The corals polyps are tiny invertebrate animals belonging to the group CNIDARIA. They belong to the jellyfish and anemone family. Their size ranges from a tiny pin head size to that of a foot. They are sessile, and feed using their tentacles tentacles to catch prey such as small fish and planktonic animals. One coral branch or mound is covered by thousands of coral polyps, which are grouped together to form a coral colony.

Why do we need coral reefs?

• Although coral reefs cover less than 1% of the Earth's surface,they are home to 25% of all marine fish species.
• Reef fish and molluscs feed between 30 and 40 million people every year. An estimated 500 million people rely on coral reefs for their food or livelihoods.
• Chemical compounds found in reefs are used to make several important medicines.
• Coral polyps turn the carbon dioxide in water into limestone. Without coral, the amount of carbon dioxide in the ware would rise, destroying precious habitats.
• Coral reefs form natural barriers that protect nearby shoreline from strong waves or currents.

When was the Coral reef formed?

• The world's first coral reefs appear around 500 million years ago.
• Modern corals first develop in the Early Triassic era, 230 million years ago.
• Mass extinction of the coral reefs happened around 199 million years ago,when 2/3ds of them were wiped away by climatic changes, at the end of the Triassic era.
• 18 million years ago the formation of Australia's Great Barrier Reef began. Its growth had started and stopped many times since then.
• Around 18,000 years ago, the temperature of the Earth fell and sea water became trapped as ice in enormous glaciers, causing sea levels to fall to their lowest levels ever. So if at all there were any corals they would have been exposed and died during this period.
• The reefs which we see today would have started to grow around 10,000 - 8,000 years ago. It was at the end of this last ice age that they began to develop. The glaciers melted and sea levels rose to the position that we still see today.

 Different kinds of corals:

• BRAIN CORAL :- The wrinkled ridges of this hard coral make it look like a giant brain.
• FAN CORAL:- The polyps of fan coral link together to form a large lacy skeleton.
• DEAD-MAN'S-FINGERS :- The tentacles of these polyps look like decomposing fingers.
• STAGHORN CORAL :- This antler-like coral is one of the speediest growers on the reef.

Different kinds of coral reefs:

• FRINGING REEFS :- These reefs follow the shorelines of continents and islands in tropical sea, and are found close to shore. This is the most common type of coral reef and it is found in the Caribbean and Red Sea.
• BARRIER REEFS :- Lying further offshore, barrier reefs are separated from land by a deep lagoon. Most famous of it is the Great Barrier Reef in Australia.
• ATOLL REEFS :- A ring of coral that grows on top of a sunken volcano, forming a lagoon, is called an atoll. Mostly they are found in the Pacific Ocean and Indian Ocean.
• PATCH REEFS :- Patches of young coral commonly grow at the bottom of the sea in the lagoon behind a barrier or atoll reef.
• PLATFORM REEFS :- When coral reaches the surface of the sea and branches out, growing horizontally, a platform reef is formed. eg. Torres Strait.

Greatest reefs of the world:

GREAT BARRIER REEF

• THE GREAT BARRIER REEF, AUSTRALIA: About 3,000 reefs combine to form the largest living structure on Earth, more than 2,010 km (1,250 miles) long. It is the home to 500 species of corals, 400 species of seaweed, 1,000 species of sea sponge, 174 species of bird, 1,500 species of fish, 30 species of mammal.
• KWAJALEIN, MARSHALL ISLAND : The world's largest atoll surrounds a lagoon 97 km (60 miles) long.
• BIKINI ISLAND, SOUTH PACIFIC
• LIGHTHOUSE REEF, BELIZE : At the centre of this Caribbean atoll lies the Great Blue Hole, 145 m deep.