Amazon of the oceans

Coral reefs and their associated communities cover an estimated 600,000 square kilometers [1], mostly between between the Tropic of Capricorn and the Tropic of Cancer. Coral reefs represent less than 0.2 percent of the total area of oceans (and cover an area equivalent to 4 percent of the world's cropland area). Coral reefs are found in shallow waters, extending to depths of 30 meters and cover 15 percent of the world's coastline. Fish production on these reefs and on the adjacent continental shelf could amount to nearly 10 percent of global fisheries production if fully exploited.

Locally, coral reefs are even more important as a food source. Throughout southeast Asia, coral reef fisheries provide 10 to 25 percent of the protein available to people living along the coastlines.

Coral reefs also protect coastal areas from erosion. In the case of coral atolls, coral provides the foundation of the island itself. In the Indian Ocean, 77 percent of isolated islands and island archipelagoes are built exclusively of reef depositions.

Coral reefs resemble tropical rainforests in two ways:

• Both thrive under nutrient-poor conditions (where nutrients are largely tied up in living matter), yet support rich communities through incredibly efficient recycling processes.
• Both exhibit very high levels of species diversity.

Coral reefs and other marine ecosystems, however, contain more varied life forms than do land habitats. All but one of the world's 33 phyla (major kinds of organisms) are found in marine environments -- 15 exclusively so.[2]

Coral reefs are noted for some of the highest levels of total (gross) productivity on earth.

• The net primary productivity of coral reefs is approximately 2,500 grams of carbon per square meter per year, compared to 2,200 grams of carbon per square meter per year for tropical forests and only 125 grams of carbon per square meter per year in the open ocean.
• Coral polyps -- the thin living layer covering reef structures -- provide much of the energy that fuels these communities. These tiny animals contain algae, which convert sunlight to fuel, deriving nutrients from polyp wastes in the process.
• Reef-building corals and certain calcareous algae (which may constitute more than half of a reef's stony substance) lay down a foundation of calcium carbonate. Over generations this accumulation results in often massive structures, providing homes and hiding places for countless other creatures. Coral reefs, then, are the net result of thousands of years of growth. As such, many are among the planet's oldest living communities.

Affiliated Ecosystems

Coral reefs stand out from other marine environments because of their species diversity, but many coral reef species also depend on other affiliated ecosystems.

Often, coral reefs, mangroves, and sea grass beds are linked physically and biologically:

• reefs serve as breakwaters that allow coastal mangroves to develop;
• the calcium of the reef provides the sand and sediment in which mangroves and sea grasses grow; and
• the mangroves and sea grass communities provide energy input into the coastal ecosystem and serve as spawning, rearing, and foraging habitat for the many of the species associated with the reefs.

Other Related Articles in Print:

1. United Nations Environment Programme (UNEP) and World Conservation Union (IUCN), Coral Reefs of the World. Volume 1: Atlantic and Eastern Pacific (Gland, Switzerland: IUCN, 1988), xvi.

2. Elliot Norse, ed., Global Marine Biological Diversity: A Strategy for Building Conservation into Decision Making (Washington, D.C.: Island Press, 1993), 14.