Original subtitles

İt is November.

A full moon rises.

Almost 400,000 kilometers away, Planet Earth falls under its spell.

Our oceans stir.

An ancient undersea ritual is underway.

The outcome of this event

will not only affect marine life in the surrounding waters,

but will also give us a clue

about the health of the entire ocean system.

The creature responsible is coraol.

And this is coral's story.

The story begins here,

with the incredible phenomenon that is mass coral spawning.

İf's an annual event, cued by the sun and the moon.

İt involves over 140 different speclies,

and has been occurring for thousands oOf yedcırs.

Although corals have no brain and no eyes,

somehow individual species spawn together,

sometimes down to the minute.

Like tiny love-letters,

the genetic material İs cast into the ocean currenİs,

connecting reefs over hundreds of kilometers.

Like us, corals take up to nine months to prepare for birth.

But many are hermaphrodites, so they gestate both egg and sperm.

On spawning night,

these are grouped into bundles and delivered through the coral's mouth.

For most, itf's a gentle birth.

Over a shorft time-span, the bundles break apart

and the egg and sperm must find their counterparts from another colony.

Billions set forth, but few survive.

Many ofher creatures choose the same conditions to spawn

and the reef waters are transformedi

into a vast İigulid womb, clouded with eggs and sperm.

Mass spawning overwhelms potential predators,

so the coral eggs have more chance to be fertilized and begin a new colony.

By daybreak, vast slicks on the surface mark their passage.

Coral is an architect not only of the ündersedc world,

but above the surface too.

Dead coral breaks down İnto sand

that eventuallly builds up to credate coral cays.

These shores and shallows provide sanctuary -

and imporfant breeding grounds -— for a varlety of other credctures.

All told, reef-building corals have colonized every tropical ocean,

shaped and proftected thousands of kilometers of coastline

and influenced marine evolution for millions of years.

Birds like these nodody terns

rely on coral reefs for food and coral cays for shelter.

Birds help vegetate cays by depositing seeds.

These seeds grow into trees and forests

which in turn provide the birds with nesting sites,

These sandy outposts are freguented by many tropical seabirds,

with some pairs returning to the same nesting sites yecir after yecır.

Primitive corals date back over 450 million years.

Modern reef-building corals first emerged around 250 million years ago

and their reefs have provided homes and sustenance

for innumerable specles ever since.

Over cordal's long history, five mass extinctions have come and gone.

During each, up to 905 of oall life-forms perished.

Two of these extinctions

occuürred during the rise of modern reef-building corals.

Rather than falter, they somehow survived,

rebuillt their reefs

and transformed the oceans anew.

Today, coral reef ecosystems are important nursery grounds

for many iİconic marine animals, such as the seda türfle.

There dare seven speciles of seda turftle

and all are long-lived and slow-growing.

They take between 10 to 30 yecrs to sexually mature and matfte af sed.

These marine reptiles are nomadic

and swim thousands of kilometers during therr lives,

But strong instinct and mysterious natural forces gulde them,

so that when a female needs to lay her egogs,

she returns to the very beach where she was born to do so.

Here, she digs a nest and coral sand becomes the womb.

Hundreds hateh, but only one or two will make it to adulthood.

They can then live for up to a century.

When a turtle hatched 100 yedcırs ago,

it would have seen the world's coral reefs in all their glory.

Pre-industrial seas were clean and clecr

and corals had enjoyed good conditions for millions of years.

Throughout the İndian and Pacific oceans,

and into the Caribbean and west Atlantic,

reefs were thriving.

The turfle spent its youth exploring these reefs

and witnessed the engineering marvel that is coral.

By harnessing the power of the sun and perfecting recyoeling,

coral bullt energy-efficient cities that put many of ours to shame.

Collectively, these cities creafed vast empires,

some visible from oufter space.

Here, the turtle found itself in great company,

for these ündersea empires were home to vast numbers of marine specles

of every imaginable shape and size

and were crowded, colorful places.

Today, reefs have one ofthe highest levels of biodiversity

of any ecosystem

and are some of the most biologically important places on Earth.

Together, turtles and corals have witnessed many changes

to their watery world.

They are some ofthe only beings

to have survived the last mass extinction event

65 million years ago.

Scientists predict that in İhe coming century,

they will face ocean conditions

as catastrophic as during that last extinction.

Wise old turtles have seen the warning signs for a while.

7055 of the world's reefs have already been destroyed

or are seriously threatenedi.

And all but one of the seven sea turtle species

are classified 'endangered' or 'eritically endangered'.

For the first time in millions of years,

the future of both turtle and coral is uncerftain.

Many things affect the hedalth of coral reefs,

in parficular, sea temperature, sea level and water chemistry.

Reefs may look mightiy, but corals themselves are fragile

and can be fatally harmed by just subtle changes in their environment.

When seda levels rise too rapidiy, corals can't grow fast enough

and reefs drown.

As atmospheric carbon dioxide levels increase,

ocedan acidification intensifies and reefs will dissolve.

And a sustadined increase of only 1-2 degrees İn ocean temperature

can codüse corals to bledch and die.

By the end of this century, it's predicted that the global climate

could be 5 degrees Celsius hotter or more.

At this rate, bleaching will become an annual occurrence,

and this colorful landscape will literally fade away.

A hedalthy coral reef is edasy to spot.

A complex structure dawash with color, variety and activity.

This is a tangled, tropical garden to rival anything on land.

Most amazing about this garden

is that many of the 'plants' are detualiy animals.

Like grasping hands,

coral mouths hungrily sift the passing currents for food

day and night.

The creature we call coral is a primitive sac-like polyp,

part animal, part plant.

The animal part feeds on plankton.

The plant part consists of microscopic algae -

called zooxanthellae - that photosynthesize using sunlight.

Each polyp is connected to its neighbor,

passing along energy and nuütrients.

These polyps mulfiply to create colonies,

which combine to form reefs.

Iİn this way, energy is produced, shared and recyeled

throughout the entire ecosystem.

With the energy they produce, corals not only thrive

but also manufacture calcilum carbonate,

the specidal concrete' that builds reefs.

This is öne secret behind corals' great empire building.

The ofther is budding.

Budding is a process where coral polyps produce

genetically identical copies of themselves

and extend their colonies without spdwning.

The calcilum carbonate foundation secreted by hard corals

can be one kilometer thick in places

and hundreds of thousands of years old.

The living reef we see today is Just a thin veneer on top,

made up of many different specles,

including soft corals...

.fan corals...

.and sponges, goörgonidans and crinoids.

All told, coral has evolved into more than 1,000 hard coral species

and over /00 soff corals,

each perfectly specialized to fill its own niche.

Ünderstanding how corals build reefs

highlights the seriousness of cliimate change

and how it threatens this complex ecosystem.

Our öoceans have always absorbed atmospheric CO2 like a giant sponge.

But now those levels are so high that the water chemistry is changing -

d process referred to as 'ocean acidification'.

Alkalinity is falling

and naturally-occurring carbonate ions are being affected.

Many marine creatures need İhese ions to produce calcium carbonate

for their shells and skeletons.

Hard corals need them to bulld reefs.

Ocean acidification seriously threatens all these processes.

But in every natural catastrophe, there are winners and İosers.

Jellyfish are distant relatives of coral,

but unlike coral, they are more adaptable

to changes İn water temperature and chemistry.

Their numbers are already on The rise,

And they are making our seas sting.

Coral's other ancient cousin is the sed anemone.

Like coral,

the anemone is a simple being that has been highliy successful.

In fact, the anemone is like a huge coral polyp.

At its center is a mouth

surrounded by a vast mantle of stinging tentacles.

Within the mouth is a big stomach filed with acidic enzymes.

Because the anemone does not have a solid physical structure or skeleton,

it does not rely on calcilum carbonate,

so İf's not as vulnerable as coral to ocedan acidification.

But, like coral, some species possess zooxanthellde algae

and warming seds will also cause them to bleach.

There are over 800 specles of sed anemone.

10 are sulitable homes for anemone fish

and this is one of the reefs most marvelous partnerships.

The anemones tentacles normally sting İnvaders.

But these fish are coated with a protective mucus

and can dance İn and out unharmedi.

The fish rarely wander more than a meter away.

Everything they need is right here -

seraps of food, protection and community.

Not surprisingily,

the fish lay their eggs near the protective folds of the anemone,

ajerating and defending them until they hatech.

And being stuck in one place hasn't harmed their sex life.

In fact, it's enhanced İT.

To keep everyone satisfied, they've mastered sex change.

If a dominant female is redulred, a male can change sex.

If a dominant male is needed,,

a subordinate moale accelerates into sexual maturity.

As öocedan conditions change, anemone fish seem more protected than most,

safe within those stinging arms.

But even they are notimmune from danger.

All fish have internal structures and organs

which may be weakened by ocedan acidification.

Even now, scientists are finding

that the ear bones of fish are being affected,

which is impacting the way they communicate.

If ocean acidification goes unchecked,

it may affect key metabolic processes for all marine animals.

Whenever conditions get more challenging,

the natural process of selection just gets more ruthless.

Those that cannot cope will be gulckly cast aside.

Every citizen must edcrn its keep.

These shrimp gather in locations referred to as cleaning stations'.

This particular station also happens to be the home of a moray eel.

But the shrimp arent running away.

If anything, theyre competing to get closer.

And although the eel finds the shrimp irritating,

he just grins and bears İt.

The readson why these entirely different species

tolerate öone another

is becaduse they have an unspoken agreemenit.

The shrimp has the important job of removing parasites

as well as dying or dead flesh.

These can be faftal to the moray,

but provide a delicious banguet for the shrimp.

Animals are engaged in complex relationships right across the reef.

Going solo is risky business.

And if youTe golng to attempt it, you'd better be very clever.

One clever survival tactic is camouflage.

Decorator crabs attach tiny sponges, corals and anemones to their shells

and look more like walking flowerbeds than animals.

Others attempt to go incognito by placing toxic sponges on İheir heads,

like these aptfly-named hat-carrying crabs.

Sponges are living creatures, but the crab doesn' care,

cutting the sponge Up into whatever size fits.

Other crabs collect forest leaves

and use them for disguise and as hang-gliders.

Boxer crabs are always ready for a fight,

with tiny polsonous anemones as boxing gloves,

Hermit crabs reinforce their own body armor by wearing second-hand shells.

Bigger shells must be found

as the crab grows

and this gives the crab lots of time to develop its own unidue İook.

More sophisticated hermit crabs collect stinging anemones

and will remove these anemones and reattach them

whenever they change shells.

Crabs date back to Jurassic times 200 million years ago

and over 10,000 specles exist.

They're hardy souls - even missing half their legs won 't slow them down.

And they're great opportunists -

some feasting inside a sea cucumber's mouth.

Sea cucumbers have some remarkable physical adaptations themselves.

They breathe through their rear end,

move on hydrauülicaliy-powered tube feet,

and have a special collagen in their body wall

that enables them to radically change shape.

They also spawn from tTheir forehead.

Sea cucumbers have few natural predators.

So it's no wonder they're a popular taxi ride for crabs and shrimp.

Because the sed cucumber stirs up food with its front end,

there's even a free meaoal as parft of the ticket.

Nudibranchs are also great to hitchhike.

These highiy poisonous sec slugs

offer guaranteed safe passage through dangerous open tTerritory,

with the shrimps scavenging on the run.

But for first-class travel,

nothing compares to a jJet-propelled jellyfish.

Magic carpets also glide above the reef, in the form of flatworms.

Flatworms and nudibranechs don't have shells,

so draw on chemical warfare as defense.

Some eat toxic hydroids and anemones

and seduester poison in their skin,

which in turn makes them poisonous to any potential predator.

They advertise their toxicity with bright, bold colors and patterns,

which have conspired to make them incredibly beautiful.

They are as wild in character as they are İn appearance.

They have gills on their backs, sex organs on Their sides

and all of them are hermaphrodlites.

And some are fierce cannibals.

Trying to eat your lover during sex is not gulfte acceptable,

but snacking on a cousin İs fine.

Joining the sea slugs on the ocedan's floor are the sea stars.

Sea stars are often referred to as starfish,

but theyre not fish at all, theyTe echinoderms.

Echinoderms date back over 500 million years,

so predate the evolution of coral.

They have evolved into a wide range of life forms

and what many have in common is the spine.

Urchins are some of the most heavily spined of all,

but for some color-coordinated crabs and shrimp, this isn't a deterrent.

They've adapted to live amongst the spines

and remadin there oll their lives.

İf's a classic case of symbiosis on a reef and worlds within worlds.

Tropical ocedans are like vast blue deserts and largely nutrient poor.

On coral reefs, nothing goes to waste.

Various specialist filter feeders have evolved

to sift the passing currents -—

capturing, digesting and recyoeling every available bit of food.

Worms are among the most numerous and diverse of all filter feeders.

20,000 marine speciles exist

and, unlike the earth worms, theyre an exotic buneh.

Befitting their name,

Christmas-tree worms unfurl festive, feathery mouth parits,

which they use like tiny nets.

Their bodies, meanwhile, are buried in the coral and rarely seen.

Egually shy are ribbon eels.

They spend most of their time concedled in deep burrows,

with just their heads peeking oUrt.

They're relatives of moray eels

and their gaping mouths make them look aggressive.

But theyre simply breathing,

with their exaggerated nostrils sniffing for food.

Adopting the same lifestyle are garden eels.

These delicate seda serpenits rise from the sand İn vast communities,

performing their hypnotic Indian snake dance.

Ever watechful for predators,

they nervously pluck plankton from passing currents,

their tails anchoring them down.

Becduse of corals'longevity on cur planet,

they're considered our living fossils.

Another living fossil still with us today is the nauütilus.

İf's an ancient mollusk, whose line eventually dropped its shell...

«and gave Trise to the age of the cephalopods.

Cephalopods are synonymous with the reef

and one of the most intriguing is İhe mimic octopus.

As its name implies,

the octopus mimics the physical likeness and movements

of more than 15 different specles,

including sea snakes, İlionfish, flounder and ghost crabs.

İf's öne of nature's great confortionists.

Ifit doesn't want to be seen, it certadinly won't be.

Many species of octopus live in the vicinity of reefs

and a İrue reef speciolist is this -

the day octopus.

These octopus are grecat huünters and fish hurry to defend their eggs.

And being so tasty themselves,

octopus have had to develop excellent martial arfts skills.

They have the most complex brain of any iİnvertebrate

and can process İnformation from all eight arms at once.

They have short as well as long-term memory

and possess a specidal way to communicate with their skin.

They'e also highiy interactive and tactile.

Courtship rituals can last for hours,

with couples intertwining all 16 arms in a sticky embrace.

Once they mate, their bodies are programmed to die.

For some species, this means a lifespan of just 6 months.

For others, up to 5 years.

Cousin of the octopus İs the sauild,

seen here delicately laying eggs in forest fronds.

We know sagulid more commonly as calamarıi,

but despite being a favored delicacy around the world,

many species are increasing İn number.

Like other cephalopods,

theyre making the most of oceans depleted of naftural predators

and seem more resilient than others to changing water conditions.

Another charismatic member of the family is the cuttlefish.

These credtures have magicaol atftributes,.

On the outside, large eyes as expressive ds ouUr own.

On the inside, three hedcarts that pump blue blood.

During their breeding season, they gather in small groups,

zooming amongst one anofher like miniature spaceships.

Masters of jet propulsion,

they can move backwards, forwards or sideways with egual edase.

Every year they return to favorite nesting sites,

like this colony of venomous fire coral.

Males üuse dramatic body displays and postures

to compete for mating rights.

So although competition is intense, it's rarely physical.

Clutching her brood of eggs in her mouth,

a female surrenders her young to the care of coral.

The flamboyant cuttlefish is one of the tiniest cephalopods,

yet lives up to its name.

İts cuttlebone is too smolll to float, so İt walks more than swims.

And it has a highiy poisonous flesh, adverftised by its pulsing skin.

İF's also a deadiy predator.

Two specidlized tentacles dre contained within a muscular sleeve,

which is launched like a speor.

With this kind of hunting prowess, it's no wonder

the cephalopods have been such a success story on İhe reef

and will no doubt rüule the seabed for eons to come.

Reefs are not only İmportant to their permanent residenis,

but also to many oceanic visitors.

Strong currents and rich upwellings of food often occur around reefs

and attract nomads such as rays.

In fact, the total number of marine crecatures dependent on coral reefs

is immedasurable.

Perhaps as many as seven million species coexist here.

Over 4,000 species of tropical fish are associated with coral reefs,

of which 755 depend on the reef for their survival.

They may look like just colorful confetti,

but each fish is its own individual.

Fish can smell, hear, see and touch.

They feel pain and have complex relationships.

The vast majority of reef fish have defined home ranges.

The reef sustains them, houses them and concedals them from predators.

Like tiny kites on invisible strings,

the fish hover above their beloved reefs,

venturing only far enough to snatch a medl,

but otfherwise inseparable.

The connection between fish and coral

is öne of nafure's most enduring İlove stories.

Humans too benefit from a healthy relationship with coral

and the seas atlarge.

Reefs create barriers to the sea and protect shorelines.

Various life-saving medicines are extracted from reefs.

Ocean-derived chemicals are üsed to treat many illnesses,

including cancer.

Microscopic marine algae processes our atmospheric CO2

and produces /70X of the oxygen we breathe.

So, like these fish, we need hedalthy ocedans to survive

and reefs to secüre our homes.

In both our terrestrial world and the undersea,

there have been constant cycles of creation and destruction.

The rüle of natuüre is chaos.

Although a reef looks harmonious,

its as chaotfic as any other ecosystem.

And oöone of the ways to survive chaos,

whether you're above or below the surface,

is t© cooperate.

This cooperation is called symbiosis,

a mutudclly beneficial relationship

between two entirely different species.

These little blue and black striped wrasse would be perfect fish food

if they hadn't made themselves so usefüul.

They're cledner wrasse and edarn İheir keep by cleaning.

So vital is this service

that none of their grateful hosts WoUld ever dare to eat tThem.

Both parties benefit and a form of balance is achieved.

There is constant tension on the reef

as different speciles work oUt this balance

and İry to maximize their moment in history.

For some of the bigger fish,

that moment used to streteh into decades.

Some even lived for a century or more.

But old age is a rarity now

and İconic reef specles are vanishing even as we waftch.

Angelfish live for 10 to 15 yedcrs in the wild

and are some of the reefs most recognizable species.,

They are highly prized by collectors

and, tragicaoally, many live out their long lives in ağuaria.

A fish in a tank is like a bird in a cage -

we're dble to observe them but we getlittle idea of their wildness.

İf's only here, on the reef,

that we can truly appreciate just how complex a fish's life can be.

Some angelfish are promiscuous,

some bond forlife,

others have male-driven harems.

And marny fish, including these delicate leafed scorpionfish,

engage in long courtship rituals.

New species of fish are discovered every week,

and with each discovery comes a wedalth of new information.

Some spawn düaily,

others do not begin breeding until they are 20 or 30 yedars old.

Many start life as a male but die a female.

Most are highliy social

and have İnftelliğgence beyond ouUr comprehension.

Like wildebeest and zebra on the African plains,

tangs and parroffish often graze together.

Both fish are herbivores

and dine on algae and even İive coral.

Other species converge on the reef crest.

This area is exposed to wave action and lots of sunlight

and İs rich in nutrients.

Fish like this rock-mover wrasse

literally move rocks in the search of worms and mollusks.

Dining this way is hard work,

and they're notf always willing to share their patech.

Others excavate the substrate and swoallow large mouthfuls of sand.

Their bodies are specioally designed to filter the sand for algae,

dispelling waste through their gills.

Access to the reef crest is limited.

İf's only at cerftain tides and during calm seas

that if's possible to feed here.

When all the conditions are right,

fish arrive from miles around to take advantage of this rare opportunity.

Some are İn couples, others dine alone,

and completely different species feed side by side.

If's biodiversity at its best.

Eccentric earth-movers, like triggerfish,

also join the dinner parity.

They use their powerful beaks to cast aside whole chunks of coral,

as they search for cams,

shrimp and crabs.

Theyre much too busy to worry about their table manners.

Like a human city,

a reef boasts an eclectic Jumble of characters

conducting themselves in a varlety of ways.

There are loners and dlrifters.

There are clandestine meetings

and ünderground movemenits.

There are the watchful and The wary.

And different forms of self-expression.

As in all of our cities, strange alliances occur...

.and odd fashion is tolerated.

Every beduty and bedcast has its place.

Just like the terrestrial world, a reef has a 24-hour eyocle.

As the afternoon light begins to fade,

fish, like these anthias, spawn wifh abandon,

knowing that night will soon follow

and conceol their eggs.

Meanwhile, tiny fish shudder their bodies,

indicating their readiness to mate.

And countless other daytime fish are inspired by the waning light

to court or breedi.

Here, a pair of flutemouths engage in a seductfive sword dance.

İf's their form of foreplay,

and they've been at it for hours.

Over the millennia, the battle between predator and prey

has fueled an evolutionary arms race under the seda.

Mother Nature is always updating her designs

and making old ones redundani?.

Animals have had to constantly refine

their offensive and defensive capaobilities.

The result can be pure science fiction.

Angler and scorpion fish are as bizarre as they come.

They're expert mimics of sponges,

but have one of the fastest strikes on Earth.

But theyrTe certdiniy not oUt to win a beduty prize.

When it comes to some of these credtions, love is certainliy blind.

This myriad life has enthralled us since the beginning of human history.

We did originally evolve from the seda.

And ever since early humans first emerged,

we've been drawn back to İts shores.

Seafood has been a favored diet.

Shells have been our money and jewelry.

Coral limestone paves our roads.

Sand cemenits our houses.

Our myfhs and legends, books and films

are all full of characters derived from the seda.

And as light fades, these characters begin to change

and the story of coral moves into C very different narrative.

Big predatory fish cruise the reefs edge, searching for a final kill.

Daytime fish hurry into hiding.

This is a dangerous time of transition.

All across the reef, there is a changing of the guard.

The night shift has begun.

Little is khnown about oUr öocedins.

The surface of Mars is better mapped.

Most living coral reefs descend to only b0 meters or so,

due to the reliance on sünlight.

But the sedafloor falls to 11 kilometers in places.

This is whaf we call the abyss.

Night-time on the reef gives us d sense

of what this abyss might be like.

The inky black is very much oalive and full of aliens.

İn special places where reefs drop to great depth,

deep sea plankton rise to the surface

to hunt shallow water phytoplankton.

They travel hundreds of meters.

They number in their billions

and they repeat the journey every night.

İf's öne of the biggest migrations in the animal kingdom.

The chase of plankton-hunter and plankton-prey

triggers a larger chain reaction right across the night-time reef.

Baitfish snateh mouthfuls,

while basking stars emerge from their lairs

and extend wehb-like arms.

The water flashes with color

as the plankton frantically communicate with one another.

Coral is not an idle bystander.

The reef has become a waoall of mouths.

The true animal nature of corol is revealed.

Eguipped with polisonous harpoons and acid,

each polyp becomes a deadiy trap from which escape İs İmpossible.

Meanwhile, catfish eat on the run.

Parroftfish sleep with eyes wide open

or conceol themselves in mMuCcUsS cocoons.

Without torches, humans are blind at night.

Underwater, we'd barely know up from down.

But the üundersea hunters are not at all disadvantaged.

Instead of sight, they use vibration, electrical impulses

and chemical traces to find what they're affer.

Stone walls are, in fact, living stonefish waiting in ambush...

.while the sharp teeth of stargazers lurk benecath the muck.

İf's easy to swim towards danger without realizing it.

This anemone has become a serlal killer.

A lucky sguid escapes, releasing ink to cover its tracks.

A pipefish looks on,

as fish scatter and more fall victim.

Down on the seabed,

scavengers collect the scraps...

.while lionfish use their long spines to herd unsuspecting prey.

There is activity in all directions,

as night hunters of every description eat therr fill.

The anglerfish is back and now completely in its elemenit.

İt may not move with grace,

but that doesn't affect its chances for a kill.

All if needs to do İs wait for a meal to come to İts mouth.

When ift comes to nocturnal hunting,

moray eels are known for their viciousness.

But other killers are not so edasy to spot.

Mantis shrimp are sophisticated and savage.

They're armed with supreme eyesight

and actively hunt live prey

while other ecrustaceans, like lobsters,

scour the seada floor for leftovers.

With a busy time ahead,

day fish try to sleep despite all the activity.

Some drrifting like ghosts in the dark.

The anemone fish are also trying to sleep, but aren 't finding it easy.

Their flat-mates, the dotted crabs, are enjoying a midnight snack.

Some of the most active night prowlers are shells.

Many of us only know them from shell shops or dead on the beach.

But shells alive are much more precious -

9ypsy caravans, varnished by the ocedans, constantiy on the move.

Darkness also suits courting mandarin fish.

They have an unusuüdlly high sex drive

and can spdwn every night if the urge takes them.

Although our ünderwater lights give us a glimpse,

we still khnow very little about what happens on a reef at night.

And our unwarranted fears have made İt harder to learn.

Our attitude to the sea has been full of contradiction.

On the öne hand we've reveredi İt,

on the other we've seen İt as an enemy -

dark and unfathomable, full of dragons and monsters.

These monsters of the deep

have long been proven figments of our collective imagination.

But some believe they still exist in the form of sharks.

How wrong they are,

These magnificent creatures predate dinosdurs.

Like coral, they've survived several mass extinctions

and have played an eduüdcllİy vital role in shaping ocedn evolution.

Sharks have been roaming our seas for over 400 million yedars.

Fossil records show that thousands of species have come and gone,

of which 370 are with us today.

They can be found worldwide,

with many dependent on coral reef ecosystems for protection and food.

As top predators,

sharks have influenced adaptation and evolution

all the way down the food chain.

But, contrary to popular myfth,

sharks are not just instinctive eating machines.

Many species exhibit powerful problem-solving skills

and their brain-to-body-mass ratio is similar to MAaNy MAMMAIİS

and other higher order vertebrates.

So they are as intelligent, curlous and socldal

as some of our more favored animals.

They nof only possess the 5 senses we do -

sight, hearing, touch, smell and taste -

but can also perceive electrical currents

and magnetic fields.

If we're in the water with them,

they can detect our presence from miles away.

They can monitor the bedating of our heart...

«and read our Moodi..

When it comes to humans, they are normally cautious creatures.

Whenever possible, they avoid us.

With good reason.

Every year, over 100 million sharks are killed,

the majority just for their fins.

Their fins are a traditional ingredient in Asian soup

and their value rivals caviar.

The sharks are offten finned oalive

and thrown back into the water to drown.

One third of all öopen-ccean shark species are now facing extinction,

primarily due to over-fishing.

So if there is a killing machine in ouUr seas, İt's not them,

İf's Uus.

No shark is safe,

not even the biggest of them all, the whale shark.

Up to 15 meters long and 12 tonsin weight, they're an impressive sight.

But theyre sirictly filter feeders and dine mostly on plankton.

Unbelievabiy, they are also victims of illegal fishing.

Whale sharks are not actudally whales but sharks.

True whales that visit the reefs inelude these, the minke.

Incredibly, these graceful animals are still being harpooned.

What trust they show us, regardless.

Before we began to plunder the seas, this is what they were İike.

Linking the abyss with the surface,

layer upon layer of shimmering silver.

A big sechool of fish is a defining image of a heolthy sedc.

İf's a show of strength and incredible physiological adaptation.

Running head to tail in most fish

İs a row oOf scales known as the lateral line.

Connected to nerves in the brain,

this line consists of specidcalized cells

that are sensitive to wafer displacement and movemenit.

Meanwhile, fishes' eyes are located on the sides of their heads

to make İf easy to see where they are in relation to one another.

So, vision helps maintain angle and distance between fish,

while the lateral line dictates speed and direction of the entire school.

In this way, many fish can move as one

and choreograph their own adudtic ballet.

Many fish school as juveniles

and around half of all fish species form aggregations

at some polnt İn their lifecyoele.

Even fish that prefer their solitude join a school from time to time.

Barracuda hunt on their own at night

but hang out in packs during the day for protectlon and company.

With their pointed hecads and streamlined bodies -

up to 2 meters long -

they fiy in unison through the blue like polished arrows.

Sechooling makes it hard for a predatfor to focus on one target

and is a great defense mechanism.

İf's also a force to be reckonedi with when it comes to feeding.

Few plankton in the areca will escape this sweep of open mouths,

as İhese rare filter-feeding mackerel make their coordinated attack.

Over the eons, the art of schooling has helped fish in many ways.

But now, ironically, it contributes to their downfall.

Just öone net can collect a ton offish at once.

And over 100 million tons of fish are havuled from the oceans each yedr.

For the few big schools left,

it must feel guite eerie moving through so much empiy liguid blue.

These days, one ofthe only safe places for schooling fish

is a marine sanctudry.

Whenever sanctuaries have been established and policed,

fish stocks have slowly increased,

helping to restore biodiversity.

A süccessful sanctuary becomes a precious time capsule...

...G reminder of how rich the seas öonce were.

And could be again.

Unlike a zoo, a marine sanctuary has no waolls.

So it has the capacity to not only replenish the immediate dreda,

but the oceans around İT.

Because we have İndividual names for oUur oceans

and have territorial borders,

we forget that there's only one system.

There is only one sea.

Water, covering 706 of our planet's surface, connecis us doll.

Whaft occurs even in our polar regions will eventually affect coral.

And,, conversely, each new marine sanctudary is another powerful step

towoacrds saving OUr seas.

And when you consider

that the global ocean makes up 995 of the living biosphere of the planet,

every step counts.

Because reefs are such important breeding grounds

for so many marine creatures,

this İs where a new future might lie.

Renewal here is a daily affair

and brings with itf magical transformation.

Here, a coral cod blushes a different color when wooed by iİts mate.

A thriving reef is an agğudatic radinbow,

And like the skin of the coral cod,

these colors have medaning and function.

Silver scales reflect light

and allow fish to blend into their watery backgrounds.

Bold, strong colors allow fish to recognize their own species

İN A Crowdl.

Color also indicates whether a fish is a juvenile or adult,

and some fish change color Aguite radicoaliy as they mature.

Once fish are palred up,

they can then use body posturing and color displays

to communicate their intentions.

A maoale parrotfish erects his dorsal fin to intimidate other males

and impress a nearby female who happens to look completely different.

And all across the reef, fish are on the lookout for a chance to mate

and pass on their precious genes.

Most seda creatures have short, intense lives compared to ours.

For some fish, a few years constitutes an entire lifetime.

So every good day on a reef is truly great.

A good decade is even greater,

the chance for countless marine creatures

to live their lives to the fullest

and give rise to new generations.

In the güuest to sürvive in these tropical seas,

animals have had to be highly inventive

and sometimes nature's own ruüles are broken.

Consider the seahorse.

These mystical creatures come in dll sizes.

Some bigger than your palm, others as small as your fingernail.

The daintiest of them c is the pygmy seahorse,

whose life is completely bound to gorgonlan coral.,

The extended seahorse family consists of 320 specles,

and includes pipefishes, pipehorses and sea dragons.

In most speciles of pipefish and sedhorse,

its the male that broods the young.

İf's not just this unusuUaAl parenting that sets them apart.

They have eguine heads,

prehensile tails...

and bony body plates instead of scoales.

Despite their dragon appearance, many fish like to eat them.

So not being noticed has become Their speciolity.

Ghost pipefish are expert mimics of other animals and plants,

including crinoids and corol.,

Their predators find it hard to see them

and so does their prey.

They spend most of their lives upside down,

focused İntentiy on the sandy bottom,

searching for the tiny crustaceans

that are their principal food.

So specific is their camouflage

that pipefish rarely wander far from a particular habitat

and perfect their mimicry down to the finest detall.

Other species concedl their true identity

by moving like eddies and currents.

While some pretend to be sand-encrusted sticks

or fallen leaves...

...Or pleces of algae.

If you know how to look, the masters of disgulise are everywhere.

In this underwater Garden of Eden,

even the snake turns out to be a fish.

Down on the seabed, deception is commonplace.

Individual reefs are often connected by areas of sand and rübble,

and this is where the so-called 'bottom dwellers' dwell.

The most numerous of these are the gobies.

There are over 2,000 species of goby,

making them one of the largest fish families.

Few of them grow bigger than your finger,

which makes them a favored food for many large predatory fish.

So theyrre always on the lookout and never far from the seabed.

They spend most of their days feeding,

filtering sand through their gills to extract tiny food particles.

Sand is everyithing to the goby.

Sand puts food in their belly

and also a roof above their heads.

Many gobies build burrows.

İts tiring excavation work,

and partners sometimes dont agree on whose turn İT is.

If the domestic argument can't be worked out,

then this species, camouflaged as big eyes,

can always go for a stroll to smooth things over.

Some clever gobies have enlisted the services of a slave.

İn a most extraordinary parfnership,

gobies and blind shrimp live together, bonded by mutual need.

The shrimps excavate a burrow in which the gobies can hide,

and they eat the göobys seraps.

The gobies act as sentinels, warning the shrimps of approaching danger.

The fish and crustacea have such a close working relationship

that they're always connectedi,

by tail or fin or feeler.

For fish close to the bottom of the food chdin,

a safe home base İs essential.

Space is limited and good reoal estate hard to come by.

Trespassing isn't tolerated.

Territorial disputes are normally gulck to work out.

But not always.

There's definitely no point picking a fight

with this mighty armored beast.

If's the crown-of-thorns starfish, corals' mortal enemy.

By disgorging their stomachs and drenching polyps with acid,

they eatliving coral and suck the life out of a reef.

The starfish play an importan 't role,

clearing space and fostering biodiversity.

And few have stood in thelir way.

The starfish have always been a natural part of the eycle.

But now the eycle is unnatural.

Agricultural pollution has increased nutrients in the water,

which in turn causes algal blooms.

Starfish juveniles are feasting on this algae

and many more are surviving into adulthood.

Plagues of crown-of-thorns starfish are now regulariy experienced

on reefs worldwide.

But not all infestations are bad news.

A perfect example is the unlikely allıance

between the edared sponge and the pink sed cucumber.

This sponge is highly toxic to most.

But the seda cucumber has adapted to live here in huge numbers,

rising off the edges to spawn.

This is an inhospitable habitat where credatures are Tthriving.

Perhaps it offers hope for life in our changing seas.

İf's certadinly proof that anything is possible.

The ocednic world is ever changing.

Nothing stays the same here for more than a moment.

Over the ages, corals have come and goöne.

Today, they are disappearing agdin.

But what sets this cycle apart from any other in geological history

is the presence of us.

For the first time in corals' existence,

humans are having a direct impact on İhe ocean's chemistry

and corals' destiny.

Many scientists believe

we are heading towards ouUr next mass extinction

and that humans are the cadüse.

Reef-building corals are now seriousliy endangered.

And as reefs disappear,

hundreds of thousands of dependent credatures disappear with them.

Furthermore, the demise of coral reefs is a clear indicator

that our ocedan İs dying,

and oUr öcedan İs our planets life-support system.

The only way to save our ocean

is to radically curb our CO2 emissions

within the next one or two decades.

We have all the tools to do İt.

And if we succeed, we will not only save our reefs,

we will ultimately save ourselves.

The future of coral, and how this story ends,

is Uup to Us.