Underwater Thailand

Coral

Coral reefs are living organisms composed of a huge variety of marine life forms, but the foundation of every reef is its ostensibly inanimate stony coral constructions such as boulder, cabbage batch, cave mushroom, bushy stag horn and brain coral. Stony coral is composed of colonies of polyps minuscule invertebrate which feed on plankton, generally depend on algae and direct sunlight for photosynthesis, and extract calcium carbonate (limestone) from sea water in order to reproduce. The polyps use this calcium carbonate to build new skeletons outside their bodies an asexual reproductive process known as budding and this is how a reef is formed. Its an extraordinarily slow process with colony growth averaging between 0.5cm and 2.8cm a year.

Fleshy, plant-like soft coral, such as dead mans fingers and elephants ear, is also composed of polyps and elephants ear, is also composed of polyps, but a variety with flaccid internal skeletons built from protein rather than calcium. The lack of an external casing means the polyps vivid colors are much more visible and, as they do not depend on direct sunlight, they flourish at greater depths, swaying with the currents and using tentacles to trap micro-organisms.

Horny coral or gorgonians, like sea whips and sea fans, are a cross between stony and soft coral, while sea anemones have much the most obvious, and poisonous, tentacles of any member of the coral family, using them to trap fish and other large prey.

Reef fish

The algae and plankton that accumulate around coral colonies attract a catalogue of fish known collectively as reef fish. Most are small in stature, with vibrant and exotically patterned skins for camouflage against the coral, and flattened bodies, broad tails and specially adapted fins for easy maneuvering around the tiniest of reel crannies.

Butterfly fish are typically well designed: named for the butterfly like movements of their thin, flat yellow-white-and-black bodies, they can swim backwards, and some also have elongated snouts for nosing into crevices; a number of even sport eye like blotches near the tail to confuse predators. Members of the similarly well-fashioned angelfish family include the luscious tangerine-and-blue-striped emperor angelfish, which makes an audible clicking sound when disturbed and can grow to 30cm in length. The Moorish idol is easily recognized by the long pennant fin trailing from its dorsal fin, the a

There are around one hundred different species of surgeons fish, each with its own distinctive markings, but they are share the feature that gives them their name a sharp blade on either slide of the tail-base that becomes erect when antagonized and can inflict serious damage.

Among the most impressive reef fish that school are huge shoals of silvery fusilier fish, which move as one changing directions an eye-catching flash of ripping silver.

Some reel fish, among them the ubiquitous parrot fish, eat coral. With the help of a bird-like beak, which is in fact several teeth fused together, the parrot fish scrapes away at the coral, leaving characteristic while scars, and then grinds the fragments down with another set of back teeth a practice reputedly responsible for the erosion of a great deal of Thailands reef.

Anemone fish are so called because, having covered themselves in the sea anemones mucus, they are able to move amongst and gain protection from the anemones venomous tentacles, which would paralyze other fish on contact.

Equally predictable is the presence of cleaner fish or cleaner wrasse, on the edges of every shoal of reel fish . Streamlined, with a long snout and jaws that act like tweezers, a cleaner fish spends its days picking parasites off the skins of other fish, such as the normally voracious grouper fish a symbiotic relationship essential of both parties. The commonly sighted coral hind is a close but more colorful relative of the grouper and is often found among bushy stag horn coral.

Larger, less frequent visitors to Thailands offshore reefs include the moray eel, whose elongated jaws of viciously pointed teeth make it a deadly predator; it hunts mainly at night and often holes up in coral caves during the day. The similarly be-fanged barracuda can grow 2m and is the worlds fastest swimming fish.

Sharks and rays

Passive leopard sharks and the more excitable white-tip reef sharks are quite common off the Andaman coast reefs, but youd be lucky indeed to encounter a whale share. Which, at up 18m long is the largest fish in the world.

It is sometimes possible to swim with a manta ray, whose extraordinary flatness, strange wing-like fins, and massive size -up to 6m across and weighting some 1600kg make it an astonishing presence.

Turtles

Turtles sometimes paddle around reef waters, too, but all for local species leatherback, Olive Ridley, green and hawksbill are fast becoming endangered in Thailand, so much so that several of their egg-laying beaches have been place under national park protection, including those on Ko Surin Tai, Ko Tarutao and Hat Mai Khao on Phuket.

Invertebrates

Thailands reefs support countless species of invertebrates, including spiral-feathered Christmas-tree worms, also sometimes evocatively known as bottle-brush worms, which embed their lower bodies in coral heads; all sorts of multi-called, multi-hued sponges, both encrusting and free-standing; and a thousand-plus species of hermaphroditic, shell-less mollusks known as nudibranchs or sea slugs, which come in an arresting array of patterns and shapes and live in shallow waters.

Of the reefs numerous spiny echinoderms, the commonest sea urchins, which also tend to live in shallow areas near shore, are those with evil-looking black spines up to 35cm in length, though some varieties are covered in short, blunt spines or even excruciatingly painful flower-like pincers.

The magnificent crown-of-thorns starfish is also protected by highly venomous spines, which sheath the twenty or so arms that extend from a body that can measure up to 50cm in diameter. Disastrously for many reefs, the crown-of-thorns starfish feeds on coral, laying waste to as much as fifty square centimeters of stony coral in a 24-hour period. The much more benign feather stars also have multiple feather stars also have multiple feather-like arms arranged in star formations and come in many versions; they feed at night, crawling along reef surfaces with the help of tiny jointed limbs, or cirri, to sway in the current.

Though hideous, the seas cucumber, which looks like a large slug and lies half-buried on the sea bed, is quite harmless. Deceptively slothful in appearance, sea cucumbers are constantly ingesting and excreting so much sand and mud that the combined force of those in a three-square-kilometers area can together redistribute one million kilograms of sea-bed material a year.

Hazardous marine life

Thailand is also home to 25 species of sea snake, whose tails are flattened to act as an efficient paddle in water. Most sea snakes are venomous, though not aggressive. Of the poisonous ones, the commonest and most easily recognized is the banded sea snake, which is silvery grey with thirty to fifty black bands and a slightly yellow underside at its front end. It grows to 1.5m and inhabits shallow coastal waters, coming onto land to lay its eggs.

Other harmful creatures to be avoided include the highly camouflaged seabed-dwelling stonefish and scorpion fish, both of whom can be very hard to spot but have extremely poisonous spines which are dangerous when trodden on.

The magnificent lionfish should also be admired from afar as its impressive plumes are poisonous if brushed against, as are the tentacles of the jellyfish.

The blue-spotted ray or stingray has two venomous spines on its long tail with which it lashes out when threatened; as it tends to bury itself with almost complete disguise in the mud or sand near reefs, it can be a particular hazard to unwary divers. Another thing to be wary of it so-called fire coral (not actually a true coral but a coral-like brownish encrustation), which is found in shallow waters on the edge of the reefs and covered in a mass of tiny, fuzz-like tentacles that can inflict a painful burn.

Top places for scuba diving – Koh Tao, Koh Chang and Similian Islands