Planet Earth

Away from all land ...

the ocean.

It covers more than half the surface of our planet,

and yet for the most part it is beyond our reach.

Much of it is virtually empty ...

a watery desert.

All life that is here is locked in a constant search to find food ...

a struggle to conserve precious energy ...

in the open ocean.

The biggest of all fish ...

30 tons in weight, 12 meters long ...

a whale shark.

It's huge bulk is sustained by mere microscopic creatures of the sea —

Plankton.

Whale sharks cruise on regular habitual routes ...

between the best feeding grounds.

In February, that takes them to the surface waters ...

far from the coast of Venezuela.

Others are already here.

Baitfish have come for the same reason to feed on the plankton.

The whale shark has timed it's arrival exactly right.

Oddly, the tiny fish swarm around it.

They're using it as a shield.

Other predatory fish are lurking nearby.

Yellowfin tuna. They seem wary of the giant.

The shark dives, as if to escape from such overcrowding.

Now the tuna have a chance to attack the unprotected baitfish.

But then ...

back comes the giant.

It has taken a vast mouthful of the baitfish itself.

Plankton, it seems, is not the only food for a whale shark.

Both shark and tuna feast together,

but the tuna must be wary.

Even they can end up in the whale shark's stomach.

Predators here must grab what they can, when they can,

for such events do not last long.

The dense shoals on which so many depend,

gather only when water conditions are perfect.

Many predators spend much of their time cruising the open ocean ...

endlessly searching.

Plankton feeding rays do so, gliding with minimum effort.

The oceanic whitetip shark —

another energy efficient traveler.

It specializes in locating prey in the emptiest areas of the open ocean ...

patrolling the top 100 meters of water.

Taste in water, is the equivalent of smell in the air.

An oceanic whitetip is able to detect even the faintest trace.

Small pilot fish swim with it.

The shark can find prey far more easily than they can,

and they'll be able to collect the scraps from it's meals.

It's long, fixed pectoral fins ...

enable it to soar through the water, with the least expenditure of energy.

This shark has found a school of rainbow runners.

It would eat one, given the chance,

but rainbow runners are swift and agile and not easily caught.

So, it bides it's time.

There's a chance that, eventually,

it may spot a weakened fish that's catchable.

The hunter ...

endlessly waiting.

Excitement far from land.

A school of dolphin 500 strong.

They've sensed there's food around, and they're racing to catch up with it.

The news has spread. Now a number of schools are on their way.

They're heading towards the Azores,

volcanic islands a thousand miles west of Portugal.

The dolphin scan the water ahead with their sonar.

They're close to their target.

This is it.

Scad mackerel.

It's difficult for a single dolphin to catch the fish.

To avoid wasting energy, they work as a group.

They drive the fish upwards, trapping them against the surface,

and there, other predators await them.

Cory's shearwaters.

They're waiting for the dolphin to drive the prey closer to the surface.

Now the shearwaters can dive down on them,

descending to 20 meters or more ...

and the dolphins block the baitball's retreat.

The dolphins leave as soon as they've had their fill ...

and, at last, the mackerel sink below the diving range of the birds.

As the Sun disappears, a profound change takes place in the ocean.

Deep water plankton start to rise from the depths,

and another hungry army prepares to receive it.

Every night, wherever conditions are right,

countless millions of creatures from the deep ...

migrate to the surface, seeking food.

A baby sailfish, 15 centimeters long,

snaps up everything in it's path.

In 3 years' time, it'll be one of the oceans most formidable hunters ...

weighing 60 kilos.

Just now, however, it's very vulnerable.

These manta rays are giants.

8 meters across and weighing over 2 tons.

The blade-like projections on either side of the head,

help to steer plankton into the manta's mouth.

Dawn returns, and the plankton sinks back into the depths.

If we are to follow, we must use a submarine.

As we descend into the darkness, the pressure builds, the temperature falls.

Below 500 meters, new, mysterious animals appear.

Their bizarre shapes help them to remain suspended in the dark space.

Some resemble creatures familiar from shallower waters,

others defy classification.

All around, organic particles drift downwards.

Marine snow, detritus from the creatures swarming in the sunlit waters above.

The snow is food for many animals here, like the sea spider,

a small relative of shrimps and crabs.

Those strange leg-like appendages are feathered, to stop it from sinking.

They can also enmesh marine snow,

which it wipes carefully into it's jaws.

A sawtooth eel hangs upright and motionless.

Gazing ever upwards, it watches for prey, silhouetted against the faint ...

glimmerings of light from the surface.

Days may pass before prey swims close enough for it to strike.

Farther down still, the blackness is complete.

No vestige of sunlight can penetrate as far as this.

Food is very scarce and nothing can afford to waste any energy.

A dumbo octopus simply flaps a fin,

no need for the jet propulsion used by it's shallow water relatives above.

The weirdest, in this world of the strange, vampyroteuthis,

the vampire squid from hell.

Disturb it. and it only retreats a little distance.

Go after it, and it has a special defense.

To see what it does, you must switch off the lights.

The vampire squid has lights of it's own.

Bioluminescent bacteria shine from pockets on it's arms ...

to confuse it's predators.

Are those eyes?

In fact they're spots at the end of it's mantle.

A bite there, would leave the head unscathed.

The threat diminishes, and vampyroteuthis disappears ...

into the blackness.

At last, the sea floor.

Over 2 miles down, the pressure here is 300 times that at the surface.

It takes several months for marine snow to drift down as far as this.

As you travel away from the rocky margins of the continents,

an immense plain stretches ahead.

It extends for thousands of miles,

gradually sinking downwards.

There are faint trails in the ooze, signs that even here there is life.

These are what made some of them —

sea urchins sifting the accumulating drifts.

Shrimps standing on elegant tiptoe,

fastidiously select the particles that appeal to them.

But, in the deep sea, as everywhere else, if there are grazers, there are hunters.

A monkfish, almost indistinguishable from the sand on which it lies.

Why waste energy chasing around, if you can attract prey towards you with a lure?

Maybe that one was a bit big.

The monkfish can wait, for days if necessary, until the right sized meal turns up.

Scavengers on the other hand, have to move around to find their food.

Crabs can detect the faintest of tastes in the water,

and that helps them locate the latest body to drift down from above.

Eels are already feeding on the corpse.

Isopods, like giant marine woodlice a third of a meter long,

are ripping into the rotting flesh.

Over the next few hours, there'll be frenzied competition ...

between scavengers of all kinds to grab a share.

Just occasionally, there is a gigantic bonanza.

The remains of a sperm whale.

It died 5 months or so ago.

There's little left but fatty blubber clinging to it's bones.

It's flesh has nourished life for miles around,

but now the feast is almost over.

Spider crabs, a meter across, still pick at the last putrid remains.

A few weeks more, and nothing will be left, but bare bones.

The crabs will have to fast, until the next carcass drifts down.

But not all food comes from the sunlit world above.

The floor of the Atlantic Ocean is split in two ...

by an immense volcanic mountain chain ...

that winds unbroken for 45,000 miles around the globe.

In places, it's riven by great fissures, from which superheated water ...

loaded with dissolved minerals blasts into the icy depths.