Corals are the endoderm species of polyps living in symbiotic relationship with an algae called zooxanthelle. They are called the 'Rainforests of the Ocean'.

Coral Bleaching It is a phenomenon of losing of colour by corals due to expulsion of zooxanthelle. The corals becomes dull and white after coral bleaching. a Coral Bleaching observed in Great Barrier Reef, Australia. The coral bleaching is a biosignature that natural conditions are undergoing changes and actions are required.

Causes of coral bleaching: (1) Rising pollution levels of water due to chemical intake caused by expulsion into sea/ocean. (2) Change in temperatures beyond 28°C increases changes of coral bleaching. (3) Acidification of ocean due to rising levels of CO2 in atmosphere and their consequent absorption by oceans causing corals CaCO3 content to dissolve. (4) Instability in water disturbs the calm nature preferred by corals and thus disrupting their habitat. Consequences of coral bleaching: (1) Loss of biodiversity - As corals constitute about 25% of Earth's biodiversity. (2) Loss of aesthetic value due to appearance of dull colour. c UNESCO is thinking of removing World Heritage tag from Great Barrier Reef, Australia. (3) Decrease in fish catch for farmers. (4) Triggering tipping points beyond which the changes are irreversible.