WHAT CORAL NEEDS

Corals need to grow in shallow water where sunlight can reach them. Since corals depend on the zooxanthellae (algae) that grow inside of them and this algae needs sunlight to survive, corals too need sunlight to survive.

Therefore, corals rarely develop deeper than 50 meters (165 feet).

Corals need clear water to survive and don't thrive well when the water is opaque. Sediment and plankton can cloud the water which decreases the amount of sunlight that reaches the zooxanthellae.

Reef building corals require warm water conditions to survive. Different corals living in different regions can withstand different temperature fluctuations. However, corals generally live in water temperatures ranging from 20 to 32 degrees Celsius (68 to 90 degrees Fahrenheit).

Corals are sensitive to pollution and sediments. Sediments can settle on coral, blocking out sunlight and smothering coral polyps. Pollution from sewage and fertilizers increases nutrient levels in the water, harming corals. When there are too many nutrients in the water, the ecological balance of the coral community is altered.

Corals need saltwater to survive and require a certain balance in the ratio of salt to water. This is why corals don't live in areas where rivers drain fresh water into the ocean.