CORAL COASTS
These are the coasts that are mainly composed of coral rocks/coral reefs.
A reef is a wave resistant ridge of coral, algae, and other calcareous organisms. They are formed from ex- skeleton of tiny marine organism called polyps. These organisms have ability to utilize lime from sea in building their building shells for their protection.
Coral reefs: A mass of coral is called a reef.
Polyps lives in colony and once they die their shells cement and form a ridge –like rock which is parallel to the shore.

CONDITION FOR THE GROWTH OF POLYPS.

• Warm temperature range which should be between 25°C and 29°C. Thus polyps are found on eastern side of continents where temperature is warm.
• Water should be shallow to allow sunlight penetration. Most polyps lives in water with depth less than 10 M however some species are found at the depth of 60 M.
• The water must be clear and salty.  For this reasons coral reefs are not found at river mouths because the water has silts and salty has been diluted.
• Plentiful supply of plant food (plankton) and enough oxygen.

Types of Coral Reefs.

• Fringing Reefs: Is a coralline platform lying close to the shore extending outwards from the mainland. i.e. is the platform of coral which forms when coral polyps start building a reef near the shore. The reef grows faster sea wards. Fringing reef is has a shallow lagoon usually forms between the coast and the reef.
• Barrier Reefs: is the reef separated from the coast by much wider and deeper channel or lagoon. Its base on the sea floor may be more than 60 M from the surface as this is the maximum depth at which polyps can survive. Barrier reefs are extensive compared to fringing reef. Examples of fringing reef include the one found in east African coast around Mayotte in Comoros, and Great Barrier Reef of the coast of Queensland Australia.
• Atolls: are circular reefs that rim lagoons. i.e. coral reefs are roughly circular in shape and which enclose a fairly deep lagoon. The encircling ring is usually broken in few places to allow the free flow of water. Atolls are found in mid-oceans, especially in the Indian and Pacific Oceans. These types of coral reefs exist in deep oceans where they form a circular pattern. Examples of an atoll include Aldabara Atoll, Maldive Islands, Bikini Atoll in pacific, Funafuti and Eniwetok Atoll.

THEORIES ON ORIGIN OF ATOLLS AND BARRIER REEFS.

The origin of Atolls and Barrier reefs is still a puzzle as the bases of these reefs are found at depths far beyond the one at which polyps can grow.
 Below are the theories on the origin of reefs and atolls.

1. Darwin’s theory (subsidence theory):  Darwin suggested that both barrier reefs and atolls form from fringing reef which develops around an island. An island begins to subside but the coral continue s growing upward to keep pace with the rising level of the sea. Growth was more outward than landward which over time led to formation of barrier reef. When the island was completely submerged and covered with water an atoll was formed. Recent research from oceanographers has revealed submergence of ocean floor hence prove Darwin theory to be the correct one.

2. Daly’s theory (glacial control theory):  he focused his attention on atolls only. He argued that during glacial period coral reef was not forming due to low temperatures. Thus waves and melting ice erode and reduced an island and flattened them to same level as the sea at that time.At the end of ice age temperature started to rise again and create favorable condition for coral formation. As water continues to rises coral reef also grows with relation to melting water to form atoll.

3. Murray’s theory: he suggested that the formation of barrier reefs does not involve the subsidence of ocean floor. He argued that barrier reefs start as fringing reefs. Waves pound on these reefs as they break.  The debris from the disintegrating reef accumulates on sea ward side. The accumulated material form base from which polyps accumulates and form barrier reefs.
Over time Atoll forms which is associated with subsidence of island.

1. SIGNIFICANCE OF OCEAN COASTS AND COASTAL FEATURES.
2. Influence on climate                   
3. Source of fresh water: ocean water can be distilled to get fresh water.
4. Water transport.                              
5. Fishing.
6. Minerals: Ocean water provides salts which is important mineral used both in domestic and industries.
7. Tourism: Ocean, coasts provide tourist attraction which promote tourism.
8. Source of power: ocean waves and tides have been used to generate electricity. Eg. St. Malo in North West France.