Original subtitles

Narrator: The ocean sprawls across 70% of our planet.

It's home to as many as one million

known species of plants and animals.

From tiny, cunning critters,

to some of the largest, most feared predators.

But it's the smallest of oceancreatures that underpins

the world's largest food web:

Plankton.

These tiny organisms drift through

the ocean's diverse habitats,

triggering a feeding cycle in their wake.

Woman: The zooplankton is what most fish feed on.

So it really starts with the nutrients

and basically you see effectsall the way up the food chain.

Narrator: Plankton may be the most important creatures on earth.

In the dead of night, two tinymandarin fish find one another,

engaging in one of nature's mostelegant mating rituals.

They rise together, cheek to cheek

and simultaneously release sperm and eggs,

which float away in the current,

on the start of an incredible journey.

It's a journey that could takethem to coral reefs,

to coastlines, to the open ocean,

or to settle on the deep ocean floor.

Along the way they will fuel an oceanic food chain,

on which much of the human racedepends for its survival.

These fish eggs aren't on this journey alone.

Masses of tiny organisms drift in the ocean

at the mercy of the currents.

They're called plankton, Greek for "drifter".

Any animal incapable of moving through the water

without the aid of currents isdefined as plankton.

Some are phytoplankton.

Tiny algae and some kinds of bacteria

smaller than the diameter of a human hair.

Or zooplankton,

tiny living animals, no largerthan a grain of rice.

Other soft, bodied animals likejellyfish are much larger.

Though because they're weak swimmers

that rely primarily on driftingwith the current

they're still classified as plankton.

But it's the tiniest of planktonic organisms

that are the most important.

Without them, life in the oceanwould cease to exist.

Just one teaspoon of ocean water

contains more than amillion microscopic organisms.

Their green hue can be seen from outer space.

Phytoplankton require sunlight to grow, as such,

they occupy the top 35 feet of the ocean.

Like land-based plants,

phytoplankton use photosynthesis.

They absorb carbon dioxide, and release oxygen.

Producing nearly two-thirds ofthe atmospheric oxygen

on our planet.

More than all rainforests

and other terrestrial plants combined.

Phytoplankton is a source of food for slightly larger

zooplankton like crab larvae, amphipods and copepods.

Copepods are the most abundantcreatures on the planet.

With an estimatedpopulation of one quintillion,

a billion-billion.

Though plankton can fill stretches of water,

it isn't evenly distributed throughout the ocean.

The vast seas can be a wastelandfor hungry travelers.

There can be nothing to eat forhundreds of miles.

Until a plankton bloom takes shape.

When currents from two separatewater systems collide,

they push nutrients, on which the plankton feed,

up the water column,

drawing the tiny organisms to one densely packed area

on the water's surface.

Small fish race in to feed on the plankton.

This creates the base for a micro food chain,

in the middle of the sea.

A pod of dolphins detects the sounds of schooling fish

from hundreds of feet away and homes in for a feast.

The shoal of sardines feels the vibrations

of approaching hunters.

They huddle into a ball for protection.

Any individual that stays out ofthe group is an easy target.

But within the bait ball, there's a fighting chance

they'll survive the onslaught to come.

Dolphins hunt as a team.

They use sonar to locate theirprey, making clicking sounds,

that travel through the open ocean.

The sound waves bounce off of potential prey

and echo back to the dolphin,

revealing the size, shape and location of a meal

as far as 250 feet away.

It's a sophisticated method that's taken the dolphin

more than 20 million years to perfect.

Dolphins prefer to hunt where the odds are stacked

in their favor.

A school of sardines feeding on plankton,

offers the perfect opportunity.

The entire pod can feed inone place.

The dolphins corral the sardinesinto a tightly packed ball

and take turns fishing.

The commotion alerts one of the ocean's greatest hunters,

the copper shark.

It detects the vibrations emitted by the panicked shoal

of sardines.

The trail leads the predator directly to its prey.

A second shark joins the hunt.

But its sights are set on a target much larger

than the sardines, a manta ray.

Sharks prefer to hunt in murky waters,

using stealth to stalk their target from behind.

Filter feeders, like this manta ray

can fall victim to the shark's cunning.

Like the schooling fish, mantarays feed close to the surface,

where plankton is most abundant.

A pair of specialized fins unrolls to guide plankton

into its enormous mouth.

But the manta's throat is no larger than a human fist,

and as a result,

its diet is restrictedalmost exclusively to plankton.

Because they're so big, manta rays don't make an easy meal

for a shark.

Many survive an attack, but thescarring and bite marks remain,

evidence of the manta having been in the wrong place

at the wrong time.

The ocean's largest fish, alsofeeds on its tiniest organisms.

As if skimming the cream off milk,

a whale shark slurps up the sheets of plankton,

that collect on the surface.

In a single day, one whale sharkwill filter nearly enough water

to fill two olympic-sized swimming pools.

A mouth as wide as a bathtub sucks in the plankton.

A set of gills, fitted with filters,

traps the tiny organisms.

When they've devoured enough plankton, the animals leave,

in search of the next pulse of life in the open ocean.

Dead plankton fall to the seabed,

where they form the basis of adifferent food chain.

Survivors continue their voyageas passengers on the current,

their fate in the ocean's hands.

An ocean surge carries the tiny organisms

through marine corridors.

Sometimes, their epic journey isinterrupted by land.

Pinnacles and peaks, rise fromthe ocean,

powerful currentssmash against the summit walls,

bringing in nutrients that sustain plankton,

which in turn feed and populate the reef.

Here, a new group of creaturesrelies on plankton,

including corals, the architectsthat built this reef.

Each coral is made up of tiny, transparent animals

called polyps, that are invisible to the naked eye.

Similar to these soft corals, polyps use their tentacles

to catch plankton, that drift by.

Polyps hide their soft, delicate bodies

in the limestone skeletons we know as corals.

Polyps connect to one another, to create colonies.

Over millions of years, these tiny engineers lay down

the foundation of the reef.

The plankton that feeds the builders of this coral city,

also feeds its residents.

For those firmly planted,

the current acts as a food delivery service.

A sea apple cucumber extends itstentacles into the stream,

to collect passing plankton.

Like arms, the tentacles bringfood to its mouth.

But for many, life on the reef is a daily fight,

against the current.

Larger residents, like these angel fish,

swim on their side to combat the surge.

Crustaceans and smaller fish tuck into nooks and crannies

seeking protection from the current,

and from lurking predators.

Eventually, the smaller fish, like these juvenile catfish,

must come out of hiding to feedon the plankton.

When they do, ambush hunters, like moray eels,

will be waiting to feed on them.

The moray eel will typically stay in its den

and wait for prey to come to it.

Other hunters are more active in their pursuit.

One of the most venomous animals on earth

slithers through the water.

A sea snake, ten times more toxic than a cobra,

the sea snake can paralyze itsprey and swallow it whole.

This ribbon eel is a favored food of the snake.

He quickly tucks back inside before he's discovered.

As the snake surfaces for a breath of air

it fills a lung that extends

nearly the entire length of its body.

A single breath will supply enough air

for two hours of underwater hunting.

Plankton, feeding fish and crustaceans

would be wise to postpone their dinner

while this predator is on the prowl.

Larger reef fish, have their sights set on

a substantial meal.

They're targeting a nest of freshly laid eggs

attached to the reef.

Left unattended, the nest is aneasy meal for the reef fish.

This protective male sergeant major

won't let the same fate happento his brood.

He stands guard to fend off hungry predators,

and hovers over a purple bed of fertilized eggs,

darting at incoming intruders.

The barber fish and king angelfish are relentless

in their pursuit.

Eventually the persistent sergeant major

repels the attackers.

Not every fish is a threat.

Some, like parrotfish, feed oncoral instead.

The parrotfish uses its large, beak-like mouth

to scrape micro-algae from the coral surface,

maintaining the health of the reef.

A hawksbill turtle, renders a similar service.

She uses her narrow, hooked beakto fetch her favorite snack,

sea sponge.

Smaller fish stick close by tonibble at her leftovers.

The hawksbill prunes this coral garden,

preserving the reef's delicate balance.

By picking off sponge, she clears some much-needed

real estate for fresh coral growth.

Though coral reef covers lessthan one percent of the ocean,

it's the most diverse of any ecosystem on earth.

Coral reefs are home to more than a quarter

of all known ocean species.

In one way or another, each ofthose species is influenced by,

and dependent on, plankton, as their nutrients move

through the food chain.

Of all the creatures on the coral reef,

fish are by far the most diverseand plentiful.

Many species, like these glass-fish,

feed directly on zooplankton.

The tiny animal-based organismsthat drift in the current.

The larger reef fish, like theselionfish, feed on them.

A vivid variety of shapes and colors,

helps the fish to hunt and hide.

Every bright color and bold pattern serves a function

in the highly organized world centered on the reef.

In this way, reef fish are strikingly different

from the silvery sheentypically associated with fish

in the open ocean.

A pancake-shaped body allowsreef fish, like this Angelfish,

to maneuver between crevices in the coral.

A specialized set of fins further enhances

a flattened frame.

A paddle-like tail and distinctive pectoral fins

help filefish to make sharp turns through the coral

to out-swim predators.

Other fish, like yellow snapper,

travel in shoals to confuse hunters.

But where there is life, energized by plankton,

predation follows.

Sharks.

Hundreds of sharks.

White tips scour the outskirtsof this coral city.

Hammerheads circle overhead.

The hammerhead shark, is one of the most skillful hunters

in these waters.

Its mallet-shaped head providesa panoramic view,

allowing the shark to see preyboth above and below.

While it cruises mid-water.

Rays hunt under the very eyes of their predator.

This blue spotted stingray usesspecialized sensors

to detect tiny electrical pulses emitted by shellfish

buried under the sand.

But this ray has lost its greatest weapon.

A shark bit off its tail and theray's stinger with it.

Now completely defenseless, theray needs to be extra cautious

in these waters.

But for now, the hammerheadsshow little interest in hunting,

which they tend to do at night, and alone.

Most of the reef's larger predators

are also nocturnal hunters, likethese white tip reef sharks,

which spend most of the daylying still to conserve energy.

Under the cover of darkness, life on the reef gives way

to a new cast of characters.

Docile filter feeding of plankton is eclipsed

by the frenetic pursuit of the predators

at the top of the food chain.

White tip reef sharks force their narrow bodies

through openings in the reef.

Pushing their heads into each nook and cranny,

as they rummage the seabed.

One of the sharks bullies a small fish out of its home.

But an agile black jack scoopsit up instead.

Despite a body tailor-made formaneuvering through coral,

The white tip reef shark is a sluggish hunter.

It has bad eyesight, and must rely

on a strong sense of smell to locate its prey.

Once a shark makes a catch, sharing is out of the question.

Though the jacks do their best to muscle in.

Each shark fends for itself ina feeding frenzy

that will continue through the night.

As the sun pierces the water's surface,

the mighty ocean welcomes a new day.

It's the calm after the storm, the night's hunters are resting.

The reef's residents come out ofhiding and new visitors arrive.

Currents fuel the reef with fresh plankton,

enticing millions of thimble jellyfish with an easy meal.

They have no brain.

They have no blood.

And are made up almost entirelyof water.

Even though they can swim to some degree,

jellyfish are consideredplankton due to their soft body,

which limits their mobility.

These ocean drifters may be low on the evolutionary scale.

And even lower on the food chain.

But as their numbers show,

simplicity can be effective in survival.

A much larger ocean wanderer turns up with the current.

A loggerhead turtle.

The largest of all hard-shelled sea turtles,

loggerheads carnivores. are carnivores.

It's come to feast on crabs and shellfish

hiding out in the seabed,

and on the planktonicjellyfish that ride the current.

But a hungry visitor approaches.

The tiger shark has just one thing on its mind.

Food.

The tiger shark is one of theocean's most-feared predators.

At 15 feet long, it's also one of the largest.

Tiger sharks live in both the open ocean,

and the coastal areas of tropical

and subtropical waters.

Often called the trashcan of the sea,

the tiger shark is known for itsvoracious appetite.

From stingrays and smaller sharks,

to car tires and license plates,

the tiger shark will eat just about anything.

No creature is safe.

The loggerhead takes a short recess from feeding

to catch a breath of air.

But she's spotted.

The shark strikes from below.

A death like this is commonplaceat the top of the food chain.

But would not be possible without plankton

providing the base for all life in the sea.

This ocean wanderer's journeyhas come to an end on the reef.

But for another, it's just beginning.

A Puddingwife wrasse releases her eggs into the current,

and a frantic race ensues.

Males release a cloud of sperm,

in an attempt to fertilize the eggs.

It's a spawning frenzy that's over in seconds.

The fertilized eggs join the spawn of thousands of

other fish species in the plankton mass

floating through the sea.

Urchins, starfish and some crustaceans,

also start their lives as plankton.

Drifting through the ocean.

They're at the mercy of the wind, the currents

and coastal upwellings,

which may bring the tiny drifters close to shore.

Here, plankton sustains a new chapter of life in the ocean.

In shallow coastal water, phytoplankton,

or microscopic algae,

thrives in the warm embrace of the sun.

Much like terrestrial plants,

phytoplankton harness energy from the sun

and convert it to food.

As the sun hits the water, it nourishes the phytoplankton

and the grassy seabed below it.

Crustaceans feed on the plankton.

And larger animals like the stingray, feed on them.

One of the largest feeders foundalong tropical coastlines

is the manatee.

This docile herbivore will graze on the sea meadow

for as long as 12 hours each day.

It's no wonder the manatee is often called the "sea cow".

In deeper coastal waters, the scene is far less peaceful.

Here, the sea lions takesadvantage of the schooling fish

brought to their doorstep by the fresh influx of plankton.

Agile and flexible, sea lions are master swimmers.

This young hunter whizzes pastafter a school of jack fish.

Methodical, and relentless in its pursuit.

From hundreds of fish, its focusbelongs to just one.

But the sea lion's presence invites another hunter.

A great white shark.

Nearly 20 feet in length.

Weighing as much as a rhino, with an appetite to match.

It's the world's largest predatory fish.

A hunter, 400 million years inthe making.

The great white shark is one ofevolution's greatest triumphs.

The shark advances slowly.

Though its torpedo-shaped bodyand powerful tail

can propel it through the water,

at speeds of more than 20 miles an hour.

The sea lion colony appears to be on high alert.

But the determined sea lion continues its chase.

At last, it's rewarded with a meal.

The sea lion swims off with its catch,

unaware of impending danger.

The great white homes in.

In these deeper coastal waters,

predatory sea lions quickly become prey.

The journey of plankton throughthe ocean is an infinite cycle.

But the isolated journeys of each organism

have a beginning and an end.

Like bus routes, currents maketheir way around the ocean.

Picking up and dropping off passengers as they push on.

But much of the plankton at some point

will drop out of the watercolumn and sink to the seabed,

where once again it is theplatform that supports all life.

Down here, away from coral reefs or seagrass beds,

food and shelter can be hard to come by.

Plankton drops into the waitingmouths and claws

of hungry bottom dwellers, like this porcelain crab.

It spreads the bristles of itsclaws to catch

and comb through falling plankton.

The crab takes shelter in an anemone sprouting

from the ocean floor.

Its stinging tentacles serve asprotection against predators.

A special coating of mucous, protects the porcelain crab from

the stinging appendages of its host.

Fish and crustaceans scour the seabed,

sifting through sand to find leftover scraps

of detritus and plankton

that may have settled on the bottom.

But they're not the only ones looking for a meal

on this seemingly barren ocean floor.

An urchin crab, carries its living armor on its back.

The crab is well protected, andthe urchin gets a free ride.

Denizens of the muck

that haven't made protective arrangements with others

seek shelter with what's available.

Because these plankton feeders

are tasty meals for other creatures.

When there's nowhere left to remain unseen.

The only option is to hide in plain sight.

Wispy strands of algae sway inthe current.

With a closer look, the seaweedgrows arms and legs.

It's a decorator crab camouflaged by debris.

What appears to be sea grass, isactually two ghost pipefish.

The ocean floor is abattlefield, where the smartest,

rather than the strongest survive.

Those who can't outwit the predator, are done for.

This is the fastest bite in theanimal kingdom.

It belongs to one of the ocean'sstrangest creatures,

the frogfish.

It uses a lure, like a fishingrod, to catch other fish.

When nothing bites, the frogfishwalks elsewhere to try its luck.

The ocean floor hides many suchcunning hunters.

If you can spot them.

They're among the most bizarrecreatures on the planet.

A master of illusion floats inthe water.

Its skin sparkles like a starry night.

Its three hearts pump blue blood.

Its eight arms grow out of itshead.

This is the cuttlefish, an alien-like creature

in the muck.

The cuttlefish hunts along theocean floor, using camouflage

to surprise its prey.

And hide from predators.

Beyond the coastal seafloor,

in the trenches of the seemingly endless ocean,

is a world even more mysterious, more alien.

It's a graveyard.

As plankton dies, it sinks to the ocean floor.

The falling plankton, nourishes a world

beyond the realm of sunlight.

With no light, resources are scarce.

Organisms must work together to survive.

What may look like one animal,

is in fact a colony of marine organisms,

called zooids, attached to one another.

Each one captures the falling plankton.

They travel and hunt, as one.

Together, they form one string-like organism,

called a siphonophore,

that can grow to be longer than a blue whale,

Although it's one of the world's longest animals,

it is incapable of independent movement.

It drifts in the black stillnessinstead.

As such, the siphonophore is thelargest planktonic organism

in the world.

As oceans churn and currents surge upward,

they carry withthem a rich supply of nutrients

that come from dead plankton

and the remains of other decayed organisms on the seabed.

The upwelling thrusts these nutrients toward the surface,

where they nourish new blooms of plankton,

and start the cycle once again.

A cycle without which, life onour planet would cease to exist.

Without plankton, the entire marine food chain

would collapse.

Plankton feeders and smaller fish

would be wiped off the face of the earth.

Without these smaller fish, oceanic mega fauna like sharks,

dolphins and rays would disappear.

Coastal mammals like sea lionswould perish.

As would billions of people

that depend directly on marine resources.

There are seven-and-a-half billion people in the world.

And every second, there are four more mouths to feed.

Nearly half need food from the ocean.

For thousands of years fishinghas been a way of life,

passed down for generations as a means to feed families.

Today, seas are overfished by commercial boats.

And corals are destroyed when fishermen drop explosives

in the water.

Wiping out reefs and killing far more fish

than are ever harvested.

Each day, more than four millionfishing boats set out to sea,

to feed a growing human population.

In 2009, Americans alone consumed 4.8 billion pounds

of seafood.

Researchers around the world are trying to understand

how to protect our oceans

from the ever-increasing demands of people.

As a conservation biologist, I have two different jobs.

One of them is to learn more about the biology

and ecology of animals.

But at the same time as you're out every day

you're almost on patrol.

Basically you're going up and down the coast

literally looking for dead animals on the beach,

nets, people poaching these animals.

And then you're reporting back to authorities.

So you're almost acting as a ranger at the same time

as you're acting as a biologist.

and that's, it's really sobering.

A lot of people have the mentality

that the oceans are just huge,

vast pools of resources.

But those resources are limited.

For a lot of different fisherieswe are reaching

that critical point were we're at that limit

of what it can actually handle.

Dr. Marshall: Over the yearsshark populations have declineddramatically.

and that's largely due to the gill nets that occur along

the coastline and also targetedfishing for sharks.

Chinese syndicates have formed along the coastline

that are buying shark fins.

So local fishermen respond by actually killing sharks.

Narrator: Recent estimates suggest that populations of large sharks

have declined by 90% or more.

Smukall: The biggest threats tosharks in general is humans.

In certain areas they're doing large beach nets

to protect surfers and swimmers.

In other areas it's the sharkfinning and just a misconception

about what type of fishing these animals can withstand.

And then the role and the importance of these animals

in the environment.

Narrator: Sharks are the ocean's apex predator.

Without them, the entire food chain collapses.

They're efficient, opportunistic hunters.

They prey on old, sick, and weak fish,

maintaining the overall health of the population.

Losing sharks would be a tragedy in itself.

But the impact of human influence is felt

at every level of the food chain.

Down to the tiny plankton thatunderpins all oceanic life.

Humans dominate the ocean's food chain.

We are the last link.

There is no greater predator.

As ocean temperatures rise due to climate change,

the cycling of chemicals in water is disturbed.

Creating a difficult environmentfor plankton growth.

Dr. Marshall: The zooplankton iswhat most fish feed on.

A lot of planktonic fish and even things like manta rays

and whale sharks,

when there's a lot of biomass of fish of course

you're going to have a lot of predatory fish.

So it really starts with the nutrients being driven up

the coastline and basically you see effects

all the way up the food chain.

Narrator: More than marine lifeneeds plankton to survive,

terrestrial life does too.

Most of all, humans.

We owe every other breath we take to phytoplankton.

The producer of nearly two-thirds of all oxygen

on our planet.

The absence of plankton wouldmark the end of life on earth.

And yet we've only scratched the surface

when it comes to learning aboutthese essential life forms.

From copepods, to snails and crab larvae

a remarkable diversity of tinydrifters floats on the current.

Triggering a feeding cycle in every habitat.

We may know little about them.

But there's one thing we do know.

These tiny microscopic organismsare the unsung heroes

of our oceans.

And their epic journey is perhaps the most important

of any creature on earth.

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