0:00:02 > 0:00:05They cover two thirds of our planet.
0:00:07 > 0:00:11They hold clues to the mysteries of our past.
0:00:11 > 0:00:15And they're vital for our future survival.
0:00:18 > 0:00:23But the secrets of our oceans have remained largely undiscovered.
0:00:23 > 0:00:25I am with a six-gill shark.
0:00:25 > 0:00:30- Yes, yes! - Explorer Paul Rose is leading
0:00:30 > 0:00:36a team of ocean experts on a series of underwater science expeditions.
0:00:36 > 0:00:43For a year, the team has voyaged across the world to build up a global picture of our seas.
0:00:43 > 0:00:46We are doing some pretty uncharted research here.
0:00:46 > 0:00:51- That is psychedelically powerful. - 'We are here to try and understand'
0:00:51 > 0:00:54the Earth's oceans and put them in a human scale.
0:00:56 > 0:01:00Our oceans are changing faster than ever.
0:01:00 > 0:01:02I've never seen ice like this before.
0:01:04 > 0:01:10There's never been a better time to explore the last true wilderness on Earth.
0:01:20 > 0:01:27The team has travelled to the edge of the mighty Southern Ocean, a vast body of wild, cold water.
0:01:29 > 0:01:33Home to the infamous Roaring Forties, it's swept by
0:01:33 > 0:01:39the strongest winds in the world, which create some of the roughest and most unpredictable seas.
0:01:43 > 0:01:46And around those cliffs there's just great boomers coming in,
0:01:46 > 0:01:51seas with a real vengeance that you just feel they're out to get you personally.
0:01:53 > 0:01:59The Southern Ocean flows around the bottom of our planet, completely encircling Antarctica.
0:02:01 > 0:02:07The Oceans team is braving some of the most remote and least chartered waters in the world.
0:02:07 > 0:02:12Hidden beneath their surface are unique marine environments,
0:02:12 > 0:02:16home to species that exist nowhere else on Earth,
0:02:16 > 0:02:21and the Southern Ocean can give us an insight into the future of all our oceans.
0:02:21 > 0:02:24It's on the front line of global climate change.
0:02:24 > 0:02:29Parts of it are warming more than twice as fast as any other ocean.
0:02:29 > 0:02:32The team has come to investigate the impact that's having.
0:02:32 > 0:02:39Climate change is happening, and understanding how it's affecting the Southern Ocean is...
0:02:39 > 0:02:42critical to understanding what's going to happen
0:02:42 > 0:02:45over the next few decades and centuries,
0:02:45 > 0:02:47for this planet and to us.
0:02:48 > 0:02:54Environmentalist Philippe Cousteau is grandson of ocean pioneer Jacques Cousteau.
0:02:54 > 0:02:57On this expedition, he will be investigating
0:02:57 > 0:03:02the profound effect that changing seas are having on the marine life here.
0:03:02 > 0:03:08Look at it, there's not a single living piece of plant material...
0:03:08 > 0:03:09anywhere.
0:03:10 > 0:03:14Tooni Mahto is a marine biologist and oceanographer.
0:03:14 > 0:03:19She'll be searching unique marine habitats for scientific discoveries.
0:03:19 > 0:03:24It's quite exceptional for a biologist to get to see these things.
0:03:24 > 0:03:27We normally only see them in several hundred metres of water.
0:03:28 > 0:03:35And maritime archaeologist Dr Lucy Blue will help to reveal the human cost of these violent seas.
0:03:35 > 0:03:41The weather effectively dictates the very huge seas that can be generated
0:03:41 > 0:03:45in the Southern Ocean. As a result, there are lots of shipwrecks.
0:03:45 > 0:03:50Only a few have actually been discovered here and not many of them have been explored extensively.
0:03:50 > 0:03:55This one has just been crushed by the power of the ocean.
0:03:55 > 0:04:00Their first task is to investigate the impact of the warming seas here.
0:04:02 > 0:04:07So they've come to Tasmania, a rugged island lying south of the mainland of Australia.
0:04:13 > 0:04:17It's home to the biggest marine plant in the world, giant kelp.
0:04:17 > 0:04:21Kelp forests are one of the most important marine eco-systems here.
0:04:21 > 0:04:25They're vital to support life in this ocean.
0:04:29 > 0:04:33The kelp should be clearly visible from the air,
0:04:33 > 0:04:36so expedition leader Paul will survey the area by helicopter.
0:04:39 > 0:04:41I haven't seen anything yet at all, nothing.
0:04:41 > 0:04:47Only ten years ago, kelp forests stretched the entire length of this coastline,
0:04:47 > 0:04:52so dense that they formed thick algal mats on the surface of the sea.
0:04:55 > 0:04:58Yeah, here we go. I think I've got something.
0:04:58 > 0:05:03It's probably about, you know, 400 metre square patch or something like that,
0:05:03 > 0:05:06but it normally would have been an extensive kelp forest.
0:05:06 > 0:05:11They use that great term, kelp forest, but that definitely is not a forest.
0:05:17 > 0:05:20Paul radios the co-ordinates through to the team.
0:05:20 > 0:05:24Tooni, Tooni, Paul? You know, it's a real shocker this,
0:05:24 > 0:05:26and it really is a patch.
0:05:26 > 0:05:30It's just a small patch. But it's the very best I can find from up here.
0:05:30 > 0:05:35- OK, got that.- I'll join you later and see you on board, over.
0:05:45 > 0:05:50Along the east coast of Tasmania, the size and number of giant kelp beds
0:05:50 > 0:05:53has declined dramatically over the past ten years.
0:05:53 > 0:05:58In places, only five per cent of the original area remains.
0:05:58 > 0:06:03Environmentalist Philippe wants to find out why.
0:06:03 > 0:06:05I'm really curious as to what's going on under there.
0:06:05 > 0:06:08From the surface, the kelp looks pretty pathetic actually.
0:06:08 > 0:06:12This is not much of a kelp forest, and it's an absolute tragedy
0:06:12 > 0:06:15to think of what's happened and how quickly.
0:06:15 > 0:06:21OK, five, four, three, two, dive.
0:06:27 > 0:06:30Like rainforests on land, these towering seaweeds provide
0:06:30 > 0:06:34food and shelter for a rich array of marine life.
0:06:34 > 0:06:40You do get that sense of flying, flying through trees.
0:06:42 > 0:06:48In good conditions, giant kelp can grow 30 metres high and shoot out half a metre a day.
0:06:50 > 0:06:52But these are not good conditions.
0:06:54 > 0:06:57And I have to say, I'm not seeing much evidence
0:06:57 > 0:07:00for a very healthy kelp forest down here.
0:07:00 > 0:07:06There's not a lot of young kelp that looks very healthy that's going to be growing to the surface to replace
0:07:06 > 0:07:10this more mature kelp that will be dying off relatively soon.
0:07:10 > 0:07:13It's not a great sign.
0:07:13 > 0:07:17Measuring the water temperature suggests a possible reason.
0:07:17 > 0:07:21I've got the temperature reading, 14 degrees Centigrade.
0:07:21 > 0:07:2657 degrees Fahrenheit, actually quite warm.
0:07:26 > 0:07:33Giant kelp can only thrive in cold water, growing best between 6 and 14 degrees Centigrade.
0:07:34 > 0:07:40So it means at the moment, they're growing right at the upper range of their temperature limit.
0:07:43 > 0:07:46But then they make another even more worrying discovery.
0:07:48 > 0:07:52Whoa, and some big, black, spiny sea urchins!
0:07:52 > 0:07:54Tooni, this is not a good sign!
0:07:54 > 0:08:00And this may help to contribute to the fact that these kelp forests are declining.
0:08:00 > 0:08:03These sea urchins are covering the rocks and they feed on
0:08:03 > 0:08:07the baby giant kelp before they have a chance to grow large.
0:08:07 > 0:08:10Oh, Tooni, I got to tell you, this is not good.
0:08:14 > 0:08:20This water should be too cold for these sea urchins to survive,
0:08:20 > 0:08:25but as it's warmed up, they've been able to migrate here and destroy the young seaweed.
0:08:28 > 0:08:30As the kelp is wiped out,
0:08:30 > 0:08:35so too is the crucial bio-diversity of these waters,
0:08:35 > 0:08:37and it's happening fast.
0:08:42 > 0:08:46Ten years to go from great kelp forests to that is excessive.
0:08:46 > 0:08:51It just means nothing's got a chance to evolve or adapt to warmer conditions.
0:08:51 > 0:08:54- It's just complete, it's wave bye-bye.- Devastation, devastation.
0:08:58 > 0:09:05The water temperature along these shores has risen 1.5 degrees in the last 50 years.
0:09:05 > 0:09:09The impact on the giant kelp has been enormous.
0:09:09 > 0:09:13A 1.5 degree rise in water temperature in this region
0:09:13 > 0:09:17has pretty much caused the decline of 95% of these kelp forests.
0:09:17 > 0:09:22It just seems like such a microscopic change, but the point about the kelp eco-systems
0:09:22 > 0:09:29is that they're such a great example of how a tiny, tiny change in such an important
0:09:29 > 0:09:33parameter such as temperature can have a completely decimating effect.
0:09:34 > 0:09:41The loss of vast areas of Tasmania's kelp forests is also threatening the marine life that depends on them.
0:09:42 > 0:09:46The most vulnerable species are those which are so well adapted to the kelp
0:09:46 > 0:09:49they can survive nowhere else.
0:09:51 > 0:09:56Philippe and Tooni are about to go in search of one of the most extraordinary.
0:09:57 > 0:10:04We are here to dive in water which hopefully harbours a quite unique and mysterious animal.
0:10:04 > 0:10:11Yes, it's well camouflaged within their environment, so it's going to be a bit of a hunt for a very...
0:10:11 > 0:10:17inconspicuous animal, but apparently, they're incredibly exquisite so it's definitely worth doing.
0:10:22 > 0:10:25Five, four, three, two, dive, dive, dive!
0:10:30 > 0:10:37So, we're looking for something about 50 centimetres long that looks exactly like a piece of seaweed.
0:10:38 > 0:10:44I'm having a good look right down underneath everything, cos the way they protect themselves
0:10:44 > 0:10:48from predators is to get right in amongst the kelp.
0:10:53 > 0:10:59- Any luck, Philippe?- No, so far, I haven't found anything, Toon.
0:10:59 > 0:11:02Of course, that's the idea for them anyway.
0:11:02 > 0:11:05Stay hidden and survive.
0:11:07 > 0:11:13- They're going a damn good job of it, if I do say so.- Apparently, you've got to look for the eye movement.
0:11:13 > 0:11:17You can just see the little eye movement amongst the kelp fronds.
0:11:20 > 0:11:24These rare animals are so perfectly evolved to blend in
0:11:24 > 0:11:28with the seaweeds that spotting one is incredibly difficult.
0:11:28 > 0:11:30Just keep looking.
0:11:39 > 0:11:43- I got one, I found one! I found one, I found one!- Woo-hoo!
0:11:43 > 0:11:46Oh, my God, it's beautiful!
0:11:46 > 0:11:48Tooni, I've got a sea dragon over here.
0:11:48 > 0:11:52- Come and look at this. - Found only in the kelp forests
0:11:52 > 0:11:57of South Australia and Tasmania, this is the weedy sea dragon.
0:11:57 > 0:12:00So brilliant!
0:12:00 > 0:12:03Blue and green and red!
0:12:03 > 0:12:07They're related to the sea horse, but they're a slightly different species.
0:12:07 > 0:12:11And how effortlessly they swim through this,
0:12:11 > 0:12:15as we're getting tossed around like we're in a washing machine.
0:12:15 > 0:12:17Its fins are all moving.
0:12:17 > 0:12:21It it just looks as though nothing is actually propelling it at all.
0:12:21 > 0:12:25Very, very fine fin on its tail there.
0:12:26 > 0:12:29You can see why it's such a perfect camouflage,
0:12:29 > 0:12:33and they're evolved just to look exactly like the kelp they live in,
0:12:33 > 0:12:37and it protects them from predators,
0:12:37 > 0:12:40cos they're not particularly fast swimmers.
0:12:40 > 0:12:46It will not only use its camouflage for evading predators, but also
0:12:46 > 0:12:52for sneaking up on its prey, small little crustaceans, things in and amongst
0:12:52 > 0:12:56and around the kelp floating in the water column. Oh!
0:12:57 > 0:13:02To help them catch prey, sea dragons have eyes that can move independently.
0:13:02 > 0:13:06While one eye looks forwards, the other can look backwards.
0:13:08 > 0:13:12This is a very rare sighting.
0:13:12 > 0:13:17Like their cousins, the sea horses, weedy sea dragons are under threat.
0:13:18 > 0:13:23It's just so sad, isn't it? With the decline of the Tasmanian kelp forest,
0:13:23 > 0:13:29that actually means that the habitat for these beautiful creatures is getting smaller and smaller.
0:13:30 > 0:13:35The thing is with something so perfectly adapted to one particular
0:13:35 > 0:13:38eco-system, it's got nowhere else to go.
0:13:41 > 0:13:44I think it's time to let her go on her way.
0:13:45 > 0:13:48Wow, what a gift!
0:14:00 > 0:14:04As our oceans continue to warm as a result of climate change,
0:14:04 > 0:14:11the devastation of this unique marine habitat offers a warning to others around the world.
0:14:13 > 0:14:19But these waters are warming much faster than any other ocean.
0:14:19 > 0:14:22The mystery is why, and will it continue?
0:14:22 > 0:14:25The team is on its way to help find out.
0:14:28 > 0:14:32There are signs it could be because of a shift in an important
0:14:32 > 0:14:36warm water current, the East Australian Current.
0:14:36 > 0:14:40This is part of a huge ocean circulation system that transports
0:14:40 > 0:14:44warm water from the Equator down the east coast of Australia.
0:14:44 > 0:14:50The way ocean circulations work is they work in these sort of giant gyres they're called,
0:14:50 > 0:14:53and it's just a huge movement of water in a circular motion.
0:14:53 > 0:14:57So the Eastern Australian Current is actually bringing warmer water
0:14:57 > 0:15:00from around the equator, but with changes in ocean currents,
0:15:00 > 0:15:05it's bringing the warmer water further and further south down the coast of Tasmania.
0:15:08 > 0:15:13The shift southwards is thought to be responsible for the rapid rise
0:15:13 > 0:15:16in water temperatures off Tasmania, but will it carry on?
0:15:19 > 0:15:23Today, the team is working with scientists at the forefront of
0:15:23 > 0:15:29ocean current research to trial a piece of cutting-edge technology.
0:15:29 > 0:15:33This glider will gather vital information about the current
0:15:33 > 0:15:35and whether it's continuing to move south.
0:15:38 > 0:15:41I'm getting some communication from the glider now.
0:15:43 > 0:15:48Five, four, three, two, one, launch!
0:15:54 > 0:15:57She's in, and looks good at the moment.
0:15:59 > 0:16:04The glider will collect data from deep within the East Australian Current.
0:16:04 > 0:16:07This will be for the first time.
0:16:07 > 0:16:11Until now, only surface readings have been taken by satellite.
0:16:11 > 0:16:17- Now, we'll set her on a mission to dive.- Oceanographer Tooni is working with senior engineer
0:16:17 > 0:16:22Lindsay MacDonald, as the glider needs to perform a successful test flight
0:16:22 > 0:16:25before it can start its first mission.
0:16:25 > 0:16:29So we'll just load that mission and send it on its merry way.
0:16:30 > 0:16:32Diving, starting to dive.
0:16:32 > 0:16:35Paul, it's starting to dive, starting to dive.
0:16:35 > 0:16:38Yes, she's away, Tooni, it's looking good.
0:16:38 > 0:16:40Six metres now, Tooni.
0:16:40 > 0:16:43It's interesting with a diver in the water to know what depth it's at.
0:16:43 > 0:16:48- I've no idea until I download the data.- We can give you real-time information.- You can.
0:16:48 > 0:16:54And she's levelled off at eight metres, and now heading back up.
0:16:54 > 0:16:57- OK, it's talking.- What does it record when it's in the water?
0:16:57 > 0:17:00- It records scientific data. - So temperature, salinity...
0:17:00 > 0:17:04Temperature, salinity, and there's an oxygen sensor in the tail.
0:17:04 > 0:17:07- So oxygen content in the water.- OK.
0:17:09 > 0:17:15Temperature, salinity and oxygen levels give each current its own unique signature.
0:17:15 > 0:17:20The glider will measure these over a series of voyages to find out how far and how deep
0:17:20 > 0:17:25the East Australian Current goes and if it's still moving further south.
0:17:28 > 0:17:30Well, this looks really good.
0:17:30 > 0:17:35She's made a whole series of descents and ascents perfectly as planned.
0:17:35 > 0:17:38That's exactly what she should be doing.
0:17:40 > 0:17:44The glider is now ready for its first month-long mission.
0:17:46 > 0:17:49It'll soon be providing information
0:17:49 > 0:17:53to help discover how ocean currents here are changing,
0:17:53 > 0:17:59and that's vital, because changes in this ocean could have a much wider impact.
0:18:01 > 0:18:03The Southern Ocean touches three other oceans.
0:18:03 > 0:18:06It touches the Pacific, the Atlantic and the Indian,
0:18:06 > 0:18:11and it carries currents all the way around the southern part of this planet.
0:18:11 > 0:18:15You disrupt those and it's going to have a domino effect,
0:18:15 > 0:18:19and it needs to be understood further, because it is on the front lines of the change
0:18:19 > 0:18:24that we are facing in this world and, as it changes, so too will everything else.
0:18:26 > 0:18:31For their next task, the team is going in search of evidence of the most fundamental change
0:18:31 > 0:18:35the Southern Ocean has ever experienced - its creation.
0:18:37 > 0:18:42That evidence lies within some of the highest sea cliffs in the world.
0:18:42 > 0:18:47These towering columns of basalt rise 300 metres out of the ocean.
0:18:47 > 0:18:52They are riddled with a vast network of underwater caves,
0:18:52 > 0:18:58carved out over millions of years by the Southern Ocean's pounding seas.
0:19:00 > 0:19:05Those same seas make diving here perilous.
0:19:05 > 0:19:12The problem here is with this big sea rolling, it's going to be booming up in those caves,
0:19:12 > 0:19:17and I've been hung up in sea caves before and you just can't be messing around in them.
0:19:17 > 0:19:21- Hold it there, Pete!- Rather than put the rest of the team at risk,
0:19:21 > 0:19:24- Paul decides to check them out first.- OK, Paul.
0:19:24 > 0:19:28He's been diving for 40 years
0:19:28 > 0:19:32and has made over 6,000 dives.
0:19:32 > 0:19:34Wow!
0:19:34 > 0:19:37There's a lot of water moving round here, boys.
0:19:37 > 0:19:41It's very, very hard to keep in position, just look at that.
0:19:41 > 0:19:44Woo, blimey! Hanging on to the weed.
0:19:53 > 0:19:58The Southern Ocean has got me in some kind of mad industrial wash cycle at the moment!
0:20:02 > 0:20:07There's no way I can get in that cave right now.
0:20:10 > 0:20:16The team has been thwarted by the power of the Southern Ocean.
0:20:17 > 0:20:22There's just no way you would get near it. And it's just...whoosh!
0:20:24 > 0:20:26Really got to try and work to come back here.
0:20:26 > 0:20:30You know, watch the waves, watch the weather, dive it at night,
0:20:30 > 0:20:33dive it at 3am. Do whatever we can. We've got to come back and dive it.
0:20:35 > 0:20:40There's now an anxious wait for tomorrow's weather forecast.
0:20:40 > 0:20:45Tooni will be diving with Paul. They've both trained as cave divers.
0:20:45 > 0:20:49'A five will develop to the south west of Tasmania today.
0:20:49 > 0:20:54'A weak cold front is passing to the south...'
0:20:54 > 0:21:00The forecast is better, but Paul is still concerned about the dangers of this cave dive.
0:21:00 > 0:21:03All I can think about is Tooni and me getting
0:21:03 > 0:21:07shoved up into a narrow groove by the force of the Southern Ocean.
0:21:07 > 0:21:12- Explain to me what the potential issues are.- What we're learning from the locals is that the surges
0:21:12 > 0:21:17come in and they call it, every once in a while they get a king swell, which is a great big one and pushes.
0:21:17 > 0:21:21Then it can push us up, and what I'm worried about is being up in the foam,
0:21:21 > 0:21:24and I think we can get stuck and trapped on the surface in there.
0:21:24 > 0:21:28- Well, then, don't go!- It looks OK. - Well, I think time is so short
0:21:28 > 0:21:33- that no matter what the conditions, almost, you and me need to get in and have a sniff of 'em.- Yeah.
0:21:33 > 0:21:37Cos if we can pull it off, it'll be blooming great and even if we can't pull it off,
0:21:37 > 0:21:40we'll get an idea what it's all about. It's worth going for.
0:21:40 > 0:21:43Yes, I agree.
0:21:45 > 0:21:48Next morning, they set out for the sea caves and a dive
0:21:48 > 0:21:52that could allow them to investigate the birth of the Southern Ocean.
0:21:52 > 0:21:58Every metre they descend will take them further back in geological time.
0:21:59 > 0:22:03They're searching these cliffs for fossils of ancient sea creatures
0:22:03 > 0:22:05that lived over 300 million years ago
0:22:05 > 0:22:10and might hold clues to the Southern Ocean's formation.
0:22:10 > 0:22:16We're looking for small boulders that we can pick up. The idea is to bring them back out of the caves,
0:22:16 > 0:22:20send them up on a lift bag, then look at them on the back of the deck,
0:22:20 > 0:22:21cos our time down there is so limited.
0:22:29 > 0:22:33This time, the surge is much more manageable.
0:22:33 > 0:22:36This is the entrance, this is it.
0:22:36 > 0:22:39But the power of this sea can never be underestimated.
0:22:42 > 0:22:45I can feel myself being pushed in by the waves.
0:22:47 > 0:22:53Once they enter the cave system, all communications with the surface will be lost.
0:22:54 > 0:22:57Gosh, it's so narrow.
0:22:57 > 0:23:02Yeah, you're right, it looks very tight indeed. But I do think it's worth going for.
0:23:02 > 0:23:07They only have enough air to dive for 30 minutes, so they need to find
0:23:07 > 0:23:11the fossils as fast as these treacherous tunnels will allow.
0:23:11 > 0:23:14It's hard work swimming against this surge.
0:23:16 > 0:23:22With metres of solid rock above them, escape to the surface is not an option.
0:23:25 > 0:23:29It's pretty tight in here as well.
0:23:29 > 0:23:33There are now 40 metres of tunnels behind them.
0:23:33 > 0:23:37They've got just 20 minutes of usable air left.
0:23:38 > 0:23:42But then they emerge into a much bigger cave strewn with rocks.
0:23:42 > 0:23:47The trick with finding these fossils is I'm not quite sure what to look for,
0:23:47 > 0:23:49because there's just loads of boulders.
0:23:51 > 0:23:55Well, we spot them by looking for something exactly like that.
0:23:55 > 0:23:58Oh, hey!
0:23:58 > 0:24:00There's a great depression in that one.
0:24:00 > 0:24:04It looks exactly like the markings of a cockle, doesn't it? See?
0:24:04 > 0:24:10That's exactly what we want, an indication that there's something more enticing inside.
0:24:10 > 0:24:12This is a fossil brachiopod,
0:24:12 > 0:24:16a type of shellfish that lived over 300 million years ago.
0:24:16 > 0:24:22It's an important clue to the Southern Ocean's past.
0:24:22 > 0:24:24Look at that one.
0:24:26 > 0:24:30It looks like a mollusc almost, something like a scallop.
0:24:30 > 0:24:33I think that's probably enough. It's quite heavy, that.
0:24:33 > 0:24:37I'm just going to put some air in this bag and lift them a little bit.
0:24:37 > 0:24:39They're too heavy for us to swim it up.
0:24:42 > 0:24:44Perfect, come on.
0:24:50 > 0:24:52Paul, surface. This is Lucy,
0:24:52 > 0:24:55have you found the fossils, over?
0:24:55 > 0:24:59Yeah, hi, Lucy, we're about to send her up, actually.
0:25:00 > 0:25:02Here she goes!
0:25:06 > 0:25:08- Here they are!- You've got them?
0:25:08 > 0:25:11- Here they are.- Wow, well done. - Was it good, was it good?
0:25:11 > 0:25:12Oh, it was a great dive.
0:25:12 > 0:25:17- Ooh!- There's the one, there it is. - You can see pretty much every crenulation of the shell.
0:25:17 > 0:25:20- Yeah, that's fantastic. - Can we hit into this one?
0:25:20 > 0:25:24We're just going to stick our masks on quick, so look out for your eyes, Lucy.
0:25:26 > 0:25:30That is a beauty. You can see the real delicate pattern in the shell.
0:25:30 > 0:25:31What is it?
0:25:31 > 0:25:36Those are brachiopods, and they used to be very, very abundant
0:25:36 > 0:25:41in sort of shallow seas, basically, where you find a lot of mussels now.
0:25:41 > 0:25:46But there's something else that's remarkable about these fossils.
0:25:46 > 0:25:48They're identical to fossils found in Antarctica
0:25:48 > 0:25:53almost 2,000 miles away - clear evidence
0:25:53 > 0:25:58that this coast and Antarctica were once joined together.
0:25:58 > 0:26:02So as Tasmania split from the Antarctic, that was the birth of the Southern Ocean,
0:26:02 > 0:26:04and we've found evidence of it.
0:26:08 > 0:26:14The separation of these two land masses started around 53 million years ago.
0:26:14 > 0:26:18They took 15 million years to tear apart.
0:26:19 > 0:26:23This was the final stage in the Southern Ocean's formation,
0:26:23 > 0:26:25and it created a body of water
0:26:25 > 0:26:29with some of the most unpredictable weather in the world.
0:26:34 > 0:26:37It feels like five minutes ago, it was a beautiful day.
0:26:37 > 0:26:44You can't guarantee a day's perfect weather here in the Southern Ocean. Just as soon as we turn around,
0:26:44 > 0:26:47we get more weather coming in. And that's exactly what's happened,
0:26:47 > 0:26:51so we'll have to pull out of here, cos it's going to be rough.
0:27:07 > 0:27:11It's amazing. I mean, I knew it was going to change quick, but maybe not quite that quick.
0:27:11 > 0:27:14- From now, it'll be a bit dodgy, then it'll ease off again. - Ease off?- Yeah.
0:27:14 > 0:27:17As you can see, there's clear sky coming again now.
0:27:22 > 0:27:27The extreme weather is largely caused by one unique feature.
0:27:27 > 0:27:29With the South Pole at its centre,
0:27:29 > 0:27:31the winds and waves of the Southern Ocean
0:27:31 > 0:27:37circle continuously eastward without any land to slow them down.
0:27:37 > 0:27:41Here, the world's longest current flows around the globe
0:27:41 > 0:27:46for 13,000 miles, driven by the world's strongest winds.
0:27:46 > 0:27:50It creates the notorious Roaring Forties,
0:27:50 > 0:27:52from 40 to 50 degrees south.
0:27:52 > 0:27:57One of the things that is significant about the context of the Southern Ocean
0:27:57 > 0:28:02is these incredibly strong winds, the Roaring Forties.
0:28:02 > 0:28:07As a result of that, she has taken many victims, as it were.
0:28:07 > 0:28:11There are literally hundreds of shipwrecks around the shores of Tasmania,
0:28:11 > 0:28:17let alone the bigger ocean, and only a very small number have actually been located.
0:28:18 > 0:28:22Maritime archaeologist Dr Lucy Blue
0:28:22 > 0:28:26has been researching the wreck of the Nord, an 80-metre long cargo vessel
0:28:26 > 0:28:31which sank while trying to evade a violent storm in 1915.
0:28:31 > 0:28:34You can see over here, these are the Hippolytes,
0:28:34 > 0:28:38and she tried to navigate between the large one and the smaller one,
0:28:38 > 0:28:42and basically hit a small rock that's... Look, you can see there
0:28:42 > 0:28:46where the water's breaking on this rock, just below the surface.
0:28:46 > 0:28:50So she obviously didn't see it, thought that she could get through, and boof!
0:28:54 > 0:29:00The captain tried to steer the Nord to safety, but huge seas swamped the ship's engines.
0:29:00 > 0:29:03She sank fast.
0:29:03 > 0:29:10These are dangerous waters, and I can't help but imagine what it was like that night when she went down.
0:29:10 > 0:29:12It would have been absolute pandemonium on board.
0:29:12 > 0:29:15I'm going to think of those men while I'm on it.
0:29:15 > 0:29:19The Nord lies in deep water.
0:29:19 > 0:29:24It's a dive only Paul has the training and experience to make.
0:29:24 > 0:29:28Lucy will be monitoring his exploration from the surface.
0:29:30 > 0:29:34They want to know how the Nord is faring after nearly 100 years
0:29:34 > 0:29:37beneath the Southern Ocean's merciless seas.
0:29:39 > 0:29:42Well, this is it, this is the wreck of the Nord.
0:29:42 > 0:29:44And just look at this thing!
0:29:44 > 0:29:48You can get an idea of the extent of the damage here.
0:29:48 > 0:29:52Some shipwrecks on the bottom look like perfect ships,
0:29:52 > 0:29:56but this one has just been crushed by the power of the ocean.
0:29:56 > 0:29:58Just look here,
0:29:58 > 0:30:03how the superstructure has sheared off so cleanly.
0:30:06 > 0:30:08As the skipper of a vessel, you're thinking
0:30:08 > 0:30:13"Right, well, I'm OK, I'm in the Southern Ocean, I've got the Westerlies behind me."
0:30:13 > 0:30:17But even though there's less land to sort of wreck against, your instinct
0:30:17 > 0:30:22when the winds pick up is to go closer to land, to take shelter, to get in the lea of the island and yet
0:30:22 > 0:30:25the winds change, and you're at the bottom.
0:30:28 > 0:30:31You can imagine at the other end of this rudder,
0:30:31 > 0:30:35those frantic movements those men will have done, trying to save her.
0:30:35 > 0:30:39I can't help but think what it must have been like for those guys.
0:30:43 > 0:30:47This ship was one of over 1,000 vessels that perished
0:30:47 > 0:30:51in the treacherous waters of this unforgiving sea.
0:30:55 > 0:31:01But the Southern Ocean was also a route for a very different cargo - human cargo.
0:31:01 > 0:31:07Paul to surface, Paul to surface, check your computer, check your computer, over.
0:31:07 > 0:31:08Yeah, computer good.
0:31:08 > 0:31:13We're now heading back to the line and slowly coming up. All good.
0:31:20 > 0:31:27Tasmania was the final destination for 75,000 convicts shipped halfway round the world from Britain.
0:31:29 > 0:31:32The journey over would have taken five to six months.
0:31:32 > 0:31:35They were pretty crammed into the boats.
0:31:35 > 0:31:41I mean, they took advantage of the Southern Ocean and the winds and the currents to bring them here
0:31:41 > 0:31:44but it's really extreme conditions out there
0:31:44 > 0:31:50and a lot of ships carrying convicts actually wrecked, so a lot of them didn't even make it here.
0:31:50 > 0:31:54But for those who did, the Southern Ocean kept them trapped here.
0:31:54 > 0:31:57No-one ever escaped from Tasmania.
0:32:02 > 0:32:09Even today, these often violent waters keep much of Tasmania virtually inaccessible.
0:32:11 > 0:32:15The south-western tip is home to some bizarre sea creatures,
0:32:15 > 0:32:20so difficult to reach that they've barely been studied.
0:32:22 > 0:32:24However, the team is hoping to do just that.
0:32:24 > 0:32:28But, to get there, the weather will have to be perfect.
0:32:28 > 0:32:34We've got probably a chance here of a two or three day decent weather window,
0:32:34 > 0:32:39and I'm not sure if in our expedition period we're going to get that again.
0:32:39 > 0:32:43But I think it would be such a good use of time if we took this weather window
0:32:43 > 0:32:45and Tooni and me went round to the south-west
0:32:45 > 0:32:49and got the target of the Sunken Valley because it's a remote spot.
0:32:49 > 0:32:54It strikes me, as such a unique place, that if we've got the opportunity to go, we should grab it.
0:32:54 > 0:33:00But what that would mean is that you two could get on with the other expedition targets based from here.
0:33:00 > 0:33:05We could push off and try and get the Sunken Valley done and then link up again in two or three days.
0:33:05 > 0:33:06Yeah, that's a good tactic.
0:33:06 > 0:33:08Thanks, guys, I'll give you a hand.
0:33:08 > 0:33:10What's first?
0:33:11 > 0:33:16Tooni and Paul are heading for a place known as the Sunken Valley.
0:33:16 > 0:33:21Here deep sea animals, normally living hundreds of metres below the surface,
0:33:21 > 0:33:24can be found thriving in shallow water.
0:33:24 > 0:33:26The deep sea is so inaccessible.
0:33:26 > 0:33:29It's so difficult to get to, it's so difficult to work in the deep sea,
0:33:29 > 0:33:34and so being able to get to the Sunken Valley and to be able to personally witness
0:33:34 > 0:33:40what's happening in a deep sea environment in six or seven metres of water, it's my ideal.
0:33:50 > 0:33:54Their journey takes them far away from civilisation.
0:33:59 > 0:34:03My first impressions are very much that Tasmania is an untouched place.
0:34:03 > 0:34:06I mean, the water's clean, the air feels clean and fresh.
0:34:06 > 0:34:10Round on the south-west out there there's no access at all.
0:34:10 > 0:34:14And it's a remote, pristine, true wilderness down there.
0:34:14 > 0:34:17They round the south-west tip of Tasmania.
0:34:17 > 0:34:23Here the sheltered waters of Bathurst Channel lead to the final passage into the sunken valley.
0:34:25 > 0:34:30Well, we're here. We've just slowed down, we're here. This is our site, this is our first site.
0:34:33 > 0:34:38The first thing that strikes them here is the stillness.
0:34:45 > 0:34:52A unique combination of landscape and elements creates a very unusual phenomenon in the Sunken Valley.
0:34:52 > 0:34:57The strange brown colour of the surface waters gives a hint of what's to come.
0:35:00 > 0:35:06It's such a beautiful place and I know that it's going to be such a special dive, so it just fills me
0:35:06 > 0:35:09with a real sense of excitement to be getting in the water in a minute.
0:35:15 > 0:35:17It's like entering an alien world.
0:35:17 > 0:35:20The water, it's kind of blood red.
0:35:22 > 0:35:29This extraordinary colour comes from tannins washed out of the peaty soil on land.
0:35:29 > 0:35:33It turns the top three metres of the water into a dark soup.
0:35:35 > 0:35:39This mimics some of the conditions that would normally only exist
0:35:39 > 0:35:42hundreds of metres below the surface.
0:35:43 > 0:35:47The tannin layer is important because it stops the light
0:35:47 > 0:35:51- penetrating through, so what you get is a deep sea community.- Got it.
0:35:52 > 0:35:58So what we're diving through now are sea whips, which are a form of deep water coral.
0:36:00 > 0:36:04It's quite exceptional as a biologist to get to see these things.
0:36:04 > 0:36:06The great thing about these sea whips
0:36:06 > 0:36:12is the fact that you normally only see them in several hundred metres of water,
0:36:12 > 0:36:14and we're in seven metres of water.
0:36:17 > 0:36:23Like many deep-sea corals, sea whips grow very slowly and may be hundreds of years old.
0:36:24 > 0:36:29Although they might look like plants, sea whips are actually colonies of animals.
0:36:29 > 0:36:32Each one is made up of hundreds of polyps
0:36:32 > 0:36:37that feed using tiny tentacles to catch plankton swept by in the current.
0:36:41 > 0:36:44- Look, look at this. This is what I wanted to see.- Yeah?
0:36:44 > 0:36:46- What is it?- This is a basket star.
0:36:46 > 0:36:49Now at the moment it's got all its tentacles retracted.
0:36:49 > 0:36:51It's kind of like a starfish,
0:36:51 > 0:36:55but it likes to use these sea whips as a base
0:36:55 > 0:36:58because it's a filter feeder.
0:36:58 > 0:37:02It climbs up the sea whip and gets its arms right out into the current
0:37:02 > 0:37:05so it can take advantage of all the food coming past it as well.
0:37:08 > 0:37:10The sea whips reveal one final secret.
0:37:10 > 0:37:12Tooni, here's one.
0:37:12 > 0:37:15Oh, there's a shark egg case, there's a shark egg case!
0:37:15 > 0:37:16Look at that!
0:37:17 > 0:37:21You can actually see the embryo inside.
0:37:21 > 0:37:23That is a shark in there!
0:37:24 > 0:37:27This has been laid by the draughtboard shark,
0:37:27 > 0:37:31another species more usually found in much deeper water.
0:37:31 > 0:37:36They've basically evolved to these conditions as well but what happens is they...
0:37:36 > 0:37:40they tie their eggs onto the sea whips because the sea whips are static.
0:37:40 > 0:37:42It's very, very intricately knotted.
0:37:44 > 0:37:47No-one's ever seen how they do this but the tangled knots are probably
0:37:47 > 0:37:51formed by the shark swimming round and round the sea whip.
0:37:55 > 0:37:57It felt really untouched to me.
0:37:57 > 0:37:59It's really diverse down there.
0:37:59 > 0:38:01There's loads of life.
0:38:01 > 0:38:04You know you get all those sea whips standing very proud
0:38:04 > 0:38:07right in the current and you can see them quivering.
0:38:09 > 0:38:16The Sunken Valley has revealed some fascinating marine life beneath its dark surface waters
0:38:16 > 0:38:20and there's another even stranger group of deep-sea animals to study.
0:38:20 > 0:38:24But with the light fading, that will have to wait until tomorrow.
0:38:32 > 0:38:39With Paul and Tooni at the Sunken Valley, Lucy and Philippe want to investigate a local marine mystery.
0:38:40 > 0:38:45They're at the south-eastern tip of Tasmania, in a small bay
0:38:45 > 0:38:51separated from the ocean by a narrow strip of land, Eaglehawk Bay.
0:38:52 > 0:38:58This is the only place in the world where dozens of octopus, the largest in the southern hemisphere,
0:38:58 > 0:38:59become stranded and die.
0:39:01 > 0:39:04Philippe wants to know why.
0:39:06 > 0:39:10- This is the spot so it's a pretty remarkable, unique place.- Why here?
0:39:10 > 0:39:14Well, I mean, you know, that's the question, that's a great question.
0:39:14 > 0:39:18We don't know so I'm thinking we have a chance to see them from the surface.
0:39:18 > 0:39:22We've got some powerful flashlights and it's shallow water.
0:39:22 > 0:39:23It's pretty clear.
0:39:27 > 0:39:33There are theories as to why these large Maori octopus are found here but no clear answers.
0:39:33 > 0:39:35We know it has something to do with the moon
0:39:35 > 0:39:40and it's right around the full moon right now, and it's coming into high tide.
0:39:40 > 0:39:44It's dusk, which is the right time to look, so I'll be thrilled if we see one.
0:39:48 > 0:39:51That's a powerful light you've got there.
0:39:52 > 0:39:53So far, no octopus.
0:39:55 > 0:39:57All I'm seeing is kind of murky murkiness.
0:39:58 > 0:40:03With no sign of them from the boat, the search moves underwater.
0:40:07 > 0:40:12You know, I'm really curious to see what it looks like in there, I mean, why are they coming here?
0:40:12 > 0:40:15But there's no precedent in the world for this,
0:40:15 > 0:40:18so, yeah, I really don't know what to expect.
0:40:18 > 0:40:20Doesn't matter how many questions you ask,
0:40:20 > 0:40:25there doesn't seem to be an answer, so I'm just, I mean, I'm just intrigued.
0:40:41 > 0:40:45Wow! Visibility is just awful.
0:40:47 > 0:40:50The seabed here is silty and featureless.
0:40:50 > 0:40:56Octopus usually like rocky crevices to hide in, so this is a very strange place for them to be found.
0:41:03 > 0:41:06- Philippe, Philippe! - That's incredible!
0:41:08 > 0:41:10At last, a Maori octopus.
0:41:11 > 0:41:13Wow! Look at that.
0:41:16 > 0:41:19They have an arm span of up to three metres.
0:41:20 > 0:41:22What do you think, Lucy?
0:41:22 > 0:41:25It's beautiful, actually.
0:41:25 > 0:41:28I've never in my life seen an octopus so huge.
0:41:33 > 0:41:36When they get this size, they're about a year or so old
0:41:36 > 0:41:41and they're at their maturity, sexual maturity, and they stop feeding,
0:41:41 > 0:41:45so definitely this animal is not here to eat.
0:41:46 > 0:41:53A fully-grown octopus like this ought to be preparing for the final act of its life, spawning.
0:41:53 > 0:41:57The problem is there's nowhere for it to effectively lay its eggs.
0:41:59 > 0:42:02They do so in a rocky substrate bottom area.
0:42:02 > 0:42:04There's nothing like that here.
0:42:11 > 0:42:13So what has drawn them here?
0:42:13 > 0:42:17Octopus would normally follow cues from the moon and tides
0:42:17 > 0:42:22to find their spawning grounds on rocky reefs in the open sea.
0:42:22 > 0:42:25Perhaps these have been led into the neck of the bay,
0:42:25 > 0:42:30only to find their final passage blocked by a narrow spit of land.
0:42:33 > 0:42:35It's a tragic, tragic story.
0:42:35 > 0:42:38Tragedy of topography.
0:42:38 > 0:42:41These octopus stay here,
0:42:41 > 0:42:44most likely unable to have the energy to leave.
0:42:46 > 0:42:51As the tide retreats, the exhausted octopus are stranded on the beach
0:42:51 > 0:42:56with just 100 metres of land separating them from the open ocean.
0:43:04 > 0:43:11At the Sunken Valley, it's day two of the team's exploration, and they're making an early start.
0:43:11 > 0:43:14It's a very atmospheric morning but it's a bit cold and damp.
0:43:14 > 0:43:18I mean, look at it, there's a whole mystery, we could be anywhere but it's good, though,
0:43:18 > 0:43:21probably the best natural harbour on the planet.
0:43:21 > 0:43:26So, a good sleep and a good breakfast, another cup of tea, go diving.
0:43:28 > 0:43:30Because the deep ocean is so difficult to get to,
0:43:30 > 0:43:34studying any kind of animal behaviour there is incredibly hard.
0:43:36 > 0:43:37But in the Sunken Valley,
0:43:37 > 0:43:43Tooni is hoping for the opportunity to record a behaviour that's never been filmed here before.
0:43:47 > 0:43:50God, it's pitch black, isn't it?
0:43:50 > 0:43:55We really are descending into the pitch black. It's like being on a night dive.
0:43:55 > 0:43:57Here's the bottom, Tooni.
0:44:00 > 0:44:06They're searching for creatures which look as though they've come from a science-fiction film...
0:44:06 > 0:44:07sea pens.
0:44:10 > 0:44:14- They're beautiful, yet very strange creatures, aren't they?- Yeah.
0:44:14 > 0:44:17They're called sea pens because they look like
0:44:17 > 0:44:21- those beautiful old feather quills that people used to write with.- OK.
0:44:21 > 0:44:27Like everything else beneath the tannin layer, these sea pens are animals.
0:44:27 > 0:44:31There's so little light here, no plants can survive.
0:44:31 > 0:44:34There are some big sea pens here, aren't there?
0:44:34 > 0:44:38Look, you can see it turning with the current.
0:44:38 > 0:44:39Yeah.
0:44:39 > 0:44:46Each of these sea pens isn't a single animal, but a colony of individuals working together as one.
0:44:46 > 0:44:50Different parts of the colony have specialised functions,
0:44:50 > 0:44:55such as pumping water, reproduction or catching prey.
0:44:55 > 0:44:57So it's like the ultimate in community living.
0:44:57 > 0:45:01I've got myself convinced that I'm at 150 metres
0:45:01 > 0:45:07because it's cold and dark, and there's loads of weird creatures down here.
0:45:12 > 0:45:14Sea pens come in and out of the sediment
0:45:14 > 0:45:18but no-one can see this behaviour because it happens so slowly.
0:45:18 > 0:45:24So the team has set up a time-lapse camera to try to record it here for the very first time.
0:45:24 > 0:45:29That one there has actually almost completely disappeared.
0:45:29 > 0:45:33They pump water into themselves to bring themselves out of the sediment
0:45:33 > 0:45:36and then when they want to go back down,
0:45:36 > 0:45:38they release that water so they can retract.
0:45:42 > 0:45:44The speeded-up footage
0:45:44 > 0:45:48shows how, over four hours, some of the sea pens gradually deflate
0:45:48 > 0:45:51and bury themselves in the seabed.
0:45:54 > 0:45:56It's thought this behaviour
0:45:56 > 0:45:59might protect sea pens from predators,
0:45:59 > 0:46:01and this may be the first time
0:46:01 > 0:46:04that evidence has been captured to confirm it.
0:46:07 > 0:46:11Close examination of the time-lapse clip shows a yellow sea slug,
0:46:11 > 0:46:17a sea pen predator, enter the scene and make contact with some of them.
0:46:17 > 0:46:22Each sea pen it touches withdraws into the sediment.
0:46:25 > 0:46:27This has never been seen before
0:46:27 > 0:46:29and will help us to understand
0:46:29 > 0:46:32this little-known world of deep-sea creatures.
0:46:41 > 0:46:47The Sunken Valley has allowed us a privileged glimpse into the lives of its deep-sea inhabitants.
0:46:47 > 0:46:50The deep sea is almost impenetrable,
0:46:50 > 0:46:56therefore the only opportunity that I get to see deep water creatures in, within my capabilities, is here.
0:46:56 > 0:47:00So I think it's been a really special part of the expedition.
0:47:17 > 0:47:19Next day, the team is re-united.
0:47:19 > 0:47:21Here they come.
0:47:23 > 0:47:24Hello!
0:47:28 > 0:47:32It's the final leg of the Southern Ocean expedition.
0:47:35 > 0:47:41As they round Tasman Island, they spot a large group of Australian fur seals.
0:47:41 > 0:47:45Oh, there are loads, there are loads of them on that flat section there.
0:47:45 > 0:47:51Hunted almost to extinction, these fur seals are now a protected species.
0:47:51 > 0:47:54But their recovery's been slow,
0:47:54 > 0:47:58so to see such a big colony is very encouraging.
0:47:59 > 0:48:00Good to go.
0:48:00 > 0:48:05Lucy and marine biologist Tooni want to check them out underwater.
0:48:09 > 0:48:12You see how much of a good look they're giving us,
0:48:12 > 0:48:14really, really looking.
0:48:17 > 0:48:19You see the way they power themselves.
0:48:19 > 0:48:22They just give that massive pull down of their front flippers
0:48:22 > 0:48:25and then they streamline and twist and turn.
0:48:32 > 0:48:33Lucy, come on!
0:48:35 > 0:48:39Australian fur seals have dense coats with coarse outer hairs
0:48:39 > 0:48:42that trap air to insulate them against the cold.
0:48:42 > 0:48:45As the seals dive, the air is released as bubbles.
0:48:47 > 0:48:50They're so streamlined underwater, aren't they?
0:48:54 > 0:49:01Their incredible speed and agility underwater allow them to catch even fast-moving prey such as squid.
0:49:04 > 0:49:06Faster than a speeding bullet.
0:49:06 > 0:49:13The presence of so many boisterous and playful seals seems to bode well for this population.
0:49:19 > 0:49:25It's clear that the waters of the Southern Ocean still support an amazing amount of marine life.
0:49:27 > 0:49:32But they are changing, and much faster than anywhere else in the world.
0:49:36 > 0:49:42The team has seen the devastating effects of warming waters here, especially on kelp forests.
0:49:44 > 0:49:46So can anything be done to save them?
0:49:46 > 0:49:51People don't care about kelp. Everyone's worried about the dolphins and the whales,
0:49:51 > 0:49:53and they should be worried about the kelp
0:49:53 > 0:49:59cos they are the ecosystem engineers, they're the ones that create the structure for rest of the habitat.
0:49:59 > 0:50:02It's one of the reasons why ecosystem management
0:50:02 > 0:50:06is one of the most important things in marine conservation and marine biology.
0:50:06 > 0:50:08You've got to look at the ecosystem,
0:50:08 > 0:50:13you can't just pick one species and attempt to conserve that - it doesn't work.
0:50:16 > 0:50:19Philippe has heard about a ground-breaking new study
0:50:19 > 0:50:23that could help restore balance to Tasmania's kelp ecosystems.
0:50:26 > 0:50:31Today, he and Tooni are joining this project to take part in a special event,
0:50:31 > 0:50:35one that's the culmination of years of research and planning.
0:50:37 > 0:50:40- Hi.- Hello. - Good morning.- I'm Tooni.
0:50:40 > 0:50:47Dr Craig Johnson and his team plan to release hundreds of large rock lobsters into damaged kelp areas.
0:50:47 > 0:50:51These guys have been out for a little while so they're fairly docile.
0:50:51 > 0:50:55He's collected the lobsters from deep offshore waters.
0:50:55 > 0:50:58They're one of the few natural predators of the sea urchins
0:50:58 > 0:51:01that have been decimating Tasmania's kelp beds.
0:51:03 > 0:51:08Craig's team is hoping that these lobsters will feast on the sea urchins.
0:51:08 > 0:51:13This could bring their numbers under control, so the dwindling kelp has a chance to recover.
0:51:15 > 0:51:21About two-thirds of the animals will be released on the urchin barren and one lot into the adjacent seaweed.
0:51:21 > 0:51:27We don't know anywhere else in the world that's moved such a large number of large lobsters
0:51:27 > 0:51:31- to look for ecosystem level effects like this.- Yeah, right.
0:51:31 > 0:51:34Oh, my God, the weight of him!
0:51:34 > 0:51:39All the lobsters need to be scanned for individual microchip numbers,
0:51:39 > 0:51:41then they can be tracked after their release.
0:51:41 > 0:51:444480, done.
0:51:47 > 0:51:49Look at that!
0:51:50 > 0:51:52A monster, it's amazing.
0:51:53 > 0:51:55Easy now, buddy.
0:51:56 > 0:51:58Oh! I've got a live one!
0:51:58 > 0:52:04We've got a revolt in the bucket over here, Tooni, a lobster rebellion.
0:52:04 > 0:52:05Behave!
0:52:05 > 0:52:09It's going on a walkabout, I know you're in Australia, but...
0:52:09 > 0:52:11The clock is ticking.
0:52:11 > 0:52:16The lobsters need to be taken to the release site and put back in the water as quickly as possible.
0:52:34 > 0:52:37At the release site, Craig's team is already in position.
0:52:37 > 0:52:43The real problem for us right now is when they're in the warmth, they do start to deteriorate
0:52:43 > 0:52:48quite quickly, so our priority now is to really try and, try and wham these down as quickly as we can.
0:52:53 > 0:52:57This has never been done before and I think it's fascinating,
0:52:57 > 0:53:01the idea of reintroducing these very mature lobsters back into the ecosystem.
0:53:01 > 0:53:03This is really cutting edge science at work,
0:53:03 > 0:53:08so being able to see kind of it happening at its inception, I think, is very exciting.
0:53:08 > 0:53:09OK...
0:53:11 > 0:53:12And let go.
0:53:17 > 0:53:23The first batch of lobsters is being released into an area that was once a lush kelp bed.
0:53:23 > 0:53:25This is definitely an urchin barren.
0:53:25 > 0:53:32I mean, look at it, there's not a single living piece of plant material anywhere.
0:53:33 > 0:53:36So this is the culprit right here.
0:53:36 > 0:53:38Look at the spines on this sucker.
0:53:39 > 0:53:41Big, nasty sea urchin.
0:53:41 > 0:53:46And so it takes these big lobsters to reach around the sea urchin,
0:53:46 > 0:53:51flip it over, and be able to get right in there.
0:53:51 > 0:53:55That is where the sea urchin is the most vulnerable, where its mouth is.
0:53:55 > 0:53:58Very little actually kills these things off.
0:53:58 > 0:54:01That's why the lobster reintroduction is so important.
0:54:04 > 0:54:10Large lobsters are a rarity in many kelp forests because they've been fished out,
0:54:10 > 0:54:13but by bringing these giants here from deeper water,
0:54:13 > 0:54:15that's about to change.
0:54:17 > 0:54:18Oh!
0:54:19 > 0:54:23They're pretty desperate to get out, I think.
0:54:23 > 0:54:27These lobsters use their powerful tails to escape from predators.
0:54:28 > 0:54:30Ow ow ow ow!
0:54:34 > 0:54:37He got me right on the hand then. That's going to leave a mark.
0:54:40 > 0:54:42Over the coming months, Craig's team will track
0:54:42 > 0:54:48the movement of these lobsters and monitor the impact they're having on the urchin population.
0:54:50 > 0:54:57If the experiment works, it could provide hope for the long-term survival of Tasmania's kelp forests.
0:54:59 > 0:55:00There we go.
0:55:00 > 0:55:05It's so fantastic to have packed these into the crates
0:55:05 > 0:55:10and now to actually bring them to their new home, where hopefully
0:55:10 > 0:55:14they're going to start eating these very big sea urchins.
0:55:19 > 0:55:21Philippe and Tooni's final job
0:55:21 > 0:55:27is to release the last few crates of lobsters into the second of Craig's study areas.
0:55:27 > 0:55:29Look in here!
0:55:29 > 0:55:34Do you know what, Philippe? I can feel mine bursting to get out.
0:55:36 > 0:55:38Here we go!
0:55:38 > 0:55:40Here the kelp is still healthy.
0:55:40 > 0:55:45The hope is that this lobster re-introduction will help keep it that way.
0:55:45 > 0:55:49This is the kind of habitat these lobsters should be in.
0:55:49 > 0:55:52There we go, one more, woo!
0:55:54 > 0:55:58There's just lobster flying everywhere!
0:55:58 > 0:56:01If it's successful, this project's approach
0:56:01 > 0:56:06could offer hope to other threatened marine ecosystems around the world.
0:56:08 > 0:56:10Woo! Mission accomplished!
0:56:13 > 0:56:15I got a bit overexcited down there.
0:56:15 > 0:56:19Well, it felt good, kind of, you know, being a part of the solution
0:56:19 > 0:56:25and you really, really hope that those lobsters are going to chow on those sea urchins.
0:56:25 > 0:56:29- There's enough of them down there. - But didn't you think for Craig and the scientists
0:56:29 > 0:56:34working on this project today, that release event is like the culmination of years of work for them?
0:56:34 > 0:56:38I just think it's fantastic that we're here to witness that.
0:56:38 > 0:56:41It's the forefront of conservation biology and that's what it's all about.
0:56:54 > 0:57:01It's the end of the Southern Ocean expedition and it's been a challenging but inspiring journey.
0:57:02 > 0:57:08The team has felt the power of these seas, and seen the damage they can inflict.
0:57:10 > 0:57:14But these waters have also revealed hidden treasures,
0:57:14 > 0:57:20extraordinary marine life in unique but often fragile habitats.
0:57:22 > 0:57:27I never appreciated just how devastated the kelp forests have become
0:57:27 > 0:57:30until I saw it with my own eyes.
0:57:30 > 0:57:34That encapsulated both the importance of the Southern Ocean
0:57:34 > 0:57:38and the peril that we face as it changes.
0:57:40 > 0:57:46There can now be no doubt that changes are having a profound impact on life in the Southern Ocean,
0:57:46 > 0:57:50but this is an ocean connected to three others,
0:57:50 > 0:57:56and what is still unknown is how the rapid changes here could affect the rest of the world.
0:58:03 > 0:58:07Next time, the Oceans team travels to the pristine southern Red Sea.
0:58:09 > 0:58:14They explore coral, thriving in some of the world's warmest waters.
0:58:15 > 0:58:20They dive a shipwreck carrying a deadly cargo.
0:58:20 > 0:58:22There are thousands of bombs here.
0:58:22 > 0:58:26And they witness the birth of an ocean.
0:58:35 > 0:58:37Subtitles by Red Bee Media Ltd
0:58:37 > 0:58:40E-mail subtitling@bbc.co.uk