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The Great Barrier Reef is the largest barrier reef in the world. Some species of fish and invertebrates are endemic. The Great Barrier Reef is a complex system of nearly 3,000 separate reefs, from tall underwater stands of living coral to coral sand islands. This wide range of conditions and habitats makes the Great Barrier Reef, which took millions of years to form, biologically important and one of the planet's most spectacular sites.
Tropical parts of the 1,200 mile (2,000 km) long ecoregion support diverse marine life. The ecoregion is home to an estimated 2,000 species of fish, 350 species of reef-building coral, more than 4,000 mollusk species, and 400 species of sea sponges. Among the submerged reefs are sandy islands that harbor important nesting sites for many seabird species.
The largest populations of dugongs in the world graze among the sea grass, while saltwater crocodiles breed in quiet spots. Sandy coasts are vital nesting areas for green and flatback turtles, which share habitat with their hawksbill, leatherback, and olive ridley cousins. Bottlenose, Irrawaddy, Indo-Pacific humpback, and spinner dolphins dive about among the reefs, and minke, killer, and humpback whales swim in deeper waters. Colonies of greater crested terns and other seabirds nest on the shore. The waters teem with black cod, dot and dash butterfly fish, and humphead wrasses. The firetail dottyback, yellow devilfish, and Queensland dotty fishes are all endemic.
The Great Barrier Reef is facing many threats-- from pollution to overfishing. Chemical runoff from agriculture causes algae to grow, which then decompose, depriving other animals of oxygen. Dumping of dredge spoil increases sedimentation. Oil production harms the coral and can pollute the waters of the reef. Overfishing, especially with trawls and lines, negatively affects marine fauna. Outbreaks of crown-of-thorns starfish feed on coral, destroying large swaths of coral habitat. Global warming is causing sea temperatures to rise and many scientists believe the affects of global warming are causing coral bleaching, which is killing the coral in many parts of the reef.
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