The Living Planet

Most of the earth is covered by water.

In fact, two-thirds of it is.

And it's only in this generation

that we have been able to move about it with any degree of freedom as I am doing now.

So perhaps it is not surprising that still most of this vast domain

is still unexplored.

And in the geographical sense,

the surface of the sea, the floor of the sea,

is even more varied than the surface of the land.

To see just how varied it is, let's take an imaginary journey across the Pacific

starting in the west where the ocean is deeper than anywhere else on the globe:

The Mariana trench.

The bottom of this immense valley seven miles below the surface is grooved by deep faults.

If Mount Everest rose from the bottom,

its summit would still be beneath 7,000 feet of water.

Down at the very bottom, the water pressure is some seven tons per square inch,

the temperature is close to freezing, and it's pitch-dark,

for it is far beyond the reach of sunlight.

As we climb up out of the trench, we move onto a plain covered with reddish mud.

A few hills rise from it, but there are still some 20,000 feet of water above us.

Travel eastwards over these plains for 1,000 miles,

and we reach a range of fantastic mountains.

Their summits are covered by a white deposit like snow,

composed of the limestone skeletons

of microscopic organisms that have drifted down from the surface.

Before they reach the lower slopes, the water pressure becomes so great they dissolve.

Currents sweeping up from the south pile the sand into dunes 150 feet high

which advance slowly across the sea floor as dunes do in a desert on land.

In places, the sand is littered with metallic lumps, some as big as cannon balls:

Manganese that under these pressures has precipitated out from the salty water.

After a journey of 4,000 miles, we reach the biggest mountains of all.

These are the flanks of the great volcanic islands of Hawaii.

Their sides are steeper than any mountain on land

for they are never eroded by frost or by rivers armed with gravel.

They rise from the sea floor 15,000 feet to the surface

and continue for an almost equal height above it,

so they can truly be reckoned the highest mountains in the world.

As we climb up their sides towards the surface,

we return once more to light and to abundant life.

Life began in sunlit waters like these some 3,000 million years ago,

and creatures very similar to those ancient primeval organisms

still flourish in shallow seas all over the world.

Feather stars like these waved their tentacles long before any fish appeared,

at a time when the land was still bare of life of any kind.

Horseshoe crabs come from an equally antique stock.

Fossils have been found in rocks 600 million years old.

Most of their relatives have died out.

These are the lonely survivors of a widespread and successful group.

Even older, indeed among the first of all living things,

microscopic plants encased in shells of limestone.

They use sunshine to build, from simple chemicals in the sea water, their own tissue.

This act of photosynthesis, transforming mineral into vegetable,

is the basis of all life in the sea.

A myriad of creatures feed on them.

Some are tiny animals, scarcely bigger than the plants that they waft into their mouths.

This floating community of plants and animals is the plankton.

Its members move endlessly through the blue seas.

Many are fragile constructions ofjelly that would collapse without the support of water.

Some are colonial, several feet long.

They call this Venus's girdle. It's two feet acros

Light catches in the beating hairs that ripple over its body

as it moves slowly through the water.

The animals of the plankton, all those that can't photosynthesise,

sweep up the tiny plants and other edible particle in many different ways.

This one extends a forest of long tentacles in which smaller organisms get entangled.

This, transparent as glass, trails stinging thread

and pulls them in whenever they catch something.

Worms actively pursue their prey.

Creatures from many families of animals have representatives in this community.

Some are permanent members, some only temporary,

joining it when they are young larvae and drifting great distances

before they grow up, change shape and settle down to a more static life.

But all are ultimately dependent on the tiny microscopic plants.

There is another way in which the drifting particles of food can be gathered.

Instead of moving with the current, you stay fixed to the rocks

and allow the currents to bring food to you.

That is the technique used by anemones and many other creatures.

As the water sweeps by, the particles it carries stick to the waving tentacles.

All kinds of creatures live in this fashion. This is a sea cucumber.

And this, a basket star.

The water brings not only food but vital oxygen.

If it doesn't bring it fast enough, it can be speeded

by pulsing as these coral polyps are doing.

It's not only simple creatures like anemones and corals that filter currents.

Other more complex animals have also taken to doing so.

This is a remote relative of the shrimps that has settled down on its back,

grown a protective shell and fishes for the passing particles with its feet

It's a barnacle.

Some crabs also rely on the currents to bring them meals,

and pluck them from the water with tiny pincers.

But the biggest of all filter-feeders propel themselves gently through the surface waters.

A manta ray, 18 feet across.

It often feeds at night

when dense swarms of the plankton move up towards the surface.

The water is channelled into its mouth by the blades on the sides of its head,

then passes through filters in the slits in the sides of its throat.

The basking shark gathers the same sort of food in a similar way.

It grows even bigger than the manta: 40 feet long and four tons in weight.

Idling through the water, it filters over 1,000 tons of water every hour.

And even bigger still, in fact, the biggest of all fish: The whale shark.

This mountain of a creature can be up to 50 feet long.

Other, more normal-sized fish live on and around it. Some collect its refuse.

Others pick off morsels that get stuck in its tiny teeth in a mouth six feet wide.

It's an astonishing proof of how sustaining and how abundant the plankton must be.

But of course, not all sharks live on plankton or are quite so amiable.

These are grey reef sharks, about six feet long.

It's some consolation to know that those sharks don't normally attack human beings.

Their prey is usually small fish or predators.

And indeed, when one looks at them, it is not so much their danger that comes into your mind

as their extraordinary beauty.

They are so perfectly streamlined,

every curve of their body, every curve of their fi

precisely matching the shape that is needed to glide through the water with the least struggle

Most beautiful things.

Sharks belong to a very ancient family that evolved this shape some 400 million years ago.

But soon after they appeared, another group of fish established itself.

These have skeletons of bone, not gristle as the sharks have,

and they have two swimming aids that the sharks lack:

Swim bladders that give them buoyancy

and paired fins that can twist in all directions

and so give them great manoeuvrability in the water.

These bony fish are the ones which today dominate the seas.

Among them are the most powerful of all hunters in the sea: The tuna.

When hunting, they can swim faster than any other fish.

Some say nearly 70 miles an hour, faster even than a cheetah can run on land.

But the fish's dominance of the sea didn't go unchallenged.

Ten million years ago, warm-blooded creatures from the land invaded the sea, mammals,

and they became equally streamlined.

Dolphins and killer whales are descended

from four-footed, land-living, air-breathing mammals that were flesh-eaters.

In the sea, they lost their limbs but not their taste for meat, nor their teeth.

Indeed, one of the family that lives only in the ice-strewn waters of the Arctic

has grown one of its teeth to an extraordinary length.

These are narwhals, and they are all males,

for only the male produces the tusk, up to nine feet long.

These without tusks are females, one with a calf.

And these are young males.

No one knows for certain what purpose the tusk serves,

but it seems likely that it is used in courtship.

That is confirmed by the fact that very rarely indeed

males have been glimpsed, as here, fencing with one another.

The best view that most of us can get for most of the time of most kinds of whales

is a brief glimpse as the animal comes to the surface to snatch a breath,

but that's not the case with the beluga, these beautiful white whales.

Up here in the Canadian Arctic, they come during those brief weeks

when the ice goes away from these shores,

and assemble in vast numbers in this bay.

There are hundreds, sometimes as many as a thousand.

We don't really know why they come here, nor what they do now that they are here.

Maybe there is some kind of specially attractive food in these shallow waters,

for they seem to stir up the gravelly bottom of the bay.

Perhaps there is valuable food for youngsters or nursing mothers,

for many that come are females with babies a few months old,

swimming skilfully in their mother's slipstream.

Whatever it is that they do here, they seem to be enjoying themselves hugely.

And they haven't lost their mammalian habit of communicating by sound.

So vocal are they that they are sometimes called sea canaries.

The most recent family to colonise the sea, also mammals,

were descended from bear-like creatures.

The walrus and its cousin the seals

are not so fully adapted to life in the sea as the whales, but they haven't been there so long.

They haven't lost their feet as the whales have, nor do they spend all their lives in the water.

They come ashore to give birth and they often haul themselves out to rest.

Nonetheless, they are superb swimmers.

So, in the 3,000 million years since living organisms first appeared in the sea,

the oceans have acquired a population of immense diversity,

from single-celled microscopic plants

to advanced and complex highly intelligent mammals.

Indeed, there are more different groups of animals living in the sea than there are on lan

The oceans were the birthplace and the nursery of life,

and they are still its main residence.

But the sea is not uniform.

Just as land has different, specialised environments

inhabited by creatures that occur nowhere else, so does the sea.

The coral lagoon is a world of its own. Corals are very demanding in their requirements.

They must have good light, clear, unpolluted water and warmth,

and they find this in the tropics,

particularly around the small islands that are the summits of submarine mountains.

There, they flourish so well that they grow outwards into the clear blue water,

building on top of their own skeletons to form wide, shallow lagoons.

The variety of corals is immense. Some are soft and rubbery,

others are hard and slightly flexible, like a horn But most are stony.

The organisms that build these structures, ton upon ton, occupy only the outer skin.

The rest is dead. As they develop, the little organisms branch,

and the particular way they do so determines the shape of the colony,

forming antlers and organ pipes, whips and fans, vases and buttons.

If the jungle is the place on land

where there are the greatest number and the greatest variety of life,

then this, the coral reef, is surely the jungle of the sea.

The number, the variety,

the sheer beauty of all these myriad fish, corals and anemones, is quite breathtaking.

Of course, the tiny anemone-like creatures that build these fans and fronds of coral

are themselves animals.

But within their tissues, there are tiny granules which are algae, plants,

and it's they that harness the sunshine and use it to build living tissue.

And onto these plates and branches of coral

come a wide variety of creatures to browse.

Some, like the parrotfish, bite off chunks.