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In the north-east of the Indian Ocean,
spanning a latitude of 6 to 16 degrees north of the Equator,
lies the Andaman Sea.
For the people of Thailand and Burma, also known as Myanmar,
the two nations bordering the eastern edge of the Andaman,
the sea has always been an integral part of life and the economy.
The Andaman's warm waters support an enormity of marine life
and they are relied upon for food as well as transport.
Limestone formations such as those which make up the Phi Phi Islands
contrast with granite outcrops like the Similan Islands.
The warm, clear water and diversity of marine life
make the Andaman an attractive dive destination
and many divers visit each year to explore and enjoy the underwater world.
And seldom is the marine landscape as diverse as it is here.
Millions of years of decay have cut the limestone pinnacles of Burma's Mergui Archipelago
into a terrain of underwater canyons and caves.
Further south, the huge granite boulders of Thailand's Similan Islands
continue beneath the waterline,
creating dramatic caves and swim-throughs.
Much of the submerged rock has been colonized by soft corals
like this mushroom leather coral at Christmas Point
or stony corals like this field of staghorn coral at Koh Bon
or this Montipora coral at East of Eden.
Elsewhere magnificent anemones have taken over.
At shallow sites such as Richelieu Rock the ebb and flow of the tide
brings the oxygen necessary for turtle weed, a type of green algae, to flourish.
Dendronephthya soft corals adorn the valleys and slopes at Hin Muang, or "purple rock" in Thai.
Elsewhere pretty crinoids, or "feather stars",
take up prime positions for filtering plankton from the water.
A feeding strategy shared by giant sea fans,
whose sieve-like skeleton makes them highly efficient filter feeders.
Here between the rocks and coral lie leopard sharks.
These gentle creatures are quite the opposite of many people's impression of the fearsome shark.
Rather than sharp teeth, their mouths contain ridged plates.
Leopard sharks can be easily and safely approached
but if divers get too close they will finally make their departure.
Although "leopard shark" is the most commonly used name in the Andaman Sea,
globally, these sharks are more commonly known as "zebra sharks",
because the rarely seen juveniles have stripes, not spots.
Bearing many similarities to leopard sharks,
nurse sharks are also normally placid.
Like leopard sharks they don't have sharp teeth.
Nurse sharks should be treated with respect however.
They have been known to bite divers when provoked,
and if they bite they tend not to let go.
During the day, tawny nurse sharks are normally found sleeping under ledges,
often piled up in groups like here at Koh Bon Pinnacle.
Although nurse sharks generally feed at night,
here at the Burma Banks they are often on the prowl looking for food during the day time too.
They have 2 barbels above the mouth which help them probe for food.
When the shark senses prey such as small fishes or crustaceans
it uses a strong sucking action to draw the food into the mouth.
Bonds between nurse sharks appear to be closer than with many other shark species
and they are often seen swimming in couples.
At Thailand's Richelieu Rock, a whale shark makes a rare appearance.
This is no whale but rather the world's largest fish.
Whale sharks can grow up to 12 meters long,
although unconfirmed reports circulate of giants up to 18 meters long.
This female is about the average size of 8 meters.
There is little to match the awe inspired by an encounter with a whale shark,
and for many divers this is the pinnacle of their underwater experience.
Their 3000 tiny teeth are rarely used.
When feeding they hold their mouths open
and feed on plankton, fish eggs and small marine creatures.
Ridges down the whale shark's back are reminiscent of those on zebra sharks' backs
and like the zebra shark, the whale shark poses little danger to humans.
She has lost the top part of her tail,
perhaps due to an attack by a predatory shark when she was a youngster,
or possibly a collision with a boat's propeller.
The shark's fins act like rudders,
helping steer it gracefully through the water.
For a long time whale sharks were thought to be oviparous,
in other words hatching from eggs laid by the mother.
However since 1995,
females have been discovered containing hundreds of hatched pups,
proving that the young complete their development inside the mother's body before birth.
As is typical of large pelagic fishes, the back is darker than the belly.
This countershading helps it blend in with its environment,
and the abstract pattern of spots and stripes on the back enhances the camouflage from above.
Some whale sharks attract shoals of fish around the head,
such as these juvenile scad,
protecting themselves from predators which may be intimidated by the shark.
The shark itself does not prey on them,
and they are careful enough to cruise in front of its cavernous mouth,
without getting sucked in.
This much younger whale shark approached boats near Western Rocky Island
and stayed around for a long time.
Although it might be tempting to touch or even hitch a ride on a whale shark,
this practise is highly discouraged.
It may modify the shark's natural behavior, or even cause infection.
It can also be dangerous for the diver or snorkeler.
Despite their usual graceful and stately motion,
whale sharks can draw on great strength if they become agitated,
and should be respected like any wild animal.
Shark fin soup is seen as a delicacy and status symbol in many Asian markets.
A single whale shark fin can fetch tens of thousands of dollars in some Chinese restaurants,
and often a whale shark fin is not eaten
but just used to advertise the availability of shark fin or shark fin soup.
Whale sharks do not reach sexual maturity until they are 25 years old,
and pregnancies are few and far between,
so their survival is particularly at risk.
Unless this culture changes,
or legislation is introduced and enforced,
whale sharks, like many other sharks,
may soon disappear forever.
From the shadows, and shoals of cardinalfish
at Burma's Shark Cave,
a grey reef shark emerges.
This strong stocky shark feeds mainly at night,
but may sometimes be seen cruising during the day.
The canyon at Shark Cave provides an excellent viewing gallery.
Although grey reef sharks can sometimes show aggression in their behaviour,
this is extremely rare amongst those found in the Andaman.
A visit to the Burma Banks will sometimes yield an interesting encounter with silvertip sharks.
These juveniles are particularly curious of divers.
As adults they will grow larger than grey reef sharks,
up to 3 meters in fact,
but they will also withdraw slightly
and become more wary of close human contact.
Already these young silvertips display the streamlined body and attractive coloration
that make them a favorite amongst shark lovers.
One of the most common sharks to be found across the Andaman Sea
is the whitetip reef shark.
Because of similar coloration of the dorsal and tail fins,
the whitetip reef shark and silvertip shark are sometimes confused,
but the whitetip has a wedge-shaped head,
and it's cigar-shaped body is slimmer than the silvertip's.
Black Rock, on the western edge of the Mergui Archipelago,
is one of the area's best dive sites,
and whitetip reef sharks are commonly encountered during the descent.
The other main order of cartilaginous fishes to be found
around the Andaman's reefs is the rays,
and most common of these is the bluespotted stingray.
This stingray's coloration and common name
make it often confused with the more circular blue-spotted stingray
found in the Gulf of Thailand,
which belongs to a different genus.
The bluespotted stingray is found on sandy bottoms
at sites such as East of Eden in the Similans.
The neutral color of the larger Jenkins whipray
camouflages it well against the seabed.
This ray has a pair of sharp and venomous spines near the base of its tail,
and the name "whipray" comes from the ray's ability to whip it's long tail over fast
and administer a nasty sting to a predator at any part of its circumference.
The ray takes water in through its spiracle, a hole just behind the eye.
This water can be blown out through the mouth
to excavate food from the substrate.
Another large stingray common to the area is the blotched fantail ray.
This impressive species can grow nearly 2 meters in diameter
and is often one of the highlights of dives in the Andaman.
Blotched fantail rays are most impressive when they aggregate in shoals.
Occasionally they can be witnessed in large numbers.
I encountered this shoal of some 30 individuals at Black Rock.
They had possibly gathered to mate.
Another visitor to Black Rock and other deep-water sites is the spotted eagle ray.
In some parts of the world eagle rays stay together in schools.
In the Andaman Sea they are normally found alone.
Just behind the short dorsal fin they have up to 6 venomous tail spines
which can inflict serious damage on attackers.
Between its wing-like fins it has a solid, heavy body and a deep head.
The smoothtail mobula is a similar size to the eagle ray
but can only usually be seen by divers in the northern Andaman
at sites like Burma's Tower Rock,
although they are occasionally seen in Thailand
at sites such as Racha Noi.
The mobula is a member of a group termed "devil rays",
so named because of 2 protruding cephalic fins either side of it's mouth.
These fins help to direct plankton and small marine creatures
into the mouth for feeding.
The mobula is a highly social fish
and is often observed in large schools.
The mobula is an impressive sight
but shares our seas with a much larger devil ray:
the king of all rays, the giant manta ray.
Mantas are frequent visitors to sites such as Koh Bon.
Giant mantas can grow to a width of over 6 meters
and a weight of over 2 tonnes.
These pelagic fish are always on the move
and like mobulas, they feed by swimming open-mouthed
and using the 2 cephalic fins to direct water into the mouth.
The gills on its white underside contain rakers
which filter out plankton and small organisms.
The markings on the back and underside of mantas are highly variable
and are useful in distinguishing individuals.
Occasionally the cephalic fins are furled up into cylinders to improve streamlining.
Mantas are one of the most intelligent fish,
with the largest brain-to-body mass ratio of all elasmobranchs.
They often seem to enjoy interaction with humans.
A gentle approach by divers is often permitted,
and mantas will sometimes approach divers,
apparently out of curiosity.
Mantas only give birth to an average of two pups every two years,
and populations have long been in decline.
The gill rakers of mantas and mobulas are used in a Chinese medicine
that is thought to detoxify the blood.
There is no scientific evidence that it works.
Nevertheless the lucrative trade is on the increase.
In November 2011
the International Union for Conservation of Nature
declared giant manta rays as "vulnerable with an elevated risk of extinction".
Down on the reef, a fish trap has caught a handful of bony fishes
including a giant moray eel.
This is the largest of all morays.
Despite their fearsome appearance,
morays are not as dangerous to humans as they look,
although larger morays can attack if provoked
and have been known to bite divers when being fed.
The mouth contains sharp teeth for capturing and restraining prey.
Once captured, a second set of jaws in the throat
is launched forward to grab the prey
and pull it down the moray's gullet.
Anemone Reef is home to several specimens of yellow-edged moray.
Like many morays they feed on small reef fishes.
Khao Lak's Boonsung tin miner wreck
has a particular concentration of honeycomb morays.
This spotted moray at the Burma Banks is a close relative.
Whitemouth morays are not at all common in the Andaman.
This rare specimen was seen at Burma's Western Rocky Island.
Another Myanmar speciality is the barredfin moray.
When feeling threatened it adopts a very snake-like posture.
Facial injuries are quite common amongst morays,
and this palechin moray at High Rock bears the scars of past conflicts.
The cartoon-like features of the greyface moray
are much more common throughout the area
and these eels are often found in pairs or small groups.
This is a small and very energetic species
and when it attacks it moves quickly.
Greyface morays don't just live with each other;
they often share their home with other species.
In this case a fimbriated moray.
And here we find a fimbriated moray with a snowflake moray.
Whereas the previous species feed mainly on fishes,
the snowflake moray feeds on shelled molluscs and crustaceans,
so it's teeth are much more blunt.
It's not difficult to see how the zebra moray got its name.
This moray also feeds on crustaceans.
Of all the marine creatures found in the Andaman Sea,
possibly the tiger tail seahorse carries the most mystique.
The seahorse finds a suitable holdfast,
such as this black sun coral,
and anchors itself to it using its striped tail.
Here at Shark Cave a seahorse has become stuck to a worm sea cucumber.
The seahorse struggled for several minutes
before finally freeing itself from the sea cucumber's adhesive body.
Perhaps the most interesting fact about the seahorse
is that it is the male of the species that becomes pregnant.
The gestating fetuses are carried in a pouch on the seahorse's belly.
Typically, litters comprise 100 or more perfectly formed babies,
each just a few millimeters in length.
Seahorses are generally monogamous,
and it is not uncommon for the male to become pregnant
several times per year with the same female mate.
The bluespotted cornetfish, sometimes known as the "smooth flutemouth",
is seen hunting for small fishes here in the canyon at Shark Cave.
Its slim profile is both streamlined for high speed,
and minimizes the chances of it being seen as it approaches prey.
The long thin snout bears a resemblance to its seahorse cousins.
Staghorn coral is found in abundance on the east side of Racha Yai island,
and this hard coral is one of the favored habitats of the trumpetfish.
It's elongated body gives it a much larger turning circle than fellow reef fishes.
Amongst coral the trumpetfish often has to make three-point turns,
relying on it's tiny pectoral fins to reverse out of a corner,
before propelling itself forward again.
The trumpetfish's dorsal and anal fins are right back on its tail
and give it a great turn of speed when attacking prey.
The bright yellow variant of the trumpetfish
can sometimes be spotted in the Similan and Surin islands.
A visit to the island of Koh Tachai
often provides a special treat for divers:
a large and easily approached school of teira batfish.
The underwater landscape here is characterized by large granite boulders
which provide the type of shelter that the batfish love.
Hanging in the current, sometimes on their side,
the batfish are very easily approached.
Batfish take their name from their elongated pair of pelvic fins.
Other varieties in the area include the pinnate batfish,
seen here at Koh Bon
And the similar golden spadefish,
seen here in a school at Koh Torinla in the Surin Islands.
This batfish's tall proportions mark it out to be a juvenile.
Very young batfish can be 3 times as tall as they are long.
This striking design belongs to a young emperor angelfish.
In adolescence, angelfish undergo a dramatic metamorphosis.
The adult's masked face and striped body are nothing like the young.
The entirely different appearance of the juveniles
is thought to protect them from adults of the same species,
which otherwise might attack them to protect their territory.
The distinctive blue ring angelfish can be seen on many Andaman dive sites
individually or in pairs.
The Similan Islands also host regal angelfish
and blueface angelfish.
This individual from Boulder City bears deep scars
and trails fishing line from its mouth.
Butterflyfish brighten up any reef
and there are many species in the Indian Ocean.
This is a pair of copperband butterflyfish at Anemone Reef.
and these are Meyer's butterflyfish in the Similans,
often found mixed with black pyramid butterflyfish.
The raccoon butterflyfish is one of the most distinctive species.
They are often mixed with redtail butterflyfish,
the most common member of the family in the area.
Bannerfishes are common throughout the area
and are characterized by a very long spine at the front of the dorsal fin.
Schooling bannerfish can be seen in shoals close to the reef
or hanging above it feeding on zooplankton.
At first glance the moorish idol may be mistaken for a bannerfish.
It bears similar form and coloration,
but belongs to a totally different family.
Nevertheless they show similar habits.
Like the bannerfish they can be seen alone or in large schools.
These sailfin tang are feeding on algae covering the boulders at Rocky Point.
Powder blue tang are seen at most sites within the Similans.
"Tang" are also known as "surgeonfish",
so named because of the razor sharp spines just in front of the tail
which can be used during combat.
The tail spines of unicornfishes are particularly prominent.
The ringtailed unicornfish also bears the spike on its head
that gave the genus it's name.
This common reef fish is appropriately named the "crescent-tail bigeye".
Bigeyes typically inhabit dark spaces such as caves,
where the large eyes help them see in low light.
They occasionally form small aggregations like this one at Rocky Point.
In open water their skin color adapts to the bright conditions
by becoming paler,
thereby making it less conspicuous.
The juvenile emperor red snapper
is one of the most distinctive of all reef fishes,
but rarely seen.
Named after the sea itself,
the boldly spotted Andaman sweetlips has a striking design.
But perhaps the most photogenic of all our reef fishes is the oriental sweetlips.
Although often found alone, this species is at its most striking in numbers.
Schools can be encountered among the enormous granite boulders
at Christmas Point and Elephant Head Rock in the Similan Islands.
The Andaman Sea is home to a large variety of groupers.
Smaller species such as this blacktip grouper
or the slightly larger longfin grouper
look nervous when approached,
but show little effort to make an escape
in comparison to many larger species.
One of the biggest bony fishes in our area is the brown-marbled grouper.
Individuals of over 1m in length
are often observed at Richelieu Rock.
This disused and broken fish trap
provides temporary protection
for one particularly large individual.
The potato grouper, or potato "cod", grows even larger.
Encounters in the Andaman are a rarity,
but Silvertip bank is home to one particularly tame
and curious individual nicknamed "Freddie".
When visiting divers feed sharks here,
Freddie invariably shows up to get a piece of the action.
The expectancy of food is undoubtedly his main motive for approaching divers,
but he does seem to enjoy contact with humans.
On a similar scale to the potato cod is the humphead wrasse:
the largest of all wrasses.
The species can grow up to 2 meters
and as it matures it develops a protruding hump on its forehead.
This individual was seen at Shark Fin Reef.
Another speciality of Shark Fin Reef, and nearby Boulder City,
is the humphead parrotfish.
The protruding lump of bone on the forehead
is used for head-butting rivals during combat.
The teeth are fused together into a parrot-like beak
which is strong enough to bite through even the hardest corals.
Several species of barracuda inhabit the Andaman.
Unlike other species, the great barracuda prefers to stay alone
or in loose associations with other individuals.
Here at Silvertip Bank, one or two great barracudas
are commonly found around the mooring line.
The barracuda possesses enormous speed and a razor sharp set of teeth
which makes it one of the reef's top level predators.
The barracuda preys on small fishes
and on occasions shiny jewellery worn by divers has been mistaken as prey,
with unfortunate results for the diver.
This giant trevally is another very fast predator.
Trevallies are often referred to as "jacks",
and like the great barracuda, they prey on small fishes.
These are bluefin trevallies,
thriving on the currents around the giant boulders at Rocky Point.
And these are young golden trevallies
in the depths at Richelieu Rock.
Back down on the reef,
we find the most common of the pufferfish family,
the blackspotted puffer.
At Black Rock these fish can often be seen just resting on the bottom,
or in this case amongst the branches of a sea fan.
This larger species is a map puffer.
Like parrotfish, puffers' teeth are fused together to form a very strong beak.
This is a blue-spotted puffer,
although this particular individual is lacking
the characteristic blue coloration around the face.
Like other pufferfish,
if it feels greatly threatened it will swallow water
to inflate its body into a ball
in order to appear more intimidating.
The largest of all pufferfish is the starry puffer.
They are fairly unfazed by the close attentions of divers.
The yellow boxfish's body is covered with hexagonal bony plates,
fused together into a rigid carapace for protection.
This fish releases toxins if stressed,
and the bright coloration serves as a warning to would-be predators.
Nevertheless, this juvenile gets a nip from an aggressive damselfish
and retreats to the shelter of the reef.
As the yellow boxfish matures
its bright yellow coloration darkens and fades,
and it gains more white spots amongst the black ones.
Large adults take on an altogether more purple hue.
The male whitespotted boxfish has a very distinct coloration.
The female of the species is a uniform black with white spots.
On Khao Lak's Boonsung wreck we find a tiny horn-nosed boxfish.
In adulthood the species develops a prominent bump on its snout.
The porcupinefish is covered with spines
which normally lie flat against its body.
When under threat, they can inflate their bodies with water, like pufferfish.
When doing so, the spines, point straight out as a defense.
This spot-fin porcupinefish has broken some of its spines,
presumably by reversing out of a hole.
The damaged spines will soon grow back.
As can be seen from this black-blotched porcupinefish,
their eyes are quite vulnerable to attack or self-inflicted damage
and it's quite common to see individuals that have been blinded in one eye.
It's diet includes bivalve molluscs,
and the porcupinefish has a strong bite
when exploring the reef for such food.
The smaller long-spine porcupinefish
is occasionally seen foraging on the seabed surrounding the reef.
Scrawled filefish, sometimes referred to as "leatherjackets",
are characterized by a long snout and tail fin,
and a long, slender dorsal spine.
Triggerfishes, such as this orange-lined triggerfish, are close relatives.
Of all the marine creatures in our area,
one of the most striking is the clown triggerfish.
Like filefishes, triggerfishes have a pronounced dorsal spine
or "trigger" that they will raise when under threat.
Unlike the larger varieties of the family,
redtooth triggerfish are sometimes seen in large shoals
like here at Silvertip Bank.
The yellowmargin triggerfish is equipped with a very strong bite.
The largest of all triggerfishes is the titan triggerfish.
This is a highly territorial species
and aggressively defends its nest against intruders and bypassers.
Here at East of Eden a painted spiny lobster is out in the open,
but soon retreats under its ledge when approached.
Spiny lobsters lack the claws that other lobsters possess,
but they have very long barbed antennae,
their main sensory device.
The whole of the front part of the lobster's body
is covered in an array of spines and blades:
a formidable defense against any attacker.
The amazing colors of the ornate spiny lobster
are not common in the Andaman,
but one spot where they can be found is Black Rock.
The tunnel through the middle of Western Rocky Island
is dominated by longlegged spiny lobsters.
Dozens of them inhabit the cracks and crevices of the cave's walls.
Decapods come in a wide range of sizes.
These tiny rock cleaner shrimps inhabit the dark hollows at Richelieu Rock.
Burma's Moving Wall was given its name
because of the masses of Durban hinge-beak shrimps living there.
They are characterized by large bulging eyes
and a body that hinges in the middle
to facilitate molting of the shell.
Banded coral shrimps have much longer claws and are always found in pairs.
Now for an entirely different type of crustacean, the swimming crab.
The swimming crab's 5th pair of legs, its hindmost,
are flattened into paddles which enable it to swim.
This red-legged swimming crab was found in deep water
and well away from the reef.
This is a territorial crab and this individual got very agitated
when it presumably mistook its reflection in the camera lens for a real rival.
Cowries are amongst the most eye-catching molluscs
that adorn the area's reefs.
This richly colored variety is a mole cowrie.
The shell is kept shiny by a bilobed mantle
which gradually extends across the shell
as the cowrie creeps along the reef.
The shells of various cowrie species are used as jewellery
and in some primitive cultures indicate the rank of the wearer.
Some shells have even been used historically as money.
Traditionally cowrie shells have been sought after by collectors
due to their highly glossy finish
and the huge variety of colors.
This species is the tiger cowrie,
one of the largest and most common.
The fully extended mantle exhibits branching papillae,
seen here with a juvenile hinge-beak shrimp in the vicinity.
This Arabian cowrie at Moving Wall
slithers past the spines of a sea urchin
and into the shelter of the rocks.
Some of the prettiest marine creatures are also some of the smallest.
Like cowries, sea slugs are found in a huge variety of colors.
Worldwide there are more than 3000 species.
They are blind, so they touch, taste and smell
with two antenna-like organs on the head
known as rhinophores.
Many of the most colorful varieties of sea slug are nudibranchs.
The word "nudibranch" means "naked gills",
referring to the branchial plume on their back
through which they breathe.
Many nudibranchs feed on stinging creatures
such as corals and hydroids.
Aeolid nudibranchs have the ability to store their prey's sting
in the cerata on their back,
and later discharge it in their own defense.
Risbecia nudibranchs often exhibit "trailing" behavior,
whereby they follow each other "top-to-tail".
It's thought this might ensure they can easily find each other
when they are ready to mate.
Nudibranchs lay their eggs in a ribbon stuck to the reef.
Like their bearers,
the egg masses vary greatly in form and color,
and are often poisonous.
Phyllidiid nudibranchs lack the external gill plumes of other families.
Their gills are under the skirt of the mantle.
The mantle itself is covered with hard tubercles.
The coloration of ocellate Phyllidia always varies
around a palette of gold, black and white.
This is a very common combination of warning colors,
and advertises the slug's unpalatability.
The varicose Phyllidia has no known predators.
If stressed, it releases a strong toxin.
At the other end of the scale in the category of molluscs
is the fluted giant clam,
which burrows its hinge into the reef. (at a shallow depth).
Giant clams are bivalves.
They siphon water through 2 holes,
extracting oxygen and plankton
for respiration and feeding.
Giant clams are often host to smaller marine creatures.
This small swimming crab finds shelter inside the clam's shell,
as does this young spotfin lionfish.
In 2003 the Thailand authorities deliberately sank a Chinese fishing vessel
off Similan Island number five in order to create an artificial reef.
The wreck later became commonly known as the "tuna wreck".
Just a few months after the sinking,
the wreck had already become home to quite a variety of marine life.
In particular, shoals of tiny cardinalfish
were already swarming in and around the wheelhouse.
Cardinalfish also find shelter in this small wreck on Racha Yai's Home Run.
Many of the Andaman's natural reefs
are similarly cloaked in shoals of tiny fish.
These luminous cardinalfish shelter amongst black sun corals.
Here at Koh Bida Nai the whole reef appears to sway with life.
While a social aggregation of fishes is known as a "shoal",
when they are more tightly organized and swim with coordinated movements,
they are known as a "school".
The tendency of fishes to form schools is a natural defense mechanism.
Each fish instinctively follows its neighbours' movements very closely,
and the resulting congregation can be confusing for predators.
The sheer number of eyes in a large school
makes it easier for the fish to spot predators.
It's all about strength in numbers.
Schooling fishes tend to choose other fishes of similar size and appearance,
but not always the same species.
If a fish stands out, it is more likely to be targeted.
This African pompano at Shark Cave made some half-hearted attempts
at catching the schools of fusilier and young barracuda.
On this occasion it left empty-mouthed.
Striped eel catfish such as these at Lucy's Reef
are invariably found in schools.
They forage for food in the day,
but are seen here resting at night.
Bigeye snappers can be seen schooling at Hin Muang.
Enormous schools of these fish are a feature of many reefs.
Bluestripe snappers form slightly smaller schools,
as do their cousins, two-spot banded snappers.
Variable-lined fusiliers, a common sight in the Similans,
often gather in their thousands,
and more often than not they're all swimming in the same direction.
The Andaman Sea is home to several species of schooling barracuda.
Large schools of bigeye barracuda are common at more inshore sites
such as the Racha Islands.
At Black Rock the larger pickhandle barracuda,
with it's distinctive yellow tail, is a common sight.
At Koh Tachai and Richelieu Rock you are more likely to find blackfin barracuda.
In the Mergui Archipelago, the similar but smaller sawtooth barracuda is more common.
At Western Rocky Island the school sometimes forms a huge vortex.
Like barracuda, dogtooth tuna prefer to socialize and hunt in numbers.
Of the trevally family, it's most likely bigeye trevallies
that form large schools in their search for small reef fishes.
Again, isolated outcrops such as Richelieu Rock and Black Rock
provide the upwellings and currents that the trevally favor.
While forming schools can provide a degree of protection for some fishes,
others will take a more direct approach to survival.
In the depths of the Mergui Archipelago,
pastel tilefish use their mouths to build enormous mounds of dead coral.
When approached, the fish literally dive head-first into the rubble.
This rare and highly pregnant dwarf whipray near the Boonsung wreck
is well disguised against the sand.
When the ray is threatened,
a quick shuffle can make it almost disappear from view.
Bluespotted stingrays occasionally hide in a similar manner.
Together with the sting on their tail, and their considerable speed,
they have the tools they need to avoid attack.
If the natural camouflage of the day octopus fails it,
then it has another defensive weapon up its sleeve.
Mimicry is another common defensive strategy.
The straightstick pipefish, a relative of the seahorse,
resembles a sea whip waving in the current,
and hence remains largely unnoticed by predators.
This is known as "passive camouflage".
This ornate ghost pipefish hangs head downwards,
mimicking the sea fan behind it.
The ghost pipefish is even able to change its body coloration
to blend in perfectly with the environment.
This juvenile cheeklined wrasse blends in perfectly with the sea fan behind it.
At first sight the giant frogfish resembles a sponge.
It actually walks around the reef using its fins which have evolved into legs.
The skin coloration is adjusted to suit the surroundings.
Frogfishes are a type of anglerfish,
and have a very cunning technique for finding food.
Their slender dorsal spine, the illicium,
is waved around like a tiny fishing rod.
Tasty bypassers attracted to the lure at the end of the illicium
are engulfed by the huge mouth in a fraction of a second.
Frogfishes sometimes use the same movement as a threat display
when they have been detected.
The bearded scorpionfish also opens its mouth in a show of aggression
if it is recognized or if it enters into a territorial dispute.
The bearded scorpionfish is a master of disguise.
It is an ambush predator,
and changes its color to blend in with the surrounding environment,
making it almost invisible to its prey.
Besides the camouflage, scorpionfishes have a formidable armoury
of stinging spines along their fins for defense.
The devil scorpionfish, sometimes known as a "false stonefish",
camouflages itself in the same manner.
Its skin is incredibly adaptable in color and texture.
But if it's disturbed enough the brightly-colored underside
of its pectoral fins can help deter attackers.
The stonefish possesses an unparalleled combination of disguise and toxicity.
Its spines contain some of the deadliest venom of any fish,
and it lies motionless, resembling a rock, waiting to attack.
Here on the Boonsung wreck a honeycomb moray barges past a stonefish
that it appears not to notice.
The stonefish's strategy when not pouncing on prey is simply to "play dead".
Large morays have been known to prey on stonefish.
In 1997 the King Cruiser, a passenger ferry,
sank between Phuket and Phi Phi Island,
creating a brand new artificial reef
and a highly popular dive site.
In the intervening years she has become home to great numbers
of another member of the scorpionfish family, the red lionfish.
Unlike it's camouflaged cousins, the lionfish makes little attempt to hide.
Instead it flares out its fins when approached,
revealing an impressive array of stinging spines
that would deter even the boldest of predators.
It's possible that some of these fish are a very similar species
commonly known as "devil firefish",
whose distribution overlaps that of the red lionfish.
Lionfish sometimes form small communities such as here at Richelieu Rock
where as many as ten can be found resting together.
The distinctive pectoral fins of the zebra lionfish
are a delight for underwater photographers but a deterrent to predators.
Richelieu Rock hosts a small community
of a slightly different different species,
commonly known as the "frillfin turkeyfish".
The spotfin lionfish is a more common sight.
Its fins are almost completely transparent.
The spines of the crown-of-thorns starfish
contain a neurotoxin intended to cause paralysis.
They feed on stony corals
and human intervention has been required in some parts of the world
where these starfish threatened to destroy entire reef systems.
The sea urchin's spines are not nearly so dangerous to humans
but they are barbed and very fragile
and the ends of the spines are designed to break off
and remain in the flesh of any attacker.
Between the spines, the sea urchin has a bulb-like anal cone
through which it expels its feces.
Some cardinalfishes are small and careful enough
to hide amongst the spines of the crown of thorns starfish or the sea urchin,
thereby using the defense of the host to protect themselves.
This is known as a "commensal" relationship,
whereby one partner in the relationship benefits
while the other receives neither benefit nor harm.
It's a similar strategy adopted by anemonefishes.
They make their home in sea anemones,
the perfect refuge from predators.
Their skin has a special immunity from the anemone's stinging tentacles.
Skunk clownfish tend to favor the magnificent sea anemone.
Clark's anemonefish are not so particular
and find their home amongst a number of species of sea anemone.
This is a mutually-beneficial relationship.
While the fish are protected,
their feces provide food for the anemone
and they help keep it free of parasites.
They also chase away polyp eaters such as butterflyfishes,
thereby defending the anemone as well as their own family.
Some even attempt to chase off passing divers.
Juvenile Clark's anemonefish are predominantly orange in color.
Saddle anemonefish are not so prevalent
and are commonly associated with bubble-tip anemones
such as here at Richelieu Rock.
Juveniles display a white stripe reminiscent of other adult species.
Anyone who has seen the film "Finding Nemo"
will already be familiar with ocellaris clownfish.
They are normally found living amongst magnificent sea anemones.
Typically an anemone hosts a dominant female matriarch and her male mate,
as well as one or more juvenile anemonefish.
When the female dies, the male transforms into a female
and the highest ranking adolescent is promoted to be her mate.
Due to abnormally warm conditions,
this anemone has lost the symbiotic zooxanthellae that give it its color,
and may or may not recover.
Other types of fish have also evolved a resistance to the sea anemone's sting.
Juvenile domino damsels are often seen around sea anemones.
Competition with anemonefishes, as well as with each other,
can be fierce and incessant.
As adults they are one of the most aggressive fish on the reef, for their size,
and become less reliant on anemones for protection.
Another creature that uses the anemone to protect itself
is the porcelain anemone crab.
At the end of the crab's third maxillipeds
is a fan of bristles known as "setae"
which the crab holds against the current to filter plankton from the water.
Any collected food is scraped into the mouth
by smaller setae on the innermost maxillipeds.
Tube anemones are often seen in isolation on the seabed.
This tube anemone's stinging tentacles provide protection for a magnificent shrimp,
as well phoronid worms which cover the tube.
A pair of whitecheek monocle bream pass by.
Jellyfishes, of course, are well known for their sting
and often attract hitchhikers such as small sardines.
The small fishes remain in the vicinity of the jellyfish,
sometimes for their whole lives.
When attacked, they find protection under the jellyfish's bell
or even right inside, past its stinging tentacles.
These hitchhikers are sheltering in a crowned jellyfish.
And this rhizostome jellyfish is harboring juvenile scad.
Older scad change from hunted to hunter.
The jellyfish's sting is no guarantee of its own survival.
This Australian spotted jellyfish at Racha Yai
comes under attack from a scrawled filefish.
Once a jellyfish has lost its defenses, a free-for-all invariably ensues.
Rainbow runners dart by,
but this feeding frenzy like many others is led by streaked spinefoots.
Although the opportunistic spinefoots have a taste for jellyfishes,
they are normally herbivores.
Here they join a shoal of Singapore parrotfish in search of food.
The top of the reef is covered in a layer of nutritious algae
which the marauders devour en masse.
Here at East of Eden bluefin trevally team up with goldsaddle goatfish
to hunt the reef for small fishes.
Smalltooth emperors join the gang too.
The emperors' skin takes on dark blotches while feeding,
but soon fades to a neutral color when the fish resume swimming.
At Racha Noi this school of mullet makes an impressive sight.
In rapid time the fish scoops a mouthful of sand from the seabed,
filters out edible organic matter, and then spits out the unwanted sand.
The defensive tactics of titan triggerfish when protecting their nest
have won the respect of many divers.
When feeding they can be an impressive sight too,
their powerful jaws enabling them to tackle even large chunks of stony coral.
On the wonderful plateau south of Koh Tachai
this triggerfish's feeding has attracted an array of hangers-on
that would do any aquarium proud.
Everything from tangs to moorish idols joins the throng,
hoping to pick up some of the triggerfish's scraps
or find some food for themselves.
The discovery of this broken mussel at Anemone Reef
has sparked another feeding frenzy
and a similar variety of reef fishes get involved in the scrap.
Blackspotted puffers often stand by at such gatherings.
Their lack of agility and awkward shape
put them at a disadvantage to other fishes.
Here at Richelieu Rock, however, this blackspotted puffer has less competition
and pecks away at the base of a small anemone while avoiding its sting.
The pufferfish retracts it's lips as it bites
so only its bony beak makes contact.
Trumpetfish often ride above a larger host such as this porcupinefish,
allowing them to sneak up on small prey such as damselfishes
that are not preyed upon by the larger host itself.
Trumpetfish sometimes craftily conceal themselves within a school of fish
such as these yellowfin goatfish.
The trumpetfish is much faster than the goatfish
and can lunge out of the school to catch unsuspecting prey.
Banded sea kraits are one of the most venomous creatures on the planet,
but they are little danger to divers.
Their mouths are tiny
and while underwater they are prepossessed with hunting
for their natural prey of eels and fishes.
The tail has evolved into a flat paddle
which the snake uses to propel itself through the water.
Although superbly adapted to life underwater,
the sea krait is still an air-breathing reptile
and it will surface to breath every few minutes.
A hawksbill turtle also takes a breath of air at the surface
and then makes its way back to the seabed in search of food.
In the Andaman the hawksbill turtle is the most common of these ancient reptiles.
Hawksbill turtles have a wide-ranging diet
that includes cnidarians such as these hammer coral polyps
and this jellyfish.
Sadly they can be quite indiscriminate in their eating habits
and are easily poisoned by eating plastic bottles
and other man-made debris.
This turtle appears to mistake my camera lens for food.
Whereas the hawksbill has two pairs of plates between its eyes,
the green turtle has just a single pair,
and a less pronounced beak.
At Donald Duck Bay, one or two green turtles
often hang around moored boats in search of food.
With care, they can be fed by hand.
Harlequin shrimps have very interesting eating habits.
Working in pairs, the shrimps take on sea stars many times their size.
Over a period of days,
the shrimps systematically sever and eat the sea star's legs.
They must be decisive however,
because the sea star will reattach its legs, given a chance.
The sea star can also regenerate its legs,
so the shrimps leave the central disc that contains its vital organs,
so that they have a chance to feed on the same individual again in the future.
The shrimp feed exclusively on sea stars
and cannot live without them.
This is known as "obligate predation".
By turning the sea star over, it is less likely to escape
and the shrimps have access to it's soft underside.
For such a small creature, the shrimps have remarkable strength.
The larger peacock mantis shrimp does things in a different way.
Two of its claws have evolved into red and white clubs
that the shrimp uses to smash or stun prey.
These formidable weapons are effectively spring-loaded.
When the shrimp deploys them
they strike their target at a velocity of some 23 meters per second,
and their sound can be heard some distance away underwater.
Amongst aquarists they have earned the nickname "thumb splitter",
and have even been known to smash the glass of aquariums when,
presumably, the shrimp mistook its reflection for a competitor.
This shrimp is trying to smash an oyster,
but occasionally stops its work to give us a colorful threat display.
Partnerships are a very important aspect of the reef ecosystem.
Skunk cleaner shrimps are often found in the presence of giant morays.
The shrimp scours the host for parasites,
so the shrimp keeps itself fed
while the moray keeps itself clean and healthy.
Such mutualism between marine creatures is a key element of survival.
Given the opportunity, the shrimps will even clean a diver's teeth.
Here at Koh Bon we see a similar example of symbiosis.
Variable-lined fusiliers gather
to get a valet from a pair of bluestreak cleaner wrasse.
The bold, longitudinal stripes of the cleaner wrasse
enable fishes to easily recognize it as their friend.
This starry puffer opens its gill wide
to afford maximum access to a pair of cleaner wrasse.
Cleaner wrasse operate out of recognized "cleaning stations":
specific locations where fishes go to be cleaned and not to feed.
The batfish at Koh Tachai know they can rely on the attentions of bluestreak cleaner wrasse.
The less-common bicolor cleaner wrasse also operate here.
Without this cleaning service,
the host fish may quickly become diseased.
Even the fearsome giant moray has entered into this silent contract.
However the cleaner's attentions are not always welcome.
This honeycomb moray seems particularly irritated by the presence of a cleaner shrimp.
And this blackspotted puffer is so annoyed by these cleaner wrasse
that it even starts to inflate,
a reflex normally reserved for times of great danger.
The false cleanerfish is a blenny
which has cunningly evolved to closely resemble the cleaner wrasse,
yet actually feeds on the flesh of its hosts.
This cuttlefish seems to get a lot more than it bargained for
when it receives a nasty nip on the eye.
Large fishes such as this zebra shark
often find themselves with company in the form of a sharksucker,
otherwise known as a "remora".
The remora's dorsal fin has evolved into a sucker
that it uses to attach itself to its host.
As well as hitching a free ride,
the sharksucker picks up scraps that it's host leaves when feeding.
Large pelagic fishes such as whale sharks
can play host to great numbers of sharksuckers.
The sharksucker lacks the swim bladder
that other fishes use to control their buoyancy,
and so it needs its host to survive.
Sharksuckers do their part
by cleaning small parasites such as isopods from the host's skin.
Sharksuckers will attach themselves to just about any moving object
significantly larger than themselves.
For example porcupinefishes,
and parrotfishes.
Even divers sometimes find themselves playing host.
Another fish that likes the slipstream of a much larger host is the cobia.
The sight of a cobia almost always indicates that something much larger is close by.
Cobias feed on the feces of their host.
Manta rays and whale sharks are particular favorites.
Shoals of blotched fantail rays can attract hundreds of cobias.
This grey reef shark has a cobia and a sharksucker for company.
But this grey reef shark is being tracked by rainbow runners, not cobias.
At first sight it might seem they are behaving in the same way,
but actually the rainbow runners' motive is different.
They rub themselves against the shark's rough skin
in order to remove algae and parasites from their own bodies.
Whitetip reef sharks sometimes get the same treatment.
These rainbow runners are cleaning themselves against a free-swimming hawksbill turtle
as it returns from breathing at the surface.
Feather duster worms are rooted statically to the reef
and feed by filtering plankton from the water with their tentacles
and passing it into the central mouth.
Colorful christmas tree worms
embed themselves into porous stony corals
such as this lobe coral.
They are highly sensitive to disturbances.
At the slightest sign of danger,
the worm retracts into the coral and seals the opening.
When they feel the coast is clear
the worms re-emerge in their full glory.