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Just 50 years ago,

we finally ventured to the Moon.

For the very first time,
we looked back at our own planet.

Since then, the human population
has more than doubled.

This series will celebrate
the natural wonders that remain

and reveal what we must preserve

to ensure people and nature thrive.

Immense shoals of fish
throng our shallow seas.

These are anchovies.

Small fish, in turn, sustain bigger ones.

Hunters, such as giant trevally...

and mobula rays.

When hunters such as these work together,
they become extremely efficient.

The rich coastal seas
are the fishing grounds of our planet

and can provide an abundance of food
for wildlife and humanity.

The seas fringing land make up
less than a tenth of the World's Oceans,

yet, astonishingly,
90 percent of all marine creatures

live in these coastal waters.

This superabundance
is due to the fact that the seafloor here

is within reach of sunlight.

Everglades National Park
in Southern Florida.

Fields of sea grass
carpet the shallow tropical waters.

Like savannas on land,

these lush marine meadows
support a great variety of animal life.

Stingrays search for prey
hiding in the sea grass.

The Everglades
are also the hunting grounds

of the coasts most ingenious fishermen.

Bottlenose dolphins.

They search for food using echolocation,
a type of sonar.

Ahead of them, a shoal of mullet.

These particular dolphins

have developed their own special way
of catching their prey.

They carefully herd the fish
into just the right place.

Then one dolphin stirs up a ring of mud
that encircles the shoal.

The fish panic and take to the air.

Most escape.

Catching flying fish isn't easy.

But the dolphins move on
and take another helping.

People aren't allowed to fish commercially
within the national park,

so there's plenty for the dolphins.

Only from the air can we really appreciate
the industry of these master fishermen.

The shallow seas are vitally important
in the fight against climate change.

Sea grass absorb
35 times as much carbon dioxide

as the same area of rainforest,

and that reduces the damage
caused by the recent warming of our seas.

Mangroves often border
the sea grass meadows.

These remarkable trees
are the only ones that can cope

with the varying saltiness
of coastal waters.

They not only protect our coasts
from the destructive forces of hurricanes

but also, like sea grass,
capture carbon dioxide.

Their tangled roots
create safe nurseries for young fish,

which will eventually leave the mangroves

and make their homes in the tropical seas
most magical wonderlands,

coral reefs.

These reefs cover
less than one percent of the seafloor,

yet they are home
to a quarter of all marine species.

None of these creatures would be here
were it not for the coral.

Corals create the structures
that provide food and shelter,

on which the entire community depends.

Every resident has a role to play
in maintaining the health of the reef.

Unfortunately, few reefs
are as pristine as they once were,

and most are now missing

one extremely important member
of the community.

Sharks.

Relentless overfishing has reduced
shark populations around the world

by over 90 percent.

Today they only thrive
in anything like their former numbers

on the very remotest of reefs.

French Polynesia,
in the middle of the Pacific Ocean.

Here, at least,
sharks are fully protected.

By day, gray reef sharks
hang in the current.

They let little wrasse
pick their teeth clean

in readiness for the night's hunt ahead.

These sharks prefer to hunt in darkness,

when their acute senses
give them an advantage over their prey.

Nightfall.

Time for small fish to take refuge
within the nooks and crannies of the reef,

beyond the reach of the gray reef sharks.

The sharks can detect
the slightest movement.

Breaking cover is dangerous.

Stay motionless
and the sharks may not detect you.

A little fish may outmaneuver
a single shark,

but with so many hunters
there is little chance of escape.

Sheltering within the coral branches
is usually the safest option,

but the arrival of a second hunter
changes everything.

White tip reef sharks.

Slender and more agile,

the white tips can get into hiding places
other hunters can't reach.

Those that are not caught by the white tips

are flushed out
to the waiting gray reef sharks.

With both kinds of sharks
hunting in partnership,

there is little respite,
even within the reef.

More and more sharks arrive,
attracted by the commotion.

Such numbers of sharks were once common
on reefs around the world.

And while so many predators
may seem damaging,

sharks, in fact, assist
in maintaining the health of the reef.

They help to keep a balance
in the fish community

by hunting the predators
that feed on small grazing fish.

The grazers, in their turn,

keep the corals
free of seaweeds and parasites

that would otherwise overgrow the reef.

A balanced community,
with sharks as top predators,

gives a coral reef much greater resilience
in the face of damage and disaster.

But today, even healthy coral reefs
are facing a greater threat.

With climate change, our seas are warming.

Microscopic plants
that live within the tissues of the corals

give them both their color
and most of their nourishment.

But if seas temperatures rise
by just a degree or two,

the corals expel their plant partners.

So they lose their main source of food...

and turn white.

Here, on Australia's Great Barrier Reef,
unusually warm seas

have caused many of the reefs
to bleach in this way.

It may look hauntingly beautiful,

but if temperatures remain high
for a few weeks,

the corals will starve
and eventually die.

The carbon dioxide
that causes global warming

is also making the seas more acidic.

No reefs can survive both changes.

And without living corals,

many of the reef's residents
will also perish.

During 2016 and 2017,

over a thousand kilometers
of the Great Barrier Reef bleached.

Six months later,

and many of the corals are dead.

The community destroyed.

Worldwide, half of all shallow coral reefs
have already died.

The rest could be gone
over the next few decades.

Away from the tropics,
in higher latitudes,

the seas are much cooler.

Storm-lashed waters bring essential
nutrients to the surface.

The enriched water,
combined with long summer days,

make these
the most productive seas on the planet.

Fur seals thrive
and even have time to ride the waves.

Spring off the coast of California

and fronds of golden kelp
floating on the surface

hint at the riches hidden beneath.

A magnificent submarine forest.

These stands of giant kelp
are as important to the oceans

as trees are to the land.

Like a rainforest,

the dense canopy provides food and shelter
for an abundant community.

In the cool, rich seas,
giant kelp can grow 50 meters high.

Air-filled floats lift the fronds
towards the sunlit surface.

Nestling in this canopy,

a sea otter.

His thick fur keeps him warm
in the chilly water.

Blowing air into it
gives him extra insulation.

Sea otters
have the densest fur of any animal,

and such a luxuriant coat
requires a great deal of attention.

They need to eat a lot to keep warm

and consume up to a quarter
of their body weight every day.

Sea urchins are a favorite food.

There's one.

And a second.

And then the otter is out of breath
and must return to the surface.

An urchin
looks like a rather prickly meal,

but if you can break the shell,
there's a feast inside.

Sea otters are crucial
to the health of the kelp forest

because they keep down
the number of sea urchins.

The urchins graze on kelp,

munching through their tough stems.

Left unchecked, they spread
across the seafloor like a plague.

Fortunately, the otters have a helper
in the fight against these spiny grazers.

Sheephead wrasse.

They have powerful teeth

and can make short work
of the smaller purple urchins.

The larger black urchins
are more of a challenge,

especially for smaller wrasse.

Only the very largest sheephead
can tackle them.

But it still has to get past
those long spines.

The urchin has to be flipped over
to expose its vulnerable underside.

Not easy when you have no hands.

Success at last.

And everybody benefits.

These fish and otters,
living within marine protected areas,

keep the kelp grazers under control.

But just outside these sanctuaries,
the urchins graze unchecked...

and fell the kelp forest.

All those that depend on the kelp
have disappeared.

In California, kelp forests
grow abundantly in protected areas

where the whole marine community
can live without pressure from people.

Here, at least, sea otters
can chill out Californian style.

Three thousand kilometers further north,
in Alaska,

spring arrives much later in the year.

After a cold, hard winter,

the first rays of the sun
trigger a great annual event.

Immense shoals of herring
rise up from the depths

and move into shallower waters.

They're gathering to breed.

But predators are waiting for them.

Steller's sea lions.

So intent on their mission,
the herring make easy prey.

Sea lions drive the fish to the surface,
within range of aerial hunters.

Bald eagles, normally solitary birds,
have assembled in numbers for the feast.

In places, the herrings reach shore,

and there the eagles
don't even need to take to the air.

Humpback whales.

They have come
all the way from the tropics,

hoping to get their first meal in months.

These whales have a remarkable way
of collecting this seasonal bounty.

They work as a team.

The lead whale dives first...

and blows a curtain of bubbles
to concentrate the fish.

A call synchronizes the attack.

By cooperating in this way,
each whale can eat a ton of fish a day.

Yet the herring are so abundant

that, in spite of the whales,
most managed to reach the shallows.

And here they spawn.

The females lay their eggs
on the sea grass.

The males follow,
fertilizing the eggs with clouds of sperm.

Once, herring thrived here in an abundance
we can barely imagine today.

They used to turn shorelines white
with spawn,

right across the North Pacific
from Japan to California.

With industrialized fishing techniques

it's all too easy
to over exploit these breeding stocks.

This is one of the few places
where a fishery still survives.

Pacific herring populations
are greatly reduced.

A mere fraction of what they once were.

This sorry tale of unsustainable fishing

has been repeated time and again
around the world.

Many of the world's fish stocks
are now in serious decline.

A third of them have collapsed altogether.

In coastal seas,

jellyfish are taking over waters
that were once dominated by fish.

Compass jellyfish have an ethereal beauty,

but they provide very little sustenance
for other wildlife or us.

These immense swarms
are becoming increasingly common.

A worrying sign of a serious imbalance
in our shallow seas.

Unless we start to fish sustainably,
our seas, once so bountiful,

will be filled with little more
than vast swarms... of jellyfish.

But the future
does not have to be like this.

On the Pacific coast of South America,
we can see how the oceans can recover.

The Atacama, the world's driest desert.

Inland it's barely able
to sustain life of any kind,

and yet the coast
could not be more different.

For centuries, seabirds have gathered
in millions on these desert shores.

But 50 years ago
the great colonies disappeared

because we over fished the local waters.

Controls were introduced,
and now the fish stocks are recovering.

So today, three million guanay cormorants
assemble each year to raise their young.

Each morning the birds head out to sea.

The colonies are so vast
they take over an hour to empty.

Joining the procession, Inca terns.

Peruvian boobies.

A great caravan of hunters,
all searching for the same thing.

Anchovies.

These little fish are so abundant

that they support
the greatest fishery on our planet.

Astonishingly, they can account
for a tenth of all the fish

we harvest from our oceans every year.

Sea lions are first to find the shoals.

As fish are driven to the surface,
they come within range of pelicans.

Cormorants dive to grab their share.

Boobies strike from heights of 20 meters.

They hit the water
at a hundred kilometers an hour.

Today, the lives of five million
cormorants and boobies

depend on the great shoals.

Yet, if we allow the anchovies
to fully recover,

they could sustain
the 25 million seabirds they once did.

It is a vivid reminder

of the astonishing riches
our coastal seas can support.

And, when given the chance,
they can recover surprisingly quickly.

The islands of Raja Ampat
in Southeast Asia.

These seas were largely stripped
of sharks and other large fish

by years of unregulated fishing.

This lagoon was once occupied
by a shark fishing camp.

Now it's a nursery for baby sharks.

The seas around Misool
were fully protected in 2007,

and the recovery has been miraculous.

Today there are 25 times more sharks
than a decade ago.

Turtles that used to be hunted
now peacefully graze on the sea grass.

Sharks are returning to local reefs,

helping to restore the balanced community,

giving them a greater resilience
against the effects of coral bleaching.

Ocean-going manta rays.

Seven meters from wing tip to wing tip.

These endangered giants

spend most of their lives
roaming the high seas.

But now they are returning
to this sanctuary

to seek the attention of cleaner wrasse.

Misool is one of the few places on Earth
where biodiversity is actually increasing.

Since protection,
there are three times more fish

than just ten years ago.

Fishermen working nearby waters
profit from the overspill.

They now catch more fish for less effort.

We have far too few marine sanctuaries,

and in many
commercial fishing is still allowed.

We need to turn
a third of all our coastal seas

into properly protected areas.

If we do that,
our planet's fishing grounds would recover

and help sustain both humanity
and the rest of the natural world.