Original subtitles

I'm here, surrounded by one of nature's greatest wonders.

A living structure so enormous, it can be seen from space.

The Great Barrier Reef.

Home to one of the most extraordinary communities of animals on the planet.

'I've been fascinated by it for almost 60 years.'

Here, unknown species are still being found.

And scientists are making astonishing discoveries

about the creatures that we thought we knew.

'In this series, our research vessel, the Alucia,

'will allow us to explore the reef as never before.'

Using the latest technology, I'll visit its mysterious depths.

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

I'll learn of its surprising origins.

And discover how this wonderfully diverse community

has been created by some of the very smallest creatures on the reef.

But visited by some of the most impressive animals on the planet.

It's an ecosystem like no other.

Vital to our oceans.

And surprisingly, we are still uncovering its many secrets.

The Great Barrier Reef lies on Australia's north-east coast.

It's 1,400 miles long...

..and at its widest, 150 miles across.

It consists of almost 3,000 individual coral reefs...

..and 900 islands.

And for me, it's truly

one of the most extraordinary places on the planet.

People say to me,

"What was the most magical thing you ever saw in your life?

"What was the most magical moment in your career as a naturalist?"

And I always say, the first time I put on a mask

and went below the surface

and moved in three dimensions just with a flick of my fin

and suddenly saw all these amazingly multicoloured things

living in communities right there.

Just astounding things.

Unforgettable beauty.

I first came to the Barrier Reef nearly 60 years ago.

And I remember very clearly how amazed I was

to see such a complexity of life.

But today, we have ways of looking at the reef,

technical ways, which we never had before

and give us a completely new vision of this wonderful place,

which is surely one of the greatest treasures of the natural world.

'Now I've returned.

'And taking me on this journey is the Alucia,

'a 56-metre state-of-the-art research and exploration vessel.

'For this expedition, we've been granted unprecedented access

'to some of the most remote corners of the Great Barrier Reef.'

Onboard is a team of experts.

And at our disposal, all the latest technology.

Our mission is to reveal a hidden world

and to complete a series of dives

that have never before been attempted on the Great Barrier Reef.

But to do that, we have had to bring in a very special piece of equipment.

This is a Triton submarine.

The very latest in submersible technology.

And the first of its kind to be brought to these waters.

The submersible's captain, Buck Taylor, will lead the dive team.

With 2,000 dives under his belt, his expertise is unparalleled.

While our film crew rigs the submersible

with no fewer than eight cameras,

Buck gathers the rest of the team together

to brief us on the dives ahead.

COMPUTER: "Welcome to the MV Alucia submersible team..."

'The submersible offers spectacular filming opportunities,

'but it's not without its dangers.'

Coming from the rescue background,

I've been in a submersible up to my waist in water,

I've had a fire in a submersible.

COMPUTER: "No smoking, smoking materials..."

'As well as these hazards, Buck is also obliged to raise

'one of the more intimate limitations of submersible life.'

We do have facilities of a toilet onboard.

Obviously, because it's quite confined, it's not very discrete,

so we do have some towels out that we can hold up around you.

It's quite interesting trying to explain about going to the toilet

in a three-man submersible in a sort of sphere

that's less than two metres diameter. It's quite intimate.

He was six foot three... LAUGHTER

We've got cameras pointing from every direction.

Good. Thank you.

Thanks very much. I'm looking forward to it a lot.

The Alucia's first mission

is to take us to the Barrier's stunning ribbon reefs

in the north of its extensive range.

It's an area of outstanding natural beauty

and the perfect place to begin our explorations.

The story of the Great Barrier Reef

starts with its most important inhabitant, the coral itself.

Hidden inside these branching structures

are the thousands of tiny creatures that build these reefs.

And they have an enormous claim to fame.

Together, they've built the largest living structure on earth.

But these fascinating coral creatures are only active at night.

So to capture their behaviour,

we'll need to do something I've never done before.

Tonight, a team of specialist divers, scientists

and programme-makers, like myself,

have gathered together to have a closer look and a longer look

at the reef at night than perhaps has ever been possible.

When I came here 60 years ago,

the idea of a night dive was almost inconceivable.

It seemed to me, a beginner, to be far too dangerous.

But now, technology is going to help me.

'Once I'm in, it's over to Buck and the support team,

'who remain onboard the Alucia,

'to make sure everything goes smoothly.'

INDISTINCT RADIO

'They've spent months preparing for this moment.'

SIREN WAILS

'Our submersible, known to the crew as the Nadir,

'has, of course, made dives like this all over the world.

'She's descended to the deepest part of the oceans,

'but she's never visited the Barrier Reef.

'It's a first for all of us.

'But before we can go anywhere, we'll need to position the Nadir

'at a safe distance from the Alucia.

'It's a substantial operation,

'but finally, we're ready to get underway.'

S.O. Nadir, just approaching the buoy. Am I clear to vent?

RADIO: "Roger, Nadir. You are clear to vent, clear to vent.

"Have a good dive, guys."

'Sinking beneath the waves is a very surreal experience.

'Your first instinct is to hold your breath.

'At night, the reef is a ghostly world.

'Tiny shrimp-like creatures dance in the lights.'

Look at that! Wow!

'With little light, there is a lot less colour,

'but this is still a very magical place.'

Ah! There's something! My first fish!

'Our submersible will eventually take us to depths of 300 metres.

'Now, we're only 30 metres down,

'but that's exciting enough for a start.'

In these dark waters, Buck needs to be careful

as we move around the front of the reef.

Coral reefs are sometimes described as marine cities.

And the comparison is indeed a good one.

We're here to take a closer look at the reef's architecture.

Its coral buildings.

There are more than 450 different species of hard coral.

The plant-like structures we can see are actually made of limestone.

And living inside are thousands of highly industrious little animals

called coral polyps.

At night, the water around the reef

becomes filled with clouds of tiny microorganisms

called the zooplankton.

And that's what the corals eat.

The coral polyps themselves emerge from their stony skeleton

and start groping in the water with their tentacles.

To see just what they're doing, we need specialised cameras.

The coral polyps never leave the safety of their limestone homes,

even at night.

If something edible comes within reach,

the polyps fire the microscopic harpoons that line their tentacles.

The prey is stunned or killed and then pulled into the polyp's mouth.

When you can't leave your home, it pays to be accurate.

The coral's stinging armoury isn't used only for collecting food.

They also use it to fight.

Because, as has been discovered only comparatively recently,

corals, like many animals that live on land,

are extremely territorial.

But in order to see the battles,

you have to speed up time.

The polyps of each colony collaborate to defend their patch.

As in any big city, space is precious.

If a rival grows too close, there will be trouble.

These fights can last for hours.

The competition is fierce

as the coral colonies jostle with one another

for the best feeding sites.

When they're not locked in battle, the corals have work to do.

'They must extract calcium carbonate from the surrounding seawater

'and with it, build their homes.'

Each coral species has its own particular way of building.

And together, they eventually create the huge reefs

that provide homes for all kinds of other, much larger creatures.

At night, the reef seems like an extraterrestrial world.

But down here, we are the aliens.

And here comes a turtle!

Attracted by our lights.

Come on!

Coming straight to us.

Isn't that great!

'Coming face-to-face with a green turtle

'in this setting is a rare privilege,

'but its presence here, along with all the other reef residents,

'is only made possible thanks to the great coral builders.'

He doesn't look very upset, does he?

It happens all the time on this reef.

It's the perfect end to my first dive.

The time has come for us to make our way back up to the Alucia.

Welcome back, gentlemen.

Diving on a reef at night is a thrilling experience.

What I want to see next is how exactly these tiny coral creatures

have created such a vast and extensive habitat.

To answer that, we'll need to look at the reef

from another angle entirely.

At this height, you can begin to appreciate

the immense size of the Barrier Reef.

It's 2,300 kilometres long, 1,400 miles.

It's the largest living structure on the planet.

Reefs much like these develop in the shallow tropical waters

that surround many an island and continental coast.

But few can match the Great Barrier

in either size or complexity.

So, what is so special about the north-eastern coast of Australia?

A clue to the answer lies in the shape of the sea floor.

If we strip away the ocean,

we can reveal the reason why such extraordinary growth is possible.

The reef has grown on a very shallow continental shelf.

Beyond which, there is a sudden and very steep 2,000-metre drop-off.

It stands in waters with an average depth of just 35 metres.

That's just about as far as sunlight can penetrate with any strength.

Light is crucially important to reef-building corals

because they have developed a special partnership

with microscopic algae -

plants that actually grow within tissues.

The algae get a safe home

and, like all plants, when they photosynthesise,

they produce energy.

The coral polyps use this energy to construct their limestone home.

Together, they've built an underwater city

on a scale that is almost impossible to comprehend.

But amazingly, just 10,000 years ago,

there was no coral here at all.

The Great Barrier Reef as we know it today simply didn't exist.

How and when these coral communities began

is something scientists have only recently started to investigate.

Marine geologist, Dr Robin Beaman,

has been leading an ambitious project to scan the entire reef.

And his data has allowed us to map the sea floor.

David, this is a three-dimensional model of the Great Barrier Reef.

In deeper waters, we tend to use sonar,

in shallow waters, we tend to use underwater laser beams

to image the sea floor.

'By combining computer modelling and radiocarbon dating,

'his team have been able to reconstruct

'the key stages in the development of the Great Barrier.

'Their research has helped identify an event

'between 10,000 and 20,000 years ago

'which may explain how the Great Barrier Reef was formed.

'But surprisingly, scientists are not the only ones to tell this story.'

Australia's Aboriginal peoples arrived on this continent

around 50,000 years ago.

They have been telling the story of how the reef was formed

long before the world's scientists even knew it existed.

To hear that story, the Alucia is taking us to Northern Queensland

to meet a community with a very special connection

to this underwater world.

They are the Gimuy Walubara Yidinji people.

And they live just outside the city of Cairns.

This community has dwelt alongside the reef for thousands of years.

THEY SPEAK YIDINY

And many of their traditions hark back to those ancient times.

THEY SING IN YIDINY

And one of them tells how the reef came into existence.

It's a legend that has been passed down from generation to generation

in the form of a dance.

Tell me the story that's connected to this dance, sir.

It's part of our law story that's told to me by my dad, my father,

and was told to him by his father and his grandfather, as well.

The part of the dance that really interests me

is the story of Gunyah and the sacred fish.

The story starts with Gunyah going out to sea.

And he saw a glitter in the water, which he thought was a fish.

And when he speared it,

he actually speared our sacred fish, the stingray.

So the fish got angry and it started to rise up.

And with its wings, it made the sea rough

and it caused the sea to rise.

Take us back to the time when the first human beings arrived here.

What was it like then?

The coastline would have been very different.

So the coastline would have been right out here,

on the edge of the Great Barrier Reef.

The sea level was much lower

and they would have fished and hunted the coastline.

These were limestone hills

that would have been eucalypts, marshlands.

There would have been mangrove swamps.

But roughly 14,000 years ago,

the climate started to dramatically change.

It was the end of the Ice Age.

And all that water started to inundate the continental shelf

and start to flood this vast, flat landscape.

And in one man's lifetime? Absolutely.

So, people living here are going to have to retreat?

Absolutely. It would have been a dramatic time for them.

They would have been following the coastline

as it prograded further and further back

as the water was flooding the shelf.

The rate of change was so great that in these very flat areas here,

the coastline would have moved back by hundreds of metres every year.

Every year? Every year.

Gosh! That's formidable.

So our story is about the sea rising.

And there used to be a cliff further out.

And past the cliff is where the ocean used to be.

Now, that's really remarkable.

Because Western science is just beginning to make discoveries

that seem to suggest that the sea,

10,000, 20,000 years ago, was way, way out there,

which is exactly what your story says.

Extraordinary. Yes.

A folk memory of an event that happened all that time ago.

Yeah. And the only way we can keep it alive

is through our song and our dance. Yes.

Just to keep that going through our culture.

So the tradition lives.

Yes. It's wonderful.

'It is truly astounding to think that this story has survived

'for so many years and across so many generations.

'And that it coincides with what scientists are now discovering

'about the age of the Great Barrier.'

The polyps that built the reef arrived as spawn,

swept here by the ocean currents.

Corals are not new to the planet.

They've been around for at least 500 million years.

The new reefs provided homes for thousands of animals,

and very quickly, a whole new community began to establish itself.

Today, the Great Barrier Reef

has one of the most diverse communities of animals on the planet.

And it's the story of these remarkable reef residents

that I want to investigate next.

To do that, the Alucia is taking me north to a very special place.

Lizard Island.

It's one of the 600 continental islands

scattered across the Great Barrier Reef.

And its shallow lagoon is known for its exceptional biodiversity.

'With the Alucia anchored in deeper water,

'a more modest mode of transport will be needed to reach the shore.

'I first visited Lizard Island in 1957.

'Then, it was completely uninhabited.

'Little did I know how important this remote outpost would become

'in helping us to understand the coral reefs.

'But today, that's exactly what this remarkable place

'is world-renowned for.'

Here, for the past few decades, there has been a research station

where scientists can study continuously and in detail

the full complexity of the community of animals that makes up the reef.

Every year, Lizard Island hosts 100 different research projects.

Here, scientists are shedding new light

on the lives of the reefs' residents

and the way in which this complex community works.

Thanks to their research, we now know that coral reefs rival rainforests

in the vast numbers of species they support.

The first question is, where does all that diversity come from?

Lizard Island reefs owe their richness

to the special plants that, in places, fringe the shores.

They link land and sea

and they're vital to the coral reef community.

They're mangroves.

Taking shelter amongst the roots

are thousands of juvenile fish of all shapes and sizes.

Many of these little fish look harmless enough,

but when they grow up, they will become

some of the most ferocious predators on the reef.

Indeed, the existence of these mangrove nurseries

is one of the reasons why the fish populations of the reef

are among the most varied and richest in the world.

The mangroves are not only nurseries, they're playgrounds.

The aim of the game here is to survive the most vulnerable stage

of any animal's life, being a juvenile.

Baby turtles...

..rays and even sharks take refuge here.

These juvenile blacktips are just a few weeks old.

And only one sixth of the size they will be

when they make it out on to the reef as adults.

For the first year of their lives,

the mangroves play a vital role in keeping them safe.

As infants, they're vulnerable to predation from larger sharks.

But the tangle of mangrove roots keeps the big predators out

and stops them making meals of the youngsters.

When the young are ready,

they will eventually leave this sheltered world behind

and make their way to the reef beyond the mangrove roots.

The next challenge will be to find their place

in one of the most crowded ecosystems on the planet.

Getting on the property ladder here is no easy feat.

Which is why one of the reefs' most celebrated characters

has developed a very special relationship.

Clownfish deal with the problem of overcrowding

by sharing space with another creature, gigantic anemones.

They've formed a relationship in which both parties benefit.

Anemones have tentacles that are packed with stinging cells.

Most fish touching one get a very nasty sting,

but not the clownfish,

thanks to the protective layer of mucus that covers its body.

The clownfish keeps the anemone in good health

by removing unwanted parasites.

And in return, the anemone offers security.

Its stinging cells ward off the sort of creatures

which would otherwise threaten the clownfish.

When the time comes for a pair to breed, that protection will be vital.

A female may lay up to 1,000 eggs

on the rock beneath her anemone home.

As she delicately attaches them,

the male follows closely behind, fertilising the eggs as he goes.

A week will pass before the young are ready to emerge.

Hatching only happens at night,

so to record it, we have to use infrared cameras

in a specialised filming environment.

This is the very first time that this behaviour has been filmed.

With gentle encouragement from their father,

the young are helped on their way.

Once the little larvae are set free, they're on their own.

They'll spend the first few weeks of their life

developing in the open ocean.

But how will the young clownfish

find their way back to the coral reefs

after drifting many miles out to sea?

To understand that, we will have to tune into a sense

we don't normally associate with this colourful underwater world.

Sound.

Coral reefs are surprisingly noisy places.

Fish and invertebrates produce a whole range of clicks

and grunts and snaps.

The healthier the reef, the more varied and numerous its inhabitants

and the louder this chorus is.

We now know that fish, just like birds,

vocalise most at dawn and dusk.

Damselfish call to defend their territory.

GRUNTING

Seahorses click to attract a mate.

CLICKING

Others create a very different soundscape

simply by carrying out their daily duties.

SQUAWKING

Parrotfish crunching through the hard coral

are a constant on the reef.

Fish perceive sound in two different ways.

Many have internal ears, but underwater,

they can also feel sound as a vibration.

The noise is a key indication that the community is in good shape.

In fact, the louder the noise on a reef,

the more inviting it is to newcomers.

Newcomers like the young clownfish.

This little male is no bigger than a button,

but the time has come for him to find his place in the big city.

At this stage, his swimming abilities leave something to be desired.

But his hearing is so sensitive, he can tell over hundreds of metres

if a reef is suitable.

His journey can last days.

The final approach is usually made at night to avoid predators.

How fish hear and respond to sound of a healthy coral reef

is a major area of study here on Lizard Island.

And the scientists have a simple way of collecting these fish for study.

A light trap, like this one at Lizard Island,

is one way of assessing the way that the reef is working.

Like moths to a flame, the young are attracted by the light.

'By sampling the newest members of the community,

'scientists can figure out how far these juvenile fish

'are willing to travel for a good home.'

In the case of the clownfish, juveniles have been known to travel

250 miles before they find a reef.

Fortunately, for the majority, it's usually a much shorter journey.

While they rarely return to the particular anemone

beside which they hatched,

60% find a new home on the same reef.

For the clownfish and the anemone, cooperation is the key

to success in this extremely crowded environment.

Other residents, however, take a very different approach.

Rather than share their home, they fiercely defend their territories.

This is a mantis shrimp.

Spotting the competition is half the battle.

There are many different species of mantis shrimp

but they all have one thing in common,

superb vision.

The 400 million-year-old visual system of the mantis shrimp

is the most complex in the entire animal kingdom.

Its eyes are mounted on two stalks, giving it independent vision,

but whereas our eyes produce binocular vision,

each one of theirs produces three different images.

Not only that, whereas we have three photoreceptors in our eyes,

the mantis shrimp has up to 16, giving it access to

parts of the spectrum that we can't even see, let alone imagine.

And they can use their amazing vision to devastating effect.

While some are armed with spears, others carry clubs.

Many are champion boxers.

They can deliver a punch

that accelerates faster than a .22 calibre bullet.

These powerful blows are used to stun their prey

and defend their burrows.

Mantis shrimps are one of the more house-proud residents on the reef.

In fact, they're compulsive cleaners.

They keep their burrows meticulously neat.

With all that effort, it's hardly surprising that they're

fiercely territorial.

In fact, mantis shrimps have earned themselves

a reputation for being somewhat ill-tempered.

But scientists have discovered that there's another side

to these macho males.

This young hopeful is trying to catch the eye of a potential mate.

He starts by showing off his paddle-like antennae.

His technique may not be very impressive to us

but he is, in fact, sending the female secret signals.

And that is possible because mantis shrimps can see

and reflect a kind of light that absolutely no other

creature in the world that we know of can see...

..including us.

The male's display is a private invitation for this female to dance.

So far, so good.

She makes her way to the dance floor.

If the male can impress the female with his performance,

she will choose him to father her offspring.

It seems that this male has all the right moves.

The final phase of courtship, however, usually takes place

out of sight, within their burrows.

The mantis shrimp is arguably one of the reefs most colourful

characters and typifies the key to survival here.

Each resident species has had to carve out its own particular niche

and that is what has created this extraordinary diversity.

Here, life can evolve 50% faster than in other marine environments.

The tiny creatures that have built this remarkable ecosystem

have created a habitat so complex that it supports all kinds of life.

But none of the reef's residents would be here

without one truly extraordinary event.

It occurs just once a year

and is one of the greatest of all natural spectacles.

It wasn't until the 1980s that scientists discovered it,

here on the Great Barrier.

On a few nights of the year

when the conditions are just right,

all along the length of the reef,

corals of many different species suddenly erupt.

It's the great spawning event

and it's one of the wonders of the natural world.

It's the one time in the year

when the corals themselves don't just grow by branching,

but reproduce sexually, and it's vital for the survival of the reef.

In recent years, we've learned a great deal

about the many factors that influenced the moment of spawning.

But even though we know it occurs within days of the full moon in

October or November, the trigger that starts it all is still a mystery.

The light of the moon is, perhaps, the most influential,

but there are many other factors,

including the temperature of the water and the state of the tides.

And as the moment approaches,

all along the length of the reef,

there's a mounting sense of excitement.

Fish and other predators gather.

This will be an opportunity for a feast.

The timing has to be exact.

Each species of coral has its own particular triggers,

but they must synchronise their behaviour to ensure their success.

Just half an hour before the big event,

there is the first sign of the spawning to come.

Small bundles of sperm and eggs bulge from the polyps.

When the moment is right, there is a mass release.

For hundreds of miles all along the coast, the corals erupt.

Only with daybreak can you see the true scale of the event.

Great ribbons of coral spawn drift over the surface of the sea.

After the coral has spawned,

the billions of developing larvae are swept far and wide

by the tides and the currents.

The vast majority will be eaten by fish and other creatures,

but the few survivors must then find a place to settle,

either on a newly-vacated site on an existing reef

or perhaps to found a new one.

The newest coral recruits will continue

the work their ancestors began almost 10,000 years ago.

They are the essential organisms on which the whole reef depends.

The Great Barrier is what it is

because the tiny coral polyps never stop building.

And what they have created is one of the wonders of the natural world.

Next time, we'll cross the Great Barrier Reef

to meet its extraordinary visitors.

I will meet turtles

that may have travelled thousands of miles to get here

and the remarkable people

who are trying to save them from disaster.

I will come face-to-face with the great predators of the reef.

Wow. There's a huge shark.

They are so beautiful in the water.

And we'll meet a whale that seeks out human contact,

a behaviour that happens nowhere else on Earth.

Some come from the open ocean,

others from the land immediately inshore

and still others from the sky,

to complicate still further the intricate community

that is known as the Great Barrier Reef.

For this series,

the production team set themselves an ambitious challenge.

They wanted me to experience the Great Barrier Reef as never before.

To achieve that, we teamed up with a very special research vessel...

..the Alucia.

There aren't many boats like this in the world and

it's a kind of magic carpet for us.

It allows us to float around the reef

and for David to tell different parts of the story.

On board, all the latest technology,

helicopters, a laboratory

and advanced mapping systems.

At the helm of Alucia,

Captain Frank Alika.

The task of getting the ship into position

for the first big submarine launch rests on his shoulders.

Some parts are charted less well than others,

but this particular bit, there's quite a lot of bombies

and things out there that are likely to jump up and bite you

on the bottom, and that's really not what you want.

Fortunately, he's a lot more hands on

than the skipper was on my first visit in 1957.

But it was very primitive.

The camera was wound up by clockwork

and it was just me and the chap with a 16mm camera

and I did the recording.

It may have been a modest shoot but it was, in its way, ground-breaking.

We worked on locations on the reef

where film crews had never been before.

60 years later, I'm told we are poised to make history once again.

This time, to reach new areas of reef,

I'll have to rely on the Triton submersible.

And she's very flexible in terms of how shallow we can come, as well.

She'll work in 1,000 metres happily,

but we can also work in the splash zone,

so her actual trim system is very good.

Amazing visibility, as you'll see when you get in.

Yes, she's a little bit flash.

With just a few short hours before the first big dive,

the excitement and pressure is building on deck.

This will be the last opportunity for the crew

to check the camera gear

and make sure everything is perfectly in place.

It's been a busy morning already.

We've had soundmen, cameramen

trying to fit all their gear into the sub.

We're sort of running out of space for bodies.

There are lots of worries when you put your 88-year-old presenter

in something like this.

I mean, it's got a very small area at the top to get into.

There are all sorts of things that can go wrong.

We're always very cautious.

And even the most limber of sub operators

will struggle getting in the sub.

David's incredibly active and fit,

but he's 88 and so we were slightly worried

about how he might get into the sub.

Yeah, that's it, that's the one.

OK, so we're just going to...

See that landing, he'll guide you right in.

And then you can put your foot there, David.

Keep coming. Nearly there. That's it. OK.

You can rest against me if you want.

Nearly sat on the pilot!

That's all right, I'm used to it. That's what he's there for.

David, as usual, defied all our thoughts

and just went straight in without any trouble

as though he was a 25-year-old.

Rest it on your lap. Is that OK? Yep.

So, that's hatch secure and we are ready.

The sub weighs almost eight tonnes

and getting it into the water is a major operation.

There's something quite extraordinary about the Triton

being launched, standing here on deck.

Suddenly, the whole back deck area of the ship comes alive.

You've got people running around.

Everything's incredibly detailed and carefully planned,

but you're sort of caught in a whirlwind as ropes fly

and the submarine starts to move forwards.

You know, this is a very exciting moment.

You know, this is a big day, even in the world of David Attenborough.

As we disappear beneath the waves,

out on a support vessel,

underwater cameraman Steve Hudson prepares to film the sub

as it explores the reef.

So, Nick and I are going to jump in the water,

descend to a maximum depth of about 30 metres

and shoot exterior shots of the submarine

as it cruises over the reef.

It can be pretty tiring.

You have to swim in front of it, swim behind it,

swim beneath it, swim above it,

trying to get a multiple of shots.

But today, because of the strong currents, visibility is poor.

At first, Steve struggles to locate the sub through the cloudy water.

Finally, he makes visual contact.

Before we descend deeper and beyond his reach,

Steve must get his exterior shots of the sub.

Lead cameraman Paul Williams

captures the action from inside the vessel.

To get the best footage,

the divers need to coordinate with the sub team.

It's a task easier said than done.

We're literally in a bubble.

We can't talk to the divers outside.

We had this rather crude hand signal.

You know, it's like,

"Get out of shot," or, you know,

"Well, just move over that way a bit."

Can you see his hand signals, yeah?

He's saying, "Thank you."

Thank you and...

We're just going to do the descent now.

'As the vessel dives deeper,

'we're treated to some spectacular sights...

Oh, how beautiful.

'..which show why the reef is one of the most dazzling

'habitats on the planet.'

Oh, look at this lot.

It's jolly nice that someone of my age

can be taken down in fantastic comfort.

Grey reef shark there.

No problem about breathing. No problem about talking.

No problem about your movements.

There's another.

You're just sitting there

and looking at one of the most extraordinary places on Earth.

A privilege given to very few.