The Blue Planet (2001): Season 1, Episode 7 - Tidal Seas - full transcript

Tidal marshes are one of the most productive parts of the world. Numerous plants support numerous animals, yet life is not easy: predators are attracted to these enormous quantities of food, forcing animals to seek constant protection from attack.

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,

two hundred and thirty
thousand 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 two hundred 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 seventy tonnes - 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 five hundred 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 Shearwaters

As the whales dive down
toward the fish

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

The flowing tide may provide
a feast for the whales,

but before long it will turn

In just six hours,
one hundred billion tonnes of water

will flow out of the bay

The sea level falling
by as much as 15 metres

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 centimetre 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 metre of its burrow

Endless practise 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

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 odour 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

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 flounder are experts
at hitching a tidal lift

They are 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 have 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 found then 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 re-emerge

After a wait of six hours under the sand,
they are desperate for food and,

unlike flounder,
they head out to sea

They are looking for
shallow open water,

where the tidal currents will
concentrate their food - plankton

In their untold thousand they stream
toward the best feeding grounds

Where they simply pick up
tiny planktonic creatures from the water

But, if they swim too far off-shore
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 racoons 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 racoon's table

For all the invertebrates
it is 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 thirty metre

long bull kelp plants bend to the current

They are 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 seven hundred 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
seventeen miles per hour

Tidal currents are not always
a damaging force

- here in the Poor Knight
Islands of 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 desmoiselle 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 desmoiselles head off
to find shelter en-masse

Safety is in numbers

More and more desmoiselles pour
towards the cave entrances

that riddle the Poor
Knight's islands

Safe at last - inside the cave

they are far less exposed
to attack from predators

Thousands of desmoiselles and blue mao mao
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 are 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 colour
comes from algae that

live inside the jellyfish's bodies
and photosynthesise energy from the sun

In open water they
are fairly safe,

but the tide is sweeping the whole
swarm gently towards the Bahamas,

where hungry mouths are waiting

Although the sea level
does not 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 is 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 is 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
razor fish beneath the sand

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

The buried fish have no defence
against this attack

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

This dolphin appears to have a razor
fish craving - well, she is pregnant

Success, at last

The incoming tide sweeps
on towards America,

flooding across vast flat
plains of seagrass

They are so shallow that,
at low tide,

all large fish are forced
to retreat into deep water channels

Like these nurse sharks...
and these 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 for now this tulip
snail it appears safe

to patrol the shallows
in search of a meal

But is it?

This I s a rather
bigger kind of snail

At five kilogrammes 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

These two metre long tarpon
are heading 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

The 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 out

manoeuvre 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 the low lying islands
like the Bahamas

are even more prone
to storm flooding

The sun's power here is immense

As the tide recedes and the
remaining flood water 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 these brine shrimp

And on the water's edge, brine flies

Both are the favourite food
of an extraordinary animal

The Caribbean Flamingo

Remarkably, they actually
seek out such briny places

- they are 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 Flamingo takes the precaution
of building next

Just in case of further flatting

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

The breeding of many animals in the ocean

is closely co-ordinated
with the tidal cycles

A half moon in November.
It is the time for small tides.

Christmas Island in the Pacific

Strange happenings are afoot

It is 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 is a great risk of drowning,

which is why they pick the
smallest tides of the month

- to minimise 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 is 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