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02:22In just a few days, the larva changes form and becomes a polyp, similar to a sea anemone.
02:31Identical copies bud off, and gradually a colony develops.
02:38Each polyp surrounds itself with a hard skeleton and from this solid base begins to grow.
03:02It increases in length by an impressive 15 centimetres a year.
03:07This branching coral is only two years old.
03:12A mature reef can be thousands.
03:27Corals provide the foundations on which the entire reef community relies.
03:32Some organisms, like the Christmas tree worms, actually live within the coral.
03:46Others climb out, away from the reef, to filter their food from the water.
04:06As the community grows, intimate relationships are formed, and different creatures become increasingly dependent on one another.
04:19Even animals that spend much of their time traveling in the open ocean return to the reef for a clean.
04:36Coral reefs can be home to astounding numbers of fish.
04:50Coral reefs can be home to astounding numbers of fish.
04:54Here swim the smallest and the largest fish in the sea.
05:07Whale sharks are only visitors.
05:10When currents bring nutrient-rich water up from the deep, they come here to feed.
05:17Coral reefs can be home to astounding numbers of fish.
05:25All these animals are here because of the coral.
05:32This extraordinary complex maze is built layer upon layer by millions and millions of individual animals.
05:42Polyps.
05:55Each polyp's flesh is supported by a limestone skin.
06:11It's the place where most of the growth occurs.
06:15Here the living tissue deposits an intricate lattice of limestone.
06:26Beneath that, the limestone skeleton is bare, having been vacated by the living coral tissues.
06:32This is the hard structure that forms the foundation of the reef, and a single reef can extend for many
06:39miles.
06:57Coral reefs are only found in the clear, warm, shallow waters of the tropics.
07:06Coral reefs are only found in the clear, warm, shallow waters of the tropics.
07:09Even though they're animals.
07:11Because inside their flesh live millions of tiny single-celled algae.
07:17Plants.
07:21And all plants need sunlight to photosynthesize sugars.
07:3698% of the food that corals consume is produced by the algae.
07:44Without them, the reef would not exist.
07:54Like any other plant, algae need just the right amount of light.
07:59Not too much, not too little.
08:06The corals regulate that with pigments that we can only see when they are illuminated by ultraviolet light.
08:16That is the best food that we eat some, is much less than one .
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08:52Most corals, for protection, spend the day withdrawn into their stony fortresses, but
08:59even then they're not safe from the jaws of these butterflyfish.
09:21At night, the corals take in water, expand their tentacles and emerge to feed.
09:45They collect plankton.
09:49Each tentacle has batteries of stinging cells which fire on contact.
09:54Once the prey is caught, it's passed down to the polyp's mouth.
10:09It's at night, when the polyps are extended, that they add to the limestone foundations
10:14beneath them.
10:25Inevitably, the corals begin to overgrow each other, and that means trouble.
10:39When neighbours get too close, they detect one another's presence chemically.
10:44The aggressor, on the right, prepares for battle.
10:57The polyps extrude their guts and simply digest their rivals alive.
11:27A no-man's land, a band of white skeleton, is the only evidence of the night's border dispute.
11:43Some corals are targeted by yet more deadly predators.
11:57Predators that can crawl in search of their victims.
12:02Crown-of-thorns starfish, poisonous, invincible eating machines.
12:08They also extrude their gut and digest coral wholesale.
12:30But some corals have help.
12:33Small crabs living within their branches resist these onslaughts and defend their home.
12:49From beneath, they launch an attack on the vulnerable underside of the starfish.
13:13Even the crown of thorns will retreat from such a determined attack, and this coral is left unharmed.
13:30Hump-head parrotfish, nearly a metre and a half in length.
13:34Their jaws are so powerful, they can bite through rock.
13:43When they descend to feed, the reef itself is under threat.
13:59They are indiscriminate feeders, taking both rock and coral alike in their quest for algae.
14:18These fish play a large part in the erosion of the reef.
14:23The rock and coral they swallow emerges later as a fine sand.
14:27On a single reef, they can produce tons of it every year.
14:45This soft sand forms the tropical beaches that we find so alluring.
15:03Over time, the sand builds up to form an island, which is then colonised by animals and plants.
15:29The guano from thousands of terns, which have chosen to nest here, enriches the sandy soil, which then can support
15:37more plants.
15:41But these terns, like other seabirds, depend on the ocean for their food.
15:57Below water, on the reef, there is not only competition for living space, but a continual contest between predators and
16:05prey.
16:13It's the arms race between them that, over millions of years, has produced today's extraordinary diversity of fawn.
16:33Jacks are one of the key predators on the reef.
16:36Their weapon is speed.
16:52They seek silversides, and their defence is to congregate in confusing shoals of shimmering silver.
17:04The jacks try to deal with that by herding the silversides onto the reef.
17:16Here, the jacks have a better chance of separating individual fish from the shoal.
17:34The jacks can now catch the isolated individuals with lightning attacks.
17:54It's far safer to be hidden on the reef itself, within the tunnels of a sponge, for example.
18:01These tiny shrimp are no bigger than grains of rice.
18:11These shrimps are unique.
18:13It's recently been discovered that they have a highly sophisticated social system, similar to that of bees.
18:19All members of the colony are the offspring of one female.
18:24She is the queen, and the only one to produce eggs.
18:36As in a colony of bees, different individuals are specialised for particular tasks.
18:45Some are guards, and are armed with particularly large and powerful claws.
18:53They are on watch at all times, ready to tackle intruders.
19:08A polychaete worm.
19:10For it, a sponge is an excellent hunting ground.
19:31In such a maze of tunnels, attack can come at any time from any quarter.
19:55In such a maze of tunnels, attack can come at any time from any quarter.
20:05Once the guards are alerted, the worm loses its advantage.
20:16Better to retreat intact than risk serious injury.
20:26The sponge not only makes a safe home for the shrimps, it also supplies them with food,
20:32so that they never need venture outside.
20:34An establishment that provides for all their needs is clearly well worth defending.
20:43Just as shrimps guard their home, other animals defend their hunting grounds.
20:52The glassfish make tempting prey for the red-mouthed grouper.
20:57Its strategy is to swim slowly amongst them until they no longer see it as a threat.
21:16There are other fish here too.
21:19Lionfish are ambush predators, taking their time and watching for the right moment.
21:28But there isn't room here for two predators.
21:38The grouper, braving the lionfish's poisonous spines, tries to evict its rival.
22:00But lionfish are persistent.
22:03This grouper spent many hours simply defending his hunting patch.
22:12But lionfish are persistent.
22:25Some animals prefer to avoid conflict whenever possible.
22:30These harlequin shrimp, having captured a starfish, are taking it back to a safe house beyond the reach of competitors
22:38and danger.
22:39The problem with starfish is that they have minds of their own and five large sticky arms.
22:49By the time the shrimps have prized off one arm, another has reattached itself.
23:06Only by manoeuvring the starfish onto its back can they have any hope of gaining the advantage.
23:23Even so, getting it back home is a major undertaking.
23:36The starfish is now a living larder.
23:40If the shrimps can hang onto it, it will feed them for days to come.
23:47The top of the reef is usually covered by a thin layer of green algae, another living larder.
23:54And many fish depend on it.
24:03Powder blue tangs defend their right to graze on a particular patch.
24:09But for a larder as well stocked as this, there is always competition.
24:36When a shoal of convict tangs decide to graze, little can stop them.
24:53The powder blue tangs try to keep them off.
25:05But they are overwhelmed by sheer numbers.
25:14The territory is stripped of algae in minutes.
25:33The blue tangs appear to be fighting a losing battle.
25:43But eventually, they begin to get the upper hand.
26:00They persist with their attacks until the marauders are well on their way.
26:20When night falls, some very strange creatures creep out of crevices and crawl over the reef.
26:39This moving bush is an animal, a basket star, which spreads out its arms to catch the night's plankton.
27:08The reef becomes uncannily tranquil.
27:15Fish retire, hiding themselves where they can.
27:37And of course, from the birds across the sea.
27:37The reflection is naturally seen their eyes.
27:38You have to look at all the distant cycles.
27:38And then the birds, they stay.
27:38The 총 of the marauders are in the river.
27:38And when do you miss aift, the parachute has been touching them.
27:38And you have to observe.
27:38You are an animal that is built on the ground.
27:38You have to beающ çalışful.
27:38You are a little afraid of a belly in the ship.
27:39You have to be a man who has to work the last four weeks.
27:40The power of the fish is aspiration.
27:40To be a man who has to be the last night's plank on the beach.
27:42The� to be a dead one night's life.
27:51I don't know.
28:16Marbled rays come out to hunt for prey buried in the sand, using electro-receptors to scan the seabed.
28:32Their activity attracts sharks.
28:54White tips.
29:19At night, when vision is of little use, sharks have a real advantage.
29:25They can still use both smell and electro-reception to track fish.
29:39These sharks are also hunting for fish concealed within the reef.
29:51Their slender shape enables them to squeeze through surprisingly narrow gaps.
30:09There is nowhere to hide.
30:29Few animals are safe during these feeding frenzies.
30:33I don't know.
30:43I don't know.
31:25Night after night, the reef animals are subjected to these raids.
31:47But life on the reef is not just about food, it's also about sex.
31:56There are many different breeding strategies, but each is aimed at maximising the number
32:02of young that will survive.
32:08Every afternoon for two months, brown surgeonfish can be seen streaming across reefs in the
32:14Red Sea.
32:16They all head for the same place, usually some prominent feature.
32:27Here, they wait for the light to fade.
32:34Suddenly, females within the group make a dash away from the reef to release their eggs.
32:39They are immediately followed by the quickest and closest of the males, all of whom are
32:45striving to fertilise the eggs.
33:02Inevitably, others come here to feast on such easy food.
33:11As the surgeonfish spawn, fusiliers move in above to eat the nutritious eggs.
33:36These are just the first of many predators which will feed on the eggs and developing larvae as
33:42they drift in the ocean during the next few weeks.
33:48Other fish are less casual about their eggs.
33:57Banded pipefish stay close to a small chosen area on the reef.
34:03Every morning at sunrise, the female leaves her sleeping site and swims to find her partner.
34:14For ten minutes or so, they remain together, reaffirming the bond that is essential to their partnership.
34:27They swim together around his territory in a simple greeting dance.
34:37Throughout the summer, when the female's eggs are ripe, courtship begins in earnest in the early morning.
34:42It takes time, and after about two hours, they rise together off the sea bed, entwining their bodies.
34:57The male rubs himself against the female, stimulating her to release her eggs.
35:08And now, swiftly, the male takes them.
35:18The eggs, now stuck to his belly, are patted down to ensure that they stay there.
35:44The female then leaves him.
35:47But every morning, she will return for a session of synchronised swimming and so ensure that their bond is maintained.
35:58Ten days later, under the cover of darkness, the male shakes his body and the young pipefish are born.
36:14Only now are they independent of their parents.
36:19Since the male takes charge of the eggs as soon as they're laid, the female can start immediately producing the
36:25next batch.
36:27Without his help, the pair could only breed every 20 days rather than every 10.
36:32So, by sharing the work, they're doubling the number of young they can produce in any one year.
36:50A flamboyant cuttlefish.
36:56Unlike most cuttlefish, this one spends much of its time walking rather than jetting across the sea bed.
37:03This is a male.
37:04A flamboyant cuttlefish.
37:12He is using his colourful display to try and seduce the larger female, who seems unimpressed.
37:29Eventually, she concedes.
37:36The final event, the transfer of sperm, is very quick.
37:47A flamboyant cuttlefish.
38:01A singing male humpback whale.
38:16Humpbacks are only visitors to the reef.
38:18After a pregnancy that lasted a whole year, the females come here to give birth and suckle
38:25their newly born young.
38:27Their investment in their single offspring is considerable, for each female will continue
38:32to nurse it for a further six to twelve months.
38:36But the males are here to mate.
38:48The lone males sing to establish their relative seniority.
38:57The louder and longer the song, the bigger and stronger the singer.
39:31The female
39:31whoaris
39:31the
39:35The better the song, the larger the male, the more mating opportunities he will get.
39:45All these different mating strategies have the same aim, to ensure that the greatest
39:50possible number of offspring will live long enough to breed themselves.
40:02Corals also reproduce sexually, but being fixed to the sea bed, they can't move to find
40:09a mate.
40:11Somehow they must synchronize their sexual activity, and they do so using the rising water temperatures
40:17of spring and the phases of the moon.
40:32A few days after the full moon, in late spring, when tidal currents are at their weakest, the
40:39corals of the Great Barrier Reef are ready to spawn.
40:50Some corals are male and release clouds of sperm.
40:55Nearby, a female will be releasing eggs.
41:16Other species of coral are both male and female.
41:24These release packages of eggs already pre-wrapped in sperm.
41:29Then, in the Halfwayheads are waiting for each being a alien, which continues to play at the
42:21Bundles of eggs and sperm float to the surface to mix with others from further along the
42:27reef.
42:33Each kind of coral times its release to a certain hour on a certain night.
42:39That maximizes the chances of cross-fertilization.
42:50The fertilized eggs drift away from the reef.
43:06The fertilized eggs drift away from the reef.
43:07The fertilized egg drift away from the reef.
43:24The stormy season brings real danger to the animals of the reef.
43:36Lobsters in the Caribbean sense a change in the water.
43:40The temperature drops and powerful ocean swells disturb the sand.
43:48Under the cover of darkness, they emerge to run before the storm and risk crossing the
43:55exposed sand flats to seek shelter in deeper water.
44:05Every year they make this journey.
44:16From all over the reef, lobsters come to join the march.
44:20They conserve their energy by travelling in one another's slipstream.
44:32And there is the added benefit of safety in numbers.
44:50By daybreak, they've reached the edge of the deep reef, and down they go.
44:56For the rest of the stormy season, they will remain in the shelter of deep water out of harm's way.
45:20Sometimes during the stormy season, a hurricane builds, and then the very structure of the
45:27reef itself is under threat.
46:12what are the next anni here?
46:21I don't know.
46:55An entire reef can be destroyed by just one big storm.
47:03Hundreds of years of growth gone in a few hours.
47:23Out in the ocean, new life continues to develop.
47:28In time, coral larvae will return to colonize the rubble,
47:32and a new reef will grow on the wasteland.
47:36In time, coral larvae will return to colonize the rubble,
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