Where Are Coral Reefs Located?

Where are coral reefs located? As with all ecosystem typess, coral reef biome distribution is mainly determined by a particular set of environmental conditions under which the dominant species that build the ecosystem thrive.

In order to understand the global distribution of coral reefs then, we need to know something of the biology and ecology of hard corals - the primary architects of coral reefs.

Ecological Requirements of Coral Reefs

First, the hard corals that build coral reefs require warm water. Although many species may survive brief exposures to more extreme temperatures, the typical limits tolerated for long periods are from about 17-34o C. Such temperature regimes are mainly restricted to tropical seas.

Coral reefs thrive only in clear warm shallow ocean waters

Second, hard corals do not tolerate sea water salinity values that exceed those normally found in the open ocean; most will not survive prolonged exposure to water outside a range of about 30-38 parts per thousand. This tolerance range is frequently exceeded in shallow coastal waters and bays of the continents.

There is also a need for sufficient sunlight to support photosynthesis. Even in the clearest of tropical seas, such amounts are only present in the relatively thin upper 200 ft layer of the water column.

Each species of hard coral differs somewhat in their ability to tolerate variations in these environmental factors either alone or in combination, but typically each does best only within an even more narrowly defined set of "optimal" conditions.

In a nutshell then, we can answer the question: "where are coral reefs located?" with a relatively simple answer: only in those places in the world's oceans where all of the ecological requirements for hard coral growth are met.

Coral Reef Distribution

Because of their restrictive ecological requirements, global coral reef distribution generally corresponds to the distribution of shallow, submarine platforms within the tropics.

Map of global coral reef distribution. Courtesy NASA.

Such geologic features happen to be concentrated towards the western ends of the three major ocean basins (Atlantic, Pacific and Indian) and this is where most of the world's coral reefs are to be found.

However, there are really only two major oceanic "provinces" of coral reef development contained within the three great oceanic basins: (1) the Indo-Pacific, and (2) the Greater Caribbean (or Tropical Western Atlantic) (see diagram, right).

There are no effective physical or ecological boundaries to prevent larval transport and dispersal between the tropical western Pacific, Indian Ocean, and the Red Sea. Therefore this enormous oceanic area is in fact but a single biologically continuous region that houses a common marine fauna.

The Indo-Pacific Region

The larger of the two major regions of coral reef development is, by far, the Indo-Pacific. This vast oceanic realm (see diagram; right) includes much of the Central and South Pacific Ocean as far north as Hawaii and southern Japan.

Further south, it includes Taiwan and coastal regions of Southeast Asia, the islands of the Philippines, northern New Zealand, and most of the Australian coast.

The easternmost part of the region includes Indonesia and most of the Indian Ocean to the east coast of Africa, as well as the entire Red Sea.

Where are coral reefs located that contain the highest marine biodiversity within this region? The greatest number of coral reef species are found in an area that extends from the southern Philippines through western New Guinea to the islands of eastern Indonesia.

The Greater Caribbean Region

The second and far smaller region of coral reef development is the tropical western Atlantic, also known as the Greater Caribbean.

This region spans the entire Caribbean Sea proper (including the Antilles), as well as The Bahamas and south Florida to the north.

North of The Bahamas, the cold, deep waters of the North Atlantic preclude successful transport and colonization of tropical species to any shallow shores (with the singular exception of Bermuda).

South of the Caribbean Sea, it also includes the northeastern coast of South America to the Amazon and Orinoco Rivers.

Where are coral reefs located that are best developed within this region? The center of marine biodiversity for the Greater Caribbean lies in the western part of the Caribbean Sea, in the vicinity of the Belize Barrier Reef.

Minor Areas of Coral Reef Development

Other than the two major bioregions discussed above, where are coral reefs located?

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.

Bermuda presents a good example of such an area. The mighty Gulf Stream carries warm water and a continual supply of new tropical "recruits" (seeds of shoreline plants, coral reef animal larvae and juvenile life stages) northward to Bermuda from the central Caribbean Sea.

This has enabled Bermuda to maintain a coral reef "outpost" far north of where one could otherwise exist, defying the general pattern of "where are coral reefs located?" in the western Atlantic Ocean.

However, only 26 of the 70 or so known Caribbean hard coral species have been found in Bermuda, and only about a third of all the shallow water species found in the central Caribbean.

Related Pages

Bahamas Diving

Caribbean Diving

Pacific Diving