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Much of our planet
still remains unexplored...

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..for most of it is covered
by water.

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Every journey below the surface
can reveal something extraordinary.

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More than a thousand new species
are discovered here every year.

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The ocean is home to 80%
of all animal life on Planet Earth.

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But today,
thriving in this varied world

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sometimes demands
the most surprising behaviour.

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The shallow seas of the tropics.

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This may look like a paradise...

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..but beneath the surface,
it is an arena

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for constant
life-and-death struggles,

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where not everything
is quite as it seems.

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A predatory lionfish...

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..on the hunt for shrimp
and small fish.

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With so many places
for its prey to hide,

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the lionfish has to be patient.

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This shrimp appears tempting.

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As the lion-fish closes in,

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it fans out its fins
to disorientate its prey.

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The hunter becomes the hunted.

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Tricked by one
of the shallow sea's

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most extraordinary predators...

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..a clown frogfish!

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On its head, it carries
a fishing rod –

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a modified dorsal fin,

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baited with a lure -
easily mistaken for a shrimp.

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But, when the fish stop biting,

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it's time to pack the rod away

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and move on.

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And, for a frogfish,
that takes time.

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Rather than swim, frogfish walk!

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Its fins have, in effect,
become feet.

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It may not look pretty,

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but what appears to be coral living
on its skin is actually camouflage.

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As every good angler knows,

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picking the right spot is important.

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Jigging the rod sends out
pressure waves

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to attract the attention
of possible prey.

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These dragonets
are certainly interested.

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Almost there.

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Hook, line, and sinker.

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Like all shallow seas,
the cold waters

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off the coast of North America,

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benefit from the intensity
of the sunshine.

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Here, that fuels

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one of the fastest-growing
organisms on the planet...

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..giant kelp.

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Towering forests
can eventually reach the height

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of a 12-storey building.

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These forests are nurseries
for young horn sharks.

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As the sun begins to set,

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they leave their daytime shelter

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and set off into the heart
of the kelp forest to find food.

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Barely half a metre long,

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this little shark
is extremely vulnerable.

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There are monsters here.

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A giant sea bass –

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weighing over 200kg...

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..and wolf-eels, with big teeth

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that can crush
little red sea urchins.

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But the biggest danger
comes from other sharks -

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houndsharks...

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..and huge broadnose sevengills.

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In this forest,
it pays to keep a low profile.

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An angel shark...

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..one of the most deadly sharks
in the kelp forest,

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and certainly
the best camouflaged.

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An angel shark
will lie in wait for days...

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..but this one has already attracted
too much attention.

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It's not welcome here.

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Now, the coast is clear.

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But angel sharks hunt
around the clock.

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Openings for breathing,
called spiracles,

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blow out sand
that helps cover its body.

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The trap is set.

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Staying close to the seabed is
a good way to avoid most predators.

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Faster than the blink of an eye.

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But it's not over yet.

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Horn sharks have a secret weapon.

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Sharp spikes keep them very much
off the menu for most.

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So, this young horn shark
can hunt in safety...

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..for now.

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Violent winter storms
batter these kelp forests.

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The plants can be ripped
from the seafloor...

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..and carried away far out to sea.

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The open ocean
is a vast, featureless desert.

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Even a small piece of drifting kelp
can become valuable.

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It's just what these fish
have been searching for.

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Here, shelter where eggs can be laid
unobtrusively is rare...

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..so they make the most of it.

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Each female produces
up to a thousand eggs,

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and the males rush in
to fertilise them.

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All this activity attracts
the attention of blue sharks.

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They can travel thousands of miles

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through the ocean
in search of food...

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..and they may not have eaten
for weeks.

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It seems that they're in luck.

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But these fish are no easy meal.

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They are flying fish!

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The blue shark, however,

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are not here for the fish...

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..they have come for the caviar.

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But flying fish lay so many eggs,

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that the sharks' feasts
hardly make an impact.

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And, in a few months' time, a new
generation will take to the skies.

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Floating islands of weed
are always attractive to creatures

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looking for shelter
out in the big blue.

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But, in today's ocean, they are
being replaced by something else...

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..plastic.

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12 million tons of it
end up in the ocean every year.

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The deadliest kind are discarded
fishing lines and nets.

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Each year, it's likely over
half a million animals are ensnared

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and killed by these "ghost nets."

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But some animals are learning

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how to take advantage
of the plastic rafts...

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..and use them for shelter,
or even as a home.

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This male Columbus crab – barely
bigger than your thumb nail –

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is a castaway.

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Clinging to his net,

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he may have been drifting
on ocean currents for months.

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Now, fully grown,
he needs to find a partner.

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But where?

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Certainly not here,

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alone on the net.

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Columbus crabs are not good
swimmers, so this male is marooned.

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Perhaps a passing loggerhead turtle
could be the chance

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to hitch a lift.

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Made it!

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But there's more than one
passenger here -

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a female Columbus crab!

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They waste no time
in getting acquainted...

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..and start to mate.

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This pair may well stay together
for the rest of their lives.

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A turtle, after all,
makes an excellent home.

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In return, the crabs provide
an onboard grooming service.

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Finding a partner in the vast ocean
is not easy.

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Dawn in the Sea of Cortez...

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..Mobula rays.

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They're gathering here,
most likely to breed.

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No-one is sure why they leap,

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but the loud splashes
certainly seem to attract more rays.

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Other creatures, however,
are also listening.

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Orca have heard the splashes.

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This female specialises
in hunting rays.

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But today, she is teaching
two youngsters

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the finer points
of Mobula ray hunting.

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The rays are fast
and can outmanoeuvre an orca.

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She knows she needs to herd
the prey into a tight group...

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..but she can't do that on her own.

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It will take teamwork,

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and that is today's lesson.

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The young orca
are quick to catch on.

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The rays are surrounded.

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They dive...

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..only to be forced back up again
by the experienced female.

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And now, with the exhausted rays
trapped against the surface,

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she attacks...

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..and the young ones
follow her lead.

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This family are the only orca
known to hunt rays like this...

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..and they are lethally efficient.

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But it appears that school
is over for today.

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For a few battle-scarred survivors,

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it's a lucky reprieve.

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With the orca gone, the rays
can resume their courtship...

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..and they do so
in astounding numbers.

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Tens of thousands of rays
in a single shoal.

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Vast areas of our ocean
are yet to be explored.

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The least known parts of it
are its great depths.

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Only highly-specialised vessels
can take you there.

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As you descend,
the sunlight rapidly fades.

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200m down,
you enter the twilight zone...

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..an alien world, inhabited
by creatures beyond imagination.

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A siphonophore – with a cloak
of lethal stinging tentacles.

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Siphonophores repeatedly
clone themselves

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and so grow to immense lengths.

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This one measures 45m and is
the longest animal ever recorded.

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With such deadly predators around,

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creatures here go
to great lengths to hide.

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A glass squid...

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..completely transparent,

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except for its eyes...

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..and stomach,

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so it is extremely difficult
to find in the gloom.

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Below 1,000m,

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all traces of sunlight
have disappeared.

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This is the midnight zone.

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Catching food in the perpetual
darkness is not easy.

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A gulper eel.

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Its giant, extendable mouth

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can engulf prey
larger than its own body.

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Two miles down,
you finally reach the ocean floor.

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We know more
about the surface of Mars.

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The pressure of the water is 300
times greater than at the surface...

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..and it's freezing cold.

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00:33:39,360 --> 00:33:44,360
Yet, amazingly,
there are animals living here.

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00:33:49,720 --> 00:33:52,639
Muusoctopus robustus,

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nicknamed the pearl octopus.

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Breeding, in these
extreme conditions poses

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a particular problem
for these animals.

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00:34:08,680 --> 00:34:10,999
At these low temperatures,

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this female's eggs could take
over ten years to develop.

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00:34:24,760 --> 00:34:29,040
So she travels
to a very special place.

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00:34:43,200 --> 00:34:48,600
This is the largest known
gathering of octopus in the world.

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00:34:58,480 --> 00:35:02,520
She joins 20,000 other females...

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..all here to lay their eggs.

206
00:35:13,800 --> 00:35:17,399
Water, heated deep
in the Earth's crust,

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00:35:17,400 --> 00:35:20,680
rises through cracks
in the seabed...

208
00:35:22,560 --> 00:35:27,840
..raising the temperature
to as much as 10 degrees Celsius.

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00:35:29,240 --> 00:35:32,080
A deep-sea thermal spa!

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00:35:37,080 --> 00:35:40,119
This warmth significantly speeds up

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00:35:40,120 --> 00:35:43,279
the development of their eggs.

212
00:35:43,280 --> 00:35:47,400
Even so, they will still take
nearly two years to hatch.

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00:35:49,600 --> 00:35:52,039
Once a female is settled,

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00:35:52,040 --> 00:35:54,600
she won't move from her spot...

215
00:35:56,080 --> 00:35:58,600
..not even to feed.

216
00:36:10,120 --> 00:36:14,199
She will constantly tend
to her brood –

217
00:36:14,200 --> 00:36:17,119
keeping them clean,

218
00:36:17,120 --> 00:36:19,199
and oxygenating them

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00:36:19,200 --> 00:36:21,840
with jets of water.

220
00:36:25,480 --> 00:36:30,600
Pearl octopus mothers must surely be
amongst the most devoted.

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00:36:47,880 --> 00:36:53,360
After almost two years,
the ordeal take its toll.

222
00:37:00,360 --> 00:37:03,120
But the vigil is almost over.

223
00:38:01,920 --> 00:38:06,280
The last of the brood
are gently encouraged to leave.

224
00:38:14,280 --> 00:38:17,240
But this will be a final act.

225
00:38:19,080 --> 00:38:25,360
Like all the mothers here, this
octopus is starved and exhausted.

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00:38:28,520 --> 00:38:31,480
Her life will soon be over.

227
00:38:49,520 --> 00:38:53,159
But this devotion means
that her offspring are among

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00:38:53,160 --> 00:38:58,039
the largest and most developed
of any octopus

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00:38:58,040 --> 00:39:00,719
and have the best chance of survival

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00:39:00,720 --> 00:39:03,560
in the demanding world of the deep.

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00:39:19,920 --> 00:39:24,280
We're finding more of these
strange hot springs every year.

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00:39:35,160 --> 00:39:39,120
In some places,
they can be astonishingly violent.

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00:39:40,560 --> 00:39:45,359
Super-heated water –
hot enough to melt lead -

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spouts from the seafloor.

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00:39:49,480 --> 00:39:51,959
Dissolved minerals
condense around them

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00:39:51,960 --> 00:39:57,040
to form towering chimneys,
known as hydrothermal vents.

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00:40:01,440 --> 00:40:05,239
They are home to unique
communities of animals

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00:40:05,240 --> 00:40:09,080
that all rely on the nutrients
in the scalding water.

239
00:40:19,040 --> 00:40:22,879
Some suggest that vents
like these could be the places

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00:40:22,880 --> 00:40:27,080
where life on Earth first began
four billion years ago.

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00:40:35,120 --> 00:40:38,199
And there is now evidence
of hydrothermal vents

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00:40:38,200 --> 00:40:41,280
on the moons of Jupiter and Saturn.

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00:40:43,200 --> 00:40:45,960
Could they too be supporting life?

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00:40:50,600 --> 00:40:54,919
Here on Earth,
the influence of these vents

245
00:40:54,920 --> 00:40:57,880
extends far beyond their chimneys.

246
00:40:59,560 --> 00:41:02,879
The essential nutrients
carried in these plumes

247
00:41:02,880 --> 00:41:07,800
can rise all the way to the surface
two miles above.

248
00:41:13,320 --> 00:41:18,159
Here, they stimulate the rapid
growth of tiny marine plants...

249
00:41:18,160 --> 00:41:20,880
..on an astronomic scale.

250
00:41:27,600 --> 00:41:31,039
This phytoplankton is so abundant

251
00:41:31,040 --> 00:41:35,320
that it produces half
of all the oxygen on Earth.

252
00:41:53,400 --> 00:41:58,000
It's also food for a host
of minute animals -

253
00:41:59,480 --> 00:42:01,800
zooplankton.

254
00:42:03,560 --> 00:42:07,279
Together, they are the basis
of the food chains

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that sustain
nearly all life in the ocean.

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00:42:16,040 --> 00:42:19,519
In the Pacific waters
off South America,

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they feed anchovy
that gather here in billions.

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00:42:37,760 --> 00:42:42,120
This is one of the world's
most productive ecosystems.

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00:42:53,800 --> 00:42:57,440
These South American
sea lions are on the hunt.

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00:43:17,760 --> 00:43:22,680
But the anchovy shoal
has already been located...

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00:43:27,280 --> 00:43:30,680
..by the planet's
most efficient hunters.

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00:43:34,040 --> 00:43:36,799
A net, over half a mile long,

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00:43:36,800 --> 00:43:38,760
encircles the shoal.

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00:43:41,720 --> 00:43:44,800
It can trap over a million fish.

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00:43:56,760 --> 00:43:59,600
But the sea lions
aren't about to go hungry.

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00:44:01,920 --> 00:44:05,520
They have learnt
to look for holes in the net.

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00:44:16,040 --> 00:44:22,640
Why waste energy when food
comes to you as easily as this?!

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00:44:29,320 --> 00:44:32,599
As more and more sea lions arrive,

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00:44:32,600 --> 00:44:35,120
some change their tactics.

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00:44:42,680 --> 00:44:45,720
They line up
on both sides of the net...

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00:44:47,360 --> 00:44:49,200
..and wait.

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00:45:03,960 --> 00:45:08,840
As the net tightens, the anchovy
panic and rush for the surface.

273
00:45:15,240 --> 00:45:19,360
This is the moment the sea lions
have been waiting for.

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00:45:33,640 --> 00:45:37,399
It's such an effective way
of hunting that the sea lions here

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00:45:37,400 --> 00:45:40,240
are changing
their natural behaviour...

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00:45:43,400 --> 00:45:47,199
..and are raiding the fishing nets

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00:45:47,200 --> 00:45:49,640
in their thousands.

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00:45:57,320 --> 00:45:59,559
With the net almost drawn in,

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00:45:59,560 --> 00:46:02,800
the fishermen beat out
a warning signal.

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00:46:06,280 --> 00:46:08,280
Time is up.

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00:46:37,680 --> 00:46:41,800
In the confusion,
not everyone manages to escape.

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00:46:50,400 --> 00:46:54,920
The trapped sea lions are in danger
of being drowned.

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00:47:16,600 --> 00:47:20,360
Pups are separated
from their mothers.

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00:48:24,120 --> 00:48:28,840
Then, at the last minute, the
fishermen briefly drop their net...

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00:48:36,240 --> 00:48:39,360
..and the trapped sea lions
can escape.

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00:48:47,640 --> 00:48:50,880
But many are not so lucky.

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00:48:52,760 --> 00:48:57,799
Around the world, millions
of animals are accidently caught

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00:48:57,800 --> 00:49:01,880
and die in fishing nets every day.

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00:49:04,280 --> 00:49:08,079
And this by-catch, as it's known,

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00:49:08,080 --> 00:49:11,480
is pushing many species
toward extinction.

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00:49:16,320 --> 00:49:19,719
Animals have evolved
in remarkable ways

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00:49:19,720 --> 00:49:22,360
to the demands of life in the ocean.

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00:49:27,040 --> 00:49:30,080
But can they now adapt
to the new challenge -

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00:49:31,320 --> 00:49:33,840
living alongside us?

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00:49:51,040 --> 00:49:54,159
The open ocean is home
to some of the largest

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00:49:54,160 --> 00:49:56,880
and most extraordinary animals
on Earth.

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00:49:59,320 --> 00:50:01,559
But here, off the Canary Islands,

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00:50:01,560 --> 00:50:05,159
the Planet Earth team are searching
for one of its smaller,

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00:50:05,160 --> 00:50:07,799
and less familiar residents.

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00:50:07,800 --> 00:50:10,359
We're looking for a tiny creature
called a Columbus crab,

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00:50:10,360 --> 00:50:12,519
which is only about the size
of your thumbnail,

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00:50:12,520 --> 00:50:16,199
which live on floating objects
in the open ocean.

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00:50:16,200 --> 00:50:19,519
Columbus crabs were once
only found on natural debris,

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00:50:19,520 --> 00:50:21,599
like driftwood or seaweed,

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00:50:21,600 --> 00:50:23,639
but the oceans are changing,

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00:50:23,640 --> 00:50:25,840
and they've been forced to adapt.

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00:50:40,240 --> 00:50:44,640
One of the most common items
they find is discarded fishing gear.

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00:50:46,960 --> 00:50:52,240
Over a million tons is left adrift
in the ocean each year.

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00:50:53,800 --> 00:50:56,599
And Columbus crabs are now
making their homes

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00:50:56,600 --> 00:50:59,120
on these unnatural materials.

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00:51:06,640 --> 00:51:09,920
Surprisingly, Columbus crabs
are thriving on this new habitat.

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00:51:15,200 --> 00:51:20,080
But, for larger ocean creatures,
these nets can be lethal.

313
00:51:22,120 --> 00:51:25,760
Loggerhead sea turtles
are especially vulnerable.

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00:51:29,400 --> 00:51:32,799
Many times, they are very injured

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00:51:32,800 --> 00:51:36,679
and many times
they don't even survive.

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00:51:36,680 --> 00:51:39,200
It's a sad situation.

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00:51:40,640 --> 00:51:44,639
As a rule, wildlife film-makers
observe natural behaviour

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00:51:44,640 --> 00:51:46,720
and do not interfere.

319
00:51:50,360 --> 00:51:53,679
But this is far from natural.

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00:51:53,680 --> 00:51:57,120
The team feel they must take action.

321
00:52:06,720 --> 00:52:09,479
Sh...

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00:52:09,480 --> 00:52:11,839
It seems that the turtle
is quite OK.

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00:52:11,840 --> 00:52:16,480
We'll just finish to cut
the plastic and then we release it.

324
00:52:32,920 --> 00:52:35,119
It's a bittersweet moment,

325
00:52:35,120 --> 00:52:40,359
as this is one of eight turtles
they rescued whilst filming here.

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00:52:40,360 --> 00:52:43,679
This situation is not natural,

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00:52:43,680 --> 00:52:47,440
it's something that is
being caused by human beings.

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00:52:49,040 --> 00:52:52,479
Sadly, the crew now face
dilemmas like this

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00:52:52,480 --> 00:52:55,800
on many of their
filming expeditions...

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00:52:57,840 --> 00:53:01,959
..including, when they travelled
to the Pacific coast of Chile,

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00:53:01,960 --> 00:53:04,919
to show how sea lions
are competing for food

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00:53:04,920 --> 00:53:07,480
with one of the biggest fisheries
on Earth.

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00:53:12,560 --> 00:53:17,320
Expedition leader Fernando Olivares
takes the team to the fleet.

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00:53:24,520 --> 00:53:28,159
Diving near fishing nets
is extremely dangerous,

335
00:53:28,160 --> 00:53:31,719
so the crew must ensure they have
the full cooperation

336
00:53:31,720 --> 00:53:33,640
of the fishermen.

337
00:53:58,040 --> 00:54:01,119
Pretty hazardous place to dive.

338
00:54:01,120 --> 00:54:03,439
It's just a case of trying
to keep an eye on the divers,

339
00:54:03,440 --> 00:54:05,999
but the sea lions also like
to go down and blow bubbles,

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00:54:06,000 --> 00:54:07,839
so you'll think
you're following the divers,

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00:54:07,840 --> 00:54:10,160
and then a sea lion will pop up.

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00:54:15,760 --> 00:54:17,879
Taking the utmost care,

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00:54:17,880 --> 00:54:19,959
the divers get a close-up view

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00:54:19,960 --> 00:54:22,520
of the sheer scale of the operation.

345
00:54:28,440 --> 00:54:31,999
This one net must have
about 15 tons of fish in it

346
00:54:32,000 --> 00:54:35,119
and there's eight or nine boats
in this one little bay,

347
00:54:35,120 --> 00:54:36,799
and these are just the small boats.

348
00:54:36,800 --> 00:54:38,879
Out there, there are huge
factory ships that are taking

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00:54:38,880 --> 00:54:41,040
even bigger catches.

350
00:54:42,280 --> 00:54:44,639
How much fish a year from just here?

351
00:54:44,640 --> 00:54:48,480
From a million tons a year
more or less.

352
00:54:56,520 --> 00:54:59,159
The catches are so vast,

353
00:54:59,160 --> 00:55:02,279
the sea lions have changed
their natural behaviour

354
00:55:02,280 --> 00:55:05,600
to collect anchovies
directly from the nets.

355
00:55:09,760 --> 00:55:11,800
But it's a risky strategy.

356
00:55:13,360 --> 00:55:17,320
The crew witnessed sea lions
caught in nets multiple times.

357
00:55:18,360 --> 00:55:21,520
Whoa, it's intense mate,
there are so many in there.

358
00:55:27,720 --> 00:55:30,319
There's a pup stuck in the net,
calling to its mother,

359
00:55:30,320 --> 00:55:33,360
and its mother's just on the outside
of the net calling back.

360
00:55:39,640 --> 00:55:42,240
That's really hard to watch.

361
00:55:47,760 --> 00:55:50,040
Oh, the pup's really panicking now.

362
00:55:52,520 --> 00:55:57,040
Sometimes, fishermen are able
to release trapped sea lions...

363
00:55:58,360 --> 00:56:00,520
..but not this time.

364
00:56:02,840 --> 00:56:05,160
The pup is in serious danger.

365
00:56:07,280 --> 00:56:10,960
Once again,
the crew decide to step in.

366
00:56:12,840 --> 00:56:16,080
Hey, he's going to go
inside of the net to save him.

367
00:56:39,800 --> 00:56:42,040
Wow.

368
00:56:45,880 --> 00:56:49,799
Nice, really nice.

369
00:56:49,800 --> 00:56:51,880
It's a relief this time...

370
00:56:54,400 --> 00:56:59,879
..but it highlights the new
realities of filming wildlife

371
00:56:59,880 --> 00:57:03,520
in today's changing ocean.

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00:57:12,560 --> 00:57:16,880
Next time, a journey to Earth's
greatest wilderness -

373
00:57:20,600 --> 00:57:24,200
deserts and grasslands...

374
00:57:29,720 --> 00:57:33,160
..where nature puts on
its most dramatic show.

375
00:57:36,040 --> 00:57:40,159
Habitat Explorer brings animals
and their habitats to life.

376
00:57:40,160 --> 00:57:43,799
Explore this free interactive
and make origami animals.

377
00:57:43,800 --> 00:57:47,879
Go to...

378
00:57:47,880 --> 00:57:50,279
And follow the links
to the Open University.

379
00:57:50,280 --> 00:57:52,439
Or to order a free printed version,

380
00:57:52,440 --> 00:57:56,200
visit the website
or call the numbers on the screen.