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00:04Off the east coast of Australia, up to 200 kilometers offshore, a line of surf rises out of the open
00:12ocean.
00:19Beneath the surface, creating these breaking waves, is the most magical marine environment on Earth.
00:26I'm Monty Halls, I'm a marine biologist and diver, and I've always been fascinated by the sea.
00:34For me, there's always been one place that is the epitome of everything that's wonderful about the marine environment.
00:42It's a true global icon, and is a mecca for anyone who's ever heard the word coral.
00:49The Great Barrier Reef!
01:00Stretching for over 2,000 kilometers up the tropical coast of Australia, it is quite simply the largest living structure
01:09on the planet.
01:20It's made up of almost 3,000 different reefs, each one with a different personality.
01:31And it's so much more than just coral.
01:53But the Great Barrier Reef is most famous for its underwater world.
01:59Here, there is more life than almost anywhere else on Earth.
02:06Many of the creatures are exquisitely beautiful, but some seem straight out of science fiction.
02:21While others can kill in an instant.
02:29And just when you think you know the reef, it changes.
02:34Every second, every hour, every day, and every year.
02:39It's a world of continual surprises.
02:50This is the amazing story of an ever-changing natural miracle.
02:56The Great Barrier Reef.
03:06The Great Barrier Reef is so large that it can be seen from space.
03:11Quite an achievement considering the size of the creatures that built it.
03:22The vast system that is the Great Barrier Reef is created by animals that are tiny.
03:29Although they might look like plants, actually they're animals called polyps.
03:36Each polyp is like a tiny upside-down jellyfish sitting in a stony cup.
03:49They live together in colonies, like underwater tower blocks.
03:59They respond to touch, temperature, currents and the cycles of the sun and moon.
04:06And their tiny movements combine to give each colony a rhythm of its own.
04:45Now are just a small
04:45Polyps can't build the reef alone.
04:47For this, they need partners that are even smaller.
04:54Within each polyp's tentacles
04:56are millions of tiny brown dots.
05:02Each is a microscopic plant,
05:04which transforms sunlight into food and energy
05:07for the corals.
05:12It's a miraculous partnership
05:14that allows the corals to turn minerals in the water
05:17into limestone, building their stony skeletons.
05:23In this way, each colony grows.
05:33If we were able to watch a reef over several years,
05:36we'd see a continually growing marine metropolis.
05:40It's intricate architecture provides homes
05:43for thousands of creatures.
05:54Even though coral reefs cover
05:56less than 1% of the world's oceans,
05:59they contain a quarter of all known marine life,
06:03and the Great Barrier Reef is the biggest of them all.
06:09I still vividly remember my first dive on a coral reef
06:14over 20 years ago.
06:22And the moment I put my head in the water,
06:25I knew what I wanted to do for the rest of my life.
06:37Even if I spent my entire life underwater,
06:41I still couldn't hope to see all the species
06:44that live on this reef.
06:45I'm going to be able to see all the species
06:47400 species of hard coral,
06:49300 of soft coral,
06:521,600 species of fish,
06:56134 species of shark and ray,
07:0030 species of whirl and dolphin,
07:036 species of turtle,
07:0514 species of sea snake,
07:093,000 species of mollusk,
07:121,300 species of crustacean.
07:16The sheer number of creatures that live here
07:19makes the reef as hectic as any human city,
07:22with a rhythm of almost perpetual rush hours.
08:05Imagine all this activity,
08:07this constant ebb and flow of life,
08:10continuing for over two, three years,
08:1230,000 kilometers.
08:24It's hard to believe that such a huge,
08:26solid structure hasn't always been here.
08:31But compared with the rest of Australia,
08:33this reef is very young.
08:3720,000 years ago,
08:39this exact spot where I'm standing,
08:41and indeed the entire length of the Great Barrier Reef
08:44would have been high and dry.
08:47Back then, in the middle of the last ice age,
08:50sea level was 120 meters lower than it is today.
08:55And the coastline was about 30 kilometers
08:57in that direction.
09:00But suppose I could go back
09:02those 20,000 years in an instant.
09:05What would it have looked like?
09:07Well, for a start,
09:09it wasn't even under water.
09:11This area would have been covered
09:12in hundreds and hundreds of miles
09:14of eucalyptus and paperbark forest,
09:16and there wouldn't have been a fish in sight.
09:28It was a land abounding with the animals
09:30of the Australian plains.
09:41Aboriginal people would have lived here too,
09:44hunting the wildlife in areas that are now deep under water.
09:54And the sea levels rose all around the world,
10:02flooding this low-lying coast.
10:06This happened only 10,000 years ago.
10:10In fact, stories of the Great Flood are still passed down
10:15in Aboriginal culture.
10:22As the sea rose, corals began to grow
10:25on the rocky fringes of the continental shelf,
10:28creating the Great Barrier Reef we see today.
10:34These shallow tropical waters are clear and warm,
10:39perfect conditions for corals to thrive.
10:41The sea is the best place to arrive.
10:58Sheltered behind this long strip of reef,
11:01a lagoon was born,
11:02an area of protected water larger in size
11:05than the whole of Great Britain.
11:09and a new coastline too, with shallow, sandy waters.
11:22The rising sea also cut off areas of high ground,
11:26creating the 600 islands that dot the lagoon.
11:34Some are little more than rocks.
11:40Others, substantial mountains covered in woodland.
11:46The first British person to see that was Captain Cook,
11:50who stood here in 1770 and for the first time realised the scale of the Great Barrier Reef.
11:56He also realised the scale of the problem that faced him.
12:00For Cook and his men, without the benefit of modern charts and sonar,
12:04it represented nothing more than a deadly labyrinth.
12:14But it's exactly this complexity and the sheer size of the reef that has created so many opportunities for life.
12:26They're a fish of almost every imaginable kind.
12:30Coral eaters, plant eaters, plankton eaters, the hunters and the hunted.
12:44Bluefin trevally.
12:49Powerful predators that hunt in packs.
12:54One minute, apparently minding their own business.
12:58The next, charging their prey with a sudden rush.
13:06Working together, they create confusion.
13:25The trevally departs as quickly as they arrived.
13:29And the colourful reef fish regroup again to feed.
13:42Beyond them, silver bait fish never let down their guard.
13:46They shimmer like a thousand tiny mirrors,
13:49swirling as one amorphous mass to confuse any attackers.
13:59It's their only defence against this, a shark mackerel.
14:07These are the greyhounds of the ocean.
14:10They need all their speed and agility against this ghostly school
14:14that is here one moment and gone the next.
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14:42sea
14:54Despite the dangers, small fish have to risk leaving the protection of the reef to feed.
15:03And perhaps none is bolder than this little wrasse.
15:13This gigantic grouper is many thousands of times her size, and an aggressive territorial
15:19predator, with one of the largest mouths on the reef.
15:29But she's not deterred from approaching.
15:39What she's about to do seems almost suicidal.
16:13She's feeding on tiny, blood-sucking parasites, which is why the grouper allows this.
16:26Nevertheless, the wrasse has to regularly vibrate her fins against the inside of his mouth,
16:32just to remind him not to swallow.
16:43A single wrasse can eat an incredible 1,200 parasites a day.
16:49And she's not fussy where she finds them.
17:04Without this decontamination, the grouper would quickly become infested.
17:11This service is so valuable that the grouper is a regular client, visiting several times
17:17a day.
17:20But even he has his limits.
17:28On the reef, there seems to be an almost infinite variety of ways of feeding.
17:33Some fish even cultivate their own food, so they're very protective of it.
17:44But there's one fish species that's so good at defending its particular patch of reef that
17:51it's responsible for more attacks on divers than any other.
18:10Much of the algae growing on the sandy seabed is edible, so the damsel farms it in green patches,
18:17encouraging some species, nipping down others and gently transforming the landscape around her.
18:32After all this hard work, she doesn't look kindly on trespassers.
18:41Anything that swims too close is chased away.
19:04But is she brave enough to try to see me off?
19:09I'm just going to edge on to its patch a little bit more.
19:13There could be trouble, I sense.
19:21She can't scare me, but she just doesn't give up.
19:25Just listen to this.
19:33This is one feisty little fish.
19:36Even though I'm so much bigger than this damselfish, it's still quite an intimidating sight.
19:49While damsels maintain areas of reef by nurturing, other fish destroy it.
19:56Bump head parrotfish, each the size of a small sheep.
20:03They have a tough beak and gigantic jaw muscles that work like bolt cutters.
20:20It might seem like a lot of hardware for a diet of soft algae and coral polyps.
20:26But the only way to get at them is by shearing off chunks of the coral rock.
20:39A second set of internal teeth then grinds the coral into a fine paste.
20:53A single bump head can chew up to five tons of coral every year, which they excrete back onto the
21:00reef as sand.
21:05As fast as the reef grows, parrotfish break it down again, creating a continually changing environment.
21:14The constant remodeling of the reef by ravenous parrotfish is nothing compared to the effect of the ocean.
21:36This is the reef crest and it's the point where the waves generated by the open ocean impact the hard
21:46surface of the coral reef.
21:51It's an unstoppable force hitting an immovable object.
21:58I'm keenly aware that these are very small waves.
22:02Believe me, in a big storm, to be here would be suicide.
22:08It's a vivid illustration of the power of the sea.
22:20Tropical storms and cyclones regularly whip in from the Pacific Ocean.
22:31The surf smashes into the reef, pulverizing the coral below.
22:38Waves and currents move the rubble and sand around and shape it into beautiful small islands.
22:47Known as coral caves.
23:09Some come and go in a matter of days, others build and grow and can last for years as plants
23:17take root and protect them from the elements.
23:38At first glance, it might seem that a sand cave is a pretty inhospitable environment, but actually it can support
23:44life in abundance.
23:50Today, it's rare to find a cave free from humans and mainland predators, but this is one of the best,
23:58Rain Island.
24:14It's home to thousands of birds and in the centre of the island, they jostle for the best available space.
24:25Nowhere else on the reef are they found in such numbers and such variety.
24:31Frigate birds, red-footed boobies and Caspian terns.
24:37In fact, 84 different species are found here.
24:42It's also the largest green turtle breeding ground in the world.
24:49Having mated offshore, thousands of females haul themselves up the beach to lay their eggs.
24:55The record is 26,000 turtles in a single night.
24:59They turn a remote desert island into a crowded frenzy of nocturnal activity.
25:32Wind and waves have created an island that, for the moment at least,
25:36has just the right conditions to support this incredible spectacle.
25:41But the island still changes, every year, every season.
25:46And the reef itself never stays the same for long.
25:51Twice a day, life along the length of the Great Barrier Reef has to cope with complete upheaval,
25:58as the rhythm of the moon causes tides to flood and drain the reef.
26:29That appears slowly in full of warm nature's
26:30This is sunny questions for the walrus.
26:31First of all, there's a wall in a while.
26:32Many pilates were used for the fusion,
26:32waiting for the mainland at the beginning of the East.
26:40During the lowest tides, the water runs off and whole sections of living coral that would
26:47normally be underwater are exposed.
27:09The level of water on the reef top decreases dramatically getting ever shallower and going
27:16from a stable environment to an ever-changing hostile one. It's almost as though some mighty
27:23force has lifted the reef right out of the water. These are extreme conditions.
27:35As the exposed corals start to heat up, the tiny polyps retract inside their stony skeletons for
27:43protection. Then they secrete mucus. It acts as a sunscreen and there's no skimping on quantity.
27:52An area no larger than the size of a coffee table can produce five litres of the stuff.
28:07As the tide retreats to the edge of the reef, it cuts off pools of water.
28:16For most animals, like these sea cucumbers and starfish, the best way to survive is by taking
28:22refuge in these rock pools.
28:36With the tropical sun beating down, the exposed flat is one of the most hostile environments on the reef.
28:43For a fish caught out here, it should mean certain death.
28:52But not for this one.
28:55It's an epaulette shark.
28:59It can't breathe out of water, but it survives here by shutting down some parts of its brain
29:05and increasing the blood supply to others.
29:12Not only that, it can walk on land.
29:19These abilities make it a specialised wreath-top hunter.
29:33Maneuvering around the confined space of a rock pool, it's master of all it surveys.
29:42Nothing is safe, not even animals hiding under the sand.
29:50It scans for smells and for tiny electric signals given off by the bodies of hidden creatures.
30:05It's detected a crab.
30:10It doesn't need shark teeth because it simply sucks up its prey.
30:24The epaulette isn't the only shark able to adapt to a change of the tides.
30:39When the sea returns, it brings cool oxygenated water back to the reef.
30:56The relief, though, is short-lived.
31:08Larger sharks gather at the reef's edge, waiting to get at the freshly accessible hunting grounds.
31:22As the water rises, more and more creatures take the opportunity to feed in a new area.
31:42For the sharks, fish that can normally outrun them are temporarily caught in the shallows,
31:48trapped between sand and surface, with few places to hide.
32:03Lemon sharks hug the shore, surrounded by schooling bait fish.
32:08For the moment, they seem to have little interest in all this food around them.
32:18They're simply waiting for help.
32:27Young trevally.
32:28They dart for the fish, causing them to panic and break ranks.
32:37By putting themselves in the midst of the shoal, the sharks are in a perfect position to exploit their chaos.
32:43Good.
32:44Come out.�
33:30For a hungry lemon shark, no water seems too shallow.
33:38The sharks are able to use these special tactics to feed inshore
33:43because of the rhythm of the tides, which change conditions every few hours.
33:55The cycle of day and night also has a dramatic effect on everything that lives on the reef.
34:32There are many enduring mysteries about the Great Barrier Reef, particularly at night.
34:37But this is one of the more enchanting ones, so watch this.
34:50This coral is fluorescing under ultraviolet light.
34:55It's this amazing light show and it covers pretty much the whole of the reef crest.
35:03Look at this, look at this.
35:06Vivid, vivid colours. Doesn't look real.
35:09Looks like some bizarre sort of galactic broccoli is what it looks like.
35:20One theory is that these magical colours are in some way caused by the coral's natural sunscreen.
35:26But despite lots of very clever people looking into it, no one really knows why this happens.
35:34And the same goes for much of the night time activity here.
36:08Even an infamous
36:09which is worth the actual poorest of the ë²½ Fears,
36:09which is responsible for publishing in the world.
36:09The body of오ain Harris
36:29A coral reef during the day is a very different place to a coral reef at night.
36:35The atmosphere changes completely. The day shift has logged off. The night shift has gone
36:42to work. It's mean and moody and the animals here mean business.
36:53Just as in human cities, there's a new cast of characters after dark.
37:02Octopus emerge from their holes to stalk their prey. A tiny soul improves his chances of survival
37:15by mimicking a toxic flatworm. Some of the strangest nocturnal creatures are relatives
37:23of the starfish, like this feather-mouthed sea cucumber sifting food from the sand.
37:33Another is the basket star. It comes alive at night, throwing out thousands of arms to filter
37:39food from the plankton-rich current.
37:49These animals can live for a very long time, up to 35 years. And there's records of these
37:55guys being seen night after night in the same place for over 15 years.
38:04The day shift is still here, of course. It's just hidden. But it's difficult to find somewhere
38:12big enough to hide if you're the size of a turtle.
38:19This green turtle has found himself a little ledge and is tucking in for the evening.
38:30Hello, big fella. He's a bit drowsy and probably quite grumpy. And we all get like that occasionally,
38:46don't we? So I'll leave him alone. Lovely sight. Sleep well, big fella.
38:55At night, many fish sleep, resting in safe nooks and crannies on the reef. Without eyelids,
39:02they enter a trance-like state, barely moving other than to keep water flowing through their
39:07gills. But they do give off a scent, and that means they can be found.
39:25This cone snail catches its prey in one of the most surprising ways imaginable. And specialises
39:34in killing fish. It sniffs them out whilst they're sleeping.
39:51This goat fish may be asleep, but it's aware of its surroundings. First, the snail must sneak
40:00close enough to bring its secret weapons into play. The snail appears to release chemicals
40:07that paralyze its victim. The goat fish seems powerless to escape, as it's swallowed alive.
40:35Moments later, a venomous barb inside the snail puts the fish out of its misery.
40:48In a place where even seashells are deadly, remaining undetected is essential if you want to survive
40:54the night. And simply hiding is not enough. Just a hint of your scent wafting into the current
41:03can attract trouble. But the parrotfish has come up with a very elegant solution. In the form
41:15of a sleeping bag made out of membrane. It stops the smell spreading along the reef
41:21and being picked up. It's a very good way, if you're a parrotfish, of ensuring you get a good night's
41:29sleep.
41:30No one has ever filmed a parrotfish making its cocoon before. It starts by exuding a layer of mucus
41:38around its body. It then draws water into its mouth and pushes it out of its gills, blowing up the
41:51mucus
41:51its bubble around it. Within half an hour, the fish is completely enveloped in a slimy cocoon,
42:14which traps its smell. But not all the reef hunters are fooled.
42:31White-tipped reef sharks do use smell to find their prey. But if that doesn't work, they have another sense.
42:39They can detect an animal's bio-electrical energy, the tiny electrical signals given off by even the smallest
42:46of its twitching muscles.
43:02This resting parrotfish risks discovery every time it moves a fin or wafts its gills.
43:12As the sharks pass, it holds its breath.
43:28But sharks don't give up that easily.
43:39White-tips are the perfect size and shape for hunting in these cramped spaces.
44:09Their snape-like bodies can wriggle into crevices.
44:19And they can fold their dorsal fin flat to squeeze through small holes.
44:27If discovered, a sleeping parrotfish wouldn't stand a chance.
44:51Once the first shark has caught its prey, the smell and commotion attracts others.
45:15Every now and then, you find yourself in moderately strange situations in life. And this is one of them.
45:24I'm in a cave with feeding sharks. They're very well designed to be in here. And I'm not sure I
45:33am quite frankly.
45:37I'm not sure I am.
45:38Uh-huh.
46:24Because of their sophisticated senses and remarkable physique, white-tips are great reef hunters.
46:30At night, they turn it into an art form, better than all other sharks.
46:43We expect sharks to be hunters, but after dark, the reef itself becomes one giant predator.
46:52By day, corals may be passive and plant-like, but by night they become active hunters.
47:10They snatch tiny animals from the current, immobilising them with stinging tentacles, just like their
47:17relatives, the jellyfish.
47:31And they're highly competitive.
47:33Here, two individual pollux are fighting for possession of a single, unfortunate creature.
47:59At night, the corals don't just hunt.
48:01When territory's at stake, whole colonies go to war with one another.
48:11Once a coral senses another is too close, it launches a barrage of stinging cells, and the enemy returns fire.
48:44It's a war of numbers.
48:46The coral with the greatest firepower will win.
49:00Eventually, the coral on the right forces its opponent to retreat.
49:12Yet another small part of the reef has been changed.
49:16Every night this goes on from one end of the Great Barrier Reef to the other.
49:23Day and night, the reef is always changing, but that's nothing compared to the impact of the seasons.
49:36In summer, warmer water means more food, making it the best time to bring new life into the world.
49:48A pair of noddy terns fly close together, over an island on the reef.
49:54These are two mates reaffirming their bond.
50:07Noddies signal to each other continually during courtship, both in the air and after landing.
50:24Once in the trees, the performance changes.
50:27They bow their heads repeatedly.
50:30It's pretty clear how they got their name.
50:56Once they've started courting, they don't like any interruption.
51:17To reinforce their relationship, the male has to collect nesting materials.
51:22And the females are famously fussy.
51:25So he chooses his present carefully.
51:42A bent twig, it seems, is just the thing.
51:45A few more of them and they'll have a nest, if you can call it that, ready for their single
51:51chick.
51:54Noddies are devoted partners, and often remain together season after season.
52:05Beneath the waves, the summer warmth triggers fish to court.
52:10In bi-colour parrotfish, the larger male leads a tender underwater ballet to woo a partner.
52:32The urge to breed spreads across the reef.
52:39These are surgeon fish.
52:42Single females dart to the surface, pursued by groups of competing males.
53:02As each female releases her eggs, the males race to fertilize them with a puff of white sperm.
53:18The rise in water temperature also sets the conditions for the most remarkable event on the reef.
53:30On only a few summer nights each year, and triggered by a particular phase of the moon, the corals spawn.
53:54This is the world's largest synchronised breeding event.
53:58On any one of these nights, trillions of eggs and sperm are released, flooding the entire 2,000 kilometre length
54:07of the reef.
54:23By spawning at this precise moment, the corals have caught a lull in the tide, allowing sperm and eggs of
54:31the same species to meet and fertilise.
54:38They form baby corals.
54:40As the tidal currents pick up, they're spread far and wide.
54:53The young corals join billions of other baby creatures floating in the plankton.
55:15A baby grouper, only a centimetre in length, that will one day grow into a giant over two metres long.
55:28Most reef animals have tiny babies like these, carried at the mercy of the currents.
55:37Many have some ability to direct themselves, and even the young corals can swim to a degree, propelling themselves with
55:45microscopic hairs.
55:54Each one of these could grow into a whole colony, and start a new coral reef.
56:04This living soup represents the future of the reef.
56:08Just one glassful has so much potential.
56:13It's remarkable to think that such a structure as the Great Barrier Reef, large enough to be seen from space,
56:21and yet complex enough to support the interwoven lives of thousands of different species,
56:25is wholly dependent on minute, fragile forms such as these.
56:35The reef is a dynamic place in constant flux, influenced by the forces of geology.
56:43Weather, wind and waves, the rhythms of the sun and moon.
56:53Yet its future depends on fragile young life forms, that must survive in the face of these powerful natural forces,
57:02and find somewhere safe to settle and grow.
57:06There can be few tails in the natural world quite so remarkable.
57:21And this is just the start of what makes the barrier reef so great.
57:28Only 7% of the ecosystem is coral.
57:31The rest is covered with rainforest and rivers, lagoon, swamp and shore.
57:42These are home to some of the world's strangest creatures.
58:08In the next program, we explore the fascinating worlds and wildlife beyond the reef,
58:14and discover their connections to this most magical place.
58:30YOLO's Jewels of Wales is here on BBC HD tomorrow evening with a long cool glass of Welsh water.
58:37That's at 7.
58:38Thanks Ben.
58:54Thanks Ben.
58:56Rebekah Teplan.
58:56There we go again.
58:58You
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