"Our Planet is the greatest living puzzle in the Universe." "A collection of worlds within worlds." "Each one a self-contained ecosystem, bursting with life." "But how do they work?" "The intricate web of relationships and the influence of natural forces, makes each microworld complex and unique." "So to discover their secrets, we need to explore them one by one." "Untangle their interlocking pieces and ultimately reveal the vital piece, the key to life itself, hidden deep within each of nature's microworlds." "At the centre of California's sunshine coast are the waters of Monterey Bay." "America's largest marine sanctuary and one of the most diverse marine ecosystems on the planet." "Below the waves is an explosion of life." "From the mammoth, to the microscopic." "All living in and around a giant kelp forest that is home to over 300 species of fish and thousands of invertebrates." "And that's just below the water." "With such abundance of life, the key to success is balance." "But what maintains this balance?" "Each species finding its niche, none out weighing the other." "This is no mean feat, it's a complex web that could be easily upset." "But Monterey has a secret weapon." "Scientists discovered that a single species holds the key to the balance of life in the entire bay." "To find out what this species is, let's journey through this remarkable place, and take a closer look at its key characters." "And what better place to start than with the most impressive." "It might not look like much from above, but below the surface of the bay is a forest, as lush and vibrant as any on land." "Spires of kelp, as tall as houses, grow from the sea floor to the surface, up to 30 meters above, forming a dense canopy." "Like a rainforest, the kelp makes a home for a myriad of incredible creatures, bizarre sea hares, flashy Garibaldis and fierce wolf eels, each one more colourful, weird or wonderful than the next." "So much diversity in fact, that as many as 100,000 creatures can be living on a square meter of kelp at any time." "Although playing the role of tree in this underwater forest, kelp is not actually a plant but a giant or macro algae." "These impressive spires can grow up to a metre a day under the right conditions." "They rely on photosynthesis, using sunlight to convert gases and nutrients into the material needed for this astonishing growth." "Holdfast fingers cling to the rocky floor, anchoring the kelp." "While floats filled with air keep it growing toward the sun." "Chlorophyll in the blades absorb the sun's energy, just like in the leaves of plants." "But this is where the similarity ends." "Kelp has no vascular system, no roots forging into the earth or internal structures to suck up water and nutrients and transport them from the root to its cells." "Kelp works in a very unusual way." "The blades directly absorb water and nutrients from their surroundings." "All types of kelp and seaweed photosynthesise in this way." "But the kelp on this stretch of California's coastline grows extraordinarily thick and fast, which is why it can support such rich marine life." "And the reason it does so well here is down to the geography of the bay itself." "Monterey sits on a gently sloping shelf, the edge of the American continent." "Where it meets the ocean, the shelf suddenly gives way to something more dramatic." "A rift deeper than the Grand Canyon plummeting 5 kilometres down to the ocean floor." "No light can penetrate to its depths, an altogether different microworld, dark, mysterious and removed from the world above." "But surprisingly it is this canyon that holds the key to the kelp's success." "The canyon floor is thick with decaying matter, the remains of life from the water column above that have sunk and slowly decomposed." "Now we see why Monterey is so unique." "Normally this nutrient soup would settle." "Instead, strong offshore winds push surface water away, forcing this deep water to rise and take its place." "And these upwellings deliver a constant stream of nutrient-rich water to the bay." "The kelp forest has all the ingredients needed for successful photosynthesis and gargantuan growth." "The forest makes the perfect habitat." "Attracting an incredible number of species." "All interacting, competing for food and space." "Kelp provides the stage for diversity but it doesn't keep the balance." "If anything, it's what makes life here so complex in the first place." "The species we are looking for must somehow keep this busy forest in check." "Just like a terrestrial forest, the spires support life at different levels, from the ground up." "The holdfasts that anchor the kelp to the seabed provide cover for spiny brittle stars, shy pygmy octopus, and the bizarre decorator crab," "a master of disguise, pain-stakingly attaching bits of kelp on to his shell until he blends in with his surroundings." "Tiny amphipods make their home in the lower blades." "Not only do they eat the kelp but they also use it as protection." "Like spiders, they produce silk," "weaving together two edges of the blade to make a safe space, a hideout from predators, protecting her and her young." "A few storeys up the flamboyant Spanish dancer, a sea slug, flaps from one blade to the next." "While young fish use the higher blades as a safe nursery before heading out to deeper waters." "The most bizarre fish is using the top reaches of the kelp." "This is the Mola Mola, or sun fish." "Unusual doesn't quite cover it." "Not only do they look like a science experiment gone wrong but they can grow to gigantic sizes." "From a tiny egg, Molas can increase in size up to 60 million times to the weight of a large car." "It's an open sea fish that has come inshore because of an uncomfortable problem." "A parasitic infestation that it can't tackle on its own." "By swimming at the surface of the kelp it can enlist the help of the half moon fish that find shelter there." "They'll happily pick off as many parasites as they can find." "And for the parasites that are tougher to shift, the Mola Mola calls in some heavy duty help." "By floating flat on the surface, it advertises its problem to a nearby gull, who is more than happy to oblige." "All these animals might seem benign and balanced within their habitat, but with so many species living on top of each other, life in the kelp is not always peaceful." "Most live under continual threat of being consumed." "This sea fern provides a disguise for the skeleton shrimp, swiping at passing plankton." "While also being nibbled by Polycera, a small sea slug." "Polycera leaves behind a slimy trail as it moves around the kelp, a line of bread crumbs for the large predatory Navanax, who uses chemoreceptors to track it down." "What looks like moss or lichen, is actually a tiny animal." "Bryozoa colonize the kelp blades," "filtering water for microscopic bits of plankton." "They hide from predators in tough shells that have a similar composition to those of crabs." "But the Garibaldi fish's mouth parts are tough enough to rip the Bryozoa from the kelp, shell and all." "This fish's spectacular colouring is a statement, space is at a premium here, it warns others off his patch." "The giant kelpfish prefers to blend in." "Imitating the kelp in both looks and movement might just save him from a hungry seal." "Although these interactions keep the food chain going, individually, they don't have enough impact to affect the balance of life." "Larger species might have more bearing." "There's a giant hiding out in the kelp." "The grey whale is not a year round inhabitant, but it's a pretty impressive visitor." "It's made the 7,500 kilometre journey from the freezing Arctic to give birth in the warmer waters of Southern California." "This is the longest migration of any mammal on the planet." "Now the calf is strong enough, they must make their way back to Arctic feeding grounds, taking them past the mouth of Monterey Bay." "But with a baby in tow, not only does this journey become slower, but far more dangerous." "They're not the only large predators out here." "The grey whale mother has a decision to make." "It can hug the coast, hiding out in the cover of the kelp forest, or cut straight across the mouth of the bay." "This is the quicker route but leaves her and her baby out in the open and vulnerable to attack." "A pack of deadly predators stalk these waters," "Orcinus orca, the aptly named killer whale." "Capable of 50 kilometre per hour bursts, the potent predators have no trouble catching up with the slow moving pair." "But the power of the mother is not to be underestimated." "Under attack, grey whales react violently, earning them the name devilfish by early hunters." "The killers must play to their strengths." "They're a third of the size but they have speed on their side, by giving chase they hope to tire the calf." "This game of cat and mouse can last hours before the mother is forced to stop for her exhausted calf." "Now the pack combine strength, forcing themselves between the whales and driving them apart." "Once the calf is separated, it's all over." "The killer pack has won and the mother must go on alone." "Battles between these large animals might not have a direct effect on the balance of life in the lower reaches of the forest, but they are still vitally connected to the kelp." "What's left of the body of the baby whale will sink to the sea floor, break down and then be recycled back to the surface by upwellings," "feeding the kelp and supporting its tenants." "Perhaps the greatest impact that large predators have on life in the kelp, is by indirectly contributing to the nutrient cycle that helps to sustain it." "The problem is that with healthy kelp comes the animals that want to eat it." "These aren't just any grazers." "If we are looking for a species that has a real impact on the kelp, well, we've found it." "A herd of Sea urchins, kelp eaters." "They reproduce fast, doubling their numbers in a matter of days and they're armoured in spines that few predators can break through." "This is an army built for a purpose." "Unlike other grazers, urchins aren't only interested in the kelp's blades." "Five sets of brutal, self-sharpening calcium carbonate teeth hit the kelp where it hurts most." "The holdfast may be tough enough to withstand winter storms, but it is no match for the urchin's jaws." "These are capable of chomping through rock." "By feeding at the base, sea urchins can cut entire spires loose and are capable of destroying whole beds of kelp at a time." "Yet despite this onslaught, the kelp proliferates." "Not because, even with nutrient-rich waters, it can outgrow urchin grazing, but because it also supports another species," "a creature equally ravenous." "Floating at the surface, lies the secret to the success of the Bay." "A raft of sea otters have rolled themselves in the kelp's fronds, anchoring themselves in place so they don't drift out to sea while they sleep." "This may be the smallest sea mammal, but with a voracious appetite and a partiality for urchin meat, it's crucially important to the kelp forest." "With an adult typically eating up to 30% of its body weight a day, that could be 50 of the spiny invaders, the otter is Monterey Bay's secret weapon of mass urchin destruction." "Although the urchins are typically found on the sea floor, otters make light work of finding them." "Holding their breath for five minutes, they will dive up to 18 metres," "prizing urchins off the rocky sea bed." "Sea otters aren't just effective hunters, they're also brilliant tool users, cracking open their prey's shell by banging it against a flat stone on their stomach, a clever way of getting past those sharp spines," "munching on its protein-rich innards." "Mothers pass on hunting techniques to their pups, although they can take a while to perfect." "So many species rely on the kelp, and therefore the otters' appetite, which keeps the urchins in check." "But the question remains, why do the otters need to eat quite so much?" "Unlike their neighbours, the harbour seals and sea lions, otters don't have a thick blubber layer, which is the usual defence against cold water." "This means that their body heat is constantly being lost to the water around them." "Otters combat this in two ways." "Firstly with their fur, the densest fur of any animal on the planet." "Up to a million hairs in an area the size of a postage stamp, trapping air, keeping the cool water at bay and providing insulation." "Their loosely jointed skeleton means they are flexible enough to fluff air back even into those tough to reach places." "In fact, this system works so well that with careful grooming, cold water never reaches the skin at all." "This remarkable fur goes a long way to keeping them warm, but to keep their core internal temperature up they must constantly burn energy" "and that means consuming calories, lots of them." "Urchin control, crucial as it is to the kelp, is really just a side effect of otter thermo-regulation." "Although populations of sea otters are relatively small, they are critical to the balance of the ecosystem." "So they are what is known as a keystone species, guardians of the kelp forest." "The importance of sea otters to the balance of the ecosystem hasn't always been known." "Sadly it was learnt the hard way." "When settlers first arrived on California's coast they treated the ocean like an open larder." "Few species were safe, and the otter fared worst of all." "It's a sad irony that the beautiful adaptation that made them so suited to life in the bay put sea otters at the brink of extinction." "Otters were hunted so heavily for their pelts that within 100 years they had vanished from California's coastline." "For scientists it was a living demonstration of the key role that otters play." "With the keystone species removed, urchin numbers rocketed, devouring the kelp." "In several areas along the Californian coastline the forests disappeared altogether." "Once sea urchins have cleared an area of kelp, enough numbers will remain in this barren area to nip any regrowth in the bud." "These urchin barrens were an ecological disaster." "Coastal fish and invertebrate populations in Monterey plummeted and so large predators were forced to move away." "Although otter hunting was officially banned in 1911, it was too late." "No otters had been seen in the area in living memory, considered extinct..." "Monterey Bay had lost its key." "Until a chance glance down a telescope in 1938 turned the fates for this failing ecosystem." "A secret community, up to 300 animals strong, living in a remote bay." "No-one knows how this fortunate community survived but their discovery heralded a new dawn for Monterey Bay." "Scientists had seen what happened to the ecosystem when the keystone species was removed." "Now they had the unique opportunity to watch the effects of its return." "With hunting banned, this otter population grew, getting down to some serious urchin eating." "Which gave kelp beds a chance to take hold and grow." "With such a ready supply of food, the secret population of hundreds became thousands and showed that where the otter went, healthy kelp followed." "Monterey's keystone species was recovering," "allowing the ecosystem to recover with it, link by link." "Today, Monterey Bay is once again one of the most diverse marine habitats on earth." "It's a real ecological success story." "We have seen just how complex the web of life is here and how quickly it can fall apart." "So it's crucially important that the bay is protected." "And with its otter guardians in place, keeping urchin grazers under control, the future looks bright for Monterey." "The balance has returned." "The kelp forest and its tenants are thriving." "The hope is, that by protecting these waters and its keystone species, this diverse marine ecosystem will continue to be spectacular." "Subtitles by Red Bee Media Ltd"