All language subtitles for The Living Planet s01e09 The Margins of the Land.eng

This is a battle ground.

In many places, the sea is forcing the land
to retreat, cutting back its cliffs

and leaving islands and towers
as markers of the territory that the land has lost

The debris is swept away

and strewn on beaches farther down the coast
as sand and gravel.

In some places, the land is advancing.

In the tropics, mangroves are moving
out into the sea, gathering mud

and building new territory
for land-living creatures.

Even in the mouths of rivers,

where fresh water laden with sediment
mingles with the salt water of the sea,

new land is being created of a sort.

I'm in an estuary in the west of England.

You might think that this mud is not
the most attractive stuff in which to live.

Certainly, animals that do live in it
have to face some severe problems.

Part of their time they're out of water like this,

part of the time they're underwater.

The saltiness of the water, too, varies.

Fresh water comes down
from the land, the tides bring in salt water.

And then there's the nature
of this extraordinarily sticky mud itself.

It is so glutinous that little oxygen gets into it

but the rewards for enduring
these unpromising conditions are high.

Edible particles
deposited on the surface of the mud

are cautiously sucked up
by the searching siphon of Scrobicularia,

a mollusc whose main body, enclosed in a shell,
hides in the mud for safety.

A tiny crustacean, Corophium, half an inch long,

grazes on the bacteria
which proliferate in millions,

breaking down rotting organic matter in the mud.

Ragworms live in burrows

and will tackle Corophium, algae, bacteria,
almost anything that's around.

The puddles are flecked with floating mucus.

It is produced by spire shells,
no bigger than grains of wheat.

The mucus attracts bacteria,
and the spire shells eat the lot.

The peacock worm fans out its tentacles
from the top of its tube

to gather food particles before they settle.

Beating threads on each filament of the fan

transport the catch
down to the mouth at the centre.

While it feeds,
it also disgorges a cement of mud and mucus

and builds up the margin of its tube.

The cockle lies with its shell agape,

filtering the water
by sucking it in through one siphon...

...and blowing it out through another.

Mussels use the same technique,
collecting within their shells

substantial quantities of the abundant
and nutritious drifting particles.

When the tide goes out,
they clamp their shells tightly together

to keep in their moisture
and to keep out attackers,

but some creatures know how to deal with that.

Each oyster-catcher has its favourite technique
for dealing with mussels.

It is usually the same as that used by its parents

though a bird needs years of practice
before it becomes really expert.

Some hunt in the shallow waters
for mussels that have not yet shut their shells.

Others carry unattached shells
away from the main flock

so they've got a little privacy.

They skilfully place the mussel in such a position
that they can cut it open along its hinge.

Other individual birds resort to brute force.

They hammer their way in through the shell itself.

As the tide retreats still further,
spire shells are exposed,

as many as 35,000 buried
within a single square yard.

All these mud feeders together
constitute a rich prize,

and there are abundant claimants.

Sandpipers, on migration, depend on them,

but at all times of the year,
wading birds come to the estuaries to feed.

The godwit,
equipped with long legs and a long bill,

can wade in water several inches deep

and collect food
before it can be reached by other birds.

The curlew prefers to work out of water.

Its long bill enables it
to probe deep into the mud for a worm,

and serves equally well as a pair of forceps.

The dunlin is a smaller bird
and goes for smaller prey:

Ragworms and insect larvae.

It feels for its food with its short bill.

The ringed plover, with a very short bill,

can only collect food
from the surface and locates it by sight.

It works alone so that its prey
won't be disturbed by pattering feet

and withdraw before being spotted.

The scything action of the avocet

collects creatures that live in the liquid mud.

Their bills are very sensitive.
As soon as they close on something edible,

the bird can juggle it up into its mouth.

The quantities of food taken by wading birds
from estuaries is enormous.

Some species consume every day
about a third of their own weight in food.

In a year, a single oyster-catcher

can consume the flesh over half a ton of cockles,

and many an estuary
supports tens of thousands of wading birds,

so these places are rich indeed.

As the river brings down
more and more particles of mud,

so the flats grow bigger and higher,

and on their surface they develop a slimy skin,

and that's formed by microscopic plants, algae.

They start the process of consolidation.

But soon, bigger plants get root,
like this glasswort,

and now the process really speeds up.

As the high tide brings in more mud particles,
they clog around the stems of the glasswort

and don't swill back to the sea when the tide fall

So with each new tide,
the flats grow higher and higher.

Glasswort is a plant
of the cold estuaries of Europe.

In the tropics, the colonisers
of mud are not small plants but trees:

Mangroves.

This mud is the pulverised remains
of rocks eroded from the Himalayas

that has been carried down
by the Ganges for 1,000 miles

and dumped on the edge of the Bay of Bengal.

This is the biggest intertidal forest of all,
the Sunderbans, 4,000 square miles of it,

and here roam many animals
that usually live in dry-land forests.

Axis deer.

Woodpeckers: The Indian golden-banded.

And wild boar.

But mangrove forests also harbour creatures
that live nowhere else at all.

The proboscis monkey eats
almost nothing but mangrove leaves.

It developed that specialism
on the island of Borneo,

and has never spread overseas,
trapped by its own specialised requirements.

Mangroves themselves
are distributed widely through the tropics,

for they have evolved
from many different plant families

and today there are
some 40 different species of them.

The flowers of this pioneering mangrove
are pollinated by the wind.

The seed doesn't immediately
leave the parent tree.

It starts to grow while it is still attached,

producing a green shoot a foot long
with a sharp end to it.

If it falls when the tide is in,

it floats horizontally in the buoyant salt water

and may be carried for miles
before being stranded.

If the tide is out, it stabs the mud
and stays in that position when the tide returns.

It puts out rootlets from the bottom
and leaves from the top,

and within a few days, it's firmly established.

Just as in cold-water estuaries,

there's a lot of organic matter in this mud.

Because it's so sticky, it isn't stirred up,
so there's little oxygen in it,

and the process of rotting
produces within the mud itself

an acid, smelly, poisonous chemical:
Hydrogen sulphide.

So these roots don't go down far into the mud.

Instead, they support the trees
by their sheer number.

But what about the other things
that normal roots do for normal trees,

like gathering nutrients and water and oxygen?

Well, these roots
deal with the nutrient problem like this.

It has this cluster of very fine roots

which don't go more than an inch or so
below the surface of the mud,

but it is on the surface of the mud
that the bulk of the nutrients are found.

As for water, there's plenty of it here,
but it's salty.

Some mangroves have a special membrane
around the cells in the root hairs

which filters off the salt.

Others absorb the salt
but then excrete it from the leaves,

or concentrate it in the leaf
and then the leaves are shed.

And oxygen, well, there are
several different solutions to that problem.

This mangrove has pores
actually in these prop roots

which absorb the oxygen directly.

This one has roots
which actually grow upwards,

so keeping pace with the rising surface
of the accumulating mud.

It's not only plants in the mangrove swamps
that have difficulty in getting oxygen.

So do animals, and this time, low tide,
is a period of particular difficulty.

Many molluscs,
like cockles and mussels elsewhere,

shut their shells to keep what moisture they have

and wait for
the food-and-oxygen-bearing water to return.

For them, it's a period of inactivity,
but for other creatures, it's just the opposite.

The mudskipper, of course, is a fish.

There are several different kinds.

This one lives near high-water mark,

and is the sort
that spends most time out of water.

It has to keep its skin moist
for it absorbs oxygen through it.

It also keeps its mouth full of water
swilling over its gills.

It feeds on the little crabs that graze on the mud

And having got one,
it needs another mouthful of water.

A second kind lives close to low-water mark,

so it is only out of water
for an hour or so each day.

It sifts the liquid mud
for small crustaceans and worms.

In between these two kinds
lives the largest of the three.

It is a vegetarian, collecting algae
and other microscopic plants from the mud.

And it, too,
nips back every now and then for a wet.

It guards its grazing rights with vigour,

building walls around its territory.

And when neighbours meet, there's trouble.

On clear mud, their territories
form a patchwork of walled ponds.

These flats are very flat,
so when a male starts to advertise for a mate,

he has to be a bit of a gymnast.

When a female is enticed into his private pond,

he can continue his courtship
at close quarters

in a more conventionally fish fashion,

with flexed fins, waggling tail
and enormous excitement.

They'll spawn in a burrow
at the bottom of the pond.

This crab is too big
to be intimidated by mudskippers,

even when it does wander
through their territories.

Its scissoring mouthparts not only
sort out its food but help it to breathe.

On top of its shell, there is a puddle of water,

and as its mouthparts move,

they circulate this into a gill chamber
within the shell,

out again and up to the reservoir on the top.

Eventually, the oxygen in the water
is exhausted

and the crab has to return to the sea,
tip it off and get a fresh supply.

Close by the edge of the sea,
the tiny soldier crabs feed with frantic haste.

No one else will steal their mud,
but they have to eat an enormous quantity

to extract the few particles
necessary to keep alive.

They have to work at it pretty well non-stop
and have no time to waste.

High up, beyond the reach
of all but the highest tides,

lives the large mangrove crab.

It keeps moist by boring its hole
as much as six feet deep to reach water.

The lure that tempts it out
is a newly fallen mangrove leaf.

And quickly back to safety.

Among the air-absorbing roots
of the mangroves, fiddler crabs are busy.

The females collect mud with both pincers,

working with the same frantic speed
as the soldier crabs.

The males need to munch
just as much mud as the females,

but work with one hand only,

for one of their claws is so big
that it is useless for feeding.

They use it instead to wave at passing females.

But it is also a weapon to brandish at rivals.

A less well-equipped male

gets a nasty hammering
even before he can get out of his hole.

The claw is long enough
to reach down into the burrow

to give his opponent a tweak
where he's least expecting it.

The purpose of the wave is to encourage
a female to follow a male into his burrow.

Is it possible perhaps just to take a moment or so
off from munching mud?

At low tide, there's lots for birds
to eat on the mangrove mud,

just as there is on estuaries elsewhere.

Terns hawk for fish that are easier to catch
now in the shallowing waters.

Kingfishers pounce on the fiddler crabs.

Great white heron stalk and stab.

The returning tide
signals "all change" for everyone.

This African mangrove snail
crops the algae growing on the mud,

but it mustn't stay there when the tide comes in,
for it would be attacked by fish.

It takes refuge up in the trees.

Its speediest climb
is barely faster than the rise of the tide,

so it has to set off in good time.

Its internal alarm clock
tells it when it should do so.

The soldier crabs are so well adapted
to their life scavenging on the exposed mud

that they have become breathers of air,
and without it they will drown.

As the tide advances,
each constructs a little igloo

which traps a bubble of air with which the crab
can breathe while the tide is in.

The mudskippers' territorial walls built with such
labour are breached by the incoming wavelets.

Higher up, the mudskippers shelter in burrows.

The incoming tide brings new creatures
into the swamps.

Shoals of fish arrive, searching for morsels
deposited by the river while the tide was out.

In the swamps of South-East Asia, archer fish
feed on insects that have fallen on the surface.

Uniquely, they also have a way
of collecting insects from above the water.

There is a groove in the roof of their mouth,

so that a sudden thrust of the tongue
produces a spurt of droplets like a water pistol.

When there is a crowd,
a marksman can't be sure of getting his prize.

So in company,
it may be better to try a direct assault.

The larger fish are themselves food for otters,

but these hunters have broad appetites

and will enthusiastically tackle snails,
crabs and even mussels.

They are great travellers, swimming for many
miles up into fresh water or down into the sea

and even out to offshore islands,

and they have an enormous appetite for play.

The largest of all living reptiles
is found among mangroves:

The estuarine crocodile,
a monster that grows to 23 feet long.

Like its ancestors that lived
when dinosaurs dominated the earth,

it's an ocean-going creature,

and, as a consequence,
it's the most widely distributed of all crocodiles

living from the Bay of Bengal
through northern Australia to the Pacific,

even reaching isolated mangrove swamps
on the islands of Fiji.

As the mangroves establish themselves
farther out into the sea,

the mudflats they've built grow higher and higher.

Rainwater washes them clean of salt,

and eventually they become dry fertile forest,
beyond the reach of the sea.

The banks of mud and sand
that the rivers lay down around their mouths,

even when they are not big enough
to rise above water,

protect the land against the attacks of the sea,
for tall waves can't travel across shallow water.

But if a current sweeping down the coast
carries away the sediment

and scours the sea floor clean,

then waves arrive at the coast full of power.

Where the land dips steeply into the sea,

the territory between the tides is not miles
across but condensed into a narrow band.

The creatures that live here, like all intertidal
creatures, are threatened by two dangers.

At the high-water mark,
there are physical problems of being dried out,

and at the low-water mark,
there are biological problems

of animals that creep up from the sea
to prey upon the intertidal creatures.

The interplay of those two sets of problems

produces a series of horizontal bands
along the coast,

each dominated by the particular species

which best deals with the problems
at that particular level.

Such bands can be seen on coasts
all over the world,

but here on the north-west coast of America,
they are strikingly clear.

The bottom band of all is only fully exposed

when the moon and the sun
are in such an alignment that they pull together

and the tide withdraws a long way
from the edge of the dry land.

Organisms here only tolerate
a brief exposure to the air

and are unable to prevent themselves
from being dried out.

The sea urchin, in water,
gnaws away at encrusting algae.

But out of water, it can do nothing
but simply hang on to the rocks.

Nearby, giant sea anemones
droop their tentacles,

and many withdraw them,
for in air there is nothing to feed on.

Sea squirts can only filter
for their food spasmodically.

Starfish are meat-eaters,
and this species feeds on mussels.

It envelops them with its adhesive arms,
wrenches apart their shells,

and feeds on the flesh within.

Below low-water mark,
they kill any mussel that tries to establish itsel

But like many of these low-level creatures,
they can't feed out of water.

So higher up, where the rocks are exposed
to air for longer, conditions favour the mussels,

and they form a dense band,

cropped at the lower edge by starfish,
but beyond their reach higher up.

The massed mussels provide shelter
for lots of other creatures:

Small starfish, too small to tackle a mussel,

worms and crustaceans,
winkles and other molluscs.

The mussels hold on to the rocks
with bundles of threads,

but can't withstand the pull of the roughest waves

and in winter storms,
sheets of them may be ripped away.

In more exposed places
where the waves beat with a particular ferocity,

mussels give way to goose-necked barnacles
which clasp the rock with a long fleshy foot.

They feed by holding out stiff, fan-like arms
which catch particles from the waves,

not when they crash in,
but as their waters flow gently back.

On the most exposed promontories,
the mussels are ousted by a plant:

An odd-looking alga known as a sea palm

which lives only
on these north-western coasts of North America.

The crown of leaves
at the top of its rubbery stem

enables the sea palm to harness the power
of the waves and use it to attack the mussels.

The plants, perhaps surprisingly, are annual.

In the spring, an individual plant
may achieve the difficult feat

of getting hold of an individual mussel
in the mussel bed, as this one has done.

When it's mature, it will produce spores,

but only when it's out of water as it is now.

So instead of the spores being distributed widely
as those of other plants are...

...the spores of the sea palm
trickle down the grooves in these leaves

and into the mussel bed here.

When the first storms of the autumn come,

they may catch
underneath the fronds of this plant and rip it up.

But the holdfast grips the mussels so firmly
that the mussels come away with it,

revealing the bare rock,

and that means
that the offspring of other nearby plants

can get a hold on the bare rock.

So by the sacrifice of one palm
growing on a mussel one year,

next year there will be a whole grove of palms
growing firmly on the bedrock.

But mussels do require
a certain amount of immersion every day

if they are not to dry out and die,

and this line marks exactly that.

Above it, no mussel can live.

The creatures that can are these: Barnacles.

Clamped tightly to the rocks, they conserve
very effectively the moisture within their shells.

They collect the minute quantities of food
they require to grow and reproduce

from the relatively infrequent submersions
at high tide,

which in some cases
may only occur for an hour once a month.

So each level on a rocky shore
is dominated by the organisms

that best deal with the precise combination
of pounding by the waves,

exposure to the air,
and attack by deep-water predators.

None, in the long run,
can claim permanent occupation,

for the attacks of the waves are unceasing.

With unfailing accuracy,
the sea picks out the softer parts of the rocks

and cuts its way into them.

Water at great pressure
is driven into joints and cracks

until it penetrates a cliff
and forms a blowhole.

On the southernmost tip of Australia, storms
of great ferocity sweeping up from the south,

with the full force
of the Antarctic gales behind them,

beat away at sandstone cliffs which have lines
of weakness that run horizontally and vertically,

so the rock is cut away in huge blocks.

The sea, having demolished the cliffs,
then works on the debris.

During storms, it picks up the boulders
and hurls them at the cliff face.

At calmer times, it rolls the rocks over the seabe
and casts them up on shingle banks.

Every movement chips and grinds the fragments
until they are reduced to sand grains,

and now even a gentle current can pick them up
and carry them for miles down the coast,

eventually to abandon them in banks and strands

in the lee of islands or in sheltered bays.

Every wave of every tide
stirs up the surface of the sand,

so plants find it impossible to get any grip on it
as they can on rocky shores or mudflats.

So a beach like this looks as lifeless
as any part of the margins of the land.

But if the sand grains
are not too small and compacted,

then each will retain around it
a thin film of moisture even when the tide is out,

and in that microscopic space, animals can live.

These translucent boulders are,
in fact, sand grains,

and the tiny snake-like animal
a worm that could sit on a pinhead.

All these inhabitants of the sand

are, necessarily,
adept at writhing, gliding and crawling

as they search for the few edible fragments
trapped between grains, or pursue one another.

This one is only a temporary lodger in the sand.
It is the larva of a mollusc.

A hydra lives here. It's like the one
that's common in freshwater ponds,

but it has one elongated tentacle
with which it anchors itself.

A nematode worm produces glue
from a gland on its tail

which helps it to maintain its position.

This is another larva
that at the beginning of its life floats in the se

but settles down into the sand
to continue its development.

It builds a tiny tube of mucus
which it carries about with it

and clings to with bristles on its flanks.

When it grows up, it does the same thing
on a larger scale, above the sand.

It's a worm called the sand mason.

Now it not only builds a tube,
but it adds long tassels to the top.

These slow down the water
so that suspended food particles fall

and can be gathered by the waving tentacles.

The tubes need constant renewal,

and this is how the sand mason does it,
speeded up 125 times.

Although plants can't grow
on these perpetually moving sands,

those dislodged from the rocky parts of the coast
by waves are washed up here,

and there are plenty of creatures
on the beach waiting for them.

These are sand-hoppers.

They hide below the surface
to avoid being baked and dried out by the sun,

but now there is food to be had.

On many beaches, their numbers are astronomic.

There can be as many as 25,000 of them
in one square yard of beach sand.

The sand-hoppers favour rotting vegetation.

Rotting flesh attracts crabs.

The remains of a squid
is a banquet for ghost crabs.

Occasionally, when there is a chance,
it may be better to cut off a length

and haul it away
to consume it in the privacy of a burrow.

The crabs and the shrimps
live close to the high-tide mark.

The incoming waters
bring with them another team of scavengers.

This periscope on a South African beach
belongs to a mollusc: A plough snail.

It inflates its plough-like foot
by pumping in water,

and it uses it not so much as a ploughshare
as a surfboard.

The waters pick it up and wash it swiftly inshore,
together with its potential food...

...a stranded jellyfish.

The plough snails detect its presence
from the taste of decay in the surrounding water

and advance on it with great speed.

To avoid being swept up the beach
and being stranded, they eat fast,

and then, while there is some food left,
they burrow into the sand.

There they wait for the tide to turn

so that they can ride back on their surfboards
to deeper water and safety.

Very few sea creatures venture
above the limit of the highest tide and survive.

One group of animals is compelled to do so
by the nature of their ancestry,

and on this one beach in Costa Rica,
they stage an astonishing invasion.

Turtles.

They are Ridleys, the smallest of
the sea-going turtles, only a couple of feet long.

Turtles are descended from land-living reptiles,

and, like all reptiles,
they lay eggs that only develop and hatch in air.

Every year, adult females,
having mated at sea, must move onto dry land.

They arrive at a rate of up to 5,000 an hour.

They use only one or two of the thousands
of beaches that seem to be suitable.

What is more, they only choose to do so
on just a few nights in the year

between August and November.

Efficient though their flippers are in water,

they are barely strong enough
to lift the turtle clear of the sand.

It has to drag itself up the beach.

This mass breeding
may be an advantage to the turtle.

Since it only occurs on a few nights a year,

their eggs can't support
a large permanent population of predators,

as they might
if the turtles were to lay over several months.

Yet, even so,
for reasons that we still don't understand,

less than one in a hundred of the eggs
produces a hatchling which reaches the sea.

Each female lays a hundred or so.

That done, she carefully fills in the hole.

A few coatimundi and vultures
come down from the forest to plunder,

but they make little impact
on the millions of eggs that are laid.

Next night, many thousands more Ridleys arrive.

On other beaches, more secretly,
other very different turtles are laying.

This is the largest of all the marine turtles.

This magnificent creature
is the giant leatherback turtle.

And it's a most mysterious animal.

It's a solitary wanderer of the oceans.

Individuals turn up almost anywhere in the tropics
but they go much farther than that.

They've been recorded as far south as Argentina,

and as far north as the British Isles
and North America.

It's a creature of mystery,
because although we know what it feeds on,

which is sea urchins and fish and, oddly enough,
jellyfish, we know little else about it.

We don't know how long they live.
We don't know how the male finds females.

We don't know how females navigate
to find nesting sites like this one.

Indeed we didn't know where
the main nesting sites were until 25 years ago.

Then it was discovered that some nested
on the Suriname coast of South America

and some nested here,
on the east coast of Malaysia.

Of course, the people here
have always known about the turtles

and have always plundered those eggs.

Today, however,
there are more people than ever here,

and the eggs are plundered more seriously,

so undoubtedly, this huge
and extraordinary creature is in danger.

But maybe the leatherback turtle has
other breeding grounds that we don't know about.

Maybe it goes to small, tiny coral islands
in the emptiness of the ocean

to find beaches far away from man.

That, indeed, is where we ourselves
will be going in the next programme.

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