- 2 days ago
How Earth's five oceans connect to form the largest ecosystem on the planet, and how its network of currents supports the health of the seas and marine wildlife.
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AnimalsTranscript
00:26A perfect planet.
00:36All life in the oceans depends on the continuous movement of water.
00:55There are not five separate oceans on Earth, but just one.
00:59Whose parts are linked by powerful, unceasing currents.
01:07Every drop of seawater on Earth rides these currents, taking a thousand years to complete
01:14a single circuit.
01:19And where there are currents, there is life.
01:40Off the coast of South Africa, dolphins are on the hunt.
01:55They have found a cold water current, and are now traveling along it, looking for food.
02:05Gannets follow them.
02:08They know that doing so is the fastest way to a meal.
02:18A shoal of mackerel, just what the dolphins have been looking for.
02:29They encircle the fish, driving them into a bait ball, and then trap them against the
02:35surface to prevent them from escaping to deeper water.
02:43Now the fish are within range of the dive-bombing gannets, who hit the water at fifty miles an hour.
03:13A sudden gathering of thousands of predators, brought together by the flow of cum.
03:20The fish are in the sea.
03:36Lost to the feast are sharks.
04:01In these vast open waters, finding food would be all but impossible without currents.
04:09The highways of the seas that bring this life together.
04:18When the bait ball has been dispersed, all that is left are scales drifting downwards.
04:30They are part of a slow, never-ending blizzard of organic waste
04:35that eventually settles on the sea floor.
04:42But it doesn't stay here forever.
04:45The currents sweep it back up into the sunlit surface waters,
04:51where it nourishes clouds of phytoplankton.
04:56Simple microscopic plants that are the pastures of the seas.
05:10There are thousands of different kinds, and together they produce half of all the oxygen in the atmosphere.
05:18More than all our forests and jungles combined.
05:25And by absorbing carbon, they are our greatest ally in combating climate change.
05:37Plankton are the foundation of almost all life in the ocean.
05:43For in those places where the currents bring nutrients to the surface,
05:47they multiply in astonishing numbers, turning the ocean green.
05:59The currents traveling through our oceans bring life to seas that would otherwise be marine deserts.
06:12The Galapagos Islands lie in the path of one of them,
06:16the deep-flowing Cromwell Current that runs for 6,000 miles across the Pacific.
06:25As it approaches Fernandina Island, it rises and delivers nutrients into its shallows.
06:45And it also brings life to this otherwise barren island.
06:50Thearent.
07:08Iguanas.
07:11There are thousands of them.
07:20And yet there's nothing on the island for these vegetarians to eat, or almost nothing.
07:34Cormorants bring seaweed ashore with which to make their nests, but what is building
07:41material for a cormorant is food for an iguana.
07:52Both these species evolved here, but that doesn't necessarily make them good neighbors.
08:02No matter.
08:04He knows where there's more elsewhere.
08:08He's a marine iguana, the only lizard in the world that gets its food from the sea.
08:32The seaweed, on which he totally relies, only grows in abundance here because of the nutrients
08:39brought by the Cormorant.
08:48Once in the water, he has just 30 minutes to find food.
09:00Any longer than that, and his muscles will seize up, and he'll drown.
09:06For like most reptiles, he can't handle the cold.
09:19Chilly water isn't a problem for a warm-blooded cormorant.
09:25She can swim in it all day, but can only hold her breath for a few minutes.
09:37He, on the other hand, completes his whole half-hour trip on one single breath.
09:45His flat face and sharp teeth make him an efficient seaweed-cropping machine, but with the clock ticking,
09:53he must eat fast.
09:58The cormorant, having caught its fish, goes back to the surface.
10:06One last mouthful, and it's also time for the iguana to head for home.
10:14But to stop his muscles from seizing up in the cold water, he must get back quickly.
10:24So he could do without the attentions of an inquisitive sea lion.
10:52Dry land is now just 30 meters away, but the biggest hurdle is still to come.
11:08The surging water now fights against him.
11:19He's out, but he's stayed in the cold so long that he's lost his strength.
11:24Thanks.
11:24Let's go.
12:05And he's made it.
12:10Few reptiles on the planet have to work harder for a meal than he does.
12:18And tomorrow, he'll have to do it all over again.
12:24Unless next time, he can outwit his neighbor.
12:34Over 100,000 marine iguanas live on Fernandina.
12:39And each owes its existence to the Cromwell Current that brings nutrients to these shores.
12:48But there is another, much bigger current, which carries water from the Pacific into the Indian Ocean.
12:59On this great journey, it travels through the islands of Indonesia, bringing together life from both oceans.
13:14A third of all the world's reef fish live here.
13:23Some call it the Coral Triangle, the most diverse marine region on Earth.
13:37The variety here is dazzling, not just of coral, but of animals of all kinds.
13:53Few are stranger than the flamboyant cuttlefish.
14:01This is a male, just five centimeters long.
14:10Swimming against the current isn't easy when you're small.
14:14So instead, he prefers to walk very, very, very slowly.
14:25He's a master of camouflage.
14:28But right now, he wants to be noticed.
14:34He's looking for a mate.
14:37His potential partner is a giant, by comparison, four times his size.
14:48When it comes to courtship, being flamboyant isn't enough.
14:58To win her over, he must dazzle.
15:08His aim is to deposit a packet of sperm inside her mouth.
15:17Close.
15:19But no cigar.
15:26He'll have to turn up the dazzle.
15:36Take two.
15:42Bingo!
15:54His job is done.
15:56Now she must find somewhere to lay their eggs.
16:02An old shell will do nicely, if she can slip past the present occupant.
16:13She fastens her eggs to the underside of the shell,
16:17where they'll be safe from predators.
16:32The current that brings so much life to the Coral Triangle
16:37now washes the eggs with clean, oxygenated water.
16:47After just three weeks, they start to hatch.
16:56Smaller than a human fingernail,
16:58the hatchlings are now carried by the current
17:01to other parts of the reef.
17:11And in just a few months,
17:14this young male will be ready to find a female of his own.
17:24By a stroke of cosmic good fortune,
17:27the Earth has a satellite, the Moon,
17:31which orbits our planet every 27 days.
17:38Its gravitational pull drags our oceans across the planet,
17:45and so gives us the tides.
17:53Unlike currents that stir the open ocean,
17:56the tides have their greatest impact on the coasts,
18:00flushing them with nutrients from both sea and land.
18:07And nowhere are they more violent and dramatic than here.
18:13Norway's Salkstraummen Strait.
18:17Every six hours, nearly half a billion tons of water
18:21are forced through a channel just 150 meters wide.
18:28Its very narrowness accelerates the water,
18:32making this the strongest tidal pull in the world.
18:52Most animals caught here would be swept away.
18:58But not these tidal specialists.
19:02Idas are one of the few ducks that depend totally on the ocean
19:06for their survival.
19:10And they're the only kind strong enough
19:13to live permanently in these racing waters.
19:24But there is food here,
19:26and in great quantity for any that can gather it.
19:31Mussels.
19:33They filter out particles of food brought to them by the tonguehead.
19:40And Ida ducks love mussels.
19:46The challenge is reaching them.
20:06Hiders seem to be the only creatures that can hold their own
20:09in the fast-flowing water.
20:14So they have the mussels all to themselves.
20:19They swallow them whole, shelled and all.
20:26Each Ida duck eats hundreds of mussels a day.
20:31A year-round feast that no others can watch.
20:46The tides here owe their power to the unique geography of the coastline.
20:53But elsewhere in our oceans,
20:56the lay of the land influences tides in a very different way.
21:03Here in the Bahamas,
21:05wide, shallow sandbanks mean the tide moves gently over the seafloor,
21:11turning what would be a sandy desert into a rich underwater habitat.
21:21This is the home of garden eels and razorfish.
21:30And fresh food arrives for them from deeper waters twice a day.
21:37Life seems unhurried and gentle.
21:42But there is trouble in paradise.
21:48These bottlenose dolphins eat razorfish,
21:52and they're not so easily fooled by vanishing tricks.
22:00They scan the sand with echolocating clicks
22:04to discover exactly where the razorfish are hiding.
22:25But knowing where they are is not the same as catching them.
22:35The more the dolphins dig, the deeper the razorfish burrow.
22:43But it's clearly not deep enough.
22:55Blowing jets of water into the sand
22:58exposes even the most hard-to-reach razorfish.
23:05Before long, the dolphins have had enough, and they move on.
23:12It looks as if they have picked the sand clean.
23:20But here, at least, there really are plenty more fish in the sea.
23:35Closer to the land, the same tides bring nourishment
23:39to one of the most threatened of coastal habitats.
23:44Mangrove forests.
23:47Part land, part sea.
23:54Mangroves are the only trees capable of surviving in salt water,
23:58and are specially adapted to it, coming and going, twice every day.
24:10As seawater floods in, fish come with it.
24:15Here, in the flooded forests,
24:18they can find both food and shelter.
24:28Stingrays ride on the incoming tide.
24:38Other commuters follow.
24:42Young lemon sharks, still far from full-grown,
24:45are looking for food.
25:02When the tide is at its highest,
25:05even adult lemon sharks can get into the mangroves.
25:11A three-meter female moves cautiously into the shallows.
25:19She can't stay here for long,
25:21but then she hasn't come here to hunt.
25:30She's come to give birth.
25:34Returning to the very place where she was born.
25:41She has nourished the pups inside her body
25:44with a placenta, as we do.
25:53The mangroves provide an ideal nursery for them,
25:57and placing them here gives them an excellent start.
26:00But that is the end of her parental care.
26:05She has to return to deeper water before the tide goes out.
26:14Her young must now fend for themselves.
26:20The pups instinctively take refuge among the roots of the mangroves.
26:28They're so small, they can swim deep into this tangled labyrinth.
26:45With the tide fast receding,
26:47even they need to find a place where they won't be left high and dry.
26:53A place like this.
26:55A permanent pool in the heart of the mangrove forest.
27:06Only the smallest sharks can get here,
27:09and only at the highest tides.
27:18The pups will spend the next two years here,
27:22perfecting the skills that make them one of the ocean's top hunters.
27:48All life at the coasts has to move to the daily rhythm of the tides.
27:54But tides are not the same throughout the year.
28:03Every month, when our planet, the moon, and the sun are all aligned,
28:09the increased gravitational pull produces particularly high tides.
28:16And this triggers a truly extraordinary event
28:20on one particular reef in the central Pacific.
28:29Thousands of resident surgeonfish begin to assemble on these high tides.
28:40And they are being followed by one of the largest fish in the sea.
28:51Manta rays.
29:02The rays spend their year moving between coral islands.
29:10But it's only now, when the tide is at its highest,
29:14and certain fish have gathered,
29:16that they appear on this particular reef.
29:23Their timing is so perfect
29:25that they rarely have to wait more than an hour
29:27for the event to begin.
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29:56the precise moment, when
29:58the tide is at its highest,
29:59At the highest, the surgeonfish begin to spawn.
30:05They release billions of eggs and sperm into the water.
30:13Breeding in this way gives their fertilized eggs
30:16the best chance of being carried on the tide
30:19away from predators that haunt the reef.
30:25All except one.
30:30The mantas move in.
30:51They gorge on the eggs, filtering them out using specially adapted gills.
30:58If the mantas had arrived just an hour later,
31:01there would have been nothing to do.
31:03There's nothing here for them to eat.
31:12No one knows how the mantas are so perfectly in tune
31:15with the rhythm of the tides.
31:23But they appear without fail whenever the surgeonfish spawn.
31:36Most of the eggs, however, are carried out into the open ocean
31:41before the mantas are able to eat them all.
31:59The rhythms of coastal life are influenced by another ocean force.
32:09Winds blowing over the sea so batter the surface
32:13is that it begins to rise and fall.
32:18These swells may travel far
32:20and reach the shores of even the most sheltered bays.
32:24As they approach shallower water, they turn into waves.
32:33A shoal of hardy heads,
32:35close to the beach of Australia's lizard island.
32:40The clearness of these glassy waters shows that they lack nutrients.
32:48But the gentle waves expose food hidden in the sand.
32:51And that's what the hardy heads are looking for.
33:04But they must beware.
33:09Packs of trevally are on the hunt.
33:20Packs of trevally are on the hunt.
33:21The hardy heads stick together.
33:24There's safety in numbers.
33:27But they're vulnerable nonetheless.
33:30But they're vulnerable nonetheless.
33:40They're so small, they can swim in the shallowest waters.
33:52Even in the body of the waves themselves,
33:56out of the reach of their enemies.
34:03But trevally aren't their only concern.
34:15Black-tip reef sharks.
34:19They are bigger and more powerful than trevally.
34:24But not as fast or as agile.
34:32The hardy heads are well aware of them.
34:35But so long as they stay just out of reach,
34:37they have little to fear.
34:53But now the sharks and the trevally join forces.
35:02They have little to fear.
35:03Together, they enter the shallows,
35:05each looking for a chance to attack.
35:25The trevally make the first move.
35:29And the hardy heads take refuge again in the waves.
35:33And this is what the sharks have been waiting for.
35:36The trevally make the first move.
35:40Surging forwards, they chase the hardy heads out of the water.
35:46Beeching themselves in a daring bid to hoover up their prey.
35:54The hardy heads that escape the sharks swim back out to deeper water.
36:00But into the mouths of the trevally.
36:14Now the receding waves help to pull the sharks back into deeper water.
36:50In the chaos, the seabirds get their chance.
36:58It's a feeding frenzy.
37:01In only 10 centimeters of water.
37:17The power of waves is dramatically evident when they crash onto our shores.
37:26But the biggest of all starts far away from land, out at sea.
37:34Great storms blowing over the surface of the ocean raise towering walls of water.
37:44Such giant swells can travel for thousands of miles.
37:50As they approach land, the shallowing sea floor begins to drag on their undersides.
37:57And they topple forward and break.
38:04This stirring of the ocean produces great riches.
38:12The falcon and islands are surrounded by some of the stormiest waters on Earth.
38:21Ideal hunting grounds for rockhopper penguins.
38:28It's the breeding season, and for the last two weeks, the males have been incubating the eggs by themselves.
38:37They're confined to the nest, with nothing to eat, while the females are out at sea, collecting food.
38:47All across the colony, eggs are starting to hatch.
38:53This male now has two youngsters to care for.
39:00But he has no food to give them, and he can't leave them unprotected.
39:06He can do nothing but wait.
39:18The females, after weeks fishing in the stormy seas, are now heading for home with food in their crops.
39:29There's just one problem.
39:32The colony sits at the top of huge cliffs.
39:38The waves that make feeding so good here, have now become major obstacles.
39:47Timing is vital.
40:04Go too early, and they could be smashed against the rocks.
40:15Too late, and they will be carried back out to sea.
40:26Hook's claws now help to get purchase on the slippery rocks.
40:33But they're not out of trouble yet.
40:41Success depends on both judgment and luck.
41:05Time and again, the waves drag her back in.
41:15She has to persevere.
41:17The lives of her chicks depend on her safe return.
41:38The waves that she daresay to swim within her lover.
41:40The maps don't fall back out to sea.
41:41The waves that she grabs over the boat.
41:45The waves are into airs to be wiped out to sea.
41:55The waves have to swim inside.
41:56She's made it.
42:07They're not called rock hoppers for nothing.
42:16With one more jump, she's home.
42:22And just in time.
42:28Her chicks are desperately hungry.
42:39This is their first proper meal.
42:51The oceans have sustained life on our planet for millions of years.
43:00But today, there's growing evidence that this is changing.
43:11As our climate warms, polar ice sheets are melting at an alarming rate.
43:21In the Arctic alone, 14,000 tons of fresh water are emptying into the sea every second.
43:36This is slowing the flow of currents around the globe.
43:42And if the atmosphere continues to warm, ocean circulation could eventually stop altogether.
43:59Our seas would then stagnate, threatening the life within them.
44:08And there are places in the oceans today where this is already beginning to happen.
44:21The Gulf of Thailand.
44:25The Gulf of Thailand.
44:31The Gulf of Thailand.
44:32Eden's whales have lived here for generations.
44:38But the world around them is changing.
44:52Today, agricultural pollution flowing from the land
44:56is beginning to suffocate this sea.
45:09Many fish now stay closer to the surface,
45:13where the water still contain enough oxygen to survive.
45:21Eden's whales depend on these fish.
45:26They swallow huge quantities of water before filtering out their prey.
45:36It takes a lot of energy to drive their 15-ton bulk through the water.
45:45And with so few fish, the rewards from feeding like this are barely worth it.
45:53So, to survive here, the whales have developed a new hunting technique.
46:03One that requires almost no effort.
46:10They simply open their mouths and wait.
46:19The panicked fish jump right in.
46:29Swimming alongside, another whale scares even more into the open jaws.
46:46With this ingenious new technique,
46:50Eden's whales have found a way to survive the pressures they now face.
46:57All across the planet, animals are having to adapt to a changing world.
47:04But the speed of these changes will be too fast for many.
47:14If we could only halt our unrestrained plunder of the ocean,
47:19its habitats and species would recover.
47:24And at a time when our over-exploited lands are already failing us,
47:29this has never been more important for humanity.
47:53The volcanic island of Fernandina in the Galapagos is home to two incredible lizards.
48:02The land iguana and the marine iguana.
48:09There are two parts to their story that cameraman Richard Woolacombe has wanted to film
48:14since he first came to these islands 25 years ago.
48:19And on a perfect planet, he got his chance.
48:27Driven by powerful currents, the cold Pacific Ocean slams into Fernandina's shores.
48:40The marine iguanas must brave these waters every day.
48:48Their journey through the big surf is what Richard and the team are here to film.
48:54But from underwater.
48:56It looks fairly benign from the surface here,
48:59but underneath it's really shallow,
49:01and there's all these really sharp rocks with lots of jagged edges.
49:05So if we were taken by the wave, it would cut us up really badly, I think.
49:20I'm a glutton for punishment, did you know?
49:25The waves are certainly punishing.
49:30With these dangerous conditions, extra protection is clearly needed for Richard and dive body Raphael.
49:37So what better than surf helmets?
49:48It isn't long before Richard realizes what he's up against.
49:55The relentless churning of the water makes it difficult to stay the right way up,
50:01let alone film the iguanas.
50:08In between the waves, the iguanas briefly appear.
50:17But Richard barely has time to line up a shot
50:21before the iguana disappears behind another wave.
50:31In the violent surge, the iguanas have learned to hang onto the rocks.
50:37A trick Richard is quick to copy to avoid being swept away.
50:43That, however, only leaves one hand to film with.
50:55But with the adrenaline carrying him through,
50:58Richard is able to get the perfect shots of iguanas in the surf.
51:09And to achieve that, totally unscathed, is a great relief.
51:14I don't need to go to the gym for months after that.
51:19Well done, mate. Good job.
51:24On the shore, land iguanas have to battle a very different force.
51:32Each year, they migrate up to the top of Fernandina's active volcano.
51:37A journey of ten days across razor-sharp lava
51:42before descending into its heart to lay their eggs in the ashy floor.
51:52It's this behaviour Richard and the team plan to film.
51:56And the scale of the expedition
51:58is one that's rarely been attempted in the Galapagos.
52:06To reach the top takes the crew ten gruelling hours.
52:20When they finally arrive on the rim, the experience doesn't disappoint.
52:27I can't believe it.
52:29It's absolutely awe-inspiring.
52:33I just can't believe the iguanas
52:36actually managed to navigate down these slopes
52:40into the bowl of this volcano.
52:44More people have been into space than to the bottom of Fernandina's crater.
52:49But that is exactly where Richard and the team must go
52:52if they are to film the nesting iguanas.
52:59From their campsite at the edge of the volcano,
53:03it's an extremely dangerous journey down to the crater floor.
53:07And assistant producer, Toby, wants to be clear with everyone
53:10what is at stake.
53:30There's only one possible route down,
53:34and as the team enter the lip of the volcano,
53:37the sound of rock fall is all around.
53:50regular earthquakes make the crater walls very unstable.
53:58It just keeps getting better.
54:01Not far away, some iguanas are making their own descent,
54:06disturbing the loose surface as they go.
54:19If a creature only a sixth the size of a person
54:22can start a deadly avalanche of razor-sharp rocks,
54:26what can a whole film crew do?
54:35It's clear the crew are going to have to be extremely cautious.
54:44On the steepest slopes, the equipment needs to be lowered with ropes.
54:57With rocks falling all around, the longer they are on the slopes,
55:01the greater the risk of an accident.
55:07But when one misstep can start an avalanche, hurrying is impossible.
55:16Finally, the prize of the crater floor is in sight.
55:19But just below there is where the iguanas are nesting.
55:23We're very close to it now, about an hour's walk.
55:27All that lies between them is a stretch of loose lava
55:30that has cascaded down the slopes after the last eruption.
55:47We're actually in the crater now, surrounded by these vertical walls.
55:54I just can't believe we really made it down here.
55:59Sometimes I doubted that, you know, we would actually make it.
56:06And there they were, iguanas using the warm volcanic ash to incubate their eggs.
56:17For Richard, after 25 years living in the Galapagos,
56:22filming this unique behaviour is a lifelong dream come true.
56:28My God, what an incredible place this is.
56:31It's such a vivid feeling to be constantly challenged
56:36by the forces of nature like that.
56:38But they have to do this every year in order to survive.
56:43I'll never forget for as long as I live.
56:47What an adventure, what an adventure.
56:53Next time, a new force.
56:57Humans, now so dominant.
57:01We are disrupting the forces of nature
57:05and the vital habitats life needs to survive.
57:11This is the most important story of our time.
57:16Where is nature? Our future!
57:19The Open University has produced a free poster
57:22exploring our perfect planet.
57:24To order, please call 0300 303 0901
57:30or go to bbc.co.uk
57:33slash perfectplanet
57:35and follow the links to The Open University.
57:42See the next episode streaming now on BBC iPlayer.
57:46New on 2, the Trump show updated
57:49from the final months of the presidency
57:51to the Capitol Hill riots.
57:54Downfall just starting.
57:55The heat is on in 70s Bangkok.
57:57Alain Gauthier at his most menacing.
58:00The serpent on BBC One.
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