The Great Barrier Reef is the world's largest coral reef system, made up of over 2,900 individual reefs and 900 islands. It spans more than 2,300 kilometers (1,400 miles) over 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 more than 61 meters (200 feet) deep. The Great Barrier Reef can be seen from space and is the world's largest structure built by living organisms. This reef is made by billions of tiny organisms called coral polyps. It supports many 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, the Queensland National Trust recognized it as a state icon of Queensland.
A large part of the reef is protected by the Great Barrier Reef Marine Park, which helps reduce the effects of human activities like fishing and tourism. Other challenges to the reef include pollution runoff, climate change and coral bleaching, dredging sludge, and 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 effects of a widespread coral bleaching event in 2020 are still being studied.
The Great Barrier Reef has been used by Aboriginal Australian and Torres Strait Islander peoples for a long time and is an important part of their cultures and beliefs. It is a popular tourist destination, especially in the Whitsunday Islands and Cairns areas. Tourism is a major source of income for the region, producing more than AUD$3 billion each year. In 2014, Google launched a 3D underwater street view of the reef.
A 2016 report found that coral bleaching was more widespread than expected, affecting the northern parts of the reef due to rising ocean temperatures. In 2016, a magazine published an article that described the reef as dying, but the article was criticized for being too early and possibly slowing efforts to help the reef recover. In 2017, a study in the journal Nature showed that large parts of the reef in the northern region had died 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 natural selection event. Many adult corals died during the 2016–2017 bleaching events, leading to fewer new corals. The types of corals that reproduced also changed, which could lead to long-term changes in the reef's ecosystem if the trend continues.
The Great Barrier Reef Marine Park Act 1975 requires a report on the reef's health, challenges, and future every five years. The last report was published in 2019. In 2022, another mass coral 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, mainly because two-thirds of the reef regrew due to fast-growing Acropora coral, which is the most common type of coral in the area.
"Discovery" and naming
The Great Barrier Reef has been lived near and used for many years 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 traveled along 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 repair the ship.
Matthew Flinders named the Great Barrier Reef after he mapped it in more detail in 1802. He used different names for different parts of the reef. He called one reef "great reef," used the term "barrier reef" to describe any reef that stops ships or waves from reaching the shore, and called the group of these reefs together "Barrier Reefs."
Geology and geography
The Great Barrier Reef is 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) in the north to the unnamed passage between Lady Elliot Island (its southernmost island) and Fraser Island in the south. Lady Elliot Island is 1,915 km (1,190 mi) southeast of Bramble Cay as the crow flies. The reef includes the smaller Murray Islands.
The plate tectonic theory shows that Australia has moved northward at a rate of 7 cm (2.8 in) per year since the Cenozoic era. In eastern Australia, tectonic uplift caused the drainage divide in Queensland to shift 400 km (250 mi) inland. During this time, volcanic eruptions in Queensland created central and shield volcanoes and basalt flows. Some of these formations 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, changes in sea level greatly influenced reef growth and decline.
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 can only grow 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 began to grow, but erosion of the Great Dividing Range led to sedimentation, creating river deltas, oozes, and turbidites that were not suitable for coral growth. Ten million years ago, a drop in sea level further increased sedimentation. The reef’s base may have needed to build up from sediment until its edge was far enough away for suspended sediments to no longer block coral growth. Around 400,000 years ago, a warm Interglacial period raised sea levels and increased water temperatures by 4°C (7°F).
The land that formed the base of 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, in rare cases, volcanoes). The Reef Research Centre found coral skeleton deposits dating back half a million years. The Great Barrier Reef Marine Park Authority (GBRMPA) says the earliest evidence of complete reef structures is 600,000 years old. According to 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. At that time, sea level was 120 meters (390 ft) lower than today.
From 20,000 to 6,000 years ago, global sea levels rose steadily. As sea levels rose, corals could grow higher on the newly submerged edges of hills on the coastal plain. By about 13,000 years ago, sea levels were only 60 meters (200 ft) lower than today, and corals began to surround the hills, which had become continental islands. As sea levels rose further, most of these islands were submerged. Corals then grew over 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 grew on limestone platforms from past (Pleistocene) reef growth phases.
Remains of an ancient barrier reef similar to the Great Barrier Reef can be 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. A previously unknown reef, 500 meters tall and 1.5 km wide at the base, was discovered 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 reef, attached to high islands like the Whitsunday Islands. Lagoonal reefs are found in the southern reef and further north, near 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 affect the reef locally by bringing up fresh water, sometimes rich in nutrients, which can lead to eutrophication.
Navigation around the reef is difficult. More than 20 ships were lost in the region between 1791 and 1850. Surveys from 1815 to 1860 by Phillip Parker King, Francis Price Blackwood, Owen Stanley, and Henry Mangles Denham improved navigation by showing 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 open sea.
Ecology
The Great Barrier Reef has a wide variety of life. This includes many species that are vulnerable or endangered, some of which are only found there.
Thirty types of cetaceans, such as the dwarf minke whale, Indo-Pacific humpback dolphin, and humpback whale, live in the Great Barrier Reef. Large numbers of dugongs live there. 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. Forty-nine species spawn in large groups, while eighty-four other species spawn elsewhere in their range. Seventeen species of sea snake live on the Great Barrier Reef in warm waters up to 50 metres (160 ft) deep. These snakes are more common in the southern than in the northern section. None of the species found in the Great Barrier Reef World Heritage Area are endemic, nor are any endangered.
Six species of sea turtles come to the reef to breed: the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle, and the olive ridley. The green sea turtles on the Great Barrier Reef have two genetically distinct populations, one in the northern part of the reef and the other in the southern part. Fifteen species of seagrass in beds attract the dugongs and turtles, and provide fish habitat. The most common types of seagrasses are Halophila and Halodule.
Saltwater crocodiles live in mangrove and salt marshes on the coast near the reef. Nesting has not been reported, and the saltwater crocodile population in the GBRWHA is wide-ranging but low density. Around 125 species of shark, stingray, skates, or chimaera live on the reef. Close to 5,000 species of mollusc have been recorded on the reef, including the giant clam and various nudibranchs and cone snails. Forty-nine species of pipefish and nine species of seahorse have been recorded. At least seven species of frog inhabit the islands.
215 species of birds (including 22 species of seabirds and 32 species of shorebirds) visit the reef or nest or roost on the islands, including the white-bellied sea eagle and roseate tern. Most nesting sites are on islands in the northern and southern regions of the Great Barrier Reef, with 1.4 to 1.7 million birds using the sites to breed. The islands of the Great Barrier Reef also support 2,195 known plant species; three of these are endemic. The northern islands have 300–350 plant species which tend to be woody, whereas the southern islands have 200 which tend to be herbaceous; the Whitsunday region is the most diverse, supporting 1,141 species. The plants are propagated by birds.
There are at least 330 species of ascidians on the reef system with the diameter of 1–10 cm (0.4–4 in). Between 300 and 500 species of bryozoans live on the reef. Four hundred coral species, both hard corals and soft corals, inhabit the reef. The majority of these spawn gametes, breeding in mass spawning events that are triggered by the rising sea temperatures of spring and summer, the lunar cycle, and the diurnal cycle. Reefs in the inner Great Barrier Reef spawn during the week after the full moon in October, while the outer reefs spawn in November and December. Its common soft corals belong to 36 genera. Five hundred species of marine algae or seaweed live on the reef, including thirteen species of genus Halimeda, which deposit calcareous mounds up to 100 metres (110 yd) wide, creating mini-ecosystems on their surface which have been compared to rainforest cover.
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. According to a 2012 study by the National Academy of Sciences, since 1985, the Great Barrier Reef has lost more than half of its corals, with two-thirds of that loss happening from 1998 due to the factors listed before. In 2022, the northern and central parts of the reef had the highest amount of coral cover since monitoring began, but the cover in the southern part had decreased, and bleaching events occurred more frequently.
The Great Barrier Reef Marine Park Authority considers climate change to be the greatest threat to the reef. Climate change causes ocean warming, which increases coral bleaching. Mass coral bleaching events due to marine heatwaves occurred in the summers of 1998, 2002, 2006, 2016, 2017, and 2020. Coral bleaching is expected to become an annual occurrence. In 2020, a study found that the Great Barrier Reef has lost more than half of its corals since 1995 due to warmer seas driven by climate change. As global warming continues, corals will not be able to keep up with increasing ocean temperatures. Coral bleaching events lead to increased disease susceptibility, which causes harmful effects for 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 also warned Australia that it will not meet the targets of the Reef 2050 report without considerable work to improve water quality.
Climate change has implications for other forms of reef life. Some fish's preferred temperature range leads them to seek new habitat, which increases chick mortality in predatory seabirds. Climate change will also affect the sea turtle's population and available habitat.
Bleaching events in benthic coral communities (deeper than 20 metres or 66 feet) in the Great Barrier Reef are not as well documented as those at shallower depths, but recent research has shown that benthic communities are just as negatively impacted in the face of rising ocean temperatures. Five Great Barrier Reef species of large benthic corals were found bleached under elevated temperatures, affirming that benthic corals are vulnerable to thermal stress.
A threat for the Great Barrier Reef is the rising levels of ocean acidification. Ocean acidification occurs when excess atmospheric carbon dioxide gets absorbed into the ocean. This causes a decrease in the pH and this alters the chemistry of the ocean's water. This reduces the amount of aragonite, a key mineral for coral to grow, in the water. The Great Barrier Reef is predicted to lose aragonite at a rate of about 0.1 per decade this century. The acidic water breaks down the materials that coral and shell building creatures need to grow.
Another key threat faced by the Great Barrier Reef is pollution and declining water quality. The rivers of north-eastern Australia pollute the Reef during tropical flood events. Over 90% of this pollution comes from farm runoff. 80% of the land adjacent to the Great Barrier Reef is used for farming, including intensive cropping of sugar cane and major beef cattle grazing. Farming practices damage the reef due to overgrazing, increased run-off of agricultural sediments, nutrients, and chemicals including fertilizers, herbicides, and pesticides, which represent a major health risk for the coral and biodiversity of the reefs.
According to a 2016 report, while higher regulation contributes to less overall pollution from "other land uses, such as industrial, mining, port development, dredging, and urban development," these can still be locally significant. Sediments containing high levels of copper and other heavy metals sourced 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. Some 67% of corals died in the reef's worst-hit northern section, the ARC Centre of Excellence for Coral Reef Studies report said.
The runoff problem is exacerbated by the loss of coastal wetlands, which act as a natural filter for toxins and help deposit sediment. It is thought that the poor water quality is due to increased light and oxygen competition from algae.
Farming fertilizer runoff releases nitrogen, phosphorus, and potassium into the oceanic ecosystem, and these limiting nutrients cause massive algal growth, which eventually leads to a reduction in oxygen available for other creatures in a process called eutrophication. This decreases the biodiversity in the affected areas, altering the species composition. A study by Katharina Fabricius and Glen Death of Australian Institute of Marine Science found that hard corals numbers were almost double on reefs that were far from agricultural areas.
Fertilizers also increase the amount of phytoplankton available for the crown-of-thorns starfish larvae to consume. A study showed that a doubling of the chlorophyll in the water leads to a tenfold increase in the crown-of-thorns starfish larvae's survival rate.
Sediment runoff from farming carries chemicals into the reef environment and reduces the amount of light available to the corals, decreasing their ability to extract energy from their environment.
Pesticides used in farming are made up of heavy metals such as lead, mercury, arsenic, and other toxins, which are released into the wider environment due to erosion of farm soil, which has a detrimental effect on the coral.
Mining company Queensland Nickel discharged nitrate-laden water into the Great Barrier Reef in 2009 and 2011 – on the later occasion releasing 516 tonnes (508 long tons; 569 short tons) of waste water. The Great Barrier Reef Marine Park Authority (GBRMPA) stated, "We have strongly encouraged the company to investigate options that do not entail releasing the material to the environment and to develop a management plan to eliminate this potential hazard; however, GBRMPA does not have legislative control over how the Yabulu tailings dam is managed."
The crown-of-thorns starfish preys on coral polyps. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the Reef Research Centre (RRC). Outbreaks are believed to occur in natural cycles, worsened by poor water quality and overfishing of the starfish's predators.
The unsustainable overfishing of keystone species, such as the giant Triton, can disrupt food chains vital to reef life. Fishing also impacts the reef through increased water pollution from boats, by-catch of unwanted species (such as dolphins and turtles), and habitat destruction from trawling, anchors, and nets. As of the middle of 2004, approximately one-third of the Great Barrier Reef Marine Park is protected from species removal of any kind, including fishing, without written permission.
Shipping accidents are a pressing concern, as several commercial shipping routes pass through the Great Barrier Reef. 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 while being repaired. There have been over 1,600 known shipwrecks in the Great Barrier Reef region. On 3 April 2010, the bulk coal carrier Shen Neng 1 ran aground on Douglas Shoals, spilling up to four tonnes of oil into the water and causing extensive damage to the reef.
The government of Queensland has a "shark control" program (shark culling) that deliberately kills sharks throughout Queensland, including in the Great Barrier Reef. Environmentalists and scientists say that this program harms the marine ecosystem; they think
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 important 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 making improvements, such as a long-term sustainability plan, a water quality improvement plan, and an investment plan to protect the reef until 2050.
The Reef 2050 Plan includes measures like improving water quality, restoring the reef, and controlling harmful starfish. However, it does not include actions to address climate change, which is caused by greenhouse gas emissions. Experts have questioned whether these steps alone will be enough to protect the reef. Another concern is that the time remaining before reaching the 1.5°C warming limit (a temperature that coral reefs can still 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 not given through proper processes that ensure fairness and transparency.
The Great Barrier Reef is important for the health of the ocean. Many species of plants, fish, and large animals depend on the reef for food, shelter, and reproduction. Problems like ocean acidification, pollution runoff, and outbreaks of harmful species, such as the crown-of-thorns starfish, have caused the reef to decline. These issues harm both the reef's wildlife and the local economy, which relies heavily on tourism related to the Great Barrier Reef.
The Australian government has aimed to protect the reef since 1972, when it established the Australian Institute of Marine Science. Together, the Australian and Queensland governments have invested about $142.5 million in the National Environmental Science Program, which has helped collect data on threats to the reef. In 2018, the Reef 2050 Water Quality Improvement Plan was introduced to help 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 pollution runoff and manage outbreaks of the 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 about 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 reef and suffered serious damage. The ship was lightened and refloated 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. 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 as beacons. Raine Island was the first example of this. 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 and banned certain activities to protect the reef. 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 conserve the reef include zoning rules, management plans, permits, education, and incentives like eco-tourism certification.
In 1999, the Australian Parliament passed the Environment Protection and Biodiversity Conservation Act. This law improved national environmental laws by providing guidance on protecting marine biodiversity. The marine bioregional planning process was created based on this law. This process helps protect marine life by considering the entire ecosystem and how species interact.
The process has two steps. First, it identifies conservation priorities in five marine regions. Second, it identifies marine reserves to add to Australia’s National Representative System of Marine Protected Areas. Marine reserves are created to protect biodiversity for future generations. These reserves are chosen based on guidelines from the Australian and New Zealand Environment and Conservation Council. These guidelines are followed nationally and applied locally using policies outlined in the "Goals and Principles for the Establishment of the National Representative System of Marine Protected Areas in Commonwealth Waters."
Conservation priorities for each region are based on human and environmental threats. Marine Bioregional Plans are created to address these threats. To assess priorities, three steps are taken: first, a bioregional profile is made, second, a plan is drafted, and third, the plan is finalized. After the plan is finalized, activities in different bioregions may be limited if they pose threats.
In 2001, the GBRMPA released a report showing declining water quality in the Great Barrier Reef and explained why this was important. In 2003, the Australian and Queensland governments started a joint program to improve water quality entering the reef. Poor water quality over the past 150 years, caused by development, has led to coral bleaching, algal blooms, and pesticide pollution. These issues have made the reef less able to handle climate change.
The plan, introduced in October 2003, originally had 65 actions based on previous 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 protect the reef’s health. To achieve these goals, the plan focused on reducing pollutants in the water and protecting areas of the reef that naturally reduce pollution. The plan targeted nutrients, pesticides, and sediment from agriculture. Other pollution from urban areas is handled by different laws.
In 2009, the plan was updated. The report found that none of the efforts to improve water quality had been successful. The new plan focused on priority outcomes, included industry and community efforts, and used new policies and regulations. 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 began in 2003, some achievements include creating the Reef Quality Partnership to set targets and monitor progress, rewarding landowners for improving land conditions, creating Water Quality Improvement Plans, establishing Nutrient Management Zones to reduce sediment loss, starting education programs to support sustainable farming, and changing land management practices through Farm Management Systems. Other efforts included the Queensland Wetland program and other water quality improvements.
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 better water quality could help the reef handle climate change. The Reefocus summit in 2008 reached similar conclusions. A working group was formed to update reef goals and work with the Australian and Queensland governments. The updated plan focuses on strategic areas and actions to meet 2013 goals, with clear targets to measure progress.
Some water quality goals include reducing nitrogen and phosphorus levels by 50% by 2013.