1. Coral reefs

4. WHAT ARE CORAL REEFS?
Coral reefs are an offshore ridge , mainly of calcium carbonate formed by the secretions of small marine animals called polyps. Polyps are soft-bodied creatures which use the calcium carbonate dissolved in sea water to build up a hard ‘casing’ of limestone to protect themselves.

5. FORMATION OF CORAL REEFS
The deposits from coral secretions also help to build up reefs and islands. Corals grow outwards and upwards , but their upward growth is inhibited by sea-level and by marine erosion. Water or calcareous algae plants assist in strengthening the reefs by absorbing the minerals in their cells. These form lime coatings on the coral limestone which are cemented together.

6. Where are they found ?
Coral reefs are somewhat broadly distributed in all three of the Earth's oceans that have portions in the tropics. This includes most of the South Pacific and Indian Oceans, and part of the western Atlantic.

8. Fringing Barrier Atoll
TYPES OF CORAL REEFS
Fringing
Barrier
Atoll

9. Fringing reefs
A low coral platform lying close to the shore of an island or continental shelf but separated from it by narrow lagoons which may disappear at low water.

10. Pictures of Fringing reefs

12. Barrier reefs
A reef lying parallel to the coast but separated from it by a wide, deep lagoon.
For example – The Great Barrier Reef off the eastern coast in Australia is the world’s largest.
The second largest reef is located off the coast of Belize.

15. Atoll reefs
This is circular, ring-like or horse- shoe in shape comprising several islands and enclosing a lagoon. The reefs are built around the rim of a sunken volcanic cone or guyots.
Guyots – flat topped, circular mountains rising from the sea floor.