23 Jan

Basic Concepts
What is a coral?
A coral is an animal organism living in colonies of polyps.
At the end of each polyp are hunting tentacles surrounding a central mouth. Using its hunting tentacles, the polyp traps its food of tiny sea creatures. Each polyp in the colony is independent and although some of the corals are single polyps, most are joined by a shared tissue.
Corals are divided into two main groups: hexacorallia and octocorallia.
The hexacorallia corals are stony corals and each polyp has six, or multiples of six, hunting tentacles. Stony corals secrete calcium which forms the skeleton of the coral. Hexacorallia is divided into subgroups: massive stony corals, branching stony corals, cushioned stony corals and collective stony corals. The massive stony corals are the reef builders – the coral growing upward is alive in its upper region while the base, which is not exposed to light, dies and creates the foundation for coral colonization.
Octocorallia corals are soft. Each polyp has only eight tentacles and some of them have limestone threads the length of the tissue. All hexacorallia and some of the octocorallia corals contain unicellular algae in their body tissue. The algae and the coral live in symbiosis. The coral protects the algae from predators and the algae supply some of the nutrients of the coral, and participate in the process of laying down calcium and building the calcified skeleton of the coral. The existence of the algae is dependent on exposure to light to create the components needed for its growth, thus the stone corals live up to depths of the penetration of sun rays. All the corals feed upon miniscule organisms called plankton. The corals reproduce both sexually and asexually.
Corals – The biological formation of the reef is created by building units called polyps. These units give rise to colonies of corals. Corals, which are a comparatively simple form of life, are characterized by the ability to lay down a large calcified skeleton resulting in the creation of a reef. Corals are the building blocks of reefs, and limestone algae, which can also deposit a calcified skeleton, are the “glue” uniting and unifying the building blocks in the creation of the entire structure. Stony corals are the main component of the reef.
Planula – Larva, the first stage of the polyp prior to the colonization and building of the reef. The larva is created from an ooctye which is deposited by a female polyp into the sea water and fertilized by sperm ejected into the water by a male polyp. The larva swims in the sea water with the help of flagellae situated on the sides of its body, until it finds a place to colonize, to grow, become a polyp and create a coral reef.
Polyp – A small animal, with six or more tentacles and a mouth centrally placed within the tentacles. It feeds on plankton drifting on the water.
From its body, the polyp secretes a substance containing calcium which assists in building an encasing rigid skeleton. This skeleton is the coral. The polyp reproduces by budding – from one polyp, additional polyps develop, leading to the growth of the polyp colony. As each polyp secretes calcium, the coral grows and the reef expands.
Plankton –Tiny organisms (flora and fauna) floating below the water surface and drifting with the water currents, mainly in seawater but also in fresh water. Plankton constitute the main food component for sea creatures.
Coral Reef – A rich marine environment which is a home for the growth/proliferation of numerous marine organisms. Corals develop in tropical and subtropical seas and oceans, (from the Greek tropikos – an area of the globe between the two sides of the equatorial zone and close to them, between the 300 N zone and the 300 S zone), the main reason being that the temperature of the warm water doesn’t go below 200 Celsius or rise above 300. Coral reefs are found in Australia , Micronesia , Madagascar, Papua New Guinea, French Polynesia , Philippines, Hawaii and Japan in the Pacific Ocean ,the Maldives, Madagascar, and the Seychelles in the Indian Ocean, Caribbean Islands in the Atlantic Ocean and in Sinai in the northern Red Sea. The coral reef in the Red Sea is the northernmost reef.

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