Updated by: Arabinda Naik
Coral reefs in shallow waters have a symbiotic relationship with photosynthetic algae known as zooxanthellae. These algae live inside the corals and contribute to forming a thick calcium carbonate outer shell. The interaction between corals and zooxanthellae is a symbiosis where the organisms collaborate for mutual benefit. The temperature of the surrounding water significantly impacts this symbiotic relationship. When the water warms, the zooxanthellae are expelled from the coral tissue, causing the corals to lose their colour and primary food source. This is known as "coral bleaching." However, coral bleaching does not always mean the Coral Reef is doomed. Corals can regain their zooxanthellae over time, which requires colder temperatures. Most reefs grew at the rate of 10-200 mm each year. Most of the existing reefs could have been formed within a period of 15,000 to 30,000 years.