All language subtitles for Natures Microworlds 11of13 The Deep Sea 720p

Our planet is the greatest living
puzzle in the universe.

A collection of worlds within worlds,

each one a self-contained ecosystem
bursting with life.

But how do they work?

The intricate web of relationships
and the influence of natural forces

makes each microworld
complex and unique.

So, to discover their secrets,
we need to explore them one by one...

..untangle their interlocking pieces,

and ultimately reveal the vital
piece - the key to life itself -

hidden deep within each
of nature's microworlds.

Over 99% of space available
for life on Earth is in the sea.

From top to bottom, the ocean
contains a volume of water

totalling 1.3 billion
cubic kilometres.

It is the single largest
ecosystem on our planet -

far, far larger
than any terrestrial ecosystem.

It's also the least explored.

We know more about
the surface of Mars than

we do about the majority
of the marine environment.

This microworld is
Earth's inner space.

Almost 90% of the ocean
lies below a kilometre,

and over 75% is deeper
than three kilometres.

The very deepest part of the ocean
lies at 11 kilometres

and would easily engulf
Mount Everest.

More people have walked on the moon
than have visited

the deepest part of the ocean.

Below the upper sunlit waters is
a foreboding world of darkness

and crushing pressures.

Despite this, it's home
to countless living things.

Some of the most bizarre and unlikely
creatures exist in the depths.

Even though they make up
the majority of creatures

upon our planet,
we know very little about them.

The vast majority of these
float or swim in the water column,

a world without walls or sunlight.

But even at the very bottom
of the ocean,

there is life somehow making a living
on a flat abyssal plain

that spans the seabed
between continents.

Recent discoveries in the deep sea
have astounded the scientific

community and given us an insight
into another world.

So just how do creatures exist
in the depths?

What is the key that connects
all these animals and allows them

to survive in a cold,
dark, hostile world?

Our journey starts at the surface
of the open ocean

in the North Atlantic.

As the sun sets, a large mass
of animals appear as if from nowhere

to feed at the sea's surface...

..millions upon millions of them.

A bizarre array of jellyfish
trail stinging tentacles,

or ingest food
directly into their bodies.

Among the throng are animals
that defy classification.

A small fish takes cover inside
the body of this pelagic jelly

for a very good reason.

Large shoals of squid arrive
to hunt at the surface.

By coming at night, they can avoid
the eyes of daytime predators.

But not all animals need eyes
to hunt.

DOLPHINS SQUEAK

Spotted dolphins use sonar
in the darkness...

..targeting their prey
with pinpoint accuracy.

So where do all these night-time
animals come from?

They ascend from a world
with little or no sunlight,

hundreds of metres down.

Every night, across the world's
oceans, 100 million tonnes of these

animals rise from the depths.

It's by far the largest migration
of animal life on the planet.

They come to exploit the abundance
of food in the surface waters.

An abundance that exists

because of something that happens
at a microscopic level -

photosynthesis.

Tiny algae and plants
known as phytoplankton

use light from the sun to turn
soluble carbon into organic matter.

This is known as primary production.

The by-product of
photosynthesis is oxygen.

The waters up here are rich
in this important element,

which is essential for life.

50 billion tonnes of phytoplankton
is produced

in the upper oceans every year.

During spring in the North Atlantic,

when conditions are right,
their blooms can be seen from space.

It forms the basis
of the marine food chain

and is fundamental
to all life in the ocean.

Phytoplankton is fed on by tiny
animals known as zooplankton.

The most common are copepods.

These crustaceans are little more
than a millimetre long

but they are the most numerous animal
in the ocean.

In the North Atlantic,
a cubic metre of seawater

may contain in excess
of 100,000 of them.

Using their legs,
they create currents which push

the microscopic phytoplankton
into their mouths.

It's the sheer numbers
of phytoplankton

and copepods that draw
deep-sea animals up at night.

When dawn returns, the migration
is reversed and the massive

army of deep-sea creatures sink
back down into the darkness.

If we're to follow them,
we must use a deep-sea submersible

capable of withstanding
immense pressures.

Without one, we could not survive
in their world.

As we descend, the sun's rays
are absorbed and scattered.

At 200 metres,
we leave the photic zone

and enter the first layer
of the deep sea -

the twilight zone.

At this depth, there's less than 1%
of the sunlight at the surface.

The pressure has increased
twentyfold, and the temperature has

dropped to four degrees, but we find
a world of extraordinary beauty.

With nowhere to hide in the
twilight zone, the best disguise

is transparency.

Like this squid with a delicate
glass-like body.

Almost nine centimetres long, this
amphipod is a giant of its kind.

It's completely transparent,
apart from its two enormous eyes

and central nervous system.

Another peculiar crustacean
lives like a hermit within

the stolen body of a jellyfish.

This shell also houses
her offspring.

Her habit of pushing this
protective shell around has led to

the nickname of pram bug.

The longest jellyfish of all
are the giant siphonophores.

Their tentacles, lined with rows
of stinging cells,

can reach 40 metres long.

Of the countless billions of animals
living below the photic zone,

only a fraction migrate into
shallower water to feed at night.

So what do these animals feed on?

Looking out of the window
of our submersible, we can see

a constant rain of particles
slowly drifting down around us.

Known as marine snow, this is a
vital food source for everything

living below 200 metres.

It rains down from the
sunlit waters above.

But what exactly is it?

The density and exuberance of life
at the surface of the ocean

far outweighs that of the deep sea.

This is where marine snow originates.

A pod of common dolphins
prepare to hunt.

They're homing in on a shoal of
mackerel swimming near the surface.

Waiting are flocks of shearwaters,
hoping for the fish

to be driven within range.

The mackerel swim
in a tight ball for safety.

Working as a group, the dolphins
drive the bait-ball upwards

towards the waiting shearwaters.

Shearwaters dive deep
to grab their share.

Caught between the birds
and the dolphins,

the mackerel have nowhere to go,
and the frenzy builds.

The commotion attracts
a school of yellowfin tuna.

These two-metre-long fish are
capable of bursts of speed

of 75 kilometres per hour.

This doesn't deter the shearwaters,
which continue to feast

on the shoal beneath.

Eventually,
nothing remains of the huge shoal

of mackerel, except for
scraps of flesh and scales.

Leftovers, faeces, dead and
dying plants and animals

have only one way to go,
and that's down.

This is marine snow.

Millions of tiny creatures, such as
this sea spider, filter the snow.

Its feathery appendages gathering
particles that are then drawn

through its jaws.

As a result, the nutritional value
of marine snow declines with depth.

Feeding activity also uses up

precious reserves
of dissolved oxygen.

Without photosynthesis to replace it,
oxygen decreases.

So, as we descend,
life begins to thin out.

But it becomes
ever more extraordinary.

At 500 metres, it appears
completely dark to human eyes.

The pressure is 50 times what it was
at the surface

and there's only the tiniest remnant
of sunlight filtering through.

Animals here have adapted to cope
with extreme pressure

and their eyes have evolved
to become disproportionately large.

The owner of THIS pair gazes
ever upwards into the gloom,

seeking the silhouette of its prey
against the faint down-welling light.

To escape the attention of
super-sensitive eyes, fish here have

evolved light-transmitting cells
on the underside of their body.

Using graphics, we can see how these
exactly match the background light.

With this, their silhouette
breaks up, making them

appear almost invisible from below.

By 800 metres, the pressure is
80 times what it was at the surface

and the temperature is below
three degrees centigrade.

Oxygen levels have also decreased
to less than 5%

of what they were at the surface.

This is called the dead zone.

But something still
manages to live here.

Vampyroteuthis infernalis -
the vampire squid from hell.

Vampire squid have lived in the
depths for 200 million years.

They share physical characteristics
with octopus and squid

and are thought to be
a missing link.

Highly specialised
blood cells allow them

to live in this
low-oxygen environment.

Despite its hellish name
and fierce look,

vampire squid are placid
creatures, averaging only

28 centimetres in length,
and are completely harmless.

Get too close to a vampire squid

and it puts on the most
amazing light display.

Bioluminescent bacteria
in its arms and on its body

dazzle and confuse
potential predators.

And with that,
it disappears into the darkness.

Beyond 1,000 metres, we enter
the dark zone, where not even

the faintest remnant of sunlight
can penetrate.

Yet when we switch off
the submersible lights,

we see bioluminescence.

There's life even here.

Furthermore, oxygen levels have risen
and that's because we are now

in a deep-water current called
the Great Ocean Conveyer.

When surface water,
enriched in oxygen by photosynthesis,

meets polar ice, it sinks
beyond the first 1,000 metres

and flows towards the equator...

..carrying oxygen to the very
deepest corners of the abyss.

Here in the dark zone, we find
the real monsters of the deep.

Oxygen may be plentiful here
but food is scarce,

and bioluminescence is
the only light available.

Most of the flashing lights we can
see come from deep-water copepods.

They provide food
for other deep-sea animals.

To a hunting squid, this
flashing light looks like food.

But in the darkness,
nothing is what it seems.

Fooled by bioluminescent bacteria
living in the antennae

of an angler fish.

The angler fish can
easily accommodate

the squid in its extendable stomach.

Many deep-sea fish have
disproportionately large stomachs.

In this sparse, cold world, it might
be many days between meals.

Natural selection has produced
lures of all shapes and sizes,

each used to tempt prey
to within easy reach.

This Wolftrap angler has a lure
hanging amidst its formidable teeth.

In this dazzling battlefield,
prey have developed

some surprising methods of escape.

Deep-water shrimps confuse
attackers by spinning

and releasing a bioluminescent glue.

While the shrimp makes its escape,
the glue sticks,

leaving the attacker glowing
in the face of its own enemies.

The shrimp's red colour
is also its camouflage.

In the dark zone,
the eyes of most predators

are tuned to the blue or green
of bioluminescent light.

So, to them, a red shrimp
is almost invisible,

but not to one deep-water resident -

the dragonfish.

This predator has evolved
red bioluminescent headlights

below its eyes
that are sensitive to red light.

Its target doesn't see it
until it's too late.

Descending ever further,
we eventually reach the sea floor,

six kilometres down.

The pressure here is more than
600 times that of the surface,

and temperatures are
close to zero degrees.

It takes many weeks for marine snow
to descend this far.

Here, it forms a vast blanket of soft
sediment over a kilometre thick -

the abyssal plain.

These plains cover a third
of the Earth's surface.

By the time the snow gets here,
it only contains

a fraction of its original energy.

Under such extreme conditions,
we would expect the abyssal plain

to be lifeless.

But even here, we find life.

Deepwater sea urchins must sift
large quantities of sediment

to survive.

The strange balloon-like sacs
on their backs may be filled

with a noxious substance
to deter predators.

Abyssal shrimps use their elongated
antennae to feel for tiny

particles of food floating
around in the darkness.

Life here may be sparse, but
because the abyssal plains cover

such a large area of
the Earth's surface,

they are home to some of the most
numerous animals on the planet.

Fish have been found living
as far down as eight kilometres.

This rattail is one of the
most common species.

The white spots around
its eyes are pores,

sensitive to the slightest movement -

vital in the inky blackness
of the abyssal plain.

Just occasionally, in this
nutrient-poor environment,

a feast arrives.

A dead tuna doesn't lie unnoticed
for long.

This deep-sea conger eel has
picked up the scent from far off.

Down here, a good sense
of smell is a lifesaver.

The carcass also attracts the
attention of one of the deep's

most elusive creatures -

the six-gilled shark.

These rarely seen sharks
are active hunters

and can grow to five metres
in length.

This type of shark has been around
for at least 200 million years.

There are many opportunistic
scavengers on the seafloor.

They'll detect even the
tiniest scent in the water

and will move in from miles around.

Deep-sea crabs and scavenging
arrowtooth eels

are soon joined by giant isopods.

Related to woodlice,
these strange-looking monsters

are half a metre long.

Within hours, the carcass
is stripped to nothing.

Even the bones are eaten.

Where food is at a premium,
nothing is wasted.

When life was first discovered
thriving in the abyss, it was

a complete surprise, but the
depths revealed another secret

that shook the foundations
of scientific thinking.

A secret that lay here
on the mid-ocean ridges.

These undersea mountain ranges
are the longest geological

structure on Earth, part of a
continuous 65,000 kilometre chain

extending across
the face of the planet.

This is the frontline
of plate tectonics.

Here, the seafloor is parting
at about two centimetres a year.

When submersibles first visited
the ridges in the 1970s,

they found towering basalt chimneys
known as black smokers

spewing hot water
and hydrogen sulphide

from deep inside the Earth's crust.

At 400 degrees centigrade, these
smokers are hot enough to melt lead.

It was here that they made

one of the most important scientific
discoveries of the 20th century -

dense populations of marine animals

living in a toxic deep-sea
environment

without any reliance
on energy from the sun.

In one location, they found
swarms of deep-sea shrimps.

In another, they found bizarre
polychaete worms tolerating

water temperatures
of 80 degrees centigrade.

No other animal on Earth is known
to exist at such temperatures.

Clams, crabs and even fish live
in large numbers around the vents.

How do all these animals survive
in such densities,

in total darkness, under conditions

of scalding heat
and intense pressure?

The answer lies in mats of bacteria
that coat the chimneys.

These bacteria are primary producers.

They substitute for phytoplankton
in a world without sunlight.

Drawing chemical energy
from the vent,

they convert soluble carbon
into organic matter -

a process known as chemosynthesis.

It is this bacteria,
not marine snow, that is

the basis of the
hydrothermal vent food chain.

But in order to exploit
this resource,

they've had to adapt to living with
high levels of hydrogen sulphide -

a poison as potent as cyanide.

These giant tube worms
approach two metres long

and they incorporate vent bacteria
within their bodies.

The bacteria provide the worms
directly with food and energy.

Despite the toxic environment,

there's thousands of times more life
at hydrothermal vents

than at the abyssal plain.

The sheer scale and diversity
of creatures here has opened up

a whole new branch of research.

New species are being discovered
on every single dive.

So, here, far away from the
sun's rays, is a self-sufficient

community thriving in the most
hostile of environments.

This may be a glimpse
of how life exists on other planets.

Our journey into the
deep-sea microworld has revealed

some of the most unusual
life forms on Earth.

What we've found at every level
is a diverse community of animals

adopting unique ways of surviving.

Many of these creatures live
well beyond the sun's rays.

But there's one thing that ties them
all together wherever they dwell -

the need for oxygen.

Even the bacteria that form the
basis of hydrothermal communities

need oxygen to make organic matter.

And oxygen can only be produced
in one way -

as a by-product of photosynthesis,

a process driven by the sun.

Even though the majority of ocean
creatures remain oblivious

to its presence,
ultimately it is the sun

that allows life to exist
in the depths of the abyss.

The sun connects all life,
from the surface...

..to the deepest reaches of the sea.

We still know more about
our neighbouring planets than

we do the deep sea.

This inner space remains
the last frontier on Earth -

a frontier that continues
to evoke awe and wonder.

Who knows what discoveries are
yet to be made in the largest

but least explored
of all our microworlds?