Original subtitles

The island of Cozumel.

A dazzling haven for marine life

in the wild-blue waters of the Caribbean Sea.

The visibility is stunning.

The coral formations are absolutely amazing.

It always takes my breath away.

Here is the world's second-largest barrier reef,

a wild hunting ground for perfect predators

at the top of the oceanic food chain.

The bull sharks are very, very big animals.

It reminds you just of your size in the ocean.

Humble and perfection is the only thing you see.

It's perfection in the water.

A perilous journey, deep inside hundreds of miles

of dark, mysterious underwater caves,

where a single wrong turn

can mean the difference between life and death.

We are far away from an exit.

A minor problem can cause a fatal accident.

A secret world, once considered sacred,

where only the bravest dare to venture.

It's like entering another world.

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Cozumel.

A lush and level island paradise

peering over the sapphire waters of the Caribbean Sea,

Less than 20 miles off the eastern coast

of Mexico's Yucatán Peninsula.

Situated on a bedrock of limestone,

Cozumel is home to the largest reef system in the Americas:

the Mesoamerican reef.

The reef is an underwater wilderness:

providing a haven for dazzling arrays of coral

and hundreds of species of fish:

from coral-crunching parrot fish

to the shy and elusive splendid toadfish.

Sparkling visibility,

vivid turquoise waters,

and hundreds of miles

of dark and mysterious underwater caves

have made Cozumel a divers' dream.

Popularized by the legendary oceanographer Jacques Cousteau

in the early 1960s,

the reef system on the south side of the island

is now a national marine park.

Coral reefs cover less than 1 percent of the world's oceans.

And yet one quarter of all marine creatures

live on a coral reef at one time in their life.

In the warm, ultra-marine waters

that separate Cozumel from the Yucatán Peninsula,

the white, sandy bottom is stirred up

by the island's apex predator: the bull shark.

Thick and powerful,

the bull shark cruises warm, shallow waters.

This stretch of the Yucatán,

near the town of Playa del Carmen,

has one of the largest populations of bull sharks

in the Caribbean.

For three months each winter, females, many of them pregnant,

make these warm, turquoise waters their home,

before migrating to nearby freshwaters to give birth.

You can normally see them in the distance circling around.

You get yourselves down on the bottom, you kneel down,

and you wait for them to come to you.

It's a very exciting experience

because you can see them in the distance

and they get closer and closer.

The bull sharks are very, very big animals as well.

It reminds you of your size in the ocean.

More than 10 feet long,

weighing as much as a grizzly bear,

bull sharks move slowly along the seabed.

Though they may appear lethargic,

bulls are capable of quick bursts of speed

to grab small and agile prey

with broad and triangular teeth

as heavily serrated as a hacksaw.

Bull sharks are relentless predators

perfectly honed over 400 million years of evolution.

In the shark's snout are small, electrical-sensing organs

called ampullae of Lorenzini

used to detect prey,

such as bony fish, smaller sharks, and rays.

Slight electrical fields radiated by animals swimming

are felt by the shark.

When an animal is in distress and floundering,

it transmits a more powerful electrical signal

that attracts the hungry shark.

Modified hair cells embedded in the skin,

called neuromasts, detect vibrations in the water

allowing the shark to decipher the direction,

and speed of prey:

meaning the shark is able to hunt in total darkness.

The bull shark has a pulverizing bite force,

eight times more powerful than a human's.

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Despite their terrible power and fearsome appearance,

these bulls are docile around humans.

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When you're diving with bull sharks,

it's nice to I guess to get a sense of fear

but also, again, proper respect for sharks

as you see them coming along.

And sitting there watching them swim around,

it's amazing.

I love sharks.

Big sharks for me are everything

and so for me to sit with bull sharks

and to have them swimming by is inspiring.

It really is.

You feel the first thing when you see these animals is humble,

humble and perfection.

It's perfection in the water.

Commonly found in shallow, coastal waters,

bull sharks also turn up in unexpected places:

freshwater rivers.

Unlike most sharks

bulls are able to survive for long periods

in both saltwater and freshwater,

and have been found in both the Amazon and Mississippi rivers.

Ancient creatures, sharks have evolved in saltwater oceans

over hundreds of millions of years,

and must retain salt internally to survive.

For most sharks, a freshwater habitat would be lethal.

Bull sharks, however, have specially developed kidneys

that recycle the salt within their bodies,

allowing them to thrive in freshwater inlets.

Firmly planted at the top of the oceanic food chain,

adult bull sharks have no natural predators.

But because they frequent coastal areas

and freshwater harbors,

they are at risk from pollution,

loss of habitat, and fishing:

caught accidentally in long lines

or killed senselessly to meet the demand for shark-fin soup.

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Apex predators like the bull shark

are an essential part of the ocean ecosystem.

Big eaters, they control the population of other species.

A drastic decline in the number of large sharks

can have a ripple effect:

allowing prey populations to bloat,

and upsetting the delicate balance of the oceanic food web.

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On this sandy ocean bottom,

the bull sharks do not hunt alone.

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A southern stingray, almost seven feet wide,

skims the seabed

in search of clams, oyster and mussels,

exposed in the sand

by vigorous flaps of its wide pectoral fins.

The stingray is perfectly adapted for life on the seabed:

its flattened body tends

to match the shade of the ocean floor,

camouflaging it from sharks and larger rays.

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A venomous barb near the base of the tail

is capable of inflicting painful wounds on predators,

or on humans who accidentally step on a ray

while it lies partially buried in the soft sand bottom.

Waders are advised to perform the 'stingray shuffle':

shuffling their feet, rather than walking,

to alert the ray of approaching danger,

and thereby avoiding

a potentially painful stingray encounter.

Two spiny lobsters hole up in a bed of coral,

antennae, longer than the rest of their entire bodies,

are waved about to fend off hungry predators

or simply unwanted attention.

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Beyond the sandy shallows,

the reef at Paso del Cedral,

65 feet below the surface,

helps turn a seemingly lifeless landscape

into a lavish garden.

Paso del Cedral is one of my favorite dive sites

on the island.

The reef itself compared to other dive sites

is a smaller reef

but it means that it's absolutely packed with life.

My personal favorite of the reefs

would be Paso del Cedral.

It has life like nothing else.

You're not getting the big coral structures

like you are further south

but there is so much life on Paso del Cedral.

Reefs like Paso del Cedral embrace about one-quarter

of all marine species on the planet.

Ocean currents collide with the reef,

carrying up from the depths nutrients

that attract a rich bounty of aquatic creatures.

A hawksbill sea turtle,

its shell streamlined to aid in swimming,

soars through the open ocean.

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Out in the distance you see a rock

that looks like it's surrounded by angelfish.

You swim a little bit closer

and you realize that rock is, in fact, a turtle feeding

and the turtle doesn't even care that you're there.

You get close to him, you can hang out with him

and watch him feed.

Hawksbill turtles are primarily found on coral reefs,

rich with their favorite food: sea sponges.

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A narrow head and hawk-like beak

are ideal for tearing sponges from crevices in the coral,

then crushing them with powerful, toothless jaws.

Some sponges are highly toxic,

even lethal to other creatures.

The turtle is able to absorb these dangerous toxins

in its body fat,

without experiencing ill effects.

Hawksbills are omnivores,

and will also feed on marine algae,

sea urchins and jellyfish.

The turtle's hard shell, and armored head,

protect it from the stinging cells of the jellyfish.

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Though they spend most of their lives underwater,

sea turtles are air-breathing reptiles,

and must surface to take in oxygen.

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A resting sea turtle might remain submerged for hours.

A turtle that uses up energy to dive for food

or escape from predators must breathe more frequently.

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Like all turtles,

the hawksbill has a wide, armored shell

that safeguards its vital organs.

The hard casing defends the turtle from predators:

such as sharks and crocodiles,

but the same shell that protects the hawksbill

has nearly led to its extinction.

Beautifully colored,

with large, scale-like structures known as scutes,

its shell is highly valued: used to make jewelry,

and other ornaments, sold as 'tortoiseshell'.

Despite its status as an endangered species,

hawksbill eggs remain a delicacy,

and adult turtles are killed for their meat and shells,

or caught accidentally in long fishing lines.

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Strong paddle-shaped front flippers

propel the turtle through the open ocean.

Hawksbills are the descendants of reptiles

that travelled the ocean more than 100 million years ago.

Graceful, ancient,

they are an irreplaceable link to our prehistoric past.

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Sea turtles have an average lifespan of about 80 years.

But they are infants

compared to the oldest animal in these waters:

the coral reefs.

Coral is a living organism,

and most established coral reefs

are between 5 and 10,000 years old.

Yet around the world,

these ancient creatures are under threat:

from pollution, destructive fishing practices,

and the effects of climate change.

High water temperatures cause algae

to leave the coral tissue,

depriving the coral of its major food source,

and leaving the reef susceptible to disease.

The reef at Paso del Cedral supports such an abundance

of marine life that it demands a closer look,

for one of the ocean's most shy and secretive creatures.

The cool thing with Paso del Cedral

is you can find the splendid toadfish, okay?

The splendid toadfish, we only have it here in Cozumel

so it's something very special.

You can find them hiding out in little holes.

They're very, very shy.

As a species, toadfish are far from powerful swimmers,

and traveling great distances is not easy.

As a result, populations of toadfish

can become geographically isolated,

potentially giving rise to endemic species.

To spot a toadfish

divers must look for the telltale signs:

lines in the sand made by the fish's beard.

Like many bottom-dwelling fish,

the toadfish has eyes at the top of its head,

to spot prey swimming above.

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Most life in these warm, tropical waters

is concentrated on the reef.

French angelfish,

swim on their side to reduce their surface area

and make it easier to move through the current.

French angels are a rare breed of ocean fish.

Whereas most fish that mate go their separate ways,

these French angels tend to stick together

feeding on the reef as a duo,

and even helping each other

defend their territory against other fish.

A pair of grey angelfish forages on the reef.

Like all angels, greys feed primarily on sponges,

tearing them from the reef with small, powerful mouths.

Overlapping rows of teeth

cut through the hard exterior of the sponge.

A thick layer of mucous, secreted by the angelfish,

then coats the meal protecting the fish's stomach

from needle-like spines in the sponge

designed to deter predators.

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Further down the reef

one of the ocean's most-striking creatures:

an electric-blue queen angelfish.

Though remarkably bright and colorful,

queen angels are able to blend in

with the reef's technicolor maze of coral.

Swimming under a darkened arch in the reef,

the queen angelfish emits a brilliant iridescent glow.

Rich in nutrients the reef at Cozumel

has transformed these shallow waters into a giant aquarium.

Sticking close to the coral

a sponge-eating rock beauty lives up to its name.

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Small fins

make the white-spotted filefish a slow swimmer.

And it avoids the open ocean, hugging the reef,

on the lookout for algae and sponges.

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When threatened,

the scrawled filefish wedges itself into crevices,

erecting spines on its head and belly

to lock itself into place.

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A honeycomb cowfish:

its body encased in hard external armor

that protects it from predators.

Openings in the shell, around the gills,

allow for respiration.

Strong, rounded rear fins help cowfish move swiftly,

as they patrol the reef for marine invertebrates.

Finding food on the reef is not easy.

The hogfish uses its elongated pig-like snout

to root around the seabed, looking for small crustaceans,

which it crushes with its powerful jaws.

Seeking an entirely different kind of prey

is one of the most remarkable creatures on the reef:

the parrotfish.

Its colors, patterns,

and even its gender can change repeatedly.

Sex changes occur when populations are low,

and either more breeding males, or more breeding females,

are needed.

The parrotfish secretes a cocoon of clear mucous,

to protect it from parasites, like bloodsucking isopods,

while it sleeps.

Isopods, known as 'the mosquitoes of the sea',

are dangerous predators:

sucking the blood from fish as they sleep.

But perhaps the most exceptional characteristic

of the parrotfish is its diet.

Parrotfish feed primarily on the coral and algae

that grow on the surface of the reef.

Hard, beak-like teeth tear into the reef,

biting off not just the coral but its hard skeleton as well.

Powerful, grinding teeth in the throat crush the coral,

freeing the algae-filled polyps that nourish the parrotfish.

The pulverized hard-coral skeletal 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.

So whenever you see a parrotfish

going by and leaving its trail behind it,

that is the sand that will, in the end, wash up on the beach.

This is part of the process

that the parrotfish gives to the reef in Cozumel.

The Yucatán rainforest.

Part of the largest continuous expanse of tropical rainforest

in Central America.

Beneath this jungle floor

lies one of the planet's last great wilderness frontiers.

A secret subterranean world...

explored by only the bravest divers.

The cenotes.

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To dive in the cenotes,

you enter

in a freshwater overhead environment.

It's very serene, it's very peaceful.

You're close to the jungle so you're very close to nature.

The jungle sits atop a thick bed of limestone,

once part of an ancient undersea reef.

Over millions of years,

rainwater, made acidic by carbon dioxide in the soil,

percolates down into the earth eating away at the limestone

and creating massive underground cave systems

flooded by pools of groundwater.

Stretching for hundreds of miles,

the world's longest underground water systems

are found in these subterranean chambers.

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Once you get inside the overhead environment,

you're surrounded by darkness.

You have your lamp, you have your guide

and you become at peace with yourself.

You become very relaxed

and it's a very slow, very peaceful dive.

Yet few have witnessed the farthest reaches

of the Yucatán's underwater galleries.

Explorers who squeeze into these tight spaces

and maze-like passageways

take their lives into their own hands.

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Cave-diving is considered

one of the most dangerous part of diving.

We are far away from an exit.

You need to be prepared with double tanks,

double regulators, technical diving equipment.

A small fail in equipment or in logistics

can lead you easily to a fatal accident.

An underwater sign warns of the dangers.

Hundreds of divers around the world

have perished in caves like these.

In the darkened depths,

with the nearest exit hundreds of feet away,

it is easy to become disoriented.

In the submerged caves of the Yucatán,

becoming lost underwater,

with a limited supply of oxygen, can be fatal.

To keep from getting lost,

cave divers unspool distance lines to mark their route.

Line markers point the way to the exit, and safety.

Daring divers were not the first

to explore these underwater cathedrals:

white catfish thrive in this lost, dark world.

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They are night-time feeders,

scouring the caverns for bottom-dwelling invertebrates.

In the darkness of the caves

monumental formations hang like icicles from the ceiling.

Stalactites.

Millions of stalactites.

Dissolved limestone in the water

escapes into the air and hardens as calcite.

Over time, minuscule amounts of calcite

build up and drip from the cave ceiling.

Air currents and the flow of water

help determine the shape of these wild sculptures,

which can range in size from mere inches

to the height of a two-story house.

Yet each begins with a single drip.

Mineral-rich water that seeps through the cave ceiling

or drips off the end of stalactites

creates stalagmites,

which emerge like traffic cones from the cavern floor.

It's hard to believe that something so close to the shore

or something in the middle of nowhere

can be so amazing under the water.

Some of them have air pockets that you come up in

and you're in this middle of this cave

in the middle of kind of nowhere.

It's different than anything else that you have here.

It's not the same kind of diving.

In the rainforest of the Yucatán Peninsula,

there are no rivers and no streams.

Cenotes,

the flooded openings to these underwater caves,

were once the only source of freshwater

for one of the world's great early civilizations:

the Maya.

The word 'cenote' means 'sacred well'.

The Maya constructed villages

around these flooded shafts,

which they believed were a gateway to the gods.

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On Cozumel's rich and colorful reef,

there is a daily battle for survival.

An abundance of prey makes these waters

a rich hunting ground for hungry predators.

Predators, like the spotted eagle ray.

Ten feet wide,

weighing as much as a grand piano,

eagles are the giants of Cozumel.

Propelled by powerful flaps of its wing-like pectoral fins,

the eagle ray soars through the open ocean.

A long whip-like tail,

equipped with two to six venomous barbs,

defends the ray against predators.

Its speed and size keep it safe

from even the largest shark

that prowls these waters:

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The nurse shark.

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In these areas you've got a really good chance

to come across the nurse sharks.

They like to hang out under the ledges

where there's a sandy bottom so they can lie down

and hide out of the current there.

Primarily nocturnal animals,

nurse sharks spend their days resting

and conserving precious energy.

Unlike other requiem sharks, which must swim constantly

to force oxygenated water over their gills,

nurse sharks are able to breathe while stationary:

using muscles around their mouths to pull in water

that then flows over their gills.

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Too slow for the daytime chase,

nurses prefer to hunt at night:

suctioning up resting prey species

through their vacuum-like windpipes.

Though sluggish swimmers

nurse sharks are imposing predators:

reaching lengths of ten feet,

and weights of more than 300 pounds,

the average body mass of an NFL lineman.

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Powerful jaws crush the hard shells of crustaceans

which are devoured by suction

and thousands of sharp, ragged teeth.

As this pair of nurse sharks slowly patrol the reef,

they are joined by more fearsome hunters:

barracudas.

Built like a hunting knife, and just as dangerous,

the barracuda is a master predator.

Small, razor-sharp teeth,

backed by a larger set of dagger-like fangs,

shred fish into small pieces for easy digestion.

Long and lean, barracudas are frighteningly quick:

capable of cutting through the water

at speeds of up to 25 miles an hour,

in pursuit of prey.

The ability to inflate and deflate its swim bladder

means the barracuda is able to squeeze

into small crevices in the coral,

to track down small reef fish.

When hunting near the reef bottom,

barracudas are able to change color,

to blend in with their surroundings

and surprise unwary prey.

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With so many barracudas on the prowl,

these schoolmaster snapper

would be wise to not drop their guard.

As the name suggests,

schoolmasters swim in classroom-size shoals

scouring the reef for crustaceans,

such as this hermit crab,

hunkered down inside the empty shell of a marine snail.

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Survival on the reef is a struggle,

and camouflage can be a lifesaver.

Rather than hiding in the sand like the hermit,

the coral crab blends in with its surroundings,

managing to match both the color,

and texture, of the coral.

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Farther along the reef

is an even craftier master of disguise:

the Caribbean reef octopus.

One of the few creatures on earth

able to alter its appearance in a flash.

Thousands of color-changing cells beneath the skin

form patterns, colors and shapes

on the surface of the skin

that match the surrounding rocks and coral.

You see them changing colors,

you see them moving around and hunting.

They are extremely good at camouflage.

Once you find them, they stop moving,

they fan themselves out

and they change their colors instantly

and it's an amazing thing to see.

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During the day,

the octopus hides out in coral overhangs on the reef.

At night, it comes out to hunt,

using a technique called 'tenting':

spreading its webbed arms into a wide canopy

used to net prey.

It is an extraordinary sight.

But here on the seabed

there are more unusual creatures to behold.

The frogfish.

Equally adept at camouflage,

lies in wait for passing prey.

They are excellent at camouflaging themselves

and they do not move at all.

So you can be staring at one

and you can hardly realize it's there.

A skilled hunter,

the frogfish wiggles its rod-like dorsal spine

to lure prey,

which is then attacked with blinding efficiency.

It may be small,

but the frogfish can expand its mouth

to twelve times its normal size,

to catch prey large prey with long needle-like teeth.

The sea cucumber has the most remarkable defense mechanism:

they actually mutilate their own bodies.

When threatened,

the sea cucumber will contract its muscles

to expel some of it internal organs through its anus.

An action that confuses and deters predators.

The missing body parts are regenerated.

Like all members of the species,

this sea cucumber breathes

by drawing oxygenated water in through the anus

and then expelling it.

A bearded fireworm feasts on the coral.

Stretching 2 to 4 inches,

it is one of the smaller creatures on the reef.

But divers must be wary:

the fireworm's bristles can penetrate the skin,

injecting a powerful venom.

The results can be painful,

and often lead to dizziness and nausea.

Even smaller than the fireworm,

a pipehorse, no larger than a human thumb,

grips the coral with its monkey-like tail.

Seahorses are not strong swimmers,

and can easily be carried away with the current.

Amid a blizzard of marine snow:

decaying organic matter falling from the waters above.

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From spectacular coral formations,

and secret subterranean worlds,

to powerful apex predators,

and magnificent, soaring giants,

the shallow seas of the Yucatán Peninsula

are home to a world among the reefs.

And one of the many wonders of the great blue wild.

In a week you can have cave diving,

shark diving, reef diving.

All in the same place.

Normally people travel all around the world

to dive different places

but here, you can do different kind of diving

in the same place.

For me in the Caribbean, Cozumel is my favorite diving.

You've got thousands of years of history

with the stalagmites and the stalactites.

The Mayans believed that it was the entrance to the underworld.

So it gives you an idea.

It's a little bit eerie, but it's stunning to see.

It's like entering another world.

(♪♪♪)

I've been to various different destinations

but there's always something about coming back to Cozumel

and getting in the water here.

It always takes my breath away.

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