Original subtitles

A jewel glistens at the southern end of the Great Barrier Reef.

One island stands at a crossroads

of coral and currents.

A place where life is on a collision course.

Its waters are full of dangerous beauty and strange partnerships.

Prodigal daughters perform secret rituals

that pit their babies against the longest of odds.

Giants roam the seas,

and life explodes at the bidding of moon and tide

at this hub of creatures, great and small,

called Lady Elliot Island.

[♪]

[Waves breaking]

It's November, early summer in Australia,

and Lady Elliot and its reefs are buzzing with life.

It's the start of breeding season.

Seabirds are courting and building nests

in all manner of precarious places.

It's also the start of the breeding season

for green sea turtles.

Just offshore, a female is making her way to the island.

She's not alone.

Dozens of female sea turtles are gathering at the reef's edge.

She is heavy with eggs.

After wandering the open ocean,

she's found her way back here

to the very same beach where she was born.

Females don't start reproducing

until they're about 40 years old.

So she would have spent at least four decades

wandering the open ocean before coming back here to breed.

No one knows exactly when or where she mated,

but she's capable of storing sperm from different males

for a number of years,

so that she can self-fertilise and develop eggs

in her own good time.

In this way,

she can produce five to seven clutches of eggs a season

without mating between each laying,

and even store sperm long enough

to fertilise clutches for future years.

She's already fertilised her first batch of eggs,

which are developing inside her

in preparation of laying.

Males, distinguished by their longer tales,

pursue females for a chance to mate again.

But once the females have started to produce egg clutches,

the males leave the island's reefs

and head sometimes hundreds of kilometres away

to their favourite foraging areas.

The females are left behind, pregnant, hungry,

and with an exhausting and protracted laying season

ahead of them.

Now she, and others like her,

have gathered to wait for the right night to come ashore

and lay their eggs.

She's weightless in the water,

but her 150 kg body will require a gargantuan effort

to move on land.

So she waits for assistance from the incoming tide,

and for darkness to fall.

As the green sea turtles prepare,

the island is in a frenzy of bird breeding activity.

Almost the entire 45 hectares hosts seabirds of some sort.

Some in newly constructed nests,

and others, in last year's recycled ones.

Like the turtles, many have just arrived on the island

for summer breeding.

Sitting at the southern extremity

of the Great Barrier Reef,

just south of the Tropic of Capricorn,

Lady Elliot Island is a true coral cay.

Built from coral, rubble, sand, and shells,

tossed up by currents, tides and waves,

separated from mainland predators,

and surrounded by a sea full of fish,

it's attractive to both nesting sea turtles and migratory birds.

[Birds chirping]

It's still early in the season,

but some black noddies have already paired up

and are busy with nest building...

while others are still courting and mating down at the beach.

Privacy can be hard to come by.

Despite the interruptions, the young lovebirds persist,

intent on creating a new generation.

They are first-time nesters

and will spend the next few weeks on the important tasks

of nest site selection and construction.

Birds who arrive early get their pick of the real estate,

but couples don't always agree on the housing options.

Most prefer the casuarina trees

on the leeward side of the island,

away from the frontline of cyclonic winds and storms

that batter the island almost yearly.

They tend to nest on sturdier branches close to the trunk.

While she works on the foundation,

he heads off to the Pisonia forest

in the centre of the island

in search of nesting material.

Up to 20 metres high,

the Pisonia trees are the tallest on the island

and form a dense, shaded stand.

They are highly sought after for nesting.

It's compact living here with as many as 42 couples per tree.

This first-time homeowner is here for the Pisonia leaves

that litter the forest floor.

And not just any leaf will do.

Moisture content and size matter,

and for this male, bigger is better.

When in short supply in the forest

more leaves can be found at the shoreline.

But some prove difficult to manoeuvre in the stiff breeze.

They cement the leaves together with their droppings.

There's urgency in the construction business now

as the cyclone season is drawing near

with its winds of 80 km/h.

It's a race to lay their eggs and fledge their chicks

before the destructive forces of nature hit the island.

With more than 30,000 pairs of black noddies on the island,

demand for nesting material runs high,

and those running behind schedule get less choosey

about their building supplies.

After a solid day of home construction and fishing,

couples reunite and retire for the evening.

The ruckus chorus

of some 90 different feathered varieties settles into silence

as darkness descends.

Under the pull of the full moon the tide is at its highest

and the giantess appears on the shore.

She must haul herself far enough above the tideline

that her eggs will not be washed away.

As if on autopilot,

she methodically scoops out a deep egg chamber

using her hind flippers as shovels.

She then begins to lay her clutch

of about 150 billiard-ball sized eggs into the chamber.

While in most animals genes determines their gender,

the sex of young sea turtles

is decided by the temperature of the sand

in which the eggs are buried.

Summer sand temperatures here for the next few weeks

will be between 28 and 30 degrees,

meaning this first clutch will hatch

as a mix of males and females.

Lower than 27 degrees would mean all males.

Higher than 31 would mean predominantly females.

During this process she weeps actual tears

that excrete excess salt

and protect her eyes from abrasive sand grains.

After depositing her last egg,

she fills in the chamber with her hind flippers, taps it down,

and tosses loose sand over the nest

to conceal it from predators.

The three hour ordeal over,

she turns back

making the most of the remaining high tide

to return to the water.

There she'll rest and recuperate for a week

before spending three days fertilising

her next batch of eggs with her stored sperm.

Within two weeks,

she will be ready to lay again.

It is a sequence that she will repeat at least five times

over the summer.

The reproductive effort over the summer is so demanding

that she can only undertake egg laying once every few years.

The black noddy couple has completed its nest

and has successfully laid a single egg,

which they'll incubate for the next 30 days.

The parents take turns heading out to fish offshore.

Once his gullet is full,

the male heads back to the nest with takeout.

The female has been waiting patiently

while attending to the egg.

So he delivers her supper directly into her waiting beak.

Living within a crowded colony comes with some downsides,

such as lice.

The couple preens meticulously

to rid each other of annoying parasites.

Other terns

have a far greater annoyance than lice to contend with,

silver gulls.

These marauding gulls stalk colonies

looking for opportunities to attack eggs and chicks.

The greater crested tern nests on the ground

in the open grassing areas

on the northwest side of the island.

In some years, when the fishing is good,

their numbers swell,

shrinking again when fish stocks are poor.

Bachelor male terns choose their nest sites.

Squabbles over turf break out everywhere

in the close quarters.

The females, however, are welcome.

Courtship involves some simple head raising

and gracious bowing.

A ritual that the young couples repeat, even after egg laying.

Most pairs lay a single egg, occasionally two,

and the couple takes turns with the month-long incubation

while the other is fishing.

They have to be constantly vigilant as their arch nemesis,

silver gulls, skulk around the edge of the colony

waiting for any opportunity.

Gulls kill more than 20% of eggs and chicks

in crested tern colonies.

They're also brazen thieves,

stealing up to half of all the fish

the terns bring back to the nest.

In defence, the terns form a feathered fortress on the edge,

stabbing their beaks and squawking their disapproval

at the pillaging gulls.

The constant harassment causes chaos among the colony.

And it's not only the gulls the terns have to be alert for.

While the island is free of mammalian

and reptilian predators,

along with the gulls,

rails and egrets pose the greatest threat

to eggs and chicks.

But synchronised nesting en mass

means more eyes on the lookout for invaders.

As the only tree nesting terns,

the black noddies are relatively safe

from the marauding predators,

but their ground nesting relatives

have to be ever vigilant

and tag team guarding their eggs and chicks.

Rather than nest in dense colonies,

bridled tern couples lay their eggs

tucked under shrubs and coral rubble.

This one has chosen the forked base of a casuarina tree.

With this woody fortress on one side,

at least the parent doesn't have to watch its back

but chicks do.

Ever protective parents don't tolerate the presence

of other chicks.

This week old bridled tern has wandered too close

to an aggressive parent on egg guarding duty

and the adult chases it off in no uncertain terms.

With its own parents perhaps lost at sea,

the chick eventually finds a tolerant foster carer

still incubating its own egg.

Yet, its chances of survival are slim

without its own dedicated parents.

The parental relay of egg incubation continues nonstop

for four weeks.

Vigilance usually pays off for bridled terns

with more than 70% of their eggs hatching successfully.

Bird density reaches its peak in summer

when the island and its surrounding waters

support more than 50,000 individual breeding seabirds.

Collectively, these thousands of seabirds

excrete tonnes of phosphate-rich guano,

or droppings, every year.

Lady Elliot Island

was once so rich in this valuable bird product

that it was intensively mined for fertiliser

in the early 19th century.

Guano miners first appeared on Lady Elliot in 1863

and remained on the island for a decade.

The destructive practise

of extracting the guano from the soil

scraped away about 90 cm of surface soil

and denuded all the vegetation on the island

except for eight remaining Pisonia trees.

Those surviving Pisonia trees propagated and flourished,

and once again bring shade to the centre of the island.

They have the birds to thank.

Their guano put some 10-20 tonnes of nitrogen

per year into the aquafer,

and the Pisonia trees feed from that ready supply

of the liquid fertiliser.

But there is a dark side to this relationship.

These flowers seem innocent enough now,

but they'll take a sinister turn in the next few weeks.

It's the height of summer,

and two weeks since the female turtle last came ashore to lay.

Her second batch of eggs

is almost ready to be laid

and she has company in the lagoon.

The rising temperatures and longer days

invite blotched fantail rays to also gather for breeding.

The males outnumber females as the jostle for mating rights.

But this female is already pregnant

and brooding her young ones inside her.

It will be another six months

before she gives birth to live pups,

which hatch from egg capsules inside her uterus.

By this time, they will be fully independent.

By mid-summer, air temperatures reach 40 degrees

and UV radiation is at its highest.

Corals have evolved a clever defence.

When exposed by the low tide,

they excrete a sticky mucus that acts like a sunscreen.

The mucus also traps nutrients

that are carried into the lagoon with the outgoing tide.

As a new day dawns,

the female turtle has completed

laying her second clutch of eggs.

This time, on an exposed part of the high dunes.

With the advance of summer, and without shade,

the sand temperatures here are already 32 degrees Celsius.

So this clutch of about 150 eggs

will likely produce mostly females.

She returns to the water

in preparation for yet another brood of eggs,

her third for the season.

Some of the island's tern chicks have begun to hatch.

The parents need to make ever more fishing trips offshore

to provide for them,

sometimes leaving them vulnerable to rails and gulls.

With its parents gone, this bridled tern chick

becomes as inconspicuous as possible.

One parent still hovers protectively above.

Away from the frenzied activity in the Pisonia forest,

a week old vulnerable red-tailed tropicbird chick

waits silently for its parents to return.

Sleeping the hours away

conserves energy that can be invested in growth.

Though simple,

its nest scrape was carefully selected by its father, out of the direct sun.

A prowling buff-banded rail considers its chances

against the chick's already formidable beak

and decides against it.

It's now early January, the summer solstice has passed

and turtle nesting is at its peak.

Each night, hundreds of mother turtles

take advantage of high tides

to make their way up the beach.

Among them, the female who has already nested

twice this season.

Further down the beach, under the casuarina tree,

her first clutch of eggs is beginning to hatch.

They're a mixed male and female clutch.

Around 5 degrees cooler and they would have all been males.

Early morning sees the sandy beaches erupt with hatchlings.

They begin a race to the sea,

a race for their lives against long odds.

The little ones are utterly defenceless.

It's a massacre.

Of the some 20,000 hatchlings

that will emerge from these sands,

only about 50% will survive the first 24 hours of their life.

If this hatchling can survive its journey

beyond the reef edge, out into the Pacific,

it could be the 1 in 1,000 that makes it to adulthood.

There is a force present just offshore

that could whisk the hatchling away from the perils

found here on Lady Elliot's reefs.

The East Australian Current, or E.A.C.,

draws warm water south from the tropics.

Travelling up to 7 km/h,

it's one of the fastest currents in the South Pacific.

It transports a staggering 40 million cubic metres of water

each second.

The current is almost 100 km wide

and more than one and a half kilometres deep.

It's this massive conveyer belt

that will carry the hatchlings to relative safety,

away from the predator-rich waters of the reef,

and south into the heart of the Pacific.

For the next 10 years, they're cast adrift in the open ocean

in what's known as the lost years,

before they return to the rich feeding areas

along the Great Barrier Reef.

Survival on the island is a numbers game.

Like the turtles, seabirds suffer high casualties.

It's now early autumn,

and a series of storms have ravaged the island.

The eastern side has taken the brunt of the winds,

dislodging trees

and chicks and eggs from their nests.

Some of the adults have also suffered.

The rookie black noddy nesters have survived,

but their precious egg has been blown to the ground,

destined to be scavenged by gulls before nightfall.

The noddy breeders

who sheltered in the Pisonia forest in the centre of the island,

have been least effected by the storm.

But nesting here poses other perils.

The Pisonia tree is also known as the catch bird tree.

At this time of year, its seed heads mature into sticky fruits

that entangle themselves in feathers.

Doomed never to fly again,

this bird's body will become a drifting raft

for the seeds of the treacherous tree.

Swept up in strong winds,

the seeds hitching a ride on the bird's carcass

can be transported to nearby islands

where they'll germinate and colonise new territories.

The tropicbird chick has also weathered the storm

under the watchful eyes of its parents.

It's still transitioning from down to flight feathers.

One parent has returned with a gullet full of fish

and none too soon for the hungry chick.

A passing buff-banded rail gives them a wide berth.

The parent's beak is sharply pointed,

it's lined with serrated edges for holding onto slippery fish

and is equally capable as a defensive weapon

against unwanted prowlers.

While elegant in the air, tropicbirds are less so on land.

Their legs and feet are set far back on the body,

and ideal centre of gravity for aerial manoeuvres

but too far back to support the bird in an upright position,

which limits movement on the ground

to an awkward shuffle.

Gaining roughly 15 grams each day,

the tropic chick still has more bulking up to do

before it's independent,

and it's constantly hungry.

To keep up with the chick's demands,

both parents need to fish,

even in stormy seas and inclement weather.

The cyclones that pound the island almost yearly,

also leave casualties on the ocean floor.

The reefs that surround Lady Elliot

can be as treacherous as they are beautiful.

Their jagged limestone structures

have long posed a danger to seafarers.

In 1999, this steel hulled yacht was sunk in a fierce storm.

In less than two decades the reef has already reclaimed it.

It's encrusted with algae and festooned with soft corals.

These sedentary organisms in turn

attract a host of pelagic life.

It's a popular hangout

for schools of surgeonfish and sweetlips.

With her body tucked into the coral,

safe from buffeting winds and waves,

the female turtle is now ready for her fifth

and final ascent to the island's shores.

It's been four months

since she laid her inaugural clutch of the season

with her first hatchlings

already swept away in the East Australian Currentto an uncertain future.

She can do little else to ensure her species survival

other than continue her mission.

She lives alongside the very creatures who eat her young

and share the same imperative to breed.

The streamlined brass striped barracuda

can swim in bursts of speed reaching 40 km/h,

easily hunting down turtle hatchlings.

But here in the open lagoon,

they revert to a classic ambush strategy,

stealthily stalking smaller fish,

crustaceans, squid, and other unwary prey.

The island's blacktip reef sharks swim in

with the incoming tide.

With plenty of turtle hatchlings on this month's menu,

they stick close to the inner reefs

where the hunting is easy.

Today, they have company.

A bottlenose dolphin is also fishing

and has a school of jacks in its sights.

Though it seems more intent on fun than food at the moment.

[♪]

The warm East Australian Current that races passed Lady Elliot,

doesn't carry the nutrient payload

typical of cold currents and upwellings.

But the coral reefs here remain vibrant

with most creatures finding what they need

in their own self-contained neighbourhood.

Garden eels poke their heads out

to feed on the plankton floating in the local current.

Only half of their graceful bodies rise up from the sand,

the other half remains safely lodged in a subterranean tube

cemented by their own mucus.

They make a quick retreat at the first hint of danger,

and they have much to fear from the dash-and-dot goatfish.

Each goatfish is armed with a pair of long chin barbels

that detect chemicals and vibrations.

They riffle through the lagoon floor

in search of worms and crustaceans.

Their digging flushes out startled prey

that appeal to other fish as well.

Opportunists, like these bigeye seabream

reap the benefits in what's known as shadow feeding.

Coral reef systems are a web of complex relationships,

and the sea cucumber can lay claim

to one of the most bizarre.

There are more than 1,500 different species

of sea cucumber

And while they differ in size, texture, and colour,

they're all bottom dwelling, slow moving creatures.

They lumber their rotund bodies across the sea floor

sucking up the sand through their mouths,

extracting the detritus and expelling the left overs

through their anus.

Remarkably, they also breathe through their anus,

and that's where this little fish has spotted an opportunity.

The pearlfish sniffs around the sea cucumber,

waits until it opens its anus to breathe

and darts into the cavity.

The pearlfish hides out

in this clever hiding place during the day

well-protected until it's time to make its feeding forays

in the evening.

Remarkably, the sea cucumber doesn't seem to mind

this strange relationship one bit.

Many of the reef relationships are mutually dependent,

or at least beneficial for both.

Clownfish have a symbiotic relationship

with the anemones they call home.

The anemones tentacles are armed with stinging cells

that fire off at intruders,

but the clownfish are covered in a protective mucus

and are immune to the stings.

While the anemone is the protector,

the clownfish returns the favour by cleaning its host,

providing nutrients in the form of waste,

and scaring away predatory fish.

And there's no better way

to ensure your value and survival

than offering a service that's always in high demand,

like cleaning.

These predatory sweetlips are gathered here

to seek the services of a pint-sized fish

that would normally be bite-sized.

Seven centimetre long striped cleaner wrasse

set up dedicated service stations in fixed locations,

so their customers know where to find them.

Reef dwellers of all shapes and sizes

come to these cleaning stations

to have their parasites and dead skin removed.

So deeply coevolved is this relationship

that the customers switch off their predatory instincts

while the cleaners go to work.

Business is brisk year round regardless of the season.

But business is just about to upscale.

The manta rays are coming.

Most of the year, they feed in deep, nutrient rich waters

further offshore.

But as autumn progresses into winter,

the depths get too chilly

and they move to the island's balmier shallows

where they expend less energy keeping warm.

[♪]

The giant rays survive on the smallest of organisms, plankton,

filtering huge amounts through structures in their gills.

Between their low tide feeding sessions

they visit the cleaning stations

to keep their massive gill rakers in peak condition.

In some years, more than 450 individual mantas

gather here for their winter break.

With a wing span of three to five metres,

they fly through the water with ease.

Lady Elliot is the largest known manta aggregation site

off the east coast of Australia.

As the water warms a few degrees with the onset of spring,

most of the mantas set off for deeper, cooler waters.

The female turtle

has also left her Lady Elliot Island nesting grounds and travelled hundreds of kilometres to foraging areas

at the northern end of the Great Barrier Reef.

Here she nourishes herself on sea grass

and recovers from the exertion of breeding.

While reef activity underwater continues to hum

throughout the spring,

above water, Lady Elliot Island is relatively serene.

Spring is the driest season on the island

with plentiful sunshine.

The migratory seabirds have left.

And the permanent residents now have the island to themselves.

Reef egrets patrol the shores and shallows.

They come in two colour forms, white and dark grey,

but are the same species.

They're ambush hunters, hunching their wings like caped crusaders

to confuse their prey with the shadow they cast.

Hunting by day or night,

egrets use the low tide to their advantage,

which traps prey in the shallows for easy picking.

[Thunder rolling]

By early summer, the rains return.

And some of the breeding seabirds come with it.

The water temperature has warmed a few degrees.

Lunar forces are having their way

with the tiniest yet most influential reef creatures

of all,

the coral polyps themselves.

Colourful, single-celled algae called zooxanthellae

live inside the coral's soft tissue.

By day, powered by the sun, they photosynthesize.

These algae also facilitate

the coral's ability to produce calcium carbonate,

which gives the corals their ridged structural support.

But by night, the polyps reveal their alter ego.

They transform into carnivores armed with stinging tentacles

that harpoon miniature prey.

Not quite as immobile as one might think.

They also engage in turf wars

with neighbours of other species.

Polyps go tentacle-to-tentacle against other species

to protect their patch of reef.

They project string-like structures,

which can attack and ultimately digest

their rivals.

Tonight, under the full moon,

something is brewing inside each polyp.

Brightly coloured bundles of coral eggs

have reached the final stages of their reproductive development.

Like some kind of magical recipe,

water temperature, day length, tide and salinity align.

Then on cue, thousands of tiny egg-filled balloons burst free.

On this one night in December,

as has happened here for thousands of years before,

millions of polyps synchronise their spawning.

The lipid filled eggs float quickly to the surface

where they're fertilised by the free swimming sperm

that have also just been released.

They develop into tiny free, swimming larvae,

which settle on the sun-drenched reef

and become new sedentary polyps.

The corals have waited a year

for these few special summer nights

to play their part

in replenishing the largest living structure on Earth,

the Great Barrier Reef.

Lady Elliot Island may be the tiny last gem

on the necklace of the reef,

but this little island has a giant role to play

in the lives of her many spectacular inhabitants

and visitors.

A host to the deeply endangered and the profligate plenty.

A stage for strange relationships

and mighty massacres,

a hub of drama for creatures from far and wide.

There's no place quite like Lady Elliot Island.

[♪]