Swaying palms, white beaches, and coral reefs—these are the "postcard" symbols of the idyllic tropical haven. Yet, there is trouble in paradise; the world's coral reef systems are in danger of disappearing. Found off the coasts of nearly 100 nations, today they cover only 0.1% of the world ocean's expanse.
Coral reefs are colonial systems of small animals called "polyps" that extract calcium carbonate from seawater to build the stony structures in which they live. They feed on plankton drifting by their fixed locations by using small tentacles to trap the microscopic organisms. Polyps also have masses of algae living within their bodies to supply them with needed calcium carbonate. In addition, the algae are the source of corals' vibrant colors and provide additional food to their hosts.