All language subtitles for The.Blue.Planet.S01E07.Tidal.Seas.1080p.AMZN.WEB-DL.DD+2.0.H.264-playWEB_track3_[eng]

There is a force
sufficiently powerful

to move the oceans
of this world.

It is a force not of this Earth.

The moon is large enough
to generate gravity,

and with sufficient force
to pull on the Earth

230,000 miles away.

As the moon orbits the Earth,

its gravity sweeps across
the face of our planet.

Its power drags a great bulge
of oceanic water in its wake...

...the rising tide.

The River Amazon in Brazil.

On some special days,

the gravitational forces
of the moon

and the sun pull together
to extraordinary effect.

A growing tidal wave
from the ocean

is being forced
200 miles inland.

This is a tidal bore.

Fortunately,
tidal bores are rare,

but the moon
does create strong tides

out in the world's oceans
on every day of the year.

The Bay of Fundy in Nova Scotia.

The tides here are
the largest in the world

and have a profound effect
on marine life,

creating a rich feeding ground.

A feast that attracts some of

the largest diners
on the planet...

...humpback whales.

But they are not the biggest
threat to the herring.

These are finback whales.

At 70 tons, the second-largest
animal on Earth,

but so beautifully streamlined

that it is the fastest
of the great whales.

This combination of
speed and immense size

makes the finback a voracious
hunter of schooling fish.

The Bay of Fundy
can attract so many fish

that during the summer,
as many as 500

of these magnificent whales
hunt here every day.

The feeding is best
where the tides run strongly,

so the whales move
further into the bay,

following tidal rips
and searching for fish.

Their movements
are closely watched

by flocks of
Cory's shearwaters.

As the whales dive down
towards the fish,

more and more birds gather,
anxious to pick up scraps.

The flowing tide
may provide a feast,

but before long,
it will turn.

In just six hours,

100 billion tons of water
will flow out of the bay,

the sea level falling by
as much as 15 meters

and exposing vast tracts
of mud and sand,

at first sight a barren place,
entirely devoid of life.

In fact,
the damp sand is packed

with microscopic life,
the meiofauna,

feeding in a sandy underworld,

quite unaffected
by the departure of the sea.

But life is not all roses
in this miniature world.

A sand bubbler crab
in Northern Australia.

It hunts meiofauna.

Just a centimeter across,

the sand bubbler works
at breakneck speed,

passing sand grains
into its mouth,

filtering out
all the meiofauna,

and kicking aside the waste.

The crab will clean
every grain of sand

within a meter of its burrow,
endless practice for

the best back heel
in the natural world.

The crabs work fast
because they can only sieve

when the sand is damp.

Remarkably,

they work the entire
surface of the beach

within just a couple of hours
of the tide retreating.

Then they simply
return to their burrows

and await the next tide.

Let's begin.

My dog is one of us.

You and me, girl.

Home protection?
Hunting.

Out here,
most folks let things go.

I guess I'm not
most folks.

I want to live.

Are you prepared to kill?

Yes.

One of us is not
leaving this island.

You ready?

Underwater,

a falling tide is the cue
for some bizarre activity.

These slow-moving clams
use their muscular feet

to bury themselves
under the sand.

If they fail
to get under cover,

the tide will leave them
exposed to the air

and they will perish.

But once underground,

they can wait
deep down in the sand,

safe beneath the beach.

And not a moment too soon.

June in Southeast Alaska,
and in just four hours,

a vast, sandy beach is
exposed by the falling tide.

The bears are hungry.

At this time of year,

the pickings on land
are few and far between.

But any food here

has long since buried itself
deep under the sand.

To a hungry adult bear,
that is no barrier.

They smell the clams
through the sand

and simply dig them out.

For such large animals,

they show quite
extraordinary dexterity

at opening
the unfortunate shellfish.

Cubs try their luck, too,
none too successfully.

But for the adults,
the shellfish feast

lasts as long as
the tide remains out.

Table Mountain in South Africa.

Every day,
the retreating waves

leave flotsam
somewhere on the beach,

and this creature
is scenting the currents

for the odor of rotting fish.

The tide carries the scent
far into the surf zone.

Responding to the smell,
snails emerge from the sand.

This is a race against the tide.

The snails need to
find their meal

before the tide leaves it
beyond their reach.

But snails are slow
and the tides fall rapidly.

These, however,
are no ordinary snails.

They can surf.

They ride the waves
up the beach,

but all too soon,

the tide leaves the fish
beyond the surf zone.

Without the sea,

there's a danger that
the snails will lose the scent,

but as long as
the sand remains damp,

they can still follow
a faint trail to the food.

Once there, they tuck in
with macabre relish.

Good things come
to those who wait.

Before long,
the heat of the sun

forces them to
retreat into the sand

to await the return
of the next tide.

February in Britain.

The falling tide is eagerly
awaited by these knot.

As the water retreats,
countless small invertebrates

are seeking shelter
under the mud.

And with good reason.

Waders are specialists
at probing in the mud,

their wide variety
of beak shapes

designed for reaching
different invertebrate dinners,

keys that unlock the safety
of the tidal flats.

But within a few hours,
the tide will turn again.

And soon, the waders are
out of their depth,

and the creatures of the mud
are safe once more.

Underwater, incoming tides
can create a strong current,

and flounders are experts
at hitching a tidal lift.

They're shaped
rather like a kite,

a perfect design
for gliding on the tide.

In Newfoundland,
on the east coast of Canada,

large numbers of flounder

ride the currents
up into the shallows.

They've come
to hunt invertebrates

that will emerge
now that the water is back.

The pickings in the shallows
can be very good.

The activity has not
gone unnoticed.

But ospreys can't dive deeply.

As long as the water
is more than a meter deep,

the flounder will be safe.

Going too far inshore
can be a risky business.

This fish buries itself
completely in the sand

at any sign of danger.

But when the tide
floods in again,

as long as the coast is clear,
these sand lancet will reemerge.

After a wait of six hours
under the sand,

they're desperate for food,

and unlike flounder,
they head out to sea.

They're looking for
shallow open water,

where the tidal currents
will concentrate their food,

plankton.

In their untold thousands,

they stream towards
the best feeding grounds,

where they simply pick up

tiny planktonic creatures
from the water.

But if they swim too far
offshore in search of food,

they risk running into
large predators

that live out
in deeper water.

Dogfish, small sharks.

The sand lancet have strayed
out of their safe depth.

The effect of the turning tide

can be totally different
on a rocky shore.

Here on the coast of
Vancouver Island in Canada,

the sun bakes the exposed rock.

It's virtually impossible
to dig underground

when the sea retreats,

so these mussels and barnacles

are fully exposed
to the heat of the sun,

literally cooking in
their own shells.

And the seaweed simply
dry to a crisp.

It can be a wait of many hours
before the water returns.

Throughout each month,

the size and strength
of the tide changes.

The biggest tides of all
happen when

the gravities of the sun
and moon pull in unison.

That happens immediately after
the new moon...

and again after the full moon.

These are called
the spring tides.

They reveal vast tracts
of sea bed

that would normally be covered.

For these raccoons,

it's a chance to look for
a seafood feast.

A mother ventures forth
with her kits.

With the spring tide,

they've come
further down the beach

than smaller tides
would normally allow.

Searching with their
extraordinarily sensitive paws,

they look for suitable prey.

With the extreme low tide,

they could find
something special.

And what could be better
than a red rock crab?

That is, if it weren't for
the risk of a painful pinch.

With large crabs,

there's no substitute
for experience.

The mother makes
an expert's catch.

But the kits learn fast.

And for those that don't,
begging is always worth a try.

All too soon,

the returning tide will cover
the raccoon's table.

For all the invertebrates,
it's a welcome relief,

but in rough weather,

they are exposed to
the worst of the waves.

Even when there are no waves,

the incoming tide can create
considerable forces underwater.

The gaps between
these small islands

on the east coast
of Vancouver Island

channel the tidal flow.

As the tide keeps rising,

gradually the water
flows faster,

and soon, these giant,

30-meter long bull kelp plants
bend to the current.

They're sufficiently flexible
to cope without too much damage,

but there are some spots

where the currents
are especially powerful.

This is the Nakwakto Rapids.

At the turn of the tide,

water from almost
700 miles of coastal fjords

will have to empty through a gap
of less than half a mile wide.

Within a few minutes,

the current is already
picking up speed,

until water roars by
at over 17 miles an hour.

Tidal currents are not always
a damaging force.

Here in the Poor Knights Islands

in New Zealand,

weak tides
run through rock arches,

making an ideal resting place
for stingrays.

These rays congregate here
in huge numbers every March.

They've come to breed.

The arches funnel the current,
which the rays can ride

with a minimum of effort,
so saving energy.

Nearby, out in open water,

a school of
two spotted demoiselle fish

are feeding on plankton,

and the current is perfect for
sweeping their food past them.

Once the current
starts to weaken,

there is insufficient food
to warrant the risks

of swimming about
out here in the open,

so the demoiselle head off
to find shelter en masse.

Safety is in numbers.

More and more demoiselles
pour towards the cave entrances

that riddle
the Poor Knight Islands.

Safe at last.

Inside the cave,

they are far less exposed
to attack from predators.

Thousands of demoiselles
and blue maomao

wait for the return
of the current,

when once again they will
head out into the open to feed.

The moon's gravitational pull

is weaker nearer to
the Earth's equator,

so the more equatorial
the location,

the smaller the tides,

and out here in
the Caribbean Sea,

the tidal movements are slight.

Even so,
they're sufficient to push

free-swimming plankton
in their path.

These are thimble jellyfish.

They swim towards the sunlight,
and invisible boundaries

formed by the tidal motion
help to herd them together

until they gather
in immense swarms.

They put the tropical sunshine
to good use.

Their brown color
comes from algae

that live inside
the jellyfish's body

and photosynthesize energy
from the sun.

In open water,
they're fairly safe,

but the tide is
sweeping the whole swarm

gently towards the Bahamas,
where hungry mouths are waiting.

Although the sea level
doesn't change much,

the tides are still pushing

an enormous volume of water
from the ocean

through the small gaps
between the island cays.

Underwater, the tidal currents
race past soft corals...

...and on over
the sandy banks themselves.

It's an immense area
of coral sand

that is only just submerged
at high tide.

This incoming tide
is bringing in

a fresh supply
of oceanic plankton,

and razorfish gather
at the best spots

to catch the pick of
the microscopic feast.

Although there's plenty here
for these small fish to eat,

gathering in one place
makes it easy

for their predators
to find them.

A nurse shark is little threat.

But this sound heralds
a quite different danger.

A bottlenose dolphin.

It's using its sonar

to locate razorfish
beneath the sand.

Once it finds a suitable target,
it simply digs out its prey.

The buried fish have no
defense against this attack.

They will simply have to wait
and hope they aren't found out.

This dolphin appears to have
a razorfish craving.

Well, she is pregnant.

Success at last.

The incoming tide
sweeps on towards America,

flooding across vast,
flat plains of seagrass.

They're so shallow
that at low tide,

all large fish
are forced to retreat

into deep water channels,
like these nurse shark.

And stingrays.

Both predators hunt crustaceans
on the seagrass beds,

but until the flooding tide
brings enough water

for them to swim in,
they will have to wait.

So now, for this tulip snail,
it appears safe

to patrol the shallows
in search of a meal.

But is it?

This is a rather bigger
kind of snail.

At five kilograms in weight,

the giant horse conch has
little to fear from any shark,

and it has a taste
for tulip snail.

Sensing the approaching danger,
the snail flees,

but in a world of snail paces,

the conch is something
of a Ferrari.

It calls for desperate measures.

Exhausted by the effort
of its last-ditch attempt,

the tulip snail
is slowly gunned down.

The tide still has to rise
for another hour

before the big predators
can feed,

but out on the flats,

the scent of dying snail
wafts away on the tide.

It's a scent that
these hermit crabs

are particularly partial to.

It's vital that the crabs have
the best possible protection

from the heavy teeth of
the waiting sharks and rays.

For that, they need the shell
with a perfect fit.

Today there is
new real estate on offer,

and competition in this
housing market is fierce.

The action becomes
even more desperate

when the shell of the devoured
snail is ready for release.

This crab simply
can't wait any longer.

But it's a decidedly
risky acquisition.

The risk paid off handsomely.

The new shell is both
lighter and stronger

than the old home,
and it's not a moment too soon,

because the tide
is flowing in strongly,

flooding the plains.

At last, the predators are free
to start their foraging.

Both the stingrays and sharks

have a highly developed
electrical sense

which they use to search
for buried invertebrates.

They can sense minute movements
beneath the sand.

Finding a promising signal,
this ray digs out its meal.

An unprotected hermit crab
would have no chance.

Within a few hours,
the tide ebbs out once more,

and all the predators
are forced to leave.

They will have to wait
until the next high tide

before making another
feeding foray.

At certain times of the year
called the equinox,

spring tides
are exceptionally large

and rise even higher
than normal.

Now predators can reach
the very shallowest fringes

of the seagrass flats,

and these two-meter-long tarpon
are going further inshore still.

They are heading
for the mangroves.

These flooded forests cover huge
areas of the coastal shallows.

Extraordinarily,

the roots of the mangrove trees
can live in salt water,

and they make a perfect nursery
for small fish.

Silversides and snapper find
sanctuary in the maze of roots.

Big predators
seldom find a way in here.

And now the tide
is falling once more.

The water starts losing
what little oxygen it contained

and quickly becomes stagnant.

Most predators have
abandoned the mangroves,

but these tarpon are still here,
trapped by the falling tide.

Dissolved oxygen
is fast running out,

but they have a vital
survival technique.

They can breathe air.

Pumped up with fresh oxygen,

they can easily outmaneuver
the dozy silversides.

The tide has turned again.

And this is no ordinary tide.

Since it is the equinox,
the tide is rising fast,

but now, out to sea,
a hurricane is on its way,

forcing the tide yet higher.

The passing storm leaves
large areas of the coast

flooded by the sea.

And low-lying islands
like the Bahamas

are particularly prone
to the storm flooding.

The sun's power here is immense.

As the tide recedes

and the remaining
floodwater evaporates,

a remarkable transformation
takes place.

The mud is coated with
a magical world of salt.

Any remaining water
is extremely salty.

Very few creatures
can survive here,

except brine shrimp.

And, on the water's edge,
brine flies.

Both are the favorite food
of an extraordinary animal...

...the Caribbean flamingo.

Remarkably, they actually
seek out such briny places.

They're the best spots
for them to find their food.

And they also provide
the protection

the flamingos need
to raise their young.

Nesting sites like this are
surrounded by corrosive brine.

It's a formidable barrier
to any predators

seeking to dine
on flamingo chicks.

The flamingos
take the precaution

of building raised mud nests

just in case
of further flooding.

Strangely, it's actually
the power of the storm tides

that gives the flamingos
both their food

and a perfect habitat
in which to breed.

A half moon in November.

It's the time of small tides.

Christmas Island
in the Pacific.

Strange happenings are afoot.

It's one of only
a few nights each year

when female
Christmas Island crabs

risk heading down
towards the sea.

Around the island,

they number in
tens of thousands,

and all of them are laden
with hundreds of eggs.

They have to shed them
into the ocean

if the eggs are to develop
into baby crabs.

But these are land crabs,

and they can neither swim
nor breathe underwater.

There's a great risk
of drowning,

which is why they pick
the smallest tides of the month

to minimize the danger.

The eggs will develop
far offshore,

and in exactly one month's time,

a great swarm of baby crabs
will return,

again choosing the perfect tide.

Whether it's the daily
or monthly cycle,

tides are the rhythm
of the ocean,

its pulsing clock,

for every tide brings
opportunity to marine life

somewhere in the world.

Now a spring tide
is flooding the shallows,

and hunters are on the prowl.

A small group of
bottlenose dolphin

are working their way inshore

to start a quite extraordinary
hunting campaign.

After one successful pass,

the dolphin move off
to start again.

One animal peels off
from the group

and swims rapidly in a circle,

stirring up the mud
and driving the mullet

towards the other
waiting dolphins.

It's a remarkable team effort,
and it's extremely effective.

The dolphin will feed like this
for as long as the tide

grants them access
to the shallows.

Eventually the falling tide

will force the dolphin
to leave the flats,

and the mullet
will be safe once more--

until the next high tide.

Because in the ocean,
every turn of the tide

spells the difference between
life and death somewhere.