Great Barrier Reef

It remained a mystery for a thousand generations...

capturing the imagination

of those who lived at its edge

but could not visit there.

Who could see only dimly into a shadowy world

both beautiful and bizarre.

Today, we can enter that world

and cast light on it.

Scientific explorers now seek to uncover

the secrets of this world.

Some of what we've learned seems remarkably similar

to the beliefs of Australia's aboriginal people.

They have endured for 50,000 years

by regarding themselves not above nature, but part of it.

Science often takes a different approach...

analyzing the living world by dissecting it

species by species.

But the aboriginals believe that no living thing

exists apart from the greater community of living things

that even the human is merely a part

of the great system of life.

Science is only now discovering

how much the aboriginals have long understood.

"It was unchanged through all of the time of my ancestors.

"From the dreamtime when animals were almost human

"and people were gods,

unchanging.

"The sea, the reef and all that lives here.

"But now, people are no longer gods

and change encircles us like the sharks."

The encroaching modern world is symbolized by vast settlements

such as Sydney, Australia's largest city.

But along the same coast lies an ancient underwater city

called by aboriginals Wogogaboo.

It is the largest structure on earth

built by living things.

The Great Barrier Reef.

More than 2,000 identifiable reefs combine

to form a rampart of coral 1,200 miles long

extending as much as 120 miles out to sea.

Erected over millions of years

it is a feature of earth's surface so immense

as to be visible from the moon.

In the great liquid space of the ocean

the reef's limestone ramparts and towers loom up

like a vast housing complex, providing its residents

with shelter from the surging sea

and from one another.

Like human cities, the reef is also a place

where the hungry can find a meal.

The concentration and interaction of life here

makes possible a steady exchange of life-giving nutrients

gathered from the surrounding sea.

Ironically, the massive reef system owes its existence

to tiny creatures called coral polyps.

Though these diminutive construction workers

are plant-like in appearance, they are animals

related to jellyfish and sea anemones.

They feed by capturing passing food in their tentacles

and protect themselves by secreting

a casing of calcium carbonate.

The calcium remains of the polyps

are compressed over time into limestone

forming the foundations

upon which new coral generations build.

An oasis in the desert of the open sea

the reef city attracts offshore travelers

like the gentle manta ray.

Such visitors enter a world of curious life-forms

where things are not always what they seem

a world where fish can inflate themselves like balloons

and an eight-legged creature, long portrayed as a monster

turns out to be remarkably intelligent and shy.

What appear to be ferns are instead, animals

sweeping the water for bits of food.

Here, some mollusks are jet-propelled...

and worms perform like Spanish dancers.

A creature shaped like a fierce snake

is actually a fish so wary it hides in a hole all day.

What appear to be feathers are poisonous spines.

A pink carnation is actually a worm.

The corals themselves exist

in an enormous array of shapes and configurations.

Many of these structures enable them to capture plankton

in barren tropical waters.

But to in ensure a steady food supply

some corals also grow their own food...

a microscopic algae

cultivated within the tissue of the cords themselves.

To provide their algae gardens with sunlight

corals take on unusual shapes.

The more surface area exposed to the sun

the better internal algae gardens grow.

As the coral generations accumulate

they rise toward the surface

creating a wall between land and sea

the barrier which gives this reef its name.

This upward growth is not without risk.

Occasional drops in sea level expose and kill the corals

turning reefs to islands.

One such tiny slip of land, Heron Island

at the southernmost end of the Great Barrier Reef

is home to a research station

operated by the University of Queensland.

Scientists from around the world gather here

to study the reef ecosystem.

In the station's labs, marine biologists seek to learn

how life transpires

in the world's greatest underwater city.

Perhaps the most important scientific research takes place

not in the labs, but on the reef itself.

Researches by the score visit the Great Barrier Reef annually.

Australians Valerie and Ron Taylor have devoted their lives

to underwater exploration and photography.

In three decades of diving here

they have helped reveal

the enormous complexity of reef life.

Although we dive the reef in the name of science

to study, photograph and count

the sheer beauty of the place draws us here

as much as the desire to better understand it.

The corals form a habitat

as lovely and magical as a fairy-tale setting.

For life here, though

the coral serves as a vital framework for survival

providing catch holds for attaching organisms

hiding places for prey and hunting grounds for predators.

A single square meter of coral can sustain dozens of species.

The coral polyps are the landlords

extracting as rent the organic debris of their tenants.

The tiny blenny keeps a wary watch

from the reef equivalent of an apartment.

Moray eels seek out crevices to occupy like day rooms.

Like many residents

the barramundi cod lays claim to a plot

and spends much of its time defending it from intruders.

Some creatures, like these bat fish

use the reef as a place to hover and rest part of each day.

Many of the fish that swim lightly through the day

commute beyond the reef at night to hunt

changing places with others that commute back

to rest all night on the reef.

The constant search for food permeates existence here.

Hunger can even lead small fish

to risk approaching a much larger stranger

in the hope of finding something to eat.

Offer food, and the fish flock like birds in a city park.

Not every creature here is a resident.

The jellyfish is a passer-by

occasionally swept over the reef as it rides the currents.

Most animals, like the shovel-nosed skate

seem timid in the presence of divers.

But the Taylors have learned to be on the lookout

for a notorious creature less likely to flee.

The abundance that draws divers to the reef

also attracts sharks.

Some sharks are permanent residents

who survive by being masters of deception.

The wobbegong, or carpet shark

has developed near-perfect camouflage

making it difficult to tell coral from carnivore.

It escapes the notice of enemies while lying in ambush for prey.

Because of their long experience diving the reef

the Taylors have often led scientific expeditions

to study the deepwater sharks lured

to this rich hunting ground.

Though frenzies are believed uncommon

sharks grow aggressive when food is on their midst

whether provided by nature

or by humans seeking to observe their behavior.

These bronze whalers provide a rare glimpse

of the streamlined power of animals fashioned by evolution

into beautiful and near-perfect hunters in the sea.

Patrolling the edges of the reef

sharks serve a vital function.

They eliminate the weak

and, over time, strengthen the breeds

of the very species they prey upon.

The history of the reef is a chronicle of constant change.

More than 25 million years ago

corals began to fringe Australia's eastern coast.

Across eons, ice ages lowered the sea levels

exposing and killing reef coral until the climate began to shift

and global warming melted the ice

allowing fresh veneers of coral to return.

Though most of the reef's story

remains hidden beneath the surface

we can more readily trace the history

of the scattered islands looming up from it.

When the seeds and spoors of life

reach these fertile outposts on the wind or currents

lush miniature worlds are born.

The islands provide both sustenance and habitat

for some of the largest bird colonies in the tropics.

The life of the islands is inextricably linked

to the encircling sea.

Nutrients are cycled from fish to bird to guano

fertilizing luxuriant vegetation.