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Narrator: Untameable and mighty.

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The oceans are our last true wilderness.

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They cover 70%
of the surface of our planet.

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Their power can fill us with awe.

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And, at times, fear.

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But, today, we are also beginning
to reveal their hidden wonders.

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Off the wild coast of South Africa,

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bottlenose dolphins face
some of the roughest seas on earth.

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But for them,
big waves are an opportunity for play.

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And why do they do it?

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To build friendships

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and strengthen family bonds.

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And, also, for the sheer joy of it.

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There is so much more
to discover about our oceans

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and their importance to us.

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Over 40% of us
live within 609 miles of the seas.

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But it is still
the least known part of our planet.

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Today, scientists and film makers

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are heading out
to explore the seven seas.

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Equipped with the latest technology,

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their mission is to bring us
a new understanding

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of life beneath the waves.

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At a time when the health of our oceans
is increasingly under threat,

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this has never been more urgent.

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Our journey begins in the warm,
clear shallows of the tropics.

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Home to coral reefs.

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They occupy less than
1% of the ocean floor.

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Yet, they are home
to a quarter of all marine species.

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Competition is fierce
in these crowded underwater cities.

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We are learning just how noisy they are

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with state-of-the-art
underwater microphones.

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Amazingly, fish can talk to each other.

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But sometimes it's better to stay quiet.

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On Australia's great barrier reef,

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one character is challenging
our understanding of fish intelligence.

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This is a tusk fish.

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He does something
few would have believed a fish could do.

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Every morning, he makes a journey
out to the edge of the reef.

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He is looking for breakfast.

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A clam.

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But how to crack it open
and get to the meat inside?

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He carries it all the way back
to his special kitchen.

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A bowl shaped coral.

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With a particular bump inside
that he always uses.

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It's not easy

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if you have no hands.

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Oops.

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Dropped it again.

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But he's got great determination.

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At last.

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So here's a fish that uses a tool.

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Some fish are much cleverer
than we ever thought.

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Even ocean creatures
that we already knew where smart

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are continuing to surprise us.

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This bottlenose dolphin mum

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is about to teach her calf
an important lesson

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here in the red seas.

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She leads him
to a particular bush-like coral

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called a gorgonian.

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The family rub themselves
through the fronds.

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The calf is watching

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and learning.

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Gorgonian fronds
are covered with a mucous

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that can have anti-inflammatory
and anti-microbial properties.

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So, maybe, the dolphins are doing this
to protect themselves from infection.

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The calf may be too young to join in,

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but his family's secret knowledge
of the coral reef

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is teaching us to search
for new medicines here, too.

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As we leave the tropics
and head into cooler waters,

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we enter the temperate seas.

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These are home
to mysterious undersea forests.

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Giant kelp, a seaweed,

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towers 200 feet high,

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growing two feet a day
under the summer sunshine.

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Marine plants
are the lungs of our planet.

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They pump out as much oxygen

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as all the forests
and grassy plains on land.

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Within their tangled undergrowth,
extraordinary discoveries await.

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In the shark-filled
kelp forests of Southern Africa

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lives one brave little octopus.

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Pyjama sharks
are every octopus' worst nightmare.

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But the octopus
has a trick up her sleeve.

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In a behaviour
previously unknown to science,

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she disguises herself with shells,

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creating a suit of armour.

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The shark can sense its prey.

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But the shells protect her.

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Superior wits allow this octopus
to stay alive.

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But just as we're getting
to know these forests,

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we're recognising their vulnerability.

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Off north America's pacific coast,
great stands of kelp

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are being felled

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by armies of ravenous sea urchins.

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They much through the roots
with razor-sharp teeth.

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But some kelp forests here
have unlikely guardians.

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Seg otters.

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Because they live their entire lives
in such cold waters,

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they need to eat

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30% of their body weight a day
to stay warm.

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One of their favourite foods
is sea urchin.

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By removing the urchins,

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the otters allow
the forests to flourish.

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And with all this food,
they're having a baby boom.

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Now, in a few remote areas,

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sea otters are creating vast rafts

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in numbers not seen
for more than a century.

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As we leave our coasts
and head for the high seas,

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we enter the open ocean.

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Covering over half our planet's surface,

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it's the world's greatest wilderness.

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A vast empty void

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where there's nowhere to hide
and little to eat.

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And, yet, it's home
to vast numbers of dolphins.

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Spinner dolphins.

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They sweep this marine desert for food

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in a superpod 5,000 strong.

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And they're leading this research vessel
to a rare feeding event.

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But to find it, they have to be fast.

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Using echolocation,
they lock on to their prey.

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Great shoals of lantern fish.

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By pinning the school
against the surface,

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the dolphins keep
this fleeting opportunity alive.

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But all this food
attracts other predators.

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Yellowfin tuna.

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They rip through the lantern fish

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in a whirling carousel
at 40 miles an hour.

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Now, the sea begins to boil.

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Finally, mobula rays

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with ten foot wing spans swoop in.

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In just 15 minutes, all that's left
is a silvery confetti of scales.

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These fleeting events are becoming rarer

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as we continue
to overfish our high seas.

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The open ocean may be featureless

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but isolated volcanic peaks
rise abruptly from deep water...

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Hinting at a secret world below.

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The deep ocean
is as challenging to explore as space.

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We know more about the surface of Mars
than we do about the deep sea.

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Now, from the research vessel alucia,

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we can dive these uncharted depths

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to discover our final frontier.

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As we descend,
the pressure increases relentlessly.

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Six hundred feet down,
we enter an alien world.

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The twilight zone.

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A pyrosome.

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A tube of jelly six-feet long.

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And, stranger still barrel eye.

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A fish with a transparent head,

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so that it can look up
through its skull.

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Eventually,
we reach the deep sea floor.

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A layer of mud. In places, a mile thick.

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Over time, the mud here slowly decays.

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Creating volcanoes of methane gas.

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The deep maybe hostile,

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but it's also home
to the weird and wonderful.

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Dancing crabs called yetis.

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Because of their hairy arms

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on which they farm bacteria to eat.

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A dumbo octopus.

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With ear-like-fins to hover
above the muddy sea floor.

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There are also corals here.

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With more species
than on shallow tropical reefs.

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Astonishingly, we're now finding
there's more life down here

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than anywhere else on earth.

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This may seem an alien world,

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but we are more closely
connected to the deep

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than we ever thought possible.

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Thanks to great ocean currents.

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These begin at the frozen poles.

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Here in Antarctica,

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the surface waters
are so cold and heavy

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that they sink.

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That creates immense rivers of water
that flow into the deep

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where they power
a global network of currents.

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These currents flow
from the frozen poles

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to the warm tropics and back again,

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linking every ocean.

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They redistribute heat around the planet

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maintaining a climate favourable
for life on earth.

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From producing the oxygen we breathe
to controlling our weather,

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the oceans are our life-support system.

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But just as we're discovering
how dependant we are on the oceans,

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there are worrying signs
that they are warming

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at a faster rate than every before
in human history.

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And nowhere is this more extreme

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than in the arctic.

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Walrus prefer to rest on sea ice.

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But with less ice than ever before,

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hundreds of quarrelsome mothers
now have to haul out on dry land.

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It's far from an ideal nursery.

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Nor is it safe from polar bears.

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A full-grown male walrus
is too big for a bear to tackle.

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So, it's looking for a walrus baby.

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This young mother

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needs to find somewhere
for her pup to rest.

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The only safe places

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are the last remaining pieces
of floating ice.

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The trouble is...

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That they're slippery...

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And some walrus pups are just too heavy.

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The best icebergs are already full.

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It only takes another one-ton mum

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to tip the balance.

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Finding a safe place
on these melting shores

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becomes harder and harder.

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Solving these problems together
helps create a bond so strong

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that the mother and her youngster

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will stay in contact
for the rest of their lives.

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Just as we're beginning to understand

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the sophisticated lives
of sea creatures,

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so we begin to recognise
the fragility of their home.

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As we explore every part
of the remote seas

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and meet astonishing animals

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We've begun to appreciate
the importance of our oceans.

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There has never been a more crucial time
to continue this journey of discovery.

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Because our future, too,
depends on a healthy blue planet.

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And who knows
what other secrets are out there...

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Waiting to be discovered.

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Man 1: The first time
I saw the tusk fish

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cracking a clam open
on its little anvil,

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I was just gobsmacked.

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He must have hit it well over 50 times.

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We call him Percy. Percy the persistent.

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Man 2: No one has previously dived
to a thousand metres in Antarctica.

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It is exciting. It is thrilling.

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And, yet, it's also slightly terrifying.

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Man 3:
Control, control, deep rover.

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My depth is 1,000 metres
on bottom. Over.

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Man 2: We can't explore
the deep ocean remotely

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without actually going there ourselves.

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And we're the first to do that here.

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Man 4: It's an ordeal to get it going

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because it's a big,
giant piece of equipment.

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But we now have it.
We're heading out to find some walrus.

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We just had our first successful shoot
with the megadome, and it was great.

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I mean, it was that classic shot
of an iceberg,

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where six-sevenths of the berg
is underwater

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and then on top was two walrus.

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Man 5: I'm feeling pretty nervous.
The erm...

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It's a big swell out there.

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This will probably be the biggest seas,
I think I've ever been out in.

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The wave actually
hit the back of the sled.

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Hit a big bump and almost bounced off
trying to hold the camera,

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and just rode out of there.

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Just another day at the office.
Created BY Pinroy Bijayan