Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system, composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately. The reef is located in the Coral Sea, off the coast of Queensland, Australia, separated from the coast by a channel wide in places and over deep. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981. CNN labelled it one of the Seven Natural Wonders of the World in 1997. Australian World Heritage places included it in its list 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, which helps to limit the impact of human use, such as fishing and tourism. Other environmental pressures on the reef and its ecosystem include runoff of humanmade pollutants, climate change accompanied by mass coral bleaching, dumping of dredging sludge and cyclic population outbreaks of the crown-of-thorns starfish. According to a study published in October 2012 by the Proceedings of the National Academy of Sciences, the reef has lost more than half its coral cover since 1985, a finding reaffirmed by a 2020 study which found over half of the reef's coral cover to have been lost between 1995 and 2017, with the effects of a widespread 2020 bleaching event not yet quantified.
The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres Strait Islander peoples, and is an important part of local groups' cultures and spirituality. The reef is a very popular destination for tourists, especially in the Whitsunday Islands and Cairns regions. Tourism is an important economic activity for the region, generating over AUD$3 billion per year. In November 2014, Google launched Google Underwater Street View in 3D of the Great Barrier Reef.
A March 2016 report stated that coral bleaching was more widespread than previously thought, seriously affecting the northern parts of the reef as a result of warming ocean temperatures. In October 2016, Outside published an obituary for the reef; the article was criticised for being premature and hindering efforts to bolster the resilience of the reef. In March 2017, the journal Nature published a paper showing that huge sections of an stretch in the northern part of the reef had died in the course of 2016 of high water temperatures, an event that the authors put down to the effects of global climate change. The percentage of baby corals being born on the Great Barrier Reef dropped drastically in 2018 and scientists are describing it as the early stage of a "huge natural selection event unfolding". Many of the mature breeding adults died in the bleaching events of 2016–17, leading to low coral birth rates. The types of corals that reproduced also changed, leading to a "long-term reorganisation of the reef ecosystem if the trend continues."
The Great Barrier Reef Marine Park Act 1975 stipulates an Outlook Report on the Reef's health, pressures, and future every five years. The last report was published in 2019. In March 2022, another mass bleaching event has been confirmed, which raised further concerns about the future of this reef system, especially when considering the possible effects of El Niño weather phenomenon.
The Australian Institute of Marine Science conducts annual surveys of the Great Barrier Reef's status, and the 2022 report showed the greatest recovery in 36 years. It is mainly due to the regrowth of two-thirds of the reef by the fast-growing Acropora coral, which is the dominant coral there.
"Discovery" and naming
The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres Strait Islander peoples, and is an important part of local groups' cultures and spirituality.The first European to sight the Great Barrier Reef was James Cook in 1770, who sailed and mapped the east coast of Australia. On 11 June 1770, Cook's ship,, ran aground on a shoal south of the present-day location of Cooktown, requiring seven weeks to repair.
It was Matthew Flinders who named the Great Barrier Reef, after his more detailed mapping of it in 1802. Flinders used various terms to describe the reefs comprising what we now call the Great Barrier Reef including "great reef", for one such reef, "barrier reef", for any reef preventing a sailing vessel in, or waves from, the open sea, from reaching the coast, and "Barrier Reefs", for the collection of such reefs.
Geology and geography
The Great Barrier Reef is a distinct feature of the East Australian Cordillera division. It reaches from Torres Strait in the north to the unnamed passage between Lady Elliot Island and Fraser Island in the south. Lady Elliot Island is located southeast of Bramble Cay as the crow flies. It includes the smaller Murray Islands.The plate tectonic theory indicates Australia has moved northwards at a rate of per year, starting during the Cenozoic. Eastern Australia experienced a period of tectonic uplift, which moved the drainage divide in Queensland inland. Also during this time, Queensland experienced volcanic eruptions leading to 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, but until about 25 million years ago, northern Queensland was still in temperate waters south of the tropicstoo cool to support coral growth. The Great Barrier Reef's development history is complex; after Queensland drifted into tropical waters, it was largely influenced by reef growth and decline as sea level changed.
Reefs can increase in diameter by per year, and grow vertically anywhere from per year; however, they grow only above a depth of due to their need for sunlight, and cannot grow above sea level. When Queensland edged into tropical waters 24 million years ago, some coral grew, but a sedimentation regime quickly developed with erosion of the Great Dividing Range; creating river deltas, oozes and turbidites, unsuitable conditions for coral growth. 10 million years ago, the sea level significantly lowered, which further enabled sedimentation. The reef's substrate may have needed to build up from the sediment until its edge was too far away for suspended sediments to inhibit coral growth. In addition, approximately 400,000 years ago there was a particularly warm Interglacial period with higher sea levels and a water temperature change.
The land that formed the substrate of the current Great Barrier Reef was a coastal plain formed from the eroded sediments of the Great Dividing Range with some larger hills.
The Reef Research Centre, a Cooperative Research Centre, has found coral 'skeleton' deposits that date back half a million years. The Great Barrier Reef Marine Park Authority considers the earliest evidence of complete reef structures to have been 600,000 years ago. According to the GBRMPA, the current, living reef structure is believed to have begun growing on the older platform about 9,000 years ago. The Australian Institute of Marine Science agrees, placing the beginning of the growth of the current reef at the time of the Last Glacial Maximum. At around that time, sea level was lower than it is today.
From 20,000 years ago until 6,000 years ago, sea level rose steadily around the world. As it rose, the corals could then grow higher on the newly submerged maritime margins of the hills of the coastal plain. By around 13,000 years ago the sea level was only lower than the present day, and corals began to surround the hills of the coastal plain, which were, by then, continental islands. As the sea level rose further still, most of the continental islands were submerged. The corals could then overgrow the submerged hills, to form the present cays and reefs. Sea level here has not risen significantly in the last 6,000 years. The CRC Reef Research Centre estimates the age of the present, living reef structure at 6,000 to 8,000 years old. The shallow water reefs that can be seen in air-photographs and satellite images cover an area of 20,679 km2, most of which has grown on top of limestone platforms that are relics of past phases of reef growth.
The 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 has been divided into 70 bioregions, of which 30 are reef bioregions. In the northern part of the Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these structures are not found in the rest of 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 distributed widely, but are most common towards the southern part of the Great Barrier Reef, attached to high islands, for example, 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 of reef in the middle of the system, for example the reefs surrounding Lizard Island. Crescentic reefs are also found in the far north of the Great Barrier Reef Marine Park, and in the Swain Reefs. Planar reefs are found in the northern and southern parts, near Cape York Peninsula, Princess Charlotte Bay, and Cairns. Most of the islands on the reef are found on planar reefs.
Wonky holes can have localised impact on the reef, providing upwellings of fresh water, sometimes rich in nutrients contributing 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 considerable navigational improvements, as they outlined the contrasting advantages and perils of the Inner Route and the Outer Route, in the open sea.