Original subtitles

The Great Barrier Reef is the largest coral reef on our planet.

It's one of the seven recognised wonders of the natural world.

The reef itself is the place that most people explore

but there's much, much more.

The coral reef is actually a very small part of this underwater world.

As little as seven per cent.

The remaining 93% of the marine park

encompasses a variety of habitats, each one remarkable in its own way.

And beyond the marine park

there are even more environments that are important to the reef.

Some close to shore.

Others inland.

Altogether there are more than a hundred different types of habitat

in and around the Barrier Reef,

each with its own distinctive plants and animals.

There are creatures that you would expect to see on a reef,

and others that you would not.

All the places in which these animals live

are linked to a vast deep-water lagoon

which lies between the coast of mainland Australia

and the outer reef.

These habitats interconnect,

and all are vital to the well being of the Great Barrier Reef.

This is the little known story of one of the most complex

and spectacular ecosystems on Earth.

The Great Barrier Reef is over two thousand kilometres long,

which means the lagoon that lies between the outer reef

and the Australian mainland is vast.

An area one and a half times the size of the British Isles.

Pick a spot anywhere in the lagoon and you'll probably find sand,

as about two-thirds of the seafloor here is a shifting underwater desert.

It looks barren, but there is life here.

It's just that you don't often see it.

Garden eels

and an unlikely alliance.

A fish and a shrimp that share a burrow.

In a world where most food is out of sight,

it takes a predator with special talents to find it.

And this is that predator...

The ray.

The ray's special skill is to find living things under the sand,

and the largest species to do this here is the stingray.

It finds its prey by detecting the minute electric fields

produced by muscles when they contract,

including the heart muscles.

Something no animal can ever switch off.

But they do have to swim directly over a beating heart

to know that it's there.

By sucking and blowing,

this stingray excavates its target deep under the soft sand.

Many rays feeding together produce a series of furrows on the sea floor

and all that puffing and blowing can attract unwelcome attention.

The hunter can just as easily become the hunted.

This is a stingray's worse nightmare.

A great hammerhead shark.

It has electro-receptors too.

They're spread across the underside of its very broad head,

which it sweeps back and forth searching for prey.

The stingray has a formidable weapon, a venomous barb.

But one hammerhead was found with 96 barbs in its body,

and seemed none the worse.

The stingray's first line of defence is to remain very still

in the hope that the shark doesn't find it.

The commotion warns the other rays to escape,

but it attracts other sharks, like jackals at a kill.

Dramas like this are played out every day on the floor of the lagoon,

but few people are there to witness them.

It seems surprising that the lagoon remains a relatively unexplored environment.

But if you're a diver, why would you explore the lagoon?

It's relatively hostile,

particularly when you compare it to the crystal clear reefs

that are short boat ride away.

Yet there's plenty of life down here.

Prawns, squid and all manner of fish species

are caught by local fishermen.

Diving here is not easy but it's well worth the effort.

Dotted across this vast underwater desert are ghostly oases

where amazing life forms have taken hold.

It's a strange, almost alien world.

And if the place seems strange,

many of the creatures living here are even stranger.

These oases are created not by plants but by animals.

They're corals, but not the normal reef building ones.

Unlike their hard coral cousins, they don't have a chalky skeleton

and they thrive at depths where the light is less intense,

capturing food from the water currents

with eight feathery tentacles.

These soft coral gardens are important

because baby fish hide amongst them.

Nearly half of all the adult fish on the reef proper

grow up in nurseries on the lagoon.

They arrive as larvae, swept in from the ocean by the tide.

Then, as the tiny fish grow,

they hop from one refuge to the next across the floor of the lagoon

to reach their final destination back on the Barrier Reef itself.

As long as they hide amongst the corals and seaweed,

they're relatively safe.

The danger comes when they break cover.

This baby Queensland grouper may just be a few centimetres long now,

but one day he'll weigh half a tonne.

That's if he lives that long. He can't stay hiding forever.

It's dangers like this camouflaged stonefish

that force all life down here to find somewhere to hide.

The floor of the lagoon is relatively flat and featureless.

It's like the plains of the desert.

But every now and then you get a little oasis of life.

And this sponge, here, has been heavily colonised

by these feather stars and it provides a vital bit of cover

for juvenile fish on their journey both to the reef

and their journey to adulthood.

And that journey includes stopovers at almost anything that sticks out above the sand,

like this tube dwelling sea anemone.

A carpet anemone becomes a welcoming roadhouse.

Even the spines of a sea urchin will do the trick.

A surprising refuge is this highly venomous Stoke's sea snake.

It's picked up some hitchhikers, baby trevally,

and become a mobile nursery.

Wherever it goes, they go.

With hiding places at a premium,

fish will go to incredible lengths to hide down here.

and none more so than this.

The pearl fish is vulnerable out in the open,

so while it's not feeding it must conceal itself.

But it has a peculiar taste in hiding places.

This is a sea cucumber.

Its body is basically a tube.

It sucks in sand at one end, extracts anything edible

and passes waste out of the other.

Just what the pearl fish has been looking for.

But NOT the mouth end.

It's attracted to the odour of the other end.

Sea cucumbers are repulsive to most predators

so the pearl fish is safe inside.

It'll stay there until it's time to feed again.

It doesn't harm its host, but the bad news for sea cucumbers

is that pearl fish are happy to share their temporary home with others.

It seems there's plenty of room for all.

The Barrier Reef we see today is comparatively young.

It began to form during the last Ice Age

when sea levels were 120 metres lower than they are today.

When the ice sheets began to melt,

the growth of corals kept pace with the rising seas,

blocking off the waters of the lagoon.

And during that one great event

another important habitat was created.

Stretching away behind me to the horizon

is the great expanse of the lagoon and yet a mere 10,000 years ago,

that's a blink of an eye in geological time,

the beach I'm standing on would have been the slope of a hill

overlooking a plain covered in Eucalyptus forest.

But the sea level rose,

the plain was inundated and the hill became an island.

These "continental islands", as they're known,

are essentially pieces of mainland cut off by the rising water.

There are six hundred of them scattered about the lagoon.

Any land animals cut off from the mainland had to adapt or perish.

And on this island one species has done so well,

it's positively flourished.

This is a yellow spotted monitor lizard,

or goanna, if you're from this neck of the woods.

And it's a very successful and abundant animal on this island.

It made a real impression on Captain Cook

when he came here in 1770.

To the degree that when he sat down to think about a name for the island,

not a terribly long process, I don't think,

he thought, "It's an island and it's covered in lizards."

"Got it! Lizard Island."

Which is rather clever, I think.

Do you see what he did there?

When hunting, the goanna is alert to any movement.

If the grasshopper remains still,

it has a chance of escaping the goanna's attention.

Balancing on its back legs and tail like a tripod

is a trick few others lizards can perform,

but it's effective to get to those just out of reach places.

The goanna's sense of smell is as important as its sight.

Its forked tongue helps it to detect food from a distance.

By comparing the strength of a smell reaching each of the two prongs

it can pinpoint where it comes from.

A rotting fish is irresistible.

They're usually solitary,

but here on Lizard Island they'll tolerate others,

as long as there's plenty of food to go round.

Small goannas give way to larger ones.

Foraging a variety of foods has helped the goannas

build a large population on Lizard Island,

but there's another important factor and that's how they react to me.

HE WHISTLES

There are people living on the island

and the goannas are not afraid of them.

In fact, quite the opposite.

He's followed the scent of my barbeque

and over the last few years these animals have adapted their behaviour

to get used to the presence of man

and use man as a potential food source.

This ability to learn and change as the environment around you changes

is a very neat evolutionary trick.

He's used to hunting invertebrates, he's changed his behaviour

to home in on this appallingly cooked barbequed sausage.

In the modern world where man has encroached on virtually every habitat

it's a very good way of ensuring your survival.

And adaptability has enabled a reptile with a more chilling interest in people to thrive in these waters.

It's the saltwater crocodile, better known locally as the 'salty'.

It's the world's largest reptile and it's common on the lagoon's islands

because it's at home in saltwater and fresh,

sometimes swimming far out at sea.

So it's not unusual to find one hauled out on an island beach.

Salties, though, start life with more modest dimensions.

This one-year-old is no more than 30 centimetres long

and it's hiding amongst the plants at the edge of the sea.

Hunting at the junction between air and water

means there's a good choice of food. Like mud skippers.

He'll have to improve as a hunter

if he's going to grow into a six-metre giant.

And he'd best better watch his back.

There's a bird about that could easily take a baby crocodile.

This is a white bellied sea eagle.

It's the second largest eagle in Australia

and it's fantastic to be this close.

This is the closest I've ever been to any eagle anywhere in the world.

They can be seen just about anywhere around the lagoon.

You're as likely to spot one amongst the trees,

as you are over the reef.

So an island is a perfect base.

They may be specialised to catch fish,

but like the goannas and crocodiles they're adaptable too.

This is a range of items taken from beneath a killing tree

of a white bellied sea eagle on a continental island.

The killing tree is where the sea eagle will take apart, dismember,

and eat its prey.

It's a very good representation of what these animals eat

and indeed their strategy for hunting.

You've got a parrot fish here, which is a deeper swimming fish.

you've got things like these long toms

which actually swim right on the surface,

you've even got birds here.

Most remarkable of all you've got these freshwater turtles,

that don't exist on the island.

They are on the mainland so that eagle has flown the mainland

taken these turtles and brought them back to the nest.

It's an excellent representation of the strategy of these animals.

If a food item is short locally in short supply on the island,

they'll actually seek alternatives.

This generalist approach makes them very, very successful

in the limited environment that an island represents.

Even so, fish make up half of its diet.

To catch them it uses huge talons.

They're also weapons it can use to have a crack at these...

fruit bats.

Spectacled fruit bats are big.

They have a wingspan of about a metre

and they roost in island forests as well as those on the mainland.

Babies have to cling on tight.

But that's the least of a mother's worries.

Diving into the tangle of branches

and grabbing a bat hanging at its roost site

is not an option for a large bird.

For the eagle to have any chance, the bats needs to be airborne.

These are little red fruit bats.

During the day, they gather in roosts of up to a million

so they're not hard to find.

An eagle's appearance creates panic.

Bats are agile flyers

but the eagle's powerful claws gave it the edge.

The continental islands are magnets for wildlife,

providing shelter, lookout points and hunting grounds.

They're oases for life but they're not the only ones.

Below the surface of the lagoon is an island of a very different kind.

A shipwreck.

This is the SS Yongala.

She sank during a cyclone in 1911

and now sits on the seabed at a depth of thirty metres.

122 people lost their lives.

But out of this human tragedy has come an opportunity.

100 years underwater has created something very, very special.

The Yongala is regarded by many as the greatest wildlife wreck on earth.

And looking around me it is very hard to disagree.

The wreck provides shelter on the featureless plain

for more than 120 fish species.

This concentration of life

is sustained by food swept in by the exceptionally strong currents.

The living is so good,

many of the young fish stay here for their entire lives,

rather than move to the outer reef when they grow up.

There are sea turtles down here too.

This one's a loggerhead.

And the wreck's a favourite hangout for another species.

This is a hawksbill turtle

and he's here to feed on the soft coral that coats the wreck.

The soft corals are one of the main reasons that all this life

is attracted to the Yongala.

Almost every available space on its once smooth hull

is covered with them.

The soft corals are a refuge for millions of small fish

but they must dart out from time to time

to feed on the plankton in the current.

And wherever small fish gather,

it's not long before something bigger turns up to eat them.

A grouper!

This is a Queensland grouper,

it's the largest bony fish that lives on the Great Barrier Reef.

Queensland groupers are real giants.

This Yongala resident is known as the VW,

because he's the same size as the car.

His mouth's so big,

he's quite capable of swallowing sharks and rays whole.

But another resident has an even deadlier bite.

Sea snakes have more potent venom

than many of their land-living relatives

and they put it to good use.

The olive sea snake doesn't really look as though it's hunting,

but when its small head disappears into a hole,

it can trap and paralyse any fish hiding there.

It's unusual for so many predators to be swimming so close to each other,

but there's so much to eat here.

Most of the action is on top of the wreck,

where the strongest currents sweep in the most food.

The waters within the immediate vicinity of the wreck

is an area of incredibly intense and violent predatory activity.

For the small fish that call the Yongala their home,

to venture into this blue water is a huge gamble

but they've got to do it, to seek out food.

And if they get it wrong and go too far,

the difference between life and death on this wreck

can be a matter of millimetres or seconds.

The amount of marine life to be found in the 100 metres

of the wreck of the Yongala is truly staggering.

Arguably it's a greater concentration

than on any spot on the Barrier Reef itself.

In contrast to the middle,

the landward edge of the lagoon is relatively shallow.

Here, bright sunlight can reach all the way to the sandy bottom,

where conditions are right for plants to grow.

This is not seaweed, but a marine relative of the water lily,

known as "sea grass".

It grows and flowers in vast meadows in clear water around islands

and along the shore of the mainland.

And it supports a creature

that ancient mariners once mistook for mermaids.

Gathering in herds of a hundred or more are dugongs or "sea cows".

They're relatives of elephants.

Each one can weigh nearly half a tonne

and munch through 40 kilos of sea grass a day.

Dugongs were once abundant

but they've had a difficult relationship with people.

Nowadays they're trapped accidentally in fishing nets

and shark protection barriers

and traditionally aboriginal hunters targeted them

because they taste good, like prime beef.

And recovery of a population is slow.

A single baby is born every three to seven years.

And this baby dugong

may not be old enough to breed until she's 17 years old.

A combination of all these factors means the population

in the southern part of the reef has halved in the last decade.

Now there are just 11,000 left in the entire Great Barrier Reef region,

yet there are still more dugongs in Australian waters

than any other place on Earth.

Dugongs are not the only animals to feed on sea grass.

Young green turtles like it too.

He's after the most tender shoots

and this is his exclusive patch.

He's very choosy about what he likes

and what he doesn't.

Like your lawn,

sea grass needs to be constantly cut short for healthy growth,

so he's actually farming his own little plot

that he'll tend for several months before moving on.

Sea grass meadows are also nurseries for baby fish,

like these domino damselfish.

They won't stay here forever.

When they're bigger,

they won't be able to hide amongst the slender stems,

and they'll look for a better hiding place, maybe one even closer to land.

Where the sea meets the coast, saltwater meets the freshwater

from rivers and streams.

But one doesn't suddenly become the other.

The water mixes slowly, creating a world unlike either,

but connected to both.

It's here that you'll find a special group of plants.

Fringing the coast of the mainland

is a habitat that has a profound impact on the ecosystem of the reef.

They're plants that have cracked a neat evolutionary trick.

They can live in brackish environments,

which is a combination of salt and fresh water.

They're the mangroves.

They grow where no other trees are able to.

Twice a day, the tide floods their roots with saltwater.

At the same time, water from rivers flows through the mangroves

and their lattice of roots acts like a giant tea strainer,

slowing it down so that any sediments washed off the land can settle out.

Bacteria break down the trapped sediment and other organic material

helping create tonnes and tonnes of sticky mud.

A whole new home for wildlife.

In a perfect world mud should be thick,

glutinous and as rich as dark chocolate.

And it should also stink to high heaven.

But this is extremely important stuff to the Great Barrier Reef.

One teaspoon full of this mud contains ten million bacteria.

All those bacteria are potential food.

And although there aren't many species that eat mud directly,

those that do, operate in large numbers.

Legions of creatures perform the unglamorous but crucial task

of breaking down the gloop.

Mud whelks and fiddler crabs both eat the mud

and their waste is the vital product that spawns an entire food chain.

Once it's in the water, clouds of shrimp devour it.

The nutrients that started in the mud are now swimming around

in small, easy to catch parcels.

All this food makes the mangrove a great place for fish,

small residents, as well as youngsters that will one day move out

to the Barrier Reef.

Reef species like these rabbit fish may look big

but they're still only one third of their adult size.

These snappers also have some growing up to do before they leave.

And these young trevally will grow up one day

and be major predators on the outer reef.

The mangroves, sea grass meadows and the soft coral oases

are vital nurseries for so many fish on the reef,

and they all provide two things,

food and shelter.

The complexity of the mangrove root system

makes it a perfect haven for small and juvenile fish.

The reason is, the latticework of the roots as they cross

means it's a very difficult for large predators to manoeuvre

and actually get at the smaller fish.

But predators like these young blacktip reef sharks hide here too.

They hunt at the edge of the mangroves,

but they can't get deep into the tangle of roots.

So the young reef fish are safe, for now.

So, it's a great environment for the small fish to actually grow up in,

to get big and strong,

before they make the big move to open sea and the reef beyond.

But when they leave the safety of the mangroves

they must cross that sandy desert

and the many hazards waiting for them in the lagoon.

This is a mantis shrimp.

From his neatly kept burrow, he surveys the world

with the most complex visual system known to science.

He's about the size of a man's forearm.

And he's got quite a reach.

Even if a young fish avoids the dangers on the seabed,

there are plenty more predators floating above.

Patrolling these inshore waters

is probably the most dangerous animal in the lagoon.

The box jellyfish,

whose stinging tentacles are quite capable of killing a person.

This creature is much more than a passive drifter.

It can move has as fast as an Olympic swimmer

and it has 24 eyes,

each complete with a lens that can form a detailed image.

It uses its tentacles like a trawl net,

when a fish makes contact, thousands of microscopic stinging capsules

explode into the prey's body, flooding it with paralysing venom.

The fish is killed quickly,

and then hauled into the mouth on the underside of the bell.

All of the habitats we've seen so far

have an obvious connection to the lagoon,

but there's one place that couldn't be more different

from the underwater world, that's critically important

to the vigour of the Great Barrier Reef ecosystem.

It's the tropical rainforest.

The Queensland rainforest is the oldest in the world,

it's older even than the Congo and even the Amazon.

And this is one of the most impressive trees in it.

This giant fig has strangled its original host

and now dominates this immediate environment.

It's an ecosystem in its own right.

But you might be asking yourself,

"What has this tree got in common with the reef?"

But, in fact, it's directly linked.

The rainforest all around me and indeed swamps and mangroves

are critical for the health of the reef.

These huge tracts of rainforest close to the Queensland coast

are essential because they regulate the flow of water

and the sediment it contains.

That's important, because there's an awful lot of water here.

Hot, humid tropical air gives rise to vast amounts of rainfall.

It pours for at least 120 days a year

and as much as 60 centimetres can fall in a single day.

It's one of the wettest places on Earth.

Left unchecked by the forest

the water would wash out sediments and smother marine life,

but the waterways flowing off the rainforest are relatively clear,

and many are spectacular.

When sediments are released slowly, the nutrients in them

help sustain life in the lagoon, so everything flourishes.

Where conditions are just right,

corals manage to grow right next to the coast.

Here, pristine tropical rainforest

grows right down to the waters edge,

a stone's throw from a coral reef.

It's a place where two worlds meet

and animals from the reef and the rainforest

can be found right next to each other.

These footprints belong to one of the biggest land animals in Australia.

The cassowary.

A flightless bird that's almost as tall as a person.

Its claws wouldn't look out of place on a dinosaur.

And its kick is so violent,

that the cassowary is said to be the world's most dangerous bird.

A parent is particularly dangerous when rearing a chick.

In fact, the cassowary is shy,

and is rarely seen in the wild.

But it's a key animal here.

It feeds on the fruits of rainforest trees and shrubs,

it's one of the few animals that spread their seeds.

The seeds of many forest trees can't germinate

without animals like the cassowary.

As the forest is directly linked to the reef

by regulating sediments entering the lagoon,

the cassowary contributes to the health of the reef itself.

But there are now less than 2000 living here

and they're becoming rarer all the time.

Before European settlers arrived

much of the coast here was covered in forest

and a lot of that was jungle just like this,

this is a vibrant ecosystem in its own right.

It's full of reptiles and birds, as you can hear all around me.

But today things have changed significantly.

Much of coastline that abuts the great Barrier Reef,

80% of it, in fact, has been cleared for agriculture

and much of that has been totally cleared for sugar cane.

Obviously this has a dramatic impact on the terrestrial environment,

but it also has a significant effect on the reef itself.

And it's not only crops.

Cattle ranches, fish farms, six large coastal cities

and many holiday resorts along the coast

all have an impact on the reef system.

Without the natural vegetation controlling the movement of water

and the sediment it carries,

heavy rain now washes millions of tonnes of silt,

often laced with damaging fertilisers and pesticides

straight into the lagoon.

Sediment plumes can be so extensive,

they sometimes spread all the way to the outer reef.

In the sea grass meadows,

the fine silt shrouds the light-dependant plants,

and fertilizers feed algal blooms that choke the life from them.

When the meadows die, the turtles, dugongs

and baby fish that depend on them die too.

Near the shore, the water can be so murky

that less light reaches the corals,

so most fringing reefs have also disappeared.

All of these habitats are interdependent.

If you ruin one, it can have an impact on many others.

And that includes the outer reef itself.

To look after all of these habitats, the Great Barrier Reef Marine Park

sits at the heart of a network of protected areas.

All interconnected and covering a vast area.

After all, the reef is an inspiration to people all over the world.

It attracts one and a half million visitors each year

who come to see the largest coral reef on earth.

Together with divers, yachtsmen and anglers,

they inject seven billion dollars a year into the local economy.

But the value to Australia is even greater than that.

Towns and cities along much of the Queensland coast

are not washed into the Pacific Ocean because the reef protects them.

It means the Barrier Reef is so much more than just a coral reef.

And there are vast tracts of rainforests, mangrove swamps,

sea grass meadows and soft coral oases in a deep-water lagoon.

It's truly an extraordinary place.

And, the reef's influence goes far beyond Australian waters.

It's vital to wildlife from many other parts of the world.

Wave after wave of voyagers arrive here from across the ocean.

From the islands of the South Pacific,

from the Asian mainland...

And from as far away as the icy seas of Antarctica.

These wildlife visitors create

some of the most impressive natural spectacles

on the Great Barrier Reef.

And all this is the subject of the next programme.

Subtitles by Red Bee Media Ltd

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