These are not visitors
from an alien planet.
Nor are they science fiction.
They are real.
Creatures of our own world.
And their destiny...
...is linked to ours.
Coral mountains rise more than half a mile
from the floor of the Caribbean Sea.
They were built, inch by inch,
over centuries...
...by billions of coral animals.
But the animals didn't do it alone.
Tiny plants living inside the coral...
...capture energy from the sun
to make its food.
Neither plant nor coral...
...can survive without the other.
And that's the key:
The whole reef community
is built on relationships.
Little fish live here.
And big fish eat little fish.
He's a 100-pound black grouper.
And he's always hungry.
But for the community
to remain in balance...
...the prey needs a fair chance
at survival too.
And nature provides some ingenious ways
to even the odds.
Take the frogfish.
He hides from predators
by looking like a sponge.
In his disguise...
...the frogfish can sit back
and attract lunch...
...with a fishing pole
mounted on his forehead.
Glassy minnows.
Like quicksilver.
That black grouper on the ledge
is hoping to catch one.
The shimmering school dances
for good reason.
It's very hard for the grouper
to isolate a single minnow.
And he often fails.
There's more diversity here
than anywhere else on Earth.
And every single citizen,
from the tiniest fish...
...to the ferocious tiger shark,
must depend upon others to survive.
The balance between predator and prey
is always shifting.
But the community stays healthy
and whole...
...because there are so many different
relationships between so many species.
Sometimes...
...even the coral itself is prey.
The crown-of-thorns sea star.
He eats coral.
Too many of these could wipe out
an entire reef.
The triton trumpet snail hunts sea stars.
Although the snail is almost blind...
...it can smell the sea star's trail.
Those nasty thorns are full of venom.
But the snail is immune.
- What's that?
- It's called a proboscis.
And he'll use it to drill through
the stars leathery hide.
Then he'll inject a venom...
...that will dissolve the sea star
from the inside out.
So the triton trumpet snail
helps save the coral.
And that helps keep
the reef's eco system in balance.
Even different species
you'd think would be enemies...
...often help each other.
This is a cleaning station.
A sort of a dermatology clinic.
The spotted coney is the patient.
The little cleaner gobies
move over his skin...
...removing and eating parasites.
Both species benefit.
It's called symbiosis.
Another cleaning station.
Away from this spot...
...the barracuda might swallow
the little Spanish hogfish whole.
When he's being cleaned,
the barracuda seems to call a truce.
The cleaning station is a sanctuary.
Green sea turtles love coming
to this reef near the island of Hawaii.
It's sort of an undersea spa.
Amazingly,
it's only the size of a living room.
But even coming from miles away...
...they somehow manage
to find this special spot.
When algae accumulates on their shells,
it can really slow them down.
But the reef fish give them a good scrub.
In exchange, the turtles give the reef fish
a healthy vegetarian feast.
Some don't even wait their turn.
They swoop in close to other turtles
to steal away the school.
With her shell beautifully polished...
...she now returns to her migrations...
...which may take her
thousands of miles away...
...through the trackless open sea...
...where jellyfish drift
through liquid skies.
That pulsing is how it swims.
Each pulse also forces
tiny animals inward...
...where they are stunned and consumed.
Thousands of different species of jellyfish
ride the currents...
...like sailors in a gale.
Most are solitary travelers.
But moon jellies sometimes swarm together
in astonishing numbers.
They know not what lies in wait below.
A monster jellyfish ensnares them
in a venomous web...
...that can stretch
more than 30 feet across.
The stinging filaments slowly drag them in
toward the translucent bell...
...where they will be dissolved
and digested.
For some mysterious reason...
...it's called the "fried egg" jellyfish.
Ocean currents can sweep
entire kelp forests...
...away from California's Channel Islands
and out into the open sea.
The drifting kelp rafts
are a favorite gathering place...
...for one of the strangest creatures
in the ocean.
It's called a Mola mola.
This one's about 5 feet across.
But he can grow
to more than 4000 pounds...
...mostly on a gossamer diet of jellyfish.
But Molas don't come here for food.
They come here to be cleaned
by halfmoon perch.
It's a cleaning station in the open sea.
Looks like this time,
the entire family came along.
Currents are as vital to life underwater
as rain is to life on land.
Along the North Pacific Coast...
...they sweep nutrients up from the depths
to nourish a dense growth of plankton.
The basket star has sensed the current...
...and opens serpentine arms
to snare passing tidbits.
Barnacles are feasting too.
They stick out their furry little legs
to catch food.
The translucent creatures
clinging to the kelp...
...are called nudibranchs.
They come in a thousand varieties.
They're close relatives
of the common garden slug...
...but much more beautiful.
These are hooded nudibranchs.
They use their hoods to scoop in water...
...then slowly squeeze out all
but the food.
The hairy arms of feather stars are great
for combing out food.
But in a pinch...
...they're even better
for escaping from marauders.
The marauder is a sun star...
...and it will eat a feather star
if it can catch one.
But it much prefers to dine
on juicy shellfish...
...especially sea scallops.
Did that one bite back?
What an intriguing landscape.
It's home to one of the oddest relationships
ever between a predator and its prey.
It's actually a forest of animals
known as tube anemones.
They protect themselves with stinging cells
hidden in their tentacles.
But there's a predator
who covets those stingers.
It's a rainbow nudibranch.
And he's a thief.
He eats tube anemone tentacles.
But he doesn't digest the stinging cells.
Instead, he'll pass them on
into the feathery gills on his back...
...where they continue to live.
So now the stolen stingers protect him.
The sun star is back...
...and he'll devour a nudibranch,
stolen venom and all.
But like any good thief...
...the nudibranch has a getaway plan.
The Irish lord.
He can hide from his enemies
and his prey.
It's not so easy for the crab to hide.
But he has great defenses:
Sharp pincers and a rock-hard shell.
The Irish lord may have bitten off
more than he can chew.
Before he can swallow his dinner...
...the crab will have to release
that death grip on his upper lip.
And now, a rare close-up look...
...at the domestic life
of the California mantis shrimp.
He's only 10 inches long...
...but he's much stronger than he looks.
He's gathering mussels for dinner.
He's got incredibly powerful claws.
In fact, those claws are as fast
as a 22-caliber bullet.
That makes him the most powerful animal,
for his size, in the world.
He's using his claw like a hammer
to smash open the mussel.
Now he's off to grab some more.
Here comes trouble.
He won't be safe in his burrow.
If he's cornered there...
...the octopus can inject a poison
that will kill him.
Something tells me he won't go down
without a fight.
His display is a warning:
"Don't mess with me."
If the octopus still doesn't get
the message...
...maybe a shot to the chops
will set him straight.
A thousand miles north,
in the frigid waters of British Columbia...
...lives an octopus
that is truly a sea monster.
The giant Pacific octopus.
This one weighs about 50 pounds...
...but he may grow up
to weigh more than 200...
...with tentacles that could stretch
more than 20 feet across.
He's a master of disguise.
As he moves, he changes both
his color and texture...
...to match his surroundings.
This octopus is on the hunt.
And his favorite food is crab.
His eyesight is only fair...
...but the lightest brush against his prey,
and the octopus attacks.
He extracts every morsel of crabmeat...
...then ejects the remains.
In the kelp forest,
there is an ever-changing balance...
...between predator and prey.
But dramatic shifts can cause
entire ecosystems to crumble.
For instance, sea urchins eat kelp.
But if the urchin population explodes,
the kelp could disappear.
Once again, there are animals
that help preserve the balance.
One of them is the wolf eel.
Certainly a face only a mother could love.
Though he looks like an ogre...
...he's important to
this whole community.
Wolf eels eat sea urchins.
And there's supper.
So as the wolf eel dines on urchins,
he helps protect the forest.
Just as the triton trumpet snail
helps protect the coral reef.
Night falls...
...and with it,
begins the largest migration on Earth.
Attracted by moonlight...
...vast swarms of plankton rise up
from the deep.
And following right behind them...
...the night hunters:
Giant manta rays.
They can span 18 feet,
wingtip to wingtip.
They feed only on plankton...
...scooping up millions of tiny prey
in a single pass.
No ocean predator is more graceful.
In the Sea of Cortes...
...nocturnal fish come up
to join the feast.
And rising to feed on them...
...the creatures of your nightmares:
Humboldt squid.
Some are more than 6 feet long
and can weigh as much as 130 pounds.
They change their color
several times each second.
Maybe it's excitement.
Or maybe it's a threat.
Maybe even rage.
They'll attack almost anything.
Sharks, humans...
...even each other.
A shipwreck lies on the ocean floor
off North Carolina.
It's a desert here, with few natural reefs.
Now the wreck itself
has become a reef...
...a shelter for these little fish.
And some not so little.
The sand tiger shark.
They like to hunt here.
But there's a surprising bond
between the sharks and these small fish.
Instead of hiding from the shark,
schools of small fish gather round...
...using him as protection
from tuna, jacks and other predators.
So the sharks provide another kind
of sanctuary for small fish...
...as they travel from wreck to wreck
across this desert of open sand.
Between lemon sharks and remoras...
...it's easy to see who benefits.
By hitching a ride on the shark,
the suckerfish can count on finding food.
We're not used to thinking of sharks
as helpful creatures.
It may not be obvious...
...but the coral reef owes its very survival
to sharks and other large predators.
They're part of the balance.
We know the balance is always shifting...
...but now it's falling apart.
In the last 50 years...
...90 percent of all the big fish
have been taken from the ocean.
We are taking more
than the ocean can give.
We now know that the killing of sharks
is one reason why coral reefs are dying.
Overfishing is decimating one species
after another.
Entire ecosystems...
...have begun to unravel.
But every year,
eight nights after the full moon in August...
...something miraculous happens.
Tonight, in the Gulf of Mexico,
on the flower garden banks...
...the entire coral reef will spawn.
Precisely one hour after sunset...
...coral polyps begin jetting spawn
into the night sea.
Brain corals begin releasing
tiny packets of eggs.
Then star corals.
How is it that millions of tiny polyps...
...from all these corals...
...choose this single moment,
on this single night...
...to spawn?
How do animals that have
no eyes to see...
...or brains to think...
...coordinate this event
with such precision?
That remains a mystery.
These drifting galaxies are the future
of the coral reef.
Most will be lost in the depths...
...but with luck,
a few tiny coral larvae...
...will settle somewhere far away...
...and give birth to new reefs.
And new life.
Not so long ago...
...we knew almost nothing about
the creatures living in this ocean world.
Now we are beginning
to acquaint ourselves with them.
This young right whale is as interested in us
as we are in him.
At last, we're beginning to learn...
...how important all species
are to each other...
...above and below the surface.
And it's clear that our own destiny...
...is linked to theirs.