[ Squeaking ] ♪♪♪ NARRATOR: In these waters lies a complex world... ...a natural realm built on relationships.

♪♪♪ It's an ancient system of give-and-take... ...where communities of life cooperate.

♪♪♪ The diversity of creatures here is dazzling.

♪♪♪ And everyone must play their part to maintain the delicate balance.

♪♪♪ Take a deep breath and discover... the Soul of the Ocean.

[ Clicking ] ♪♪♪ ♪♪♪ ♪♪♪ [ Squeaking ] ♪♪♪ NARRATOR: Hold your breath.

♪♪♪ Listen.

[ Animals singing ] [ Squeaking ] Watch.

♪♪♪ Understand.

♪♪♪ The more you look... the more it changes your perspective.

♪♪♪ ♪♪♪ ♪♪♪ Animals and places reach out to you.

[ Clicking ] ♪♪♪ They are all part of a global and ancient system that could explain everything.

♪♪♪ Hold your breath... dive... into a better world.

♪♪♪ [ Whales singing ] Sound travels further underwater, and whale songs can cross an ocean.

[ Whales singing ] Humpback whales have left Antarctica and are heading for French Polynesia in the middle of the Pacific.

[ Wind whipping ] The humpbacks come 4,000 miles to this reef to give birth and sing.

[ Whales singing ] Males escort each family, hoping to mate.

There's constant communication.

[ Whales singing ] A calf nurses, sloppily, 50 gallons of milk a day.

The milk is so rich that it doesn't dissolve in the water, but forms white droplets.

[ Whales singing ] The humpback bulls sing on their heads.

We don't know why.

[ Whales singing ] The songs are complex, constantly changing as part of a rich culture.

There are elements of music and language, but their meaning to each other we don't yet understand.

[ Whales singing ] ♪♪♪ The song spreads from Polynesia and echoes across thousands of miles of ocean.

♪♪♪ ♪♪♪ Tides and currents, ripples and upwellings connect the furthest reaches.

[ Whales singing ] ♪♪♪ The ocean transports nutrients and animals in a way impossible on land.

♪♪♪ This is a single home, miles deep, and full of life that can link almost anywhere.

♪♪♪ In November, when the calves are strong enough, the families return south to feed.

[ Whales singing ] Humpback whales connect the ocean, but the coral reef is where their song starts.

♪♪♪ Each reef is a global city, with waves of traffic and sounds and tastes, even cultures, moving back and forth over thousands of miles.

♪♪♪ The city is fueled by an extraordinary alliance between sunlight and coral.

♪♪♪ Coral polyps are animals, and living inside them are plants -- photosynthetic algae.

♪♪♪ The algae are powered by sunlight to build sugars, and the coral polyps gather nutrients and proteins.

This cosmopolitan community is built on relationships, on creatures working together.

Each species of anemone fish has its own anemone, a symbiotic friendship that neither can live without.

The stinging arms defend their personal clownfish from reef predators like moray eels.

If an anemone fish feels really threatened, it even can hide in the anemone's stomach.

It's also a safe home to a porcelain crab.

And specialist shrimp and baby damselfish make it their home.

Companionships are everywhere you look.

An urchin and a crab.

Pygmy seahorses hide on gorgonian corals.

They've evolved to match their home.

Different kinds of fan corals have different kinds of seahorses.

If a fan coral goes, its seahorses die, too.

♪♪♪ Each species is like a cell in a body, working together and part of a vast system that only can exist because everything is connected.

It's different from land, with its isolated islands and habitats.

♪♪♪ The consequences of this are only beginning to be understood.

♪♪♪ Beyond the reef, cooperation can become even more personal.

♪♪♪ Offshore of the Philippines, a shrimp goby guards a burrow in the coral rubble.

♪♪♪ A companion shrimp excavates and does the housework.

Gobies have good eyesight.

They scan for predators.

The shrimp is almost blind and will only venture to the entranceway if he, or she, can touch the goby with its antenna.

The physical contact between lifelong friends is the heart of the relationship.

How they originally find each other to set up home is a puzzle.

They are never seen living alone.

There are dozens of different species, and each partnership is specific.

Both shrimp and goby usually have a mate, and the couples get along well.

They may also take in lodgers.

These ones are dartfish.

The shrimp never leaves the burrow, so what does he eat?

Well, the goby's food is... recycled to the shrimp.

Perfect.

At least one shrimp antenna is always in contact with one goby.

They both react as one.

Relationships are not always so balanced.

Sharing the same reef is a family of convict blennies, living in a burrow.

The baby blennies mimic venomous striped catfish, and their disguise is convincing enough to discourage predators from eating them.

The youngsters feed on plankton above the reef without any danger.

Meanwhile, the adults hide.

They stay at home and clean and maintain the burrow.

They have never been seen to eat.

Only the youngsters feed, on life drifting in from maybe thousands of miles away.

♪♪♪ How the parents survive has long puzzled scientists.

Researchers studying them now believe that the seemingly perfect parents actually eat a few of their babies each night.

[ Ominous music plays ] Cooperation raises some difficult questions.

♪♪♪ In nature, there is dark, as well as light... and all shades in between.

♪♪♪ In communities full of competing interests, hunger, and betrayal, why would a shrimp go near a dangerous moray eel?

♪♪♪ ♪♪♪ It's a cleaner shrimp.

The moray holds its breath.

Cleaner shrimps dedicate their lives to others, and an extraordinary trust has built up between them and the moray eels.

Everywhere you look, animals are not eating each other, but cleaning each other.

Fish travel to a particular cleaning station and often change color as a signal that they're hoping to be cleaned.

They come far more often than they need to.

There's something about it that they like and keeps them coming back.

♪♪♪ Specialist cleaning stations are on every reef across the Pacific.

♪♪♪ Around Hawaii, green turtles come regularly, often from hundreds of miles away.

Surgeonfish remove a green fuzz of algae.

The fuzz slows a turtle down, so a clean shell is important.

♪♪♪ ♪♪♪ This turtle cleaning station is a very specific outcrop.

50 feet from here, surgeonfish have other jobs and ignore the turtles.

There are service centers like this all over.

It's a global network.

3,000 miles to the east, off Mexico, Clarion angelfish wait for a different customer.

♪♪♪ A manta ray may have traveled thousands of miles between appointments.

♪♪♪ Injuries are tended to... and tiny parasites or algae removed.

♪♪♪ The angelfish gets a meal, but that can't quite explain the relationship completely.

There's a much older alchemy, an ancient biochemistry that creates a physiological buzz out of doing things together.

Symbiosis can be traced back as far as bacteria.

Cooperation was built into life right from the start.

And mantas, angelfish, and us -- we all feel it.

♪♪♪ ♪♪♪ ♪♪♪ [ Ominous music plays ] ♪♪♪ Even a tiger shark has companions.

♪♪♪ ♪♪♪ Remoras are constant attendants to sharks and manta rays.

But the sharks have other relationships.

A bull shark, a hammerhead, and a nurse shark hang out together in the Bahamas, like three amigos.

♪♪♪ ♪♪♪ The hammerhead is searching beneath the sand.

Her head is a scanner.

[ Whoosh ] [ Crackling ] We may think of sharks as frightening, but the majority of fish near them seem relaxed.

Life here is not simple.

Schools of snapper hang out with the gang, though they keep a respectful distance.

It was thought that remoras rode with sharks to share their food, but this lemon shark has stopped to allow its remoras to clean it.

Lemon sharks cruise around the Caribbean and may meet males from the Gulf of Mexico to keep the gene pool healthy.

They are all international travelers with their own entourage of personal groomers.

♪♪♪ ♪♪♪ Not all arrangements with suckerfish are as comfortable.

♪♪♪ This dugong in the Philippines has two sets of companions -- the streamlined remoras seen on sharks and mantas... and striped golden jacks.

♪♪♪ The placid dugong grazes the seagrass meadows.

♪♪♪ The golden jacks grab small shrimps that the dugong stirs up.

♪♪♪ He seems content to have them around.

The remoras, on the other hand, seem to trouble him.

They don't seem to be useful cleaners.

In fact, they only want to eat what the shrimp goby feeds his shrimp.

Most remoras are poop-eaters, just like the shrimp.

The dugong hates it.

It must be very uncomfortable.

♪♪♪ ♪♪♪ First, he tries to rub them off, but that doesn't work.

Plan B.

He rolls around, creating a cloud of silt and sand.

♪♪♪ He tries to bat them away.

♪♪♪ ♪♪♪ Once he's got a dense cloud cover going, he sneaks off with his golden jacks... and only one remora.

♪♪♪ The wild has often been seen as mindless competition.

Animals were violent and unsophisticated, nature red in tooth and claw.

Survival was for the fittest.

♪♪♪ We felt that the ocean was heartless, friendless.

We fear what we are not part of.

♪♪♪ Cold upwellings on America's West Coast are rich in plankton, and tube anemones catch the current's tiny passengers on stinging tentacles.

♪♪♪ But we certainly never thought of them as part of anything bigger.

♪♪♪ Tube anemones here are taller than most, up to a foot tall, probably because of the rainbow nudibranchs.

Nudibranchs are sea slugs.

This one is Dendronotus, and it eats the tube anemone's stinging tentacles.

♪♪♪ ♪♪♪ The anemone recoils.

Too late.

But look closer.

He only takes a tentacle or two.

♪♪♪ Many nudibranchs do not even digest the stinging cells from anemones, but incorporate them into their skin for their own defense.

He takes as little as he needs to keep the supply alive.

He's more farmer than predator.

It's a partnership that has been finely tuned over millions of years.

♪♪♪ The colder currents take us north along California.

♪♪♪ The upwellings are colder here, and there are beds of giant kelp.

♪♪♪ If the tropical coral reefs are the ocean's cities, then these are the sea's ancient forests.

♪♪♪ It's a nursery for juvenile sardines.

They're individuals, yet they move like a single organism, to the frustration of the cormorants.

♪♪♪ Sea lions, growing up, spend hours just playing together.

♪♪♪ ♪♪♪ Solitary sevengill sharks emerge from the freezing depths like forgotten dinosaurs.

Some may live for centuries and come up to visit sometimes.

♪♪♪ Giant sea bass live long, slow lives here.

♪♪♪ A wolf eel marks the decades.

♪♪♪ Rockfish can live to be 200 years old.

An anemone can live on the same boulder for a century.

Part of a community matured and refined over millennium.

♪♪♪ The rockfish have ritualized a boundary dispute so that neither gets hurt.

Intelligent animals reach out to each other, for reasons we barely understand.

♪♪♪ The instinct to be part of something draws animals together, sometimes in huge numbers.

♪♪♪ A plague of pelagic red crabs, millions of them, arrive from the open ocean.

♪♪♪ The kelp forest is a global hub for many creatures.

♪♪♪ Another tide, and millions of moon jellies arrive.

♪♪♪ ♪♪♪ Following one multitude, another.

Pacific sea nettle jellyfish, 2 and 1/2 feet wide and 15 feet long.

♪♪♪ Jellyfish can't see or hear, yet they travel together.

♪♪♪ ♪♪♪ Many of the jellyfish have passengers.

A juvenile slender crab holds on until he's big enough to survive alone.

♪♪♪ Delicate Medusafish live in a fragile mobile home.

A pod of basking sharks can accompany jellyfish.

Jellyfish are a clue to food along colder currents.

♪♪♪ They're feeding on copepods.

The causes of these planktonic blooms may be thousands of miles away and due to variations in temperature and nutrients that are hard for us to measure.

Yet, sharks and dolphins and whales can follow these global cycles.

They seem to know when and where everything should be.

♪♪♪ [ Birds calling ] Sea otters live in the kelp only a few miles from Los Angeles, one of our own global hubs.

The sea otter mothers wrap themselves in the kelp, so as not to drift away.

They rub air into their fur as insulation.

The babies are rambunctious and demanding, and the mothers put up with a lot.

Eventually they settle down to nurse... ...and the parents to snooze together.

♪♪♪ It's winter, and storms from the Pacific sweep in.

♪♪♪ [ Thunder crashes ] ♪♪♪ The surge tears at the kelp and stirs up nutrients that will feed the kelp forest all summer.

♪♪♪ In the wake of the storm, sometimes whole kelp plants are ripped off the reef.

♪♪♪ As the mothership was torn from its moorings, baby rockfish became passengers.

This whole community may travel hundreds of miles and colonize new shores.

Six-foot Mola molas and other fish appear, and the drifting kelp becomes a mobile cleaning station.

♪♪♪ Schools of open-ocean fish find some sanctuary.

Harbor seals hide here, too, from orcas and great white sharks.

[ Ominous music plays ] ♪♪♪ ♪♪♪ He's not hunting.

Just...swimming by.

The companions of the great white are sardines, who find safety around him.

Sardines look for any security, for any protective relationship.

For sardines in the open ocean, they can only rely on each other, against some very frightening predators.

♪♪♪ The sailfish work together like wolves.

The sardines coordinate their defense.

It's a battle of cooperation.

It requires good communication and trust.

Dark bronze means "I'm attacking."

Silver means waiting in line to feed.

♪♪♪ ♪♪♪ Fish coordinate their movements through electromagnetic and pressure sensors, almost like a single nervous system.

♪♪♪ ♪♪♪ ♪♪♪ The sardines are soon gone.

Only scales remain, filling the water with silver.

♪♪♪ Hunting and being hunted in schools evolved alongside an ancient imperative.

There are coordinated gathering places, where schools like these big-eye jacks arrive when it's time to breed.

♪♪♪ It's the ultimate form of cooperation.

They communicate in subtle postures and colors, in a slow waltz.

♪♪♪ ♪♪♪ Some travel far to a gathering, like these hammerheads at Cocos Island, off Costa Rica.

♪♪♪ We can see that they communicate using posture, but it's probably just a small part of their dance, like any courtship.

♪♪♪ In shallow tropical water, there's courtship, too.

Longer-term relationships are forming or being renewed.

♪♪♪ Animals take time to choose each other.

A slow courtship builds commitment and trust.

♪♪♪ ♪♪♪ ♪♪♪ Off South Australia, a 3-foot-long giant cuttlefish is warning off rival males.

♪♪♪ Courtship is over.

He's guarding a female and a cave hiding her eggs.

Working together is for more than comfort or your own protection... or even mating.

Parents all over are getting ready.

Off the Philippines, anemone fish have their home and their stinging anemone protector, but they still need more space to lay their eggs.

They have a problem and need to figure out how to deal with it.

They could use a coconut husk, if it was with the anemone.

Their solution -- moving what they need for a custom remodel of their home -- is not simply mindless instinct.

There's a whole new science about how animals think and solve problems, and it turns out that fish are pretty remarkable.

It takes good communication for all relationships to work.

♪♪♪ There is coordination somehow across the whole reef, even for the simplest animals.

Barrel sponges organize their spawning, communicating chemically with each other and following tides.

♪♪♪ When the moon is right, blue sea stars stand on tiptoe to spawn... ...and sea cucumbers reach up.

It's as though all the threads linking every animal were being pulled by the moon.

♪♪♪ ♪♪♪ [ Hissing ] Male corals release sperm.

And then females release egg packets.

The magic only happens one night each year.

♪♪♪ Once adrift, the packets break open, and fertilized eggs start their journey.

♪♪♪ Nothing in the ocean can happen in isolation.

The pull of the moon and tides is felt globally, and migrants arrive in perfect time for the feast.

The ocean's largest mouths will come a long way for nights like these.

♪♪♪ ♪♪♪ The mantas eat what they can, but the quantity is overwhelming.

♪♪♪ ♪♪♪ ♪♪♪ From the depths along the colder Pacific Coast, opalescent squid rise toward the full moon.

♪♪♪ A male grabs a female, and his tentacles flush red.

He passes a sperm package to her.

They drift inshore, and by the time they arrive, the females are carrying pods of growing embryos.

They attach them to anything solid, even decorating a decorator crab.

Once their eggs have been laid, all the adults die.

Their purpose in the chain of generations is fulfilled.

Almost everything will eat the dying parents, but not so the eggs.

The egg cases carry toxins, and most animals only try them once.

Inside each carefully protected home, the squid are already growing.

♪♪♪ The squid will all hatch together, and the eruption of life will trigger so much more.

The majority of larvae are swept away and become part of the plankton, the biggest nursery on the planet.

♪♪♪ The ocean itself looks after them, feeds and protects them.

♪♪♪ A tiny seahorse clings to a cotton thread.

♪♪♪ Flounders grow long tendrils to keep them from falling into the depths.

A baby nautilus clings to a fragment of plastic as if it were kelp.

An iridescent ctenophore is vast next to a tiny squid.

♪♪♪ A jellyfish and a crab start their journey together.

Right from the start, animals are drawn to each other.

A Medusafish hides in a tiny jelly.

♪♪♪ A juvenile filefish holds on, as well, not to eat, but so as not to be alone.

♪♪♪ ♪♪♪ Uncomfortable as it is, we can't ignore our part in this story.

[ Birds crying ] ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ Look beyond the desolation... and the mistakes.

It's not too late.

♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ A fire urchin is venomous and untouchable.

Not an ideal friend, but maybe there's not much else.

He's a carrier crab.

The urchin gets a free ride, and nothing will attack the crab now.

They're companions.

It's very equal.

It seems an unlikely relationship -- a plain crab and a venomous beauty -- but partnerships like these are the heart and soul of the ocean.

♪♪♪ The eggs and larvae travel the planet.

They are a microscopic chance of renewal and repair.

♪♪♪ Not all we do turns out bad.

Machines that set out to destroy life now nurture it.

♪♪♪ ♪♪♪ A new home is built.

♪♪♪ ♪♪♪ Between wreck and reef, home improvements are finished for the clownfish.

The coconut husk is now a nursery.

♪♪♪ The most precious relationship in the ocean is between parent and young.

♪♪♪ Look.

Their hearts are beating.

♪♪♪ A home must be protected.

Despite the stinging tentacles, hawksbill turtles eat anemones.

Many of the anemones on the reef protect a nursery, and the parents must defend their anemone at all costs.

They know that the hawksbill's vulnerability is his eyes.

The Clark's anemonefish attack anything threatening their anemone, including us.

They can bite you hard enough to draw blood.

The hawksbill is off to find an easier meal.

♪♪♪ All around us, baby fish are being protected.

Urchins provide a favorite kindergarten.

♪♪♪ ♪♪♪ We are piecing together clues, like a jigsaw puzzle, slowly revealing parts of the picture.

♪♪♪ Our rare help is often accidental.

But the wreckage we have made of our world is most chilling by what's not there.

500 years ago, there was maybe 10 times as many fish.

It's hard to imagine.

It's not just the individuals lost.

It's their delicate partnerships, their families, all the connections between lives, severed.

♪♪♪ ♪♪♪ ♪♪♪ The natural world is built on relationships.

But what we are only beginning to discover is the ancient biochemistry of cooperation.

Single cells united to form animals and plants, and they needed to breed, to create homes and communities, and so ancient neurotransmitters and hormones began rewarding collaboration.

The instincts are strong.

Being together, a part of something, just feels right.

♪♪♪ ♪♪♪ ♪♪♪ [ Whales singing ] Animals are very trusting.

♪♪♪ ♪♪♪ ♪♪♪ It may seem foolish to want to be a part of this.

Some here could easily kill us.

They may be hungry, and we are edible, but you don't need to feel afraid -- just respectful.

Listen.

Listen.

They have something to say.

Here's a thought.

How about a bit of give-and-take?

♪♪♪ We can feel what it is like to be trusted, and we can help protect what we're part of.

♪♪♪ [ Whales singing ] ♪♪♪ Holding your breath long enough is the hardest part.

But it's worth it.

[ Whale sings ] Look.

They are reaching out to us.

[ Whales singing ] ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ ♪♪♪ To learn more about what you've seen on this "Nature" program, visit pbs.org.

♪♪♪