Original subtitles

SIAN PHILLIPS (VO): It's spring tide.

The Atlantic Ocean is being squeezed between Ramsey Island

and the Pembrokeshire mainland.

Known as the Bitches

these are some of the fastest ocean rapids on Earth.

Here, the water races over the shallow reef below.

Dangerous whirlpools and eddies become a white-water playground...

for thrill-seekers.

The shallow seas below them...

as exciting and dramatic as anything that rides above.

MAN SHOUTS

With rich habitats as varied as anything on land.

Populated with creatures straight from Welsh myth.

Transforming shape...

colour...

and even sex.

All bursting into life...

for a few short months.

Thanks to the magical powers of the sun's caress.

This is an adventure...

into the kingdom of myths.

Woo!

SIAN (VO): Wales is a coastal nation.

The sea is in our soul.

Full of hidden treasures...

wonders...

and giants.

A sea of mythical coasts...

with extraordinary creatures...

secretive shallows...

and hidden depths.

These are the Wonders of the Celtic Deep.

BIRDS CAW

The Llyn Peninsula in North Wales.

This narrow finger of land, some 45 kilometres long

is surrounded by shallow seas.

They make up just seven percent of the ocean

but are home to nearly a third of all marine animals.

By May, these shallows are bursting with life.

Human visitors are also arriving.

Out enjoying the calm, crystal-clear water.

Just beneath them lies an extraordinary marine world.

One of the most productive eco-systems on Earth.

A mysterious underwater forest.

This is the kingdom...

of the giant kelp.

Each plant here is home to some 8,000 microscopic creatures

bringing in a vast array of larger animals.

Hiding in the canopy...

a ballan wrasse patrols its territory...

using oar-like fins to row through the water...

on the lookout for its next meal.

Its bee-stung lips hide a set of teeth

which can crush through crab shells with ease.

But not every animal is looking for a meal just yet.

Also weaving through the forest is a female catshark.

At a metre long, she's looking out for a safe place to lay a precious cargo.

But this kelp is too exposed.

She heads onto the forest floor...

and finds the ideal spot.

Tucked into the undergrowth is an egg case known as a mermaid's purse.

Inside...

is a tiny embryo.

In a few months' time, if the kelp holds firm...

it will hatch into a perfectly-formed catshark.

Across the seafloor is a tangled thicket of smaller seaweeds

which need less light to grow.

Home to a group of otherworldly-looking creatures...

including the sea hare.

These strict vegetarians have a voracious appetite.

Both for food...

and for love.

Round here, it's not just the water temperature that's rising.

This individual is looking for a mate.

And here he comes.

Or is it a she?

It's of no importance.

For sea hares are hermaphrodites.

They are both male...

and female.

Once our pair have decided they want to hook up...

they release invisible pheromones which waft out across the forest floor.

This magical love potion

soon attracts another sea hare...

and another...

and another!

Over the next three days, many more sea hares join in this love—athon.

Each sea hare being male at the front end of their body...

and female at the rear.

Soon, a string of eggs lace around a feathery boudoir.

Several million in a single chain.

But all good swinging parties must come to an end.

Exhausted...

the lascivious libertines retreat into their leafy hideaways.

SEABIRDS CRY

Ceibwr Bay, Pembrokeshire.

WOMAN: Woo!

SIAN (VO): Above the water, it's clear summer hasn't quite arrived.

But a group of daring souls have come in search of adventure.

The only burst of colour in this seemingly bare coastline.

MAN: Woah!

SIAN (VO): But as in Welsh folklore

nothing is quite what it seems.

Rocks shaped by wind and waves over the millennia.

But it's the cliffs beneath the waves...

SEABIRDS CRY

...where those legends become a reality.

This is where the magic happens.

Heading down the cliffs and into the shallow sea...

here, a mountainous landscape is revealed...

cloaked with exotic gardens of sponges and soft corals.

The Great Barrier Reef of Wales.

Thanks to the sunlight that breaches this shallow mountain world

there's a dazzling display of shapes and colours.

The rare scarlet and gold star coral.

Anemones, strange soft-bodied creatures...

that look like flowers.

They feed on a rich soup of plankton...

that drift in on the tidal currents that buffet the cliffs.

But this land has larger predators.

An ancient, armoured hunter rules over this realm.

A rare, spiny lobster nearly half a metre long.

He's ready for a feast...

and mussels are on the menu.

He uses delicate but dexterous claws

like a knife and fork

to prise open the mollusc.

Systematically tearing the life out of his prey.

Feeding it into his waiting mandibles.

The mussel is devoured.

Feast over, he's returned to his cave.

Heading into deeper water, there's a mountain plateau.

This is the domain of an alien-like predator...

which evolved in the shallow seas some 450 million years ago.

The spiny starfish.

Beneath each of its five arms are hundreds of feet, tipped with suckers

that detect chemical traces in the water...

used in the search for prey.

Navigating using tiny pink eye spots at the tip of each arm

it's locked on to its next victim.

A king scallop.

The starfish must approach very carefully...

for the scallop has amazing underwater vision.

Peering out from the fringe of tentacles lining its shell

are 200 tiny, metallic blue eyes.

But the scallop doesn't have eyes in the back of his shell.

And this is a stealth attack from the rear.

The scallop has also evolved hundreds of millions of years ago

and has a trick of its own.

It has lightening reflexes to deal with its old enemy.

Transforming into a pair of flying castanets.

It can only swim a few metres at one time.

But it's enough to escape.

The starfish won't be eating king scallop tonight.

It's early summer...

and the shallow waters are being warmed by the sun.

Beneath the mountain, a stranger struts in from the deep.

A young spider crab is travelling north

on an epic pilgrimage.

He's heading for an annual gathering with other crabs...

congregating to shed their shells at the end of the summer.

This should be his final moult.

As he makes the step into adulthood...

he's on a 160-kilometre journey...

that's full of dangers.

BIRDS TWITTER

PEOPLE SHOUT AND LAUGH

As summer progresses

holidaymakers flock to the coast.

By June...

the beaches of Abersoch are completely packed.

Here, the sandy shore gently slopes out to sea

forming a vast submarine desert.

It may look devoid ot life...

but there's plenty here, if you Know where to look.

The desert plains are a favourite hunting ground for catsharks.

Right now, she's just surveying the seabed.

Catsharks normally hunt at night.

But the local sand-loving inhabitants...

aren't taking any chances.

With nowhere to hide...

everyone has to find their own camouflage solution.

The sandy-coloured brill hides in plain sight...

while this hermit crab has a completely different strategy.

It's decorated its shell with seaweed

topped off with a tiny hitchhiker...

a translucent fan worm to provide extra cover.

Other animals seem to know they're safe from the catshark...

and are making an exhibition of themselves.

From across the seabed comes the sound of distant drums.

LOW RAPID DRUMMING SOUND

Astonishingly...

DRUMMING SOUND CONTINUES

...it's a vocalisation from a tiny fish

only six centimetres long.

The painted goby.

He's trying to attract a mate.

But he's not alone.

There's a whole gang competing for female attention.

The males able to drum the longest and with the most consistency...

DRUMMING SOUND

...are most likely to get the girls.

A female comes in.

She doesn't Know which way to turn.

So the stakes are raised.

Behind her, a male drums

showing off his brightly-coloured dorsal fin.

So much choice!

This male may hold the trump card

showing off his ready-made shell home.

Perfect for her eggs.

She comes in for an inspection.

If she agrees to mate...

he'll be the one looking after the babies.

But the fickle female heads off.

He won't see her for dust.

The young spider crab is halfway through his journey north.

Spider crabs all moult in one place, at one time

to protect themselves from predators.

So, he's on a date with destiny

and mustn't be late.

He can move quickly through this flat expanse

and has come close to the beach.

He may not be fully mature...

but this young knight already has an impressive suit of armour.

And his exoskeleton is about to be put to the test.

This older male has claimed this desert land as his own...

and stands defiantly between the young crab

and his destination.

Up to 20 centimetres wide...

spider crabs are the largest crabs in the Celtic Sea

and notoriously combative.

As they square up for battle, the older crab takes the first swipe.

And with his mace-like claw...

he pins the young crab to the seafloor.

Using some nimble footwork, he escapes.

But his adversary is a veteran fighter.

Rearing up on his hind legs, he has the advantage...

and takes another swipe.

He misses.

But the young pretender knows he's been defeated.

There's nothing left to do, but stage a dignified retreat.

He'll have to find a long way round.

He still has many kilometres to go.

Some animals drawn in by the sun's rays come from much further afield.

It's the summer solstice.

The sun is rising on the longest day of the year.

BIRDS CAW

Revered by druids

the Island of Anglesey has an influx of noisy sunseekers.

BIRDS CAW

Arctic terns make the longest migrations of any bird on Earth.

They constantly follow the sun to stay in perpetual summer.

They've come from Antarctica to Cemlyn Bay, a sanctuary for tern colonies.

Effortless flyers, in a 30-year lifetime an Arctic tern can travel

the distance to the moon and back...

three times.

But for a few short months

this group will join both Common and Sandwich terns

to make home here.

Raising their chicks

until they're strong enough to head back south.

BIRDS CHIRP

The chicks are so demanding, adults even have to drink on the wing...

TERN CAWS

... regularly exchanging calls with their young.

TERNS CHIRP

Once a fish is spotted

a tern will hover in mid-air like a hummingbird

and from a height of up to six metres

they'll dive...

plunging beneath the surface to spear their prey.

This parent has caught a sand eel.

He has an older chick, who's extremely vocal.

TERN CHICK CHIRPS

But as every parent knows, as youngsters get bigger

they get more fussy.

But he tries again.

TERN CHIRPS RAPIDLY

Success!

And the hard-working dad heads back to the water to fish.

SEABIRDS CRY

Anchored between Anglesey and Aberdaron to the south

Caernarfon Bay is a picture postcard

nestled in the lap of the Irish sea.

BIRDS CHIRP -— INSECTS CHITTER

It seems everyone is out enjoying the tranquil blue water.

But not all days are like today.

The cliff boasts razor teeth of jagged rock.

They warn of a reef that sits just beneath the waves.

One, which over the centuries, has proved deadly to many ships.

One and a half kilometres from shore lies one such unlucky vessel.

This is the rotting carcass of the SS Gwynfaen.

A former 300-tonne cargo ship, long since dragged down to a watery grave.

Her bare bones have become a post-apocalyptic marine city.

And like all good urban environments

it's home to a diverse range of characters.

Attached to the structure...

are fleshy mounds of a soft coral.

The aptly named dead man's fingers.

Huge sea urchins the size of saucers

slowly patrol the city limits...

grazing on the thick crust of barnacles.

The Gwynfaen's spacious hull

provides a protected gathering place for large shoals of fish.

This gang of bib are members of the cod family.

There's safety in numbers.

Along their flanks is a line of sensors used as a mini sonar system.

If any one individual senses dangev...

the entire shoal...

darts away.

The bib have reason to be on their guard.

In the engine room lives a real-life sea monster.

A female conger eel.

These are the largest eels in the Celtic seas

up to three metres in length.

During the day, she hides within the old boiler.

Her powerful jaws contain rows of densely packed teeth.

Most of the residents of the wreck keep a wide berth.

But not everyone.

Halfway down the conger eel

this little gang of prawns choose to dance with death.

These scavengers snack on the leftovers from her hunting forays...

while staying well clear of the conger's business end.

On the far side of the engine room

lives the ship's captain...

a huge lobster more than 50 centimetres long.

With his powerful muscular claws, he is the original Captain Hook.

His massive left-hand pincer can crush through shells with ease.

And his smaller righthand claw makes a Superb cutlass...

to slice through flesh.

He's 30 years old, relatively young for a lobster

and he could live much longer and grow even bigger...

thanks to an enzyme in his cells

which allows them to regenerate.

An elixir of life.

As long as he remains in the ship

and keeps shedding and re-growing his shell

it's just possible...

he could live... forever.

But perhaps the most diverse adaptation to life in this dystopian world

belongs to small shoal of fish

that looks like they've just swam in from the Caribbean.

These are female Cuckoo wrasse, part of a hareem headed up by a single male.

With his blue and orange stripes, he's a real head turner.

His female companions have different but equally tropical colours.

Coral pink...

topped by a fringe of distinctive black and white blotches.

In the bottom of the wreck...

another shoal of wrasse is under threat.

These females have no male.

He fell victim to the conger eel.

But, in a twist, straight from ancient Welsh myth

there is a strange sexual sorcery at work here.

The senior female...

has just started to sport male colours.

In a few weeks' time

an extraordinary transformation will take place...

which could potentially save them.

Just inshore from the Gwynfaen...

lies the tiny fishing village of Porthdinllaen.

This sheltered bay has been a safe harbour for generations of seafarers and fishermen.

And provides the perfect conditions

for one of the rarest marine habitats in the world.

Hidden beneath these crystal-clear waters

lies a vast sea grass meadow.

The size of 28 rugby fields, it's one of the largest in Wales.

These lush pastures are dependent on direct sunlight

so only grow in shallow water.

Sea grass is the ocean's only pollinating plant

and takes in huge quantities of carbon dioxide.

Metre for metre...

more than the Amazon rainforest.

In Summer...

the meadow is a nursery

for fish of all shapes and sizes.

Elegant eels...

corkwing wrasse...

and a polka-—dotted plaice.

The sea grass also offers a resting place for the intrepid spider crab.

His battle scars are healing

and he's back on schedule

for his date with destiny.

Near the back of the meadow

a male sea stickleback is busily constructing a nest.

He's not fussy about where he gets his building materials.

These wispy strands of sargassum originally floated here from the Pacific.

He interweaves the delicate threads to create a cosy nest.

He's something of a perfectionist.

He wants to ensure his home can withstand the summer storms ahead.

When it comes to raising a family...

it's definitely advisable to have a penthouse suite...

for big beasts prowl the floor below.

Across the meadow, this bull huss shark is keeping a close eye

on another dad-to-be.

This pipe fish is the straight bodied cousin of the sea horse.

He doesn't need to make a nest

because remarkably...

he's pregnant!

In 20 days' time, he'll give birth to live young.

The seagrass camouflages him from predators...

and is also full of plankton and tiny crustations he can feed on.

Luckily, he has the most extraordinary eyes.

Each eye moves independently

allowing him to spot minute prey

which he sucks up with his straw-like snout.

Back across the seagrass meadow...

the sea stickleback may be in luck.

A female has spotted his nest.

He's still making adjustments.

If she decides to lay her eggs in his nest...

she'll leave him to raise their offspring!

She's definitely impressed...

and makes her way towards the nest.

A final bit of sprucing up...

and she's in...

and laying her eggs.

If all goes well

he will soon be the proud father of a brood of baby sticklebacks.

As one sea ruler sets...

another rises.

By night...

the world of shallows is full...

of mystery...

and monsters.

Back in the sandy bed close to Abersoch

a pair of huge eyes peeps out from the seabed.

They belong to a small but tenacious nocturnal hunter.

An Atlantic bobtail squid.

No bigger than a golf ball.

But she's doesn't want to become someone else's dinner.

So, like a supernatural shape shifter

she changes colour...

to match the sandy bottom.

Once she reaches the red kelp...

another transformation!

With an enormous brain for her size

she's triggered strong muscle contractions

that move pigment and light-reflecting cells.

Back in the sand...

her cloak of invisibility is used yet again.

But her vanishing act doesn't fool everyone.

A male Atlantic bobtail also lives in the neighbourhood.

His large eyes are especially adapted for seeing in the dark.

And he's set his sights on her.

He pounces...

grasping hold of her with his tentacles.

They start to mate...

under the moon light...

for over an hour.

The night isn't just for lovers.

This is the time for catsharks to start hunting.

She too has superb night vision...

and an extraordinary sixth-sense...

of electro-reception in her snout.

Capable of detecting the tiny electric currents

that emit from all living animals.

The bobtail acts quickly.

Using her two front arms

she buries herself with gravel.

But for the cat shark...

prey hidden in the sand make easy pickings.

This time...

it wasn't the bobtail.

As the summer comes to an end

there's a danger waiting...

that comes from the sea itself.

A challenge to every animal in the shallow waters.

Llyr, the God of the ocean

is about to unleash his furious hand

across the entire Welsh coastline.

As the planet warms

summer storms become stronger and more frequent.

While the ancient cliffs can withstand the battering...

underwater, it's a different story.

The fragile sea grass nursery is being ripped from its roots.

The tall kelp is smashed against the rocks.

The shipwreck provides shelter for some.

While the fish shoals are torn apart.

In the marine desert...

a seaborn sandstorm...

tears through the subterranean homes.

BIRDS TWITTER

The following morning...

the storm has passed.

But the sea god has left his mark.

SEABIRDS CALL

Beneath the now calm water in Porthdinllaen's harbour...

there's devastation.

Large swathes of seagrass have been uprooted.

And the sea stickleback's nest has been destroyed.

There are no signs of any eggs.

And dad is missing too.

SEABIRDS CALL

Nearby, on board the Gwynfaen...

the once female Cuckoo wrasse has survived the battering.

With the sex change complete...

he now leads his hareem...

ensuring the future of the shoal.

For all the devastation they wreaked

the storms have not defeated one dogged traveller.

Some three months after setting out on his epic journey

our determined young spider crab...

has finally reached his destination.

He's joining hundreds of other spider crabs

all drawn here for an annual mass gathering.

Their arrival is perfectly synchronised with the end of the summer.

When the sea is at its warmest.

The ideal conditions when you're about to moult.

The young knight casts off his old carapace

to reveal a new suit of armour.

He's succeeded in his right of passage

and won't moult again.

In a day or two, he'll start his long journey back to the deep.

This time, to find a mate.

SEABIRDS CALL

As the days shorten and the sun's power starts to fade

the tourists have gone.

Now, the beach is littered with the husks

left behind by the spider crabs.

And in the kelp forests off Pembrokeshire...

the female cat shark has returned.

The tough mermaid's purse held firm in the storm.

The baby is still alive

and has more than doubled in size.

In a few weeks, a fully formed cat shark will hatch out.

Time to move on.

Over the winter, the shallow kelp forest

will continue to protect her offspring.

BIRDS CAW

Off the coast of Anglesey...

the Arctic terns are heading south.

Their young now strong enough to fly.

They'll be back next year...

having flown some 35,000 kilometres.

Back to the shallows of Wales.

Back in search of the sun.