0:00:04 > 0:00:05In this series,
0:00:05 > 0:00:09I have travelled the length and breadth of the Great Barrier Reef...
0:00:13 > 0:00:16..and used the latest techniques to watch its wildlife.
0:00:26 > 0:00:30But the reef has one more story to tell.
0:00:32 > 0:00:35The residents of this marine paradise
0:00:35 > 0:00:39have seen their habitat change rapidly within the last few decades.
0:00:41 > 0:00:43And time is running out for them.
0:00:48 > 0:00:51The Barrier Reef is facing one of the most serious challenges
0:00:51 > 0:00:54to its continued existence -
0:00:54 > 0:00:56the effect of human beings.
0:00:57 > 0:00:59But there is hope.
0:01:01 > 0:01:04This time, our research vessel, the Alucia,
0:01:04 > 0:01:07will be taking me to meet teams of scientists
0:01:07 > 0:01:10who are developing new ways to try and save it.
0:01:11 > 0:01:14And I'll be going to its deepest parts,
0:01:14 > 0:01:16where new discoveries are being made
0:01:16 > 0:01:19that might hold clues to its survival.
0:01:19 > 0:01:22Nobody has ever dived as deep as this before
0:01:22 > 0:01:24on the Great Barrier Reef.
0:01:26 > 0:01:31This is one of the greatest and most important ecosystems on the planet -
0:01:31 > 0:01:34and what happens here affects us all.
0:01:35 > 0:01:39So, what does the future hold for this complex wonder?
0:01:51 > 0:01:54I'm travelling along Australia's north east coast
0:01:54 > 0:01:55to look at one of the greatest
0:01:55 > 0:01:59and most splendid natural treasures that the world possesses -
0:01:59 > 0:02:02a chain of tropical islands and coral reefs
0:02:02 > 0:02:05that lies between the coast and the open ocean.
0:02:12 > 0:02:15I will never forget the first time I came here.
0:02:18 > 0:02:20YOUNGER DAVID: 'And what a world this was -
0:02:20 > 0:02:23'beneath me lay an endless landscape of coral,
0:02:23 > 0:02:26'of every conceivable colour and shape.'
0:02:38 > 0:02:42It was unimaginable then to think that we might ever lose the reef.
0:02:47 > 0:02:51But now, I've returned, and I can see that the reef is changing.
0:02:54 > 0:02:58In the last 30 years, almost half the coral has disappeared.
0:03:02 > 0:03:06The greatest concern now is that we might lose the reef altogether.
0:03:17 > 0:03:20Parts of the Great Barrier Reef still remain a mystery.
0:03:20 > 0:03:22Its immense size and remote depths
0:03:22 > 0:03:25make it extremely difficult to explore.
0:03:29 > 0:03:32But today, exciting new technology has made it possible
0:03:32 > 0:03:37to survey the entire reef from top to bottom.
0:03:37 > 0:03:40And that is revealing extraordinary things
0:03:40 > 0:03:43about the way in which the reef itself has evolved over time.
0:03:45 > 0:03:47By looking into the reef's past,
0:03:47 > 0:03:50we may discover something about its future.
0:03:52 > 0:03:56So, I'm meeting marine geologist Dr Robin Beaman.
0:03:58 > 0:04:00'He is on board the Alucia
0:04:00 > 0:04:03'and shows me some of his remarkable discoveries.'
0:04:04 > 0:04:08This is a depth model of the Great Barrier Reef -
0:04:08 > 0:04:10of the entire Great Barrier Reef.
0:04:10 > 0:04:12And there's a whole lot of different tools we use,
0:04:12 > 0:04:14the main one being multibeam echosounders,
0:04:14 > 0:04:17so it gives you a scan of the seafloor
0:04:17 > 0:04:22and we can actually map great areas of the continental shelf.
0:04:22 > 0:04:24This white part is land?
0:04:24 > 0:04:25That's right.
0:04:25 > 0:04:30So, everything that's coloured rainbow colours is under water.
0:04:30 > 0:04:33'By combining computer modelling and deep sea surveying,
0:04:33 > 0:04:36'Beaman has discovered new evidence
0:04:36 > 0:04:39'that the reef has already experienced great changes.'
0:04:42 > 0:04:44As a scientist - as geological scientists -
0:04:44 > 0:04:46we're trying to understand how the Great Barrier Reef
0:04:46 > 0:04:48has responded to changes in the past
0:04:48 > 0:04:51and there are clues there as to what the Great Barrier Reef has done,
0:04:51 > 0:04:55so if I zoom back, you can see, geologically,
0:04:55 > 0:04:57it's gone through some dramatic changes.
0:05:01 > 0:05:05Beaman's scans showed traces of an ancient reef
0:05:05 > 0:05:08that thrived over the last half million years
0:05:08 > 0:05:11and is now hidden along the edge of this great drop-off.
0:05:14 > 0:05:18This earlier reef existed long before the one we know today.
0:05:18 > 0:05:20It lay up to 70 metres deep
0:05:20 > 0:05:24and stretched nearly unbroken for more than 500 miles.
0:05:27 > 0:05:30It's been described as the world's largest fossil.
0:05:33 > 0:05:36This is what the older Great Barrier Reef looked like.
0:05:36 > 0:05:38And we call these "drowned reefs" -
0:05:38 > 0:05:41they're drowned in the sense that the water over them is so deep
0:05:41 > 0:05:43that the reef no longer grows.
0:05:45 > 0:05:48These ancient reefs were drowned by dramatic climate changes
0:05:48 > 0:05:50that caused sea levels to rise.
0:05:52 > 0:05:55This last happened less than 14,000 years ago.
0:05:56 > 0:06:00So, water released from the melting icecaps
0:06:00 > 0:06:03- is going to start flooding across here, is it?- That's right.
0:06:03 > 0:06:06The sea level was high enough to actually inundate
0:06:06 > 0:06:08and cover these old limestone hills
0:06:08 > 0:06:12and created the Great Barrier Reef that we know today.
0:06:12 > 0:06:15So, the changes that we're seeing going on now
0:06:15 > 0:06:18are nothing new, in terms of change.
0:06:18 > 0:06:21I mean, the Barrier Reef has always been changing.
0:06:21 > 0:06:23We do find it's quite robust.
0:06:23 > 0:06:24It has actually reformed,
0:06:24 > 0:06:30despite these catastrophic changes that have occurred.
0:06:31 > 0:06:36It's been exposed and flooded at least four times that we know of.
0:06:36 > 0:06:38To us, it's astounding.
0:06:41 > 0:06:44This new insight into the ancient history of the reef
0:06:44 > 0:06:48shows that, given enough time, it can regenerate.
0:06:53 > 0:06:56It seems that if seawater is clear and warm,
0:06:56 > 0:06:58simple organisms will eventually evolve
0:06:58 > 0:07:01that can build limestone homes to protect themselves
0:07:01 > 0:07:03from the waves and their enemies.
0:07:05 > 0:07:10But most of these events started long before human beings appeared on Earth
0:07:10 > 0:07:13and took many thousands of years to complete.
0:07:16 > 0:07:20We now know the reef has dwindled and recovered
0:07:20 > 0:07:23many times in its long history,
0:07:23 > 0:07:27but it also has to withstand a major change every 24 hours,
0:07:27 > 0:07:30as the tide retreats and comes back.
0:07:35 > 0:07:38At low tide, the water drains away very quickly,
0:07:38 > 0:07:42leaving the topmost community of creatures dangerously exposed.
0:07:48 > 0:07:50Some are washed out with the tide.
0:07:56 > 0:07:58Others swim to safety.
0:08:01 > 0:08:03But the coral polyps can't move.
0:08:08 > 0:08:10Temperatures on the surface of the reef
0:08:10 > 0:08:13can now reach a scorching 30 degrees centigrade.
0:08:16 > 0:08:19The exposed corals could easily dry out
0:08:19 > 0:08:22and be damaged by intense ultraviolet rays.
0:08:24 > 0:08:27But corals have ways of protecting themselves.
0:08:29 > 0:08:33When exposed to air, they produce huge amounts of mucus,
0:08:33 > 0:08:36which keeps them wet and acts like a sunscreen.
0:08:38 > 0:08:43This remarkable slime actually increases its UV resistance,
0:08:43 > 0:08:45becoming stronger if the temperatures soar.
0:08:47 > 0:08:52So, the coral manages to survive for the few hours that it's out of water.
0:08:55 > 0:09:00But there's one fish that manages to turn this exposure to its advantage.
0:09:13 > 0:09:18The epaulette shark remains on the reef even when the tide goes out.
0:09:18 > 0:09:20Of course, with so little water,
0:09:20 > 0:09:23it doesn't get as much oxygen as it requires normally,
0:09:23 > 0:09:27but it deals with that possibility by shutting off a part of its brain
0:09:27 > 0:09:30and so, reducing its oxygen demands.
0:09:31 > 0:09:35As the retreating tide exposes the topmost branches of the corals,
0:09:35 > 0:09:39the shark remains in the little pools between them for as long as it can.
0:09:42 > 0:09:46And then, it sets off to try and find food -
0:09:46 > 0:09:51shrimps, crabs and small worms that live on the reef.
0:09:51 > 0:09:55And it does that by exploiting another talent it has.
0:09:55 > 0:09:57It can, in effect, walk.
0:10:10 > 0:10:14It may be slow-going, but the little shark manages to make its way
0:10:14 > 0:10:18between the rocky pools to look for prey that may be imprisoned in them.
0:10:26 > 0:10:28It has the run of the place,
0:10:28 > 0:10:31until the tide returns once more to flood the reeftop.
0:10:46 > 0:10:50So, the inhabitants of the reef, each in its own way,
0:10:50 > 0:10:53deal with the daily hazards brought by exposure.
0:11:00 > 0:11:03But there is one catastrophe that can strike each year
0:11:03 > 0:11:05against which there is no defence.
0:11:14 > 0:11:15From November onwards,
0:11:15 > 0:11:18warm, moisture-laden winds from the northwest
0:11:18 > 0:11:22sweep down across these tropic seas
0:11:22 > 0:11:24and it's then that cyclones form.
0:11:27 > 0:11:32They are, in fact, the biggest killers of the reef's corals.
0:11:34 > 0:11:38But that doesn't mean that the corals are permanently destroyed.
0:11:38 > 0:11:41Their resilience once more comes apparent.
0:11:45 > 0:11:49And there's an extraordinary example of that
0:11:49 > 0:11:51in the most unlikely of places.
0:12:07 > 0:12:11This is the wreck of the SS Yongala.
0:12:14 > 0:12:17It was sunk by a cyclone in 1911.
0:12:23 > 0:12:27It lies 30 metres below the surface on a barren, sandy plain...
0:12:31 > 0:12:34..miles away from any natural coral reefs.
0:12:39 > 0:12:42By the time it was discovered, decades later,
0:12:42 > 0:12:44it had become an artificial reef...
0:12:47 > 0:12:51..and had been colonised by an extraordinary variety of life.
0:12:57 > 0:13:00It was an oasis in the featureless ocean.
0:13:16 > 0:13:18But in the century since it sank,
0:13:18 > 0:13:22the wreck has been hit repeatedly by more cyclones.
0:13:27 > 0:13:29The waters here are not deep
0:13:29 > 0:13:34so the turbulence created by a cyclone can reach the sea floor.
0:13:43 > 0:13:46THUNDERCLAP
0:13:52 > 0:13:55Cyclones travelling towards the coast
0:13:55 > 0:13:57can rip up hundreds of miles of coral.
0:14:02 > 0:14:06Captain Trevor Jackson, who has been diving on this wreck for decades,
0:14:06 > 0:14:13saw the devastating effects caused in 2011 by a category five cyclone.
0:14:14 > 0:14:16Cyclone Yahtzee, a massive system,
0:14:16 > 0:14:19crossed the coast just north of here.
0:14:19 > 0:14:20The cyclone was so large,
0:14:20 > 0:14:23it generated waves that exposed the top of the Yongala.
0:14:28 > 0:14:31THUNDERCLAP
0:14:40 > 0:14:42There was a lifting action...
0:14:45 > 0:14:46..and in the process,
0:14:46 > 0:14:49this scoured the top of the reef of all marine life.
0:15:01 > 0:15:06What was once a thriving ecosystem was now an almost bare skeleton.
0:15:10 > 0:15:13But amazingly, the reef on the Yongala
0:15:13 > 0:15:16began to repair itself within months.
0:15:21 > 0:15:23Green algae appeared on the wreck.
0:15:25 > 0:15:28Barnacles followed, allowing corals to get a grip.
0:15:36 > 0:15:39And soon, a new community had established itself.
0:16:05 > 0:16:08One of the things that makes the Yongala so unique
0:16:08 > 0:16:12is the way it rejuvenates itself after a major weather event.
0:16:12 > 0:16:15In the course of the last four or five years,
0:16:15 > 0:16:17about 80% of the reef has re-grown.
0:16:26 > 0:16:30The story of the Yongala shows that a coral reef can, remarkably,
0:16:30 > 0:16:32recover from natural disaster.
0:16:43 > 0:16:46And such recovery can be surprisingly quick
0:16:46 > 0:16:49when a reef is healthy and in balance.
0:16:52 > 0:16:55Most of the reef's inhabitants depend on one another for survival.
0:17:12 > 0:17:15But it is the coral that is the foundation of the reef
0:17:15 > 0:17:19and it plays a crucial role in many of the relationships.
0:17:28 > 0:17:32This is the crown-of-thorns starfish.
0:17:34 > 0:17:37For it, coral is food
0:17:37 > 0:17:40and it will eat relentlessly if not kept in check.
0:17:41 > 0:17:43But to other creatures, like the guard crab,
0:17:43 > 0:17:45coral is home.
0:17:50 > 0:17:53The crab is prepared to defend its patch
0:17:53 > 0:17:57from the carnivorous starfish at all costs.
0:18:02 > 0:18:03The crown-of-thorns, however,
0:18:03 > 0:18:06is much larger than most other starfish on the reef,
0:18:06 > 0:18:11so the tiny crab is forced to take a more stealthy approach.
0:18:15 > 0:18:19Hidden within the coral, it waits for its moment to attack.
0:18:34 > 0:18:37The starfish has left itself dangerously exposed,
0:18:37 > 0:18:40but the crab is cautious.
0:18:44 > 0:18:47When it can, the crab uses its powerful pincers
0:18:47 > 0:18:51to snip at the starfish's spines and tube-like feet...
0:19:04 > 0:19:08..before retreating back into the safety of the coral.
0:19:10 > 0:19:12The crab has won this battle.
0:19:15 > 0:19:17But recently, something has changed
0:19:17 > 0:19:19and the balance has been upset.
0:19:23 > 0:19:26The number of crown-of-thorns has increased dramatically
0:19:26 > 0:19:29and they've become a big problem on the reef.
0:19:35 > 0:19:37To find out more,
0:19:37 > 0:19:41the Alucia is taking me to a research station in the far north of the reef.
0:19:50 > 0:19:55It's situated on Lizard Island, where we can observe this problem up close.
0:20:00 > 0:20:04Lizard is surrounded by some of the most spectacular reefs
0:20:04 > 0:20:06on the entire barrier.
0:20:07 > 0:20:11But they are under attack from the coral-eating starfish.
0:20:13 > 0:20:16And at the island's research station,
0:20:16 > 0:20:20they've been studying why we might be seeing more of them than we used to.
0:20:29 > 0:20:32They have an extraordinary ability
0:20:32 > 0:20:37to suddenly increase vastly in numbers, like a plague.
0:20:37 > 0:20:41There have been three such plagues since the 1960s
0:20:41 > 0:20:43and, unfortunately,
0:20:43 > 0:20:46it seems as though we're in the middle, now, of a fourth.
0:20:48 > 0:20:52You might think that these plagues are just another natural disaster
0:20:52 > 0:20:55that the reef has had to withstand, like cyclones.
0:20:55 > 0:20:58There are reasons to suppose that, in fact,
0:20:58 > 0:21:01the plagues have been affected by human activity -
0:21:01 > 0:21:06either through an accumulation of run-off of fertilisers from the land
0:21:06 > 0:21:10that creates more food for the young starfish,
0:21:10 > 0:21:12or because we have overfished
0:21:12 > 0:21:15and so destroyed the natural balance of the reef.
0:21:16 > 0:21:20The starfish outbreaks have been responsible
0:21:20 > 0:21:23for over 40% of the coral loss of the last 30 years.
0:21:24 > 0:21:29It's just one of the huge changes here witnessed by Dr Charlie Veron.
0:21:31 > 0:21:33In 1972, Charlie was appointed
0:21:33 > 0:21:37the reef's first full-time coral scientist.
0:21:37 > 0:21:40He's gone on to become a world authority on coral
0:21:40 > 0:21:43and has identified a third of the world's known species.
0:21:45 > 0:21:49He was one of the first scientists to spend time in this underwater world
0:21:49 > 0:21:52and that was due to a particular piece of technology.
0:21:54 > 0:21:58What we knew about corals at the beginning of the scuba era
0:21:58 > 0:22:00was just almost nothing.
0:22:00 > 0:22:03So, scuba gear must have changed things radically.
0:22:03 > 0:22:05It changed everything.
0:22:05 > 0:22:07When you went down the face of a coral reef,
0:22:07 > 0:22:11you could see how corals fed, how they fought each other,
0:22:11 > 0:22:13how they reproduced and still,
0:22:13 > 0:22:15we're only just scratching the surface.
0:22:15 > 0:22:18Think of all the things that happen in a rainforest,
0:22:18 > 0:22:19how much we know about it.
0:22:19 > 0:22:22We haven't got a thousandth part of that information on the coral reef yet.
0:22:22 > 0:22:25'But since Charlie's first discoveries,
0:22:25 > 0:22:27'the reef has altered dramatically.'
0:22:27 > 0:22:33I've been going back to the same spots 10, 20, 30, 40 years ago
0:22:33 > 0:22:36and every time I go back,
0:22:36 > 0:22:39I'm sickened by some of the changes I've seen.
0:22:39 > 0:22:42Sometimes, I go back, I know it's the same spot
0:22:42 > 0:22:43and I can barely recognise it.
0:22:43 > 0:22:46Some species have been wiped out in the shallows now.
0:22:46 > 0:22:48It's already happened.
0:22:50 > 0:22:54What Charlie had witnessed were the effects of mankind upon the reef.
0:22:58 > 0:23:03When I myself first visited the Queensland coast almost 60 years ago,
0:23:03 > 0:23:05it was very different.
0:23:14 > 0:23:17Since then, like many coastlines around the world,
0:23:17 > 0:23:20there has been a massive increase in population
0:23:20 > 0:23:22and an explosion of industry.
0:23:37 > 0:23:42By 1975, the reef had been declared a National Marine Park.
0:23:42 > 0:23:46It was the biggest one of its kind in the world.
0:23:46 > 0:23:49But then, a new threat began to be recognised -
0:23:49 > 0:23:53not only to the reef, but to the world's oceans -
0:23:53 > 0:23:54climate change.
0:23:56 > 0:24:00THUNDERCLAPS
0:24:02 > 0:24:06There is more carbon dioxide in our atmosphere now
0:24:06 > 0:24:09than there has been in 800,000 years.
0:24:12 > 0:24:15Industrialised nations have been burning fossil fuels
0:24:15 > 0:24:17at an alarming rate.
0:24:19 > 0:24:22Global warming is slowly heating up our planet
0:24:22 > 0:24:24and threatens to cause huge problems for us all.
0:24:27 > 0:24:32Around 30% of the carbon dioxide we produce is absorbed by the ocean.
0:24:35 > 0:24:39As a result, we're seeing an increase in the temperature
0:24:39 > 0:24:40and acidity of our seas.
0:24:43 > 0:24:46Both are killing the inhabitants of the reef.
0:24:51 > 0:24:54But how quickly is it being damaged?
0:24:57 > 0:25:02To find out, I'm heading to meet Professor Ove Hoegh-Guldberg
0:25:02 > 0:25:05He's studying the effects of climate change on coral.
0:25:10 > 0:25:12Ove is based on Heron Island,
0:25:12 > 0:25:16near the southern end of the Great Barrier.
0:25:16 > 0:25:20Heron is a low, sandy island, 50 miles out from the mainland,
0:25:20 > 0:25:22right on the reef itself...
0:25:24 > 0:25:28..so its research station is very well-placed.
0:25:29 > 0:25:32Here, Ove is carrying out an experiment
0:25:32 > 0:25:34to see how the reef is going to cope.
0:25:35 > 0:25:37At the research station here,
0:25:37 > 0:25:41the experiment we're running is really climate change sped up.
0:25:42 > 0:25:46Because it's often hard for people to really get their heads around
0:25:46 > 0:25:48when you talk about global change over decades
0:25:48 > 0:25:51and what might happen to coral reefs.
0:25:51 > 0:25:54We have, essentially, in these experiments, sped things up
0:25:54 > 0:25:56so that you can literally, over a year,
0:25:56 > 0:26:00see the impacts of what might be occurring over the next hundred.
0:26:03 > 0:26:07Each of these tanks contains a miniature coral reef
0:26:07 > 0:26:09with the same species of coral.
0:26:09 > 0:26:11But each is being subjected to
0:26:11 > 0:26:15slightly different conditions of temperature and acidity -
0:26:15 > 0:26:19the two factors that are most likely to alter with climate change.
0:26:24 > 0:26:29Using these tanks, scientists have shown that increasing acidity
0:26:29 > 0:26:32restricts hard corals from building their limestone skeletons.
0:26:35 > 0:26:37And a rise in temperature -
0:26:37 > 0:26:40a single degree centigrade warmer than normal -
0:26:40 > 0:26:42can cause corals to become so stressed
0:26:42 > 0:26:45that they eject the photosynthesising algae
0:26:45 > 0:26:48that enable them to grow and give some colour.
0:26:53 > 0:26:57So they bleach, turning ghostly white.
0:27:07 > 0:27:09If you go back in time,
0:27:09 > 0:27:13you can see the big swings between ice ages and the warm periods
0:27:13 > 0:27:16where the Great Barrier Reef disappears and regrows
0:27:16 > 0:27:18and that's happened numerous times.
0:27:18 > 0:27:21So, we've always had changes,
0:27:21 > 0:27:25but we're talking about changes over 10,000 years, in those cases.
0:27:25 > 0:27:29But we're now seeing is the equivalent in a few decades.
0:27:29 > 0:27:32And that, of course, is stretching life's capacity to keep up.
0:27:39 > 0:27:44Organisms, ecosystems are falling behind as the world changes,
0:27:44 > 0:27:47faster than it has in this enormous amount of time.
0:27:53 > 0:27:58It's been shown here that a rise of just two degrees centigrade
0:27:58 > 0:28:01will turn a healthy reef into a decimated one.
0:28:02 > 0:28:06And such a rise will almost certainly happen in these seas
0:28:06 > 0:28:09if we continue to do what we are doing.
0:28:19 > 0:28:21As Ove's tests suggest,
0:28:21 > 0:28:24this man-made problem has reached the point
0:28:24 > 0:28:26where it needs a man-made solution.
0:28:31 > 0:28:33I'm returning to mainland Australia
0:28:33 > 0:28:36to meet the scientists who are approaching this problem
0:28:36 > 0:28:37in a radically new way.
0:28:39 > 0:28:44The Australian Institute of Marine Science, AIMS,
0:28:44 > 0:28:47is based in northeast Queensland, right on the coast.
0:28:51 > 0:28:55Here, pioneering research is pushing the boundaries of coral science.
0:29:00 > 0:29:04Over three million litres of filtered seawater
0:29:04 > 0:29:07are pumped through these tanks every day.
0:29:08 > 0:29:11So, it's possible for scientists to study the minute
0:29:11 > 0:29:16and often very complex changes that can affect coral's health.
0:29:20 > 0:29:22So, here, they're also conducting research
0:29:22 > 0:29:25to see whether it might not be possible
0:29:25 > 0:29:29to devise techniques of restoring damaged reefs back to health.
0:29:31 > 0:29:35In these tanks, they can simulate the exact conditions of the reef.
0:29:37 > 0:29:40They've been so successful that remarkably,
0:29:40 > 0:29:44the corals respond to the same astronomic and seasonal rhythms
0:29:44 > 0:29:46as those out in the ocean.
0:29:49 > 0:29:53And that is proving useful for one particular experiment.
0:29:56 > 0:29:59Corals are usually able to adapt to changing circumstances,
0:29:59 > 0:30:01given enough time.
0:30:05 > 0:30:09And that is partly due to the way they reproduce.
0:30:12 > 0:30:14After the first full moon in October,
0:30:14 > 0:30:18the great synchronised coral spawning event begins.
0:30:38 > 0:30:42It's a wonderful, annual rejuvenation.
0:30:48 > 0:30:53Hundreds of species release sperm and eggs into the ocean.
0:30:57 > 0:31:01Just as pollen from plants is blown far and wide by the wind,
0:31:01 > 0:31:04so coral spawn is swept away by the ocean currents.
0:31:07 > 0:31:10And at the same time, under the same moonlight,
0:31:10 > 0:31:14the corals will spawn here in the laboratory tanks.
0:31:19 > 0:31:22Using red light, so as not to disturb the process,
0:31:22 > 0:31:25scientists wait for the moment of release.
0:31:39 > 0:31:41And when it finally happens,
0:31:41 > 0:31:44they move fast to collect the sperm and the eggs.
0:31:49 > 0:31:52It's their one chance to get all the samples they need
0:31:52 > 0:31:54for a year's worth of research.
0:31:57 > 0:32:00But what exactly are they planning to do with them?
0:32:03 > 0:32:08Here, Dr Madeleine van Oppen has been selectively breeding them,
0:32:08 > 0:32:13using much the same techniques that we've used to produce crops on land
0:32:13 > 0:32:16that are resistant to drought and disease.
0:32:16 > 0:32:18It's the first time that selective breeding
0:32:18 > 0:32:21has been used in marine conservation.
0:32:25 > 0:32:27They release their sperm and eggs in bundles
0:32:27 > 0:32:30and those bundles float to the surface of the tank.
0:32:30 > 0:32:34We then agitate that to separate the eggs from the sperm.
0:32:37 > 0:32:38And we use that to set up
0:32:38 > 0:32:41our specific in vitro processes, basically.
0:32:45 > 0:32:48In the ocean, there is the potential
0:32:48 > 0:32:51for different species of coral to breed with each other.
0:32:52 > 0:32:54So, here, scientists wonder
0:32:54 > 0:32:57if you might be able to produce a new kind of coral
0:32:57 > 0:33:01that proves more successful in the changing waters of the reef.
0:33:03 > 0:33:05The problem that corals are facing now is that
0:33:05 > 0:33:08the change of the environment is extremely fast -
0:33:08 > 0:33:10much faster than ever recorded -
0:33:10 > 0:33:12so we need to help them a little bit in the lab.
0:33:12 > 0:33:16We need to speed up those natural processes of evolution.
0:33:18 > 0:33:23Van Oppen's aim is to use selective breeding to produce strains of coral
0:33:23 > 0:33:27that are able to withstand the worst effects of climate change...
0:33:29 > 0:33:34..and to use them to bring life back to worst-affected part of the reef.
0:33:37 > 0:33:39Maybe in five years or so,
0:33:39 > 0:33:42we will be allowed to place those corals
0:33:42 > 0:33:45onto a real reef, a disturbed reef -
0:33:45 > 0:33:48and test it and these selectively-bred corals
0:33:48 > 0:33:50will be able to restore that reef faster.
0:33:51 > 0:33:55And you have to realise, this is really a last resort option.
0:33:55 > 0:33:58We wouldn't want to do that if the reef is able to restore itself.
0:34:04 > 0:34:08But is there a chance that the reef, damaged by our activities,
0:34:08 > 0:34:10could restore itself without our help?
0:34:13 > 0:34:15Well, we now think that there may be clues
0:34:15 > 0:34:18in the reef's most distant and mysterious regions.
0:34:25 > 0:34:28There are still parts of the Great Barrier Reef
0:34:28 > 0:34:31that are virtually unexplored.
0:34:31 > 0:34:35But today, we have got remarkable new underwater vessels,
0:34:35 > 0:34:38like this submersible, that can take us to places
0:34:38 > 0:34:42where no unprotected human being could possibly go.
0:34:42 > 0:34:47What they will find down there, nobody knows.
0:34:47 > 0:34:49But I'm lucky enough to be one of those
0:34:49 > 0:34:51who's about to go down to find out.
0:34:54 > 0:34:56At the outer edge of the reef,
0:34:56 > 0:35:01the continental shelf plunges down over 2,000 metres to the seafloor.
0:35:05 > 0:35:09The Alucia has brought us over the edge of the drop-off,
0:35:09 > 0:35:1290 miles out into the Coral Sea...
0:35:15 > 0:35:17..out to Osprey Reef.
0:35:19 > 0:35:23Here at Osprey, this sheer vertical drop of the seafloor
0:35:23 > 0:35:26enables us to see corals at a variety of depths.
0:35:28 > 0:35:31Between 100 and 150 metres down,
0:35:31 > 0:35:33daylight is reduced to a glimmer.
0:35:33 > 0:35:36This is the mesophotic zone.
0:35:36 > 0:35:40Here, a mysterious community of corals is thriving,
0:35:40 > 0:35:43despite the damage being done to the reef above.
0:35:43 > 0:35:46The Great Barrier Reef, it's a marvel beyond marvels.
0:35:46 > 0:35:51It's a million species living in this symbiotic tangle,
0:35:51 > 0:35:53half of which we don't know.
0:35:53 > 0:35:55I mean, when you get to mesophotic depths,
0:35:55 > 0:35:58we know very few of the species down there.
0:35:58 > 0:36:01It literally is one of the last frontiers of biology,
0:36:01 > 0:36:03to understand this system.
0:36:06 > 0:36:09Scientists are now beginning to wonder if these corals
0:36:09 > 0:36:14might have the potential to restore the damaged parts of the reef.
0:36:15 > 0:36:17- RADIO:- '..Down about 100 metres...'
0:36:23 > 0:36:25Our state-of-the-art submersible
0:36:25 > 0:36:29is going to take me to see these deep corals for myself
0:36:29 > 0:36:31and even bring back a sample.
0:36:36 > 0:36:38Nadir in position.
0:36:38 > 0:36:40Are we clear to vent?
0:36:40 > 0:36:43You are clear to vent, clear to vent.
0:36:43 > 0:36:45Roger. Venting now.
0:36:57 > 0:37:00We are descending into the twilight zone.
0:37:07 > 0:37:10As we drop down the face of the reef,
0:37:10 > 0:37:12the light begins to dim.
0:37:21 > 0:37:23At about 100 metres,
0:37:23 > 0:37:26we enter the mesophotic zone.
0:37:26 > 0:37:29"Mesophotic" literally means "middle light".
0:37:32 > 0:37:35The corals here are beginning to look very different.
0:37:37 > 0:37:40Despite the apparent lack of light down here,
0:37:40 > 0:37:44there's still enough for some corals to photosynthesise,
0:37:44 > 0:37:46just like their relations closer to the surface.
0:37:46 > 0:37:50And to do that, they've formed these flat, broad plates
0:37:50 > 0:37:53to collect what little light there is.
0:37:57 > 0:38:02Mesophotic corals lie mostly out of reach of cyclones and bleaching.
0:38:04 > 0:38:08So, one of the big questions facing scientists is,
0:38:08 > 0:38:13could these deeper corals naturally repopulate the damaged reefs above?
0:38:24 > 0:38:27We've now passed beyond the mesophotic zone.
0:38:31 > 0:38:33The light begins to disappear completely
0:38:33 > 0:38:36and the reef changes again.
0:38:47 > 0:38:50Most of the light that filters down from above
0:38:50 > 0:38:53comes from the blue end of the spectrum,
0:38:53 > 0:38:58so the rock surface ahead of me looks very dull.
0:38:58 > 0:39:01But turn on the lights and it looks very different.
0:39:25 > 0:39:27Despite their remoteness,
0:39:27 > 0:39:30these strange relatives of reef-building corals
0:39:30 > 0:39:33are still part of the great reef system.
0:39:35 > 0:39:38To understand how they're connected, we need to study them closely.
0:39:41 > 0:39:44So, this seems an excellent place to collect a sample.
0:39:47 > 0:39:51But manoeuvring our eight-tonne submersible close to the rock face
0:39:51 > 0:39:53is a delicate operation.
0:40:12 > 0:40:14Oh, that's great.
0:40:22 > 0:40:26The chances are that this could well be a species
0:40:26 > 0:40:28that no-one has ever seen before.
0:40:31 > 0:40:34But things don't go quite to plan.
0:40:36 > 0:40:39- Oh, no!- We're going to have to go and fetch that.
0:40:52 > 0:40:54There it is.
0:41:08 > 0:41:09Oh, terrific!
0:41:14 > 0:41:15Success!
0:41:25 > 0:41:28As we descend past the 200 metre mark,
0:41:28 > 0:41:32the coral finally begins to disappear altogether.
0:41:37 > 0:41:39Surface, surface, Nadir.
0:41:39 > 0:41:44My depth now, 300 metres. Over.
0:41:45 > 0:41:50At this depth, the pressure bearing down on the submersible's sphere
0:41:50 > 0:41:53is more than 30 times that at the surface.
0:41:55 > 0:41:59That's an incredible 450 pounds per square inch.
0:42:03 > 0:42:06Here, there's a sediment that is drifting down from above,
0:42:06 > 0:42:09cloaking the surface of the reef.
0:42:09 > 0:42:11That means it's very difficult for any organism
0:42:11 > 0:42:16to get a hold of the rock, because it's continually being swept down.
0:42:16 > 0:42:21The sediment itself is the result of the erosion of the coral skeletons from high above,
0:42:21 > 0:42:25but also from the remains of coral
0:42:25 > 0:42:28that parrot fish have munched and excreted
0:42:28 > 0:42:30and it's slowly drifting down here.
0:42:30 > 0:42:34So, this is so deep, it's almost barren.
0:42:44 > 0:42:46But not quite.
0:42:48 > 0:42:51At almost the deepest point of our dive,
0:42:51 > 0:42:53something pays us a visit.
0:42:56 > 0:42:59There's a fish to your right, David. On your shoulder.
0:42:59 > 0:43:01Look at this!
0:43:07 > 0:43:09It's a deep-water grouper.
0:43:09 > 0:43:13No-one has ever seen them up close like this, at this depth.
0:43:21 > 0:43:24'It appears to find the sub and its occupants fascinating.'
0:43:27 > 0:43:30And he's big, this boy. He must be...
0:43:32 > 0:43:35..four, five feet long - a couple of metres, almost.
0:43:38 > 0:43:39Hello.
0:43:39 > 0:43:41Oh, gosh!
0:43:45 > 0:43:49And why he is down here, what he's looking for - who knows?
0:43:56 > 0:43:58He's going up.
0:44:00 > 0:44:01So are we.
0:44:11 > 0:44:16As we ascend, light and colour returns to the reef around us.
0:44:58 > 0:45:02'Our on-board reef scientist, Professor Justin Marshall,
0:45:02 > 0:45:05'is on hand to retrieve the sample we gathered in the darkness.'
0:45:05 > 0:45:08- What do you reckon? - Well, it's fantastic.
0:45:08 > 0:45:12This is one of the deepest samples ever from Osprey Reef.
0:45:12 > 0:45:14- It's wonderful.- Will it survive? Will it still live?
0:45:14 > 0:45:17It will still live and we'll take samples back
0:45:17 > 0:45:20- to the University of Queensland and work on it there.- Great.
0:45:22 > 0:45:25In fact, they think this coral has never been reported
0:45:25 > 0:45:29in this part of the world before and may be new to science.
0:45:33 > 0:45:36We are a long way off from having a solution
0:45:36 > 0:45:39to the threats which now face the Great Barrier Reef.
0:45:41 > 0:45:43But in these deep water samples
0:45:43 > 0:45:46and in the scientists' experimental tanks,
0:45:46 > 0:45:48there is a small glimmer of hope.
0:45:51 > 0:45:53But time is not on our side -...
0:45:57 > 0:46:01..an opinion shared by many of the scientists I've met along the way.
0:46:05 > 0:46:08Are you fearful for the future of the reef?
0:46:08 > 0:46:10There will be change, for sure.
0:46:10 > 0:46:14I mean, we're seeing change within our own human lives' timescales now.
0:46:14 > 0:46:16And what's your prediction about
0:46:16 > 0:46:19what it's going to look like in another hundred years?
0:46:19 > 0:46:21The sea levels will be higher.
0:46:21 > 0:46:24We want to know - as a scientist, we want to know
0:46:24 > 0:46:26how the Great Barrier Reef will respond.
0:46:26 > 0:46:30Whether it has the resilience to bounce back
0:46:30 > 0:46:35with the future changes to the climate remains to be seen.
0:46:39 > 0:46:41Here on the Great Barrier Reef,
0:46:41 > 0:46:45we've lost about 50% of the coral since the early 1980s.
0:46:47 > 0:46:51Coral provides a habitat for over a million species.
0:46:51 > 0:46:54This is such a fundamental part of our oceans
0:46:54 > 0:46:57and the fact that it's going to disappear on our watch,
0:46:57 > 0:46:58it's incredible.
0:47:16 > 0:47:20When the Great Barrier Reef starts to go seriously backwards,
0:47:20 > 0:47:21the next generation is going to say,
0:47:21 > 0:47:25"Why didn't you guys do something about it when you had a chance?"
0:47:25 > 0:47:27And well may they ask that
0:47:27 > 0:47:30because we're not doing what we should be doing
0:47:30 > 0:47:32and we're going to pay the price.
0:47:51 > 0:47:54The Great Barrier Reef is in grave danger.
0:47:54 > 0:47:57The twin perils brought by climate change
0:47:57 > 0:48:02and increase in the temperature of the ocean and in its acidity
0:48:02 > 0:48:05threaten its very existence.
0:48:05 > 0:48:08If they continue to rise at the present rate,
0:48:08 > 0:48:11the reefs will be gone within decades.
0:48:11 > 0:48:15And that would be a global catastrophe.
0:48:18 > 0:48:22About one quarter of the species of fish in the world
0:48:22 > 0:48:25spend some part of their lives in the reefs.
0:48:25 > 0:48:29If the reefs go, the fish will also disappear.
0:48:30 > 0:48:33And that could affect the livelihood
0:48:33 > 0:48:36and diet of human communities worldwide.
0:48:38 > 0:48:42But there's surely another reason why we should protect the reefs.
0:48:42 > 0:48:46They are among this planet's richest, most complex
0:48:46 > 0:48:49and most beautiful ecosystems.
0:49:05 > 0:49:10Do we really care so little about the Earth on which we live
0:49:10 > 0:49:14that we don't wish to protect one of its greatest wonders
0:49:14 > 0:49:17from the consequences of our behaviour?
0:49:42 > 0:49:45For this series, the production team were determined
0:49:45 > 0:49:47to show the Barrier Reef in a new way,
0:49:47 > 0:49:50by filming in some of its most remote areas...
0:49:53 > 0:49:54..and allowing me to meet
0:49:54 > 0:49:58some of its more unusual and surprising inhabitants.
0:50:00 > 0:50:03'This took us out onto the top of Heron Island's reef,
0:50:03 > 0:50:05'which is only exposed at low tide.
0:50:09 > 0:50:12'But we had to tread carefully, accompanied by guides,
0:50:12 > 0:50:15'to ensure that we didn't damage any of the coral.'
0:50:16 > 0:50:19Anybody who's coming on here, it's weird at first,
0:50:19 > 0:50:22but just try and walk on the dead coral - the concrete stuff.
0:50:22 > 0:50:24'We were there to film an elusive creature
0:50:24 > 0:50:28'that feeds in this special habitat when the tide is out -
0:50:28 > 0:50:30'the epaulette shark.'
0:50:31 > 0:50:34There's one with a tail - the first one is there.
0:50:34 > 0:50:37- Just gone.- It's gone under there.
0:50:39 > 0:50:44'Professor Gillian Renshaw has been studying these sharks for 20 years.'
0:50:44 > 0:50:46It's very hard to see the epaulettes
0:50:46 > 0:50:50because they're cryptically coloured and blend in very well
0:50:50 > 0:50:53with the fingers of coral that are rising out of the reef platform.
0:50:55 > 0:50:58'It's a challenging location, not least because
0:50:58 > 0:51:00'it's only accessible for short periods of time.'
0:51:03 > 0:51:05We've got probably about 40 minutes
0:51:05 > 0:51:07to get all of the shots that we need,
0:51:07 > 0:51:10so I shouldn't really be talking to you, we should be getting this.
0:51:10 > 0:51:15- OK, quiet please! - Camera's rolling. And action, David.
0:51:15 > 0:51:18The epaulette shark remains on the reef,
0:51:18 > 0:51:20even when the tide goes out.
0:51:21 > 0:51:23Of course, with so little water,
0:51:23 > 0:51:27it doesn't get as much oxygen as it requires normally, but...
0:51:29 > 0:51:30'Although my piece is done,
0:51:30 > 0:51:34'the team must now film the shark's unique walking behaviour.'
0:51:34 > 0:51:36The water is literally pouring in around the equipment
0:51:36 > 0:51:38and over our feet.
0:51:38 > 0:51:41We've got about 10 to 15 minutes to get this sequence finished
0:51:41 > 0:51:43and get back in the boats before we're literally cut off
0:51:43 > 0:51:45and we can't get back to the boats.
0:51:47 > 0:51:50'The tide creeps in around us.'
0:51:55 > 0:51:58He's walking beautifully, now. Look at that.
0:52:00 > 0:52:03Let's try and get it in the water a bit.
0:52:03 > 0:52:06Really nice performance from the epaulette shark.
0:52:08 > 0:52:11'Now, it's a race against time to get off the reef.'
0:52:12 > 0:52:13Are we ready for the boat, now?
0:52:13 > 0:52:16Geraldine, can we get David on, please?
0:52:21 > 0:52:23Yeah, looked stunning. Worth the stress.
0:52:25 > 0:52:28'This trip took us from the very top of the reef
0:52:28 > 0:52:30'down almost to its bottom...
0:52:31 > 0:52:34'..for our most ambitious sequence of the series -...
0:52:36 > 0:52:38'..to attempt the deepest dive in this area
0:52:38 > 0:52:42'and collect a sample of the mysterious coral that survives there.
0:52:43 > 0:52:46'And it's down to cameraman Paul Williams
0:52:46 > 0:52:48'to film our mission single-handedly.'
0:52:50 > 0:52:52I'm on my own down there.
0:52:52 > 0:52:54I've gone over it and over it again in my mind,
0:52:54 > 0:52:57about what we're trying to do and how we're going to do it,
0:52:57 > 0:52:59so I think I've got it locked in.
0:52:59 > 0:53:01I hope haven't forgotten anything.
0:53:01 > 0:53:03'It's something of a squeeze in the sub,
0:53:03 > 0:53:06'with all of Paul's filming equipment.'
0:53:06 > 0:53:08Do you mind if I just give you that for a moment?
0:53:09 > 0:53:12'But our third crew member is essential.
0:53:12 > 0:53:14'He's the pilot, Buck Taylor.'
0:53:19 > 0:53:22I'm sitting with a big camera on my shoulder
0:53:22 > 0:53:25and two other cameras, which were outside the sub,
0:53:25 > 0:53:28controlled by laptops which were both on my lap.
0:53:32 > 0:53:35The sound kit was under Buck's feet.
0:53:35 > 0:53:36It was tight in there.
0:53:44 > 0:53:46David, do you mind?
0:53:46 > 0:53:49- Would you get your towel and just give that a little wipe there?- Yup.
0:53:49 > 0:53:50Thank you, sir.
0:53:53 > 0:53:55'For the first part of the dive,
0:53:55 > 0:53:58'underwater cameramen filmed the sub's descent.
0:53:59 > 0:54:02'But at about 60 metres, they reached their limit.
0:54:05 > 0:54:07'It's only possible to venture further
0:54:07 > 0:54:09'within the protection of the submarine.
0:54:10 > 0:54:14'As we enter the mesophotic zone, around 100 metres down,
0:54:14 > 0:54:15'we're on our own.
0:54:20 > 0:54:22'To get the best shots of the reef beyond,
0:54:22 > 0:54:25'Paul requires all of Buck's skill as a pilot.'
0:54:26 > 0:54:29Do you want to try some other light options?
0:54:29 > 0:54:32- What have you got? - I can give you that.
0:54:32 > 0:54:35Yeah, put the higher ones on, take the lower ones off.
0:54:35 > 0:54:39- How's that?- Yes. Actually, that looks better.- Isn't it lovely?
0:54:39 > 0:54:42- Probably full of nooks and crannies.- Yeah.
0:54:42 > 0:54:44Buck, the sub driver, was brilliant.
0:54:44 > 0:54:46He'd find a drift in the currents
0:54:46 > 0:54:48and then we'd just drift across the coral.
0:54:48 > 0:54:50What's nice is, I can actually see the wall.
0:54:50 > 0:54:53- That's a very good angle for me. - Is it?- Yeah.
0:54:53 > 0:54:56So, just let us drift a tiny bit to starboard.
0:54:56 > 0:54:58And...action, David.
0:54:58 > 0:55:04This wall of rock ahead of me is actually the flank of Osprey Reef -
0:55:04 > 0:55:07an oasis for life.
0:55:07 > 0:55:09'But we weren't down here just to look.
0:55:09 > 0:55:13'We also wanted to collect samples for deep reef scientists...
0:55:15 > 0:55:18'..and that proved easier said than done.'
0:55:18 > 0:55:21- Oh, no! - We have to go and fetch that.
0:55:21 > 0:55:22We'll take that on film.
0:55:25 > 0:55:28'As we descended beyond 250 metres,
0:55:28 > 0:55:31'we entered a landscape rarely seen with the naked eye.
0:55:33 > 0:55:37'It was the perfect opportunity simply to explore.'
0:55:38 > 0:55:40This is the first time that manned submersibles
0:55:40 > 0:55:42have worked at this depth
0:55:42 > 0:55:45and it gives one the ability to look and observe
0:55:45 > 0:55:48and just do curiosity-driven research.
0:55:48 > 0:55:50It's fantastic.
0:55:50 > 0:55:52The visibility down here spectacular, isn't it?
0:55:52 > 0:55:55It's absolutely pure, yeah.
0:55:55 > 0:55:58There were many times when I had to take my eye away from the eyepiece
0:55:58 > 0:56:01because I just had to look with my own eyes,
0:56:01 > 0:56:04so it goes into the brain properly
0:56:04 > 0:56:05in the right perspective.
0:56:07 > 0:56:09'Soon, we reached our target depth.'
0:56:12 > 0:56:14There it is. 300.
0:56:15 > 0:56:21Nobody before has ever been as deep as this on the Great Barrier Reef.
0:56:21 > 0:56:22I like it.
0:56:22 > 0:56:25LAUGHTER
0:56:25 > 0:56:28So, it hasn't even come up on here - 290 metres,
0:56:28 > 0:56:31but we've heard that they've just reached 300 metres.
0:56:31 > 0:56:34Another thing to add to the things that David's done on this planet.
0:56:34 > 0:56:37'The purpose of our record-breaking trip
0:56:37 > 0:56:40'was to raise awareness of the reef's fragility.
0:56:40 > 0:56:44'Fortunately, while production continued on the series,
0:56:44 > 0:56:47'the dive caught the attention of a president.'
0:56:48 > 0:56:52- Mr President. - When I heard that you had gone down,
0:56:52 > 0:56:55you dove into the Great Barrier Reef again...
0:56:56 > 0:56:58..60 years after the first time you did it?
0:56:58 > 0:57:00- Yes.- That impressed me.
0:57:00 > 0:57:02Ah, but I was in a sub.
0:57:02 > 0:57:05I mean, I was in a very, very remarkable research sub
0:57:05 > 0:57:07and we went down to over 300 metres.
0:57:07 > 0:57:10Oh, so you went really deep.
0:57:10 > 0:57:11And that was just mind-blowing.
0:57:13 > 0:57:16The deep dive proved a truly memorable moment for me
0:57:16 > 0:57:19and allowed us the unique opportunity of revealing
0:57:19 > 0:57:23a part of this great reef that has never before been seen.