Original subtitles

The giant squid, a near mythical monster

that lives in the deep ocean.

And other creatures there, so strange

and bizarre they could come from a nightmare.

(upbeat music)

Others are exquisitely beautiful and dazzle us

with their lights and colors.

(bells tinkling)

Almost all live at depths of around a thousand meters

that we've only just begun to explore.

Now however, we're developing technology

that can take us to places where the ocean

is 10 times deeper.

(upbeat music)

An international team of scientists is setting out

to discover what if anything lives

at these much greater depths.

Down there the water pressure can be a thousand times

that on the surface, and there's little food.

(water bubbling)

Until recently man scientists assumed

that such waters must be barren.

How could any creature survive in such conditions.

We now know that there is life down there,

but we still know very little about it.

(upbeat music)

This is an expedition to explore the earth's

deepest frontier.

(upbeat music)

We are heading for the middle of the Pacific Ocean.

The sea floor between Japan and Australia

is cut by an enormous marine trench

that stretches for two and half thousand kilometers.

It's the deepest in the world, the Mariana Trench.

Such immense trenches are rare

and most are found in the Pacific.

Around its rim, there are deep cracks created

by movements far below in the earth's crust.

At many points along them, that's what's created

a series of underwater trenches.

(water splashing)

To dive here is to enter another world.

As we descend it gets darker and darker

until 200 meters down, there is hardly any light at all.

Many of the creatures living here have huge eyes

that enable them to gather what little light there is.

(light music)

And some produce their own light.

(bells tinkling)

Below 1000 meters, there is no sunlight whatever.

Finding food in the blackness is not easy.

Some fish here have gigantic mouths

so that they can tackle almost anything edible

that comes their way.

Others stand on stilts above the sea floor

waiting for a meal to drift by.

The pressure in these black depths is immense.

An experiment with a large steel ball

shows how great it is.

Under pressure equivalent to that

a depth of 2000 meters,

(loud blast)

the thick steel walls collapse.

(light music)

How can animals living in such conditions survive?

The bodies of most marine creatures are largely made

up of water, which is uncompressable.

So such creatures are not crushed by it.

But below a certain depth, the huge pressure

creates a different problem.

Where the sea floor drops to more than 6000 meters,

the pressure is so enormous that it destroys

the structure of the cells of which

an animal is made.

This part of the ocean is called the hadal zone.

And here life is near impossible.

(suspenseful music)

But not totally.

There are a few living things here,

but they're very few and hard to find.

(upbeat music)

The expedition's aim is to look for them

in the Mariana Trench.

Scientists from one of Japan's leading deep sea

research institutes are leading the project.

The first stage will be to send down a platform

and establish it on the sea floor.

They call it the lander.

It carries a high-resolution camera specially modified

to work at these extreme depths.

Pieces of raw fish are attached to one of lander's arms

to attract any deep sea creatures

that might be down here.

Well I'm not sure what kind of marine life

we'll be able to capture on camera

but fingers crossed.

The lander is ready to go.

(waves crashing)

The water is crystal clear.

Slowly the lander descends.

The Mariana Trench is thousands of miles from land

and these seas contain very few nutrients.

So there's little food here for marine life.

Nearly three and a half hours have passed

and at last the lander is nearing the bottom.

(metal clinking)

It's over eight kilometers deep.

Here the water pressure is 800 times that

of the surface.

What kind of creature could survive here?

And will the camera on the lander glimpse them?

They recognize them.

They're amphipods, shrimp-like creatures

about three centimeters long.

Until now they have only ever been found

in the hadal zone.

They seem to have little difficulty in dealing

with the enormous pressure.

The lander's camera is programed to be turned on

for an hour every three hours.

Now the team will have to wait until it switches on again.

Wow, look at that.

There's been a extraordinary change.

The bate is covered in amphipods.

This is incredible.

It looks like a pile of sushi.

Every time the camera turns on,

the numbers are greater.

The amphipods have stripped the fish bait

down to the bones.

But the amphipods themselves might now attract

other hungry, bigger creatures.

The scientists watch intently.

The lander is 8,178 meters below the surface.

No true fish has ever been seen this deep.

If one appeared, it would be a record.

(suspenseful music)

The lander has been sitting on the sea floor

now for 18 hours.

The team are beginning to lose hope

of seeing anything new.

(men yell)

Hey, what do we have here?

This is a strange looking creature.

And it seems to be some kind of a fish.

It looks a little like a tadpole,

but it clearly has a backbone.

It's about 20 centimeters long and must be

a fish of some kind.

Here it is again at the bottom.

The researchers think it may be

the same species as one discovered

in another part of the Mariana Trench

by another team three years ago.

It's known simply as the Mariana snail fish.

It's definite proof that fish can actually

come down to this depth.

(applause)

We did it!

Only one fish was found in the 18 hours.

It must mean the population density is very low.

That's probably what this indicates.

When the lander was lowered again

to seven and a half kilometers, it also recorded

some exciting pictures.

A huge white amphipod, a giant, more than 10 times

the size of the first they saw.

It's called the super giant amphipod.

(light music)

And after some time, the lander is surrounded

by ghostly white shapes, more Mariana snail fish.

They're attracted to the small amphipods

feeding on the bait.

Their eyes could probably see little

in the dark, but they have special sensory pores

around the mouth that allow them to detect

movements in the water.

(upbeat music)

The snail fish appears almost waif-like

and yet it must be tough to withstand the conditions here.

No other fish is known to live as deep as this.

(waves crashing)

To understand just how animals survive

at these extreme depths, a team of international scientists

have come together.

They all bring different skills to the table

and all are passionate about uncovering the mysteries

of the deep seas.

So our target area is about 200 meter.

They're now planning to capture

a snail fish alive at a depth of 8000 meters

so that they can examine the workings

of its body in detail.

Dr. Jeff Drazen is from the United States.

He's been working on the ecology of the deep sea

for many years.

If you go to the top of Mount Everest

and look around and say that there is snow and ice

and that is Mount Everest, you miss most

of that mountain.

And it is the same thing with the trench.

So it's very important now for modern hadal

investigations to sample the entire trench,

various depths and various different kinds

of habitats within this place.

(light music)

Dr. Alan Jamieson is from Britain.

He's an expert on the deep sea and has been

at the forefront of designing technology

to explore it.

So we've got three systems that are gonna be

at the point today looking for the snail fish.

The first one is a baited camera.

We have baits on the seafloor here

and it's being filmed by two separate cameras.

So this second system's a large fish trap.

So this will lure a snail fish into the trap

and recover a physical specimen.

Quite often the depths are working on are so unknown

that quite often we see things for the first time.

And the last one's fairly exciting.

It's my passion, the deepest places.

The places where no one had been before.

Places we not dare to go.

The team will use a range

of different landers designed in different countries.

Each will be lowered to around 8000 meters,

the depth of which snail fish are known to occur.

The first kind carries a fish trap.

Once fish have entered the basket, they can't escape.

(loud splash)

Next in line is the Adaka One, also designed

to catch animals alive and built by a group

of small firms in Tokyo.

I'm sure it will come back tomorrow

and we'll have some fish.

(upbeat music)

The next day the landers are brought back

to the surface.

There, yeah, I got it, I got it.

The first one up is Adaka One.

(men yelling)

There's something trapped inside the net.

But they all look like super giant amphipod,

allisella gigantea, seven, eight, nine.

(mumbles) This is great.

These amphipods are truly monsters.

Like most crustaceans their bodies are encased

in hard shell-like armor, and they have sharp pointed tails.

They use these tails so fish can't eat them.

They use that if the fish tries to eat,

it gets poked.

All of this here is just oily fluid

that helps them float.

You'll see it in the videos.

They kind of float.

So there's almost no muscle there.

Nothing to eat.

The super giant amphipods are the largest

in the world and could grow to over

30 centimeters in length.

How they do so is still a mystery.

(men talking)

The fish trip has also returned.

(men yelling)

And it's brought back what they've been hoping for,

a snail fish.

It's rushed back to the lab for immediate examination.

So, this is one of our snail fish,

a Mariana snail fish.

That's perfect I think.

We are very excited.

We've been working on it for a long time.

The body of the fish is soft and gelatinous.

It has no scales, and its skin is transparent

so one can see right through it

to the muscles beneath.

Its small eyes are probably useless

but no one knows for sure.

Some blind fish still retain rudimentary eyes

underneath the skin.

So fish have a number of sensory pores

on their heads, do you see them, yeah.

Most of the snail fish's pores

are located around its mouth and are used

for detecting movements in the water.

But they go away very quickly,

magic disappearing pores.

They're gone now.

The skin is extremely delicate

and the pores disappear almost instantly.

The researchers quickly make a note

of the position of each pore.

And then this is underneath looking up

so this is the mouth here.

And the underside of the jaw you can see

lots of little holes, but there's some very, very

small ones behind the eyes and coming down

the sides of the head, like little sensory,

so its vibrations in the water.

The pores probably help the snail fish hunt

for prey in the darkness of the deep.

Even the tiniest movement made by a small crustacean

will be picked up by these specialized organs.

(suspenseful music)

A closer look at the bodies of deep sea fish

is also starting to explain how they survive

the extreme pressures of the deep sea.

Dr. Paul Yancey has been trying to answer

this question for a long time.

His research has led him to a substance

commonly found in salt water fish.

It's called Trimethylamine oxide or TMAO.

It's a chemical that most people are probably

familiar with if they've been to a fish market.

It's that faint fishy odor that is coming out

of all these different species here.

And TMAO helps animals survive the high pressure

of the deep.

The water pressure in the hadal zone

is so great that it almost destroys body cells.

But exactly how does that happen?

There are proteins inside the cells that carry out

essential life functions.

It seems that under high pressure water molecules

are pushed into the proteins and stop them from functioning.

And this is where TMAO helps.

It binds tightly to the water molecules

and prevents them from disrupting the way

that the proteins work.

(light music)

Dr. Yancey has discovered that deep sea fish

have higher levels of TMAO than others

and the Mariana snail fish has the highest of all.

This remarkable finding suggests that the

Mariana snail fish may be better adapted

to life in the deep than any other species.

The Mariana Trench started to form around

50 million years ago.

That's relatively recent in the earth's long history

where few creatures alive today seem to have

evolved ways of surviving in its depths.

We think that fish has evolved in shallow waters

and most of the major groups of fishes

have not made it into the deep sea.

So it seems to be very difficult for animals

to evolve the ability to work under pressure.

So we imagine it's taken millions of years

and only a few types of fishes have made it down.

(waves crashing)

The team are preparing to launch

another lander to get some more footage

of the snail fish in their natural habitat.

(water bubbling)

They wait eagerly to see if their bait

attracts any visitors.

Oh, there he is.

There are snail fish here.

Two of them, there's two.

That was cool.

The lander has settled on the ocean floor

at about 8000 meters below the surface.

The bait has already attracted both amphipods

and snail fish, and the team get a wonderful

view of life in the very deepest part

of the earth's oceans.

Look at that, he just ate.

That's fantastic here.

To their delight the camera is recording

a fish feeding on amphipods.

It's just the kind of behavior that the researchers

were hoping to see.

The snail fish may look like a harmless tadpole

but it has some formidable weapons.

A CT scan reveals the details of its internal anatomy.

It has over 100 sharp teeth that ensure its prey

can't escape.

And at the back of the throat, there is a second

set of jaws with more teeth.

It's a complex system that enables the fish

to crush and grind food and so feed

on a great variety of prey.

And it may be one of the reasons why the Mariana

snail fish is able to live at such extreme depths

where food is so scarce.

In the deep sea you kind of don't know

when your next meal will be.

So you wanna be adapted to eat anything

that you can find.

Maybe that's where they are devoting their energy

is to making a very strong jaw for crushing prey.

They do seem quite fragile but they seem very successful.

We are beginning to get some understanding

of how the Mariana snail fish and other

deep sea creatures manage to survive

in the deepest parts of our oceans.

The first to gather at a fresh carcass

are the scavenging amphipods.

Following them come larger predatory amphipods.

And these in turn are hunted by Mariana snail fish

which crush the amphipods' shells

with their specialized jaws.

Astonishingly there appears to be an entire

community of animals that flourishes

as deep as eight kilometers down in the sea.

But what does the smallest of these creatures

usually feed on?

These amphipods are scavengers that eat dead

and decaying matter.

But very little food ever reaches these depths.

Now new research has shown they don't rely

just on the occasional animal carcass,

but also on something more surprising, driftwood.

Wood is notoriously difficult to digest

but the amphipods have evolved a powerful

wood-busting enzyme that could break it down

and extract energy from it.

(light music)

Chunks of wood do sometimes sink into the ocean trenches.

These may form a significant part

of the amphipods' diet and enable it

to live where few other creatures can.

(suspenseful music)

We have a long ways to go in exploring the deep ocean.

We have a lot of questions left.

And we're just going to have to keep exploring

the trenches to find it and to try

to answer a whole lot of other questions that we have.

(waves crashing)

The team are now heading for a location

near the entrance of the Mariana Trench.

(mechanical cables lifting)

This time they're dispatching a remotely

operated vehicle, an ROV.

They're hoping to find a place that was discovered

several years ago 5,700 meters below the surface.

The ROV moves along the steep rocky slopes of the trench.

And as it comes around a corner, it finds

what they've been looking for.

(people speaking foreign language)

It's a ghostly site resembling the stalactite formations

in a dark cave.

(light music)

And there is also life within this strange

underwater landscape.

A tangle of deep sea tube worms.

And on the sea floor a bed of giant white clams.

They've not been seen in the trench before.

(light music)

All these lifeforms can only exist here

because the water seeping from deep below

is rich in dissolved chemicals which can

be converted into food by a whole community

of deep sea creatures.

The seeps in the Mariana Trench are still mysterious

and largely unexplored.

(light music)

The expedition is now heading towards the deepest

part of the Mariana Trench.

It's a slot of the southern edge called

the Challenger Deep.

On the 23rd of January, 1960, the US Navy

made history by sending down the first manned

deep sea vessel into its depths.

Its two-man crew sat inside a small sphere

on the underside of the submersible.

The rest of the ship was a float chamber

filled with gasoline to give it buoyancy.

And the two men who attempted the journey

were lieutenant Don Walsh and scientist Jacque Picard.

The dissent took nearly five hours

but they reached the bottom and a depth

of nearly 11 kilometers.

The submersible that made this historic voyage

is called the Trieste and is now kept

in the US Navy Museum in Washington.

Don Walsh remembers the epic journey well.

As you can see this window here is not straight ahead.

It's pointed down to the seafloor.

He claims to have seen something remarkable

on the ocean floor.

We had outside lights, which are on the bottom part

of the balloon here.

So we could see from here out to about 10 meters

on the seafloor.

Well just before we landed on the bottom,

we saw a flat fish, like a sole or a halibut.

Jacque was at the window.

He said come here, look, fish.

And he moved away from the window.

I moved up, looked at it, and that's what

it looked like to me.

This is almost a quick snapshot.

'Cause soon as we landed, poof, our vision went away.

This is Don's drawing of the fish

he thinks he saw.

But most scientists are skeptical.

And they have good reason.

Deep sea fish need high levels of TMAO

to withstand the enormous water pressure.

But at extreme depths of over 8000 meters,

it's thought that the fish would need

so much TMAO that their bodies would cease

to function properly.

I know that many marine biologists

and fish specialists said we didn't see a fish

because one couldn't live at that depth

and so on and so forth.

I'm willing to allow or admit that maybe

we didn't see what we saw.

But for now, until they can prove us wrong,

I'll have to stick with fish 'cause I know

what the fish looks like.

After the descent of the Trieste,

over 50 years ago, only unmanned vessels

made the journey into the Challenger Deep.

Then in 2012, film director James Cameron

became the third man to descend to the bottom.

In the small area of the trench that he explored

he saw a number of deep sea creatures but no fish.

The question as to whether there are fish

in the deepest parts of our ocean is a fascinating one.

Japanese scientists have teamed up

with filmmakers to develop a new type

of ROV that might be able to answer the question.

It's one that can move freely along the ocean floor

at a depth of 10,000 meters.

All its parts are specially designed

to be able to withstand extreme pressure.

It's taken a whole year to complete its construction.

Now the ROV is heading out into the Challenger Deep

for the first time.

The engineers carry out the final safety checks.

The ROV is equipped with high resolution cameras

that can be operated from the surface.

It's a unique system where the ROV and its launcher

are dispatched together.

The two parts are coupled together during descent

lowered by a main cable from the mother ship.

At 7,000 meters the smaller vehicle is separated

from the launcher and a one millimeter fiber optic

cable is now the only connection between the two.

Once uncoupled, the lighter vehicle can move around

more freely to explore the ocean floor.

(upbeat music)

It's four in the morning.

The team prepare to launch the new system.

It will take six hours for the ROV to reach the bottom

so they start well before dawn.

(loud splash)

(man talking)

The ROV sends back images to the ship's control room

as it descends.

1000 meters.

After three hours the ROV and launcher

are 7000 meters down.

They'll now be uncoupled.

All systems go, commence separation.

Everyone is on edge.

During testing the thin fiber optic cable

repeatedly snapped at this stage.

They watch nervously.

It's free, keep going.

Good, it's all right.

Separation complete, time 7:57.

This is nerveracking.

The uncoupling went without a hitch

and the ROV continues its dive to the bottom

of the trench.

8000 meters.

It's now beyond the depth at which

fish can survive.

10,000 meters.

And it's more than 10 kilometers

below the surface.

50 meters to the bottom.

The countdown to the bottom has begun.

30 meters, five meters.

It's hard to see the sea floor.

Are we seeing it?

Ah, there it is, yup.

That's definite.

But after six hours and 20 minutes

the ROV has finally reached the bottom.

This is the deepest place in all the oceans

of the earth.

The temperature is 2.4 degrees above freezing

and the ocean floor is covered by a thick layer of sediment.

This barren lunar landscape seems lifeless.

The ROV slowly starts to move across the ocean floor.

The water pressure at this depth is so enormous

it's equal to a one ton weight placed

on the end of your finger.

Can anything really survive here?

The team watch intently for any sign of life.

And there it is, a small white shrimp-like creature.

Given the enormous pressure it's under,

it's swimming with surprising speed.

It appears to be an amphipod.

It's the first time one has been observed at this depth.

Here, this.

The team have spotted something else.

It's a type of sea cucumber, the soft bodied

marine creature.

It's closest relatives are star fish and sea urchins.

Most sea cucumbers feed on plankton and waste matter

on the sea floor.

The researchers have not seen this kind before.

It could be a new species.

(men talking)

Then the ROV finds even more.

The ocean floor around them seems disturbed.

It looks like they've been feeding.

Sea cucumbers do that by sucking in sediment

and filtering out the edible particles.

The rest is ejected and returned to the sea floor.

The ROV then continues on its journey.

(men talking)

The researchers are thrilled.

They never imagined there would be such large numbers

of sea cucumbers at this depth.

These animals are all aligned in the same direction.

That suggests that there is a current flowing

along the bottom, and the sea cucumbers

may be facing the flow to save energy.

So it seems that the deepest reaches

of our oceans hold more life than we once thought possible.

What appears to be a desolate landscape

is in fact home to some highly specialized creatures.

But how is it that sea cucumbers and amphipods

are not crushed to death by water

over 10 kilometers deep?

Recent research has revealed that another chemical

substance may hold the answer.

It's been found in large quantities along with TMAO

in deep sea amphipods and it's called scyllo inositol.

It has a flat molecular structure that may allow it

to wedge itself between protein molecules

and counteract the effect of water pressure.

And scyllo inositol may protect proteins

in a way TMAO cannot.

TMAO will only work up to a certain depth.

In deeper waters, the proteins stick together

and cease to work properly.

If scyllo inositol is present, it may wedge itself

between the proteins and restore their function.

We don't yet know whether other creatures

that live in these depths have high levels

of scyllo inositol.

And it's not inconceivable that some fish

could make use of a substance like this.

If so, then Don Walsh could have been right

when he claimed to have seen one some 50 years ago.

Our expeditions that dive into the deepest parts

of the Mariana Trench has revealed sea cucumbers

and amphipods.

But it's been unable to find any fish.

For now this will remain one of the unsolved mysteries

of the trench.

(light music)

While deep sea exploration has unraveled

some of the mysteries of our oceans,

one question continues to puzzle scientists.

Where did the animals that live in the Mariana Trench

come from?

Doctor Hiroshi Kitazato has studied deep sea creatures

for many years and has an extraordinary theory.

DNA analysis of the lifeforms in the hadal zone

has made great progress in recent years.

Based on those results, we can say

with some degree of confidence that these creatures

are likely to have come from antarctic waters.

In fact, the Mariana Trench

and the antarctic have one thing in common.

Their waters are very cold and poor in food.

The amphipods from the Mariana Trench were also found

to have the same cold tolerance gene

that is found in antarctic amphipods.

As for snail fish, they are common throughout our oceans

but they're more abundant in antarctic waters.

So the Mariana snail fish may have its origin

in the antarctic seas.

There are in fact deep ocean currents

that connect the antarctic with the Mariana Trench.

Cold antarctic water sits at the bottom

and flows out along the seafloor into other oceans.

In the Pacific one of them crosses the equator

and flows into the Mariana Trench.

Animals found in the Mariana Trench today

could have made the journey by adapting

to their new environments along the way.

The trench only reached its currently depth

10 million years ago, so the creatures

that live here must have evolved relatively recently.

Only animals like snail fish and amphipods

already adapted to living in the cold

would have been able to make this epic journey.

The Mariana Trench is just one of the many

deep gorges hidden beneath our oceans.

But it has given us a brief glimpse

of some remarkable animals that manage

to survive in one of the most inhospitable places

on the planet.

If creatures like these can remain unknown

for so long, what others might there still be hiding

in the deep.

It's a reminder of how little we still know

about the deepest reaches of our oceans.

(light music)