Planet Earth is so spectacular,
it's easy to miss the smaller things in life.
But take a closer look...
and there's a whole undiscovered world.
A world where tiny heroes...
and little monsters...
need incredible superpowers...
to help them triumph against giant odds.
Coral reefs are some of the most diverse places on the planet.
Home to massive shoals and magnificent creatures.
But beneath them...
is a miniature metropolis...
bustling with extraordinary little lives.
These animals may be small...
but the work they do is essential.
And right now, they're busier than ever.
Once a year, the reef stages a spectacular breeding event...
vital to securing its future.
But it's not easy being a small fish on a big reef.
Tiny animals must overcome huge challenges to keep their coral city alive.
The coral reef is as complex and crowded as any city.
Each day starts busy and noisy.
All the citizens calling to each other in a rousing underwater dawn chorus...
of popping muscles...
snapping claws...
and chattering teeth.
Only a healthy reef with a thriving community of tiny creatures
sings this loud.
Half the fish here are barely bigger than a bottle cap.
But their services are in high demand.
A turtle checks into the cleaning station...
for a little shell shine.
It's a job too big for a tiny blenny to manage alone.
So a crew of algae-removal specialists help polish it off.
A clown fish family is busy tending their anemone home.
Few predators dare enter its stinging tentacles.
But clown fish have a protective shield of mucus
that allows them to live here permanently.
In return, they keep the anemone clean and oxygenated.
Hidden underneath, the male has 500 eggs to look after.
Each smaller than a grain of rice.
If they hatch on the same night the reef breeds,
it will give them the best chance of survival.
Until then, they should be safe.
This is one of the most secure homes on the reef.
And the family never stray far.
Out here, there's always a bigger fish.
The leopard coral grouper.
Little damselfish take cover in the maze of coral...
beyond the grouper's reach.
But this smart fish doesn't give up.
He just calls in...
more arms.
An octopus may seem an unlikely accomplice.
But together, they make a killer team.
When the grouper changes its colors to camouflage...
the hunt is on.
It's double trouble for damselfish.
The grouper locates their hiding place.
Then turns pale to point it out.
Tentacles descend.
Fish panic.
Straight into the grouper's jaws.
It's a terrible choice.
Stay put, and risk the octopus's deadly reach.
Or flee...
and get picked off by the grouper.
With no safe escape...
sometimes the only option is to fight back.
The damselfish mob the octopus...
and try to drive it away.
But the commotion attracts even bigger fish.
It's a chance for the little fish to make their escape.
With sharks circling...
suddenly, it's everyone for themselves.
So much for teamwork.
Large sharks don't bother with small fry.
But by scaring off other predators, they help tiny animals get back to work.
Grazers keep the reef free of algae.
Allowing slow-growing coral to thrive.
Coral is actually made up of colonies of tiny animals.
And each one contains microscopic plant cells that convert light into food.
An amazing alliance on which the whole reef is built.
Together, billions of little lives...
create the largest living structures on Earth.
But these coral cities are fragile.
Vulnerable to warming seas...
pollution...
overfishing...
and invasion.
Crawling on hundreds of tubed feet.
Armed with venomous spines.
A monstrous...
coral-eating...
crown-of-thorns starfish.
It can devour hundreds of corals each year.
And there's not just one.
There's a whole army of them...
decimating the homes of all the tiny creatures.
But unaware of the threat heading their way...
the residents of the reef are busy, preparing to breed.
And searching for food.
The most complex eyes in the animal kingdom.
With four times as many color receptors as a human's...
the peacock mantis shrimp sees the world in a completely different light.
She's no bigger than a tube of toothpaste, but far from defenseless.
She packs a punch that rivals the acceleration of a 9-millimeter bullet.
So fast, it vaporizes water.
And can even create a flash of light.
But even well-armed mantis shrimp need a safe place.
Her burrow, and soon to be her nursery.
Once renovations are complete.
She already has a male visitor...
looking for a mate.
Or to steal her home.
Either way...
her lightning fists will make it very clear...
she's not ready for guests.
But this is a dangerous place to be caught out in the open.
A voracious predator.
The size of a...
teacup.
A dwarf cuttlefish.
If this one is to reach breeding condition, he needs to get bigger.
And that means a lot of eating.
But he's a soft target himself.
So the trick is to hunt without being hunted.
This master of disguise can change the color and texture of his skin...
to outwit predators...
and prey.
He'll live less than a year, so he needs to grow fast...
eating pretty much anything that moves.
Waving its arms to catch a meal of plankton...
a button-sized boxer crab seems oblivious to the threat.
A painful mistake.
This crab holds miniature stinging anemones in its claws.
Tiny Tasers to fend off predators.
They're so effective,
rivals will do anything to get hold of them.
It's a remarkably delicate struggle.
Neither crab wants to damage the anemones.
With his opponent in a lock, the rival carefully extracts his prize.
Now they have one each,
both crabs will split them to regrow a full pair of stinging gloves.
Anemones offer protection to all kinds of little creatures.
Tiny see-through anemone shrimp.
Cohabiting with the clown fish.
They may only be the size of a paper clip...
but they are brave enough to do business with the big fish on the reef.
The shrimp advertise their services by rocking.
And if the customer is a predator...
they make sure their sales pitch is absolutely clear...
by clapping.
Once she's sure it's safe,
one little shrimp gets to work.
Exfoliating dead skin...
picking off parasites...
and cleaning the gills.
She even braves the jaws for a little dental hygiene.
Health services provided by tiny cleaners
are essential for keeping big fish in top condition.
All over the reef preparations for mating are underway.
The mantis shrimp is almost done building her nursery.
She's lifted a massive 3 kilos of debris to make it secure.
And cleared her emergency exits, so she can keep her enemies guessing.
Her building work is so extensive, others find a home here too.
But she has one neighbor who's more of a problem.
A tuskfish.
One of the few fish known to use tools.
It even has its own anvil for cracking clams.
He's unlikely to eat a mantis shrimp.
But his smash-and-grab approach to feeding could wreck her home.
He shifts huge piles of rubble looking for food.
He's got what he wanted.
But now her nursery construction is way behind schedule.
As the day draws to a close, the reef is getting busier.
The clown fish eggs are close to hatching.
And a fleet of cleaner wrasse are hard at work.
Only the length of a finger,
they're easily identified by their black and blue stripes.
But not all are quite as well-intentioned as they appear.
A fangblenny.
This impostor changes his colors to mimic cleaner wrasse
and slips among them unnoticed.
But he's not here to clean.
Raking his fangs across the skin of the unsuspecting fish...
he steals a meal of scales.
And before his victims know what hit them...
this devious trickster disappears...
back to his lair.
Operating undercover helps many little animals survive on a big reef.
It's how the dwarf cuttlefish has managed to stay alive...
and stay fed.
With each hunting success, he grows bigger.
This female seems impressed.
And for once, food isn't his first priority.
The mantis shrimp has been getting her home back in order.
Clearing out clutter.
Making sure everything's in place.
And adding the finishing touches.
Finally, she's ready to receive a guest.
Just as the reef is set for the most important event of the year,
the coral killers arrive.
Hordes of crown-of-thorns starfish.
Extruding their stomachs, they digest the coral's living tissue.
And leave only the white skeletons behind.
There seems to be little the reef residents can do
to stop the swarm of starfish from devouring every coral in their path.
The home of this tiny crab is next on the menu.
No matter how hard she tries...
the starfish's body is almost impenetrable.
But the soft sensitive base of its spines...
is the chink in its armor.
Time for one little crab...
to take down a monster.
Contending with guard crabs just isn't worth the pain.
A diverse community of tiny creatures...
all playing their part...
keeps coral reefs healthy and far more resilient to the many threats they face.
Even damaged areas of these living cities can regenerate.
Once a year
the perfect tide and the perfect temperature coincide.
Tonight is the night...
when the reef itself begins to breed.
A tiny bundle, only the size of a peppercorn.
All the ingredients to make baby corals in one package.
The coral is spawning.
Many other little reef animals are breeding too.
The dwarf cuttlefish has secured his mate.
Now it's time for her to tuck their eggs safely into the coral.
The mantis shrimp also has eggs.
Twenty thousand of them.
And after one more cleaning from Dad...
hundreds of clown fish larvae are cast adrift.
Spawning together ensures as many new lives as possible...
are carried safely away on the tide.
Soon, small wonders are growing.
No bigger than a peanut,
a cuttlefish hatchling is just beginning its ocean adventure.
And perhaps most important of all, a one-millimeter coral planula.
Drawn toward the sound of the reef...
a tiny brick that will grow into a mighty coral.
And help build a future for all the residents of this coral city.