Original subtitles

In a vast ocean...

along a wild continent.

An incredible place of sanctuary.

These pristine beaches, the tidal forests

and the most southerly submerged reef are a hotspot of diversity.

A crowded home to thousands of species,

where some inhabitants work together...

and others are solitary hunters.

And for two of the ocean's nomadic giants,

this coast is the key to the survival of their species.

This is the Indian Ocean's secret refuge.

This is Africa's ocean sanctuary.

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Spanning two hemispheres and touching three continents,

The Indian Ocean covers over 28 million square miles.

Here, off the east coast of Southern Africa,

it washes up against a shoreline

of subtropical bush and golden beaches.

A lush, abundant landscape.

Where mangrove forests and dune fields meet an inviting ocean.

With a climate created by the warm Agulhas current,

its warm waters are a sanctuary for a diverse collection

of marine species.

And yet, the apparent abundance of this world is deceptive.

This African shoreline is gentle and warm,

but life here is a relative struggle

compared to that enjoyed by species

just six hundred miles down the coast,

where these azure waters give way

to the violent Atlantic washing up on a semi-desert world.

Southern Africa's Atlantic coast is pounded by huge surf

whipped up by constant winds.

But those winds also draw water up from the depths,

bringing with it vast amounts of nutrients

from a millennia of decomposing plant matter.

This bonanza of food supports massive populations

of marine species on the west coast -

over two million Cape fur seals jostle for space

in large breeding colonies.

They are fed by enormous shoals of pelagic fish such as sardines

that are drawn here by the cold, nutrient-rich water.

But along the east coast,

the prevailing winds are gentler.

Without the battering gales,

there is no upwelling of nutrients from the depths.

The water might be warm and tranquil,

but it doesn't have the benefit of the west coast's

endless conveyor belt of food brought up from the deep.

What it does have, though, is coral:

a living landscape thriving on a symbiotic relationship

between coral polyps and single-celled algae.

As the algae photosynthesize and give off oxygen for the polyps,

and the polyps give off carbon dioxide for the algae,

they create a solar-powered oasis,

offering food and shelter for the creatures

that are drawn here.

It's a vibrant concentration of life,

a safe zone created by a unique confluence

of geography and climate;

where Africa's marine animals gather together

to form a vibrant community

in one of the last great wilderness strongholds.

Out in the open ocean, some of this region's great migrants

are ending long journeys.

Drawn to the warm waters and relative safety of the coast,

turtles and Ragged-tooth sharks

make an annual journey to gestate.

This Ragged-tooth shark is pregnant.

She has come to these waters to bring her pups closer to term.

The Hawksbill turtle, too, is returning to these waters,

but her nesting grounds are further up

the African coast in Mozambique.

She knows these waters well.

She has travelled this way every two years

since she was old enough to breed.

Now she is gathering her strength for the last leg

of our journey.

It's been a long trek.

One young Hawksbill was found to have swum from the Cocos Islands

southwest of Sumatra to Tanzania -

a journey of 3,800 miles.

She's not alone.

Somewhere out beyond the reef, other female turtles

are reaching the end of their own epic journeys.

Now, though, she's focused on her meal.

She's tired.

The current is powerful.

But it's worth persevering.

The reef hides her favorite meal - soft sponges.

The coral reef is built on ancient foundations.

Millions of years ago, sand dunes on a prehistoric beach

solidified into something like sandstone.

Slowly swallowed up by the ocean,

they became the bedrock upon which this coral reef grew.

Coral is a living creature,

a soft-bodied organism

that attaches to bedrock and grows,

creating hard calcium carbonate tubes.

Colonies are formed, creating reefs

and in turn, entire habitats.

They grow slowly -

just four inches per year -

but when they are left undisturbed for millennia,

their colonies can build up into entire landscapes like this one.

This is the southernmost submerged reef

along the African coast.

It's also deep.

Its shallowest outcrop is still 33 feet below the surface.

The deeper the reef, the less sunlight reaches the algae

on which it depends.

And yet, enough filters down here

to make this one of the most diverse ecosystems

on the planet.

The location of the reef might seem arbitrary:

these corals could have settled on any rocky outcrop

anywhere along the hundreds of miles of this shore.

And yet, it owes its success as a center of diversity

to a quirk of geography that makes it part

of a uniquely interlocking ecosystem.

Just beyond the dunes, an estuary winds towards the sea.

At the head of its mysterious waterways

lies a forest unlike any other along this shore.

A mangrove forest,

able to survive in the salt water

that floods it with every high tide.

Every day, this unique forest drops tons of plant matter

into the waterlogged mud around its roots.

Much of that waste is dragged underground

by the mangrove's composter-in-chief,

the Red-claw mangrove crab.

Alerted by the soft vibrations of an impact on the mud,

these tireless recyclers keep the forest floor clean -

and keep the entire estuary system flooded with nutrients.

Tons of pods and leaves quickly become tons of compost.

As the tide comes in, flooding the forest with salt water,

the water fills with dissolved nutrients.

When it retreats, all of that food is washed out into the sea,

bringing a feast to the filter feeders of the nearby reef.

The ebb and flow of the tides in the mangrove forest

keeps the reef well fed.

But it provides more than food to the fish of this coast.

It also provides a nursery.

At high tide, an unbroken passage

stretches from ocean to forest.

Now these beaches are no longer a barrier between worlds,

as channels open for new visitors.

A waterway deep into the mangrove forest

is an invitation to the reef's baby fish.

Young reef fish have evolved to follow

the incoming tide upstream.

The journey from coral to coast is a long one for a small fish,

but it's worth the effort.

Submerged mangrove roots:

the fish have reached the outskirts of the forest,

where salt- and fresh water are mingling.

Pulled together by the promise of the mangroves,

a new community forms.

An underwater nursery for young fish.

They come in the thousands.

The mangroves are a sanctuary,

offering a few vital months of abundant food

and safety from the reef's predators.

Here the fish will mature, growing bigger and stronger

until they're ready to take on the challenges

of the open ocean.

For a world struggling for sustenance,

the nutrient-rich water of the forest is a bonanza

and its effects are dramatic:

tropical fish species have been found to be

up to twice as abundant

on reefs bordering mangroves on this coast.

But not all of the reef's inhabitants

have access to a convenient nursery.

They cannot disappear for a few months

until they are ready to compete.

Instead, they disappear right where they are - in plain sight.

On an exposed reef offering few places to hide,

the art of camouflage becomes a vital weapon

in the battle for survival.

Indistinguishable from the textured backdrop

of the rocks and coral,

a predator waits for a catch.

The Frogfish is a type of Anglerfish,

using a lure attached to its head to attract hungry victims.

It's easy to miss him.

His unique skin makes him a master of disguise.

Instead of scales, Frogfish are covered with fleshy spines,

hairy extensions and tiny skin flaps

to blur any recognizable features.

All the better to be mistaken

for a piece of algae-covered sponge.

Since his camouflage depends on him being motionless,

the Frogfish doesn't move much.

When he does, he reveals a unique waddling walk,

as he makes his way along the seabed

using his jointed pelvic fins.

He's not a strong swimmer,

but these feet-like fins

brace him against the current as he waddles across the reef.

When he finds his next hiding place,

he will settle down and become invisible

against the rock, biding his time until his next meal.

He's not the only undetectable hunter lying in wait.

The Crocodile fish is intricately marked and textured,

and pressed against the reef, it all but disappears.

Even its eyes are camouflaged.

All is not what it seems on this reef.

To unsuspecting passersby this may look like

just another dead leaf waving in the current.

But this dead leaf is very much alive.

Paper fish snap up any small, unsuspecting fish

and crustaceans that venture too close.

Most of these predators are prey as well.

Camouflage not only allows them to ambush their prey,

but it also hides them from the animals that prey on them.

For some, it's not about being invisible.

Instead, it's about looking like the fish next to you.

This cloud of yellow fish is made up of several

similar-looking species.

Most of them are Blue banded snapper,

but mixed in among them

are a number of Yellow stripe goatfish.

For both the snapper and the goatfish,

there's safety in numbers.

The more similar-looking the fish in the group,

the better the odds to survive an attack by a predator.

Shoaling increases the chance of survival

for each individual fish.

More eyes means more surveillance

on potential threats.

Should they be attacked,

the swirling mass of yellow bodies

might disorientate or distract a predator,

making individual fish less likely to be picked out.

It's a relationship that benefits both species.

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But one famous fish has taken interspecies co-operation

to an extreme level -

happily living in a death-trap.

Clownfish find safety among the fronds of sea anemones.

It seems like an unlikely refuge.

The anemone's stinging nettles make a meal

of anything small and unwary enough to venture close.

But for the Clownfish, the tentacles aren't killers -

they're home.

It's a unique "exchange of services" arrangement.

While the anemone provides shelter, food and protection

for its little keeper, the Clownfish returns the favor

by keeping its home clean and healthy.

The Clownfish are able to survive the stings,

thanks to a life-saving layer of mucus that covers their body.

This mucus is up to four times thicker

than that produced by other fish.

More importantly, it's laced

with traces of the anemone's own venom.

Each anemone houses its own Clownfish

and it is believed that the fish tailor-makes

its own specific anti-venom by rubbing against the anemone -

literally taking the sting out of these nettles.

This death-defying performance has an audience:

a group of baby Domino damsel-fish.

These territorial animals are also able

to withstand anemone stings;

they've been using this one as a hideout.

But while the bigger Clownfish is having a turn,

they keep a respectful distance.

Turtles are the great nomads of the planet's oceans.

Covering huge distances to feed or to breed,

they spend most of their lives away from land.

Africa's Indian Ocean coast is 4,000 miles long,

spanning five countries and two hemispheres.

And yet when they migrate here,

they are heading for one special place on one specific beach.

The place where they were born.

The females know exactly where they need to go.

Turtles are highly sensitive to the Earth's magnetic field.

They use it to navigate in the open ocean,

following tiny fluctuations or gradients

as if they were lines on a map.

This beach, too, has its own magnetic markers,

like invisible GPS co-ordinates.

But this female Hawksbill will swim on.

Her inner compass is directing her to a beach

far north of here.

She knows exactly where she will find it:

the beach's co-ordinates were imprinted on her

when she was born.

The beaches of this African sanctuary, however,

are calling to other turtles.

They were born here, many years ago

and are now returning to complete an ancient cycle.

This Loggerhead female has followed her magnetic signal

back to the beach where she was born.

This moment has been a long time coming.

It can take up to 35 years for Loggerheads

to reach breeding age.

Now ready to lay, she begins to excavate her nest.

Up here, above the high-water mark,

her eggs will be safe.

Her babies will have a fighting chance.

The sex of baby turtles is heavily influenced

by the temperature in the nest.

In warmer nests, most embryos develop into females.

Cooler clutches are more likely to produce males.

Nearby, another long-distance nomad is also nesting.

A female Leatherback has dragged herself ashore,

hauling her huge weight up the dunes.

These massive turtles can grow to be over six feet long

and weigh almost a ton.

Her migrations are vast -

sometimes over 4,300 miles each way -

and she can reach depths of almost 4,000 feet

down into the abyss.

But none of her journeys have been as important

as this short one from the surf to the dunes,

to lay her hundred eggs and start a new generation

of ocean wanderers.

The Loggerhead female has laid her eggs

and covered up her nest.

Exhausted by the night's exertion,

she drags herself back towards the surf.

But she's not alone.

Out in the night, eyes are watching.

Ghost crabs.

The mortal enemy of her babies.

But for tonight, her work is done.

She will return to this beach three or four more times

in the coming weeks to lay more eggs in new nests.

But the hatchlings will have to fend for themselves.

As silently and secretly as she arrived, she slips out of sight.

A new day and under coral overhangs

away from strong currents,

fish are gathering to get a much-needed clean-up

from one of this reef's most industrious workers:

the Cleaner shrimp.

This is a safe place, where predators and prey alike

put aside their differences in the quest

for the perfect full-body treatment.

For the weary and worn, it's a welcome relief

to get rid of parasites and damaged skin.

For the team it means a hearty meal.

Waving their white legs and antennae,

the shrimp flag down interested customers.

The usually dangerous Rock cod are not here to cause trouble,

and move in slowly to show they mean no harm,

changing colors and gently opening their mouths.

A Cleaner leaps to work.

A stingray approaches hoping to secure a slot.

Like the Rock cod, she too comes

waving the proverbial white flag.

She lifts her body off the sand with undulating movements.

But she's come too late.

The shrimps are busy now and like it or not

she'll have to come back later to try again.

The Cleaner shrimp's cousin, the Harlequin shrimp,

has more refined tastes.

Not for these refined diners is scraping together meals

consisting of dead skin and scraps stuck between teeth.

They are hunters.

And today's target is their favorite delicacy: starfish.

They're dressed for dinner, suited up in magnificent shells.

They can afford to be showy,

since their prey will not be able to escape them.

Starfish have hundreds of tubular feet that allow them

to move smoothly, but slowly, across the ocean floor.

A slow-moving target is an easy target

and some starfish have developed hard bodies

to protect themselves

But not this one.

The Harlequin shrimp have used their delicate sensory antenna

to smell out their prey.

Now, they climb on top of it and get to work

trying to turn it over.

If they are going to get to its vulnerable underbelly,

they need to immobilize it.

And then, with chilling precision,

they will set about slicing off its tender feet

with their specialized claws,

working slowly towards to the starfish's juicy central body.

The starfish will feed these meticulous killers for days.

Elsewhere on the reef, other predators

are starting their day,

or recovering from the night's hunt.

A Leopard shark has spent the night prowling the reef,

stalking crabs and shrimp.

They are small morsels, but they are abundant.

With enough food, these placid sharks

can grow up to six feet long.

Tired after the night's hunt, it rests on the sandy bottom,

keeping exertion to a minimum.

Sharks have ancient origins,

going back hundreds of millions of years,

but next to these silent hunters,

drifting over the reef, they are relative newcomers.

The first jellyfish floated through the world's oceans

500 million years ago,

long before there were even plants on land.

They are the oldest multi-organ animal on Earth.

But they are not quite as primitive as they seem.

Instead of being passive drifters,

they move by contracting the rims of their bells

in subtle pulsing movements that displaces the water

they're moving through.

They also have a complex nervous system

that helps them adapt and react to the environment,

sensing current flows,

identifying other jellyfish,

and even testing the salinity of seawater.

The bodies of jellyfish are soft and fragile,

but they can be lethal.

When they encounter their prey,

they react with overwhelming force,

pumping their victim full of neurotoxins.

Most animals in this ocean give them a wide berth,

but for turtles, they're a staple diet.

Leatherbacks gorge on jellyfish in the open ocean,

in summer sometimes eating up to 70% of their body weight

every day.

This predator chooses to stay close to the reef

rather than roam the open ocean like the jellyfish.

The Honeycomb moray eel coils itself in and among the crevices

of the reef, venturing out occasionally for a stop

at the cleaning station or to hunt.

Often mistaken for a of type sea-snake,

the moray is actually a fish.

Its open mouth looks intimidating,

but this is less a show of force than simple respiration.

An open mouth allows a constant stream of water

to flow through its gills -

little holes situated behind its head.

They may look frightening and anti-social,

but eels are relatively peaceful neighbors -

when they're well fed.

Where nooks and crannies are scarce on the reef,

they might even live side by side with other eels:

a fearsome-looking pair

that is just trying to get by like everyone else.

These fish can swim close to the eels' open mouths

with little to fear...

until feeding time.

Another ancient creature of the ocean

has made her way to the coast.

Female Ragged-tooth sharks

migrate to these warm waters to gestate.

They are extremely sensitive to temperature changes

and will move along the coastline to warmer waters

when they are carrying young.

She has two wombs and will produce eggs

as long as she's gestating.

She will give birth to two pups - one from each womb.

Most of her energy is going into growing her pups.

And yet during this time she eats very little.

Algae on her mouth and teeth is testament to her fast.

Almost nothing has passed through these jaws for weeks.

But just because she's not eating,

it doesn't mean her pups are going hungry.

The unborn sharks are building their strength -

by eating their siblings.

The biggest pups eat their weaker brothers and sisters -

inside their mother's body.

First the embryos and then any unfertilized eggs

in their reach.

The extra eggs are a vital source of baby food.

As their mother cruises in the warm water,

her unborn pups have already learnt

their first lesson in life:

only the strongest survive.

She will spend two months here in this sanctuary,

but as the time comes for her to give birth,

she will swim south toward cooler waters.

It will take up to 9 months for them to be born.

When they enter the world, her pups will be up to 3 feet long

- half her size - and already formidable predators.

But for now they are growing.

Two months have passed

since the Loggerhead laid her eggs on this beach.

Up above the high-water mark, the dunes are stirring.

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The first of the brood makes its way out of the nest.

Instinct tells the rest to stay motionless for now,

but this one is precocious.

It's a bad move.

Dangers lurk in the darkness.

Ghost crabs are waiting at the water's edge,

gathering for the kill.

These opportunists are one of the key predators

of baby turtles.

If the babies are going to reach the safety of the ocean,

they will have to avoid being caught.

The rest are staying put.

There is safety in numbers.

But their impatient sibling is on his way.

Out in the open, alone, there is nowhere to hide.

A crab closes in for the easy kill.

Unaware of the tragedy on the beach,

the rest of the brood is surfacing.

Up to 120 babies are pushing up out of the nest,

all intent on one, all-important dash

down the dunes and across the beach.

For the tiny, soft, awkward babies,

not made for moving on land,

it will be a monumental struggle.

Even small dune plants present major obstacles.

The journey is just a few dozen yards,

but for the hatchlings it's an exhausting trek

across an apparently endless desert.

A desert full of dangers.

A life-and-death struggle.

A baby has been snared by a ghost crab under the sand.

The unlucky do not survive, but this baby is tough.

It battles on through the night,

rejoining its brothers and sisters as the march goes on.

This is the first and last time the males will walk on land.

The rest of their lives will be spent at sea.

At last, they reach the water's edge.

They are together for now,

but they are starting solitary lives.

Turtles are self-sufficient from the moment they hatch

and already they are going their separate ways,

beginning decades of wandering across the world's seas.

The magnetic signature of this beach

has already imprinted on them

and one day, twenty or thirty years from now,

the females will begin to return here to lay their own eggs.

Now, they will let the currents guide them.

The warm Mozambique current will take them south,

skirting the African continent

and then out into the Southern Ocean.

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A new day over the reefs of Southern Africa.

The baby turtles are gone.

The secret ritual of the night before has passed

as mysteriously as it started.

But life on the reef goes on, as urgently as always.

There are fish to be scrubbed.

Dangers to be avoided.

The daily work of survival in the Indian Ocean.

The Raggies will linger here for many weeks more,

drifting in these warm waters as their pups reach full term.

And then they too will leave this coast,

to swim south to give birth.

Another migration in an ocean full of ancient nomads.

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Life in the Indian Ocean might be challenging,

but here, off the coast of Southern Africa,

it flourishes in a natural sanctuary like no other.

A protected area, made abundant by the interplay

between subtropical reef and life-giving mangroves.

From its sweeping beaches to its coral landscapes...

safe nurseries...

to secret nesting sites.

This is a place that offers shelter

and abundance to those that throng here.

Whether they call it home, or are just passing through.

A hideaway.

A stronghold.

An island of diversity in the great Indian Ocean.

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