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Our planet is the greatest
living puzzle in the universe.
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A collection of worlds
within worlds.
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Each one a self-contained ecosystem
bursting with life.
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00:00:17,900 --> 00:00:19,260
But how do they work?
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00:00:21,220 --> 00:00:24,620
The intricate web of relationships
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00:00:24,620 --> 00:00:27,980
and the influence of natural forces
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makes each microworld
complex and unique.
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So, to discover their secrets,
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00:00:35,580 --> 00:00:38,220
we need to explore them one by one,
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00:00:40,300 --> 00:00:44,100
untangle their interlocking pieces
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and, ultimately,
reveal the vital piece,
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the key to life itself
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00:00:49,980 --> 00:00:54,180
hidden deep within
each of nature's microworlds.
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00:01:09,020 --> 00:01:12,980
And we may think it's brimming
with life from shore to shore,
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but, actually,
that's not quite true.
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In fact, in most of this ocean,
life can be hard to come by.
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Instead, most marine species
are condensed into intense pockets,
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crammed along the coasts.
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And, in tropical seas,
these colourful coastlines
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are the most diverse ecosystems
in the ocean -
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the coral reef.
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These coral reefs are found
across the world,
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but one of them
is the master of them all.
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It is simply the largest
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living structure on Earth.
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The Great Barrier Reef.
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00:02:01,260 --> 00:02:02,900
Of all the reefs on the planet,
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how has this one managed to achieve
this incredible size?
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00:02:08,420 --> 00:02:12,220
But scale isn't the only success
of this microworld.
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The water that this reef basks in
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lacks many of the nutrients
vital for life.
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So such a vibrant ecosystem
should have struggled
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to get a foothold here.
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So how has this enormous place
managed to survive?
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00:02:35,500 --> 00:02:36,980
To understand this,
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we first need to find out
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what it was that allowed the
Great Barrier Reef to get so big.
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The reef stretches along
the north-eastern coast of Australia
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for over 2,000 kilometres -
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a distance equivalent to that
between Britain and North Africa.
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00:03:02,460 --> 00:03:05,660
Underwater,
it's a marine metropolis
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00:03:05,660 --> 00:03:08,900
and home to a hustling, bustling
whirlwind of life.
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00:03:11,700 --> 00:03:15,820
But this microworld encompasses
more than just a reef.
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All along its lengths are lagoons,
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islands and seagrass meadows.
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00:03:22,740 --> 00:03:26,180
On the western boundary
is the Australian mainland.
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And to the east,
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the open Pacific Ocean,
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where the outer wall
of the Great Barrier Reef
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meets the deep blue sea.
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00:03:36,700 --> 00:03:40,140
In our search for the key factors
that make this place so big,
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00:03:40,140 --> 00:03:43,300
we need to look at some
of these habitats in more detail.
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And, to begin,
the one that dominates all others...
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..the underwater world of coral,
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00:03:53,980 --> 00:03:57,300
home to the majority of species
on the Great Barrier Reef.
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00:03:59,300 --> 00:04:03,380
The fish are perhaps the most
conspicuous of all the animals here
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00:04:03,380 --> 00:04:05,940
and there are some 1,500 species,
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00:04:07,660 --> 00:04:10,060
each with their own way
of making a living.
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00:04:14,260 --> 00:04:16,260
Clownfish live amongst anemones.
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00:04:17,620 --> 00:04:20,020
There are more than seven species
of these fish
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00:04:20,020 --> 00:04:22,100
that live along this reef
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00:04:22,100 --> 00:04:24,420
and each species depends
on the presence
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00:04:24,420 --> 00:04:27,260
of their host anemone to survive.
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00:04:27,260 --> 00:04:30,980
Spiny damselfish
are another reef resident.
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00:04:30,980 --> 00:04:35,220
And they face the challenges
of parenthood in a watery world.
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00:04:35,220 --> 00:04:39,820
They keep their school of miniature
offspring in sight at all times,
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00:04:39,820 --> 00:04:44,420
only venturing away from the safety
of the reef to grab a quick snack
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00:04:44,420 --> 00:04:48,020
before returning back to the cover
of their coral cave.
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00:04:51,140 --> 00:04:53,660
This diversity of fish
is only the beginning
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00:04:53,660 --> 00:04:55,580
of the Great Barrier Reef story.
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This microworld is jam-packed
with thousands of other species,
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like mantis shrimp
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00:05:01,620 --> 00:05:03,060
and feather stars.
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00:05:04,860 --> 00:05:07,780
All these lives play out
against a backdrop
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00:05:07,780 --> 00:05:09,780
of hundreds of coral species,
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00:05:09,780 --> 00:05:12,660
which can stretch
as far as the eye can see.
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00:05:14,100 --> 00:05:17,300
This huge array of life
may be impressive,
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00:05:17,300 --> 00:05:21,140
but it doesn't set the Great Barrier
Reef apart from other reefs.
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00:05:23,020 --> 00:05:25,860
Amongst all of these players,
it isn't the fish,
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the invertebrates or even the corals
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00:05:28,140 --> 00:05:30,380
that explain why
this reef is so big.
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00:05:32,940 --> 00:05:35,300
We need to look further.
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We need to visit
the other environments
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00:05:37,580 --> 00:05:40,420
that make up the Great Barrier Reef.
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00:05:40,420 --> 00:05:43,900
And one of these is seagrass.
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00:05:45,420 --> 00:05:49,420
Remarkably, seagrass
is actually a flowering plant -
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the only one adapted
to live in the ocean.
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00:05:53,340 --> 00:05:56,620
And like huge grasslands,
such as the Serengeti,
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00:05:56,620 --> 00:06:00,980
seagrass provide important
feeding grounds for herbivores.
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00:06:07,180 --> 00:06:11,220
More related to the elephant
than to any dolphins or whales,
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00:06:11,220 --> 00:06:14,020
these are herbivores
that can hold their breath.
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00:06:15,460 --> 00:06:17,460
This is a dugong.
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00:06:21,180 --> 00:06:24,780
Meadows of seagrass stretch
right along the Great Barrier Reef
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00:06:24,780 --> 00:06:29,700
and cover up to 40,000 square
kilometres of the sandy bottom.
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00:06:29,700 --> 00:06:33,620
This huge area allows
impressive numbers of dugongs
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00:06:33,620 --> 00:06:36,820
to congregate in these southern
stretches of the coast.
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00:06:39,620 --> 00:06:42,460
But what part do these vast
areas of seagrass play
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in the Great Barrier Reef's size?
99
00:06:47,340 --> 00:06:49,740
Well, the seagrass supports
massive creatures
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00:06:49,740 --> 00:06:51,740
and provides additional habitat...
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00:06:53,740 --> 00:06:57,900
..but this seagrass is just a
product of the reef, not its cause.
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00:07:00,100 --> 00:07:02,740
In fact, the seagrass actually
depends on the reef
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for the material in which it grows.
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00:07:08,180 --> 00:07:09,420
Sand.
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00:07:10,820 --> 00:07:13,860
And some of that sand comes
from animal life.
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00:07:22,220 --> 00:07:25,460
The aptly-named parrotfish
is a conspicuous sight
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to come across on any reef.
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00:07:29,300 --> 00:07:31,060
And, by following these fish,
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we soon see where some of this sand
comes from.
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The fish's teeth
are fused into a parrot-like beak
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that crunches its way
through the calcium structure
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00:07:53,620 --> 00:07:56,300
of dead and living coral alike.
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00:07:58,220 --> 00:08:03,260
But what seems to be pure
destruction has a surprising twist.
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The digested bits of coral skeleton
115
00:08:05,820 --> 00:08:08,860
are ground down
inside the humphead parrotfish
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into a fine calcium powder
117
00:08:11,540 --> 00:08:14,020
and excreted as sand...
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..sand that builds up
with other bits of calcium rubble
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00:08:19,700 --> 00:08:24,620
and, with wind and waves, becomes
mounds that push up above the water.
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00:08:25,100 --> 00:08:26,700
The beginnings of islands
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00:08:26,700 --> 00:08:29,620
that allow other creatures
to prosper on the reef.
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00:08:32,100 --> 00:08:36,380
There are some 600 islands
dotted all along this coast.
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00:08:36,380 --> 00:08:39,660
Oases of life that have been
colonised by plants
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00:08:39,660 --> 00:08:42,660
and become vibrant ecosystems
of their own.
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00:08:44,900 --> 00:08:47,700
Some of the islands in the southern
reaches of the reef
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00:08:47,700 --> 00:08:52,540
have become central to generation
after generation of green turtles.
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Every year, 38,000 female turtles
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00:08:57,140 --> 00:09:00,060
come to the sandy beaches
of the Great Barrier Reef
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to lay their eggs.
130
00:09:06,620 --> 00:09:10,900
This female was born on this
same beach over 45 years ago
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00:09:10,900 --> 00:09:15,900
and she's now returned to lay
her own clutch of around 100 eggs.
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It might sound like a lot
but of each 1,000 eggs laid,
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only one turtle might survive
to adulthood.
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00:09:28,500 --> 00:09:30,780
So the reef's protected
sandy beaches
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provide vital nesting habitat
for an ancient and iconic reptile.
136
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But the islands have brought
other life to the reef too.
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They have become important
breeding grounds
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for the 20 or so species
of seabirds.
139
00:09:51,140 --> 00:09:54,380
And white-capped noddies
are here in their thousands.
140
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They produce a single egg
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and build their nests
among the trees and shrubs
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00:10:00,300 --> 00:10:02,260
of coral sand islands.
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00:10:06,740 --> 00:10:09,100
Without the sand
that built these islands,
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00:10:09,100 --> 00:10:12,820
these birds would never be able
to nest here in such great numbers.
145
00:10:16,140 --> 00:10:18,100
So sand plays a vital role
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00:10:18,100 --> 00:10:21,100
in creating the islands and seagrass
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that allow a rich diversity of
animals to make the reef their home.
148
00:10:28,820 --> 00:10:32,820
But sand is just one of the reasons
it's so vast.
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The Great Barrier Reef
has 2,900 reef systems,
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00:10:46,580 --> 00:10:49,220
600 tropical islands
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and more than 270,000
square kilometres of coral.
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00:10:54,820 --> 00:10:57,500
To find the ultimate reason
for this immense size,
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we need to look wider still.
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And the answer is right under
its feet.
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Seen from space,
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the reef sticks out from the coast.
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It's sitting up on a huge platform.
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This is an extension
of the continental shelf -
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over 2,000 kilometres long
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and up to 200 kilometres wide -
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that provides the reef
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with the perfect shallow-water stage
on which to grow.
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But there's another reason
why it's so massive.
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In the northern section of the reef,
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a gap in the coral
allows a huge current
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to pour in from the Coral Sea.
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It's the East Australian Current
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and it's far from just a trickle.
169
00:11:51,580 --> 00:11:54,740
This movement of water
can be up to 100 kilometres wide
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and 500 metres deep.
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It carries over 30 million
cubic metres of water per second.
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And the current is a vehicle
that carries life.
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Combined with wind-driven currents,
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planktonic animals are transported
for hundreds of kilometres
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up and down the reef.
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It's a great highway
that has spread life
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to all its individual parts
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and it's joined up
this massive ecosystem
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to make the longest reef
on the planet.
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00:12:38,020 --> 00:12:40,740
So the Great Barrier Reef's
immense size
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is a product of the huge
shallow-water platform
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created by Australia's
continental shelf,
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combined with the effects
of a great current
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that spreads colonising life
right along the coast.
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00:12:53,740 --> 00:12:56,660
And it's this unique
set of circumstances
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that has led to such success.
187
00:13:02,500 --> 00:13:06,300
But survival on this coast
is far from guaranteed.
188
00:13:07,980 --> 00:13:12,820
The Great Barrier Reef is an
ecosystem in an impoverished ocean.
189
00:13:14,860 --> 00:13:17,140
So how does it actually work?
190
00:13:23,140 --> 00:13:24,620
It's almost unbelievable
191
00:13:24,620 --> 00:13:28,060
but all of this is created
by a tiny creature.
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An animal
just one millimetre across,
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which barely looks alive at all.
194
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The coral polyp.
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00:13:42,060 --> 00:13:43,700
This is a reef-building coral
196
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and it literally manufactured
the Great Barrier Reef
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from the ground up.
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00:13:49,140 --> 00:13:52,060
It's made by a creature you can
barely see with the naked eye,
199
00:13:52,060 --> 00:13:54,260
and it's created enough coral reef
200
00:13:54,260 --> 00:13:57,140
to cover the entire land area
of the United Kingdom.
201
00:13:58,980 --> 00:14:01,900
270 billion square metres.
202
00:14:03,580 --> 00:14:04,940
How does it do it?
203
00:14:07,180 --> 00:14:11,540
Reef-building corals
are made up of tiny polyps
204
00:14:11,540 --> 00:14:15,820
and they each live in a little
box of calcium carbonate.
205
00:14:15,820 --> 00:14:20,340
This stony structure
is called their skeleton
206
00:14:20,340 --> 00:14:23,100
and they deposit it beneath them
in order to grow.
207
00:14:26,780 --> 00:14:30,380
Each colourful structure here
is a colony
208
00:14:30,380 --> 00:14:35,180
and each has slowly built up
their fortified-calcium castle
209
00:14:35,180 --> 00:14:37,420
of all shapes and sizes.
210
00:14:53,180 --> 00:14:56,140
They look like sturdy rock giants
211
00:14:56,140 --> 00:15:00,740
but, remarkably, the living tissue
forms a thin veneer on the outside
212
00:15:00,740 --> 00:15:04,260
of sometimes metres
of inanimate coral rock.
213
00:15:09,060 --> 00:15:13,620
This tiny layer of life
makes corals incredibly fragile
214
00:15:13,620 --> 00:15:15,660
and vulnerable to attack.
215
00:15:20,620 --> 00:15:24,260
The dainty mouths of angelfish
might appear harmless
216
00:15:24,260 --> 00:15:26,620
but they actually eat coral.
217
00:15:29,020 --> 00:15:31,140
And, for the coral under attack,
218
00:15:31,140 --> 00:15:34,580
the daytime is best spent
hiding indoors.
219
00:15:36,380 --> 00:15:39,460
But, at night,
when the reef goes quiet,
220
00:15:39,460 --> 00:15:41,460
the coral polyps emerge,
221
00:15:41,460 --> 00:15:44,060
and, finally, we get to see
the animals within.
222
00:15:46,060 --> 00:15:49,940
All across the tropics,
stone coral statues come to life.
223
00:15:52,980 --> 00:15:55,620
The coral animals
are relatives of the anemone
224
00:15:55,620 --> 00:15:57,980
and are equipped
with stinging tentacles
225
00:15:57,980 --> 00:16:00,820
that they use to gather
the plankton floating by.
226
00:16:17,860 --> 00:16:21,820
These corals are clearly
far from lifeless rocks.
227
00:16:24,500 --> 00:16:26,860
And, on some of these crammed reefs,
228
00:16:26,860 --> 00:16:30,860
these tiny animals will even
wage war on their neighbours.
229
00:16:35,140 --> 00:16:38,220
The growing corals
send out digesting tentacles
230
00:16:38,220 --> 00:16:41,220
that, over hours,
can eat away at their neighbours
231
00:16:41,220 --> 00:16:43,740
in a quest for dominance.
232
00:16:43,740 --> 00:16:47,740
And their thin layer of living
tissue is soon stripped back
233
00:16:47,740 --> 00:16:49,540
to their limestone skeleton.
234
00:16:51,580 --> 00:16:55,300
But, for the most part,
these corals can grow peacefully.
235
00:16:55,300 --> 00:16:57,100
And, in good conditions,
236
00:16:57,100 --> 00:16:59,860
will deposit new layers
of their calcium skeleton
237
00:16:59,860 --> 00:17:01,940
at up to five centimetres per year.
238
00:17:06,060 --> 00:17:09,340
This remarkable process
is what lays down
239
00:17:09,340 --> 00:17:11,780
the limestone building blocks
of the reef.
240
00:17:13,660 --> 00:17:16,380
Between them, the polyps
of the Great Barrier Reef
241
00:17:16,380 --> 00:17:21,100
lay down one billion tonnes
of calcium carbonate every year,
242
00:17:21,100 --> 00:17:23,100
creating the foundations
243
00:17:23,100 --> 00:17:26,140
for this awe-inspiring
shallow-water ecosystem.
244
00:17:32,260 --> 00:17:34,980
But building their skeletons
is demanding
245
00:17:34,980 --> 00:17:38,020
of both energy and nutrients
246
00:17:38,020 --> 00:17:41,420
and the coral animals
can't manage such a feat alone.
247
00:17:45,660 --> 00:17:48,380
The crystal-clear water
of the Great Barrier Reef
248
00:17:48,380 --> 00:17:50,860
might seem like the stuff
of postcards and dreams...
249
00:17:54,180 --> 00:17:58,260
..but this bright blue sea is
missing something vital for life.
250
00:18:01,780 --> 00:18:03,420
It lacks the nutrients
251
00:18:03,420 --> 00:18:06,300
that microscopic plants
and animals need to grow -
252
00:18:07,900 --> 00:18:09,780
the nitrates and phosphates
253
00:18:09,780 --> 00:18:11,620
that fuel plankton blooms,
254
00:18:11,620 --> 00:18:13,620
which are the base
of the food chain.
255
00:18:17,940 --> 00:18:20,460
So, despite feeding every night,
256
00:18:20,460 --> 00:18:23,780
the coral simply can't get
enough energy to survive here
257
00:18:23,780 --> 00:18:25,420
from plankton alone.
258
00:18:27,540 --> 00:18:29,700
But deep in its evolutionary
history,
259
00:18:29,700 --> 00:18:32,740
coral developed a clever trick
to get around this.
260
00:18:38,260 --> 00:18:41,060
The key to this
is a remarkable association
261
00:18:41,060 --> 00:18:43,380
between the coral
and a single-celled algae,
262
00:18:43,380 --> 00:18:44,980
called zooxanthellae.
263
00:18:48,620 --> 00:18:53,620
These tiny single-celled algae are
incorporated into the coral tissues,
264
00:18:54,260 --> 00:18:57,060
at up to five million
per square centimetre.
265
00:19:00,540 --> 00:19:04,620
The coral's waste products feed the
algae with the nutrients they need.
266
00:19:07,860 --> 00:19:12,500
And, in return,
the algae develops inside the coral,
267
00:19:12,500 --> 00:19:17,140
photosynthesising, using sunlight
to create oxygen and sugars.
268
00:19:20,020 --> 00:19:22,620
These much-needed sugars
are the vital energy
269
00:19:22,620 --> 00:19:24,220
that the coral needs to grow.
270
00:19:27,420 --> 00:19:30,820
So this unique partnership
allows coral to thrive
271
00:19:30,820 --> 00:19:33,540
in the nutrient-poor waters
along this coast.
272
00:19:36,100 --> 00:19:41,140
But this relationship also sets
the rules for this entire ecosystem.
273
00:19:43,340 --> 00:19:45,700
By having an algae
within its tissue,
274
00:19:45,700 --> 00:19:50,420
the coral effectively becomes
half plant and half animal.
275
00:19:50,420 --> 00:19:55,460
And so, like plants,
coral has become a slave to the sun.
276
00:19:57,580 --> 00:20:00,620
It needs the sunlit waters
of the tropics to grow.
277
00:20:07,900 --> 00:20:10,300
But these shallow tropical waters
278
00:20:10,300 --> 00:20:13,140
leave the coral exposed
279
00:20:13,140 --> 00:20:15,620
because each Australian summer,
280
00:20:15,620 --> 00:20:18,740
destructive forces
move towards the coast.
281
00:20:54,180 --> 00:20:57,460
150kmph winds.
282
00:20:57,460 --> 00:20:59,660
Destructive waves.
283
00:20:59,660 --> 00:21:02,140
Tropical cyclones develop
over the warm seas
284
00:21:02,140 --> 00:21:04,060
of the South-Western Pacific
285
00:21:04,060 --> 00:21:06,860
and hit parts of the
Great Barrier Reef every year.
286
00:21:15,060 --> 00:21:17,900
Huge waves smash the fragile
coral skeletons,
287
00:21:17,900 --> 00:21:19,700
breaking them up into rubble
288
00:21:19,700 --> 00:21:21,860
which tumbles down the reef edge...
289
00:21:52,260 --> 00:21:55,860
..leaving behind a wasteland
of coral skeletons.
290
00:21:58,500 --> 00:22:00,860
This coral takes the brunt
of the storm
291
00:22:00,860 --> 00:22:04,220
and, in doing so,
protects other parts of the reef.
292
00:22:09,060 --> 00:22:12,660
The seagrass is sheltered
in protected lagoons
293
00:22:12,660 --> 00:22:16,140
and the rich island ecosystems
are kept intact.
294
00:22:18,100 --> 00:22:21,700
The sturdy outer wall of coral
protects this coastline
295
00:22:21,700 --> 00:22:25,500
from the wild forces of the Pacific
Ocean that roll in every year.
296
00:22:29,780 --> 00:22:32,220
But if life in these shallow waters
297
00:22:32,220 --> 00:22:34,780
is threatened
on such a regular basis,
298
00:22:34,780 --> 00:22:37,340
how has this coral reef
managed to survive?
299
00:22:41,620 --> 00:22:43,940
The secret to this reef's success
300
00:22:43,940 --> 00:22:46,140
is that it's bigger than any storm.
301
00:22:49,060 --> 00:22:51,980
And to see how this saves the reef
from ruin,
302
00:22:51,980 --> 00:22:55,700
we need to take a look at what
happens when the dust settles.
303
00:22:59,900 --> 00:23:04,900
This coral graveyard is not an
untimely death but an opportunity.
304
00:23:05,660 --> 00:23:08,020
An opportunity for new life.
305
00:23:11,740 --> 00:23:14,380
Not all of the reef
was damaged in the storm.
306
00:23:14,380 --> 00:23:16,900
Even in the worst cyclones,
307
00:23:16,900 --> 00:23:20,420
85% of it can escape damage
308
00:23:20,420 --> 00:23:24,620
and new life comes from these
undamaged parts each November
309
00:23:24,620 --> 00:23:28,820
when the reef experiences
an incredible reproductive event.
310
00:23:32,980 --> 00:23:34,380
In the moonlit night,
311
00:23:34,380 --> 00:23:36,660
the corals of the Great Barrier Reef
312
00:23:36,660 --> 00:23:40,020
start to release eggs and sperm
into the water
313
00:23:40,020 --> 00:23:42,260
and it becomes alive.
314
00:23:56,060 --> 00:23:58,620
Tiny coral nomads take shape.
315
00:24:02,180 --> 00:24:05,780
But they don't just settle on
the reef where they were released.
316
00:24:09,140 --> 00:24:12,740
This is where the ocean current
comes into play.
317
00:24:14,380 --> 00:24:18,460
It carries the larvae of coral,
fish and invertebrates
318
00:24:18,460 --> 00:24:19,860
all along the reef.
319
00:24:23,780 --> 00:24:27,700
This allows bits of damaged reef
to be re-colonised with life.
320
00:24:35,740 --> 00:24:38,380
A single coral polyp.
321
00:24:39,980 --> 00:24:42,260
The beginning of a new colony.
322
00:24:48,220 --> 00:24:51,140
And a renewed stretch of reef.
323
00:24:53,620 --> 00:24:57,100
The new life created by
the annual coral spawn
324
00:24:57,100 --> 00:25:00,300
helps rebuild damaged parts
of the reef...
325
00:25:02,780 --> 00:25:04,980
..allowing them to flourish
once more.
326
00:25:10,700 --> 00:25:13,060
This process repairs the ramparts
327
00:25:13,060 --> 00:25:15,740
and can help replenish the reef edge
328
00:25:15,740 --> 00:25:18,180
before the next cyclone arrives.
329
00:25:21,460 --> 00:25:24,180
It might seem like a pointless
reconstruction
330
00:25:24,180 --> 00:25:28,180
but the re-growth of coral on
a bedrock of dead calcium skeleton
331
00:25:28,180 --> 00:25:32,700
is vitally important
to the continuation of life here.
332
00:25:32,700 --> 00:25:34,860
And, to see just why this is,
333
00:25:34,860 --> 00:25:36,980
we need to look back in time.
334
00:25:41,780 --> 00:25:44,020
Just some 10,000 years ago,
335
00:25:44,020 --> 00:25:47,980
this whole stretch of coastline
was completely different.
336
00:25:47,980 --> 00:25:50,380
Since the end of the last ice age,
337
00:25:50,380 --> 00:25:52,980
sea levels have been rising
338
00:25:52,980 --> 00:25:54,540
and as they rise,
339
00:25:54,540 --> 00:25:57,380
flooded land gives way
to shallow seas.
340
00:26:00,900 --> 00:26:05,900
The sea surface was about
100 metres lower than it is today
341
00:26:05,900 --> 00:26:10,060
and this shallow-water ecosystem
used to be on dry land.
342
00:26:14,140 --> 00:26:16,340
And the sea hasn't stopped there.
343
00:26:16,340 --> 00:26:18,940
It continues to rise
344
00:26:18,940 --> 00:26:21,660
and threatens to flood the reef too,
345
00:26:21,660 --> 00:26:25,500
leaving it in the dark depths
of the seabed.
346
00:26:25,500 --> 00:26:29,700
This could have spelled the end
for the Great Barrier Reef
347
00:26:29,700 --> 00:26:31,580
but not yet.
348
00:26:31,580 --> 00:26:34,540
In the same way
that it recovers from cyclones,
349
00:26:34,540 --> 00:26:36,940
the reef builds up on itself,
350
00:26:36,940 --> 00:26:39,100
layer by layer.
351
00:26:39,100 --> 00:26:42,260
The dead coral skeletons of the past
are cemented together
352
00:26:42,260 --> 00:26:44,300
by colourful coralline algae.
353
00:26:46,540 --> 00:26:50,140
A living mortar that binds
the calcium reef together.
354
00:26:53,660 --> 00:26:57,620
From here, new life is brought
on the currents to colonise
355
00:26:57,620 --> 00:27:00,940
and the reef spreads ever upwards.
356
00:27:00,940 --> 00:27:03,380
Keeping up pace with the rising seas
357
00:27:03,380 --> 00:27:06,820
and creating the shallow-water
ecosystem that we see today.
358
00:27:09,420 --> 00:27:11,900
This exceptional process
not only ensures
359
00:27:11,900 --> 00:27:14,260
that the coral stays
near the surface
360
00:27:14,260 --> 00:27:17,620
so that its algae
can photosynthesise
361
00:27:17,620 --> 00:27:19,180
but, in doing so,
362
00:27:19,180 --> 00:27:22,380
it allows this whole shallow-water
ecosystem to exist.
363
00:27:25,340 --> 00:27:30,380
The Great Barrier Reef
is more than just coral and fish.
364
00:27:30,380 --> 00:27:35,300
It's a network of thousands of
islands, reefs and other habitats
365
00:27:35,300 --> 00:27:38,460
that allow animals
both large and small to prosper.
366
00:27:40,180 --> 00:27:42,180
The reef is remarkably resilient.
367
00:27:45,540 --> 00:27:49,980
Not only can it withstand some of
the most ferocious forces of nature
368
00:27:49,980 --> 00:27:53,220
but it has also managed
to exist in nutrient-poor waters
369
00:27:53,220 --> 00:27:55,220
that could otherwise be lifeless.
370
00:27:59,380 --> 00:28:03,420
But the reason this reef has got
bigger than any other on Earth
371
00:28:03,420 --> 00:28:05,820
is the massive
shallow-water platform
372
00:28:05,820 --> 00:28:08,060
of the Australian continental shelf,
373
00:28:09,420 --> 00:28:12,780
the great current
that runs right along the coast
374
00:28:12,780 --> 00:28:15,780
and the simple partnership
between a one-millimetre coral
375
00:28:15,780 --> 00:28:17,860
and a single-celled algae.
376
00:28:19,660 --> 00:28:23,620
These are the secrets
of the Great Barrier Reef.
30892
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