"Coral reefs around the world are getting hit by the double whammy of global warming and an intense El Niño this year. Record and near-record warmth spread across large parts of the world’s major oceans are prolonging the longest global coral die-off on record.
“We’re maybe looking at a 2- to 2.5-year-long event. Some areas have already seen bleaching two years in a row,” said Mark Eakin, a biological oceanographer with the National Oceanic and Atmospheric Administration in College Park, Maryland, and coordinator of the agency’s Coral Reef Watch.
When corals are stressed by conditions such as high temperatures, they expel the symbiotic algae that live in their tissues. Without the algae, corals lose a significant source of food and are more vulnerable to disease. In a severe bleaching event, large swaths of reef-building corals die. This causes reefs to erode, destroying fish habitat and exposing previously protected shorelines to the destructive force of ocean waves."