All language subtitles for 5) -2001- The Blue Planet-Seasonal Seas

There are some seas
where fish swarm in millions...

...and plankton blossoms
in vast clouds.

The sheer quantity of life here is
unmatched anywhere in the oceans.

These are the most productive seas
on Earth.

They are the Seasonal Seas.

The Seasonal Seas border
the temperate zones,

where conditions change
through the year.

The seasons also affect
the underwater world.

The power of the sun
is constantly changing.

In the far north,
during the summer,

there are long hours of sunlight,

but in winter, that dwindles,
and there can be weeks of darkness.

The summers are warm and gentle,

the winters
racked by savage storms.

In conditions like this,
life of any sort

has to struggle to survive.

January on Sable Island
off the coast of Nova Scotia.

Gray seals
have managed to get ashore

through the crashing breakers.

Gales here can blow
for days on end.

Sable Island has the world's
largest colony of gray seals.

100,000 come here
to breed each year,

just when the weather
is at its worst.

To add insult to injury,

the pups, having suck/ed for
only 18 days, are then abandoned.

Their mothers must return to
the sea to find food for themselves.

As yet unable to dive,
the pups are marooned,

sustained only
by their fatty blubber.

It will be five weeks before
they are strong enough to swim,

but then it will be spring and
the ocean will be teeming with food.

By May, spring has reached
the coasts of Scotland.

Underwater; it arrived
rather earlier.

In March,
the seas had warmed enough

to trigger
a magical transformation.

These are phytoplankton -

tiny floating algae,
each much smaller than a pinhead.

They multiply with amazing speed

to produce more annual growth
than all the plants on land together -

six billion tons of it.

This immense bloom spreads
across the face of the ocean

and, Within a couple of months,

turns vast areas of it
a dense green.

Animal life
reacts to the blooming sea.

These look like small anemones,
but they're about to change.

They separate, revealing themselves
to be tiny common jellyfish.

They are less
than three millimeters across.

Within a few months, they Will
have assembled into vast swarms.

Minute copepods
are part of their staple diet.

These appear every spring
in vast numbers

and graze
on the phytoplankton bloom.

Their beating legs create currents
that sweep the little algae

into the filters
round their mouths.

On this microscopic scale,
water is so viscous

that the phytoplankton
can't swim against the current.

Whilst feeding,
sensors on the copepod's antennae

give warning of dangers ahead.

Lighting by lasers

reveals that feeding copepods
leave wakes behind them,

like jet trails in the sky.

Slightly larger floating predators

are able to use these trails
to find their prey.

A close call, but some predators
are simply too large to avoid.

Jellyfish.

They may appear to be delicate
as well as beautiful,

but they are deadly hunters.

With every pulse
of the delicate bells,

plankton-rich water is drawn
into their lacy throats

and pushed out again, leaving
copepods stuck to the membranes.

A single sea-nettle jellyfish,
only a few centimeters across,

can collect thousands
of copepods in a day.

So, the killing power of giants
like these is hard to estimate.

Each of these jellyfish
weighs up to 30 kilos

and has tentacles
stretching over eight meters.

But there are even greater dangers
awaiting the copepods.

By late spring, the baby
common jellyfish are fully grown.

They gather in millions,

forming swarms
hundreds of meters long,

which filter out all the small
planktonic animals in their path.

Nevertheless, there are such
astronomic numbers of copepods

that enough will survive
to form swarms of their own.

A basking shark.

This huge eight-ton fish
feeds on plankton and nothing else.

Every hour it filters 1,000 tons
of seawater through its gills.

Numbers of these shark appear
when the bloom is at its peak

and travel along currents
where the plankton is thickest.

Even so, the supply of plankton
is so abundant

that another group of animals
can feast -

animals that live on the sea floor.

Every centimeter of rock is covered
with invertebrates of some kind -

anemones, sea squirts, gorgonians -

all trapping plankton
from the passing water.

Not all life in the Seasonal Seas
depends upon plankton.

It is early spring
in British Columbia.

Seaweed has started to grow slowly
in the cold water.

As the hours of sunlight increase
and the water warms,

these small plants turn into
great beds of bull kelp.

The immense 30-meter long strands

have small gas-filled floats
which keep them high in the water,

within reach
of the energy-giving sunlight.

Further south,
the sunshine is more powerful,

so here,
on the coast of California,

the biggest kelp of all can grow.

This is giant kelp,
and by midsummer;

each plant is growing in length
by nearly a meter a day.

The main stem is fixed
to the bottom 35 meters below

by a small
but immensely strong holdfast.

Fully grown,

these gigantic plants
are 100 meters long

and they form vast marine forests.

Great schools of fish
find sanctuary here.

These are blacksmith fish.

They are plankton feeders
and, whenever it seems safe,

they head into open water to feed
where the plankton is thickest.

But at the first hint of danger...

...they rush back to the safety
of the forest.

Fish are not the only creatures
that shelter here.

Californian sea otters
gather in the kelp forest

to rest and snooze in safety.

To prevent themselves
being carried away

into dangerous open water
where the big predators cruise,

they anchor themselves by winding
straps of kelp around their body.

Sooner or later,
they have to find food,

and that lies on the seabed
a long way below them.

Sea otters, however, can stay
underwater for up to ten minutes,

ample time to find
the shellfish they need.

Many of the smaller creatures
that live in these forests,

such as urchins, graze on the kelp

and can seriously damage it
if their numbers are unchecked.

The sea otters
feed on some of these grazers

and prevent them
getting too numerous.

So, in effect, the sea otters
are the guardians of the forest.

Garibaldi fish do not,
in fact, damage the kelp.

If anything, they help it

by picking off tiny animals
that encrust the leaves.

They graze on bryozoans,
tiny colonial animals

which build their colonies

like a patchwork of white skins
on the leaves.

When night falls, there are
fewer predatory fish around,

and the bryozoans emerge
from their White shelters.

Now, just like coral polyps,

they start filtering out the
plankton under cover of darkness.

They're not the only animals
to venture out at this time.

This is an amphipod,
just two centimeters long,

and it does eat kelp.

In turn,

it is excellent food
for many predators.

To protect itself, it produces
silk, just like a spider,

and uses it to sew together
two sides of a kelp frond

and so form a shelter.

This one is in particular need
of a secure home.

She's a mother.

There are over 50 youngsters
clustered on her abdomen,

so her home is becoming
somewhat cramped.

They will soon
be old enough to leave,

and, whenever she can,
she kicks them out

to get a taste of the outside world.

Dawn.

Beds of eel grass
grow in the shallows

between the kelp forest
and the shore.

A harbor seal
has found sanctuary here,

and is sleeping
after a hard night's foraging.

But not for long.

A male seal gives a wake-up call.

More seals are attracted
from all directions.

It's June, the time
when young male harbor seals

start their strange
mating displays.

One listens attentively to the
grunting noises made by the other.

These calls are almost certainly
a way of establishing

which of the two will be dominant.

But if the animals are closely
matched in size and experience,

grunts won 't settle the issue.

The rivals
will have to come to blows.

And seals can be
surprisingly violent.

In a month 's time,

the breeding season will start
and then fights will be in earnest,

but now, in midsummer,
these exchanges are harmless.

They're just playing.

Many of the creatures
that shelter in the kelp

have to venture out
in order to feed.

The bat ray for one.

Unlikely though it seems,

the sandy floor of the open sea

is, for the bat ray,
a rich feeding ground.

There is food
hidden within the sand,

and the bat ray has
a special technique for finding it.

It uses jets of water

to blow the sand aside
and expose small invertebrates.

A kelp bass hangs about alongside
waiting for scraps.

Other hunters
are also on the prowl.

The fan-tailed sole.

There are mantid shrimps here,
living in tunnels.

But, once again, hunger compels
them to venture into the open.

That, of course, is a gamble.

They will either eat...

...or be eaten.

A sea slug called Jana/us.

Its colors suggest
that it is poisonous,

and so it is, to everything
except another kind of sea slug...

...the predatory Navanax.

Navanax pulls itself
along the trail of slime

that Janolus leaves behind it.

Once caught,
Janolus mils into a ball.

All Navanax gets
is a few yellow tentacles.

And Janolus is swept to safety
by the current.

It's now midsummer, and the sun is
shining at full strength.

The increasing warmth is the cue

for an Atlantic lobster
to start on a long journey.

She's spent the winter 250 meters down,
far beyond the reach of the storms.

But it was cold down there and now
she needs to find warmer water,

so she's marching
towards the shallows.

They, however,
are 150 kilometers away.

After a month of walking, she arrives
at her favored sand bank.

But she is not the first here.

Dozens of other lobsters
have already dug homes in the sand

and they don't intend
to surrender them to newcomers.

Size counts for everything
in these battles.

The new arrival
is in need of a pit,

and since she weighs a hefty seven
kilos, she'll probably get one.

She has won.

These battles continue
for the next two months,

and they are crucial,

for the females must have shelter
and warm water to raise young.

For the last seven months,

each female has been carrying
about 20,000 fertilized eggs,

but their task
is approaching its end.

The warmth of the shallows
is speeding the eggs' development.

Two more months
and the eggs are ready to hatch.

At first, they're not very good
at swimming.

But Within a few minutes,

the babies are able to set off
in a purposeful way.

At this time of the year,
the sea is full of larval animals.

This one is a day old lobster.

And this - a three-week-old crab -

just ready to start its life
on the sea floor.

Its feet touch the bottom
for the first time.

At this stage, it's a vegetarian
with a taste for sea lettuce.

As it grows,
it will repeatedly molt

and expand into a bigger,
thicker skin.

The chances are it will be eaten,

but if it survives for five years,
it will become an armored giant.

Now it eats meat,

and special adaptations
enable it to hunt in the dark.

Its jointed feet
are covered in sensors

which detect the slightest chemical
change in its surroundings.

As it walks through the darkness,

its feet can, literally,
taste the sand.

As soon as it finds suitable food,

it passes it forward
to its powerful crushing claws,

which make light work
of the soft flesh.

And those claws are also
very useful for defense.

A one and a half meter long
common octopus glides by.

The jet-propelled giant
is both powerful and very clever.

With octopus about, it's risky
for even a crab to be in the open.

Even in the dark,
the octopus's eyes are sensitive

to the slightest movement.

Against a hunter like this,
the crab's claws are useless.

Late summer in South East Alaska.

The water is still warming,

and mysid shrimp
swarm near the surface.

It's a final feast
for Pacific salmon

returning to the coast
from the open Pacific.

They are heading inshore to breed
and they arrive in huge numbers.

They have to swim
far up the rivers to spawn,

but this river's level
is still too low.

They'll have to wait
till rain causes it to rise.

For now, they are trapped
in the sea, close to the shore,

the worst place to be.

A three meter long salmon shark,

a close relation
of the great white.

This one has sensed

minute electrical signals
from the salmon nearby.

Shark can maintain
their blood temperature

at a higher level
than the surrounding water.

And that means they have the energy
to be quick.

Quicker than salmon.

Early autumn in Vancouver Island
in Canada, 600 miles to the south.

The ocean temperature
is slowly dropping.

40 meters below the surface,

this year's baby herring feed
on the last of the summer plankton.

Their movements attract attention
from the skies above.

Gulls can 't dive,

so for now,
the fish are still safe.

But there are birds which CAN dive.

Auklets and murres swim with ease
down beneath the school.

The panicked herring are forced
towards the surface.

They gather into a giant
defensive ball of swirling fish.

The commotion attracts
yellowtail rockfish.

They, too, are hunters.

The marauding fish
scatter the herring.

Repeated attacks split the ball
into numerous smaller groups.

Now, it's easier for the divers

to keep the confused fish
penned at the surface.

Even the gulls can get at them.

Attacked from all sides, the little
fish have virtually no chance.

More and more divers
are attracted to the scene.

They harry the shrinking numbers
of herring

right down
to the very last individual.

Far bigger predators
cruise here, too.

Pacific White-sided dolphin.

But the dolphin
are mainly nocturnal hunters.

During the day,
they concentrate on socializing.

They display by releasing streams
of bubbles

and they play games.

Games like pass the seaweed,
for example.

Exactly eight months ago,
in the winter off Western Scotland,

an egg was laid and securely fixed
to a strand of kelp.

Inside, a tiny embryo
started to develop.

Protected by the tough egg case,

it endured
the worst of the winter storms.

By summer, it was half-grown.

Now, at last, in late autumn,
it's nearly ready to hatch.

A fully-formed miniature shark
swims free.

This year's plankton Will soon die,

but the dogfish is so well developed

that it can hunt immediately
for larger prey.

The days are getting shorter now.

In British Columbia,
the water begins to chill.

This bizarre-looking creature
is searching the kelp for food.

This is Melibe -
the hooded sea slug.

It catches plankton
with its net-like head.

As winter approaches,
plankton is becoming scarce,

but Melibe
is an assiduous searcher.

It can swim.

It flaps away to look
for a better feeding spot,

but its search is becoming
increasingly difficult.

Within the next two weeks, most of
the plankton will have disappeared.

As the sunlight
becomes ever more feeble,

the kelp starts to die,
gradually rotting away to nothing.

Soon, it will be Winter.

But 9,000 miles to the south,
the sun is rising on a new spring day.

The southern hemisphere, too,
has temperate regions.

And now the plankton is beginning
to bloom around Tasmania.

Just as in the north,

the Southern Seasonal Seas
have areas of rich green water...

...With their own kelp forests...

...and their own swarms of plankton.

Some of the inhabitants
of these seas

live only
in the southern hemisphere.

This is one of them -
the handfish -

that strolls around
on modified fins.

But, when needs must,
it can resort to tail power.

Every summer, visitors come
to the shallows around Tasmania.

These are Australian squid,
about half a meter long.

They are here to breed.

The larger males compete
for the attentions of a female,

displaying towards her
and to one another,

by putting on a ballet,
continually changing costume color.

Eventually,

they form pairs.

A male passes a packet of sperm
across to the female.

After the eggs
have been fertilized,

they are deposited
in tough, rubbery egg cases

that other creatures find poisonous.

Within three weeks,
the babies are ready to hatch out.

They are already
able to change color,

but aren't so good at swimming.

There is another animal here
that is a rather more devoted parent.

This is a male leafy sea dragon,

an exquisitely-decorated relative
of the sea horse.

He is carrying his partner's eggs
around with him.

They would be a nutritious snack
for any predator that found them.

But that's not easy
because the eggs are attached

to their father's
perfectly-camouflaged body.

They could scarcely be
in a safer place.

By November,
10,000 miles to the north,

Winter has arrived.

Norway now gets less than
five hours of daylight in every 24.

The temperature is falling rapidly.

But, despite the cold,
the sea is far from deserted.

Every winter, 500 million tons
of adult herring

seek shelter in these deep waters.

They will stay here
for four months,

living entirely
on the fat they accumulated

during the summer feasts
of plankton.

But they are not alone.

Orca.

This pod is part of a population
of some 500 killer whales

that specialize in hunting
North Atlantic herring.

(WHALE SONG)

Using their echo location,
they have detected a shoal of herring

50 meters below them.

With enough air
for a ten-minute dive,

they swim deep below the herring

and drive the fish upwards.

Bubbles stream from the rising fish

as gas in their swim bladders
expands and escapes.

Even an area finds it difficult
to catch a healthy herring.

But they have a devastating weapon
all their own.

They use their tails to club the fish
with waves of water pressure.

Then it's simply a matter
of collecting the stunned casualties.

The herrings have no chance.

Both area and gulls
will eat as much as they can

every day for the next four months.

But there are so many fish
wintering here,

over five billion individuals,

that the losses
are almost unnoticeable.

Violent as this winter weather
may be,

it's essential for the renewal
of the riches of the Seasonal Seas.

Out in the open oceans,

the surging waters stir up
nutrients from the depths.

By the end of Winter,

the Seasonal Seas Will be
full of minerals once more,

ready for the return of the sun
and the next great plankton bloom.