Coral Reef

Coral Reef Formations | Coral Reef Biology | Hazards to Reefs | Coral Reefs Maps | Coral Reef Articles

"Coral reefs are the most biodiverse of all known marine ecosystems, and maintain much higher genetic diversity than tropical rainforests. They therefore represent the world’s most significant storehouse of potential future products." (John McManus, The International Coral Reef Initiative: Partnership Building and Framework Development, report of the ICRI Workshop, Dumaguete City, The Philippines, 29 May-2 June 1995.)

The term "coral reef" generally refers to a marine ecosystem in which the main organisms are corals that house algal symbionts within their tissues. These ecosystems require:

1) fully marine waters;
2) warm temperatures; and
3) ample sunlight.

They are therefore restricted to shallow waters of tropical and subtropical regions.

Coral Reef

Corals that do not have algal symbionts can also form significant reef communities in deeper, darker, and colder waters, but these communities are distinguished as cold-water coral bioherms.

The more technical definition of "coral reef" includes an additional geological requirement that the reef organisms produce enough calcium carbonate to build the physical reef structure. The coral reef community lives only on the surface veneer of the reef, on top of already existing skeletal material left behind by previous reef-builders. Many processes act to break down the skeletal material and reef as soon it is laid down by organisms. These include mechanical processes such as waves and currents, and a wide array of biological processes (e.g., bioerosion). Some of the best known bioeroders are large organisms such as parrotfish and sponges, but much of the bioerosion occurs at the microscopic scale by organisms such as algae and fungi. A coral reef is produced only if the coral reef community produces more calcium carbonate than is removed. Indeed, some coral reef communities grow too slowly to build a reef.

Coral reefs can take a variety of forms, defined in following;

Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.
Fringing reef – reef that is directly attached to a shore or borders it with an intervening shallow channel or lagoon.
Barrier reef – reef separated from a mainland or island shore by a deep lagoon; see Great Barrier Reef.
Patch reef – an isolated, often circular reef, usually within a lagoon or embayment.
Ribbon reef – long, narrow, somewhat winding reef, usually associated with an atoll lagoon.
Table reef – isolated reef, approaching an atoll type, but without a lagoon.
Atoll reef – a more or less circular or continuous barrier reef extending all the way around a lagoon without a central island; see atoll.
Bank Reef – Bank reefs are larger than patch reefs and are linear or semi-circular in outline.

Coral Reef Biology

Image of a healthy reef Thousands of corals species exist worldwide. Stony (hermatypic) corals are the best recognized because of their elaborate and colorful formations. One trait of stony corals is their capacity to build reef structures that range from tens, to thousands of meters across. As they grow, reefs provide structural habitats for hundreds to thousands of different vertebrate and invertebrate species.

Although corals are found throughout the world, reef-building corals are confined to waters that exhibit a narrow band of characteristics. The water must be warm, clear, and saline. These waters are almost always nutrient-poor as well. Physiologically and behaviorally, corals have evolved to take advantage of this unique environment and thrive.

Not only are reef-building corals confined by a specific range of environmental conditions, but as adults, almost all of them are sessile. This means that for their entire lives, they remain on the same spot of the sea floor. Thus, reef-building corals have developed reproductive, feeding, and social behaviors that allow them to gain the maximum survival benefit from their situation. (Reference: NOAA)

Hazards to Coral Reefs

Corals weakened by a combination of natural and anthropogenic stresses may be unable to recover from disease outbreaks. Coral reefs face numerous hazards and threats. As human populations and coastal pressures increase, reef resources are more heavily exploited, and many coral habitats continue to decline. Current estimates note that 10 percent of all coral reefs are degraded beyond recovery. Thirty percent are in critical condition and may die within 10 to 20 years. Experts predict that if current pressures are allowed to continue unabated, 60 percent of the world’s coral reefs may die completely by 2050 (CRTF, 2000). Most scientists believe coral reef degradation occurs in response to both natural and anthropogenic (human-caused) stresses. (Reference: NOAA)

Coral Reefs Maps

Atlantic and Eastern Pacific Coral Reef Maps

Indian Ocean, Red Sea and Gulf Coral Reef Maps

Central and Western Pacific Coral Reef Maps

These maps, from the book Coral Reefs of the World by Susan M. Wells, are posted with permission of the publishers IUCN Conservation Monitoring Center and United Nations Environment Programme(UNEP).

UNEP/IUCN(1988). Coral Reefs of the World.Volume 1, Volume 2 and Volume 3: UNEP Regional Seas Directories and Bibliographies. IUCN, Gland, Switzerland and Cambridge, U.K./UNEP, Nairobi, Kenya. ISBN: 2-88032-943-4, 2-88032-944-2, 2-88032-945-0

Coral Reef

Coral Reef Formations

Coral Reef Biology

Hazards to Coral Reefs

Coral Reefs Maps

Coral Reefs Articles

Coral Reef Glossary