1 00:00:07,160 --> 00:00:08,840 SIAN PHILLIPS (VO): It's spring tide. 2 00:00:12,200 --> 00:00:16,120 The Atlantic Ocean is being squeezed between Ramsey Island 3 00:00:16,240 --> 00:00:18,200 and the Pembrokeshire mainland. 4 00:00:21,160 --> 00:00:22,880 Known as the Bitches 5 00:00:23,200 --> 00:00:26,680 these are some of the fastest ocean rapids on Earth. 6 00:00:30,800 --> 00:00:34,360 Here, the water races over the shallow reef below. 7 00:00:38,80 --> 00:00:42,880 Dangerous whirlpools and eddies become a white-water playground... 8 00:00:44,80 --> 00:00:45,520 for thrill-seekers. 9 00:00:50,120 --> 00:00:52,280 The shallow seas below them... 10 00:00:54,720 --> 00:00:58,880 as exciting and dramatic as anything that rides above. 11 00:01:00,640 --> 00:01:01,800 MAN SHOUTS 12 00:01:04,720 --> 00:01:08,160 With rich habitats as varied as anything on land. 13 00:01:11,960 --> 00:01:15,160 Populated with creatures straight from Welsh myth. 14 00:01:18,760 --> 00:01:20,640 Transforming shape... 15 00:01:22,320 --> 00:01:23,520 colour... 16 00:01:25,720 --> 00:01:27,760 and even sex. 17 00:01:31,160 --> 00:01:33,440 All bursting into life... 18 00:01:35,40 --> 00:01:37,200 for a few short months. 19 00:01:42,760 --> 00:01:45,880 Thanks to the magical powers of the sun's caress. 20 00:01:47,680 --> 00:01:49,80 This is an adventure... 21 00:01:50,520 --> 00:01:52,800 into the kingdom of myths. 22 00:01:54,760 --> 00:01:55,880 Woo! 23 00:02:00,360 --> 00:02:03,200 SIAN (VO): Wales is a coastal nation. 24 00:02:05,880 --> 00:02:08,400 The sea is in our soul. 25 00:02:11,760 --> 00:02:13,440 Full of hidden treasures... 26 00:02:16,800 --> 00:02:18,00 wonders... 27 00:02:20,320 --> 00:02:22,80 and giants. 28 00:02:24,560 --> 00:02:27,400 A sea of mythical coasts... 29 00:02:28,320 --> 00:02:30,320 with extraordinary creatures... 30 00:02:32,560 --> 00:02:34,560 secretive shallows... 31 00:02:35,600 --> 00:02:37,320 and hidden depths. 32 00:02:39,560 --> 00:02:44,80 These are the Wonders of the Celtic Deep. 33 00:02:47,640 --> 00:02:49,640 BIRDS CAW 34 00:02:56,720 --> 00:02:59,680 The Llyn Peninsula in North Wales. 35 00:03:00,440 --> 00:03:04,440 This narrow finger of land, some 45 kilometres long 36 00:03:05,240 --> 00:03:07,880 is surrounded by shallow seas. 37 00:03:09,760 --> 00:03:12,920 They make up just seven percent of the ocean 38 00:03:14,400 --> 00:03:19,40 but are home to nearly a third of all marine animals. 39 00:03:22,560 --> 00:03:26,480 By May, these shallows are bursting with life. 40 00:03:29,00 --> 00:03:31,440 Human visitors are also arriving. 41 00:03:33,80 --> 00:03:37,160 Out enjoying the calm, crystal-clear water. 42 00:03:39,40 --> 00:03:43,120 Just beneath them lies an extraordinary marine world. 43 00:03:44,520 --> 00:03:48,00 One of the most productive eco-systems on Earth. 44 00:03:50,240 --> 00:03:53,480 A mysterious underwater forest. 45 00:03:56,200 --> 00:03:57,760 This is the kingdom... 46 00:03:58,760 --> 00:04:00,640 of the giant kelp. 47 00:04:09,400 --> 00:04:14,440 Each plant here is home to some 8,000 microscopic creatures 48 00:04:16,400 --> 00:04:19,640 bringing in a vast array of larger animals. 49 00:04:29,00 --> 00:04:30,840 Hiding in the canopy... 50 00:04:32,640 --> 00:04:35,800 a ballan wrasse patrols its territory... 51 00:04:38,80 --> 00:04:41,440 using oar-like fins to row through the water... 52 00:04:43,760 --> 00:04:46,00 on the lookout for its next meal. 53 00:04:50,320 --> 00:04:53,280 Its bee-stung lips hide a set of teeth 54 00:04:53,360 --> 00:04:56,360 which can crush through crab shells with ease. 55 00:05:02,440 --> 00:05:05,880 But not every animal is looking for a meal just yet. 56 00:05:07,800 --> 00:05:11,440 Also weaving through the forest is a female catshark. 57 00:05:14,440 --> 00:05:19,880 At a metre long, she's looking out for a safe place to lay a precious cargo. 58 00:05:25,560 --> 00:05:27,760 But this kelp is too exposed. 59 00:05:31,560 --> 00:05:33,800 She heads onto the forest floor... 60 00:05:40,240 --> 00:05:43,40 and finds the ideal spot. 61 00:06:00,360 --> 00:06:06,240 Tucked into the undergrowth is an egg case known as a mermaid's purse. 62 00:06:07,600 --> 00:06:08,880 Inside... 63 00:06:09,440 --> 00:06:11,320 is a tiny embryo. 64 00:06:16,320 --> 00:06:19,600 In a few months' time, if the kelp holds firm... 65 00:06:21,00 --> 00:06:24,680 it will hatch into a perfectly-formed catshark. 66 00:06:30,400 --> 00:06:35,240 Across the seafloor is a tangled thicket of smaller seaweeds 67 00:06:36,360 --> 00:06:38,80 which need less light to grow. 68 00:06:42,320 --> 00:06:46,560 Home to a group of otherworldly-looking creatures... 69 00:06:47,240 --> 00:06:49,880 including the sea hare. 70 00:06:53,520 --> 00:06:57,400 These strict vegetarians have a voracious appetite. 71 00:06:58,400 --> 00:06:59,760 Both for food... 72 00:07:01,880 --> 00:07:03,200 and for love. 73 00:07:12,880 --> 00:07:17,480 Round here, it's not just the water temperature that's rising. 74 00:07:21,00 --> 00:07:23,760 This individual is looking for a mate. 75 00:07:26,160 --> 00:07:28,200 And here he comes. 76 00:07:29,600 --> 00:07:31,00 Or is it a she? 77 00:07:32,240 --> 00:07:34,00 It's of no importance. 78 00:07:39,00 --> 00:07:41,720 For sea hares are hermaphrodites. 79 00:07:43,280 --> 00:07:44,720 They are both male... 80 00:07:46,200 --> 00:07:47,480 and female. 81 00:07:51,240 --> 00:07:54,440 Once our pair have decided they want to hook up... 82 00:07:57,760 --> 00:08:03,40 they release invisible pheromones which waft out across the forest floor. 83 00:08:05,400 --> 00:08:07,760 This magical love potion 84 00:08:08,720 --> 00:08:11,160 soon attracts another sea hare... 85 00:08:12,960 --> 00:08:14,00 and another... 86 00:08:16,00 --> 00:08:17,240 and another! 87 00:08:20,600 --> 00:08:25,640 Over the next three days, many more sea hares join in this love—athon. 88 00:08:27,400 --> 00:08:31,80 Each sea hare being male at the front end of their body... 89 00:08:31,720 --> 00:08:33,800 and female at the rear. 90 00:08:37,160 --> 00:08:41,760 Soon, a string of eggs lace around a feathery boudoir. 91 00:08:42,800 --> 00:08:45,680 Several million in a single chain. 92 00:08:51,640 --> 00:08:55,240 But all good swinging parties must come to an end. 93 00:09:01,200 --> 00:09:02,600 Exhausted... 94 00:09:03,40 --> 00:09:07,800 the lascivious libertines retreat into their leafy hideaways. 95 00:09:13,200 --> 00:09:14,680 SEABIRDS CRY 96 00:09:18,40 --> 00:09:19,960 Ceibwr Bay, Pembrokeshire. 97 00:09:20,40 --> 00:09:21,360 WOMAN: Woo! 98 00:09:23,760 --> 00:09:27,840 SIAN (VO): Above the water, it's clear summer hasn't quite arrived. 99 00:09:29,280 --> 00:09:33,40 But a group of daring souls have come in search of adventure. 100 00:09:34,240 --> 00:09:37,840 The only burst of colour in this seemingly bare coastline. 101 00:09:37,920 --> 00:09:39,80 MAN: Woah! 102 00:09:42,600 --> 00:09:44,360 SIAN (VO): But as in Welsh folklore 103 00:09:44,440 --> 00:09:46,600 nothing is quite what it seems. 104 00:09:52,880 --> 00:09:56,560 Rocks shaped by wind and waves over the millennia. 105 00:09:57,800 --> 00:10:00,00 But it's the cliffs beneath the waves... 106 00:10:00,80 --> 00:10:01,360 SEABIRDS CRY 107 00:10:01,440 --> 00:10:03,680 ...where those legends become a reality. 108 00:10:05,800 --> 00:10:08,520 This is where the magic happens. 109 00:10:12,560 --> 00:10:15,640 Heading down the cliffs and into the shallow sea... 110 00:10:17,120 --> 00:10:20,760 here, a mountainous landscape is revealed... 111 00:10:23,80 --> 00:10:27,00 cloaked with exotic gardens of sponges and soft corals. 112 00:10:29,160 --> 00:10:32,40 The Great Barrier Reef of Wales. 113 00:10:38,80 --> 00:10:41,800 Thanks to the sunlight that breaches this shallow mountain world 114 00:10:42,920 --> 00:10:46,120 there's a dazzling display of shapes and colours. 115 00:10:52,640 --> 00:10:55,960 The rare scarlet and gold star coral. 116 00:11:01,00 --> 00:11:04,960 Anemones, strange soft-bodied creatures... 117 00:11:06,480 --> 00:11:08,40 that look like flowers. 118 00:11:13,200 --> 00:11:15,840 They feed on a rich soup of plankton... 119 00:11:17,800 --> 00:11:21,640 that drift in on the tidal currents that buffet the cliffs. 120 00:11:26,880 --> 00:11:29,760 But this land has larger predators. 121 00:11:38,440 --> 00:11:42,600 An ancient, armoured hunter rules over this realm. 122 00:11:54,520 --> 00:11:59,400 A rare, spiny lobster nearly half a metre long. 123 00:12:01,960 --> 00:12:03,640 He's ready for a feast... 124 00:12:08,920 --> 00:12:11,80 and mussels are on the menu. 125 00:12:22,440 --> 00:12:25,800 He uses delicate but dexterous claws 126 00:12:25,880 --> 00:12:27,600 like a knife and fork 127 00:12:27,680 --> 00:12:29,760 to prise open the mollusc. 128 00:12:32,640 --> 00:12:36,360 Systematically tearing the life out of his prey. 129 00:12:43,00 --> 00:12:45,960 Feeding it into his waiting mandibles. 130 00:12:52,40 --> 00:12:54,80 The mussel is devoured. 131 00:12:57,360 --> 00:13:00,760 Feast over, he's returned to his cave. 132 00:13:15,00 --> 00:13:18,480 Heading into deeper water, there's a mountain plateau. 133 00:13:20,880 --> 00:13:24,160 This is the domain of an alien-like predator... 134 00:13:28,520 --> 00:13:33,600 which evolved in the shallow seas some 450 million years ago. 135 00:13:36,80 --> 00:13:38,200 The spiny starfish. 136 00:13:42,160 --> 00:13:48,40 Beneath each of its five arms are hundreds of feet, tipped with suckers 137 00:13:48,120 --> 00:13:51,40 that detect chemical traces in the water... 138 00:13:53,680 --> 00:13:55,960 used in the search for prey. 139 00:13:57,800 --> 00:14:02,760 Navigating using tiny pink eye spots at the tip of each arm 140 00:14:03,560 --> 00:14:05,920 it's locked on to its next victim. 141 00:14:07,400 --> 00:14:08,800 A king scallop. 142 00:14:15,640 --> 00:14:18,560 The starfish must approach very carefully... 143 00:14:21,360 --> 00:14:24,520 for the scallop has amazing underwater vision. 144 00:14:27,80 --> 00:14:30,120 Peering out from the fringe of tentacles lining its shell 145 00:14:30,200 --> 00:14:33,800 are 200 tiny, metallic blue eyes. 146 00:14:36,920 --> 00:14:39,920 But the scallop doesn't have eyes in the back of his shell. 147 00:14:42,520 --> 00:14:45,320 And this is a stealth attack from the rear. 148 00:15:02,560 --> 00:15:07,520 The scallop has also evolved hundreds of millions of years ago 149 00:15:08,880 --> 00:15:11,40 and has a trick of its own. 150 00:15:17,80 --> 00:15:20,760 It has lightening reflexes to deal with its old enemy. 151 00:15:25,960 --> 00:15:29,200 Transforming into a pair of flying castanets. 152 00:15:32,480 --> 00:15:35,240 It can only swim a few metres at one time. 153 00:15:38,160 --> 00:15:40,120 But it's enough to escape. 154 00:15:42,640 --> 00:15:46,320 The starfish won't be eating king scallop tonight. 155 00:15:52,360 --> 00:15:53,760 It's early summer... 156 00:15:54,960 --> 00:15:57,920 and the shallow waters are being warmed by the sun. 157 00:16:03,00 --> 00:16:06,720 Beneath the mountain, a stranger struts in from the deep. 158 00:16:10,280 --> 00:16:13,520 A young spider crab is travelling north 159 00:16:15,00 --> 00:16:16,800 on an epic pilgrimage. 160 00:16:20,40 --> 00:16:23,80 He's heading for an annual gathering with other crabs... 161 00:16:24,840 --> 00:16:28,160 congregating to shed their shells at the end of the summer. 162 00:16:30,520 --> 00:16:32,840 This should be his final moult. 163 00:16:35,400 --> 00:16:37,920 As he makes the step into adulthood... 164 00:16:39,800 --> 00:16:42,600 he's on a 160-kilometre journey... 165 00:16:43,880 --> 00:16:45,440 that's full of dangers. 166 00:16:47,600 --> 00:16:49,400 BIRDS TWITTER 167 00:16:49,800 --> 00:16:51,840 PEOPLE SHOUT AND LAUGH 168 00:16:55,680 --> 00:16:57,160 As summer progresses 169 00:16:57,600 --> 00:17:00,40 holidaymakers flock to the coast. 170 00:17:02,200 --> 00:17:03,200 By June... 171 00:17:04,200 --> 00:17:07,760 the beaches of Abersoch are completely packed. 172 00:17:10,800 --> 00:17:14,840 Here, the sandy shore gently slopes out to sea 173 00:17:15,120 --> 00:17:17,720 forming a vast submarine desert. 174 00:17:25,440 --> 00:17:28,200 It may look devoid ot life... 175 00:17:29,800 --> 00:17:33,320 but there's plenty here, if you Know where to look. 176 00:17:41,120 --> 00:17:44,960 The desert plains are a favourite hunting ground for catsharks. 177 00:17:50,680 --> 00:17:53,920 Right now, she's just surveying the seabed. 178 00:17:57,440 --> 00:17:59,400 Catsharks normally hunt at night. 179 00:18:02,40 --> 00:18:04,480 But the local sand-loving inhabitants... 180 00:18:05,520 --> 00:18:07,520 aren't taking any chances. 181 00:18:13,160 --> 00:18:14,640 With nowhere to hide... 182 00:18:15,800 --> 00:18:19,200 everyone has to find their own camouflage solution. 183 00:18:21,360 --> 00:18:24,760 The sandy-coloured brill hides in plain sight... 184 00:18:25,800 --> 00:18:29,240 while this hermit crab has a completely different strategy. 185 00:18:30,760 --> 00:18:33,920 It's decorated its shell with seaweed 186 00:18:34,800 --> 00:18:37,400 topped off with a tiny hitchhiker... 187 00:18:38,240 --> 00:18:42,160 a translucent fan worm to provide extra cover. 188 00:18:53,240 --> 00:18:57,40 Other animals seem to know they're safe from the catshark... 189 00:18:58,800 --> 00:19:01,80 and are making an exhibition of themselves. 190 00:19:04,200 --> 00:19:08,560 From across the seabed comes the sound of distant drums. 191 00:19:08,640 --> 00:19:10,440 LOW RAPID DRUMMING SOUND 192 00:19:10,720 --> 00:19:12,240 Astonishingly... 193 00:19:12,320 --> 00:19:14,280 DRUMMING SOUND CONTINUES 194 00:19:16,840 --> 00:19:20,80 ...it's a vocalisation from a tiny fish 195 00:19:20,160 --> 00:19:22,520 only six centimetres long. 196 00:19:24,520 --> 00:19:26,280 The painted goby. 197 00:19:28,520 --> 00:19:30,520 He's trying to attract a mate. 198 00:19:34,600 --> 00:19:35,960 But he's not alone. 199 00:19:41,360 --> 00:19:45,200 There's a whole gang competing for female attention. 200 00:19:48,760 --> 00:19:53,960 The males able to drum the longest and with the most consistency... 201 00:19:54,40 --> 00:19:56,120 DRUMMING SOUND 202 00:19:56,760 --> 00:19:59,320 ...are most likely to get the girls. 203 00:20:01,520 --> 00:20:03,240 A female comes in. 204 00:20:09,480 --> 00:20:11,560 She doesn't Know which way to turn. 205 00:20:12,840 --> 00:20:14,440 So the stakes are raised. 206 00:20:14,960 --> 00:20:17,600 Behind her, a male drums 207 00:20:17,680 --> 00:20:20,640 showing off his brightly-coloured dorsal fin. 208 00:20:22,360 --> 00:20:24,520 So much choice! 209 00:20:25,960 --> 00:20:28,280 This male may hold the trump card 210 00:20:28,600 --> 00:20:31,640 showing off his ready-made shell home. 211 00:20:33,280 --> 00:20:35,200 Perfect for her eggs. 212 00:20:37,440 --> 00:20:39,320 She comes in for an inspection. 213 00:20:41,880 --> 00:20:43,800 If she agrees to mate... 214 00:20:44,680 --> 00:20:47,600 he'll be the one looking after the babies. 215 00:20:49,360 --> 00:20:51,760 But the fickle female heads off. 216 00:20:57,680 --> 00:21:00,00 He won't see her for dust. 217 00:21:06,600 --> 00:21:10,120 The young spider crab is halfway through his journey north. 218 00:21:11,720 --> 00:21:15,960 Spider crabs all moult in one place, at one time 219 00:21:16,40 --> 00:21:18,280 to protect themselves from predators. 220 00:21:19,00 --> 00:21:21,240 So, he's on a date with destiny 221 00:21:21,800 --> 00:21:23,160 and mustn't be late. 222 00:21:26,40 --> 00:21:28,800 He can move quickly through this flat expanse 223 00:21:28,880 --> 00:21:31,80 and has come close to the beach. 224 00:21:33,680 --> 00:21:35,680 He may not be fully mature... 225 00:21:37,400 --> 00:21:41,160 but this young knight already has an impressive suit of armour. 226 00:21:42,880 --> 00:21:46,720 And his exoskeleton is about to be put to the test. 227 00:21:55,40 --> 00:21:59,80 This older male has claimed this desert land as his own... 228 00:22:03,360 --> 00:22:06,880 and stands defiantly between the young crab 229 00:22:07,320 --> 00:22:08,880 and his destination. 230 00:22:13,800 --> 00:22:16,00 Up to 20 centimetres wide... 231 00:22:17,320 --> 00:22:20,880 spider crabs are the largest crabs in the Celtic Sea 232 00:22:21,680 --> 00:22:24,120 and notoriously combative. 233 00:22:33,920 --> 00:22:38,400 As they square up for battle, the older crab takes the first swipe. 234 00:22:40,840 --> 00:22:42,880 And with his mace-like claw... 235 00:22:44,120 --> 00:22:46,800 he pins the young crab to the seafloor. 236 00:22:50,320 --> 00:22:52,960 Using some nimble footwork, he escapes. 237 00:22:58,160 --> 00:23:00,840 But his adversary is a veteran fighter. 238 00:23:03,00 --> 00:23:06,400 Rearing up on his hind legs, he has the advantage... 239 00:23:09,880 --> 00:23:11,680 and takes another swipe. 240 00:23:14,720 --> 00:23:15,640 He misses. 241 00:23:16,600 --> 00:23:19,680 But the young pretender knows he's been defeated. 242 00:23:24,40 --> 00:23:28,240 There's nothing left to do, but stage a dignified retreat. 243 00:23:32,240 --> 00:23:34,560 He'll have to find a long way round. 244 00:23:37,960 --> 00:23:40,440 He still has many kilometres to go. 245 00:23:51,00 --> 00:23:56,00 Some animals drawn in by the sun's rays come from much further afield. 246 00:23:56,680 --> 00:23:58,600 It's the summer solstice. 247 00:24:00,240 --> 00:24:03,960 The sun is rising on the longest day of the year. 248 00:24:04,560 --> 00:24:06,520 BIRDS CAW 249 00:24:07,120 --> 00:24:08,880 Revered by druids 250 00:24:09,120 --> 00:24:13,320 the Island of Anglesey has an influx of noisy sunseekers. 251 00:24:13,800 --> 00:24:15,760 BIRDS CAW 252 00:24:16,240 --> 00:24:21,680 Arctic terns make the longest migrations of any bird on Earth. 253 00:24:23,840 --> 00:24:28,320 They constantly follow the sun to stay in perpetual summer. 254 00:24:29,880 --> 00:24:35,560 They've come from Antarctica to Cemlyn Bay, a sanctuary for tern colonies. 255 00:24:37,280 --> 00:24:42,760 Effortless flyers, in a 30-year lifetime an Arctic tern can travel 256 00:24:42,840 --> 00:24:45,160 the distance to the moon and back... 257 00:24:45,800 --> 00:24:47,200 three times. 258 00:24:49,00 --> 00:24:50,680 But for a few short months 259 00:24:50,760 --> 00:24:54,00 this group will join both Common and Sandwich terns 260 00:24:54,320 --> 00:24:55,480 to make home here. 261 00:24:57,00 --> 00:24:58,520 Raising their chicks 262 00:24:58,600 --> 00:25:00,880 until they're strong enough to head back south. 263 00:25:00,960 --> 00:25:02,960 BIRDS CHIRP 264 00:25:04,560 --> 00:25:09,640 The chicks are so demanding, adults even have to drink on the wing... 265 00:25:10,640 --> 00:25:11,720 TERN CAWS 266 00:25:12,440 --> 00:25:15,680 ... regularly exchanging calls with their young. 267 00:25:15,760 --> 00:25:17,200 TERNS CHIRP 268 00:25:25,560 --> 00:25:27,360 Once a fish is spotted 269 00:25:28,00 --> 00:25:31,520 a tern will hover in mid-air like a hummingbird 270 00:25:32,640 --> 00:25:35,00 and from a height of up to six metres 271 00:25:35,960 --> 00:25:36,960 they'll dive... 272 00:25:38,560 --> 00:25:41,840 plunging beneath the surface to spear their prey. 273 00:25:43,720 --> 00:25:46,80 This parent has caught a sand eel. 274 00:25:52,960 --> 00:25:56,480 He has an older chick, who's extremely vocal. 275 00:25:56,560 --> 00:25:58,520 TERN CHICK CHIRPS 276 00:25:59,640 --> 00:26:02,960 But as every parent knows, as youngsters get bigger 277 00:26:03,40 --> 00:26:04,480 they get more fussy. 278 00:26:05,880 --> 00:26:07,440 But he tries again. 279 00:26:10,840 --> 00:26:12,520 TERN CHIRPS RAPIDLY 280 00:26:15,640 --> 00:26:16,760 Success! 281 00:26:21,920 --> 00:26:25,760 And the hard-working dad heads back to the water to fish. 282 00:26:27,80 --> 00:26:29,80 SEABIRDS CRY 283 00:26:31,520 --> 00:26:34,640 Anchored between Anglesey and Aberdaron to the south 284 00:26:34,920 --> 00:26:37,680 Caernarfon Bay is a picture postcard 285 00:26:37,760 --> 00:26:40,200 nestled in the lap of the Irish sea. 286 00:26:40,760 --> 00:26:43,240 BIRDS CHIRP -— INSECTS CHITTER 287 00:26:46,120 --> 00:26:50,800 It seems everyone is out enjoying the tranquil blue water. 288 00:26:53,880 --> 00:26:56,840 But not all days are like today. 289 00:26:59,40 --> 00:27:02,960 The cliff boasts razor teeth of jagged rock. 290 00:27:06,80 --> 00:27:10,80 They warn of a reef that sits just beneath the waves. 291 00:27:12,480 --> 00:27:16,760 One, which over the centuries, has proved deadly to many ships. 292 00:27:29,200 --> 00:27:33,480 One and a half kilometres from shore lies one such unlucky vessel. 293 00:27:37,120 --> 00:27:41,760 This is the rotting carcass of the SS Gwynfaen. 294 00:27:42,480 --> 00:27:48,00 A former 300-tonne cargo ship, long since dragged down to a watery grave. 295 00:27:52,840 --> 00:27:57,200 Her bare bones have become a post-apocalyptic marine city. 296 00:27:59,160 --> 00:28:01,920 And like all good urban environments 297 00:28:03,40 --> 00:28:06,160 it's home to a diverse range of characters. 298 00:28:10,360 --> 00:28:12,120 Attached to the structure... 299 00:28:12,880 --> 00:28:15,600 are fleshy mounds of a soft coral. 300 00:28:16,360 --> 00:28:19,560 The aptly named dead man's fingers. 301 00:28:23,600 --> 00:28:26,920 Huge sea urchins the size of saucers 302 00:28:28,200 --> 00:28:30,800 slowly patrol the city limits... 303 00:28:32,840 --> 00:28:35,400 grazing on the thick crust of barnacles. 304 00:28:44,360 --> 00:28:46,640 The Gwynfaen's spacious hull 305 00:28:46,720 --> 00:28:50,440 provides a protected gathering place for large shoals of fish. 306 00:28:53,80 --> 00:28:56,440 This gang of bib are members of the cod family. 307 00:28:59,40 --> 00:29:00,840 There's safety in numbers. 308 00:29:02,440 --> 00:29:07,400 Along their flanks is a line of sensors used as a mini sonar system. 309 00:29:11,720 --> 00:29:14,360 If any one individual senses dangev... 310 00:29:15,560 --> 00:29:17,00 the entire shoal... 311 00:29:18,80 --> 00:29:18,920 darts away. 312 00:29:21,520 --> 00:29:24,200 The bib have reason to be on their guard. 313 00:29:26,760 --> 00:29:31,640 In the engine room lives a real-life sea monster. 314 00:29:33,840 --> 00:29:36,240 A female conger eel. 315 00:29:37,200 --> 00:29:40,360 These are the largest eels in the Celtic seas 316 00:29:41,40 --> 00:29:43,160 up to three metres in length. 317 00:29:45,40 --> 00:29:48,760 During the day, she hides within the old boiler. 318 00:29:50,80 --> 00:29:54,440 Her powerful jaws contain rows of densely packed teeth. 319 00:29:57,840 --> 00:30:01,360 Most of the residents of the wreck keep a wide berth. 320 00:30:03,120 --> 00:30:04,360 But not everyone. 321 00:30:10,920 --> 00:30:13,240 Halfway down the conger eel 322 00:30:13,440 --> 00:30:17,640 this little gang of prawns choose to dance with death. 323 00:30:20,00 --> 00:30:24,480 These scavengers snack on the leftovers from her hunting forays... 324 00:30:25,560 --> 00:30:29,360 while staying well clear of the conger's business end. 325 00:30:38,240 --> 00:30:40,800 On the far side of the engine room 326 00:30:41,200 --> 00:30:43,240 lives the ship's captain... 327 00:30:45,160 --> 00:30:49,520 a huge lobster more than 50 centimetres long. 328 00:30:53,200 --> 00:30:58,240 With his powerful muscular claws, he is the original Captain Hook. 329 00:30:59,280 --> 00:31:04,920 His massive left-hand pincer can crush through shells with ease. 330 00:31:07,80 --> 00:31:11,360 And his smaller righthand claw makes a Superb cutlass... 331 00:31:12,560 --> 00:31:15,80 to slice through flesh. 332 00:31:17,160 --> 00:31:21,360 He's 30 years old, relatively young for a lobster 333 00:31:21,920 --> 00:31:26,160 and he could live much longer and grow even bigger... 334 00:31:28,440 --> 00:31:31,240 thanks to an enzyme in his cells 335 00:31:32,200 --> 00:31:34,400 which allows them to regenerate. 336 00:31:36,120 --> 00:31:38,240 An elixir of life. 337 00:31:39,320 --> 00:31:41,960 As long as he remains in the ship 338 00:31:42,40 --> 00:31:45,00 and keeps shedding and re-growing his shell 339 00:31:45,80 --> 00:31:46,880 it's just possible... 340 00:31:47,240 --> 00:31:49,640 he could live... forever. 341 00:31:52,480 --> 00:31:57,120 But perhaps the most diverse adaptation to life in this dystopian world 342 00:31:57,840 --> 00:32:00,400 belongs to small shoal of fish 343 00:32:00,920 --> 00:32:04,840 that looks like they've just swam in from the Caribbean. 344 00:32:07,00 --> 00:32:13,00 These are female Cuckoo wrasse, part of a hareem headed up by a single male. 345 00:32:14,680 --> 00:32:18,400 With his blue and orange stripes, he's a real head turner. 346 00:32:20,440 --> 00:32:24,800 His female companions have different but equally tropical colours. 347 00:32:26,360 --> 00:32:27,720 Coral pink... 348 00:32:28,160 --> 00:32:31,480 topped by a fringe of distinctive black and white blotches. 349 00:32:34,800 --> 00:32:36,480 In the bottom of the wreck... 350 00:32:37,280 --> 00:32:39,760 another shoal of wrasse is under threat. 351 00:32:43,00 --> 00:32:45,360 These females have no male. 352 00:32:47,440 --> 00:32:50,40 He fell victim to the conger eel. 353 00:32:52,80 --> 00:32:55,840 But, in a twist, straight from ancient Welsh myth 354 00:32:57,00 --> 00:33:00,840 there is a strange sexual sorcery at work here. 355 00:33:03,00 --> 00:33:04,680 The senior female... 356 00:33:05,480 --> 00:33:09,320 has just started to sport male colours. 357 00:33:13,520 --> 00:33:15,160 In a few weeks' time 358 00:33:15,240 --> 00:33:18,760 an extraordinary transformation will take place... 359 00:33:21,840 --> 00:33:24,840 which could potentially save them. 360 00:33:30,160 --> 00:33:32,320 Just inshore from the Gwynfaen... 361 00:33:32,920 --> 00:33:36,720 lies the tiny fishing village of Porthdinllaen. 362 00:33:39,760 --> 00:33:45,600 This sheltered bay has been a safe harbour for generations of seafarers and fishermen. 363 00:33:50,160 --> 00:33:53,80 And provides the perfect conditions 364 00:33:53,600 --> 00:33:57,240 for one of the rarest marine habitats in the world. 365 00:34:03,960 --> 00:34:06,760 Hidden beneath these crystal-clear waters 366 00:34:07,880 --> 00:34:10,800 lies a vast sea grass meadow. 367 00:34:12,160 --> 00:34:17,440 The size of 28 rugby fields, it's one of the largest in Wales. 368 00:34:21,320 --> 00:34:24,920 These lush pastures are dependent on direct sunlight 369 00:34:26,40 --> 00:34:28,480 so only grow in shallow water. 370 00:34:36,00 --> 00:34:39,920 Sea grass is the ocean's only pollinating plant 371 00:34:41,760 --> 00:34:45,200 and takes in huge quantities of carbon dioxide. 372 00:34:46,960 --> 00:34:48,480 Metre for metre... 373 00:34:49,240 --> 00:34:51,880 more than the Amazon rainforest. 374 00:35:00,280 --> 00:35:01,400 In Summer... 375 00:35:02,200 --> 00:35:03,960 the meadow is a nursery 376 00:35:04,40 --> 00:35:06,560 for fish of all shapes and sizes. 377 00:35:12,600 --> 00:35:14,200 Elegant eels... 378 00:35:19,160 --> 00:35:20,720 corkwing wrasse... 379 00:35:25,40 --> 00:35:27,40 and a polka-—dotted plaice. 380 00:35:31,320 --> 00:35:36,640 The sea grass also offers a resting place for the intrepid spider crab. 381 00:35:37,840 --> 00:35:40,00 His battle scars are healing 382 00:35:40,480 --> 00:35:42,280 and he's back on schedule 383 00:35:42,840 --> 00:35:44,720 for his date with destiny. 384 00:35:47,360 --> 00:35:48,960 Near the back of the meadow 385 00:35:49,40 --> 00:35:52,760 a male sea stickleback is busily constructing a nest. 386 00:35:56,280 --> 00:35:59,280 He's not fussy about where he gets his building materials. 387 00:36:01,920 --> 00:36:06,800 These wispy strands of sargassum originally floated here from the Pacific. 388 00:36:09,360 --> 00:36:13,600 He interweaves the delicate threads to create a cosy nest. 389 00:36:16,800 --> 00:36:19,40 He's something of a perfectionist. 390 00:36:22,440 --> 00:36:27,160 He wants to ensure his home can withstand the summer storms ahead. 391 00:36:32,240 --> 00:36:34,320 When it comes to raising a family... 392 00:36:35,280 --> 00:36:38,600 it's definitely advisable to have a penthouse suite... 393 00:36:41,760 --> 00:36:45,200 for big beasts prowl the floor below. 394 00:36:48,720 --> 00:36:53,960 Across the meadow, this bull huss shark is keeping a close eye 395 00:36:54,40 --> 00:36:55,880 on another dad-to-be. 396 00:36:59,800 --> 00:37:03,920 This pipe fish is the straight bodied cousin of the sea horse. 397 00:37:06,480 --> 00:37:08,240 He doesn't need to make a nest 398 00:37:09,240 --> 00:37:10,680 because remarkably... 399 00:37:12,80 --> 00:37:13,560 he's pregnant! 400 00:37:15,440 --> 00:37:19,520 In 20 days' time, he'll give birth to live young. 401 00:37:23,360 --> 00:37:26,400 The seagrass camouflages him from predators... 402 00:37:28,720 --> 00:37:33,240 and is also full of plankton and tiny crustations he can feed on. 403 00:37:34,720 --> 00:37:37,680 Luckily, he has the most extraordinary eyes. 404 00:37:41,80 --> 00:37:44,200 Each eye moves independently 405 00:37:44,920 --> 00:37:47,680 allowing him to spot minute prey 406 00:37:49,240 --> 00:37:52,00 which he sucks up with his straw-like snout. 407 00:37:57,960 --> 00:38:00,160 Back across the seagrass meadow... 408 00:38:01,840 --> 00:38:04,280 the sea stickleback may be in luck. 409 00:38:06,520 --> 00:38:08,800 A female has spotted his nest. 410 00:38:13,880 --> 00:38:16,40 He's still making adjustments. 411 00:38:18,680 --> 00:38:22,200 If she decides to lay her eggs in his nest... 412 00:38:23,280 --> 00:38:26,440 she'll leave him to raise their offspring! 413 00:38:33,400 --> 00:38:35,720 She's definitely impressed... 414 00:38:37,720 --> 00:38:40,80 and makes her way towards the nest. 415 00:38:42,160 --> 00:38:44,280 A final bit of sprucing up... 416 00:38:46,560 --> 00:38:48,00 and she's in... 417 00:38:49,200 --> 00:38:50,960 and laying her eggs. 418 00:38:52,920 --> 00:38:54,680 If all goes well 419 00:38:55,00 --> 00:38:59,120 he will soon be the proud father of a brood of baby sticklebacks. 420 00:39:05,120 --> 00:39:07,360 As one sea ruler sets... 421 00:39:09,640 --> 00:39:11,320 another rises. 422 00:39:17,240 --> 00:39:18,400 By night... 423 00:39:19,200 --> 00:39:21,960 the world of shallows is full... 424 00:39:22,880 --> 00:39:24,120 of mystery... 425 00:39:25,400 --> 00:39:26,960 and monsters. 426 00:39:33,320 --> 00:39:36,640 Back in the sandy bed close to Abersoch 427 00:39:37,680 --> 00:39:41,760 a pair of huge eyes peeps out from the seabed. 428 00:39:46,160 --> 00:39:50,480 They belong to a small but tenacious nocturnal hunter. 429 00:39:52,360 --> 00:39:54,880 An Atlantic bobtail squid. 430 00:39:57,680 --> 00:39:59,760 No bigger than a golf ball. 431 00:40:00,920 --> 00:40:03,880 But she's doesn't want to become someone else's dinner. 432 00:40:08,40 --> 00:40:11,320 So, like a supernatural shape shifter 433 00:40:12,80 --> 00:40:13,720 she changes colour... 434 00:40:14,760 --> 00:40:16,880 to match the sandy bottom. 435 00:40:22,120 --> 00:40:24,320 Once she reaches the red kelp... 436 00:40:25,440 --> 00:40:27,80 another transformation! 437 00:40:29,120 --> 00:40:32,00 With an enormous brain for her size 438 00:40:32,80 --> 00:40:34,920 she's triggered strong muscle contractions 439 00:40:35,00 --> 00:40:38,640 that move pigment and light-reflecting cells. 440 00:40:43,320 --> 00:40:44,720 Back in the sand... 441 00:40:46,00 --> 00:40:48,920 her cloak of invisibility is used yet again. 442 00:40:52,680 --> 00:40:55,480 But her vanishing act doesn't fool everyone. 443 00:40:59,880 --> 00:41:04,40 A male Atlantic bobtail also lives in the neighbourhood. 444 00:41:07,240 --> 00:41:11,760 His large eyes are especially adapted for seeing in the dark. 445 00:41:14,200 --> 00:41:16,800 And he's set his sights on her. 446 00:41:21,280 --> 00:41:22,440 He pounces... 447 00:41:23,480 --> 00:41:25,880 grasping hold of her with his tentacles. 448 00:41:27,240 --> 00:41:28,880 They start to mate... 449 00:41:36,480 --> 00:41:38,160 under the moon light... 450 00:41:44,160 --> 00:41:45,920 for over an hour. 451 00:41:56,560 --> 00:41:58,880 The night isn't just for lovers. 452 00:42:00,240 --> 00:42:03,280 This is the time for catsharks to start hunting. 453 00:42:07,720 --> 00:42:10,600 She too has superb night vision... 454 00:42:12,440 --> 00:42:14,840 and an extraordinary sixth-sense... 455 00:42:16,160 --> 00:42:19,80 of electro-reception in her snout. 456 00:42:22,880 --> 00:42:26,160 Capable of detecting the tiny electric currents 457 00:42:26,520 --> 00:42:29,00 that emit from all living animals. 458 00:42:34,00 --> 00:42:35,800 The bobtail acts quickly. 459 00:42:35,880 --> 00:42:37,560 Using her two front arms 460 00:42:37,640 --> 00:42:39,520 she buries herself with gravel. 461 00:42:43,360 --> 00:42:44,960 But for the cat shark... 462 00:42:46,320 --> 00:42:49,640 prey hidden in the sand make easy pickings. 463 00:43:02,640 --> 00:43:03,760 This time... 464 00:43:04,720 --> 00:43:06,320 it wasn't the bobtail. 465 00:43:10,640 --> 00:43:12,760 As the summer comes to an end 466 00:43:13,320 --> 00:43:15,120 there's a danger waiting... 467 00:43:15,880 --> 00:43:18,520 that comes from the sea itself. 468 00:43:19,120 --> 00:43:22,480 A challenge to every animal in the shallow waters. 469 00:43:27,320 --> 00:43:29,800 Llyr, the God of the ocean 470 00:43:29,880 --> 00:43:33,00 is about to unleash his furious hand 471 00:43:33,280 --> 00:43:35,960 across the entire Welsh coastline. 472 00:43:45,960 --> 00:43:47,760 As the planet warms 473 00:43:47,840 --> 00:43:50,960 summer storms become stronger and more frequent. 474 00:43:52,520 --> 00:43:55,560 While the ancient cliffs can withstand the battering... 475 00:43:58,280 --> 00:44:00,880 underwater, it's a different story. 476 00:44:03,720 --> 00:44:09,520 The fragile sea grass nursery is being ripped from its roots. 477 00:44:18,240 --> 00:44:21,240 The tall kelp is smashed against the rocks. 478 00:44:29,640 --> 00:44:32,400 The shipwreck provides shelter for some. 479 00:44:36,280 --> 00:44:38,920 While the fish shoals are torn apart. 480 00:44:47,880 --> 00:44:49,520 In the marine desert... 481 00:44:52,200 --> 00:44:54,440 a seaborn sandstorm... 482 00:44:57,120 --> 00:45:00,40 tears through the subterranean homes. 483 00:45:14,400 --> 00:45:16,480 BIRDS TWITTER 484 00:45:17,200 --> 00:45:18,760 The following morning... 485 00:45:19,520 --> 00:45:21,520 the storm has passed. 486 00:45:27,240 --> 00:45:30,320 But the sea god has left his mark. 487 00:45:32,80 --> 00:45:34,80 SEABIRDS CALL 488 00:45:36,640 --> 00:45:41,200 Beneath the now calm water in Porthdinllaen's harbour... 489 00:45:43,520 --> 00:45:45,160 there's devastation. 490 00:45:49,800 --> 00:45:53,520 Large swathes of seagrass have been uprooted. 491 00:45:55,680 --> 00:45:59,00 And the sea stickleback's nest has been destroyed. 492 00:46:03,240 --> 00:46:05,760 There are no signs of any eggs. 493 00:46:07,80 --> 00:46:08,960 And dad is missing too. 494 00:46:10,400 --> 00:46:12,400 SEABIRDS CALL 495 00:46:17,760 --> 00:46:20,320 Nearby, on board the Gwynfaen... 496 00:46:23,720 --> 00:46:27,760 the once female Cuckoo wrasse has survived the battering. 497 00:46:34,320 --> 00:46:36,480 With the sex change complete... 498 00:46:40,160 --> 00:46:42,240 he now leads his hareem... 499 00:46:47,760 --> 00:46:50,40 ensuring the future of the shoal. 500 00:47:00,40 --> 00:47:02,480 For all the devastation they wreaked 501 00:47:03,280 --> 00:47:06,840 the storms have not defeated one dogged traveller. 502 00:47:12,280 --> 00:47:15,480 Some three months after setting out on his epic journey 503 00:47:16,320 --> 00:47:18,360 our determined young spider crab... 504 00:47:19,600 --> 00:47:22,360 has finally reached his destination. 505 00:47:25,840 --> 00:47:29,440 He's joining hundreds of other spider crabs 506 00:47:30,200 --> 00:47:33,640 all drawn here for an annual mass gathering. 507 00:47:35,760 --> 00:47:39,920 Their arrival is perfectly synchronised with the end of the summer. 508 00:47:40,760 --> 00:47:42,880 When the sea is at its warmest. 509 00:47:45,40 --> 00:47:48,920 The ideal conditions when you're about to moult. 510 00:47:51,600 --> 00:47:54,720 The young knight casts off his old carapace 511 00:47:55,600 --> 00:47:58,120 to reveal a new suit of armour. 512 00:48:01,80 --> 00:48:03,560 He's succeeded in his right of passage 513 00:48:03,640 --> 00:48:05,280 and won't moult again. 514 00:48:06,560 --> 00:48:11,440 In a day or two, he'll start his long journey back to the deep. 515 00:48:13,40 --> 00:48:15,200 This time, to find a mate. 516 00:48:16,840 --> 00:48:18,400 SEABIRDS CALL 517 00:48:18,480 --> 00:48:22,240 As the days shorten and the sun's power starts to fade 518 00:48:22,800 --> 00:48:24,560 the tourists have gone. 519 00:48:25,200 --> 00:48:27,720 Now, the beach is littered with the husks 520 00:48:27,800 --> 00:48:29,920 left behind by the spider crabs. 521 00:48:33,720 --> 00:48:36,640 And in the kelp forests off Pembrokeshire... 522 00:48:37,920 --> 00:48:40,760 the female cat shark has returned. 523 00:48:44,200 --> 00:48:48,840 The tough mermaid's purse held firm in the storm. 524 00:48:50,280 --> 00:48:52,880 The baby is still alive 525 00:48:53,520 --> 00:48:55,760 and has more than doubled in size. 526 00:48:57,800 --> 00:49:02,800 In a few weeks, a fully formed cat shark will hatch out. 527 00:49:05,600 --> 00:49:07,40 Time to move on. 528 00:49:08,920 --> 00:49:12,00 Over the winter, the shallow kelp forest 529 00:49:12,80 --> 00:49:14,720 will continue to protect her offspring. 530 00:49:21,960 --> 00:49:23,760 BIRDS CAW 531 00:49:24,840 --> 00:49:26,560 Off the coast of Anglesey... 532 00:49:29,200 --> 00:49:32,120 the Arctic terns are heading south. 533 00:49:39,200 --> 00:49:42,240 Their young now strong enough to fly. 534 00:49:43,760 --> 00:49:45,920 They'll be back next year... 535 00:49:47,840 --> 00:49:51,320 having flown some 35,000 kilometres. 536 00:49:55,840 --> 00:49:58,40 Back to the shallows of Wales. 537 00:50:00,960 --> 00:50:03,360 Back in search of the sun.