Coral reefs first developed about 500 million years ago, forming on hard surfaces in the ocean. There are several types of coral reefs including fringing reefs, barrier reefs, and atolls which start as fringing reefs but become ring-shaped as the underlying land mass shrinks. Corals come in soft and hard varieties, with hard corals having calcium carbonate skeletons and being the main builders of tropical reef structures. Corals reproduce both asexually through division and sexually via mass spawning events where eggs and sperm are released and may develop into new colonies. However, coral reefs are severely threatened by bleaching, dynamite fishing, and rising water temperatures.

1. Coral ReefsBy: Beatriz &Somekid

2. About Coral ReefsThe world's first coral reefs occurred about 500 million years ago, and the first close relatives of modern corals developed in southern Europe about 230 million years ago. Most modern reefs have formed on hard surfaces in the ocean, such as a base of an old reef that died during a period when sea level was lower, or the edge of a rocky island. Some coral reefs form in the deep ocean and are called atolls.An atoll starts life as a fringing reef, then becomes more of a ring growing on the shrinking land-mass, until the land disappears and just the coral circle remains. Depending on how they start out, several types of reefs can form.

3. Types of Coral ReefsCorals come in a variety of shapes, sizes and color. But there are two types of corals: Soft Corals and Hard Corals.

4. Soft Corals do not have hard, rigid permanent skeletons.

5. Hard Coral has hard skeletons made of calcium carbonate.

6. The soft coral group is made up of the Gorgonians and the Black Corals.

7. The hard coral group is made up of the hydrocorals and the stony corals.Different CoralsSoft CoralHard Coral

8. Groups of coralThere are two kinds of hydrocorals: fire and lace corals.

9. Fire coral, sometimes called stinging coral, gives you a painful, burning feeling when it touches your bare skin. The sting is not dangerous but the rash can itch for a few days.

10. Stony corals are the basic building blocks of tropical coral reefs.