Original subtitles

Ten million species

live on planet Earth.

Each one is remarkable.

But none can survive on its own.

All life depends upon connections.

Unexpected, invariably complex,

beautiful relationships between millions of plants and animals.

In our waterworlds,

I want to show you why

this crab needs a tiger... TIGER GROWLS

..why this giant otter needs a snail...

..and why this shark needs a sponge.

Connections like these form the planet's great ecosystems.

They're vital for all life.

I want to show you our world as you've never seen it before.

This is the Gullfoss waterfall in Iceland.

100 cubic metres of water are falling here every second.

So this is just about as close as I want to get,

because this is a dangerous and volatile environment.

But for all of that danger, these raging torrents contain

an ingredient which is absolutely vital for life.

And the clue is in the name.

"Gullfoss" means "Golden Falls."

The colour is produced by millions of tonnes of raging water,

relentlessly carving through rock and soil.

And accumulating that golden sediment.

And there's something else vital being carried in this water...

oxygen.

Together, these are incredibly potent ingredients.

At the moment, all of this is just cargo,

being swept along by this very fast-moving water.

But with ingredients like this,

if the environment changes, then the potential for life is huge.

It doesn't matter where you are.

Most life on Earth depends on the simple ingredients

that start upstream.

Places where, normally,

just a few specially-adapted creatures can survive.

So, how do mere oxygen and sediment

ignite such a richness of life downstream?

To find out, I'm going to witness

one of the greatest explosions of life on Earth.

Over millions of years, waters from the Brazilian highlands

have flooded into a vast lowland basin...

..the Pantanal.

Look at this!

These murky waters are virtually boiling with fish.

I've never seen so much life so densely packed into one place.

Every river and every tributary that we've paddled up in the Pantanal...

CAIMANS SPLASH ..has been lined with these animals.

An estimate suggests there might be as many as ten million caiman living in the Pantanal.

That would make it the largest concentration of land vertebrates anywhere on Earth.

But the really staggering thing about the animals in the Pantanal

is their sheer size.

Look at this wonderful bird.

It's called the jabiru stork.

The tallest flying bird in South America.

This really is a land of the giants.

The world's largest snake, the green anaconda,

which can grow to nine metres long.

Even the plants are monsters.

Look at this splendid spread of giant water lilies.

Absolutely fabulous things.

A single plant produces around 40 leaves

and each leaf can grow to three metres wide.

BIRD CHEEPS

Even the rodents here are the largest in the world.

These are capybara.

They're the dominant herbivore in the Pantanal,

and they occur here in huge numbers.

And what does it take to catch such an overgrown rat?

(Look at that! Look at that!)

We're about six metres from a wild jaguar. It's unbelievable.

The jaguars in the Pantanal are the biggest cats

anywhere in the Americas.

(Oh, my goodness!)

And then, there's the apex predator -

the king of the river.

OTTER SQUEAKS Giant otters.

Remarkable animals.

OTTERS SQUEAK

They're supremely adapted for their aquatic lifestyle.

And given the size of these animals and their abundance here,

this has to mean that this water is literally full of fish.

It's like an Eden, it's just packed - packed with life!

So, how did that cargo from those barren mountain streams

help create this magical place?

Here's a jar of water.

I've just collected it from the creek behind me.

And look, if I shake it, to mimic the action of a waterfall,

swirling and frothing in a violent eddy,

you can see that all of the material here

is now held in suspension.

But what's so important about that material?

What's so important about that cargo?

Well, when water tumbles down from the mountains,

through the fast-flowing streams, along the giant rivers,

it's constantly grinding away at the bedrock and the soil,

picking up material, so that when it arrives here in the Pantanal,

it's filled full of silt, sediment and detritus -

a heady cocktail of inorganic and organic material.

And it's filled full of things which are essential for life -

things like nitrogen and phosphorus.

And look - now the water in my jar has begun to slow down,

the material in it has started to settle out.

And this exactly replicates what is happening here in the Pantanal.

In fact, it's settled out right here,

and what I'm standing on is a great plain of fertility.

BIRDS CHIRP

This land of giants is exceptionally fertile

because that cocktail of nutrients deposited by the rivers

has been trapped here.

Gradually, they've built up, year-on-year,

over millions of years.

But this hugely productive process has only been possible

thanks to the tireless work of one species of animal.

It's so important that even the giant otter

depends upon it for its survival.

Now, you might expect my hero of the Pantanal

to be one of the large creatures that we've already seen,

but brace yourselves... My hero...

is this, the apple snail.

And I can tell you that, without this humble animal,

the Pantanal wouldn't - couldn't - be such a rich environment.

But how on Earth can a snail be so important?

The apple snail spends much of its life on the river bed,

safe from most of its predators.

It has a fish-like gill that can remove oxygen from the water,

so it can breathe beneath the surface.

Here, there's plenty of food...

..because there's nothing that an apple snail likes more to eat,

than dead and decaying vegetation.

Its teeth can saw through the toughest plant fibres

and, unlike most animals, it can digest cellulose.

But like all animals, it needs to relieve itself

and that's when the magic happens.

It's miraculously recycled all that dead material

back into accessible nitrogen and phosphorous.

Five-star fertiliser for the next generation of plants.

But that's not the only way this species

recycles essential nutrients.

For hundreds of predators, apple snails make a very tasty meal.

Young caimans particularly enjoy them.

And each mouthful

helps spread the vital ingredients of all life around the Pantanal.

It's thanks to all of this recycling by the apple snail

that the Pantanal is so full of so many giants.

But, in order to carry out this pivotal role,

the snail has to overcome one huge challenge -

one which puts the whole ecosystem of the Pantanal on a knife edge.

THUNDERCLAP

April brings rains to the highlands across central South America.

For months, the Pantanal has been drying into a patchwork

of small pools and grass.

But now, the rivers swell.

They burst their banks and drown the grassy plains.

This is the most dangerous time for this ecosystem,

because the most important ingredient for life is running out.

Clearly, there's no shortage of sunshine here.

Nor is there any shortage of nutrients.

No, what's in surprisingly short supply in these waters, is oxygen.

As billions of tonnes of grass is swamped, it begins to decay...

..stagnating the water and robbing it of that oxygen.

The Pantanal is suffocating.

It will only survive if that rotting grass

is rapidly recycled into new forms of life.

The Pantanal now needs the apple snail more than ever.

But without oxygen, not even it can survive.

Thankfully, it has a secret weapon.

Uniquely amongst snails,

it possesses a beautifully-evolved, telescopic appendage...

..a snorkel!

The snail pumps air straight into a special lung.

And when it's breathed enough, it returns to what it does best -

processing that rotting grass.

So whatever this place throws at them,

billions of apple snails keep munching away

and fertilising the Pantenal.

The aquatic ecosytem flourishes,

supporting enough fish to satisfy the king of the river.

OTTERS SCREECH

The giant otter.

OTTERS SNORT AND SCREECH

SCREECHING CONTINUES

Just listen to that!

Their vocalisations are constant, this family party,

constantly in touch with one another.

These screeching calls are territorial -

warning other animals that this group owns this stretch of river,

and all of the fish in it.

Any rivals are aggressively dealt with.

The whole family regularly patrols a stretch of up to 20km.

And there's nothing that frightens them -

not even caimans.

Now that they've got the river to themselves,

it's down to the business of catching fish.

And their appetites are insatiable.

Each animal needs to eat a tenth of its bodyweight every day.

In the Pantanal, there really is plenty for everyone,

and it's all thanks to a mollusc.

For me the most important species in the Pantanal is the apple snail.

It's a true keystone species,

involved in everything that's going on here.

It converts fish and other matter into grass.

Grass and aquatic vegetation into food.

It's even food itself,

and it can survive anything that this place can throw at it.

It shapes and structures the Pantanal.

Therefore, it's what we call an ecosystem engineer.

Without it, all those millions of caimans, the capybara,

the jaguar, and especially the giant otter,

would struggle to live here.

And that's why the giant otter needs the snail.

I like that. I love the connectedness!

The tireless work of apple snails over millions of years

has helped to create the Pantanal.

And all over the planet, from the Florida Everglades,

to the Fens of East Anglia,

to the Nile, freshwater snails and other wetland creatures

recycle material on an epic scale,

sustaining watery ecosystems, and making them rich in life.

And thanks to these animals, the impact of wetlands

on the planet is huge.

At one end of the wetland, the raging water from mountain streams

is soaked up like a giant sponge.

At the other, it's released in a steady flow.

In doing so, these wetlands ensure

that the rivers and the animals downstream

get a reliable supply of water.

But as the river makes its way to the sea,

life in the water faces a much bigger challenge.

This is the end of the line for the mighty Ganges.

It's the swamp of the Sundarbans, on the coast of Bangladesh.

On the ground here, it feels and smells like an alien world.

The whole place is pervaded by the stench of rotten eggs,

generated by sulphur-belching bacteria.

It's certainly a lot less inviting than the Pantanal.

It's surprising that anything survives here at all,

because life in this place

has to survive some pretty tough challenges.

For a start, the silt.

You see, when the water reaches the coast,

only the finest particles are held in suspension

and when they drop out, they form this...

..thick, gloopy mud. Whoa!

It's so thick, that not even air can penetrate it,

so no oxygen can get into the soil.

And, as if that wasn't bad enough, twice a day,

with the rise and fall of the tide,

this whole place floods.

Precious nutrients, in the form of leaves, are flushed out to sea.

And, worst of all, everything is drenched in bitter salty water,

which very few plants can tolerate.

But the Sundarbans is not the hell on Earth that it might seem.

Look at this beauty!

A black-capped kingfisher.

A brahminy kite.

There are enough fish here to support millions of people.

Macaque monkeys...

..chital deer, too.

And there's one creature that is very special.

But it's extremely well hidden.

It's also a man-eater.

Tiger!

I can see the stripes on its back.

It's got its rump facing towards me,

its head's lying on the ground.

Wow!

It's about the worst ever view of an animal that I've ever had,

and yet it's one of the best!

It's getting up.

Which way did it go?

After that tantalising and remarkable view of an animal,

we've been able to follow a diary of its movements, here in the mud.

And, if you look, you can see that the tiger has come here.

Here's a pug mark, here's another, here are three more.

But I think what's happened here

is that the tiger has come to this point, it's changed its mind,

and it's turned around, headed back this way.

There's another print there.

And it's gone off, into the forest.

And this is not a one-off.

Pictures from our camera traps reveal,

that living in this salty, drowned forest

is a large population of Bengal tigers.

Surely one of nature's most magnificent predators.

And despite the fact that population estimates vary,

we think that a quarter

of the world's wild tiger population

might be living here in the Sundarbans.

So, there has to be enough food for them,

this has to be a productive ecosystem.

But how can a muddy, salty, sulphurous bog support so much life?

Well, the secret of the Sundarbans, lies in beautiful

relationships that have evolved between the most unlikely species -

including the tiger.

And it all starts with a very peculiar plant...

..the mangrove - the only trees that can survive in salty water.

They even expel some of that salt through their leaves.

And as for the lack of oxygen in the soil,

mangroves have a spectacular solution -

not unlike that of the apple snail.

Now normally, plants access oxygen through their roots

from tiny pockets of air in the soil.

But in this sticky ooze,

these pockets are virtually non-existent.

But then, the mangrove is a pretty special plant.

All of these spikes sticking out of the soil here are roots,

and they act a bit like snorkels, sucking in oxygen out of the air

when the plant can't get it out of this thick mud.

But then, the mangrove doesn't just rely on its snorkels.

There's something else going on here,

something you can only appreciate at low tide.

Millions of crabs!

Leaf-eating crabs and fiddler crabs.

They're called fiddler crabs,

because they have this vastly-enlarged front claw.

And when they're feeding, it looks like they're playing the fiddle.

They also wave them at any adversaries

in a relative show of size and strength.

In fact, when they're fully grown, that claw can represent 65%

of the crab's body weight -

quite an investment for something to wave around

at your enemies.

These fiddlers are displaying to defend their territories.

And their most valuable real estate is underground.

This little fiddler is excavating mud to create a burrow.

When he's finished,

it's going to be more than half a metre deep.

His burrow gives him somewhere to hide from predators,

like this stork.

And when the tide comes in, from predatory fish.

These leaf-eaters live in communal burrows,

and together, their tunnels form an underground labyrinth.

All of these burrows are vital for the mangrove.

At low tide, they channel an air supply through the mud,

direct to the roots.

And it's not just oxygen.

The crabs even supply the trees with food.

The first ingredient is all those smelly bacteria.

Look really carefully, and you can see this crab feeding.

It's picking up particles of soil and passing them to its mandibles.

When it gets enough, it forms them into a ball,

and it gradually removes all of the organic material,

detritus and bacteria,

and then it discards the ball.

And you can see those that it's processed lying on the surface here.

And if the crabs didn't do this, this mud wouldn't be very nice -

a nasty, sulphurous ooze.

Racing against the tide,

this fiddler is taking bacteria-rich mud back to his burrow.

Here, he'll recycle it and release nutrients

for the roots of the mangrove.

Further up the beach, this leaf-eater is also working hard

to gather his food before the tide steals it.

These crabs collect a staggering 80% of the leaves

that fall here in the Sunderbans

and store them at the bottom of their burrows.

Where they, too, will essentially fertilise the mangrove.

But best of all,

the burrows even help control the saltiness of the swamp.

When the tide comes in,

toxic seawater flows into the burrows

and mixes with fresh water.

And this allows the mangrove

to expend less of its energy excreting salt,

and more on actually growing.

Without these burrows,

the Sundarbans simply couldn't survive.

Together, the crabs make a vast network -

a sort of Sundarbans tube system.

The scale of the tube system is unbelievable.

Just one square metre can have 300 tunnels.

Crabs are ecosystem engineers.

Without the many millions of them,

living in this mangrove, the Sundarbans simply couldn't work.

That's why the tiger needs the crab.

So the tiger needs the crab. But it's more magical than that.

And there's an even more unusual relationship...

..one that protects the Sundarbans from a lethal threat.

Thanks to the crabs gardening the mangroves,

the Sundarbans support some large herbivores.

But too many eating too much would soon damage the forest,

so it needs protection.

The monkeys have sounded a warning.

This family of chital deer won't be staying much longer.

It's the very presence of these terrifying predators

that protects the Sundarbans.

You see, in any ecosystem,

top predators exert what we call "an ecology of fear".

And this influences the behaviour and movement of their prey.

Here, that might be monkeys, or deer, or humans.

In the Sundarbans, the tigers keep

large numbers of people out of the forest,

and they also keep all the herbivores on the move,

so they don't damage the trees.

So, in a way, the tiger needs the crab to help build this place,

but then the crab needs the tiger to help protect it.

You've got to admit, that's pretty neat.

And the result is this -

the largest mangrove forest in the world!

This mangrove ecosystem is dependent on a complex web of relationships

between species as diverse as crabs and tigers to make it functional.

But surprisingly, these connections don't end here,

because what happens on the coast, where the river meets the sea,

actually has a profound effect on what happens out there.

Across the planet, coastal ecosystems, like the Sundarbans,

are essential for both the land and the sea.

They act as barriers, protecting the land from storms.

And they provide vital nurseries for ocean-going fish.

But, more importantly, they trap much of the silt and sediment,

so that clean water flows out to sea.

And in the tropics, this has a profound effect

on the world's richest marine habitats...

..coral reefs.

And one of the finest on Earth is here - the Maldives,

There's something very odd about coral reefs.

Look at the water - it's clear. It's absolutely crystal clear.

I can see a vast and colourful coral city.

And across the world's oceans,

these are home to a quarter of all marine species...

..from tiny clown fish...

..to the black-tipped reef shark.

This really is

the ocean equivalent of a rainforest.

But it's also a puzzle.

The waters around this reef aren't just low in sediment,

they're consequently low in nutrients.

So, how on Earth can they support so much life?

It was a puzzle that stumped the world's most famous biologist,

Charles Darwin.

And thus it became known as Darwin's Paradox.

And it took science more than 100 years to figure it out.

And guess what the key was?

Connections. Wonderful connections between the species that live here.

Take the coral itself.

It's not made from one,

but from two organisms.

First, tiny creatures, just a few millimetres in length,

called polyps.

Polyps spend their lives filtering

microscopic particles in the clear waters.

But up to 90% of their food comes from their coral partners.

Sheltering within the safety of the polyps,

are colourful specks -

algae.

Like plants, these tiny algae get most of their food

through photosynthesis, to make sugars, powered by the sunlight.

So, whilst the polyps provide the algae with protection,

in return, the algae supply the polyps with food.

But this ecosystem just doesn't add up.

As Darwin knew, this fabulous diversity of life here

can't be sustained by just sunlight alone.

It also needs vital nutrients, things like nitrogen,

phosphorous and potassium.

And if it doesn't get these from silt,

then where does it get them from?

Well, all of the animals

that live in these waters excrete valuable nutrients.

But the constant tidal currents quickly wash them away.

So, what the reef needs is something that can hold on to those nutrients.

Well, there is such a thing,

and there's also a very special creature

that's going to lead me straight to it.

The hawksbill turtle.

They're strong swimmers,

but I need to keep up with it, to see where it goes.

And I'm really hoping that this one is hungry.

It's a rather odd-looking meal - a sponge.

It's tough, but the sharp beak of the hawksbill

can bite through its sinuous flesh.

What's clearly much harder

is actually keeping hold of it in the swirling currents.

So turtles love to eat them,

but why does the reef need the sponge?

Well, sponges are creatures that live embedded amongst the coral.

And there are thousands of species.

They are amongst the most bizarre animals on the planet.

They don't have eyes, a heart, or a nervous system.

But the weirdest thing about a sponge is the way that it feeds.

The sponge sucks the coloured water out of this syringe.

The plunger isn't even being touched.

As sponges siphon water through their bodies,

they extract the nutrients.

Although those nutrients are in tiny concentrations,

if the sponge pumps quickly, it can get enough.

Their secret is the scale with which they can do this.

A sponge like this one can pump five times its own volume of water

through its feeding canal in just one minute!

And a sponge, just 60cm in length,

can filter the equivalent of an Olympic-sized swimming pool

in just five days!

So, as the animals on the reef excrete nutrients,

it's the sponges that capture and concentrate these viable food.

It's these nutrients that help feed the reef,

benefiting everything that lives here,

from the coral, right up to the top predator.

This large-scale recycling of nutrients

helps keep these nutrients around the reef for longer,

delaying the inevitable leaking away into the open ocean.

For that reason, it's the sponges that are my coral reef heroes.

What I've learned here, is nothing short of a revelation, really.

Everything is connected - the fish, the turtles, the corals.

But it's not just these animals - it's the sponges, too.

And further upstream, the tiger and the snails.

And when all of these things come together,

the connections make this place work.

And it really does work,

because this is one of the richest ecosystems on our planet.

Around the world, ecosystems in shallow seas like these,

convert scarce nutrients in the water,

to provide a haven for a huge variety of sea life.

But the most miraculous place of all is further out to sea...

..in the deep ocean.

And in this endless expanse,

it appears there's nothing living here

and nothing to eat.

On the face of it, it's devoid of life.

But, of course, it's not.

It's home to the world's largest animals.

Thanks to connections that lead back to those wetlands, upstream -

all the way back to that apple snail.

All of the silt, the sediment, and recycled organic material,

that's washed down from the wetlands, the mangroves

and the coral reef, where's it all gone?

Has it just washed out into the open ocean,

to be lost for ever?

And if it has, what are the animals that live here feeding upon?

Well, potentially, it could have been a great waste of food,

if it weren't for the way that the water moves.

All of those valuable nutrients

fall like marine snow on the sea bed, far below.

But they're not lost for ever.

Deep sea currents of unimaginable power,

stir up the oceans on a global scale.

It may take centuries, but carried by these upwelling currents,

many of those lost nutrients eventually resurface.

A sudden bounty of all the ingredients needed to sustain life.

And a feast for all the microscopic algae - phytoplankton.

The plankton that live here on the surface are dependent

on these upwellings of nutrients.

And when they're able to combine them

with bright sunlight, their population explodes.

These multiplying plankton soon attract millions

of small crustaceans, krill, larvae of all kinds

and many other creatures.

And together, they combine

to create the biggest frenzy of life on our planet...

..a plankton bloom.

And plankton blooms attract some awe-inspiring creatures.

Here, in the Indian Ocean,

I've come to witness one of the most enchanting...

..the manta ray.

They fly through the water,

filtering and feeding on the plankton.

They can eat 30 kg a day.

Astonishing! Astonishing! Just so graceful!

And it's not just rays.

The plankton bloom has attracted the world's largest fish.

This whale shark, may have swum thousands of kilometres,

just to feast on this plankton bloom.

And this great spectacle of life is all thanks to connections

that stretch back, right across our planet.

All of the debris of life on Earth ultimately ends up here,

in the ocean.

And that's why the marine environment

is so dependent on healthy terrestrial ecosystems -

places like the Pantanal wetlands and the mangroves in the Sunderbans.

That's why the ray needs the snail.

A giant fish needs a moderately-sized mollusc,

thousands of miles away.

Unexpected, undeniably complex, but a certainly beautiful connection.

But this is really only the beginning.

Because the presence of this plankton affects

not just life in the ocean, but all life on Earth.

And that's because plankton blooms are so dramatic

they can even affect the weather.

When the blooms reach their peak, they alter the temperature

of the ocean's surface,

driving weather systems across the whole planet -

systems that create rain.

So, here we are, back at the beginning!

Some of the water that's evaporated from the oceans,

is now pouring down on these highlands,

and beginning its long journey back to the sea.

It's remarkable to think that this rain,

falling in this remote corner of the North Atlantic,

is actually dependent upon the activity

of microscopic plankton in the sea.

And that those plankton, in turn, in order to flourish,

are dependent upon the interconnectedness

of all of our waterways and the life that lives in them.

And that is truly remarkable!

If you'd like to know more

about the fascinating web of links between species,

the Open University has produced some material

both to inform and inspire you.

For your free copy,

or to find out more about Open University programmes,

phone...

or go to the website...

and then follow the links to Open University.

Subtitles by Red Bee Media Ltd