0:00:02 > 0:00:06Our Planet is the greatest living puzzle in the Universe.
0:00:06 > 0:00:08A collection of worlds within worlds.
0:00:08 > 0:00:13Each one a self-contained ecosystem, bursting with life.
0:00:17 > 0:00:19But how do they work?
0:00:20 > 0:00:27The intricate web of relationships and the influence of natural forces,
0:00:27 > 0:00:32makes each microworld complex and unique.
0:00:33 > 0:00:37So to discover their secrets, we need to explore them one by one.
0:00:39 > 0:00:45Untangle their interlocking pieces
0:00:45 > 0:00:48and ultimately reveal the vital piece, the key to life itself,
0:00:48 > 0:00:54hidden deep within each of nature's microworlds.
0:01:01 > 0:01:04At the centre of California's sunshine coast
0:01:04 > 0:01:07are the waters of Monterey Bay.
0:01:07 > 0:01:12America's largest marine sanctuary
0:01:12 > 0:01:16and one of the most diverse marine ecosystems on the planet.
0:01:18 > 0:01:21Below the waves is an explosion of life.
0:01:26 > 0:01:29From the mammoth,
0:01:29 > 0:01:31to the microscopic.
0:01:31 > 0:01:38All living in and around a giant kelp forest
0:01:38 > 0:01:45that is home to over 300 species of fish and thousands of invertebrates.
0:01:45 > 0:01:48And that's just below the water.
0:01:49 > 0:01:55With such abundance of life, the key to success is balance.
0:01:55 > 0:01:57But what maintains this balance?
0:01:57 > 0:02:03Each species finding its niche, none out weighing the other.
0:02:04 > 0:02:07This is no mean feat,
0:02:07 > 0:02:12it's a complex web that could be easily upset.
0:02:14 > 0:02:16But Monterey has a secret weapon.
0:02:19 > 0:02:22Scientists discovered that a single species holds the key
0:02:22 > 0:02:25to the balance of life in the entire bay.
0:02:28 > 0:02:30To find out what this species is,
0:02:30 > 0:02:32let's journey through this remarkable place,
0:02:32 > 0:02:37and take a closer look at its key characters.
0:02:42 > 0:02:46And what better place to start than with the most impressive.
0:02:48 > 0:02:52It might not look like much from above,
0:02:52 > 0:02:57but below the surface of the bay is a forest,
0:02:57 > 0:03:01as lush and vibrant as any on land.
0:03:05 > 0:03:07Spires of kelp, as tall as houses,
0:03:07 > 0:03:12grow from the sea floor to the surface,
0:03:12 > 0:03:17up to 30 meters above, forming a dense canopy.
0:03:20 > 0:03:24Like a rainforest, the kelp makes a home
0:03:24 > 0:03:28for a myriad of incredible creatures,
0:03:28 > 0:03:31bizarre sea hares,
0:03:31 > 0:03:33flashy Garibaldis
0:03:33 > 0:03:34and fierce wolf eels,
0:03:34 > 0:03:40each one more colourful, weird or wonderful than the next.
0:03:41 > 0:03:46So much diversity in fact, that as many as 100,000 creatures
0:03:46 > 0:03:51can be living on a square meter of kelp at any time.
0:03:53 > 0:03:58Although playing the role of tree in this underwater forest,
0:03:58 > 0:04:03kelp is not actually a plant but a giant or macro algae.
0:04:05 > 0:04:08These impressive spires can grow up to a metre a day
0:04:08 > 0:04:10under the right conditions.
0:04:10 > 0:04:13They rely on photosynthesis,
0:04:13 > 0:04:17using sunlight to convert gases and nutrients
0:04:17 > 0:04:21into the material needed for this astonishing growth.
0:04:23 > 0:04:28Holdfast fingers cling to the rocky floor, anchoring the kelp.
0:04:31 > 0:04:36While floats filled with air keep it growing toward the sun.
0:04:37 > 0:04:42Chlorophyll in the blades absorb the sun's energy,
0:04:42 > 0:04:46just like in the leaves of plants.
0:04:47 > 0:04:50But this is where the similarity ends.
0:04:52 > 0:04:54Kelp has no vascular system,
0:04:54 > 0:04:58no roots forging into the earth or internal structures to suck up
0:04:58 > 0:05:03water and nutrients and transport them from the root to its cells.
0:05:03 > 0:05:07Kelp works in a very unusual way.
0:05:07 > 0:05:14The blades directly absorb water and nutrients from their surroundings.
0:05:16 > 0:05:21All types of kelp and seaweed photosynthesise in this way.
0:05:21 > 0:05:25But the kelp on this stretch of California's coastline
0:05:25 > 0:05:29grows extraordinarily thick and fast,
0:05:29 > 0:05:32which is why it can support such rich marine life.
0:05:34 > 0:05:36And the reason it does so well here
0:05:36 > 0:05:40is down to the geography of the bay itself.
0:05:43 > 0:05:47Monterey sits on a gently sloping shelf,
0:05:47 > 0:05:49the edge of the American continent.
0:05:51 > 0:05:53Where it meets the ocean,
0:05:53 > 0:05:57the shelf suddenly gives way to something more dramatic.
0:06:00 > 0:06:03A rift deeper than the Grand Canyon
0:06:03 > 0:06:07plummeting 5 kilometres down to the ocean floor.
0:06:08 > 0:06:12No light can penetrate to its depths, an altogether different
0:06:12 > 0:06:18microworld, dark, mysterious and removed from the world above.
0:06:18 > 0:06:21But surprisingly it is this canyon
0:06:21 > 0:06:24that holds the key to the kelp's success.
0:06:26 > 0:06:31The canyon floor is thick with decaying matter, the remains of life
0:06:31 > 0:06:37from the water column above that have sunk and slowly decomposed.
0:06:39 > 0:06:43Now we see why Monterey is so unique.
0:06:43 > 0:06:48Normally this nutrient soup would settle.
0:06:48 > 0:06:53Instead, strong offshore winds push surface water away,
0:06:53 > 0:06:57forcing this deep water to rise and take its place.
0:06:59 > 0:07:02And these upwellings deliver a constant stream
0:07:02 > 0:07:05of nutrient-rich water to the bay.
0:07:07 > 0:07:10The kelp forest has all the ingredients needed
0:07:10 > 0:07:15for successful photosynthesis and gargantuan growth.
0:07:20 > 0:07:24The forest makes the perfect habitat.
0:07:24 > 0:07:27Attracting an incredible number of species.
0:07:27 > 0:07:33All interacting, competing for food and space.
0:07:33 > 0:07:36Kelp provides the stage for diversity
0:07:36 > 0:07:38but it doesn't keep the balance.
0:07:40 > 0:07:46If anything, it's what makes life here so complex in the first place.
0:07:46 > 0:07:49The species we are looking for
0:07:49 > 0:07:52must somehow keep this busy forest in check.
0:07:57 > 0:07:59Just like a terrestrial forest,
0:07:59 > 0:08:04the spires support life at different levels, from the ground up.
0:08:08 > 0:08:12The holdfasts that anchor the kelp to the seabed provide cover
0:08:12 > 0:08:16for spiny brittle stars,
0:08:16 > 0:08:20shy pygmy octopus,
0:08:20 > 0:08:24and the bizarre decorator crab,
0:08:25 > 0:08:30a master of disguise, pain-stakingly attaching bits of kelp
0:08:30 > 0:08:35on to his shell until he blends in with his surroundings.
0:08:38 > 0:08:43Tiny amphipods make their home in the lower blades.
0:08:43 > 0:08:48Not only do they eat the kelp but they also use it as protection.
0:08:50 > 0:08:54Like spiders, they produce silk,
0:08:57 > 0:09:02weaving together two edges of the blade to make a safe space,
0:09:02 > 0:09:08a hideout from predators, protecting her and her young.
0:09:16 > 0:09:22A few storeys up the flamboyant Spanish dancer, a sea slug,
0:09:22 > 0:09:25flaps from one blade to the next.
0:09:28 > 0:09:32While young fish use the higher blades as a safe nursery
0:09:32 > 0:09:36before heading out to deeper waters.
0:09:37 > 0:09:41The most bizarre fish is using the top reaches of the kelp.
0:09:43 > 0:09:47This is the Mola Mola, or sun fish.
0:09:47 > 0:09:51Unusual doesn't quite cover it.
0:09:51 > 0:09:55Not only do they look like a science experiment gone wrong
0:09:55 > 0:10:00but they can grow to gigantic sizes.
0:10:00 > 0:10:07From a tiny egg, Molas can increase in size up to 60 million times
0:10:07 > 0:10:09to the weight of a large car.
0:10:11 > 0:10:14It's an open sea fish that has come inshore
0:10:14 > 0:10:17because of an uncomfortable problem.
0:10:20 > 0:10:24A parasitic infestation that it can't tackle on its own.
0:10:26 > 0:10:30By swimming at the surface of the kelp it can enlist the help
0:10:30 > 0:10:34of the half moon fish that find shelter there.
0:10:35 > 0:10:39They'll happily pick off as many parasites as they can find.
0:10:41 > 0:10:45And for the parasites that are tougher to shift,
0:10:45 > 0:10:48the Mola Mola calls in some heavy duty help.
0:10:51 > 0:10:55By floating flat on the surface, it advertises its problem
0:10:55 > 0:11:00to a nearby gull, who is more than happy to oblige.
0:11:15 > 0:11:20All these animals might seem benign and balanced within their habitat,
0:11:20 > 0:11:26but with so many species living on top of each other,
0:11:26 > 0:11:30life in the kelp is not always peaceful.
0:11:30 > 0:11:34Most live under continual threat of being consumed.
0:11:40 > 0:11:43This sea fern provides a disguise for the skeleton shrimp,
0:11:43 > 0:11:48swiping at passing plankton.
0:11:50 > 0:11:57While also being nibbled by Polycera, a small sea slug.
0:11:57 > 0:12:01Polycera leaves behind a slimy trail as it moves around the kelp,
0:12:01 > 0:12:08a line of bread crumbs for the large predatory Navanax,
0:12:08 > 0:12:12who uses chemoreceptors to track it down.
0:12:18 > 0:12:25What looks like moss or lichen, is actually a tiny animal.
0:12:25 > 0:12:28Bryozoa colonize the kelp blades,
0:12:32 > 0:12:37filtering water for microscopic bits of plankton.
0:12:39 > 0:12:42They hide from predators in tough shells
0:12:42 > 0:12:45that have a similar composition to those of crabs.
0:12:47 > 0:12:50But the Garibaldi fish's mouth parts are tough enough
0:12:50 > 0:12:54to rip the Bryozoa from the kelp, shell and all.
0:12:56 > 0:13:01This fish's spectacular colouring is a statement,
0:13:01 > 0:13:07space is at a premium here, it warns others off his patch.
0:13:11 > 0:13:15The giant kelpfish prefers to blend in.
0:13:15 > 0:13:19Imitating the kelp in both looks and movement
0:13:19 > 0:13:23might just save him from a hungry seal.
0:13:25 > 0:13:29Although these interactions keep the food chain going,
0:13:29 > 0:13:32individually, they don't have enough impact
0:13:32 > 0:13:34to affect the balance of life.
0:13:36 > 0:13:40Larger species might have more bearing.
0:13:44 > 0:13:47There's a giant hiding out in the kelp.
0:13:47 > 0:13:52The grey whale is not a year round inhabitant,
0:13:52 > 0:13:56but it's a pretty impressive visitor.
0:13:56 > 0:14:01It's made the 7,500 kilometre journey from the freezing Arctic
0:14:01 > 0:14:05to give birth in the warmer waters of Southern California.
0:14:05 > 0:14:10This is the longest migration of any mammal on the planet.
0:14:10 > 0:14:14Now the calf is strong enough, they must make their way back
0:14:14 > 0:14:19to Arctic feeding grounds, taking them past the mouth of Monterey Bay.
0:14:19 > 0:14:25But with a baby in tow, not only does this journey become slower,
0:14:25 > 0:14:28but far more dangerous.
0:14:28 > 0:14:33They're not the only large predators out here.
0:14:33 > 0:14:38The grey whale mother has a decision to make.
0:14:38 > 0:14:42It can hug the coast, hiding out in the cover of the kelp forest,
0:14:42 > 0:14:46or cut straight across the mouth of the bay.
0:14:46 > 0:14:49This is the quicker route but leaves her and her baby
0:14:49 > 0:14:53out in the open and vulnerable to attack.
0:14:54 > 0:15:00A pack of deadly predators stalk these waters,
0:15:00 > 0:15:05Orcinus orca, the aptly named killer whale.
0:15:06 > 0:15:11Capable of 50 kilometre per hour bursts, the potent predators
0:15:11 > 0:15:16have no trouble catching up with the slow moving pair.
0:15:16 > 0:15:21But the power of the mother is not to be underestimated.
0:15:21 > 0:15:26Under attack, grey whales react violently,
0:15:26 > 0:15:31earning them the name devilfish by early hunters.
0:15:31 > 0:15:36The killers must play to their strengths.
0:15:36 > 0:15:41They're a third of the size but they have speed on their side,
0:15:41 > 0:15:45by giving chase they hope to tire the calf.
0:15:46 > 0:15:50This game of cat and mouse can last hours
0:15:50 > 0:15:55before the mother is forced to stop for her exhausted calf.
0:15:58 > 0:16:01Now the pack combine strength,
0:16:03 > 0:16:07forcing themselves between the whales and driving them apart.
0:16:10 > 0:16:15Once the calf is separated, it's all over.
0:16:18 > 0:16:20The killer pack has won
0:16:22 > 0:16:27and the mother must go on alone.
0:16:32 > 0:16:36Battles between these large animals might not have a direct effect
0:16:36 > 0:16:41on the balance of life in the lower reaches of the forest,
0:16:41 > 0:16:44but they are still vitally connected to the kelp.
0:16:47 > 0:16:53What's left of the body of the baby whale will sink to the sea floor,
0:16:53 > 0:16:59break down and then be recycled back to the surface by upwellings,
0:17:01 > 0:17:04feeding the kelp and supporting its tenants.
0:17:06 > 0:17:09Perhaps the greatest impact that large predators
0:17:09 > 0:17:14have on life in the kelp, is by indirectly contributing to
0:17:14 > 0:17:17the nutrient cycle that helps to sustain it.
0:17:18 > 0:17:21The problem is that with healthy kelp
0:17:21 > 0:17:25comes the animals that want to eat it.
0:17:25 > 0:17:27These aren't just any grazers.
0:17:30 > 0:17:33If we are looking for a species that has a real impact on the kelp,
0:17:33 > 0:17:36well, we've found it.
0:17:38 > 0:17:44A herd of Sea urchins, kelp eaters.
0:17:44 > 0:17:50They reproduce fast, doubling their numbers in a matter of days
0:17:50 > 0:17:54and they're armoured in spines that few predators can break through.
0:17:54 > 0:17:58This is an army built for a purpose.
0:17:59 > 0:18:02Unlike other grazers,
0:18:02 > 0:18:06urchins aren't only interested in the kelp's blades.
0:18:08 > 0:18:12Five sets of brutal, self-sharpening calcium carbonate teeth
0:18:12 > 0:18:15hit the kelp where it hurts most.
0:18:18 > 0:18:23The holdfast may be tough enough to withstand winter storms,
0:18:23 > 0:18:26but it is no match for the urchin's jaws.
0:18:27 > 0:18:31These are capable of chomping through rock.
0:18:41 > 0:18:47By feeding at the base, sea urchins can cut entire spires loose
0:18:50 > 0:18:54and are capable of destroying whole beds of kelp at a time.
0:18:58 > 0:19:03Yet despite this onslaught, the kelp proliferates.
0:19:03 > 0:19:07Not because, even with nutrient-rich waters,
0:19:07 > 0:19:10it can outgrow urchin grazing,
0:19:10 > 0:19:16but because it also supports another species,
0:19:18 > 0:19:21a creature equally ravenous.
0:19:24 > 0:19:30Floating at the surface, lies the secret to the success of the Bay.
0:19:32 > 0:19:36A raft of sea otters have rolled themselves in the kelp's fronds,
0:19:36 > 0:19:38anchoring themselves in place
0:19:38 > 0:19:42so they don't drift out to sea while they sleep.
0:19:45 > 0:19:48This may be the smallest sea mammal,
0:19:48 > 0:19:54but with a voracious appetite and a partiality for urchin meat,
0:19:54 > 0:19:58it's crucially important to the kelp forest.
0:20:00 > 0:20:06With an adult typically eating up to 30% of its body weight a day,
0:20:08 > 0:20:12that could be 50 of the spiny invaders,
0:20:12 > 0:20:18the otter is Monterey Bay's secret weapon of mass urchin destruction.
0:20:21 > 0:20:25Although the urchins are typically found on the sea floor,
0:20:25 > 0:20:28otters make light work of finding them.
0:20:30 > 0:20:34Holding their breath for five minutes,
0:20:34 > 0:20:38they will dive up to 18 metres,
0:20:43 > 0:20:47prizing urchins off the rocky sea bed.
0:20:50 > 0:20:54Sea otters aren't just effective hunters,
0:20:54 > 0:21:00they're also brilliant tool users, cracking open their prey's shell
0:21:00 > 0:21:04by banging it against a flat stone on their stomach,
0:21:04 > 0:21:08a clever way of getting past those sharp spines,
0:21:08 > 0:21:11munching on its protein-rich innards.
0:21:13 > 0:21:18Mothers pass on hunting techniques to their pups,
0:21:18 > 0:21:22although they can take a while to perfect.
0:21:24 > 0:21:30So many species rely on the kelp, and therefore the otters' appetite,
0:21:30 > 0:21:32which keeps the urchins in check.
0:21:32 > 0:21:35But the question remains,
0:21:35 > 0:21:38why do the otters need to eat quite so much?
0:21:40 > 0:21:43Unlike their neighbours, the harbour seals and sea lions,
0:21:43 > 0:21:46otters don't have a thick blubber layer,
0:21:46 > 0:21:50which is the usual defence against cold water.
0:21:50 > 0:21:53This means that their body heat is constantly being lost
0:21:53 > 0:21:55to the water around them.
0:21:55 > 0:21:57Otters combat this in two ways.
0:21:57 > 0:22:03Firstly with their fur, the densest fur of any animal on the planet.
0:22:06 > 0:22:11Up to a million hairs in an area the size of a postage stamp,
0:22:11 > 0:22:16trapping air, keeping the cool water at bay and providing insulation.
0:22:19 > 0:22:23Their loosely jointed skeleton means they are flexible enough
0:22:23 > 0:22:26to fluff air back even into those tough to reach places.
0:22:28 > 0:22:32In fact, this system works so well that with careful grooming,
0:22:32 > 0:22:35cold water never reaches the skin at all.
0:22:43 > 0:22:46This remarkable fur goes a long way to keeping them warm,
0:22:46 > 0:22:50but to keep their core internal temperature up
0:22:50 > 0:22:53they must constantly burn energy
0:22:55 > 0:22:57and that means consuming calories,
0:22:59 > 0:23:01lots of them.
0:23:03 > 0:23:07Urchin control, crucial as it is to the kelp,
0:23:07 > 0:23:13is really just a side effect of otter thermo-regulation.
0:23:13 > 0:23:16Although populations of sea otters are relatively small,
0:23:16 > 0:23:22they are critical to the balance of the ecosystem.
0:23:22 > 0:23:26So they are what is known as a keystone species,
0:23:26 > 0:23:29guardians of the kelp forest.
0:23:30 > 0:23:34The importance of sea otters to the balance of the ecosystem
0:23:34 > 0:23:37hasn't always been known.
0:23:37 > 0:23:40Sadly it was learnt the hard way.
0:23:42 > 0:23:46When settlers first arrived on California's coast
0:23:46 > 0:23:50they treated the ocean like an open larder.
0:23:50 > 0:23:56Few species were safe, and the otter fared worst of all.
0:23:57 > 0:24:02It's a sad irony that the beautiful adaptation that made them
0:24:02 > 0:24:07so suited to life in the bay put sea otters at the brink of extinction.
0:24:09 > 0:24:14Otters were hunted so heavily for their pelts that within 100 years
0:24:14 > 0:24:18they had vanished from California's coastline.
0:24:19 > 0:24:22For scientists it was a living demonstration
0:24:22 > 0:24:25of the key role that otters play.
0:24:27 > 0:24:33With the keystone species removed, urchin numbers rocketed,
0:24:33 > 0:24:36devouring the kelp.
0:24:40 > 0:24:44In several areas along the Californian coastline
0:24:44 > 0:24:47the forests disappeared altogether.
0:24:50 > 0:24:54Once sea urchins have cleared an area of kelp,
0:24:54 > 0:24:58enough numbers will remain in this barren area
0:24:58 > 0:25:01to nip any regrowth in the bud.
0:25:01 > 0:25:06These urchin barrens were an ecological disaster.
0:25:08 > 0:25:14Coastal fish and invertebrate populations in Monterey plummeted
0:25:17 > 0:25:22and so large predators were forced to move away.
0:25:26 > 0:25:30Although otter hunting was officially banned in 1911,
0:25:30 > 0:25:32it was too late.
0:25:32 > 0:25:36No otters had been seen in the area in living memory,
0:25:36 > 0:25:39considered extinct...
0:25:42 > 0:25:46Monterey Bay had lost its key.
0:25:52 > 0:25:57Until a chance glance down a telescope in 1938
0:25:57 > 0:26:02turned the fates for this failing ecosystem.
0:26:02 > 0:26:05A secret community, up to 300 animals strong,
0:26:05 > 0:26:08living in a remote bay.
0:26:08 > 0:26:12No-one knows how this fortunate community survived
0:26:12 > 0:26:17but their discovery heralded a new dawn for Monterey Bay.
0:26:19 > 0:26:22Scientists had seen what happened to the ecosystem
0:26:22 > 0:26:26when the keystone species was removed.
0:26:26 > 0:26:31Now they had the unique opportunity to watch the effects of its return.
0:26:31 > 0:26:35With hunting banned, this otter population grew,
0:26:35 > 0:26:38getting down to some serious urchin eating.
0:26:41 > 0:26:46Which gave kelp beds a chance to take hold and grow.
0:26:46 > 0:26:49With such a ready supply of food,
0:26:49 > 0:26:55the secret population of hundreds became thousands
0:26:55 > 0:26:59and showed that where the otter went, healthy kelp followed.
0:27:03 > 0:27:08Monterey's keystone species was recovering,
0:27:12 > 0:27:18allowing the ecosystem to recover with it,
0:27:18 > 0:27:22link by link.
0:27:22 > 0:27:25Today, Monterey Bay is once again
0:27:25 > 0:27:30one of the most diverse marine habitats on earth.
0:27:30 > 0:27:34It's a real ecological success story.
0:27:36 > 0:27:40We have seen just how complex the web of life is here
0:27:40 > 0:27:44and how quickly it can fall apart.
0:27:44 > 0:27:48So it's crucially important that the bay is protected.
0:27:48 > 0:27:51And with its otter guardians in place,
0:27:51 > 0:27:54keeping urchin grazers under control,
0:27:54 > 0:27:57the future looks bright for Monterey.
0:27:59 > 0:28:03The balance has returned.
0:28:03 > 0:28:07The kelp forest and its tenants are thriving.
0:28:14 > 0:28:15The hope is,
0:28:15 > 0:28:21that by protecting these waters and its keystone species,
0:28:21 > 0:28:26this diverse marine ecosystem will continue to be spectacular.
0:28:54 > 0:28:57Subtitles by Red Bee Media Ltd