The Great Barrier Reef is the world's largest coral reef system. It is made up of more than 2,900 separate reefs and 900 islands. These reefs and islands stretch over 2,300 kilometers (1,400 miles) and cover an area of about 344,400 square kilometers (133,000 square miles). The reef is located in the Coral Sea, off 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 can be seen from outer space and is the world's largest single structure made by living organisms. This structure is built by billions of tiny organisms called coral polyps. The reef supports many different types of life and was chosen as a World Heritage Site in 1981. It was named one of the Seven Natural Wonders of the World by CNN in 1997 and listed by Australian World Heritage places in 2007. The Queensland National Trust named it a state icon of Queensland in 2006.
A large part of the reef is protected by the Great Barrier Reef Marine Park. This protection helps reduce the effects of human activities, such as fishing and tourism. Other challenges to the reef include pollution from human activities, climate change, coral bleaching, the dumping of dredging sludge, and outbreaks of the crown-of-thorns starfish. A study from 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 major bleaching event in 2020 are still being studied.
The Great Barrier Reef has been used and valued 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 tourist destination, especially in the Whitsunday Islands and Cairns regions. Tourism is an important source of income for the area, generating over AUD$3 billion each year. In 2014, Google launched an underwater 3D view of the Great Barrier Reef.
A report from 2016 showed that coral bleaching was more widespread than previously thought, especially in the northern parts of the reef due to warmer ocean temperatures. In 2016, a magazine published an article suggesting the reef might be dying, but the article was criticized for being too early and possibly hindering efforts to protect it. A 2017 study in the journal Nature found that large areas of the reef in the north had died due to high water temperatures, linked to global climate change. In 2018, the number of baby corals born on the reef dropped sharply. Scientists say this is the early stage 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 reproduced 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 last report was published in 2019. In 2022, another major 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 regularly checks the reef's condition. The 2022 report showed the greatest recovery in 36 years. This recovery is 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 known to and used by Aboriginal Australian and Torres Strait Islander peoples for a long time. It is an important part of the cultures and spiritual beliefs of these groups.
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 named the Great Barrier Reef 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," used "barrier reef" to describe any reef that blocked ships and waves from the open sea from reaching the coast, and used "Barrier Reefs" to refer to the group of these reefs.
Geology and geography
The Great Barrier Reef is a unique part of the East Australian Cordillera division. It stretches from 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 located 1,915 km (1,190 mi) southeast of Bramble Cay as the crow flies. It includes the smaller Murray Islands.
The plate tectonic theory explains that 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 created 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 Great Barrier Reef’s development 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 centimetres (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 metres (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 a sedimentation process developed due to erosion of the Great Dividing Range, creating river deltas, oozes, and turbidites, which were unsuitable for coral growth. Ten million years ago, sea levels dropped significantly, which increased 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 hinder coral growth. About 400,000 years ago, there was a warm Interglacial period with higher sea levels and a 4 °C (7 °F) increase in water temperature.
The land that formed the current Great Barrier Reef’s substrate 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 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 the older platform 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. Around that time, sea level was 120 metres (390 ft) lower than it is today.
From 20,000 to 6,000 years ago, sea levels rose steadily worldwide. As sea levels rose, corals could grow higher on the newly submerged edges of the coastal plain’s hills. By around 13,000 years ago, sea level was only 60 metres (200 ft) lower than today, and corals began to surround the hills, which had become continental islands. As sea levels rose further, most of the continental 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 age of the current living reef structure as 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 Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these structures are not found elsewhere in the reef system. A previously undiscovered reef, 500 metres 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, such as the Whitsunday Islands. Lagoonal reefs are found in the southern Great Barrier 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 a local impact on the reef, providing upwellings of fresh water, sometimes rich in nutrients, which can contribute 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
Ecology
The Great Barrier Reef is home to a wide variety of life, including many species that are vulnerable or endangered. Some of these species are found only in the reef system.
Thirty types of whales and dolphins, such as the dwarf minke whale, Indo-Pacific humpback dolphin, and humpback whale, live in the reef. Large numbers of dugongs also live there. Over 1,500 kinds of fish, including clownfish, red bass, red-throat emperor, and several types of snapper and coral trout, are found on the reef. Forty-nine fish species spawn together in large groups, while eighty-four other species spawn in other areas of their habitats. Seventeen types of sea snakes live in warm waters up to 50 meters (160 feet) deep. These snakes are more common in the southern part of the reef than the northern part. None of the sea snakes in the Great Barrier Reef World Heritage Area are found only there, nor are they 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. Green sea turtles in the reef have two groups with different genetic makeup, one in the northern part and the other in the southern part. Fifteen types of seagrass grow in beds that attract dugongs and turtles and provide habitat for fish. The most common seagrass types are Halophila and Halodule.
Saltwater crocodiles live in mangrove forests and salt marshes near the reef. No nesting has been reported, and the crocodile population in the Great Barrier Reef World Heritage Area is spread out but not very dense. Around 125 types of sharks, stingrays, skates, or chimaeras live on the reef. Nearly 5,000 types of mollusks, such as giant clams, nudibranchs, and cone snails, have been recorded 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 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 sites to breed. The islands also support 2,195 types of plants, three of which are found only there. Northern islands have 300–350 plant types, often woody plants, while southern islands have 200 plant types, often herbaceous plants. The Whitsunday region has the most plant diversity, with 1,141 species. Birds help spread these plants.
There are at least 330 types of ascidians on the reef, each with a size between 1–10 cm (0.4–4 in). Between 300 and 500 types of bryozoans live on the reef. Four hundred types of coral, both hard and soft, live on the reef. Most corals release reproductive cells during mass spawning events, which happen when sea temperatures rise in spring and summer, along with the lunar and daily cycles. Inner reef areas spawn the week after the full moon in October, while outer reefs spawn in November and December. Common soft corals belong to 36 different groups. Five hundred types of marine algae or seaweed live 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, similar to rainforests.
Environmental threats
The Great Barrier Reef faces several major threats. These include climate change, pollution, crown-of-thorns starfish, and fishing. Other threats are shipping accidents, oil spills, and tropical cyclones. A disease called Skeletal Eroding Band, caused by a type of protozoan, affects 31 coral species. A 2012 study by the National Academy of Sciences found that the Great Barrier Reef has lost more than half of its corals since 1985, with two-thirds of that loss happening from 1998. In 2022, the northern and central parts of the reef had the highest coral cover since monitoring began, but the southern part saw a decrease in coral cover and more frequent bleaching events.
The Great Barrier Reef Marine Park Authority says climate change is the greatest threat to the reef. Climate change causes ocean warming, which increases coral bleaching. Major coral bleaching events happened in the summers of 1998, 2002, 2006, 2016, 2017, and 2020. Coral bleaching is expected to happen every year. A 2020 study found that the reef has lost more than half of its corals since 1995 due to warmer seas caused by climate change. As global warming continues, corals may not survive rising ocean temperatures. Coral bleaching increases the risk of disease, which harms reef ecosystems.
In July 2017, UNESCO expressed concern about the impact of coral bleaching on the reef. The organization warned Australia that it may not meet the goals of the Reef 2050 plan without improving water quality.
Climate change also affects other reef life. Some fish move to new habitats because of changing temperatures, which can increase chick deaths in seabirds. It also impacts sea turtles and their habitats.
Bleaching events in deeper parts of the reef (below 20 meters or 66 feet) are less studied than those in shallow areas. However, recent research shows that deep coral communities are also harmed by rising ocean temperatures. Five species of large deep-water corals were found to be bleached under high temperatures, showing that these corals are vulnerable to heat stress.
Ocean acidification is another threat. This happens when carbon dioxide from the atmosphere dissolves in ocean water, lowering the pH and changing ocean chemistry. This reduces aragonite, a mineral important 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 harms the materials coral and shell-building creatures need to grow.
Pollution and poor water quality are major threats. Rivers in northeastern Australia pollute the reef during floods. Over 90% of this pollution comes from farms. About 80% of the land near the reef is used for farming, including sugar cane and cattle grazing. Farming practices harm the reef through overgrazing, runoff of sediments, nutrients, and chemicals like fertilizers, herbicides, and pesticides.
A 2016 report said that while regulations reduce pollution from industrial and urban activities, these sources can still cause local problems. Sediments with high levels of copper and other heavy metals from the Ok Tedi Mine in Papua New Guinea may pollute the northern reef and Torres Strait areas. A study found that 67% of corals died in the northern reef’s worst-hit area.
The runoff problem is made worse by the loss of coastal wetlands, which naturally filter toxins and trap sediment. Poor water quality may be linked to increased light and oxygen competition from algae.
Fertilizer runoff releases nitrogen, phosphorus, and potassium into the ocean, causing algal growth. This process, called eutrophication, reduces oxygen levels and harms biodiversity. A study found that hard coral numbers were almost double on reefs far from farms.
Fertilizers also increase phytoplankton, which crown-of-thorns starfish larvae eat. A study showed that doubling chlorophyll levels in water leads to a tenfold increase in the survival rate of these larvae.
Sediment from farming carries chemicals into the reef, reducing light for corals and their ability to produce energy. Pesticides used in farming contain heavy metals like lead, mercury, and arsenic, which harm coral.
In 2009 and 2011, Queensland Nickel released nitrate-laden water into the reef. The Great Barrier Reef Marine Park Authority encouraged the company to find safer waste management solutions but does not control how the Yabulu tailings dam is managed.
Crown-of-thorns starfish eat coral polyps. Large outbreaks can destroy reefs. A 2000 study found that an outbreak caused a 66% loss of live coral on sampled reefs. Outbreaks occur naturally but are worsened by poor water quality and overfishing of the starfish’s predators.
Overfishing of key species, like the giant Triton, disrupts reef food chains. Fishing also harms the reef through pollution from boats, by-catch of species like dolphins and turtles, and habitat damage from trawling, anchors, and nets. About one-third of the Great Barrier Reef Marine Park is protected from fishing without permission.
Shipping accidents are a concern because many commercial routes pass through the reef. Over 1,600 shipwrecks have been recorded in the area. In 2010, the coal carrier Shen Neng 1 ran aground, spilling oil and damaging the reef.
Queensland’s "shark control" program, which kills sharks, harms the marine ecosystem. Scientists and environmentalists say this program negatively affects the reef’s balance.
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 global heritage until 2050. This 35-year plan, called the "Reef 2050 Plan," outlines steps to manage long-term challenges such as pollution, climate change, and other threats to the reef’s health 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.
The Reef 2050 Plan includes actions like improving water quality, restoring damaged areas of the reef, and reducing the impact of predatory starfish. However, the plan does not address climate change, which is caused by greenhouse gas emissions. Scientists have questioned whether these steps alone will be enough to protect the reef. Another concern is that the time remaining to stay below the 1.5°C warming limit, which is the maximum temperature coral reefs can handle, 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 awarded through standard bidding or open processes.
The Great Barrier Reef supports the health of the ocean ecosystem. Many species of plants, fish, and large animals rely on the reef for food, shelter, and breeding. Threats such as acidic ocean water, pollution from land, and outbreaks of harmful species like the crown-of-thorns starfish have caused the reef to decline. These threats harm both the reef’s wildlife and the local economy, which depends on tourism revenue from 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 the National Environmental Science Program, which has helped gather 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 pollution runoff 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 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 was seriously damaged. The ship was saved by lightening it and re-floating it during a high tide. A famous wreck was the HMS Pandora, which sank on August 29, 1791, killing 35 men. Since 1983, the Queensland Museum has led archaeological work on the wreck of the Pandora. Because the reef had no atolls, it was not studied much in the 19th century. During this time, some islands were mined for guano, and lighthouses were built to guide ships. Raine Island is an example of the earliest lighthouse. In 1922, the Great Barrier Reef Committee began researching the reef.
In 1975, the Australian government created the Great Barrier Reef Marine Park to protect the reef and 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. Rules like zoning, management plans, permits, education, and incentives (such as eco-tourism certification) are used to protect the reef.
In 1999, the Australian Parliament passed the Environment Protection and Biodiversity Conservation Act. This law helped improve national environmental laws by providing guidance for protecting marine biodiversity. A process called marine bioregional planning was created to 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 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 used nationally and applied locally through policies outlined in the "Goals and Principles for the Establishment of the National Representative System of Marine Protected Areas in Commonwealth Waters."
Each region’s priorities are based on human and environmental threats. Marine Bioregional Plans are created to address these threats. To assess priorities, three steps are taken: creating a bioregional profile, drafting a plan, and finalizing the plan. After the plan is complete, activities in 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 its importance. 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, making the reef less able to survive climate change.
The plan introduced in 2003 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 protect the reef’s health. To achieve this, the plan focused on reducing pollutants and protecting areas that naturally reduce water pollution. It targeted nutrients, pesticides, and sediment from agriculture. Urban pollution is handled by other laws.
In 2009, the plan was updated. The update noted that earlier efforts to improve water quality had not been successful. The new plan focused on key goals, included industry and community efforts, and used new policies. The 2009 report found that 41 of the 65 actions met their goals, but 18 had slow progress, and 6 had poor progress.
Some achievements since 2003 include creating the Reef Quality Partnership to set targets and monitor progress, rewarding landowners for improving land conditions, developing Water Quality Improvement Plans, creating Nutrient Management Zones to reduce sediment loss, starting education programs for sustainable farming, and changing land management practices through Farm Management Systems and codes of practice. The Queensland Wetland program was also created.
A group of scientists was formed to study the plan’s impact on water quality. They found that many goals had not yet been met but noted that improving water quality could help the reef survive climate change. The Reefocus summit in 2008 reached similar conclusions. A working group was formed to update the plan’s goals and objectives. The updated plan focuses on key areas and actions to meet 2013 goals, with clear targets to measure progress.
Examples of water quality goals include reducing nitrogen and phosphorus loads by 50% by 2013.