Planet Earth (2006) s01e09 Episode Script

1
Our planet's continents are fringed
by shallow seas.
Rarely more than 200 hundred meters deep,
they lie on the continental shelves,
which may stretch sometimes
for hundreds of miles
before the sea floor drops into
deeper darker waters.
All together, they constitute
a mere 8% of the world's oceans,
but they contain the vast majority
of it's marine life.
A male humpback whale sings
to attract a mate.
The whales have just returned
to their breeding grounds
in the shallow seas of the tropics.
The calf is no more
than a few weeks old.
Despite being 3 meters long
and weighing nearly a ton,
he is nonetheless vulnerable.
but his mother watches over him,
and, as he begins to tire, she
supports him close to the surface
so that he can breathe more easily.
These shallows around the equator
are excellent nurseries.
They're warm, calm, and contain
very few predators.
The playful calf is now drinking
500 liters of milk a day,
but his mother must starve.
There is nothing for her to eat here.
Like many tropical shallow seas,
these crystal clear waters
are virtually lifeless.
They receive year round sunlight,
but they lack the nutrients
essential for the growth of plankton.
The mother will be trapped here
for the next 5 months
until her calf is strong enough
to make the journey to the
feeding grounds, near the poles.
Coral reefs are oases
in a watery desert.
Most tropical shallows are barren,
but these coral havens contain one-quarter
of all the marine life on our planet.
Reefs are the work of polyps,
tiny colonial animals
like minute sea anemones,
yet the great barrier reef is so big,
it can be seen from the Moon.
It's actually 2,000 separate reefs
that together form a barrier stretching
for over a thousand miles
along Australia's northeastern coast.
Despite it's vast size,
this reef does not contain the greatest
variety of marine life on the planet.
For that, one must travel north
to Indonesia.
There are individual reefs in Indonesia that
contain almost as many kinds of fish
as live in the whole of the Caribbean.
There are also 10 times the number
of coral species.
Corals thrive in these waters with the
help of microscopic plants, algae
that grow within the tissues
of the polyps,
and the polyps feed by snaring passing
morsels with their tentacles.
At night, the algae are inactive but then,
the polyps put out even more tentacles,
so coral in effect
feeds around the clock.
This well balanced alliance brings
benefits to both polyps and algae,
and between them, they turn the
barren seas into rich gardens.
The Indonesian reefs contain
such a variety of life
because they lie at a giant crossroads.
This is the meeting place for different
seas the Indian Ocean and the Pacific.
Here, everything demands a closer look.
On the surface of this sea fan, there
are two polyps that are not polyps.
They're pygmy sea horses, the world's
smallest, less than 2 centimeters high.
They are males, settling a territorial
dispute, by head butting.
An electric flash?
No, the display of a file clam.
Perhaps this extraordinary pulsation
of the clam's fleshy mantle
is a warning to frighten away nibbling
fish, but no one really knows.
And there are snakes here, too,
lots of them.
These are banded sea crates.
They lay their eggs on land,
but they hunt here in the water.
They're too slow to catch fish
in a straight chase,
so they seek prey that is hiding
in the nooks and crannies of the coral.
Their bite is highly venomous
and paralyzes their victims.
And on this reef,
the snakes do not hunt alone.
Shoals of yellow goatfish and trivali
are seeking similar prey.
And they attract the snakes' attention.
As one group of hunters searches the reef,
they're joined by the other.
At least 30 snakes
have now joined the caravan.
The big fish scare the prey into cracks
and there the snakes can catch them
And anything fleeing from the crates will swim
straight into the mouths of the waiting trivali.
There's nowhere to hide.
As the raiders scour the reef,
more and more snakes join the hunt.
This cooperation between snakes
and fish, spectacular though it is,
has only recently been observed,
for it only happens on the most
remote reefs in Indonesia.
Perhaps such hunting alliances
were once a common sight,
but today no more than 6% of Indonesia's
reefs are in their pristine state.
Beyond the coral
stretches a world of shifting sand.
Out there with nowhere to hide,
survival is not easy
and camouflage can be crucial.
If this wasn't moving, you might
think it was a shell or a rock.
In fact it's an octopus.
A gurnard. It's huge pectoral
fins disguise it's shape,
and they can also help in clearing
away sand when searching for food.
The jawfish hides underground.
The wonderpus octopus on the other
hand has such a powerful bite
that it has a special warning display
to tell others to keep out of it's way.
Here and there,
plants manage to take root
and they're cropped by green turtles.
Sea-grasses are the only flowering plants
that have managed to grow in the sea,
although they put out
a few ribbon-like leaves,
they produce very extended networks
of fleshy stems, risomes,
that are buried in the sand.
At their lushest,
they can transform the sea bed
into an underwater meadow.
The largest expanse grows in the shallow
waters of Shark Bay, in Western Australia.
These vast aquatic grasslands
stretch for 1,500 square miles,
and like terrestrial prairies,
they support herds of grazers.
Dugongs.
Dugongs are the largest
herbivores in the sea.
They can be 3 meters long
and weigh half a ton
and they eat nothing but sea-grass,
mostly the fleshy risomes,
which they excavate
with their mobile lips.
A herd can clear a patch of sea-grass
the size of a football pitch
in a single day.
Food is not evenly distributed
in the tropical shallow seas,
and it can take a lot of finding,
but bottlenose dolphins are inquisitive,
energetic, and very intelligent,
and they have discovered
a shoal of baitfish.
Together, they ride a wave, using it
to carry them into the shallows,
and there, it will be easier
to make the catch.
In Western Australia,
these dolphins have taken on
an ever tougher challenge.
The fish have taken refuge
close to the beach
where the water is only
a few centimeters deep.
Tail slapping is a method dolphins
often use to stun their prey,
but it doesn't seem to work here.
The fish are tantalizingly close,
but they're still out of reach,
so the dolphins try another technique.
Vigorously pumping their tails,
they work up some speed,
and then, they hydroplane.
Their momentum carries them right
through the shallowest waters,
and onto the fish.
Now they're in real danger
of being stranded,
but fortune favors the brave.
Younger dolphins lie alongside,
watching,
but so far only 8 individuals here
have mastered this daring technique.
Although most life in tropical waters is
concentrated around the coral reefs
and the sea-grass meadows,
there are some spectacular exceptions.
The desert of Bahrain seems
a very unlikely place
to find a crowded bustling
colony of seabirds,
but every year, a hundred
thousand socotra cormorants
gather here to breed.
It's swelteringly hot,
and only vigorous panting can prevent
the birds from fatal overheating.
This hardly seems a good place
to rear young,
but at least, there are no
land-based predators here.
The only source of trouble
is likely to be the neighbors,
so each nest is built
just beyond pecking reach.
But what about food?
There's only bare sand
and the warm shallow sea beyond.
Neither seem likely to produce enough
nourishment to support bird life on this scale.
The answer is blowing in the wind.
Sand whipped up
by Shamals offshore winds
blows into the seas of the Arabian Gulf.
With the grains come nutrients,
which act as fertilizer,
and they transform the shallow sea
into a rich fishing ground.
So, paradoxically, it's the roasted sands
of Arabia that prevent the gulf
from being another desert in the sea.
The whale calf is now 5 months old.
He's almost doubled in size,
and his days in his tropical
nursery are coming to an end.
It has been a warm and safe place
in which to grow up,
but there's nothing to eat here
for his mother.
She has been living off her fat
reserves for the last 8 months
and she's close to starving.
She must leave now, while she
still has enough energy
to guide and protect her calf,
on the long voyage ahead.
All across the tropics, humpbacks are
heading away from the Equator
towards the rich temperate seas of both
the southern and the northern hemispheres.
These are colder, rougher,
and more dangerous waters.
Mother and calf must stay close.
They can send sound signals
to one another,
above the roar of the ocean
by slapping fins on the surface.
In winter, the temperate seas
are lashed by violent storms.
The turbulence stirs the water, and
draws nutrients up from the depths,
but nutrients alone
can not support life.
There must also be sunlight.
In the spring, as the sun
daily climbs higher in the sky,
the algae start to grow.
Blooms the size of the Amazon
Rainforest turn the seas green.
Individually, the algae are tiny,
but together, they produce three-quarters
of all the oxygen in our atmosphere.
They're eaten by an array
of bewildering creatures.
Salps appear in the plankton soup.
Individuals link together to form chains
which can stretch for 15 meters.
Pumping water through their bodies, they
strain out algae and other edible particles.
Comb jellies cruise through the water.
They too flourish
in this seasonal soup,
and for short periods, they appear
in astounding numbers.
Krill — shrimp-like creatures.
By weight they're the most
abundant animals on the planet.
A single swarm can contain
2 million tons of them
and that is a lot of fish food.
The shallow temperate seas support the
greatest concentrations of fish on our planet.
Huge shoals migrate from their
overwintering grounds in the depths
to feed in these rich waters.
It's these shoals that support most
of the world's sea mammals.
Sea lions have all the agility and speed
needed to collect what they want
and seemingly delight in doing so.
Dusky dolphin, often in pods 200 strong,
work together to reap the harvest.
They break up the shoals into
smaller, more manageable balls,
and all the hunters benefit.
By midsummer, the surface nutrients
have all been absorbed.
The algae die
and the food chain collapses.
In a few special places, however,
the temperate seas sustain these
levels of life throughout the summer.
Along the coast of California, ocean
currents carry a constant supply
of nutrients up from the depths
to the surface layers.
These upwellings fertilize forests of giant
kelp, that thrive in the summer sunshine.
The algal towers are
as high as a three story house,
and they can grow
by half a meter a day.
Life in the kelp is as full of drama,
as in any other forest,
but the cast is less familiar.
An army of sea urchins
is mounting an attack.
The urchin plague strikes
at the kelp's holdfasts,
their crucial attachments
to the rock.
Holdfasts are extremely tough,
but each urchin has 5 teeth,
which are self sharpening
and are replaced every few months.
Urchins fell vast areas of kelp forest,
creating clearings
known as urchin barrens.
Yet barrens is a poor description.
Millions of invertebrates
invade the seabed.
The most fearsome predator here
is a giant.
The sunflower starfish is a meter across,
with an appetite for brittle stars.
It uses it's feet to taste for prey.
When it's actions are speeded up,
it becomes clear
that the predator's fondness
for the brittle stars
is almost matched by the brittle stars
ability to get out of the way.
Sand dollars flat sea urchins
cluster together as a defense.
But it doesn't seem to work
against the sunflower starfish.
The predator extrudes it's stomach,
and wraps it around it's victims,
liquefying their soft parts.
Nothing is left of them,
except their white skeletons.
The Californian upwellings are
seasonal and relatively small,
but in Southern Africa,
they're so big
they create seas rich enough to support
colonies of over a million seals.
The Benguela Current sweeps along the
western coastline of Southern Africa,
driving nutrient rich waters
up to the surface,
and then,
at the southern tip of Africa,
it meets the Agulhas Current,
arriving from the east.
The result — even richer waters.
The seals here
thrive on a diet of fish and squid.
In temperate seas, there may actually
be more squid than fish.
These are chokker squid, and
they lay their egg capsules
in sandy shallows bathed
by the warmer Agulhas Current.
Each capsule contains
a hundred tiny squid.
Within a few days,
they develop spots of pigment,
which, when they're adult, they will
use to communicate with one another.
With females continuing to lay eggs,
and males still preoccupied
with repelling rivals,
the squid drop their guard.
Stingray.
Short-tailed stingray
can be up to 2 meters across.
They're the largest of all the stingrays,
and they have appetites to match.
Another predator is on the prowl —
the aptly named ragged tooth shark.
Raggies grow to 3 meters long,
but they share these waters
with a shark twice their size.
The great white —
The largest predatory fish
on the planet.
Each dawn, cape fur seals leave
their colony to go fishing.
To reach the open sea, they must
cross a narrow strip of water,
and that is patrolled
by great whites.
Each seal is indeed swimming
for it's life.
The shark relies on surprise.
The great white's turn of speed
is powered by a high metabolism.
They only thrive
in cold temperate seas,
for only these waters contain
sufficient food necessary
to fuel such a ravenous predator.
As you travel towards the poles,
north or south,
the colder, stormier seas
can become even richer.
Midway between South Africa
and the South Pole
lies the isolated island of Marion.
The island sits in the infamous
"Roaring Forties"
where incessant gale force winds
draw nutrients up from the depths,
ensuring plenty of food
for king penguins.
The kings are returning from a
three-day fishing trip,
with food for their chicks,
But first they must cross
a crowded beach,
threading their way
between gigantic
and bad tempered elephant seals.
The 200,000 penguins breeding here
are testament to the richness
of the fishing.
King chicks are dependent on
their mothers for over a year,
and this puts a great deal
of pressure on the parents.
Being flightless, the returning penguins
must cross the open beach on foot.
Fur seals, that have come to the
beach to breed, are waiting for them.
Fur seals normally live on krill,
but these have now acquired an unexpected
taste for blubber-rich penguins.
Penguins may be featherweights
by comparison,
but they have razor sharp bills
and a feisty character.
The seal could easily lose an eye.
The only safe way to grab a
penguin is from behind,
and the birds are
well aware of that.
Both animals are clumsy
on this terrain,
but the penguin has the more to lose.
Made it.
2 out of 3 penguins
survive the seal attacks
and succeed in reaching
their ever hungry chicks.
The humpbacks are nearing the end
of their epic journeys.
After 2 months and thousands of miles,
they're entering the polar seas
both in the north and the south.
In the far north, winter is over at
last and the ice is starting to melt.
The Aleutian Island chain
running west from Alaska
is the gateway to the Bearing Sea.
With the retreating ice,
rough weather and ferocious
currents stir up these shallow seas.
Add sunshine, and the mix
is spectacularly productive.
5 million shearwaters have flown almost
10,000 miles from Australia to get here.
In all, 80 million seabirds
come here for the summer,
the greatest concentration
to be found anywhere on Earth.
The humpbacks have finally arrived.
The giant shearwater flocks
hunt the krill swarms,
sometimes diving to depths
of 40 meters to reach them.
A large humpback
eats 3 tons of krill a day.
The polar seas in summer are the
most productive on the planet,
and the whales gorge themselves
round the clock.
The fat reserves they lay down now will
keep them alive during the year to come,
but it may not always be this way.
Fish and krill stocks
are declining so rapidly,
that spectacles like this
may soon be part of history.
Once the mother and calf have reached
their feeding grounds, they will separate.
With luck, the calf will make the
epic journey across the oceans
from equator to pole
another 70 times,
cruising back and forth
between the shallow seas
where life proliferates so
abundantly on our planet.