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In a far corner
of S oath-East Asia,
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00:00:42,628 --> 00:00:45,297
lies the Coral Triangle.
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00:00:48,842 --> 00:00:52,721
A cluster of the richest coral reefs,
in the world.
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00:00:58,644 --> 00:01:02,564
Undersea cities crammed full of life.
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00:01:09,529 --> 00:01:12,074
As in any crowded metropolis,
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00:01:12,532 --> 00:01:15,410
there is fierce rivalry for space,
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00:01:19,998 --> 00:01:21,333
for food
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00:01:26,338 --> 00:01:27,714
and for a partner.
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But the reef is also a place
full of opportunity.
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00:01:48,193 --> 00:01:49,361
A cuttlefish.
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00:02:06,586 --> 00:02:10,799
It specialises in hunting crabs.
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00:02:19,641 --> 00:02:23,103
But a large crab is a dangerous quarry.
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00:02:31,403 --> 00:02:33,488
It has powerful claws.
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00:02:37,617 --> 00:02:41,246
The cuttlefish, however,
has a remarkable talent.
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00:02:47,294 --> 00:02:50,797
Its skin contains millions
of pigment cells
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with which it can create
ever-changing colours
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00:02:53,675 --> 00:02:55,010
and patterns.
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00:03:04,811 --> 00:03:08,857
And that apparently hypnotises the crab.
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00:03:32,130 --> 00:03:33,799
A cuttlefish may be clever,
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00:03:34,341 --> 00:03:35,967
but a shark is bigger.
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00:03:38,845 --> 00:03:40,889
And it eats cuttlefish.
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Time to disappear.
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00:04:02,327 --> 00:04:03,829
Back to the hunt.
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00:04:06,998 --> 00:04:11,086
A new target,
but the same mesmerising technique.
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00:04:27,769 --> 00:04:32,357
For those that manage to establish
themselves in these bustling
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00:04:32,524 --> 00:04:33,900
undersea cities,
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00:04:34,192 --> 00:04:36,862
there can be great rewards.
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00:04:57,799 --> 00:05:01,219
Corals build themselves
homes of limestone,
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00:05:01,386 --> 00:05:04,723
in the warm, clear,
shallow seas of the Tropics.
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00:05:08,977 --> 00:05:11,646
Their reefs occupy less than one tenth
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of one percent of the ocean floor.
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Yet, they're home to a quarter
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of all known marine species.
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They are complex,
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infinitely variant structures,
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providing all kinds of homes
for their many residents,
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00:05:40,967 --> 00:05:42,511
from penthouse suites,
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00:05:44,471 --> 00:05:46,348
to backstreet dens.
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00:05:52,604 --> 00:05:55,440
Here, on Australia's Great Barrier Reef,
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a coral grouper lives
by hunting for small fish.
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00:06:05,992 --> 00:06:07,827
But how do you get a meal here,
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when you're too big
to squeeze into crevices?
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00:06:21,132 --> 00:06:24,511
And the grouper also has a rival,
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one which is highly intelligent,
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and seeks the same kind of prey.
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An octopus.
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It can reach into really narrow cracks.
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00:07:17,689 --> 00:07:19,024
Even so,
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its prey often escapes.
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What if they could work together?
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The grouper turns pale,
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00:07:59,314 --> 00:08:02,651
and tries to attract
the octopus's attention.
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00:08:08,406 --> 00:08:10,116
It performs a head stand.
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00:08:17,290 --> 00:08:20,460
Not only is the grouper signalling
to the octopus,
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00:08:20,835 --> 00:08:23,797
it's indicating
where the prey is hiding.
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00:08:37,644 --> 00:08:39,979
The octopus reaches inside.
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The fish take fright.
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00:08:49,322 --> 00:08:53,618
And swim straight into
the grouper's jaws.
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00:09:01,626 --> 00:09:04,295
Sometimes, the octopus gets the reward,
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00:09:05,797 --> 00:09:08,508
sometimes, the grouper does.
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Two very different species
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have discovered
that teamwork can bring success,
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00:09:20,729 --> 00:09:22,814
in reef city.
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00:09:39,998 --> 00:09:43,668
Teamwork, in fact,
is the very foundation of life
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on the reef.
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00:09:53,178 --> 00:09:57,265
The corals themselves
also rely on a partnership.
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00:09:58,725 --> 00:10:02,103
But one of a much more intimate kind.
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Corals are colonies
of anemone-like animals,
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polyps.
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00:10:17,118 --> 00:10:20,121
Some as small as grains of sand.
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00:10:23,082 --> 00:10:25,919
Living inside the tissues of each polyp,
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are minute plant-like cells,
invisible to the naked eye.
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00:10:37,222 --> 00:10:40,225
By day flourishing in tropical sunshine,
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00:10:40,600 --> 00:10:43,269
the plant-like cells provide the polyps
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with up to 90% of their food.
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00:10:59,744 --> 00:11:03,331
And when it's dark,
the polyps continue to feed
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00:11:03,665 --> 00:11:09,254
by using their tentacles to grab
edible particles drifting by.
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00:11:17,470 --> 00:11:21,349
The polyps also extract
calcium carbonate from the sea water,
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00:11:21,599 --> 00:11:25,603
and use it to build a stony housing
for themselves.
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00:11:28,773 --> 00:11:32,443
Coral colonies
can continue to grow for centuries.
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00:11:33,194 --> 00:11:34,779
Possibly millennia.
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And they can build structures
that can reach the size of a house.
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00:11:59,137 --> 00:12:02,640
The biggest of their cities,
is the Great Barrier Reef.
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It runs for over 7400 miles
along the coast of North East Australia.
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00:12:22,076 --> 00:12:26,664
Activity in coral reefs,
wherever they are, never ceases.
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00:12:29,000 --> 00:12:31,544
At dawn, the day shift begins.
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00:12:32,587 --> 00:12:37,175
Accompanied by a chorus
of submarine song,
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00:12:37,592 --> 00:12:42,013
created by fish, shrimps,
and other inhabitants of the reef.
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00:12:56,694 --> 00:12:59,864
Every resident in this city,
has its role.
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00:13:00,865 --> 00:13:03,201
Scavengers, like the sea cucumber,
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recycle the waste of others.
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00:13:08,206 --> 00:13:11,000
These parrot fish,
bite off chunks of coral
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00:13:11,084 --> 00:13:14,587
and crunch it
to extract the contents.
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00:13:27,475 --> 00:13:30,395
And then, excrete the rest as sand.
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00:13:46,953 --> 00:13:49,747
Green turtles, here in Borneo,
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pay regular visits
to a particular patch of coral.
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00:13:59,590 --> 00:14:04,512
This little female is up early
and one step ahead of the others.
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00:14:24,782 --> 00:14:29,287
Turtles travel long distances along
the reef in order to get here.
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00:14:33,124 --> 00:14:35,376
This is their destination.
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00:14:35,960 --> 00:14:37,462
Turtle Rock.
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Generations of visiting turtles
have worn a hollow in its top.
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00:15:02,987 --> 00:15:05,740
This is home to blennies
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00:15:06,866 --> 00:15:08,534
and surgeon fish.
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00:15:10,078 --> 00:15:15,249
They clean the visitors picking off
any algae, parasites and dead skin,
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that they can find.
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00:15:21,589 --> 00:15:24,509
Other client are close behind.
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00:15:32,683 --> 00:15:34,727
A queue is forming.
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00:15:51,953 --> 00:15:54,622
The big males barge their way in.
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00:16:10,888 --> 00:16:14,559
And the smaller female is forced out.
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00:16:23,609 --> 00:16:26,404
She takes a quick turn around the block,
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00:16:31,909 --> 00:16:33,452
while the others are squabbling.
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00:16:47,592 --> 00:16:49,969
And then, she sneaks back in.
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00:17:02,273 --> 00:17:05,193
So the cleaners get a nutritious meal,
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and their customers are freed of
their parasites and other encumbrances.
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00:17:15,995 --> 00:17:20,875
And it's now thought, that a spot
of pampering at a cleaning station
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may even reduce stress.
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00:17:39,727 --> 00:17:43,314
The lands of the Middle East
are so hot and dry,
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that much of their surface
is almost lifeless.
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00:17:48,569 --> 00:17:50,655
But here in the Red Sea,
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Coral Reefs flourish wonderfully.
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00:17:56,911 --> 00:17:58,412
The waters offshore,
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are almost as rich
in life as a rainforest.
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00:18:05,044 --> 00:18:07,255
And some animals come to the reefs
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00:18:07,505 --> 00:18:10,716
simply for rest and relaxation.
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00:18:31,279 --> 00:18:33,823
The family of bottlenose dolphins
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are resting on the reef
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00:18:35,700 --> 00:18:38,286
after a night's feeding offshore.
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00:18:59,307 --> 00:19:02,143
Whilst the adult and their babies sleep,
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00:19:03,936 --> 00:19:07,231
the adolescents set of the explore...
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00:19:11,277 --> 00:19:13,904
...and they appear to make up games.
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00:19:23,622 --> 00:19:26,584
You might call this one,
"Catch the coral."
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The rules aren't entirely clear.
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00:19:52,860 --> 00:19:55,613
They pick up different bits
of broken coral,
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00:19:58,699 --> 00:19:59,992
and drop them.
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00:20:02,328 --> 00:20:04,038
Some fall fast.
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00:20:08,125 --> 00:20:10,127
Others sink more slowly.
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00:20:28,479 --> 00:20:30,898
And some seem to be descending in a way
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that pleases everybody.
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00:20:48,999 --> 00:20:54,713
Only the most successful city residents
can afford the luxury of playing games.
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00:20:57,174 --> 00:20:59,885
But, such games do that their value.
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They may help the youngsters develop
the coordination and the agility
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that they will need when
they start hunting in the open sea.
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00:21:20,614 --> 00:21:24,034
Every reef
has a sharply defined boundary.
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00:21:26,871 --> 00:21:28,706
Its city walls.
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00:21:34,211 --> 00:21:37,381
On the outer side is the drop off.
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00:21:38,424 --> 00:21:42,136
These ramparts protect the city
from the ocean waves.
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00:21:46,557 --> 00:21:50,436
But twice a day, the walls are covered
by the incoming tide.
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00:22:00,821 --> 00:22:05,910
In the Bahamas, the rush of the water
creates a truly strange phenomenon.
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00:22:18,005 --> 00:22:21,967
Seamen once told tales
of a giant sea monster,
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00:22:22,134 --> 00:22:24,637
lurking here deep inside the reef,
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00:22:25,429 --> 00:22:28,265
that would drag sailors to their doom.
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00:22:47,284 --> 00:22:53,123
Today, we know it is in fact a whirlpool
created by the incoming tide
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rushing over deep coral caves.
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These currents bring in fresh supplies
of microscopic food to the reef
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from the open ocean.
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00:23:11,684 --> 00:23:15,145
And in the Maldives,
on the biggest tides,
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one particular coral lagoon
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become so flooded with plankton,
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00:23:22,486 --> 00:23:26,156
that it attracts hundreds
of ocean giants.
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00:23:28,993 --> 00:23:30,828
Manta Rays.
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00:23:32,705 --> 00:23:35,040
With three-metre wing spans.
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With their huge sloth
like mouths wide open
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00:23:49,930 --> 00:23:52,057
they filter out the plankton.
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00:24:01,734 --> 00:24:05,362
And the mantas create
a vortex of their own
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that further concentrates their food.
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00:24:52,826 --> 00:24:57,581
This behaviour has been called
the manta cyclone.
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Then the tide changes,
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00:25:11,804 --> 00:25:13,931
and the supply of food is cut of.
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00:25:17,768 --> 00:25:20,312
The mantas leave the lagoon.
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00:25:30,280 --> 00:25:35,119
Life on the sheltered side of the reef
is tranquil and peaceful.
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In these suburbs,
any creature wishing to escape
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from the bustling crowds of reef city,
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can find plenty of space.
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00:25:53,679 --> 00:25:54,847
On the other hand,
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there is nowhere to hide.
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That, at night,
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makes it a dangerous place.
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00:26:16,160 --> 00:26:19,663
Nocturnal predators,
such as this lion fish,
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patrol the reef edge.
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00:26:54,698 --> 00:26:57,868
The hunter has become the hunted.
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00:27:17,763 --> 00:27:19,056
A hobbit,
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a giant carnivorous worm
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with jaws as sharp as daggers.
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00:27:31,068 --> 00:27:35,906
It has an ancestry that stretches back
more than four hundred million years.
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00:27:44,122 --> 00:27:46,166
It's a metre long.
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00:28:07,312 --> 00:28:10,774
It tastes for scent.
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00:28:17,531 --> 00:28:20,117
And feels for movement.
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00:29:06,705 --> 00:29:11,710
Dawn, and with light,
the reef becomes a safer place.
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Little bream return to foraging.
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00:29:27,517 --> 00:29:29,686
The bobbit might still be hungry.
191
00:29:32,564 --> 00:29:36,276
But now in daylight
the odds have shifted.
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00:29:39,571 --> 00:29:41,907
The bream can see the bobbit.
193
00:29:46,954 --> 00:29:48,789
Instead of retreating,
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they join together to blow away
the sand covering the worm.
195
00:30:00,050 --> 00:30:04,388
So, taking away
its advantage of surprise.
196
00:30:10,143 --> 00:30:12,729
By revealing the [rabbit's hiding place,
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00:30:12,938 --> 00:30:15,482
they will all be able
to feed more safely.
198
00:30:19,736 --> 00:30:21,780
But it pays to remember
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00:30:31,748 --> 00:30:33,500
there is a bobbit about.
200
00:30:46,596 --> 00:30:48,765
Out here, on the sand flats,
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there is safe accommodation for some.
202
00:31:01,611 --> 00:31:07,200
The family of saddleback clownfish
have found an excellent home.
203
00:31:10,037 --> 00:31:13,790
The tentacles
of this carpet anemone can kill.
204
00:31:16,626 --> 00:31:19,337
But the clownfish
are immune to the poison,
205
00:31:25,969 --> 00:31:28,055
so they can shelter from danger.
206
00:31:33,226 --> 00:31:37,814
In return, the fish keep the anemone
clean of debris.
207
00:31:42,861 --> 00:31:44,529
As with all clownfish,
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00:31:44,654 --> 00:31:47,991
the family is ruled by a big female.
209
00:31:49,993 --> 00:31:53,705
Her white face marks her out
as the boss.
210
00:31:59,169 --> 00:32:01,922
The diminutive male
has to prove his worth,
211
00:32:02,589 --> 00:32:04,716
so he works tirelessly,
212
00:32:05,175 --> 00:32:09,012
removing debris and generally keeping
on top of the housework.
213
00:32:31,284 --> 00:32:35,205
His greatest challenge
is to find a safe place
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00:32:35,372 --> 00:32:37,916
where the boss can lay her eggs.
215
00:32:41,378 --> 00:32:44,923
But there's nothing solid here
for the female to lay them on.
216
00:32:51,388 --> 00:32:53,640
A nearby shell could be the solution.
217
00:33:05,110 --> 00:33:09,239
If only he can move it
to the protection of the anemone.
218
00:33:17,581 --> 00:33:18,748
Too heavy.
219
00:33:23,128 --> 00:33:25,755
Besides, it has a mind of its own.
220
00:33:30,010 --> 00:33:31,261
The hermit crab.
221
00:33:40,770 --> 00:33:43,023
But out here, twice a day,
222
00:33:43,982 --> 00:33:47,110
the anemone is swept by tidal currents,
223
00:33:47,277 --> 00:33:49,529
and they bring in new opportunities.
224
00:33:52,782 --> 00:33:54,659
An old plastic bottle.
225
00:33:59,372 --> 00:34:00,790
Perhaps, this will do.
226
00:34:09,132 --> 00:34:10,467
Not heavy enough.
227
00:34:23,480 --> 00:34:24,814
A coconut shell.
228
00:34:30,570 --> 00:34:32,489
It looks just right.
229
00:34:33,365 --> 00:34:35,825
But it's a long way from home.
230
00:34:55,345 --> 00:34:58,056
And he can't move it by himself.
231
00:35:10,777 --> 00:35:13,613
So the pair now work together.
232
00:35:56,906 --> 00:35:59,909
A little adjustment
to the anemone's tentacles,
233
00:35:59,993 --> 00:36:01,786
in order to clear a space for it.
234
00:36:05,081 --> 00:36:07,250
And the shell is tucked in.
235
00:36:13,173 --> 00:36:14,674
The female lays.
236
00:36:15,425 --> 00:36:17,927
A safe nursery at last.
237
00:36:34,611 --> 00:36:38,365
He has proved himself worthy
to father her young.
238
00:36:38,948 --> 00:36:40,492
And he fertilizes them.
239
00:36:45,288 --> 00:36:48,708
Now he will meticulously tend the eggs,
240
00:36:56,800 --> 00:36:59,719
keeping them clean
and healthy until they hatch
241
00:37:01,137 --> 00:37:02,555
in 10 days time.
242
00:37:17,195 --> 00:37:22,659
Reef creatures go to great lengths to
give their young a head start in life.
243
00:37:32,043 --> 00:37:33,837
And nowhere more so
244
00:37:34,045 --> 00:37:37,507
than on the remotest reefs in the world.
245
00:37:40,009 --> 00:37:41,719
French Polynesia,
246
00:37:42,178 --> 00:37:45,056
the very heart of the South Pacific.
247
00:37:52,063 --> 00:37:54,149
Protected by their isolation,
248
00:37:54,232 --> 00:37:58,027
some of the reefs here,
are still virtually pristine.
249
00:38:08,246 --> 00:38:13,543
This marbled grouper has made it
in the city and reached adulthood.
250
00:38:14,878 --> 00:38:17,547
Now, it's the time to mate.
251
00:38:19,549 --> 00:38:25,263
To find a partner, he must head
to the most dangerous part of this reef:
252
00:38:26,556 --> 00:38:27,599
The drop off.
253
00:38:33,104 --> 00:38:36,316
Patrolled by grey reef sharks,
254
00:38:39,569 --> 00:38:40,820
hundreds of them.
255
00:38:48,119 --> 00:38:49,662
They seem to be resting,
256
00:38:52,790 --> 00:38:53,958
for now.
257
00:39:04,928 --> 00:39:09,307
Thousands of other groupers
have gathered on the seabed below.
258
00:39:26,616 --> 00:39:29,953
The females are almost bursting
with eggs.
259
00:39:35,041 --> 00:39:36,459
But to mate with one,
260
00:39:37,794 --> 00:39:41,548
he must first get through the crowd
of other waiting males.
261
00:39:43,800 --> 00:39:47,387
And they all have the same thing
on their minds.
262
00:39:54,978 --> 00:39:58,815
They jostle to get as close as possible
to a female.
263
00:40:27,677 --> 00:40:30,680
This male may have
secured pole position,
264
00:40:31,764 --> 00:40:35,268
but the female won't release
her eggs for him to fertilize,
265
00:40:35,893 --> 00:40:38,354
until conditions are just right.
266
00:40:51,367 --> 00:40:54,370
Now the sharks begin to close in,
267
00:40:55,121 --> 00:40:58,958
sensing that
the critical moment is approaching.
268
00:41:26,903 --> 00:41:29,572
The tide is beginning to turn.
269
00:41:32,617 --> 00:41:35,286
This could be the moment to spawn.
270
00:41:43,419 --> 00:41:47,423
Suddenly, the females rush up
towards the surface
271
00:41:47,590 --> 00:41:50,259
releasing their clouds
of eggs as they go.
272
00:41:52,428 --> 00:41:56,516
The males pursue them,
simultaneously releasing their sperm.
273
00:42:13,282 --> 00:42:16,786
It's an act
the groupers seem prepared to die for.
274
00:42:21,290 --> 00:42:24,460
It's now or never.
275
00:43:14,218 --> 00:43:15,762
The fertilized eggs,
276
00:43:16,179 --> 00:43:17,722
will now be swept away
277
00:43:18,556 --> 00:43:22,518
from the many hungry mouths
of the reef dwellers.
278
00:43:34,697 --> 00:43:38,117
Most of the billions of eggs
that cloud the sea,
279
00:43:38,367 --> 00:43:39,702
will be eaten.
280
00:43:41,871 --> 00:43:43,122
But a few,
281
00:43:43,247 --> 00:43:45,541
a tiny but crucial minority,
282
00:43:46,375 --> 00:43:48,252
will find another reef
283
00:43:48,920 --> 00:43:50,588
and make it their home.
284
00:44:05,061 --> 00:44:09,232
But today's coral reefs
are facing a new threat.
285
00:44:14,403 --> 00:44:16,572
The seas are warming.
286
00:44:20,409 --> 00:44:23,287
A rise in temperature
of just one for two degrees
287
00:44:23,788 --> 00:44:25,331
for just a few weeks,
288
00:44:25,998 --> 00:44:31,921
can be enough to cause the coral polyps
to eject their plant-like cells.
289
00:44:40,096 --> 00:44:44,183
When that happens,
the corals lose both their colour,
290
00:44:44,767 --> 00:44:47,103
and their main source of food.
291
00:44:54,777 --> 00:44:57,363
If the high temperatures are sustained,
292
00:44:58,197 --> 00:45:00,616
coral, bleached in this way,
293
00:45:01,033 --> 00:45:02,702
is likely to die.
294
00:45:09,375 --> 00:45:13,880
In recent years, it's thought that
half the world's coral reefs
295
00:45:14,171 --> 00:45:16,132
have been affected by bleaching.
296
00:45:23,639 --> 00:45:26,559
Including, since 2016,
297
00:45:26,809 --> 00:45:30,229
around two thirds
of the shallow water corals,
298
00:45:30,396 --> 00:45:32,982
on Australia's Great Barrier Reef.
299
00:45:46,203 --> 00:45:49,415
These once crowded submarine cities,
300
00:45:51,500 --> 00:45:52,668
are reduced
301
00:45:53,252 --> 00:45:54,837
to bleak ruins.
302
00:45:57,340 --> 00:46:00,843
and many of their inhabitants,
left homeless.
303
00:46:16,359 --> 00:46:20,404
Some scientists predict
that by the end of the century,
304
00:46:21,864 --> 00:46:24,033
coral reef cities as we know them,
305
00:46:25,034 --> 00:46:27,203
could be a thing of the past.
306
00:46:44,387 --> 00:46:49,475
Is there any future for these most
precious of ocean treasures?
307
00:46:58,401 --> 00:47:03,155
Well, that ultimately depends
on how fast they heat up,
308
00:47:03,447 --> 00:47:05,783
and how warm the seas become.
309
00:47:10,079 --> 00:47:11,914
And there is a glimmer of hope,
310
00:47:12,289 --> 00:47:16,252
because of the way
the corals reproduce themselves.
311
00:47:23,259 --> 00:47:25,594
On one special night of the year,
312
00:47:26,345 --> 00:47:30,433
the full moon triggers
an extraordinary event:
313
00:47:49,160 --> 00:47:51,829
The spawning of the coral.
314
00:48:01,630 --> 00:48:06,302
With extraordinary synchrony,
entire reefs reproduce.
315
00:48:23,152 --> 00:48:26,197
Billions of fertilized eggs drift away
316
00:48:29,366 --> 00:48:31,702
carried by the ocean currents.
317
00:48:38,501 --> 00:48:41,879
And it's not just the corals that spawn,
318
00:48:43,881 --> 00:48:47,218
so do many other residents of the reef.
319
00:48:53,015 --> 00:48:55,184
A whole range of young
320
00:48:55,434 --> 00:48:57,520
are swept through the oceans,
321
00:48:58,270 --> 00:49:01,065
ready to settle on a vacant site,
322
00:49:01,398 --> 00:49:05,194
and bring back into existence
the complex community,
323
00:49:05,611 --> 00:49:07,738
that is a coral reef.
324
00:49:20,042 --> 00:49:24,088
We may not know what the future
hold for our seas,
325
00:49:27,383 --> 00:49:30,219
but coral reefs can regenerate.
326
00:49:30,928 --> 00:49:33,639
As long as some reefs survive,
327
00:49:35,266 --> 00:49:38,102
some hope can remain.
328
00:49:51,157 --> 00:49:55,161
Next time, we head
into the vastness of the open ocean.
329
00:49:58,205 --> 00:50:02,293
To survive in this blue wilderness,
some are fast,
330
00:50:03,169 --> 00:50:05,504
others use deadly strategies,
331
00:50:06,881 --> 00:50:10,926
and a few rely on the closeness
of their families.
27555
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