All language subtitles for The Blue Planet - S01E05 - Seasonal Seas.eng

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 parts of the world,

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
eventually 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 in North America

Grey 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 grey 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 suckled 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

and sustained by nothing
except their fatty blubber

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

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

By May, Spring has reached
the coasts of Scotland

Underwater it arrived rather earlier

During March, the seas had warmed enough
to trigger a magical transformation

These are Phytoplankton,
tiny floating algae,

each much smaller than a pinhead

And they multiply with amazing speed
to produce more annual growth

than all the plants on land put together
- 6 billion tonnes 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

Although these polyps look
like small anemones,

They're about to change
into something else

As they separate, they reveal
themselves to be tiny, common jellyfish

They are less than
3 millimetres 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 basket-like filters
around 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,

rather 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 behind copepods stuck
to the membranes

A single sea-nettle jellyfish
only a few centimetres

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 8 metres

But there are even greater dangers
awaiting the copepods

By the late spring the baby common
jellyfish are fully grown

They gather in millions, forming
immense swarms hundreds of metres 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 tonne fish feeds
on plankton and nothing else

Every hour it filters a thousand
tonnes of seawater through its gills

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

and travel along those water currents
where the plankton is thickest

Even so, the supply of plankton
is so abundant

that another group of animals'
is able to share in the feast

- animals that live on the seafloor

Every centimetre 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 the plankton

It's 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 metre 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 metre a day

The main stem is fixed to
the bottom 35 metres below

by a small but immensely
strong holdfast

Fully grown, these gigantic plants
are a hundred metres 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 off 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 10 minutes and that's 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, however,
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 in places 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 are not the only animals
to venture out at this time

This is an amphipod, just two
centimetres 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 fifty youngsters
clustered on her abdomen,

so her home is becoming
somewhat cramped

They will soon be old enough to leave
and now 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 harbour 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 harbour 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 mid-summer 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

A 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 Janolus

Its colours suggest that it's
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 rolls
into a ball...

All Navanax gets is a few
yellow tentacles

And Janolus is swept to safety
by the current

It's now mid-summer 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 has spent the winter 250 metres 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 kilometres away

After a month of walking she finally
arrives at her favoured sand bank

But she's not the first here

Dozens of other lobsters have already
dug themselves homes in the sand

and they don't intent to
surrender them to newcomers

Size counts for everything
in these battles

The new arrival is in urgent need of a pit
and since she weighs a hefty 7 kilos,

she stands a good chance
of getting one

She's won

These battles continue for the
next two months and they're crucial,

for the females must
have both shelter

and warm water if they're
to raise their young

For the last seven months, each of
these females has been carrying

around about twenty thousand
fertilised 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 year the sea
is full of larval animals

- this one is a 1 day old lobster

And this ... a 3 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 in its life it's a
vegetarian, with a taste for sea lettuce

As it grows, so it will repeatedly
moult and expand into a bigger, thicker skin

The chances are it will be eaten,
but if it survives for five years

it will have become a magnificent
armoured 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

And 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 defence

A one and half metre 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 are swarming 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
until rain causes it to rise

So, for now they are trapped
in the sea,

close to the shore,
the worst place to be

A three metre 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 sea water

And that means they have
the energy to be quick

Quicker even than salmon

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

The ocean temperature
is slowly dropping

Forty metres below the surface,

this year's baby herring are feeding
on the last of the summer's 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 effortlessly
down beneath the school

The panic herring
a force 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

and there 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 socialising

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 the west coast of 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 the late autumn
- it's nearly ready to hatch

A fully formed miniature
shark swims free

This year's plankton will soon die
but the young dogfish

is so well developed that it can't 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 through 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

also 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 metre 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,

during which they continually change
the colour of their costumes

Eventually they form pairs

A male passes a packet of sperm
across to the female

After the eggs have been fertilised,
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 colour

- but they're not quite
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 highly 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 5 hours
of daylight in every twenty four

The temperature is
falling rapidly

But despite the cold,
the sea is far from deserted

Every winter, 500 million
tonnes 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's his small pod is part
of a population

of some five hundred
killer whales

that specialise in hunting
North Atlantic herring

Using their echo-location
they have detected a shoal

of herring 50 metres below them

With enough air for a 10 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 orca finds it difficult
to catch a healthy herring

But they have a devastating
weapon all their own

They use their tail 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 and both orca
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 5 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