The Deep The Blue Planet

Over 60% of our planet is covered by ocean more than a mile deep.

That - the deep sea - is by far the largest habitat on Earth,

and it's largely unknown.

Join us on a journey to the very bottom of the deep sea,

to an alien world never revealed before.

It's home to some of the strangest animals on Earth.

Fish flash in the darkness.

New species are discovered on almost every dive.

More people have travelled into space than have ventured this deep.

Come on a journey into the abyss.

A sperm whale takes a breath -

its last for over an hour.

It's about to leave the warm, well-lit surface waters

and dive far down into the cold, dark depths of the deep ocean.

At the surface, it took in air at the same pressure as we breathe it.

But it's going to look for food at more than 1,000m down,

where pressure is 100 times that on the surface,

crushing the whale's lungs to just 1% of their volume.

For us to follow the whale, we need the very latest submersible.

A reinforced acrylic sphere, with walls 12cm thick

protects a pilot and our cameraman from the enormous pressure below

and allows the submarine to dive to just over 900m.

With every passing metre, pressure increases

and sunlight diminishes.

'1,000ft.'

By 300m, it's already very dark

and the water temperature is dropping fast.

We are entering a twilight zone,

a weird world of gloom, where many animals

have become completely transparent.

In this twilight, an animal needs to see

and yet, as far as possible, must avoid being seen.

A giant amphipod, 12cm long,

and almost perfectly transparent.

Its head is completely filled

by two huge eyes, with which it strains to detect its prey.

Another twilight monster - Phronima, inspiration for the Alien movies.

She and her developing pink offspring

live like parasites, in the stolen body of a jelly.

This impressive cutlery set and its huge eyes

make Phonima a powerful predator.

Even really complex animals

have become transparent in the twilight zone.

Squids are among the most advanced of invertebrates,

but this one never meets a hard surface in its entire life,

so its body need not be as robust as that of its cousins.

There's a rich variety of jellies

that live nowhere else but in the deep sea.

Thousands of tiny cilia propel them through a world without walls.

Invisible in the gloom,

they grope blindly for their prey.

Comb jellies let out long sticky nets

to catch passing copepods.

But the most extensive death trap

is set by siphonophores.

This pulsating bell is the head of a colonial jelly,

that can be 40 metres long.

Millions of tiny stinging cells drifting through the sea.

500 metres down and in even the clearest tropical waters

only the faintest vestige of the sunlight remains.

So little, that our eyes can't detect it. But others can.

Survival in the twilight zone

is all about seeing, yet not being seen.

Hatchet fish are masters at hide-and-seek.

They have the large sensitive eyes needed for seeking prey,

but their bodies are flat.

And their sides are highly silvered.

Head on, they are just visible, thin though they are.

But as soon as they turn,

their mirrored sides reflect remnants of blue light from the surface

and they disappear into the gloom. Whole shoals can hide in this way.

But what about from below?

The tubular eyes of many predators, even in this gloom,

are able to distinguish their prey

silhouetted against the scarcely detectable light from above.

Hatchet fish have a way of confusing any eyes searching for them.

Their bellies carry light-producing cells called photophores.

They can use these to exactly match

the changing colour of light from the surface far above.

This counter-shading breaks up their silhouette,

making them almost invisible from below.

Almost.

But these are no ordinary eyes.

The enormous yellow lenses

enable their owner to distinguish between light made by photophores

and sunlight.

So one device for escape is countered by one for attack

in an evolutionary arms race waged for millions of years.

Descend below 1,000 metres,

and you enter the dark zone.

No sunlight penetrates this deep.

The water is below four degrees centigrade.

The pressure is 100 times that at the surface.

Life becomes ever more sparse.

It's a dark, dangerous world.

Relative to body size,

these are the largest teeth in the ocean.

They're so big, their owner can't even close its mouth.

They belong to the fang tooth.

Unlike most deep-sea fish,

this has powerful muscles and is an aggressive hunter.

With food in such short supply at this depth,

dark-zone predators have to be able to deal with a meal of any size.

Many animals here are dark red, like this deep-sea jelly.

Caught in the lights of the submersible,

it's a spectacular firework display of colour.

Normally, no red light penetrates as deep as this,

so animals with red pigment appear completely black -

perfectly concealed.

Predators here don't just rely on vision - many have tiny eyes.

Instead, their bodies are lined with organs sensitive to movement.

This monster, half a metre across,

is a hairy angler.

This is the first time it's been seen.

It's covered with hundreds of sensitive antennae,

capable of detecting the movements of any prey

careless enough to stray too close to this motionless predator.

But this must be the strangest of all the deep-sea fish yet discovered.

A highly-sensitive metre-long tail

hangs down from the head that makes up a quarter of its body.

Its eyes are tiny, but its mouth is truly enormous.

It's called the gulper eel,

because it can engulf a meal of almost any size.

Hanging motionless in mid-water,

its enormous gape enables it to deal with passing prey,

whether it's small...or large.

Gulper eels can swallow prey as big as themselves,

very useful in a world where you never know where the next meal is.

Even in the dark zone, there is some light.

Turn off the submersible headlights

and you see a pyrotechnic display outside.

These lights are created by animals.

This is bioluminescence.

A deep-sea angler fish flashes in the darkness.

The light is generated by bacteria

that live permanently inside the lure,

which attracts prey to these murderous teeth.

There are all sorts of lures out in the darkness.

"Come into my mouth, little fish."

What is the purpose of this lure,

suspended on a long rod way below its owner's terrifying teeth?

It's difficult to be sure.

But this monster has another lure,

much closer to its mouth.

These fish are called anglers

because they use their lures in the same way as fly fishermen

use their imitation flies.

For a hunting squid, with huge eyes, this glimmer is intriguing.

It might just be food.

A satisfying meal

for a fish with a highly-extendable stomach.

Attracting a mate in this darkness

can be even harder than finding food.

Flashing lures may be helpful.

Certainly, only female anglers have them.

The tiny males are just a tenth the size of the females.

Their only purpose is to find a mate in the darkness.

She releases chemicals into the water,

which the males scent with a special white organ in front of their eyes.

Having found a partner,

the male bites at her belly, with specially-designed teeth.

He needs to get permanently attached.

Within a matter of weeks,

the male is fused to the female.

There he will stay for the rest of his life.

Her blood provides him with his sustenance.

In return, she gets a continuous, reliable supply of sperm.

A brilliant solution to finding a mate

in the vast emptiness of the deep sea.

To help in the constant battle between predators and prey,

some fish have developed headlights.

These light-producing photophores beneath their eyes

may be used to search out prey in the darkness.

Most bioluminescence in the deep sea is blue or greenish-blue.

But a very few predatory fish produce red light.

With this, red prey becomes obvious in the darkness.

Red light is rare down here.

Most animal eyes can't see it. Only these fish can do so.

This gives them a sniperscope - a headlight invisible to targets.

This copepod, unalarmed, takes no avoiding action.

Bioluminescence is useful in escape as well as attack.

A shrimp senses a threat.

It spins in the water, releasing a bioluminescent glue.

This acts like a burglar alarm, startling the fish

and leaving it illuminated and vulnerable to predators.

These twinkling lights in the darkness

are produced by copepods.

They probably flash like this to communicate with one another

and confuse their predators.

The most sensitive eyes belong to an ostracod called gigantocypris.

It's the size of a pea.

That's enormous for an ostracod.

Copepods are a favourite prey

and it actively searches for their flashes in the darkness.

But this copepod has a way of confusing a hunting gigantocypris.

It discharges a packet of bioluminescent liquid.

The flash is delayed, like a depth charge.

Spinning confused in the water,

gigantocypris chases after the flashes...

..and the copepod slips away, unseen, into the darkness.

The ultimate bioluminescent defence mechanism

has to be the light show created by the deep-sea jellyfish, periphylla.

That, presumably, is the way it scares away its enemies.

These bright lights are produced by firefly squid.

Normally they live way down, at 300m.

beyond the reach of these Japanese fishermen's nets.

But for a few months each spring,

they come to the surface every night.

The lights come from bioluminescent tips of their two front tentacles,

but only in the dark of the deep sea

can you fully appreciate the complexity of their displays.

Their whole bodies are covered in photophores.

The exact function is not clear.

It may be for attracting mates or dazzling predators.

The rest may be camouflage, providing counter-shading

as they journey up into the twilight zone.

Every night in the season,

hundreds of thousands of squid journey into shallow water to spawn.

Before dawn, they will return to the depths,

leaving their eggs to develop in the shallows.

The daily cycle of the sun

has a profound influence on life in the deep ocean.

As the sun sets,

it triggers the largest migration of organisms on our planet.

One thousand million tonnes of animals travel up from the dark zone

into richer, shallower water every night.

Tiny grazers are first up,

searching for the microscopic plants that only grow in shallow waters.

Predators follow the grazers.

An enormous variety of different animals join the convoy,

or feed off it, as it passes.

Many will travel towards the surface and then, at dawn,

finding themselves at risk from predators,

the visitors return to the safer darkness of the depths.

The sun only has a direct effect

in the top 100 metres of the ocean.

It's only here that photosynthesis can take place and reefs flourish.

Leave this slice of life and travel over its altiface -

you quickly enter a demanding world.

Below 150 metres, photosynthesis becomes impossible.

You find no plants,

just animals.

Here, the animals are adapted to catch marine snow -

particles of dead animals and plants that drift down from above.

So they depend, second-hand,

on energy captured from the sun by organisms living in surface waters.

Travelling close to the sea floor,

we're going to take a journey to the very bottom of the deep sea.

To a world separate from the mid-water above.

At around 300 metres,

the drop-off levels out and we move onto the continental slope.

This stretches for about 150 miles from the coast,

sloping in a gentle gradient down to a maximum depth of 4,000 metres.

Water temperatures drop below four degrees centigrade,

and the pressure reaches 400 times that at the surface.

Without the lights of the submersible,

it would be completely dark.

The water is crystal clear because there's so little organic matter.

Only 3% of potential food at the surface reaches here.

At first sight, it appears a lifeless desert.

But take a closer look and you notice a network of tracks.

There is life even down here.

These animals would die immediately if brought to the surface in nets.

You can only see them behaving normally from submersibles.

Many are new to science.

The deep sea floor is dominated by echinoderms -

sea cucumbers, brittle-stars and sea urchins.

There are literally millions of them,

marching across the sea bed,

hoovering up edible particles in the sediment.

They come in all shapes and sizes.

Though thinly spread, the deep ocean floor is so vast

these are among the most numerous animals on the planet.

Their spikes are good for locomotion and defence,

but not so good for mating.

Finding a mate in this largely empty sea floor could be a problem.

Some urchins stay in herds,

to be sure they're never too far from a potential partner.

Rocky outcrops provide good anchorage for animals

that rely on food that might drift past.

These sea lilies look like plants, but are, in fact, animals.

Their long stalks ensure their umbrella of feeding tentacles

are positioned to best effect in the current.

Particles are swept onto the arms

and carried to a mouth in the middle.

These sudden movements

swat away tiny amphipods that try to steal the sea lily's captures.

Coral reefs are not supposed to exist in total darkness.

But recently, a new kind of coral was found as deep as 2,000 metres.

In the cold waters of a Norwegian fjord

there was a deep-sea reef 30m high and 200m long.

This coral gets no energy from the sun,

so it has to be efficient in catching food.

Its polyps are far larger than those of shallow-water corals.

These are, in fact, the largest coral polyps in the ocean.

They belong to the deep-sea mushroom coral.

Their 3cm-long tentacles can catch far larger prey

than other corals can.

This necessity to capture every particle of food

in this near-desert

has radically changed many animals.

Most tunicates are filter feeders,

but this one has become a predator

and its greatly-enlarged siphon has been converted into a trap.

Most sea cucumbers stay firmly on the bottom.

But not this extraordinary deep-sea species.

Its skirts of skin

allow it to swim hundreds of metres above the sea floor.

Eventually, it will descend and, with luck,

land on fresh feeding grounds.

This, though, has to be the most extraordinary animal design of all.

It's a polycheate worm

and you'd expect the long body to be stuck on the sediment.

This worm - alone in its group - swims in the open water.

Propelling itself with its yellow frill,

it finds new sources of food

or maybe escapes from a predator.

This is chimaera, a relative of the sharks, less than a metre long.

Sensory pits on its chin help it hunt prey on the bottom,

while its surprisingly large eyes may help it spot bioluminescence.

Large fish are rare down here.

There's simply not enough live prey to sustain them.

Most have become scavengers.

A dead tuna has attracted a deep sea conger eel...

.. and a sixgill shark.

These monsters grow to eight metres long.

Sixgills are living fossils.

For 150 million years, they've existed unchanged,

living in water as deep as 2,500m.

Very few people have ever been lucky enough to glimpse these sharks

and we know almost nothing about their behaviour.

The body of a tuna is a substantial meal, but occasionally,

a really gigantic corpse drifts down to the deep-sea floor.

This is the freshly dead carcass of a 30-tonne grey whale.

It's resting on the sea floor a mile down.

It's only been on the bottom for six weeks

but already it has attracted hundreds of hagfish.

These ancient scavengers are often the first to discover a fallen body

and are attracted from miles around.

They lack jaws, and rasp at the flesh

with two rows of horny teeth on each side of their mouths.

Next to arrive, a sleeper shark, a real deep-sea specialist.

They grow to over seven metres long

and have never been filmed at such a depth before.

The gaping wounds in the whale's flank are its work.

Unlike the hagfish, it has powerful jaws,

so is able to rip off huge chunks of meat.

Sharks, hagfish and a whole succession of deep-sea scavengers

will feast on the carcass for years before all its nutriment has gone.

18 months later, when we returned to this whale,

all that was left was a perfect skeleton, stripped bare.

It was almost as if a museum specimen

had been carefully laid out on the sea floor.

At first, the skeleton seemed totally abandoned,

but even after so long, there was still some flesh left in the head.

Hagfish have a skeleton of cartilage

and are so flexible that they can tie themselves into knots

and get a better purchase on the flesh they feed on.

But smaller organisms had fed here.

A band of white bacteria had formed on the mud

outlining the shape of the whale.

And on the skeleton itself,

colonies of bacteria extract energy from the bones.

Most remarkably, and in huge abundance,

polychaete worms were collecting the last edible fragments.

These are a new species that, so far,

have only been found on the fallen bodies of whales.

Scientists have found 178 different animals on one whale vertebra,

most of which have been found nowhere else.

This whale, lying over a mile down,

was not filmed from a submersible with an acrylic sphere.

Such craft can't go as deep as this.

To withstand the pressure here, you need a far stronger submersible.

This is Alvin, a sphere with just enough room in it

for a pilot and two observers. Its walls are made of titanium.

The viewing ports have to be tiny.

Any larger and the submersible would implode under the pressure here.

Alvin can dive to 4,500m, three miles below the surface.

Around 3,000 metres, the continental slope finally flattens out

and joins the abyssal plain.

This covers over half the Earth's surface.

Mostly it's completely flat,

but, in places, it's gashed by huge trenches, hundreds of miles wide.

The deepest of these is the Mariana trench,

which drops to over seven miles below sea level.

Only five manned submersibles can reach the abyssal plain.

Between them so far, they have explored less than 1% of it.

1,000 times fewer large animals live here than on the continental slope,

but in places, hundreds of brittle stars

march over the sea bed, in search of food.

Fish have been found right down to the bottom of the deepest trenches.

Most come from one family, the aptly named rat-tails.

They forage near the sea floor

and use their battery of sensory pits

to follow odour trails from rotting carcasses.

They travel long distances across the abyssal plain in search of food,

but others prefer to sit and wait.

This is a tripod fish.

It supports itself on two specially adapted fin rays

and can sit motionless for hour after hour.

It does have tiny eyes, but it's almost totally blind.

It locates potential prey with a pair of fins behind its head,

which are sensitive to even tiny movements.

We know more about the moon's surface than about the abyssal plain.

Every dive still produces complete surprises.

This deep-sea octopus is about the size of a beach ball

and has been nicknamed Dumbo.

An umbrella of skin between its tentacles and its flapping ears

allow Dumbo to hover effortlessly over the sea floor

as it searches for food.

Right in the middle of the abyssal plain

lie the largest geological structures on our planet...

..the mid-ocean ridges.

Rising almost two miles off the sea floor,

the ridges extend for 28,000 miles, the largest mountain chain on Earth.

When submersibles finally succeeded in reaching the ridges in the 1970s,

they found an extraordinary world with miles of once molten rock

that had welled up from the deep in the past and had now solidified.

They discovered towering chimneys,

pouring out water as hot as molten lead.

At the surface, water becomes steam at 100 degrees centigrade,

but down here, under the immense pressure of the ocean,

it remains liquid at temperatures as hot as 400 degrees centigrade.

A submersible has to move carefully. Disaster is very close,

when surrounded by such enormous temperatures and pressures.

And here, where the water is loaded with hydrogen sulphides

poisonous to normal life processes, they found living creatures.

Some of the chimneys were encrusted with white tubes.

The tubes were inhabited by a new species of polychaete worm

that was exposed to temperatures as high as 80 degrees centigrade.

No other animal on Earth was known to tolerate such high temperatures,

so the scientists call them Pompeii worms.

But this was just the beginning. Nearby, there were chimneys

completely covered by whole communities of different organisms.

The bottom of the vent was encrusted with large mussels.

There were swarms of white crabs

and dominating the chimney were hundreds of bright red tube worms,

each two metres long and four centimetres wide.

Until these creatures were discovered,

all life on earth was thought to be dependent on the sun.

But here in the darkness of the deep,

they discovered a density of life that derived no energy from the sun.

So, what do they live on?

The answer was found within the tube worms themselves.

They were full of specialised bacteria, that are able to derive

energy from the sulphides pouring from the vents.

The worms' plumes were red with haemoglobin

that carries sulphides and oxygen down to the bacteria.

These bacteria are the primary source of energy for the life here.

The mussels were packed with them.

As green plants are the basis of life for animals living in the sun,

these bacteria and other microbes

are at the foot of the food chain on which over 500 species depend.

Crabs and shrimps feed off bacteria

and even try to steal pieces of tube worm plumes.

Since the vents were first visited by biologists in 1979,

a new species has been described every ten days.

At the top of the food chain, fish that never stray far from the vents.

But they, or their descendants, will move eventually,

for we know that individual vents are only active for a few decades.

Such a density of life, living in such harsh conditions,

in the middle of a vast, and otherwise barren, abyssal plain,

astounded the biologists who first saw it.

It seemed to them that here was evidence of how life on this planet,

which certainly started in the sea, might have begun.

Deep-sea submersibles made an even more extraordinary discovery

in 1990.

Over half a mile down, at the bottom of the Gulf of Mexico,

they came across what appeared to be an underwater lake over 20m long,

with its own sandy shore.

Around its edge there even seemed to be a tide line.

But this couldn't be, of course. This was under water.

In fact, the lapping edge was created by a soup of salty brine,

far heavier than the surrounding sea water,

and the sand was made up of hundreds of thousands of mussels.

Once again, in the midst of a totally barren sea bed,

a rich oasis of life, totally independent of the sun's energy.

The source of energy this time was methane,

bubbling out of the sea bed.

Again, the mussels carried special bacteria

capable of fixing the methane's energy.

Just like the hot vents,

a complete ecosystem had developed, based on the bacteria.

There was an enormous variety of completely new species -

shrimps, weird squat lobsters and bright red polychaete worms.

These oases were called cold seeps

and were surprisingly similar to the hot vents.

The geological processes in the sea floor that produce methane

can also result in the release of hydrogen sulphides.

It was hardly surprising, then, that nearby they found tube worms.

Extensive fields of tube worms, that stretch for hundreds of metres.

This new species also uses bacteria to fix energy from sulphides,

but it extracts them directly from the ground.

Their beautiful gills are only used to supply oxygen to the bacteria.

Amazingly, these tube worms are over 200 years old.

Hot vent tube worms are the fastest growing invertebrates in the sea,

but these appear to be far slower.

All the more reason to protect your gills from biting amphipods.

The energy sources exploited by the hot vent animals may suddenly fail,

but here life can enjoy a more stable geological future.

To discover, within ten years, two new ecosystems

both independent of the sun's energy, has been quite extraordinary.

So far we have explored just 1% of the deep ocean floor.

Who knows what is still out there to be discovered?

The waters of the deep ocean are so clear

it looks as if these pictures were filmed in a tank.

Nothing could be farther from the truth.

These tube worms live a mile down, where pressure is so great

that a large polystyrene cup attached to the submersible was crushed down

to this tiny thimble.

It's a pressure that could kill a human immediately

and only a handful of submersibles worldwide can dive that deep.

To add camera equipment, then to film remotely from the capsule,

seems almost impossible.

But with the help of some highly-professional submarine crews,

our Blue Planet teams did bring back these extraordinary pictures

from another world.

'You have permission to surface.'

The Johnson Sea Link submersible surfaces after a successful dive.

In the Gulf of Mexico, it's used in the oil industry

to survey the sea floor.

But on this occasion, Blue Planet cameraman Mike DeGruy

has been filming a remarkable phenomenon

over half a mile down on the sea floor.

He can hardly contain his excitement.

The place is amazing. You're travelling across the mud,

there's nothing, except the odd fish, sea cucumber swimming around.

You come up to the mussels - a band about eight feet wide -

encircling what looks like a black hole.

You're literally floating on salt.

The sub is trying to sink and it bounces off the top.

You can't get any lower.

Mike is describing a unique new community of animals

first discovered in 1990.

A super-salty lake under the sea

which has never been documented.

It's an extremely dangerous place for the unwary.

Fish will come swimming across the mussels and think,

"This is interesting." Into the lake they go.

When they hit the top, they start gaping, roll over on their side.

I've got a shot of one barely making it across.

He makes it and lives. It must be full of dead animals.

It's a fantastic place.

Mike's task for his last dive was to film

creatures called tube worms, that live around pockets of gas

seeping from the sea bed 1,000 metres down.

At 6.00am the next morning, the Sea Link sets off

on Mike's dive to find the tubeworms.

All the lights and cameras are fitted and checked.

All Mike can do is hope everything works out 1,000 metres down.

The journey down will take 20 minutes.

The submersible has enough power for six hours' work.

The crew inside have constant contact with the mothership.

One seven six.

The only sense they have that they're descending

comes from quickly diminishing light.

-1-84 at 600 feet.

-Roger that.

By 500m, most of the light from the surface has gone

and strange creatures start to pass by.

We're sitting on the bottom. Our depth is 17-55, 1-7-5-5.

Temperature is seven degrees, visibility is 30-35 feet.

I've got zero to one tenth...

Below 500 metres, creatures like this rabbit fish

exist in a world where daylight never penetrates.

Filming moving animals with a submersible

requires a lot of skill from the pilot,

since it's very easy to disturb the ancient silt on the sea bed.

At least tube worms don't move around

and Mike had a few hours to concentrate on high quality images

before the submersible's batteries ran down.

First, the lights attached to the manipulator arm

had to be positioned to get the right look.

But the real challenge was the big close-ups.

At high magnifications every tiny movement is crucial.

Eventually, he was satisfied.

Oh, that's beautiful.

These beautiful creatures take 200 years to grow to this size,

and, for millions of years they have evolved in the deep sea,

out of the sight of mankind, until now.