Where Are Coral Reefs Located?

In the vastness of all our oceans, just where are coral reefs located?

Coral reefs are found in all three of the Earth's oceans that have portions in the tropics.

These include the Pacific Ocean, Atlantic Ocean, and Indian Ocean (including the Red Sea). However, unlike the Caribbean and Pacific oceans, no land barriers effectively (from a genetic standpint) isolate the tropical Pacific and Indian Ocean regions.

Thus there are really only two truly isolated coral reef regions; The Caribbean and Indo-Pacific. Nonetheless, because the Red Sea has very restricted water exchange with the rest of the Indo-Pacific region, many coral reef biologists still recognize three main regions of coral reef development:

• Indo-Pacific Region
• Wider Caribbean
• Red Sea (often included as part of Indo-Pacific Region)

Despite a broad distribution pattern, coral reefs are by no means randomly scattered throughout these oceans. Rather, as with all biomes, coral reef distribution is mainly determined by a particular set of environmental conditions under which the dominant species that build that kind of ecosystem thrive.

World map of coral reef distribution. Courtesy NASA

In order to understand the global coral reef distribution 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.

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.

Coral reefs thrive only in clear warm shallow ocean waters

There is also a need for sufficient sunlight to support photosynthesis. Even in the clearest of tropical seas, photosynthesis only occurs in the relatively thin uppermost 200 ft. 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.

Major Regions of Coral Reef Development

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

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.

The Indo-Pacific Region

The larger of the two major regions of coral reef development is, by far, the Indo-Pacific.

Map of Indo-Pacific region of coral reef development.

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.

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

However, because the Red Sea is connected to the rest of the Indo-Pacific region by a relatively restricted passage, there is far less water exchange between the Red Sea and the rest of this vast region.

As a result, the Red Sea has extreme (compared to the open water of the Pacific and Indian Oceans) temperature and salinity regimes. These factors - restricted water exchange and extreme conditions - have combined to create a high degree of endemism in the Red Sea coral reef biota, and we therefore discuss this fascinating area as a separate "region" on our website's related pages on each of the major regions of coral reef development (see below).

Where are coral reefs located that contain the highest marine biodiversity within the entire Indo-Pacific 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.

Map of the Greater Caribbean region.

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 with the most animal and plant species in the Greater Caribbean region?

The best developed and most biologically diverse coral reefs are found in the western part of the Caribbean Sea proper (see map), in the vicinity of the central portion of the Belize Barrier Reef.

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.

Map of Gulf Stream and Bermuda, with sea water temperatures indicated

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 animal and plant species found in the central Caribbean.

Summary: Where Are Coral Reefs Located?

In a nutshell, 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 (see above) for hard coral growth are met.

A separate page of this website is devoted to each of three distinctive areas of coral reef development. These pages may be accessed by the links provided in the Section Navigation Menu (top left).