Tyler Eddy, a research scientist who co-authored a new study at the Memorial University of Newfoundland, says, “Coral reefs have been in decline worldwide. I think that’s pretty commonly accepted. We didn’t necessarily know the magnitude of how much.” The in-depth analysis reveals half of coral reefs have been lost since the 1950s. Climate change, overfishing and pollution are decimating coral reef cover, biodiversity and fish abundance. In another study, scientists with the Global Coral Reef Monitoring Network determined the world lost 14 percent of its coral between 2009 and 2018 alone.

Coral reefs provide habitat for fish and protection for coastal communities, and they generate billions of dollars for the fishing and tourism industries. Corals are extremely sensitive to changes in water temperature and acidity. The living polyps rely on zooxanthellae—algae that live in their tissue—to produce food the corals need. When the polyps are stressed by changes in light, water temperature or acidity, they expel the algae in a process called bleaching. There is a brief time frame in which they can replenish the algae, but if corals are stressed for too long, their death is irreversible. “We are running out of time: We can reverse losses, but we have to act now,” says Inger Andersen, head of the United Nations Environment Program.