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  • 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.

In the liquid skin of planet Earth live creatures of unearthly beauty.

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奧地利的大堡礁 - 國家地理 (有字幕) (Austraila's Great Barrier Reef - National Geographic (With Subtitles))

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    不信中原不姓朱 發佈於 2021 年 01 月 14 日
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