Where Are Coral Reefs Located?
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.
Instead it is clear that most are 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.
This is no coincidence, for the broad-scale distribution of coral reefs is largely determined by the restrictive ecological requirements of reef-building corals:
(1) First, the Scleractinian corals that build tropical reefs require sunlight found in clear, shallow ocean waters. These needs are tied to the coral animals' dependence upon the algal partners (zooxanthellae) dwelling within the coral tissues. Even in the clearest of tropical seas, most photosynthesis only occurs in the relatively thin uppermost 100-200 ft. of the water column.
(2) 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.
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.
A Biogeographic Perspective
Coral reefs are not just piles of undersea "rocks" - they are ecologically and economically important ecosystems composed in part of highly diverse assemblages of marine organisms.
Thus, our discussion of coral reef distribution would not be complete without looking at it from the perspective of biogeography - the distribution of species that comprise the coral reef communities of the world.
Major Regions of Coral Reef Development
From that perspective, 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 informaation on these regions, use the links (above) to visit the page of our website devoted to each.
Minor Areas of Coral Reef Development
Smaller, fragmented areas of coral reef development occur in the eastern Pacific, tropical eastern Atlantic, off western Australia, along the east coast of southern Brazil, off southern Japan, and around the island of Bermuda in the western Atlantic.
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.