Great Barrier Reef

An aerial photograph of a section of the Great Barrier Reef.

The Great Barrier Reef is the world's largest coral reef system, composed of roughly 3,000 individual reefs and 900 islands, that stretch for 1,616 miles covering an area of approximately 214,000 square miles. The reef is located in the Coral Sea, off the coast of Queensland in northeast Australia. A large part of the reef is protected by the Great Barrier Reef Marine Park.

The Great Barrier Reef can be seen from outer space and is sometimes referred to as the single largest organism in the world. In reality, it is made up of many millions of tiny organisms, known as coral polyps. The reef was also selected as a UNESCO World Heritage Site in 1981, and it has been labelled it one of the seven natural wonders of the world. The Queensland National Trust has named it a state icon of Queensland. Each year, some two million tourists from around the world come to swim, fish, and enjoy the magnifident ecosystem of the Great Barrier Reef. In recent years, concern has grown that climate change and global warming have become serious threats to the reef.

Geology and Geography

Satellite image of part of the Great Barrier Reef adjacent to the Queensland coastal areas of Proserpine and Mackay.

According to the Great Barrier Reef Marine Park Authority, the current, living reef structure is believed to have begun growing on an older platform about 20,000 years ago. The Reef Research Centre, a Cooperative Research Centre, has found coral 'skeleton' deposits that date back half a million years.

From 20,000 years ago until 6,000 years ago, the sea level rose steadily. As the sea level rose, the corals could grow higher on the hills of the coastal plain. By around 13,000 years ago the sea level was 60 metres lower than the present day, and corals began to grow around the hills of the coastal plain - by then, continental islands. As the sea level rose further still, most of the continental islands were submerged. The corals could then overgrow the hills, to form the present cays and reefs. Sea level on the Great Barrier Reef has not risen significantly in the last 6,000 years.

In the northern part of the Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these reef structures are not found in the rest of the Great Barrier Reef system.

Species of the Great Barrier Reef

Green Sea Turtle on the Great Barrier Reef

The Great Barrier Reef supports a diversity of life, including many vulnerable or endangered species. Thirty species of whales, dolphins, and porpoises have been recorded in the reef, including the Dwarf Minke Whale, Indo-Pacific Humpback Dolphin, and the Humpback Whale. Also, large populations of dugongs live there. Six species of sea turtle come to the reef to breed – Green Sea Turtle, Leatherback Sea Turtle, Hawksbill turtle, Loggerhead Sea Turtle, Flatback Turtle and the Olive Ridley. There are 15 species of seagrass that attract the dugongs and turtles.

Over 200 species of birds (including 40 species of waterbirds) live on the Great Barrier Reef, including the White-bellied Sea Eagle and Roseate Tern. Some 5000 species of mollusc have been recorded on the reef, including the Giant Clam and various nudibranches and cone snails, as well as 17 species of sea snake. More than 1500 species of fish live on the reef, including the Clownfish, Red Bass, Red-Throat Emperor, and several species of Snapper and Coral Trout. Four-hundred species of corals, both hard corals and soft corals, are found on the reef. Five-hundred species of marine algae or seaweed live on the reef, along with the irukandji jellyfish.

Environmental threats

Water quality

Storage Silos on the Gladstone waterfront - An industrial area in the water catchment area.

Unlike most reef environments worldwide, the Great Barrier Reef's water catchment area is home to industrialized urban areas, and where extensive areas of coastal lands and rangelands have been used for agricultural and pastoral purposes.

The coastline of north eastern Australia has no major rivers. It also has several major urban centres including Cairns, Townsville, Mackay, Rockhampton, and the industrial city of Gladstone. Cairns and Townsville are the largest of these coastal cities with populations of approximately 150,000 each.

Due to the range of human uses made of the water-catchment area adjacent to the Great Barrier Reef, some 400 of the 3000 reefs are within a risk zone where water quality has declined owing to sediment and chemical runoff from farming, and to loss of coastal wetlands which are a natural filter. The principal agricultural activity is sugar cane farming in the wet tropics and cattle grazing in the dry tropics regions. Both are considered significant factors affecting water quality.

It is thought that the mechanism behind poor water quality affecting the reefs is due to increased light and oxygen competition from algae, but it has also been suggested that poor water quality encourages the spread of infectious diseases among corals. Copper, a common industrial pollutant in the waters of the Great Barrier Reef, has been shown to interfere with the development of coral polyps.

Climate change

Bioerosion (coral damage) such as this may be caused by coral bleaching.

Some people believe that the most significant threat to the status of the Great Barrier Reef and of the planet's other tropical reef ecosystems is climate change—comprised of global warming and the El Niño effect. Many of the corals of the Great Barrier Reef are currently living at the upper edge of their temperature tolerance, as demonstrated in the coral bleaching events of the summers of 1998, 2002 and most recently 2006.

Under the stress of waters that remain too warm for too longorals expel their photosynthesising zooxanthellae and turn colorless, revealing their white, calcium carbonate skeletons. If the water does not cool within about a month, the coral will die. Australia experienced its warmest year on record in 2005. Abnormally high sea temperatures during the summer of 2005-2006 have caused massive coral bleaching in the Keppel Island group. A draft report by the UN Intergovernmental Panel on Climate Change states that the Great Barrier Reef is at grave risk and will be "functionally extinct" by 2030, warning that coral bleaching likely will become an annual occurence.

Global warming may have triggered the collapse of reef ecosystems throughout the tropics. Increased global temperatures are thought by some to bring more violent tropical storms, but reef systems are naturally resilient and recover from storm battering. While some believe that an upward trend in temperature will cause much more coral bleaching, others suggest that while reefs may die in certain areas, other areas will become habitable for corals, and form coral reefs.

However, Kleypas et al. in their 2006 report suggest that the trend towards ocean acidification indicates that as the sea's pH decreases, corals will become less able to secrete calcium carbonate.Reef scientist Terry Done has predicted a one-degree rise in global temperature would result in 82 percent of the reef bleached, two degrees resulting in 97 percent and three degrees resulting in 'total devastation'.

Crown-of-thorns starfish

Crown-of-thorns starfish

The crown-of-thorns starfish is a coral-reef predator that preys on coral polyps by climbing onto them, extruding the stomach over them, and releasing digestive enzymes to then absorb the liquified tissue. An individual adult of this species can wipe out up to 19.6 square feet of living reef in a single year

Although large outbreaks of these starfish are believed to occur in natural cycles, human activity in and around the Great Barrier Reef can worsen the effects. Reduction of water quality associated with agriculture can cause the crown-of-thorns starfish larvae to thrive. Overfishing of its natural predators, such as the Giant Triton, is also considered to contribute to an increase in the number of crown-of-thorns starfish.

Overfishing

The unsustainable overfishing of keystone species, such as the giant triton, can cause disruption to food chains vital to life on the reef. Fishing also impacts the reef through increased pollution from boats, by-catch of unwanted species, and reef habitat destruction from trawling, anchors and nets. As of the middle of 2004, approximately one-third of the Great Barrier Reef Marine Park was protected from species removal of any kind, including fishing, without written permission

Shipping

Shipping accidents are also a real concern, as several commercial shipping routes pass through the Great Barrier Reef. From 1985-2001, there were 11 collisions and 20 groundings on the inner Great Barrier Reef shipping route. The leading cause of shipping accidents in the Great Barrier Reef is human error.

Although the route through the Great Barrier Reef is not easy, reef pilots consider it safer than outside the reef in the event of mechanical failure, since a ship can sit safely in its protected waters while being repaired. On the outside, wind and swell will push a ship towards the reef and the water remains so deep right up to the reef, that anchoring is impossible.

Waste and foreign species discharged in ballast water from ships are a further biological hazard to the Great Barrier Reef. In addition,Tributyltin (TBT) compounds found in certain paints on ship hulls leaches into seawater and is toxic to marine organisms and humans. Efforts are underway to restrict its use.

Oil

Oil drilling is not permitted on the Great Barrier Reef, yet oil spills are still considered one of the biggest threats to the reef, with a total of 282 oil spills between 1987-2002. It is believed that the reef may sit above a major natural oil reservoir. In the 1960s and early 1970s, there was some speculation about drilling for oil and gas there.

Human use

Starfish on coral - typically, tourists photograph the natural beauty of the reef.

The Great Barrier Reef has long been known to and utilized by Indigenous Australian people, whose occupation of the continent is thought to extend back 40,000 to 60,000 years or more.For these 70 or so clan groups, the reef is also an important part of their Dreamtime.

The Reef first became known to Europeans when the HM Bark Endeavour, captained by explorer James Cook, ran aground there on June 11, 1770 and sustained considerable damage. It was finally saved after lightening the ship as much as possible and re-floating it during an incoming tide.

Management

In 1975, the Government of Australia created the Great Barrier Reef Marine Park and defined what activities were prohibited on the Great Barrier Reef. The park is managed, in partnership with the Government of Queensland, through the Great Barrier Reef Marine Park Authority to ensure that it is widely understood and used in a sustainable manner. A combination of zoning, management plans, permits, education, and incentives (such as eco-tourism certification) are used in the effort to conserve the Great Barrier Reef.

In July 2004, a new zoning plan was brought into effect for the entire Marine Park, and has been widely acclaimed as a new global benchmark for the conservation of marine ecosystems. While protection across the Marine Park was improved, the highly protected zones increased from 4.5 percent to over 33.3 percent.

A scuba diver looking at a giant clam on the Great Barrier Reef.

Tourism

Due to its vast biodiversity, warm, clear waters and its accessibility from the floating guest facilities called 'live aboards,' the reef is a very popular destination for tourists, especially scuba divers. Many cities along the Queensland coast offer boat trips to the reef on a daily basis. Several continental islands have been turned into resorts.

As the largest commercial activity in the region, tourism in the Great Barrier Reef generated some 4.16 billion dollars, according to a 2005 estimate.) There are approximately two million visitors to the Great Barrier Reef each year. Although most of these visits are managed in partnership with the marine tourism industry, there are some very popular areas near shore (such as Green Island) that have suffered damage due to overfishing and land based run off.

A glass-bottomed boat on the Great Barrier Reef.

A variety of boat tours and cruises are offered, from single day trips, to longer voyages. Boat sizes range from dinghies to superyachts. Glass-bottomed boats and underwater observatories are also popular, as are helicopter flights. But by far, the most popular tourist activities on the Great Barrier Reef are snorkelling and diving. Pontoons are often used for snorkelling and diving. When a pontoon is used, the area is often enclosed by nets. The outer part of the Great Barrier Reef is favored for such activities, due to water quality.

Management of tourism in the Great Barrier Reef is geared towards making tourism ecologically sustainable. A daily fee is levied that goes towards research of the Reef.

Fishing

The fishing industry in the Great Barrier Reef, controlled by the Queensland Government, is worth some 816 million dollars annually. It employs approximately 2000 people, and fishing in the Great Barrier Reef is pursued commercially, for recreation, and as a traditional means for feeding one's family. Wonky holes in the reef provide particularly productive fishing areas.

References

ISBN links support NWE through referral fees

• Doubilet, David. Great Barrier Reef (National Geographic Insight), National Geographic, 2002. ISBN 978-0792264750

• Mylne, Lee. Frommer's Portable Australia's Great Barrier Reef, Frommer's, 2007. ISBN 978-0792264750

• Zell, Len. Lonely Planet Diving & Snorkling the Great Barrier Reef, Lonely Planet Publications, 2006. ISBN 978-1746191232

External links

• Travel guide to Great Barrier Reef from Wikitravel
• Great Barrier Reef Marine Park Authority
• CRC Reef Research Centre
• Biological monitoring of coral reefs of the GBR
• Great Barrier Reef (World Wildlife Fund)
• Dive into the Great Barrier Reef from National Geographic
• Underwater photo gallery from the Great Barrier Reef

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