Episode 1 The Deep – A thousand metres down, in the twilight zone, animals play a constant game of hide and seek. Most are transparent, hoping to pass unnoticed. Hatchet fish have flattened bodies and silvered sides that reflect any light and make them invisible. A fish called winteria looks like an underwater bushbaby with its two tubular eyes designed to look up at the surface to spot the silhouettes of potential prey. Below 1,000 metres you enter the dark zone and an alien world. In a world where red light does not exist, dark red jellyfish and shrimps float by, confident that they are almost completely invisible. Predators here have massive teeth and enormous mouths as food comes along so rarely that they have to grab prey of any size. The hairy angler is the size of a beach ball and its body is covered in long antennae designed to pick out the movements of any prey foolish enough to venture close to its terrifying teeth. The fangtooth has the largest teeth in the ocean for its size, so big it can’t close its mouth. Gulper eels can swallow prey as big as themselves.
Episode 2 Open Oceans – An unfortunate shoal of sardines is first attacked by three metre long striped marlin with metre long, needle sharp javelins on their heads. The commotion attracts juvenile yellowfin tuna and then a 14 metre Sei whale scoops up the remains. Sir David Attenborough says: “Predators and prey are locked in a deadly three dimensional contest of hide and seek, played out over immense distances.” None are better at tracking down food than dolphins. A school of spotted dolphins herd mackerel, but the noise of their sonar attracts one of the most glamorous fish in the sea, a sailfish. With a top speed of over 120km/h, it herds the fleeing fish with its unique sail before gunning them down with ease.
Episode 3 Frozen Seas – In winter the temperature drops to below -50 degrees centigrade and in Antarctica most animals escape the weather. But emperor penguins stay put and huddle together, incubating their eggs and rearing their chicks in the worst weather on the planet. Weddell seals also remain, keeping their breathing holes open by scraping away the ice with their teeth. In the Arctic, animals that do stay north for the winter are forced to seek refuge in any patches of open water that haven’t frozen over. Sometimes whales become trapped in these isolated tiny holes in the ice. A group of belugas are 22km from open ocean and it will be two months before the ice melts. They are painfully thin and horribly scarred. Their wounds are not inflicted by the ice but by polar bears that have spotted an easy meal. Aware of the danger, the whales stay submerged as long as they can, but they can only hold their breathe for 20 minutes. Eventually a bear makes a catch.
Episode 4 Seasonal Seas – Just when the weather is at its worst, 100,000 grey seals haul themselves up through the surf on to Sable Island off Nova Scotia. This is the world’s largest colony of grey seals and perversely they’ve come to breed in winter. Within 18 days the pups are abandoned, but spring is on its way with plenty of food. An eight tonne basking shark filters 1,000 tonnes of seawater through its gills every hour to sieve out plankton, and large numbers are attracted to plankton blooms. On the seafloor, seaweed stretches towards the sunlight, and off the coast of California, underwater forests of giant kelp grow up to 100 metres high. Massive schools of fish shelter here and sea otters snooze at the surface winding strands of kelp around themselves as anchors.
Episode 5 Coral Seas – Life on a coral reef starts with one coral larva which lands in the right place and grows. Soon it’s a coral head, cemented and secure on the seabed. A tiny algae that lives in its tissues allows the coral to grow night and day and as more corals settle, a reef develops. Overcrowding follows as corals expand and soon they’re fighting, digesting their neighbours alive under cover of darkness. Corals are protected by a hard, limestone skeleton, but bumphead parrot fish bite straight through rock and coral with their powerful jaws. These fish erode the coral and the material they swallow comes out the other end as fine sand. On a single reef they can produce tonnes of sand every year. This soft sand forms beautiful tropical white beaches and eventually creates tropical islands!
Episode 6 Tidal Seas – A huge tidal wave, sweeps 200 miles inland up the River Amazon. It’s an event that only happens on key days each month, when the moon and sun combine their gravitational pull to maximum effect. The force of the wave shatters immense rainforest trees. As the moon orbits the Earth its gravitational pull causes the sea level all over the world to rise and fall. In the Bay of Fundy, Canada, two billion tonnes of water flow in and out each day, more than all the rivers on Earth combined. Five hundred finback whales come here to gorge on the rich herring pickings.
Episode 7 Coasts – Each year the entire population of green turtles that live off the coast of Brazil undertakes a massive 5,000 mile migration to the tiny seven mile wide island of Ascension, lost in the middle of the Atlantic. How they manage to navigate remains a mystery but each year 5,000 female turtles make it to the island to lay their eggs. After laying three to four clutches of eggs each every two weeks or so, they have to make the return journey to Brazil. The whole cycle takes six months and the turtles do not feed at all during this time. Four hundred thousand Ridley’s turtles co-ordinate their return to land in a massive simultaneous egg lay called an arribada. It’s hard enough for turtles to drag themselves up the beach but what about fish? Every year, millions of capelin appear along the coasts of Newfoundland. They literally throw themselves out of the sea and for miles the beach is covered with writhing fish. Like the turtles, they are here to lay their eggs.
Episode 8 Deep Trouble – Scientists believe many species that are eaten every day are now seriously threatened. Most people have no idea where the fish they buy come from let alone how endangered they might be. As fish stocks dry up, supermarkets are now offering new and strange species from the deep sea. Bizarre looking creatures are being dragged up in vast fishing nets from depths of 1,000 metres or more. The methods used to catch them are horrifying. As the nets drag along the sea bed they rip up 100 year old corals and sponges, destroying the habitat. So even these new species may not be available for long.