❄Desert Seas Narrated by David Attenborough | National Geographic Documentary

There is a world that's been out of reach until now. Two seas lie on either side of Saudi Arabia. One sea is beautiful, flamboyant and sophisticated. The other is across the desert, a younger sea. Secretive, tougher, different. Little in these two sister seas is as it appears. This is a story of miracles, where you would least expect them. The two seas reach around the desert peninsula of Arabia like two arms. Millions of years ago, this was underwater. On the seafloor, a deep compost built up. It's still here. The wealth of a long-gone sea now fuels our world. The natural riches of the past, as well as the present, are part of this story. 10,000 years ago, the Gulf was a swampy flood plain. When the sea level rose, it disappeared underwater. The Red Sea was formed much earlier as Africa and Arabia's tectonic plates pulled apart, leaving a chasm a mile deep now filled with seawater. The edges, fringed with coral, disappear into the depths. The reef is a jeweled city perched on the clifftop. It's a community with amazing relationships between animals. Five centimetre wrasse groom sweetlips, even combing the tender gills. They eat any parasites and dead skin, a reward for their trouble. A moray eel, the two and a half metre dragon of the reef, is attended by shrimps. They enter the jaws of death to keep razor-sharp teeth clean in exchange for any morsels they find. No opportunity is wasted, however desperate it may seem. Damselfish hide in an anemone, protected by tentacles that would paralyse other fish. An anemone can close and the local clownfish is finding his home a tight squeeze. Every relationship can have difficult moments. This underwater community lies along the shores of ancient human settlements. The Middle East is the birthplace of our civilisation. Over 4,000 years ago, the first cities rose here, the cradle of mathematics, astronomy and medicine. If the Garden of Eden's rivers flowed anywhere, it was into the Gulf. Ancient Mesopotamia was on the northern shoreline, with Persia to the east. The two sister seas are very different. The Gulf shyly hides its wealth. The ageing Red Sea flaunts extravagance. But the diamond-clear water of the Red Sea reveals the truth. Unlike the muddy Gulf, the reef has few nutrients in the water. The oasis seems to grow out of nothing. A reef is built by tiny animals. Coral polyps construct limestone tower blocks, protection against fish and crabs. Microscopic plants, algae, live in the polyps and convert sunlight to sugar, which feeds the coral. This city is solar-powered. For millennia, the entrepreneurs here have slowly evolved an intricate society. The edge falls away, and any nutrients from the reef fall away too, like food tumbling off the edge of a table. Tiny mouths try and grab a meal as it sinks into the dark, unexplored depths a mile below. Along these city limits, gangsters prowl. Blue-finned trevally are predatory hunters, cruising the hood. The wolves of the Red Sea reef, trevallies, are hunting through a nursery school of juvenile fusiliers. The trevally continue along the wall, searching for anything that strays too far for falling scraps. Two-metre wire corals reach further than most, and an enterprising little shrimp has made his home out on a limb. He survives by collecting passing morsels. His front teeth are a great help. One tear post puts him into a shoal of sleek unicorn fish. The drop-off attracts large schools, but there is an even greater wildlife gathering on the other side of Saudi Arabia. The Gulf is a hot, shallow sea, hardly an enticing destination. Yet here are a quarter of a million Socotra cormorants, three-quarters of the world population. They search for schools of baitfish and rest in rafts. Socotra cormorants breed here in winter on isolated islands. Featherless chicks shiver each morning. Nights are cold here. Life in the colony is dangerous, loud and smelly. Chicks are of various ages, and the older ones hang out in gangs. The younger chicks still need babysitters. Everyone is hungry. Gulls attack undefended chicks. Even cannibalism is common. Temperatures swing from too cold to too hot in a few hours. Birds can't sweat and pant desperately to keep cool. There's no shade and no food. Salvation appears first as a thin black line. After a morning's fishing, tens of thousands of parents return to the colony with food. The first problem for families is to find each other. The lucky ones are fed quickly. After all that, the last thing you want is to be mugged for the only meal of the day. Hungry cormorants and reef herons wait until chicks are being fed, then swoop in. Just when you thought it couldn't get any tougher, the wind becomes a sandstorm. Sand and dirt are blown into the sea. The gulf waters become a foggy soup. The silt reaches the seagrass meadows and animals turn grey. Out of adversity, a miracle. The dust fertilizes the seagrass prairies with nitrogen, iron and phosphorus. Productivity is phenomenal, more than most intensive agriculture. In February and March, green turtles begin their journey to their breeding grounds. Across the gulf, sandstorms called chamals carry millions of tons of nutrients into the water. Plankton bloom and feed everything from cauliflower jellies to fish. Cormorants rely on the dust storms to bring life to the gulf. Terns arrive from the Indian Ocean and striped mackerel just swim with their mouths open. Whale sharks arrive, 15 meters long and as heavy as several elephants. They're the biggest fish in the world, yet they eat tiny plankton. The chamal sandstorms are the making of this place. Dolphins and cormorants follow the schools, which follow the plankton, which follow the dust. It's extraordinary, considering what happened here 20 years ago in history. The gulf's marine life was decimated. Miraculously, survivors returned. Wildlife has suffered heat, salt, dust, wars and oil. Almost unnoticed, animals adapt and battle on. The other side of Arabia is another story. For most of the Red Sea reefs, sandstorms deliver few nutrients. The oasis has to be self-sufficient. Storms and tides could stir up fertility, but mostly they just sweep the reef clean. Nutrients disappear over the edge to the sea floor far below. There are patches of sand, but even this is not what it seems. Bumphead parrotfish are a meter long and weigh about 20 kilograms. They bite off coral and grind it up to digest the polyps. It comes out the other end as fine, clean sand. The coral sand settles, little bits of desert in the oasis. Goatfish and sea cucumbers search hungrily through the sand. Speed it up, we can see how busy they are. Sea cucumbers are part of an army of garbage collectors and street cleaners. Starfish search for food too, but it's a risky business. Titan triggerfish are hunters, and one of the few able to take apart the starfish's spiny body. The neighbours soon spot a meal they couldn't normally enjoy. Starfish are able to regenerate from a single arm. A dismembered limb is overlooked and slowly crawls away. Nervous garden eels emerge from their burrows. They eat plankton. It'll take them all day to connect enough. They vanish if anything bigger passes by. A blue-spotted ray hunts for shellfish under the sand like a minesweeper. It can detect a shrimp's minute electrical signal and digs it out. Smaller fish hope to catch anything stirred up by the ray. Its most reliable follower is a sand perch. Life in the Red Sea requires patience like a garden eel, or specialist equipment like a ray, or a helpful companion. The relationship can often be complex. The sand perch may be keeping guard. Understanding these animals has only just begun. A two-metre wide-tipped reef shark is recognised and feared. So are barracuda, casting a shadow over the reef. Barracuda gather in hundreds by the drop-off. They're waiting for evening. The nocturnal pack hunters form the wheel of death. Schools of fusiliers become nervous towards dusk. As the day ends, a new drama will begin. Twilight in the Red Sea, and the moray eel emerges to hunt. Everything changes at night. Many corals come to life. Soft corals swell, polyps open. Basket stars, cousins of the starfish, climb onto a peak and unfurl their arms into a net. Lionfish with poisonous spines are ambush predators. They conceal their fish shape under waving flags. So, small reef fish hide in the coral. A parrotfish makes a bubble of mucus, disguising scent and protecting it from danger. Here it hides until dawn breaks over the Red Sea. A thousand kilometres east, and its late spring, in the Gulf. In May, the green turtle males are first to reach the sandy shallows. They're waiting for mates to arrive. Spring happens underwater as well as on land. Phantail rays are leading the way. The first female turtle arrives and courtship begins. The male holds on with hooks on his flippers. Unsuccessful suitors try to dislodge him. The couple may remain together all day, surfacing every 10 minutes or so for a breath. The sandstorms have eased and the islands welcome terns. They wash off the dust before heading for the party. Crested terns are courting. They reach up to appear taller, more attractive. Compared to the cormorants, these are dressy dancers. A small gift between white-cheeked terns seals their union. The air is full of the coming and going of these most graceful birds. As the sand heats to 60 degrees, the terns need to do more than just shade the egg, and they're overheating themselves. Luckily, they have a trick. When the tern colony overheats, one of the parents goes skimming over the water, drinking and wetting their breast feathers. The damp feathers hold just enough moisture for evaporation to cool the egg. Very few other birds have learned this trick. Each of the gulf's characters face domestic life in their own way. A little goby lives in a burrow. He has a battle with the sand. Every day, his home needs spring cleaning. Another goby and another strategy. A shrimp dug his burrow and still lives here, cleaning out the sand. The shrimp has poor eyesight and relies on the goby as a guard. There's a tenderness between this odd couple. The shrimp always has a tentacle touching the goby, and the goby warns the shrimp with flicks of his fins. A so-harl surgeonfish passes. The goby pushes the shrimp down the burrow. The hard-working housekeeper rarely goes out. Instead, it removes dirt and small visitors and parasites by eating them. The gulf's characters may be less colourful than the Red Seas, but are no less wonderful. Around the gulf, the seawater gets hotter through the summer. Corals generally bleach and die if sea temperatures rise even a little. The gulf is about the hottest sea in the world, and corals here, like Acropora, are specially adapted and work with different algae. With sea temperatures expected to rise everywhere, some scientists think that the magical gulf corals could be the salvation of the world's reefs. By August in the gulf, the tern chicks are adult-size in mottled adolescent plumage. Their parents are trying to feed them for their journey home. As the sun falls, tracks in the sand lead to one of our green turtles. She'll dig a nest about a metre deep and lay about a hundred eggs. Over her lifetime, she'll lay several thousand. The chances are very few will survive. The riches of the gulf are hidden under sand and water and dust. The natural wealth buried here that has most changed us. The stakes here, for wildlife and for us, are very high. Oil tankers go around Arabia to the Red Sea, heading for the Suez Canal and Europe. The Red Sea reefs sit vulnerable beside one of the busiest shipping channels in the world. Below, casualties. A century-old wreck sits harmlessly at 20 fathoms. This was a cargo steamer en route through the Suez Canal. Now, it's part of the reef. The Red Sea and the Mediterranean were linked by the Suez Canal almost a century and a half ago. The wreck has been colonised by eggs and larvae from the reef. Leather corals reach out from below decks. Coral grouper and glassfish are in adjacent cabins. A red-mouthed grouper acts as a protector to the glassfish, guarding them from other groupers or jacks. But the babysitter snatches a few glassfish for himself. The price of his protection. In order to colonise a wreck or regenerate the reef, eggs and young must survive. Staying alive yourself is hard enough. Starting a family here, securing a future, is an extraordinary story. Love has reached the Red Sea reef. Bannerfish take turns on the dance floor. Couples are preparing for a family. Fish time their spawnings carefully, but the chances are that almost all their precious young will be eaten. To avoid this tragedy, some fish have become better parents. A titan triggerfish is behaving strangely. She may be lying on top of her eggs to protect them. Triggerfish lay a jelly-like blob of eggs in depressions in the coral rubble. The dedicated parent defends the eggs from the multi-coloured thieves. The triggerfish's mate comes to the rescue. A few eggs might survive, but the longer-term future for coral reefs seems less hopeful. Half the reefs worldwide are dying or have died. Scientists blame us. Pollution and a changing climate with warmer seas. Twilight offers a glimpse into a darker future. Gorgonian fan corals seem like decaying lace. A ghost town, a reminder of what is at stake. On the other side of Saudi Arabia is another vision of the future. In a sea beyond platforms and refineries, there is salvation and new life. In August, on one magical night in the Gulf, the sandstorms and the summer of growth have had an extraordinary effect. Slowly at first, eggs and larvae are released in millions. This wasn't known to happen here on this scale, let alone filmed before. Polola worms release wriggling egg cases that fragment into capsules of eggs. Packages explode with new life. The specially adapted Gulf corals, the hardest survivors of a superheated sea, will release eggs too, and egg eaters can't possibly eat them all. Eggs and larvae begin a journey to regenerate the ocean. Ctenophores are joined by bigger jellies. This jellyfish is like a mobile reef, a lifeboat full of shrimps and fish and eggs. A Noah's Ark. On the islands where cormorants and terns nested and dust storms blew nutrients into the sea, now baby green turtles start on their journey. They join in eggs and larvae, the gift of the Gulf. One lucky hatchling might survive to return here in about 20 years' time. By then, tougher corals from the Gulf may be helping the Red Sea Reef to cope with warmer times. The Gulf at first seemed like the ugly duckling of the two seas. Now, it seems the Gulf may perform a final miracle and restock the reef. The two seas are an extraordinary reflection of each other. The parade of riches in the Red Sea relies on almost nothing. The harshness of the Gulf has become its true wealth.