0:00:07 > 0:00:09As dusk gives way to twilight,
0:00:09 > 0:00:12the encroaching darkness is lit by life.
0:00:16 > 0:00:23These dancing lights around me are produced by fireflies -
0:00:23 > 0:00:27creatures that have the strange ability to produce light.
0:00:27 > 0:00:29They bioluminesce.
0:00:32 > 0:00:35And fireflies are not alone.
0:00:35 > 0:00:38Scientists are finding ever more strange and wonderful
0:00:38 > 0:00:41glowing life forms all around the world.
0:00:46 > 0:00:49Living light has always fascinated me.
0:00:49 > 0:00:53And the discovery of more and more luminous creatures raises more
0:00:53 > 0:00:55and more questions.
0:00:55 > 0:00:59Why? What is the light for? And how is it made?
0:01:02 > 0:01:03In recent years,
0:01:03 > 0:01:07scientists have begun to find answers to those questions.
0:01:07 > 0:01:08And in doing so,
0:01:08 > 0:01:12they've taken us into a world that is utterly unlike our own.
0:01:18 > 0:01:22However astonishing these images look, they are all real.
0:01:27 > 0:01:31With help from new cameras, one designed just for this film,
0:01:31 > 0:01:33we can reveal this extraordinary phenomenon
0:01:33 > 0:01:35as it has never been seen before.
0:01:53 > 0:01:57Bioluminescence holds many mysteries.
0:01:57 > 0:02:01But we do know that fireflies use it to attract the opposite sex.
0:02:15 > 0:02:21Each species has its own flash code and WE can join in the conversation.
0:02:28 > 0:02:33I'm going to use this rod to fish for fireflies.
0:02:34 > 0:02:38It's the actual rod used by the scientist who was the first
0:02:38 > 0:02:42to decipher the various call signs of fireflies.
0:02:42 > 0:02:47And there are 15 different species, at least, around here.
0:02:47 > 0:02:49Each with its own signal.
0:02:49 > 0:02:54Biologist Jim Lloyd used the rod to imitate male fireflies
0:02:54 > 0:02:58and so decode their various light patterns.
0:02:58 > 0:03:02He discovered that the call sign consisted partly in
0:03:02 > 0:03:05the actual flight path of the species concerned.
0:03:05 > 0:03:08There are, for example,
0:03:08 > 0:03:12some fireflies which move steadily horizontally, like that.
0:03:12 > 0:03:14And there are others which
0:03:14 > 0:03:18turn their light on as they climb, like that.
0:03:19 > 0:03:24But in addition to the flight path, they flash a particular signal.
0:03:24 > 0:03:26It's rather like Morse code.
0:03:27 > 0:03:30So I should be able to use this light myself.
0:03:32 > 0:03:36There is a female amongst these leaves here,
0:03:36 > 0:03:38which will emit a single flash.
0:03:38 > 0:03:45And the male of her species waits for precisely four seconds,
0:03:45 > 0:03:48and then answers back with a flash.
0:03:48 > 0:03:53Whereupon she immediately gives another flash, like that.
0:03:54 > 0:03:58And the male then knows that he is going to be a welcome visitor.
0:04:00 > 0:04:03But the message has recently been shown to be more than
0:04:03 > 0:04:05a simple signal for sex.
0:04:07 > 0:04:10A female judges the quality of a male's genes
0:04:10 > 0:04:13by the precision of his timing and the brightness of his light.
0:04:19 > 0:04:24She encourages her chosen suitor by directing her lanterns towards him.
0:04:35 > 0:04:39And it seems this male sent out all the right signals.
0:04:44 > 0:04:46We are now discovering that
0:04:46 > 0:04:49this language of light even has local dialects.
0:04:54 > 0:04:58Throughout the summer months, from Florida to southern Canada,
0:04:58 > 0:05:02gardens, fields and forests sparkle with these mating messages.
0:05:07 > 0:05:09Time-lapse photography reveals
0:05:09 > 0:05:11the extraordinary extent of this courtship.
0:05:17 > 0:05:21Some species flash only at dusk.
0:05:23 > 0:05:26Others prefer the forest canopy for their light show.
0:05:31 > 0:05:35Some species make their flashes more conspicuous by choosing
0:05:35 > 0:05:38the very darkest places in which to display.
0:05:39 > 0:05:44I can see virtually nothing here, except the flashes.
0:05:46 > 0:05:50And this particular species has another trick, too.
0:05:51 > 0:05:53It synchronises the displays.
0:05:53 > 0:05:56Individuals flash together.
0:06:00 > 0:06:03Each individual is triggered by its neighbour,
0:06:03 > 0:06:07and soon waves of light pulse through the woods.
0:06:13 > 0:06:16Speeded up, the wave becomes clearer.
0:06:25 > 0:06:26Between the waves,
0:06:26 > 0:06:31an impressed female can respond with two flashes of her own.
0:06:33 > 0:06:35And the males home in on her.
0:06:37 > 0:06:39But she can only choose one.
0:06:44 > 0:06:48These displays peak for just a few nights in June,
0:06:48 > 0:06:52which could explain why they were only recently discovered.
0:06:54 > 0:06:57Why they all flash together is still a mystery.
0:07:05 > 0:07:10It's surprising how little we know about bioluminescence.
0:07:11 > 0:07:13Fireflies are perhaps the best understood
0:07:13 > 0:07:18but some living light is still very perplexing indeed.
0:07:18 > 0:07:22With dawn, the sexual signals of the fireflies are drowned
0:07:22 > 0:07:25by the increasing flood of light.
0:07:25 > 0:07:27The flies take refuge in the undergrowth,
0:07:27 > 0:07:31away from the sharp-eyed predators of the day.
0:07:31 > 0:07:33But right now,
0:07:33 > 0:07:37light is being produced by life in the soil under my feet.
0:07:41 > 0:07:46The threads of certain fungi form a glowing underground network.
0:07:55 > 0:07:59But why would a fungus shine in the permanent darkness of the soil?
0:07:59 > 0:08:01We simply don't know.
0:08:03 > 0:08:07And for years, fungus bioluminescence,
0:08:07 > 0:08:10like much other living light, was written off as a beautiful
0:08:10 > 0:08:13by-product of evolution with no function.
0:08:16 > 0:08:20But some species only glow above ground and only at night,
0:08:20 > 0:08:23when their intense green light is very obvious.
0:08:28 > 0:08:31If it was just a biochemical accident then surely
0:08:31 > 0:08:33they would shine all the time.
0:08:33 > 0:08:36The glow certainly attracts insects
0:08:36 > 0:08:39and the theory is that these visitors spread the fungal spores.
0:08:52 > 0:08:55So here, too, just as with fireflies,
0:08:55 > 0:08:58we're learning new things all the time.
0:09:04 > 0:09:08But much living light remains a beautiful enigma.
0:09:11 > 0:09:12And throughout history,
0:09:12 > 0:09:16stories of bioluminescence were often thought to be pure fiction.
0:09:18 > 0:09:23In the 1870s, Jules Verne, the French science-fiction novelist,
0:09:23 > 0:09:28wrote this in his book, 20,000 Leagues Under The Sea.
0:09:29 > 0:09:33"At seven o'clock in the evening, our ship, half-immersed,
0:09:33 > 0:09:37"was sailing in a sea of milk.
0:09:37 > 0:09:40"At first sight, the ocean seemed lactified.
0:09:40 > 0:09:44"The whole sky seemed black by contrast with
0:09:44 > 0:09:47"the whiteness of the waters."
0:09:47 > 0:09:50Jules Verne may have based this story
0:09:50 > 0:09:52on a myth told to him by sailors.
0:09:52 > 0:09:57But in 1995, the captain of a British vessel wrote
0:09:57 > 0:10:00a real-life account in his ship's log.
0:10:00 > 0:10:04"At 18:00 hours on a clear moonless night,
0:10:04 > 0:10:08"while 150 miles east of the Somalian coast,
0:10:08 > 0:10:11"a whitish glow was observed on the horizon.
0:10:11 > 0:10:16"And after 15 minutes of steaming, the ship was completely surrounded
0:10:16 > 0:10:23"by a sea of milky white colour with a fairly uniform luminescence.
0:10:23 > 0:10:26"And it appeared as though the ship was sailing over
0:10:26 > 0:10:30"a field of snow or gliding over the clouds."
0:10:33 > 0:10:36Reports like this are rarer than the supposed sightings
0:10:36 > 0:10:38of the Loch Ness Monster.
0:10:38 > 0:10:41And there was no photographic evidence.
0:10:44 > 0:10:48Some scientists, including marine biologist Steven Haddock,
0:10:48 > 0:10:52were curious, and sought confirmation from above.
0:10:54 > 0:10:57We wondered if you could find one of these ship reports where
0:10:57 > 0:11:00they record sailing through one of these milky seas,
0:11:00 > 0:11:03and actually find the corresponding satellite data that cover
0:11:03 > 0:11:06that area at that same time.
0:11:06 > 0:11:09So we looked at the satellite from the ship report in 1995
0:11:09 > 0:11:12and it was somewhat of a eureka moment.
0:11:12 > 0:11:15We cleaned up the noisy sensor image from the camera,
0:11:15 > 0:11:19we mapped it onto the ship track, and this 300km feature
0:11:19 > 0:11:24emerged on the map matching exactly with what the ship had reported.
0:11:24 > 0:11:27So it was really an amazing moment.
0:11:27 > 0:11:30We were able to document the full extent of the milky sea over
0:11:30 > 0:11:34three successive nights as it rotated with the currents.
0:11:34 > 0:11:38So satellite images from the space age validated
0:11:38 > 0:11:40a piece of maritime folklore.
0:11:42 > 0:11:45On rare occasions, the oceans do glow.
0:11:48 > 0:11:49But what was causing a glow
0:11:49 > 0:11:52so bright that it could be seen from space?
0:11:54 > 0:11:58The answer can be found at the back of a neglected fridge.
0:12:04 > 0:12:09Left for a couple of days, this sea bream starts to glow.
0:12:18 > 0:12:22The fish itself has no light-producing ability.
0:12:23 > 0:12:27The glow is, in fact, produced by bacteria that are found
0:12:27 > 0:12:31in almost all seawater when they start to feed on decaying fish.
0:12:33 > 0:12:37On rare occasions when currents and temperatures cause a large bloom of
0:12:37 > 0:12:42algae in the ocean, these very same bacteria also feed on dying algae.
0:12:44 > 0:12:46Once they reach a critical concentration,
0:12:46 > 0:12:50their secretions trigger others to glow.
0:12:52 > 0:12:54They were glowing in such numbers that they can be
0:12:54 > 0:12:56detected by a satellite in orbit.
0:13:07 > 0:13:10Bacteria are among the most ancient forms of life,
0:13:10 > 0:13:14so they may have been the very first living things to glow.
0:13:14 > 0:13:17But why they did so is still debated.
0:13:18 > 0:13:22Today some animals have stolen the genes of the bacteria,
0:13:22 > 0:13:24and incorporated them into their own DNA.
0:13:26 > 0:13:29Others have simply kidnapped the bacteria themselves.
0:13:38 > 0:13:41These lights are made by captives,
0:13:41 > 0:13:45which are farmed in special organs below the eyes of flashlight fish.
0:13:55 > 0:13:58They have harnessed the bacterial glow for many purposes.
0:14:01 > 0:14:05We can only see them because our special cameras use infrared light.
0:14:07 > 0:14:10But to a predator, the fish look like this.
0:14:12 > 0:14:15A confusion of lights which makes it hard to pick a single target.
0:14:24 > 0:14:28Just before they change direction, the fish give a quick blink.
0:14:36 > 0:14:38These lights have other functions, too.
0:14:40 > 0:14:44They act as headlights to illuminate the sea floor
0:14:44 > 0:14:46as the fish search for food.
0:14:55 > 0:14:59They may even help a fish to flirt with the opposite sex.
0:15:06 > 0:15:08Unlike their captive bacteria,
0:15:08 > 0:15:13flashlight fish use living light for functions we now understand.
0:15:16 > 0:15:19But how is the light made?
0:15:19 > 0:15:21While it might appear magic,
0:15:21 > 0:15:25it's actually a straightforward chemical reaction that happens
0:15:25 > 0:15:31when a substance is mixed with a particular enzyme, like this.
0:15:37 > 0:15:39Hey, presto, light.
0:15:42 > 0:15:46The exact chemical formula varies according to the species.
0:15:46 > 0:15:52The reaction is very similar to that with which bacteria produce energy.
0:15:52 > 0:15:56Indeed, it could well be that the first luminescence was
0:15:56 > 0:15:58a by-product of that process.
0:15:59 > 0:16:03An evolutionary accident that has been co-opted by the fish to
0:16:03 > 0:16:05help them survive.
0:16:07 > 0:16:10The chemicals involved are quite harmless.
0:16:10 > 0:16:14In fact, you can actually buy a lollipop which,
0:16:14 > 0:16:19when you put it in hot water, glows.
0:16:20 > 0:16:27But to be truthful, I don't really find that very appetising.
0:16:27 > 0:16:31Perhaps, at the back of my mind, there's a memory of those
0:16:31 > 0:16:34bacteria on rotting fish, which tells me
0:16:34 > 0:16:38that things that glow aren't all that nice to eat.
0:16:40 > 0:16:43Bacteria may have been the first living lights,
0:16:43 > 0:16:47but then many other organisms also developed the ability.
0:16:48 > 0:16:51From jellyfish to fungi and insects,
0:16:51 > 0:16:56bioluminescence has evolved independently over 50 times,
0:16:56 > 0:17:00and is now produced by thousands of different species.
0:17:02 > 0:17:05And defence seems to be a common function.
0:17:11 > 0:17:14Millipedes are found across the globe.
0:17:14 > 0:17:16Many are active during the day,
0:17:16 > 0:17:18scuttling across the damp forest floor.
0:17:20 > 0:17:24They can do this with impunity, because they are deadly poisonous.
0:17:24 > 0:17:28Their bright colours are a clear message to predators -
0:17:28 > 0:17:32"Do not eat me. I am laced with cyanide."
0:17:39 > 0:17:42But what about millipedes that are active at night?
0:17:45 > 0:17:49They are no less toxic than those that are active during the day.
0:17:51 > 0:17:56But, of course, colours at night are no warning at all.
0:17:56 > 0:18:00Could it be that luminescence is a way
0:18:00 > 0:18:03of warning off night-time predators?
0:18:04 > 0:18:07These extraordinary millipedes are only found
0:18:07 > 0:18:10in the high mountains of California.
0:18:11 > 0:18:14Their bioluminescence has never been filmed before.
0:18:16 > 0:18:20They can't be sending signals to one another, because they're blind.
0:18:23 > 0:18:26Their living light evolved separately from bacteria,
0:18:26 > 0:18:30from a chemical process that helps millipedes conserve water
0:18:30 > 0:18:32in dry environments.
0:18:32 > 0:18:35But since the millipedes already contain cyanide,
0:18:35 > 0:18:37the light evolved a function.
0:18:39 > 0:18:43To my eyes, he doesn't look very bright.
0:18:43 > 0:18:48But my eyes are not the eyes of a night-time predator,
0:18:48 > 0:18:51or indeed of our specialist camera.
0:18:51 > 0:18:53And to both of them,
0:18:53 > 0:18:57this could look very bright indeed and be a real warning.
0:18:59 > 0:19:02When scientists made clay models of these millipedes,
0:19:02 > 0:19:03half of which glowed,
0:19:03 > 0:19:08nocturnal predators were more likely to attack those that didn't glow.
0:19:13 > 0:19:16This simple experiment produced a clear result.
0:19:16 > 0:19:20Living light can act as a warning.
0:19:23 > 0:19:27But proving the function of bioluminescence is not always
0:19:27 > 0:19:30so easy, as a recent discovery has shown.
0:19:35 > 0:19:40These, surely, are like creatures from science-fiction.
0:19:40 > 0:19:43Luminous earthworms.
0:19:43 > 0:19:44A few years ago,
0:19:44 > 0:19:49a lady living in the Loire Valley in central France went out during the
0:19:49 > 0:19:54evening to look for her dog which was digging a hole in the garden.
0:19:54 > 0:19:59And in the bottom of the hole, the soil was glowing.
0:19:59 > 0:20:03It was these earthworms. She could hardly believe her eyes.
0:20:03 > 0:20:06And she went and told people what she had seen
0:20:06 > 0:20:08and few people would believe her.
0:20:08 > 0:20:12The species of worm was already known, it lived over quite
0:20:12 > 0:20:16a lot of France, but no-one had ever seen it glow before.
0:20:16 > 0:20:20Perhaps that's because few people went out in the middle of the night
0:20:20 > 0:20:23digging a hole, especially without a light.
0:20:23 > 0:20:27But eventually, science recognised these creatures.
0:20:27 > 0:20:32But why should they luminesce in the darkness of the soil?
0:20:33 > 0:20:35Nobody knew.
0:20:38 > 0:20:43This blue light had gone unnoticed by science until 2010,
0:20:43 > 0:20:48when biologist Marcel Koken first saw their eerie glow.
0:20:50 > 0:20:54We are trying to find out why this animal produces light.
0:20:54 > 0:20:58A thing living underground. Why produce light?
0:20:58 > 0:21:01No use for it, apparently.
0:21:01 > 0:21:04Is it just a by-product of some internal chemistry?
0:21:04 > 0:21:07Or could the glow be used to frighten off attackers?
0:21:09 > 0:21:13These ground beetles are voracious predators and they love earthworms.
0:21:16 > 0:21:19The worms look like ordinary ones until the light goes out.
0:21:20 > 0:21:22Our special camera gives us
0:21:22 > 0:21:25a privileged view of what's happening in the dark.
0:21:30 > 0:21:34Marcel's experiments have shown that the worms can
0:21:34 > 0:21:36control their brightness.
0:21:36 > 0:21:40When the beetle touches part of the worm, its light gets brighter.
0:21:42 > 0:21:46So it could be that in case a predator tries to bite it,
0:21:46 > 0:21:49it lights up, that scares the predator.
0:21:49 > 0:21:52The predator goes off and the earthworm can escape.
0:21:53 > 0:21:56The beetle bites, and the worm's entire body
0:21:56 > 0:21:59bursts into light as it struggles to break free.
0:22:00 > 0:22:03But the beetle doesn't seem put off by the glow.
0:22:07 > 0:22:10If this is defence, it isn't working here.
0:22:12 > 0:22:14Marcel is still looking for the function.
0:22:17 > 0:22:20Perhaps other predators are put off or perhaps the worms use
0:22:20 > 0:22:22light to find each other.
0:22:26 > 0:22:31So it seems that this beautiful glow has a function which
0:22:31 > 0:22:32we still don't understand.
0:22:35 > 0:22:39The world of living light is full of mysteries.
0:22:39 > 0:22:41The French worms went unnoticed for so long
0:22:41 > 0:22:45because they produce their eerie light underground.
0:22:47 > 0:22:49But there are rare occasions
0:22:49 > 0:22:52when luminous life is all about revealing yourself.
0:23:02 > 0:23:04May 2015.
0:23:04 > 0:23:08While the southern aurora illuminates the night sky above,
0:23:08 > 0:23:11the sea below produces a strange blue glow.
0:23:21 > 0:23:24Each wave causes a ripple of intense colour.
0:23:38 > 0:23:41The animals in the bay notice it first.
0:23:43 > 0:23:46Wading birds are attracted to small crustaceans
0:23:46 > 0:23:47caught in the glow.
0:23:51 > 0:23:54Each movement alerts others to this rare spectacle.
0:23:54 > 0:23:58People gather to marvel at this once-in-a-lifetime event.
0:24:02 > 0:24:03That is amazing!
0:24:03 > 0:24:06I've never seen anything like this before in my life.
0:24:09 > 0:24:10That's wicked.
0:24:13 > 0:24:17LAUGHTER
0:24:24 > 0:24:28It may look like something from Willy Wonka's chocolate factory,
0:24:28 > 0:24:30but the phenomenon is real.
0:24:31 > 0:24:35A mass bloom of microscopic organisms caused by a rare
0:24:35 > 0:24:39combination of climate and nutrients.
0:24:39 > 0:24:44Under this microscope, I've got a drop of ordinary seawater.
0:24:44 > 0:24:49And it's full of tiny organisms, invisible to the naked eye,
0:24:49 > 0:24:50called dinoflagellates.
0:24:51 > 0:24:54And if I disturb them in some way,
0:24:54 > 0:24:59they combine two chemicals in their body to produce a flash of light.
0:24:59 > 0:25:01Watch.
0:25:17 > 0:25:19Dinoflagellates are one of the
0:25:19 > 0:25:22biggest single-celled organisms known.
0:25:24 > 0:25:27They are 1,000 times bigger than bacteria.
0:25:27 > 0:25:29They are neither animal nor plant,
0:25:29 > 0:25:32but have characteristics of them both,
0:25:32 > 0:25:36and when conditions are right in the sea, as they were in Tasmania,
0:25:36 > 0:25:38they bloom in enormous numbers.
0:25:41 > 0:25:45Bioluminescent tides like this one are certainly rare.
0:25:48 > 0:25:53However, dinoflagellates are found in huge numbers all over the world.
0:25:53 > 0:25:58They are among the most widespread of all bioluminescent life.
0:25:58 > 0:26:00Wherever they exist,
0:26:00 > 0:26:04these single-celled creatures highlight anything that moves.
0:26:07 > 0:26:12But why do dinoflagellates behave in this way?
0:26:12 > 0:26:16It's certainly not to entertain us, though it obviously does.
0:26:16 > 0:26:19Well, it could be that it is a kind of burglar alarm -
0:26:19 > 0:26:22that when a shrimp or some other animal
0:26:22 > 0:26:25that feeds on the dinoflagellates by filtering them out,
0:26:25 > 0:26:27comes along and starts to feed,
0:26:27 > 0:26:30it is, in doing so, illuminating itself.
0:26:33 > 0:26:37So that attracts the attention of perhaps bigger fish that might
0:26:37 > 0:26:39feed on the shrimp.
0:26:41 > 0:26:45Just as a flashing burglar alarm alerts the police to a thief,
0:26:45 > 0:26:49the dinoflagellates expose their attacker to its enemies.
0:26:54 > 0:26:58The shrimp is revealed to a cuttlefish, with fatal results.
0:27:02 > 0:27:06And so the cuttlefish can hunt in total darkness.
0:27:08 > 0:27:11But while the dinoflagellates' light can work in this way,
0:27:11 > 0:27:14it is still debated if that's why they do it.
0:27:18 > 0:27:21Whatever the reason, the magic created by their light can be
0:27:21 > 0:27:24one of nature's most magical spectacles.
0:27:40 > 0:27:44Bow-riding dolphins are revealed as dazzling outlines.
0:27:51 > 0:27:56Whenever these lights appear, the way life in the ocean hunts
0:27:56 > 0:27:58and hides is transformed.
0:27:59 > 0:28:02Perhaps dolphins are guided to their prey by the light
0:28:02 > 0:28:03of the dinoflagellates.
0:28:16 > 0:28:21Only now has it become possible to film these scenes with such clarity.
0:28:21 > 0:28:25But every night, spectacular light shows like this play out
0:28:25 > 0:28:28somewhere in the vastness of the oceans.
0:28:44 > 0:28:48While exactly how dinoflagellates use bioluminescence remains
0:28:48 > 0:28:51unproven, there are other instances
0:28:51 > 0:28:55when the burglar alarm effect has been clearly demonstrated.
0:29:03 > 0:29:05Caribbean coral reefs are some of the
0:29:05 > 0:29:08most well-dived waters in the world...
0:29:09 > 0:29:10..by day.
0:29:22 > 0:29:26At night, it's a different world.
0:29:28 > 0:29:31A crab searches for a tasty morsel.
0:29:34 > 0:29:37This is just what it's looking for, the delicate
0:29:37 > 0:29:41tentacles of a brittle star, a relative of starfish.
0:29:52 > 0:29:56But the brittle star has a surprisingly effective defence.
0:29:59 > 0:30:03When disturbed, it unleashes a dazzling weapon, raising the alarm.
0:30:06 > 0:30:09Having been revealed, the crab makes a run for it.
0:30:15 > 0:30:19And the normally well camouflaged crustacean becomes easy prey
0:30:19 > 0:30:22for the octopus, even in the gloom.
0:30:24 > 0:30:28Scientists have only recently proved the light helps the
0:30:28 > 0:30:32brittle star drive off predators or, better still, to get them eaten.
0:30:39 > 0:30:42It's in the open water, where there's nowhere to hide, that the
0:30:42 > 0:30:45burglar alarm defence is most effective.
0:30:47 > 0:30:51Fish hunt small invertebrates silhouetted against the night sky.
0:30:53 > 0:30:57Ostracods, tiny crustaceans no bigger than a grain of sand,
0:30:57 > 0:30:58emerge from the reef.
0:31:00 > 0:31:04Cardinal fish are common predators of the small and unwary.
0:31:06 > 0:31:08But when they strike an ostracod,
0:31:08 > 0:31:10they get more than they bargained for.
0:31:13 > 0:31:16The ostracod discharges a bioluminescent flash bomb,
0:31:16 > 0:31:19one of the brightest forms of living light.
0:31:19 > 0:31:21And the cardinal fish quickly spits it out.
0:31:26 > 0:31:29The light is so bright that it shines through
0:31:29 > 0:31:33the body of the fish, temporarily blinding it, and this normally
0:31:33 > 0:31:36invisible fish becomes an easy target for a predator.
0:31:47 > 0:31:49Ostracods, with their flash bomb defence,
0:31:49 > 0:31:52are found throughout the world's oceans.
0:31:58 > 0:32:00But in the Caribbean,
0:32:00 > 0:32:03they employ their glow to attract as well as to repel.
0:32:06 > 0:32:09It's something that researchers Gretchen Gerrish
0:32:09 > 0:32:11and Trevor Rivers are studying.
0:32:11 > 0:32:14The spectacular mating display of ostracods.
0:32:16 > 0:32:19But they can't even begin to work until the moon has set.
0:32:21 > 0:32:25A fully moonlit night is not dark in the eyes of an organism that
0:32:25 > 0:32:29depends on their own light that they create, and so darkness truly
0:32:29 > 0:32:34is just a starlit sky, no moon present in the sky at all.
0:32:44 > 0:32:47Diving without torches in near total darkness, Gretchen
0:32:47 > 0:32:51and Trevor are entering a world that few people ever witness.
0:32:55 > 0:32:58You are immersed in darkness, you are immersed in water.
0:32:59 > 0:33:03And you see streaming stars floating past you and they're being
0:33:03 > 0:33:07produced by these tiny crustaceans that we barely understand.
0:33:08 > 0:33:11By releasing small amounts of glowing liquid as they swim,
0:33:11 > 0:33:15male ostracods leave a trail of lights in their wake.
0:33:17 > 0:33:21The series of precisely timed dots tell the female where
0:33:21 > 0:33:23he will be in exactly half a second.
0:33:25 > 0:33:30But as one male starts to display, another and another join him.
0:33:37 > 0:33:38And as they synchronise,
0:33:38 > 0:33:42they fan out into this firework-like display of light.
0:33:47 > 0:33:50It's one of the most awe-inspiring things I've ever seen.
0:34:01 > 0:34:05With every research trip, Trevor and Gretchen discover new species,
0:34:05 > 0:34:08each with its own light language.
0:34:23 > 0:34:26Ostracods and fireflies use bioluminescence
0:34:26 > 0:34:28to find potential mates.
0:34:28 > 0:34:32And it can be an efficient means of getting your message across,
0:34:32 > 0:34:35but it's not foolproof.
0:34:35 > 0:34:37Those messages can be hacked.
0:34:39 > 0:34:42There's a love cheat in this situation.
0:34:42 > 0:34:47There's also a female of a particular species here that,
0:34:47 > 0:34:52when she sees the males of a different species fly past,
0:34:52 > 0:34:56answers with their particular call sign, and that attracts them.
0:34:56 > 0:35:00And when they arrive, instead of mating with them,
0:35:00 > 0:35:03she has her own dastardly way with them.
0:35:06 > 0:35:09She mimics the flash patterns of other species.
0:35:13 > 0:35:16An unsuspecting male is lured in.
0:35:32 > 0:35:37Fireflies contain toxins thought to protect them against most predators.
0:35:37 > 0:35:40But this femme fatale is not put off.
0:35:42 > 0:35:45And she eats him alive.
0:35:45 > 0:35:48In fact, it may be the toxins that she is after.
0:35:50 > 0:35:53She can't produce such chemicals herself.
0:35:53 > 0:35:59So she tricks and then devours males of different species to obtain them.
0:36:04 > 0:36:08If she can't get males to come to her, she goes after them.
0:36:10 > 0:36:14And a good place to look for one is on a spider's web.
0:36:19 > 0:36:22A male firefly is ensnared.
0:36:22 > 0:36:24As the spider venom takes effect,
0:36:24 > 0:36:27his flashing turns to a constant glow.
0:36:34 > 0:36:37The femme fatale is alerted by the dim glow,
0:36:37 > 0:36:42and she flies straight onto the web to steal the spider's catch.
0:36:44 > 0:36:46As the spider struggles to keep its prey,
0:36:46 > 0:36:48she dazzles it with her lantern.
0:36:56 > 0:36:59Using her light, the firefly can clearly see the spider
0:36:59 > 0:37:01and avoid the web.
0:37:06 > 0:37:08The confused spider loses out.
0:37:16 > 0:37:21Predation turns out to be one area where light-making life
0:37:21 > 0:37:23has been very creative.
0:37:28 > 0:37:31Like a scene from the surface of an alien planet,
0:37:31 > 0:37:35these termite mounds have lodgers living in their walls.
0:37:43 > 0:37:47The luminous larvae of click beetles wait in burrows.
0:37:55 > 0:37:59Insects are drawn to their death by the green glow,
0:37:59 > 0:38:00like moths to a flame.
0:38:03 > 0:38:05And the beetle larvae gorge
0:38:05 > 0:38:09on the steady supply of unsuspecting victims.
0:38:19 > 0:38:22These predators work as individuals.
0:38:25 > 0:38:29There is another insect that excels in deception.
0:38:31 > 0:38:34But it works alongside thousands of its own kind.
0:38:38 > 0:38:41From outside, this cave shows no sign of the astonishing
0:38:41 > 0:38:43things that go on inside.
0:38:49 > 0:38:53The entrance is fringed with a curtain of silk,
0:38:53 > 0:38:55woven by the larvae of a kind of gnat.
0:38:57 > 0:38:59They move back and forth along the rocks,
0:38:59 > 0:39:04lowering sticky strings of saliva from the roof of the cave.
0:39:09 > 0:39:11As night falls, the walls
0:39:11 > 0:39:15and ceiling of this cavern become nature's very own planetarium.
0:39:26 > 0:39:27The trap is set.
0:39:30 > 0:39:35The cool, blue light produced in each larva's tail is the lure.
0:39:41 > 0:39:42Other insects that hatch
0:39:42 > 0:39:47and emerge in the cave instinctively fly upwards to the sky.
0:39:47 > 0:39:51But this is not a starlit sky. It's a deathtrap.
0:40:04 > 0:40:07Bioluminescence is clearly a powerful tool
0:40:07 > 0:40:10to these life forms that possess it.
0:40:10 > 0:40:13But it is only effective in darkness.
0:40:13 > 0:40:15Each dawn,
0:40:15 > 0:40:19the bright rays of the sun overwhelm the power of living light.
0:40:24 > 0:40:27For all of the wonders of bioluminescence
0:40:27 > 0:40:30in the plains and woodlands of the Earth, there is
0:40:30 > 0:40:35one place where living light is virtually the key to existence.
0:40:35 > 0:40:39The world of eternal darkness, the deep sea.
0:40:48 > 0:40:51The Western Fire is one of the world's most advanced
0:40:51 > 0:40:53deep sea research vessels.
0:40:55 > 0:40:58In the black depths there are no edges.
0:40:59 > 0:41:01No boundaries, nowhere to hide.
0:41:03 > 0:41:06Predators and prey have therefore had to develop some
0:41:06 > 0:41:08extraordinary strategies to stay alive.
0:41:08 > 0:41:11And many do so with the help of light.
0:41:13 > 0:41:17Dr Steven Haddock has spent the last 25 years studying the
0:41:17 > 0:41:21least known part of our planet, the ocean depths.
0:41:23 > 0:41:26I think people look at bioluminescence,
0:41:26 > 0:41:30this ability to make light, they think of it as a very magical thing,
0:41:30 > 0:41:34but once you see the diversity and the range of functions that
0:41:34 > 0:41:37bioluminescence serves for animals in the ocean, it is
0:41:37 > 0:41:40clear that it is a critical part of the whole ecology
0:41:40 > 0:41:41of the system.
0:41:41 > 0:41:44Until recently, it was all but impossible
0:41:44 > 0:41:49to collect living bioluminescent creatures from the deep.
0:41:49 > 0:41:52But this remote submersible, known as the Doc Ricketts,
0:41:52 > 0:41:55is equipped to do just that.
0:41:56 > 0:41:58They are trying to find new life
0:41:58 > 0:42:02and clues as to why light-making has evolved in so many forms.
0:42:11 > 0:42:14In the control room, thousands of metres above, Steve
0:42:14 > 0:42:18and the crew navigate past alien-like life forms.
0:42:18 > 0:42:19Nice.
0:42:22 > 0:42:23Wow.
0:42:23 > 0:42:26But in truth, it is us who are the aliens down here.
0:42:43 > 0:42:46Although very sophisticated, the Doc Ricketts'
0:42:46 > 0:42:51own remote cameras are not sensitive enough to record bioluminescence,
0:42:51 > 0:42:54so they use bright lights to find and film these creatures.
0:42:57 > 0:43:00To have any hope of observing their light-making powers,
0:43:00 > 0:43:04the research team needs to bring them to the surface.
0:43:05 > 0:43:09Gentle suction and remotely controlled canisters are used to
0:43:09 > 0:43:12delicately scoop up the rare sea creatures.
0:43:18 > 0:43:19Vampire squid.
0:43:26 > 0:43:27Yes!
0:43:29 > 0:43:30Viper fish.
0:43:34 > 0:43:36Perfect.
0:43:36 > 0:43:38Oh, look at that!
0:43:38 > 0:43:39And dragonfish.
0:43:42 > 0:43:45They don't just sound like something from a sailor's tale of
0:43:45 > 0:43:48fantasy monsters, they look like them, too.
0:43:51 > 0:43:54This is one of the few dragonfish that has ever been seen alive.
0:43:57 > 0:44:01And it's one of the even fewer that have been captured unharmed.
0:44:05 > 0:44:09- Yes!- Yay!- Oh, my gosh.
0:44:14 > 0:44:17Once they arrive on the ship, thousands of metres
0:44:17 > 0:44:21above their normal environment, there is no time to waste.
0:44:21 > 0:44:24The enormous pressure change is likely to cause any
0:44:24 > 0:44:27bioluminescence abilities to disappear.
0:44:30 > 0:44:33The race is on to try and observe those abilities
0:44:33 > 0:44:35and understand their functions.
0:44:39 > 0:44:41Wow.
0:44:48 > 0:44:50In some species, it seems to be defensive.
0:44:52 > 0:44:56Like the circling flashes of the Atolla jellyfish.
0:44:59 > 0:45:03Or the rippling light waves of the Beroe comb jelly.
0:45:14 > 0:45:17In other species, like this viper fish,
0:45:17 > 0:45:21light is used not only for defence, but to lure prey.
0:45:26 > 0:45:31These pyrosomes, colonies of minute translucent creatures,
0:45:31 > 0:45:34use light to communicate within the colony.
0:45:34 > 0:45:39The team's experiment shows that as one colony begins to glow,
0:45:39 > 0:45:41its neighbours light up in response.
0:45:43 > 0:45:45What could they be saying?
0:45:49 > 0:45:53Thanks to the delicate sampling methods of the Doc Ricketts,
0:45:53 > 0:45:55the team are able to observe a living
0:45:55 > 0:46:00and luminescing dragonfish, a sight few have ever witnessed.
0:46:03 > 0:46:04Whatever their function,
0:46:04 > 0:46:08one thing unites all these types of bioluminescence -
0:46:08 > 0:46:10their otherworldly beauty.
0:46:16 > 0:46:20And this beauty is the result of an evolutionary arms race
0:46:20 > 0:46:24where light is a weapon to blind or deceive.
0:46:27 > 0:46:32In response, some animals have evolved the most sophisticated
0:46:32 > 0:46:35and bizarre eyes on the planet.
0:46:38 > 0:46:43The rare barreleye fish has eyes that can only look upwards,
0:46:43 > 0:46:46through the top of its translucent head.
0:46:46 > 0:46:47Searching for prey above.
0:46:50 > 0:46:51It is so rare,
0:46:51 > 0:46:54catching even a glimpse of it alive is a huge achievement.
0:47:01 > 0:47:04And the same is true for the cock-eyed squid.
0:47:04 > 0:47:08It has one normal eye and one strange, upward-looking eye.
0:47:18 > 0:47:22At this depth, it is too dark for human eyes.
0:47:22 > 0:47:24But the faintest light from the surface,
0:47:24 > 0:47:29half a kilometre above, can just reach this twilight zone.
0:47:32 > 0:47:35Firefly squid normally live at these depths.
0:47:35 > 0:47:38To prevent themselves from being seen from below,
0:47:38 > 0:47:43they hide themselves with light.
0:47:43 > 0:47:45It's a strange paradox.
0:47:45 > 0:47:48In this dark world, light can be used for camouflage.
0:47:53 > 0:47:57At close range, the light-emitting cells, called photophores,
0:47:57 > 0:47:59are easy to see.
0:47:59 > 0:48:02But from a distance, they break up the outline of the squid
0:48:02 > 0:48:04and it merges with the background.
0:48:10 > 0:48:13It's an elegant solution used by many creatures
0:48:13 > 0:48:16when a silhouette can be a death sentence.
0:48:24 > 0:48:27In shallower waters, the colour of the light changes
0:48:27 > 0:48:33so the squid, as it gets closer to the surface, uses green photophores.
0:48:43 > 0:48:46The lives of firefly squid are short.
0:48:46 > 0:48:48When they are only a year old,
0:48:48 > 0:48:52mated females make their final journey, to the surface to spawn.
0:48:57 > 0:49:01But even in their final moments, they are both spectacular
0:49:01 > 0:49:02and valuable.
0:49:11 > 0:49:13All along the coast here,
0:49:13 > 0:49:16these squid, which die naturally after spawning,
0:49:16 > 0:49:18are gathered as a local delicacy.
0:49:20 > 0:49:23It's largely through this fishery that we know
0:49:23 > 0:49:26anything at all about the firefly squid.
0:49:28 > 0:49:30Like so many deep sea creatures,
0:49:30 > 0:49:33their daily lives are still virtually unknown.
0:49:34 > 0:49:39What we do know is that their world is dominated by bioluminescence.
0:49:43 > 0:49:46We've come a long way from watching fireflies
0:49:46 > 0:49:49in the woodlands of Pennsylvania.
0:49:49 > 0:49:54Organisms that produce light on land may be exceptional
0:49:54 > 0:49:55but in the sea,
0:49:55 > 0:49:59creatures that do so, like these comb jellies,
0:49:59 > 0:50:01are, in fact, the norm.
0:50:06 > 0:50:09In the oceans and on land,
0:50:09 > 0:50:13living creatures of many kinds have harnessed the power of light in
0:50:13 > 0:50:20extraordinary ways, to mate, to lie, even to hide under a cloak of light.
0:50:24 > 0:50:27Yet, with the latest cameras and technology, we are
0:50:27 > 0:50:31only beginning to understand the lives of luminous creatures.
0:50:34 > 0:50:40There remain many mysteries. But what a beautiful world they create.
0:50:42 > 0:50:46And what a beautiful world awaits the scientists of the future.
0:51:03 > 0:51:06During this programme, we've had to use cameras
0:51:06 > 0:51:08that are far more sensitive than our own eyes
0:51:08 > 0:51:13and about as sensitive as many of the animals that we are showing.
0:51:17 > 0:51:20The eye is one of evolution's greatest achievements.
0:51:20 > 0:51:24And nature has certainly devised some fiendishly complex
0:51:24 > 0:51:26and sensitive examples.
0:51:26 > 0:51:30Some of which are designed specifically to see bioluminescence.
0:51:34 > 0:51:39When we enter the dark, we barely notice bioluminescence.
0:51:39 > 0:51:41But after a few minutes, physiological changes
0:51:41 > 0:51:46take place in our eyes that enable us to see living light.
0:51:47 > 0:51:49Cameras have always struggled to replicate
0:51:49 > 0:51:51what the human eye can do,
0:51:51 > 0:51:53but with special low-light cameras,
0:51:53 > 0:51:57we can now record glowing light at least as well,
0:51:57 > 0:52:00and sometimes better, than we can see it ourselves.
0:52:02 > 0:52:06But being able to film the glow is only one part of the solution.
0:52:06 > 0:52:10To really understand light on Earth, you need to be able to record
0:52:10 > 0:52:13the creature themselves as they make the light.
0:52:14 > 0:52:16This camera allows you to film
0:52:16 > 0:52:20in low-light levels in a completely new way.
0:52:20 > 0:52:23The beam of light comes in through the single lens,
0:52:23 > 0:52:28but it is then split into two, and one camera records on one
0:52:28 > 0:52:33light frequency, and the other on a different light frequency.
0:52:33 > 0:52:37One of the cameras is sensitive to infrared light, invisible to
0:52:37 > 0:52:41most animals, but which allows the camera to record in the dark.
0:52:42 > 0:52:46The second camera records only the bioluminescence,
0:52:46 > 0:52:48which is mostly blue or green.
0:52:49 > 0:52:52The two are then combined into one picture.
0:52:56 > 0:52:59And that way you can get pictures at a low-light level,
0:52:59 > 0:53:01not only of bioluminescent animals,
0:53:01 > 0:53:05but even the environment in which they are living.
0:53:05 > 0:53:08This technique, pioneered by film-maker Martin Dohrn,
0:53:08 > 0:53:12allows us to enter the world of bioluminescent creatures,
0:53:12 > 0:53:16and also to contribute to new science.
0:53:16 > 0:53:18With this type of camera, there are many things
0:53:18 > 0:53:22I see on these images which I wouldn't be able to see normally.
0:53:24 > 0:53:28In the past, scientist Marcel Koken has been unable to
0:53:28 > 0:53:31study the worm and beetle without using a light.
0:53:31 > 0:53:34But when he did, the light would frighten the beetle
0:53:34 > 0:53:37and overpower the worm's bioluminescence.
0:53:37 > 0:53:41With the help of Martin's camera, Marcel is able to observe
0:53:41 > 0:53:46and record the beetle and worm encounter for the first time.
0:53:46 > 0:53:49Having decided working with two cameras simultaneously wasn't
0:53:49 > 0:53:54already hard enough, the team decide to take them underwater.
0:53:54 > 0:53:56The objective was to film
0:53:56 > 0:54:00the beautiful mating display of ostracods -
0:54:00 > 0:54:04tiny, one millimetre long crustaceans in the dark
0:54:04 > 0:54:09swirling currents of their natural habitat. A huge challenge.
0:54:09 > 0:54:12- Martin, how was it tonight? - We had a lot of problems.
0:54:12 > 0:54:16Tonight, it went smoother. It's calmer. Much, much calmer.
0:54:16 > 0:54:20A lot of what I saw looked utterly amazing.
0:54:22 > 0:54:25Martin's beam-splitting system makes it possible to film
0:54:25 > 0:54:29the bioluminescence as well as the tiny ostracods, as they leave
0:54:29 > 0:54:31lights in their wake.
0:54:31 > 0:54:34However, the scientists are not done.
0:54:35 > 0:54:39Marine biologist Gretchen Gerrish hopes the camera will enable
0:54:39 > 0:54:42her to film groups of males that aren't flashing,
0:54:42 > 0:54:45swimming alongside the individual that is.
0:54:45 > 0:54:48Something that has only ever been seen in the lab.
0:54:51 > 0:54:55These males, known as sneakers, are invisible to a normal camera,
0:54:55 > 0:54:57because they leave no night trail.
0:54:57 > 0:55:02But our camera, nicknamed Bertha, could change all that.
0:55:02 > 0:55:05- So, how was Bertha? - Bertha is awesome.
0:55:05 > 0:55:10She was filming sneakers and you could see them swimming.
0:55:10 > 0:55:13She's a bit of a beast.
0:55:13 > 0:55:16What do you think, Trevor? Did you get any good footage?
0:55:16 > 0:55:17It was just awesome.
0:55:17 > 0:55:19This is opening the doors for so much.
0:55:21 > 0:55:24The scientists are keen to get their first look at the combined
0:55:24 > 0:55:26images from Bertha.
0:55:31 > 0:55:34The infrared does show there is a spiralling group of males,
0:55:34 > 0:55:38intent on intercepting the female, before she can reach the male
0:55:38 > 0:55:41that has done all the hard work of attracting her.
0:55:45 > 0:55:47And there are far more competing males
0:55:47 > 0:55:50than the scientists had expected.
0:55:51 > 0:55:53It's an ostracod soup. There's thousands of them.
0:55:54 > 0:55:59What, to our eyes, is a beautiful, orderly display is in fact
0:55:59 > 0:56:01an ostracod free-for-all.
0:56:01 > 0:56:04Lots of males try to cash in on the efforts of a few.
0:56:04 > 0:56:07The amount of information you could fire from this is something
0:56:07 > 0:56:09we've been trying to do for the last five years.
0:56:09 > 0:56:11Yeah, that's a paper, right there.
0:56:11 > 0:56:13What? You mean in that short clip? There's not a paper there.
0:56:13 > 0:56:16Close to it.
0:56:16 > 0:56:20But having hi-tech kit is only part of the story.
0:56:20 > 0:56:22Since much of the bioluminescence is little-known,
0:56:22 > 0:56:26just finding it is often the biggest hurdle.
0:56:26 > 0:56:31The crew are about to head out on their most ambitious shoot.
0:56:31 > 0:56:32Tonight, we're going to try
0:56:32 > 0:56:35and film something that we know is found all over the world,
0:56:35 > 0:56:39and it happens every night in every ocean, almost anywhere,
0:56:39 > 0:56:43and yet, in terms of getting information from people
0:56:43 > 0:56:44as to where we might find it,
0:56:44 > 0:56:47and when the best time is, there is nothing.
0:56:49 > 0:56:54As night falls, they head away from shore and any artificial light.
0:56:56 > 0:56:59And soon, they are sailing in the sea laced with dinoflagellates.
0:57:01 > 0:57:03These blue flashes can be seen
0:57:03 > 0:57:07in almost any ocean at night, with the lights out.
0:57:07 > 0:57:10But this alone is not what the crew came for.
0:57:10 > 0:57:12They are hoping to meet some special visitors.
0:57:23 > 0:57:26Working on a rocking boat in complete darkness with
0:57:26 > 0:57:29a prototype camera is one of the trickiest challenges Martin
0:57:29 > 0:57:31has faced in his career.
0:57:34 > 0:57:38After a week searching the dark sea, here they are.
0:57:38 > 0:57:40Dolphins.
0:57:48 > 0:57:52To be out at night, with clear skies and beautiful stars,
0:57:52 > 0:57:56and everywhere there are flashes of light,
0:57:56 > 0:58:00and when dolphins turn up, the show just gets more extraordinary still.
0:58:00 > 0:58:04It really is one of the most amazing things I've ever seen in my life.
0:58:06 > 0:58:10Scenes like this are happening across the oceans,
0:58:10 > 0:58:14yet this is one of the few times they've ever been caught on camera.
0:58:17 > 0:58:21New technologies and new ideas are creating
0:58:21 > 0:58:25a revolution in our way of seeing the world.
0:58:25 > 0:58:28And of understanding life that glows.