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In a far corner of South-East Asia,
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00:00:42,627 --> 00:00:45,296
lies the Coral Triangle.
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00:00:48,841 --> 00:00:52,720
A cluster of the richest coral reefs,
in the world.
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Undersea cities crammed full of life.
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00:01:09,528 --> 00:01:12,073
As in any crowded metropolis,
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00:01:12,531 --> 00:01:15,409
there is fierce rivalry for space,
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for food
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00:01:26,337 --> 00:01:27,713
and for a partner.
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But the reef is also a place
full of opportunity.
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00:01:48,192 --> 00:01:49,360
A cuttlefish.
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00:02:06,585 --> 00:02:10,798
It specialises in hunting crabs.
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00:02:19,640 --> 00:02:23,102
But a large crab is a dangerous quarry.
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00:02:31,402 --> 00:02:33,487
It has powerful claws.
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00:02:37,616 --> 00:02:41,245
The cuttlefish, however,
has a remarkable talent.
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00:02:47,293 --> 00:02:50,796
Its skin contains millions
of pigment cells
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with which it can create
ever-changing colours
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00:02:53,674 --> 00:02:55,009
and patterns.
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00:03:04,810 --> 00:03:08,856
And that apparently hypnotises the crab.
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A cuttlefish may be clever,
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but a shark is bigger.
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And it eats cuttlefish.
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Time to disappear.
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Back to the hunt.
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00:04:06,997 --> 00:04:11,085
A new target,
but the same mesmerising technique.
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00:04:27,768 --> 00:04:32,356
For those that manage to establish
themselves in these bustling
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00:04:32,523 --> 00:04:33,899
undersea cities,
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there can be great rewards.
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00:04:57,798 --> 00:05:01,218
Corals build themselves
homes of limestone,
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00:05:01,385 --> 00:05:04,722
in the warm, clear,
shallow seas of the Tropics.
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00:05:08,976 --> 00:05:11,645
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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00:05:40,966 --> 00:05:42,510
from penthouse suites,
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00:05:44,470 --> 00:05:46,347
to backstreet dens.
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00:05:52,603 --> 00:05:55,439
Here, on Australia's Great Barrier Reef,
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a coral grouper lives
by hunting for small fish.
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00:06:05,991 --> 00:06:07,826
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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00:06:21,131 --> 00:06:24,510
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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00:07:04,925 --> 00:07:08,929
It can reach into really narrow cracks.
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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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00:07:59,313 --> 00:08:02,650
and tries to attract
the octopus's attention.
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00:08:08,405 --> 00:08:10,115
It performs a head stand.
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00:08:17,289 --> 00:08:20,459
Not only is the grouper signalling
to the octopus,
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00:08:20,834 --> 00:08:23,796
it's indicating
where the prey is hiding.
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00:08:37,643 --> 00:08:39,978
The octopus reaches inside.
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The fish take fright.
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And swim straight into
the grouper's jaws.
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00:09:01,625 --> 00:09:04,294
Sometimes, the octopus gets the reward,
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00:09:05,796 --> 00:09:08,507
sometimes, the grouper does.
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00:09:14,304 --> 00:09:16,473
Two very different species
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have discovered
that teamwork can bring success,
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00:09:20,728 --> 00:09:22,813
in reef city.
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00:09:39,997 --> 00:09:43,667
Teamwork, in fact,
is the very foundation of life
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on the reef
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The corals themselves
also rely on a partnership.
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00:09:58,724 --> 00:10:02,102
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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00:10:17,117 --> 00:10:20,120
Some as small as grains of sand.
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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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By day flourishing in tropical sunshine,
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the plant-like cells provide the polyps
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with up to 90% of their food.
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00:10:59,743 --> 00:11:03,330
And when it's dark,
the polyps continue to feed
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00:11:03,664 --> 00:11:09,253
by using their tentacles to grab
edible particles drifting by.
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00:11:17,469 --> 00:11:21,348
The polyps also extract
calcium carbonate from the sea water,
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00:11:21,598 --> 00:11:25,602
and use it to build a stony housing
for themselves.
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00:11:28,772 --> 00:11:32,442
Coral colonies
can continue to grow for centuries.
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00:11:33,193 --> 00:11:34,778
Possibly millennia.
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And they can build structures
that can reach the size of a house.
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00:11:59,136 --> 00:12:02,639
The biggest of their cities,
is the Great Barrier Reef
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It runs for over1400 miles
along the coast of North East Australia.
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Activity in coral reefs,
wherever they are, never ceases.
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00:12:28,999 --> 00:12:31,543
At dawn, the day shift begins.
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00:12:32,586 --> 00:12:37,174
Accompanied by a chorus
of submarine song,
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00:12:37,591 --> 00:12:42,012
created by fish, shrimps,
and other inhabitants of the reef
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00:12:56,693 --> 00:12:59,863
Every resident in this city,
has its role.
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00:13:00,864 --> 00:13:03,200
Scavengers, like the sea cucumber,
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recycle the waste of others.
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00:13:08,205 --> 00:13:10,999
These parrot fish,
bite off chunks of coral
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00:13:11,083 --> 00:13:14,586
and crunch it
to extract the contents.
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00:13:27,474 --> 00:13:30,394
And then, excrete the rest as sand.
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00:13:46,952 --> 00:13:49,746
Green turtles, here in Borneo,
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pay regular visits
to a particular patch of coral.
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00:13:59,589 --> 00:14:04,511
This little female is up early
and one step ahead of the others.
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00:14:24,781 --> 00:14:29,286
Turtles travel long distances along
the reef in order to get here.
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00:14:33,123 --> 00:14:35,375
This is their destination.
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00:14:35,959 --> 00:14:37,461
Turtle Rock.
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Generations of visiting turtles
have worn a hollow in its top.
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00:15:02,986 --> 00:15:05,739
This is home to blennies
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00:15:06,865 --> 00:15:08,533
and surgeon fish.
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00:15:10,077 --> 00:15:15,248
They clean the visitors picking off
any algae, parasites and deadskin,
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that they can find.
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00:15:21,588 --> 00:15:24,508
Other client are close behind.
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00:15:32,682 --> 00:15:34,726
A queue is forming.
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00:15:51,952 --> 00:15:54,621
The big males barge their way in.
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00:16:10,887 --> 00:16:14,558
And the smaller female is forced out.
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00:16:23,608 --> 00:16:26,403
She takes a quick turn around the block,
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00:16:31,908 --> 00:16:33,451
while the others are squabbling.
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00:16:47,591 --> 00:16:49,968
And then, she sneaks back in.
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00:17:02,272 --> 00:17:05,192
So the cleaners get a nutritious meal,
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00:17:05,859 --> 00:17:10,447
and their customers are freed of
their parasites and other encumbrances.
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00:17:15,994 --> 00:17:20,874
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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00:17:39,726 --> 00:17:43,313
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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00:17:48,568 --> 00:17:50,654
But here in the Red Sea,
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Coral Reefs flourish wonderfully.
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00:17:56,910 --> 00:17:58,411
The waters offshore,
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are almost as rich
in life as a rainforest.
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00:18:05,043 --> 00:18:07,254
And some animals come to the reefs
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00:18:07,504 --> 00:18:10,715
simply for rest and relaxation.
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00:18:31,278 --> 00:18:33,822
The family of bottlenose dolphins
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are resting on the reef
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00:18:35,699 --> 00:18:38,285
after a night's feeding offshore.
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00:18:59,306 --> 00:19:02,142
Whilst the adult and their babies sleep,
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00:19:03,935 --> 00:19:07,230
the adolescents set of the explore...
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00:19:11,276 --> 00:19:13,903
...and they appear to make up games.
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00:19:23,621 --> 00:19:26,583
You might call this one,
"Catch the coral."
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The rules aren't entirely clear.
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00:19:52,859 --> 00:19:55,612
They pick up different bits
of broken coral,
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00:19:58,698 --> 00:19:59,991
and drop them.
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00:20:02,327 --> 00:20:04,037
Some fall fast.
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00:20:08,124 --> 00:20:10,126
Others sink more slowly.
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00:20:28,478 --> 00:20:30,897
And some seem to be descending in a way
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that pleases everybody.
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00:20:48,998 --> 00:20:54,712
Only the most successful city residents
can afford the luxury of playing games.
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00:20:57,173 --> 00:20:59,884
But, such games do that their value.
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00:21:00,260 --> 00:21:04,180
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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00:21:20,613 --> 00:21:24,033
Every reef
has a sharply defined boundary.
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00:21:26,870 --> 00:21:28,705
Its city walls.
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00:21:34,210 --> 00:21:37,380
On the outer side is the drop off
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00:21:38,423 --> 00:21:42,135
These ramparts protect the city
from the ocean waves.
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00:21:46,556 --> 00:21:50,435
But twice a day, the walls are covered
by the incoming tide.
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00:22:00,820 --> 00:22:05,909
In the Bahamas, the rush of the water
creates a truly strange phenomenon.
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00:22:18,004 --> 00:22:21,966
Seamen once told tales
of a giant sea monster,
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00:22:22,133 --> 00:22:24,636
lurking here deep inside the reef,
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00:22:25,428 --> 00:22:28,264
that would drag sailors to their doom.
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00:22:47,283 --> 00:22:53,122
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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00:23:01,798 --> 00:23:06,469
These currents bring in fresh supplies
of microscopic food to the reef
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00:23:06,636 --> 00:23:08,137
from the open ocean.
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00:23:11,683 --> 00:23:15,144
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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00:23:22,485 --> 00:23:26,155
that it attracts hundreds
of ocean giants.
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00:23:28,992 --> 00:23:30,827
Manta Rays.
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00:23:32,704 --> 00:23:35,039
With three-metre wing spans.
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00:23:45,008 --> 00:23:48,011
With their huge sloth
like mouths wide open
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00:23:49,929 --> 00:23:52,056
they filter out the plankton.
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00:24:01,733 --> 00:24:05,361
And the mantas create
a vortex of their own
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that further concentrates their food.
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00:24:52,825 --> 00:24:57,580
This behaviour has been called
the manta cyclone.
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Then the tide changes,
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00:25:11,803 --> 00:25:13,930
and the supply of food is cut of
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00:25:17,767 --> 00:25:20,311
The mantas leave the lagoon.
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00:25:30,279 --> 00:25:35,118
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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00:25:53,678 --> 00:25:54,846
On the other hand,
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there is nowhere to hide.
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00:26:05,356 --> 00:26:06,649
That, at night,
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makes it a dangerous place.
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00:26:16,159 --> 00:26:19,662
Nocturnal predators,
such as this lion fish,
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patrol the reef edge.
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00:26:54,697 --> 00:26:57,867
The hunter has become the hunted.
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00:27:17,762 --> 00:27:19,055
A bobbit,
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a giant carnivorous worm
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with jaws as sharp as daggers.
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00:27:31,067 --> 00:27:35,905
It has an ancestry that stretches back
more than four hundred million years.
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00:27:44,121 --> 00:27:46,165
It's a metre long.
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00:28:07,311 --> 00:28:10,773
It tastes for scent.
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00:28:17,530 --> 00:28:20,116
And feels for movement.
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00:29:06,704 --> 00:29:11,709
Dawn, and with light,
the reef becomes a safer place.
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00:29:15,338 --> 00:29:17,840
Little bream return to foraging.
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00:29:27,516 --> 00:29:29,685
The bobbit might still be hungry.
191
00:29:32,563 --> 00:29:36,275
But now in daylight
the odds have shifted.
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00:29:39,570 --> 00:29:41,906
The bream can see the bobbit.
193
00:29:46,953 --> 00:29:48,788
Instead of retreating,
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they join together to blow away
the sand covering the worm.
195
00:30:00,049 --> 00:30:04,387
So, taking away
its advantage of surprise.
196
00:30:10,142 --> 00:30:12,728
By revealing the bobbit's hiding place,
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00:30:12,937 --> 00:30:15,481
they will all be able
to feed more safely.
198
00:30:19,735 --> 00:30:21,779
But it pays to remember
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00:30:31,747 --> 00:30:33,499
there is a bobbit about.
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00:30:46,595 --> 00:30:48,764
Out here, on the sand flats,
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00:30:49,015 --> 00:30:51,976
there is safe accommodation for some.
202
00:31:01,610 --> 00:31:07,199
The family of saddleback clownfish
have found an excellent home.
203
00:31:10,036 --> 00:31:13,789
The tentacles
of this carpet anemone can kill.
204
00:31:16,625 --> 00:31:19,336
But the clownfish
are immune to the poison,
205
00:31:25,968 --> 00:31:28,054
so they can shelter from danger.
206
00:31:33,225 --> 00:31:37,813
In return, the fish keep the anemone
clean of debris.
207
00:31:42,860 --> 00:31:44,528
As with all clownfish,
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00:31:44,653 --> 00:31:47,990
the family is ruled by a big female.
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00:31:49,992 --> 00:31:53,704
Her white face marks her out
as the boss.
210
00:31:59,168 --> 00:32:01,921
The diminutive male
has to prove his worth,
211
00:32:02,588 --> 00:32:04,715
so he works tirelessly,
212
00:32:05,174 --> 00:32:09,011
removing debris and generally keeping
on top of the housework.
213
00:32:31,283 --> 00:32:35,204
His greatest challenge
is to find a safe place
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00:32:35,371 --> 00:32:37,915
where the boss can lay her eggs.
215
00:32:41,377 --> 00:32:44,922
But there's nothing solid here
for the female to lay them on.
216
00:32:51,387 --> 00:32:53,639
A nearby shell could be the solution.
217
00:33:05,109 --> 00:33:09,238
If only he can move it
to the protection of the anemone.
218
00:33:17,580 --> 00:33:18,747
Too heavy.
219
00:33:23,127 --> 00:33:25,754
Besides, it has a mind of its own.
220
00:33:30,009 --> 00:33:31,260
The hermit crab.
221
00:33:40,769 --> 00:33:43,022
But out here, twice a day,
222
00:33:43,981 --> 00:33:47,109
the anemone is swept by tidal currents,
223
00:33:47,276 --> 00:33:49,528
and they bring in new opportunities.
224
00:33:52,781 --> 00:33:54,658
An old plastic bottle.
225
00:33:59,371 --> 00:34:00,789
Perhaps, this will do.
226
00:34:09,131 --> 00:34:10,466
Not heavy enough.
227
00:34:23,479 --> 00:34:24,813
A coconut shell.
228
00:34:30,569 --> 00:34:32,488
It looks just right.
229
00:34:33,364 --> 00:34:35,824
But it's a long way from home.
230
00:34:55,344 --> 00:34:58,055
And he can't move it by himself
231
00:35:10,776 --> 00:35:13,612
So the pair now work together.
232
00:35:56,905 --> 00:35:59,908
A little adjustment
to the anemone's tentacles,
233
00:35:59,992 --> 00:36:01,785
in order to clear a space for it.
234
00:36:05,080 --> 00:36:07,249
And the shell is tucked in.
235
00:36:13,172 --> 00:36:14,673
The female lays.
236
00:36:15,424 --> 00:36:17,926
A safe nursery at last.
237
00:36:34,610 --> 00:36:38,364
He has proved himself worthy
to father her young.
238
00:36:38,947 --> 00:36:40,491
And he fertilizes them.
239
00:36:45,287 --> 00:36:48,707
Now he will meticulously tend the eggs,
240
00:36:56,799 --> 00:36:59,718
keeping them clean
and healthy until they hatch
241
00:37:01,136 --> 00:37:02,554
in 10 days time.
242
00:37:17,194 --> 00:37:22,658
Reef creatures go to great lengths to
give their young a head start in life.
243
00:37:32,042 --> 00:37:33,836
And nowhere more so
244
00:37:34,044 --> 00:37:37,506
than on the remotest reefs in the world.
245
00:37:40,008 --> 00:37:41,718
French Polynesia,
246
00:37:42,177 --> 00:37:45,055
the very heart of the South Pacific.
247
00:37:52,062 --> 00:37:54,148
Protected by their isolation,
248
00:37:54,231 --> 00:37:58,026
some of the reefs here,
are still virtually pristine.
249
00:38:08,245 --> 00:38:13,542
This marbled grouper has made it
in the city and reached adulthood.
250
00:38:14,877 --> 00:38:17,546
Now, it's the time to mate.
251
00:38:19,548 --> 00:38:25,262
To find a partner, he must head
to the most dangerous part of this reef:
252
00:38:26,555 --> 00:38:27,598
The drop off
253
00:38:33,103 --> 00:38:36,315
Patrolled by grey reef sharks,
254
00:38:39,568 --> 00:38:40,819
hundreds of them.
255
00:38:48,118 --> 00:38:49,661
They seem to be resting,
256
00:38:52,789 --> 00:38:53,957
for now.
257
00:39:04,927 --> 00:39:09,306
Thousands of other groupers
have gathered on the seabed below.
258
00:39:26,615 --> 00:39:29,952
The females are almost bursting
with eggs.
259
00:39:35,040 --> 00:39:36,458
But to mate with one,
260
00:39:37,793 --> 00:39:41,547
he must first get through the crowd
of other waiting males.
261
00:39:43,799 --> 00:39:47,386
And they all have the same thing
on their minds.
262
00:39:54,977 --> 00:39:58,814
They jostle to get as close as possible
to a female.
263
00:40:27,676 --> 00:40:30,679
This male may have
secured pole position,
264
00:40:31,763 --> 00:40:35,267
but the female won't release
her eggs for him to fertilize,
265
00:40:35,892 --> 00:40:38,353
until conditions are just right.
266
00:40:51,366 --> 00:40:54,369
Now the sharks begin to close in,
267
00:40:55,120 --> 00:40:58,957
sensing that
the critical moment is approaching.
268
00:41:26,902 --> 00:41:29,571
The tide is beginning to turn.
269
00:41:32,616 --> 00:41:35,285
This could be the moment to spawn.
270
00:41:43,418 --> 00:41:47,422
Suddenly, the females rush up
towards the surface
271
00:41:47,589 --> 00:41:50,258
releasing their clouds
of eggs as they go.
272
00:41:52,427 --> 00:41:56,515
The males pursue them,
simultaneously releasing their sperm.
273
00:42:13,281 --> 00:42:16,785
It's an act
the groupers seem prepared to die for.
274
00:42:21,289 --> 00:42:24,459
It's now or never.
275
00:43:14,217 --> 00:43:15,761
The fertilized eggs,
276
00:43:16,178 --> 00:43:17,721
will now be swept away
277
00:43:18,555 --> 00:43:22,517
from the many hungry mouths
of the reef dwellers.
278
00:43:34,696 --> 00:43:38,116
Most of the billions of eggs
that cloud the sea,
279
00:43:38,366 --> 00:43:39,701
will be eaten.
280
00:43:41,870 --> 00:43:43,121
But a few,
281
00:43:43,246 --> 00:43:45,540
a tiny but crucial minority,
282
00:43:46,374 --> 00:43:48,251
will find another reef
283
00:43:48,919 --> 00:43:50,587
and make it their home.
284
00:44:05,060 --> 00:44:09,231
But today's coral reefs
are facing a new threat.
285
00:44:14,402 --> 00:44:16,571
The seas are warming.
286
00:44:20,408 --> 00:44:23,286
A rise in temperature
of Just one for two degrees
287
00:44:23,787 --> 00:44:25,330
for just a few weeks,
288
00:44:25,997 --> 00:44:31,920
can be enough to cause the coral polyps
to eject their plant-like cells.
289
00:44:40,095 --> 00:44:44,182
When that happens,
the corals lose both their colour,
290
00:44:44,766 --> 00:44:47,102
and their main source of food.
291
00:44:54,776 --> 00:44:57,362
If the high temperatures are sustained,
292
00:44:58,196 --> 00:45:00,615
coral, bleached in this way,
293
00:45:01,032 --> 00:45:02,701
is likely to die.
294
00:45:09,374 --> 00:45:13,879
In recent years, it's thought that
half the world's coral reefs
295
00:45:14,170 --> 00:45:16,131
have been affected by bleaching.
296
00:45:23,638 --> 00:45:26,558
Including, since 2016,
297
00:45:26,808 --> 00:45:30,228
around two thirds
of the shallow water corals,
298
00:45:30,395 --> 00:45:32,981
on Australia's Great Barrier Reef
299
00:45:46,202 --> 00:45:49,414
These once crowded submarine cities,
300
00:45:51,499 --> 00:45:52,667
are reduced
301
00:45:53,251 --> 00:45:54,836
to bleak ruins.
302
00:45:57,339 --> 00:46:00,842
and many of their inhabitants,
left homeless.
303
00:46:16,358 --> 00:46:20,403
Some scientists predict
that by the end of the century,
304
00:46:21,863 --> 00:46:24,032
coral reef cities as we know them,
305
00:46:25,033 --> 00:46:27,202
could be a thing of the past.
306
00:46:44,386 --> 00:46:49,474
Is there any future for these most
precious of ocean treasures?
307
00:46:58,400 --> 00:47:03,154
Well, that ultimately depends
on how fast they heat up,
308
00:47:03,446 --> 00:47:05,782
and how warm the seas become.
309
00:47:10,078 --> 00:47:11,913
And there is a glimmer of hope,
310
00:47:12,288 --> 00:47:16,251
because of the way
the corals reproduce themselves.
311
00:47:23,258 --> 00:47:25,593
On one special night of the year,
312
00:47:26,344 --> 00:47:30,432
the full moon triggers
an extraordinary event:
313
00:47:49,159 --> 00:47:51,828
The spawning of the coral.
314
00:48:01,629 --> 00:48:06,301
With extraordinary synchrony,
entire reefs reproduce.
315
00:48:23,151 --> 00:48:26,196
Billions of fertilized eggs drift away
316
00:48:29,365 --> 00:48:31,701
carried by the ocean currents.
317
00:48:38,500 --> 00:48:41,878
And it's not just the corals that spawn,
318
00:48:43,880 --> 00:48:47,217
so do many other residents of the reef
319
00:48:53,014 --> 00:48:55,183
A whole range of young
320
00:48:55,433 --> 00:48:57,519
are swept through the oceans,
321
00:48:58,269 --> 00:49:01,064
ready to settle on a vacant site,
322
00:49:01,397 --> 00:49:05,193
and bring back into existence
the complex community,
323
00:49:05,610 --> 00:49:07,737
that is a coral reef
324
00:49:20,041 --> 00:49:24,087
We may not know what the future
hold for our seas,
325
00:49:27,382 --> 00:49:30,218
but coral reefs can regenerate.
326
00:49:30,927 --> 00:49:33,638
As long as some reefs survive,
327
00:49:35,265 --> 00:49:38,101
some hope can remain.
328
00:49:51,156 --> 00:49:55,160
Next time, we head
into the vastness of the open ocean.
329
00:49:58,204 --> 00:50:02,292
To survive in this blue wilderness,
some are fast,
330
00:50:03,168 --> 00:50:05,503
others use deadly strategies,
331
00:50:06,880 --> 00:50:10,925
and a few rely on the closeness
of their families.
25223
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