Biodiversity and Coral Reefs

Coral reefs have often been described as the Rainforests of the Sea. 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. Additionally, 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.

The most species-rich reefs are found in a swath extending through Southeast Asia to the Great Barrier Reef, off northeastern Australia.

• More than 700 species of corals alone are found in this region.
• The Indo-West-Pacific supports more than 16 percent of the world's estimated 19,000 species of freshwater and marine fish.
• The Great Barrier Reef, the world's largest system of coral reefs, covers 349,000 square kilometers and occupying only one-tenth of one percent of the ocean surface, supports:
  • nearly 8 percent (1,500) of the world's fish species,
  • more than 700 species of coral,
  • over 4,000 species of mollusks.
  • 252 species of birds nest and breed on the coral cays, five species of turtles live on the reef, and several species of whales and dolphins are associated with it.
• In the Philippines -- The Bolinao Reef Complex, Tubbataha Reef, and Apo and Balicasag Island Reefs) -- more than 2,000 fish species live on or near coral reefs, compared to only 448 in the waters surrounding Hawaii and 507 in the Bahamas.

The diversity of species in smaller portions of coral reefs is equally impressive.

• The Capricorn reefs at the southern end of the Great Barrier account for only 3 percent of the area of the Great Barrier Reef complex yet support 859 species of fish and 72 percent of the complex's coral species. This richness of fish species (4.5 percent of the world's total) compares roughly with Costa Rica's richness of plant (3 percent of the world's total) and mammal (4.7 percent) species, yet Costa Rica is four times as large as the Capricorn portion of the Great Barrier Reef.

Compare these estimates of diversity to that in other coral reef ecosystems:

• The coastal waters of the Mediterranean sea support less than 25 percent as many fish species as the Great Barrier Reef and less than 20 percent as many as the Philippines.
• The mid-Atlantic seaboard of the United States, roughly comparable in length to the Great Barrier Reef, has only 250 species of fish -- less than one fifth as many as the Great Barrier Reef supports.

However, reefs outside of the Indo-West-Pacific region are important for the distinct populations and species they contain.

• Although fewer types of corals are found in the Red Sea, this basin contains more endemics (species found nowhere else) than other portions of the Eastern Indian Ocean.

Although coral reefs share numerous attributes with tropical forests, the level of local species endemism is much lower on reefs.

• Within the Indo-Pacific, for example, the vast majority of coral species are found throughout the region.
• Because coral reef species disperse readily, locally endemic species occur only on isolated oceanic islands. For instance, 20 percent of the corals and 30 percent of the inshore fishes in Hawaii are endemic to that island chain.

Because coral-related species tend to be widely distributed, they are less threatened than tropical forests are by species extinction. However, degradation threatens both ecosystems' ability to meet human needs. -

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Sources:
1. D. Bryant et al. Reefs at Risk: A map-based indicator of threats to the world's coral reefs. (Washington DC: World resources Institute, 1998)
2. www.wri.org/biodiv/marine_diversity.html