Previous Year Question

Microscopic photosynthetic algae called Zooxanthellae live within the tissues of corals. Corals and these algae have a symbiotic relationship; the algae provide an important part of the coral's food and also give it its colour.

When sea-water temperature rises beyond its normal range, corals experience thermal stress. Under stress, corals expel the Zooxanthellae living in their tissues, exposing their white calcium carbonate skeleton. This condition is known as Coral Bleaching.

Coral bleaching can result from several types of environmental stress, such as pollution, excessive sunlight or changes in salinity; however, abnormally high sea temperature is the leading cause of large-scale coral bleaching.

In many reef regions, temperatures remaining about 1°C above the normal summertime maximum can produce bleaching stress. If the stress is short-lived, corals may recover, but prolonged bleaching can increase coral mortality.