行星地球第十集：季節(jié)森林 Seasonal Forests

[00:27.87]Away from all land [00:30.87] [00:31.59]the ocean. [00:33.04] [00:34.22]It covers more than half the surface of our planet [00:37.69] [00:37.69]and yet for the most part it is beyond our reach. [00:42.54] [00:45.74]Much of it is virtually empty [00:48.56] [00:49.86]a watery desert. [00:51.96] [00:57.31]All life that is here is locked in a constant search to find food [01:03.92] [01:04.88]a struggle to conserve precious energy [01:08.13] [01:08.32]in the open ocean. [01:10.90] [01:29.81]The biggest of all fish [01:32.86] [01:33.08]thirty tons in weight, twelve meters long [01:37.28] [01:37.60]a whale shark. [01:39.88] [01:40.89]It's huge bulk is sustained by mere microscopic creatures of the sea [01:47.18] [01:47.71]Plankton. [01:49.33] [01:51.11]Whale sharks cruise on regular habitual routes [01:55.05] [01:55.28]between the best feeding grounds. [01:58.35] [02:02.14]In February, that takes them to the surface waters [02:05.85] [02:05.89]far from the coast of Venezuela. [02:08.79] [02:11.82]Others are already here. [02:14.03] [02:14.83]Baitfish have come for the same reason to feed on the plankton. [02:19.64] [02:20.23]The whale shark has timed it's arrival exactly right. [02:24.97] [02:26.30]Oddly, the tiny fish swarm around it. [02:30.42] [02:37.95]They're using it as a shield. [02:40.61] [02:44.12]Other predatory fish are lurking nearby. [02:47.89] [02:50.69]Yellowfin tuna. They seem wary of the giant. [02:55.97] [03:02.02]The shark dives, as if to escape from such overcrowding. [03:06.99] [03:11.46]Now the tuna have a chance to attack the unprotected baitfish [03:16.33] [03:28.02]but then [03:29.09] [03:29.30]back comes the giant. [03:31.99] [03:38.24]It has taken a vast mouthful of the baitfish itself. [03:42.06] [03:42.28]Plankton, it seems, is not the only food for a whale shark. [03:47.97] [03:57.89]Both shark and tuna feast together [04:01.24] [04:16.56]but the tuna must be wary. [04:19.07] [04:22.89]Even they can end up in the whale shark's stomach. [04:27.01] [04:35.03]Predators here must grab what they can, when they can [04:39.19] [04:39.47]for such events do not last long. [04:42.13] [04:45.15]The dense shoals, on which so many depend [04:47.91] [04:48.07]gather only when water conditions are perfect. [04:51.37] [05:05.13]Many predators spend much of their time cruising the open ocean [05:09.76] [05:09.90]endlessly searching. [05:12.23] [05:16.57]Plankton feeding rays do so, gliding with minimum effort. [05:21.78] [05:35.98]The oceanic whitetip shark [05:38.95] [05:41.15]another energy efficient traveler. [05:44.17] [05:46.41]It specializes in locating prey in the emptiest areas of the open ocean [05:51.84] [05:51.99]patrolling the top one hundred meters of water. [05:55.40] [06:03.72]Taste in water, is the equivalent of smell in the air. [06:08.45] [06:08.64]An oceanic whitetip is able to detect even the faintest trace. [06:13.78] [06:17.31]Small pilot fish swim with it. [06:19.61] [06:19.82]The shark can find prey far more easily than they can [06:23.02] [06:23.26]and they'll be able to collect the scraps from it's meals. [06:26.78] [06:31.58]It's long, fixed pectoral fins [06:34.80] [06:34.93]enable it to soar through the water, with the least expenditure of energy. [06:40.59] [06:45.20]This shark has found a school of rainbow runners. [06:49.56] [06:49.91]It would eat one, given the chance [06:52.59] [06:52.74]but rainbow runners are swift and agile and not easily caught [06:56.58] [07:00.10]so, it bides it's time. [07:02.38] [07:02.76]There's a chance that, eventually, it may spot a weakened fish that's catchable. [07:08.26] [07:12.02]The hunter [07:13.12] [07:13.47]endlessly waiting. [07:15.58] [07:26.19]Excitement far from land. [07:28.57] [07:37.72]A school of dolphin five hundred strong. [07:41.24] [07:56.51]They've sensed there's food around, and they're racing to catch up with it. [08:01.12] [08:09.25]The news has spread. Now a number of schools are on their way. [08:13.97] [08:27.49]They're heading towards the Azores [08:29.81] [08:29.92]volcanic islands a thousand miles west of Portugal. [08:34.08] [08:44.54]The dolphin scan the water ahead with their sonar. [08:47.65] [08:47.78]They're close to their target. [08:49.98] [08:58.24]This is it. [08:59.64] [08:59.89]Scad mackerel. [09:02.03] [09:04.77]It's difficult for a single dolphin to catch the fish. [09:08.90] [09:09.82]To avoid wasting energy the work as a group. [09:13.65] [09:20.60]They drive the fish upwards, trapping them against the surface [09:25.02] [09:27.09]and there, other predators await them. [09:30.64] [09:33.51]Cory's shearwaters. [09:35.85] [09:36.40]They're waiting for the dolphin to drive the prey closer to the surface. [09:41.23] [09:50.89]Now the shearwaters can dive down on them, descending to twenty meters or more [09:56.72] [10:00.94]and the dolphins block the baitball's retreat. [10:04.90] [10:34.72]The dolphins leave as soon as they've had their fill [10:38.58] [10:43.04]and, at last, the mackerel sink below the diving range of the birds. [10:49.23] [11:11.78]As the Sun disappears, a profound change takes place in the ocean. [11:17.46] [11:18.61]Deep water plankton start to rise from the depths [11:22.14] [11:22.19]and another hungry army prepares to receive it. [11:27.07] [11:50.44]Every night, wherever conditions are right, [11:53.58] [11:53.70]countless millions of creatures from the deep migrate to the surface, seeking food. [12:00.30] [12:08.91]A baby sailfish, fifteen centimeters long [12:12.87] [12:12.95]snaps up everything in it's path. [12:15.35] [12:15.89]In three years' time, it'll be one of the oceans most formidable hunters [12:20.49] [12:20.68]weighing sixty kilos. [12:23.07] [12:23.90]Just now, however, it's very vulnerable. [12:27.31] [13:08.36]These manta rays are giants. [13:11.83] [13:12.25]Eight meters across and weighing over two tons. [13:16.69] [13:19.64]The blade-like projections on either side of the head help to steer plankton into the manta's mouth. [13:26.71] [13:45.71]Dawn returns, and the plankton sinks back into the depths. [13:50.70] [13:52.66]If we are to follow, we must use a submarine. [13:56.93] [14:00.07]As we descend into the darkness, the pressure builds, the temperature falls. [14:06.65] [14:10.06]Below five hundred meters, new, mysterious animals appear. [14:14.97] [14:20.28]Their bizarre shapes help them to remain suspended in the dark space. [14:26.47] [14:29.54]Some resemble creatures familiar from shallower waters [14:34.64] [14:42.07]others defy classification. [14:45.69] [14:50.76]All around, organic particles drift downwards. [14:56.29] [14:57.21]Marine snow, detritus from the creatures swarming in the sunlit waters above. [15:04.07] [15:05.77]The snow is food for many animals here, like the sea spider [15:10.73] [15:11.02]a small relative of shrimps and crabs. [15:15.02] [15:25.72]Those strange leg-like appendages are feathered, to stop it from sinking. [15:32.24] [15:34.05]They can also enmesh marine snow [15:37.13] [15:37.37]which it wipes carefully into it's jaws. [15:41.24] [15:56.40]A sawtooth eel hangs upright and motionless. [16:01.74] [16:04.31]Gazing ever upwards, it watches for prey, silhouetted against the faint [16:08.93] [16:09.01]glimmerings of light from the surface. [16:12.71] [16:18.23]Days may pass before prey swims close enough for it to strike. [16:24.11] [16:28.89]Farther down still, the blackness is complete. [16:32.80] [16:33.59]No vestige of sunlight can penetrate as far as this. [16:38.84] [16:41.79]Food is very scarce and nothing can afford to waste any energy. [16:48.05] [16:50.66]A dumbo octopus simply flaps a fin [16:54.41] [16:54.79]no need for the jet propulsion used by it's shallow water relatives above. [17:00.34] [17:29.99]The weirdest, in this world of the strange, vampyroteuthis [17:35.57] [17:35.87]the vampire squid from hell. [17:39.36] [17:43.71]Disturb it and it only retreats a little distance. [17:48.69] [17:51.57]Go after it, and it has a special defense. [17:55.88] [17:59.46]To see what it does, you must switch off the lights. [18:03.58] [18:05.93]The vampire squid has lights of it's own. [18:10.06] [18:12.07]Bioluminescent bacteria shine from pockets on it's arms to confuse it's predators. [18:18.80] [18:19.80]Are those eyes? [18:21.66] [18:25.87]In fact they're spots at the end of it's mantle. [18:28.34] [18:28.55]A bite there, would leave the head unscathed. [18:31.96] [18:34.24]The threat diminishes, and vampyroteuthis disappears into the blackness. [18:41.65] [18:56.62]At last, the sea floor. [18:58.90] [18:59.20]Over two miles down, the pressure here is three hundred times that at the surface. [19:06.25] [19:06.98]It takes several months for marine snow to drift down as far as this. [19:13.50] [19:16.94]As you travel away from the rocky margins of the continents [19:21.01] [19:21.07]an immense plain stretches ahead. [19:24.55] [19:27.09]It extends for thousands of miles [19:29.96] [19:30.36]gradually sinking downwards. [19:33.08] [19:39.41]There are faint trails in the ooze, signs that even here there is life. [19:46.38] [19:53.20]These are what made some of them [19:55.93] [19:56.36]sea urchins sifting the accumulating drifts. [20:01.41] [20:05.09]Shrimps standing on elegant tiptoe [20:08.12] [20:08.28]fastidiously select the particles that appeal to them [20:12.09] [20:19.76]but, in the deep sea, as everywhere else if there are grazers, there are hunters. [20:27.39] [20:35.95]A monkfish, almost indistinguishable from the sand on which it lies. [20:42.06] [20:46.55]Why waste energy chasing around, if you can attract prey towards you with a lure? [20:53.01] [21:10.93]Maybe that one was a bit big. [21:13.84] [21:16.55]The monkfish can wait, for days if necessary, until the right sized meal turns up. [21:23.38] [21:26.77]Scavengers on the other hand, have to move around to find their food. [21:31.71] [21:34.50]Crabs can detect the faintest of tastes in the water [21:37.82] [21:37.82]and that helps them locate the latest body to drift down from above. [21:43.24] [21:44.38]Eels are already feeding on the corpse. [21:47.89] [21:54.36]Isopods, like giant marine woodlice a third of a meter long [21:58.80] [21:59.00]are ripping into the rotting flesh. [22:01.63] [22:02.86]Over the next few hours there'll be frenzied competition [22:06.14] [22:06.21]between scavengers of all kinds to grab a share. [22:10.02] [22:39.05]Just occasionally, there is a gigantic bonanza. [22:43.70] [22:52.52]The remains of a sperm whale. [22:55.37] [22:55.96]It died five months or so ago. [22:58.82] [22:59.12]There's little left but fatty blubber clinging to it's bones. [23:03.79] [23:06.47]It's flesh has nourished life for miles around [23:09.99] [23:10.15]but now the feast is almost over. [23:13.21] [23:17.87]Spider crabs, a meter across, still pick at the last putrid remains. [23:24.26] [23:31.37]A few weeks more, and nothing will be left, but bare bones. [23:36.63] [23:37.27]The crabs will have to fast, until the next carcass drifts down. [23:42.56] [23:48.93]But not all food comes from the sunlit world above. [23:53.61] [23:54.45]The floor of the Atlantic Ocean is split in two by an immense volcanic mountain chain [24:01.05] [24:01.13]that winds unbroken for forty five thousand miles around the globe. [24:06.39] [24:10.14]In places, it's riven by great fissures, from which superheated water [24:15.68] [24:15.86]loaded with dissolved minerals blasts into the icy depths. [24:20.69] [24:31.61]Clouds of sulfides solidify into towering chimneys, as tall as a three story house. [24:38.91] [24:43.13]At four hundred degrees this scalding cocktail of chemicals [24:47.25] [24:47.29]would be lethally toxic to most forms of life [24:51.15] [24:53.05]but astoundingly, a particular kind of bacteria thrives here [24:57.88] [24:58.39]and feeding on the bacteria, vast numbers of shrimps. [25:03.49] [25:12.99]So, beyond the farthest reach of the Sun's power [25:16.48] [25:16.61]a rich independent community exists, that draws all it's energy [25:21.20] [25:21.20]directly from the Earth's molten core. [25:24.74] [25:39.44]On the other side of the planet, in the western Pacific bordering Japan [25:44.07] [25:45.54]the dragon chimneys, another series of hot vents, erupting in the darkness. [25:52.70] [25:59.06]Here, more, but different bacteria thrive in a similar way. [26:05.10] [26:10.03]And here, too, more crustaceans, but quite different species [26:14.44] [26:14.44]from those around the hot vents in the Atlantic. [26:17.44] [26:23.64]These are squat lobsters, clad in furry armor [26:28.12] [26:28.28]jostling with one another beside the jets of superheated water [26:32.36] [26:32.49]for the best places, from which to graze on bacteria. [26:36.54] [26:42.58]These vents, too, like those in the Atlantic are isolated oases [26:47.88] [26:48.03]so widely separated, that each community is unique. [26:52.97] [27:03.12]Cross to the other side of the Pacific, to the deep near the Galapagos Islands [27:08.54] [27:08.70]and there are yet other fissures venting superheated water. [27:13.04] [27:18.72]One and a half miles down, at a site known as Nine North [27:23.56] [27:23.71]towering chimneys support a spectacular display of giant tubeworms. [27:29.92] [27:35.44]These vents give off so much energy [27:38.00] [27:38.08]that some of the worms reach three meters in length. [27:41.97] [27:42.32]They're the fastest growing marine invertebrates known. [27:46.23] [27:50.96]All told, over fifty different species have so far been found living here. [27:57.05] [28:01.21]The inhabitants of these bustling communities may grow at speed [28:06.08] [28:06.32]but their existence can also be short, for the vents do not erupt indefinitely. [28:12.42] [28:12.90]Suddenly, unpredictably, they may become inactive. [28:17.19] [28:21.83]Nine months have passed at Nine North. [28:25.17] [28:25.57]What were only recently chimneys teeming with life [28:28.94] [28:29.10]have turned into cold, sterile mineral monuments. [28:34.02] [28:37.34]Some eddy, deep in the Earth's crust [28:40.59] [28:40.81]diverted the volcanic energy elsewhere [28:43.82] [28:43.95]and, an entire microworld was extinguished. [28:48.73] [28:56.38]In places, volcanoes have erupted to build great submarine mountains. [29:01.95] [29:02.59]There are thought to be around thirty thousand such volcanoes [29:06.86] [29:07.18]some, measured from the sea floor, are taller than Everest. [29:12.26] [29:17.94]Sheer cliffs soaring to drowned volcanic peaks. [29:23.13] [29:34.43]Powerful currents sweep up the mountains' flanks [29:37.72] [29:37.78]transporting nutrients from deep water towards the summits. [29:42.59] [29:45.29]The hard rock provides excellent anchorage [29:48.08] [29:48.14]for communities of great variety and stunning color. [29:52.80] [29:54.61]Soft corals, several meters across collect the marine snow as it drifts past. [30:02.12] [30:04.35]Whip corals stretch out into the current. [30:08.29] [30:10.44]Giant sponges filter nourishment from the cold water. [30:15.21] [30:29.49]A richly varied community flourishes here [30:32.50] [30:32.81]sustained by the nutrients and detritus in the icy currents that flow around the peak. [30:39.57] [30:44.24]Yet it is all blossoming on an extinct volcano [30:48.32] [30:48.46]a mile below the reach of the Sun. [30:51.78] [31:16.26]A nautilus. It spends it's days hiding four hundred meters down [31:21.12] [31:21.23]But as night falls, it ascends up to the reefs, to look for food. [31:26.75] [31:31.69]It's graceful shell contains gas filled floatation chambers, that control it's depth. [31:38.73] [31:40.98]It's powered by a jet of water, squirting from a siphon [31:45.96] [31:47.69]but it travels shell first, so it can't see exactly where it's going. [31:53.19] [31:58.29]It's nearest living relatives are squid and octopus [32:01.78] [32:01.90]which, over evolutionary time, have both lost their shells [32:06.58] [32:06.76]and the octopus has become one of the nautilus' major predators. [32:11.38] [32:11.84]It's a master of disguise. [32:14.73] [32:20.67]The nautilus keeps well clear of them. [32:23.91] [32:26.13]It's small tentacles carry highly developed chemical sensors [32:30.54] [32:30.67]which can detect traces of both predators and prey. [32:35.40] [32:40.55]It uses it's water jet to dig in the sand. [32:45.03] [32:49.78]Because it devotes so little energy to swimming, it only needs a meal once a month. [32:55.76] [33:00.68]Got something. And just as well. Dawn is approaching and it has to puff it's way [33:07.20] [33:07.20]back, to deeper waters. [33:10.63] [33:31.05]Thirty miles away, shoals of squid are jetting upwards towards the surface. [33:36.85] [33:38.26]By night, they seek small fish among the plankton, but they're cautious. [33:43.28] [33:50.77]Pacific spotted dolphin. [33:53.46] [33:57.11]They're guided by their sonar. [33:59.70] [34:04.32]The dolphin, as so often, are working as a team, synchronizing their attacks [34:09.69] [34:09.86]to confuse their prey. [34:11.98] [34:30.16]As dawn approaches, squid and fish and plankton retreat downwards, to shelter in the darkness. [34:38.30] [35:03.71]Some of these isolated volcanoes [35:06.39] [35:06.39]rise as much as nine thousand meters from the sea floor, reaching close to the surface. [35:12.86] [35:16.34]Around these peaks invigorated by daily sunshine [35:20.00] [35:20.11]marine life flourishes in spectacular abundance. [35:25.29] [35:33.68]Fish crowd here, because the volcano forces nutrients to the surface [35:38.99] [35:39.19]encouraging the plankton to bloom. [35:42.57] [36:00.71]An oceanic wanderer, a mola mola [36:03.56] [36:03.68]stops by to be cleaned by reef fish, at the sea mount edge. [36:08.90] [36:16.46]Butterfly-fish pluck string-like parasites from it's flanks. [36:22.02] [36:28.27]The huge fish lives on jellyfish over a thousand meters down [36:32.69] [36:32.83]where the water is twenty degrees colder [36:36.08] [36:36.77]so, a brushup near the surface, allows it to warm up [36:41.11] [36:41.20]before making more deep water forays. [36:45.44] [36:52.17]The summit of this volcanic mountain rises above the surface of the sea. [36:57.91] [36:58.70]It's Ascension Island [37:01.22] [37:01.60]eight hundred miles from any other land, a welcome vital haven for long distance travelers. [37:10.08] [37:14.09]Frigatebirds spend months continuously airborne at sea [37:18.44] [37:18.66]but at nesting time, they come to Ascension from all over the ocean. [37:24.13] [37:28.32]The island's barren slopes of volcanic ash and lava [37:32.15] [37:32.22]might seem to offer perfectly good sites for a nest [37:36.86] [37:37.93]but the frigates choose an even more isolated site [37:42.41] [37:43.94]Boatswain Bird Island, a lonely pillar, just of Ascension's coast. [37:49.81] [37:57.76]Frigates are the world's lightest bird, relative to their wingspan [38:02.21] [38:02.48]and they can soar for weeks on end with minimal effort. [38:07.25] [38:10.94]They seem much more at home in the skies, than in a crowded colony on land [38:15.87] [38:16.19]but nest, they must. [38:18.85] [38:20.51]They come from all over the Atlantic to this, their only colony. [38:25.59] [38:28.72]There are boobys here, too. [38:30.81] [38:35.78]To raise their young, seabirds worldwide seek such remote islands. [38:42.09] [38:52.44]Swimmers also come to Ascension to breed. [38:56.03] [38:57.52]A female green turtle approaches the coast. [39:01.48] [39:04.22]She's not eaten once, in two months. [39:07.65] [39:09.02]She may have traveled one thousand miles from her feeding grounds [39:12.94] [39:13.21]the greatest journey of her kind. [39:16.40] [39:23.27]Many others are here, too, resting on the sandy sea floor [39:27.21] [39:27.21]awaiting the darkness of night, when it'll be safer to visit the beaches. [39:32.59] [39:38.44]Eggs that were laid a few weeks ago, at the start of the season [39:42.40] [39:42.48]are beginning to hatch. [39:44.87] [39:56.87]Most hatchings happen at night. [39:59.55] [40:00.16]Now, in the light of day, the young are extremely vulnerable. [40:05.02] [40:10.68]They must get to the sea as soon as possible [40:13.80] [40:16.16]but their trials have only just begun. [40:19.76] [40:32.15]Many will drown in the pounding waves. [40:36.47] [41:00.32]During the next twenty years, the vast majority will inevitably die [41:05.83] [41:05.93]but those that survive will, eventually, as their mothers did before them, [41:10.21] [41:10.44]return to the very same beach where they were hatched. [41:14.63] [41:16.57]How they find their way back [41:18.38] [41:18.47]across thousands of miles of open ocean, we still have no idea. [41:23.99] [41:32.02]A frigate soars. [41:34.60] [41:35.70]Somewhere, beneath the surface below, [41:38.41] [41:38.68]there is the food it must have. [41:41.28] [41:41.90]But where? [41:43.75] [41:45.39]Those that fly above the ocean [41:47.55] [41:47.59]must be able to read the signs of fresh supplies, or perish. [41:52.47] [41:55.66]A hundred miles from the Mexican coast, and keen eyes have spotted movement. [42:01.54] [42:05.99]Sailfish, three meters long, are closing in on prey. [42:11.58] [42:17.07]They will only use just enough energy to make their kill [42:21.43] [42:22.07]never wasting a fin stroke. [42:24.70] [42:29.01]Nearly a hundred sailfish have surrounded a single school of baitfish. [42:33.60] [42:33.60]It's very rare to see so many of these hunters in one place. [42:38.27] [42:40.91]To herd their prey, the predators raise their huge dorsal fins. [42:45.76] [43:03.53]A mistimed strike by one sailfish, could fatally damage another [43:08.00] [43:08.00]but each continually changes it's color, from blue, to striped, to black [43:13.21] [43:13.50]that warns it's companions of it's intentions and also confuses the prey. [43:19.17] [43:21.91]As the shoal is driven nearer the surface, it comes within the range of the seabirds. [43:27.91] [43:42.01]Out here, in the open ocean, there is nowhere for the baitfish to hide. [43:47.35] [44:29.63]Sailfish live a high octane life. [44:33.31] [44:33.74]To survive, they must find prey daily [44:37.26] [44:37.68]so their entire existence will be spent on the move. [44:42.60] [44:53.14]Over ninety percent on the living space for life on our planet, is in the oceans [45:00.25] [45:00.84]Home to the biggest animal that exists [45:04.50] [45:04.63]or has ever existed. [45:07.16] [45:08.53]the blue whale. [45:11.44] [45:18.26]Some weigh nearly two hundred tons [45:21.64] [45:21.88]twice the size of the largest dinosaur. [45:25.38] [45:30.07]Despite their great size, we still have little idea of where they travel in the vast oceans [45:36.86] [45:37.02]and none at all of where they go to breed. [45:41.20] [46:09.67]The largest animal on Earth feeds almost exclusively [46:14.01] [46:14.25]on one of the smallest krill, shrimp-like crustaceans. [46:20.30] [46:21.40]They take many tons of water into their ballooning throats in a single gulp [46:27.01] [46:27.19]and sieve out what it contains. [46:30.81] [46:36.78]Every day, each one swallows some four million krill. [46:43.51] [46:45.60]Such gargantuan harvests depend on the continuing fertility of the oceans [46:52.52] [46:54.77]But global changes now threaten the great blooms of plankton [46:59.25] [46:59.34]on which the whales depend. [47:01.91] [47:04.00]Once and not so long ago [47:06.83] [47:07.25]three hundred thousand blue whales roamed the oceans [47:11.28] [47:11.93]now, less than three percent of that number remains. [47:16.64] [47:20.65]Our planet is still full of wonders. [47:24.21] [47:24.51]As we explore them, so we gain not only understanding, but power. [47:31.03] [47:32.63]It's not just the future of the whale that today lies in our hands [47:37.44] [47:37.66]it's the survival of the natural world in all parts of the living planet. [47:43.96] [47:45.03]We can now destroy, or we can cherish. [47:49.54] [47:51.88]The choice is ours. [47:58.70]

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