Original subtitles

For centuries, we've fantasized

about alien life on other planets.

And because life as we know it needs water,

we imagined seas on the moon,

rivers on Mars,

and lakes beneath Europa's icy surface.

So far, we've discovered only dust...

except on this watery blue marble,

where inner space hides creatures

as weird as anything extraterrestrial.

There are oceans of oddballs with strange shapes,

strange rituals,

and strange bedfellows

right here in Earth's own "Alien Abyss."

Oceans, the great unknown.

To understand this weird world,

first you got to leave that land brain of yours

on the beach and dive right in.

Lesson number one-- forget what you already know,

because down here, nothing is as it seems...

not a plant...

not a rock.

This won't kill you.

This surely will.

But in this mysterious underworld,

being bizarre alone

won't win you life's daily battles.

What you need is help from a friend...

an accomplice,

or even a significant other.

Teamwork is the name of the game.

And the stranger the relationship, the better.

Yesterday's adversaries...

could today be your allies.

What do you picture when you hear the words

"alien invasion"?

This?

Maybe this?

Or even...

Who--who are you?

We're from Mars. Don't be afraid.

But did you think a small, spiny sea creature

that's only as big as a golf ball...

Cute, right?

Wrong.

Our story begins in sunny California.

These folks don't know it,

but a pestilence is wreaking havoc in their local seas.

Unearthly invaders rule the seabed here.

And they devour everything.

Under their relentless attack,

the ocean floor is a desert.

But it wasn't always like this.

15 years ago,

giant kelp forests covered these coastal seas.

Kelp were the OGs of these California waters.

Their forests remove millions of tonnes of carbon

from the atmosphere each year.

And many species flourished within their foliage.

This was once a bustling underwater metropolis,

and life was good.

The kelp's only annoyance were sea urchins

that nibbled on their fronds.

But that was okay because sea stars kept them in check.

However, that all changed when higher sea temperatures

began killing the sea stars.

With them out of the picture,

urchin populations exploded.

Disaster for kelp.

Their soft fronds have absolutely no defense

against urchin teeth that can cut stone.

Today conquering urchin hordes

wipe out entire kelp forests...

creating what are called urchin barrens.

Nothing can stop them.

Well, almost nothing.

There is a place along this coast

where sea urchins finally meet their match.

This is the realm of the sea otter.

A marine hunter extraordinaire,

guardian of kelp forests,

and sea urchin connoisseur.

For these predators,

no hunt is easier than an urchin hunt.

Tough spiny shells? Not a problem.

Otters bite through the underside,

where spines are shortest.

It's an all-you-can-eat buffet.

And the otters make the most of it.

A single otter will polish off

up to 1,000 urchins each day.

That's enough to keep the rampant urchins

from spreading unchecked.

Maybe through this interspecies relationship,

kelp all along the coast can get a respite

from pillaging urchins

and rediscover their former glory...

Because where there are otters,

there is happier kelp and healthier seas.

And that is how the alien abyss works...

a complex web of relationships

where fortunes are intertwined...

and help comes from the most unexpected quarters.

But things aren't always this complicated.

Some weird relationships are much more straightforward...

like the one between the snapping shrimp

and its neighbour, the goby.

The shrimp is an obsessive burrower.

It digs all day,

clearing rubble away from the entrance to its burrow.

It really doesn't do much else.

The shrimp even finds food in the debris that it moves.

And all this while,

its neighbour just stands there and watches.

But see, here's the twist.

The goby is its personal bodyguard...

because the shrimp's got a problem.

It's nearly blind

and useless at detecting danger.

Case in point.

It's no good having a fortified bunker

if you don't know exactly when to duck in.

And that's where the goby comes in.

With powerful bulbous eyes to spot danger,

it's a perfect protector.

While the shrimp goes about its business,

it keeps one of its sensitive antennae on the goby.

Incoming!

In return, the little fish wants to share the bunker.

And the shrimp is okay with the arrangement.

It's the least you can do

for someone who's just saved your life.

eard of a toxic relationship?

Well, in these mysterious depths,

that's actually a good thing.

Meet one half of this deadly romance...

sea anemones.

No relation to their harmless terrestrial namesakes.

Don't be fooled by their benign looks,

because these things are killers...

Much like their distant free-moving cousins,

the jellyfish.

Armed with stinging nematocysts on their tentacles,

anemones inject a toxic chemical cocktail

into their victims...

which paralyze them.

This anemone has no time for subtleties

and consumes its prey alive.

So, yeah, an all-round nasty customer.

As these poor fish will soon find out, too.

Wait for it.

Any moment now.

Strangely, the anemone doesn't attack...

because the clownfish-anemone alliance

is a love story for the ages.

These fish proliferate the warmer shallow seas

around the world...

Always in partnership with the anemones.

Their noxious affair starts early.

Clownfish lay eggs in coral niches close to anemones.

It's a surefire way to keep egg burglars at bay.

They know better than to get close to the vicious tentacles.

A week after hatching, young clowns don't stick around.

All on its own,

this baby clownfish attracts unwanted attention.

Eventually, something will come along that wants to eat it.

The only way to survive

is to find its very own toxic partner.

This anemone is perfect.

The clownfish is born with a layer of slime

that makes it immune to the anemone sting.

Safe from predators, these stinging tentacles

become a sanctuary for baby clownfish.

But it's a two-way street down here.

In return, when clownfish are older,

they chase away larger fish that want to feed

on the anemone's tentacles.

It takes out the trash

and even delivers scraps of food.

Without clownfish, anemones often die.

But by means of this unique partnership, everyone wins.

So, basically, friends turn up to help when you're in need.

But spare a thought for the loners,

the recluses, and the outcasts.

Making friends isn't easy

when you're just plain weird.

Remember when we said,

"These things are killers"?

Now let's take a closer look.

Closer still...

and hold.

That right there, stuck in the anemone's vicious coils,

is a pearlfish.

These eel-like fish--

Hmm, try that again.

Pearlfish are found in the--

As you can see,

pearlfish are useless at defending themselves.

Out in the open,

weird, alien-like killers give him no chance.

This pearlfish desperately needs a place to hide.

The rear end of a defenseless deep-sea dweller

is just the place.

Right, we can't just brush past that information.

Sea cucumber are large, spineless beasties

that some would describe as a "walking colon."

You'll soon find out why.

They're a simple marine organism

with a no-frills lifestyle.

A leathery skin covers a spongy, tubular body.

And inside, a digestive tract with openings at each end.

At the top end, their fan-like tube feet filter out

floating particles of algae, tiny animals...

and organic matters off the sea floor.

Which brings us to...

That's clean sand, by the way.

Poop-scooping scientists calculated

that on just one reef,

sea cucumbers dump five Eiffel Towers' weight

in sand every year.

Their words, not ours.

And that's not all.

The sea cucumber is basic.

But it's also basic.

When their gut breaks down sand,

it creates calcium carbonate,

which they then poop out.

This lowers the acidity of its surrounding water...

and helps coral form their calcium carbonate skeletons.

So sea cucumbers are vital

for the health of the planet's reefs.

They're real nice guys.

So nice, in fact, that when the pearlfish wants sanctuary,

the sea cucumber welcomes it.

And the little fish

benefits from this open-door policy.

It's safe in there because most predators

find the sea cucumber rather disgusting.

When it moves around on the sea floor,

the pearlfish has access to new feeding grounds

while still staying at home.

Food, lodging, and a free ride...

now, that's a vacation.

But what the sea cucumber gets

out of this strange relationship,

we'll never know.

The best relationshipse all about g

But what if the givers and takers never meet each other...

never really interact with each other?

In the eccentric world of misfits,

that's still a very important relationship,

like this one between a hermit crab

and the maker of the shell he's borrowed.

Hermit crabs are true nomads.

Wherever it goes, its home goes, too.

But the shell is just a hand-me-down.

Unlike many other crab-like beings,

hermits can't grow their own.

So they form partnerships with mollusks,

squishy, snail-like things.

Well, really just their shells,

and only after their owners have discarded them.

It's prime real estate

because it's relatively light and protects them from attack.

But for these crabs,

each shell is only as good as the next one.

Every time they outgrow their shell,

they must discard it and move into a new one.

It's a relentless lifelong quest.

But the world is changing around them.

Suddenly they find themselves

surrounded by alien beings...

us humans.

And we are destroying the only home

the hermit crab has ever known.

In the aftermath of cyclones,

beaches of Southeast Asia are littered with trash.

It's a particularly rough time for hermit crabs.

Shells are in short supply.

But among all this debris,

pragmatic hermits find a solution.

With declining mollusk population,

they've found a new, completely oblivious partner...

Us.

Bottle caps,

measuring cups...

film roll containers.

Anything goes.

Soon, the beaches teem with alien trash-robot hybrids,

half crab, half plastic.

They aren't exactly tailored to the crabs' contours,

but no one's complaining.

Desperate times, desperate measures.

Deep within the coral crevices of the North Pacific...

Lives a creature with a face for radio...

A beast that looks like it's graduated from alien school...

But, in fact, lives a life

that's straight out of the 1950s.

This male's mission-- find a wife.

With misshapen, crooked teeth, mottled, bumpy skin,

and an unblinking stare,

the wolf eel won't be winning any beauty pageants.

But it doesn't bother about what the world thinks.

Only one opinion truly matters...

that of this female wolf eel.

In the wolf eel world,

she is his, and he is hers

for now and forever.

Theirs is a tender, old-fashioned affair

that is incredibly unusual under the sea.

Old-fashioned or not,

what comes next should be no surprise...

a baby boom.

Secure within their intertwined coils

lies the fruits of their relationship...

up to 10,000 newly laid eggs.

The loving male now turns protector

of his unborn children.

For four long months,

the parents will guard their precious cargo.

But it's a full-time job.

Hunger soon pushes the male out of his cozy love nest.

Breakfast is served.

You can see why the eel's teeth

aren't in the best shape.

But every winter,

he'll replace his old worn-out teeth with new ones.

Having eaten his fill, he heads back to his lair

to swap places with his partner.

That's right, wolf eels only look unearthly.

Their everyday life is decidedly not weird at all.

In fact, their whole life cycle is pretty mundane.

Grow up...

find a partner...

put food on the table...

start a family...

over and over and over again

for the rest of their lives.

There's only one thing that they don't have to do.

That is raise their weird-looking,

but otherwise unremarkable kids.

After hatching...

baby eels are on their own.

They head into the North Pacific Ocean

looking to forge their very own super-normal,

unweird, prosaic futures.

Allies

But there are some weirdos in this alien abyss

that have nothing to give...

but specialize in mooching off others.

Say hello to the freeloaders.

Take a moment to consider the remora.

From below, it looks like a fairly normal fish.

But from above...

This fish wears a permanent alien suction disk helmet.

It's a marvel of natural engineering.

The head disk is a device that helps the remora

get past a crucial design flaw.

Without an air bladder to control buoyancy...

it struggles to do normal fish things,

like swim and stay afloat.

So, for transportation, gangs of these suckerfish hang about,

waiting for a ride.

This shipwreck serves as a station of sorts.

It's their Grand Central Terminal.

Transit route number one--

reef sharks.

Reef sharks are the express train.

They're fast swimmers,

and there's almost always onboard dining.

Great for the remora in a hurry.

But the travellers have other options.

Transit route number two--

gigantic whale sharks

and manta rays.

They're more like the cruise liner--

not as fast but definitely roomier

and more likely to travel long-distance.

It's a chance for remora

to get to better feeding grounds

and even to find new mates.

Remoras will even catch a lift...

on a dugong.

Really?

Might as well walk.

But sometimes holding on can become tough.

But sensory organs below the remora's sticky disk

tell them when they lose traction,

which gives them time to readjust.

Not everyone is thrilled with this rideshare arrangement.

For ocean dwellers, hydrodynamics is everything.

The ease of moving through water

with as little drag as possible...

is the cornerstone of marine locomotion.

Clingy fish hanging off

kind of puts the brakes on this.

The Romans were right when they named these fish "remora,"

Latin for "hindrance."

Remoras are like hitchhikers.

They catch a free ride,

but eventually they get off.

But there are some freeloaders that don't let up...

ever.

They spend their whole lives scrounging off their hosts.

Take, for instance, barnacles.

Yeah, they can harmlessly stick to rocks and stuff,

but they also have a nasty habit

of sticking to living, moving creatures...

forever.

It all starts here...

baby barnacles.

For a few brief weeks, they swim free.

This part of their life, this little part,

is called settling down.

It's when they decide where they want to live

for the rest of their lives.

What these barnacle larvae want are a modern mobile associate.

No one knows when or how they climb aboard,

but they do.

Turtles offer a good surface to work with.

And, of course, these guys.

Actually, these are manatees, not dugongs...

just as slow, just as easy for fledgling freeloaders

to grab a hold.

But the best lodging sites of all...

whales.

These living, breathing underwater blimps

are moving islands of flesh and blubber.

For larvae wanting a contemporary space

to settle...

whales are the real deal.

Using cementing enzymes,

they clamp down on spots like the head and chin,

where water flow is consistent,

so that when they pass through plankton-rich waters,

they can grab tasty titbits, like so.

Of course, this was filmed on a rock.

I mean, there's no way our camera operator's gonna get

that close to a whale.

Trust us, barnacles work the same either way.

As the whales migrate throughout the year...

the barnacles get a free ride to nutrient-rich waters,

feeding all the time.

And what of the whales?

Well, they don't come out of this relationship

as complete chumps.

Whales fight over mates,

and hard barnacles are like brass knuckles.

It adds an edge to their punches,

and sometimes even acts as armour plating,

which helps them take a blow or two.

So remora are annoying but temporary.

Barnacles are lifelong but don't really do any harm.

Just freeloaders being opportunistic,

or is this a slippery slope?

Enter the harlequin shrimp...

a male and a female out to get some food.

First things first, catch a ride.

Sea stars could be the perfect shrimp transport...

but the bizarre shrimp takes the concept of catching a ride

way too literally...

because sea stars are not just their way

to get from point A to point B.

It also happens to be their favourite chow.

That's right, these dainty shrimp

are a criminal couple.

Talk about taking onboard dining to the next level.

What better way to keep your meal fresh

than jumping on it...

and chomping away at it...

all while still riding it?

However, some sea stars have a strategy

to get the deadly duo off their backs.

While ravenous shrimp focus on eating their fill,

a desperate sea star sheds its arm...

A ruse to divert the killers' attention.

It might just be able to sneak away.

If the plan works, it can later regrow its lost arm...

but it isn't that lucky.

The sea star's shed arm

only momentarily distracts the killer couple.

They're right back on it.

So that escalated quickly.

As far as unhealthy relationships go,

losing an arm in the process

seems just about par for the course.

Where some see hideous alien monsters...

others see friends...

and vice versa.

It's all a matter of perspective down here.

Out on the sea floor, crabs are patsies.

Their shells give off an illusion of invincibility.

But they're just not always enough.

Enter the fire urchin.

Armed with venom-tipped spines,

they're all-round vicious customers.

But for some, these prickly freaks are saviours.

Their spines make

for an impenetrable mobile fortress...

a boon for the beleaguered crabs,

like these little guys.

Zebra crabs ride their fiery chariots

all day and all night,

never once getting off.

The urchin protects them from potential killers

and carries them around.

And how do these freeloaders show their gratitude?

By slowly, imperceptibly gnawing away

on urchin tissue for food.

However, the damage is so minimal

that it doesn't kill the urchins.

But the crab family soon find a way to redeem themselves...

By turning this eccentric relationship on its head.

This crab's modified back legs have just one purpose...

To haul urchins around.

Having a venomous pincushion for a headdress

keeps predators at bay.

Unlike their parasitic cousins, the zebra crabs,

the carrier crab isn't just a taker.

It's also a giver.

In exchange for full-time protection,

the crab carries the urchin around to new feeding grounds

faster than the urchin could go on its own tube feet.

It's like having a chauffeur on call...

the only downside being you go where the chauffeur wants

and not the other way round.

And because you're wondering,

yes, this means it's possible

to have a crab riding an urchin...

riding a crab.

Carrying bodyguards around for protection is so effective

that yet another crab has picked up

on this nifty trick, too.

This pom-pom crab's oddly shaped pincers

are, in fact, not pincers at all.

These alien, tentacle-like appendages

are actually deadly anemones.

Remember them?

Jellyfish family, venom-tipped...

killer.

The defenseless crab knows all this, too...

which is why it holds two small anemone clumps

in its front pincers like a freaky cheerleader.

Perfect to ward off anyone that comes too close.

And that's not all.

In return, when the crab forages,

the anemones get food scraps and more oxygen

from the flowing water.

For a change, this story has a happy ending.

The crab-anemone collab is a prime example

of two completely different organisms

getting along just fine.

There are other alliances in this alien abyss,

where predators and their prey

set aside their differences for a common good.

In the depths of the Earth's own alien abyss,

there are some that have cracked the code to survival.

It's this...

not every killer is out to get you...

So long as you are willing to help them out...

because predators have problems of their own...

ectoparasites.

As is the norm in these alien oceans,

weird problems warrant weirder solutions.

Cleaning stations...

designated "no kill" safe zones

where an enterprising bunch of tiny oddballs

run a cleaning service.

And their shop is now open for business.

This glass shrimp has its first customer of the day--

a pufferfish.

The shrimp gets started,

gorging on parasites and dead skin

from the fish's body.

The puffer must rein in its natural hunting instinct...

Because a shrimp this size could be an ideal snack.

Thanks to the reef's unspoken peace pact...

the shrimp can totally concentrate on the job at hand.

Just above,

domino damselfish hover in anticipation...

waiting for the shrimp to flush out parasites.

And now for the tricky bit-- the deep clean.

The gills are a parasite's favourite hiding spots.

Left unchecked, they can infect and even kill the puffer.

But not if the cleaner shrimp has its way.

It picks them off expertly,

making sure to get into all the nooks and crannies.

On other cleaning stations around the world,

business is always brisk,

Specialist cleaners attend to busier clients on the go.

Cleaner wrasses remove dead and damaged scales...

And even simulate mucus production,

often the first line of fish immune defense system.

Most importantly for the clients,

it probably feels fantastic.

Who doesn't love a backrub?

Not even this mysterious,

deep-sea-dwelling freak of nature...

the mola mola.

This slow-moving, tailless giant

looks decidedly otherworldly.

But he's a distant cousin of the tiny pufferfish.

Only, he's three meters long

and weighs a tonne.

That's almost as big as a small car.

He usually likes to hunt in the deepest, darkest chasms

of tropical oceans.

But today he's come up to the surface...

Because today is spa day.

A bit of exfoliation, a bit of sun,

and to get rid of teeming parasites.

Cleaners like these bannerfish

enjoy a parasite banquet...

because each mola mola can have up to 54 species of parasites

on them at any given time.

If it weren't for the dedicated cleaners,

these blood suckers would infest the giant fish

and cause them a great deal of discomfort.

In the hands of the tactless, it can be a dangerous job.

But years of evolution has helped these cleaners

master the fine art of getting a meal

without becoming a meal.

Getting along and working together for mutual benefit

is the surest path to survival in this alien abyss.

When you're small and powerless,

banding together with others of your kind

is not just advantageous, it's necessary.

On the sea floor around Indonesia,

a dark cloud hangs about...

An advancing alien swarm that's bewitching,

hypnotic, ominous.

These are baby striped eel catfish.

Advancing in unison,

their movements mimic a larger beast.

It strikes fear into the hearts of predators...

ones that would readily attack

and devour a lone young catfish.

Confident in their invincibility,

the swarm begins to feed.

They completely work over the seafloor

in a mesmerizing steamroller fashion.

Fish at the rear swimming over the ones at the front,

only to be replaced again.

This way, they leave no bit of seabed untouched

in their search for invertebrates and algae.

While the ones at the front are facedown in the sand,

the ones at the back keep an eye out for predators.

A ribbon eel is the only one that dares.

But young catfish have a secret weapon--

toxic pectoral and dorsal spines.

And the eel gets a mouthful of it.

Back to formation for the young escapee.

And back to the drawing board for the chastened eel.

Tightly packed shimmering, shapeshifting shoals

can confuse your typical, run-of-the-mill predators.

But can it hold its own

against some of the smartest brains

on the planet?

For far too long, we've searched for intelligent life

above our heads,

when we should have been beaming signals downwards

into our oceans...

because that's where you'll find

the second-largest brains on the planet...

with an IQ greater than that of chimps and gorillas.

Alien intelligence?

You're looking at the leading contender--

orcas.

Their remarkable intellect has helped them rule

all of our planet's oceans--

that's more than 70% of Earth's surface...

For more than 6 million years,

which is far longer than we've walked the planet.

Maybe they really are hyperintelligent beings.

Not convinced?

Well, let's put their smarts to the test.

Introducing the test subjects...

Hungry Norwegian orcas.

And here's what they're after--

large shoals of herring--

fatty, juicy, rich source of protein.

And now here's the problem.

As we discovered earlier, tightly packed,

fast-moving small fish are spectacularly hard to catch.

Not least when you're a 6-tonne beast

in a sea with no cover.

It's a code they must crack,

and their time starts now.

Step one, turn on their secret superpower--

echolocation.

Pinging out sound waves and catching it back,

they get a mental picture of anything in their way

and even see inside it...

like an X-ray.

The herring are tantalizingly close.

Step two, trap the small fish.

Orcas turn to their most potent weapon--

their brains.

No one knows exactly how they communicate,

but soon, orca brains are syncing up.

Working as one, the pod pushes them towards the shallows.

Now the small fish are stuck between the sea floor,

the shore, and the orcas.

Step three, immobilize fast-moving fish

with their very own stun gun...

Their tails.

Powerful tail slaps shock the living daylights

out of the small fish.

And the slap-happy orcas pick them off one by one.

Game, set, and match.

Social beings--tick.

Problem-solving brains-- tick.

Phenomenal superpowers--

tick and tick.

So, you see, these giants could easily be aliens...

who've mastered a strange and inhospitable environment...

to become the kings of these alien oceans.

Working together works...

because in the end, every critter that lives

in these ungodly depths

has the very same goal--

survival.

And as is the norm, stranger the problem...

weirder the alliance...

in this alien abyss.