Wildest Places

- It covers 1/3 of the world's surface.

Ringed by fire.

Constantly reshaped

by the almighty clash of Earth's tectonic plates.

Creating lifeforms that, in turn,

become the architects of underwater empires.

Here the world's most primitive life forms

have outlived dinosaurs,

and found astonishing ways

to adapt and survive

in one of the most competitive environments on the planet.

This is "The Wildest Pacific."

The Pacific Ocean spans more

than 155 million square kilometers.

Its depths are less mapped

than the surface of Mars.

As we forge further into the underwater frontier,

numbering species are being uncovered

at a rate of nearly 2,000 each year.

The Pacific Ocean's terrains

are as varied as the land mirrored above.

From hulking sea mounts,

island atolls and lagoons,

to a monumental network of barrier reef

so long it can be seen from space.

The complex ecosystems of reefs

are the lifeblood of the Pacific.

One of the most important reef areas

is known as The Coral Triangle.

This small western corner of the Pacific

has scientists enthralled.

Below the water line,

a vast empire of coral reefs

has flourished from Indonesia,

north to the Philippines,

and west to the Solomon Islands.

This area packs in 3/4 of the planet's coral species

and is home to the world's largest

and smallest fish.

Like an underwater Amazon,

the coral triangle has the highest concentration

of marine biodiversity on the planet.

There are single reefs

that contain more species

than the entire Caribbean.

Here major ocean currents converge,

allowing species to intermingle.

Millennia of stable temperature

have given evolution time to do

its astonishing work.

The triangle is flanked by volcanic activity,

sandy beaches, and the world's

densest concentration of mangrove forests.

This range of topography in such a small area

has forced nature's hand

into specialized and curious adaptations.

Reefs flourish on submerged continental shelves,

on remnants of collapsed volcanoes,

or take hold on new sea mounts

rising up to meet the surface.

Over time, a reef develops zones

with varying currents, temperature, and structure.

Like rainforests on land,

coral reefs form huge, complex ecosystems

spanning hundreds of kilometers.

Each habitat hothouses its own variations of life.

From algae to crustaceans.

The smallest fish to apex predators.

Each tier of the food chain

supports the one above

and those at the top

keep populations in check.

It's an intricate dance

that has surged and subsided time and time again

for some 400 million years.

Modern reefs have risen

in the evolutionary blink of an eye

as sea levels for the past 10,000 years or so

have remained somewhat stable.

These immense underwater empires

are engineered from the tiniest of building blocks.

Coral.

Often thought of as a plant or rocklike mineral,

its neither.

A coral polyp is an animal,

a tiny carnivore just millimeters wide

feeding on passing zooplankton.

Little more than a mouth encircled

by stinging tentacles.

Coral does, however, have vegetable and mineral qualities.

Polyps themselves are clear.

A reef's striking color

comes from an even tinier organism within.

Algae called zooxanthellae.

Like terrestrial plants,

the algae photosynthesizes,

converting sunlight to energy.

Hard corals build limestone exoskeletons.

New polyps grow in the remnants

of the forebearers,

creating the structural framework of a reef city.

Hundreds of millions of years ago

coral cousins broke free to become swimmers.

Today seen as jellyfish.

An evolutionary explosion

took place in the seas.

Swimmers became walkers.

Sea life adapted to poorly oxygenated waters

with tubes and gills.

The first vertebrates appeared as bony fish.

Then amphibians, reptiles, and animals graduated on land.

Occasionally, taking an evolutionary U-turn

and returning to the sea.

The reef itself is engineered,

not only by the living coral,

but by the animals around it.

From drifting algae and plankton

up to the apex hunters,

is one of the most complex

and delicately balanced ecosystems on Earth.

This titan triggerfish

is one the reef's hardest workers.

It has strong, rounded teeth

designed to crunch into coral walls and seabeds

in search of tiny crabs and molluscs.

The titan's mouth is so strong,

it's able to life large lumps of coral and rock

to uncover the best of the reef's hidden smorgasbord.

An intelligent fish,

the titan will spit water jets to uncover food.

Today this trigger has an unearthed a clam.

The shell is too tough to crack

even for a titan.

But this is one of the few tool using fish.

The titan drops the clam onto the seabed

in an effort to crack it open.

This trigger fish hasn't quite found the right tools today.

The sand here is too soft.

The clam's hard casing remains unbreached.

Reef builders like titans and parrotfish

aren't just a part of this environment.

They help shape it.

With formidable teeth fused into beaks,

they gnaw into the limestone coral

to reach the algae within.

This fish excrete the hard parts they don't digest

as calcium carbonate, or sand.

A single fish can create up to 90 kilograms of sand

every year this way.

Nearly every animal on the reef

contributes in some manner.

Shells, carapaces, bony skeletons,

all break down into tiny mineral fragments.

Their remains line beaches,

form islands,

line bays and burrows

of new lives just beginning.

The sand surrounding a reef

is made up of its last tiny remnants.

Over time, it builds up

and births new kingdoms.

Between reef and land is the inshore zone.

These areas are protected from incoming waves

but the shallows are exposed to harsh elements,

lower oxygen levels, and UV rays.

Only the hardiest of corals survive here.

Dense boulder and brain corals dominate.

There's enough gentle tidal flow

for nutrients to pass through

and protection from strong currents and waves.

Inshore animals can maneuver comfortably

and develop ingenious methods to do so.

Boulder corals grow at a rate

of just three centimeters a year.

Some are estimated to be over 1,000 years old.

A master of the boulder domain

emerges from its coral lair to begin dawn patrol.

While most octopuses prefer to hunt at night,

the day octopus takes advantage

of the less competitive sunlight hours.

This boldness is backed

with exceptional camouflage skills.

The day octopus can change body color

in just 3/10 of a second.

A sophisticated network

of pigmented chromatophore organs in its skin

allows it to not only change color

but its entire texture.

Every second the day octopus

reassess where it is

and where it wants to go

and dresses appropriately to hide

or to hunt.

This hunting technique

is an all in approach.

Try everything at once

and see what morsels the reef gives up.

Boulder corals are a haven

for small fish and crabs.

Staples of the octopus diet.