Coral reef deterioration stages

Healthy corals support healthy marine ecosystems, but corals are in crisis on many fronts. High levels of carbon dioxide are warming ocean waters and causing them to become more acidic. Pollution and overfishing put pressure on reef populations. Large algal blooms deprive shallow waters of oxygen, which harms stationary animals, such as corals, and strong tropical storms can physically damage reefs. (Illustration by Natalie Renier, © Woods Hole Oceanographic Institution)