Last year, it had spread to 97. It's tough to pin down a precise cause. Some researchers believe a natural fungus is to blame. But there may also be complicating factors. Poor water quality caused by everything from boating to agricultural runoff probably weakens the coral.
Coral are complex and poorly understood animals.
Unfortunately, we may be destroying them faster than we're learning about them. The EnvironMinute is produced in cooperation with the National Safety Council and made possible by the Teresa and H. John Heinz III Foundation.