During tropical floods, runoff containing fertilizer and pesticides is dispensed into the reef's waters and harms its delicately balanced ecosystem. Pollution is another concern, as another oil spill occurred in 2010, when the Chinese coal-carrying ship Shen Neng1 ran aground on the reef, leaking a 1.86-mile-long (3 km) ribbon of oil and destroying precious coral and marine life.ĭeclining water quality is a major factor in the pollution of the Great Barrier Reef.
There is widespread concern that such intense tourism might be harming the fragile reefs. Ī tourism hotspot, approximately 2 million people visit the Great Barrier Reef every year, according to the Australian government. Lagoonal reefs are found in the southern Great Barrier Reef, and further north, off the coast of Princess Charlotte Bay. Most occur in the southern part of the Great Barrier Reef and are attached to high islands such as the Whitsunday Islands. The northern part of the Great Barrier Reef features ribbon reefs, which are narrow and winding, and deltaic reefs, which, as the name implies, resemble river deltas.įringing reefs, which attach to the mainland, are infrequent. These types of reefs are found surrounding Lizard Island as well as far north of the Great Barrier Reef Marine Park and in the Swain Reefs.įlat reefs known as planar reefs are found in the northern and southern parts, near Cape York Peninsula, Princess Charlotte Bay and Cairns. The Great Barrier Reef World Heritage Area is divided into 30 bioregions that consist of different types of reefs.Ĭresentic reefs - shaped like crescents as the name implies - are the most common shape of reef in the middle of the system. Most of the continental islands were submerged, and the coral remained to form the reefs and cays (low-elevation sandy islands) of today. The sea level continued to rise during a warming period as glaciers melted. About 13,000 years ago, the sea level was 200 feet (61 meters) lower than the current level, and corals began to grow around the hills of the coastal plain, which had become continental islands. The land that forms the base of the Great Barrier Reef is the remains of the sediments of the Great Dividing Range, Australia's largest mountain range. This period, which occurred from about 26,500 years ago to 19,000 to 20,000 years ago, ushered in significant environmental changes in the region, including a dramatic drop in sea levels. Reefs on Australia's continental shelf have taken on many forms, depending on the sea level, and the current formation is about 6,000 to 8,000 years old.Īccording to the Australian Institute of Marine Science and other scientific research, the current reef began to form during the Last Glacial Maximum. The Great Barrier Reef is about 500,000 years old, but it hasn't always looked as it does today. The reefs are vital to the survival of several endangered species, so much so that in 2004, the Great Barrier Reef Marine Park Authority (GBRMPA) increased the amount of highly protected zones by almost 30 percent.
The most common types of seagrasses are Halophila and Halodule. The 15 species of seagrass found along the reef attract the dugongs and turtles and provide habitats for the fish. The white-bellied sea eagle and roseate tern are frequently sighted. The Great Barrier Reef is home to 215 species of birds (including 22 species of seabirds and 32 species of shorebirds) that visit the reef or nest or roost on the islands. Saltwater crocodiles live in mangrove and salt marshes on the coast near the reef.
Six species of sea turtles - the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle, and the olive ridley - come to the reef to breed. Seventeen species of sea snake live on the Great Barrier Reef in warm waters up to 160 feet (49 meters) deep and are more common in the south than in the northern section. About 5,000 species of mollusks live on the reef. More than 1,500 fish species live on the reef, including the clownfish, red bass, red-throat emperor, and several species of snapper and coral trout. Large populations of dugongs, large marine mammals that are relatives of the manatees, make their home along the reef. They all live in different coastal areas of the ocean. This dugong is one of four seacow, or Sirenians, species in the world.