Original subtitles

In the far north, after three dark months of winter,

a world is waiting

for a trigger. The sunshine of spring.

Starfish are the first to respond.

They race for the highest point

and sensing changes in the water with the tips of their tube feet.

They spawn.

Sea cucumbers, with only their mouths exposed, now emerge.

They collect as many starfish eggs as they can,

which is quite a lot when you've got ten arms.

Now sea pens rise up to claim a share.

The creatures here must grab what they can of this annual banquet.

For the light has also set in motion the greatest transformation of all.

Fronds of kelp, a marine alga, rise towards the

surface, lifted by their gas-filled bladders.

Soon, a marine forest has materialised,

teeming with life of all kinds.

These green seas are some of the most productive,

but fiercely competitive waters in all the oceans.

The southern tip of Africa.

Here, two great oceans collide.

In the shallows, fed by rich currents, are bountiful forests of kelp.

Barely visible, except for the pulsating siphon through

which it breathes, a common octopus waiting for prey to pass

by.

A crab will do.

The octopus sets off in pursuit.

And then lurks with the patience of an ambush hunter.

But the octopus shares the cape waters with a great concentration of other predators.

Fur seals and sharks.

They all eat octopus if they can find one.

And pyjama sharks are experts at hunting in the undergrowth.

Time to disappear.

But these tough-skinned little sharks are small enough to reach deep into crevices.

But the octopus is far from finished.

She slips her tentacles into the shark's

gills. That prevents the shark from breathing.

So the shark has to let go.

When caught out in the open and vulnerable, this octopus

does something truly extraordinary. And never recorded

before.

She disguises herself with a protective armor of shells.

She's hiding in plain sight.

The shark can sense its prey.

But the shells confuse it.

In a forest full of hungry mouths, superior winds allow this octopus to stay alive.

Forests of kelp flourish in seasonal waters around the globe.

Particularly along the Pacific coast of North America.

Here, the biggest kelps of all grow in vast forests, stretching for hundreds of miles.

In some places, the giant fronds rise up to 60 meters tall.

The thickets they create are crowded with life.

Competition here for space and food is intense.

A challenging problem for the Garibaldi fish.

He tends to his patch of seaweed filled with tiny creatures that he eats.

As with most farmers, his work never ends.

He removes snails and any other grazers that come to eat his algae.

No matter how big they are.

He has to deal with pests of all kinds.

This can be the worst of them. Sea urchins that can scrape

off every vestige of algae from a rock. Its spines are

needle sharp.

Somehow, the Garibaldi must remove it.

But the problem with sea urchins...

is that they just keep coming.

When evening arrives and the light fades, he has to

stop. He not only needs a rest, he needs to hide.

Because at night, he has to go to sleep. Predators prowl through these forests.

A torpedo ray capable of stunning its victim with 45 volts of electricity.

While the Garibaldi hides, the urchins can feed without interruption.

The light returns...

and he finds his farm is once again under attack.

Urchins, like locusts, have the ability to swarm.

And this can be disastrous, not just for the Garibaldi,

but for the kelp forest itself. The sea urchins can be

dangerous.

All the vegetation is now under attack.

The urchins move through the forest, cutting through

the kelp fronds and leaving behind vast barrens.

These urchin armies have felled many kelp forests along

the coast, along the Pacific coast of North America.

But help is at hand.

Sea otters.

All other kinds of otters spend much of their lives

on land, but sea otters rarely leave the water.

At first, a newly born pup is not a very good swimmer, so

its mother spends hours grooming its fur to make it buoyant.

But to provide her youngster with milk and keep herself

warm, she must eat up to 30% of her body weight every day.

She does that by eating shellfish.

And urchins are among a sea otter's favorite delicacies.

In the past, sea otters were hunted so intensively

for their fur that they came close to extinction.

With them gone, many kelp forests were replaced with urchin barrens.

Today, sea otters are protected.

And as their numbers slowly return, many of the kelp forests are recovering too.

Now, in some remote places, sea otters are so numerous, they assemble in huge rafts.

Something that hasn't been seen for over a century.

This is one of the largest shallows of Australia. Kelp is

replaced by the sea's only flowering plants. Sea grass.

The most extensive of these marine grasslands

can stretch for over 3,000 square miles.

All across the tropics, they're patrolled by tiger sharks.

They can grow up to 5 meters in length.

And have powerful crushing jaws.

Green turtles are their prey.

The turtles feed almost entirely on sea grass. A

single one can consume up to 2 kilos of it in a day.

But they can never rest easy.

Healthy turtles are their prey. The turtles

will keep well away from an approaching shark.

And just by keeping the turtles on the move, the sharks

prevent any one patch of sea grass from being overgrazed.

And that has benefits for us all.

A patch of sea grass can absorb and store 35 times as

much carbon dioxide as the same area of a rainforest.

Though the prairies and their sharks are surprising

allies in the fight against a warming climate.

The struggle to survive in our green seas can have far

-reaching consequences. Once a year, one particular meadow

in Australia is transformed.

Around the first full moon of winter, an army materializes.

Spider crabs.

For the past year, they've been feeding in deeper waters.

Now they march across the sea grass plains.

Hundreds of thousands of them.

They clamber over one another.

Creating great mounds.

Nearly a hundred meters long.

They're not seeking mates, neither are they

laying eggs. They have come here in order to grow.

Like all crabs, their bodies are enclosed in a hard,

unexpandable shell. So to grow, they have to break out of

it.

And that allows a soft one that has developed belief to expand.

It will take days for the new shell to harden.

Its legs are so limp that they won't work properly.

The crab is unprotected and in great danger.

A smooth stingray.

It's huge, about four meters long. It wants a soft,

freshly -melted crab that will be easier to eat.

The crabs try to stick together.

But now, disturbed by the ray, they're scattering.

A newly-melted crab is too weak to keep up with the crowd.

The safest place is right in the middle of the

pile. That is why they have all assembled here.

There is safety in numbers.

But the vast majority of the crabs escape. And within the

next few days, they will be ready to return to the depths

and resume their lonely wanderings in search of food.

This is no graveyard.

But the triumph of 100,000 crabs, successfully molted.

The green seas of southern Australia are

particularly rich in such spectacular assemblies.

But most of the creatures come together for a very different reason. To breed.

The giant cuttlefish. The largest of all cuttlefish.

They live for just one or two years.

Now, as the Australian summer draws to an end, they have one last act to complete.

To find a mate.

But there are over 100,000 males competing for the arriving females in this one bay.

Among them, a giant, a true Goliath. He probably weighs about 10 kilos.

Bands of color sweep across his skin. That's how cuttlefish communicate.

This smaller male couldn't possibly take him on.

Beside Goliath and under his protection, a female who

has just mated with a giant, is trying to mate with him.

But other rivals are still interested.

It seems a small male wouldn't stand a chance. The female

is now displaying a white stripe along her side nearest

Goliath.

It's a clear signal that she no longer wants to mate with him.

It's all the encouragement that the little male needs.

He's going to have to use trickery.

He tones down his colors and tucks in the white

stripe. It's just the right size to mimic a female.

Goliath is deceived.

The small male now displays a white stripe, just

like the real female, to deter his advances.

He slips beside her. And they mate.

By mating with multiple partners, the female ensures the

greatest distance and genetic diversity for her young.

The sneaky male leaves, his final act complete.

So even among giant cuttlefish, it seems,

it's not all about size.

Other males in these Australian green pastures

take greater responsibility for their young.

A weedy sea dragon.

This is a male, and he's carrying a precious cargo. While

mating with the female, he collected the eggs and attached

them to his underside.

Now he's leaving the seaweed thickets. And traveling

into more open waters, where elaborate camouflage is less

effective.

And there are many predators out here.

And this is what the fathers risk their lives for.

Dense clouds of minute shrimp.

And the sea dragon. Mices.

One of a sea dragon's favorite foods.

They're drawing other sea dragons out here, too.

Finally, it's time for the young to break free. But

algae has grown over these developing eggs, and it risks

smothering them.

And now, the young. Nonetheless, the babies are emerging.

They've hatched successfully.

The father's return to the Tangle of Kelp, where they're virtually invisible.

While the young remain out here.

But they will grow bigger and bigger, grow quickly,

surrounded as they are by their ideal food.

Vast numbers of the ocean's young fish start their lives in the green seas.

One of the richest nurseries of all are the mangrove forests.

Fringing the coastline of the tropics, they form a natural

protective barrier between land and sea. And are some of the

world's most productive forests.

Below the water, their arching aerial roots give them a firm footing.

Here, the land is full of fresh water, and there's abundant food for baby fish.

While the Tangle roots protect them from bigger

fish and other predators that haunt the channels.

But in northern Australia, with the receding tide,

the little fish are forced to leave their shelter.

And the small fish are forced to go back to their homes. And now, they're vulnerable.

It's the most deadly assassin in the green seas.

The zebra mantis shrimp, a male almost 40 centimetres long.

But he's not hunting just for himself.

He's collecting food for his mate. She may have been his partner for 20 years.

She relies on him to bring her food. And puts her energy into her eggs instead.

In a world so full of food, this would seem a sensible strategy.

But it's also a risky one.

And now, it's time.

Were her male to disappear, she could starve.

Something has caught this male's attention.

Perhaps an irresistible odour, or a distant call.

Whatever the reason, a male will leave his burrow and his lifelong mate.

An even larger hole.

Females who have lost their mates appear to

send out distress signals to call in a new male.

A larger female will produce more eggs, so by

mating with her, he will father more offspring.

But infidelity comes at a price.

A larger partner demands more food.

It's time.

The richer a sea, the greater the competition. And there

is one green sea that supports more life than all the rest

combined.

Unlike the mangrove forests and the seagrass prairies,

its location is in the open seas and only temporary and

unpredictable.

This greenness comes not from rooted plants, but from clouds of floating ones.

Billions of microscopic phytoplankton are proliferating.

And in such numbers that they fuel one of the greatest feasts of all.

Off America's Pacific coast, hundreds of common dolphins are rushing to a banquet.

They're not the only ones homing in. They're

not the only ones homing in. So are sea lions.

They're heading for Monterey Bay, California, where algal

blooms have caused an explosion in plankton feeders.

Anchovies, millions of them.

The dolphins herd the anchovies towards the surface.

Sea birds and sea lions take advantage of the show's appearance.

It's a race to grab a share before others arrive.

Humpback whales.

Hundreds of them.

With every upward lunge, they sieve out upward waves. Up to 100 kilos of fish.

They're claiming the biggest share of one of the biggest feasts on Earth.

So crucial are these tiny plankton that almost all

marine life ultimately depends on them. It's the

green seas, not the blue, that are the basis

of almost all life in the world's oceans.

It's the green seas,

that are the basis of almost all life To capture the

magnificence of the undersea forests and the surprising

creatures living here, the Blue Planet 2 team

have developed a series of specialist camera rigs.

Another dome, recording half-in, half-out shots at the top of the towering canopy.

Two state-of-the-art time-lapse equipment that speeds

up time to reveal the secret life of the forest floor.

But of all the creatures living in these forests, filming

one in the waters off the Cape of South Africa was to prove

the greatest challenge of all.

Naturalist Craig Foster has developed a fascination

for its most secretive resident, a common octopus.

There are also many other species There are almost 100

species of shark in these waters, but that doesn't deter

Craig, who's swum here every morning for the past six years.

When you find that really small, tiny little oval hole, then

you know it's been killed by an octopus. And then if you

look very, very carefully, they're often in the vicinity of that.

Craig has witnessed the antics of these octopuses and

wants to share his remarkable discoveries with Blue Planet

cameraman Roger Horrocks.

Roger is immediately charmed by the strength of their personalities.

It's really been astounding to see how individual these

characters are. The common octopus all display different

behaviours.

Some were extremely timid, some were very, very bold.

They have variety. And it's really endeared me today.

After weeks of filming different individuals, they finally

meet one octopus that's not only seemingly unafraid of the

camera, but willing to perform for it.

She just came right out, whoop! And then came right through

underneath the tripod in between my legs. Yeah, that's cool,

amazing. She very quickly just completely accepted both of

us. So we've actually been getting these really intimate

behaviours, it's amazing.

I've watched this octopus for many months. It's just

trusting us in the water, carrying on with normal

activities, which is just so fantastic.

Months later, the team finally film their star octopus on the hunt.

But then discover the grave consequences of sharing the

forest with so many other predators. Pajama sharks. Pound

-for-pound, these sharks are far more brazen and aggressive

than a great white. They're like guided missiles. The

slightest smell that octopus makes just gives off, that shark will find it.

The pajama shark actually got hold of the

octopus, and I mean, I just assumed that was it.

After spending so much time with this animal, it

was just so difficult watching her get attacked.

Then, to their amazement, she fights back.

She put her tentacles down, you could see them coming

through the gill, basically closed the mouth. The shark

couldn't breathe, and that's what enabled her to escape. And

just witnessing that whole thing was, you know, it was an

incredibly intense experience. The team are relieved by her escape.

But when caught out in the open, her next trick astonishes them even more.

It lifts its arms and legs over its head, and at the

same time, pulled shell material with it and created this

extraordinary arm ring. Octopus had armored up, and then

that guy came through from the back. He could kind of smell

something. He's not seeing an octopus shape, he's seeing

that strange arm ring. And then he was bumping the octopus,

and it was just incredible to see how that octopus outwitted

that shark, using the arm, using all his knowledge. It's

just absolutely phenomenal.

She's a rock star, man, a proper little rock star. Thanks

to Craig's and Roger's dedication, the octopus's astonishing

behaviors are now known to science. What else might we

find as we continue to explore these fascinating undersea

forests?

Next time on Blue Planet 2, we meet the

creatures that live where two worlds collide

and discover how they cope with the demands of the ever -changing coasts.

Thanks for watching. you