the reef,

the light begins to dim.

At about 100 metres,

we enter the mesophotic zone.

"Mesophotic" literally means
"middle light".

The corals here are beginning
to look very different.

Despite the apparent
lack of light down here,

there's still enough for some
corals to photosynthesise,

just like their relations
closer to the surface.

And to do that, they've formed
these flat, broad plates

to collect what
little light there is.

Mesophotic corals lie mostly out
of reach of cyclones and bleaching.

So, one of the big questions
facing scientists is,

could these deeper corals naturally
repopulate the damaged reefs above?

We've now passed beyond
the mesophotic zone.

The light begins to
disappear completely

and the reef changes again.

Most of the light that
filters down from above

comes from the blue end
of the spectrum,

so the rock surface
ahead of me looks very dull.

But turn on the lights
and it looks very different.

Despite their remoteness,

these strange relatives
of reef-building corals

are still part of
the great reef system.

To understand how they're connected,
we need to study them closely.

So, this seems an excellent place
to collect a sample.

But manoeuvring our eight-tonne
submersible close to the rock face

is a delicate operation.

Oh, that's great.

The chances are that this
could well be a species

that no-one has ever seen before.

But things don't go quite to plan.

Oh, no! We're going to have
to go and fetch that.

There it is.

Oh, terrific!

Success!

As we descend past
the 200 metre mark,

the coral finally begins
to disappear altogether.

Surface, surface, Nadir.

My depth now, 300 metres. Over.

At this depth, the pressure bearing
down on the submersible's sphere

is more than 30 times
that at the surface.

That's an incredible
450 pounds per square inch.

Here, there's a sediment that is
drifting down from above,

cloaking the surface of the reef.

That means it's very difficult
for any organism

to get a hold of the rock, because
it's continually being swept down.

The sediment itself is the
result of the erosion of the
coral skeletons from high above,

but also from the remains of coral

that parrot fish have
munched and excreted

and it's slowly drifting down here.

So, this is so deep,
it's almost barren.

But not quite.

At almost the deepest point
of our dive,

something pays us a visit.

There's a fish to your right,
David. On your shoulder.

Look at this!

It's a deep-water grouper.

No-one has ever seen them up close
like this, at this depth.

'It appears to find the sub
and its occupants fascinating.'

And he's big, this boy. He must be...

..four, five feet long -
a couple of metres, almost.

Hello.

Oh, gosh!

And why he is down here,
what he's looking for - who knows?

He's going up.

So are we.

As we ascend, light and colour
returns to the reef around us.

'Our on-board reef scientist,
Professor Justin Marshall,

'is on hand to retrieve the sample
we gathered in the darkness.'

What do you reckon?
Well, it's fantastic.

This is one of the deepest
samples ever from Osprey Reef.

It's wonderful. Will it survive?
Will it still live?

It will still live
and we'll take samples back

to the University of Queensland
and work on it there. Great.

In fact, they think this coral
has never been reported

in this part of the world before
and may be new to science.

We are a long way off
from having a solution

to the threats which now face
the Great Barrier Reef.

But in these deep water samples

and in the scientists'
experimental tanks,

there is a small glimmer of hope.

But time is not on our side -...

..an opinion shared by many of the
scientists I've met along the way.

Are you fearful for
the future of the reef?

There will be change, for sure.

I mean, we're seeing change within
our own human lives' timescales now.

And what's your prediction about

what it's going to look like
in another hundred years?

The sea levels will be higher.

We want to know - as
a scientist, we want to know

how the Great Barrier Reef
will respond.

Whether it has
the resilience to bounce back

with the future changes to
the climate remains to be seen.

Here on the Great Barrier Reef,

we've lost about 50% of the coral
since the early 1980s.

Coral provides a habitat
for over a million species.

This is such a fundamental
part of our oceans

and the fact that it's going
to disappear on our watch,

it's incredible.

When the Great Barrier Reef
starts to go seriously backwards,

the next generation is going to say,

"Why didn't you guys do something
about it when you had a chance?"

And well may they ask that

because we're not doing
what we should be doing

and we're going to pay the price.

The Great Barrier Reef
is in grave danger.

The twin perils brought
by climate change

and increase in the temperature of
the ocean and in its acidity

threaten its very existence.

If they continue to rise
at the present rate,

the reefs will be gone
within decades.

And that would be
a global catastrophe.

About one quarter of the
species of fish in the world

spend some part of their lives
in the reefs.

If the reefs go,
the fish will also disappear.

And that could affect the livelihood

and diet of human
communities worldwide.

But there's surely another reason
why we should protect the reefs.

They are among this planet's
richest, most complex

and most beautiful ecosystems.

Do we really care so little about
the Earth on which we live

that we don't wish to protect
one of its greatest wonders

from the consequences
of our behaviour?

For this series, the
production team were determined

to show the Barrier Reef
in a new way,

by filming in some of
its most remote areas...

..and allowing me to meet

some of its more unusual
and surprising inhabitants.

'This took us out onto the top
of Heron Island's reef,

'which is only exposed at low tide.

'But we had to tread carefully,
accompanied by guides,

'to ensure that we didn't
damage any of the coral.'

Anybody who's coming on here,
it's weird at first,

but just try and walk on the
dead coral - the concrete stuff.

'We were there to film
an elusive creature

'that feeds in this special habitat
when the tide is out -

'the epaulette shark.'

There's one with a tail -
the first one is there.

Just gone. It's gone under there.

'Professor Gillian Renshaw has been
studying these sharks for 20 years.'

It's very hard to see
the epaulettes

because they're cryptically
coloured and blend in very well

with the fingers of coral that are
rising out of the reef platform.

'It's a challenging location,
not least because

'it's only accessible for
short periods of time.'

We've got probably about 40 minutes

to get all of the shots
that we need,

so I shouldn't really be talking
to you, we should be getting this.

OK, quiet please!
Camera's rolling. And action, David.

The epaulette shark
remains on the reef,

even when the tide goes out.

Of course, with so little water,

it doesn't get as much oxygen
as it requires normally, but...

'Although my piece is done,

'the team must now film the shark's
unique walking behaviour.'

The water is literally pouring
in around the equipment

and over our feet.

We've got about 10 to 15 minutes
to get this sequence finished

and get back in the boats
before we're literally cut off

and we can't get back to the boats.

'The tide creeps in around us.'

He's walking beautifully, now.
Look at that.

Let's try and get it
in the water a bit.

Really nice performance
from the epaulette shark.

'Now, it's a race against time
to get off the reef.'

Are we ready for the boat, now?

Geraldine, can we get
David on, please?

Yeah, looked stunning.
Worth the stress.

'This trip took us from
the very top of the reef

'down almost to its bottom...

'..for our most ambitious
sequence of the series -...

'..to attempt
the deepest dive in this area

'and collect a sample of the
mysterious coral that survives there.

'And it's down to
cameraman Paul Williams

'to film our mission
single-handedly.'

I'm on my own down there.

I've gone over it and over it
again in my mind,

about what we're trying to do
and how we're going to do it,

so I think I've got it locked in.

I hope haven't forgotten anything.

'It's something of
a squeeze in the sub,

'with all of Paul's
filming equipment.'

Do you mind if I just
give you that for a moment?

'But our third crew member
is essential.

'He's the pilot, Buck Taylor.'

I'm sitting with a big
camera on my shoulder

and two other cameras,
which were outside the sub,

controlled by laptops
which were both on my lap.

The sound kit was under Buck's feet.

It was tight in there.

David, do you mind?

Would you get your towel and just
give that a little wipe there? Yup.

Thank you, sir.

'For the first part of the dive,

'underwater cameramen
filmed the sub's descent.

'But at about 60 metres,
they reached their limit.

'It's only possible
to venture further

'within the protection
of the submarine.

'As we enter the mesophotic zone,
around 100 metres down,

'we're on our own.

'To get the best shots
of the reef beyond,

'Paul requires all of
Buck's skill as a pilot.'

Do you want to try
some other light options?

What have you got?
I can give you that.

Yeah, put the higher ones on,
take the lower ones off.

How's that? Yes. Actually,
that looks better. Isn't it lovely?

Probably full of nooks
and crannies. Yeah.

Buck, the sub driver, was brilliant.

He'd find a drift in the currents

and then we'd just drift
across the coral.

What's nice is,
I can actually see the wall.

That's a very good angle for me.
Is it? Yeah.

So, just let us drift
a tiny bit to starboard.

And...action, David.

This wall of rock ahead of me is
actually the flank of Osprey Reef -

an oasis for life.

'But we weren't down here
just to look.

'We also wanted to collect samples
for deep reef scientists...

'..and that proved
easier said than done.'

Oh, no!
We have to go and fetch that.

We'll take that on film.

'As we descended beyond 250 metres,

'we entered a landscape rarely
seen with the naked eye.

'It was the perfect opportunity
simply to explore.'

This is the first time
that manned submersibles

have worked at this depth

and it gives one the ability
to look and observe

and just do curiosity-driven
research.

It's fantastic.

The visibility down here
spectacular, isn't it?

It's absolutely pure, yeah.

There were many times when I had to
take my eye away from the eyepiece

because I just had to
look with my own eyes,

so it goes into the brain properly

in the right perspective.

'Soon, we reached our target depth.'

There it is. 300.

Nobody before has ever been as deep
as this on the Great Barrier Reef.

I like it.

LAUGHTER

So, it hasn't even come up
on here - 290 metres,

but we've heard that they've
just reached 300 metres.

Another thing to add to the things
that David's done on this planet.

'The purpose of our
record-breaking trip

'was to raise awareness
of the reef's fragility.

'Fortunately, while production
continued on the series,

'the dive caught
the attention of a president.'

Mr President.
When I heard that you had gone down,

you dove into
the Great Barrier Reef again...

..60 years after the first time
you did it?

Yes. That impressed me.

Ah, but I was in a sub.

I mean, I was in a very,
very remarkable research sub

and we went down to over 300 metres.

Oh, so you went really deep.

And that was just mind-blowing.

The deep dive proved
a truly memorable moment for me

and allowed us the unique
opportunity of revealing

a part of this great reef
that has never before been seen.