0:00:04 > 0:00:09I'm here, surrounded by one of nature's greatest wonders.
0:00:09 > 0:00:14A living structure so enormous, it can be seen from space.
0:00:18 > 0:00:19The Great Barrier Reef.
0:00:25 > 0:00:29Home to one of the most extraordinary communities of animals on the planet.
0:00:34 > 0:00:37'I've been fascinated by it for almost 60 years.'
0:00:45 > 0:00:49Here, unknown species are still being found.
0:00:52 > 0:00:54And scientists are making astonishing discoveries
0:00:54 > 0:00:57about the creatures that we thought we knew.
0:01:00 > 0:01:03'In this series, our research vessel, the Alucia,
0:01:03 > 0:01:06'will allow us to explore the reef as never before.'
0:01:10 > 0:01:14Using the latest technology, I'll visit its mysterious depths.
0:01:16 > 0:01:21Nobody has ever dived as deep as this before on the Great Barrier Reef.
0:01:23 > 0:01:25I'll learn of its surprising origins.
0:01:28 > 0:01:32And discover how this wonderfully diverse community
0:01:32 > 0:01:35has been created by some of the very smallest creatures on the reef.
0:01:38 > 0:01:43But visited by some of the most impressive animals on the planet.
0:01:53 > 0:01:55It's an ecosystem like no other.
0:01:57 > 0:01:59Vital to our oceans.
0:02:04 > 0:02:08And surprisingly, we are still uncovering its many secrets.
0:02:34 > 0:02:37The Great Barrier Reef lies on Australia's north-east coast.
0:02:41 > 0:02:43It's 1,400 miles long...
0:02:47 > 0:02:50..and at its widest, 150 miles across.
0:02:53 > 0:02:57It consists of almost 3,000 individual coral reefs...
0:03:00 > 0:03:02..and 900 islands.
0:03:05 > 0:03:07And for me, it's truly
0:03:07 > 0:03:10one of the most extraordinary places on the planet.
0:03:12 > 0:03:14People say to me,
0:03:14 > 0:03:17"What was the most magical thing you ever saw in your life?
0:03:17 > 0:03:22"What was the most magical moment in your career as a naturalist?"
0:03:22 > 0:03:27And I always say, the first time I put on a mask
0:03:27 > 0:03:29and went below the surface
0:03:29 > 0:03:33and moved in three dimensions just with a flick of my fin
0:03:33 > 0:03:38and suddenly saw all these amazingly multicoloured things
0:03:38 > 0:03:41living in communities right there.
0:03:42 > 0:03:44Just astounding things.
0:03:44 > 0:03:46Unforgettable beauty.
0:03:54 > 0:03:57I first came to the Barrier Reef nearly 60 years ago.
0:03:57 > 0:04:01And I remember very clearly how amazed I was
0:04:01 > 0:04:04to see such a complexity of life.
0:04:04 > 0:04:08But today, we have ways of looking at the reef,
0:04:08 > 0:04:11technical ways, which we never had before
0:04:11 > 0:04:14and give us a completely new vision of this wonderful place,
0:04:14 > 0:04:18which is surely one of the greatest treasures of the natural world.
0:04:25 > 0:04:27'Now I've returned.
0:04:27 > 0:04:30'And taking me on this journey is the Alucia,
0:04:30 > 0:04:34'a 56-metre state-of-the-art research and exploration vessel.
0:04:39 > 0:04:43'For this expedition, we've been granted unprecedented access
0:04:43 > 0:04:46'to some of the most remote corners of the Great Barrier Reef.'
0:04:54 > 0:04:57Onboard is a team of experts.
0:04:57 > 0:05:00And at our disposal, all the latest technology.
0:05:03 > 0:05:06Our mission is to reveal a hidden world
0:05:06 > 0:05:08and to complete a series of dives
0:05:08 > 0:05:12that have never before been attempted on the Great Barrier Reef.
0:05:15 > 0:05:20But to do that, we have had to bring in a very special piece of equipment.
0:05:22 > 0:05:25This is a Triton submarine.
0:05:29 > 0:05:32The very latest in submersible technology.
0:05:34 > 0:05:37And the first of its kind to be brought to these waters.
0:05:40 > 0:05:44The submersible's captain, Buck Taylor, will lead the dive team.
0:05:44 > 0:05:49With 2,000 dives under his belt, his expertise is unparalleled.
0:05:55 > 0:05:57While our film crew rigs the submersible
0:05:57 > 0:05:59with no fewer than eight cameras,
0:05:59 > 0:06:01Buck gathers the rest of the team together
0:06:01 > 0:06:04to brief us on the dives ahead.
0:06:04 > 0:06:07- COMPUTER:- "Welcome to the MV Alucia submersible team..."
0:06:07 > 0:06:10'The submersible offers spectacular filming opportunities,
0:06:10 > 0:06:13'but it's not without its dangers.'
0:06:13 > 0:06:15Coming from the rescue background,
0:06:15 > 0:06:18I've been in a submersible up to my waist in water,
0:06:18 > 0:06:21I've had a fire in a submersible.
0:06:21 > 0:06:24- COMPUTER:- "No smoking, smoking materials..."
0:06:25 > 0:06:29'As well as these hazards, Buck is also obliged to raise
0:06:29 > 0:06:32'one of the more intimate limitations of submersible life.'
0:06:32 > 0:06:35We do have facilities of a toilet onboard.
0:06:35 > 0:06:38Obviously, because it's quite confined, it's not very discrete,
0:06:38 > 0:06:42so we do have some towels out that we can hold up around you.
0:06:42 > 0:06:46It's quite interesting trying to explain about going to the toilet
0:06:46 > 0:06:49in a three-man submersible in a sort of sphere
0:06:49 > 0:06:52that's less than two metres diameter. It's quite intimate.
0:06:52 > 0:06:55He was six foot three... LAUGHTER
0:06:55 > 0:06:57We've got cameras pointing from every direction.
0:06:57 > 0:06:59- Good.- Thank you.
0:06:59 > 0:07:02Thanks very much. I'm looking forward to it a lot.
0:07:08 > 0:07:10The Alucia's first mission
0:07:10 > 0:07:13is to take us to the Barrier's stunning ribbon reefs
0:07:13 > 0:07:15in the north of its extensive range.
0:07:19 > 0:07:22It's an area of outstanding natural beauty
0:07:22 > 0:07:25and the perfect place to begin our explorations.
0:07:29 > 0:07:32The story of the Great Barrier Reef
0:07:32 > 0:07:36starts with its most important inhabitant, the coral itself.
0:07:40 > 0:07:42Hidden inside these branching structures
0:07:42 > 0:07:46are the thousands of tiny creatures that build these reefs.
0:07:51 > 0:07:54And they have an enormous claim to fame.
0:07:55 > 0:07:58Together, they've built the largest living structure on earth.
0:08:04 > 0:08:08But these fascinating coral creatures are only active at night.
0:08:08 > 0:08:10So to capture their behaviour,
0:08:10 > 0:08:13we'll need to do something I've never done before.
0:08:16 > 0:08:21Tonight, a team of specialist divers, scientists
0:08:21 > 0:08:23and programme-makers, like myself,
0:08:23 > 0:08:27have gathered together to have a closer look and a longer look
0:08:27 > 0:08:31at the reef at night than perhaps has ever been possible.
0:08:34 > 0:08:36When I came here 60 years ago,
0:08:36 > 0:08:40the idea of a night dive was almost inconceivable.
0:08:41 > 0:08:46It seemed to me, a beginner, to be far too dangerous.
0:08:46 > 0:08:49But now, technology is going to help me.
0:08:54 > 0:08:57'Once I'm in, it's over to Buck and the support team,
0:08:57 > 0:08:59'who remain onboard the Alucia,
0:08:59 > 0:09:02'to make sure everything goes smoothly.'
0:09:02 > 0:09:04INDISTINCT RADIO
0:09:06 > 0:09:10'They've spent months preparing for this moment.'
0:09:10 > 0:09:12SIREN WAILS
0:09:12 > 0:09:16'Our submersible, known to the crew as the Nadir,
0:09:16 > 0:09:19'has, of course, made dives like this all over the world.
0:09:19 > 0:09:24'She's descended to the deepest part of the oceans,
0:09:24 > 0:09:27'but she's never visited the Barrier Reef.
0:09:27 > 0:09:28'It's a first for all of us.
0:09:34 > 0:09:38'But before we can go anywhere, we'll need to position the Nadir
0:09:38 > 0:09:41'at a safe distance from the Alucia.
0:09:45 > 0:09:47'It's a substantial operation,
0:09:47 > 0:09:49'but finally, we're ready to get underway.'
0:09:51 > 0:09:55S.O. Nadir, just approaching the buoy. Am I clear to vent?
0:09:57 > 0:10:00- RADIO:- "Roger, Nadir. You are clear to vent, clear to vent.
0:10:00 > 0:10:02"Have a good dive, guys."
0:10:10 > 0:10:13'Sinking beneath the waves is a very surreal experience.
0:10:16 > 0:10:19'Your first instinct is to hold your breath.
0:10:28 > 0:10:32'At night, the reef is a ghostly world.
0:10:38 > 0:10:41'Tiny shrimp-like creatures dance in the lights.'
0:10:50 > 0:10:52Look at that! Wow!
0:10:53 > 0:10:57'With little light, there is a lot less colour,
0:10:57 > 0:11:00'but this is still a very magical place.'
0:11:05 > 0:11:07Ah! There's something! My first fish!
0:11:08 > 0:11:13'Our submersible will eventually take us to depths of 300 metres.
0:11:13 > 0:11:16'Now, we're only 30 metres down,
0:11:16 > 0:11:18'but that's exciting enough for a start.'
0:11:25 > 0:11:28In these dark waters, Buck needs to be careful
0:11:28 > 0:11:31as we move around the front of the reef.
0:11:37 > 0:11:41Coral reefs are sometimes described as marine cities.
0:11:41 > 0:11:43And the comparison is indeed a good one.
0:11:46 > 0:11:49We're here to take a closer look at the reef's architecture.
0:11:49 > 0:11:51Its coral buildings.
0:11:56 > 0:12:00There are more than 450 different species of hard coral.
0:12:02 > 0:12:06The plant-like structures we can see are actually made of limestone.
0:12:06 > 0:12:09And living inside are thousands of highly industrious little animals
0:12:09 > 0:12:11called coral polyps.
0:12:17 > 0:12:19At night, the water around the reef
0:12:19 > 0:12:23becomes filled with clouds of tiny microorganisms
0:12:23 > 0:12:25called the zooplankton.
0:12:28 > 0:12:30And that's what the corals eat.
0:12:35 > 0:12:39The coral polyps themselves emerge from their stony skeleton
0:12:39 > 0:12:43and start groping in the water with their tentacles.
0:12:46 > 0:12:50To see just what they're doing, we need specialised cameras.
0:12:53 > 0:12:57The coral polyps never leave the safety of their limestone homes,
0:12:57 > 0:12:59even at night.
0:13:03 > 0:13:06If something edible comes within reach,
0:13:06 > 0:13:10the polyps fire the microscopic harpoons that line their tentacles.
0:13:15 > 0:13:19The prey is stunned or killed and then pulled into the polyp's mouth.
0:13:21 > 0:13:24When you can't leave your home, it pays to be accurate.
0:13:26 > 0:13:30The coral's stinging armoury isn't used only for collecting food.
0:13:30 > 0:13:32They also use it to fight.
0:13:32 > 0:13:36Because, as has been discovered only comparatively recently,
0:13:36 > 0:13:39corals, like many animals that live on land,
0:13:39 > 0:13:41are extremely territorial.
0:13:41 > 0:13:44But in order to see the battles,
0:13:44 > 0:13:46you have to speed up time.
0:13:52 > 0:13:56The polyps of each colony collaborate to defend their patch.
0:13:59 > 0:14:02As in any big city, space is precious.
0:14:04 > 0:14:06If a rival grows too close, there will be trouble.
0:14:10 > 0:14:12These fights can last for hours.
0:14:17 > 0:14:19The competition is fierce
0:14:19 > 0:14:21as the coral colonies jostle with one another
0:14:21 > 0:14:23for the best feeding sites.
0:14:30 > 0:14:34When they're not locked in battle, the corals have work to do.
0:14:36 > 0:14:39'They must extract calcium carbonate from the surrounding seawater
0:14:39 > 0:14:42'and with it, build their homes.'
0:14:48 > 0:14:51Each coral species has its own particular way of building.
0:14:51 > 0:14:55And together, they eventually create the huge reefs
0:14:55 > 0:15:00that provide homes for all kinds of other, much larger creatures.
0:15:13 > 0:15:19At night, the reef seems like an extraterrestrial world.
0:15:19 > 0:15:22But down here, we are the aliens.
0:15:26 > 0:15:27And here comes a turtle!
0:15:30 > 0:15:32Attracted by our lights.
0:15:32 > 0:15:34Come on!
0:15:39 > 0:15:40Coming straight to us.
0:15:51 > 0:15:53Isn't that great!
0:15:53 > 0:15:55'Coming face-to-face with a green turtle
0:15:55 > 0:15:57'in this setting is a rare privilege,
0:15:57 > 0:16:01'but its presence here, along with all the other reef residents,
0:16:01 > 0:16:05'is only made possible thanks to the great coral builders.'
0:16:05 > 0:16:07He doesn't look very upset, does he?
0:16:11 > 0:16:13It happens all the time on this reef.
0:16:23 > 0:16:27It's the perfect end to my first dive.
0:16:30 > 0:16:35The time has come for us to make our way back up to the Alucia.
0:16:45 > 0:16:47Welcome back, gentlemen.
0:16:52 > 0:16:56Diving on a reef at night is a thrilling experience.
0:16:59 > 0:17:03What I want to see next is how exactly these tiny coral creatures
0:17:03 > 0:17:06have created such a vast and extensive habitat.
0:17:10 > 0:17:12To answer that, we'll need to look at the reef
0:17:12 > 0:17:14from another angle entirely.
0:17:51 > 0:17:53At this height, you can begin to appreciate
0:17:53 > 0:17:56the immense size of the Barrier Reef.
0:17:56 > 0:18:01It's 2,300 kilometres long, 1,400 miles.
0:18:01 > 0:18:05It's the largest living structure on the planet.
0:18:08 > 0:18:12Reefs much like these develop in the shallow tropical waters
0:18:12 > 0:18:15that surround many an island and continental coast.
0:18:18 > 0:18:20But few can match the Great Barrier
0:18:20 > 0:18:22in either size or complexity.
0:18:24 > 0:18:28So, what is so special about the north-eastern coast of Australia?
0:18:31 > 0:18:35A clue to the answer lies in the shape of the sea floor.
0:18:37 > 0:18:39If we strip away the ocean,
0:18:39 > 0:18:43we can reveal the reason why such extraordinary growth is possible.
0:18:45 > 0:18:49The reef has grown on a very shallow continental shelf.
0:18:49 > 0:18:53Beyond which, there is a sudden and very steep 2,000-metre drop-off.
0:18:56 > 0:19:00It stands in waters with an average depth of just 35 metres.
0:19:00 > 0:19:05That's just about as far as sunlight can penetrate with any strength.
0:19:08 > 0:19:12Light is crucially important to reef-building corals
0:19:12 > 0:19:15because they have developed a special partnership
0:19:15 > 0:19:17with microscopic algae -
0:19:17 > 0:19:21plants that actually grow within tissues.
0:19:24 > 0:19:27The algae get a safe home
0:19:27 > 0:19:30and, like all plants, when they photosynthesise,
0:19:30 > 0:19:31they produce energy.
0:19:35 > 0:19:40The coral polyps use this energy to construct their limestone home.
0:19:45 > 0:19:48Together, they've built an underwater city
0:19:48 > 0:19:52on a scale that is almost impossible to comprehend.
0:19:56 > 0:19:59But amazingly, just 10,000 years ago,
0:19:59 > 0:20:02there was no coral here at all.
0:20:06 > 0:20:11The Great Barrier Reef as we know it today simply didn't exist.
0:20:15 > 0:20:18How and when these coral communities began
0:20:18 > 0:20:22is something scientists have only recently started to investigate.
0:20:24 > 0:20:26Marine geologist, Dr Robin Beaman,
0:20:26 > 0:20:31has been leading an ambitious project to scan the entire reef.
0:20:31 > 0:20:35And his data has allowed us to map the sea floor.
0:20:36 > 0:20:40David, this is a three-dimensional model of the Great Barrier Reef.
0:20:40 > 0:20:42In deeper waters, we tend to use sonar,
0:20:42 > 0:20:46in shallow waters, we tend to use underwater laser beams
0:20:46 > 0:20:48to image the sea floor.
0:20:51 > 0:20:55'By combining computer modelling and radiocarbon dating,
0:20:55 > 0:20:57'his team have been able to reconstruct
0:20:57 > 0:21:01'the key stages in the development of the Great Barrier.
0:21:02 > 0:21:04'Their research has helped identify an event
0:21:04 > 0:21:07'between 10,000 and 20,000 years ago
0:21:07 > 0:21:11'which may explain how the Great Barrier Reef was formed.
0:21:14 > 0:21:19'But surprisingly, scientists are not the only ones to tell this story.'
0:21:20 > 0:21:24Australia's Aboriginal peoples arrived on this continent
0:21:24 > 0:21:26around 50,000 years ago.
0:21:30 > 0:21:34They have been telling the story of how the reef was formed
0:21:34 > 0:21:37long before the world's scientists even knew it existed.
0:21:39 > 0:21:43To hear that story, the Alucia is taking us to Northern Queensland
0:21:43 > 0:21:46to meet a community with a very special connection
0:21:46 > 0:21:48to this underwater world.
0:21:57 > 0:22:01They are the Gimuy Walubara Yidinji people.
0:22:01 > 0:22:04And they live just outside the city of Cairns.
0:22:11 > 0:22:15This community has dwelt alongside the reef for thousands of years.
0:22:17 > 0:22:19THEY SPEAK YIDINY
0:22:21 > 0:22:25And many of their traditions hark back to those ancient times.
0:22:25 > 0:22:28THEY SING IN YIDINY
0:22:30 > 0:22:34And one of them tells how the reef came into existence.
0:22:34 > 0:22:38It's a legend that has been passed down from generation to generation
0:22:38 > 0:22:40in the form of a dance.
0:22:44 > 0:22:47Tell me the story that's connected to this dance, sir.
0:22:47 > 0:22:52It's part of our law story that's told to me by my dad, my father,
0:22:52 > 0:22:56and was told to him by his father and his grandfather, as well.
0:22:59 > 0:23:01The part of the dance that really interests me
0:23:01 > 0:23:04is the story of Gunyah and the sacred fish.
0:23:07 > 0:23:10The story starts with Gunyah going out to sea.
0:23:10 > 0:23:14And he saw a glitter in the water, which he thought was a fish.
0:23:14 > 0:23:17And when he speared it,
0:23:17 > 0:23:22he actually speared our sacred fish, the stingray.
0:23:22 > 0:23:25So the fish got angry and it started to rise up.
0:23:25 > 0:23:30And with its wings, it made the sea rough
0:23:30 > 0:23:32and it caused the sea to rise.
0:23:34 > 0:23:39Take us back to the time when the first human beings arrived here.
0:23:39 > 0:23:40What was it like then?
0:23:40 > 0:23:42The coastline would have been very different.
0:23:42 > 0:23:45So the coastline would have been right out here,
0:23:45 > 0:23:47on the edge of the Great Barrier Reef.
0:23:47 > 0:23:49The sea level was much lower
0:23:49 > 0:23:52and they would have fished and hunted the coastline.
0:23:52 > 0:23:53These were limestone hills
0:23:53 > 0:23:55that would have been eucalypts, marshlands.
0:23:55 > 0:23:58There would have been mangrove swamps.
0:24:01 > 0:24:04But roughly 14,000 years ago,
0:24:04 > 0:24:08the climate started to dramatically change.
0:24:08 > 0:24:10It was the end of the Ice Age.
0:24:10 > 0:24:13And all that water started to inundate the continental shelf
0:24:13 > 0:24:18and start to flood this vast, flat landscape.
0:24:18 > 0:24:20- And in one man's lifetime? - Absolutely.
0:24:20 > 0:24:24So, people living here are going to have to retreat?
0:24:24 > 0:24:27Absolutely. It would have been a dramatic time for them.
0:24:27 > 0:24:29They would have been following the coastline
0:24:29 > 0:24:31as it prograded further and further back
0:24:31 > 0:24:33as the water was flooding the shelf.
0:24:33 > 0:24:37The rate of change was so great that in these very flat areas here,
0:24:37 > 0:24:41the coastline would have moved back by hundreds of metres every year.
0:24:41 > 0:24:43- Every year?- Every year.
0:24:44 > 0:24:47Gosh! That's formidable.
0:25:02 > 0:25:05So our story is about the sea rising.
0:25:05 > 0:25:09And there used to be a cliff further out.
0:25:09 > 0:25:12And past the cliff is where the ocean used to be.
0:25:12 > 0:25:13Now, that's really remarkable.
0:25:13 > 0:25:18Because Western science is just beginning to make discoveries
0:25:18 > 0:25:21that seem to suggest that the sea,
0:25:21 > 0:25:2510,000, 20,000 years ago, was way, way out there,
0:25:25 > 0:25:27which is exactly what your story says.
0:25:27 > 0:25:29- Extraordinary.- Yes.
0:25:29 > 0:25:33A folk memory of an event that happened all that time ago.
0:25:33 > 0:25:37Yeah. And the only way we can keep it alive
0:25:37 > 0:25:40- is through our song and our dance. - Yes.
0:25:40 > 0:25:43Just to keep that going through our culture.
0:25:44 > 0:25:46So the tradition lives.
0:25:46 > 0:25:48- Yes.- It's wonderful.
0:25:52 > 0:25:56'It is truly astounding to think that this story has survived
0:25:56 > 0:25:59'for so many years and across so many generations.
0:26:03 > 0:26:07'And that it coincides with what scientists are now discovering
0:26:07 > 0:26:09'about the age of the Great Barrier.'
0:26:13 > 0:26:16The polyps that built the reef arrived as spawn,
0:26:16 > 0:26:19swept here by the ocean currents.
0:26:21 > 0:26:23Corals are not new to the planet.
0:26:23 > 0:26:27They've been around for at least 500 million years.
0:26:34 > 0:26:38The new reefs provided homes for thousands of animals,
0:26:38 > 0:26:42and very quickly, a whole new community began to establish itself.
0:26:46 > 0:26:48Today, the Great Barrier Reef
0:26:48 > 0:26:51has one of the most diverse communities of animals on the planet.
0:26:56 > 0:27:00And it's the story of these remarkable reef residents
0:27:00 > 0:27:02that I want to investigate next.
0:27:04 > 0:27:09To do that, the Alucia is taking me north to a very special place.
0:27:11 > 0:27:13Lizard Island.
0:27:21 > 0:27:23It's one of the 600 continental islands
0:27:23 > 0:27:25scattered across the Great Barrier Reef.
0:27:30 > 0:27:35And its shallow lagoon is known for its exceptional biodiversity.
0:27:39 > 0:27:42'With the Alucia anchored in deeper water,
0:27:42 > 0:27:46'a more modest mode of transport will be needed to reach the shore.
0:27:49 > 0:27:52'I first visited Lizard Island in 1957.
0:27:54 > 0:27:57'Then, it was completely uninhabited.
0:28:00 > 0:28:03'Little did I know how important this remote outpost would become
0:28:03 > 0:28:06'in helping us to understand the coral reefs.
0:28:09 > 0:28:12'But today, that's exactly what this remarkable place
0:28:12 > 0:28:14'is world-renowned for.'
0:28:18 > 0:28:21Here, for the past few decades, there has been a research station
0:28:21 > 0:28:26where scientists can study continuously and in detail
0:28:26 > 0:28:30the full complexity of the community of animals that makes up the reef.
0:28:34 > 0:28:39Every year, Lizard Island hosts 100 different research projects.
0:28:42 > 0:28:44Here, scientists are shedding new light
0:28:44 > 0:28:46on the lives of the reefs' residents
0:28:46 > 0:28:49and the way in which this complex community works.
0:28:52 > 0:28:57Thanks to their research, we now know that coral reefs rival rainforests
0:28:57 > 0:29:00in the vast numbers of species they support.
0:29:03 > 0:29:06The first question is, where does all that diversity come from?
0:29:11 > 0:29:13Lizard Island reefs owe their richness
0:29:13 > 0:29:17to the special plants that, in places, fringe the shores.
0:29:19 > 0:29:21They link land and sea
0:29:21 > 0:29:24and they're vital to the coral reef community.
0:29:25 > 0:29:27They're mangroves.
0:29:29 > 0:29:32Taking shelter amongst the roots
0:29:32 > 0:29:37are thousands of juvenile fish of all shapes and sizes.
0:29:37 > 0:29:40Many of these little fish look harmless enough,
0:29:40 > 0:29:43but when they grow up, they will become
0:29:43 > 0:29:46some of the most ferocious predators on the reef.
0:29:46 > 0:29:49Indeed, the existence of these mangrove nurseries
0:29:49 > 0:29:53is one of the reasons why the fish populations of the reef
0:29:53 > 0:29:56are among the most varied and richest in the world.
0:30:00 > 0:30:04The mangroves are not only nurseries, they're playgrounds.
0:30:07 > 0:30:11The aim of the game here is to survive the most vulnerable stage
0:30:11 > 0:30:14of any animal's life, being a juvenile.
0:30:19 > 0:30:21Baby turtles...
0:30:22 > 0:30:25..rays and even sharks take refuge here.
0:30:30 > 0:30:34These juvenile blacktips are just a few weeks old.
0:30:34 > 0:30:36And only one sixth of the size they will be
0:30:36 > 0:30:40when they make it out on to the reef as adults.
0:30:42 > 0:30:43For the first year of their lives,
0:30:43 > 0:30:46the mangroves play a vital role in keeping them safe.
0:30:49 > 0:30:53As infants, they're vulnerable to predation from larger sharks.
0:30:55 > 0:30:59But the tangle of mangrove roots keeps the big predators out
0:30:59 > 0:31:02and stops them making meals of the youngsters.
0:31:07 > 0:31:08When the young are ready,
0:31:08 > 0:31:11they will eventually leave this sheltered world behind
0:31:11 > 0:31:15and make their way to the reef beyond the mangrove roots.
0:31:21 > 0:31:24The next challenge will be to find their place
0:31:24 > 0:31:27in one of the most crowded ecosystems on the planet.
0:31:35 > 0:31:39Getting on the property ladder here is no easy feat.
0:31:41 > 0:31:45Which is why one of the reefs' most celebrated characters
0:31:45 > 0:31:47has developed a very special relationship.
0:31:51 > 0:31:55Clownfish deal with the problem of overcrowding
0:31:55 > 0:31:59by sharing space with another creature, gigantic anemones.
0:32:05 > 0:32:08They've formed a relationship in which both parties benefit.
0:32:11 > 0:32:15Anemones have tentacles that are packed with stinging cells.
0:32:15 > 0:32:19Most fish touching one get a very nasty sting,
0:32:19 > 0:32:21but not the clownfish,
0:32:21 > 0:32:25thanks to the protective layer of mucus that covers its body.
0:32:29 > 0:32:31The clownfish keeps the anemone in good health
0:32:31 > 0:32:33by removing unwanted parasites.
0:32:35 > 0:32:39And in return, the anemone offers security.
0:32:39 > 0:32:42Its stinging cells ward off the sort of creatures
0:32:42 > 0:32:44which would otherwise threaten the clownfish.
0:32:49 > 0:32:54When the time comes for a pair to breed, that protection will be vital.
0:32:59 > 0:33:02A female may lay up to 1,000 eggs
0:33:02 > 0:33:05on the rock beneath her anemone home.
0:33:09 > 0:33:11As she delicately attaches them,
0:33:11 > 0:33:15the male follows closely behind, fertilising the eggs as he goes.
0:33:20 > 0:33:23A week will pass before the young are ready to emerge.
0:33:27 > 0:33:30Hatching only happens at night,
0:33:30 > 0:33:33so to record it, we have to use infrared cameras
0:33:33 > 0:33:35in a specialised filming environment.
0:33:38 > 0:33:42This is the very first time that this behaviour has been filmed.
0:33:44 > 0:33:47With gentle encouragement from their father,
0:33:47 > 0:33:49the young are helped on their way.
0:33:57 > 0:34:01Once the little larvae are set free, they're on their own.
0:34:03 > 0:34:05They'll spend the first few weeks of their life
0:34:05 > 0:34:07developing in the open ocean.
0:34:10 > 0:34:12But how will the young clownfish
0:34:12 > 0:34:14find their way back to the coral reefs
0:34:14 > 0:34:17after drifting many miles out to sea?
0:34:25 > 0:34:28To understand that, we will have to tune into a sense
0:34:28 > 0:34:32we don't normally associate with this colourful underwater world.
0:34:35 > 0:34:36Sound.
0:34:42 > 0:34:46Coral reefs are surprisingly noisy places.
0:34:46 > 0:34:50Fish and invertebrates produce a whole range of clicks
0:34:50 > 0:34:52and grunts and snaps.
0:34:52 > 0:34:57The healthier the reef, the more varied and numerous its inhabitants
0:34:57 > 0:34:59and the louder this chorus is.
0:35:02 > 0:35:05We now know that fish, just like birds,
0:35:05 > 0:35:08vocalise most at dawn and dusk.
0:35:11 > 0:35:14Damselfish call to defend their territory.
0:35:14 > 0:35:17GRUNTING
0:35:18 > 0:35:21Seahorses click to attract a mate.
0:35:21 > 0:35:23CLICKING
0:35:26 > 0:35:29Others create a very different soundscape
0:35:29 > 0:35:31simply by carrying out their daily duties.
0:35:31 > 0:35:33SQUAWKING
0:35:36 > 0:35:39Parrotfish crunching through the hard coral
0:35:39 > 0:35:41are a constant on the reef.
0:35:44 > 0:35:47Fish perceive sound in two different ways.
0:35:47 > 0:35:50Many have internal ears, but underwater,
0:35:50 > 0:35:53they can also feel sound as a vibration.
0:35:56 > 0:36:02The noise is a key indication that the community is in good shape.
0:36:02 > 0:36:04In fact, the louder the noise on a reef,
0:36:04 > 0:36:07the more inviting it is to newcomers.
0:36:07 > 0:36:11Newcomers like the young clownfish.
0:36:16 > 0:36:19This little male is no bigger than a button,
0:36:19 > 0:36:23but the time has come for him to find his place in the big city.
0:36:29 > 0:36:34At this stage, his swimming abilities leave something to be desired.
0:36:39 > 0:36:42But his hearing is so sensitive, he can tell over hundreds of metres
0:36:42 > 0:36:44if a reef is suitable.
0:36:47 > 0:36:49His journey can last days.
0:36:51 > 0:36:54The final approach is usually made at night to avoid predators.
0:36:56 > 0:37:00How fish hear and respond to sound of a healthy coral reef
0:37:00 > 0:37:03is a major area of study here on Lizard Island.
0:37:03 > 0:37:07And the scientists have a simple way of collecting these fish for study.
0:37:08 > 0:37:11A light trap, like this one at Lizard Island,
0:37:11 > 0:37:15is one way of assessing the way that the reef is working.
0:37:17 > 0:37:22Like moths to a flame, the young are attracted by the light.
0:37:24 > 0:37:26'By sampling the newest members of the community,
0:37:26 > 0:37:29'scientists can figure out how far these juvenile fish
0:37:29 > 0:37:32'are willing to travel for a good home.'
0:37:36 > 0:37:40In the case of the clownfish, juveniles have been known to travel
0:37:40 > 0:37:44250 miles before they find a reef.
0:37:51 > 0:37:55Fortunately, for the majority, it's usually a much shorter journey.
0:37:59 > 0:38:02While they rarely return to the particular anemone
0:38:02 > 0:38:03beside which they hatched,
0:38:03 > 0:38:0760% find a new home on the same reef.
0:38:13 > 0:38:17For the clownfish and the anemone, cooperation is the key
0:38:17 > 0:38:20to success in this extremely crowded environment.
0:38:27 > 0:38:31Other residents, however, take a very different approach.
0:38:33 > 0:38:38Rather than share their home, they fiercely defend their territories.
0:38:41 > 0:38:43This is a mantis shrimp.
0:38:46 > 0:38:49Spotting the competition is half the battle.
0:38:51 > 0:38:54There are many different species of mantis shrimp
0:38:54 > 0:38:56but they all have one thing in common,
0:38:56 > 0:38:58superb vision.
0:38:58 > 0:39:02The 400 million-year-old visual system of the mantis shrimp
0:39:02 > 0:39:07is the most complex in the entire animal kingdom.
0:39:07 > 0:39:12Its eyes are mounted on two stalks, giving it independent vision,
0:39:12 > 0:39:15but whereas our eyes produce binocular vision,
0:39:15 > 0:39:19each one of theirs produces three different images.
0:39:20 > 0:39:25Not only that, whereas we have three photoreceptors in our eyes,
0:39:25 > 0:39:30the mantis shrimp has up to 16, giving it access to
0:39:30 > 0:39:34parts of the spectrum that we can't even see, let alone imagine.
0:39:37 > 0:39:42And they can use their amazing vision to devastating effect.
0:39:47 > 0:39:50While some are armed with spears, others carry clubs.
0:39:57 > 0:39:59Many are champion boxers.
0:39:59 > 0:40:01They can deliver a punch
0:40:01 > 0:40:04that accelerates faster than a .22 calibre bullet.
0:40:10 > 0:40:12These powerful blows are used to stun their prey
0:40:12 > 0:40:14and defend their burrows.
0:40:19 > 0:40:24Mantis shrimps are one of the more house-proud residents on the reef.
0:40:25 > 0:40:27In fact, they're compulsive cleaners.
0:40:35 > 0:40:38They keep their burrows meticulously neat.
0:40:41 > 0:40:44With all that effort, it's hardly surprising that they're
0:40:44 > 0:40:45fiercely territorial.
0:40:48 > 0:40:50In fact, mantis shrimps have earned themselves
0:40:50 > 0:40:53a reputation for being somewhat ill-tempered.
0:40:55 > 0:40:58But scientists have discovered that there's another side
0:40:58 > 0:40:59to these macho males.
0:41:01 > 0:41:05This young hopeful is trying to catch the eye of a potential mate.
0:41:06 > 0:41:09He starts by showing off his paddle-like antennae.
0:41:13 > 0:41:16His technique may not be very impressive to us
0:41:16 > 0:41:19but he is, in fact, sending the female secret signals.
0:41:22 > 0:41:26And that is possible because mantis shrimps can see
0:41:26 > 0:41:29and reflect a kind of light that absolutely no other
0:41:29 > 0:41:31creature in the world that we know of can see...
0:41:33 > 0:41:34..including us.
0:41:36 > 0:41:41The male's display is a private invitation for this female to dance.
0:41:50 > 0:41:51So far, so good.
0:41:51 > 0:41:54She makes her way to the dance floor.
0:42:01 > 0:42:05If the male can impress the female with his performance,
0:42:05 > 0:42:07she will choose him to father her offspring.
0:42:17 > 0:42:20It seems that this male has all the right moves.
0:42:25 > 0:42:28The final phase of courtship, however, usually takes place
0:42:28 > 0:42:32out of sight, within their burrows.
0:42:38 > 0:42:41The mantis shrimp is arguably one of the reefs most colourful
0:42:41 > 0:42:44characters and typifies the key to survival here.
0:42:49 > 0:42:54Each resident species has had to carve out its own particular niche
0:42:54 > 0:42:58and that is what has created this extraordinary diversity.
0:43:00 > 0:43:05Here, life can evolve 50% faster than in other marine environments.
0:43:07 > 0:43:11The tiny creatures that have built this remarkable ecosystem
0:43:11 > 0:43:17have created a habitat so complex that it supports all kinds of life.
0:43:21 > 0:43:23But none of the reef's residents would be here
0:43:23 > 0:43:26without one truly extraordinary event.
0:43:28 > 0:43:30It occurs just once a year
0:43:30 > 0:43:33and is one of the greatest of all natural spectacles.
0:43:37 > 0:43:41It wasn't until the 1980s that scientists discovered it,
0:43:41 > 0:43:43here on the Great Barrier.
0:43:45 > 0:43:47On a few nights of the year
0:43:47 > 0:43:48when the conditions are just right,
0:43:48 > 0:43:50all along the length of the reef,
0:43:50 > 0:43:55corals of many different species suddenly erupt.
0:43:55 > 0:43:58It's the great spawning event
0:43:58 > 0:44:00and it's one of the wonders of the natural world.
0:44:02 > 0:44:04It's the one time in the year
0:44:04 > 0:44:07when the corals themselves don't just grow by branching,
0:44:07 > 0:44:13but reproduce sexually, and it's vital for the survival of the reef.
0:44:13 > 0:44:15In recent years, we've learned a great deal
0:44:15 > 0:44:19about the many factors that influenced the moment of spawning.
0:44:22 > 0:44:25But even though we know it occurs within days of the full moon in
0:44:25 > 0:44:29October or November, the trigger that starts it all is still a mystery.
0:44:34 > 0:44:38The light of the moon is, perhaps, the most influential,
0:44:38 > 0:44:40but there are many other factors,
0:44:40 > 0:44:44including the temperature of the water and the state of the tides.
0:44:44 > 0:44:47And as the moment approaches,
0:44:47 > 0:44:49all along the length of the reef,
0:44:49 > 0:44:51there's a mounting sense of excitement.
0:44:55 > 0:44:58Fish and other predators gather.
0:44:58 > 0:45:01This will be an opportunity for a feast.
0:45:09 > 0:45:11The timing has to be exact.
0:45:13 > 0:45:16Each species of coral has its own particular triggers,
0:45:16 > 0:45:20but they must synchronise their behaviour to ensure their success.
0:45:22 > 0:45:25Just half an hour before the big event,
0:45:25 > 0:45:27there is the first sign of the spawning to come.
0:45:31 > 0:45:35Small bundles of sperm and eggs bulge from the polyps.
0:45:41 > 0:45:44When the moment is right, there is a mass release.
0:46:11 > 0:46:15For hundreds of miles all along the coast, the corals erupt.
0:46:38 > 0:46:43Only with daybreak can you see the true scale of the event.
0:46:48 > 0:46:52Great ribbons of coral spawn drift over the surface of the sea.
0:47:00 > 0:47:02After the coral has spawned,
0:47:02 > 0:47:05the billions of developing larvae are swept far and wide
0:47:05 > 0:47:07by the tides and the currents.
0:47:08 > 0:47:13The vast majority will be eaten by fish and other creatures,
0:47:13 > 0:47:17but the few survivors must then find a place to settle,
0:47:17 > 0:47:21either on a newly-vacated site on an existing reef
0:47:21 > 0:47:23or perhaps to found a new one.
0:47:31 > 0:47:33The newest coral recruits will continue
0:47:33 > 0:47:36the work their ancestors began almost 10,000 years ago.
0:47:48 > 0:47:53They are the essential organisms on which the whole reef depends.
0:48:00 > 0:48:02The Great Barrier is what it is
0:48:02 > 0:48:05because the tiny coral polyps never stop building.
0:48:08 > 0:48:12And what they have created is one of the wonders of the natural world.
0:48:21 > 0:48:24Next time, we'll cross the Great Barrier Reef
0:48:24 > 0:48:26to meet its extraordinary visitors.
0:48:34 > 0:48:35I will meet turtles
0:48:35 > 0:48:39that may have travelled thousands of miles to get here
0:48:39 > 0:48:40and the remarkable people
0:48:40 > 0:48:43who are trying to save them from disaster.
0:48:48 > 0:48:53I will come face-to-face with the great predators of the reef.
0:48:53 > 0:48:55Wow. There's a huge shark.
0:48:55 > 0:48:57They are so beautiful in the water.
0:49:02 > 0:49:05And we'll meet a whale that seeks out human contact,
0:49:05 > 0:49:08a behaviour that happens nowhere else on Earth.
0:49:10 > 0:49:12Some come from the open ocean,
0:49:12 > 0:49:15others from the land immediately inshore
0:49:15 > 0:49:18and still others from the sky,
0:49:18 > 0:49:22to complicate still further the intricate community
0:49:22 > 0:49:26that is known as the Great Barrier Reef.
0:49:45 > 0:49:46For this series,
0:49:46 > 0:49:50the production team set themselves an ambitious challenge.
0:49:50 > 0:49:54They wanted me to experience the Great Barrier Reef as never before.
0:49:58 > 0:50:02To achieve that, we teamed up with a very special research vessel...
0:50:04 > 0:50:06..the Alucia.
0:50:06 > 0:50:08There aren't many boats like this in the world and
0:50:08 > 0:50:10it's a kind of magic carpet for us.
0:50:10 > 0:50:13It allows us to float around the reef
0:50:13 > 0:50:15and for David to tell different parts of the story.
0:50:18 > 0:50:21On board, all the latest technology,
0:50:21 > 0:50:23helicopters, a laboratory
0:50:23 > 0:50:25and advanced mapping systems.
0:50:30 > 0:50:31At the helm of Alucia,
0:50:31 > 0:50:33Captain Frank Alika.
0:50:35 > 0:50:37The task of getting the ship into position
0:50:37 > 0:50:41for the first big submarine launch rests on his shoulders.
0:50:43 > 0:50:45Some parts are charted less well than others,
0:50:45 > 0:50:48but this particular bit, there's quite a lot of bombies
0:50:48 > 0:50:50and things out there that are likely to jump up and bite you
0:50:50 > 0:50:53on the bottom, and that's really not what you want.
0:50:56 > 0:50:58Fortunately, he's a lot more hands on
0:50:58 > 0:51:01than the skipper was on my first visit in 1957.
0:51:06 > 0:51:08But it was very primitive.
0:51:08 > 0:51:10The camera was wound up by clockwork
0:51:10 > 0:51:13and it was just me and the chap with a 16mm camera
0:51:13 > 0:51:14and I did the recording.
0:51:16 > 0:51:20It may have been a modest shoot but it was, in its way, ground-breaking.
0:51:22 > 0:51:24We worked on locations on the reef
0:51:24 > 0:51:26where film crews had never been before.
0:51:29 > 0:51:3360 years later, I'm told we are poised to make history once again.
0:51:36 > 0:51:38This time, to reach new areas of reef,
0:51:38 > 0:51:42I'll have to rely on the Triton submersible.
0:51:42 > 0:51:46And she's very flexible in terms of how shallow we can come, as well.
0:51:46 > 0:51:48She'll work in 1,000 metres happily,
0:51:48 > 0:51:51but we can also work in the splash zone,
0:51:51 > 0:51:54so her actual trim system is very good.
0:51:54 > 0:51:57Amazing visibility, as you'll see when you get in.
0:51:57 > 0:51:59Yes, she's a little bit flash.
0:52:02 > 0:52:05With just a few short hours before the first big dive,
0:52:05 > 0:52:08the excitement and pressure is building on deck.
0:52:12 > 0:52:14This will be the last opportunity for the crew
0:52:14 > 0:52:16to check the camera gear
0:52:16 > 0:52:18and make sure everything is perfectly in place.
0:52:21 > 0:52:22It's been a busy morning already.
0:52:22 > 0:52:24We've had soundmen, cameramen
0:52:24 > 0:52:26trying to fit all their gear into the sub.
0:52:26 > 0:52:29We're sort of running out of space for bodies.
0:52:31 > 0:52:34There are lots of worries when you put your 88-year-old presenter
0:52:34 > 0:52:36in something like this.
0:52:36 > 0:52:39I mean, it's got a very small area at the top to get into.
0:52:39 > 0:52:41There are all sorts of things that can go wrong.
0:52:41 > 0:52:42We're always very cautious.
0:52:46 > 0:52:47And even the most limber of sub operators
0:52:47 > 0:52:49will struggle getting in the sub.
0:52:49 > 0:52:51David's incredibly active and fit,
0:52:51 > 0:52:53but he's 88 and so we were slightly worried
0:52:53 > 0:52:55about how he might get into the sub.
0:52:57 > 0:52:59Yeah, that's it, that's the one.
0:52:59 > 0:53:01OK, so we're just going to...
0:53:01 > 0:53:04See that landing, he'll guide you right in.
0:53:04 > 0:53:07And then you can put your foot there, David.
0:53:07 > 0:53:09Keep coming. Nearly there. That's it. OK.
0:53:11 > 0:53:12You can rest against me if you want.
0:53:12 > 0:53:14Nearly sat on the pilot!
0:53:14 > 0:53:17- That's all right, I'm used to it. - That's what he's there for.
0:53:19 > 0:53:21David, as usual, defied all our thoughts
0:53:21 > 0:53:23and just went straight in without any trouble
0:53:23 > 0:53:25as though he was a 25-year-old.
0:53:25 > 0:53:28- Rest it on your lap. Is that OK? - Yep.
0:53:33 > 0:53:37So, that's hatch secure and we are ready.
0:53:40 > 0:53:42The sub weighs almost eight tonnes
0:53:42 > 0:53:45and getting it into the water is a major operation.
0:53:48 > 0:53:50There's something quite extraordinary about the Triton
0:53:50 > 0:53:52being launched, standing here on deck.
0:53:52 > 0:53:56Suddenly, the whole back deck area of the ship comes alive.
0:53:56 > 0:53:57You've got people running around.
0:53:57 > 0:54:00Everything's incredibly detailed and carefully planned,
0:54:00 > 0:54:03but you're sort of caught in a whirlwind as ropes fly
0:54:03 > 0:54:05and the submarine starts to move forwards.
0:54:05 > 0:54:07You know, this is a very exciting moment.
0:54:07 > 0:54:11You know, this is a big day, even in the world of David Attenborough.
0:54:17 > 0:54:19As we disappear beneath the waves,
0:54:19 > 0:54:21out on a support vessel,
0:54:21 > 0:54:25underwater cameraman Steve Hudson prepares to film the sub
0:54:25 > 0:54:26as it explores the reef.
0:54:29 > 0:54:32So, Nick and I are going to jump in the water,
0:54:32 > 0:54:35descend to a maximum depth of about 30 metres
0:54:35 > 0:54:37and shoot exterior shots of the submarine
0:54:37 > 0:54:39as it cruises over the reef.
0:54:41 > 0:54:42It can be pretty tiring.
0:54:42 > 0:54:45You have to swim in front of it, swim behind it,
0:54:45 > 0:54:47swim beneath it, swim above it,
0:54:47 > 0:54:49trying to get a multiple of shots.
0:54:51 > 0:54:54But today, because of the strong currents, visibility is poor.
0:54:59 > 0:55:03At first, Steve struggles to locate the sub through the cloudy water.
0:55:21 > 0:55:23Finally, he makes visual contact.
0:55:30 > 0:55:32Before we descend deeper and beyond his reach,
0:55:32 > 0:55:35Steve must get his exterior shots of the sub.
0:55:37 > 0:55:39Lead cameraman Paul Williams
0:55:39 > 0:55:41captures the action from inside the vessel.
0:55:43 > 0:55:45To get the best footage,
0:55:45 > 0:55:47the divers need to coordinate with the sub team.
0:55:49 > 0:55:52It's a task easier said than done.
0:55:52 > 0:55:53We're literally in a bubble.
0:55:53 > 0:55:56We can't talk to the divers outside.
0:55:56 > 0:55:58We had this rather crude hand signal.
0:55:58 > 0:55:59You know, it's like,
0:55:59 > 0:56:02"Get out of shot," or, you know,
0:56:02 > 0:56:04"Well, just move over that way a bit."
0:56:20 > 0:56:22Can you see his hand signals, yeah?
0:56:34 > 0:56:36He's saying, "Thank you."
0:56:36 > 0:56:37Thank you and...
0:56:37 > 0:56:39We're just going to do the descent now.
0:56:48 > 0:56:49'As the vessel dives deeper,
0:56:49 > 0:56:53'we're treated to some spectacular sights...
0:56:53 > 0:56:54Oh, how beautiful.
0:56:56 > 0:56:59'..which show why the reef is one of the most dazzling
0:56:59 > 0:57:00'habitats on the planet.'
0:57:06 > 0:57:08Oh, look at this lot.
0:57:08 > 0:57:10It's jolly nice that someone of my age
0:57:10 > 0:57:13can be taken down in fantastic comfort.
0:57:13 > 0:57:15Grey reef shark there.
0:57:15 > 0:57:18No problem about breathing. No problem about talking.
0:57:18 > 0:57:21No problem about your movements.
0:57:21 > 0:57:22There's another.
0:57:24 > 0:57:26You're just sitting there
0:57:26 > 0:57:29and looking at one of the most extraordinary places on Earth.
0:57:29 > 0:57:31A privilege given to very few.