There are too few study sites, and few long-term studies. Many studies emphasize basic research and few use similar methods. The survey was by far the largest ever undertaken and was based on the use of one method at all sites so that comparisons could be made among sites. The results confirmed that reefs in different parts of the world share similar problems. Overfishing was shown to be far worse than expected, particularly at remote locations.
Corals are animals, but they also have microscopic, single-celled plants living in their tissues.
Like other animals, coral polyps capture and eat food, but the plant cells provide an additional source of nutritious compounds to the coral. These algae give most corals their characteristic brownish-green color. The extra energy from the algae allows corals to secrete a calcium carbonate skeleton. When many living and dead skeletons fuse together over time, a coral reef is formed. Coral reefs are the largest structures made by living organisms.