0:00:29 > 0:00:32The oceans, seemingly limitless,
0:00:32 > 0:00:34invoke in us a sense of awe
0:00:34 > 0:00:37and wonder, and also sometimes fear.
0:00:37 > 0:00:41They cover 70% of the surface of our planet,
0:00:41 > 0:00:44and yet they are still the least explored.
0:00:46 > 0:00:51Hidden beneath the waves, right beneath my feet,
0:00:51 > 0:00:54there are creatures beyond our imagination.
0:01:09 > 0:01:13With revolutionary technology, we can enter new worlds...
0:01:19 > 0:01:22..and shine a light on behaviours in ways that were impossible
0:01:22 > 0:01:25just a generation ago.
0:01:32 > 0:01:35In this extended special, we celebrate
0:01:35 > 0:01:37some of the highlights from the series.
0:01:40 > 0:01:42We will journey across the globe...
0:01:48 > 0:01:51..from the warm waters of the tropics...
0:01:56 > 0:01:59..to the coldest seas around the poles...
0:02:01 > 0:02:04..and down into the unexplored depths...
0:02:04 > 0:02:07WHOOSHING
0:02:09 > 0:02:13..to bring us a new understanding of life beneath the waves.
0:02:13 > 0:02:14BIRDS SQUAWK
0:02:21 > 0:02:24This is Blue Planet II.
0:03:23 > 0:03:27The surface of the ocean conceals the many creatures that
0:03:27 > 0:03:28live beneath.
0:03:40 > 0:03:42But not all.
0:03:45 > 0:03:48Bottlenose dolphins.
0:03:50 > 0:03:53They are extremely intelligent.
0:04:03 > 0:04:06And with this intelligence comes playfulness.
0:04:13 > 0:04:15They surf...
0:04:17 > 0:04:21..and as far as we can tell, they do so for the sheer joy of it.
0:04:50 > 0:04:52But to properly appreciate their true character...
0:04:52 > 0:04:54DOLPHINS SING
0:04:54 > 0:04:58..you have to travel with them into THEIR world.
0:05:10 > 0:05:14A pod of bottlenose dolphins is visiting a
0:05:14 > 0:05:16coral reef in the Red Sea.
0:05:19 > 0:05:23For the youngsters, there are things to be learned here.
0:05:23 > 0:05:25DOLPHINS SING
0:05:31 > 0:05:35The adults lead a calf to a particular bush-like coral
0:05:35 > 0:05:39called a gorgonian.
0:05:46 > 0:05:49And here the adults behave rather strangely.
0:05:56 > 0:05:59They deliberately rub themselves through the fronds.
0:06:13 > 0:06:16Their calf seems reluctant to do so.
0:06:28 > 0:06:30By watching his elders,
0:06:30 > 0:06:34he may be realising that this is something he ought to do.
0:06:41 > 0:06:44Gorgonian fronds, in fact, are covered with a mucus
0:06:44 > 0:06:49that can have anti-inflammatory and anti-microbial properties.
0:06:54 > 0:06:57So maybe the adult dolphins are doing this to protect
0:06:57 > 0:06:59themselves from infection.
0:07:09 > 0:07:14The dolphins' intimate knowledge of the reef is spurring us
0:07:14 > 0:07:17to search for new medicines here, too.
0:07:27 > 0:07:32Tropical coral reefs occupy only a tenth of 1% of the ocean floor.
0:07:35 > 0:07:40But their shallow warm waters and stable year-round conditions
0:07:40 > 0:07:44support some of the most crowded and varied communities
0:07:44 > 0:07:46to be found anywhere in the oceans.
0:07:49 > 0:07:54And there are new discoveries to be made on every one of them.
0:08:14 > 0:08:17One creature on Australia's Great Barrier Reef
0:08:17 > 0:08:22is challenging our understanding of fish intelligence.
0:08:23 > 0:08:28A tusk fish, and you can see why it gets its name.
0:08:32 > 0:08:37He does something few would have believed a fish could do.
0:08:43 > 0:08:47Every morning, he travels to the edge of the reef.
0:09:02 > 0:09:05He's searching for something special to eat amongst the coral rubble
0:09:05 > 0:09:07and sand.
0:09:10 > 0:09:12Here's one.
0:09:14 > 0:09:15A small clam.
0:09:22 > 0:09:26But how to crack it open and get to the meat?
0:09:37 > 0:09:41He takes it all the way back to his special kitchen...
0:09:50 > 0:09:55..a bowl-shaped coral that has a particular bump on the inside
0:09:55 > 0:09:58that he always uses.
0:10:15 > 0:10:17It's not easy
0:10:17 > 0:10:19if you have no hands.
0:10:26 > 0:10:27Oops!
0:10:27 > 0:10:30There it goes again.
0:10:34 > 0:10:38But he's got great determination...
0:10:43 > 0:10:45..and surprising accuracy.
0:11:05 > 0:11:06At last.
0:11:09 > 0:11:12So here is a fish that uses tools.
0:11:14 > 0:11:18Some fish are much cleverer than you might suppose.
0:11:35 > 0:11:39The density of the animals on tropical reefs makes
0:11:39 > 0:11:42competition inevitable and extreme...
0:11:43 > 0:11:46..not only for those that live within the reefs,
0:11:46 > 0:11:49but for the birds that fly above them.
0:11:49 > 0:11:53BIRDS SQUAWK
0:11:53 > 0:11:58During the dry season, over half a million terns crowd onto
0:11:58 > 0:12:01this remote atoll in the Indian Ocean.
0:12:08 > 0:12:13Their chicks are still in their dark juvenile plumage.
0:12:28 > 0:12:31Those just starting to learn to fly use the
0:12:31 > 0:12:35shallow lagoon that occupies the centre of the atoll
0:12:35 > 0:12:37as their training ground.
0:12:39 > 0:12:42It's difficult for some of them to stay aloft for long.
0:13:07 > 0:13:09Giant trevallies!
0:13:21 > 0:13:25Usually, they are solitary hunters,
0:13:25 > 0:13:29but about 50 of them have come here from neighbouring reefs,
0:13:29 > 0:13:32attracted by this abundance of potential prey.
0:13:40 > 0:13:44The fledglings stay out of the water if they can.
0:13:45 > 0:13:48They even drink on the wing.
0:14:05 > 0:14:11If the trevally are to catch one now, they have to up their game.
0:14:20 > 0:14:24So there is a fish here that, amazingly, has a brain
0:14:24 > 0:14:28capable of calculating the air speed,
0:14:28 > 0:14:31altitude and trajectory of a bird.
0:15:02 > 0:15:05The time comes when every fledgling has
0:15:05 > 0:15:08to take to the air and collect food for itself.
0:15:32 > 0:15:35Their parents lead them to the training grounds.
0:16:03 > 0:16:05BIRDS SQUAWK
0:17:10 > 0:17:15If they are to survive, they must learn quickly.
0:17:23 > 0:17:27After a month of practising over the lagoon, the youngsters start
0:17:27 > 0:17:31to leave and take their chances out over the open sea.
0:17:39 > 0:17:44The oceans hold 97% of all the water in the world.
0:17:47 > 0:17:50As the sun warms their surface, water evaporates.
0:17:51 > 0:17:53The vapour rises into the sky
0:17:53 > 0:17:58until it cools and condenses into towering clouds.
0:17:58 > 0:18:00THUNDER CRASHES
0:18:00 > 0:18:03And they generate huge storms.
0:18:07 > 0:18:11The spin of the Earth deflects these storms, north and south,
0:18:11 > 0:18:13into cooler latitudes.
0:18:22 > 0:18:24As they travel across the sea,
0:18:24 > 0:18:28storm-driven winds create huge swells.
0:18:32 > 0:18:34When the swells reach shallower water,
0:18:34 > 0:18:37they rise into gigantic waves.
0:18:55 > 0:18:58In its lifetime, a large storm can release
0:18:58 > 0:19:03energy that is the equivalent of 10,000 nuclear bombs.
0:19:28 > 0:19:31These are the seasonal seas.
0:19:33 > 0:19:38And when they warm in spring, they can suddenly explode with life.
0:19:53 > 0:19:56Mobula rays have gathered in Mexico's
0:19:56 > 0:19:58Sea of Cortez in vast numbers.
0:20:06 > 0:20:08Why do they leap?
0:20:11 > 0:20:13Is it to tell others that they're here?
0:20:16 > 0:20:18No-one knows.
0:20:21 > 0:20:23They feed mostly at night,
0:20:23 > 0:20:28for that is when vast swarms of plankton rise from the depths.
0:20:34 > 0:20:37The disturbance in the water stimulates
0:20:37 > 0:20:41many of the planktonic creatures to luminesce.
0:20:43 > 0:20:45Only now do we have the technology to
0:20:45 > 0:20:47record their faint glow.
0:20:56 > 0:20:59The feasting rays swim through them,
0:20:59 > 0:21:03creating an extraordinary ballet of life and death.
0:21:51 > 0:21:56The richness of these waters is based on microscopic plants,
0:21:56 > 0:21:58phytoplankton, which bloom on
0:21:58 > 0:22:02such a massive scale, they benefit us all.
0:22:05 > 0:22:09They, together with seaweeds and seagrasses,
0:22:09 > 0:22:11produce as much oxygen as
0:22:11 > 0:22:14all the forests and grassy plains on land.
0:22:26 > 0:22:29In the shallow waters of the seasonal seas
0:22:29 > 0:22:31lie great undersea forests.
0:22:40 > 0:22:44Giant kelp towers 60 metres high.
0:22:55 > 0:23:00These enchanted forests are crowded with life.
0:23:03 > 0:23:06Creatures jostle for space and food.
0:23:15 > 0:23:19In the fiercely competitive kelp forests off Southern Africa,
0:23:19 > 0:23:22survival can demand great ingenuity.
0:23:25 > 0:23:27A common octopus.
0:23:30 > 0:23:33She is waiting for prey to pass by.
0:23:38 > 0:23:40A crab will do.
0:23:46 > 0:23:49The octopus sets off in pursuit...
0:24:04 > 0:24:10..and then lurks with the patience of an ambush hunter.
0:24:36 > 0:24:39But the octopus shares the Cape waters with a great
0:24:39 > 0:24:42concentration of other predators.
0:24:49 > 0:24:51Fur seals...
0:24:53 > 0:24:55..and sharks.
0:24:58 > 0:25:00They all eat octopus...
0:25:00 > 0:25:03..if they can find one.
0:25:11 > 0:25:14And pyjama sharks are experts...
0:25:17 > 0:25:19..at hunting in the undergrowth.
0:25:28 > 0:25:30Time to disappear.
0:25:36 > 0:25:39But these tough-skinned little sharks are
0:25:39 > 0:25:42small enough to reach deep into crevices.
0:26:01 > 0:26:04But the octopus is far from finished.
0:26:07 > 0:26:10She slips her tentacles into the shark's gills.
0:26:12 > 0:26:14That prevents the shark from breathing.
0:26:19 > 0:26:21So the shark HAS to let go.
0:26:33 > 0:26:36When caught out in the open and vulnerable,
0:26:36 > 0:26:39this octopus does something truly extraordinary...
0:26:41 > 0:26:43..and never recorded before.
0:26:54 > 0:26:56She disguises herself...
0:26:59 > 0:27:01..with a protective armour of shells.
0:27:07 > 0:27:10She's hiding in plain sight.
0:27:21 > 0:27:24The shark can sense its prey.
0:27:38 > 0:27:40But the shells confuse it.
0:27:46 > 0:27:49In a forest full of hungry mouths,
0:27:49 > 0:27:53superior wits allow this octopus to stay alive.
0:28:06 > 0:28:09In the underwater forests off northern Japan...
0:28:14 > 0:28:17..the residents of this sunken wreck
0:28:17 > 0:28:19are waiting for the summer temperatures to reach
0:28:19 > 0:28:2116 degrees Celsius.
0:28:25 > 0:28:28That, for some, is the time for mating.
0:28:42 > 0:28:46A kind of giant wrasse called a kobudai.
0:28:53 > 0:28:54This is a male...
0:29:00 > 0:29:02..and in female terms,
0:29:02 > 0:29:04he's particularly handsome.
0:29:11 > 0:29:15He's a metre long and weighs 15 kilos...
0:29:18 > 0:29:22..much larger than the diminutive female.
0:29:25 > 0:29:28And he is ready to breed.
0:29:31 > 0:29:33He attempts to mate with her,
0:29:33 > 0:29:37and with any of the other dozen or so females
0:29:37 > 0:29:39that live in his territory...
0:29:39 > 0:29:42..whenever he gets the chance.
0:29:56 > 0:29:59But females from around ten years old take
0:29:59 > 0:30:02little notice of his advances.
0:30:30 > 0:30:33This is because, when any large female reaches a critical
0:30:33 > 0:30:38body size, she can begin a dramatic transformation.
0:30:56 > 0:30:58Over just a few months,
0:30:58 > 0:31:01particular enzymes inside her body cease to work...
0:31:04 > 0:31:07..and male hormones start to circulate.
0:31:12 > 0:31:16As time passes, her head expands
0:31:16 > 0:31:19and her chin gets longer.
0:31:22 > 0:31:25A "she" has changed into a "he".
0:31:35 > 0:31:38And with this comes a change in temperament.
0:31:45 > 0:31:47The old male who ruled all the females here...
0:31:49 > 0:31:52..is challenged to a face-off.
0:31:59 > 0:32:04The more bulbous the head, the more it intimidates an opponent.
0:32:31 > 0:32:34The territory has a new ruler.
0:32:46 > 0:32:50Only the largest females transform themselves in this way.
0:32:55 > 0:32:59But the change enables them to have more mates,
0:32:59 > 0:33:04so they will have many more offspring carrying their genes.
0:33:10 > 0:33:13But a new male can't afford to be complacent.
0:33:15 > 0:33:19Inside the body of every kobudai female
0:33:19 > 0:33:22there is a new male-in-waiting.
0:33:40 > 0:33:42At the height of summer, there is an
0:33:42 > 0:33:46explosion in the population of another forest resident.
0:33:48 > 0:33:52But this one is out to attack the very forest itself.
0:33:56 > 0:33:58Off the Pacific coast of North America,
0:33:58 > 0:34:02armies of sea urchins cut through the kelp fronds.
0:34:10 > 0:34:12Protected by a coat of spines,
0:34:12 > 0:34:17with their mouths full of razor teeth, they fell the great stalks.
0:34:36 > 0:34:38Behind them, they leave a wasteland,
0:34:38 > 0:34:41known as an urchin barren.
0:34:56 > 0:34:58But help is at hand.
0:35:07 > 0:35:09Sea otters.
0:35:13 > 0:35:15All other kinds of otters spend much of
0:35:15 > 0:35:19their lives on land, but sea otters rarely
0:35:19 > 0:35:20leave the water.
0:35:24 > 0:35:29At first, a newly born pup is not a very good swimmer,
0:35:29 > 0:35:33so its mother spends hours grooming its fur to make it buoyant.
0:35:40 > 0:35:44But to provide her youngster with milk and keep herself warm,
0:35:44 > 0:35:48she must eat up to 30% of her body weight every day.
0:36:08 > 0:36:11She does that by eating shellfish.
0:36:16 > 0:36:21And urchins are among a sea otter's favourite delicacies.
0:36:39 > 0:36:43In the past, sea otters were hunted so intensively
0:36:43 > 0:36:46for their fur that they came close to extinction.
0:36:52 > 0:36:58With them gone, many kelp forests were replaced with urchin barrens.
0:37:08 > 0:37:10Today, sea otters are protected.
0:37:13 > 0:37:16And as their numbers slowly return,
0:37:16 > 0:37:19many of the kelp forests are recovering, too.
0:37:35 > 0:37:39Now, in some remote places, sea otters are so numerous,
0:37:39 > 0:37:42they assemble in huge rafts...
0:37:47 > 0:37:51..something that hasn't been seen for over a century.
0:38:24 > 0:38:29Coasts are the most swiftly changing of all ocean habitats...
0:38:36 > 0:38:38..because of the tides.
0:38:50 > 0:38:55Tides are created as the moon's gravity pulls at the sea.
0:39:05 > 0:39:10As the moon circles our planet, the seas rise and fall...
0:39:12 > 0:39:14..typically twice a day...
0:39:16 > 0:39:20..creating the most constantly dynamic landscapes on Earth.
0:39:30 > 0:39:35Nowhere else do sea-living creatures face such changeable conditions...
0:39:39 > 0:39:44..with the daily risk of drying out and being scorched by the sun.
0:39:50 > 0:39:53Where the tide retreats across a rocky shore,
0:39:53 > 0:39:56it can leave behind a temporary oasis.
0:40:04 > 0:40:06A rock pool.
0:40:16 > 0:40:19Seemingly, it's a haven of calm.
0:40:22 > 0:40:24But not for long.
0:40:26 > 0:40:28Turning minutes into seconds reveals
0:40:28 > 0:40:30unexpected dramas.
0:40:44 > 0:40:46In rock pools, grazers,
0:40:46 > 0:40:49scavengers and filter-feeders must all make the most of
0:40:49 > 0:40:53the few short hours before the tide returns.
0:41:10 > 0:41:14Anemones gulp down anything they can reach...
0:41:16 > 0:41:19..though some meals are harder to digest than others.
0:41:19 > 0:41:21LOW RUMBLING
0:41:28 > 0:41:32These magical worlds soon become battlegrounds.
0:41:35 > 0:41:41A deadly predator with five arms and, on the underside, a mouth.
0:41:44 > 0:41:47The ochre starfish.
0:41:51 > 0:41:54And it's in search of limpets.
0:42:13 > 0:42:16For some, there is no escape.
0:42:16 > 0:42:18It engulfs them.
0:42:26 > 0:42:29But other limpets have a secret defence.
0:42:32 > 0:42:34They deploy a slippery shield...
0:42:37 > 0:42:40..which allows them to slide to safety.
0:42:46 > 0:42:50And this limpet has its own personal bodyguard.
0:42:58 > 0:43:01A scale worm, with a nasty nip!
0:43:06 > 0:43:11The starfish prefers food that doesn't bite back.
0:43:13 > 0:43:14The limpet carries on,
0:43:14 > 0:43:18its bodyguard tucked safe under its shell.
0:43:20 > 0:43:25But there is one creature that limpets have no defence against.
0:43:29 > 0:43:31A clingfish.
0:43:33 > 0:43:36It has teeth that can lever under the shell..
0:43:38 > 0:43:41..and twist the limpet off like a bottle top.
0:43:45 > 0:43:49The clingfish then swallows it, shell and all.
0:43:58 > 0:44:02Rock pool dramas like these last just a few short hours
0:44:02 > 0:44:05before the tide returns.
0:44:09 > 0:44:11Every day, the sea becomes land,
0:44:11 > 0:44:14and the land becomes sea...
0:44:22 > 0:44:24..bringing new opportunities.
0:44:28 > 0:44:30A Sally Lightfoot crab.
0:44:33 > 0:44:37One of thousands of shore crabs just waiting for their moment.
0:44:40 > 0:44:43Every day, they gather on the rocky shores of Brazil...
0:44:47 > 0:44:50..waiting for the tide to go out...
0:44:59 > 0:45:02..which exposes their feeding grounds...
0:45:02 > 0:45:07..seaweed-covered rocks, 100 metres from the shore.
0:45:16 > 0:45:19Getting there is a race against the tide.
0:45:25 > 0:45:28They leap from rock to rock.
0:45:42 > 0:45:46These crabs seem to be afraid of the water.
0:45:59 > 0:46:01And for good reason.
0:46:12 > 0:46:14A moray eel.
0:46:16 > 0:46:20The chain moray is a specialist crab-hunter.
0:46:25 > 0:46:30Its blunt teeth can easily grip and crush a crab's shell.
0:46:36 > 0:46:39It's the crab's deadliest enemy.
0:46:49 > 0:46:53But the crabs' feeding grounds are still a long way off.
0:46:59 > 0:47:02They must press on.
0:47:24 > 0:47:26Halfway.
0:47:30 > 0:47:33But their enemy has other ideas...
0:47:39 > 0:47:41..crossing the land...
0:47:47 > 0:47:50..to reset the ambush.
0:47:53 > 0:47:56To feed, the crabs must keep going.
0:48:02 > 0:48:04But nowhere is safe.
0:48:09 > 0:48:11An octopus, also a crab-killer.
0:48:37 > 0:48:39The crabs make a dash for it.
0:49:06 > 0:49:07Made it!
0:49:16 > 0:49:21Risking life and limb to graze on these seaweed pastures.
0:49:25 > 0:49:29But in two hours' time, when the tide starts to turn,
0:49:29 > 0:49:33they will have to run the gauntlet all over again.
0:49:52 > 0:49:56As we leave our coasts and head for the high seas,
0:49:56 > 0:49:58we enter the big blue.
0:50:07 > 0:50:10Covering over half our planet's surface,
0:50:10 > 0:50:12it's the world's greatest wilderness.
0:50:23 > 0:50:27Here, there is nowhere to hide and little to eat.
0:50:32 > 0:50:34It's the marine equivalent of a desert.
0:50:39 > 0:50:41But there are rare moments
0:50:41 > 0:50:45when these empty seas are filled with life.
0:50:54 > 0:50:59Lanternfish, off the Pacific coast of Costa Rica.
0:50:59 > 0:51:02They're scarcely bigger than minnows, but what they lack in size,
0:51:02 > 0:51:05they make up for in numbers.
0:51:08 > 0:51:12They are one of the most numerous fish anywhere.
0:51:19 > 0:51:22Normally, they only come to the surface at night,
0:51:22 > 0:51:24to feed on plankton,
0:51:24 > 0:51:27but this immense shoal has risen during the day,
0:51:27 > 0:51:29almost certainly in order to spawn.
0:51:38 > 0:51:42For open-ocean hunters, this would be a bonanza.
0:51:47 > 0:51:49DOLPHINS SING
0:51:52 > 0:51:54Spinner dolphins.
0:51:58 > 0:52:01They're named after their acrobatic leaps.
0:52:06 > 0:52:09They stick together in a super-pod, 5,000 strong.
0:52:13 > 0:52:17And now they have located the shoal, using their echo-sounding calls.
0:52:18 > 0:52:21But they have to get to it quickly.
0:52:24 > 0:52:26They are not the only hunters here.
0:52:26 > 0:52:30Yellowfin tuna have also detected the shoal.
0:52:39 > 0:52:43And behind them, with their two-metre wingspans, mobula rays.
0:52:53 > 0:52:57Now sailfish, one of the fastest fish in the sea,
0:52:57 > 0:52:59have joined the chase.
0:53:05 > 0:53:09The lanternfish may return to the deep at any moment.
0:53:16 > 0:53:19But now the dolphins have got here.
0:53:19 > 0:53:22DOLPHINS SING
0:53:46 > 0:53:49They swim beneath the shoal, pinning it to the surface
0:53:49 > 0:53:53and forcing the lanternfish to pack more closely together.
0:54:00 > 0:54:03And now the sea begins to boil.
0:54:12 > 0:54:16The tuna charge into the shoal at over 40mph.
0:54:47 > 0:54:50The slower-swimming rays arrive at last.
0:54:57 > 0:54:59With their immense mouths agape,
0:54:59 > 0:55:02they scoop up the lanternfish by the hundred.
0:55:05 > 0:55:09The shoal has now been largely dispersed,
0:55:09 > 0:55:12and the sailfish pick off the survivors.
0:55:15 > 0:55:19In just 15 minutes, all that's left is a
0:55:19 > 0:55:21silvery confetti of scales.
0:55:33 > 0:55:37But here, such feasts are only too infrequent.
0:55:45 > 0:55:49Whilst the dolphins perform great feats of endurance,
0:55:49 > 0:55:51others are driven to even greater extremes
0:55:51 > 0:55:55to find food in this ocean desert.
0:56:13 > 0:56:15A sleeping giant.
0:56:19 > 0:56:21A sperm whale.
0:56:28 > 0:56:32This family is resting between bouts of feeding.
0:56:39 > 0:56:43Who knows what the owners of the biggest brain in the planet
0:56:43 > 0:56:45dream about?
0:56:51 > 0:56:53One has a calf.
0:56:55 > 0:56:59It's about two weeks old, but still dependent on its mother's milk.
0:56:59 > 0:57:01It's hungry.
0:57:05 > 0:57:08It communicates with its mother using a
0:57:08 > 0:57:10pattern of clicks.
0:57:10 > 0:57:12CLICKING
0:57:15 > 0:57:18But its mother slumbers on.
0:57:23 > 0:57:28The calf, covered in suckerfish, of which it can't yet rid itself,
0:57:28 > 0:57:30has to be patient.
0:57:57 > 0:58:00Sleep over and refreshed,
0:58:00 > 0:58:02the whales move on.
0:58:04 > 0:58:07Sperm whales don't wait for their prey to
0:58:07 > 0:58:09rise to the surface.
0:58:09 > 0:58:12They swim down into the depths to find it.
0:58:17 > 0:58:20They take a series of heavy breaths...
0:58:23 > 0:58:25..to saturate their blood with oxygen...
0:58:28 > 0:58:30..then down they go.
0:58:39 > 0:58:42This entire family dives together in search of squid.
0:58:51 > 0:58:54A mother will push her body to the limits of her endurance,
0:58:54 > 0:58:59and already it's hard for her calf to keep up with her.
0:58:59 > 0:59:01CLICKING
0:59:09 > 0:59:12The calf sticks to its mother as closely as it can...
0:59:12 > 0:59:14CLICKING
0:59:14 > 0:59:16..touching her frequently...
0:59:18 > 0:59:20..as if for reassurance.
0:59:33 > 0:59:36But 300 metres down,
0:59:36 > 0:59:39it seems the calf can't hold its breath any longer.
1:00:03 > 1:00:08In their early years, calves are forced to sit out the hunt.
1:00:13 > 1:00:16The adults continue their dive.
1:00:29 > 1:00:33The mother changes her calls into a series of louder
1:00:33 > 1:00:35and more rapid clicks.
1:00:35 > 1:00:38CLICKING
1:00:41 > 1:00:45She's now using sonar to hunt down shoals of squid.
1:00:53 > 1:00:56At 800 metres, a burst of clicks.
1:00:56 > 1:00:59CLICKING QUICKENS
1:01:06 > 1:01:08Then silence.
1:01:10 > 1:01:12She's made a catch.
1:01:24 > 1:01:27A calf can have a long wait at the surface.
1:01:33 > 1:01:38A mother returns from the deep after as much as an hour.
1:01:40 > 1:01:43She has a stomach full of squid.
1:02:02 > 1:02:06Finally, this hungry calf can take some milk.
1:02:12 > 1:02:15It's one of the richest produced by any mammal,
1:02:15 > 1:02:19and the calf guzzles a bath full of it a day.
1:02:35 > 1:02:41It may be six years before a calf masters the art of deep diving
1:02:41 > 1:02:44and is able to find food for itself.
1:03:05 > 1:03:10Over half of all animals in the open ocean drift in currents.
1:03:26 > 1:03:29Jellyfish cross entire oceans,
1:03:29 > 1:03:31feeding on whatever happens
1:03:31 > 1:03:34to tangle with their tentacles.
1:03:43 > 1:03:45And when, by lucky chance,
1:03:45 > 1:03:48they encounter a patch of sea rich in plankton...
1:03:51 > 1:03:53..their numbers explode.
1:04:04 > 1:04:08It's such a successful strategy that jellies are
1:04:08 > 1:04:12one of the most common life forms on the planet.
1:04:25 > 1:04:28But among the jellies, and looking somewhat like them,
1:04:28 > 1:04:31is a rather more complex and sinister creature.
1:04:37 > 1:04:40The Portuguese man o' war.
1:04:44 > 1:04:48It floats with the help of a gas-filled bladder,
1:04:48 > 1:04:50topped by a vertical membrane.
1:04:51 > 1:04:55With that serving as a sail, it maintains a
1:04:55 > 1:04:57steady course through the waves.
1:05:00 > 1:05:02Long tentacles trail behind it.
1:05:05 > 1:05:10Each is armed with many thousands of stinging cells.
1:05:12 > 1:05:16A single tentacle could kill a fish or, in rare cases, a human.
1:05:27 > 1:05:31A tentacle has caught this one and reels it in.
1:05:38 > 1:05:40It's already paralysed.
1:05:44 > 1:05:46This voracious man o' war may collect
1:05:46 > 1:05:49over 100 small fish in a day.
1:05:56 > 1:05:59BIRDS SQUAWK
1:06:08 > 1:06:12Parts of the open ocean are deeper than the highest mountains
1:06:12 > 1:06:14that rise on the land.
1:06:22 > 1:06:26Now we can dive these uncharted depths to discover what
1:06:26 > 1:06:28secrets lie beneath.
1:06:42 > 1:06:47The deep ocean is as challenging to explore as space.
1:06:55 > 1:06:58Ready to carry on with the launch. All clear.
1:07:00 > 1:07:02We know more about the surface of Mars
1:07:02 > 1:07:06than we do about the deepest parts of our seas.
1:07:14 > 1:07:17As we descend into the deep,
1:07:17 > 1:07:19the pressure increases...
1:07:21 > 1:07:25..and the lights from above all but disappears.
1:07:27 > 1:07:30INDISTINCT RADIO CHATTER
1:07:30 > 1:07:33200 metres down, we enter an alien world...
1:07:36 > 1:07:39..the twilight zone,
1:07:39 > 1:07:41a sea of eternal gloom.
1:07:52 > 1:07:56Survival here means making the most of every last glimmer.
1:08:00 > 1:08:03A squid, but this is one that lives only here.
1:08:05 > 1:08:08Its right eye looks permanently downwards.
1:08:10 > 1:08:14But its left eye is much bigger and trained upwards to detect the
1:08:14 > 1:08:17silhouettes of prey swimming nearer the surface.
1:08:19 > 1:08:23No wonder it's nicknamed "the cockeyed squid".
1:08:29 > 1:08:31And even stranger...
1:08:33 > 1:08:36this is barreleye...
1:08:38 > 1:08:41..a fish with a transparent head,
1:08:41 > 1:08:45filled with jelly, so that it can look up
1:08:45 > 1:08:47through its skull.
1:09:01 > 1:09:04We now know that the twilight zone is a
1:09:04 > 1:09:09refuge for an incredible 90% of all fish in the ocean.
1:09:12 > 1:09:14CRASHING THUD
1:09:16 > 1:09:18Humboldt squid.
1:09:30 > 1:09:32Two metres long
1:09:32 > 1:09:33and 50 kilos in weight.
1:09:39 > 1:09:42Like most squid, they're voracious hunters.
1:09:48 > 1:09:51They've found a shoal of lanternfish,
1:09:51 > 1:09:55hiding 800 metres down, off the coast of South America.
1:10:06 > 1:10:10Their tentacles are armed with powerful suckers
1:10:10 > 1:10:12with which they grab their prey.
1:10:28 > 1:10:32And when there are no more lanternfish to be found,
1:10:32 > 1:10:35they turn on each other.
1:10:46 > 1:10:50This squid has caught a smaller one in its tentacles.
1:10:55 > 1:10:57To hide its capture from the rest,
1:10:57 > 1:11:00it releases a smokescreen of black ink.
1:11:12 > 1:11:15But then an even bigger one challenges it...
1:11:21 > 1:11:24..and steals its catch.
1:11:34 > 1:11:37Below the twilight zone lies a world
1:11:37 > 1:11:39of perpetual blackness...
1:11:48 > 1:11:52..leading, eventually, to the deep sea floor.
1:11:58 > 1:12:02Here, there is a layer of mud, in places a mile thick.
1:12:24 > 1:12:28The deep seabed may at first appear lifeless...
1:12:31 > 1:12:35..but it's home to a unique cast of mud-dwellers.
1:12:41 > 1:12:43The sea toad.
1:12:47 > 1:12:52This fish has been living for so long here that its fins have
1:12:52 > 1:12:55changed into something more useful.
1:13:00 > 1:13:02Feet.
1:13:06 > 1:13:10They help it shuffle about on the sea floor.
1:13:28 > 1:13:31The flapjack octopus.
1:13:35 > 1:13:38It hovers just above the surface of the mud
1:13:38 > 1:13:42as it delicately sifts through it, searching for worms.
1:13:58 > 1:14:03Down here, over time, organic matter slowly decays...
1:14:05 > 1:14:07WHOOSHING
1:14:07 > 1:14:11..creating a volcano of methane gas.
1:14:13 > 1:14:17RUMBLING AND WHOOSHING
1:14:50 > 1:14:52In the Gulf of Mexico,
1:14:52 > 1:14:56these eruptions also release a super-salty liquid.
1:15:00 > 1:15:02Brine.
1:15:13 > 1:15:15Heavier than seawater,
1:15:15 > 1:15:18it accumulates in great pools on the sea floor.
1:15:23 > 1:15:28A lake of concentrated saltwater, 15 metres deep,
1:15:28 > 1:15:31at the bottom of the sea.
1:15:44 > 1:15:47Cut-throat eels, scavengers,
1:15:47 > 1:15:50come to the shores of the brine lake
1:15:50 > 1:15:52in search of something edible.
1:16:23 > 1:16:28Spending too long in it can send an eel into toxic shock.
1:16:40 > 1:16:42Its only hope is to rise above it.
1:16:57 > 1:16:59It manages to escape.
1:17:08 > 1:17:11Conditions in the deep sea may be hostile...
1:17:18 > 1:17:21..but, astonishingly, there is more life
1:17:21 > 1:17:24down here than anywhere else on Earth.
1:17:38 > 1:17:42As far down as 3½ miles, there are more
1:17:42 > 1:17:47species of coral in the deep than on the shallow tropical reefs.
1:17:54 > 1:17:57The deep may be full of alien-like creatures,
1:17:57 > 1:18:00but we are more closely connected to it
1:18:00 > 1:18:03than we ever thought possible...
1:18:09 > 1:18:11..thanks to great ocean currents.
1:18:24 > 1:18:28These currents begin in the frozen poles.
1:18:39 > 1:18:40Antarctica.
1:18:55 > 1:19:00Here, the surface waters are so cold and heavy that they sink...
1:19:03 > 1:19:08..and that creates immense rivers of water that flow into the deep.
1:19:11 > 1:19:15This is the start of a giant network of currents...
1:19:18 > 1:19:21..that flow from the poles to the tropics
1:19:21 > 1:19:22and back again...
1:19:25 > 1:19:27..linking every ocean.
1:19:32 > 1:19:36These currents are in fact crucial to the wellbeing of our planet.
1:19:39 > 1:19:41They distribute the sun's heat,
1:19:41 > 1:19:45maintaining a favourable climate for life on Earth.
1:19:50 > 1:19:53From creating the weather to producing oxygen,
1:19:53 > 1:19:56the seas keep our world healthy.
1:20:04 > 1:20:08But just as we are discovering how dependent we are on the oceans,
1:20:08 > 1:20:13there are worrying signs that they are warming at a faster rate than
1:20:13 > 1:20:16ever before in human history.
1:20:20 > 1:20:23And nowhere is this more extreme than in the Arctic.
1:20:27 > 1:20:29Here, in the past 30 years,
1:20:29 > 1:20:34the extent of the ice in summer has been reduced by 40%.
1:20:35 > 1:20:37This sudden warming,
1:20:37 > 1:20:40most likely a consequence of human activity,
1:20:40 > 1:20:44is having a profound impact on its wildlife.
1:20:48 > 1:20:53Walruses are among those that are seriously affected.
1:20:55 > 1:20:57LOW GROWLING
1:20:57 > 1:21:01The sea ice is retreating from much of the walrus's traditional range,
1:21:01 > 1:21:04so they now have to haul out on dry land.
1:21:04 > 1:21:08But a herd of hundreds of quarrelsome mothers,
1:21:08 > 1:21:13some weighing almost a ton, is not an ideal nursery.
1:21:13 > 1:21:16THEY GRUNT AND GROWL
1:21:22 > 1:21:26Walruses on land stick together for good reason.
1:21:28 > 1:21:31Polar bears.
1:21:33 > 1:21:37A full-grown male walrus is gigantic -
1:21:37 > 1:21:40too big for even a polar bear to tackle.
1:21:42 > 1:21:46So the bear is looking for a walrus baby.
1:21:49 > 1:21:52THEY SNARL
1:21:52 > 1:21:55The scent of the bear spreads alarm through the colony.
1:22:02 > 1:22:05The walruses retreat into the sea.
1:22:23 > 1:22:27The bear knows it won't be able to catch them there.
1:22:36 > 1:22:39But she too has young ones to feed.
1:22:46 > 1:22:49What is a mother to do?
1:22:57 > 1:22:59WALRUS BARKS
1:22:59 > 1:23:02A mother walrus still needs to find a place
1:23:02 > 1:23:04where her young can rest.
1:23:12 > 1:23:14A melting iceberg might do.
1:23:15 > 1:23:18But she is not the first to find this one.
1:23:26 > 1:23:28Suitable places are already taken.
1:24:02 > 1:24:04Other mothers don't want to share.
1:24:09 > 1:24:12They too need a patch of ice where they
1:24:12 > 1:24:14can protect their young.
1:24:18 > 1:24:23The desperate mother has no choice but to barge her way in.
1:24:23 > 1:24:27THEY GROWL AND SNARL
1:24:47 > 1:24:50So, this time, everyone loses.
1:25:15 > 1:25:18Finding the right place on these melting shores
1:25:18 > 1:25:20gets harder and harder.
1:25:56 > 1:26:01Solving these problems together helps create a bond so strong that
1:26:01 > 1:26:06the mother will stay in contact with her young for the rest of her life.
1:26:18 > 1:26:22But who knows now what their future will be?
1:26:35 > 1:26:39As we understand more about the complexity of the lives
1:26:39 > 1:26:41of sea creatures,
1:26:41 > 1:26:46so we begin to appreciate the fragility of their home.
1:26:55 > 1:26:58We are at a unique stage in our history.
1:26:58 > 1:27:03Never before have we had such an awareness of what we are
1:27:03 > 1:27:05doing to the planet,
1:27:05 > 1:27:09and never before have we had the power
1:27:09 > 1:27:11to do something about that.
1:27:13 > 1:27:16Surely we have a responsibility to care for our Blue Planet.
1:27:18 > 1:27:20The future of humanity,
1:27:20 > 1:27:23and indeed all life on Earth,
1:27:23 > 1:27:26now depends on us.
1:27:30 > 1:27:32To find out more about our oceans with
1:27:32 > 1:27:37this free poster, call...
1:27:37 > 1:27:42..or go to...
1:27:42 > 1:27:45..and follow the links to the Open University.