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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.