[00:30.12]Our planet's continents are fringed by shallow seas.
[00:36.93]Rarely more than two hundred meters deep they lie on the continental shelves
[00:41.78]which may stretch sometimes for hundreds of miles
[00:44.84]before the sea floor drops into deeper darker waters.
[00:54.70]All together they constitute a mere eight percent of the world's oceans
[00:59.42]but they contain the vast majority of it's marine life.
[01:37.25]A male humpback whale sings to attract a mate.
[02:03.12]The whales have just returned to their breeding grounds
[02:07.06]in the shallow seas of the tropics.
[02:16.75]The calf is no more than a few weeks old.
[02:25.85]Despite being three meters long and weighing nearly a ton
[02:30.30]he is nonetheless vulnerable.
[02:36.90]but his mother watches over him
[02:39.07]and, as he begins to tire, she supports him close to the surface
[02:44.08]so that he can breathe more easily.
[03:09.84]These shallows around the equator are excellent nurseries.
[03:14.47]They're warm, calm, and contain very few predators.
[03:22.13]The playful calf is now drinking five hundred liters of milk a day
[03:27.45]but his mother must starve.
[03:30.19]There is nothing for her to eat here.
[03:40.42]Like many tropical shallow seas
[03:43.01]these crystal clear waters are virtually lifeless.
[03:46.45]They receive year round sunlight
[03:48.75]but they lack the nutrients essential for the growth of plankton.
[03:53.41]The mother will be trapped here for the next five months
[03:56.45]until her calf is strong enough to make the journey to the feeding grounds, near the poles.
[04:25.60]Coral reefs are oases in a watery desert.
[04:30.79]Most tropical shallows are barren
[04:33.64]but these coral havens contain one quarter of all the marine life on our planet.
[04:58.35]Reefs are the work of polyps
[05:00.71]tiny colonial animals like minute sea anemones
[05:04.84]yet the great barrier reef is so big it can be seen from the Moon.
[05:16.55]It's actually two thousand separate reefs
[05:19.85]that together form a barrier stretching for over a thousand miles
[05:24.24]along Australia's northeastern coast.
[05:30.46]Despite it's vast size
[05:32.79]this reef does not contain the greatest variety of marine life on the planet.
[05:39.46]For that one must travel north to Indonesia.
[06:10.00]There are individual reefs in Indonesia that contain almost as many kinds of fish
[06:15.76]as live in the whole of the Caribbean.
[06:20.17]There are also ten times the number of coral species.
[06:26.87]Corals thrive in these waters with the help of microscopic plants, algae
[06:32.35]that grow within the tissues of the polyps
[06:41.37]and the polyps feed by snaring passing morsels with their tentacles.
[06:58.45]At night, the algae are inactive but then, the polyps put out even more tentacles
[07:04.73]so coral in effect feeds around the clock.
[07:25.61]This well balanced alliance brings benefits to both polyps and algae
[07:31.77]and between them, they turn the barren seas into rich gardens.
[07:46.77]The Indonesian reefs contain such a variety of life
[07:50.72]because they lie at a giant crossroads.
[07:53.91]This is the meeting place for different seas the Indian Ocean and the Pacific.
[08:02.79]Here everything demands a closer look.
[08:06.27]On the surface of this sea fan, there are two polyps that are not polyps.
[08:12.01]They're pygmy sea horses, the world's smallest, less than two centimeters high.
[08:30.38]They are males, settling a territorial dispute, by head butting.
[08:44.75]An electric flash?
[08:48.21]No, the display of a file clam.
[08:56.73]Perhaps this extraordinary pulsation of the clam's fleshy mantle
[09:01.03]is a warning to frighten away nibbling fish, but no one really knows
[09:20.86]And there are snakes here, too, lots of them.
[09:30.70]These are banded sea crates. They lay their eggs on land
[09:36.30]but they hunt here in the water.
[09:43.74]They're too slow to catch fish in a straight chase
[09:47.63]so they seek prey that is hiding in the nooks and crannies of the coral.
[09:54.56]Their bite is highly venomous and paralyzes their victims.
[10:03.64]And on this reef the snakes do not hunt alone.
[10:13.78]Shoals of yellow goatfish and trivali are seeking similar prey
[10:19.05]And they attract the snakes' attention. As one group of hunters searches the reef
[10:24.81]they're joined by the other.
[10:35.03]At least thirty snakes have now joined the caravan.
[10:45.05]The big fish scare the prey into cracks and there the snakes can catch them
[10:51.76]And anything fleeing from the crates will swim straight into the mouths of the waiting trivali.
[10:58.56]There's nowhere to hide.
[11:05.96]As the raiders scour the reef, more and more snakes join the hunt.
[11:32.87]This cooperation between snakes and fish, spectacular though it is,
[11:37.92]has only recently been observed, for it only happens on the most remote reefs in Indonesia.
[11:53.46]Perhaps such hunting alliances were once a common sight
[11:57.33]but today no more than six percent of Indonesia's reefs are in their pristine state.
[12:30.57]Beyond the coral stretches a world of shifting sand.
[12:35.70]Out there with nowhere to hide survival is not easy
[12:39.68]and camouflage can be crucial.
[12:44.91]If this wasn't moving, you might think it was a shell or a rock. In fact it's an octopus.
[12:53.55]A gurnard. It's huge pectoral fins disguise it's shape
[12:58.43]and they can also help in clearing away sand when searching for food.
[13:07.03]The jawfish hides underground.
[13:12.26]The wonderpus octopus on the other hand has such a powerful bite
[13:16.35]that it has a special warning display to tell others to keep out of it's way.
[13:32.77]Here and there, plants manage to take root
[13:36.69]and they're cropped by green turtles.
[13:39.98]Seagrasses are the only flowering plants that have managed to grow in the sea
[13:45.03]although they put out a few ribbon like leaves
[13:47.61]they produce very extended networks of fleshy stems, risomes,
[13:52.03]that are buried in the sand.
[14:00.97]At their lushest they can transform the sea bed
[14:04.29]into an underwater meadow.
[14:07.58]The largest expanse grows in the shallow waters of Shark Bay, in Western Australia.
[14:16.00]These vast aquatic grasslands stretch for fifteen hundred square miles
[14:21.84]and, like terrestrial prairies, they support herds of grazers.
[14:41.83]Dugongs are the largest herbivores in the sea.
[14:45.45]They can be three meters long and weigh half a ton
[14:48.36]and they eat nothing but seagrass, mostly the fleshy risomes,
[14:52.54]which they excavate with their mobile lips.
[15:10.31]A herd can clear a patch of seagrass the size of a football pitch
[15:15.13]in a single day.
[15:40.13]Food is not evenly distributed in the tropical shallow seas
[15:44.52]and it can take a lot of finding
[15:46.95]but bottlenose dolphins are inquisitive, energetic,1 and very intelligent
[15:52.88]and they have discovered a shoal of baitfish.
[16:03.79]Together, they ride a wave, using it to carry them into the shallows
[16:08.82]and there, it will be easier to make the catch.
[16:38.30]In Western Australia
[16:40.29]these dolphins have taken on an ever tougher challenge.
[16:45.12]The fish have taken refuge close to the beach
[16:48.25]where the water is only a few centimeters deep.
[16:55.32]Tail slapping is a method dolphins often use to stun their prey
[17:00.66]but it doesn't seem to work here.
[17:12.83]The fish are tantalizingly close
[17:15.91]but they're still out of reach, so the dolphins try another technique.
[17:25.77]Vigorously pumping their tails, they work up some speed
[17:30.39]and then, they hydroplane.
[17:59.74]Their momentum carries them right through the shallowest waters, and onto the fish.
[18:16.36]Now they're in real danger of being stranded
[18:20.32]but fortune favors the brave.
[18:31.11]Younger dolphins lie alongside, watching
[18:34.46]but so far only eight individuals here
[18:37.57]have mastered this daring technique.
[19:29.16]Although most life in tropical waters is concentrated around the coral reefs
[19:34.57]and the seagrass meadows,
[19:36.42]there are some spectacular exceptions.
[19:45.77]The desert of Bahrain seems a very unlikely place
[19:49.82]to find a crowded bustling colony of seabirds
[19:54.02]But every year, a hundred thousand socotra cormorants gather here to breed.
[20:06.65]It's swelteringly hot
[20:08.50]and only vigorous panting can prevent the birds from fatal overheating.
[20:14.11]This hardly seems a good place to rear young
[20:19.50]but at least, there are no land based predators here.
[20:23.63]The only source of trouble is likely to be the neighbors
[20:27.26]so each nest is built just beyond pecking reach
[20:46.68]But what about food?
[20:48.99]There's only bare sand and the warm shallow sea beyond.
[20:53.44]Neither seem likely to produce enough nourishment to support bird life on this scale.
[21:03.21]The answer is blowing in the wind.
[21:08.61]Sand whipped up by Shamals offshore winds
[21:12.60]blows into the seas of the Arabian Gulf.
[21:16.20]With the grains come nutrients, which act as fertilizer
[21:19.92]and they transform the shallow sea into a rich fishing ground
[21:30.22]So, paradoxically, it's the roasted sands of Arabia that prevent the gulf
[21:35.71]from being another desert in the sea.
[21:51.58]The whale calf is now five months old.
[21:55.10]He's almost doubled in size
[21:57.18]and his days in his tropical nursery are coming to an end.
[22:01.43]It has been a warm and safe place in which to grow up
[22:05.00]but there's nothing to eat here for his mother.
[22:09.81]She has been living off her fat reserves for the last eight months
[22:14.52]and she's close to starving.
[22:17.42]She must leave now, while she still has enough energy
[22:20.03]to guide and protect her calf, on the long voyage ahead.
[22:41.95]All across the tropics, humpbacks are heading away from the Equator
[22:46.87]towards the rich temperate seas of both the southern and the northern hemispheres.
[22:55.76]These are colder, rougher, and more dangerous waters.
[23:12.44]Mother and calf must stay close.
[23:33.76]They can send sound signals to one another, above the roar of the ocean
[23:38.15]by slapping fins on the surface.
[24:01.54]In winter, the temperate seas are lashed by violent storms.
[24:24.01]The turbulence stirs the water, and draws nutrients up from the depths
[24:38.27]but nutrients alone can not support life.
[24:42.67]There must also be sunlight.
[24:48.20]In the spring, as the sun daily climbs higher in the sky
[24:52.41]the algae start to grow.
[24:55.47]Blooms the size of the Amazon Rainforest turn the seas green.
[25:03.75]Individually the algae are tiny
[25:06.82]but together, they produce three quarters of all the oxygen in our atmosphere.
[25:16.26]They're eaten by an array of bewildering creatures.
[25:20.46]Salps appear in the plankton soup.
[25:28.94]Individuals link together to form chains which can stretch for fifteen meters.
[25:45.29]Pumping water through their bodies they strain out algae and other edible particles.
[26:01.66]Comb jellies cruise through the water.
[26:04.94]They too flourish in this seasonal soup
[26:08.32]and for short periods, they appear in astounding numbers.
[26:13.59]Krill, shrimp like creatures.
[26:16.16]By weight they're the most abundant animals on the planet.
[26:19.49]A single swarm can contain two million tons of them
[26:32.12]and that is a lot of fish food.
[26:44.71]The shallow temperate seas support the greatest concentrations of fish on our planet.
[26:50.28]Huge shoals migrate from their overwintering grounds in the depths
[26:54.30]to feed in these rich waters.
[27:05.76]It's these shoals that support most of the world's sea mammals.
[27:12.29]Sea lions have all the agility and speed needed to collect what they want
[27:17.89]and seemingly delight in doing so.
[27:54.59]Dusky dolphin, often in pods two hundred strong
[27:58.78]work together to reap the harvest.
[28:04.00]They break up the shoals into smaller, more manageable balls, and all the hunters benefit.
[28:36.14]By midsummer, the surface nutrients have all been absorbed.
[28:41.21]The algae die and the food chain collapses.
[28:50.00]In a few special places, however
[28:52.43]the temperate seas sustain these levels of life throughout the summer.
[28:57.76]Along the coast of California, ocean currents carry a constant supply
[29:02.31]of nutrients up from the depths to the surface layers.
[29:06.86]These upwellings fertilize forests of giant kelp, that thrive in the summer sunshine.
[29:20.13]The algal towers are as high as a three story house
[29:24.24]and they can grow by half a meter a day.
[29:41.50]Life in the kelp is as full of drama, as in any other forest
[29:46.79]but the cast is less familiar.
[29:50.14]An army of sea urchins is mounting an attack.
[29:56.52]The urchin plague strikes at the kelp's holdfasts their crucial attachments to the rock.
[30:17.43]Holdfasts are extremely tough, but each urchin has five teeth, which are self sharpening
[30:24.61]and are replaced every few months.
[30:34.35]Urchins fell vast areas of kelp forest
[30:37.97]creating clearings know as urchin barrens
[30:45.39]yet barrens is a poor description.
[30:52.93]Millions of invertebrates invade the seabed.
[31:11.50]The most fearsome predator here is a giant.
[31:15.04]The sunflower starfish is a meter across, with an appetite for brittle stars.
[31:39.37]It uses it's feet to taste for prey.
[31:47.91]When it's actions are speeded up, it becomes clear that the predator's fondness for the brittle stars
[31:54.01]is almost matched by the brittle stars ability to get out of the way.
[32:10.96]Sand dollars flat sea urchins cluster together as a defense
[32:21.94]But it doesn't seem to work against the sunflower starfish.
[32:26.70]The predator extrudes it's stomach, and wraps it around it's victims liquefying their soft parts.
[32:34.28]Nothing is left of them, except their white skeletons.
[32:45.26]The Californian upwellings are seasonal and relatively small
[32:49.89]but in Southern Africa they're so big
[32:52.61]they create seas rich enough to support colonies of over a million seals.
[33:03.13]The Benguela Current sweeps along the western coastline of Southern Africa
[33:08.22]driving nutrient rich waters up to the surface
[33:13.42]and then, at the southern tip of Africa it meets the Agulhas Current, arriving from the east.
[33:20.66]The result: even richer waters.
[33:35.36]The seals here thrive on a diet of fish and squid.
[33:42.27]In temperate seas there may actually be more squid than fish.
[33:54.50]These are chokker squid, and they lay their egg capsules
[33:58.59]in sandy shallows bathed by the warmer Agulhas Current.
[34:11.83]Each capsule contains a hundred tiny squid.
[34:21.21]Within a few days they develop spots of pigment
[34:24.00]which, when they're adult, they will use to communicate with one another.
[34:40.58]With females continuing to lay eggs
[34:43.48]and males still preoccupied with repelling rivals, the squid drop their guard.
[35:02.64]Short tailed stingray can be up to two meters across.
[35:12.83]They're the largest of all the stingrays, and they have appetites to match.
[35:46.04]Another predator is on the prowl.
[35:51.16]The aptly named ragged tooth shark.
[35:58.71]Raggies grow to three meters long, but they share these waters with a shark twice their size.
[36:21.55]The great white.
[36:25.60]The largest predatory fish on the planet.
[36:35.69]Each dawn cape fur seals leave their colony to go fishing.
[36:41.84]To reach the open sea, they must cross a narrow strip of water
[36:46.58]and that is patrolled by great whites.
[36:59.47]Each seal is indeed swimming for it's life.
[37:25.77]The shark relies on surprise.
[38:27.53]The great white's turn of speed is powered by a high metabolism.
[38:32.74]They only thrive in cold temperate seas
[38:35.67]for only these waters contain sufficient food necessary to fuel such a ravenous predator.
[39:13.54]As you travel towards the poles north or south
[39:17.35]the colder, stormier seas can become even richer.
[39:23.77]Midway between South Africa and the South Pole
[39:27.57]lies the isolated island of Marion.
[39:36.65]The island sits in the infamous "roaring forties"
[39:40.58]where incessant gale force winds draw nutrients up from the depths
[39:45.40]ensuring plenty of food for king penguins.
[39:51.85]The kings are returning from a three day fishing trip, with food for their chicks
[39:57.16]But first they must cross a crowded beach, threading their way between gigantic
[40:02.82]and bad tempered elephant seals.
[40:16.70]The two hundred thousand penguins breeding here
[40:19.88]are testament to the richness of the fishing.
[40:27.19]King chicks are dependent on their mothers for over a year
[40:30.85]and this puts a great deal of pressure on the parents.
[40:48.59]Being flightless, the returning penguins must cross the open beach on foot.
[41:26.15]Fur seals, that have come to the beach to breed, are waiting for them.
[41:38.68]Fur seals normally live on krill
[41:41.56]but these have now acquired an unexpected taste for blubber rich penguins.
[42:37.81]Penguins may be featherweights by comparison
[42:40.80]but they have razor sharp bills and a feisty character.
[42:47.81]The seal could easily lose an eye.
[42:50.22]The only safe way to grab a penguin is from behind, and the birds are well aware of that.
[43:17.79]Both animals are clumsy on this terrain
[43:20.64]but the penguin has the more to lose.
[43:37.55]Two out of three penguins survive the seal attacks
[43:40.83]and succeed in reaching their ever hungry chicks.
[44:13.64]The humpbacks are nearing the end of their epic journeys.
[44:23.19]After two months and thousands of miles, they're entering the polar seas
[44:28.84]both in the north and the south.
[44:42.19]In the far north, winter is over at last and the ice is starting to melt.
[44:52.59]The Aleutian Island chain running west from Alaska
[44:56.09]is the gateway to the Bearing Sea.
[44:58.89]With the retreating ice, rough weather and ferocious currents stir up these shallow seas.
[45:05.72]Add sunshine and the mix is spectacularly productive.
[45:20.20]Five million shearwaters have flown almost ten thousand miles from Australia to get here.
[45:27.30]In all eighty million seabirds come here for the summer
[45:30.78]the greatest concentration to be found anywhere on Earth.
[45:47.98]The humpbacks have finally arrived.
[46:09.80]The giant shearwater flocks hunt the krill swarms
[46:13.91]sometimes diving to depths of forty meters to reach them.
[46:40.99]A large humpback eats three tons of krill a day.
[46:58.07]The polar seas in summer are the most productive on the planet
[47:02.40]and the whales gorge themselves round the clock.
[47:12.84]The fat reserves they lay down now will keep them alive during the year to come
[47:19.43]but it may not always be this way.
[47:22.15]Fish and krill stocks are declining so rapidly
[47:25.62]that spectacles like this may soon be part of history.
[47:39.03]Once the mother and calf have reached their feeding grounds, they will separate.
[47:47.79]With luck, the calf will make the epic journey across the oceans
[47:52.08]from equator to pole another seventy times
[47:56.62]cruising back and forth between the shallow seas
[48:00.43]where life proliferates so abundantly on our planet.
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