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Over 60 per cent of our planet
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is covered by ocean
more than a mile deep.
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That, the deep sea,
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is by far the largest habitat
on Earth
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and it's largely unknown.
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Join us on a journey
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to the very bottom of the deep sea,
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to an alien world
never revealed before.
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It's home to some
of the strangest animals on Earth.
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Fish flash in the darkness.
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New species are discovered
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on almost every dive.
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More people have travelled
into space
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than have ventured this deep.
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Come on a journey
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into the abyss.
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A sperm whale takes a breath,
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its last for over an hour.
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It's about to leave
the warm, well—lit surface waters
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and dive far down
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into the cold, dark depths
of the deep ocean.
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At the surface
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it took in air at the same pressure
as we breath it.
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But it's going to look for food
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at more than 1,000 metres down,
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where pressure is 100 times
that on the surface,
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crushing the whale's lungs
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to just one per cent
of their volume.
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For us to follow the whale,
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we need the very latest submersible.
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A reinforced acrylic sphere
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with walls 12 centimetres thick
protects a pilot and our cameraman
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from the enormous pressure below,
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and allows the submarine to dive
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to just over 900 metres.
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(PILOT) 900 feet,
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With every passing metre,
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pressure increases
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and sunlight diminishes.
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(PILOT) 1,000 feet,
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By 300 metres,
it's already very dark
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and the temperature of the water
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is dropping fast.
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We are entering the twilight zone,
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a weird world of gloom
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where many animals have become
completely transparent.
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In this twilight,
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and animal needs to see,
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and yet, as far as possible,
must avoid being seen.
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A giant amphipod,
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12 centimetres long
and almost perfectly transparent.
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Its head is completely filled
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by two huge eyes
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with which it strains
to detect its prey.
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Another twilight monster, phronima,
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the inspiration
for the Alien movies.
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She and her developing
pink offspring
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live like parasites
in the stolen body of a jelly.
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This impressive cutlery set
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and its huge eyes
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make phronima a powerful predator.
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Even really complex animals
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have become transparent
in the twilight zone.
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Squids are among
the most advanced of invertebrates,
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but this one never meets
a hard surface in its entire life,
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so its body need not be as robust
as that of its shallow water cousins.
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There's a rich variety of jellies
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that live nowhere else
but in the deep sea.
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Thousands of tiny cilia propel them
through a world without walls.
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Invisible in the gloom,
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they grope blindly for their prey.
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Comb jellies let out long sticky
nets to catch passing copepods.
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But the most extensive death trap
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is set by siphonophores.
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This pulsating bell
is the head of a colonial jelly
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that can be 40 metres long.
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Millions of tiny stinging cells
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drifting through the sea.
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500 metres down,
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and in even
the clearest tropical waters
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only the faintest vestige
of the sunlight remains —
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so little that our eyes
can't detect it, but others can.
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Survival in the twilight zone
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is all about seeing,
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yet not being seen.
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Hatchet fish
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are masters of the game
of hide and seek.
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They have the large, sensitive eyes
needed for seeking prey
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but their bodies are flat...
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and their sides are highly silvered.
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Head on, they are just visible,
thin though they are,
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but as soon as they turn,
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their mirrored sides
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reflect the remnants of blue light
from the surface,
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and they disappear into the gloom.
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Viewed from the side,
whole shoals can hide in this way,
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but what about from below?
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The tubular eyes
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of many of the predators,
even in this gloom,
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are able to distinguish their prey
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silhouetted against the faint
glimmer of light from above.
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Hatchet fish, however,
have a way of confusing any eyes
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that might be searching for them
from below.
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Their bellies carry rows
of light—producing cells
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called photophores.
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They can use these
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to exactly match the changing colour
of light from the surface far above.
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This counter shading
breaks up their silhouette,
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making them almost invisible
from below...
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almost.
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But these are no ordinary eyes.
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The enormous yellow lenses
enable their owner to distinguish
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between light produced
by photophores and sunlight.
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So, one device for escape
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is countered by another
equally subtle one for attack
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in an evolutionary arms race that
has been waged for millions of years.
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Descend below 1,000 metres,
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and you enter the dark zone.
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No sunlight whatsoever
penetrates this deep.
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The temperature of the water
is below four degrees Centigrade.
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The pressure is more than 100 times
that at the surface.
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Life becomes ever more sparse.
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It's a dark, dangerous world.
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Relative to body size,
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these are the largest teeth
in the ocean.
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They are so big
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that their owner
can't close its mouth.
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They belong to the fang tooth.
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Unlike most deep sea fish,
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this has powerful muscles
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and is an aggressive hunter.
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With food in such short supply
at this depth,
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dark zone predators have to be able
to deal with a meal of any size.
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Many animals here are dark red,
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like this deep sea jelly.
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Caught in the lights
of the submersible,
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it's a spectacular firework display
of colour.
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Normally, no red light
penetrates as deep as this,
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so animals with red pigment
appear completely black down here,
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perfectly concealed.
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Predators here, however,
don't just rely on vision —
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many have tiny eyes.
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Instead, their thin, rod—like bodies
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are lined with organs sensitive
to tiny movements in the water.
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This monster, half a metre across,
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is a hairy angler.
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This is the first time
it's been seen.
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It's covered with hundreds
of sensitive antennae,
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which detect the movements
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of any prey careless enough
to stray too close
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to this motionless predator.
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But this, surely,
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must be the strangest of all
the deep sea fish yet discovered.
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A highly sensitive metre—long tail
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hangs down from the head
that makes up a quarter of its body.
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Its eyes are tiny,
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but its mouth is truly enormous.
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It's called the gulper eel
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because it can engulf a meal
of almost any size.
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Hanging motionless in mid—water,
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its enormous gape enables it
to deal with passing prey,
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whether it's small,
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or large.
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Gulper eels can swallow prey
as big as themselves,
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which is very useful in a world
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where you never know
when the next meal is coming along.
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Even in the dark zone,
there is SOME light.
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Turn off the submersible headlights,
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and you see a pyrotechnic display
outside.
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These lights are created by animals.
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This is bioluminescence.
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A deep sea angler fish
flashes in the darkness.
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The light is generated by bacteria
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that live permanently
inside the lure
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which attracts prey
to these murderous teeth.
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There are all sorts of lures
out in the darkness.
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Come into my mouth, little fish!
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And what is the purpose
of THIS lure,
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suspended on a long rod,
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way below its owner's
terrifying set of teeth?
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It's difficult to be sure,
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but then, this monster does have
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another giant flashing lure
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much closer to its mouth.
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These fish are called anglers
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because they use their lures
in much the same way
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as fly fishermen
use their imitation flies.
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For a hunting squid with huge eyes
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this glimmer is intriguing.
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It might just be food.
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A satisfying meal
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for a fish
with a highly extendible stomach.
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Attracting a mate
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in this endless darkness
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can be even harder
than finding food.
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Flashing lures may be helpful;
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certainly, only female anglers
have them.
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The tiny males are just a tenth
the size of the females.
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Their only purpose is somehow
to find a mate in the darkness.
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She releases chemicals
into the water
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which the males scent with a special
white organ in front of their eyes.
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Having found a partner,
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the male bites at her belly
with specially designed teeth.
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He needs to get
permanently attached.
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Within a matter of weeks,
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the male is completely fused
to the female,
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and there he will stay
for the rest of his life.
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Her blood circulating in his body
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provides him
with all the sustenance he needs.
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In return, she gets a continuous,
reliable supply of sperm —
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a brilliant solution to the problem
of finding a mate
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in the vast emptiness
of the deep sea.
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To help in the constant battle
between predators and prey,
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00:16:10,320 --> 00:16:12,312
some fish in the dark zone
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00:16:12,480 --> 00:16:14,472
have developed headlights.
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00:16:20,560 --> 00:16:24,190
These light—producing photophores
beneath their eyes
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00:16:24,360 --> 00:16:27,432
may be used to search out prey
in the darkness.
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00:16:29,640 --> 00:16:32,712
Most bioluminescence in the deep sea
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is blue or greenish—blue,
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but a very few predatory fish
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produce red light.
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00:16:44,000 --> 00:16:45,480
With this,
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00:16:45,640 --> 00:16:48,314
red prey becomes obvious
in the darkness.
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Red light is rare down here
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and most animal eyes can't see it.
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Only these fish can do so.
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This gives them a sniper scope —
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a headlight invisible
to their targets.
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00:17:08,600 --> 00:17:10,592
This copepod, unalarmed,
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00:17:10,760 --> 00:17:12,752
takes no avoiding action.
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Bioluminescence
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is useful in escape
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as well as attack.
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00:17:31,560 --> 00:17:33,552
A shrimp senses a threat.
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It spins in the water,
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00:17:39,680 --> 00:17:41,911
releasing a bioluminescent glue.
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This acts like a burglar alarm,
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00:17:47,320 --> 00:17:49,312
startling the attacking fish
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00:17:49,480 --> 00:17:51,995
and leaving it illuminated
in the dark,
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00:17:52,160 --> 00:17:54,550
and vulnerable to its own predators.
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These twinkling lights
in the darkness
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are produced by copepods.
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They probably flash like this
to communicate with one another
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and confuse their predators.
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The most sensitive eyes in the ocean
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belong to an ostracod
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called gigantocypris.
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00:18:22,400 --> 00:18:23,800
It's the size of a pea,
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00:18:23,960 --> 00:18:25,440
but that's enormous
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00:18:25,600 --> 00:18:27,080
for an ostracod.
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Copepods are a favourite prey,
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00:18:30,680 --> 00:18:34,469
and it actively searches
for their flashes in the darkness...
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00:18:38,160 --> 00:18:42,837
but this copepod has a way of
confusing a hunting gigantocypris.
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It discharges a packet
of bioluminescent liquid.
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The flash is delayed,
like a depth charge.
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00:19:00,000 --> 00:19:02,595
Spinning, confused, in the water,
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00:19:02,760 --> 00:19:05,753
gigantocypris chases
after the flashes...
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00:19:13,280 --> 00:19:14,680
and the copepod
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00:19:14,840 --> 00:19:16,479
slips away unseen
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00:19:16,640 --> 00:19:18,154
into the darkness.
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00:19:26,840 --> 00:19:30,072
The ultimate bioluminescent
defence mechanism
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has to be the light show
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00:19:31,920 --> 00:19:35,152
created by the deep sea jellyfish,
periphylla.
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00:19:46,000 --> 00:19:49,596
That, presumably, is the way
it scares away its enemies.
265
00:20:05,600 --> 00:20:09,310
These bright lights
are all produced by firefly squid.
266
00:20:09,480 --> 00:20:12,917
Normally, they live way down
at around 300 metres,
267
00:20:13,080 --> 00:20:16,676
beyond the reach of
these Japanese fishermen's nets...
268
00:20:16,840 --> 00:20:21,119
but for a few months each spring,
they come to the surface each night.
269
00:20:25,320 --> 00:20:28,677
The brightest lights
come from the bioluminescent tips
270
00:20:28,840 --> 00:20:30,718
of their two front tentacles,
271
00:20:30,880 --> 00:20:33,395
but it's only in the dark
of the deep sea,
272
00:20:33,560 --> 00:20:38,112
that you can really appreciate
the full complexity of their displays.
273
00:20:38,280 --> 00:20:40,272
It's not just their tentacles
274
00:20:40,440 --> 00:20:44,036
but their whole bodies
that are covered in photophores.
275
00:20:46,400 --> 00:20:48,392
The exact function is not clear.
276
00:20:48,560 --> 00:20:51,951
The bright tentacle tips
may be for attracting mates
277
00:20:52,120 --> 00:20:53,600
or dazzling predators.
278
00:20:54,800 --> 00:20:56,712
The rest may be camouflage,
279
00:20:56,880 --> 00:20:59,475
providing counter shading
for the squid
280
00:20:59,640 --> 00:21:02,314
as they journey up
into the twilight zone.
281
00:21:05,120 --> 00:21:06,793
Every night in the season,
282
00:21:06,960 --> 00:21:08,952
hundreds of thousands of squid
283
00:21:09,120 --> 00:21:11,874
journey up into the shallow water
to spawn.
284
00:21:16,520 --> 00:21:19,592
Before dawn,
they will return to the depths,
285
00:21:19,760 --> 00:21:22,753
leaving their eggs
to develop in the shallows.
286
00:21:33,520 --> 00:21:35,193
The daily cycle of the sun
287
00:21:35,360 --> 00:21:38,592
has a profound influence on life
in the deep ocean.
288
00:21:39,520 --> 00:21:42,672
As the sun sets,
it triggers the largest migration
289
00:21:42,840 --> 00:21:45,116
of living organisms on our planet.
290
00:21:46,000 --> 00:21:48,390
One thousand million tonnes
of animals
291
00:21:48,560 --> 00:21:50,517
travel up from the dark zone
292
00:21:50,680 --> 00:21:53,832
into richer, shallower water
every night.
293
00:21:57,680 --> 00:21:59,672
Tiny grazers are first up,
294
00:21:59,840 --> 00:22:02,275
searching for the microscopic plants
295
00:22:02,440 --> 00:22:05,114
that only grow
in shallow, sunlit waters.
296
00:22:06,600 --> 00:22:08,876
Predators follow the grazers.
297
00:22:11,040 --> 00:22:14,192
An enormous variety
of different animals
298
00:22:14,360 --> 00:22:15,840
join the convoy
299
00:22:16,000 --> 00:22:17,992
or feed off it as it passes.
300
00:22:23,720 --> 00:22:27,475
Many will travel up hundreds
of metres towards the surface,
301
00:22:27,640 --> 00:22:31,316
and, at dawn, finding themselves
at risk from predators,
302
00:22:31,480 --> 00:22:35,076
the visitors return
to the safer darkness of the depths.
303
00:22:42,760 --> 00:22:45,275
The sun's rays
only have a direct effect
304
00:22:45,440 --> 00:22:48,160
in the top 100 metres
or so of the ocean.
305
00:22:48,960 --> 00:22:52,192
It's only here that photosynthesis
can take place
306
00:22:52,360 --> 00:22:54,352
and coral reefs can flourish.
307
00:22:54,520 --> 00:22:56,751
Leave this thin, rich slice of life
308
00:22:56,920 --> 00:22:59,515
and travel over the outer face
of the reef
309
00:22:59,680 --> 00:23:02,912
and you quickly enter
a far more demanding world.
310
00:23:12,080 --> 00:23:13,594
Below 150 metres,
311
00:23:13,760 --> 00:23:16,559
photosynthesis becomes impossible.
312
00:23:18,760 --> 00:23:20,274
You find no plants,
313
00:23:20,440 --> 00:23:21,920
just animals.
314
00:23:24,400 --> 00:23:27,711
Here, the animals are adapted
to catch marine snow —
315
00:23:27,880 --> 00:23:32,033
particles of dead animals and plants
that drift down from above.
316
00:23:32,200 --> 00:23:36,194
So they depend second—hand
on the energy captured from the sun
317
00:23:36,360 --> 00:23:38,670
by organisms in the surface waters.
318
00:23:48,960 --> 00:23:51,191
Travelling close to the sea floor,
319
00:23:51,360 --> 00:23:54,353
we're going to take a journey
to the very bottom
320
00:23:54,520 --> 00:23:55,920
of the deep sea...
321
00:23:57,000 --> 00:24:00,755
to a world completely separate
from the mid—water above.
322
00:24:10,000 --> 00:24:12,151
At around 300 metres,
323
00:24:12,320 --> 00:24:16,712
the drop—off levels out, and we move
out onto the continental slope.
324
00:24:19,560 --> 00:24:22,075
This stretches for about 150 miles
325
00:24:22,240 --> 00:24:23,799
from the coast,
326
00:24:23,960 --> 00:24:25,838
sloping in a gentle gradient,
327
00:24:26,000 --> 00:24:28,515
down to a maximum depth
of 4,000 metres.
328
00:24:31,120 --> 00:24:33,032
Water temperatures down here
329
00:24:33,200 --> 00:24:35,510
drop below four degrees Centigrade
330
00:24:35,680 --> 00:24:39,594
and the pressure can reach
up to 400 times that of the surface.
331
00:24:46,800 --> 00:24:49,315
Without the lights
of the submersible,
332
00:24:49,480 --> 00:24:51,472
it would be completely dark.
333
00:24:52,320 --> 00:24:56,792
The water is crystal clear because
there's so little organic matter.
334
00:24:56,960 --> 00:25:00,271
Only three per cent of any food
in the surface waters
335
00:25:00,440 --> 00:25:02,511
reaches the continental slope.
336
00:25:06,800 --> 00:25:09,713
At first sight,
it appears a lifeless desert,
337
00:25:09,880 --> 00:25:11,997
but take a closer look
338
00:25:12,160 --> 00:25:14,959
and you notice a network
of tracks and trails.
339
00:25:15,120 --> 00:25:17,874
There is life even down here.
340
00:25:21,360 --> 00:25:23,636
These animals would die immediately
341
00:25:23,800 --> 00:25:25,951
if brought to the surface in nets,
342
00:25:26,120 --> 00:25:28,874
so you can only see them
behaving normally
343
00:25:29,040 --> 00:25:30,554
from submersibles.
344
00:25:30,720 --> 00:25:32,712
Many are new to science.
345
00:25:36,520 --> 00:25:38,671
The deep sea floor is dominated
346
00:25:38,840 --> 00:25:40,399
by echinoderms —
347
00:25:40,560 --> 00:25:42,836
sea cucumbers, brittle stars
348
00:25:43,000 --> 00:25:44,480
and sea urchins.
349
00:25:44,640 --> 00:25:47,200
There are literally millions
of them,
350
00:25:47,360 --> 00:25:49,352
marching across the sea bed,
351
00:25:49,520 --> 00:25:51,751
hoovering up any edible particles
352
00:25:51,920 --> 00:25:53,400
in the sediment.
353
00:25:54,800 --> 00:25:56,951
They come in all shapes and sizes,
354
00:25:57,120 --> 00:25:59,874
and though they are thinly spread,
355
00:26:00,040 --> 00:26:02,714
these are among
the most numerous animals
356
00:26:02,880 --> 00:26:04,633
on the planet.
357
00:26:06,080 --> 00:26:09,312
Their spikes are good
for locomotion and defence,
358
00:26:09,480 --> 00:26:12,871
but perhaps not quite so good
when it comes to mating.
359
00:26:16,160 --> 00:26:19,437
Finding a mate
in this largely empty sea floor
360
00:26:19,600 --> 00:26:21,080
could be a problem,
361
00:26:21,240 --> 00:26:23,800
so some urchins
stay together in herds
362
00:26:23,960 --> 00:26:27,954
to be sure that they're never
too far from a potential partner.
363
00:26:30,080 --> 00:26:32,595
Rocky outcrops
provide good anchorage
364
00:26:32,760 --> 00:26:36,071
for animals that rely on food
that might drift past.
365
00:26:36,920 --> 00:26:39,913
These crinoids or sea lilies
look like plants,
366
00:26:40,080 --> 00:26:42,072
but are, in fact, animals.
367
00:26:45,160 --> 00:26:49,473
Their long stalks ensure that
their umbrella of feeding tentacles
368
00:26:49,640 --> 00:26:52,553
are positioned to best effect
in the current.
369
00:26:52,720 --> 00:26:54,951
Particles are swept onto the arms,
370
00:26:55,120 --> 00:26:58,716
and carried down to a mouth
in the middle of the umbrella.
371
00:27:00,720 --> 00:27:03,030
These sudden movements swat away
372
00:27:03,200 --> 00:27:07,479
tiny amphipods that try to steal
the sea lily's captures.
373
00:27:16,800 --> 00:27:20,316
Coral reefs are not supposed
to exist in total darkness,
374
00:27:20,480 --> 00:27:22,517
but recently, a new kind of coral
375
00:27:22,680 --> 00:27:25,275
was found as deep as 2,000 metres.
376
00:27:26,440 --> 00:27:29,399
In the cold waters
of a Norwegian fjord,
377
00:27:29,560 --> 00:27:33,315
there was a deep sea reef
30 metres high and 200 metres long.
378
00:27:35,680 --> 00:27:39,674
This coral gets no energy from
the sun, so it has to be very efficient
379
00:27:39,840 --> 00:27:41,240
in catching food.
380
00:27:41,400 --> 00:27:45,155
Its polyps are far larger
than those of shallow water corals.
381
00:27:51,680 --> 00:27:53,160
These are, in fact,
382
00:27:53,320 --> 00:27:56,233
the largest coral polyps
in the ocean.
383
00:27:57,160 --> 00:28:00,915
They belong
to the deep sea mushroom coral.
384
00:28:02,160 --> 00:28:04,834
Their three—centimetre—long
tentacles
385
00:28:05,000 --> 00:28:06,559
can catch far larger prey
386
00:28:06,720 --> 00:28:08,234
than other corals can.
387
00:28:11,400 --> 00:28:14,393
This necessity to capture
every particle of food
388
00:28:14,560 --> 00:28:17,314
that comes within reach
in this near desert
389
00:28:17,480 --> 00:28:19,870
has radically changed many animals.
390
00:28:21,280 --> 00:28:22,680
Most tunicates
391
00:28:22,840 --> 00:28:24,320
are filter feeders,
392
00:28:24,480 --> 00:28:26,631
but this one has become a predator
393
00:28:26,800 --> 00:28:28,951
and its greatly enlarged siphon
394
00:28:29,120 --> 00:28:31,112
has been converted into a trap.
395
00:28:42,520 --> 00:28:44,079
Most sea cucumbers
396
00:28:44,240 --> 00:28:46,311
stay firmly on the bottom,
397
00:28:46,480 --> 00:28:49,757
but not this extraordinary
deep sea species.
398
00:28:54,280 --> 00:28:55,794
Its skirts of skin
399
00:28:55,960 --> 00:28:58,191
allow it to swim hundreds of metres
400
00:28:58,360 --> 00:28:59,840
above the sea floor.
401
00:29:14,120 --> 00:29:16,874
Eventually, it will descend
402
00:29:17,040 --> 00:29:18,520
and, with luck,
403
00:29:18,680 --> 00:29:20,990
will land on fresh feeding grounds.
404
00:29:28,000 --> 00:29:31,755
This has to be the most
extraordinary animal design of all.
405
00:29:31,920 --> 00:29:33,434
It's a polychaete worm
406
00:29:33,600 --> 00:29:37,276
and, normally, you would expect
the long, pulsating body
407
00:29:37,440 --> 00:29:39,716
to be stick firmly in the sediment.
408
00:29:42,680 --> 00:29:44,160
This worm,
409
00:29:44,320 --> 00:29:45,800
alone in its group,
410
00:29:45,960 --> 00:29:47,440
swims in the open water.
411
00:29:51,920 --> 00:29:54,594
Propelling itself
with its yellow frill,
412
00:29:54,760 --> 00:29:56,240
it moves about
413
00:29:56,400 --> 00:29:58,471
and so finds new sources of food,
414
00:29:58,640 --> 00:30:01,712
or maybe succeeds
in escaping from a predator.
415
00:30:07,440 --> 00:30:10,512
This is chimaera,
a close relative of the sharks,
416
00:30:10,680 --> 00:30:12,160
less than a metre long.
417
00:30:14,200 --> 00:30:17,750
Sensory pits on its chin
help it hunt prey on the bottom,
418
00:30:17,920 --> 00:30:22,392
while its surprisingly large eyes
may help it spot bioluminescence.
419
00:30:30,200 --> 00:30:32,795
Large fish are rare down here —
420
00:30:32,960 --> 00:30:35,873
there's not enough live prey
to sustain them.
421
00:30:36,040 --> 00:30:38,032
Most have become scavengers.
422
00:30:38,200 --> 00:30:41,352
A dead tuna has attracted
a deep sea conger eel...
423
00:30:43,800 --> 00:30:45,553
and a six—gilled shark.
424
00:30:45,720 --> 00:30:47,359
These monsters grow
425
00:30:47,520 --> 00:30:49,318
to eight metres long.
426
00:31:03,920 --> 00:31:06,435
Six gills are living fossils.
427
00:31:06,600 --> 00:31:09,991
For 150 million years,
they've existed unchanged,
428
00:31:10,160 --> 00:31:14,074
living in water
as deep as 2,500 metres.
429
00:31:17,680 --> 00:31:22,436
Very few people have glimpsed
these sharks from submersibles,
430
00:31:22,600 --> 00:31:25,832
and we know almost nothing
about their behaviour.
431
00:31:33,080 --> 00:31:36,198
The body of a tuna
is a substantial meal,
432
00:31:36,360 --> 00:31:37,953
but just occasionally,
433
00:31:38,120 --> 00:31:39,713
a really gigantic corpse
434
00:31:39,880 --> 00:31:42,031
drifts down to the deep sea floor.
435
00:31:46,760 --> 00:31:48,956
This is the freshly dead carcass
436
00:31:49,120 --> 00:31:51,112
of a 30—tonne grey whale.
437
00:31:51,280 --> 00:31:54,034
It's resting on the sea floor
a mile down.
438
00:31:55,000 --> 00:31:57,913
It's only been on the bottom
for six weeks,
439
00:31:58,080 --> 00:32:01,312
but already it has attracted
hundreds of hagfish.
440
00:32:03,320 --> 00:32:04,913
These ancient scavengers
441
00:32:05,080 --> 00:32:08,710
are nearly always the first
to discover a fallen body,
442
00:32:08,880 --> 00:32:11,270
and are attracted from miles around.
443
00:32:15,160 --> 00:32:19,279
They lack jaws and rasp at the flesh
with two rows of horny teeth
444
00:32:19,440 --> 00:32:22,274
on either side
of their sucker—like mouths.
445
00:32:27,760 --> 00:32:29,752
Next to arrive,
446
00:32:29,920 --> 00:32:33,391
a sleeper shark —
a real deep sea specialist.
447
00:32:33,560 --> 00:32:35,870
They grow to over seven metres long,
448
00:32:36,040 --> 00:32:39,192
and have never been filmed
at such a depth before.
449
00:32:44,000 --> 00:32:47,198
The gaping wounds
in the whale's flank are its work.
450
00:32:54,720 --> 00:32:57,713
Unlike the hagfish,
it has powerful jaws,
451
00:32:57,880 --> 00:33:00,918
so is able to rip off
huge chunks of meat.
452
00:33:08,240 --> 00:33:09,720
Sharks, hagfish
453
00:33:09,880 --> 00:33:13,271
and a whole succession
of different deep sea scavengers
454
00:33:13,440 --> 00:33:17,514
will feast on the carcass for years
before all its nutriment is gone.
455
00:33:20,320 --> 00:33:21,800
Eighteen months later,
456
00:33:21,960 --> 00:33:23,952
when we returned to this whale,
457
00:33:24,120 --> 00:33:27,670
all that was left was
a perfect skeleton stripped bare.
458
00:33:35,840 --> 00:33:38,150
It was almost
as if a museum specimen
459
00:33:38,320 --> 00:33:41,040
had been carefully laid out
on the sea floor.
460
00:33:45,000 --> 00:33:48,118
At first, the skeleton
seemed totally abandoned,
461
00:33:48,280 --> 00:33:52,513
but even after so long, there was
still some flesh left in the head.
462
00:33:59,000 --> 00:34:02,596
Hagfish have a skeleton
of cartilage and are so flexible
463
00:34:02,760 --> 00:34:05,070
that they tie themselves into knots
464
00:34:05,240 --> 00:34:08,631
and so get a better purchase
on the flesh they feed on.
465
00:34:14,800 --> 00:34:17,395
But smaller organisms had fed here.
466
00:34:18,000 --> 00:34:19,832
A thick band of white bacteria
467
00:34:20,000 --> 00:34:21,400
had formed on the mud
468
00:34:21,560 --> 00:34:24,553
outlining the original shape
of the whale,
469
00:34:24,720 --> 00:34:26,552
and on the skeleton itself,
470
00:34:26,720 --> 00:34:29,030
colonies of specialised bacteria
471
00:34:29,200 --> 00:34:32,511
were extracting energy
from the bones themselves.
472
00:34:35,320 --> 00:34:38,313
Most remarkably,
and in huge abundance,
473
00:34:38,480 --> 00:34:42,474
polychaete worms were collecting
the last edible fragments.
474
00:34:42,640 --> 00:34:44,120
These are a new species
475
00:34:44,280 --> 00:34:48,274
that so far have only been found
on the fallen bodies of whales.
476
00:34:50,440 --> 00:34:53,751
Scientists have discovered
178 different animals
477
00:34:53,920 --> 00:34:55,912
on a single whale vertebra,
478
00:34:56,080 --> 00:34:58,834
most of which have been found
nowhere else.
479
00:34:59,000 --> 00:35:01,390
This whale, lying over a mile down,
480
00:35:01,560 --> 00:35:05,839
was not filmed from a submersible
with an acrylic sphere.
481
00:35:06,000 --> 00:35:08,515
Such craft can't go as deep as this.
482
00:35:10,000 --> 00:35:12,071
To withstand the pressure here,
483
00:35:12,240 --> 00:35:14,630
you need a far stronger submersible.
484
00:35:14,800 --> 00:35:16,280
This is Alvin,
485
00:35:16,440 --> 00:35:19,638
a two—metre—wide sphere
with just enough room in it
486
00:35:19,800 --> 00:35:21,792
for a pilot and two observers.
487
00:35:21,960 --> 00:35:23,838
Its walls are made of titanium.
488
00:35:24,000 --> 00:35:26,640
The viewing ports have to be tiny —
489
00:35:26,800 --> 00:35:29,793
any larger,
and the submersible would implode
490
00:35:29,960 --> 00:35:32,600
under the enormous pressure
down here.
491
00:35:33,800 --> 00:35:35,439
Alvin can dive
492
00:35:35,600 --> 00:35:37,557
to 4,500 metres,
493
00:35:37,720 --> 00:35:39,712
three miles below the surface.
494
00:35:44,040 --> 00:35:48,512
Around 3,000 metres, the continental
slope finally flattens out
495
00:35:48,680 --> 00:35:50,797
and joins the abyssal plain.
496
00:35:51,400 --> 00:35:54,393
This covers over half
the earth's surface.
497
00:35:54,560 --> 00:35:56,552
Mostly it's completely flat,
498
00:35:56,720 --> 00:35:59,792
but in places
it's gashed by massive trenches
499
00:35:59,960 --> 00:36:01,952
hundreds of miles wide.
500
00:36:08,120 --> 00:36:10,794
The deepest of these
is the Mariana Trench,
501
00:36:10,960 --> 00:36:14,351
which drops to over seven miles
below sea level.
502
00:36:21,800 --> 00:36:25,430
There are just five manned
submersibles world—wide
503
00:36:25,600 --> 00:36:27,751
that can reach the abyssal plain,
504
00:36:27,920 --> 00:36:29,479
and between them so far,
505
00:36:29,640 --> 00:36:32,633
they have explored
less than one per cent of it.
506
00:36:34,240 --> 00:36:37,790
There are a thousand times
fewer large animals down here
507
00:36:37,960 --> 00:36:39,952
than on the continental slope,
508
00:36:40,120 --> 00:36:41,600
but in places,
509
00:36:41,760 --> 00:36:45,720
hundreds of brittle stars
cross the sea bed in search of food.
510
00:36:47,840 --> 00:36:52,312
Fish have been found right down to
the bottom of the deepest trenches.
511
00:36:52,480 --> 00:36:54,472
Most come from one family —
512
00:36:54,640 --> 00:36:56,632
the aptly named rattails.
513
00:36:59,800 --> 00:37:01,792
They forage near the sea floor
514
00:37:01,960 --> 00:37:04,316
and use their battery
of sensory pits
515
00:37:04,480 --> 00:37:07,598
to follow odour trails
from rotting carcasses.
516
00:37:07,760 --> 00:37:09,956
Rattails can travel long distances
517
00:37:10,120 --> 00:37:11,713
across the abyssal plain
518
00:37:11,880 --> 00:37:13,360
in search of food,
519
00:37:13,520 --> 00:37:16,558
but others down here
prefer to sit and wait.
520
00:37:20,120 --> 00:37:21,873
This is a tripod fish.
521
00:37:22,040 --> 00:37:25,431
It supports itself
on two specially adapted fin rays
522
00:37:25,600 --> 00:37:28,354
and can sit motionless
for hour after hour.
523
00:37:30,680 --> 00:37:32,160
It does have tiny eyes,
524
00:37:32,320 --> 00:37:34,312
but it's almost totally blind.
525
00:37:34,480 --> 00:37:36,472
It locates potential prey
526
00:37:36,640 --> 00:37:38,791
with a pair of fins behind its head
527
00:37:38,960 --> 00:37:42,237
which are sensitive
to even tiny movements.
528
00:37:48,400 --> 00:37:50,869
We know more about the surface
of the moon
529
00:37:51,040 --> 00:37:53,157
than we do about the abyssal plain.
530
00:37:53,800 --> 00:37:57,396
Every dive still produces
complete surprises.
531
00:38:03,680 --> 00:38:05,160
This deep sea octopus
532
00:38:05,320 --> 00:38:07,312
is about the size of a beach ball
533
00:38:07,480 --> 00:38:09,597
and has been nicknamed Dumbo.
534
00:38:20,000 --> 00:38:22,959
An umbrella of skin
between its tentacles
535
00:38:23,120 --> 00:38:25,510
and its extraordinary flapping ears
536
00:38:25,680 --> 00:38:27,911
allow Dumbo to hover effortlessly
537
00:38:28,080 --> 00:38:29,560
over the sea floor
538
00:38:29,720 --> 00:38:31,757
as it searches for food.
539
00:38:48,880 --> 00:38:51,395
Right in the middle
of the abyssal plain
540
00:38:51,560 --> 00:38:55,190
lie the largest geological
structures on our planet...
541
00:39:02,080 --> 00:39:04,197
the mid—ocean ridges.
542
00:39:10,800 --> 00:39:13,679
Rising almost two miles
off the sea floor,
543
00:39:13,840 --> 00:39:16,912
the ridges extend
for over 28,000 miles,
544
00:39:17,080 --> 00:39:19,640
the largest mountain chain on Earth.
545
00:39:26,000 --> 00:39:28,560
When submersibles finally succeeded
546
00:39:28,720 --> 00:39:31,030
in reaching the ridges in the 1970s,
547
00:39:31,200 --> 00:39:33,431
they found an extraordinary world
548
00:39:33,600 --> 00:39:36,035
with mile upon mile
of once molten rock
549
00:39:36,200 --> 00:39:40,433
that had welled up from the deep
in the past and had now solidified.
550
00:39:44,040 --> 00:39:46,999
They discovered towering chimneys,
551
00:39:47,160 --> 00:39:50,073
pouring out water
as hot as molten lead.
552
00:40:17,400 --> 00:40:21,474
At the surface, water becomes steam
at 100 degrees Centigrade,
553
00:40:21,640 --> 00:40:24,872
but here, under the immense pressure
of the ocean,
554
00:40:25,040 --> 00:40:29,432
it remains liquid at temperatures
as hot as 400 degrees Centigrade.
555
00:40:34,000 --> 00:40:37,072
The submersible
has to move carefully.
556
00:40:37,240 --> 00:40:40,278
Disaster is very close
when surrounded
557
00:40:40,440 --> 00:40:43,274
by such enormous temperatures
and pressures.
558
00:40:44,000 --> 00:40:46,515
And here,
where the very water is loaded
559
00:40:46,680 --> 00:40:50,674
with hydrogen sulphides
poisonous to normal life processes,
560
00:40:50,840 --> 00:40:52,832
they found living creatures.
561
00:40:56,800 --> 00:41:00,680
Some of the chimneys
were encrusted with white tubes.
562
00:41:00,840 --> 00:41:02,593
The tubes were inhabited
563
00:41:02,760 --> 00:41:04,991
by a new species of polychaete worm
564
00:41:05,160 --> 00:41:09,473
that was exposed to temperatures
as high as 80 degrees Centigrade.
565
00:41:11,640 --> 00:41:16,192
No other animal on Earth was known
to tolerate such high temperatures,
566
00:41:16,360 --> 00:41:20,036
so the scientists called
these creatures Pompeii worms.
567
00:41:22,520 --> 00:41:24,591
But this was just the beginning.
568
00:41:24,760 --> 00:41:26,752
Nearby, there were chimneys
569
00:41:26,920 --> 00:41:30,675
covered by whole communities
of different organisms.
570
00:41:30,840 --> 00:41:34,470
The bottom of the vent
was encrusted with large mussels.
571
00:41:37,200 --> 00:41:39,351
There were swarms of white crabs,
572
00:41:39,520 --> 00:41:41,352
and, most spectacular of all,
573
00:41:41,520 --> 00:41:45,480
dominating the chimney were
hundreds of bright red tubeworms,
574
00:41:45,640 --> 00:41:48,712
each two metres long
and four centimetres wide.
575
00:41:50,680 --> 00:41:53,275
Until these creatures
were discovered,
576
00:41:53,440 --> 00:41:56,990
all life on Earth was thought
to be dependent on the sun,
577
00:41:57,160 --> 00:42:00,153
but here, in the complete darkness
of the deep,
578
00:42:00,320 --> 00:42:03,040
they had discovered
a rich density of life
579
00:42:03,200 --> 00:42:05,556
that derived no energy from the sun.
580
00:42:12,360 --> 00:42:14,352
So what do they live on?
581
00:42:14,520 --> 00:42:18,070
The answer was found
within the tubeworms themselves.
582
00:42:18,240 --> 00:42:21,233
They were packed full
of specialised bacteria
583
00:42:21,400 --> 00:42:23,676
that are able to derive energy
584
00:42:23,840 --> 00:42:26,878
from the sulphides
that pour from the vents.
585
00:42:30,600 --> 00:42:33,911
The worms' plumes were bright red
with haemoglobin
586
00:42:34,080 --> 00:42:37,676
that carries sulphides and oxygen
down to the bacteria.
587
00:42:38,120 --> 00:42:40,112
These bacterial colonies
588
00:42:40,280 --> 00:42:43,956
are the primary source of energy
for all that lives here.
589
00:42:44,120 --> 00:42:46,351
The mussels were packed with them.
590
00:42:46,520 --> 00:42:48,000
Just as green plants
591
00:42:48,160 --> 00:42:51,392
are the basis of life
for animals living in the sun,
592
00:42:51,560 --> 00:42:53,870
so these bacteria and other microbes
593
00:42:54,040 --> 00:42:56,032
are at the foot of the food chain
594
00:42:56,200 --> 00:42:58,590
on which over 500 species depend.
595
00:43:04,840 --> 00:43:07,719
Crabs and shrimps feed off bacteria
596
00:43:07,880 --> 00:43:11,112
and even try to steal pieces
of tubeworm plumes.
597
00:43:16,640 --> 00:43:21,271
Since the vents were first visited
by biologists in 1979,
598
00:43:21,440 --> 00:43:24,990
a new species has been described
every ten days.
599
00:43:27,000 --> 00:43:31,313
At the top of the food chain, fish
that never stray far from the vents,
600
00:43:32,200 --> 00:43:35,318
but they or their descendants
will move eventually,
601
00:43:35,480 --> 00:43:39,030
for we now know that
individualvents are rarely active
602
00:43:39,200 --> 00:43:41,078
for more than a few decades.
603
00:43:55,000 --> 00:43:56,639
Such a density of life
604
00:43:56,800 --> 00:43:59,360
living in such harsh conditions
605
00:43:59,520 --> 00:44:03,355
in the middle of a vast
and otherwise barren abyssal plain
606
00:44:03,520 --> 00:44:06,638
astounded the biologists
who first saw it.
607
00:44:09,800 --> 00:44:14,033
It seemed to them that here was
evidence of how life on this planet,
608
00:44:14,200 --> 00:44:17,637
which certainly started in the sea,
might have begun.
609
00:44:23,000 --> 00:44:24,798
Deep sea submersibles
610
00:44:24,960 --> 00:44:28,840
made an even more
extraordinary discovery in 1990.
611
00:44:39,800 --> 00:44:41,280
Over half a mile down,
612
00:44:41,440 --> 00:44:43,875
at the bottom of the Gulf of Mexico,
613
00:44:44,040 --> 00:44:47,636
they came across what appeared
to be an underwater lake,
614
00:44:47,800 --> 00:44:49,314
over 20 metres long,
615
00:44:49,480 --> 00:44:51,437
with its own sandy shore.
616
00:44:52,800 --> 00:44:56,111
Around its edge,
there even seemed to be a tide line,
617
00:44:56,280 --> 00:44:58,351
but this couldn't be, of course,
618
00:44:58,520 --> 00:45:00,512
this was underwater.
619
00:45:01,640 --> 00:45:04,030
In fact, the lapping edge
was created
620
00:45:04,200 --> 00:45:06,590
by a thick soup of salty brine
621
00:45:06,760 --> 00:45:09,594
far heavier than
the surrounding sea water,
622
00:45:09,760 --> 00:45:11,240
and the sand was made up
623
00:45:11,400 --> 00:45:13,790
of hundreds of thousands of mussels.
624
00:45:14,920 --> 00:45:18,960
Once again, in the midst
of a totally barren sea bed,
625
00:45:19,120 --> 00:45:21,555
an extraordinarily
rich oasis of life
626
00:45:21,720 --> 00:45:24,394
totally independent
of the sun's energy.
627
00:45:28,280 --> 00:45:31,478
The source of energy this time
was not sulphides
628
00:45:31,640 --> 00:45:35,190
but methane bubbling
out of the sea bed, and once again,
629
00:45:35,360 --> 00:45:38,114
the mussels carried special bacteria
630
00:45:38,280 --> 00:45:41,273
capable of fixing
the methane's energy.
631
00:45:41,440 --> 00:45:43,432
Just like the hot vents,
632
00:45:43,600 --> 00:45:47,560
a complete ecosystem had developed
based on the bacteria.
633
00:45:47,720 --> 00:45:52,237
There was an enormous variety
of completely new species — shrimps,
634
00:45:52,400 --> 00:45:54,756
weird squat lobsters,
635
00:45:54,920 --> 00:45:56,320
and bright red
636
00:45:56,480 --> 00:45:58,073
polychaete worms.
637
00:46:07,000 --> 00:46:09,799
These oases were called cold seeps
638
00:46:09,960 --> 00:46:13,032
and were surprisingly similar
to the hot vents.
639
00:46:18,000 --> 00:46:22,074
The geological processes
in the sea floor that produce methane
640
00:46:22,240 --> 00:46:25,916
also tend to result in the release
of hydrogen sulphides.
641
00:46:26,080 --> 00:46:28,151
It was hardly surprising, then,
642
00:46:28,320 --> 00:46:30,471
when, not far from the brine pool,
643
00:46:30,640 --> 00:46:32,279
they found tubeworms...
644
00:46:33,760 --> 00:46:36,320
extensive fields of tubeworms
645
00:46:36,480 --> 00:46:38,870
that stretch for hundreds of metres.
646
00:46:39,040 --> 00:46:41,600
This new species also uses bacteria
647
00:46:41,760 --> 00:46:43,752
to fix energy from sulphides,
648
00:46:43,920 --> 00:46:46,913
but it extracts them directly
from the ground.
649
00:46:51,000 --> 00:46:52,673
Their beautiful gills
650
00:46:52,840 --> 00:46:56,356
are only used to supply oxygen
to the bacteria.
651
00:46:59,240 --> 00:47:03,519
Amazingly, these tubeworms
are over 200 years old.
652
00:47:04,240 --> 00:47:05,879
While hot vent tubeworms
653
00:47:06,040 --> 00:47:09,351
may be the fastest—growing
invertebrates in the sea,
654
00:47:09,520 --> 00:47:11,398
these appear to be far slower —
655
00:47:11,560 --> 00:47:15,520
all the more reason to protect
your gills from biting amphipods.
656
00:47:20,400 --> 00:47:23,837
The energy sources exploited
by the hot vent animals
657
00:47:24,000 --> 00:47:25,480
may suddenly fail,
658
00:47:25,640 --> 00:47:29,236
but here, life can enjoy
a more stable geological future.
659
00:47:33,720 --> 00:47:37,634
To discover within ten years
two completely new ecosystems,
660
00:47:37,800 --> 00:47:40,793
both totally independent
of the sun's energy,
661
00:47:40,960 --> 00:47:42,952
has been quite extraordinary.
662
00:47:43,120 --> 00:47:47,080
So far, we have explored just one
per cent of the deep ocean floor.
663
00:47:47,240 --> 00:47:50,790
Who knows what is still out there
to be discovered?