♪♪ -The oceans are full of wonder, an alien world waiting to be explored.
A place of extraordinary life-forms with intriguing social lives and incredible intelligence.
[ Dolphin squeaking ] To reveal their secrets, a hidden team goes undercover.
♪♪ The most innovative undersea robots in the world.
They not only look like the animals they film, they interact with them as no human can.
♪♪ Equipped with hidden cameras... ♪♪ ...they reveal their astonishing lives.
As our spies join their undersea world, they shed light on some of the mysteries of the deep.
♪♪ ♪♪ ♪♪ -On our spies' latest mission, they reveal the extraordinary relationships that exist among the creatures of the ocean.
♪♪ In Australia, an astonishing event is underway.
Cued by the full moon, spider crabs rise up from the abyss deep below.
To reveal what's going on, Spy Crab joins the march.
Eight robotic legs give the traction it needs.
♪♪ Like the real thing, a hard shell protects its innards -- in this case, a camera.
Over the next two weeks, thousands upon thousands of these usually solitary creatures will gather.
Then, a hint at why they're here.
Spy Crab discovers that some are emerging from their shells.
♪♪ Squeezing out can take 15 minutes or more.
♪♪ Enzymes oil the process, helping her slip away.
♪♪ Freed from what's become a prison, she now has space to grow.
♪♪ Her new shell will take weeks to harden.
Until then, she'll hide among the better protected.
For now, she'll make do with our spy.
She has good reason to hide away.
There are plenty out to get her.
A 13-foot stingray can eat 50 crabs a day.
They vacuum up any who've lost their shell.
Our spy becomes the crab's defender.
♪♪ ♪♪ The ray will look for an easier meal.
Those with hard shells aren't worth the trouble.
Males even stand and fight.
Those with soft shells hide among the hordes.
Despite their brave defenders, the ray can hunt them down.
It makes short work of separating meat from shell.
The crab-in-hiding makes her getaway.
She needs to get lost in the crowd.
The ray's victim is just an empty husk.
But the ray is yet to satisfy his 50-a-day appetite.
And the fleeing crab is still in the open.
♪♪ She's made it.
Now, to vanish among the masses.
The greater the numbers, the harder it is for the ray.
♪♪ Those with hard shells form an armored fortress, with the soft-shelled hidden beneath.
♪♪ Left in the open, Spy Crab is now a sitting target.
It gets the full death-ray treatment.
♪♪ A crab's-eye view of an untimely end.
♪♪ But it's still live and kicking.
And it's not over yet.
♪♪ This time, the ray did it a favor!
Back firmly on its own eight feet, our spy heads to the fortress.
It has a tower of crustaceans to climb.
But there's no need.
The crabs come to our spy.
♪♪ They create a shield of legs and armor -- a living citadel built on sand and a brief monument to the strength of teamwork.
Many sea creatures have found value in being together.
Sharks may have a reputation as solitary killers, but many are surprisingly social.
Scalloped hammerheads are among the most sociable of all.
They travel in their hundreds as they head to a remote island 300 miles off the coast of Colombia.
Today, they have a spy in their midst.
A mechanical marvel, propelled by its sharklike tail.
It hardly makes a sound, vital when filming these surprisingly shy creatures.
♪♪ As well as a camera in each eye... it has another in its fin, one with 360 vision.
♪♪ It can even film through its jaws.
♪♪ Our spy has much to reveal.
Most of these hammerheads are female, with the largest in the middle and the smallest outside.
Some even choose a travel companion for their journey.
♪♪ They're all swimming towards a special destination.
Malpelo is a magnetic anomaly.
A place where the earth's magnetic field is distorted by the rocks below.
Hammerheads use the magnetic field as a compass, so this place has unseen significance.
They gather here, having returned from their feeding grounds.
They are met by a surprising welcoming party -- king angelfish that provide a personal grooming service to these would-be killers.
♪♪ Wounds are attended to and parasites removed.
♪♪ Hammerheads feed in the deep ocean, so the angelfish here are safe.
While they get a meal, the sharks enjoy a makeover.
♪♪ In this topsy-turvy world, fish seem to like sharks so much even our spy gains a following.
♪♪ Galapagos sharks also visit this undersea spa and receive the same warm welcome.
♪♪ Pilot fish cluster around the shark's jaws but are never taken.
Instead, they benefit from the shark's protection.
In return, they clean its teeth and gain a meal in the bargain.
Rainbow chub are also shark lovers They rub themselves on the shark's serrated scales... ...a trick thought to scrape off parasites.
In this place of apparent harmony, other intriguing relationships can be found.
Spy Moray Eel joins the team.
Like the real thing, it moves silently.
Its mechanical spine creates the waves that propel its body.
This is what it came to see.
A community of moray eels.
Despite their ghoulish looks and razor-sharp teeth, they live in relative harmony.
♪♪ Spy Moray is here to study the partnership they share.
Their unlikely partners are leather bass groupers.
Our robotic moray soon attracts their attention.
For the fish are here to wake up the eels.
Their snooze alarm could hardly be gentler.
But, one by one, they stir.
The groupers signal it's time to follow.
♪♪ With some gentle encouragement, the eels oblige.
♪♪ To discover the reason, Spy Moray follows behind.
♪♪ ♪♪ They're heading to a spot the fish have checked out before.
♪♪ ♪♪ A place where smaller fish are hiding.
A headstand marks the spot.
A signal to the eels.
And they slink in where groupers can't and flush out the fish.
Most are too quick to catch.
♪♪ But in the scrum, there's enough for both groupers and eels, despite the ones that get away.
It's a perfect relationship where both gain.
But Spy Moray is experiencing a technical malfunction... [ Mechanical whirring ] ...a loss of transmission.
But still keeps filming.
The groupers act as if our spy is part of the hunt and has found something.
Soon our spy is completely smothered.
But help has arrived.
A spy to shepherd them away.
The signal finally gets through.
Like others in this undersea community, our spies can use teamwork too.
In the oceans, working in partnership is surprisingly common.
For bottlenose dolphins, it's a way of life.
To strengthen the bonds between them, they spend a lot of time at play.
To find out who else might join their games, Spy Pelican follows from above, while Spy Dolphin films from below.
Together, our roving spy creatures find a possible playmate.
A southern right whale.
A species not known for its fun-loving lifestyle.
It will need some coaxing.
Something to get it in the mood.
Already, it seems to be working.
♪♪ Some dolphins show their bellies -- a sign they want to play.
♪♪ The whale even attempts a leap.
The dolphins have the playmate they're after.
♪♪ But who can compete with a dolphin?
♪♪ The whale does his best.
♪♪ ♪♪ ♪♪ Another whale joins.
It's now double the fun.
[ Dolphin squeaking ] ♪♪ ♪♪ Still more arrive.
♪♪ ♪♪ But you can have too much of a good thing.
The dolphins decide it's time to leave.
To discover that whales and dolphins play together is a revelation.
For our spies, there are always new surprises to uncover.
[ Whale singing ] Even sociable creatures like manatees can't always choose who they mix with.
Spy Manatee is now fully accepted into the group.
[ Manatee chirps ] It's discovering that even here they have friends they like, and then there are the hangers-on.
Latched onto her body are remora fish.
Totally harmless, their relationship is extraordinary.
They feed on skin flakes and parasites and whatever the manatee poos.
What was once a fin has evolved into a suction pad on their heads.
As well as food, the manatees provide an energy-saving way to get around, while keeping water flowing through the remoras' gills.
♪♪ ♪♪ Those on top travel upside down.
If they move to the belly, they're more easily shooed away.
Even so, there's always another free ride.
While remora can be a nuisance, sergeant major fish are welcomed.
Our spy investigates why they're accepted so readily.
The fish provide a cleaning service.
They graze on the algae that grows on the manatee's skin.
♪♪ ♪♪ For a full-body treatment, manatees strike a pose, letting the fish tackle those hard-to-reach places.
It sends them into a state of bliss... ...until they nod off.
♪♪ The spa is popular.
Everyone wants a makeover.
♪♪ But not all the fish here are friendly.
Nurse sharks patrol the coral heads, while stingrays search the sandy seabed.
These predators could be the ultimate test for our spy.
♪♪ ♪♪ Rays and sharks can detect electromagnetic signals.
Spy Manatee has plenty of those.
♪♪ An exploratory nibble.
But there's nothing here to be found.
Like most of our spies, Spy Manatee attracts the curious rather than the aggressive.
In Indonesia, Spy Hammerhead continues its own journey of discovery.
It soon finds that across the ocean similar partnerships have evolved.
Here it's cleaner wrasse that take on cleaning duties.
They even act as dental hygienists, with trapped food the reward.
But these pearly whites have nothing to offer.
An olive sea snake shows his inquisitive side.
He's one of the most venomous snakes in the world.
Today, he's on the hunt.
He can hold his breath for up to two hours -- useful when searching for a meal.
He's after the fish that hide in the coral.
To catch them, he needs help.
And on the reef, support is rarely far away.
A female who's also hunting.
♪♪ Like moray eels, the snakes have formed a partnership with a fish.
But here it's trevally who know where food can be found.
♪♪ When they arrive, the trevally show them where to look.
Like moray eels, snakes can go where others can't.
But these snakes have a problem.
They aren't the only ones hunting.
Soon there are too many after the same meal.
The snakes and trevally grab what they can.
But there's a limited supply.
This partnership works best with fewer numbers.
Today, there's not enough fish to go around.
But the snake couple won't go unrewarded, it's now a relationship of a more amorous kind.
They head to the surface... ...joining together in a serpentine embrace.
One that briefly forms a fitting symbol.
♪♪ ♪♪ ♪♪ ♪♪ They'll stay entwined for up to an hour before going their separate ways.
Of all the relationships found in the ocean, few can beat the spinner dolphins.
As well as gathering in huge numbers, they are the acrobats of the dolphin world.
They can leap over 10 feet high and spin seven times in a jump.
Today they're on a hunting expedition.
Spy Dolphin is here to find out how they work as a team.
Their bubbles provide a clue.
On closer inspection, they plainly come from the dolphin's blowholes.
A sign they are whistling to each other.
[ Dolphins whistling ] They use these calls to bring the pod together.
They also have a unique whistle to announce who they are -- the dolphin equivalent of a name.
[ Dolphins whistling ] ♪♪ As well as whistles, they use clicks to communicate too.
Some clicks are ultrasonic, far above our hearing range.
All this works at close range, but to contact dolphins far away they use their corkscrew leaping.
For an aerial view of what's going on, Spy Frigate films from above.
The leaps can be seen by distant dolphins... ...while the splashing can be heard from far and wide.
[ Dolphins whistling and clicking ] United, they can hunt as a super team.
Our spy is in the midst of an extraordinary gathering... ...one of the greatest mega pods ever filmed.
♪♪ ♪♪ Spy dolphin is here to witness this astonishing moment.
And there's yet more to discover.
Yellowfin tuna also heard the splashing and join the dolphins' quest for a meal.
♪♪ As the dolphins and tuna travel together, the ocean becomes a superhighway.
♪♪ Above, frigate birds join the travelers, including our spy version.
As they near their goal, the dolphins leap into action.
♪♪ A synchronized wave, thousands strong.
♪♪ ♪♪ Spy Frigate records the moment they close in on their target.
A squadron of flying fish chased into the air by the hunting dolphins.
The tuna even try to grab them as they fly.
♪♪ With dolphins and tuna working together, few escape.
♪♪ ♪♪ ♪♪ The frigates too take what they can.
♪♪ ♪♪ It's a feast made possible by extraordinary teamwork.
♪♪ As the day ends, they have reason to celebrate, and they do it in true dolphin style.
♪♪ ♪♪ Off Mexico, shoals of mackerel are gathering too.
Upwellings of nutrients have caused plankton to bloom.
It's not only mackerel that relish the feast.
♪♪ A tuna crab, a type of squat lobster.
It won't be alone for long.
More are rising from the depths.
♪♪ ♪♪ As always, there's a spy for every occasion... ♪♪ ...with a subject worthy of special attention.
Tuna crabs only come together when conditions are perfect.
♪♪ ♪♪ They may all look the same, but they are not short on character.
A blade of sea grass covered in plankton becomes something to fight over.
♪♪ ♪♪ It's now a tug of war... ♪♪ ...with both a winner and a loser.
Spy Tuna Crab arrived at a special moment, an event that has rarely been filmed.
♪♪ Hundreds soon become thousands.
Then thousands become millions.
♪♪ ♪♪ They devour all the plankton they can.
When they've had their fill, they descend to the deep once more.
Those that leave are soon replaced, and so the cycle goes on.
♪♪ ♪♪ Such numbers have seldom been seen.
A magical moment before they vanish into the depths once more.
♪♪ When autumn brings storms to the Caribbean, another gathering begins.
Spiny lobsters leave their hideaways and start to assemble.
They're preparing to migrate to calmer and warmer waters.
One has yet to join them.
As the storm builds, conditions worsen.
♪♪ ♪♪ Alone, they're vulnerable -- not just to currents, but predators too.
So they'll make their journey together.
Already Spy Lobster has company.
♪♪ Others also couple up.
♪♪ Everyone joins the great migration... ...including our spy and its newfound buddy.
As the lobsters come together, it becomes a game of follow the leader.
♪♪ Latecomers race to join up.
Including our spy.
A chain soon starts to form.
♪♪ ♪♪ It becomes a lobster conga line, their antennae keeping each in line.
♪♪ The members can number 50 or more.
No one wants to be left behind.
♪♪ As they head for deeper water, walking in line reduces drag and keeps them on course.
Guided by the Earth's magnetic field, they can march like this for days.
♪♪ Already they are vanishing into the deep, leaving Spy Lobster far behind.
Shipwrecks are testament to the power of the storms.
They are now a refuge for those sheltering from the turmoil above.
♪♪ Another place, another spy.
This time -- Spy Nautilus.
♪♪ It finds that every nook and cranny is occupied.
With little shelter elsewhere, the wreck is a magnet for the vulnerable.
♪♪ ♪♪ Spy Lobster joins the search.
Then, a promising sign.
Two lobsters hiding beneath the broken bow.
They're not the only ones.
In every crevice, more can be found.
With no claws to protect them, wrecks like this keep them safe.
For them, the journey has been worth it.
Here they'll spend the winter until the shallows warm once more.
♪♪ There is one place our spies have yet to visit.
The islands of the Galapagos are home to a rich community of sea creatures.
On the volcanic rocks that hug the coastline, marine iguanas bask in the morning sun.
It's a time to socialize as they warm up for the day ahead.
Among the masses is a visitor from outside -- A spy adapted to both land and sea.
It needs both talents, for iguanas feed on vegetation, and the land has little to offer.
Once they're up to temperature, they take the plunge.
Where they go, our spy must follow.
Iguanas are coldblooded, so their time in the cold sea is limited to just half an hour.
That includes battling the surf.
Spy Iguana swims just like the real thing, propelled by its articulated tail.
When an iguana dives, our spy dives too.
The best feeding grounds lie deep beneath the waves.
Our spy will join them there.
♪♪ ♪♪ Unlike the barren land, the sea is rich in nutrients.
It nourishes the algae the iguanas depend on.
♪♪ They eat almost nothing else.
♪♪ ♪♪ Each has a chosen spot to graze.
Spy Iguana hardly causes a stir.
There's no rivalry here.
But the real iguanas are on borrowed time.
He must eat what he can while he can.
♪♪ ♪♪ Leave too late, and he'll be too cold to make it back.
♪♪ But he knows when his time is up.
♪♪ ♪♪ He heads to the surface and returns to land.
♪♪ Our spy has many other inhabitants to meet.
The most playful of all are Galapagos sea lions.
And who better to play with than our spy creature?
But playing games is not in our spy's repertoire... ...no matter the encouragement it receives.
The sea lion seeks a more playful partner.
But he leaves Spy Iguana in the best possible spot, just in time to meet a true wonder of the deep -- Mola mola, a type of sunfish.
Its only means of propulsion are its elongated fins.
One of the largest bony fish in the ocean, it reaches 10 feet in length.
They visit for one reason only -- to be cleaned by angelfish and hogfish.
As our spies have found, almost all undersea communities have their own grooming specialists.
Job done, they return to the deep blue yonder.
♪♪ Our spy has one last inhabitant to find.
The shallows are home to a colony of damselfish.
♪♪ ♪♪ They are suspicious of outsiders.
♪♪ They're avid gardeners, so trespassers aren't welcome here.
♪♪ They spend their time tending their lawns of algae.
Like an allotment, it's divided into plots.
To attract a mate, each male has his own patch to care for.
They must beware of intruders.
A sea urchin, looking uncannily like a naval mine.
It creates its own kind of devastation.
It will graze their precious algae down to the rock.
To remove it they must work together... ♪♪ ...and use a bit of extra oomph.
♪♪ ♪♪ It's now out of his patch and onto his neighbor's.
Each damselfish passes it along to the next fish.
♪♪ ♪♪ They'll persevere until it's finally gone.
♪♪ Nearly there.
♪♪ But our spies' adventures aren't over.
Spy Hammerhead has arrived in the Galapagos, along with the hammerheads last seen off Colombia.
The sharks are completing a round trip that began in the seas around these islands.
Hammerheads, like other long-distance travelers, connect distant communities in a network of partnerships that reach across the globe.
As our spies have found, ocean life is interconnected in ways we could hardly imagine.
♪♪ It's an undersea world built on extraordinary relationships.
Next time, we discover some of the trouble sea creatures face and what happens to spies when things go horribly wrong.
♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ To learn more about what you've seen on this "Nature" program, visit pbs.org.