All language subtitles for Z01

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.

[♪]