The Great Barrier Reef is the largest coral reef system in the world. It includes over 2,900 separate reefs and 900 islands. These reefs and islands stretch for more than 2,300 kilometers (1,400 miles) across an area of about 344,400 square kilometers (133,000 square miles). The reef is located in the Coral Sea, near the coast of Queensland, Australia. It is separated from the coast by a channel that is 160 kilometers (100 miles) wide in some places and over 61 meters (200 feet) deep. The Great Barrier Reef is visible from space and is the largest structure on Earth built by living things. This structure is made by billions of tiny organisms called coral polyps. It supports many different types of life and was chosen as a World Heritage Site in 1981. In 1997, CNN named it one of the Seven Natural Wonders of the World. In 2007, it was added to Australia's list of World Heritage places. In 2006, it was named a state icon of Queensland by the Queensland National Trust.
A large part of the reef is protected by the Great Barrier Reef Marine Park. This protection helps reduce harm from human activities, such as fishing and tourism. Other challenges to the reef include pollution from human-made sources, climate change that causes coral bleaching, the dumping of dredging sludge, and recurring outbreaks of the crown-of-thorns starfish. A study published in 2012 found that the reef has lost more than half of its coral cover since 1985. A 2020 study confirmed that over half of the reef's coral cover was lost between 1995 and 2017. The full impact of a major bleaching event in 2020 is still being studied.
The Great Barrier Reef has been used by Aboriginal Australian and Torres Strait Islander peoples for a long time. It is an important part of their cultures and spiritual beliefs. The reef is a popular place for tourists, especially in the Whitsunday Islands and Cairns areas. Tourism is an important source of income for the region, bringing more than AUD$3 billion each year. In 2014, Google launched an underwater 3D view of the Great Barrier Reef.
A 2016 report showed that coral bleaching was more widespread than previously believed, especially in the northern parts of the reef due to rising ocean temperatures. In 2016, a magazine published an article that described the reef as dying. This article was criticized for being too early and for possibly slowing efforts to help the reef recover. In 2017, a study in the journal Nature found that large areas of the reef in the north had died in 2016 because of high water temperatures, which scientists linked to global climate change. In 2018, the number of baby corals born on the reef dropped sharply. Scientists say this is the beginning of a major change in the reef's ecosystem. Many adult corals died during the 2016–2017 bleaching events, leading to fewer baby corals being born. The types of corals that reproduce have also changed, which could lead to long-term changes in the reef if the trend continues.
The Great Barrier Reef Marine Park Act of 1975 requires a report on the reef's health, challenges, and future every five years. The most recent report was published in 2019. In 2022, another mass bleaching event was confirmed, raising concerns about the reef's future, especially with the possible effects of the El Niño weather pattern.
The Australian Institute of Marine Science studies the reef's condition each year. The 2022 report showed the greatest recovery in 36 years. This recovery was mainly due to the regrowth of two-thirds of the reef by a fast-growing type of coral called Acropora, which is the most common coral in the area.
"Discovery" and naming
The Great Barrier Reef has been lived near and used for a long time by the Aboriginal Australian and Torres Strait Islander peoples. It is an important part of their cultures and beliefs.
The first European to discover the Great Barrier Reef was James Cook in 1770. He sailed and mapped the east coast of Australia. On June 11, 1770, Cook’s ship, HMS Endeavour, hit a shallow area south of the present-day location of Cooktown. It took seven weeks to fix the ship.
Matthew Flinders gave the reef its name after he mapped it in more detail in 1802. He used different terms to describe the reefs that make up what we now call the Great Barrier Reef. He called one reef "great reef," another "barrier reef" because it stopped ships or waves from reaching the shore, and the group of reefs together "Barrier Reefs."
Geology and geography
The Great Barrier Reef is a unique part of the East Australian Cordillera division. It stretches from the Torres Strait, between Bramble Cay (its northernmost island) and the south coast of Papua New Guinea, to the unnamed passage between Lady Elliot Island (its southernmost island) and Fraser Island. Lady Elliot Island is 1,915 km (1,190 mi) southeast of Bramble Cay in a straight line. It includes the smaller Murray Islands.
According to the plate tectonic theory, Australia has moved northward at a rate of 7 cm (2.8 in) per year since the Cenozoic era. Eastern Australia experienced tectonic uplift, which shifted the drainage divide in Queensland 400 km (250 mi) inland. During this time, Queensland had volcanic eruptions that formed central and shield volcanoes and basalt flows. Some of these became volcanic islands. After the Coral Sea Basin formed, coral reefs began to grow in the Basin. However, until about 25 million years ago, northern Queensland was in temperate waters south of the tropics, which were too cool for coral growth. The development of the Great Barrier Reef is complex; after Queensland moved into tropical waters, reef growth and decline were influenced by changes in sea level.
Reefs can grow in diameter by 1 to 3 cm (0.39 to 1.18 in) per year and vertically by 1 to 25 cm (0.39 to 9.84 in) per year. However, they grow only above a depth of 150 meters (490 ft) because they need sunlight, and they cannot grow above sea level. When Queensland moved into tropical waters 24 million years ago, some coral grew, but erosion of the Great Dividing Range caused sediment buildup, forming river deltas, oozes, and turbidites, which were not suitable for coral growth. Ten million years ago, sea levels dropped, increasing sedimentation. The reef’s substrate may have needed to build up from sediment until its edge was far enough for suspended sediments to no longer block coral growth. Around 400,000 years ago, a warm Interglacial period occurred, with higher sea levels and a 4°C (7°F) increase in water temperature.
The land that formed the current Great Barrier Reef was a coastal plain made from eroded sediments of the Great Dividing Range, with some larger hills (most of which were remnants of older reefs or, rarely, volcanoes). The Reef Research Centre, a Cooperative Research Centre, found coral skeleton deposits dating back half a million years. The Great Barrier Reef Marine Park Authority (GBRMPA) considers the earliest evidence of complete reef structures to be 600,000 years ago. According to the GBRMPA, the current living reef structure began growing on older platforms about 9,000 years ago. The Australian Institute of Marine Science agrees, placing the start of the current reef’s growth at the time of the Last Glacial Maximum, when sea levels were 120 meters (390 ft) lower than today.
From 20,000 to 6,000 years ago, sea levels rose globally. As they rose, corals could grow higher on the newly submerged edges of coastal plain hills. By around 13,000 years ago, sea levels were only 60 meters (200 ft) lower than today, and corals began surrounding the hills, which had become continental islands. As sea levels rose further, most of these islands were submerged. Corals then overgrew the submerged hills, forming the present cays and reefs. Sea levels have not risen significantly in the last 6,000 years. The CRC Reef Research Centre estimates the current living reef structure to be 6,000 to 8,000 years old. Shallow water reefs visible in air-photographs and satellite images cover 20,679 km², most of which (about 80%) grew on limestone platforms from past (Pleistocene) reef growth phases.
Remains of an ancient barrier reef similar to the Great Barrier Reef are found in The Kimberley, Western Australia.
The Great Barrier Reef World Heritage Area is divided into 70 bioregions, 30 of which are reef bioregions. In the northern part of the reef, ribbon reefs and deltaic reefs have formed; these structures are not found elsewhere in the reef system. A previously undiscovered reef, 500 meters tall and 1.5 km wide at the base, was found in the northern area in 2020. There are no atolls in the system, and reefs attached to the mainland are rare.
Fringing reefs are widespread but most common in the southern part of the Great Barrier Reef, attached to high islands like the Whitsunday Islands. Lagoonal reefs are found in the southern reef and further north, off the coast of Princess Charlotte Bay. Crescentic reefs are the most common shape in the middle of the system, such as those surrounding Lizard Island. Crescentic reefs are also found in the far north of the Great Barrier Reef Marine Park and in the Swain Reefs (20–22 degrees south). Planar reefs are found in the northern and southern parts, near Cape York Peninsula, Princess Charlotte Bay, and Cairns. Most islands on the reef are located on planar reefs.
Wonky holes can have localized effects on the reef, causing upwelling of fresh water, sometimes rich in nutrients that may lead to eutrophication.
Navigation through and around the reefs is a major challenge. More than 20 ships were recorded lost in the region between 1791 and 1850. Surveys between 1815 and 1860 by Phillip Parker King in the Mermaid, Francis Price Blackwood in HMS Fly, Owen Stanley in the Rattlesnake, and Henry Mangles Denham in the Herald led to significant navigational improvements. These surveys outlined the advantages and dangers of the Inner Route (between Australia’s east coast and the western edge of the reefs) and the Outer Route in the open sea.
Ecology
The Great Barrier Reef is home to a wide variety of life, including many species that are at risk of becoming endangered or are found only in this area.
Thirty types of whales and dolphins live in the Great Barrier Reef, such as the dwarf minke whale, Indo-Pacific humpback dolphin, and humpback whale. Large numbers of dugongs also live there. More than 1,500 kinds of fish live on the reef, including clownfish, red bass, red-throat emperor, and several types of snapper and coral trout. Forty-nine species spawn in large groups, while eighty-four other species spawn in other parts of their habitat. Seventeen types of sea snakes live in the reef’s warm waters up to 50 meters (160 feet) deep. These snakes are more common in the southern part of the reef than in the northern part. No species found in the Great Barrier Reef World Heritage Area are unique to the area, and none are endangered.
Six types of sea turtles come to the reef to lay eggs: the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle, and olive ridley. The green sea turtles on the reef have two genetically different groups, one in the northern part and one in the southern part. Fifteen types of seagrass grow in beds that attract dugongs and turtles and provide homes for fish. The most common seagrass types are Halophila and Halodule.
Saltwater crocodiles live in mangrove forests and salt marshes near the reef. Nesting has not been reported, and the saltwater crocodile population in the Great Barrier Reef World Heritage Area is spread out but has few individuals. Around 125 types of sharks, stingrays, skates, or chimaeras live on the reef. Close to 5,000 types of mollusks, including giant clams and various nudibranchs and cone snails, have been found on the reef. Forty-nine types of pipefish and nine types of seahorses live there. At least seven types of frogs live on the islands.
About 215 types of birds, including 22 types of seabirds and 32 types of shorebirds, visit the reef or nest and rest on the islands. These include the white-bellied sea eagle and roseate tern. Most nesting areas are on islands in the northern and southern parts of the reef, with 1.4 to 1.7 million birds using these areas to breed. The islands of the Great Barrier Reef also support 2,195 known plant species, three of which are unique to the area. Northern islands have 300–350 plant species that are often woody, while southern islands have 200 plant species that are often herbaceous. The Whitsunday region has the most plant diversity, with 1,141 species. Birds help spread the plants.
At least 330 types of ascidians, which are small, sponge-like creatures, live on the reef. Between 300 and 500 types of bryozoans, which are tiny colonial animals, also live there. Four hundred types of coral, both hard and soft, grow on the reef. Most of these corals release gametes during mass spawning events triggered by rising sea temperatures in spring and summer, the lunar cycle, and the daily cycle. Corals in the inner reef spawn the week after the full moon in October, while corals on the outer reef spawn in November and December. Common soft corals belong to 36 different groups. Five hundred types of marine algae or seaweed grow on the reef, including thirteen types of the genus Halimeda. These algae create calcareous mounds up to 100 meters (110 yards) wide, forming small ecosystems on their surfaces that resemble rainforests.
Environmental threats
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The main threats to the health of the reef system are climate change, pollution, crown-of-thorns starfish, and fishing. Other threats include shipping accidents, oil spills, and tropical cyclones. A disease called Skeletal Eroding Band, caused by the protozoan Halofolliculina corallasia, affects 31 coral species. A 2012 study by the National Academy of Sciences found that since 1985, the Great Barrier Reef has lost more than half of its corals, with two-thirds of the loss happening from 1998 due to these factors. In 2022, the northern and central parts of the reef had the highest coral cover since monitoring began, but the southern part had less cover and more frequent bleaching events.
The Great Barrier Reef Marine Park Authority considers climate change the greatest threat to the reef. Climate change causes ocean warming, which increases coral bleaching. Mass coral bleaching events due to marine heatwaves happened in the summers of 1998, 2002, 2006, 2016, 2017, and 2020. Coral bleaching is expected to happen more often each year. A 2020 study found that the Great Barrier Reef has lost more than half of its corals since 1995 due to warmer seas from climate change. As global warming continues, corals will not be able to keep up with rising ocean temperatures. Coral bleaching increases the risk of disease, which harms reef communities.
In July 2017, UNESCO published a draft decision expressing serious concern about the impact of coral bleaching on the Great Barrier Reef. The draft decision warned Australia that it will not meet the goals of the Reef 2050 report without significant improvements in water quality.
Climate change affects other reef life. Some fish move to new habitats due to changes in water temperature, which can increase chick mortality in seabirds. Climate change also affects sea turtles and their habitat.
Bleaching events in deeper coral communities (more than 20 meters or 66 feet) are not as well studied as those in shallower areas, but recent research shows that these deeper corals are also negatively affected by rising ocean temperatures. Five large benthic coral species were found to be bleached under high temperatures, showing that these corals are also vulnerable to thermal stress.
Ocean acidification is another threat to the Great Barrier Reef. Ocean acidification happens when excess carbon dioxide from the atmosphere is absorbed by the ocean, lowering the pH and changing the ocean's chemistry. This reduces the amount of aragonite, a key mineral for coral growth. The Great Barrier Reef is expected to lose aragonite at a rate of about 0.1 per decade this century. Acidic water breaks down the materials that corals and shell-building creatures need to grow.
Pollution and poor water quality are also major threats. Rivers in northeastern Australia pollute the reef during floods. Over 90% of this pollution comes from farm runoff. About 80% of the land near the Great Barrier Reef is used for farming, including sugar cane and beef cattle grazing. Farming practices harm the reef through overgrazing, increased runoff of sediments, nutrients, and chemicals like fertilizers, herbicides, and pesticides, which are harmful to corals and reef biodiversity.
A 2016 report said that higher regulations help reduce pollution from other land uses, such as industrial, mining, port development, dredging, and urban development. However, these sources can still be significant locally. Sediments with high levels of copper and other heavy metals from the Ok Tedi Mine in Papua New Guinea are a potential pollution risk for the far northern Great Barrier Reef and Torres Strait regions. A report said that about 67% of corals died in the northern section of the reef.
The runoff problem is made worse by the loss of coastal wetlands, which act as natural filters for toxins and help deposit sediment. Poor water quality is thought to be caused by increased light and oxygen competition from algae.
Fertilizer runoff from farms releases nitrogen, phosphorus, and potassium into the ocean, leading to large algal growth. This reduces oxygen levels in the water, a process called eutrophication. This lowers biodiversity and changes the species composition. A study by Katharina Fabricius and Glen Death found that hard coral numbers were almost double on reefs far from agricultural areas.
Fertilizers also increase the amount of phytoplankton available for crown-of-thorns starfish larvae to eat. A study showed that doubling the amount of chlorophyll in the water leads to a tenfold increase in the survival rate of crown-of-thorns starfish larvae.
Sediment runoff from farming carries chemicals into the reef environment, reducing the amount of light available to corals and decreasing their ability to get energy from the environment.
Pesticides used in farming contain heavy metals like lead, mercury, and arsenic, which are released into the environment through soil erosion. These toxins harm coral.
In 2009 and 2011, the mining company Queensland Nickel released nitrate-laden water into the Great Barrier Reef. The Great Barrier Reef Marine Park Authority encouraged the company to find ways to avoid releasing waste into the environment and to develop a management plan to eliminate this risk. However, the authority does not have legal control over how the Yabulu tailings dam is managed.
The crown-of-thorns starfish eats coral polyps. Large outbreaks can severely damage reefs. A study by the Reef Research Centre found that an outbreak in 2000 caused a 66% loss of live coral cover on sampled reefs. Outbreaks are believed to happen naturally but are worsened by poor water quality and overfishing of the starfish's predators.
Overfishing of keystone species, like the giant Triton, can disrupt food chains important to reef life. Fishing also affects the reef through water pollution from boats, by-catch of unwanted species like dolphins and turtles, and habitat destruction from trawling, anchors, and nets. About one-third of the Great Barrier Reef Marine Park is protected from species removal, including fishing, without written permission.
Shipping accidents are a major concern, as several commercial shipping routes pass through the Great Barrier Reef. Although the route is not easy, reef pilots consider it safer than outside the reef in case of mechanical failure because a ship can be repaired safely. There have been over 1,600 known shipwrecks in the Great Barrier Reef region. On April 3, 2010, the bulk coal carrier Shen Neng 1 ran aground on Douglas Shoals, spilling up to four tonnes of oil and causing extensive damage to the reef.
The government of Queensland has a "shark control" program that deliberately kills sharks throughout Queensland, including in the Great Barrier Reef. Environmentalists and scientists say that this program harms the marine ecosystem.
Protection and preservation: Reef 2050 plan
In March 2015, the Australian and Queensland governments created a plan to protect and preserve the Great Barrier Reef’s universal heritage until 2050. This 35-year plan, called the "Reef 2050 Plan," outlines possible steps to manage long-term challenges such as pollution, climate change, and other threats to the reef’s survival and value. The plan includes details for measuring progress and improving conditions, such as a long-term sustainability plan, a water quality improvement plan, and an investment plan to protect the reef until 2050.
However, the Reef 2050 Plan includes measures like improving water quality, restoring the reef, and controlling harmful starfish. It does not include steps to address the main cause of the problem—climate change, which is caused by greenhouse gas emissions. Because of this, experts questioned whether the plan would be enough to protect the reef. Another concern is that the time remaining to stay below the 1.5°C warming threshold (a temperature limit that coral reefs can survive) is very short.
In 2018, the Australian government gave the Great Barrier Reef Foundation a grant of AUD$443 million. This decision faced criticism because the grant was awarded without following proper tender and transparency processes.
The Great Barrier Reef is important for the health of the marine ecosystem. Many species of plants, fish, and large animals depend on the reef for food, shelter, and reproduction. Threats like ocean acidification, pollution runoff, and outbreaks of harmful species, such as the crown-of-thorns starfish, have caused the reef’s ecosystem to decline. These threats harm the reef’s organisms and also affect the region’s economy, which relies heavily on tourism related to the reef.
The Australian government has aimed to protect the Great Barrier Reef since 1972, when it established the Australian Institute of Marine Science. The Australian and Queensland governments have invested about $142.5 million in their National Environmental Science Program, which has helped collect data about threats to the reef. In 2018, the Reef 2050 Water Quality Improvement Plan was introduced to help local communities, farmers, and industries adopt more sustainable practices. This plan will work with the Queensland government and the Great Barrier Reef Marine Park Authority to reduce runoff reaching the reef and control outbreaks of crown-of-thorns starfish.
Human use
The Great Barrier Reef has been known to and used by Aboriginal Australian and Torres Strait Islander peoples for many years. Aboriginal Australians have lived in the area for at least 40,000 years, and Torres Strait Islanders have lived there for about 10,000 years. For these 70 or so clan groups, the reef is an important part of their culture.
In 1768, Louis de Bougainville saw the reef but did not explore it. On June 11, 1770, the ship HM Bark Endeavour, led by explorer James Cook, ran aground on the Great Barrier Reef and suffered serious damage. The ship was lightened and floated again during a high tide, which saved it. One of the most famous shipwrecks was HMS Pandora, which sank on August 29, 1791, killing 35 men. Since 1983, the Queensland Museum has led archaeological work at the wreck site of Pandora. Because the reef had no atolls, it was not studied much in the 19th century. During this time, some of the reef's islands were mined for guano, and lighthouses were built to guide ships. An example is Raine Island, the earliest lighthouse built there. In 1922, the Great Barrier Reef Committee began early research on the reef.
In 1975, the Australian government created the Great Barrier Reef Marine Park to stop harmful activities. The Marine Park does not cover the entire Great Barrier Reef Province. It is managed by the Great Barrier Reef Marine Park Authority, in partnership with the Queensland government, to ensure the reef is used in a sustainable way. Efforts to protect the reef include zoning plans, management strategies, permits, education, and programs like eco-tourism certification.
In 1999, the Australian Parliament passed the Environment Protection and Biodiversity Conservation Act. This law improved how national environmental laws work by providing guidance on protecting marine biodiversity. A process called marine bioregional planning was created to help protect marine life by considering how ecosystems and species interact.
This process has two steps. First, it identifies conservation priorities in five marine regions. Second, it finds areas to add to Australia’s National Representative System of Marine Protected Areas. These protected areas, like those on land, help protect biodiversity for future generations. Marine reserves are chosen based on guidelines created by the Australian and New Zealand Environment and Conservation Council. These guidelines are used nationally and applied locally according to Australian policies.
Each region’s priorities are based on human and environmental threats. Marine Bioregional Plans are created to address these priorities. To assess priorities, three steps are taken: creating a bioregional profile, drafting a plan, and finalizing it. After the plan is done, activities in different areas may be limited if they pose specific threats.
In 2001, the Great Barrier Reef Marine Park Authority released a report about declining water quality in the reef and explained why this was important. In 2003, the Australian and Queensland governments started a joint initiative to improve water quality entering the reef. Poor water quality over the past 150 years has caused coral bleaching, algal blooms, and pesticide pollution. These issues have made the reef less able to survive climate change.
When the plan was introduced in October 2003, it had 65 actions based on earlier laws. Its goal was to stop and reverse the decline in water quality by 2013. By 2020, the plan aimed to improve water quality enough to avoid harming the reef. To reach these goals, the plan focuses on reducing pollutants in the water and protecting areas of the reef that naturally help reduce pollution. The plan targets nutrients, pesticides, and sediment from agriculture. Other pollution from urban areas is handled by different laws.
In 2009, the plan was updated. The report said that none of the earlier efforts to improve water quality had been successful. The new plan focuses on key goals, combines industry and community efforts, and uses new policies. The 2009 report found that 41 of the 65 actions met their goals, but 18 were not progressing well, and 6 had poor progress.
Since the plan started in 2003, some achievements include creating the Reef Quality Partnership to set targets and monitor progress, rewarding landowners for improving land conditions with longer leases, creating Water Quality Improvement Plans to identify regional goals, establishing Nutrient Management Zones to reduce sediment loss, starting education programs to support sustainable farming, changing land management practices through Farm Management Systems, and launching the Queensland Wetland program.
A group of scientists was formed to study the plan’s impact on water quality. They found that many goals had not been met but saw evidence that improving water quality could help the reef survive climate change. A meeting called Reefocus in 2008 reached similar conclusions. A working group was formed to update reef goals and objectives. The new plan focuses on key areas and sets measurable goals to check progress.
Some water quality goals include reducing nitrogen and phosphorus levels by 50% by 2013.