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In the vastness of the Pacific,
there's a place unlike any other.

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Enchanted volcanic islands
that are home to a remarkable

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collection of animals and plants.

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Here, evolution is proceeding
at extraordinary speed.

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Galapagos.

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A place of wonders.

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Millions of years ago,

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the islands were colonised
by a strange cast of characters.

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But to settle in this harsh,
unforgiving landscape,

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those new arrivals had to
dramatically adapt their bodies.

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Today, revelatory discoveries
are still being made about them.

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And from their story,
we can piece together how Galapagos

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came to be one of the most diverse
environments on our planet.

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It's perhaps surprising that the
Galapagos should have become famous

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for its biodiversity,

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for the fact is that living
conditions here are very tough.

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On the equator, the heat is intense.
There's very little water.

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Much of the land is covered
by bare volcanic rock.

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And yet,
every species that lives here

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is descended from an ancestor
from the continents

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that have taken on these conditions
and won.

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And the way in which they did so
is extraordinary.

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The total land area of the
16 islands and rocky outcrops

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that make up Galapagos is less than
half that of Wales.

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Yet, for its size,

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there are more unique species here
than anywhere else on Earth.

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Why should that be?

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There are clues hidden
within the landscape.

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This crescent-shape strip of cliff,

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rising steeply from the Pacific
Ocean, is the island of Tortuga.

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And like all the Galapagos Islands,

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it's a wonderful place
to see wildlife.

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Here and there, there's a sea lion.

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Above that, nesting seabirds.

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Boobies and Galapagos gulls.

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But you only really appreciate
the true character of this island

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from the air.

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From here,

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it's clear that this is the last
fragment of an extinct volcano.

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These curving cliffs are all that
remains of what was once

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a completely circular crater.

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And that's an indication
of something very significant

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about all these islands.

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They change
with enormous rapidity.

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The history of these islands
is very much the same.

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Each is born
on the bottom of the sea,

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and rises up through the waters
to emerge as a volcano.

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(VOLCANO BLASTS)

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This is a typical Galapagos island
in its infancy.

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But then, after a million years
of eruptions,

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volcanic activity ceases.

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Two million years
after its first appearance,

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the island is approaching
middle age.

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It has a moist climate
and is covered by forest.

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It begins to sink under
its own weight of ash and lava.

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It's battered by erosion,
and after four million years,

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it's near the end of its existence.

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Low-lying and arid
with little rainfall,

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it's surrounded by beaches
of soft sand.

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The waves and rain continue
to take their toll,

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until all that's left is
a craggy outcrop of rock.

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These islands, in geological terms,
are very short-lived.

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Today, there are islands
in the Galapagos archipelago

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that illustrate every stage
in this history.

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The youngest in the west are arid,
black and still breathing fire.

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The oldest in the east have
long since ceased to erupt.

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But each island provides its
colonists with a range of habitats.

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And it's the youngest active islands
that pose the greatest problems

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for any animals that
attempt to colonise them.

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In the far west of the archipelago
lies Fernandina.

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This is the youngest
of the Galapagos Islands.

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It's forbiddingly desolate
and inhospitable.

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But one animal has colonised
its shoreline.

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This creature is a specialist
at surviving in this harsh terrain.

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And, in adapting to this place,

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it has become like no other animal
on Earth.

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Behold the marine iguana.

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The ancestors of these iguanas
almost certainly

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lived in the jungles
of Central America.

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There still today you can see
iguanas in the trees

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overhanging the rivers, nibbling
leaves, or on rafts of reeds.

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Just occasionally,
some are swept out to sea,

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and the vast majority
of course die there.

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But just a few, a long time ago,
were fortunate enough to be swept

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by a favourable current out
to the ocean and pitched up here.

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In their ancestral rainforest
habitat, iguanas are vegetarians.

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(IGUANA GROWLS)

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Here, they browse on juicy leaves.

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But the iguanas that
first appeared in the Galapagos

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could find no such things.

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So these iguanas, to survive,

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had to eat the only kind of leaf
that was available.

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Seaweed.

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And to get the best of that,

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they had to do something
even more radical.

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They had to swim.

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They even learned to dive.

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They acquired the ability to
hold their breath for up to an hour

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so that they could swim down
to a depth of 20 metres.

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Their claws strengthened,

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so they could cling
to the rocks on the seabed.

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And under the water, they found
an endless supply of seaweed

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which grew in abundance
in the nutrient-rich currents

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that flow around the islands.

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But that was not all.

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Their snouts became flatter
to help them graze.

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And their teeth became sharper
to grip the slippery seaweed.

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But cold water can be
dangerous for cold-blooded reptiles.

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After a few minutes feeding at sea,
the iguanas are seriously chilled

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and in urgent need of a warm-up.

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And their skin enables them
to get that.

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It is black.

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Dark objects absorb heat and each
scale in the marine iguana's skin

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is like an element
in a miniature solar panel.

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Now all a marine iguana needs to do

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to bring its body
back up to temperature

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is to bask in the hot equatorial
sun for an hour or two.

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But eating nothing but seaweed
creates another problem -

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too much salt.

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The marine iguanas dealt with that
in a very particular way.

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They evolved a special gland
in their nose.

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They simply sneeze the excess salt
from their blood.

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These changes had to happen very
quickly in evolutionary terms

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if the iguanas were to survive.

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But here,
conditions sometimes change.

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And then, even iguanas
struggle to keep up.

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Every three to seven years,

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the weather becomes very extreme
and irregular.

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It's a phenomenon called El Nino.

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And it can have a devastating effect
on wildlife.

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Evolutionary biologist
Maren Vitousek

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has studied the effects of El Nino
on the Galapagos marine iguanas.

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She discovered that it decimates
their food.

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Pressed as 1.0.

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Marine iguanas usually eat red
and green algae, and that algae

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dies off completely during El Ninos,
during strong El Ninos.

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And it's replaced by a brown algae.

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Marine iguanas aren't able to digest
the brown algae,

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so they eat it, but it sits in their
stomach, basically in a big lump.

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And so you can find iguanas
dead on the beach of starvation

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with stomachs full of this brown
algae that they just can't digest.

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The marine iguana is worst-affected
of all Galapagos animals

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during an El Nino.

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As many as 90% of them can perish.

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It's bad news for iguanas...

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...but good news for scavengers.

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And new research has shown that
the iguanas have evolved

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a special ability that enables them
to survive the famine.

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Their bodies shrink.

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They lose not just fat and muscle,
but bone.

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The iguanas
can actively reduce their skeletons

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over just a few months.

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So we saw that the largest animals
were decreasing their body length

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by as much as 20%.

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And the magnitude of that means
that it can't be simply that they're

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changing their cartilage
or connective tissue

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or resorbing muscles.

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Those things together
count for about 10% of length.

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So, instead, 20% of shrinkage really
indicates that it's got to be

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the skeleton itself that's
decreasing in length.

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This amazing ability to do reabsorb
bone in times of hardship

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is unique to these reptiles.

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It's most recent discovery
in understanding how marine iguanas

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managed to survive on the coastlines
of the youngest Galapagos Islands.

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But iguanas were not alone

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in adapting
to these desolate volcanic shores.

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This is the lava heron.

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It's well camouflaged.

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It's grey feathers make it
relatively inconspicuous

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against the blackened lava rocks.

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So, moving stealthily, it
can hunt very effectively.

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Its favourite prey
is the Sally Lightfoot crab,

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whose striking red shell stands
out against the jet-black lava.

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But the adult crabs have
tough shells and sharp pincers

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and herons know better
than to attack a full-grown one.

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Juvenile crabs will be a much
more attractive prospect.

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But they have responded
to the landscape of Fernandina.

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They have black shells that
make them far less conspicuous

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to prowling herons.

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This time, the lava heron

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will have to make do
with a really tiny snack -

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a Sally Lightfoot hatchling.

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On the shorelines
of this infant Galapagos island,

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life is tough.

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Habitats are limited.

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Opportunities are scarce.

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But away from the coast,
survival is almost impossible.

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There, it's too dry and too hot
for most forms of life.

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But, in time, that will change.

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As the island ages,

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this hostile landscape
will become a little more welcoming.

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It will one day
support a rich forest,

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full of new places
for animals to live.

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This change is driven
by the volcanic hotspot

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which brought the island
into existence.

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The eruptions continue.

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95% of its final bulk
will accumulate

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in the next few hundred thousand
years.

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By the time the eruptions
have ceased,

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it's grown so large
that it has acquired a new power.

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It has the ability to create
its own weather.

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Humid, oceanic winds
blowing across the Pacific

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hit this mountain of lava
and are so forced upwards.

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That caused them so that they can no
longer hold their load of moisture,

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and it condenses as mist and rain.

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And that allows plants to thrive.

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Santa Cruz,
in the centre of the archipelago,

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is typical of these
middle-aged islands.

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(THUNDER RUMBLES)

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Its slopes are covered
by a mantle of green.

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This might seem to be a forest
of giant trees supporting a rich

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population of animals of all kinds.

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00:20:18,600 --> 00:20:23,280
But, this being Galapagos,
this forest is different.

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These plants are not true trees.

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Trees tend to have big seeds,

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and few of those made it across
the oceans to the Galapagos,

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and certainly none up here
into the highlands.

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But smaller plants
have smaller seeds.

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Some, so small
they can float on the wind.

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And one member of the dandelion
family made it up here.

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And without competition
from other trees, they grew big.

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This, you could say,
is a forest of giant dandelions.

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This very special kind of dandelion
is called scalesia.

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It's unique to the Galapagos,
and flourishes on the high slopes

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of Santa Cruz
and other middle-aged islands.

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It's become the host
for a whole community

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that could not exist without it.

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Because scalesia performs
a conjuring trick that gives life

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to the rest of the forest.

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There's no ground water
in these thin, volcanic soils,

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but the scalesia trees are
tall enough to collect moisture

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from the sky -
from clouds and from mist -

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and that is sufficient to sustain

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a whole community
of plants and animals.

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High in the canopy,
mist condenses on the spindly,

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crisscrossed branches
of the scalesia.

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Water trickles down
their wooded trunks.

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00:22:34,480 --> 00:22:38,360
Ferns root themselves in the damp
moss that clings to their bark.

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00:22:44,880 --> 00:22:48,119
The moisture creates conditions
where spiders

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and other small creatures can live.

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And on the forest floor,
pools appear.

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Here, dragonflies thrive and,
once again,

243
00:23:13,800 --> 00:23:17,720
they belong to a species that occurs
nowhere else but here.

244
00:23:25,040 --> 00:23:27,719
But the Galapagos climate
is changeable

245
00:23:27,720 --> 00:23:30,199
and the mists sometimes dry up,

246
00:23:30,200 --> 00:23:32,239
leaving this delicate ecosystem

247
00:23:32,240 --> 00:23:35,720
exposed to the burning
equatorial heat.

248
00:23:37,800 --> 00:23:41,760
Some trees, however, have evolved
a way of protecting themselves.

249
00:23:43,800 --> 00:23:47,959
This tree has developed a mutually
beneficial relationship

250
00:23:47,960 --> 00:23:49,960
with the lichen that grows on it.

251
00:23:50,720 --> 00:23:54,479
The lichen shields the tree
from the sun,

252
00:23:54,480 --> 00:23:56,639
preventing it from getting scorched.

253
00:23:56,640 --> 00:24:01,479
And the tree provides the lichen
with moisture and nutriment.

254
00:24:01,480 --> 00:24:04,319
But if the weather gets really sunny

255
00:24:04,320 --> 00:24:07,039
then the lichen shrivels

256
00:24:07,040 --> 00:24:10,039
and stops taking nutriment
and moisture from the tree

257
00:24:10,040 --> 00:24:14,320
but, at the same time, still
prevents it from getting sunburnt.

258
00:24:15,720 --> 00:24:19,520
And when the moisture returns,
the lichen can grow back.

259
00:24:20,800 --> 00:24:25,040
So, plant and lichen make the best
of the two extremes of climate.

260
00:24:29,800 --> 00:24:33,999
Fresh water anywhere on land
creates opportunities.

261
00:24:34,000 --> 00:24:36,919
But on volcanic islands
like Galapagos,

262
00:24:36,920 --> 00:24:40,000
it gets to some very strange places.

263
00:24:42,800 --> 00:24:45,359
Deep in the rocks beneath
the scalesia forest

264
00:24:45,360 --> 00:24:49,560
there is a network of hundreds
of tunnels called lava tubes.

265
00:24:51,000 --> 00:24:54,559
Here, the species-transforming power
of the Galapagos

266
00:24:54,560 --> 00:24:56,560
is as active as everywhere else.

267
00:25:09,760 --> 00:25:14,279
For scientists like caver Aaron
Addison and biologist Steve Taylor,

268
00:25:14,280 --> 00:25:19,759
these lava tubes are the Galapagos
Islands' new frontier of discovery.

269
00:25:19,760 --> 00:25:24,679
It's difficult to imagine or indeed
believe that there are still

270
00:25:24,680 --> 00:25:27,199
such untouched areas within
a place that's so well-known

271
00:25:27,200 --> 00:25:29,799
as the Galapagos
and so well studied.

272
00:25:29,800 --> 00:25:32,999
But we do find those areas,
and those areas then lead us

273
00:25:33,000 --> 00:25:35,719
to a new species
that are unknown to science,

274
00:25:35,720 --> 00:25:38,720
that haven't been described
by anyone else, ever.

275
00:25:46,640 --> 00:25:50,359
Black volcanic rock
still lies only a few inches down

276
00:25:50,360 --> 00:25:53,719
beneath the forest trees
of Santa Cruz.

277
00:25:53,720 --> 00:25:57,119
It erupted millions of years ago
and flowed down the sides

278
00:25:57,120 --> 00:26:02,239
of the volcano in rivers of molten,
red-hot lava.

279
00:26:02,240 --> 00:26:04,479
As the surface of the lava cooled,

280
00:26:04,480 --> 00:26:07,040
it solidified
and formed a rocky skin.

281
00:26:08,600 --> 00:26:13,119
And when the eruption ceased,
liquid lava continued to flow away,

282
00:26:13,120 --> 00:26:16,000
leaving behind these huge,
empty caverns.

283
00:26:19,280 --> 00:26:22,999
And now, a constant trickle
of life-giving water

284
00:26:23,000 --> 00:26:25,640
drips down into the winding tunnels.

285
00:26:29,120 --> 00:26:32,440
Steve Taylor
is an expert on underground life.

286
00:26:37,080 --> 00:26:40,400
The subterranean world
is full of surprises.

287
00:26:44,200 --> 00:26:48,199
It's just really exciting, cos
these animals are pale and eyeless.

288
00:26:48,200 --> 00:26:51,479
There's no selective pressure
to maintain eyes in a cave,

289
00:26:51,480 --> 00:26:53,399
so they're blind.

290
00:26:53,400 --> 00:26:56,559
And they often have
elongated appendages

291
00:26:56,560 --> 00:26:59,680
so they can either find prey
or avoid prey.

292
00:27:02,200 --> 00:27:05,679
This amblypygid,
half-scorpion, half-spider,

293
00:27:05,680 --> 00:27:07,920
is a predator and a scavenger.

294
00:27:09,800 --> 00:27:13,680
It might seem ungainly, but it's
well adapted to this black habitat.

295
00:27:15,560 --> 00:27:20,639
Eyes are useless down here,
and it's become almost blind.

296
00:27:20,640 --> 00:27:24,039
Instead, it feels its way
through the cave

297
00:27:24,040 --> 00:27:26,160
with great skill and sensitivity.

298
00:27:28,440 --> 00:27:31,159
Two of its eight legs
are greatly elongated

299
00:27:31,160 --> 00:27:34,400
and capable of extending
to twice the length of its body.

300
00:27:39,040 --> 00:27:42,639
This millipede
has lost all its colour.

301
00:27:42,640 --> 00:27:46,239
Why spend precious energy creating
a pigment in a place where

302
00:27:46,240 --> 00:27:47,720
no-one can see it?

303
00:27:50,240 --> 00:27:52,800
Spiders, too, haunt the lava tubes.

304
00:27:56,440 --> 00:27:59,519
And just like the tortoises
and iguanas,

305
00:27:59,520 --> 00:28:03,320
these creatures have evolved
into many different species.

306
00:28:04,920 --> 00:28:07,760
There are 90 of them,
all unique to the Galapagos.

307
00:28:11,440 --> 00:28:14,800
But spiders don't just differ
from island to island.

308
00:28:17,360 --> 00:28:21,400
They do so dramatically,
even within a single lava tube.

309
00:28:23,400 --> 00:28:26,239
Some that have been here
for a long time are blind

310
00:28:26,240 --> 00:28:28,279
and feel their way through the cave.

311
00:28:28,280 --> 00:28:30,200
A few have lost their eyes entirely.

312
00:28:36,200 --> 00:28:39,839
But living just centimetres
from them are more recent colonists,

313
00:28:39,840 --> 00:28:42,680
species that still retain
their eyes.

314
00:28:53,400 --> 00:28:58,559
Such variety in such a small area
seems extraordinary,

315
00:28:58,560 --> 00:29:01,080
but in the Galapagos,
it's almost common.

316
00:29:05,280 --> 00:29:09,439
The huge number of differing
habitats has made Santa Cruz

317
00:29:09,440 --> 00:29:11,600
a centre of biological diversity.

318
00:29:16,280 --> 00:29:19,760
And, as an island ages,
so it develops more habitats.

319
00:29:24,600 --> 00:29:26,760
Now, it's entering its old age.

320
00:29:29,560 --> 00:29:31,200
It's no longer growing.

321
00:29:35,080 --> 00:29:38,959
The sheer mass is too heavy
for the earth's crust to support.

322
00:29:38,960 --> 00:29:41,600
It begins to sink
under its own weight.

323
00:29:46,080 --> 00:29:49,599
And now, the rainwater that has been
falling on it throughout

324
00:29:49,600 --> 00:29:52,960
its middle age begins to carve away
its substance.

325
00:29:55,800 --> 00:29:59,680
So the island becomes smaller,
drier and flatter.

326
00:30:05,800 --> 00:30:08,440
That is what has happened
to Espanola.

327
00:30:15,120 --> 00:30:17,920
It's nearing four million years old.

328
00:30:22,520 --> 00:30:24,880
Its forests have gone.

329
00:30:28,040 --> 00:30:31,160
But it now has a different range
of habitats.

330
00:30:34,720 --> 00:30:40,039
Millions of years of erosion
have created beaches of soft sand.

331
00:30:40,040 --> 00:30:42,680
And they suit some animals
very well.

332
00:30:54,920 --> 00:31:00,080
This is a natural bathing beach
for Galapagos sea lions.

333
00:31:09,000 --> 00:31:13,879
They are just one of the very few
mammal species that are unique

334
00:31:13,880 --> 00:31:15,360
to the Galapagos.

335
00:31:20,240 --> 00:31:22,559
And the beach of an ageing island

336
00:31:22,560 --> 00:31:24,920
provides them with
an excellent nursery.

337
00:31:26,400 --> 00:31:30,320
Here, sea lion pups can suckle
in complete safety.

338
00:31:31,600 --> 00:31:34,200
Though they can be
a little irritating.

339
00:31:37,680 --> 00:31:41,119
And, in a protected cove
close by the beach,

340
00:31:41,120 --> 00:31:43,680
parents can teach
their youngsters to swim.

341
00:32:10,840 --> 00:32:15,640
After a swimming lesson, the beach
is a perfect place to relax.

342
00:32:41,160 --> 00:32:45,319
Sea lions seem to have
an idyllic life,

343
00:32:45,320 --> 00:32:47,639
but there is just one irritant...

344
00:32:47,640 --> 00:32:49,399
(FLIES BUZZ)

345
00:32:49,400 --> 00:32:51,120
...flies.

346
00:32:53,840 --> 00:32:57,239
On younger islands
with rocky coastlines,

347
00:32:57,240 --> 00:33:02,200
sea lions have help to keep
the flies at bay - lava lizards.

348
00:33:04,200 --> 00:33:06,960
(FLY BUZZES)

349
00:33:10,920 --> 00:33:13,519
But on the sandy beaches
of Espanola,

350
00:33:13,520 --> 00:33:16,759
the lava lizards
are nowhere to be seen.

351
00:33:16,760 --> 00:33:19,840
They prefer the nearby rocks,
which are warmer.

352
00:33:24,280 --> 00:33:28,200
So here the sea lions must deal
with the fly problem by themselves.

353
00:33:37,320 --> 00:33:39,319
Espanola's soft sand beaches

354
00:33:39,320 --> 00:33:42,280
are also gratefully valued
by another species -

355
00:33:46,800 --> 00:33:48,840
the waved albatross.

356
00:33:56,480 --> 00:33:59,599
The islands provides
an excellent nesting ground

357
00:33:59,600 --> 00:34:01,600
for these huge seabirds.

358
00:34:03,800 --> 00:34:06,119
With a wingspan
of two-and-a-half metres,

359
00:34:06,120 --> 00:34:08,159
the albatross is so big and heavy

360
00:34:08,160 --> 00:34:12,520
that it has to get up a considerable
ground speed in order to take off.

361
00:34:15,240 --> 00:34:17,480
And that's what the beach provides.

362
00:34:22,400 --> 00:34:25,999
As you might expect, the species
of albatross that lives here

363
00:34:26,000 --> 00:34:30,599
is slightly different from those
found in other parts of the world.

364
00:34:30,600 --> 00:34:34,359
These wavelike patterns on its
neck feathers distinguish it

365
00:34:34,360 --> 00:34:36,560
from all other albatross species.

366
00:34:53,120 --> 00:34:56,239
All albatrosses spend
most of their lives on the wing,

367
00:34:56,240 --> 00:34:59,040
travelling across entire oceans.

368
00:35:06,360 --> 00:35:11,319
But here on Espanola,
the waved albatrosses can nest.

369
00:35:11,320 --> 00:35:15,200
(SQUAWKING)

370
00:35:18,000 --> 00:35:21,999
The isolation of the Galapagos and
the protected soft shingle beaches

371
00:35:22,000 --> 00:35:24,839
of Espanola make this ageing island

372
00:35:24,840 --> 00:35:27,719
an excellent breeding ground
for them.

373
00:35:27,720 --> 00:35:30,400
35,000 settle here each year.

374
00:35:33,000 --> 00:35:37,360
Waved albatrosses are monogamous -
they mate for life.

375
00:35:39,000 --> 00:35:43,679
But how do you find a new mate
or recognise your old partner

376
00:35:43,680 --> 00:35:45,480
in such a crowded colony?

377
00:35:48,360 --> 00:35:50,599
You dance.

378
00:35:50,600 --> 00:35:53,920
(RHYTHMIC SQUAWKING)

379
00:36:02,960 --> 00:36:05,800
The whole performance
can last for nearly an hour.

380
00:36:08,240 --> 00:36:12,040
And it's repeated
several times every day.

381
00:36:13,960 --> 00:36:17,480
Sometimes, a potential rival
steps in to try his luck.

382
00:36:18,960 --> 00:36:22,639
The female in the middle dances
with both enthusiastic males

383
00:36:22,640 --> 00:36:24,160
at the same time.

384
00:36:35,160 --> 00:36:38,440
The reward for the victorious male
is great.

385
00:36:42,400 --> 00:36:43,960
A mate.

386
00:36:45,400 --> 00:36:48,520
And an opportunity
to pass on his genes.

387
00:36:54,640 --> 00:36:59,279
The many habitats of Espanola
and all ageing Galapagos Islands

388
00:36:59,280 --> 00:37:03,480
were created by the erosive power
of sea and weather.

389
00:37:10,800 --> 00:37:14,520
But erosion can have
only one final result.

390
00:37:21,680 --> 00:37:23,160
Destruction.

391
00:37:36,000 --> 00:37:40,599
So, a Galapagos island worn down
by the waves and the weather

392
00:37:40,600 --> 00:37:44,320
eventually reaches
the last stage of its existence.

393
00:37:51,000 --> 00:37:53,679
After millions of years
sustaining life,

394
00:37:53,680 --> 00:37:57,880
all that remains of it above water
is a rocky, curving cliff.

395
00:38:05,560 --> 00:38:07,200
Like Tortuga.

396
00:38:17,440 --> 00:38:22,000
There are many relic islands
like Tortuga in the Galapagos.

397
00:38:33,720 --> 00:38:37,919
Devil's Crown in the south
of the archipelago is even closer

398
00:38:37,920 --> 00:38:40,480
to disappearing altogether
below the waves.

399
00:38:42,720 --> 00:38:45,079
But even in its final days,

400
00:38:45,080 --> 00:38:48,200
a Galapagos island
provides a habitat for some.

401
00:38:50,800 --> 00:38:54,599
Its rock has been turned by erosion
into sediment, and now,

402
00:38:54,600 --> 00:38:59,280
that fertilises the marine life
around its submerged remains.

403
00:39:04,000 --> 00:39:08,400
A ring of coral two metres wide
encircles its dwindling stump.

404
00:39:12,200 --> 00:39:15,080
So, a whole new animal community
develops.

405
00:39:21,440 --> 00:39:23,440
Corals are at its centre.

406
00:39:25,880 --> 00:39:27,999
Bristle worms hide inside them,

407
00:39:28,000 --> 00:39:31,040
occasionally emerging
to browse on passing morsels.

408
00:39:42,280 --> 00:39:46,159
Fish find safety among the branches.

409
00:39:46,160 --> 00:39:50,120
And some of the species, once again,
are unique to the Galapagos.

410
00:40:04,840 --> 00:40:07,000
The reef teems with life.

411
00:40:40,000 --> 00:40:44,199
But the presence of warm water
corals here in the Galapagos seas

412
00:40:44,200 --> 00:40:46,200
is something of a surprise.

413
00:40:47,600 --> 00:40:52,240
Because penguins that need
cold water live here too.

414
00:40:55,800 --> 00:40:59,960
So how can tropical corals
and penguins co-exist?

415
00:41:01,760 --> 00:41:05,000
The Galapagos Islands have
one more trick up their sleeve.

416
00:41:08,240 --> 00:41:10,399
The archipelago lies
at the confluence

417
00:41:10,400 --> 00:41:12,559
of several deep ocean currents.

418
00:41:12,560 --> 00:41:16,360
And that creates a bizarre
mixture of marine habitats.

419
00:41:17,520 --> 00:41:21,599
The subantarctic Humboldt Current
flows around the islands

420
00:41:21,600 --> 00:41:25,880
and chills the water just enough
for the penguins to survive.

421
00:41:26,760 --> 00:41:29,599
The corals can't grow
in such cold water

422
00:41:29,600 --> 00:41:33,440
but they can go into a state of
semi-hibernation for short periods.

423
00:41:35,600 --> 00:41:38,479
When warm water from
Central America is dominant,

424
00:41:38,480 --> 00:41:41,280
the temperature
rises by about seven degrees.

425
00:41:43,040 --> 00:41:45,240
Now the corals can grow...

426
00:41:46,800 --> 00:41:48,919
...and the penguins can find refuge

427
00:41:48,920 --> 00:41:52,879
in the few remaining pockets
of cold water in the coves and bays

428
00:41:52,880 --> 00:41:54,560
that still remain.

429
00:41:57,200 --> 00:42:00,559
So, even in the last stages
of its life,

430
00:42:00,560 --> 00:42:04,160
a Galapagos island can support
a rich animal community.

431
00:42:05,480 --> 00:42:10,080
But remarkably, even this
is not the end of the story.

432
00:42:11,400 --> 00:42:15,999
Because even when an island totally
disappears beneath the waves,

433
00:42:16,000 --> 00:42:20,400
it continues to influence life
in the surrounding seas.

434
00:42:22,520 --> 00:42:25,639
The remains of ancient
Galapagos islands

435
00:42:25,640 --> 00:42:29,040
stretch for hundreds of miles
across the Pacific seabed.

436
00:42:30,880 --> 00:42:34,279
These were once volcanoes
like Fernandina,

437
00:42:34,280 --> 00:42:36,799
vegetated mountains like Santa Cruz

438
00:42:36,800 --> 00:42:39,080
and low-lying nurseries
like Espanola.

439
00:42:42,200 --> 00:42:45,279
Today,
those environments are long gone,

440
00:42:45,280 --> 00:42:49,479
but the remnants of the islands
under the sea are still key

441
00:42:49,480 --> 00:42:53,160
in the lives of one of the ocean's
most magnificent inhabitants.

442
00:42:56,280 --> 00:43:00,040
Up to 12 metres long,
it's the largest fish in the world.

443
00:43:03,440 --> 00:43:04,840
The whale shark.

444
00:43:08,760 --> 00:43:12,199
Whale sharks come to the Galapagos
in large numbers

445
00:43:12,200 --> 00:43:13,920
at the same time every year.

446
00:43:16,560 --> 00:43:18,960
But why they do so is a mystery.

447
00:43:27,400 --> 00:43:31,359
Marine biologists Alex Hearn
and Jonathan Green have spent

448
00:43:31,360 --> 00:43:35,239
the last five years trying
to solve the puzzle.

449
00:43:35,240 --> 00:43:38,759
If you think about how Galapagos
is formed and how currents work,

450
00:43:38,760 --> 00:43:41,439
the most productive waters
are actually out west,

451
00:43:41,440 --> 00:43:44,679
so you would've thought that if
whale sharks were here to feed,

452
00:43:44,680 --> 00:43:47,759
they'd be out in the west
of the archipelago, and they're not.

453
00:43:47,760 --> 00:43:49,479
They're up north.

454
00:43:49,480 --> 00:43:53,200
So, why are they coming here?
It's clearly not to feed.

455
00:43:54,880 --> 00:43:59,719
What we found out recently is that
it's mainly large, pregnant females.

456
00:43:59,720 --> 00:44:02,159
Are they coming here to give birth?

457
00:44:02,160 --> 00:44:06,919
This may be the pupping ground for
whale sharks. I'm slightly sceptical.

458
00:44:06,920 --> 00:44:10,200
I think we'd have seen juveniles,
and we don't.

459
00:44:12,040 --> 00:44:14,919
So, that brings back the question,
well, then,

460
00:44:14,920 --> 00:44:17,759
if they aren't pupping here
and they aren't feeding here,

461
00:44:17,760 --> 00:44:19,240
why are they coming?

462
00:44:32,520 --> 00:44:36,159
To understand the whale sharks'
migratory patterns,

463
00:44:36,160 --> 00:44:40,400
Hearn and Green attach satellite
tags to the sharks they encounter.

464
00:44:48,120 --> 00:44:51,680
This enables them
to track their movements.

465
00:44:53,840 --> 00:44:57,720
And it's revealing some
extraordinary new facts.

466
00:45:02,480 --> 00:45:06,639
First, the sharks swim
open-mouthed through the rich waters

467
00:45:06,640 --> 00:45:08,680
off the west coast of South America.

468
00:45:10,160 --> 00:45:14,480
Then they continue their journey
westwards to the Galapagos.

469
00:45:15,360 --> 00:45:19,520
But they only spend a few days
at a time in the islands' waters,

470
00:45:20,400 --> 00:45:23,880
before continuing westwards
out into the open ocean.

471
00:45:32,600 --> 00:45:36,239
Nobody has yet proved why
the whale sharks do this,

472
00:45:36,240 --> 00:45:40,959
but Alex Hearn has begun
to formulate some ideas.

473
00:45:40,960 --> 00:45:43,079
I think there are two possibilities.

474
00:45:43,080 --> 00:45:47,359
Firstly, they may be using Galapagos
as a waypoint which directs them

475
00:45:47,360 --> 00:45:49,039
towards their pupping grounds.

476
00:45:49,040 --> 00:45:53,279
The other option is Galapagos may be
providing a service along way,

477
00:45:53,280 --> 00:45:55,559
and that service may be cleaning,

478
00:45:55,560 --> 00:45:58,479
because we do see a lot of cleaning
behaviour from the reef fish,

479
00:45:58,480 --> 00:46:00,679
or it may be a combination
of the two.

480
00:46:00,680 --> 00:46:05,679
The long line of submerged Galapagos
islands could play a central role

481
00:46:05,680 --> 00:46:08,240
in the whale sharks'
extraordinary journey.

482
00:46:09,960 --> 00:46:12,519
It might be that they
serve as signposts

483
00:46:12,520 --> 00:46:14,519
by which the sharks navigate.

484
00:46:14,520 --> 00:46:16,799
If you start looking at
where they're going,

485
00:46:16,800 --> 00:46:19,799
especially the tracks that we have,
along those ridges

486
00:46:19,800 --> 00:46:22,919
and then up to the next ridge
and back down again, it certainly

487
00:46:22,920 --> 00:46:26,559
seems that they're associating with
those ridges for one reason

488
00:46:26,560 --> 00:46:29,239
or another, and that could be
geomagnetism or it could also be

489
00:46:29,240 --> 00:46:33,599
something to do with the biology of
the water column above the ridges,

490
00:46:33,600 --> 00:46:35,760
but certainly something is going on.

491
00:46:51,720 --> 00:46:54,199
From their birth to their death,

492
00:46:54,200 --> 00:46:58,399
the islands have acted like
evolutionary pressure cookers.

493
00:46:58,400 --> 00:47:01,599
From the youngest islands
like Fernandina,

494
00:47:01,600 --> 00:47:07,000
middle-aged ones like Santa Cruz
and the old islands like Espanola...

495
00:47:09,120 --> 00:47:13,680
...they are extremely varied,
with contrasted conditions.

496
00:47:19,880 --> 00:47:23,999
Deserts, rainforests
and polar waters crowded together

497
00:47:24,000 --> 00:47:25,720
in a very small area.

498
00:47:54,280 --> 00:47:59,479
These huge variations have created
a wide range of opportunities

499
00:47:59,480 --> 00:48:02,400
for the few animals
that have managed to reach here.

500
00:48:12,520 --> 00:48:14,280
As they colonised...

501
00:48:17,960 --> 00:48:20,360
...so they adapted.

502
00:48:21,880 --> 00:48:24,120
And consequently, flourished.

503
00:48:32,320 --> 00:48:37,800
That explains many of the oddities
of the inhabitants of these islands.

504
00:48:46,080 --> 00:48:50,919
Including that most fundamental
phenomenon of all -

505
00:48:50,920 --> 00:48:53,880
the appearance of new species.

506
00:48:58,560 --> 00:49:02,559
The giant tortoise is the
very emblem of the Galapagos,

507
00:49:02,560 --> 00:49:05,799
and in their heyday, there were
hundreds of thousands of them.

508
00:49:05,800 --> 00:49:09,039
Not only that,
there were 15 different species

509
00:49:09,040 --> 00:49:11,519
each in its own locality.

510
00:49:11,520 --> 00:49:14,359
But why should there be
so many species

511
00:49:14,360 --> 00:49:17,079
within such a comparatively
restricted area?

512
00:49:17,080 --> 00:49:21,679
In the next programme, we'll look
at the deep geological forces

513
00:49:21,680 --> 00:49:24,919
that can make a single species
produce many,

514
00:49:24,920 --> 00:49:28,000
and turn the Galapagos
into this wonderland.

515
00:49:40,720 --> 00:49:42,840
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