Arabian Seas (2017–…): Season 1, Episode 4 - Defenders of the Reef - full transcript

In the Gulf of Oman, survival is all about defense. Some species of sea urchins and sea slugs rely on toxins to keep predators at bay, while guitarfish use their size and armored bodies to stay off the menu.

The coral reefs of Arabia are
teeming with large predators.

Small residents
need strong defensive
strategies to survive.

Some are equipped with
body armor...

..or chemical weaponry.

Neighbors help neighbors
in times of need.

And often attack can be
the best line of defense.

These are the
defenders of the reef.

(Birds call and hoot)

It's summer
in the Gulf of Oman.

The scorching hot Arabian
sun heats the shallow waters

to around 86 degrees.

The warmth boosts
the growth of algae

across a vast coral reef...

..attracting thousands of
hungry herbivores.

It is the setting of a
fish-versus-fish turf war.

Many of these competing fish
are spectacular,

sporting bright colors
and bold designs.

But not so the humble
domino fish,

silver-gray, with a white
spot on either side.

With his drab appearance,

this male is easy
to overlook.

But what he lacks in color
and size...

..he makes up for
in attitude.

This little guy
will stand up

to any of the big bullies
on the reef.

Even a parrotfish
many times his own size.

He'll need his confidence
in the coming weeks,

because this little fish
is on a mission.

He's about to breed
for the first time.

Step one: he needs to
establish his territory

and lay claim to a small
patch of algae

to cultivate
and call his own.

This is not a food store.

It's a giant advertisement,
like a billboard,

that says
to female domino fish

"eligible bachelor
in residence".

A large, well-maintained
algal lawn will demonstrate

his abilities to protect
and nurture a nursery,

something the females
will find irresistible.

But on his first attempt
at selecting real estate,

he makes a rookie error.

His new territory
is too exposed.

Large numbers of hungry

including other domino fish,

can decimate
new green growth.

Non-breeding dominos are
darker in color.

Despite his best defensive

the lighter-colored male is

The hungry domino fish
strip his new lawn clean.

The setback means
he has to start again,

find a safer spot
to defend

away from the hungry masses.

He sets off in search of
somewhere new.

The reef is part of a marine
paradise lying nine miles

off the coast of Arabia

called the Damaniyat Islands.

The archipelago consists
of nine main islands

and a string of rocky
outcrops in the Gulf of Oman.

The bare, jagged cliffs are
in stark contrast

to the treasures
that lie beneath.

The area lies at the heart

of one of the world's
five largest upwellings.

Here, cold nutrient waters
well up in the Arabian Sea,

triggering plankton blooms

that fuel
the region's productivity.

exceptionally diverse

and promote
dramatic coral growth.

A coral reef is like
an underwater fortress,

providing protection,
food and family homes

to a stunning array
of marine creatures.

It is also an underwater

of predators and prey...

..of attack and defense,

as each plays
its critical part

in protecting the delicate
balance of life.

This is not a safe place
for little fish.

The fusilier has been
bitten by a predator.

The nasty wound's a reminder

of the many dangers
of the reef.

The odds seem stacked
against the domino fish.

A number of large, deadly
hunters patrol.

At just over a foot long,
the yellowfin hind
hunts fish.

Active by day,
this ambush predator

sneaks around the gullies
and escarpments.

Skirting the fringes
of the reef,

a huge bowmouth guitarfish

patrols the exposed areas
of the vast seabed.

Guitarfish can reach
up to nine feet

and his size provides
some defense

against most larger
predators like sharks.

He looks like a cross
between a shark and a ray

and is actually
a type of skate.

Like his relatives,

he can detect even the
faintest electrical signal

from prey
buried in the sand.

His back has built-in
body armor, scaly thorns

to dissuade anything larger
from biting him.

He's not alone
in having bio-armor.

On this dangerous reef,

many species have physical
defenses to keep them safe.

Trunkfish have only a few
large scales

fused together to form
a solid box-like body.

This armament makes them

for other fish to swallow.

Some go further, secreting
toxic mucous,

making them
quite unpalatable.

Their body shape limits
their movements,

leaving just a hinge-like
joint in the tail

to help them get around.

But despite appearances,

they're streamlined
and good at cornering.

Porcupinefish, too, are
a tough act to swallow.

If threatened, they can fill
their bodies with seawater,

making themselves
three times bigger

and erecting sharp spines
that lie flat on their skin.

It's also poisonous.

As it consumes shellfish,
it recycles their toxins

and secretes them
from its skin.

This gives off a scent
warning to predators

not to eat it.

Not all species
have built-in defenses.

Some must find other ways
to protect themselves.

A tiger pistol shrimp hides
within a burrow,

using his broad,
stout pincers

as shovels to excavate.

He's an excellent digger,
but has very poor eyesight.

While he's at work,

he could easily miss
an approaching predator.

So, to help him, he enlists
a goby as lookout.

This triple-spot goby is
also low on the food chain

and needs refuge.

Unlike the shrimp, it has
excellent eyesight

and it can dash away
at a moment's notice.

But it lacks the digging
skills to make a safe home.

So the two join forces.

While the shrimp
plows away,

it always keeps
one of its long antennae

in contact with
its watch-dog.

An important defense,

for there's predators lurking
in every nook and cranny.

This huge honeycomb moray eel

can reach six feet long.

He's a master of camouflage,
thanks to his mottled skin

that resembles the
surrounding coral.

He rarely leaves his sentry
post during the day,

but, under the cover of

he stalks the smaller fish
as they sleep.

In addition to the fish,

he'd pounce on an unwary
crustacean given the chance.

Luckily, pistol shrimps have
goby lookouts.

This co-operative behavior
is known as "mutualism".

Both species benefit
from the relationship.

And predators go hungry.

Away from the prying eyes of
the moray eels,

the little domino fish has
found a new patch

on which to cultivate
his algae.

This time, he's chosen
a less-obvious spot,

closer to the sea floor,

under the protection
of a steep coral cliff.

This patch should be easier
to defend.

It will serve as a nest site
- if he can attract a female.

Females prefer a neat lawn.

It shows that the male
is fit and strong

and capable of defending
his patch.

His lawn is
coming on nicely.

By protecting the area
from grazers,

he's given the algae a chance
to take hold and flourish.

Now he's ready to start
his advertising campaign

and lure in
a potential mate.

His circular dance draws in
the first female.

But she doesn't stick around.

He's going to have to try
harder to impress.

He'll have to improve
his dance moves

and grow more algae
if he's to succeed.

The domino isn't
the only fish

to tend and defend
a garden.

His flashier neighbor,
a sohal surgeonfish,

is one of the most
territorial gardeners
on the reef.

Unlike the domino's
little lawn,

this algae isn't
for breeding.

It's for him to eat.

The surgeonfish's vast lawn
of algae

can stretch out over 40 feet.

It's a large area of food to
defend, but he's well-armed.

The surgeonfish gets his name

from the yellow,
scalpel-like blade

on either side of its tail.

The blades are usually tucked
into a groove in the skin

but, like a switch-blade,

they can be unleashed
to slash at trespassers.

Apart from occasionally

to sample his algal crop,

the surgeon is endlessly
on border patrol.

While he's very aggressive
to some species...

..he ignores others.

He needs to keep out
other algae-feeders,

especially the large
and numerous parrotfish,

with their powerful and
destructive parrot-like jaws.

The surgeonfish uses attack
to defend his territory,

from hungry fish,
but also from coral,

which could take up space,

where he'd rather be
growing algae.

The coral itself is made up
of tiny creatures.

They're colonizers,
always looking to expand.

Individually, they are
known as "polyps",

but they are never alone.

They live in vast colonies,

their own defensive strategy
against predator attack.

Some create hard
calcium-carbonate shells

to defend their soft bodies.

New generations
of these hard corals

build on top of the last,

creating vast structures that
can be over 3,000 feet high.

Black-spotted butterfly fish
feed mostly on coral.

Eye-catching Arabian

use their tiny, tweezer-like
jaws to gently nip out

the soft, living body parts
of the coral.

Butterflyfish are believed
to consume

around 6% of live corals
each year.

They play a key role
in the reef's size,

shape and distribution.

By clearing the coral,

they help the surgeonfish
increase his crop.

It's not just the fish
that threaten the coral.

Even the algae
can fight back.

Here in Oman's tropical
shallow waters,

photosynthesizing algae
reproduce rapidly.

They can slowly smother
the coral,

making it harder for the tiny
animals to filter food.

To fight back, corals have
their own protectors.

Large herbivores, like
parrotfish, constantly graze

on the algae,
cutting back the growth.

And on a smaller scale,

individual corals hire
their own mini army.

A host of little,
live-in bodyguards.

Tiny coral crabs
weed out the algae.

They look heavy-handed,

but can pluck the algae
with precision

and use their pincers

to pass it to
their grinding mouth parts.

They're assisted by
citron gobies,

so-called for their bright
yellow color.

The goby only eats small
amounts of algae,

preferring to nibble
on the coral itself.

But his occasional nip is
a small sacrifice,

as he guards the coral

from larger voracious

like the butterflyfish.

The goby, unlike most fish,
doesn't have any scales.

Just smooth skin,

from which he secretes
a slimy, toxic mucus.

He's only two inches long,

so relies on this chemical
defense for his own safety.

Like the domino fish,

the goby is ready to start
a family.

The coral branches provide
a safe haven and a nest site.

Both parents look identical.

They will be faithful
to each other for life

and will stay loyal
to this one patch of coral.

Other species of fish
come and go,

but only one alpha pair
of citrons

will breed on the coral.

Young animals have a queuing
system and wait in line.

They will only mature

if either of the alpha pair

When that happens, one of the
smaller, darker juveniles

will quickly develop
to take their place.

All the youngsters
are female,

but if the adult male
is lost,

the largest will undergo
a sex change to replace him.

This female has already laid
around 100 eggs,

tiny baubles of jelly,

almost invisible,

which hang under the arch
of coral in neat rows.

The male rolls upside down

to deposit sperm over
the eggs to fertilize them.

He will stand guard
over his microscopic family

and do his best to protect
them from hungry mouths.

Fish eggs are a favorite
food for many reef species.

The sneaky yellowfin hind
is a constant threat.

It will certainly vacuum up
the eggs,

if it can get to them.

Too big to take on,

the goby relies
on the coral's structure

to protect his eggs.

The citron goby
has chosen well.

The nest site is
just out of reach.

The hind doesn't stick

He heads on, arriving at
the domino's nest site.

But the male domino fish has
yet to impress a female

and gain some eggs.

He practices his best
defensive move

and scares off
the hungry hind.

The commotion attracts

A light gray female
investigates his lawn.

Her color indicates
she's also ready to breed.

Using a white ovipositor,
a mobile tube,

she precisely deposits
up to 20,000 eggs.

Each is sticky and will
adhere to the algal lawn.

He follows, releasing sperm
over the clutch.

The whole courtship and
laying lasts 20 minutes.

Then she saunters off,

leaving the male
to defend the eggs.

The female plays no further
role in raising their young.

Instead, she will visit

other males tending lawns
in the neighborhood.

The male has to stand guard
24 hours a day for a week,

until the eggs hatch.

It's a long time
for a little fish

on a big and dangerous reef,

where monstrous predators

The wide gape of a honeycomb
moray eel reveals a glimpse

of its powerful weaponry.

Its teeth are needle-sharp
and there are lots of them,

up to 38, with not two,

but four pairs of large
canines at the front.

A third row lines the roof
of its mouth.

It has a second set of jaws
in its throat,

which help drag any victim
in, crushing it as it goes.

If disturbed or challenged
in its den,

the eel can strike
with devastating effect.

Defense may be futile against
this monster of the reef.

Its jaws never rest.

Unlike other fish, it doesn't
have structured gill flaps

to pump water through,

so it must continuously
force water over its gills.

Many species of moray eel

also secrete a toxic mucous
on their skin

that has the ability
to destroy red blood cells.

It may be a defense against
their own predators.

Some species might also
transfer the toxins

with their serrated teeth
when they bite their prey.

It looks like this fish

is taking its life
in its own hands.

But it's a cleaner wrasse,

one of the few small fish
the moray won't eat.

The wrasse is
a defender of health,

a marine doctor and dentist

that gives the reef

a thorough check-up and eats
their pesky parasites.

Observations suggest that
a single cleaner wrasse

will tend to over 2,000 fish

and remove up to 1,200
parasites a day.

They're a vital part
of a healthy reef.

Beyond the defensive walls of
coral lies a no-man's land.

A vast open seabed
has little cover

for animals to escape danger.

This is where the big guys

Heavily-armored predators,
like the guitarfish.

Those who brave the open
need ingenious adaptations

to better their chances of

Kangaroo nudibranchs are
one of 3,000 known species

of colorful, shell-less
sea slugs.

The word "nudibranch"
means "naked gill"

and this one's
are on full display.

With an unprotected
soft body,

it should be very vulnerable
to predators.

But this sea slug

has a defensive trick
up its sleeve.

It mostly eats
toxic sponges.

It recycles the dangerous
parts of its dinner...

..storing the toxins
in a sheath over its gills.

This makes it repellent

to anything that might try
to eat it.

Its bright colors act
as a warning not to nibble.

Armed with these chemical

the sea slug is even able
to flirt out in the open.

This behavior is known
as "tailgating".

One slug follows the slime
trail of another

to make sure it doesn't lose
it on the vast seabed.

It's a rare sight

and is thought to be
a precursor to mating.

Long-spined sea urchins
appear equally unappetizing

with their intimidating

Moving on tiny,
suckered arms,

they patrol the open sea
floor grazing on algae.

It's been recently discovered
that their tiny legs

are also eyes, capable of
detecting light,

and guiding the urchins
across the reef.

As added protection, their
long spines are covered

in microscopic barbs
and toxic mucus.

Despite this heavy defense,
they're not immune to attack.

This foot-long
Picasso triggerfish,

for the bold abstract
markings on its face,

will eat just about anything.

Including sea urchins.

But it requires
some shooting practice.

With its big, strong jaws,

it can squirt a jet of water
that'll flip an urchin over,

enabling its powerful teeth
to break through

their more vulnerable

But it's not a done deal.

When caught in the open,

the urchins form big,
prickly herds...

..making it even harder
to reach their weak spot.

The urchins are a magnet
for some species

and for good reason.

Glass shrimps are delicate

They survive with help from
their prickly neighbors.

By using the urchin's
ten-inch spines as cover,

the shrimp hitchhike to
travel to areas of the reef

normally out of their reach.

Their very own
mobile safety cage.

The long, tubular snout
of a trumpetfish

is built to suck up
small creatures.

Glass shrimp make
a good snack.

But whilst they're protected
by the urchin,

the hungry trumpetfish stands
no chance of getting one.

The glass shrimp aren't
freeloaders, though.

As the shrimp forage around
the urchin,

they remove smaller parasites
that could attack their host.

Yellow-striped cardinalfish

also use the urchins
for defense.

These tiny nervous creatures

hide amongst the spines
during the day,

only venturing out to feed
under the cover of darkness.

The plucky male domino fish
has been guarding

his microscopic eggs
for three days.

So far, so good.

He's not let anyone
take them from under him.

But there's egg-thieving
trouble on the horizon.

A pack of hungry
crescent wrasse.

Across the reef,

his domino neighbor's eggs
are under attack.

Domino fish
are fierce fighters.

They can drive away
one or two attackers.

But the wrasse use
their numbers

to overwhelm the guards.

Once one family is

..the greedy gang moves on
to the next.

With each raid, they're
moving closer and closer

to the male and his eggs.

He's chosen a good spot
for the lawn,

low-down and out of sight.

But little escapes
the attention

of a hungry mob of wrasse.

The wrasse home in on the
male and his exposed family.

Suddenly, an unlikely hero

comes to
the male domino's aid.

A surgeonfish.

His size, weapons
and assertive defense

are enough to send
the wrasse packing.

The surgeonfish
isn't deliberately
helping the domino,

he just doesn't
want the trespassers

on his patch of reef.

The domino's lawn
is on the fringes

of the larger fish's

Far enough to be tolerated,

but close enough
to reap the benefits

of the security guard.

The surgeonfish sees off
the intruders

and the domino's eggs
survive the attack.

The male just needs
to protect them

for three more days.

The surgeonfish's large lawn

is close to the steep slopes
of the shore.

Twice a day, the changing
tide churns the water.

The movement
in the water column

often triggers
a movement of creatures.

Crabs make the most
of their ability

to move freely
between reef and shore.

When the low tide exposes
the rocks,

they tuck into the algae
and other food

that's now out of reach of
the solely aquatic species.

Below the waves, the churning
waters stir up nutrients,

attracting large shoals of
hungry fish.

Among them are foraging

They mostly eat algae

and will munch through
anything to get to it.

The parrotfish get their
name from their strong beak,

which enables them
to power through
whole chunks of coral.

Everything goes in.

The edible is processed and
whatever they can't digest

comes out the other end.

In such great numbers, this
attack looks destructive,

but parrotfish play a curious
role in defending the reef.

By clearing an area
like this,

parrotfish level
the playing field

and increase diversity
on the reef.

By removing
the dominating algae

and fast-growing corals,

they give slow-growing
species, like hard corals,

the chance to develop.

Beneficial or not,

they're still trespassing on
the surgeonfish's algal lawn.

He turns on his side,

flashing his yellow
fin markings

as a reminder
of his secret-blade weapons.

The surgeon keeps close tabs
on who's on his patch.

He's mostly solitary,

but does allow
female surgeonfish

to share parts of
his territory.

It's times like this when
roomies are a good idea.

They work together to clear
the hungry intruders.

But there are some grazers
that just won't budge.

The green turtles have
found his stash of algae

that's too good to miss.

And they won't be moved.

Try as he might,

the surgeonfish just can't
persuade them to leave.

(Waves roar and crash)

The fish are constantly

waging war
with their neighbors

and defending
their resources.

But one individual's efforts
have paid off.

Our fearless father's vigil
is at an end.

After a week on guard duty,
his eggs have hatched.

The tiny baby domino fish
drift out into the current.

There are too many dangers
on the reef itself

for the microscopic fry.

Their chances of survival
are increased

by floating amongst
the plankton

out in the vast tracts
of ocean.

After a few weeks,

they will smell their way
back to the reef.

But the male's parental
duties are done.

He makes one final sweep
of his lawn,

then swims off to re-join
the other domino fish...

..and the protection
of the shoal.

A multitude of fish
use this technique

of schooling over the reef
for defense.

When fish school, they seem
to turn with a sixth sense,

without bumping into
each other.

The fluidity of their

is mostly based on sight.

They watch their neighbors

and when their neighbors
move, they do, too.

Their ability to school
might also be helped

by the lateral line
along their sides.

This fluid-filled canal in
their skin detects vibrations

and changes in water

which might also help them
to space evenly

from one another.

Moving as one vast mass
makes it hard for a predator

to pick out an individual.

Hidden among the coral, the
moray eel watches and waits.

The sneaky yellowfin hind
waits with him.

Then they set out to hunt.


It's seldom-seen behavior,

combining the eel's ability
to squeeze into tight spaces

with the hind's
lightning-fast reactions.

For potential prey,
this is double trouble.

Anything trying to escape
the hind risks swimming

straight into the jaws
of the eel.

Anything flushed
from the reef by the eel

may get picked off
by the hind.

They could be competitors,

but teaming up creates
greater success for both.

Observations show
each performs better

with their partner
by their side.

This level
of co-operative hunting

two different species

is extremely rare.

With neighbors like this,

the pistol shrimp's going to
need his protective bunker...

..and the sharp eyes
of the goby.

Hidden among the coral
branches, a family reunites.

The goby's eggs hatched long
ago and the babies dispersed.

But now they've returned from
their time in the plankton

as fish fry by using
their sense of smell

to guide them
back to the coral.

The young citron gobies can
settle into their new homes.

While the gobies look for
sanctuary in the coral,

the baby domino fish also
return from the plankton

and seek protection among the
long spines of a sea urchin.

It's a perfect nursery.

The tiny juveniles live up
to their name,

looking like
little dominoes.

It will take several years

for them to be
sexually mature

and fade to the dull gray
color of the breeding adults.

As they get older, they will
become more aggressive
and territorial

and ready
to tend a lawn of their own.

Just like their father.

They will learn to keep
an eye out for predators,

like the moray eel,
the guitarfish...

..and the hungry gangs
of wrasse.

These hunters often
seem like the bad guys,

but they're vital

for keeping populations of
reef fish in check.

Creatures of the reef
walk a fine line

between success and failure,

using adaptations for attack
and defense.

Their relationships forge
cunning tricks

and powerful alliances.

Here, the brave
and hardworking thrive,

defending themselves,
their family

and even protecting the
health of the reef itself.