Coral reef bleaching is a stress response of corals to various environmental disturbances such as global warming and increased UV radiation due to ozone depletion. This whitening response of corals occurs when symbiotic single cell algae are released due to stress. When the single cell algae, also known as zooxantheallae are expelled, the coral loses its pigment, leading to a bleached or completely white appearance. Beginning in the 1980s, the frequency and widespread distribution of reported coral reef bleaching events increased.