Shallow tropical reefs in the Indian and Pacific oceans boast the most coral species.
Reef-building corals are restricted in their geographic distribution by factors such as the temperature and the salinity (salt content) of the water. The water must also be clear to permit high light penetration. Because of these environmental restrictions, reefs generally are confined to tropical and semitropical waters. The diversity of reef corals (the number of species), decreases in higher latitudes up to about 30° north and south, beyond which reef corals are usually not found. [a]
To date, over 1,500 species of reef-building corals have been identified, with new discoveries occuring each year. [b] Of the known species, over 1,400 are found in the Indian and Pacific oceans—an area known as the Indo-Pacific region—and only approximately 70 are found in the Atlantic/Caribbean region. [c] There are over 500 species of coral found in the Coral Triangle alone—a region encompassing the waters around the Phillipines, Malaysia, Indonesia, Timor-Leste, Papua New Guinea, and the Solomon Islands—making this region one of the global hotspots of coral diversity. Even outside of the Coral Triangle, a typical reef in the Indo-Pacific region contains nearly twice as many coral species as an Atlantic/Caribbean reef. The diversity of other species found on Indo-Pacific reefs is also much greater than in the Atlantic/Caribbean.