0:00:02 > 0:00:07The Great Barrier Reef is the largest coral reef on our planet.
0:00:16 > 0:00:21It's one of the seven recognised wonders of the natural world.
0:00:27 > 0:00:32The reef itself is the place that most people explore
0:00:32 > 0:00:35but there's much, much more.
0:00:37 > 0:00:42The coral reef is actually a very small part of this underwater world.
0:00:42 > 0:00:44As little as seven per cent.
0:00:48 > 0:00:51The remaining 93% of the marine park
0:00:51 > 0:00:57encompasses a variety of habitats, each one remarkable in its own way.
0:01:00 > 0:01:02And beyond the marine park
0:01:02 > 0:01:06there are even more environments that are important to the reef.
0:01:09 > 0:01:12Some close to shore.
0:01:14 > 0:01:16Others inland.
0:01:17 > 0:01:22Altogether there are more than a hundred different types of habitat
0:01:22 > 0:01:26in and around the Barrier Reef,
0:01:26 > 0:01:30each with its own distinctive plants and animals.
0:01:33 > 0:01:38There are creatures that you would expect to see on a reef,
0:01:38 > 0:01:40and others that you would not.
0:01:57 > 0:02:01All the places in which these animals live
0:02:01 > 0:02:04are linked to a vast deep-water lagoon
0:02:04 > 0:02:07which lies between the coast of mainland Australia
0:02:07 > 0:02:09and the outer reef.
0:02:13 > 0:02:15These habitats interconnect,
0:02:15 > 0:02:20and all are vital to the well being of the Great Barrier Reef.
0:02:22 > 0:02:26This is the little known story of one of the most complex
0:02:26 > 0:02:30and spectacular ecosystems on Earth.
0:02:39 > 0:02:43The Great Barrier Reef is over two thousand kilometres long,
0:02:43 > 0:02:46which means the lagoon that lies between the outer reef
0:02:46 > 0:02:49and the Australian mainland is vast.
0:02:49 > 0:02:53An area one and a half times the size of the British Isles.
0:03:00 > 0:03:07Pick a spot anywhere in the lagoon and you'll probably find sand,
0:03:07 > 0:03:13as about two-thirds of the seafloor here is a shifting underwater desert.
0:03:14 > 0:03:17It looks barren, but there is life here.
0:03:17 > 0:03:20It's just that you don't often see it.
0:03:27 > 0:03:29Garden eels
0:03:29 > 0:03:33and an unlikely alliance.
0:03:33 > 0:03:37A fish and a shrimp that share a burrow.
0:03:38 > 0:03:42In a world where most food is out of sight,
0:03:42 > 0:03:46it takes a predator with special talents to find it.
0:03:46 > 0:03:49And this is that predator...
0:03:49 > 0:03:51The ray.
0:03:52 > 0:03:57The ray's special skill is to find living things under the sand,
0:03:57 > 0:04:01and the largest species to do this here is the stingray.
0:04:08 > 0:04:12It finds its prey by detecting the minute electric fields
0:04:12 > 0:04:15produced by muscles when they contract,
0:04:15 > 0:04:17including the heart muscles.
0:04:17 > 0:04:21Something no animal can ever switch off.
0:04:21 > 0:04:25But they do have to swim directly over a beating heart
0:04:25 > 0:04:27to know that it's there.
0:04:33 > 0:04:36By sucking and blowing,
0:04:36 > 0:04:40this stingray excavates its target deep under the soft sand.
0:04:55 > 0:04:59Many rays feeding together produce a series of furrows on the sea floor
0:04:59 > 0:05:05and all that puffing and blowing can attract unwelcome attention.
0:05:05 > 0:05:08The hunter can just as easily become the hunted.
0:05:16 > 0:05:19This is a stingray's worse nightmare.
0:05:21 > 0:05:24A great hammerhead shark.
0:05:27 > 0:05:29It has electro-receptors too.
0:05:29 > 0:05:32They're spread across the underside of its very broad head,
0:05:32 > 0:05:36which it sweeps back and forth searching for prey.
0:05:38 > 0:05:42The stingray has a formidable weapon, a venomous barb.
0:05:42 > 0:05:46But one hammerhead was found with 96 barbs in its body,
0:05:46 > 0:05:48and seemed none the worse.
0:05:51 > 0:05:56The stingray's first line of defence is to remain very still
0:05:56 > 0:05:59in the hope that the shark doesn't find it.
0:06:18 > 0:06:21The commotion warns the other rays to escape,
0:06:21 > 0:06:25but it attracts other sharks, like jackals at a kill.
0:06:44 > 0:06:49Dramas like this are played out every day on the floor of the lagoon,
0:06:49 > 0:06:51but few people are there to witness them.
0:06:52 > 0:06:58It seems surprising that the lagoon remains a relatively unexplored environment.
0:06:58 > 0:07:00But if you're a diver, why would you explore the lagoon?
0:07:00 > 0:07:02It's relatively hostile,
0:07:02 > 0:07:05particularly when you compare it to the crystal clear reefs
0:07:05 > 0:07:07that are short boat ride away.
0:07:12 > 0:07:14Yet there's plenty of life down here.
0:07:14 > 0:07:17Prawns, squid and all manner of fish species
0:07:17 > 0:07:19are caught by local fishermen.
0:07:23 > 0:07:27Diving here is not easy but it's well worth the effort.
0:07:36 > 0:07:41Dotted across this vast underwater desert are ghostly oases
0:07:41 > 0:07:43where amazing life forms have taken hold.
0:07:59 > 0:08:02It's a strange, almost alien world.
0:08:09 > 0:08:12And if the place seems strange,
0:08:12 > 0:08:15many of the creatures living here are even stranger.
0:09:11 > 0:09:15These oases are created not by plants but by animals.
0:09:15 > 0:09:19They're corals, but not the normal reef building ones.
0:09:22 > 0:09:27Unlike their hard coral cousins, they don't have a chalky skeleton
0:09:27 > 0:09:31and they thrive at depths where the light is less intense,
0:09:31 > 0:09:34capturing food from the water currents
0:09:34 > 0:09:36with eight feathery tentacles.
0:09:39 > 0:09:41These soft coral gardens are important
0:09:41 > 0:09:44because baby fish hide amongst them.
0:09:44 > 0:09:48Nearly half of all the adult fish on the reef proper
0:09:48 > 0:09:50grow up in nurseries on the lagoon.
0:09:53 > 0:09:57They arrive as larvae, swept in from the ocean by the tide.
0:10:00 > 0:10:02Then, as the tiny fish grow,
0:10:02 > 0:10:06they hop from one refuge to the next across the floor of the lagoon
0:10:06 > 0:10:11to reach their final destination back on the Barrier Reef itself.
0:10:12 > 0:10:15As long as they hide amongst the corals and seaweed,
0:10:15 > 0:10:17they're relatively safe.
0:10:17 > 0:10:20The danger comes when they break cover.
0:10:22 > 0:10:27This baby Queensland grouper may just be a few centimetres long now,
0:10:27 > 0:10:29but one day he'll weigh half a tonne.
0:10:31 > 0:10:35That's if he lives that long. He can't stay hiding forever.
0:10:48 > 0:10:51It's dangers like this camouflaged stonefish
0:10:51 > 0:10:55that force all life down here to find somewhere to hide.
0:10:58 > 0:11:02The floor of the lagoon is relatively flat and featureless.
0:11:02 > 0:11:05It's like the plains of the desert.
0:11:05 > 0:11:09But every now and then you get a little oasis of life.
0:11:11 > 0:11:15And this sponge, here, has been heavily colonised
0:11:15 > 0:11:20by these feather stars and it provides a vital bit of cover
0:11:20 > 0:11:25for juvenile fish on their journey both to the reef
0:11:25 > 0:11:28and their journey to adulthood.
0:11:29 > 0:11:35And that journey includes stopovers at almost anything that sticks out above the sand,
0:11:35 > 0:11:38like this tube dwelling sea anemone.
0:11:44 > 0:11:49A carpet anemone becomes a welcoming roadhouse.
0:11:49 > 0:11:52Even the spines of a sea urchin will do the trick.
0:11:56 > 0:12:01A surprising refuge is this highly venomous Stoke's sea snake.
0:12:02 > 0:12:05It's picked up some hitchhikers, baby trevally,
0:12:05 > 0:12:07and become a mobile nursery.
0:12:15 > 0:12:17Wherever it goes, they go.
0:12:34 > 0:12:37With hiding places at a premium,
0:12:37 > 0:12:41fish will go to incredible lengths to hide down here.
0:12:41 > 0:12:43and none more so than this.
0:12:48 > 0:12:51The pearl fish is vulnerable out in the open,
0:12:51 > 0:12:55so while it's not feeding it must conceal itself.
0:12:55 > 0:12:59But it has a peculiar taste in hiding places.
0:13:01 > 0:13:03This is a sea cucumber.
0:13:05 > 0:13:08Its body is basically a tube.
0:13:08 > 0:13:11It sucks in sand at one end, extracts anything edible
0:13:11 > 0:13:15and passes waste out of the other.
0:13:15 > 0:13:17Just what the pearl fish has been looking for.
0:13:19 > 0:13:22But NOT the mouth end.
0:13:22 > 0:13:26It's attracted to the odour of the other end.
0:13:43 > 0:13:46Sea cucumbers are repulsive to most predators
0:13:46 > 0:13:49so the pearl fish is safe inside.
0:13:49 > 0:13:52It'll stay there until it's time to feed again.
0:13:55 > 0:13:59It doesn't harm its host, but the bad news for sea cucumbers
0:13:59 > 0:14:04is that pearl fish are happy to share their temporary home with others.
0:14:09 > 0:14:12It seems there's plenty of room for all.
0:14:20 > 0:14:23The Barrier Reef we see today is comparatively young.
0:14:23 > 0:14:26It began to form during the last Ice Age
0:14:26 > 0:14:31when sea levels were 120 metres lower than they are today.
0:14:35 > 0:14:37When the ice sheets began to melt,
0:14:37 > 0:14:41the growth of corals kept pace with the rising seas,
0:14:41 > 0:14:44blocking off the waters of the lagoon.
0:14:47 > 0:14:49And during that one great event
0:14:49 > 0:14:52another important habitat was created.
0:14:53 > 0:14:56Stretching away behind me to the horizon
0:14:56 > 0:15:00is the great expanse of the lagoon and yet a mere 10,000 years ago,
0:15:00 > 0:15:03that's a blink of an eye in geological time,
0:15:03 > 0:15:06the beach I'm standing on would have been the slope of a hill
0:15:06 > 0:15:09overlooking a plain covered in Eucalyptus forest.
0:15:09 > 0:15:10But the sea level rose,
0:15:10 > 0:15:14the plain was inundated and the hill became an island.
0:15:20 > 0:15:23These "continental islands", as they're known,
0:15:23 > 0:15:28are essentially pieces of mainland cut off by the rising water.
0:15:31 > 0:15:35There are six hundred of them scattered about the lagoon.
0:15:45 > 0:15:49Any land animals cut off from the mainland had to adapt or perish.
0:15:51 > 0:15:55And on this island one species has done so well,
0:15:55 > 0:15:58it's positively flourished.
0:16:01 > 0:16:03This is a yellow spotted monitor lizard,
0:16:03 > 0:16:06or goanna, if you're from this neck of the woods.
0:16:06 > 0:16:09And it's a very successful and abundant animal on this island.
0:16:09 > 0:16:11It made a real impression on Captain Cook
0:16:11 > 0:16:14when he came here in 1770.
0:16:14 > 0:16:17To the degree that when he sat down to think about a name for the island,
0:16:17 > 0:16:20not a terribly long process, I don't think,
0:16:20 > 0:16:24he thought, "It's an island and it's covered in lizards."
0:16:24 > 0:16:26"Got it! Lizard Island."
0:16:26 > 0:16:28Which is rather clever, I think.
0:16:28 > 0:16:30Do you see what he did there?
0:16:46 > 0:16:51When hunting, the goanna is alert to any movement.
0:16:53 > 0:16:55If the grasshopper remains still,
0:16:55 > 0:16:59it has a chance of escaping the goanna's attention.
0:17:25 > 0:17:28Balancing on its back legs and tail like a tripod
0:17:28 > 0:17:31is a trick few others lizards can perform,
0:17:31 > 0:17:36but it's effective to get to those just out of reach places.
0:17:45 > 0:17:49The goanna's sense of smell is as important as its sight.
0:17:49 > 0:17:53Its forked tongue helps it to detect food from a distance.
0:17:54 > 0:17:57By comparing the strength of a smell reaching each of the two prongs
0:17:57 > 0:18:01it can pinpoint where it comes from.
0:18:04 > 0:18:07A rotting fish is irresistible.
0:18:22 > 0:18:24They're usually solitary,
0:18:24 > 0:18:27but here on Lizard Island they'll tolerate others,
0:18:27 > 0:18:30as long as there's plenty of food to go round.
0:18:44 > 0:18:47Small goannas give way to larger ones.
0:18:56 > 0:19:00Foraging a variety of foods has helped the goannas
0:19:00 > 0:19:02build a large population on Lizard Island,
0:19:02 > 0:19:09but there's another important factor and that's how they react to me.
0:19:09 > 0:19:13HE WHISTLES
0:19:20 > 0:19:22There are people living on the island
0:19:22 > 0:19:24and the goannas are not afraid of them.
0:19:24 > 0:19:26In fact, quite the opposite.
0:19:36 > 0:19:38He's followed the scent of my barbeque
0:19:38 > 0:19:42and over the last few years these animals have adapted their behaviour
0:19:42 > 0:19:44to get used to the presence of man
0:19:44 > 0:19:47and use man as a potential food source.
0:19:48 > 0:19:53This ability to learn and change as the environment around you changes
0:19:53 > 0:19:56is a very neat evolutionary trick.
0:19:56 > 0:20:00He's used to hunting invertebrates, he's changed his behaviour
0:20:00 > 0:20:04to home in on this appallingly cooked barbequed sausage.
0:20:04 > 0:20:08In the modern world where man has encroached on virtually every habitat
0:20:08 > 0:20:11it's a very good way of ensuring your survival.
0:20:15 > 0:20:24And adaptability has enabled a reptile with a more chilling interest in people to thrive in these waters.
0:20:31 > 0:20:37It's the saltwater crocodile, better known locally as the 'salty'.
0:20:38 > 0:20:43It's the world's largest reptile and it's common on the lagoon's islands
0:20:43 > 0:20:47because it's at home in saltwater and fresh,
0:20:47 > 0:20:49sometimes swimming far out at sea.
0:20:56 > 0:21:01So it's not unusual to find one hauled out on an island beach.
0:21:04 > 0:21:08Salties, though, start life with more modest dimensions.
0:21:12 > 0:21:16This one-year-old is no more than 30 centimetres long
0:21:16 > 0:21:19and it's hiding amongst the plants at the edge of the sea.
0:21:20 > 0:21:23Hunting at the junction between air and water
0:21:23 > 0:21:27means there's a good choice of food. Like mud skippers.
0:21:59 > 0:22:02He'll have to improve as a hunter
0:22:02 > 0:22:05if he's going to grow into a six-metre giant.
0:22:07 > 0:22:10And he'd best better watch his back.
0:22:10 > 0:22:13There's a bird about that could easily take a baby crocodile.
0:22:16 > 0:22:17This is a white bellied sea eagle.
0:22:17 > 0:22:20It's the second largest eagle in Australia
0:22:20 > 0:22:22and it's fantastic to be this close.
0:22:22 > 0:22:26This is the closest I've ever been to any eagle anywhere in the world.
0:22:29 > 0:22:33They can be seen just about anywhere around the lagoon.
0:22:33 > 0:22:36You're as likely to spot one amongst the trees,
0:22:36 > 0:22:37as you are over the reef.
0:22:37 > 0:22:40So an island is a perfect base.
0:22:49 > 0:22:52They may be specialised to catch fish,
0:22:52 > 0:22:57but like the goannas and crocodiles they're adaptable too.
0:22:57 > 0:23:01This is a range of items taken from beneath a killing tree
0:23:01 > 0:23:05of a white bellied sea eagle on a continental island.
0:23:05 > 0:23:08The killing tree is where the sea eagle will take apart, dismember,
0:23:08 > 0:23:10and eat its prey.
0:23:10 > 0:23:13It's a very good representation of what these animals eat
0:23:13 > 0:23:16and indeed their strategy for hunting.
0:23:16 > 0:23:20You've got a parrot fish here, which is a deeper swimming fish.
0:23:20 > 0:23:22you've got things like these long toms
0:23:22 > 0:23:24which actually swim right on the surface,
0:23:24 > 0:23:26you've even got birds here.
0:23:26 > 0:23:29Most remarkable of all you've got these freshwater turtles,
0:23:29 > 0:23:31that don't exist on the island.
0:23:31 > 0:23:34They are on the mainland so that eagle has flown the mainland
0:23:34 > 0:23:38taken these turtles and brought them back to the nest.
0:23:38 > 0:23:42It's an excellent representation of the strategy of these animals.
0:23:42 > 0:23:46If a food item is short locally in short supply on the island,
0:23:46 > 0:23:48they'll actually seek alternatives.
0:23:48 > 0:23:52This generalist approach makes them very, very successful
0:23:52 > 0:23:55in the limited environment that an island represents.
0:23:56 > 0:24:00Even so, fish make up half of its diet.
0:24:00 > 0:24:03To catch them it uses huge talons.
0:24:07 > 0:24:12They're also weapons it can use to have a crack at these...
0:24:12 > 0:24:13fruit bats.
0:24:17 > 0:24:20Spectacled fruit bats are big.
0:24:20 > 0:24:23They have a wingspan of about a metre
0:24:23 > 0:24:27and they roost in island forests as well as those on the mainland.
0:24:40 > 0:24:42Babies have to cling on tight.
0:24:46 > 0:24:48But that's the least of a mother's worries.
0:24:54 > 0:24:56Diving into the tangle of branches
0:24:56 > 0:24:59and grabbing a bat hanging at its roost site
0:24:59 > 0:25:01is not an option for a large bird.
0:25:04 > 0:25:08For the eagle to have any chance, the bats needs to be airborne.
0:25:23 > 0:25:26These are little red fruit bats.
0:25:26 > 0:25:29During the day, they gather in roosts of up to a million
0:25:29 > 0:25:31so they're not hard to find.
0:25:47 > 0:25:50An eagle's appearance creates panic.
0:26:42 > 0:26:44Bats are agile flyers
0:26:44 > 0:26:47but the eagle's powerful claws gave it the edge.
0:26:51 > 0:26:54The continental islands are magnets for wildlife,
0:26:54 > 0:26:58providing shelter, lookout points and hunting grounds.
0:26:58 > 0:27:02They're oases for life but they're not the only ones.
0:27:08 > 0:27:13Below the surface of the lagoon is an island of a very different kind.
0:27:17 > 0:27:19A shipwreck.
0:27:23 > 0:27:25This is the SS Yongala.
0:27:34 > 0:27:38She sank during a cyclone in 1911
0:27:38 > 0:27:41and now sits on the seabed at a depth of thirty metres.
0:27:44 > 0:27:48122 people lost their lives.
0:27:58 > 0:28:01But out of this human tragedy has come an opportunity.
0:28:10 > 0:28:16100 years underwater has created something very, very special.
0:28:35 > 0:28:40The Yongala is regarded by many as the greatest wildlife wreck on earth.
0:28:41 > 0:28:44And looking around me it is very hard to disagree.
0:28:46 > 0:28:49The wreck provides shelter on the featureless plain
0:28:49 > 0:28:52for more than 120 fish species.
0:28:52 > 0:28:54This concentration of life
0:28:54 > 0:28:59is sustained by food swept in by the exceptionally strong currents.
0:29:06 > 0:29:08The living is so good,
0:29:08 > 0:29:11many of the young fish stay here for their entire lives,
0:29:11 > 0:29:15rather than move to the outer reef when they grow up.
0:29:37 > 0:29:39There are sea turtles down here too.
0:29:39 > 0:29:41This one's a loggerhead.
0:29:49 > 0:29:52And the wreck's a favourite hangout for another species.
0:29:55 > 0:29:57This is a hawksbill turtle
0:29:57 > 0:30:01and he's here to feed on the soft coral that coats the wreck.
0:30:04 > 0:30:07The soft corals are one of the main reasons that all this life
0:30:07 > 0:30:09is attracted to the Yongala.
0:30:20 > 0:30:24Almost every available space on its once smooth hull
0:30:24 > 0:30:26is covered with them.
0:30:37 > 0:30:41The soft corals are a refuge for millions of small fish
0:30:41 > 0:30:43but they must dart out from time to time
0:30:43 > 0:30:46to feed on the plankton in the current.
0:30:47 > 0:30:50And wherever small fish gather,
0:30:50 > 0:30:54it's not long before something bigger turns up to eat them.
0:30:56 > 0:30:58A grouper!
0:31:01 > 0:31:03This is a Queensland grouper,
0:31:03 > 0:31:07it's the largest bony fish that lives on the Great Barrier Reef.
0:31:12 > 0:31:15Queensland groupers are real giants.
0:31:15 > 0:31:19This Yongala resident is known as the VW,
0:31:19 > 0:31:21because he's the same size as the car.
0:31:22 > 0:31:24His mouth's so big,
0:31:24 > 0:31:27he's quite capable of swallowing sharks and rays whole.
0:31:33 > 0:31:37But another resident has an even deadlier bite.
0:31:39 > 0:31:41Sea snakes have more potent venom
0:31:41 > 0:31:44than many of their land-living relatives
0:31:44 > 0:31:46and they put it to good use.
0:31:51 > 0:31:54The olive sea snake doesn't really look as though it's hunting,
0:31:54 > 0:31:57but when its small head disappears into a hole,
0:31:57 > 0:32:01it can trap and paralyse any fish hiding there.
0:32:03 > 0:32:08It's unusual for so many predators to be swimming so close to each other,
0:32:08 > 0:32:10but there's so much to eat here.
0:32:11 > 0:32:13Most of the action is on top of the wreck,
0:32:13 > 0:32:16where the strongest currents sweep in the most food.
0:32:17 > 0:32:22The waters within the immediate vicinity of the wreck
0:32:22 > 0:32:27is an area of incredibly intense and violent predatory activity.
0:32:28 > 0:32:32For the small fish that call the Yongala their home,
0:32:32 > 0:32:36to venture into this blue water is a huge gamble
0:32:36 > 0:32:38but they've got to do it, to seek out food.
0:32:39 > 0:32:43And if they get it wrong and go too far,
0:32:43 > 0:32:47the difference between life and death on this wreck
0:32:47 > 0:32:51can be a matter of millimetres or seconds.
0:33:36 > 0:33:39The amount of marine life to be found in the 100 metres
0:33:39 > 0:33:43of the wreck of the Yongala is truly staggering.
0:33:43 > 0:33:46Arguably it's a greater concentration
0:33:46 > 0:33:49than on any spot on the Barrier Reef itself.
0:33:59 > 0:34:01In contrast to the middle,
0:34:01 > 0:34:04the landward edge of the lagoon is relatively shallow.
0:34:06 > 0:34:11Here, bright sunlight can reach all the way to the sandy bottom,
0:34:11 > 0:34:13where conditions are right for plants to grow.
0:34:17 > 0:34:21This is not seaweed, but a marine relative of the water lily,
0:34:21 > 0:34:22known as "sea grass".
0:34:25 > 0:34:29It grows and flowers in vast meadows in clear water around islands
0:34:29 > 0:34:31and along the shore of the mainland.
0:34:35 > 0:34:37And it supports a creature
0:34:37 > 0:34:40that ancient mariners once mistook for mermaids.
0:34:44 > 0:34:49Gathering in herds of a hundred or more are dugongs or "sea cows".
0:34:49 > 0:34:51They're relatives of elephants.
0:35:04 > 0:35:07Each one can weigh nearly half a tonne
0:35:07 > 0:35:10and munch through 40 kilos of sea grass a day.
0:35:32 > 0:35:34Dugongs were once abundant
0:35:34 > 0:35:37but they've had a difficult relationship with people.
0:35:38 > 0:35:41Nowadays they're trapped accidentally in fishing nets
0:35:41 > 0:35:43and shark protection barriers
0:35:43 > 0:35:46and traditionally aboriginal hunters targeted them
0:35:46 > 0:35:51because they taste good, like prime beef.
0:35:54 > 0:35:58And recovery of a population is slow.
0:35:58 > 0:36:02A single baby is born every three to seven years.
0:36:03 > 0:36:05And this baby dugong
0:36:05 > 0:36:09may not be old enough to breed until she's 17 years old.
0:36:16 > 0:36:19A combination of all these factors means the population
0:36:19 > 0:36:24in the southern part of the reef has halved in the last decade.
0:36:24 > 0:36:29Now there are just 11,000 left in the entire Great Barrier Reef region,
0:36:29 > 0:36:32yet there are still more dugongs in Australian waters
0:36:32 > 0:36:34than any other place on Earth.
0:36:44 > 0:36:48Dugongs are not the only animals to feed on sea grass.
0:36:48 > 0:36:51Young green turtles like it too.
0:37:05 > 0:37:10He's after the most tender shoots
0:37:10 > 0:37:14and this is his exclusive patch.
0:37:25 > 0:37:29He's very choosy about what he likes
0:37:29 > 0:37:31and what he doesn't.
0:37:36 > 0:37:37Like your lawn,
0:37:37 > 0:37:41sea grass needs to be constantly cut short for healthy growth,
0:37:41 > 0:37:44so he's actually farming his own little plot
0:37:44 > 0:37:48that he'll tend for several months before moving on.
0:37:54 > 0:37:58Sea grass meadows are also nurseries for baby fish,
0:37:58 > 0:38:00like these domino damselfish.
0:38:05 > 0:38:07They won't stay here forever.
0:38:08 > 0:38:10When they're bigger,
0:38:10 > 0:38:14they won't be able to hide amongst the slender stems,
0:38:14 > 0:38:18and they'll look for a better hiding place, maybe one even closer to land.
0:38:25 > 0:38:30Where the sea meets the coast, saltwater meets the freshwater
0:38:30 > 0:38:32from rivers and streams.
0:38:36 > 0:38:40But one doesn't suddenly become the other.
0:38:41 > 0:38:45The water mixes slowly, creating a world unlike either,
0:38:45 > 0:38:48but connected to both.
0:38:53 > 0:38:56It's here that you'll find a special group of plants.
0:39:05 > 0:39:07Fringing the coast of the mainland
0:39:07 > 0:39:11is a habitat that has a profound impact on the ecosystem of the reef.
0:39:11 > 0:39:15They're plants that have cracked a neat evolutionary trick.
0:39:15 > 0:39:17They can live in brackish environments,
0:39:17 > 0:39:21which is a combination of salt and fresh water.
0:39:21 > 0:39:22They're the mangroves.
0:39:25 > 0:39:28They grow where no other trees are able to.
0:39:31 > 0:39:35Twice a day, the tide floods their roots with saltwater.
0:39:46 > 0:39:51At the same time, water from rivers flows through the mangroves
0:39:51 > 0:39:55and their lattice of roots acts like a giant tea strainer,
0:39:55 > 0:40:01slowing it down so that any sediments washed off the land can settle out.
0:40:06 > 0:40:11Bacteria break down the trapped sediment and other organic material
0:40:11 > 0:40:15helping create tonnes and tonnes of sticky mud.
0:40:18 > 0:40:21A whole new home for wildlife.
0:40:28 > 0:40:30In a perfect world mud should be thick,
0:40:30 > 0:40:33glutinous and as rich as dark chocolate.
0:40:33 > 0:40:37And it should also stink to high heaven.
0:40:37 > 0:40:41But this is extremely important stuff to the Great Barrier Reef.
0:40:41 > 0:40:47One teaspoon full of this mud contains ten million bacteria.
0:40:50 > 0:40:54All those bacteria are potential food.
0:40:54 > 0:40:58And although there aren't many species that eat mud directly,
0:40:58 > 0:41:01those that do, operate in large numbers.
0:41:06 > 0:41:11Legions of creatures perform the unglamorous but crucial task
0:41:11 > 0:41:12of breaking down the gloop.
0:41:23 > 0:41:27Mud whelks and fiddler crabs both eat the mud
0:41:27 > 0:41:31and their waste is the vital product that spawns an entire food chain.
0:41:38 > 0:41:42Once it's in the water, clouds of shrimp devour it.
0:41:45 > 0:41:48The nutrients that started in the mud are now swimming around
0:41:48 > 0:41:51in small, easy to catch parcels.
0:42:05 > 0:42:09All this food makes the mangrove a great place for fish,
0:42:09 > 0:42:14small residents, as well as youngsters that will one day move out
0:42:14 > 0:42:15to the Barrier Reef.
0:42:22 > 0:42:25Reef species like these rabbit fish may look big
0:42:25 > 0:42:29but they're still only one third of their adult size.
0:42:31 > 0:42:35These snappers also have some growing up to do before they leave.
0:42:40 > 0:42:43And these young trevally will grow up one day
0:42:43 > 0:42:46and be major predators on the outer reef.
0:42:48 > 0:42:53The mangroves, sea grass meadows and the soft coral oases
0:42:53 > 0:42:56are vital nurseries for so many fish on the reef,
0:42:56 > 0:42:59and they all provide two things,
0:42:59 > 0:43:01food and shelter.
0:43:05 > 0:43:08The complexity of the mangrove root system
0:43:08 > 0:43:11makes it a perfect haven for small and juvenile fish.
0:43:11 > 0:43:15The reason is, the latticework of the roots as they cross
0:43:15 > 0:43:18means it's a very difficult for large predators to manoeuvre
0:43:18 > 0:43:21and actually get at the smaller fish.
0:43:26 > 0:43:31But predators like these young blacktip reef sharks hide here too.
0:43:31 > 0:43:33They hunt at the edge of the mangroves,
0:43:33 > 0:43:36but they can't get deep into the tangle of roots.
0:43:42 > 0:43:46So the young reef fish are safe, for now.
0:43:47 > 0:43:51So, it's a great environment for the small fish to actually grow up in,
0:43:51 > 0:43:52to get big and strong,
0:43:52 > 0:43:56before they make the big move to open sea and the reef beyond.
0:44:01 > 0:44:04But when they leave the safety of the mangroves
0:44:04 > 0:44:06they must cross that sandy desert
0:44:06 > 0:44:09and the many hazards waiting for them in the lagoon.
0:44:22 > 0:44:25This is a mantis shrimp.
0:44:37 > 0:44:41From his neatly kept burrow, he surveys the world
0:44:41 > 0:44:44with the most complex visual system known to science.
0:44:53 > 0:44:56He's about the size of a man's forearm.
0:45:02 > 0:45:05And he's got quite a reach.
0:45:18 > 0:45:22Even if a young fish avoids the dangers on the seabed,
0:45:22 > 0:45:25there are plenty more predators floating above.
0:45:27 > 0:45:29Patrolling these inshore waters
0:45:29 > 0:45:33is probably the most dangerous animal in the lagoon.
0:45:35 > 0:45:37The box jellyfish,
0:45:37 > 0:45:40whose stinging tentacles are quite capable of killing a person.
0:45:44 > 0:45:48This creature is much more than a passive drifter.
0:45:48 > 0:45:51It can move has as fast as an Olympic swimmer
0:45:51 > 0:45:53and it has 24 eyes,
0:45:53 > 0:45:56each complete with a lens that can form a detailed image.
0:46:02 > 0:46:05It uses its tentacles like a trawl net,
0:46:05 > 0:46:11when a fish makes contact, thousands of microscopic stinging capsules
0:46:11 > 0:46:15explode into the prey's body, flooding it with paralysing venom.
0:46:24 > 0:46:26The fish is killed quickly,
0:46:26 > 0:46:30and then hauled into the mouth on the underside of the bell.
0:46:36 > 0:46:39All of the habitats we've seen so far
0:46:39 > 0:46:41have an obvious connection to the lagoon,
0:46:41 > 0:46:44but there's one place that couldn't be more different
0:46:44 > 0:46:48from the underwater world, that's critically important
0:46:48 > 0:46:51to the vigour of the Great Barrier Reef ecosystem.
0:46:56 > 0:46:59It's the tropical rainforest.
0:47:00 > 0:47:03The Queensland rainforest is the oldest in the world,
0:47:03 > 0:47:06it's older even than the Congo and even the Amazon.
0:47:06 > 0:47:09And this is one of the most impressive trees in it.
0:47:09 > 0:47:12This giant fig has strangled its original host
0:47:12 > 0:47:15and now dominates this immediate environment.
0:47:15 > 0:47:17It's an ecosystem in its own right.
0:47:17 > 0:47:19But you might be asking yourself,
0:47:19 > 0:47:21"What has this tree got in common with the reef?"
0:47:21 > 0:47:24But, in fact, it's directly linked.
0:47:24 > 0:47:28The rainforest all around me and indeed swamps and mangroves
0:47:28 > 0:47:30are critical for the health of the reef.
0:47:33 > 0:47:37These huge tracts of rainforest close to the Queensland coast
0:47:37 > 0:47:40are essential because they regulate the flow of water
0:47:40 > 0:47:42and the sediment it contains.
0:47:44 > 0:47:48That's important, because there's an awful lot of water here.
0:48:29 > 0:48:34Hot, humid tropical air gives rise to vast amounts of rainfall.
0:48:34 > 0:48:37It pours for at least 120 days a year
0:48:37 > 0:48:41and as much as 60 centimetres can fall in a single day.
0:48:45 > 0:48:48It's one of the wettest places on Earth.
0:49:01 > 0:49:03Left unchecked by the forest
0:49:03 > 0:49:07the water would wash out sediments and smother marine life,
0:49:07 > 0:49:12but the waterways flowing off the rainforest are relatively clear,
0:49:12 > 0:49:14and many are spectacular.
0:50:06 > 0:50:09When sediments are released slowly, the nutrients in them
0:50:09 > 0:50:13help sustain life in the lagoon, so everything flourishes.
0:50:22 > 0:50:24Where conditions are just right,
0:50:24 > 0:50:27corals manage to grow right next to the coast.
0:50:34 > 0:50:37Here, pristine tropical rainforest
0:50:37 > 0:50:39grows right down to the waters edge,
0:50:39 > 0:50:42a stone's throw from a coral reef.
0:50:48 > 0:50:51It's a place where two worlds meet
0:50:51 > 0:50:54and animals from the reef and the rainforest
0:50:54 > 0:50:56can be found right next to each other.
0:51:04 > 0:51:08These footprints belong to one of the biggest land animals in Australia.
0:51:15 > 0:51:16The cassowary.
0:51:19 > 0:51:23A flightless bird that's almost as tall as a person.
0:51:25 > 0:51:28Its claws wouldn't look out of place on a dinosaur.
0:51:35 > 0:51:37And its kick is so violent,
0:51:37 > 0:51:42that the cassowary is said to be the world's most dangerous bird.
0:51:55 > 0:51:59A parent is particularly dangerous when rearing a chick.
0:52:11 > 0:52:13In fact, the cassowary is shy,
0:52:13 > 0:52:17and is rarely seen in the wild.
0:52:17 > 0:52:19But it's a key animal here.
0:52:19 > 0:52:23It feeds on the fruits of rainforest trees and shrubs,
0:52:23 > 0:52:27it's one of the few animals that spread their seeds.
0:52:29 > 0:52:33The seeds of many forest trees can't germinate
0:52:33 > 0:52:35without animals like the cassowary.
0:52:38 > 0:52:41As the forest is directly linked to the reef
0:52:41 > 0:52:44by regulating sediments entering the lagoon,
0:52:44 > 0:52:48the cassowary contributes to the health of the reef itself.
0:52:51 > 0:52:54But there are now less than 2000 living here
0:52:54 > 0:52:57and they're becoming rarer all the time.
0:53:00 > 0:53:02Before European settlers arrived
0:53:02 > 0:53:05much of the coast here was covered in forest
0:53:05 > 0:53:07and a lot of that was jungle just like this,
0:53:07 > 0:53:10this is a vibrant ecosystem in its own right.
0:53:10 > 0:53:14It's full of reptiles and birds, as you can hear all around me.
0:53:14 > 0:53:18But today things have changed significantly.
0:53:18 > 0:53:22Much of coastline that abuts the great Barrier Reef,
0:53:22 > 0:53:2580% of it, in fact, has been cleared for agriculture
0:53:25 > 0:53:28and much of that has been totally cleared for sugar cane.
0:53:28 > 0:53:32Obviously this has a dramatic impact on the terrestrial environment,
0:53:32 > 0:53:35but it also has a significant effect on the reef itself.
0:53:39 > 0:53:41And it's not only crops.
0:53:41 > 0:53:45Cattle ranches, fish farms, six large coastal cities
0:53:45 > 0:53:48and many holiday resorts along the coast
0:53:48 > 0:53:51all have an impact on the reef system.
0:53:58 > 0:54:03Without the natural vegetation controlling the movement of water
0:54:03 > 0:54:05and the sediment it carries,
0:54:05 > 0:54:07heavy rain now washes millions of tonnes of silt,
0:54:07 > 0:54:11often laced with damaging fertilisers and pesticides
0:54:11 > 0:54:13straight into the lagoon.
0:54:16 > 0:54:19Sediment plumes can be so extensive,
0:54:19 > 0:54:23they sometimes spread all the way to the outer reef.
0:54:24 > 0:54:26In the sea grass meadows,
0:54:26 > 0:54:30the fine silt shrouds the light-dependant plants,
0:54:30 > 0:54:35and fertilizers feed algal blooms that choke the life from them.
0:54:36 > 0:54:39When the meadows die, the turtles, dugongs
0:54:39 > 0:54:43and baby fish that depend on them die too.
0:54:44 > 0:54:46Near the shore, the water can be so murky
0:54:46 > 0:54:48that less light reaches the corals,
0:54:48 > 0:54:51so most fringing reefs have also disappeared.
0:55:00 > 0:55:03All of these habitats are interdependent.
0:55:04 > 0:55:08If you ruin one, it can have an impact on many others.
0:55:09 > 0:55:12And that includes the outer reef itself.
0:55:14 > 0:55:19To look after all of these habitats, the Great Barrier Reef Marine Park
0:55:19 > 0:55:23sits at the heart of a network of protected areas.
0:55:23 > 0:55:26All interconnected and covering a vast area.
0:55:39 > 0:55:43After all, the reef is an inspiration to people all over the world.
0:55:46 > 0:55:50It attracts one and a half million visitors each year
0:55:50 > 0:55:54who come to see the largest coral reef on earth.
0:56:06 > 0:56:09Together with divers, yachtsmen and anglers,
0:56:09 > 0:56:15they inject seven billion dollars a year into the local economy.
0:56:19 > 0:56:24But the value to Australia is even greater than that.
0:56:25 > 0:56:28Towns and cities along much of the Queensland coast
0:56:28 > 0:56:33are not washed into the Pacific Ocean because the reef protects them.
0:56:36 > 0:56:41It means the Barrier Reef is so much more than just a coral reef.
0:56:51 > 0:56:55And there are vast tracts of rainforests, mangrove swamps,
0:56:55 > 0:57:01sea grass meadows and soft coral oases in a deep-water lagoon.
0:57:01 > 0:57:05It's truly an extraordinary place.
0:57:06 > 0:57:10And, the reef's influence goes far beyond Australian waters.
0:57:12 > 0:57:16It's vital to wildlife from many other parts of the world.
0:57:19 > 0:57:24Wave after wave of voyagers arrive here from across the ocean.
0:57:24 > 0:57:28From the islands of the South Pacific,
0:57:28 > 0:57:30from the Asian mainland...
0:57:34 > 0:57:39And from as far away as the icy seas of Antarctica.
0:57:51 > 0:57:53These wildlife visitors create
0:57:53 > 0:57:56some of the most impressive natural spectacles
0:57:56 > 0:57:58on the Great Barrier Reef.
0:58:04 > 0:58:08And all this is the subject of the next programme.
0:58:36 > 0:58:39Subtitles by Red Bee Media Ltd
0:58:39 > 0:58:44E-mail subtitling@bbc.co.uk