All language subtitles for LOCA ASI

As dusk gives way to twilight,

the encroaching darkness is lit by life.

These dancing lights around me
are produced by fireflies,

creatures that have the strange ability
to produce light.

They bioluminesce.

And fireflies are not alone.

Scientists are finding ever more strange
and wonderful glowing life forms

all around the world.

Living light has always fascinated me.

And the discovery of more and more
luminous creatures

raises more and more questions.

Why?

What is the light for?

And how is it made?

In recent years,
scientists have begun to find answers

to those questions,

and in doing so,
they've taken us into a world

that is utterly unlike our own.

However astonishing these images look,
they are all real.

With help from new cameras,
one designed just for this film,

we can reveal this extraordinary
phenomenon

as it has never been seen before.

Bioluminescence holds many mysteries,

but we do know that fireflies use it

to attract the opposite sex.

Each species has its own flash code

and we can join in the conversation.

I'm going to use this rod

to fish for fireflies.

It's the actual rod
used by the scientist

who was the first to decipher
the various call signs of fireflies.

And there are 15 different species,
at least, around here,

each with its own signal.

Biologist Jim Lloyd used the rod
to imitate male fireflies

and so decode
their various light patterns.

He discovered that the call sign

consisted partly
in the actual flight path

of the species concerned.

There are, for example, some fireflies

which move steadily horizontally
like that,

and there are others which
turn their light on as they climb,

like that.

But in addition to the flight path,

they flash a particular signal.

It's rather like morse code.

So I should be able to use
this light myself.

There's a female
amongst these leaves here

which will emit a single flash,

and the male of her species
waits for precisely four seconds

and then answers back with a flash,

whereupon she immediately
gives another flash, like that.

And the male then knows that
he's going to be a welcome visitor.

But the message has recently been shown
to be more than a simple signal for sex.

A female judges the quality of a male's
genes by the precision of his timing

and the brightness of his light.

She encourages her chosen suitor

by directing her lanterns towards him.

And it seems that this male

sent out all the right signals.

We are now discovering
that this language of light

even has local dialects.

Throughout the summer months
from Florida to southern Canada,

gardens, fields and forests sparkle
with these mating messages.

Time-lapse photography reveals

the extraordinary extent
of this courtship.

Some species flash only at dusk.

Others prefer the forest canopy
for their light show.

Some species make their flashes
more conspicuous

by choosing the very darkest
places in which to display.

I can see virtually nothing here
except the flashes.

And this particular species
has another trick too.

It synchronises the displays
individuals flash together.

Each individual is
triggered by its neighbour

and soon waves of light
pulse through the woods.

Speeded up, the wave becomes clearer.

Between the waves,

an impressed female
can respond with two flashes of her own.

And the males home in on her.

But she can only choose one.

These displays peak
for just a few nights in June,

which could explain why
they were only recently discovered.

Why they all flash together
is still a mystery.

It's surprising how little we know

about bioluminescence.

Fireflies are perhaps
the best understood

but some living light
is still very perplexing indeed.

With dawn,
the sexual signals of the fireflies

are drowned by the increasing
flood of light.

The flies take refuge
in the undergrowth,

away from the sharp-eyed predators
of the day.

But right now, light is being
produced by life in the soil

under my feet.

The threads of certain fungi

form a glowing, underground network.

But why would a fungus shine
in the permanent darkness of the soil?

We simply don't know.

And for years, fungus bioluminescence,
like much other living light,

was written off as a beautiful
by-product of evolution

with no function.

But some species only glow above ground

and only at night

when their intense green light
is very obvious.

If it was just a biochemical accident,

then surely they would shine
all the time.

The glow certainly attracts insects,

and the theory is that these visitors
spread the fungal spores.

So here too, just as with fireflies,

we're learning new things all the time.

But much living light remains
a beautiful enigma.

And throughout history,
stories of bioluminescence

were often thought to be pure fiction.

In the 1870s, Jules Verne,
the French science fiction novelist,

wrote this in his book
20,000 Leagues Under the Sea.

"At 7 o'clock in the evening,
our ship, half immersed,

"was sailing in a sea of milk.

"At first sight,
the ocean seemed lactified.

"The whole sky seemed black

"by contrast with
the whiteness of the waters."

Jules Verne may have based this story
on a myth told to him by sailors.

But in 1995,

the captain of a British vessel wrote
a real-life account in his ship's log.

"At 1800 hours on a clear,
moonless night,

"while 150 miles east
of the Somalian coast,

"a whitish glow was
observed on the horizon

"and after 15 minutes of steaming,

"the ship was completely surrounded
by a sea of milky white colour

"with a fairly uniform luminescence,

"and it appeared as though the ship
was sailing over a field of snow

"or gliding over the clouds."

Reports like this are rarer

than the supposed sightings
of the Loch Ness Monster,

and there was no photographic evidence.

Some scientists, including marine
biologist Stephen Haddock,

were curious,
and sought confirmation from above.

We wondered if you could find
one of these ship reports

where they record sailing through
one of these milky seas,

and actually find
the corresponding satellite data

that cover that area at that same time,

so we looked at this satellite
from the ship report in 1995,

and it was somewhat of a eureka moment.

We cleaned up the noisy sensor image
from the camera,

we mapped it onto the ship track,

and this 300km feature
emerged on the map

matching exactly with what the ship
had reported.

So it was really an amazing moment.

We were able to document the full
extent of the milky sea

over three successive nights
as it rotated with the currents.

So satellite images
from the space age

validated a piece of maritime folklore.

On rare occasions, the oceans do glow.

But what was causing a glow so bright
that it could be seen from space?

The answer can be found
at the back of a neglected fridge.

Left for a couple of days,

this sea bream starts to glow.

The fish itself
has no light-producing ability.

The glow is, in fact,
produced by bacteria

that are found in almost all sea water

when they start to feed
on decaying fish.

On rare occasions when currents
and temperatures

cause a large bloom of algae
in the ocean,

these very same bacteria
also feed on dying algae.

Once they reach
a critical concentration,

their secretions trigger others to glow.

They were glowing in such numbers

that they can be detected
by a satellite in orbit.

Bacteria are among
the most ancient forms of life,

so they may have been the very first
living things to glow.

But why they did so is still debated.

Today, some animals have stolen
the genes of the bacteria

and incorporated them
into their own DNA.

Others have simply kidnapped
the bacteria themselves.

These lights are made by captives,

which are farmed in special organs
below the eyes of flashlight fish.

They have harnessed the bacterial
glow for many purposes.

We can only see them because
our special cameras use infra-red light.

But to a predator,
the fish look like this...

..a confusion of lights which makes
it hard to pick a single target.

Just before they change direction,
the fish give a quick blink.

These light have other functions too.

They act as headlights
to illuminate the sea floor

as the fish search for food.

They may even help a fish to flirt
with the opposite sex.

Unlike their captive bacteria,

flashlight fish use living light
for functions we now understand.

But how is the light made?

While it might appear magic,

it's actually a straightforward
chemical reaction,

that happens when a substance is mixed

with a particular enzyme like this.

Hey presto! Light.

The exact chemical formula
varies according to the species.

The reaction is very similar to that
with which bacteria produce energy.

Indeed, it could well be
that the first luminescence

was a by-product of that process.

An evolutionary accident
that has been co-opted by the fish

to help them survive.

The chemicals involved
are quite harmless.

In fact, you can actually buy a lollipop

which, when you put it in hot water...

..glows.

But to be truthful,

I don't really find that
very appetising.

Perhaps at the back of my mind,

there's a memory of those
bacteria on rotting fish

which tells me that things that glow

aren't all that nice to eat.

Bacteria may have been
the first living lights,

but then many other organisms
also developed the ability.

From jellyfish to fungi and insects,

bioluminescence has evolved
independently over 50 times

and is now produced
by thousands of different species.

And defence seems to be
a common function.

Millipedes are found across the globe.

Many are active during the day,
scuttling across the damp forest floor.

They can do this with impunity
because they're deadly poisonous.

Their bright colours
are a clear message to predators,

"Do not eat me. I'm laced with cyanide."

But what about millipedes
that are active at night?

They're no less toxic

than those that are active
during the day.

But, of course, colours at night
are no warning at all.

Could it be that luminescence is a way
of warning off night-time predators?

These extraordinary millipedes

are only found in the high mountains
of California.

Their bioluminescence
has never been filmed before.

They can't be sending signals
to one another because they're blind.

Their living light evolved
separately from bacteria,

from a chemical process that helps
millipedes conserve water

in dry environments.

But since the millipedes
already contain cyanide,

the light evolved a function.

To my eyes, he doesn't look very bright,

but my eyes are not the eyes
of a night-time predator

or, indeed, of our specialist camera.

And to both of them,
this could look very bright indeed,

and be a real warning.

When scientists made clay
models of these millipedes,

half of which glowed,

nocturnal predators were more likely
to attack those that didn't glow.

This simple experiment
produced a clear result.

Living light can act as a warning.

But proving the function of
bioluminescence is not always so easy,

as a recent discovery has shown.

These surely are like creatures
from science fiction.

Luminous earthworms.

A few years ago, a lady living
in the Loire Valley in central France

went out during the evening
to look for her dog,

which was digging a hole in the garden.

And in the bottom of the hole,
the soil was glowing.

It was these earthworms.

She could hardly believe her eyes.

And she went and told people
what she had seen

and few people would believe her.

The species of worm was already known.

It lived over quite a lot of France.

But no-one had ever seen it glow before.

Perhaps that's because
few people went out

in the middle of the night
digging a hole,

especially without a light.

But eventually science recognised
these creatures.

But why should they luminesce
in the darkness of the soil?

Nobody knew.

This blue light had gone
unnoticed by science

until 2010

when biologist Marcel Koken

first saw their eerie glow.

We're trying to find out why
this animal produces light.

A thing living underground -
why produce light?

No use for it apparently.

Is it just a by-product
of some internal chemistry

or could the glow be used
to frighten off attackers?

These ground beetles
are voracious predators

and they love earthworms.

The worms look like ordinary ones
until the light goes out.

Our special camera gives us
a privileged view

of what's happening in the dark.

Marcel's experiments have shown that the
worms can control their brightness.

When the beetle touches
part of the worm,

its light gets brighter.

So it could be that in case
a predator tries to bite it,

it lights up, that scares the predator.

Predator goes off
and the earthworm can escape.

The beetle bites and the
worm's entire body bursts into light

as it struggles to break free.

But the beetle doesn't seem
put off by the glow.

If this is defence,

it isn't working here.

Marcel is still looking
for the function.

Perhaps other predators are put off

or perhaps the worms use light
to find each other.

So it seems that this beautiful glow

has a function which
we still don't understand.

The world of living light
is full of mysteries.

The French worms went unnoticed
for so long

because they produce their eerie light
underground.

But there are rare occasions
when luminous life

is all about revealing yourself.

May 2015.

While the Southern Aurora
illuminates the night sky above,

the sea below produces
a strange blue glow.

Each wave causes a ripple
of intense colour.

The animals in the bay notice it first.

Wading birds are attracted to small
crustaceans caught in the glow.

Each movement alerts others
to this rare spectacle.

People gather to marvel
at this once-in-a-lifetime event.

- Look at that.
- Oh, wow!

Oh, that is amazing!

I have never seen
anything like this before in my life.

That's wicked.

It may look like something
from Willy Wonka's Chocolate Factory,

but the phenomenon is real.

A mass bloom of microscopic organisms

caused by a rare combination
of climate and nutrients.

Under this microscope,

I've got a drop of ordinary sea water,

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're a thousand times bigger
than bacteria.

They're 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're 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's
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 cuttlefish
with fatal results.

And so the cuttlefish can hunt
in total darkness.

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

it's 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.

Two, three...

Diving without torches
in near total darkness,

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

You're immersed in darkness,
you're 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 the display,
another and another join him.

And as the 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's 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.

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's 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 Flyer 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 Stephen 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's clear that it's 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're 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.

Even with it. In.

Down. Yes!

Viperfish.

Perfect.

Oh, look! Oh!

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 viperfish,
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 barrel-eyed fish has eyes
that can only look upwards

through the top of its translucent head,
searching for prey above.

It's 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,

where 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're 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.

To make this program,
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're 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.

Cameras have always struggled
to replicate what the human eye can do,

but with special low-light cameras,
we can now record glowing light

at least as well -
and sometimes better -

than we can see it ourselves.

But being able to film the glow
is only one part of the solution.

To really understand light on earth,

you need to be able to record
the creature themselves

as they make the light.

This camera allows you to film in low
light levels in a completely new way.

The beam of light comes in
through the single lens,

but it's then split into two,

and one camera records
on one light frequency

and the other
on a different light frequency.

One of the cameras
is sensitive to infra-red right,

invisible to most animals, but which
allow the camera to record in the dark.

The second camera records
only the bioluminescence,

which is mostly blue or green.

The two are then combined
into one picture.

And that way, you can get pictures
at a low light level,

not only of bioluminescent animals,

but even the environment
in which they are living.

This technique,
pioneered by filmmaker Martin Dohrn,

allows us to enter the world
of bioluminescent creatures

and also to contribute to new science.

It's this type of camera,
the many things I see on these images,

which I wouldn't be able to see
normally.

In the past, scientist Marcel Koken

has been unable to study the worm
and beetle without using a light.

But when he did,
the light would frighten the beetle

and overpower the worm's
bioluminescence.

With the help of Martin's camera,
Marcel is able to observe and record

the beetle and worm encounter
for the first time.

Having decided working with
two cameras simultaneously

wasn't already hard enough,
the team decide to take them underwater.

The objective was to film the beautiful
mating display of ostracods,

tiny, one-millimetre-long crustaceans,

in the dark, swirling currents of their
natural habitat - a huge challenge.

- Martin, how was it tonight?
- We've had a lot of problems.

Tonight it went smoother,
it's calmer - much, much calmer.

A lot of what I saw
looked utterly amazing.

Martin's beam-splitting system

makes it possible to film
the bioluminescence,

as well as the tiny ostracods,
as they leave light in their wake.

However, the scientists are not done.

Marine biologist Gretchen Gerrish
hopes the camera

will enable her to film
groups of males that aren't flashing,

swimming alongside
the individual that is,

something that has only ever
been seen in the lab.

These males, known as sneakers,
are invisible to a normal camera

because they leave no light trail.

But our camera, nicknamed Bertha,
could change all that.

So, how was Bertha?

Bertha is awesome!

She was filming the sneakers
and you could see them swimming.

She's a bit of a beast.

What do you think, Trevor?
Did you get any good footage?

It was just awesome.
This is opening the doors for so much.

The scientists
are keen to get their first look

at the combined images from Bertha.

So this here,
two little forms. Look at that.

The infra-red does show
there is a spiralling group of males

intent on intercepting the female
before she can reach the male

that's done all the hard work
of attracting her.

And there are far more competing males
than the scientists had expected.

It's an ostracod soup.
There's thousands of them.

What, to our eyes,
is a beautiful, orderly display,

is, in fact, an ostracod free-for-all.

Lots of males try to cash in
on the efforts of a few.

The amount of information
you could farm from this

is something we've been
trying to do for the last five years.

That's a paper right there.

What, you mean in that...?
There's not a paper there.

- Maybe.
- Close to it.

But having high-tech kit
is only part of the story.

Since much of the bioluminescence
is little-known,

just finding it
is often the biggest hurdle.

The crew are about to head out
on their most ambitious shoot.

Tonight, we're going to try
and film something

that we know is found all over the world

and it happens every night
in every ocean, almost anywhere.

And yet, in terms of getting information
from people as to where we might find it

and when the best time is,
there's nothing.

As night falls,

they head away from shore
and any artificial light.

And soon they're sailing in a sea
laced with dinoflagellates.

These blue flashes can be seen in almost
any ocean at night, with the lights out.

But this alone
is not what the crew came for.

They're hoping to meet
some special visitors.

Working on a rocking boat in complete
darkness with a prototype camera

is one of the trickiest challenges
Martin has faced in his career.

After a week searching the dark sea,

here they are - dolphins!

To be out at night
with clear skies and beautiful stars

and everywhere
there are flashes of light,

and when Dolphins turn up, the show
just gets more extraordinary still.

It really is one of the most amazing
things I've ever seen in my life.

Scenes like this
are happening across the oceans,

yet this is one of the few times
they've ever been caught on camera.

New technologies and new ideas

are creating a revolution
in our way of seeing the world

and of understanding life that glows.