Original subtitles

Off Africa's east coast, a small fish searches for a home

along a coral reef. He's a model toby, and in order to find

a mate, he needs to claim a territory.

This turf is already taken.

Luckily for the Toby, he lives in a shallow

water paradise, where reef space is abundant.

His home is on the eastern border of the Bazaruto archipelago.

This series of five islands lies 15

kilometers off the east coast of Mozambique.

The islands are the centerpieces of a marine protected area

and national park that covers some 1,400 square kilometers.

The islands were formed during rising sea levels

between five and seven thousand years ago.

Today, sun-soaked shallows surround them on all sides.

To the east lie underwater walls of fossilized sand,

remnants of an ancient coastline. These rocky barriers

enclose coral gardens, living metropolises feeding on sunlight.

To the islands west, extensive sand flats form

perfect habitats for broad beds of seagrass.

Where the shallows meet the shore, mangrove forests

form a bridge between two worlds, the wet and the dry.

As the rising tide floods this shallow realm, it

feeds and shapes this diverse array of living spaces.

Life here harnesses the natural elements of this dynamic environment,

reflecting the sun's light in displays of brilliant color

and feeding off the nutrient-rich water in the flowing

current. With a variety of strategies and adaptations, the

many creatures fill every niche in the light-bathe shallows

of Bazaruto.

To the east of the Bazaruto archipelago lie coral reefs

growing as deep as 20 meters below the surface. Even at

these depths, the clear water allows sunlight to reach the

coral. These are the outer limits of the coral's range, as a

little further east the seabed drops off into the depths of the Indian Ocean.

Large fish move slowly along the low, widespread reefs, feeding as they go.

A white-barred rubberlip eats mainly small

invertebrates it sifts from sand between the coral.

An ember parrotfish scrapes algae from the reef with its beak-like mouth.

These sizable fish live mostly without companions of their

own species, and they aren't the only lonely characters in

the Bazaruto archipelago. The Bazaruto archipelago

is one of the most beautiful waters in the depths.

A honeycomb moray spends its life alone in its cave.

Its hidden body is up to two meters of pure muscle.

Concealed in the rocks, it launches ambushes on unsuspecting prey.

But not all down here live alone in the shadows.

A raised section of reef is the site of colorful commotion.

Among the largest here are penciled surgeonfish, gathering to graze on algae.

Alongside, sea goldies congregate in shoals to feed on zooplankton in the water.

This larger male lives and mates with his harem of more brightly colored females.

When he dies, the dominant female will take his place.

Incredibly, in just a few days, he will be able to take

his place. After two weeks, her ovaries will transform into

testes, and her color will change to the male coloration.

But when it comes to changing color, one fish outdoes all the rest.

An emperor angelfish feeds on algae and invertebrates from the rocks.

His striking stripes make him among the most beautiful of all fish.

But believe it or not, he's become less flashy with age.

A juvenile emperor swims surreptitiously through the coral.

Its colors will begin to change when it reaches around 14 centimeters.

What it loses in colorful contrast, it'll gain in confidence.

The adult has no problem being seen. This patch of reef is

his. And should other adult emperors trespass, they risk an

aggressive attack.

With markings that signal it poses no threat, the

juvenile can swim here without fearing the adult.

All this color can only be appreciated thanks to the sunlight reaching the reef.

Almost all corals rely on their relationship with

photosynthesizing algae to grow. At 20 meters down, corals

employ two very different strategies for absorbing as much light as possible.

Some, like these plate corals, grow outwards in

massive disks, maximizing their surface area.

This whip coral has a far more direct approach.

Instead of spreading itself out and waiting for the light to

come to it, it grows towards the light in single cords that

can reach more than three meters long.

This green tree coral is misleading in its appearance.

Despite its layer of dark green fleshy

tissue, it lacks any photosynthesizing algae.

It gets its green color from its own pigments.

This coral thrives in deep water, especially in areas with

strong currents. And there's no shortage of those here. The

Mozambique current flows rapidly south along Bazaruto's eastern edge.

On the brink of the deep ocean, this reef is also exposed

to the full force of sea swells. Though tropical storms can

break even the most robust coral plates, remarkably

they can weld themselves back onto the reef over time.

In the shallower water not far away, a

sandstone wall rises all the way to the surface.

This wall marks the point where the island's shore lay,

some thousands of years ago when sea levels were lower.

Known as beach rock, the sandstone was gradually cemented

when fresh water percolating through the sand deposited

minerals where it met the sea.

The wall now forms a divide between two very different,

shallow worlds. One barren and turbulent, exposed to the

deep ocean, the other calm and packed with life, protected

by the divide. In the sandstone reefs on the more turbulent

side of the wall, the water may seem calm, but looks can be seen. It can be deceiving.

Little coral lives here.

The Mozambique current surges at up to two metres per second

down this coast, carrying large amounts of sand with it.

The regular disturbance and inundation with sand means

little coral can grow and reef fish are few and far between.

But there is life here nonetheless.

Little nooks and crannies define this world.

A predatory trumpetfish has evolved a streamlined

body to penetrate the crevices as it hunts.

While some are long and slender, the others are not. Others are short and stout.

The boxfishes.

These are some of the few vertebrates to grow a complete carapace of bone.

There's more to this rigid suit of armour than meets the eye.

Its special shape reduces drag as the boxfish swims through the water.

It also plays a crucial role in increasing the boxfish's manoeuvrability.

The flow of water around the hard carapace constantly

destabilises the boxfish, pushing it in different

directions.

It maintains a course by steadily working its pectoral fins.

But when it needs to turn, it lets the flow of water take over, turning it on the spot.

In this way, boxfish have evolved especially

for a life navigating the tight spaces.

At the base of the turbulent realm's barren rocks lie

deep deposits of sand carried by the strong currents.

These provide cover for inhabitants that

couldn't be more different from the boxfish.

Stingrays have broad, flat bodies, evolved for gliding

ever so slowly. They swim effortlessly through the water.

They find their food in the sand and have a sting for

protection, so they have no need for quick manoeuvres

through tight spaces.

They may not be reef residents, but these visitors

will readily take advantage of the services on offer.

Blue streak cleaner wrasse are known as the doctors of the reef.

They make their living by feeding on parasites

from the skin of other, larger creatures.

The stingray enjoys a good clean in the comfort of the sand.

The cleaner wrasse are some of the few permanent residents of the sandstone reef.

But visitors come from far and wide, looking for an easy meal.

On the protected inland side of the wall, a very different world exists.

As waves come crashing in, they break

against the wall and their energy dissipates.

The resulting calm zone is an epicentre of life that

offers shelter and food to a plethora of species.

At just three metres below the surface, the reef is bathed in sun.

Staghorn coral dominates here.

These fast-growing dense labyrinths form perfect cover for small fish.

In the bright light of the shallows, these reefs are

even more colourful than their deeper counterparts.

Within the large schools of surgeonfish, one species is drab, another dazzling blue.

These herbivores play an important role in controlling algae on the reef.

Alongside them, threadfin butterflyfish add yellows and whites to the dreamy scene.

Perhaps the most eye-catching here are the psychedelic gold bar wrasses.

Only sexually mature males sport the gold streaks that give them their names.

It's not just fish and coral that live here.

Among the most impressive creatures on the reef are these.

Magnificent anemones.

Growing to 80 centimetres in diameter, these are

the world's second largest species of anemone.

Not to be outdone by the fish, they can

close to reveal bright colours of their own.

Their long tentacles have stinging cells that pack a

powerful punch. But there are some fish that are immune to

the stings.

Nose-stripe anemonefish have a layer of protective mucus covering their bodies.

Their small families include a dominant female,

her male mate, and a handful of juveniles.

When the female dies, the male dies. The male will change

sex to take her place. The biggest juvenile will then

develop into the mature male.

In this remarkable way, there are always fish to fill each

reproductive role in each anemone. Between the long stinging

tentacles, the anemonefish find safety from the reef's predators.

But some of the most vulnerable creatures here

have evolved chemical defences of their own.

They don't come more seemingly vulnerable than nudibranchs.

These shellless sea slugs extract noxious chemicals from their diet of sea sponges.

They then store these chemicals in their organs,

giving them a disgusting taste to discourage predators.

Their bright colours are a warning to stay away. In

the shallows, beauty and danger often go hand in hand.

Delicate underwater roses decorate the reef.

They're coiled ribbons of nudibranch eggs, and they

carry a toxic deterrent just like their parents.

Nearby, the model toby is still searching for a territory on the reef.

Like the nudibranchs, he has what's known as aposematic

colouring. His vivid black and yellow body warns predators

of deadly toxins in his skin. It's the natural world's

equivalent of a biohazard sign, and it means he can wander

the reef at ease.

Eventually, he finds some caves that'll serve well as a home base.

Here, he has cover from a gentle current reaching the reef.

Not far away, the water flows a whole lot quicker.

There are places where the ocean's force breaches the wall,

pushing water through large gaps and flooding the shallows with nutrients.

Where the flow is strongest, it has formed a giant basin known as the fishbowl.

No reefs grow here, leaving a huge hollow some

14 metres deep that's mainly covered in sand.

But at its centre, a different environment thrives.

A field of daisy coral, hundreds of metres wide, sways in the current.

It feeds on plankton that it catches in its tentacle-like polyps.

It may look like soft coral, but this is actually the only

hard coral that extends its polyps permanently during the

day, giving it its other name, diurnal coral.

It's not just those growing on the bottom that feed on the current.

A school of devil rays glides through the water.

They get their name from the horn-like fins projecting in front of their mouths.

But far from instruments of evil, these fins

help the rays guide plankton into their mouths.

The rich, rapidly flowing water above the fishbowl

provides enough food for a multitude of animals.

As the rays pass through, they soar above a

far more sedentary set of fishbowl inhabitants.

Spotted garden eels live their lives in burrows that they

dig in the sand. Once nestled inside, they secrete mucus

from their skin to cement the burrow walls. From this

safe haven, they emerge to pluck plankton from the passing

current.

Above them, a much larger visitor is also cashing in.

It's a whale shark, the biggest of all fish. Like the coral,

rays, and eels, it's here to feed on plankton in the rich

water in undisturbed waters.

The whale shark is just visiting the shallows to

eat its fill before returning to the deep ocean.

For many, the fishbowl is a more permanent source of food.

Pufferfish swim slowly through the water. They forage

on algae and invertebrates from beneath the coral.

Their grumpy scowls give them the appearance

of the least friendly fish in the shallows.

But this title belongs to a far bigger brute.

Though finding him at all is a challenge.

Lying motionless in the corals, a Malabar rock

cod waits for unsuspecting fish and crustaceans.

Ambush is the best tactic for such a cumbersome swimmer.

This huge fish is a meter and a half long. His military-like

camouflage is perfect for the coral environment.

He's a successful hunter here.

There's an unwelcome rock cod in his territory.

It doesn't take much for the senior fish to banish the

intruder. The smaller specimen will have to look elsewhere

for a suitable ambush site.

At the reef wall, on the edge of the fishbowl, another

ambush predator plies its trade. The long-head flathead is a

true master of disguise. It can disappear in plain

sight and makes the Malabar rock cod look like a novice.

As the bully of the seabed approaches, the flathead keeps faith in its own disguise.

To the very end.

But one bite is enough for it to get the message. It's not welcome here either.

In the light-bathe shallows, visual

deception is an important means of survival.

Camouflage isn't its only form.

A pair of model tobies swims calmly above the diurnal coral.

With their aposematic coloration, they need not fear attack

from the likes of the rock cod.

Not far away, another fish looks just like the tobies. But he's a fraud.

He's a black-saddle mimic, a non-poisonous species that's

evolved to look just like the tobies for its safety.

While some mimic for defense, others do so with more sinister intentions.

And what better fish to imitate than everybody's favorite

cleaner? Mimic blennies look exactly like the blue streak

cleaner ass.

This allows them to swim right up to bigger fish,

which are in for a nasty surprise.

The blennies have a pair of huge canines in their lower

jaws that they use to bite chunks of flesh from their

unsuspecting victims.

As the tide rises, water flows through deep channels and

across the broad sand flats on the western side of the

archipelago's islands.

Here, the water sweeps over beds of seagrass

that cover some 88 square kilometers.

Remarkably, these completely submerged plants evolved from

terrestrial ancestors and reproduce via water-pollinated

flowers. Their pollen sticks together in long rope-like

masses that can be carried by the current from one plant to

another.

The seagrasses are crucial to the nearby reefs. Their roots

stabilize the sand, preventing it from being swept up in the

current. This keeps the water clear so sunlight can get

through, powering life on the reef. These eerie beds are

home to a remarkable diversity of life of their own.

Some are familiar, like rays, and young fish sheltering in the grass.

Among the recognizable live other, more curious life forms.

As the current flows through the seagrass, a pipefish drifts

along with it.

His slender build offers fantastic camouflage amongst the stalks.

This male carries a clutch of eggs embedded in the skin on his belly.

His mate deposited them, and he will carry them until they're ready to hatch.

As the current continues to flow, it carries food into

trawlers. These are traps laid by other strange and

beautiful creatures. A sea pen is a type of coral that

spreads a sail to filter the water for plankton. Feather

dusted tube worms have a similar strategy. A red-knob

starfish adds a splash of color to the environment. It moves

in super slow motion across the sand in search of sponges to eat.

Possibly the weirdest of all are the sea cucumbers.

Some look like giant caterpillars. Others bear more

resemblance to the vegetables they're named after.

Despite their name, these are in fact animals, relatives

of starfish and sea urchins. They're the recyclers of this

underwater realm. They feed on waste from the seabed and

plankton from the water. They then break their food down

into smaller particles, recycling them into the system much

like earthworms do on land. When attacked, some will eject a

long sticky mass of toxic threads to entangle the predator.

Others have a less messy way of dealing with threats. They employ help.

This diagonal bar goby lives in an underground burrow.

But he didn't dig it himself.

He is a lodger in the home of a male and female pistol

shrimp. These shrimp are famous for their ability to stun

prey with a powerful burst of sound from their snapping

pincers. But they're completely blind, which makes them

vulnerable.

That's where the goby comes in. He keeps watch

as the shrimps come out to do burrow maintenance.

With their long antennae, the shrimps keep constant contact with the goby.

And when he gives the signal, everyone disappears in a

flash. In return for keeping watch, the shrimp share their

safe tunnel with the goby.

As the tide rises, the water continues to inundate the sandy beds.

Eventually, it reaches the shallowest environment of all.

Like the seagrass, these mangrove trees are adapted to survive in salt water.

When the tide retreats, the roots are exposed. But

when it rises, they create an underwater forest.

The roots offer crucial cover to the water. They attract

to young reef fish, contributing to the health of the reef

ecosystem, just as the seagrass beds do.

Bunches of oysters cling to the branches. During low

tide, they seal their shells tight to avoid dehydrating.

But now, they can filter food from the water once again.

A hermit crab climbs across the branches, looking for

something to eat. As he grows, he'll need to find a larger shell.

Luckily, the sandy bed is littered with potential new homes.

As the tide comes in, schools of fish take to the shallows.

Above the surface, many water birds eagerly anticipate the opportunity to go fishing.

But the fish have many places to hide.

They congregate in huge numbers among the pillars beneath a man-made jetty.

Beneath them, flamboyant characters gather.

A lionfish's flag-like spines may be beautiful, but they

inject a lot of water into the water. They also inject

poison that inflicts terrible pain on any attackers.

Brightly colored boxfish can also pack a powerful punch.

Even the smallest baby can feed on algae without fear of attack.

Cute as it might seem, it has one of the more aggressive means of defense.

Most poisonous creatures here only release

toxins when an attacker makes physical contact.

Boxes have the ability to actively release their toxins

whenever they want. These toxins disperse quickly through

the water and are incredibly potent.

They burst red blood cells around the attackers'

gills, effectively suffocating and killing them.

This chemical defense makes a seemingly innocuous little

fish one of the most deadly creatures in its tropical home.

The huge numbers of moonies gathering under the pier owe

their abundance to the success of Bazaruto's protection.

As the tide recedes again, the flow of water will

reverse, leaving the jetty and mangroves dry once more.

But for most of Bazaruto's inhabitants, these rhythms pass unnoticed.

Their homes will remain submerged, soaked in salt water and tropical sun.

Whether they've evolved to stand out or blend in, these

creatures make the most of the many niches available in this

varied and wonderful underwater world.