Increased ocean temperatures and changing ocean chemistry are the greatest global threats to coral reef ecosystems. These threats are caused by warmer atmospheric temperatures and increasing levels of carbon dioxide in seawater.
As atmospheric temperatures rise, so do seawater temperatures. This warming causes corals to lose the microscopic algae that produce food that corals need, placing stress on the corals. Without this algae coral also lose their coloration—a condition known as coral bleaching— because the loss of algae reveals the white color of the calcium carbonate structure underlying the polyps.
Severe or prolonged bleaching can kill coral colonies or leave them more vulnerable to other threats such as infectious disease.
