Coral reefs are found throughout the oceans, from deep, cold waters to shallow, tropical waters. Temperate and tropical reefs however are formed only in a zone extending at most from 30°N to 30°S of the equator; the reef-building corals prefering to grow at depths shallower than 30 m (100 ft), or where the temperature range is between 16-32oc, and light levels are high.
Based on current estimates, shallow water coral reefs occupy somewhere between 284,000 and 512,000 km2 of the planet (cold-water (deep) coral reefs occupy even more area). If all the world's shallow water coral reefs were crammed together, the space would equal somewhere between an area of land ranging from the country of Ecuador (the low estimate) to Spain (the higher estimate). This area-about 198 thousand square miles in an ocean of 140 million square miles-represents less than 0.015 percent of the ocean. Yet coral reefs harbor more than one quarter of the ocean's biodiversity. That's an amazing statistic when you think about it: no other ecosystem occupies such a limited area with more life forms.
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