1 00:00:52,619 --> 00:00:56,749 The waters that cover most of the planet are in constant movement. 2 00:00:57,290 --> 00:00:59,554 As the moon circles around the spinning earth, 3 00:00:59,793 --> 00:01:04,196 so the pull of its gravity causes the oceans to rise and fall, 4 00:01:04,397 --> 00:01:10,029 and twice every day, the sea surges up and down the coasts of the continents. 5 00:01:18,845 --> 00:01:20,870 In the Bay of Fundy in North America, 6 00:01:21,047 --> 00:01:24,107 the shape of the coast and the slope of the seabed 7 00:01:24,284 --> 00:01:28,448 produces the highest tides of all, rising 50 feet. 8 00:01:39,365 --> 00:01:43,529 Living in this in-between world, which is neither sea nor land, 9 00:01:43,703 --> 00:01:46,433 demands very special talents. 10 00:01:54,547 --> 00:01:56,981 This is a battle ground. 11 00:02:09,963 --> 00:02:14,366 In many places, the sea is forcing the land to retreat, cutting back its cliffs 12 00:02:14,534 --> 00:02:19,267 and leaving islands and towers as markers of the territory that the land has lost 13 00:02:20,006 --> 00:02:21,667 The debris is swept away 14 00:02:21,841 --> 00:02:25,902 and strewn on beaches farther down the coast as sand and gravel. 15 00:02:30,350 --> 00:02:33,183 In some places, the land is advancing. 16 00:02:33,419 --> 00:02:37,617 In the tropics, mangroves are moving out into the sea, gathering mud 17 00:02:37,790 --> 00:02:40,918 and building new territory for land-living creatures. 18 00:02:43,429 --> 00:02:44,919 Even in the mouths of rivers, 19 00:02:45,098 --> 00:02:49,762 where fresh water laden with sediment mingles with the salt water of the sea, 20 00:02:49,936 --> 00:02:53,736 new land is being created of a sort. 21 00:02:59,078 --> 00:03:02,275 I'm in an estuary in the west of England. 22 00:03:02,515 --> 00:03:07,885 You might think that this mud is not the most attractive stuff in which to live. 23 00:03:08,188 --> 00:03:12,955 Certainly, animals that do live in it have to face some severe problems. 24 00:03:13,226 --> 00:03:16,957 Part of their time they're out of water like this, 25 00:03:17,197 --> 00:03:19,529 part of the time they're underwater. 26 00:03:19,799 --> 00:03:21,767 The saltiness of the water, too, varies. 27 00:03:21,935 --> 00:03:26,201 Fresh water comes down from the land, the tides bring in salt water. 28 00:03:26,439 --> 00:03:32,002 And then there's the nature of this extraordinarily sticky mud itself. 29 00:03:32,946 --> 00:03:35,642 It is so glutinous that little oxygen gets into it 30 00:03:35,815 --> 00:03:40,445 but the rewards for enduring these unpromising conditions are high. 31 00:03:45,158 --> 00:03:48,355 Edible particles deposited on the surface of the mud 32 00:03:48,528 --> 00:03:53,591 are cautiously sucked up by the searching siphon of Scrobicularia, 33 00:03:53,833 --> 00:03:58,827 a mollusc whose main body, enclosed in a shell, hides in the mud for safety. 34 00:03:59,305 --> 00:04:02,706 A tiny crustacean, Corophium, half an inch long, 35 00:04:02,875 --> 00:04:05,969 grazes on the bacteria which proliferate in millions, 36 00:04:06,246 --> 00:04:09,215 breaking down rotting organic matter in the mud. 37 00:04:11,117 --> 00:04:12,448 Ragworms live in burrows 38 00:04:12,619 --> 00:04:17,056 and will tackle Corophium, algae, bacteria, almost anything that's around. 39 00:04:25,999 --> 00:04:28,524 The puddles are flecked with floating mucus. 40 00:04:28,701 --> 00:04:32,501 It is produced by spire shells, no bigger than grains of wheat. 41 00:04:32,772 --> 00:04:37,232 The mucus attracts bacteria, and the spire shells eat the lot. 42 00:04:50,957 --> 00:04:54,484 The peacock worm fans out its tentacles from the top of its tube 43 00:04:54,661 --> 00:04:57,653 to gather food particles before they settle. 44 00:05:10,043 --> 00:05:12,273 Beating threads on each filament of the fan 45 00:05:12,445 --> 00:05:15,710 transport the catch down to the mouth at the centre. 46 00:05:20,253 --> 00:05:23,950 While it feeds, it also disgorges a cement of mud and mucus 47 00:05:24,123 --> 00:05:26,318 and builds up the margin of its tube. 48 00:05:32,765 --> 00:05:34,960 The cockle lies with its shell agape, 49 00:05:35,134 --> 00:05:38,661 filtering the water by sucking it in through one siphon... 50 00:05:40,740 --> 00:05:43,641 ...and blowing it out through another. 51 00:05:45,745 --> 00:05:48,771 Mussels use the same technique, collecting within their shells 52 00:05:48,948 --> 00:05:54,580 substantial quantities of the abundant and nutritious drifting particles. 53 00:06:00,059 --> 00:06:03,256 When the tide goes out, they clamp their shells tightly together 54 00:06:03,429 --> 00:06:06,694 to keep in their moisture and to keep out attackers, 55 00:06:06,999 --> 00:06:09,331 but some creatures know how to deal with that. 56 00:06:18,544 --> 00:06:22,878 Each oyster-catcher has its favourite technique for dealing with mussels. 57 00:06:23,249 --> 00:06:25,683 It is usually the same as that used by its parents 58 00:06:25,852 --> 00:06:31,222 though a bird needs years of practice before it becomes really expert. 59 00:06:31,691 --> 00:06:36,151 Some hunt in the shallow waters for mussels that have not yet shut their shells. 60 00:06:40,767 --> 00:06:44,794 Others carry unattached shells away from the main flock 61 00:06:44,971 --> 00:06:46,598 so they've got a little privacy. 62 00:06:46,906 --> 00:06:51,775 They skilfully place the mussel in such a position that they can cut it open along its hinge. 63 00:07:05,224 --> 00:07:08,751 Other individual birds resort to brute force. 64 00:07:08,995 --> 00:07:11,463 They hammer their way in through the shell itself. 65 00:07:22,308 --> 00:07:26,438 As the tide retreats still further, spire shells are exposed, 66 00:07:26,612 --> 00:07:30,605 as many as 35,000 buried within a single square yard. 67 00:07:30,850 --> 00:07:34,115 All these mud feeders together constitute a rich prize, 68 00:07:34,287 --> 00:07:36,482 and there are abundant claimants. 69 00:07:50,770 --> 00:07:53,739 Sandpipers, on migration, depend on them, 70 00:07:53,906 --> 00:07:57,899 but at all times of the year, wading birds come to the estuaries to feed. 71 00:08:01,113 --> 00:08:03,741 The godwit, equipped with long legs and a long bill, 72 00:08:03,916 --> 00:08:05,884 can wade in water several inches deep 73 00:08:06,052 --> 00:08:08,987 and collect food before it can be reached by other birds. 74 00:08:10,823 --> 00:08:13,291 The curlew prefers to work out of water. 75 00:08:13,659 --> 00:08:16,890 Its long bill enables it to probe deep into the mud for a worm, 76 00:08:17,129 --> 00:08:19,620 and serves equally well as a pair of forceps. 77 00:08:24,604 --> 00:08:27,869 The dunlin is a smaller bird and goes for smaller prey: 78 00:08:28,107 --> 00:08:29,574 Ragworms and insect larvae. 79 00:08:29,876 --> 00:08:32,470 It feels for its food with its short bill. 80 00:08:56,269 --> 00:08:58,396 The ringed plover, with a very short bill, 81 00:08:58,704 --> 00:09:02,265 can only collect food from the surface and locates it by sight. 82 00:09:02,542 --> 00:09:06,672 It works alone so that its prey won't be disturbed by pattering feet 83 00:09:06,846 --> 00:09:09,212 and withdraw before being spotted. 84 00:09:11,517 --> 00:09:13,075 The scything action of the avocet 85 00:09:13,252 --> 00:09:15,584 collects creatures that live in the liquid mud. 86 00:09:24,830 --> 00:09:28,698 Their bills are very sensitive. As soon as they close on something edible, 87 00:09:28,868 --> 00:09:31,462 the bird can juggle it up into its mouth. 88 00:10:12,378 --> 00:10:16,712 The quantities of food taken by wading birds from estuaries is enormous. 89 00:10:16,882 --> 00:10:21,376 Some species consume every day about a third of their own weight in food. 90 00:10:21,554 --> 00:10:24,114 In a year, a single oyster-catcher 91 00:10:24,290 --> 00:10:27,316 can consume the flesh over half a ton of cockles, 92 00:10:27,593 --> 00:10:31,962 and many an estuary supports tens of thousands of wading birds, 93 00:10:32,164 --> 00:10:34,462 so these places are rich indeed. 94 00:10:38,137 --> 00:10:41,197 As the river brings down more and more particles of mud, 95 00:10:41,440 --> 00:10:44,432 so the flats grow bigger and higher, 96 00:10:44,644 --> 00:10:49,775 and on their surface they develop a slimy skin, 97 00:10:50,082 --> 00:10:54,018 and that's formed by microscopic plants, algae. 98 00:10:54,353 --> 00:10:57,254 They start the process of consolidation. 99 00:10:57,990 --> 00:11:02,222 But soon, bigger plants get root, like this glasswort, 100 00:11:02,395 --> 00:11:05,228 and now the process really speeds up. 101 00:11:08,834 --> 00:11:13,897 As the high tide brings in more mud particles, they clog around the stems of the glasswort 102 00:11:14,073 --> 00:11:17,167 and don't swill back to the sea when the tide fall 103 00:11:17,643 --> 00:11:21,170 So with each new tide, the flats grow higher and higher. 104 00:11:23,849 --> 00:11:27,012 Glasswort is a plant of the cold estuaries of Europe. 105 00:11:27,253 --> 00:11:32,816 In the tropics, the colonisers of mud are not small plants but trees: 106 00:11:32,992 --> 00:11:34,357 Mangroves. 107 00:11:37,096 --> 00:11:41,055 This mud is the pulverised remains of rocks eroded from the Himalayas 108 00:11:41,233 --> 00:11:44,464 that has been carried down by the Ganges for 1,000 miles 109 00:11:44,637 --> 00:11:47,128 and dumped on the edge of the Bay of Bengal. 110 00:11:47,573 --> 00:11:52,977 This is the biggest intertidal forest of all, the Sunderbans, 4,000 square miles of it, 111 00:11:53,279 --> 00:11:57,079 and here roam many animals that usually live in dry-land forests. 112 00:11:58,617 --> 00:11:59,948 Axis deer. 113 00:12:11,664 --> 00:12:14,690 Woodpeckers: The Indian golden-banded. 114 00:12:20,773 --> 00:12:22,240 And wild boar. 115 00:12:26,445 --> 00:12:30,973 But mangrove forests also harbour creatures that live nowhere else at all. 116 00:12:31,383 --> 00:12:35,080 The proboscis monkey eats almost nothing but mangrove leaves. 117 00:12:35,354 --> 00:12:38,050 It developed that specialism on the island of Borneo, 118 00:12:38,257 --> 00:12:42,887 and has never spread overseas, trapped by its own specialised requirements. 119 00:12:50,102 --> 00:12:53,936 Mangroves themselves are distributed widely through the tropics, 120 00:12:54,206 --> 00:12:57,300 for they have evolved from many different plant families 121 00:12:57,476 --> 00:13:00,775 and today there are some 40 different species of them. 122 00:13:02,081 --> 00:13:05,676 The flowers of this pioneering mangrove are pollinated by the wind. 123 00:13:05,951 --> 00:13:09,853 The seed doesn't immediately leave the parent tree. 124 00:13:10,089 --> 00:13:12,387 It starts to grow while it is still attached, 125 00:13:12,591 --> 00:13:17,119 producing a green shoot a foot long with a sharp end to it. 126 00:13:19,732 --> 00:13:21,461 If it falls when the tide is in, 127 00:13:21,634 --> 00:13:23,864 it floats horizontally in the buoyant salt water 128 00:13:24,036 --> 00:13:27,062 and may be carried for miles before being stranded. 129 00:13:27,339 --> 00:13:32,902 If the tide is out, it stabs the mud and stays in that position when the tide returns. 130 00:13:33,279 --> 00:13:37,739 It puts out rootlets from the bottom and leaves from the top, 131 00:13:37,917 --> 00:13:40,818 and within a few days, it's firmly established. 132 00:13:43,222 --> 00:13:45,452 Just as in cold-water estuaries, 133 00:13:45,624 --> 00:13:48,058 there's a lot of organic matter in this mud. 134 00:13:48,427 --> 00:13:54,161 Because it's so sticky, it isn't stirred up, so there's little oxygen in it, 135 00:13:54,333 --> 00:13:57,894 and the process of rotting produces within the mud itself 136 00:13:58,070 --> 00:14:03,474 an acid, smelly, poisonous chemical: Hydrogen sulphide. 137 00:14:04,844 --> 00:14:09,474 So these roots don't go down far into the mud. 138 00:14:09,782 --> 00:14:14,310 Instead, they support the trees by their sheer number. 139 00:14:14,687 --> 00:14:18,851 But what about the other things that normal roots do for normal trees, 140 00:14:19,024 --> 00:14:23,484 like gathering nutrients and water and oxygen? 141 00:14:23,796 --> 00:14:27,664 Well, these roots deal with the nutrient problem like this. 142 00:14:34,740 --> 00:14:38,972 It has this cluster of very fine roots 143 00:14:39,144 --> 00:14:43,137 which don't go more than an inch or so below the surface of the mud, 144 00:14:43,315 --> 00:14:48,014 but it is on the surface of the mud that the bulk of the nutrients are found. 145 00:14:48,554 --> 00:14:52,752 As for water, there's plenty of it here, but it's salty. 146 00:14:52,992 --> 00:14:59,329 Some mangroves have a special membrane around the cells in the root hairs 147 00:14:59,498 --> 00:15:01,830 which filters off the salt. 148 00:15:02,201 --> 00:15:06,467 Others absorb the salt but then excrete it from the leaves, 149 00:15:06,639 --> 00:15:10,871 or concentrate it in the leaf and then the leaves are shed. 150 00:15:11,277 --> 00:15:15,941 And oxygen, well, there are several different solutions to that problem. 151 00:15:16,115 --> 00:15:19,915 This mangrove has pores actually in these prop roots 152 00:15:20,085 --> 00:15:22,883 which absorb the oxygen directly. 153 00:15:23,622 --> 00:15:26,682 This one has roots which actually grow upwards, 154 00:15:26,859 --> 00:15:31,159 so keeping pace with the rising surface of the accumulating mud. 155 00:15:31,630 --> 00:15:36,693 It's not only plants in the mangrove swamps that have difficulty in getting oxygen. 156 00:15:36,869 --> 00:15:43,274 So do animals, and this time, low tide, is a period of particular difficulty. 157 00:15:44,176 --> 00:15:47,077 Many molluscs, like cockles and mussels elsewhere, 158 00:15:47,279 --> 00:15:49,975 shut their shells to keep what moisture they have 159 00:15:50,149 --> 00:15:53,516 and wait for the food-and-oxygen-bearing water to return. 160 00:15:53,752 --> 00:15:59,987 For them, it's a period of inactivity, but for other creatures, it's just the opposite. 161 00:16:12,571 --> 00:16:14,835 The mudskipper, of course, is a fish. 162 00:16:15,074 --> 00:16:16,769 There are several different kinds. 163 00:16:16,976 --> 00:16:19,103 This one lives near high-water mark, 164 00:16:19,278 --> 00:16:22,179 and is the sort that spends most time out of water. 165 00:16:23,148 --> 00:16:26,982 It has to keep its skin moist for it absorbs oxygen through it. 166 00:16:27,186 --> 00:16:30,587 It also keeps its mouth full of water swilling over its gills. 167 00:16:34,293 --> 00:16:37,319 It feeds on the little crabs that graze on the mud 168 00:16:41,934 --> 00:16:45,097 And having got one, it needs another mouthful of water. 169 00:16:53,612 --> 00:16:56,581 A second kind lives close to low-water mark, 170 00:16:56,749 --> 00:16:59,843 so it is only out of water for an hour or so each day. 171 00:17:00,085 --> 00:17:03,953 It sifts the liquid mud for small crustaceans and worms. 172 00:17:14,533 --> 00:17:17,730 In between these two kinds lives the largest of the three. 173 00:17:17,970 --> 00:17:22,703 It is a vegetarian, collecting algae and other microscopic plants from the mud. 174 00:17:29,481 --> 00:17:33,008 And it, too, nips back every now and then for a wet. 175 00:17:37,489 --> 00:17:39,855 It guards its grazing rights with vigour, 176 00:17:40,025 --> 00:17:41,959 building walls around its territory. 177 00:17:51,370 --> 00:17:53,964 And when neighbours meet, there's trouble. 178 00:18:04,883 --> 00:18:08,683 On clear mud, their territories form a patchwork of walled ponds. 179 00:18:08,954 --> 00:18:13,118 These flats are very flat, so when a male starts to advertise for a mate, 180 00:18:13,292 --> 00:18:15,226 he has to be a bit of a gymnast. 181 00:18:27,873 --> 00:18:30,808 When a female is enticed into his private pond, 182 00:18:31,043 --> 00:18:33,307 he can continue his courtship at close quarters 183 00:18:33,479 --> 00:18:35,811 in a more conventionally fish fashion, 184 00:18:36,014 --> 00:18:40,576 with flexed fins, waggling tail and enormous excitement. 185 00:19:13,485 --> 00:19:16,215 They'll spawn in a burrow at the bottom of the pond. 186 00:19:20,826 --> 00:19:23,920 This crab is too big to be intimidated by mudskippers, 187 00:19:24,096 --> 00:19:26,758 even when it does wander through their territories. 188 00:19:36,008 --> 00:19:40,809 Its scissoring mouthparts not only sort out its food but help it to breathe. 189 00:19:41,079 --> 00:19:43,138 On top of its shell, there is a puddle of water, 190 00:19:43,315 --> 00:19:44,907 and as its mouthparts move, 191 00:19:45,083 --> 00:19:48,382 they circulate this into a gill chamber within the shell, 192 00:19:48,554 --> 00:19:51,546 out again and up to the reservoir on the top. 193 00:19:52,090 --> 00:19:54,490 Eventually, the oxygen in the water is exhausted 194 00:19:54,660 --> 00:19:59,097 and the crab has to return to the sea, tip it off and get a fresh supply. 195 00:20:03,035 --> 00:20:07,665 Close by the edge of the sea, the tiny soldier crabs feed with frantic haste. 196 00:20:07,906 --> 00:20:13,845 No one else will steal their mud, but they have to eat an enormous quantity 197 00:20:14,012 --> 00:20:17,038 to extract the few particles necessary to keep alive. 198 00:20:17,316 --> 00:20:21,685 They have to work at it pretty well non-stop and have no time to waste. 199 00:20:30,696 --> 00:20:33,256 High up, beyond the reach of all but the highest tides, 200 00:20:33,432 --> 00:20:35,730 lives the large mangrove crab. 201 00:20:36,101 --> 00:20:41,129 It keeps moist by boring its hole as much as six feet deep to reach water. 202 00:20:41,406 --> 00:20:45,536 The lure that tempts it out is a newly fallen mangrove leaf. 203 00:20:50,148 --> 00:20:51,877 And quickly back to safety. 204 00:20:56,655 --> 00:21:01,058 Among the air-absorbing roots of the mangroves, fiddler crabs are busy. 205 00:21:01,493 --> 00:21:03,723 The females collect mud with both pincers, 206 00:21:03,895 --> 00:21:07,592 working with the same frantic speed as the soldier crabs. 207 00:21:10,168 --> 00:21:12,898 The males need to munch just as much mud as the females, 208 00:21:13,105 --> 00:21:14,936 but work with one hand only, 209 00:21:15,107 --> 00:21:18,702 for one of their claws is so big that it is useless for feeding. 210 00:21:21,246 --> 00:21:24,477 They use it instead to wave at passing females. 211 00:21:30,922 --> 00:21:34,016 But it is also a weapon to brandish at rivals. 212 00:21:39,264 --> 00:21:40,492 A less well-equipped male 213 00:21:40,666 --> 00:21:44,227 gets a nasty hammering even before he can get out of his hole. 214 00:21:55,547 --> 00:21:57,811 The claw is long enough to reach down into the burrow 215 00:21:57,983 --> 00:22:01,350 to give his opponent a tweak where he's least expecting it. 216 00:22:09,027 --> 00:22:13,987 The purpose of the wave is to encourage a female to follow a male into his burrow. 217 00:22:26,812 --> 00:22:31,146 Is it possible perhaps just to take a moment or so off from munching mud? 218 00:22:34,853 --> 00:22:38,050 At low tide, there's lots for birds to eat on the mangrove mud, 219 00:22:38,223 --> 00:22:40,987 just as there is on estuaries elsewhere. 220 00:22:41,226 --> 00:22:45,925 Terns hawk for fish that are easier to catch now in the shallowing waters. 221 00:22:47,699 --> 00:22:50,293 Kingfishers pounce on the fiddler crabs. 222 00:22:58,176 --> 00:23:01,703 Great white heron stalk and stab. 223 00:23:19,898 --> 00:23:23,959 The returning tide signals "all change" for everyone. 224 00:23:29,441 --> 00:23:32,933 This African mangrove snail crops the algae growing on the mud, 225 00:23:33,111 --> 00:23:37,673 but it mustn't stay there when the tide comes in, for it would be attacked by fish. 226 00:23:38,316 --> 00:23:40,682 It takes refuge up in the trees. 227 00:23:40,919 --> 00:23:44,286 Its speediest climb is barely faster than the rise of the tide, 228 00:23:44,456 --> 00:23:46,822 so it has to set off in good time. 229 00:23:47,225 --> 00:23:51,992 Its internal alarm clock tells it when it should do so. 230 00:24:05,243 --> 00:24:09,907 The soldier crabs are so well adapted to their life scavenging on the exposed mud 231 00:24:10,081 --> 00:24:13,676 that they have become breathers of air, and without it they will drown. 232 00:24:14,553 --> 00:24:18,080 As the tide advances, each constructs a little igloo 233 00:24:18,256 --> 00:24:22,625 which traps a bubble of air with which the crab can breathe while the tide is in. 234 00:24:40,612 --> 00:24:46,551 The mudskippers' territorial walls built with such labour are breached by the incoming wavelets. 235 00:24:49,888 --> 00:24:52,721 Higher up, the mudskippers shelter in burrows. 236 00:25:01,099 --> 00:25:04,933 The incoming tide brings new creatures into the swamps. 237 00:25:05,170 --> 00:25:11,473 Shoals of fish arrive, searching for morsels deposited by the river while the tide was out. 238 00:25:15,981 --> 00:25:21,851 In the swamps of South-East Asia, archer fish feed on insects that have fallen on the surface. 239 00:25:28,727 --> 00:25:33,255 Uniquely, they also have a way of collecting insects from above the water. 240 00:25:35,367 --> 00:25:37,130 There is a groove in the roof of their mouth, 241 00:25:37,302 --> 00:25:42,501 so that a sudden thrust of the tongue produces a spurt of droplets like a water pistol. 242 00:25:50,282 --> 00:25:53,979 When there is a crowd, a marksman can't be sure of getting his prize. 243 00:26:06,197 --> 00:26:09,724 So in company, it may be better to try a direct assault. 244 00:26:33,358 --> 00:26:36,725 The larger fish are themselves food for otters, 245 00:26:36,962 --> 00:26:39,157 but these hunters have broad appetites 246 00:26:39,331 --> 00:26:44,598 and will enthusiastically tackle snails, crabs and even mussels. 247 00:27:01,086 --> 00:27:05,853 They are great travellers, swimming for many miles up into fresh water or down into the sea 248 00:27:06,024 --> 00:27:08,219 and even out to offshore islands, 249 00:27:08,593 --> 00:27:11,721 and they have an enormous appetite for play. 250 00:27:23,541 --> 00:27:28,240 The largest of all living reptiles is found among mangroves: 251 00:27:28,613 --> 00:27:34,051 The estuarine crocodile, a monster that grows to 23 feet long. 252 00:28:19,431 --> 00:28:22,958 Like its ancestors that lived when dinosaurs dominated the earth, 253 00:28:23,134 --> 00:28:25,261 it's an ocean-going creature, 254 00:28:25,503 --> 00:28:29,371 and, as a consequence, it's the most widely distributed of all crocodiles 255 00:28:29,541 --> 00:28:33,477 living from the Bay of Bengal through northern Australia to the Pacific, 256 00:28:33,645 --> 00:28:39,242 even reaching isolated mangrove swamps on the islands of Fiji. 257 00:28:40,919 --> 00:28:44,548 As the mangroves establish themselves farther out into the sea, 258 00:28:44,723 --> 00:28:47,658 the mudflats they've built grow higher and higher. 259 00:28:47,959 --> 00:28:50,052 Rainwater washes them clean of salt, 260 00:28:50,295 --> 00:28:55,392 and eventually they become dry fertile forest, beyond the reach of the sea. 261 00:28:58,903 --> 00:29:02,031 The banks of mud and sand that the rivers lay down around their mouths, 262 00:29:02,207 --> 00:29:04,732 even when they are not big enough to rise above water, 263 00:29:04,909 --> 00:29:11,314 protect the land against the attacks of the sea, for tall waves can't travel across shallow water. 264 00:29:11,950 --> 00:29:15,351 But if a current sweeping down the coast carries away the sediment 265 00:29:15,520 --> 00:29:17,715 and scours the sea floor clean, 266 00:29:17,956 --> 00:29:21,255 then waves arrive at the coast full of power. 267 00:29:49,287 --> 00:29:51,551 Where the land dips steeply into the sea, 268 00:29:51,790 --> 00:29:57,092 the territory between the tides is not miles across but condensed into a narrow band. 269 00:29:57,495 --> 00:30:03,730 The creatures that live here, like all intertidal creatures, are threatened by two dangers. 270 00:30:04,435 --> 00:30:08,929 At the high-water mark, there are physical problems of being dried out, 271 00:30:09,140 --> 00:30:12,200 and at the low-water mark, there are biological problems 272 00:30:12,377 --> 00:30:17,405 of animals that creep up from the sea to prey upon the intertidal creatures. 273 00:30:17,615 --> 00:30:20,311 The interplay of those two sets of problems 274 00:30:20,485 --> 00:30:24,649 produces a series of horizontal bands along the coast, 275 00:30:24,923 --> 00:30:27,551 each dominated by the particular species 276 00:30:27,725 --> 00:30:32,128 which best deals with the problems at that particular level. 277 00:30:32,430 --> 00:30:36,332 Such bands can be seen on coasts all over the world, 278 00:30:36,534 --> 00:30:41,335 but here on the north-west coast of America, they are strikingly clear. 279 00:30:42,006 --> 00:30:44,406 The bottom band of all is only fully exposed 280 00:30:44,576 --> 00:30:48,512 when the moon and the sun are in such an alignment that they pull together 281 00:30:48,680 --> 00:30:51,979 and the tide withdraws a long way from the edge of the dry land. 282 00:30:52,684 --> 00:30:56,176 Organisms here only tolerate a brief exposure to the air 283 00:30:56,387 --> 00:31:00,414 and are unable to prevent themselves from being dried out. 284 00:31:06,297 --> 00:31:10,324 The sea urchin, in water, gnaws away at encrusting algae. 285 00:31:12,604 --> 00:31:16,597 But out of water, it can do nothing but simply hang on to the rocks. 286 00:31:17,342 --> 00:31:20,641 Nearby, giant sea anemones droop their tentacles, 287 00:31:20,812 --> 00:31:24,213 and many withdraw them, for in air there is nothing to feed on. 288 00:31:40,064 --> 00:31:43,932 Sea squirts can only filter for their food spasmodically. 289 00:31:45,436 --> 00:31:50,066 Starfish are meat-eaters, and this species feeds on mussels. 290 00:31:50,308 --> 00:31:54,301 It envelops them with its adhesive arms, wrenches apart their shells, 291 00:31:54,479 --> 00:31:56,003 and feeds on the flesh within. 292 00:31:56,381 --> 00:32:00,909 Below low-water mark, they kill any mussel that tries to establish itsel 293 00:32:01,152 --> 00:32:05,316 But like many of these low-level creatures, they can't feed out of water. 294 00:32:05,590 --> 00:32:11,825 So higher up, where the rocks are exposed to air for longer, conditions favour the mussels, 295 00:32:11,996 --> 00:32:13,657 and they form a dense band, 296 00:32:13,831 --> 00:32:18,200 cropped at the lower edge by starfish, but beyond their reach higher up. 297 00:32:24,275 --> 00:32:28,541 The massed mussels provide shelter for lots of other creatures: 298 00:32:28,713 --> 00:32:31,773 Small starfish, too small to tackle a mussel, 299 00:32:32,016 --> 00:32:36,578 worms and crustaceans, winkles and other molluscs. 300 00:32:44,495 --> 00:32:47,487 The mussels hold on to the rocks with bundles of threads, 301 00:32:47,699 --> 00:32:50,532 but can't withstand the pull of the roughest waves 302 00:32:50,768 --> 00:32:54,169 and in winter storms, sheets of them may be ripped away. 303 00:33:08,486 --> 00:33:12,616 In more exposed places where the waves beat with a particular ferocity, 304 00:33:12,857 --> 00:33:18,727 mussels give way to goose-necked barnacles which clasp the rock with a long fleshy foot. 305 00:33:29,674 --> 00:33:35,169 They feed by holding out stiff, fan-like arms which catch particles from the waves, 306 00:33:35,346 --> 00:33:39,407 not when they crash in, but as their waters flow gently back. 307 00:33:59,637 --> 00:34:05,269 On the most exposed promontories, the mussels are ousted by a plant: 308 00:34:05,543 --> 00:34:07,670 An odd-looking alga known as a sea palm 309 00:34:07,845 --> 00:34:11,440 which lives only on these north-western coasts of North America. 310 00:34:14,318 --> 00:34:16,752 The crown of leaves at the top of its rubbery stem 311 00:34:16,921 --> 00:34:23,622 enables the sea palm to harness the power of the waves and use it to attack the mussels. 312 00:34:23,961 --> 00:34:27,522 The plants, perhaps surprisingly, are annual. 313 00:34:27,799 --> 00:34:33,032 In the spring, an individual plant may achieve the difficult feat 314 00:34:33,271 --> 00:34:38,709 of getting hold of an individual mussel in the mussel bed, as this one has done. 315 00:34:39,844 --> 00:34:43,280 When it's mature, it will produce spores, 316 00:34:43,448 --> 00:34:47,077 but only when it's out of water as it is now. 317 00:34:47,385 --> 00:34:53,847 So instead of the spores being distributed widely as those of other plants are... 318 00:34:54,058 --> 00:34:59,018 ...the spores of the sea palm trickle down the grooves in these leaves 319 00:34:59,197 --> 00:35:01,757 and into the mussel bed here. 320 00:35:02,667 --> 00:35:05,864 When the first storms of the autumn come, 321 00:35:06,304 --> 00:35:13,039 they may catch underneath the fronds of this plant and rip it up. 322 00:35:13,377 --> 00:35:19,043 But the holdfast grips the mussels so firmly that the mussels come away with it, 323 00:35:19,217 --> 00:35:20,582 revealing the bare rock, 324 00:35:20,751 --> 00:35:26,621 and that means that the offspring of other nearby plants 325 00:35:26,791 --> 00:35:30,192 can get a hold on the bare rock. 326 00:35:30,628 --> 00:35:36,828 So by the sacrifice of one palm growing on a mussel one year, 327 00:35:37,101 --> 00:35:43,700 next year there will be a whole grove of palms growing firmly on the bedrock. 328 00:35:54,919 --> 00:36:00,084 But mussels do require a certain amount of immersion every day 329 00:36:00,258 --> 00:36:02,749 if they are not to dry out and die, 330 00:36:03,027 --> 00:36:05,723 and this line marks exactly that. 331 00:36:06,130 --> 00:36:08,462 Above it, no mussel can live. 332 00:36:08,733 --> 00:36:12,863 The creatures that can are these: Barnacles. 333 00:36:13,638 --> 00:36:19,668 Clamped tightly to the rocks, they conserve very effectively the moisture within their shells. 334 00:36:19,877 --> 00:36:24,109 They collect the minute quantities of food they require to grow and reproduce 335 00:36:24,282 --> 00:36:27,649 from the relatively infrequent submersions at high tide, 336 00:36:27,885 --> 00:36:32,447 which in some cases may only occur for an hour once a month. 337 00:36:57,848 --> 00:37:01,614 So each level on a rocky shore is dominated by the organisms 338 00:37:01,786 --> 00:37:06,223 that best deal with the precise combination of pounding by the waves, 339 00:37:06,424 --> 00:37:09,791 exposure to the air, and attack by deep-water predators. 340 00:37:10,161 --> 00:37:13,096 None, in the long run, can claim permanent occupation, 341 00:37:13,264 --> 00:37:16,131 for the attacks of the waves are unceasing. 342 00:37:44,528 --> 00:37:48,521 With unfailing accuracy, the sea picks out the softer parts of the rocks 343 00:37:48,699 --> 00:37:50,326 and cuts its way into them. 344 00:37:50,635 --> 00:37:54,435 Water at great pressure is driven into joints and cracks 345 00:37:54,605 --> 00:37:58,132 until it penetrates a cliff and forms a blowhole. 346 00:38:02,513 --> 00:38:07,746 On the southernmost tip of Australia, storms of great ferocity sweeping up from the south, 347 00:38:07,918 --> 00:38:10,887 with the full force of the Antarctic gales behind them, 348 00:38:11,122 --> 00:38:18,585 beat away at sandstone cliffs which have lines of weakness that run horizontally and vertically, 349 00:38:18,929 --> 00:38:21,955 so the rock is cut away in huge blocks. 350 00:38:58,069 --> 00:39:01,766 The sea, having demolished the cliffs, then works on the debris. 351 00:39:02,006 --> 00:39:05,908 During storms, it picks up the boulders and hurls them at the cliff face. 352 00:39:06,143 --> 00:39:11,672 At calmer times, it rolls the rocks over the seabe and casts them up on shingle banks. 353 00:39:12,049 --> 00:39:17,681 Every movement chips and grinds the fragments until they are reduced to sand grains, 354 00:39:17,988 --> 00:39:22,857 and now even a gentle current can pick them up and carry them for miles down the coast, 355 00:39:23,060 --> 00:39:26,086 eventually to abandon them in banks and strands 356 00:39:26,263 --> 00:39:29,289 in the lee of islands or in sheltered bays. 357 00:40:42,840 --> 00:40:47,709 Every wave of every tide stirs up the surface of the sand, 358 00:40:47,945 --> 00:40:55,283 so plants find it impossible to get any grip on it as they can on rocky shores or mudflats. 359 00:40:55,586 --> 00:41:02,992 So a beach like this looks as lifeless as any part of the margins of the land. 360 00:41:03,461 --> 00:41:07,557 But if the sand grains are not too small and compacted, 361 00:41:07,798 --> 00:41:12,895 then each will retain around it a thin film of moisture even when the tide is out, 362 00:41:13,103 --> 00:41:16,903 and in that microscopic space, animals can live. 363 00:41:19,743 --> 00:41:24,180 These translucent boulders are, in fact, sand grains, 364 00:41:24,381 --> 00:41:29,546 and the tiny snake-like animal a worm that could sit on a pinhead. 365 00:41:44,168 --> 00:41:46,102 All these inhabitants of the sand 366 00:41:46,270 --> 00:41:50,764 are, necessarily, adept at writhing, gliding and crawling 367 00:41:50,941 --> 00:41:57,005 as they search for the few edible fragments trapped between grains, or pursue one another. 368 00:42:08,959 --> 00:42:14,192 This one is only a temporary lodger in the sand. It is the larva of a mollusc. 369 00:42:18,669 --> 00:42:22,230 A hydra lives here. It's like the one that's common in freshwater ponds, 370 00:42:22,406 --> 00:42:26,365 but it has one elongated tentacle with which it anchors itself. 371 00:42:28,312 --> 00:42:32,078 A nematode worm produces glue from a gland on its tail 372 00:42:32,249 --> 00:42:34,547 which helps it to maintain its position. 373 00:42:43,394 --> 00:42:47,194 This is another larva that at the beginning of its life floats in the se 374 00:42:47,398 --> 00:42:50,856 but settles down into the sand to continue its development. 375 00:42:51,435 --> 00:42:54,836 It builds a tiny tube of mucus which it carries about with it 376 00:42:55,005 --> 00:42:57,803 and clings to with bristles on its flanks. 377 00:43:06,650 --> 00:43:11,587 When it grows up, it does the same thing on a larger scale, above the sand. 378 00:43:11,956 --> 00:43:14,424 It's a worm called the sand mason. 379 00:43:16,226 --> 00:43:19,821 Now it not only builds a tube, but it adds long tassels to the top. 380 00:43:20,064 --> 00:43:23,864 These slow down the water so that suspended food particles fall 381 00:43:24,034 --> 00:43:26,332 and can be gathered by the waving tentacles. 382 00:43:27,071 --> 00:43:30,268 The tubes need constant renewal, 383 00:43:30,474 --> 00:43:35,502 and this is how the sand mason does it, speeded up 125 times. 384 00:44:18,055 --> 00:44:21,513 Although plants can't grow on these perpetually moving sands, 385 00:44:21,792 --> 00:44:26,491 those dislodged from the rocky parts of the coast by waves are washed up here, 386 00:44:26,830 --> 00:44:30,129 and there are plenty of creatures on the beach waiting for them. 387 00:44:42,579 --> 00:44:44,342 These are sand-hoppers. 388 00:44:44,581 --> 00:44:48,540 They hide below the surface to avoid being baked and dried out by the sun, 389 00:44:48,786 --> 00:44:51,084 but now there is food to be had. 390 00:45:07,771 --> 00:45:10,433 On many beaches, their numbers are astronomic. 391 00:45:10,708 --> 00:45:16,374 There can be as many as 25,000 of them in one square yard of beach sand. 392 00:45:28,926 --> 00:45:31,952 The sand-hoppers favour rotting vegetation. 393 00:45:32,596 --> 00:45:35,793 Rotting flesh attracts crabs. 394 00:45:44,241 --> 00:45:48,371 The remains of a squid is a banquet for ghost crabs. 395 00:46:09,333 --> 00:46:12,427 Occasionally, when there is a chance, it may be better to cut off a length 396 00:46:12,603 --> 00:46:16,061 and haul it away to consume it in the privacy of a burrow. 397 00:46:20,811 --> 00:46:24,269 The crabs and the shrimps live close to the high-tide mark. 398 00:46:24,515 --> 00:46:29,009 The incoming waters bring with them another team of scavengers. 399 00:46:30,587 --> 00:46:35,889 This periscope on a South African beach belongs to a mollusc: A plough snail. 400 00:46:40,931 --> 00:46:44,594 It inflates its plough-like foot by pumping in water, 401 00:46:44,835 --> 00:46:48,965 and it uses it not so much as a ploughshare as a surfboard. 402 00:46:49,473 --> 00:46:54,877 The waters pick it up and wash it swiftly inshore, together with its potential food... 403 00:46:58,382 --> 00:46:59,974 ...a stranded jellyfish. 404 00:47:09,226 --> 00:47:14,061 The plough snails detect its presence from the taste of decay in the surrounding water 405 00:47:14,264 --> 00:47:16,664 and advance on it with great speed. 406 00:47:53,403 --> 00:47:57,669 To avoid being swept up the beach and being stranded, they eat fast, 407 00:47:57,841 --> 00:48:02,210 and then, while there is some food left, they burrow into the sand. 408 00:48:02,779 --> 00:48:04,713 There they wait for the tide to turn 409 00:48:04,882 --> 00:48:09,444 so that they can ride back on their surfboards to deeper water and safety. 410 00:48:16,326 --> 00:48:21,559 Very few sea creatures venture above the limit of the highest tide and survive. 411 00:48:21,899 --> 00:48:26,836 One group of animals is compelled to do so by the nature of their ancestry, 412 00:48:27,037 --> 00:48:32,236 and on this one beach in Costa Rica, they stage an astonishing invasion. 413 00:48:33,644 --> 00:48:34,906 Turtles. 414 00:48:35,445 --> 00:48:40,246 They are Ridleys, the smallest of the sea-going turtles, only a couple of feet long. 415 00:48:41,218 --> 00:48:43,652 Turtles are descended from land-living reptiles, 416 00:48:43,820 --> 00:48:48,621 and, like all reptiles, they lay eggs that only develop and hatch in air. 417 00:48:48,892 --> 00:48:54,660 Every year, adult females, having mated at sea, must move onto dry land. 418 00:48:59,503 --> 00:49:03,769 They arrive at a rate of up to 5,000 an hour. 419 00:49:04,207 --> 00:49:08,735 They use only one or two of the thousands of beaches that seem to be suitable. 420 00:49:08,979 --> 00:49:13,211 What is more, they only choose to do so on just a few nights in the year 421 00:49:13,383 --> 00:49:15,442 between August and November. 422 00:49:23,160 --> 00:49:25,151 Efficient though their flippers are in water, 423 00:49:25,362 --> 00:49:29,423 they are barely strong enough to lift the turtle clear of the sand. 424 00:49:29,666 --> 00:49:31,998 It has to drag itself up the beach. 425 00:49:33,904 --> 00:49:37,305 This mass breeding may be an advantage to the turtle. 426 00:49:37,474 --> 00:49:40,068 Since it only occurs on a few nights a year, 427 00:49:40,410 --> 00:49:43,868 their eggs can't support a large permanent population of predators, 428 00:49:44,147 --> 00:49:47,241 as they might if the turtles were to lay over several months. 429 00:49:47,951 --> 00:49:50,977 Yet, even so, for reasons that we still don't understand, 430 00:49:51,221 --> 00:49:56,818 less than one in a hundred of the eggs produces a hatchling which reaches the sea. 431 00:49:57,894 --> 00:50:00,727 Each female lays a hundred or so. 432 00:50:13,910 --> 00:50:16,811 That done, she carefully fills in the hole. 433 00:50:34,398 --> 00:50:38,767 A few coatimundi and vultures come down from the forest to plunder, 434 00:50:39,002 --> 00:50:42,403 but they make little impact on the millions of eggs that are laid. 435 00:50:50,781 --> 00:50:54,740 Next night, many thousands more Ridleys arrive. 436 00:51:03,293 --> 00:51:09,027 On other beaches, more secretly, other very different turtles are laying. 437 00:51:10,867 --> 00:51:17,773 This is the largest of all the marine turtles. 438 00:51:18,041 --> 00:51:22,876 This magnificent creature is the giant leatherback turtle. 439 00:51:23,113 --> 00:51:25,843 And it's a most mysterious animal. 440 00:51:26,183 --> 00:51:29,482 It's a solitary wanderer of the oceans. 441 00:51:29,786 --> 00:51:36,123 Individuals turn up almost anywhere in the tropics but they go much farther than that. 442 00:51:36,460 --> 00:51:39,190 They've been recorded as far south as Argentina, 443 00:51:39,396 --> 00:51:42,729 and as far north as the British Isles and North America. 444 00:51:43,066 --> 00:51:46,900 It's a creature of mystery, because although we know what it feeds on, 445 00:51:47,070 --> 00:51:53,805 which is sea urchins and fish and, oddly enough, jellyfish, we know little else about it. 446 00:51:54,044 --> 00:51:58,777 We don't know how long they live. We don't know how the male finds females. 447 00:51:58,982 --> 00:52:05,387 We don't know how females navigate to find nesting sites like this one. 448 00:52:05,622 --> 00:52:11,458 Indeed we didn't know where the main nesting sites were until 25 years ago. 449 00:52:11,628 --> 00:52:17,225 Then it was discovered that some nested on the Suriname coast of South America 450 00:52:17,467 --> 00:52:21,335 and some nested here, on the east coast of Malaysia. 451 00:52:21,671 --> 00:52:25,835 Of course, the people here have always known about the turtles 452 00:52:26,009 --> 00:52:29,103 and have always plundered those eggs. 453 00:52:29,346 --> 00:52:33,339 Today, however, there are more people than ever here, 454 00:52:33,583 --> 00:52:37,314 and the eggs are plundered more seriously, 455 00:52:37,487 --> 00:52:42,857 so undoubtedly, this huge and extraordinary creature is in danger. 456 00:52:43,860 --> 00:52:49,355 But maybe the leatherback turtle has other breeding grounds that we don't know about. 457 00:52:49,566 --> 00:52:55,402 Maybe it goes to small, tiny coral islands in the emptiness of the ocean 458 00:52:55,572 --> 00:52:58,939 to find beaches far away from man. 459 00:52:59,176 --> 00:53:04,307 That, indeed, is where we ourselves will be going in the next programme.