Australia's Great Barrier Reef
In the liquid skin of planet Earth live creatures of unearthly beauty.
These tiny animals have crossed oceans of space
and time in an epic bid for survival.
Wanderers through inner space,
they carry the future of their species.
On their odyssey
they have faced extinction and awesome planetary force.
Theirs is an evolutionary success story,
made possible by a remarkable reproductive strategy.
Reefs are exotic interruptions in otherwise barren tropical seas.
They're oases of life, vibrant, colorful and competitive.
But this vast canvas of living art
has not just materialized out of the blue.
Coral and its cohorts have arrived from somewhere.
Though they seem solid and unmoving,
reefs have spread themselves throughout the tropical oceans.
How have they overcome their immobility?
The answer has its origin
in one of life's most fundamental acts - sex.
But the reproductive rites of
coral communities are shrouded in mystery.
It's only in the last ten years
that the reef has begun to reveal its private life.
For animals sex is a fact of life,
but for the 'rocks' of the reef
a sex life would seem out of the question.
But corals are not rocks, they're colonies of tiny animals.
Only the outer surface of these colonies is alive;
a living skin populated by polyps.
Their structure is simple,
a tube with a mouth surrounded by stinging tentacles.
These tiny animals a few millimeters across build reefs
The beauty of the individual rivals that of the colony as a whole.
A single pioneering polyp clones
or buds itself endlessly to produce a colony of hundreds,
even thousands, of identical individuals.
In theory a polyp could live forever this way,
unchanging and unmoving.
But change and mobility are essential to all species.
On the reef sex achieves both in one elegantly simple solution.
It's a brief extravaganza, cued by the summer moon,
and for the rest of the year
the priority is coping with life's demands.
Inside the reff's barrier, garden eels vie for tasty morsels.
They inspect drifting particles.
Some are food,
some just broken parts of other reef creatures,
but in the quiet lagoon every particle is inspected by somebody.
A goatfish snuffles industriously.
Within a self-made sandstorm it feasts on small worms
and molluscs which it locates using sensitive barbels.
But the real heavy mover in the sand business are sea cucumbers.
The basic design is a long hollow tube
that creeps around the lagoon floor.
They push sand in one end... and out the other.
Some sea cucumbers mop the reef with sticky feet,
passing edible particles into their mouths.
Nature constantly tests and refines its designs
the basic theme remains, only the detail varies.
With its body completely buried in sand another sea cucmber unfurls
its feathery arms to net drifting debris.
Every particle of sand in the lagoon was once part of the animals
and plants that make up the reef.
Sand production is aided by heavy-jawed grazers
like the bumphead parrotfish.
Moving in herds like buffalo over the reef
they bite off pieces of coral,
crush it to powder and
leave clouds of new sand in their wake.
The reef supports an endless variety of grazers,
scrapers, and biters.
Many seem to bite at dead reef
but are actually cropping back a fuzz of algae that grows by day.
The wastes of these schools of fishes act
as fertiliser to the plants they crop.
The waters surrounding the reef are poor in nutrients,
so recycling of its limited resources is essential.
It begins with the invisible haze of life called plankton,
It continually showers the reef.
Just as plankton gather nutrients from the ocean,
fish like the spiny chromis gather plankton so nutrients
from the ocean are imported into the reef's economy.
Poised like ghostly daggers, barracuda cruise the coral fringe;
they are after more than planktonic prey.
These larger predators are drawn to the rich life of the reef.
Compared to the impoverished oceans the reef is a prosperous economy.
Built up from nothing by the labours of tiny animals
and plants it attracts investment from thousands of other species.
It becomes a bank, or storehouse, of the ocean's resources.
But some creatures are a storehouse in themselves.
A sleek manta ray wings its way through the late afternoon.
It owes its huge bulk,
and wingspan of five meters to the millions of minute plankton
it sieves from tropical waters.
Mantas are free agents, opportunists.
They exploit the reef as and when it focuses their food supply.
They feed and then move on,
leaving each reef a little poorer for their passing.
The blubber jelly voyages at the whim of wind and tide,
feeding on plankton as it drifts.
Billowing in the currents its an occasional visitor to the reef.
Like all jellyfish it's a free-living relative
of the unmoving corals on the reef below.
Building on the skeletons of others,
hard corals extract calcium from sea water.
Tiny polyps toil in limestone
to craft their biological works of art.
From the hard coral foundation has arisen a rambling architecture.
This ever expanding labyrinth has another dimension:
It creates living space for related corals.
Bold against blue,
lace-like Gorgonians strain against the current.
On the reef slope, soft corals sweep the same current.
Their flexible arms house polyps but, unlike hard corals,
these are no reef builders.
Lacking a solid skeleton,
they draw support from
tiny limestone spines within their tissues.
When the soft coral dies it disappears,
leaving no lasting monument.
Reef plants appear to be just as
ephemeral but their role is fundamental,
All capture energy from sunlight
some also contribute to the reef structure,
The brittle green Halimeda is mainly limestone.
It constantly sheds gritty lakes into the lagoon.
The stony skin of pink coralline algae glues
the limestone blocks of the reef together.
Filamentous algae seems little more than a green fur on rocks.
But it's the pasture of the reef,
and essential to all the reef grazers.
But the ties that bind algae and the reef together go deeper.
Like algae, hard corals also require sunlight to grow.
This is a clue to an intimate relationship
that literally fuels the reef.
Corals are twin-engined.
They're animals that have harnessed the power of plants
to build the vast and
elaborate limestone structures we call the reef.
How have they done it?
Somewhere in their evolutionary past coral struck
a deal with microscopic
single-celled algae called zooxanthellae.
The algae is sheltered inside the polyp tissue,
producing sugars from sunlight and recycling coral waste products.
This partnership became a most powerful evolutionary achievement.
Between them they built reefs.
It's not until the sun sets
that coral's second, animal, engine is revealed.
As darkness falls, plankton begins its nightly ascent
into the waters surrounding the reef.
From their stony lairs emerge... the polyps.
Wreathed with stinging tentacles,
each polyp is poised to reap a grisly harvest.
Other members of the night shift emerge to feed.
Feather stars take up strategic positions in the current.
They sieve plankton and particles with their arms.
Slender prey,
a formation of razorfish expertly mimic the harp coral
that hides their knifelike bodies.
A chaotic ball of eel-tailed catfish swarms in mid-water between feeding.
Lagoon sands below them are loaded with hidden delicacies.
These miniature catfish scout for their supper in rank and file,
aided by sensitive chin whiskers.
Lagoon sediments provide dainty pickings
for the feather-mouthed sea cucumber
Little more than an elastic tube filled with water,
it delicately wipes each feathered finger across its mouth,
collecting food along with sand.
More robust sea cucumbers have rubbery bodies
that make them unpalatable to predators.
They continue their slow work of shunting sediment day and night
and have no need to hide...
unlike the sophisticates of the night shift.
A hunter by night,
an octopus is able to change both colour and texture.
Hiding and bluffing...
this stealthy camouflage expert is both actor and magician.
Its relative the cuttlefish shares
the octopus's talent for lightning colour change.
Shunning camouflage altogether,
the flamboyant spanish dancer flounces through the night.
Its colourful costume is a signal to predators.
Like other nudibranchs, or sea slugs,
the Spanish dancer looks much better than it tastes.
Overcome by darkness,
parrotfish retire into the fabric of the reef.
Some of these daytime dandies
sleep in a gossamer cocoon of their own weaving.
Perhaps this mucous bubble disguises their scent
to unwelcome visitors.
A fast-moving vegetarian,
the parrotfish grazes algae with its bird-like beak.
Clownfish may be left out in the dark
when their protective anemone shuts up for the night.
This is the reef's best known example of shared lives
The reef is a multi-layered organisation
and its inhabitants have perfected
the art of living on and in each other.
Liaisons are everywhere but some may be hard to find.
An ornamented anemone harbours colour-coordinated shrimp
Competition for the reef's limited resources is tough.
When citizens live together there are winners and losers.
The blood-sucking fish louse
has a one-way relationship with its suffering host.
Even corals are not exempt from exploitation by others.
Down among the valleys of the polyps lies another world.
A world that's never been seen.
Among the heaving tissues of the polyp,
live flatworms the size of a pinhead.
Living on the thin veneer of the coral's mucous
these tiny lodgers appear to do no harm,
gliding like magic carpets in a world of altered reality.
On the reef every opportunity has been investigated.
Space is at a premium, and overcrowding a fact of life.
Invariably property disputes develop and borders are drawn.
Where two different species meet, encounters can be nasty.
Nightly 'space wars,' fought by special stinging tentacles,
leave a conspicuous white saw of conflict.
Surrounded, this fatal siege may last months.
A plate coral spreads outward to meet itself.
Here the problem is resolved by a fence of self-recognition.
Over time this living evolves.
Territorial struggles shape the reef
as a multitude of species vie for position.
Shading its competitors from light,
the fast-growing plate corals
borrow a strategy from the forest canopy.
Other inhabitants can neither outgrow
nor out-sting their competitors.
For sponges chemical warfare is the way.
Their tissues are loaded with toxins,
a kind of natural anti-fouling that preserves their space.
Just as space invaders are part of life, so too are space makers.
Sometimes an opening comes by chance.
Storms and ocean swells damage the reef,
tearing long-lived corals from their foundations.
But not all space is created by the elements.
The crown of thorns starfish, a coral predator,
opens up new territory with each meal.
And new settlers are in ready supply.
Out of the blue curtain of distance
the currents propel a sea full of eager immigrants,
a multitude of microscopic larvae.
This humble bean, covered with beating hairs,
is the beginning of a new coral.
Equally disguised,
a larval sea urchin is a long way from its final form,
Even the giant clam begins life microscopically.
All reef larvae are designed to voyage in the plankton.
To become citizens of a reef
they will need to take on their adult form,
but first they must find a safe place to settle.
Journeying day and night they may stumble upon a reef,
a sentinel in the dark sea.
But their sanctuary is in fact a snare.
Night has unmasked the reef.
Poised and armed, it has become a waiting wall of mouths.
The graceful Gorgonian is now a web of death,
its animal nature revealed.
Thousands of tiny polyps wait outstretched.
A feather star sways in the gathering storm.
A million mouths wait in silence
for the microscopic voyagers
to blunder their way into outstretched arms.
The weaponry of the reef is revealed,
a sinister array of traps, sieves,
harpoons and clutching tentacles
The methods may vary
but the final sentence will always be the same.
And night after night this random microscopic rain falls.
Millions of epic voyages end in tiny, but titanic, struggles.
Despite huge losses some larvae
survive their perilous voyage and settle.
They grow to become solid citizens of the reef,
joining the wall of mouths and waging space wars with each other.
This endless lottery of settlement and survival
weaves a visual tapestry of species, colour, pattern and form.
But beauty and harmony is a mask it hides chaos and competition.
Reef society is shaped in a war zone of relentless conflict.
The reef thrives in adversity,
prospering despite its internal struggles.
But reefs have also endured struggles
of planetary dimension over enormous geological time.
Through the millennia continents drift,
climates change, sea levels rise and fall.
As the world moves around them
coral reefs remain, as always, immobile.
They seem at the mercy of geology yet
today's have somehow survived 214 million years of global upheaval.
Coral reefs rim continental shelves
and cap volcanic sea mounts throughout tropical oceans.
But once, reefs lived in an ancient sea called the Tethys.
It lay between two supercontinents which split apart,
causing Africa and India to drift northwards.
The broad Tethys Sea, evolutionary home of modern reef animals,
was squeezed out of existence.
Over millions of years
it became a war zone of continental collision,
earthquakes and sea level change
and the animals evolving here came under siege.
Amidst these shunting continents reef life had two choices:
Extinction or escape.
Today's reefs are built by immobile creatures
that somehow dispersed and
evolved from their ancestral communities in the Tethys.
But to escape the ravages of geology
they had to play an evolutionary Ace.
This ace not only allowed them to move, but to change.
It was sex.
And every summer the age-old ritual unfolds.
Shoals of tiny fry appear,
with their parents, the spiny chromis.
Their behaviour is unusual among reef fish;
they guard their growing offspring.
A female cuttlefish holds an egg daintily in her tentacles.
She chooses a nest with great care
and places the fertile egg securely within.
But despite her plump maternalism
this is the extent of her parenting.
From the time the egg is placed in its coral cradle
the young cuttlefish will be on its own.
This careful handling of individual eggs requires more time
and effort than most other reef dwellers invest.
The giant clam makes no attempt to nurture its young.
However it does invest enormous energy producing
and broadcasting many millions of eggs and sperm.
With each mighty contraction the waters of the lagoon turn milky.
Fish dart closer, feasting on the seasonal delicacy.
Other, perhaps more prudent species will wait for dusk
before they begin to spawn.
The male coral trout emerge in sober courting colours.
With his tail flagged black he patrols his territory.
Females are lying low on the reef,
their swollen bellies heavy with eggs.
Concealed in the watery twilight they await the male's advances.
His elaborate dance is designed to tempt a female from her retreat.
Reluctantly she leaves the reef's protection,
encouraged by the ardent male.
The climax of their courting ritual is a spawning rush...
A split second when eggs and
sperm are released near the surface...
...leaving the future to chance, once again,
As summer waters warm other biological clocks are ticking.
The reef below begins to stir.
Cued by the full moon in November,
countless coral polyps bulge.
They are ripe with packets of egg
and sperm that have taken months to prepare.
Their time has come.
Others respond to an unseen urge.
Crown of Thorns starfish begin their slow creep
to high points on the reef.
Even inert creatures are stirring.
Sea cucumbers scurry... at their own pace...
away from the lagoon floor to the coral ledges above.
Here they begin a sinuous dance,
swaying to an ancient evolutionary rhythm...
Even the fragile feather mouth rises to the occasion.
This is an event too compelling to miss.
From within the bulging polyp comes an answering movement...
...building to a slow spiral as each puts the finishing touches
to its precious bundle of eggs and sperm.
This living jewel is the coral's passport to mobility.
While polyps turn in time,
the hypnotic dance of
the sea cucumbers has reached its silent climax.
Males begin exuding sperm from tiny pores on their heads.
They rear and sway to scatter their sperm throughout the lagoon,
perhaps to meet the eggs released by females.
The Crown of Thorns smoulders dramatically,
releasing a misty cloud of sperm.
It drapes itself across coral that would normally be its food.
Now begins one of the most monumental
and secret events in nature,
mass spawning on the Great Barrier Reef.
In unison, polyps pucker
and propel their fragile spheres into space.
Locked in limestone they cannot move to mate.
Instead they reach out to each other with tiny voyaging probes.
Their cue is exact;
each year each species will spawn at the same time on the same day.
We are privileged to be spectators
as the reef stages this unearthly performance.
Each night, for a week following the full moon,
the intensity builds...
new species adding to the growing curtain of new life.
Along 1200 kilometres of the northeast coast of Australia,
countless millions of polyps spawn in unison.
Some corals are hermaphrodites
while others have separate colonies of females and males...
Whatever their sex, each has its own pace and style.
The synchronised spawning creates a web of drifting food
for those with an appetite for it.
A hermit crab picks off eggs as they emerge.
But predators take only a fraction of the coral's output.
Most pass unhindered into the sea.
And still the outpouring continues.
For these few nights of the year,
space wars seem insignificant.
Adversaries are united by powerful ancient forces.
The reef acts like a single organism...
intent on securing its future.
Living rocks erupt in a frenzy of colour
and movement but the climax is yet to come.
Six nights after the full moon, silent and unheralded,
there is a kaleidoscopic finale.
The giant plate corals,
each with hundreds of thousands of polyps,
explode into ascending galaxies of pink and white.
The sea is now a soup of coloured eggs against the black depths,
but the performance is not yet over.
Incredibly, there is one final encore.
The lagoon becomes laced with streamers,
the reproductive segments of polychaete worms,
seeming to bid bon voyage to the millions of new lives
who set sail tonight,
As the frenzy of release subsidies,
the tide plays its part in the completion of the night's magic.
The moon stills the restless sea
as egg and sperm bundles rise to the surface.
Somehow, in this vast and chaotic scramble,
the right egg and right sperm will meet, fertilise, and develop.
Each morning the sea bears witness to the night's toil
as the future hopes of the reef community drift away.
Here is the solution to the reef's immobility.
From this floating slick
the tiny developing larvae begin their odyssey.
Opportunists take advantage of the annual bounty,
but against the overwhelming
abundance they make little impression.
However, in the vast ocean
this ribbon of new life will remain vulnerable.
As plankton blooms mound the spawning raft,
more opportunists gather.
Larvae may end their journey
on the stinging tentacles of a jellyfish...
...or engulfed by the ballooning jaws of marauding manta rays.
Up here, invisible, could be the beginning of a new coral.
Out of the countless millions
dispersed only a few will survive their journey.
Far fewer will evade the wall of mouths
and find a safe place to settle.
But despite incredible odds
the survival of just one coral larva is enough.
They cross the trackless oceans,
minute in size, monumental in importance.
Time will see their strategy prevail.
Even the perilous flanks of an active volcano may be journey's end.
Having crossed ofcean wastes as an invisible mist in the plankton,
coral larvae settle to found a reef.
Its volcanic support will subside but, once established,
a reef outpost will build and maintain itself,
gathering the rare larval voyagers over time.
Each new atoll is a stepping stone to the next.
In this way corals have marched
through time and great ocean distance.
They have established collections
of living art in the galleries of empty oceans.
Reefs are portrayed as
'fragile ecosystems' with a 'delicate beauty',
and yet they're robust enough to
have survived millions of years
of fierce competition and planetary upheaval.
They're exquisite,
but they're also dynamic and adaptive communities.
They've adopted mass spawning
and dispersal as their incredible solution to the problems of tme,
change and immobility.
The architects of the mighty atolls
and the Great Barrier Reef are simple animals and plants.
The limestone fortresses they build
are monuments to the evolutionary success of Sex on the Reef.