1 00:00:24,561 --> 00:00:28,001 Ati'en borough: The ocean, the largest habitat on earth 2 00:00:28,081 --> 00:00:32,361 and an inhospitable place for those of us who live on land. 3 00:00:36,641 --> 00:00:38,721 Yet, for a billion years, 4 00:00:38,801 --> 00:00:42,441 this was the only place on the planet where life existed. 5 00:00:49,881 --> 00:00:53,601 Today, descendants of those early life forms 6 00:00:53,681 --> 00:00:55,561 continue to thrive. 7 00:01:00,281 --> 00:01:05,081 They share the sea with fish but outnumber them by 70 to one. 8 00:01:07,641 --> 00:01:09,361 They have no backbones 9 00:01:09,441 --> 00:01:12,561 and have evolved into countless different forms. 10 00:01:16,641 --> 00:01:21,361 Some are huge, large-brained and intelligent. 11 00:01:28,041 --> 00:01:30,001 Others are miniscule, 12 00:01:30,081 --> 00:01:33,801 yet build the largest natural structures on the planet. 13 00:01:46,721 --> 00:01:50,961 They are marine in vertebrates, the creatures of the deep. 14 00:02:05,681 --> 00:02:08,441 They ha ve colonised every corner of the ocean 15 00:02:08,521 --> 00:02:10,721 and have a mind-boggling range 16 00:02:10,801 --> 00:02:14,561 of solutions to the problem of staying alive. 17 00:02:33,321 --> 00:02:36,441 The ocean is by no means uniform. 18 00:02:36,521 --> 00:02:40,521 Differences in depth, temperature, sunlight and currents 19 00:02:40,601 --> 00:02:42,921 pose particular challenges. 20 00:02:44,721 --> 00:02:48,961 One and a half miles down, these h ydro-thermal vents 21 00:02:49,041 --> 00:02:54,721 spew out super-heated water at 450 degrees centigrade 22 00:02:54,801 --> 00:02:57,201 from cracks in the earth's crust. 23 00:02:59,361 --> 00:03:01,161 Despite the enormous pressure, 24 00:03:01,241 --> 00:03:04,641 the total darkness and the scaldingl y high temperatures, 25 00:03:04,721 --> 00:03:07,361 the ancestors of all life may have evolved 26 00:03:07,441 --> 00:03:09,481 in a place just like this. 27 00:03:13,441 --> 00:03:15,481 Pompeii worms, 28 00:03:15,561 --> 00:03:19,801 so named for their ability to survive volcanic heat. 29 00:03:24,401 --> 00:03:29,041 They share the vents with crabs and two-metre-long tube worms. 30 00:03:31,201 --> 00:03:33,001 They can only survive here 31 00:03:33,081 --> 00:03:37,801 because the y're able to feed on bacteria that thrive around the vents. 32 00:03:45,441 --> 00:03:47,881 These colonies are extremely rare. 33 00:03:51,081 --> 00:03:55,681 Not surprisingly, most life thrives nearer the surface, 34 00:03:55,761 --> 00:03:59,121 where feeding is considerably easier. 35 00:04:06,361 --> 00:04:10,441 These are krill, tiny shrimp-like crustaceans. 36 00:04:11,921 --> 00:04:16,801 5 warms can reach astounding numbers, 60, 000 per cubic metre. 37 00:04:21,041 --> 00:04:25,441 During the night, they rise towards the surface to feed on plankton. 38 00:04:28,761 --> 00:04:31,841 Here, in the sea of Cortez off Mexico, 39 00:04:31,921 --> 00:04:34,721 the swarms attract hunters of all kinds, 40 00:04:34,801 --> 00:04:38,601 from humpback whales to shoals of preda Tory fish. 41 00:04:46,961 --> 00:04:51,321 Yet another hunter arrives. It's one from the deep. 42 00:04:54,841 --> 00:04:56,961 A humboldt squid. 43 00:05:00,081 --> 00:05:03,241 Two metres long, they ha ve a local reputation 44 00:05:03,321 --> 00:05:04,801 as man-eaters. 45 00:05:08,801 --> 00:05:12,241 Alone they are formidable enough. 46 00:05:12,321 --> 00:05:16,641 But this is a pack of hundreds. 47 00:05:21,121 --> 00:05:23,361 T he y're highly intelligent hunters. 48 00:05:23,441 --> 00:05:25,201 Their eyesight is exceptional. 49 00:05:25,281 --> 00:05:29,921 They have powerful tentacles, suckers ringed with 70, 000 hooks 50 00:05:30,001 --> 00:05:33,321 and a razor-sharp beak for tearing through flesh. 51 00:05:39,721 --> 00:05:42,881 Now the fish find that they are under attack, 52 00:05:42,961 --> 00:05:45,561 and so group together for safety. 53 00:05:50,961 --> 00:05:55,481 But the humboldt squid work as a team, herding the fish against the rocks. 54 00:06:15,001 --> 00:06:17,441 It's thought that the squid flash red and white 55 00:06:17,521 --> 00:06:19,441 not only to confuse their prey, 56 00:06:19,521 --> 00:06:23,521 but also to signal to each other when they are about to attack. 57 00:07:05,881 --> 00:07:09,401 Humboldt squid numbers are growing rapidly, 58 00:07:10,841 --> 00:07:13,001 but they remain mysterious. 59 00:07:14,761 --> 00:07:19,561 As fast as they arrived, they disappear back into the deep. 60 00:07:30,641 --> 00:07:33,201 Eight hundred miles from the south pole, 61 00:07:33,281 --> 00:07:36,681 in the shadow of a smouldering mount erebus. 62 00:07:44,761 --> 00:07:48,601 Winter temperatures are a punishing minus 40. 63 00:07:52,401 --> 00:07:57,921 This, perhaps, is the last place you might expect to find marine life. 64 00:08:17,521 --> 00:08:21,281 Now it's the beginning of the polar spring 65 00:08:21,361 --> 00:08:26,641 and for the first time in months, light reaches the sea beneath the ice. 66 00:08:35,681 --> 00:08:37,121 It's extremely cold 67 00:08:37,201 --> 00:08:39,921 and completely dark for much of the year, 68 00:08:40,001 --> 00:08:43,521 so conditions are not unlike those of the deep ocean. 69 00:08:49,481 --> 00:08:53,681 Yet in McMurdo sound life flourishes. 70 00:09:11,561 --> 00:09:15,121 The creatures here grow extremely slowly, 71 00:09:15,201 --> 00:09:20,681 but that does mean they can reach a great age and great size. 72 00:09:20,761 --> 00:09:24,321 And they occur in surprisingly large numbers. 73 00:09:38,241 --> 00:09:42,161 Three-metre-long carnivorous nemertine worms, 74 00:09:42,241 --> 00:09:47,401 red sea stars and urchins carpet the sea floor. 75 00:09:55,081 --> 00:09:58,721 This monster worm will eat almost anything 76 00:09:58,801 --> 00:10:02,001 and is constantly scanning the sea floor for food. 77 00:10:15,001 --> 00:10:19,641 Animals are swarming here in such numbers because of this, 78 00:10:20,801 --> 00:10:22,601 a dead seal pup. 79 00:10:26,641 --> 00:10:31,561 Such a great quantity of food may only arrive once in 70 years. 80 00:10:31,641 --> 00:10:34,681 But a seal's body won't be easy to eat. 81 00:10:41,521 --> 00:10:44,481 Nemertines have a snout like a harpoon, 82 00:10:44,561 --> 00:10:47,921 that enables them to puncture the skin of the corpse. 83 00:10:57,481 --> 00:11:00,321 It's harder work for the sea stars. 84 00:11:00,401 --> 00:11:04,321 They feed by pushing out their stomachs through their mouths. 85 00:11:08,321 --> 00:11:12,761 As this sea star presses its stomach against the seal's skin, 86 00:11:12,841 --> 00:11:17,921 it secrets digestive juices that dissolve the seal's tissue. 87 00:11:18,001 --> 00:11:19,761 But that takes time. 88 00:11:27,081 --> 00:11:30,281 These scavengers will feed here throughout the summer, 89 00:11:30,361 --> 00:11:32,841 until all that remains of the seal 90 00:11:32,921 --> 00:11:35,681 will be a skeleton stripped bare. 91 00:11:43,201 --> 00:11:47,961 The shallows are only a tiny part of the marine world, 92 00:11:48,041 --> 00:11:51,401 9096 of it is open water. 93 00:11:54,521 --> 00:11:58,521 Its currents carry life for thousands of miles. 94 00:12:02,681 --> 00:12:07,121 The masters of this nomadic existence are jellyfish. 95 00:12:09,441 --> 00:12:14,161 A life spent drifting in the empty ocean could be a lonely one, 96 00:12:14,241 --> 00:12:17,641 but not for this jellyfish. 97 00:12:19,161 --> 00:12:20,681 A urelia. 98 00:12:23,161 --> 00:12:26,401 S warms like this are not accidental. 99 00:12:26,481 --> 00:12:29,041 These individuals all hatched together 100 00:12:29,121 --> 00:12:32,321 when the temperature and currents were just right. 101 00:12:35,761 --> 00:12:39,481 Their timing has ensured that they can make the most of feeding 102 00:12:39,561 --> 00:12:42,281 on a late summer plankton bloom. 103 00:13:06,201 --> 00:13:10,201 Jellyfish have no brain and no blood. 104 00:13:10,281 --> 00:13:12,321 But they do have eyespots 105 00:13:12,401 --> 00:13:16,201 that enable them to tell the difference between light and dark. 106 00:13:16,281 --> 00:13:18,881 And they can move independently of the current 107 00:13:18,961 --> 00:13:21,481 by a simple form of jet propulsion. 108 00:13:30,601 --> 00:13:35,241 All jellyfish have stinging tentacles with which to catch their food. 109 00:13:35,321 --> 00:13:38,641 As they pulse their bodies, the tentacles trap plankton, 110 00:13:38,721 --> 00:13:42,201 which is then passed towards their mouth in the centre. 111 00:14:03,641 --> 00:14:07,761 A swarm of 700, 000 stinging jellyfish 112 00:14:07,841 --> 00:14:11,161 might seem a daunting prospect for a predator. 113 00:14:13,801 --> 00:14:16,001 But not for this one. 114 00:14:16,601 --> 00:14:19,481 A huge fried egg jellyfish. 115 00:14:20,801 --> 00:14:22,361 It is a killer. 116 00:14:26,761 --> 00:14:31,081 Its weapons are harpoon-like cells that cover its tentacles. 117 00:14:33,761 --> 00:14:36,401 When they come into contact with a victim, 118 00:14:36,481 --> 00:14:38,081 they spear it. 119 00:14:52,521 --> 00:14:55,761 The fried egg then hauls in its prey. 120 00:15:03,601 --> 00:15:08,121 A few luckyaurelia do manage to pull themselves free. 121 00:15:14,721 --> 00:15:17,801 But for the majority there's only one outcome, 122 00:15:19,001 --> 00:15:20,161 death. 123 00:15:35,361 --> 00:15:38,681 Jellyfish, like a great many marine in vertebrates, 124 00:15:38,761 --> 00:15:41,281 have soft, vulnerable bodies. 125 00:15:46,121 --> 00:15:49,601 They are protected by stinging cells. 126 00:15:54,561 --> 00:15:57,681 But there are other kinds of defence. 127 00:16:02,281 --> 00:16:04,041 Armour plating. 128 00:16:19,161 --> 00:16:21,881 These are spider crabs. 129 00:16:21,961 --> 00:16:25,761 They spend most of their lives in deep water. 130 00:16:25,841 --> 00:16:29,361 But once a year, off the coast of southern Australia, 131 00:16:29,441 --> 00:16:31,521 a quarter of a million crabs 132 00:16:31,601 --> 00:16:35,001 set off on a long journey to the shallows. 133 00:16:42,281 --> 00:16:45,401 They're here because they all share a problem. 134 00:16:45,481 --> 00:16:50,321 Each crab has been wearing the same suit of armour for a year now. 135 00:16:55,041 --> 00:16:58,321 And it's getting uncomfortably tight. 136 00:17:03,121 --> 00:17:07,121 So each crab eventually has to shed its shell 137 00:17:07,201 --> 00:17:10,241 and produce a bigger one. 138 00:17:10,321 --> 00:17:15,361 Replacing an old shell is, understandably, a tricky process. 139 00:17:18,201 --> 00:17:19,801 First, the crab grows 140 00:17:19,881 --> 00:17:23,881 an entirely new skin within the old shell. 141 00:17:27,081 --> 00:17:29,921 It then flexes its body to force its shell 142 00:17:30,001 --> 00:17:32,041 to split along the back... 143 00:17:35,961 --> 00:17:38,441 Before gingerly backing itself out. 144 00:17:47,481 --> 00:17:51,841 The spider crabs are not only here to moult, but to mate. 145 00:17:54,281 --> 00:17:58,401 And they grab the opportunity with considerable enthusiasm. 146 00:18:06,561 --> 00:18:10,481 Coming together in such numbers does, however, have a drawback. 147 00:18:14,001 --> 00:18:16,521 It attracts predators. 148 00:18:20,161 --> 00:18:21,721 A stingray. 149 00:18:36,601 --> 00:18:39,321 Despite there being so many potential prey, 150 00:18:39,401 --> 00:18:42,281 the stingray seems to ignore them. 151 00:18:42,361 --> 00:18:44,881 Perhaps there's safety in numbers. 152 00:18:47,361 --> 00:18:51,241 Although not all the crabs are prepared to rely on it. 153 00:18:58,841 --> 00:19:01,641 Alarm spreads amongst the crabs. 154 00:19:11,121 --> 00:19:13,761 But in fact, most of them are safe. 155 00:19:13,841 --> 00:19:15,921 This ray is being very choosy. 156 00:19:16,001 --> 00:19:18,521 It's only interested in the softest-shelled 157 00:19:18,601 --> 00:19:20,841 most recently moulted crabs. 158 00:19:33,761 --> 00:19:37,521 Once a target is singled out, there is no escape. 159 00:20:07,961 --> 00:20:10,241 When their new armour has hardened, 160 00:20:10,321 --> 00:20:13,961 the crabs return to the comparative safety of the deep, 161 00:20:14,041 --> 00:20:17,801 leaving behind only their old empty shells. 162 00:20:21,921 --> 00:20:25,441 Like spider crabs, the behaviour of most marine creatures 163 00:20:25,521 --> 00:20:29,921 is controlled by a very simple nervous system. 164 00:20:30,001 --> 00:20:32,161 But there are exceptions. 165 00:20:37,641 --> 00:20:42,081 This cuttlefish is one of the cle verest animals in the ocean. 166 00:20:43,401 --> 00:20:45,601 She has a very large brain. 167 00:20:45,681 --> 00:20:48,081 In fact, it's larger for her size 168 00:20:48,161 --> 00:20:50,601 than that of most fish or reptiles. 169 00:20:53,201 --> 00:20:57,361 Her life is both complex and full of intrigue. 170 00:20:59,681 --> 00:21:03,001 Giant Australian cuttlefish usually live alone, 171 00:21:03,081 --> 00:21:06,961 but once in their short lives they must come together to mate. 172 00:21:18,561 --> 00:21:21,801 As she approaches the traditional mating grounds, 173 00:21:21,881 --> 00:21:25,601 one of the largest males starts to show interest in her. 174 00:21:33,241 --> 00:21:37,281 She moves him away from his rivals to a quieter spot, 175 00:21:37,361 --> 00:21:41,001 a place where she will be able to lay her eggs in safety. 176 00:21:52,201 --> 00:21:57,241 The male takes the female in his arms and turns her to face him, 177 00:21:57,321 --> 00:22:01,041 before using one of his arms to pass sacks of sperm 178 00:22:01,121 --> 00:22:03,321 to an opening near her mouth. 179 00:22:39,641 --> 00:22:42,521 Once mated, he hovers over her, 180 00:22:42,601 --> 00:22:45,841 standing guard until she's laid her eggs. 181 00:22:52,601 --> 00:22:54,521 But he's got a problem. 182 00:22:54,601 --> 00:22:57,801 Males outnumber females four to one, 183 00:22:57,881 --> 00:23:02,081 so keeping her to himself is a constant battle. 184 00:23:25,001 --> 00:23:28,761 This larger rival is more difficult to intimidate. 185 00:23:31,161 --> 00:23:33,601 Cuttlefish can make very drama tic changes 186 00:23:33,681 --> 00:23:37,201 to their skin pattern in order to signal their moods. 187 00:23:42,921 --> 00:23:47,201 Flashes of bright colour and stripes that pulse along his side 188 00:23:47,281 --> 00:23:49,361 tell the rival to keep off. 189 00:24:00,441 --> 00:24:04,601 Most rivals back down at this stage, but not this one. 190 00:24:07,241 --> 00:24:10,841 Although the male's flashing signals get more and more emphatic, 191 00:24:10,921 --> 00:24:14,201 in the end he has no choice but to fight. 192 00:24:51,561 --> 00:24:55,761 I/ictory! And the male can return to guard his female. 193 00:24:59,641 --> 00:25:02,241 Cuttlefish are great communicators 194 00:25:02,321 --> 00:25:04,321 but there is a flipside. 195 00:25:04,401 --> 00:25:07,041 They can also be masters of deception. 196 00:25:16,761 --> 00:25:20,361 This male is too small to fight for a mate 197 00:25:20,441 --> 00:25:24,121 but he has another plan and it's sneaky. 198 00:25:26,601 --> 00:25:28,801 He approaches the couple cautiously, 199 00:25:28,881 --> 00:25:31,441 holding his tentacles tucked up at the front, 200 00:25:31,521 --> 00:25:35,201 mimicking a female that wants to mate. 201 00:25:35,281 --> 00:25:36,961 To complete his disguise, 202 00:25:37,041 --> 00:25:40,561 he changes colour to appear even more like a female. 203 00:25:43,081 --> 00:25:45,121 The guarding male seems convinced 204 00:25:45,201 --> 00:25:47,841 maybe he thinks his luck is in. 205 00:25:47,921 --> 00:25:50,841 Another female to add to his conquests. 206 00:26:08,161 --> 00:26:12,761 The sly, cross-dressing male edges closer and closer to the female 207 00:26:12,841 --> 00:26:14,441 holding his nerve. 208 00:26:14,521 --> 00:26:17,841 As long as he avoids being grabbed in a mating embrace, 209 00:26:17,921 --> 00:26:19,601 the sneak is safe. 210 00:26:29,881 --> 00:26:34,521 At what point the female guesses his true identity is unclear. 211 00:26:34,601 --> 00:26:36,241 But she isn't choosy, 212 00:26:36,321 --> 00:26:38,521 and surreptitiously mates with him 213 00:26:38,601 --> 00:26:41,361 right under the larger male's tentacles. 214 00:27:06,841 --> 00:27:10,401 It's time for the female to lay her eggs. 215 00:27:10,481 --> 00:27:13,041 Using the sperm from both males, 216 00:27:13,121 --> 00:27:15,921 she fertilises her eggs one by one 217 00:27:16,001 --> 00:27:18,961 and glues them to a rock in a hidden crevice. 218 00:27:22,361 --> 00:27:25,561 With luck, she will now have a mix of offspring. 219 00:27:25,641 --> 00:27:28,161 Some may become masterful males 220 00:27:28,241 --> 00:27:30,321 and others little sneaks. 221 00:27:30,401 --> 00:27:32,881 She'll have all the bases covered. 222 00:27:38,561 --> 00:27:41,601 The coastal waters of British Columbia, 223 00:27:46,601 --> 00:27:51,641 home to this four-metre-long pacific giant octopus. 224 00:27:58,401 --> 00:28:01,081 She is a formidable predator, 225 00:28:01,161 --> 00:28:04,481 but at the moment hunting isn't on her mind. 226 00:28:12,161 --> 00:28:15,121 She has just mated for the first time. 227 00:28:16,841 --> 00:28:20,041 And now she's searching for a safe refuge. 228 00:28:34,121 --> 00:28:36,281 She makes her choice carefully. 229 00:28:36,361 --> 00:28:40,201 This is going to be her home for many months to come. 230 00:28:54,401 --> 00:28:57,081 I t's her nursery den. 231 00:28:59,321 --> 00:29:02,721 A hundred thousand eggs hang from its ceiling 232 00:29:02,801 --> 00:29:05,601 and she's guarding them with her life. 233 00:29:09,201 --> 00:29:10,881 Without her to protect them, 234 00:29:10,961 --> 00:29:14,641 they would be eaten by predators or become diseased. 235 00:29:17,241 --> 00:29:20,161 She caresses them with her tentacles, 236 00:29:20,241 --> 00:29:24,801 ensuring that algae don't grow on them and that fish don't eat them. 237 00:29:26,721 --> 00:29:29,961 She constantly keeps the water moving around them 238 00:29:30,041 --> 00:29:32,641 so the y're well supplied with oxygen. 239 00:29:43,121 --> 00:29:46,321 She cares for them for six months, 240 00:29:46,401 --> 00:29:50,041 and during all this time she doesn't eat a thing. 241 00:29:58,841 --> 00:30:03,801 And now, as they are hatching, she is dying. 242 00:30:14,361 --> 00:30:17,641 One night, as the baby octopus emerge, 243 00:30:17,721 --> 00:30:21,041 she jets water over them for the last time, 244 00:30:21,121 --> 00:30:23,161 helping them on their way. 245 00:30:28,001 --> 00:30:30,521 This will be her final act. 246 00:30:36,641 --> 00:30:40,281 This is the only time she will reproduce 247 00:30:40,361 --> 00:30:45,521 and to give her young their best chance, she sacrifices her life. 248 00:30:56,081 --> 00:30:58,761 Out of the depths comes one of the largest 249 00:30:58,841 --> 00:31:01,681 and most aggressive starfish in the ocean. 250 00:31:02,881 --> 00:31:06,401 Pycnopodia, a giant sun star 251 00:31:06,481 --> 00:31:09,081 the size of a dustbin lid. 252 00:31:15,921 --> 00:31:17,201 It's a hunter. 253 00:31:17,281 --> 00:31:20,721 Each arm is covered by supersensitive tube feet 254 00:31:20,801 --> 00:31:23,561 that can detect prey by touch and smell. 255 00:31:31,001 --> 00:31:33,921 But the sun star is also partial to carrion 256 00:31:34,001 --> 00:31:38,161 and it detects the carcass of the giant octopus mother. 257 00:31:46,881 --> 00:31:48,881 The miniature suckers on its feet 258 00:31:48,961 --> 00:31:52,561 tamp onto the corpse and drag it out of the cave. 259 00:32:03,281 --> 00:32:06,241 Other scavengers rush to join the feast. 260 00:32:22,041 --> 00:32:24,281 Although it's a fearsome predator, 261 00:32:24,361 --> 00:32:27,241 pycnopodia doesn't have it all its own way. 262 00:32:29,081 --> 00:32:32,281 These sea urchins aren't speedy enough to escape, 263 00:32:32,361 --> 00:32:35,001 but they do have a formidable defence. 264 00:32:36,241 --> 00:32:38,841 The sharp spines are hard to get past. 265 00:32:38,921 --> 00:32:42,721 And what's more, the urchins can move each spine independently, 266 00:32:42,801 --> 00:32:45,401 pinching the starfish's probing arms. 267 00:32:57,841 --> 00:32:59,961 Trapped by an army of urchins, 268 00:33:00,041 --> 00:33:04,001 pycnopodia is spotted by an enormous king crab. 269 00:33:12,001 --> 00:33:14,361 Pycnopodia has more than met its match 270 00:33:14,441 --> 00:33:18,321 and within seconds, the crab rips off one of its arms. 271 00:33:28,721 --> 00:33:32,361 But that is just a temporary inconvenience. 272 00:33:32,801 --> 00:33:37,041 Starfish are able to quickly regrow a lost limb. 273 00:33:42,641 --> 00:33:46,161 The most impressive in vertebrates may seem to be the giants, 274 00:33:46,241 --> 00:33:50,841 but in fact, it's some of the smallest that can make the biggest impact. 275 00:33:54,001 --> 00:33:56,121 Every square inch of this island 276 00:33:56,201 --> 00:34:00,321 has been created by an ever-growing living superstructure, 277 00:34:00,401 --> 00:34:02,161 a coral reef. 278 00:34:03,601 --> 00:34:06,561 It's taken thousands of years to reach this size 279 00:34:06,641 --> 00:34:10,721 and it all began with creatures smaller than a pin head. 280 00:34:32,921 --> 00:34:35,721 A reef can't be built just anywhere. 281 00:34:35,801 --> 00:34:38,761 It needs something to give it a firm footing. 282 00:34:43,201 --> 00:34:47,321 A wreck like this provides an excellent foundation. 283 00:35:00,521 --> 00:35:02,881 As soon as it settles on the seabed, 284 00:35:02,961 --> 00:35:05,601 the wreck comes under attack from invaders, 285 00:35:05,681 --> 00:35:08,841 plankton, carried here by ocean currents. 286 00:35:13,721 --> 00:35:18,001 These are the microscopic larvae of barnacles, sponges 287 00:35:18,081 --> 00:35:20,681 and most importantly, corals. 288 00:35:30,761 --> 00:35:33,801 The larvae must attach themselves to the wreck. 289 00:35:34,401 --> 00:35:38,841 Once there, they can develop into young corals called polyps. 290 00:35:41,961 --> 00:35:44,441 But the polyps are very slow-growing 291 00:35:44,521 --> 00:35:47,881 and there is lots of competition from other invaders. 292 00:35:56,241 --> 00:35:58,481 Algae quickly cover the wreck 293 00:35:58,561 --> 00:36:01,321 and that's a problem for the young coral. 294 00:36:14,841 --> 00:36:17,761 Algae attract grazers. 295 00:36:24,161 --> 00:36:26,601 The polyps are in danger of being eaten 296 00:36:26,681 --> 00:36:29,481 before they've even got a proper foothold. 297 00:36:32,441 --> 00:36:37,081 If conditions are right, the survivors can go on to build a reef. 298 00:36:40,801 --> 00:36:42,601 Position is critical. 299 00:36:44,161 --> 00:36:48,601 T 00 deep, and not enough light will reach the corals for them to grow. 300 00:36:49,201 --> 00:36:53,921 T 00 shallow, and they risk being exposed to the air at low tide. 301 00:36:56,161 --> 00:36:58,081 For the reef to really flourish, 302 00:36:58,161 --> 00:37:01,801 it also needs to be in the path of currents carrying food. 303 00:37:13,041 --> 00:37:15,881 Fast-forward half a dozen years or so 304 00:37:15,961 --> 00:37:19,561 and the wreck will begin to show the first signs of corals 305 00:37:19,641 --> 00:37:21,641 visible to the naked eye. 306 00:37:27,961 --> 00:37:31,481 A decade later and the wreck will be transformed. 307 00:37:37,641 --> 00:37:40,921 Thousands of polyps will form coral heads 308 00:37:41,001 --> 00:37:43,001 that encrust its surface. 309 00:37:47,121 --> 00:37:50,161 This ship was sunk during the second world war 310 00:37:51,001 --> 00:37:55,321 and there has been enough time for a substantial reef to develop. 311 00:37:59,401 --> 00:38:01,081 After decades of gro wth, 312 00:38:01,161 --> 00:38:05,281 different species of corals dominate particular areas of the wreck. 313 00:38:13,081 --> 00:38:17,441 The fastest growing types grow best on the edges and overhangs, 314 00:38:17,521 --> 00:38:20,841 reaching far out into the water and up to the light. 315 00:38:23,401 --> 00:38:26,441 They need only a small area to establish themselves, 316 00:38:26,521 --> 00:38:31,321 yet they can rapidly grow dozens of plates or branches crammed with polyps 317 00:38:31,401 --> 00:38:33,921 to gather as much light as possible. 318 00:38:52,321 --> 00:38:56,881 Slower-growing, much more robust corals, like these brain corals, 319 00:38:56,961 --> 00:39:00,401 are better suited to the heart of the developing reef. 320 00:39:03,401 --> 00:39:07,401 It's these that give the reef their structure and permanence. 321 00:39:11,041 --> 00:39:13,801 There could be nearly 500 different species here, 322 00:39:13,881 --> 00:39:17,841 each striving to win a foothold on the rusting hulk. 323 00:39:21,561 --> 00:39:25,281 The pace of life for corals may seem to be so slow 324 00:39:25,361 --> 00:39:29,001 that it's hard to imagine that there is any conflict here. 325 00:39:33,321 --> 00:39:37,721 But as night falls, the mood on the reef changes. 326 00:39:40,841 --> 00:39:44,321 Corals are, in fact, extremely aggressive 327 00:39:44,401 --> 00:39:47,681 and will fight to death to expand their territory. 328 00:39:49,561 --> 00:39:51,761 There can be no honourable retreat. 329 00:39:51,841 --> 00:39:55,321 A winner will literally eat its enemy alive. 330 00:39:59,121 --> 00:40:02,441 Along the battlefront, the polyps of both combatants 331 00:40:02,521 --> 00:40:06,041 extrude their guts, long threadlike filaments, 332 00:40:06,121 --> 00:40:07,921 over their opponents. 333 00:40:10,481 --> 00:40:14,161 At the fringe, all that remains of the destroyed polyps 334 00:40:14,241 --> 00:40:16,001 are their skeletons. 335 00:40:17,721 --> 00:40:21,601 The coral that can digest fastest wins. 336 00:40:26,721 --> 00:40:28,721 Corals constantly grow 337 00:40:28,801 --> 00:40:31,481 over the skeletons of their dead comrades, 338 00:40:31,561 --> 00:40:33,601 building a bigger and bigger reef. 339 00:40:36,121 --> 00:40:40,961 Then, just once a year, a few days after the November full moon, 340 00:40:41,041 --> 00:40:44,841 the corals take part in a mass spawning event. 341 00:40:51,641 --> 00:40:55,161 Millions of eggs and sperm are released into the water 342 00:40:55,241 --> 00:40:57,641 and join to develop into larvae 343 00:40:57,721 --> 00:41:00,521 that drift in search of a place to settle. 344 00:41:38,241 --> 00:41:42,761 Eventually, every inch of the wreck's surface will be colonised. 345 00:41:42,841 --> 00:41:47,281 The steel will rust away and the reef will be on its own. 346 00:41:57,321 --> 00:42:01,481 Most reefs grow without the help of a wreck to start them off. 347 00:42:02,321 --> 00:42:06,681 But given time, they can create something as huge as this, 348 00:42:06,761 --> 00:42:11,001 the great barrier reef the largest living structure on earth. 349 00:42:27,921 --> 00:42:32,921 A coral reef rivals even a rainforest for its diversity of life, 350 00:42:33,721 --> 00:42:38,121 yet corals like this are found in waters where food is very scarce. 351 00:42:41,681 --> 00:42:43,041 All the creatures here 352 00:42:43,121 --> 00:42:46,961 have had to adopt a different and highly specialised way 353 00:42:47,041 --> 00:42:49,441 to gather every nourishing scrap. 354 00:42:55,201 --> 00:43:00,041 Christmas tree worms bore into the coral's skeleton for protection, 355 00:43:00,121 --> 00:43:04,241 swirling out and grabbing food particles with their feathery gills. 356 00:43:06,601 --> 00:43:09,921 Coral barnacles are, in fact, related to lobsters. 357 00:43:10,001 --> 00:43:12,401 They lie on their backs, waving their feet 358 00:43:12,481 --> 00:43:14,921 to gather any food floating past. 359 00:43:23,001 --> 00:43:26,881 Crabs have evolved many different ways of gathering food. 360 00:43:28,521 --> 00:43:30,361 This porcelain crab 361 00:43:30,441 --> 00:43:33,481 has a fan of filaments on his front legs. 362 00:43:38,401 --> 00:43:42,441 A boxer crab attaches a tiny sea anemone to each fist. 363 00:43:42,841 --> 00:43:44,121 As well as for defence, 364 00:43:44,201 --> 00:43:48,081 he uses their sticky tentacles to gather passing plankton. 365 00:43:52,521 --> 00:43:56,801 This orangutan crab's whole body is coated with sticky hairs, 366 00:43:56,881 --> 00:43:59,801 in this case, perhaps just a bit too sticky. 367 00:44:25,361 --> 00:44:29,361 This strange creature is a sea cucumber. 368 00:44:29,441 --> 00:44:33,041 It uses its tentacles to grab food from the sediment. 369 00:44:35,081 --> 00:44:40,001 There are hunters here, too, like these nudibranchs or sea slugs. 370 00:44:41,961 --> 00:44:45,481 Their vibrant colours are a warning that they are toxic. 371 00:44:45,561 --> 00:44:50,201 There are over 3, 000 species, many hunt just one specific prey. 372 00:44:51,041 --> 00:44:52,841 Some hunt each other. 373 00:44:58,321 --> 00:45:03,081 This emperor shrimp makes the most of the poisonous nature of its host. 374 00:45:03,681 --> 00:45:06,321 But it's a rather one-sided affair. 375 00:45:06,401 --> 00:45:10,081 As it feeds, the shrimp gets protection and a free ride. 376 00:45:16,641 --> 00:45:20,361 Other shrimps have developed a more balanced relationship. 377 00:45:20,441 --> 00:45:22,961 Some even solicit for partners. 378 00:45:24,961 --> 00:45:27,401 These dance for their dinner. 379 00:45:37,721 --> 00:45:43,361 And these advertise to passers-b y that they are open for business. 380 00:45:46,241 --> 00:45:48,961 They are a parasite removal team, 381 00:45:49,041 --> 00:45:51,921 providing a service for countless fish on the reef 382 00:45:52,001 --> 00:45:54,881 including those that could happily eat them. 383 00:46:03,161 --> 00:46:07,561 In return for their bra very, they get a meal that comes to them. 384 00:46:27,401 --> 00:46:31,081 Coral reefs, built by the tiniest of creatures, 385 00:46:31,161 --> 00:46:35,161 occupy less than half of 7 % of the ocean's floor. 386 00:46:37,801 --> 00:46:41,681 Yet they support a quarter of all marine species. 387 00:47:16,521 --> 00:47:22,841 Marine creatures, all without backbones, from corals to cuttlefish to crabs, 388 00:47:22,921 --> 00:47:26,321 make up the majority of life in the oceans. 389 00:47:27,681 --> 00:47:31,241 But they have also had a surprisingly important impact 390 00:47:31,321 --> 00:47:33,281 beyond the marine world. 391 00:47:34,601 --> 00:47:38,001 Their fossilised bodies, shells and skeletons 392 00:47:38,081 --> 00:47:41,881 form the limestone and chalk that now covers huge tracts 393 00:47:41,961 --> 00:47:44,361 of Asia, Europe and the Americas. 394 00:47:45,121 --> 00:47:49,401 They may be small, but over their two billion year history, 395 00:47:49,481 --> 00:47:53,081 they have literally changed the world. 396 00:48:02,601 --> 00:48:05,561 To capture some of the sequences in this episode, 397 00:48:05,641 --> 00:48:10,041 the life team had to take underwater filming into uncharted territory. 398 00:48:12,081 --> 00:48:16,321 One shoot meant spending weeks diving under two metres of ice, 399 00:48:16,401 --> 00:48:21,281 another involved laying the foundation for a new coral reef in the tropics. 400 00:48:28,121 --> 00:48:32,401 A sunken ship can make an ideal location for corals to grow. 401 00:48:32,481 --> 00:48:36,481 So with this in mind, the life team set themselves a challenge, 402 00:48:36,561 --> 00:48:38,961 to make their very own shipwreck. 403 00:48:42,441 --> 00:48:43,801 A fter months of searching, 404 00:48:43,881 --> 00:48:46,881 they find a boat in The Bahamas that might be suitable. 405 00:48:46,961 --> 00:48:50,641 But there's a lot to do before it can be sunk to the seabed. 406 00:48:50,721 --> 00:48:53,481 This prow been here for how many years? Eight years on the jetty? 407 00:48:53,561 --> 00:48:56,441 All this fibreglass insulation, it's all got to be removed. 408 00:48:56,521 --> 00:48:58,241 - Man: Yes. - And, um... 409 00:48:58,321 --> 00:49:00,121 - It's all hands to the pump, Ian. - It is. 410 00:49:00,201 --> 00:49:02,361 I'm going to go and get a pair of overalls. 411 00:49:02,481 --> 00:49:07,401 Ati'en borough: The team have to put away their cameras and get their hands dirty. 412 00:49:08,481 --> 00:49:12,521 I've got a 50-tonne boat and I'm trying to clean it with a paint scraper. 413 00:49:12,601 --> 00:49:13,937 A'i'i'en borough: Thoroughly cleaning the boat 414 00:49:13,961 --> 00:49:16,561 increases the chance that coral will grow on it 415 00:49:16,641 --> 00:49:18,441 and ensures it won't pollute the sea. 416 00:49:18,521 --> 00:49:20,761 Like changing rooms, isn't it? 417 00:49:21,681 --> 00:49:24,321 Ati'en borough: After eight years rusting on the jetty, 418 00:49:24,401 --> 00:49:26,761 there's no guarantee that she will even float. 419 00:49:26,841 --> 00:49:29,441 We actually... we do have some holes. 420 00:49:30,481 --> 00:49:32,001 Pull up. 421 00:49:32,081 --> 00:49:36,401 To get this ship ready in time for the inspectors is a massive task. 422 00:49:36,481 --> 00:49:40,321 And they're doing a brilliantjob, and we're cutting panels through 423 00:49:40,401 --> 00:49:44,121 to let the water rush through it when she starts sinking. 424 00:49:44,201 --> 00:49:48,081 Right, in you go. That's the last bit. Okay, guys. 425 00:49:48,161 --> 00:49:50,321 - Vamoose! - Man: Yeah. 426 00:49:50,401 --> 00:49:52,121 Ati'en Bo roug h: Ship-shape at last. 427 00:49:53,561 --> 00:49:57,521 Well, she's clean, she's been inspected, she's ready to be sunk. 428 00:49:57,601 --> 00:49:59,441 What can go wrong now? 429 00:50:00,961 --> 00:50:04,001 - Anchorwoman: Here's I(Evin. - Christina, here's the very la test... 430 00:50:04,081 --> 00:50:07,441 Ati'en borough: As the tail end of hurricane Dean sweeps through, 431 00:50:07,521 --> 00:50:10,561 the team are forced to put their plans on hold. 432 00:50:10,681 --> 00:50:14,361 Kevin: Winds of 750 miles an hour... 433 00:50:14,441 --> 00:50:17,081 Ati'en borough: Luck doesn't seem to be on their side. 434 00:50:23,641 --> 00:50:26,961 But two days later, good weather returns. 435 00:50:27,041 --> 00:50:29,721 Here comes the crane. Finally. 436 00:50:33,041 --> 00:50:35,921 Fingers crossed, arms crossed, legs crossed, everything is crossed. 437 00:50:36,001 --> 00:50:38,761 Ati'en borough: They urgently need to get the boat into the water 438 00:50:38,841 --> 00:50:42,481 or they won't reach the chosen wreck site before nightfall. 439 00:50:45,921 --> 00:50:48,921 She's safely in the water. So far, so good. 440 00:50:49,001 --> 00:50:50,321 It floats! 441 00:50:52,961 --> 00:50:54,601 Ati'en borough: Her final voyage. 442 00:50:56,441 --> 00:51:01,401 Cameras are mounted around the deck to film her sinking below the surface. 443 00:51:01,481 --> 00:51:05,721 We've spent a week preparing for this and finally the afternoon's arrived. 444 00:51:05,801 --> 00:51:09,641 But the light's going very quickly so we have to make a move. 445 00:51:10,921 --> 00:51:13,281 Ati'en borough: A last few holes are cut. 446 00:51:13,361 --> 00:51:17,121 It's time to pump in water and to abandon ship. 447 00:51:21,641 --> 00:51:24,561 The crew dive in, ready to film her descent, 448 00:51:24,641 --> 00:51:28,001 while the support boat moves away to a safe distance. 449 00:51:29,921 --> 00:51:32,241 There's nothing more to do but wait. 450 00:51:32,321 --> 00:51:33,721 Here we go, look at this! 451 00:51:33,801 --> 00:51:36,561 Man: Great bounce, great bounce, great bounce! 452 00:52:02,241 --> 00:52:04,601 Ati'en borough: She gently comes to rest, 453 00:52:04,681 --> 00:52:08,081 and the right way up, just as the y'd hoped. 454 00:52:18,681 --> 00:52:21,801 Now it's time to let nature take its course. 455 00:52:21,881 --> 00:52:24,161 The crew will be back over the next two years 456 00:52:24,241 --> 00:52:26,321 to see how life takes hold. 457 00:52:27,481 --> 00:52:29,881 A t this site, the wreck has a very good chance 458 00:52:29,961 --> 00:52:32,241 that it'll be colonised by coral. 459 00:52:32,321 --> 00:52:36,281 With luck and time, it will eventually become a full-scale reef. 460 00:52:39,841 --> 00:52:42,201 Meanwhile, at the other end of the world, 461 00:52:42,281 --> 00:52:45,161 the life team's challenge is very different. 462 00:52:49,201 --> 00:52:53,161 Here in Antarctica, just getting underwater will be tough. 463 00:52:58,441 --> 00:53:01,081 In order to work in such a demanding location, 464 00:53:01,161 --> 00:53:04,601 the team needed the help of the national science foundation 465 00:53:04,681 --> 00:53:07,321 at the McMurdo polar research station. 466 00:53:12,001 --> 00:53:17,161 Everyone here has to be able to cope out on the ice if there's an emergency. 467 00:53:17,681 --> 00:53:20,681 So the life team joins research scientists 468 00:53:20,761 --> 00:53:24,641 for survival training, to prepare them for any situation. 469 00:53:27,401 --> 00:53:29,121 Even one like this. 470 00:53:38,201 --> 00:53:41,001 A colleague lost in a whiteout is very serious. 471 00:53:41,081 --> 00:53:44,921 This training might mean the difference between rescue or not. 472 00:53:46,161 --> 00:53:49,081 This is supposed to simulate a whiteout. 473 00:53:49,161 --> 00:53:51,241 We'll be looking for someone who's been lost. 474 00:53:51,321 --> 00:53:55,361 And you wear the bucket so that you cannot see at all what is going on. 475 00:53:55,441 --> 00:53:57,481 And it does actually work. 476 00:53:57,561 --> 00:54:00,561 It's just... You can't see anything in this. 477 00:54:03,121 --> 00:54:04,297 Ati'en borough: With the training over, 478 00:54:04,321 --> 00:54:07,561 it's time to travel over the ice to the dive site, 479 00:54:07,641 --> 00:54:11,601 ready to go beneath the frozen surface of the Ross sea. 480 00:54:14,401 --> 00:54:17,721 But to get through this ice, thick enough to land a jet on, 481 00:54:17,801 --> 00:54:21,361 needs the help of McMurdo's specialist drilling team. 482 00:54:46,521 --> 00:54:48,041 Once the hole is drilled, 483 00:54:48,121 --> 00:54:51,561 a specially designed hut is slid into position. 484 00:54:57,361 --> 00:55:01,561 This will be the team's base for the next four weeks of diving. 485 00:55:03,241 --> 00:55:07,281 Look, this is all we need. All we need to go in here. 486 00:55:08,241 --> 00:55:10,241 The door to another world. 487 00:55:10,321 --> 00:55:12,801 Ati'en borough: All the equipment the team need for the shots 488 00:55:12,881 --> 00:55:15,121 must come in and out of this hole. 489 00:55:15,201 --> 00:55:18,641 And this is as far south as it's possible to dive. 490 00:55:18,721 --> 00:55:23,761 The ice, eight feet thick, it's here for eleven and a half months of the year. 491 00:55:23,841 --> 00:55:26,321 And we're gonna go down underneath and have a look 492 00:55:26,401 --> 00:55:29,001 to see just what it's like underneath here. 493 00:55:29,081 --> 00:55:32,401 Ati'en borough: Doug and the team venture below the ice. 494 00:56:03,921 --> 00:56:08,201 The under-ice landscape is both surprising and spectacular. 495 00:56:08,281 --> 00:56:11,081 But it's the animals they've come to film. 496 00:56:14,521 --> 00:56:18,961 So specialist time-lapse cameras are moved into position. 497 00:56:26,001 --> 00:56:29,761 The animals move very slowly at these freezing temperatures, 498 00:56:30,241 --> 00:56:34,601 but by using time-lapse to speed up the action 500 times, 499 00:56:34,681 --> 00:56:39,481 the team hopes to re veal the behaviour of these creatures for the first time. 500 00:56:51,641 --> 00:56:55,321 With air and warmth running out for this dive, 501 00:56:55,401 --> 00:56:59,121 Doug makes his way back to the lifeline and the surface. 502 00:57:21,881 --> 00:57:26,041 That is amazing! That is so beautiful down there. 503 00:57:26,121 --> 00:57:27,801 All sorts of colours, 504 00:57:27,881 --> 00:57:30,001 beautiful stalactites made of ice crystals 505 00:57:30,081 --> 00:57:32,481 hanging down from the top of the ice. 506 00:57:32,561 --> 00:57:35,481 All sorts of things on the bottom, starfish, urchins. 507 00:57:35,561 --> 00:57:37,841 Just an amazing profusion of life. 508 00:57:37,921 --> 00:57:41,041 Really lovely, totally unique, not like anywhere else. 509 00:57:41,121 --> 00:57:44,921 However, after an hour underwater, it is getting pretty cold. 510 00:57:45,001 --> 00:57:48,521 So can you give me a hand up, please? Thanks. 511 00:57:50,801 --> 00:57:54,921 Ati'en borough: There would be another month here, and over 700 dives 512 00:57:55,001 --> 00:57:57,961 before the sequence was eventually completed.