1 00:00:34,117 --> 00:00:36,203 A Perfect Planet. 2 00:00:43,919 --> 00:00:49,800 All life in the oceans depends on the continuous movement of water. 3 00:01:03,897 --> 00:01:07,442 There are not five separate oceans on Earth, 4 00:01:07,568 --> 00:01:09,027 but just one... 5 00:01:09,152 --> 00:01:13,949 whose parts are linked by powerful, unceasing currents. 6 00:01:16,326 --> 00:01:20,831 Every drop of seawater on Earth rides these currents, 7 00:01:20,956 --> 00:01:25,085 taking a thousand years to complete a single circuit. 8 00:01:28,880 --> 00:01:31,008 And where there are currents... 9 00:01:31,133 --> 00:01:33,010 there is life. 10 00:01:51,194 --> 00:01:53,572 Off the coast of South Africa, 11 00:01:53,697 --> 00:01:55,532 dolphins are on the hunt. 12 00:02:06,835 --> 00:02:09,421 They have found a cold-water current 13 00:02:09,546 --> 00:02:13,050 and are now travelling along it looking for food. 14 00:02:16,094 --> 00:02:18,555 Gannets follow them. 15 00:02:20,515 --> 00:02:24,645 They know that doing so is the fastest way to a meal. 16 00:02:31,026 --> 00:02:32,694 A shoal of mackerel - 17 00:02:32,819 --> 00:02:35,322 just what the dolphins have been looking for. 18 00:02:41,912 --> 00:02:45,499 They encircle the fish, driving them into a bait ball, 19 00:02:45,624 --> 00:02:48,669 and then trap them against the surface 20 00:02:48,794 --> 00:02:51,713 to prevent them from escaping to deeper water. 21 00:02:56,718 --> 00:02:59,554 Now the fish are within range of the dive-bombing gannets, 22 00:02:59,680 --> 00:03:03,433 who hit the water at 50 miles an hour. 23 00:03:27,708 --> 00:03:32,003 A sudden gathering of thousands of predators brought together 24 00:03:32,129 --> 00:03:35,340 by the flow of currents. 25 00:03:51,690 --> 00:03:54,151 Last to the feast are sharks. 26 00:04:18,675 --> 00:04:20,761 In these vast open waters, 27 00:04:20,886 --> 00:04:26,183 finding food would be all but impossible without currents, 28 00:04:26,308 --> 00:04:30,729 the highways of the seas that bring this life together. 29 00:04:35,609 --> 00:04:38,069 When the bait ball has been dispersed, 30 00:04:38,195 --> 00:04:42,866 all that is left are scales drifting downwards. 31 00:04:47,871 --> 00:04:53,960 They are part of a slow, never-ending blizzard of organic waste 32 00:04:54,085 --> 00:04:57,881 that eventually settles on the sea floor. 33 00:05:00,509 --> 00:05:03,136 But it doesn't stay here for ever. 34 00:05:04,221 --> 00:05:08,517 The currents sweep it back up into the sunlit surface waters... 35 00:05:10,018 --> 00:05:13,230 where it nourishes clouds of phytoplankton... 36 00:05:15,690 --> 00:05:20,487 simple microscopic plants that are the pastures of the seas. 37 00:05:30,705 --> 00:05:33,667 There are thousands of different kinds, 38 00:05:33,792 --> 00:05:38,004 and together they produce half of all the oxygen in the atmosphere... 39 00:05:39,339 --> 00:05:43,301 more than all our forests and jungles combined. 40 00:05:45,554 --> 00:05:48,056 And by absorbing carbon, 41 00:05:48,181 --> 00:05:52,519 they are our greatest ally in combating climate change. 42 00:05:57,607 --> 00:06:03,113 Plankton are the foundation of almost all life in the ocean, 43 00:06:03,238 --> 00:06:08,368 for in those places where the currents bring nutrients to the surface, 44 00:06:08,493 --> 00:06:11,663 they multiply in astonishing numbers... 45 00:06:12,998 --> 00:06:15,125 turning the ocean green. 46 00:06:21,673 --> 00:06:26,761 The currents travelling through our oceans bring life to seas 47 00:06:26,887 --> 00:06:29,681 that would otherwise be marine deserts. 48 00:06:34,811 --> 00:06:38,481 The Galépagos Islands lie in the path of one of them, 49 00:06:38,607 --> 00:06:41,026 the deep-flowing Cromwell Current 50 00:06:41,151 --> 00:06:44,362 that runs for 6,000 miles across the Pacific. 51 00:06:48,033 --> 00:06:51,119 As it approaches Fernandina Island, 52 00:06:51,244 --> 00:06:55,582 it rises and delivers nutrients into its shallows. 53 00:07:09,012 --> 00:07:13,600 And it also brings life to this otherwise barren island. 54 00:07:32,327 --> 00:07:34,371 Iguanas. 55 00:07:36,122 --> 00:07:38,333 There are thousands of them. 56 00:07:45,340 --> 00:07:50,220 And yet there's nothing on the island for these vegetarians to eat. 57 00:07:52,931 --> 00:07:54,182 Or... 58 00:07:54,307 --> 00:07:56,476 almost nothing. 59 00:07:59,479 --> 00:08:04,484 Cormorants bring seaweed ashore with which to make their nests. 60 00:08:06,277 --> 00:08:09,364 But what is building material for a cormorant 61 00:08:09,489 --> 00:08:11,324 is food for an iguana. 62 00:08:18,289 --> 00:08:20,709 Both these species evolved here, 63 00:08:20,834 --> 00:08:24,254 but that doesn't necessarily make them good neighbours. 64 00:08:28,842 --> 00:08:33,138 No matter. He knows where there's more elsewhere. 65 00:08:34,597 --> 00:08:37,183 He's a marine iguana... 66 00:08:42,939 --> 00:08:45,316 the only lizard in the world 67 00:08:45,442 --> 00:08:47,402 that gets its food from the sea. 68 00:08:59,706 --> 00:09:02,584 The seaweed on which he totally relies 69 00:09:02,709 --> 00:09:05,462 only grows in abundance here 70 00:09:05,587 --> 00:09:10,008 because of the nutrients brought by the Cromwell Current. 71 00:09:16,806 --> 00:09:21,186 Once in the water, he has just 30 minutes to find food. 72 00:09:29,360 --> 00:09:31,154 Any longer than that, 73 00:09:31,279 --> 00:09:34,365 and his muscles will seize up and he'll drown... 74 00:09:36,201 --> 00:09:39,996 for, like most reptiles, he can't handle the cold. 75 00:09:49,547 --> 00:09:53,676 Chilly water isn't a problem for a warm-blooded cormorant. 76 00:09:54,969 --> 00:09:57,347 She can swim in it all day, 77 00:09:57,472 --> 00:10:00,183 but can only hold her breath for a few minutes. 78 00:10:07,565 --> 00:10:09,609 He, on the other hand, 79 00:10:09,734 --> 00:10:12,278 completes his whole half-hour trip 80 00:10:12,403 --> 00:10:14,864 on one single breath. 81 00:10:16,991 --> 00:10:19,077 His flat face and sharp teeth 82 00:10:19,202 --> 00:10:22,497 make him an efficient seaweed-cropping machine, 83 00:10:22,622 --> 00:10:26,126 but with the clock ticking, he must eat fast. 84 00:10:30,588 --> 00:10:33,508 The cormorant, having caught its fish, 85 00:10:33,633 --> 00:10:36,094 goes back to the surface. 86 00:10:38,513 --> 00:10:40,223 One last mouthful, 87 00:10:40,348 --> 00:10:43,977 and it's also time for the iguana to head for home. 88 00:10:47,397 --> 00:10:50,775 But to stop his muscles from seizing up in the cold water, 89 00:10:50,900 --> 00:10:52,986 he must get back quickly. 90 00:10:57,323 --> 00:11:01,953 So he could do without the attentions of an inquisitive sea lion. 91 00:11:26,603 --> 00:11:29,939 Dry land is now just 30 metres away, 92 00:11:30,064 --> 00:11:33,401 but the biggest hurdle is still to come. 93 00:11:43,161 --> 00:11:47,457 The surging water now fights against him. 94 00:11:54,339 --> 00:11:55,632 He's out, 95 00:11:55,757 --> 00:12:00,053 but he stayed in the cold so long that he's lost his strength. 96 00:12:42,720 --> 00:12:44,597 And he's made it. 97 00:12:47,684 --> 00:12:53,481 Few reptiles on the planet have to work harder for a meal than he does. 98 00:12:56,317 --> 00:12:57,527 And tomorrow, 99 00:12:57,652 --> 00:12:59,821 he'll have to do it all over again... 100 00:13:02,782 --> 00:13:04,659 unless next time 101 00:13:04,784 --> 00:13:07,036 he can outwit his neighbour. 102 00:13:13,042 --> 00:13:17,380 Over 100,000 marine iguanas live on Fernandina... 103 00:13:18,840 --> 00:13:22,468 and each owes its existence to the Cromwell Current 104 00:13:22,593 --> 00:13:25,263 that brings nutrients to these shores. 105 00:13:28,099 --> 00:13:31,019 But there is another, much bigger current 106 00:13:31,144 --> 00:13:36,149 which carries water from the Pacific into the Indian Ocean. 107 00:13:39,444 --> 00:13:44,157 On this great journey, it travels through the islands of Indonesia, 108 00:13:44,282 --> 00:13:47,243 bringing together life from both oceans. 109 00:13:54,625 --> 00:13:59,172 A third of all the world's reef fish live here. 110 00:14:03,343 --> 00:14:06,429 Some call it the Coral Triangle, 111 00:14:06,554 --> 00:14:09,891 the most diverse marine region on Earth. 112 00:14:18,399 --> 00:14:22,195 The variety here is dazzling, not just of coral, 113 00:14:22,320 --> 00:14:25,198 but of animals of all kinds. 114 00:14:36,000 --> 00:14:40,129 Few are stranger than the flamboyant cuttlefish. 115 00:14:43,424 --> 00:14:47,387 This is a male, just five centimetres long. 116 00:14:52,975 --> 00:14:57,021 Swimming against the current isn't easy when you're small, 117 00:14:57,146 --> 00:15:00,817 so, instead, he prefers to walk... 118 00:15:02,068 --> 00:15:04,612 very, very slowly. 119 00:15:08,866 --> 00:15:11,577 He's a master of camouflage. 120 00:15:11,702 --> 00:15:14,831 But right now he wants to be noticed. 121 00:15:17,834 --> 00:15:19,794 He's looking for a mate. 122 00:15:21,754 --> 00:15:24,882 His potential partner is a giant by comparison, 123 00:15:25,007 --> 00:15:26,884 four times his size. 124 00:15:32,390 --> 00:15:34,308 When it comes to courtship, 125 00:15:34,434 --> 00:15:36,853 being flamboyant isn't enough. 126 00:15:43,317 --> 00:15:45,862 To win her over, he must dazzle. 127 00:15:53,119 --> 00:15:57,123 His aim is to deposit a packet of sperm 128 00:15:57,248 --> 00:15:59,208 inside her mouth. 129 00:16:02,086 --> 00:16:03,421 Close... 130 00:16:04,589 --> 00:16:06,382 but no cigar. 131 00:16:12,680 --> 00:16:15,183 He'll have to turn up the dazzle. 132 00:16:22,023 --> 00:16:23,774 Take two. 133 00:16:28,321 --> 00:16:29,655 Bingo! 134 00:16:41,042 --> 00:16:42,960 His job is done. 135 00:16:43,085 --> 00:16:46,964 Now she must find somewhere to lay their eggs. 136 00:16:48,966 --> 00:16:52,303 An old shell will do nicely 137 00:16:52,428 --> 00:16:55,473 if she can slip past the present occupant. 138 00:17:00,728 --> 00:17:04,815 She fastens her eggs to the underside of the shell, 139 00:17:04,941 --> 00:17:07,818 where they'll be safe from predators. 140 00:17:21,582 --> 00:17:25,920 The current that brings so much life to the Coral Triangle 141 00:17:26,045 --> 00:17:30,508 now washes the eggs with clean, oxygenated water. 142 00:17:36,889 --> 00:17:39,058 After just three weeks, 143 00:17:39,183 --> 00:17:41,060 they start to hatch. 144 00:17:45,189 --> 00:17:47,900 Smaller than a human fingernail, 145 00:17:48,025 --> 00:17:51,237 the hatchlings are now carried by the current 146 00:17:51,362 --> 00:17:53,823 to other parts of the reef. 147 00:18:01,455 --> 00:18:04,166 And in just a few months, 148 00:18:04,292 --> 00:18:09,297 this young male will be ready to find a female of his own. 149 00:18:15,303 --> 00:18:18,014 By a stroke of cosmic good fortune, 150 00:18:18,139 --> 00:18:19,849 the Earth has a satellite, 151 00:18:19,974 --> 00:18:21,517 the moon, 152 00:18:21,642 --> 00:18:25,688 which orbits our planet every 27 days. 153 00:18:29,525 --> 00:18:34,530 Its gravitational pull drags our oceans across the planet... 154 00:18:37,283 --> 00:18:40,161 and so gives us the tides. 155 00:18:44,915 --> 00:18:48,294 Unlike currents that stir the open ocean, 156 00:18:48,419 --> 00:18:51,672 the tides have their greatest impact on the coasts, 157 00:18:51,797 --> 00:18:56,719 flushing them with nutrients from both sea and land. 158 00:18:59,430 --> 00:19:03,434 And nowhere are they more violent and dramatic than here... 159 00:19:05,269 --> 00:19:08,022 Norway's Saltstraumen strait. 160 00:19:10,816 --> 00:19:12,026 Every six hours, 161 00:19:12,151 --> 00:19:14,612 nearly half a billion tonnes of water 162 00:19:14,737 --> 00:19:15,946 are forced through a channel 163 00:19:16,072 --> 00:19:19,158 just 150 metres wide. 164 00:19:20,826 --> 00:19:24,538 Its very narrowness accelerates the water... 165 00:19:25,665 --> 00:19:31,003 making this the strongest tidal pull in the world. 166 00:19:45,726 --> 00:19:50,064 Most animals caught here would be swept away. 167 00:19:53,192 --> 00:19:56,445 But not these tidal specialists. 168 00:19:56,570 --> 00:19:58,989 Eiders are one of the few ducks 169 00:19:59,115 --> 00:20:01,242 that depend totally on the ocean 170 00:20:01,367 --> 00:20:03,411 for their survival. 171 00:20:06,163 --> 00:20:09,083 And they're the only kind strong enough 172 00:20:09,208 --> 00:20:12,712 to live permanently in these racing waters. 173 00:20:20,302 --> 00:20:22,722 But there is food here, and in great quantity, 174 00:20:22,847 --> 00:20:25,433 for any that can gather it... 175 00:20:26,809 --> 00:20:28,185 mussels. 176 00:20:29,520 --> 00:20:35,234 They filter out particles of food brought to them by the tide. 177 00:20:36,569 --> 00:20:39,029 And eider ducks love mussels. 178 00:20:42,366 --> 00:20:45,035 The challenge is reaching them. 179 00:21:03,387 --> 00:21:05,556 Eiders seem to be the only creatures 180 00:21:05,681 --> 00:21:09,685 that can hold their own in the fast-flowing water... 181 00:21:12,188 --> 00:21:15,232 so they have the mussels all to themselves. 182 00:21:17,276 --> 00:21:20,863 They swallow them whole, shell and all. 183 00:21:25,284 --> 00:21:28,496 Each eider duck eats hundreds of mussels a day... 184 00:21:30,372 --> 00:21:31,999 a year-round feast 185 00:21:32,124 --> 00:21:33,876 that no others can reach. 186 00:21:46,263 --> 00:21:48,682 The tides here owe their power 187 00:21:48,808 --> 00:21:52,144 to the unique geography of the coastline. 188 00:21:53,729 --> 00:21:55,397 But elsewhere in our oceans, 189 00:21:55,523 --> 00:21:58,609 the lay of the land influences tides 190 00:21:58,734 --> 00:22:00,736 in a very different way. 191 00:22:03,864 --> 00:22:05,533 Here in the Bahamas, 192 00:22:05,658 --> 00:22:09,954 wide, shallow sandbanks mean the tide moves gently 193 00:22:10,079 --> 00:22:11,747 over the sea floor... 194 00:22:13,207 --> 00:22:15,876 turning what would be a sandy desert 195 00:22:16,001 --> 00:22:18,420 into a rich underwater habitat. 196 00:22:21,841 --> 00:22:26,762 This is the home of garden eels and razorfish. 197 00:22:31,058 --> 00:22:36,188 And fresh food arrives for them from deeper waters twice a day. 198 00:22:38,941 --> 00:22:42,444 Life seems unhurried and gentle... 199 00:22:44,196 --> 00:22:47,324 but there is trouble in paradise. 200 00:22:50,703 --> 00:22:53,497 These bottlenose dolphins eat razorfish, 201 00:22:53,622 --> 00:22:57,877 and they're not so easily fooled by vanishing tricks. 202 00:23:03,382 --> 00:23:06,886 They scan the sand with echolocating clicks 203 00:23:07,011 --> 00:23:11,432 to discover exactly where the razorfish are hiding. 204 00:23:29,074 --> 00:23:32,828 But knowing where they are is not the same as catching them. 205 00:23:38,584 --> 00:23:40,753 The more the dolphins dig, 206 00:23:40,878 --> 00:23:43,756 the deeper the razorfish burrow. 207 00:23:47,593 --> 00:23:49,887 But it's clearly not deep enough. 208 00:24:00,439 --> 00:24:02,775 Blowing jets of water into the sand 209 00:24:02,900 --> 00:24:06,820 exposes even the most hard-to-reach razorfish. 210 00:24:10,574 --> 00:24:15,371 Before long, the dolphins have had enough and they move on. 211 00:24:17,623 --> 00:24:20,501 It looks as if they have picked the sand clean... 212 00:24:26,256 --> 00:24:27,841 but here, at least, 213 00:24:27,967 --> 00:24:31,887 there really are plenty more fish in the sea. 214 00:24:42,272 --> 00:24:45,901 Closer to the land, the same tides bring nourishment 215 00:24:46,026 --> 00:24:49,530 to one of the most threatened of coastal habitats... 216 00:24:51,156 --> 00:24:52,866 mangrove forests... 217 00:24:54,493 --> 00:24:56,161 part land... 218 00:24:56,286 --> 00:24:58,205 part sea. 219 00:25:01,208 --> 00:25:03,168 Mangroves are the only trees 220 00:25:03,293 --> 00:25:06,255 capable of surviving in salt water 221 00:25:06,380 --> 00:25:11,343 and are specially adapted to it coming and going twice every day. 222 00:25:18,642 --> 00:25:22,563 As seawater floods in, fish come with it. 223 00:25:24,231 --> 00:25:26,442 Here, in the flooded forests, 224 00:25:26,567 --> 00:25:29,486 they can find both food and shelter. 225 00:25:36,160 --> 00:25:40,122 Stingrays ride on the incoming tide. 226 00:25:47,296 --> 00:25:50,382 Other commuters follow. 227 00:25:50,507 --> 00:25:54,470 Young lemon sharks, still far from full-grown, 228 00:25:54,595 --> 00:25:56,305 are looking for food. 229 00:26:12,529 --> 00:26:15,074 When the tide is at its highest, 230 00:26:15,199 --> 00:26:17,576 even adult lemon sharks 231 00:26:17,701 --> 00:26:19,328 can get into the mangroves. 232 00:26:22,247 --> 00:26:26,376 A three-metre female moves cautiously into the shallows. 233 00:26:30,297 --> 00:26:32,049 She can't stay here for long, 234 00:26:32,174 --> 00:26:34,885 but then she hasn't come here to hunt. 235 00:26:42,059 --> 00:26:43,936 She's come to give birth... 236 00:26:46,396 --> 00:26:50,275 returning to the very place where she was born. 237 00:26:53,195 --> 00:26:57,866 She has nourished the pups inside her body with a placenta, 238 00:26:57,991 --> 00:26:59,493 as we do. 239 00:27:06,208 --> 00:27:09,628 The mangroves provide an ideal nursery for them, 240 00:27:09,753 --> 00:27:13,257 and placing them here gives them an excellent start, 241 00:27:13,382 --> 00:27:17,136 but that is the end of her parental care. 242 00:27:18,720 --> 00:27:20,681 She has to return to deeper water 243 00:27:20,806 --> 00:27:23,100 before the tide goes out. 244 00:27:26,854 --> 00:27:31,066 Her young must now fend for themselves. 245 00:27:34,027 --> 00:27:38,699 The pups instinctively take refuge among the roots of the mangroves. 246 00:27:41,660 --> 00:27:47,708 They're so small they can swim deep into this tangled labyrinth. 247 00:27:59,428 --> 00:28:01,471 With the tide fast receding, 248 00:28:01,597 --> 00:28:03,640 even they need to find a place 249 00:28:03,765 --> 00:28:06,810 where they won't be left high and dry... 250 00:28:07,895 --> 00:28:09,688 a place like this... 251 00:28:11,231 --> 00:28:15,652 a permanent pool in the heart of the mangrove forest. 252 00:28:22,242 --> 00:28:25,287 Only the smallest sharks can get here, 253 00:28:25,412 --> 00:28:27,623 and only at the highest tides. 254 00:28:35,130 --> 00:28:37,841 The pups will spend the next two years here, 255 00:28:37,966 --> 00:28:43,222 perfecting the skills that make them one of the ocean's top hunters. 256 00:28:46,975 --> 00:28:48,602 And it seems... 257 00:28:49,645 --> 00:28:51,772 that there's a lot to learn. 258 00:28:58,362 --> 00:28:59,988 Got one! 259 00:29:05,452 --> 00:29:12,042 All life at the coasts has to move to the daily rhythm of the tides, 260 00:29:12,167 --> 00:29:15,754 but tides are not the same throughout the year. 261 00:29:21,760 --> 00:29:27,683 Every month, when our planet, the moon and the sun are all aligned, 262 00:29:27,808 --> 00:29:33,689 the increased gravitational pull produces particularly high tides. 263 00:29:35,440 --> 00:29:38,735 And this triggers a truly extraordinary event 264 00:29:38,860 --> 00:29:41,989 on one particular reef in the central Pacific. 265 00:29:49,037 --> 00:29:52,165 Thousands of resident surgeonfish 266 00:29:52,291 --> 00:29:55,460 begin to assemble on these high tides. 267 00:30:00,382 --> 00:30:05,262 And they are being followed by one of the largest fish in the sea... 268 00:30:11,310 --> 00:30:13,228 manta rays. 269 00:30:22,696 --> 00:30:28,285 The rays spend their year moving between coral islands. 270 00:30:30,954 --> 00:30:34,916 But it's only now, when the tide is at its highest 271 00:30:35,042 --> 00:30:36,626 and the surgeonfish have gathered, 272 00:30:36,752 --> 00:30:40,547 that they appear on this particular reef. 273 00:30:44,634 --> 00:30:46,178 Their timing is so perfect 274 00:30:46,303 --> 00:30:49,556 that they rarely have to wait more than an hour 275 00:30:49,681 --> 00:30:51,850 for the event to begin. 276 00:31:19,044 --> 00:31:23,340 At the precise moment when the tide is at its highest, 277 00:31:23,465 --> 00:31:26,426 the surgeonfish begin to spawn. 278 00:31:28,845 --> 00:31:32,974 They release billions of eggs and sperm into the water. 279 00:31:37,437 --> 00:31:40,357 Breeding in this way gives their fertilised eggs 280 00:31:40,482 --> 00:31:43,485 the best chance of being carried on the tide 281 00:31:43,610 --> 00:31:46,071 away from predators that haunt the reef... 282 00:31:49,783 --> 00:31:51,660 all except one. 283 00:31:55,163 --> 00:31:57,624 The mantas move in. 284 00:32:16,268 --> 00:32:18,395 They gorge on the eggs, 285 00:32:18,520 --> 00:32:22,399 filtering them out using specially adapted gills. 286 00:32:24,317 --> 00:32:27,320 If the mantas had arrived just an hour later, 287 00:32:27,446 --> 00:32:30,949 there would have been nothing here for them to eat. 288 00:32:37,664 --> 00:32:41,293 No-one knows how the mantas are so perfectly in tune 289 00:32:41,418 --> 00:32:43,628 with the rhythm of the tides. 290 00:32:50,135 --> 00:32:54,639 But they appear without fail whenever the surgeonfish spawn. 291 00:33:03,190 --> 00:33:05,108 Most of the eggs, however, 292 00:33:05,233 --> 00:33:07,652 are carried out into the open ocean 293 00:33:07,777 --> 00:33:10,739 before the mantas are able to eat them all. 294 00:33:28,006 --> 00:33:33,803 The rhythms of coastal life are influenced by another ocean force. 295 00:33:37,807 --> 00:33:42,145 Winds blowing over the sea so batter the surface 296 00:33:42,270 --> 00:33:45,190 that it begins to rise and fall. 297 00:33:47,234 --> 00:33:49,194 These swells may travel far 298 00:33:49,319 --> 00:33:52,739 and reach the shores of even the most sheltered bays. 299 00:33:53,740 --> 00:33:56,284 As they approach shallower water, 300 00:33:56,409 --> 00:33:58,203 they turn into waves. 301 00:34:03,124 --> 00:34:05,043 A shoal of hardyheads, 302 00:34:05,168 --> 00:34:09,881 close to the beach of Australia's Lizard Island. 303 00:34:11,091 --> 00:34:16,137 The clearness of these glassy waters shows that they lack nutrients. 304 00:34:17,722 --> 00:34:21,560 But the gentle waves expose food hidden in the sand, 305 00:34:21,685 --> 00:34:25,063 and that's what the hardyheads are looking for. 306 00:34:35,073 --> 00:34:37,075 But... they must beware. 307 00:34:41,037 --> 00:34:43,999 Packs of trevally are on the hunt. 308 00:34:52,048 --> 00:34:54,759 The hardyheads stick together. 309 00:34:55,844 --> 00:34:57,804 There's safety in numbers. 310 00:34:59,472 --> 00:35:01,308 But they're vulnerable nonetheless. 311 00:35:13,194 --> 00:35:17,032 They're so small, they can swim in the shallowest waters... 312 00:35:25,498 --> 00:35:28,460 even in the body of the waves themselves, 313 00:35:28,585 --> 00:35:31,087 out of the reach of their enemies. 314 00:35:36,635 --> 00:35:39,137 But trevally aren't their only concern. 315 00:35:49,105 --> 00:35:51,358 Blacktip reef sharks. 316 00:35:53,401 --> 00:35:56,863 They are bigger and more powerful than trevally... 317 00:35:59,115 --> 00:36:01,534 but not as fast or as agile. 318 00:36:07,248 --> 00:36:09,751 The hardyheads are well aware of them, 319 00:36:09,876 --> 00:36:13,713 but so long as they stay just out of reach, they have little to fear. 320 00:36:29,062 --> 00:36:32,857 But now the sharks and the trevally join forces. 321 00:36:39,030 --> 00:36:41,366 Together, they enter the shallows, 322 00:36:41,491 --> 00:36:44,119 each looking for a chance to attack. 323 00:37:01,970 --> 00:37:04,097 The trevally make the first move... 324 00:37:05,682 --> 00:37:09,144 and the hardyheads take refuge again in the waves. 325 00:37:10,437 --> 00:37:13,732 And this is what the sharks have been waiting for. 326 00:37:17,736 --> 00:37:22,115 Surging forwards, they chase the hardyheads out of the water... 327 00:37:23,450 --> 00:37:28,455 beaching themselves in a daring bid to hoover up their prey. 328 00:37:32,417 --> 00:37:34,294 The hardyheads that escape the sharks 329 00:37:34,419 --> 00:37:37,589 swim back out to deeper water... 330 00:37:39,382 --> 00:37:42,427 but into the mouths of the trevally. 331 00:37:53,897 --> 00:37:57,150 Now the receding waves help to pull the sharks back 332 00:37:57,275 --> 00:37:58,735 into deeper water. 333 00:38:30,308 --> 00:38:34,270 In the chaos, the seabirds get their chance. 334 00:38:39,317 --> 00:38:41,903 It's a feeding frenzy 335 00:38:42,028 --> 00:38:45,156 in only ten centimetres of water. 336 00:38:59,045 --> 00:39:02,757 The power of waves is dramatically evident 337 00:39:02,882 --> 00:39:04,926 when they crash onto our shores. 338 00:39:07,887 --> 00:39:13,601 But the biggest of all start far away from land, out at sea. 339 00:39:16,688 --> 00:39:19,983 Great storms blowing over the surface of the ocean 340 00:39:20,108 --> 00:39:23,027 raise towering walls of water. 341 00:39:26,614 --> 00:39:31,244 Such giant swells can travel for thousands of miles. 342 00:39:33,955 --> 00:39:35,665 As they approach land, 343 00:39:35,790 --> 00:39:40,253 the shallowing sea floor begins to drag on their undersides, 344 00:39:40,378 --> 00:39:42,338 and they topple forward... 345 00:39:42,463 --> 00:39:44,132 and break. 346 00:39:48,344 --> 00:39:53,016 This stirring of the ocean produces great riches. 347 00:39:56,978 --> 00:40:02,150 The Falkland Islands are surrounded by some of the stormiest waters on Earth... 348 00:40:05,987 --> 00:40:09,908 ideal hunting grounds for rockhopper penguins. 349 00:40:12,744 --> 00:40:14,120 It's the breeding season, 350 00:40:14,245 --> 00:40:19,542 and for the last two weeks, the males have been incubating the eggs by themselves. 351 00:40:21,961 --> 00:40:25,214 They're confined to the nest with nothing to eat, 352 00:40:25,340 --> 00:40:28,259 while the females are out at sea collecting food. 353 00:40:32,639 --> 00:40:36,893 All across the colony, eggs are starting to hatch. 354 00:40:39,354 --> 00:40:42,774 This male now has two youngsters to care for. 355 00:40:45,693 --> 00:40:50,448 But he has no food to give them, and he can't leave them unprotected. 356 00:40:52,450 --> 00:40:54,786 He can do nothing but wait. 357 00:41:05,088 --> 00:41:08,967 The females, after weeks fishing in the stormy seas, 358 00:41:09,092 --> 00:41:13,137 are now heading for home with food in their crops. 359 00:41:17,058 --> 00:41:19,769 There's just one problem. 360 00:41:19,894 --> 00:41:24,774 The colony sits at the top of huge cliffs. 361 00:41:26,818 --> 00:41:30,363 The waves that make feeding so good here 362 00:41:30,488 --> 00:41:33,324 have now become major obstacles. 363 00:41:35,576 --> 00:41:37,704 Timing is vital. 364 00:41:52,760 --> 00:41:54,095 Go too early... 365 00:41:55,680 --> 00:41:58,558 and they could be smashed against the rocks. 366 00:42:04,856 --> 00:42:07,108 Too late... 367 00:42:07,233 --> 00:42:10,278 and they will be carried back out to sea. 368 00:42:16,242 --> 00:42:18,745 Hooked claws now help to get purchase 369 00:42:18,870 --> 00:42:20,830 on the slippery rocks. 370 00:42:24,125 --> 00:42:26,544 But they're not out of trouble yet. 371 00:42:31,340 --> 00:42:34,052 Success depends on both judgment... 372 00:42:34,177 --> 00:42:35,595 and luck. 373 00:42:56,282 --> 00:43:00,578 Time and again, the waves drag her back in. 374 00:43:07,460 --> 00:43:09,504 She has to persevere. 375 00:43:09,629 --> 00:43:14,550 The lives of her chicks depend on her safe return. 376 00:43:47,416 --> 00:43:49,544 Finally... 377 00:43:49,669 --> 00:43:51,879 she's made it. 378 00:44:02,056 --> 00:44:04,517 They're not called rockhoppers for nothing. 379 00:44:10,398 --> 00:44:13,192 With one more jump, she's home. 380 00:44:16,571 --> 00:44:18,281 And just in time. 381 00:44:23,953 --> 00:44:26,539 Her chicks are desperately hungry. 382 00:44:34,380 --> 00:44:36,757 This is their first proper meal. 383 00:44:48,060 --> 00:44:53,107 The oceans have sustained life on our planet for millions of years. 384 00:44:57,612 --> 00:45:02,241 But today, there's growing evidence that this is changing. 385 00:45:08,372 --> 00:45:10,499 As our climate warms, 386 00:45:10,625 --> 00:45:14,503 polar ice sheets are melting at an alarming rate. 387 00:45:18,799 --> 00:45:23,554 In the Arctic alone, 14,000 tonnes of fresh water 388 00:45:23,679 --> 00:45:27,058 are emptying into the sea every second. 389 00:45:35,024 --> 00:45:39,487 This is slowing the flow of currents around the globe. 390 00:45:41,405 --> 00:45:44,617 And if the atmosphere continues to warm, 391 00:45:44,742 --> 00:45:48,871 ocean circulation could eventually stop altogether. 392 00:45:57,129 --> 00:46:01,008 Our seas would then stagnate, 393 00:46:01,133 --> 00:46:03,552 threatening the life within them. 394 00:46:07,640 --> 00:46:10,309 And there are places in the oceans today 395 00:46:10,434 --> 00:46:13,562 where this is already beginning to happen. 396 00:46:22,613 --> 00:46:24,699 The Gulf of Thailand. 397 00:46:32,290 --> 00:46:36,335 Eden's whales have lived here for generations. 398 00:46:38,963 --> 00:46:42,049 But the world around them is changing. 399 00:46:51,809 --> 00:46:56,981 Today, agricultural pollution flowing from the land... 400 00:46:58,024 --> 00:47:01,360 is beginning to suffocate this sea. 401 00:47:11,746 --> 00:47:15,166 Many fish now stay closer to the surface, 402 00:47:15,291 --> 00:47:19,420 where the waters still contain enough oxygen to survive. 403 00:47:23,966 --> 00:47:27,511 Eden's whales depend on these fish. 404 00:47:29,764 --> 00:47:31,390 They swallow huge quantities of water 405 00:47:31,515 --> 00:47:34,435 before filtering out their prey. 406 00:47:39,815 --> 00:47:45,780 It takes a lot of energy to drive their 15-tonne bulk through the water. 407 00:47:49,200 --> 00:47:50,951 And with so few fish, 408 00:47:51,077 --> 00:47:54,872 the rewards from feeding like this are barely worth it. 409 00:47:56,874 --> 00:47:59,210 So, to survive here, 410 00:47:59,335 --> 00:48:02,963 the whales have developed a new hunting technique... 411 00:48:07,760 --> 00:48:11,305 one that requires almost no effort. 412 00:48:14,100 --> 00:48:17,186 They simply open their mouths... 413 00:48:17,311 --> 00:48:19,105 and wait. 414 00:48:24,777 --> 00:48:27,738 The panicked fish jump right in. 415 00:48:35,162 --> 00:48:37,081 Swimming alongside, 416 00:48:37,206 --> 00:48:41,001 another whale scares even more into the open jaws. 417 00:48:52,888 --> 00:48:55,724 With this ingenious new technique, 418 00:48:55,850 --> 00:49:01,147 Eden's whales have found a way to survive the pressures they now face. 419 00:49:04,191 --> 00:49:05,860 All across the planet, 420 00:49:05,985 --> 00:49:07,987 animals are having to adapt 421 00:49:08,112 --> 00:49:10,072 to a changing world. 422 00:49:11,907 --> 00:49:13,993 But the speed of these changes 423 00:49:14,118 --> 00:49:16,495 will be too fast for many. 424 00:49:20,624 --> 00:49:26,338 If we could only halt our unrestrained plunder of the ocean, 425 00:49:26,464 --> 00:49:29,842 its habitats and species would recover. 426 00:49:32,761 --> 00:49:37,433 And at a time when our overexploited lands are already failing us, 427 00:49:37,558 --> 00:49:42,730 this has never been more important for humanity.