Attenbobough's Life That Glows Page #4

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From outside, this cave shows no sign of the astonishing

things that go on inside.

The entrance is fringed with a curtain of silk,

woven by the larvae of a kind of gnat.

They move back and forth along the rocks,

lowering sticky strings of saliva from the roof of the cave.

As night falls, the walls

and ceiling of this cavern become nature's very own planetarium.

The trap is set.

The cool, blue light produced in each larva's tail is the lure.

Other insects that hatch

and emerge in the cave instinctively fly upwards to the sky.

But this is not a starlit sky. It's a deathtrap.

Bioluminescence is clearly a powerful tool

to these life forms that possess it.

But it is only effective in darkness.

Each dawn,

the bright rays of the sun overwhelm the power of living light.

For all of the wonders of bioluminescence

in the plains and woodlands of the Earth, there is

one place where living light is virtually the key to existence.

The world of eternal darkness, the deep sea.

The Western Fire is one of the world's most advanced

deep sea research vessels.

In the black depths there are no edges.

No boundaries, nowhere to hide.

Predators and prey have therefore had to develop some

extraordinary strategies to stay alive.

And many do so with the help of light.

Dr Steven Haddock has spent the last 25 years studying the

least known part of our planet, the ocean depths.

I think people look at bioluminescence,

this ability to make light, they think of it as a very magical thing,

but once you see the diversity and the range of functions that

bioluminescence serves for animals in the ocean, it is

clear that it is a critical part of the whole ecology

of the system.

Until recently, it was all but impossible

to collect living bioluminescent creatures from the deep.

But this remote submersible, known as the Doc Ricketts,

is equipped to do just that.

They are trying to find new life

and clues as to why light-making has evolved in so many forms.

In the control room, thousands of metres above, Steve

and the crew navigate past alien-like life forms.

Nice.

Wow.

But in truth, it is us who are the aliens down here.

Although very sophisticated, the Doc Ricketts'

own remote cameras are not sensitive enough to record bioluminescence,

so they use bright lights to find and film these creatures.

To have any hope of observing their light-making powers,

the research team needs to bring them to the surface.

Gentle suction and remotely controlled canisters are used to

delicately scoop up the rare sea creatures.

Vampire squid.

Yes!

Viper fish.

Perfect.

Oh, look at that!

And dragonfish.

They don't just sound like something from a sailor's tale of

fantasy monsters, they look like them, too.

This is one of the few dragonfish that has ever been seen alive.

And it's one of the even fewer that have been captured unharmed.

- Yes!

- Yay!

- Oh, my gosh.

Once they arrive on the ship, thousands of metres

above their normal environment, there is no time to waste.

The enormous pressure change is likely to cause any

bioluminescence abilities to disappear.

The race is on to try and observe those abilities

and understand their functions.

Wow.

In some species, it seems to be defensive.

Like the circling flashes of the Atolla jellyfish.

Or the rippling light waves of the Beroe comb jelly.

In other species, like this viper fish,

light is used not only for defence, but to lure prey.

These pyrosomes, colonies of minute translucent creatures,

use light to communicate within the colony.

The team's experiment shows that as one colony begins to glow,

its neighbours light up in response.

What could they be saying?

Thanks to the delicate sampling methods of the Doc Ricketts,

the team are able to observe a living

and luminescing dragonfish, a sight few have ever witnessed.

Whatever their function,

one thing unites all these types of bioluminescence -

their otherworldly beauty.

And this beauty is the result of an evolutionary arms race

where light is a weapon to blind or deceive.

In response, some animals have evolved the most sophisticated

and bizarre eyes on the planet.

The rare barreleye fish has eyes that can only look upwards,

through the top of its translucent head.

Searching for prey above.

It is so rare,

catching even a glimpse of it alive is a huge achievement.

And the same is true for the cock-eyed squid.

It has one normal eye and one strange, upward-looking eye.

At this depth, it is too dark for human eyes.

But the faintest light from the surface,

half a kilometre above, can just reach this twilight zone.

Firefly squid normally live at these depths.

To prevent themselves from being seen from below,

they hide themselves with light.

It's a strange paradox.

In this dark world, light can be used for camouflage.

At close range, the light-emitting cells, called photophores,

are easy to see.

But from a distance, they break up the outline of the squid

and it merges with the background.

It's an elegant solution used by many creatures

when a silhouette can be a death sentence.

In shallower waters, the colour of the light changes

so the squid, as it gets closer to the surface, uses green photophores.

The lives of firefly squid are short.

When they are only a year old,

mated females make their final journey, to the surface to spawn.

But even in their final moments, they are both spectacular

and valuable.

All along the coast here,

these squid, which die naturally after spawning,

are gathered as a local delicacy.

It's largely through this fishery that we know

anything at all about the firefly squid.

Like so many deep sea creatures,

their daily lives are still virtually unknown.

What we do know is that their world is dominated by bioluminescence.

We've come a long way from watching fireflies

in the woodlands of Pennsylvania.

Organisms that produce light on land may be exceptional

but in the sea,

creatures that do so, like these comb jellies,

are, in fact, the norm.

In the oceans and on land,

living creatures of many kinds have harnessed the power of light in

extraordinary ways, to mate, to lie, even to hide under a cloak of light.

Yet, with the latest cameras and technology, we are

only beginning to understand the lives of luminous creatures.

There remain many mysteries. But what a beautiful world they create.

And what a beautiful world awaits the scientists of the future.

During this programme, we've had to use cameras

that are far more sensitive than our own eyes

and about as sensitive as many of the animals that we are showing.

The eye is one of evolution's greatest achievements.

And nature has certainly devised some fiendishly complex

and sensitive examples.

Some of which are designed specifically to see bioluminescence.

When we enter the dark, we barely notice bioluminescence.

But after a few minutes, physiological changes

take place in our eyes that enable us to see living light.

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