Coral reefs are fragile ecosystems that have been created through complex interactions between the four spheres of the biophysical environment over time. Conditions for Optimal Coral Growth show how the four spheres interact to create this unique ecosystem:
Corals thrive best in shallow waters between 2 and 30 metres where the light is strongest so that the ZOOXANTHELLAE can go through the process of photosynthesis
The best temperature range for coral polyps to create their limestone exoskeleton is 26 to 27°C. Temperatures lower than this result in a lower build up of limestone.
Coral needs clear water with low concentrations of nutrients (chemicals) such as nitrogen, phosphate and ammonium. Corals do not like phosphates as they interfere with the development of their skeletal structure. Reefs are rarely found near the mouth of a river for this reason. The agricultural and mining runoff from rivers is often heavy in phosphates and ammonium and has a harmful impact on near shore reefs.
Corals dies if there are sudden drops in salinity (salt) levels. Heavy rainfall resulting from a tropical cyclone can make fresh water pond on top of reefs and cause coral death.
Corals do best where the water is continually oxygenated by wave activity as on the outer edge of the reef. When waves crash down they have millions of tiny air bubbles that contain oxygen.
Coral needs sunlight to be able to photosynthesise thus, the water needs to be clear of sediment for sunlight to penetrate. Coral that gets covered in sediment (dirt, soil, silt etc) often die. Hence, the coral needs low turbidity (suspended sediment) in the water.