Attenbobough's Life That Glows Page #3

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Under this microscope, I've got a drop of ordinary seawater.

And it's full of tiny organisms, invisible to the naked eye,

called dinoflagellates.

And if I disturb them in some way,

they combine two chemicals in their body to produce a flash of light.

Watch.

Dinoflagellates are one of the

biggest single-celled organisms known.

They are 1,000 times bigger than bacteria.

They are neither animal nor plant,

but have characteristics of them both,

and when conditions are right in the sea, as they were in Tasmania,

they bloom in enormous numbers.

Bioluminescent tides like this one are certainly rare.

However, dinoflagellates are found in huge numbers all over the world.

They are among the most widespread of all bioluminescent life.

Wherever they exist,

these single-celled creatures highlight anything that moves.

But why do dinoflagellates behave in this way?

It's certainly not to entertain us, though it obviously does.

Well, it could be that it is a kind of burglar alarm -

that when a shrimp or some other animal

that feeds on the dinoflagellates by filtering them out,

comes along and starts to feed,

it is, in doing so, illuminating itself.

So that attracts the attention of perhaps bigger fish that might

feed on the shrimp.

Just as a flashing burglar alarm alerts the police to a thief,

the dinoflagellates expose their attacker to its enemies.

The shrimp is revealed to a cuttlefish, with fatal results.

And so the cuttlefish can hunt in total darkness.

But while the dinoflagellates' light can work in this way,

it is still debated if that's why they do it.

Whatever the reason, the magic created by their light can be

one of nature's most magical spectacles.

Bow-riding dolphins are revealed as dazzling outlines.

Whenever these lights appear, the way life in the ocean hunts

and hides is transformed.

Perhaps dolphins are guided to their prey by the light

of the dinoflagellates.

Only now has it become possible to film these scenes with such clarity.

But every night, spectacular light shows like this play out

somewhere in the vastness of the oceans.

While exactly how dinoflagellates use bioluminescence remains

unproven, there are other instances

when the burglar alarm effect has been clearly demonstrated.

Caribbean coral reefs are some of the

most well-dived waters in the world...

..by day.

At night, it's a different world.

A crab searches for a tasty morsel.

This is just what it's looking for, the delicate

tentacles of a brittle star, a relative of starfish.

But the brittle star has a surprisingly effective defence.

When disturbed, it unleashes a dazzling weapon, raising the alarm.

Having been revealed, the crab makes a run for it.

And the normally well camouflaged crustacean becomes easy prey

for the octopus, even in the gloom.

Scientists have only recently proved the light helps the

brittle star drive off predators or, better still, to get them eaten.

It's in the open water, where there's nowhere to hide, that the

burglar alarm defence is most effective.

Fish hunt small invertebrates silhouetted against the night sky.

Ostracods, tiny crustaceans no bigger than a grain of sand,

emerge from the reef.

Cardinal fish are common predators of the small and unwary.

But when they strike an ostracod,

they get more than they bargained for.

The ostracod discharges a bioluminescent flash bomb,

one of the brightest forms of living light.

And the cardinal fish quickly spits it out.

The light is so bright that it shines through

the body of the fish, temporarily blinding it, and this normally

invisible fish becomes an easy target for a predator.

Ostracods, with their flash bomb defence,

are found throughout the world's oceans.

But in the Caribbean,

they employ their glow to attract as well as to repel.

It's something that researchers Gretchen Gerrish

and Trevor Rivers are studying.

The spectacular mating display of ostracods.

But they can't even begin to work until the moon has set.

A fully moonlit night is not dark in the eyes of an organism that

depends on their own light that they create, and so darkness truly

is just a starlit sky, no moon present in the sky at all.

Diving without torches in near total darkness, Gretchen

and Trevor are entering a world that few people ever witness.

You are immersed in darkness, you are immersed in water.

And you see streaming stars floating past you and they're being

produced by these tiny crustaceans that we barely understand.

By releasing small amounts of glowing liquid as they swim,

male ostracods leave a trail of lights in their wake.

The series of precisely timed dots tell the female where

he will be in exactly half a second.

But as one male starts to display, another and another join him.

And as they synchronise,

they fan out into this firework-like display of light.

It's one of the most awe-inspiring things I've ever seen.

With every research trip, Trevor and Gretchen discover new species,

each with its own light language.

Ostracods and fireflies use bioluminescence

to find potential mates.

And it can be an efficient means of getting your message across,

but it's not foolproof.

Those messages can be hacked.

There's a love cheat in this situation.

There's also a female of a particular species here that,

when she sees the males of a different species fly past,

answers with their particular call sign, and that attracts them.

And when they arrive, instead of mating with them,

she has her own dastardly way with them.

She mimics the flash patterns of other species.

An unsuspecting male is lured in.

Fireflies contain toxins thought to protect them against most predators.

But this femme fatale is not put off.

And she eats him alive.

In fact, it may be the toxins that she is after.

She can't produce such chemicals herself.

So she tricks and then devours males of different species to obtain them.

If she can't get males to come to her, she goes after them.

And a good place to look for one is on a spider's web.

A male firefly is ensnared.

As the spider venom takes effect,

his flashing turns to a constant glow.

The femme fatale is alerted by the dim glow,

and she flies straight onto the web to steal the spider's catch.

As the spider struggles to keep its prey,

she dazzles it with her lantern.

Using her light, the firefly can clearly see the spider

and avoid the web.

The confused spider loses out.

Predation turns out to be one area where light-making life

has been very creative.

Like a scene from the surface of an alien planet,

these termite mounds have lodgers living in their walls.

The luminous larvae of click beetles wait in burrows.

Insects are drawn to their death by the green glow,

like moths to a flame.

And the beetle larvae gorge

on the steady supply of unsuspecting victims.

These predators work as individuals.

There is another insect that excels in deception.

But it works alongside thousands of its own kind.

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