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00:00A place where land meets sea.
00:13Shaped into different habitats over time.
00:20Each a stage telling its own story.
00:23It was here waves washed the very first creatures onto the shore.
00:37Since then, this boundary joining two realms has given rise to a profusion of life.
00:44And by harnessing nature's most powerful forces, our coast continues to write new chapters in the story of life.
00:58Take a dive into our planet's mesmerizing world of water.
01:14From the monumental open ocean to the rugged coasts that serve as the dividing line between two worlds.
01:31From the changing rivers that carve through continents.
01:38To mysterious lakes and swamps.
01:43Immerse yourself in the magic that unfolds.
01:51As we reveal...
01:55The secrets of our enchanted waters.
01:58The coast can offer a variety of opportunities to many different creatures.
02:17A refuge.
02:19A source of food.
02:20Or for those smart enough, it can even be deployed as a trap.
02:29Beneath the waves...
02:33A silent shadow glides through the waters of the North Atlantic.
02:38Sleek.
02:41Powerful.
02:43And clever.
02:45Orca are one of the animal kingdom's most intelligent hunters.
02:57With a playbook of tactics they can call upon in any eventuality.
03:02This female is heading towards the coast.
03:14She knows this world intimately.
03:17Every twist of shoreline.
03:19Even the contours of the shallow seabed have been committed to memory.
03:29She and her pod have been visiting this area for years.
03:33For years.
03:36They've devised a well-rehearsed strategy to hunt their favourite prey.
03:44The harbour seal.
03:53Everyone in the pod knows the plan.
03:56The changing tide is going to offer the best odds.
04:13As the water level rises, the seal's sanctuary of rocks starts to disappear.
04:20And the deeper water allows the orca to get much closer to the coastline.
04:27As she approaches, the seals instinctively head to the refuge of land.
04:34But it's all part of the orca's plan.
04:37Subtly driving one seal into a channel of deeper water flanked by rocks.
04:42Then the pod splits up, making sure every escape route out of the channel is sealed off.
04:51Except one.
04:53The youngest orca shadows his mum.
04:56Go too shallow, and they risk getting stranded.
04:57But she knows from experience exactly how far she can push it.
05:10The seal is fooled into thinking it has found a way out of the channel.
05:16But its escape is blocked by the waiting pod.
05:19Who drive it from the safety of land out into the open sea.
05:28It's now a game of cat and mouse.
05:33The seal may be fast, but the orca are faster.
05:43The strike is swift.
05:49And lethal.
05:51Teamwork, shared knowledge, and a deep understanding of every patch of this coastline have elevated the orcopod into formidable hunters.
06:12Learn how to use its powers, and the coast can be a very accommodating ally.
06:24An ever-changing stage, ready to support a medley of players.
06:30When the North Atlantic is raging, the sheer cliffs it has created may seem the safest place to find refuge.
06:47But sometimes, a leap of faith is needed to take the first step into a new world.
06:53These guillemots are perennial seabirds.
07:03But this summer, they are compelled to seek out a cliff-top home, so they can raise a chick.
07:10Alongside tens of thousands of others.
07:14It's the only time the birds ever spend on land.
07:27But it's not a pleasant stay.
07:31Each family is perched on a ledge only a couple of inches wide.
07:37As guillemots raise just one chick a year, there's no room for error.
07:48Their eggs are even pear-shaped to prevent them from rolling off into the sea.
07:57Nope, this one's not going anywhere.
07:59And once the eggs hatch, the ledge becomes even more cramped.
08:08But as uncomfortable as their coastal home is, Dad still has access to food.
08:14It's just a bit further away.
08:19He takes turns with his partner, fishing these abundant coastal waters to satisfy the chick's ever-growing appetite.
08:27But every trip to the sea leaves the chick vulnerable, with just one parent to stand guard.
08:40Their nest is surrounded by neighbors, equally protective of their young.
08:46And hungry gulls threaten from the air, and closer to home.
08:59They, too, have been lured here by the coast's opportunities.
09:06It's time for the young guillemot to move on.
09:08The ocean is calling below them.
09:29Dad fights his way to a jumping-off point.
09:32It's just a short flight for an adult.
09:38But it's a giant leap for his chick.
09:42Only a few weeks old, and without fully developed wings, the chick can't yet fly.
09:48The chick can't yet fly.
09:58But he can...fall.
10:00And Dad is right behind him.
10:13And Dad is right behind him.
10:15The escape plan pays off.
10:30These coastal seas are teeming with food.
10:35Allowing Dad to dive around the clock.
10:46Delivering twice as much fish than if they'd remained on land.
10:53Every summer, thousands of young guillemots take this leap of faith.
10:57Some, reluctantly.
11:00Plunging into the depths.
11:05To join the others in this more welcoming world.
11:10Free from the confines of the land.
11:15From now on, it's the Dad that takes on soul-parenting duties.
11:20Ushering the chicks into the next chapter of their lives.
11:25As a real sea bird.
11:30Here, the chick will mature into a skilled swimmer.
11:35Even before he learns to fly.
11:42He'll grow faster in the water, and will spend as many as five years constantly out at sea.
11:48Only returning to these cliffs when it's his turn to become a dad.
12:05These towering sentinels of the coastline have been sculpted by the onslaught of waves.
12:10But the ocean has another power it can harness.
12:16To drive the movement of its waters.
12:19The rhythmic ebb and flow of every coastline is motivated by its tides.
12:31High and low.
12:32This pulse is driven by a force far beyond our world.
12:42The moon wields a secret power over our seas.
12:46Its gravitational pull causes the oceans to bulge out on the side closest to the moon.
13:01But also, it leaves a second bulge on the opposite side, farthest away from it.
13:10It's these bulges that create high tides.
13:16As the Earth spins, the oceans rise and fall in an eternal cycle.
13:22The position of the sun and the Earth's orbit also exert their influence, magnifying the seasonal push and pull.
13:34As the incoming water plays one of the most important roles in the coastal ecosystem.
13:41It's this constant motion that brings a wealth of goodness from the deep ocean to the shallows.
13:58Mix this marine fertility with sunlight and a share of the land's rich nutrients.
14:04And coastal waters are transformed into some of the most productive areas of the world's oceans.
14:19Our shorelines are brimming with life.
14:22All sustained by the tidal waters.
14:36Offering a gateway for creatures to switch their allegiance between land and sea.
14:52Scotland's intricate coastline of jagged cliffs and rocky bays work with the strong tidal currents to make sure deep sea nutrients are delivered directly to their shores.
15:09Making the coast so bountiful, it has converted one staunch river dweller into an ocean expert.
15:16This otter mum and her three-month-old pups are waiting for the low tide.
15:35They are officially river otters, but the bounty of food here is too good to ignore.
15:40If you know how to find it.
15:54And mum is ready to deliver a lesson in coastal living.
15:59First, see what the tide left behind.
16:05Stranded amongst the heaps of seaweed by a whole host of creatures.
16:11Looks like the female pup has cracked it.
16:19Just beyond the land, the intertidal zone is packed with even more crabs, mollusks and fish.
16:39But that means braving the sea.
16:47River otters are used to hunting in water.
16:50But these pups must get to grips with salt water, strong currents and powerful waves.
16:57As they dive to scour the seabed for food, the growing swell proves too much for the female pup.
17:14But this is a great spot to watch and learn from the best teacher.
17:23It's octopus for dinner.
17:32And mum has her own way of quite literally disarming it.
17:37While the female pup prefers to study from afar, her brother is fast getting familiar with the seafood.
17:50As fruitful as these waters are, the otter can be found in the sea.
17:51The otter can be found in the sea.
17:52The otter can be found in the sea.
17:53While the female pup prefers to study from afar.
17:56As fruitful as these waters are, the otters are not designed for swimming in the sea.
18:09And their fur requires some aftercare to keep it in the best condition.
18:27So mum encourages them to rub themselves in the seaweed.
18:33This sloughs off any salt residue.
18:36Helping keep their coats waterproof to insulate them from the cold seas.
18:46It's a minor inconvenience when the living here is this good.
18:51So good, that half of Scotland's river otters have now adapted to live on the coast.
19:01And they're a valuable addition to the area.
19:10As top predators, the otters will help maintain the balance of this tidal ecosystem.
19:18Just as they would in a river.
19:20By preying on the most abundant species, they keep populations in check.
19:28Helping to maintain the diversity in these waters.
19:31Away from the strong tides and crashing waves, a tranquil, sandy beach offers a more welcoming side of the coastline.
19:57Setting the scene for a special appearance from a so-called living fossil.
20:07This female horseshoe crab is carrying thousands of eggs beneath her shell.
20:13She's one of hundreds of females that are coming inshore to find a mate and lay their eggs.
20:31They're more closely related to spiders than modern crabs.
20:35These tiny tanks predate the dinosaurs and have survived multiple mass extinctions.
20:43Remaining unchanged for over 450 million years.
20:49So they know what they like when it comes to finding a suitable coastline.
20:57First, these ladies like to take life easy when they're carrying eggs.
21:03So they want a sheltered shoreline, free from powerful waves that might bowl them over.
21:11And they prefer a gentle slope to the beach.
21:15No hiking up the soft sand for them.
21:19The type of sand is also important.
21:21It must be coarse enough to allow proper drainage.
21:25And create pockets of air to oxygenate the eggs once she's laid them.
21:31There is one bit of coastline that fits all these criteria.
21:39Delaware Bay in North America.
21:47Which is why horseshoe crabs have been using this area as their spawning grounds since it became a tidal bay over 4,000 years ago.
21:59It's the right location.
22:02Now she needs to reach the actual beach.
22:07But in her way are a gamut of males.
22:11Eager to fertilize those eggs of hers.
22:17She doesn't get to pick who.
22:21It's more a case of who gets there first.
22:27As she tries to battle through, the males attempt to sabotage each other's efforts.
22:37It's slow motion, armor-plated chaos.
22:49Finally, she emerges, with one determined male clasped onto her shell.
23:07Once out of the water, she digs a hollow in the grainy sand and releases her eggs.
23:17And her hanger-on gets his reward.
23:21To fertilize them.
23:23Over the coming nights, as the tides rise and fall, this ancient act will play out again and again.
23:35Over 30 million horseshoe crabs visit this special bay during breeding season.
23:47With each female laying up to 100,000 eggs.
23:53But as she heads back out to the open sea, her precious offspring are already being devoured.
24:09The trillions of crab eggs serve a purpose far beyond their species.
24:27Thousands of migratory shorebirds time their arrival specifically to coincide with this spawning event.
24:37A stopover at this bay holds enough food for these sandpipers to fuel the next leg of their migration across the globe.
24:55And high tide delivers a share of the banquet to the fish and crabs waiting in the shallows.
25:01An intricate food web creating a bond between land, sea and sky that has lasted for eons.
25:13Fortunately, the sheer abundance of eggs ensures plenty will still develop safely beneath the sand.
25:27To guarantee the next generation of one of Earth's oldest survivors.
25:33The horseshoe crabs have found a specific beach that works for them.
25:45But there are countless different types out there.
25:49Sand's colour depends on its origin.
25:53Black sand comes from volcanic rocks or cooled lava that shatters into tiny fragments.
26:05Pink beaches get their attractive hue from the crushed up shells of tiny marine creatures washed ashore.
26:11But for most sandy beaches, their journey starts high in the peaks millions of years ago.
26:25As mountains slowly crumble under the persistent work of wind and rain,
26:31great shards of rock break free and tumble into rivers below.
26:41Carried downstream by churning currents,
26:43they break into fragments and are slowly ground into smaller pieces.
26:47Once at the coast, powerful ocean waves and shifting tides take over,
27:01grinding the once mighty stones down even further.
27:09The more energetic waves create pebble beaches.
27:11As the power of the water throws rocks up the slope before they have the chance to be worn down.
27:21While more sheltered beaches create waves with less energy that repeatedly smooth over the same areas,
27:27breaking pebbles down into fine grains of sand.
27:31But in tropical waters, most of the fine white sand that looks so idyllic comes from a more surprising source.
27:47Parrot fish.
27:53Blessed with teeth harder than iron,
27:55they chew up chunks of coral as they graze algae off the reef.
28:13Each parrot fish can produce up to 1,000 pounds of this fine white sand each year.
28:21In the Caribbean,
28:25it's estimated that 70% of that beautiful,
28:29pristine sand has been pooped out by a parrot fish.
28:45When sea and sand work together,
28:47they can create a special magic to help determine the future of an entire species.
28:59The ocean is home to this green turtle.
29:03She's traversed its deep waters in search of food.
29:13But now she's heading inshore.
29:19Where better to lay her eggs than the exact beach that first welcomed her into the world?
29:31She has navigated her way over 1,000 miles to return to this one spot,
29:39using the sea floor as her compass.
29:43From the moment she was born, she's been creating a magnetic field map,
29:49starting with her birthplace,
29:51and then all across the ocean.
29:55A mental map that now guides her back to the coast.
30:01She is built for elegance in the water.
30:13But a sandy beach is the perfect terrain to lay her eggs,
30:19as long as she picks the right spot.
30:25For sea turtles, it's not chromosomes that'll determine the sex of their offspring.
30:31It's the sand.
30:33If the sand is too cool and moist, the clutch will all be male.
30:43Too dry and hot, and all females will emerge.
30:49A mix of sexes is the ideal, so she needs to judge the position of her nest just right.
30:57And let the sand work its sorcery.
31:01She scoops out a sandy vault nearly three feet deep.
31:13Fit for a hundred precious eggs.
31:19But she won't stay to look after them.
31:31She leaves that job to the beach.
31:45For the following two months,
31:47the sand protects and incubates the eggs.
31:51Then the tiny hatchlings finally break through the sand.
32:01These newborns, barely two inches long,
32:05are swimming machines.
32:09Programmed to just keep going.
32:15They instinctively head down the beach,
32:19toward the light reflected off the ocean.
32:21But even under the cloak of darkness,
32:25their 300-foot dash to the sea is not easy.
32:29An army of ghost crabs block their route.
32:41They might not be much bigger in size,
32:47but these guys carry weapons.
32:51And they have been waiting for this moment.
32:57The late developers hope a daylight escape might offer better chances.
33:11But they too must navigate past the waiting crabs.
33:25The survivors are greeted by the surf,
33:39but they're not out of danger quite yet.
33:43Despite never having seen water before,
33:47instinctively their ocean compass kicks in.
33:53At just a few minutes old,
33:55the tiny swimmers can read the push and pull of the water
33:59as the waves pass overhead.
34:01Using its direction,
34:03using its direction,
34:05they orient themselves to swim straight out to sea,
34:09to escape the shoreline
34:11and the predators that might lurk in the shallows.
34:15Only one in a thousand green turtles make it to adulthood,
34:21where they'll disappear into the deep.
34:27With such low survival rates,
34:30these turtles rely on protected natal grounds
34:34to give hatchlings the best start.
34:36But with the loss of these vital beaches,
34:45many sea turtle populations face an uncertain future.
34:56The coast is the final stop on the sea's journey.
35:02While tides and waves are instrumental
35:04in delivering nutrients to the shorelines.
35:10They also leave behind any unwanted ocean detritus.
35:16But there's no such thing as waste in nature.
35:25This bubbler crab is very pleased with his setup.
35:31He has fought off the competition
35:33to secure his own piece of beach territory.
35:38He just needs to dig himself a burrow
35:40and his home will be complete.
35:43Not bad for a creature the size of a little fingernail.
35:47And as the high tide starts to creep in,
35:50his food is delivered right to his door.
35:54Once the water has gone,
35:56he gets stuck straight in.
35:57But it's not the sand itself he's after.
36:06Each grain is coated in a thin layer of organic matter.
36:11A delicious mixture of decomposing plants and rotten plankton,
36:15which are scraped off each grain as they pass through his mouth.
36:28Then the clean, indigestible sand is formed into neat little balls by his pincers.
36:33But he's not the only one emerging to feed.
36:42He shares the shore with other hungry bubbler crabs.
36:47Each one sticks within its territory, creating its own sandball galaxy.
36:59Which help to define boundaries and guarantee no time is wasted filtering the same patch of beach twice.
37:07But this legion of busy bubbler crabs aren't just insatiable gluttons.
37:16They're also inadvertently helping to maintain this coastline.
37:22Their appetite for rotting matter means they're actually cleaning every single grain of sand as they eat,
37:30leaving behind a healthier beach.
37:32And as they work the sand into their signature bubbles,
37:38they aerate it and help distribute nutrients throughout the entire beach ecosystem.
37:45Once again, the changing tide signals feeding time is over.
37:51Better retreat back to his burrow and wait for this new high tide to deliver a fresh coating of food across the sand.
38:02Every coastal creature, however tiny or giant, works with the ocean to help maintain their shoreline ecosystem.
38:13But the ocean can be an unpredictable partner.
38:18Its immense force means the coast is often required to take on yet another role.
38:24That of protector.
38:25Our coasts are the last line of defense against the power of the ocean.
38:42Natural coastlines have built-in fortifications that protect land against flooding, erosion, and storms.
38:51But only 15% of the world's coastlines remain in their native state.
39:02And one of the most threatened is the mangrove forest.
39:06Here, these remarkable salt-tolerant trees temper the water's energy by slowing its flow.
39:21Filter contaminants from the water, and anchor the coastline firmly in place.
39:26These super trees are also among the planet's most important carbon sinks.
39:38They remove more carbon dioxide from the atmosphere than terrestrial trees.
39:44And store it away in the surrounding soil.
39:46But for the wildlife that live amongst the mangrove trees, they serve an even more immediate purpose.
39:56A much-needed refuge.
39:59Hidden amidst the mangrove roots lies a world of growth and learning.
40:17And a secret school for cold-blooded killers.
40:21As the mangrove trees stretch their gnarled fingers into the shallows, they form a natural barricade to keep out large predators.
40:34Creating a safe place to cradle the fragile beginnings of countless tropical fish.
40:40However, this nursery is also home to baby sharks.
40:53They may be natural-born killers.
40:59But right now, like all the others here, they're just inexperienced young fish.
41:04For the juvenile lemon sharks, this is a sanctuary and a school.
41:20Born in these clear and calm coastal waters, they were left alone to fend for themselves.
41:26But without a parent around to guide them, how do these lemon sharks mature into an apex predator?
41:36By learning from one another.
41:39The youngest pups join up with slightly older juveniles, where they can observe the basics.
41:47Where to find food.
41:50Where to hide.
41:52And any dangers to avoid.
41:54With that groundwork complete, they then form peer groups of the same age, size, and similar level of expertise.
42:06Essentially, these young sharks are making friends and hanging out together.
42:11Learning through adventure and mistakes.
42:14But this shark school is only possible because of the mangrove forest they're born into.
42:23This protective enclave provides them with plenty of food, warm waters to help them grow, and a safe learning ground to practice their hunting skills.
42:37And if one shark learns a new trick, like how to stir up the seabed to flush out buried crustaceans, he'll show his friends how to do it too.
42:55After years, the group is ready to leave the sanctuary of the sanctuary of the mangroves.
43:04And together, they venture out into the big wide ocean.
43:09Unlike most sharks, their species is surprisingly social and learns through shared knowledge, showcasing a higher intelligence.
43:19The bonds they form in these coastal shallows set them up for life.
43:26It's not known if the friendships made in their youth remain throughout adulthood.
43:31But the lessons they learn there certainly do.
43:39Every part of our coast is different.
43:43And so too are the needs it caters for.
43:48Offering support, food, and sanctuary.
43:52These precious habitats are essential to the future of life along the water's edge.
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