[Tom Hiddleston] The night.
A shadowy world that hides more than half the animals on our planet.
Until now, cameras only offered a glimpse into their lives.
But with next-generation technology,
we can see the night as clear as day.
With cameras a hundred times more sensitive than the human eye...
we can now capture the beauty of night...
in color.
Alien landscapes.
Strange creatures brought to life by the darkness.
Unseen behaviors.
Now we can follow the lives of animals
in Earth's last true wilderness.
The night.
Evening is falling over the tropical islands of Indonesia.
And hidden beneath the waves...
lie some of the planet's most pristine underwater worlds.
Coral reefs...
our seas' treasure troves of life.
Across the world, they cover less than one percent of the seabed...
but support over a third of life in our oceans.
The reef is a bustling undersea city...
with creatures of all shapes and sizes busy feeding.
Humphead parrotfish, the reef's bulldozers,
munch coral with birdlike beaks...
while hawksbill turtles snack on the softer sponges
that grow beneath the hard corals.
For the ingenious, food can be found in the most unlikely of places.
Small cleaner wrasse offer an intimate service.
As they nibble food stuck in their neighbors' mouths.
Evening is rush hour on the reef,
with the residents making the most of the light while it lasts.
But this busy world...
is about to change.
Because there is another side to coral reefs...
that only emerges when the sun goes down.
With the latest filming techniques...
we can see into this hidden realm...
and witness the drama of the world's coral reefs at night.
As darkness falls, smaller fish shoal together for safety in numbers.
The beginning of night is the most dangerous time on the reef.
Cornetfish.
A meter long and armed with a rifle-like snout.
The reef's nocturnal marksman.
With large, light-sensitive eyes...
they line up on the school of fish...
and let fire with deadly precision.
[whooshes]
They trap their prey in their syringe-like mouth.
[whoosh]
And pick off fish one at a time.
As they swallow their prize...
all that's left of the catch...
is a puff of scales.
But cornetfish aren't the only hunters lurking in the darkness.
The reef's residents hide deep in cracks and crevices...
because bigger, deadlier predators are now emerging.
And each stalks the night reef in its own way.
This whitetip reef shark will devour fish that linger too long above the reef.
And she's not alone.
A stingray, every little fish's nightmare.
For his victims, the night appears almost pitch black.
They can't see him coming.
But our cameras reveal...
how he stalks the reef.
He uses electroreceptors...
not eyesight, to sense the movement of fish hiding in the coral...
or crabs buried in the sand.
[water whooshes]
Wings up to two meters wide trap them on the seabed.
Flushing away the sand exposes the victim...
[water whooshes]
...before his vacuum-like mouth...
[whooshes]
...gobbles them up.
With so many predators about at night...
[whooshes]
...it's best to keep your head down.
But despite the dangers...
one colorful little fish is about to leave the safety of the reef.
A mandarinfish.
And this male...
is on the lookout for love.
Tonight, he's hoping to court up to eight females in under an hour.
But to find them, he's going to have to move very carefully.
Through the darkness, he spies...
a female...
having her evening meal of tiny, shrimp-like copepods.
But she's as picky about her lovers...
as she is about her food.
To win her affections, the male now spreads his fins...
to appear as big and irresistible as possible.
She's impressed.
But to mate, it's now time for an even bolder move...
and to use the darkness to their advantage.
With fish that would eat their eggs hiding amongst the coral...
the new couple rise above the reef...
to spawn in a dazzling courtship dance.
With their nighttime display over...
the couple retreat to the safety of the coral...
but not for long.
With up to seven more females to find...
this Casanova is off to brave the dark
in search of his next dancing partner.
As the night draws on...
the darkness triggers one of nature's most astonishing hidden wonders...
an event that will bring a magical change to the reef.
From the ocean depths, an army of tiny animals is emerging...
as if from an alien world.
It's the greatest migration of creatures anywhere on the planet,
and it happens every night in our oceans.
Over a billion tons of planktonic life
rise from the depths to feed in the surface waters.
These creatures, some no bigger than a grain of rice...
are the lifeblood of the ocean.
With ingenious forms of luminescence and propulsion...
they capture morsels of food adrift in the dark.
Some creatures live entirely in this hidden world.
Others, like this mantis shrimp larvae,
spend only the first part of their lives in this alien existence
and will return to live on the reef once they grow.
This rising tide of life...
now triggers the coral reef to undergo a magical transformation.
Seemingly dormant rocks come to life.
Coral reefs are made up of colossal colonies of tiny animals.
By day, the reef absorbs energy from the sun.
But at night...
these animals spread their tentacles to become hunters...
of a microscopic nocturnal realm.
For the tiny animals drifting in...
this colorful garden has turned into a deadly wall of millions of mouths.
This nighttime feast provides corals with the nutrients
that are essential for the reef to grow.
And we now know, as coral reefs struggle with rising sea temperatures,
this nighttime feeding is more vital than ever for their survival.
But it's not just the tiny corals that rely on the nighttime tide of plankton.
Other far larger creatures are gathering for the night's final feast:
a manta ray, gliding on wings up to four meters wide.
Though usually solitary...
there are places in the tropical seas where the plankton is so rich,
mantas come together to feed.
Most astonishing, these one-ton giants
are sustained by the tiny planktonic animals that rise in the sea at night.
With hornlike fins, they funnel the plankton into their open mouths...
and sift out the morsels of food.
Now in the dead of night...
they reveal their mastery in feeding on the night's riches.
By barrel-rolling over and over...
they target the greatest concentrations of plankton...
which they then devour.
We now know that manta rays possess the largest brains of any fish.
But how they navigate huge distances to find food
in the vastness of the dark ocean remains a mystery.
It's one of many secrets still to be discovered...
in our seas at night.
To capture the nighttime dramas of coral reefs,
the Earth at Night team filmed in some of the world's most pristine tropical waters.
For cameraman David Reichert,
the biggest challenge was filming the reef's predators hunting at night.
Sharks and other predators can be more active at night...
but can also be very hard to approach safely.
[man] Filming at night is a whole new world.
We just don't know what's gonna come out of the dark.
We'll find out. We're about to jump in.
[Tom Hiddleston] David had to plan his dives around the full moon,
when strong currents wash food into the reef...
and can make the predators more active.
But it creates a big problem.
Surface to divers, surface to divers. How is the current?
-[static] -Not good. The current is too strong.
[Reichert] We're boarding. Coming up.
Current is ripping down there right now,
making it almost impossible to stay put.
Well, that was terrible.
Yeah...
[Reichert] There's more action, more things to film,
more life when the currents are up...
[male diver] Still too strong.
[Reichert] But we are struggling just to be there.
That's kinda the game we're playing.
[Tom Hiddleston] Over the coming nights, as the full moon wanes, the currents ease.
But although it makes diving easier, the reefs are empty.
[male diver] Yeah.
Yeah, current kinda died, and then, uh, I guess that was--
Yeah, everybody just went home.
-Yeah. -Yeah.
[Tom Hiddleston] As the team searched for the right conditions...
they discover they have to hit a tiny window...
when the water slackens between currents.
[Reichert] It's tough to film like that,
because it can be maybe 6:00 p.m. right when the sun sets,
but then as soon as we miss that window, suddenly it's 4:00 a.m.
So we get in these terrible schedules
where we having to, like, wait all night for a 40-minute dive.
[yawns] Gimme a cup of tea.
[exhales deeply]
[Tom Hiddleston] With perseverance and many sleepless nights...
David and the team finally begin to capture
the new behaviors they've been searching for.
[Reichert] I've never seen these cornet fish attack like that before.
You don't win 'em all, but I think we won that one.
[Tom Hiddleston] Each predator had their own way of stalking their prey.
Moray eels were venturing into the reef to hunt.
[Reichert] The moray was, like, working the top of the reef.
And there was, like, a little hole that it kinda went down through.
Sure enough, there was a little fish down there,
and the moray came down there.
Well, there it is.
And then, boom.
[whooshes]
Got it! Right in front of the camera. Right in the hole too. That was good.
There's a lot going on on these reefs.
You start to see this really vibrant community down there
that seems to just come alive at night.
[Tom Hiddleston] The crew had managed to capture unique new insights
into this magical underwater world.