行星地球第九集：多樣淺海 Shallow Seas

[00:30.12]Our planet's continents are fringed by shallow seas. [00:35.56] [00:36.93]Rarely more than two hundred meters deep they lie on the continental shelves [00:41.64] [00:41.78]which may stretch sometimes for hundreds of miles [00:44.77] [00:44.84]before the sea floor drops into deeper darker waters. [00:49.37] [00:54.70]All together they constitute a mere eight percent of the world's oceans [00:59.37] [00:59.42]but they contain the vast majority of it's marine life. [01:04.48] [01:37.25]A male humpback whale sings to attract a mate. [01:42.74] [02:03.12]The whales have just returned to their breeding grounds [02:06.96] [02:07.06]in the shallow seas of the tropics. [02:10.28] [02:16.75]The calf is no more than a few weeks old. [02:20.99] [02:25.85]Despite being three meters long and weighing nearly a ton [02:30.18] [02:30.30]he is nonetheless vulnerable. [02:33.55] [02:36.90]but his mother watches over him [02:38.84] [02:39.07]and, as he begins to tire, she supports him close to the surface [02:43.95] [02:44.08]so that he can breathe more easily. [02:47.67] [03:09.84]These shallows around the equator are excellent nurseries. [03:14.41] [03:14.47]They're warm, calm, and contain very few predators. [03:19.60] [03:22.13]The playful calf is now drinking five hundred liters of milk a day [03:26.98] [03:27.45]but his mother must starve. [03:29.67] [03:30.19]There is nothing for her to eat here. [03:33.59] [03:40.42]Like many tropical shallow seas [03:42.94] [03:43.01]these crystal clear waters are virtually lifeless. [03:46.23] [03:46.45]They receive year round sunlight [03:48.66] [03:48.75]but they lack the nutrients essential for the growth of plankton. [03:52.54] [03:53.41]The mother will be trapped here for the next five months [03:56.31] [03:56.45]until her calf is strong enough to make the journey to the feeding grounds, near the poles. [04:03.21] [04:25.60]Coral reefs are oases in a watery desert. [04:29.72] [04:30.79]Most tropical shallows are barren [04:33.50] [04:33.64]but these coral havens contain one quarter of all the marine life on our planet. [04:39.76] [04:58.35]Reefs are the work of polyps [05:00.55] [05:00.71]tiny colonial animals like minute sea anemones [05:04.43] [05:04.84]yet the great barrier reef is so big it can be seen from the Moon. [05:10.88] [05:16.55]It's actually two thousand separate reefs [05:19.66] [05:19.85]that together form a barrier stretching for over a thousand miles [05:24.20] [05:24.24]along Australia's northeastern coast. [05:27.23] [05:30.46]Despite it's vast size [05:32.73] [05:32.79]this reef does not contain the greatest variety of marine life on the planet. [05:38.03] [05:39.46]For that one must travel north to Indonesia. [05:43.74] [06:10.00]There are individual reefs in Indonesia that contain almost as many kinds of fish [06:15.63] [06:15.76]as live in the whole of the Caribbean. [06:18.58] [06:20.17]There are also ten times the number of coral species. [06:24.26] [06:26.87]Corals thrive in these waters with the help of microscopic plants, algae [06:32.33] [06:32.35]that grow within the tissues of the polyps [06:35.97] [06:41.37]and the polyps feed by snaring passing morsels with their tentacles. [06:46.78] [06:58.45]At night, the algae are inactive but then, the polyps put out even more tentacles [07:04.60] [07:04.73]so coral in effect feeds around the clock. [07:08.60] [07:25.61]This well balanced alliance brings benefits to both polyps and algae [07:31.53] [07:31.77]and between them, they turn the barren seas into rich gardens. [07:37.02] [07:46.77]The Indonesian reefs contain such a variety of life [07:50.58] [07:50.72]because they lie at a giant crossroads. [07:53.66] [07:53.91]This is the meeting place for different seas the Indian Ocean and the Pacific. [08:00.05] [08:02.79]Here everything demands a closer look. [08:06.03] [08:06.27]On the surface of this sea fan, there are two polyps that are not polyps. [08:11.42] [08:12.01]They're pygmy sea horses, the world's smallest, less than two centimeters high. [08:18.39] [08:30.38]They are males, settling a territorial dispute, by head butting. [08:36.49] [08:44.75]An electric flash? [08:47.05] [08:48.21]No, the display of a file clam. [08:52.23] [08:56.73]Perhaps this extraordinary pulsation of the clam's fleshy mantle [09:00.93] [09:01.03]is a warning to frighten away nibbling fish, but no one really knows [09:07.32] [09:20.86]And there are snakes here, too, lots of them. [09:25.42] [09:30.70]These are banded sea crates. They lay their eggs on land [09:36.14] [09:36.30]but they hunt here in the water. [09:39.65] [09:43.74]They're too slow to catch fish in a straight chase [09:47.44] [09:47.63]so they seek prey that is hiding in the nooks and crannies of the coral. [09:52.12] [09:54.56]Their bite is highly venomous and paralyzes their victims. [09:58.89] [10:03.64]And on this reef the snakes do not hunt alone. [10:08.43] [10:13.78]Shoals of yellow goatfish and trivali are seeking similar prey [10:18.81] [10:19.05]And they attract the snakes' attention. As one group of hunters searches the reef [10:24.61] [10:24.81]they're joined by the other. [10:27.44] [10:35.03]At least thirty snakes have now joined the caravan. [10:39.37] [10:45.05]The big fish scare the prey into cracks and there the snakes can catch them [10:51.08] [10:51.76]And anything fleeing from the crates will swim straight into the mouths of the waiting trivali. [10:57.39] [10:58.56]There's nowhere to hide. [11:00.64] [11:05.96]As the raiders scour the reef, more and more snakes join the hunt. [11:11.76] [11:32.87]This cooperation between snakes and fish, spectacular though it is, [11:37.92] [11:37.92]has only recently been observed, for it only happens on the most remote reefs in Indonesia. [11:44.86] [11:53.46]Perhaps such hunting alliances were once a common sight [11:57.16] [11:57.33]but today no more than six percent of Indonesia's reefs are in their pristine state. [12:03.31] [12:30.57]Beyond the coral stretches a world of shifting sand. [12:34.90] [12:35.70]Out there with nowhere to hide survival is not easy [12:39.43] [12:39.68]and camouflage can be crucial. [12:42.45] [12:44.91]If this wasn't moving, you might think it was a shell or a rock. In fact it's an octopus. [12:51.57] [12:53.55]A gurnard. It's huge pectoral fins disguise it's shape [12:57.94] [12:58.43]and they can also help in clearing away sand when searching for food. [13:02.77] [13:07.03]The jawfish hides underground. [13:10.34] [13:12.26]The wonderpus octopus on the other hand has such a powerful bite [13:16.31] [13:16.35]that it has a special warning display to tell others to keep out of it's way. [13:21.00] [13:32.77]Here and there, plants manage to take root [13:36.03] [13:36.69]and they're cropped by green turtles. [13:39.52] [13:39.98]Seagrasses are the only flowering plants that have managed to grow in the sea [13:44.72] [13:45.03]although they put out a few ribbon like leaves [13:47.53] [13:47.61]they produce very extended networks of fleshy stems, risomes, [13:51.86] [13:52.03]that are buried in the sand. [13:54.43] [14:00.97]At their lushest they can transform the sea bed [14:04.14] [14:04.29]into an underwater meadow. [14:06.60] [14:07.58]The largest expanse grows in the shallow waters of Shark Bay, in Western Australia. [14:13.63] [14:16.00]These vast aquatic grasslands stretch for fifteen hundred square miles [14:21.47] [14:21.84]and, like terrestrial prairies, they support herds of grazers. [14:26.70] [14:27.38]Dugongs. [14:28.91] [14:41.83]Dugongs are the largest herbivores in the sea. [14:45.05] [14:45.45]They can be three meters long and weigh half a ton [14:48.20] [14:48.36]and they eat nothing but seagrass, mostly the fleshy risomes, [14:52.46] [14:52.54]which they excavate with their mobile lips. [14:55.79] [15:10.31]A herd can clear a patch of seagrass the size of a football pitch [15:14.78] [15:15.13]in a single day. [15:16.74] [15:40.13]Food is not evenly distributed in the tropical shallow seas [15:44.42] [15:44.52]and it can take a lot of finding [15:46.45] [15:46.95]but bottlenose dolphins are inquisitive, energetic,1 and very intelligent [15:52.66] [15:52.88]and they have discovered a shoal of baitfish. [15:56.38] [16:03.79]Together, they ride a wave, using it to carry them into the shallows [16:08.38] [16:08.82]and there, it will be easier to make the catch. [16:12.50] [16:38.30]In Western Australia [16:40.10] [16:40.29]these dolphins have taken on an ever tougher challenge. [16:44.32] [16:45.12]The fish have taken refuge close to the beach [16:48.12] [16:48.25]where the water is only a few centimeters deep. [16:51.57] [16:55.32]Tail slapping is a method dolphins often use to stun their prey [17:00.36] [17:00.66]but it doesn't seem to work here. [17:03.14] [17:12.83]The fish are tantalizingly close [17:15.55] [17:15.91]but they're still out of reach, so the dolphins try another technique. [17:21.65] [17:25.77]Vigorously pumping their tails, they work up some speed [17:30.08] [17:30.39]and then, they hydroplane. [17:32.63] [17:59.74]Their momentum carries them right through the shallowest waters, and onto the fish. [18:06.18] [18:16.36]Now they're in real danger of being stranded [18:19.92] [18:20.32]but fortune favors the brave. [18:22.95] [18:31.11]Younger dolphins lie alongside, watching [18:34.18] [18:34.46]but so far only eight individuals here [18:37.46] [18:37.57]have mastered this daring technique. [18:40.44] [19:29.16]Although most life in tropical waters is concentrated around the coral reefs [19:34.51] [19:34.57]and the seagrass meadows, [19:36.25] [19:36.42]there are some spectacular exceptions. [19:39.77] [19:45.77]The desert of Bahrain seems a very unlikely place [19:49.71] [19:49.82]to find a crowded bustling colony of seabirds [19:53.39] [19:54.02]But every year, a hundred thousand socotra cormorants gather here to breed. [20:00.14] [20:06.65]It's swelteringly hot [20:08.27] [20:08.50]and only vigorous panting can prevent the birds from fatal overheating. [20:13.36] [20:14.11]This hardly seems a good place to rear young [20:17.56] [20:19.50]but at least, there are no land based predators here. [20:23.14] [20:23.63]The only source of trouble is likely to be the neighbors [20:26.98] [20:27.26]so each nest is built just beyond pecking reach [20:31.55] [20:46.68]But what about food? [20:48.54] [20:48.99]There's only bare sand and the warm shallow sea beyond. [20:53.11] [20:53.44]Neither seem likely to produce enough nourishment to support bird life on this scale. [20:59.20] [21:03.21]The answer is blowing in the wind. [21:06.71] [21:08.61]Sand whipped up by Shamals offshore winds [21:12.49] [21:12.60]blows into the seas of the Arabian Gulf. [21:15.76] [21:16.20]With the grains come nutrients, which act as fertilizer [21:19.82] [21:19.92]and they transform the shallow sea into a rich fishing ground [21:24.30] [21:30.22]So, paradoxically, it's the roasted sands of Arabia that prevent the gulf [21:35.52] [21:35.71]from being another desert in the sea. [21:39.05] [21:51.58]The whale calf is now five months old. [21:54.89] [21:55.10]He's almost doubled in size [21:57.05] [21:57.18]and his days in his tropical nursery are coming to an end. [22:00.99] [22:01.43]It has been a warm and safe place in which to grow up [22:04.68] [22:05.00]but there's nothing to eat here for his mother. [22:08.12] [22:09.81]She has been living off her fat reserves for the last eight months [22:14.23] [22:14.52]and she's close to starving. [22:16.69] [22:17.42]She must leave now, while she still has enough energy [22:20.03] [22:20.03]to guide and protect her calf, on the long voyage ahead. [22:25.16] [22:41.95]All across the tropics, humpbacks are heading away from the Equator [22:46.74] [22:46.87]towards the rich temperate seas of both the southern and the northern hemispheres. [22:52.92] [22:55.76]These are colder, rougher, and more dangerous waters. [23:00.85] [23:12.44]Mother and calf must stay close. [23:15.51] [23:33.76]They can send sound signals to one another, above the roar of the ocean [23:37.90] [23:38.15]by slapping fins on the surface. [23:41.17] [24:01.54]In winter, the temperate seas are lashed by violent storms. [24:07.06] [24:24.01]The turbulence stirs the water, and draws nutrients up from the depths [24:30.31] [24:38.27]but nutrients alone can not support life. [24:41.91] [24:42.67]There must also be sunlight. [24:45.10] [24:48.20]In the spring, as the sun daily climbs higher in the sky [24:52.18] [24:52.41]the algae start to grow. [24:54.60] [24:55.47]Blooms the size of the Amazon Rainforest turn the seas green. [25:00.89] [25:03.75]Individually the algae are tiny [25:06.42] [25:06.82]but together, they produce three quarters of all the oxygen in our atmosphere. [25:12.86] [25:16.26]They're eaten by an array of bewildering creatures. [25:20.16] [25:20.46]Salps appear in the plankton soup. [25:23.41] [25:28.94]Individuals link together to form chains which can stretch for fifteen meters. [25:35.33] [25:45.29]Pumping water through their bodies they strain out algae and other edible particles. [25:51.30] [26:01.66]Comb jellies cruise through the water. [26:04.68] [26:04.94]They too flourish in this seasonal soup [26:08.10] [26:08.32]and for short periods, they appear in astounding numbers. [26:12.60] [26:13.59]Krill, shrimp like creatures. [26:15.87] [26:16.16]By weight they're the most abundant animals on the planet. [26:19.30] [26:19.49]A single swarm can contain two million tons of them [26:23.53] [26:32.12]and that is a lot of fish food. [26:35.59] [26:44.71]The shallow temperate seas support the greatest concentrations of fish on our planet. [26:49.78] [26:50.28]Huge shoals migrate from their overwintering grounds in the depths [26:54.20] [26:54.30]to feed in these rich waters. [26:57.16] [27:05.76]It's these shoals that support most of the world's sea mammals. [27:11.44] [27:12.29]Sea lions have all the agility and speed needed to collect what they want [27:17.32] [27:17.89]and seemingly delight in doing so. [27:20.99] [27:54.59]Dusky dolphin, often in pods two hundred strong [27:58.69] [27:58.78]work together to reap the harvest. [28:01.18] [28:04.00]They break up the shoals into smaller, more manageable balls, and all the hunters benefit. [28:09.78] [28:36.14]By midsummer, the surface nutrients have all been absorbed. [28:40.77] [28:41.21]The algae die and the food chain collapses. [28:45.58] [28:50.00]In a few special places, however [28:52.32] [28:52.43]the temperate seas sustain these levels of life throughout the summer. [28:57.35] [28:57.76]Along the coast of California, ocean currents carry a constant supply [29:02.31] [29:02.31]of nutrients up from the depths to the surface layers. [29:05.96] [29:06.86]These upwellings fertilize forests of giant kelp, that thrive in the summer sunshine. [29:13.20] [29:20.13]The algal towers are as high as a three story house [29:24.06] [29:24.24]and they can grow by half a meter a day. [29:27.79] [29:41.50]Life in the kelp is as full of drama, as in any other forest [29:46.44] [29:46.79]but the cast is less familiar. [29:49.61] [29:50.14]An army of sea urchins is mounting an attack. [29:54.22] [29:56.52]The urchin plague strikes at the kelp's holdfasts their crucial attachments to the rock. [30:03.38] [30:17.43]Holdfasts are extremely tough, but each urchin has five teeth, which are self sharpening [30:24.41] [30:24.61]and are replaced every few months. [30:27.13] [30:34.35]Urchins fell vast areas of kelp forest [30:37.80] [30:37.97]creating clearings know as urchin barrens [30:42.55] [30:45.39]yet barrens is a poor description. [30:49.13] [30:52.93]Millions of invertebrates invade the seabed. [30:56.91] [31:11.50]The most fearsome predator here is a giant. [31:14.65] [31:15.04]The sunflower starfish is a meter across, with an appetite for brittle stars. [31:22.08] [31:39.37]It uses it's feet to taste for prey. [31:43.06] [31:47.91]When it's actions are speeded up, it becomes clear that the predator's fondness for the brittle stars [31:53.97] [31:54.01]is almost matched by the brittle stars ability to get out of the way. [31:59.27] [32:10.96]Sand dollars flat sea urchins cluster together as a defense [32:16.44] [32:21.94]But it doesn't seem to work against the sunflower starfish. [32:26.31] [32:26.70]The predator extrudes it's stomach, and wraps it around it's victims liquefying their soft parts. [32:33.39] [32:34.28]Nothing is left of them, except their white skeletons. [32:38.30] [32:45.26]The Californian upwellings are seasonal and relatively small [32:49.53] [32:49.89]but in Southern Africa they're so big [32:52.50] [32:52.61]they create seas rich enough to support colonies of over a million seals. [32:58.45] [33:03.13]The Benguela Current sweeps along the western coastline of Southern Africa [33:08.04] [33:08.22]driving nutrient rich waters up to the surface [33:12.08] [33:13.42]and then, at the southern tip of Africa it meets the Agulhas Current, arriving from the east. [33:20.28] [33:20.66]The result: even richer waters. [33:24.04] [33:35.36]The seals here thrive on a diet of fish and squid. [33:40.65] [33:42.27]In temperate seas there may actually be more squid than fish. [33:47.37] [33:54.50]These are chokker squid, and they lay their egg capsules [33:58.50] [33:58.59]in sandy shallows bathed by the warmer Agulhas Current. [34:03.67] [34:11.83]Each capsule contains a hundred tiny squid. [34:16.13] [34:21.21]Within a few days they develop spots of pigment [34:23.93] [34:24.00]which, when they're adult, they will use to communicate with one another. [34:28.45] [34:40.58]With females continuing to lay eggs [34:43.48] [34:43.48]and males still preoccupied with repelling rivals, the squid drop their guard. [34:50.30] [34:53.76]Stingray. [34:55.35] [35:02.64]Short tailed stingray can be up to two meters across. [35:07.09] [35:12.83]They're the largest of all the stingrays, and they have appetites to match. [35:18.14] [35:46.04]Another predator is on the prowl. [35:49.11] [35:51.16]The aptly named ragged tooth shark. [35:54.76] [35:58.71]Raggies grow to three meters long, but they share these waters with a shark twice their size. [36:05.01] [36:21.55]The great white. [36:24.26] [36:25.60]The largest predatory fish on the planet. [36:29.31] [36:35.69]Each dawn cape fur seals leave their colony to go fishing. [36:40.64] [36:41.84]To reach the open sea, they must cross a narrow strip of water [36:45.85] [36:46.58]and that is patrolled by great whites. [36:50.72] [36:59.47]Each seal is indeed swimming for it's life. [37:03.36] [37:25.77]The shark relies on surprise. [37:28.87] [38:27.53]The great white's turn of speed is powered by a high metabolism. [38:32.46] [38:32.74]They only thrive in cold temperate seas [38:35.67] [38:35.67]for only these waters contain sufficient food necessary to fuel such a ravenous predator. [38:42.15] [39:13.54]As you travel towards the poles north or south [39:17.27] [39:17.35]the colder, stormier seas can become even richer. [39:22.01] [39:23.77]Midway between South Africa and the South Pole [39:27.17] [39:27.57]lies the isolated island of Marion. [39:31.08] [39:36.65]The island sits in the infamous "roaring forties" [39:40.47] [39:40.58]where incessant gale force winds draw nutrients up from the depths [39:45.29] [39:45.40]ensuring plenty of food for king penguins. [39:48.92] [39:51.85]The kings are returning from a three day fishing trip, with food for their chicks [39:56.94] [39:57.16]But first they must cross a crowded beach, threading their way between gigantic [40:02.66] [40:02.82]and bad tempered elephant seals. [40:06.19] [40:16.70]The two hundred thousand penguins breeding here [40:19.88] [40:19.88]are testament to the richness of the fishing. [40:23.24] [40:27.19]King chicks are dependent on their mothers for over a year [40:30.78] [40:30.85]and this puts a great deal of pressure on the parents. [40:34.93] [40:48.59]Being flightless, the returning penguins must cross the open beach on foot. [40:54.98] [41:26.15]Fur seals, that have come to the beach to breed, are waiting for them. [41:30.59] [41:38.68]Fur seals normally live on krill [41:41.37] [41:41.56]but these have now acquired an unexpected taste for blubber rich penguins. [41:47.19] [42:37.81]Penguins may be featherweights by comparison [42:40.61] [42:40.80]but they have razor sharp bills and a feisty character. [42:44.86] [42:47.81]The seal could easily lose an eye. [42:50.06] [42:50.22]The only safe way to grab a penguin is from behind, and the birds are well aware of that. [42:56.17] [43:17.79]Both animals are clumsy on this terrain [43:20.50] [43:20.64]but the penguin has the more to lose. [43:23.30] [43:35.14]Made it. [43:36.54] [43:37.55]Two out of three penguins survive the seal attacks [43:40.77] [43:40.83]and succeed in reaching their ever hungry chicks. [43:44.39] [44:13.64]The humpbacks are nearing the end of their epic journeys. [44:18.00] [44:23.19]After two months and thousands of miles, they're entering the polar seas [44:28.65] [44:28.84]both in the north and the south. [44:32.01] [44:42.19]In the far north, winter is over at last and the ice is starting to melt. [44:48.83] [44:52.59]The Aleutian Island chain running west from Alaska [44:55.88] [44:56.09]is the gateway to the Bearing Sea. [44:58.65] [44:58.89]With the retreating ice, rough weather and ferocious currents stir up these shallow seas. [45:05.58] [45:05.72]Add sunshine and the mix is spectacularly productive. [45:10.41] [45:20.20]Five million shearwaters have flown almost ten thousand miles from Australia to get here. [45:26.56] [45:27.30]In all eighty million seabirds come here for the summer [45:30.70] [45:30.78]the greatest concentration to be found anywhere on Earth. [45:35.42] [45:47.98]The humpbacks have finally arrived. [45:51.40] [46:09.80]The giant shearwater flocks hunt the krill swarms [46:13.87] [46:13.91]sometimes diving to depths of forty meters to reach them. [46:18.41] [46:40.99]A large humpback eats three tons of krill a day. [46:46.23] [46:58.07]The polar seas in summer are the most productive on the planet [47:02.24] [47:02.40]and the whales gorge themselves round the clock. [47:05.93] [47:12.84]The fat reserves they lay down now will keep them alive during the year to come [47:17.94] [47:19.43]but it may not always be this way. [47:21.86] [47:22.15]Fish and krill stocks are declining so rapidly [47:25.41] [47:25.62]that spectacles like this may soon be part of history. [47:30.07] [47:39.03]Once the mother and calf have reached their feeding grounds, they will separate. [47:44.82] [47:47.79]With luck, the calf will make the epic journey across the oceans [47:52.04] [47:52.08]from equator to pole another seventy times [47:56.03] [47:56.62]cruising back and forth between the shallow seas [48:00.10] [48:00.43]where life proliferates so abundantly on our planet. [48:07.47]

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