Great Barrier Reef is the world’s largest system of coral reefs. A coral reef is a type of underwater environment shaped by limestone formations. The Great Barrier Reef is made up of more than 3,000 individual reefs that extend about 1,400 miles (2,300 kilometers) along the northeast coast of Australia. The Great Barrier Reef is famous for its beauty and for the variety of its wildlife. Many fish, other animals, and plants live on its reefs and in nearby sea-grass beds and mangrove swamps—that is, coastal wetlands where the spreading roots of mangrove trees catch and hold soil.
Ocean animals called corals form the limestone structures of the Great Barrier Reef. About 400 species of corals occur on the reef. The soft tissues of corals contain single-celled algae called zooxanthellae, which help the corals grow and make limestone skeletons. When corals die, their skeletons accumulate and become cemented together to form reefs.
Loading the player...Great Barrier Reef
The Great Barrier Reef began to form millions of years ago. But drops in sea level during ice ages have repeatedly interrupted its formation. About 14,000 years ago, the level of the oceans was lower than it is today, and the reef was above water. About 6,000 years ago, the oceans reached their current level, allowing corals to recolonize shallow coastal areas. Today, the reef is one of the world’s largest marine parks. In 1981, it was added to the UNESCO World Heritage List of sites recognized for their great cultural or natural value. The economic value of the reef lies primarily in a huge tourism industry.
Dugong
The Great Barrier Reef Marine Park Authority works to protect the reef. Such activities as oil exploration and the harvesting of rare species are outlawed or closely regulated. But the reef remains threatened. Starting in the late 1960’s, large, coral-eating crown-of-thorns starfish repeatedly invaded the reef. Pollution from land and rivers threaten near-shore habitats. The populations of sharks, turtles, and sea mammals called dugongs have declined.
The main threat to the reef is bleaching caused by global warming. Unusually high water temperatures have caused many coral species to lose their zooxanthellae, bleach (turn white), and die prematurely, thereby leading to a decline in reef building. Scientists predict that bleaching will reduce diversity among corals and the creatures that depend on them. In 2004, the Parliament of Australia passed a law prohibiting all commercial activities, except tourism, in one-third of the reef’s area. Scientists hope that reducing pollution and limiting human activities around the reef will reduce stress on the corals so that they can recover from bleaching.
During the 2000’s, severe and widespread bleaching has occurred more frequently than before on the Great Barrier Reef. Thousands of miles of coral reef can bleach during periods of extremely high water temperatures. Such large-scale disasters are known as mass bleaching events. The Great Barrier Reef experienced mass bleaching events in 2016, 2017, 2020, 2022, and 2024. From 2021 to 2022, bleaching impacted about 90 percent of the reef’s corals.
