The current El Nino is not only affecting weather patterns across the US and the Caribbean, but it has also set in motion another widespread coral bleaching event. Coral bleaching occurs when ocean temperatures rise too much above average, and the coral organism reacts by discharging the algae it depends on for food. After this happens the coral will die, leaving behind its white skeleton of pure calcium carbonate. This is how the event gets its name ‘coral bleaching’.
Coral bleaching causes a devastating side effect since the entire reef ecosystem is based on the food base provided by coral. Tropical seas where coral reefs abound are traditionally nutrient poor areas of the ocean, and the ecosystems in these areas are dependent on the coral providing food for almost everything inhabiting these areas. The snowballing effect of removing the food base causes many species of fish and other organisms to either move or die off completely. So bleaching events are noted as being major eco system changing events.
For more information please read this excellent article describing the current coral bleaching event around the globe along with its many severe consequences.