Original subtitles

Palau, a remote and tiny island chain near the equator,

is home to one of the world's richest reef ecosystems.

It is also home to giants.

Massive Second World War wrecks harbor dark secrets on the

ocean floor. I turn around, there's a huge monster wreck

behind me. My heart went whoop. Undersea trenches, deep

enough to swallow mountains, offer a glimpse into the abyss.

The old phrase that we know more about the surface of the

moon and Mars than we know about the bottom of the ocean

holds true. And large and mysterious creatures soar through

its azure waters. You turn around and all you see is these

big gaping mouths coming out of the blue. It's basically

like a mouth with wings on it coming at you. Here, in this

land of the giants.

At the southern end of the Palau Islands, near a dive site

called German Channel, Manta researcher Mandy Eppteson

prepares to descend into the blue.

During the German occupation of Palau prior to the First

World War, miners blasted and dredged a channel here to

create a shipping route between the islands. Today, strong

currents carry plankton to the mouth of the channel, making

it an ideal feeding site for one of the ocean's most graceful and gentle giants.

The manta ray. One of the largest creatures in the sea

survives by feeding almost entirely on one of the smallest.

It's sort of like a bottleneck, so the plankton gets

concentrated here, and that's why it's famous for mantas. So

we're hoping to see mantas, obviously, and if we're lucky,

maybe a new individual that hasn't been recorded yet so we

can add it to our database.

Mandy began the Palau Manta ID project in 2009, identifying

each animal by the spots on its belly. The spot formation on

a manta is as unique as a fingerprint. We started taking

pictures of the bellies to identify the mantas, and trying

to show, especially Palau government, that we don't need

to hurt the animals or tag them to be able to find out more

about them. We've identified over 280 right now. Five years

ago, nobody would have believed we have that many mantas in

Palau. A simple ID project can do a lot. By tracking the

numbers and movements of mantas, Mandy and the UK-based

Manta Trust can identify any population decline caused by

illegal fishing, and whether or not tourism may be driving

mantas away from German Channel.

Tourism is on the rise in Palau, a collection of more than

200 islands, nearly 1,000 miles east of the Philippines, in

the western Pacific Ocean. The tourists that flock here to

explore its natural wonders contribute about $125 million to

the economy, more than half of Palau's gross domestic

product. Hundreds of miles of sky-blue ocean surround the

archipelago.

Limestone islands, blanketed in thick and pristine jungle,

rise like mushrooms from the sea. They appear to be floating

gardens.

Scuba divers from across the globe are drawn to Palau for

what lies beneath the emerald lagoons. One of the world's

richest reef ecosystems.

These coral gardens overflow with 1,500 species of fish,

500 species of coral, and more than 100 species of sharks

and rays. Palau's seas may contain more species of marine

life than anywhere else on Earth, and provide researchers

an exceptional window into a vanishing underwater world.

The explosion of marine life here is due to marine geology.

Palau sits on the tip of an underwater mountain that formed

70 million years ago. Far below the island peaks, currents

crash against the drowned mountain, then surge upward,

carrying the nutrients that underpin the oceanic food chain.

There is another reason for the sheer numbers of fish

that throng these waters. Palau has a long history of

conservation.

For centuries, Palauans have lived in harmony

with the sea, never taking more than they needed.

In 2009, Palau created the world's first shark

sanctuary. Making it illegal to catch sharks in its seas.

Then in 2014, it expanded its conservation efforts

and banned all foreign fishing within its waters.

Palau is now home to the world's largest marine sanctuary,

a swath of protected ocean nearly the size of California.

Marine law officers patrol the Palauan seas,

on the lookout for illegal fishing vessels.

As a result, the big fish that have been all but wiped out

in some areas of the Pacific are still very much alive in

Palau.

Hefty gray reef sharks.

Five-foot-long Napoleon wrasses.

And of course, manta rays, the marine giants that patrol these seas.

Though smaller than their oceanic cousins, reef mantas

are still among the largest fish in the sea. They have an

average wingspan of 11 feet and reach weights of more than

3 ,000 pounds. Mantas have exceptionally large brains,

specifically the region responsible for hearing, touch and

vision. They are highly social and curious about humans.

If you've been diving a long time, you interact with

different animals. You can see the difference, for instance,

between a guppy or a Napoleon wrasse. In a Napoleon wrasse,

you can tell there's somebody home, there's an intelligent

being in there. And it's the same with mantas. When you

look at them and you start realizing they're actually, in my

opinion, they can recognize certain dive guides. They will

go over a dive group and go straight for the dive guide. And

especially the newborn mantas, they will play with divers

when it's not too crowded. You can see it's an intelligent

animal, like a dog or a cat, and they can learn.

At German Channel, mantas swim against the current to feed

on large concentrations of plankton swept into the channel

entrance.

Fins curving around its face direct water into the manta's large open mouth.

You turn around and all you see is these big gaping mouths

coming out of the blue. It's basically like a mouth with

wings on it coming at you. It's an amazing sight. Tissue

between the manta's gills sift tiny crustaceans and plankton

from the water. A manta is like a giant filtering machine

capable of vacuuming up more than 400 pounds of plankton in

a single week.

At times, manta feeding can be a dizzying display. Depending

on the current and the wind direction, sometimes they'll

feed by themselves and roll. They call it barrel rolling.

It's like an underwater ballet. Really nice to watch.

The manta may look like it's chasing its tail, but by

rolling, it pushes more plankton into its waiting mouth.

When the current is strong, usually right before a full

moon, mantas adopt an entirely different but equally

captivating feeding strategy known as train feeding.

So you can get anywhere from 2 to 20 or 200, if there are

that many, feeding together in a train, which is an amazing

sight. And they'll just keep going back and forth

across the line where the plankton gets trapped.

One of the largest creatures in the sea, mantas are also

one of the most mysterious. Research into their mating and

birthing behaviour has barely begun. For hundreds of

years, mantas were simply known as devil fish, due to their

imposing size and bat-like appearance. But they're very,

very gentle. When the current is strong, sometimes when

you're taking photos or video, it's very hard to stay out

of their way, especially when there's that many of them. So

when you're freediving and you dive down to take a picture,

they'll come straight at you and sometimes you get thrown in

their path, basically. And they'll just very gently lift

their wing and try not to touch you. They're very careful

with people, which is amazing. They could just slap you if they wanted to.

Mandy believes that physically tagging

mantas can cause harm to these gentle giants.

A mantis' skin is like rubber, and wounds can take years to

heal. Even though they might be able to recover from it, it

leaves scars. And by photographing the mantas at German

Channel, we've seen how long it can take for those scars to

heal. By photographing them every season, you can start

seeing those results. So we prefer to not do actual tagging.

Previous tagging studies enabled scientists to track the

movement of mantas. Photo IDs can't do that, but Mandy has

developed an alternative that is unveiling more secrets

of their behavior. She places time-lapse cameras at the

cleaning stations, spots on the reef where small fish rid

the mantas of dead skin and parasites. It takes pictures

every 10 seconds or 30 seconds, and normally we put four or

five around the cleaning station. And then when you pick it

up, you've got thousands of pictures to go through. In the

previous year, Mandy was able to identify 44 new mantas from

thousands of time-lapse photos.

It's a lot of effort, but worth it in the end. Because

instead of acoustic tagging where you can just see a beep

how many times a manta passed by, you can actually see the

manta and what they're doing, and learn about their behavior

at the same time without hurting them. Mantas are curious

creatures and will closely inspect the cameras left behind

on the reef. When we put the time-lapse cameras, we start

realizing that they're immediately aware of something

changing in their cleaning station. So they come up to the

cameras and they unfold their cephalic flaps, which are sort

of like feelers for them also. So they're doing like this to

the camera to see like, what is this thing that's sitting on

my cleaning station? So those are the kind of

things you would never find out any other way.

Today at German Channel, one of the busiest manta

sites in Palau, there are no mantas to be seen.

Currents, which should be incoming based on the moon cycle,

have switched to outgoing, which means no plankton is

flowing into the channel, and that means fewer mantas.

Mandy spots something on the bottom, a feather-tailed

stingray, buried up to its eyes in the sand.

Finally, she sites a large male manta.

It's one called Uncle Fester, a regular at German

Channel that has fed here for at least 10 years.

On this day, Mandy sites just three other mantas. One

pregnant female already logged in the database, and two

others that passed by without stopping at the cleaning station.

Mantas may be large, but they are dwarfed by

another giant living in the waters of Palau.

It's Barrier Reef.

Coral reefs are the world's largest living structures, made

up of millions of tiny plant-like animals known as coral

polyps. Reefs begin when a polyp attaches itself to a

surface on the ocean floor, then divides into thousands of

clones, which secrete a calcium carbonate skeleton.

Together, the polyps act as a single, immense organism.

Coral reefs are always growing. When coral dies, it leaves

behind the rock-like skeleton. The next generation of coral

grows on the old skeleton. Coral reefs are the rainforests of the sea.

They cover fewer than 2% of the ocean floor, and yet they

provide food and shelter for about one quarter of all ocean

species. One billion people depend on coral reefs for food

and income from fishing and tourism. Reefs also provide

protection from hurricanes and typhoons. The Palau Reef,

believed to have formed about two million years ago, may be

the most essential giant in these waters.

The bone-white beaches of the low-lying rock islands

are built from sand that originated as coral.

Reef animals like this parrotfish feed on coral

and algae that grows on the surface of the reef.

The parrotfish's hard, beef-like teeth bite off

not just the coral, but its hard skeleton as well.

The pulverized hard coral material ingested by the fish

passes through its digestive system and is deposited back

into the ocean in clouds of fine white coral sand.

One parrotfish can produce 200 pounds of sand in a single year.

These rock islands, built by coral sand and topped by lush

and untouched Pacific jungle, are a major tourist draw.

Palau is a country of just 20,000 people. In

2015, it received more than 150,000 visitors.

This tiny island nation is struggling to find a balance

between the profit tourism generates and its impact on the

reef.

The research that we're doing is to look at the sites that

are visited by tourists and to try to look at their impact

on the reef communities, including the corals and

the fish and the animals that live around the reef.

Today we're trying to look to see the impacts of snorkelers

on shallow coral reefs. So with Palau's tourism boom, we've

seen an increase of tourists on our snorkeling reefs and a

lot of them, as we've noticed, have very little or little

confident swimming skills. So we want to see if that has

any impact on the corals and if they're breaking corals or

standing on them. And the effects of that.

To determine the health of the coral at this site, Evelyn

uses a sampling square called a quadrat. She throws it

randomly 50 to 60 times at a given site.

When the quadrat lands on the lagoon floor, she photographs the area within the frame.

Researchers study the photos for evidence of coral damage

and compare the sample photos taken at busy snorkeling sites

with those taken at sites untouched by tourists.

Initial research by Dr. Golbu's team reveals that the reefs

at crowded snorkeling sites are dominated by broken coral,

which seriously threatens the health of the reef. But the

team is studying more than just corals today. Gary is going

to be counting fish today. He's one of our experts at the

Coral Reef Center. He knows a lot of our fish species, their

common names, their Palau names, as well as their Latin

names. So what he will do is he will go and measure any fish

that comes within a five meter radius of him, which is what

we call a stationary fish count. So he'll stay in one spot

for three minutes and he'll count any commercially important

fish that comes in that five meter radius and then write

down their sizes in centimeters.

The fish count, like the reef survey, is designed

to assess the impact of tourism on the lagoon.

Although it's prohibited, tour operators have been known

to feed fish to attract them to tourist snorkeling sites.

Hand-feeding fish makes them associate humans with food and

can interfere with their natural feeding cycles. This study

will help determine the effect fish feeding has had

on both the size and numbers of fish in the lagoon.

On a global level, coral reefs face a threat

far greater than tourism. Ocean acidification.

Humans have produced more and more carbon dioxide

emissions through the burning of fossil fuels.

More than one quarter of carbon dioxide pumped into the

atmosphere is dissolved into the oceans, where it upsets the

chemical balance, making water more acidic.

The acidification threatens the survival of the animals on

the reef. The skeletons of most marine organisms, including

crustaceans and fish, are made from calcium carbonate.

If the acidity of the water increases, there are fewer

carbonate ions in the water, and it becomes harder for these

animals to form a skeleton. Acidity can be increased to the

point where even coral can no longer make a skeleton. Even

before that stage, the struggle to make a skeleton can leave

coral weak and vulnerable. You might have a coral, but it's

not strong, and it's able to clear a storm and it would

break. Or you would have very high bioerosion. A lot of

other organisms would be able to live inside and break a

skeleton of a coral. It's yet another threat on the

Palau Barrier Reef that was already stressed by reckless

overfishing. For decades, foreign fishing vessels plundered

these seas, brutally raking fish from the reef. The reef is

an ecosystem, and you need corals and you need fish. And if

you take all the fish from the system, then it would affect

the reefs. It would affect its health and its recovery from

disturbance. And so that is one of the main issues that we

need to ensure that we still have enough fish in

the reef to allow the reef function to continue.

Not all of Palau's reefs are two million years old. Some are

relative youngsters that can be traced back just 70 years,

to a time when battles raged over Palau's tropical waters.

At the bottom of Malacal Harbor, a massive,

broken skeleton appears slowly from the blue.

It is the Iroh, a Japanese Navy tanker that met its doom

during the Second World War, when U.S. airplanes rained

explosives on the Japanese fleet.

Over the decades, the Iroh has transformed into an

artificial reef, providing shelter for prey, food for

predators, and a breeding ground for the hard and soft

corals that have taken hold of the ship. She's a spectacular

wreck to dive now. She is teeming with life. And it's just

an amazing wreck dive because you have all that history, you

have all that drama of the sinking of the vessel, and now

70 years plus later, you look at it and it's just the most

beautiful, spectacular reef there is around there. The

Iroh sits upright in its watery grave, 130 feet below the

surface.

It's a colossal wreck, nearly 500 feet long, weighing

upwards of 14,000 tons, and remains largely intact, except

for the damage caused when a massive explosion

in the engine room sent the ship to the bottom.

On the bow sits a turret gun, its barrel an armored shield draped in soft coral.

Wrecks like the Iroh provide a stable setting for coral.

Corals spawn in the water column. Eggs are

carried by the current and can land anywhere.

The shallow depth, warm water, and relative stillness of

this lagoon make an ideal breeding ground for the algae that

cements coral reefs together.

The Iroh is alive with stony staghorn coral,

ivory tube sponges, and

black coral trees.

Fish make their home on or near the wreck as well.

Clouds of fry,

lionfish, and

pacific spadefish.

Three masts reach toward a distant sky and provide

an ideal surface for sun-seeking organisms,

including huge colonies of bubble tip anemones.

A close relative of both jellyfish and coral, the bubble

tip anemone is equipped with sweeping venom-filled tentacles

that ensnare passing prey.

The slightest touch triggers the tentacles, which inject a

paralyzing neurotoxin into its victim. But not to the tomato

clownfish nestled inside its tentacles. To defend itself and

ensure it has enough to eat, the bubble tip anemone forms an

unlikely alliance. A layer of mucus on the clownfish's

skin makes it immune to the anemone's lethal sting.

It's a symbiotic relationship. The anemone protects the

clownfish from predators and snacks on its leftover meals.

In return, the clownfish drives off intruders

and cleans the anemone of parasites.

The coral-encrusted Iroh is just one of more

than 60 Second World War wrecks in Palau.

In March 1944, U.S. Navy planes appeared high above the

islands, bombarding the Japanese fleet with rockets and

torpedoes and sending most of its vessels to the bottom.

The coordinated attack was codenamed Operation Desecrate 1.

In September 1944, the island of Peleliu was the scene of

one of the bloodiest battles of the Second World War. U.S.

Marines made an amphibious assault on these beaches to

liberate the island from Japanese forces. Fighting lasted

for months and took the lives of 10,000 Japanese and 1,800

American soldiers.

Today, the island is surreally peaceful, although scattered

amid the lush vegetation are the reminders of past horrors.

A crippled Japanese fighter plane reclaimed by the jungle.

A gutted U.S. Marine landing craft corroded by the elements.

And sobering memorials to the thousands, Japanese and

American, that spent their final moments on what was once an

island paradise.

Francis Torabiang is a native Palauan who grew

up on the islands in the years following the war.

He founded Palau's first dive operation and, in the

1980s, helped discover more than 30 Japanese wrecks.

Including the 285-foot-long Chuyo Maru.

Like the Iro, it sits upright and is overgrown with corals, sponges and oysters.

The Chuyo Maru was a coastal freighter sent to the bottom

during Operation Desecrate 1 and discovered by Torabiang in

1989.

I followed the anchor line down and there's nothing there.

I turn around, there's a huge monster wreck behind me. My

heart went whoop. I got scared. Actually I got a little bit

scared because it's a huge thing right behind me. I did not

see it because I was going down this way. That was exciting.

I mean, that completely changed my way of diving. Today when

I take people diving, I don't try to explain everything. I

talk about safety, the depth, time, and how you go around

this wreck. And I tell them, that's good enough. I don't

want to go beyond that. Why? I say I want you to have that

excitement like I do. I want you to have that feeling. It's

hard to explain, but when things are in the water for last

50-some years, 70 years, and then the first time you go, it's a really exciting dive.

The Chuyo Maru shares its watery grave with a mystery ship.

Its true name remains unknown. No records of the ship can be

found in Japanese Navy archives. Though like most wrecks in

Palau, it was sunk along with most of the

Japanese fleet during Operation Desecrate 1.

Today, it's known simply as the Helmet Wreck, or Depth

Charge Wreck, for the dozens of bombs found in its hold.

Divers are warned not to touch any of the charges. Many

of Palau's wrecks are laden with live ammunition that can

explode if disturbed. In fact, it's illegal for divers to

take anything from Palau's sunken historical treasures. The

Depth Charge Wreck is a trove of Second World War artifacts.

The cylinder poking out of the wreck is a clinometer used to

measure the height of clouds to predict incoming storms.

These sake bottles and a corroded Japanese gas mask are grim

reminders that men died here in what is now a living museum

of the sea. When I take the Japanese diving there, I can

see they have a goose bump. They tell me a little bit eerie.

That's the way they do. I respect that. So it's a part

of history and part of our relationship with Japan and

something that people need to understand that we need to

respect other people. These once mighty wrecks won't last

forever. Saltwater corrodes and eats away at the steel

skeletons. Eventually, the lagoon will swallow these

remains.

Over the eons, saltwater erosion has also carved stunning

caverns and tunnels into Palau's limestone geography.

Hidden 12 feet below the surface, Chandelier Cave is one of

the largest cave systems in Palau. At one time, it was an

open-air cave on the surface of the Rock Islands.

After the last ice age, oceans rose, filling the

cave with seawater and concealing the entrance.

Stalactites, formed from calcite deposited by water dripping

from the cave ceiling, hang like glittering light fixtures,

giving Chandelier Cave its name.

Inside the cave, there is no sunlight to nourish plankton.

Free from these microscopic organisms, the water is crystal clear.

At Siais Tunnel, divers drop down to enter a

chamber that reaches depths of more than 140 feet.

Even this far below the surface, sunlight penetrates

the tunnel to illuminate gorgeous orange sea fans and

lionfish nibbling on soft corals. Palau is

a jumping-off point for some of the deepest diving in the

Pacific. It sits atop what is essentially a sunken mountain

range. A steep drop-off, more than 30,000 feet deep, fringes

the islands. This is the Palau Trench. It just drops off and

it plummets into the abyss and very, very close to shore as

well. So people always talk about the Marianas Trench, the

deepest part of the planet, Challenger Deep. That's nearly

300 kilometers offshore. We've got massively deep water

within 15 or 20 kilometers of our shoreline, so it's very,

very unique. The Palau Trench is deep enough to completely

submerge Mount Everest.

Scuba divers typically descend about 130 feet, less

than half of one percent of the depth of the trench.

Divers have only just scratched its surface. What is known

about what's down the Palau Trench, honestly, very, very

little. The old phrase that we've all heard that we know

more about the surface of the Moon and Mars than we know

about the bottom of the ocean, holds true. Collins has

compiled a 3D map of the trench from satellite-derived

gravity data and sonar measurements collected on dives. The

green shows the Palau Islands, just the tip of a massive

underwater mountain. You can see that some of these sheer

walls, they plummet miles, literally miles, two or three

miles, before they might have a slight shelf and another

feature. And again, before they just plummet into the

abyssal plain at over 9,000 meters deep. Once we look over

the edge of that reef, sometimes it's a little daunting

because you have the beautiful colors, the shallow waters,

and you just look over and it's literally looking down a

cliff. And especially knowing how deep that is, so

sometimes it can be a little bit daunting and a little bit

disorientating, but it's also a bit thrilling.

A short boat ride from Siez Tunnel lies a marine environment

so spectacular, it's considered one of the seven underwater

wonders of the world.

Palau is home to more than 50 marine lakes. When glaciers

melted at the end of the last ice age 10,000 years ago,

ocean levels rose, filling low-lying areas with seawater.

Fishers and tunnels in the limestone connect these saltwater lakes to the ocean.

Beneath the surface of a 100-foot deep marine lake, on the

uninhabited coral island of El Malek, is an astonishing

sight.

Millions of rippling jellyfish pack the fluorescent green

water, their shimmering bodies casting a luminescent glow.

This is Jellyfish Lake.

These golden jellyfish have thrived in the lake for more than 10,000 years.

In this closed system, there are few predators, so the

jellyfish have lost their need to sting. They possess

stinging cells, just not ones powerful enough to cause

serious harm to humans. Getting to swim through that many

jellyfish is a pretty weird but wonderful experience. When

you find a very dense patch of them, the whole lake is

essentially pulsating these jellyfish, so it's very cool

to see. They're not harmful unless you have very sensitive

skin. They're very soft. They're just doing their own thing, cruising along.

There's another, even more remarkable way in which these

jellyfish differ from their cousins in Palau's nearby ocean

lagoons. Most species of jellyfish, like this moon jelly,

drift serenely on ocean currents, just as their ancestors

have since before the age of the dinosaurs.

The five million specimens at Jellyfish Lake are far from

passive. They may look like they're drifting aimlessly, but

in fact, they're on a journey. Migrating almost a mile, they

follow the same path and same schedule every day. As the sun

rises in the east, the jellyfish swim toward its life-giving

rays. They have to make the trek to survive. The body of

each jellyfish contains a crop of algae, its main source

of food. The algae processes sunlight to produce sugar that

feeds the jellyfish. For hours, they swim east toward

the sun, pumping water through their bells and rotating

counterclockwise to provide even exposure to the sun for the

algae in their bodies. Trees that surround and shelter the

lake also cast shadows on the surface. The jellyfish must

avoid the shade. They need to absorb as much sunlight as

possible to maximize the energy created by the algae within

their bells. So what they do is they follow the sun around

the lake, so at a given time during the day, they'll be in

the brightest spot of the lake finding the most food. As the

sun begins to set in the west, the dense bloom of jellyfish

reverses course and heads back to the western shore. All

this swimming churns up nutrients in the water that form the

base of the lake's food chain. When the sun disappears into

the horizon, the jellyfish sink 50 feet down, where nitrogen

-rich waters help sustain the algae in their bodies, before

ascending to the surface before dawn, to start their complex migration once more.

Of Palau's 52 marine lakes, five are home to

persistent populations of golden jellyfish.

Fragile creatures, they have shown an outstanding ability

to adapt in these landlocked lakes. Lakes that were once

connected to the ocean, that defines and sustains this tiny island nation.

For thousands of years, Palauans have depended on their

coral reef for survival. It's such a diverse habitat, so if

we lose that, we really lost a lot of our ocean, a lot of

biodiversity in our ocean. Billions of people live near the

coast and they depend on coral reefs. So all of those, and

especially us on these small islands, we would be severely

affected and our way of life is totally changed. It

would be a devastation to us not to have the reef.

These Pacific Islanders hold two traditions of deep respect

for the sea. Yesterday, one of my customers asked me,

Francie, don't you get tired of coming out here in the

ocean? And I said, it's amazing. Not one day is the same as

another day, never the same. The clouds, the sun, the rain,

the wind, the tide, the movement. So it's never the same, so

that's why I don't get tired of going to the ocean. In

these protected waters that contain more species of marine

creatures than almost anyplace else on earth, long lost war

wrecks, claimed by the power of the ocean, burst with energy

and life. Yawning trenches plunge into unseen depths, and

manta rays soar, here in this exotic land of the giants.

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