Coral reefs are found in all three of the Earth’s oceans that have portions in the tropics – the Atlantic, Pacific and Indian.
However, coral reefs are not randomly scattered throughout each of these great ocean basins (see map below).
Why? Because the global distribution of coral reefs is largely determined by the ecological requirements of the reef-building corals themselves.
The coral animals that build tropical reefs require sunlight found in clear, shallow ocean waters.
This need for light is tied to the corals’ dependence upon their photosynthetic partners (zooxanthellae) dwelling within the animal tissues. Even in the clearest of tropical seas, most photosynthesis only occurs in the relatively thin uppermost 100-200 ft. of the sea.
Reef-building corals also require warm water. Although many species may survive brief exposures to more extreme temperatures, the limits tolerated for long periods are from about 17-34 degrees C. – annual temperature regimes mainly restricted to tropical seas.
Thus, the Earth’s coral reefs are mainly concentrated towards their western margins (see global map, below), a distribution pattern that generally corresponds to the occurrence of shallow submarine platforms within tropical seas.
Each species of hard coral differs somewhat in their ability to tolerate variations in these environmental factors, but each does best only within an even more narrowly defined set of “optimal” conditions – and shallow tropical seas are those parts of the oceans where “optimal conditions” for coral growth are most frequently found.
Global distribution of coral reefs.
Globally, three major regions of coral reef development are generally recognized, each with a somewhat distinctive biota. These are:
(1) The Indo-Pacific – Includes most of the Indian Ocean (excluding the Red Sea), and the western Pacific.
(2) The Wider Caribbean (tropical western Atlantic) – Includes Florida, The Bahamas, Caribbean Sea proper, and coastal waters off northeastern S. America.
(3) The Red Sea
For more information on these regions, use the links (above) to visit the page of our website devoted to each.
In the Atlantic Ocean basin, smaller, fragmented areas of coral reef development occur in the tropical eastern Atlantic,along the east coast of southern Brazil, and around the island of Bermuda.
The Pacific basin houses similar small pockets of limited reef development in the eastern Pacific, off western Australia, and off southern Japan.
For the most part, these areas are at the extreme margins of the ecological tolerances of hard corals, where environmental conditions are only minimally capable of sustaining only a fraction of the hard coral species found in the two main regions of reef development.
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