Ecology. Coral reef biodiversity--habitat size matters.

Coral reefs are the most diverse of all marine ecosystems (1), with estimates of reef species ranging from 600,000 to more than 9 million species worldwide (2, 3). This biodiversity is most pronounced in the western Pacific and Indian Oceans (1, 4), but decreases with increasing distance from the Indo-Australian archipelago. For example, reefs in the central Indo-Pacific have more than 10 times as many coral and fish species as reefs of the Galapagos Islands in the eastern Pacific (4) (see the figure). This striking gradient of biodiversity deserves an explanation (1, 4, 5). On page 1532 of this issue, Bellwood and Hughes (6) present their attempt to explain this biodiversity gradient by analyzing the numbers of coral and fish species associated with 113 reef communities stretching from the Red Sea to the Gulf of California. They discovered that the area of suitable reef habitat surrounding the study sites was by far the best predictor of biodiversity at these sites.