Corals is limestone rock made by accumulation of skeletons of tiny marine organisms called coral polyps. Reefs are shallow, mostly submarine features, build primarily by colonies of living marine organisms, including corals, sponges and shellfish. Coral reefs occur only in the places coral polyps can survive and thrive .
The following are five conditions which favor occurrence of coral reefs;
- Sunlight – coral reefs need to grow in shallow water where sunlight can reach them. Corals depend on the zooxanthellae (algae) that grow inside of them for oxygen and other things, and since these algae need sunlight to survive corals also need sunlight to survive. Corals rarely develop in water deeper than 50 meters since sunlight can not penetrate beyond this point.
- Clean water, corals need clean water that lets the sunlight through. They do not thrive well in muddy like near river mouth. Sediments and plankton can cloud water which decrease the amount of sunlight that reaches the zooxanthellae
- Warm water – reef building corals require warm water condition to survive. Different corals living in different regions can withstand various temperature fluctuations. However corals generally in water temperature of 20 – 30 degree Celsius, this is the reason why coral reef appear on the eastern part of continents due to presence of warm currents.
- salty water – corals need salty water to survive and require certain balance in the ratio of salt to water. this is why corals do not live in areas where rivers drain fresh water into the sea.
- Corals in order to grow also need plentiful supply of plankton and enough oxygen. This is important because like any other living organism corals polyps need food and oxygen so as to grow and be able to reproduce