www.able.co.nz Captions were made with the support of NZ On Air. Able 2017 (WIND HOWLS) (ICE CREAKS AND GROANS) In the far north, after three dark months of winter,... a world is waiting... for a trigger. The sunshine of spring. (PEACEFUL MUSIC) Starfish are the first to respond. They race for the highest point... and, sensing changes in the water with the tips of their tube feet,... they spawn. (UNSETTLING MUSIC) Sea cucumbers, with only their mouths exposed, now emerge. They collect as many starfish eggs as they can. Which is quite a lot when you've got 10 arms. Now sea pens rise up to claim a share. The creatures here must grab what they can of this annual banquet,... for the light has also set in motion the greatest transformation of all. Fronds of kelp, a marine alga, rise towards the surface, lifted by their gas-filled bladders. Soon, a marine forest has materialised,... teeming with life of all kinds. These green seas are some of the most productive but fiercely competitive waters in all the oceans. The southern tip of Africa. Here, two great oceans collide. (SEA ROARS) In the shallows, fed by rich currents, are bountiful forests of kelp. Barely visible except for the pulsating siphon through which it breathes - a common octopus, waiting for prey to pass by. A crab will do. The octopus sets off in pursuit. (INTRIGUING MUSIC) (SUSPENSEFUL MUSIC) (MUSIC BUILDS) And then lurks... with the patience of an ambush hunter. (SUDDEN DRAMATIC MUSIC) But the octopus shares the Cape waters with a great concentration of other predators. Fur seals... and sharks. They all eat octopus... if they can find one. (TENSE MUSIC) And pyjama sharks are experts... at hunting in the undergrowth. Time to disappear. (TENSE MUSIC CONTINUES) But these tough-skinned little sharks are small enough to reach deep into crevices. (DRAMATIC MUSIC) But the octopus is far from finished. She slips her tentacles into the shark's gills. That prevents the shark from breathing. So the shark has to let go. When caught out in the open and vulnerable, this octopus does something truly extraordinary... and never recorded before. (EXCITING MUSIC) She disguises herself... with a protective armour of shells. She's hiding... in plain sight. The shark can sense its prey. (EXCITING MUSIC BUILDS) But the shells confuse it. In a forest full of hungry mouths, superior wits allow this octopus to stay alive. (VACUUM CLEANER WHIRRS) (CELL PHONE BEEPS) Oh! To help keep you safe if there's an emergency, all compatible mobile phones are now able to receive emergency mobile alerts. (CELL PHONES BEEP) Huh? Oh! (WHOOSH!) (BARKS) So when you hear this sound,... (CELL PHONE BEEPS) ...stop doing what you're doing and follow the instructions. (BEEP! BEEP!) 1 Forests of kelp flourish in seasonal waters around the globe,... particularly along the Pacific Coast of North America. Here, the biggest kelps of all grow in vast forests stretching for hundreds of kilometres. In some places, the giant fronds rise up to 60 metres tall. (MAJESTIC MUSIC) The thickets they create are crowded with life. Competition here for space and food is intense. A challenging problem for the Garibaldi fish. He tends to his patch of seaweed, filled with tiny creatures that he eats. As with most farmers, his work never ends. He removes snails and any other grazers that come to eat his algae,... no matter how big they are. He has to deal with pests of all kinds. This can be the worst of them - sea urchins that can scrape off every vestige of algae from a rock. Its spines are needle-sharp. Somehow, the Garibaldi must remove it. But the problem with sea urchins... is that they just keep coming. When evening arrives and the light fades, he has to stop. He not only needs a rest, he needs to hide... because at night, predators prowl through these forests. A torpedo ray, capable of stunning its victim with 45 volts of electricity. (TENSE MUSIC) While the Garibaldi hides,... the urchins can feed without interruption. The light returns,... and he finds his farm is once again under attack. (ROUSING MUSIC) Urchins, like locusts, have the ability to swarm. And this can be disastrous, not just for the Garibaldi, but for the kelp forest itself. All the vegetation is now under attack. The urchins move through the forest, cutting through the kelp fronds and leaving behind vast barrens. These urchin armies have felled many kelp forests along the Pacific Coast of North America. But help is at hand. (SQUEAKS) Sea otters. All other kinds of otters spend much of their lives on land, but sea otters rarely leave the water. At first, a newly-born pup is not a very good swimmer, so its mother spends hours grooming its fur to make it buoyant. But to provide her youngster with milk and keep herself warm, she must eat up to 30% of her body weight every day. (INTRIGUING MUSIC) She does that by eating shellfish. And urchins are among a sea otter's favourite delicacies. In the past, sea otters were hunted so intensively for their fur that they came close to extinction. With them gone, many kelp forests were replaced with urchin barrens. Today, sea otters are protected,... (SQUEAKS) and as their numbers slowly return, many of the kelp forests are recovering too. (SOFT MUSIC) Now, in some remote places, sea otters are so numerous they assemble in huge rafts,... something that hasn't been seen for over a century. (OTTERS SQUEAK) 1 In the sun-drenched shallows off Australia,... kelp is replaced by the sea's only flowering plants - seagrass. The most extensive of these marine grasslands can stretch for over 8,000 square kilometres. (MAJESTIC MUSIC) All across the tropics, they're patrolled by tiger sharks. They can grow up to 5 metres in length... and have powerful crushing jaws. Green turtles are their prey. The turtles feed almost entirely on seagrass. A single one can consume up to 2 kilos of it in a day. (BIRDS CHATTER) (SUSPENSEFUL MUSIC) But they can never rest easy. Healthy turtles will keep well away from an approaching shark. And just by keeping the turtles on the move, the sharks prevent any one patch of seagrass from being overgrazed. (UPLIFTING MUSIC) And that has benefits for us all. A patch of seagrass can absorb and store 35 times as much carbon dioxide as the same area of a rainforest. So the prairies and their sharks are surprising allies in the fight against a warming climate. (WAVES SPLASH SOFTLY) The struggle to survive in our green seas can have far-reaching consequences. Once a year, one particular meadow in Australia is transformed. Around the first full moon of winter, an army materialises. Spider crabs. For the past year, they've been feeding in deeper waters. Now they march across the seagrass plains. (MAJESTIC MUSIC) Hundreds of thousands of them. They clamber over one another,... creating great mounds... nearly 100 metres long. They're not seeking mates, neither are they laying eggs. They have come here in order to grow. Like all crabs, their bodies are enclosed in a hard, un-expandable shell. So to grow, they have to break out of it. And that allows the soft one that has developed beneath to expand. It will take days for the new shell to harden. Its legs are so limp that they won't work properly. The crab is unprotected and in great danger. (DRAMATIC MUSIC) A smooth stingray. It's huge - about 4 metres long. It wants a soft, freshly-moulted crab that will be easier to eat. (DRAMATIC MUSIC CONTINUES) The crabs try to stick together. But now, disturbed by the ray, they're scattering. A newly-moulted crab is too weak to keep up with the crowd. (CRUNCHING) The safest place is right in the middle of the pile. That is why they have all assembled here. There is safety in numbers. (HIGHLY DRAMATIC MUSIC) (MUSIC FADES) But the vast majority of the crabs escape,... and within the next few days, they will be ready to return to the depths and resume their lonely wanderings in search of food. This is no graveyard,... but the triumph of a 100,000 crabs successfully moulted. (WAVES SPLASH GENTLY) 1 The green seas of Southern Australia are particularly rich in such spectacular assemblies. But most of the creatures come together for a very different reason - to breed. The giant cuttlefish, the largest of all cuttlefish. (INTRIGUING MUSIC) They live for just one or two years. Now, as the Australian summer draws to an end, they have one last act to complete - to find a mate. (TENSE MUSIC) But there are over 100,000 males competing for the arriving females in this one bay. Among them a giant - a true Goliath. He probably weighs about 10 kilos. Bands of colour sweep across his skin. That's how cuttlefish communicate. (DRAMATIC MUSIC) This smaller male couldn't possibly take him on. Beside Goliath and under his protection, a female who has just mated with him. But other rivals are still interested. It seems a small male wouldn't stand a chance. The female is now displaying a white stripe along her side nearest Goliath. It's a clear signal that she no longer wants to mate with him. (GENTLE MUSIC) It's all the encouragement that the little male needs. He's going to have to use trickery. (INTRIGUING MUSIC) He tones down his colours and tucks in his arms. He's just the right size to mimic a female. Goliath is deceived. The small male now displays a white stripe, just like the real female, to deter his advances. He slips beside her,... and they mate. By mating with multiple partners,... the female ensures the greatest genetic diversity for her young. The sneaky male leaves, his final act complete. So even among giant cuttlefish, it seems... it's not all about size. Other males in these Australian green pastures take greater responsibility for their young. A weedy sea dragon. This is a male, and he's carrying a precious cargo. While mating with the female, he collected the eggs and attached them to his underside. Now he's leaving these seaweed thickets... and travelling into more open waters where elaborate camouflage is less effective. (TENSE MUSIC) And there are many predators out here. And this is what the fathers risk their lives for. (MAJESTIC MUSIC) Dense clouds of minute shrimp. Mysids - one of a sea dragon's favourite foods. They're drawing other sea dragons out here too. Finally, it's time for the young to break free. But algae has grown over these developing eggs,... and it risks smothering them. Nonetheless, the babies are emerging. (TENDER MUSIC) They've hatched successfully. The fathers return to the tangle of kelp, where they're virtually invisible,... while the young remain out here. But they will grow quickly, surrounded as they are by their ideal food. 1 (TINKLING MUSIC) Vast numbers of the oceans' young fish start their lives in the green seas. One of the richest nurseries of all are the mangrove forests. Fringing the coastline of the tropics, they form a natural protective barrier between land and sea... and are some of the world's most productive forests. Below the water, their arching aerial roots give them a firm footing. Here, there's abundant food for baby fish,... while the tangled roots protect them from bigger fish and other predators that haunt the channels. But in Northern Australia, with the receding tide,... the little fish are forced to leave their shelter. And now they are vulnerable. (SUDDEN DRAMATIC MUSIC) (UNSETTLING MUSIC) It's the most deadly assassin in the green seas. The zebra mantis shrimp - a male, almost 40 centimetres long. But he's not hunting just for himself. He's collecting food for his mate. She may have been his partner for 20 years. She relies on him to bring her food... and puts her energy into her eggs instead. In a world so full of food, this would seem a sensible strategy. But it's also a risky one. Were her male to disappear, she could starve. Something has caught this male's attention. Perhaps an irresistible odour... or a distant call. Whatever the reason, a male will leave his burrow and his lifelong mate. An even larger hole. Females who have lost their mates appear to send out distress signals to call in a new male. A larger female will produce more eggs, so by mating with her, he will father more offspring. But infidelity comes at a price. A larger partner demands more food. (BIRDS AND INSECTS CHATTER) The richer a sea, the greater the competition. And there is one green sea that supports more life than all the rest combined. Unlike the mangrove forests and the seagrass prairies, its location is in the open seas and only temporary and unpredictable. This greenness comes not from rooted plants,... but from clouds of floating ones. Billions of microscopic phytoplankton are proliferating. And in such numbers that they fuel one of the greatest feasts of all. (DRAMATIC MUSIC) Off America's Pacific Coast, hundreds of common dolphins are rushing to a banquet. (DOLPHINS WHINE) (BIRDS SQUAWK) They're not the only ones homing in. (DRAMATIC MUSIC CONTINUES) So are sea lions. (MUSIC SETTLES) They're heading for Monterey Bay, California, where algal blooms have caused an explosion in plankton feeders. Anchovies - millions of them. The dolphins herd the anchovies towards the surface. Sea birds and sea lions take advantage of the shoal's appearance. It's a race to grab a share before others arrive. (DRAMATIC MUSIC CONTINUES) (WHALE GROANS) Humpback whales - hundreds of them. With every upward lunge, they sieve out up to 100 kilos of fish. (BIRDS SQUAWK) They're claiming the biggest share of one of the biggest feasts on Earth. (WHALE GROANS) (GENTLE MUSIC) (WHALE GROANS) So crucial are these tiny plankton that almost all marine life ultimately depends upon them. It's the green seas, not the blue,... that are the basis of almost all life in the world's oceans. (MAJESTIC MUSIC) (MUSIC SETTLES) Next time on Blue Planet II, we meet the creatures that live where two worlds collide... and discover how they cope with the demands of the ever-changing coasts. (SEALS BELLOW) www.able.co.nz Captions were made with the support of NZ On Air.