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Article Index
Coral
Reproduction
Sexual
Asexual
Reefs
Types
Ahermatypic corals
Evolutionary history
Environmental effects
Live corals
Coral as a gemstone
Ancient corals
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Page 1 of 12

Coral.

coral phuket thailand reefsCorals are marine organisms from the class Anthozoa and exist as small sea anemone–like polyps, typically in colonies of many identical individuals. The group includes the important reef builders that are found in tropical oceans, which secrete calcium carbonate to form a hard skeleton.

A coral "head", commonly perceived to be a single organism, is formed from thousands of individual but genetically identical polyps, each polyp only a few millimeters in diameter. Over thousands of generations, the polyps lay down a skeleton that is characteristic of their species. A head of coral grows by asexual reproduction of the individual polyps. Corals also breed sexually by spawning, with corals of the same species releasing gametes simultaneously over a period of one to several nights around a full moon.coral phuket thailand reefs

Although corals can catch small fish and animals such as plankton using stinging cells on their tentacles, these animals obtain most of their nutrients from photosynthetic unicellular algae called zooxanthellae. Corals coordinate common behaviour by communication processes. Consequently, most corals depend on sunlight and grow in clear and shallow water, typically at depths shallower than 60 m (200 ft). These corals can be major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not have associated algae and can live in much deeper water, such as in the Atlantic or Pacific, with the cold-water genus Lophelia surviving as deep as 3000 m. Examples of these can be found living on the Darwin Mounds located north-west of Cape Wrath, Scotland. Corals have also been found off the coast of Washington State and the Aleutian Islands in Alaska.

Anatomy

While a coral head appears to be a single organism, it is actually a head of many individual, yet genetically identical, polyps. The polyps are multicellular organisms that feed on a variety of small organisms, from microscopic plankton to small fish.

Polyps are usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radially symmetrical with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which both food is ingested and waste expelled.coral phuket thailand reefs

The stomach closes at the base of the polyp, where the epithelium produces an exoskeleton called the basal plate or calicle (L. small cup). This is formed by a thickened calciferous ring (annular thickening) with six supporting radial ridges (as shown below). These structures grow vertically and project into the base of the polyp. When polyps are physically stressed, they contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements (Barnes, R.D., 1987; Sumich, 1996).
The polyp grows by extension of vertical calices which are occasionally septated to form a new, higher, basal plate. Over many generations this extension forms the large calciferous (Calcium containing) structures of corals and ultimately coral reefs.

Formation of the calciferous exoskeleton involves deposition of the mineral aragonite by the polyps from calcium ions they acquire from seawater. The rate of deposition, while varying greatly between species and environmental conditions, can be as much as 10 g / m² of polyp / day (0.3 ounce / sq yd / day). This is light dependent, with night-time production 90% lower than that during the middle of the day
The polyp's tentacles trap prey using stinging cells called nematocysts. These are cells modified to capture and immobilize prey, such as plankton, by injecting poisons, firing very rapidly in response to contact. These poisons are usually weak but in fire corals they are potent enough to harm humans. Nematocysts can also be found in jellyfish and sea anemones. The toxins injected by nematocysts immobilize or kill prey, which can then be drawn into the polyp's stomach by the tentacles through a contractile band of epithelium called the pharynx.

The polyps are interconnected by a complex and well developed system of gastrovascular canals allowing significant sharing of nutrients and symbiotes. In soft corals these range in size from 50-500 μm in diameter and to allow transport of both metabolites and cellular components.
Aside from feeding on plankton, many corals as well as other cnidarian groups such as sea anemones (e.g. Aiptasia), form a symbiotic relationship with a class of algae, zooxanthellae, of the genus Symbiodinium. The sea anemone Aiptasia, while considered a pest among coral reef aquarium hobbyists, has served as a valuable model organism in the scientific study of cnidarian-algal symbiosis. Typically a polyp will harbor one particular species of algae. Via photosynthesis, these provide energy for the coral, and aid in calcification. The algae benefit from a safe environment, and use the carbon dioxide and nitrogenous waste produced by the polyp. Due to the strain the algae can put on the polyp, stress on the coral often triggers ejection of the algae, known on a large scale as coral bleaching, as it is the algae that contribute to the brown coloration of corals; other colors, however, are due to host coral pigments, such as GFPs (green fluorescent protein). Ejecting the algae increases the polyps' chances of surviving stressful periods - they can regain the algae at a later time. If the stressful conditions persist, the polyps, and corals, will eventually die.

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Koh Racha Yai:

Dive sites at Koh Racha Yai:

Bungalow Bay, Home Run, Lucy's reef, Eastern coast, Siam Bay etc.

Bungalow Bay:

Bungalow bay is situated on the west coast of Koh Racha Yai. Average depth is around 17 meters / maximum depth 30 meters. This site can be split; you can opt to follow either of the bay's shorelines.

The rocky formations visible above the surface continue underwater, with a good presence of reef fish. Around the rocks swim surgeonfish and fusiliers, while below you can see inquisitive paired goatfish, nudibranchs, urchins and plenty of blue spotted ribbontail rays.

Eastern Coast:

The first site begins at the northeast tip of Koh Racha Yai and heads south, the second follows the southeastern apex. Average depth is around 12 meters / maximum depth 22 meters. This is a very popular diving destination and is suitable for all levels of diver. There's also enjoyable snorkeling around the rocks in the shallow waters off the islands coastline.

The shallower sections of the reef feature table corals and smaller examples of leaf corals; the deeper waters have similar species, but larger. There are many featherstars, lionfish, puffers and a few parrotfish and wrasse.

The site's southern end has the bonus of encountering mating cuttlefish along with a greater display of reef creatures, including good sized titan triggerfish, moray eels and octopus; plus on a smaller scale, a better selection of colorful fish and invertebrates. Leopard sharks and hawksbill turtles are occasionally seen around the coastline.


Koh Racha Noi:

Dive sites at Koh Racha Noi:

The rock, North Pinnacle, Kanpela point. The beach, South pinnacle.

Northern Tip:

Average diving depth is around 17 meters / maximum diving depth 30 meters at Koh Racha Noi. A very reasonable multilevel dive site, which takes divers around pinnacles and large rocks. There is a fair display of hard corals and soft corals, and the usual reef fish are present in reasonable quantities.

If you are lucky you should be able to sight small reef sharks, but the main attraction is probably the presence of large bullet-head parrotfish, and the magical manta rays. However, diving here can be demanding because of the currents.

Southern Tip:

Average diving depth around 23 meters / maximum diving depth 40 meters +. This is a really great dive for the experienced diver. The underwater terrain is similar to that around the island's northern tip, but much deeper, the shallowest part of any consequence is at 18 meters.

Fine soft corals highlight the smooth sided boulders. Crinoids and featherstars are well represented. There are fairly plentiful, reasonably sized fish, including lionfish, parrotfish, wrasse and triggerfish, as well as large visiting pelagic's such as barracuda, rainbow runners and trevally.

Manta rays and marbled rays frequently seen here as are whale sharks, although with slightly less regularity. All in all, this site can be compared with some sites found around Ko Similan Marine National Park, Thailand.


Phi Phi Islands:

Dive sites at phi Phi Islands:

Koh Bida Nok, Koh Bida Nai, Maya Bay.

The spectacular Phi Phi islands lie in the mouth of the Phang Nga Bay and form the Haad Nopparattara Mo Koh Phi Phi National Park. White limestone crags splashed with greenery jut vertically up wards out of the clear turquoise waters to tower over magnificent sandy beaches.

You will see an amazing variety of fish life, beautiful soft corals, staghorn coral gardens and huge sea fans. On the sandy bottom, leopard sharks can be found resting. Diving in the Phi Phi islands is an experience not to be missed. From shallow sheltered bays to wall and drift dives, there's something for every level of diver.

Visibility ranges on average from 10-25 meters with weak to moderate currents. Water temperature remains a fairly constant 27 - 30C throughout the year, depths from 10 - 30 meters, and, there's plenty of marine life! For non divers the Phi Phi area offers superb snorkeling, with the opportunity to see not only beautiful coral gardens but also some of the larger fish at shallow depths.


Koh Doc Mai:

Koh Doc Mai is a small island off Phuket, In Thai language Doc Mai means "Tiny Flower".

When you scuba dive here you will see why this island has this name. Koh Doc Mai's underwater area is famous for its hard and soft corals covering the vertical outcrop. Also famous for its circumnavigational wall dropping down to 30 meters.

Koh Doc Mai also has a few caves were you will find some weird and wonderful reef species. Perfect for macro photographers who want to spot that little yellow seahorse. Lots of soft and hard corals, white eyed moray eels, schools of trevally, trigger fish and lots lots more.


For more detailed dive site information: Koh Doc Mai, Kata Beach, King Cruiser, Koh Poo, Koh Racha Yai, Koh Racha Yai Bays, Koh Racha Noi, Anemone Reef, Similan Islands,Anita's Reef, Beacon Reef, Boonsung Wreck, Boulder City, Breakfast Bend, Christmas Point, Deep Six, Donald Duck Bay, East Of Eden, Elephant Head Rock, Honeymoon Bay, Koh Bon, Richelieu Rock, Rocky Point, Shark Fin Reef, Tachai Pinnacle, Tachai Reef, Turtle Rock, Waterfall Bay, West Of Eden.