scuba dive vacations

in the liquid skin of planet earthlive creatures of unearthly beauty. these tiny animals have crossedoceans of space and time in an epic bidfor survival. wanderers through inner space, they carry the future oftheir species. on their odyssey they have faced extinction andawesome planetary force. theirs isan evolutionary success story, made possible by a remarkablereproductive strategy.

reefs are exotic interruptions inotherwise barren tropical seas. they're oases of life, vibrant,colorful and competitive. but this vast canvas of living art has not just materializedout of the blue. coral and its cohorts have arrivedfrom somewhere. though they seem solid and unmoving, reefs have spread themselvesthroughout the tropical oceans. how have they overcometheir immobility? the answer has its origin

in one of life's most fundamentalacts - sex. but the reproductive rites of coral communities are shroudedin mystery. it's only in the last ten years that the reef has begun toreveal its private life. for animals sex is a fact of life, but for the 'rocks' of the reef a sex life would seem out ofthe question. but corals are not rocks,they're colonies of tiny animals.

only the outer surface ofthese colonies is alive; a living skin populated by polyps. their structure is simple, a tube with a mouth surroundedby stinging tentacles. these tiny animalsa few millimeters across build reefs the beauty of the individual rivalsthat of the colony as a whole. a single pioneering polyp clones or buds itself endlessly toproduce a colony of hundreds, even thousands,of identical individuals.

in theory a polyp could liveforever this way, unchanging and unmoving. but change and mobility areessential to all species. on the reef sex achieves both inone elegantly simple solution. it's a brief extravaganza,cued by the summer moon, and for the rest of the year the priority is coping withlife's demands. inside the reff's barrier,garden eels vie for tasty morsels. they inspect drifting particles.

some are food, some just broken parts ofother reef creatures, but in the quiet lagoon everyparticle is inspected by somebody. a goatfish snuffles industriously. within a self-made sandstorm itfeasts on small worms and molluscs which it locatesusing sensitive barbels. but the real heavy mover in thesand business are sea cucumbers. the basic design isa long hollow tube that creeps around thelagoon floor.

they push sand in one end...and out the other. some sea cucumbers mop the reefwith sticky feet, passing edible particlesinto their mouths. nature constantly tests andrefines its designs the basic theme remains,only the detail varies. with its body completely buriedin sand another sea cucmber unfurls its feathery arms tonet drifting debris. every particle of sand in thelagoon was once part of the animals and plants that make up the reef.

sand production is aided byheavy-jawed grazers like the bumphead parrotfish. moving in herds like buffaloover the reef they bite off pieces of coral, crush it to powder and leave clouds of new sandin their wake. the reef supports an endlessvariety of grazers, scrapers, and biters. many seem to bite at dead reef

but are actually cropping back afuzz of algae that grows by day. the wastes of these schools offishes act as fertiliser tothe plants they crop. the waters surrounding the reefare poor in nutrients, so recycling of itslimited resources is essential. it begins with the invisible hazeof life called plankton, it continually showers the reef. just as plankton gather nutrientsfrom the ocean, fish like the spiny chromisgather plankton so nutrients

from the ocean are imported intothe reef's economy. poised like ghostly daggers,barracuda cruise the coral fringe; they are after more thanplanktonic prey. these larger predators are drawnto the rich life of the reef. compared to the impoverished oceansthe reef is a prosperous economy. built up from nothingby the labours of tiny animals and plants it attracts investmentfrom thousands of other species. it becomes a bank, or storehouse,of the ocean's resources. but some creatures area storehouse in themselves.

a sleek manta ray wings its waythrough the late afternoon. it owes its huge bulk, and wingspan of five meters tothe millions of minute plankton it sieves from tropical waters. mantas are free agents,opportunists. they exploit the reef as andwhen it focuses their food supply. they feed and then move on, leaving each reef a little poorerfor their passing. the blubber jelly voyagesat the whim of wind and tide,

feeding on plankton as it drifts. billowing in the currents itsan occasional visitor to the reef. like all jellyfishit's a free-living relative of the unmoving coralson the reef below. building on the skeletons of others, hard corals extract calciumfrom sea water. tiny polyps toil in limestone to craft their biologicalworks of art. from the hard coral foundationhas arisen a rambling architecture.

this ever expanding labyrinthhas another dimension: it creates living spacefor related corals. bold against blue, lace-like gorgonians strainagainst the current. on the reef slope,soft corals sweep the same current. their flexible arms house polypsbut, unlike hard corals, these are no reef builders. lacking a solid skeleton, they draw support from

tiny limestone spineswithin their tissues. when the soft coral dies itdisappears, leaving no lasting monument. reef plants appear to be just as ephemeral but their role isfundamental, all capture energy from sunlight some also contribute tothe reef structure, the brittle green halimeda ismainly limestone. it constantly sheds gritty lakesinto the lagoon.

the stony skin ofpink coralline algae glues the limestone blocks ofthe reef together. filamentous algae seems littlemore than a green fur on rocks. but it's the pasture of the reef, and essential toall the reef grazers. but the ties that bind algaeand the reef together go deeper. like algae, hard corals alsorequire sunlight to grow. this is a clue toan intimate relationship that literally fuels the reef.

corals are twin-engined. they're animals that haveharnessed the power of plants to build the vast and elaborate limestone structureswe call the reef. how have they done it? somewhere in theirevolutionary past coral struck a deal with microscopic single-celled algaecalled zooxanthellae. the algae is sheltered insidethe polyp tissue,

producing sugars from sunlightand recycling coral waste products. this partnership became a mostpowerful 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, planktonbegins its nightly ascent into the waterssurrounding the reef. from their stony lairs emerge...the polyps. wreathed with stinging tentacles,

each polyp is poised toreap a grisly harvest. other members ofthe night shift emerge to feed. feather stars take up strategicpositions in the current. they sieve plankton andparticles with their arms. slender prey, a formation of razorfishexpertly mimic the harp coral that hides their knifelike bodies. a chaotic ball of eel-tailed catfishswarms in mid-water between feeding. lagoon sands below them areloaded with hidden delicacies.

these miniature catfish scout fortheir supper in rank and file, aided by sensitive chin whiskers. lagoon sediments providedainty pickings for the feather-mouthed sea cucumber little more than an elastic tubefilled with water, it delicately wipes each featheredfinger across its mouth, collecting food along with sand. more robust sea cucumbers haverubbery bodies that make them unpalatableto predators.

they continue their slow workof shunting sediment day and night and have no need to hide... unlike the sophisticatesof the night shift. a hunter by night, an octopus is able to changeboth colour and texture. hiding and bluffing... this stealthy camouflage expertis both actor and magician. its relative the cuttlefish shares the octopus's talent forlightning colour change.

shunning camouflage altogether, the flamboyant spanish dancerflounces through the night. its colourful costume isa signal to predators. like other nudibranchs,or sea slugs, the spanish dancer looksmuch better than it tastes. overcome by darkness, parrotfish retire intothe fabric of the reef. some of these daytime dandies sleep in a gossamer cocoon oftheir own weaving.

perhaps this mucous bubbledisguises their scent to unwelcome visitors. a fast-moving vegetarian, the parrotfish grazes algaewith its bird-like beak. clownfish may be left outin the dark when their protective anemoneshuts up for the night. this is the reef'sbest known example of shared lives the reef is a multi-layered organisation and its inhabitants have perfected

the art of living on andin each other. liaisons are everywherebut some may be hard to find. an ornamented anemone harbourscolour-coordinated shrimp competition for the reef'slimited resources is tough. when citizens live togetherthere are winners and losers. the blood-sucking fish louse has a one-way relationshipwith its suffering host. even corals are not exemptfrom exploitation by others. down among the valleysof the polyps lies another world.

a world that's never been seen. among the heaving tissuesof the polyp, live flatwormsthe size of a pinhead. living on the thin veneerof the coral's mucous these tiny lodgers appear to dono harm, gliding like magic carpets ina world of altered reality. on the reef every opportunityhas been investigated. space is at a premium,and overcrowding a fact of life. invariably property disputesdevelop and borders are drawn.

where two different species meet,encounters can be nasty. nightly 'space wars,' foughtby special stinging tentacles, leave a conspicuous whitesaw of conflict. surrounded, this fatal siegemay last months. a plate coral spreads outwardto meet itself. here the problem is resolved bya fence of self-recognition. over time this living evolves. territorial struggles shape the reef as a multitude of speciesvie for position.

shading its competitors from light, the fast-growing plate corals borrow a strategy fromthe forest canopy. other inhabitants can neitheroutgrow nor out-sting their competitors. for sponges chemical warfareis the way. their tissues areloaded with toxins, a kind of natural anti-foulingthat preserves their space. just as space invaders are partof life, so too are space makers.

sometimes an opening comesby chance. storms and ocean swellsdamage the reef, tearing long-lived coralsfrom their foundations. but not all space iscreated by the elements. the crown of thorns starfish,a coral predator, opens up new territorywith each meal. and new settlers arein ready supply. out of the blue curtainof distance the currents propel a seafull 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 isa long way from its final form, even the giant clam beginslife microscopically. all reef larvae are designed tovoyage in the plankton. to become citizens of a reef they will need to take ontheir adult form,

but first they must finda safe place to settle. journeying day and nightthey may stumble upon a reef, a sentinel in the dark sea. but their sanctuary isin fact a snare. night has unmasked the reef. poised and armed, it has becomea waiting wall of mouths. the graceful gorgonian isnow a web of death, its animal nature revealed. thousands of tiny polyps waitoutstretched.

a feather star swaysin the gathering storm. a million mouths wait in silence for the microscopic voyagers to blunder their wayinto outstretched arms. the weaponry of the reefis revealed, a sinister array of traps, sieves, harpoons and clutching tentacles the methods may vary but the final sentence willalways be the same.

and night after night thisrandom microscopic rain falls. millions of epic voyages end intiny, but titanic, struggles. despite huge losses some larvae survive their perilousvoyage and settle. they grow to become solid citizensof the reef, joining the wall of mouths andwaging space wars with each other. this endless lottery ofsettlement and survival weaves a visual tapestry of species,colour, pattern and form. but beauty and harmony is a maskit hides chaos and competition.

reef society is shaped in a warzone of relentless conflict. the reef thrives in adversity, prospering despiteits internal struggles. but reefs have alsoendured struggles of planetary dimension overenormous geological time. through the millenniacontinents drift, climates change,sea levels rise and fall. as the world moves around them coral reefs remain,as always, immobile.

they seem at the mercyof geology yet today's have somehow survived 214million years of global upheaval. coral reefs rim continental shelves and cap volcanic sea mountsthroughout tropical oceans. but once, reefs lived inan ancient sea called the tethys. it lay between two supercontinentswhich split apart, causing africa and india todrift northwards. the broad tethys sea, evolutionaryhome of modern reef animals, was squeezed out of existence.

over millions of years it became a war zone ofcontinental collision, earthquakes and sea level change and the animals evolving herecame under siege. amidst these shunting continentsreef life had two choices: extinction or escape. today's reefs are built byimmobile creatures that somehow dispersed and evolved from their ancestralcommunities in the tethys.

but to escape the ravagesof geology they had to playan evolutionary ace. this ace not only allowed themto move, but to change. it was sex. and every summer the age-oldritual unfolds. shoals of tiny fry appear, with their parents,the spiny chromis. their behaviour is unusualamong reef fish; they guard their growing offspring.

a female cuttlefish holds anegg daintily in her tentacles. she chooses a nest with great care and places the fertile eggsecurely within. but despite her plump maternalism this is the extent ofher parenting. from the time the egg isplaced in its coral cradle the young cuttlefish will beon its own. this careful handling of individualeggs requires more time and effort than most other reefdwellers invest.

the giant clam makes no attemptto nurture its young. however it does invest enormousenergy producing and broadcasting many millionsof eggs and sperm. with each mighty contraction thewaters of the lagoon turn milky. fish dart closer, feastingon the seasonal delicacy. other, perhaps more prudentspecies will wait for dusk before they begin to spawn. the male coral trout emergein sober courting colours. with his tail flagged black hepatrols his territory.

females are lying low on the reef, their swollen bellies heavywith eggs. concealed in the watery twilightthey await the male's advances. his elaborate dance is designed totempt a female from her retreat. reluctantly she leavesthe reef's protection, encouraged by the ardent male. the climax of their courtingritual is a spawning rush... a split second when eggs and sperm are released nearthe surface...

...leaving the future to chance,once again, as summer waters warm otherbiological 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 takenmonths to prepare. their time has come. others respond to an unseen urge.

crown of thorns starfish begintheir slow creep to high points on the reef. even inert creatures are stirring. sea cucumbers scurry...at their own pace... away from the lagoon floorto the coral ledges above. here they begin a sinuous dance, swaying to anancient evolutionary rhythm... even the fragile feather mouthrises to the occasion. this is an eventtoo compelling to miss.

from within the bulging polypcomes an answering movement... ...building to a slow spiral aseach puts the finishing touches to its precious bundle ofeggs and sperm. this living jewel is the coral'spassport to mobility. while polyps turn in time, the hypnotic dance of the sea cucumbers has reachedits silent climax. males begin exuding spermfrom tiny pores on their heads. they rear and sway to scattertheir sperm throughout the lagoon,

perhaps to meet the eggsreleased by females. the crown of thorns smouldersdramatically, releasing a misty cloud of sperm. it drapes itself across coralthat would normally be its food. now begins one ofthe most monumental and secret events in nature, mass spawningon the great barrier reef. in unison, polyps pucker and propel their fragilespheres into space.

locked in limestone they cannotmove to mate. instead they reach out to eachother with tiny voyaging probes. their cue is exact; each year each species will spawnat the same time on the same day. we are privileged to be spectators as the reef stagesthis unearthly performance. each night, for a week followingthe full moon, the intensity builds... new species adding to thegrowing curtain of new life.

along 1200 kilometres ofthe northeast coast of australia, countless millions ofpolyps spawn in unison. some corals are hermaphrodites while others have separate coloniesof females and males... whatever their sex, each hasits own pace and style. the synchronised spawning createsa web of drifting food for those with an appetite for it. a hermit crab picks off eggsas they emerge. but predators take only a fractionof 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 powerfulancient forces. the reef acts likea single organism... intent on securing its future. living rocks erupt ina frenzy of colour and movement but the climaxis yet to come.

six nights after the full moon,silent and unheralded, there is a kaleidoscopic finale. the giant plate corals, each with hundreds ofthousands of polyps, explode into ascending galaxiesof pink and white. the sea is now a soup of colouredeggs against the black depths, but the performance is not yet over. incredibly, there isone final encore. the lagoon becomes lacedwith streamers,

the reproductive segments ofpolychaete worms, seeming to bid bon voyage tothe millions of new lives who set sail tonight, as the frenzy of release subsidies, the tide plays its part in thecompletion of the night's magic. the moon stills the restless sea as egg and sperm bundlesrise to the surface. somehow, in this vast andchaotic scramble, the right egg and right sperm willmeet, fertilise, and develop.

each morning the sea bears witnessto the night's toil as the future hopes of the reefcommunity drift away. here is the solution tothe reef's immobility. from this floating slick the tiny developing larvaebegin their odyssey. opportunists take advantageof the annual bounty, but against the overwhelming abundance they makelittle impression. however, in the vast ocean

this ribbon of new life willremain vulnerable. as plankton blooms moundthe spawning raft, more opportunists gather. larvae may end their journey on the stinging tentaclesof a jellyfish... ...or engulfed by the ballooningjaws of marauding manta rays. up here, invisible, could be thebeginning of a new coral. out of the countless millions dispersed only a few willsurvive their journey.

far fewer will evadethe wall of mouths and find a safe place to settle. but despite incredible odds the survival of just one corallarva is enough. they cross the trackless oceans, minute in size,monumental in importance. time will seetheir strategy prevail. even the perilous flanks of anactive volcano may be journey's end. having crossed ofcean wastes asan invisible mist in the plankton,

coral larvae settle to found a reef. its volcanic support willsubside but, once established, a reef outpost will buildand maintain itself, gathering the rare larval voyagersover time. each new atoll isa stepping stone to the next. in this way corals have marched through time andgreat ocean distance. they have established collections of living art in the galleriesof empty oceans.

reefs are portrayed as 'fragile ecosystems' witha 'delicate beauty', and yet they're robust enough to have survived millions of years of fierce competition andplanetary upheaval. they're exquisite, but they're also dynamic andadaptive communities. they've adopted mass spawning and dispersal as their incrediblesolution to the problems of tme,

change and immobility. the architects of the mighty atolls and the great barrier reef aresimple animals and plants. the limestone fortresses they build are monuments to the evolutionarysuccess of sex on the reef.