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Great Barrier Reef

Great Barrier Reef

The Great Barrier Reef lies off the northeastern coast of Australia and is the largest structure ever made by living organisms including human beings, consisting of the skeletons of tiny coral polyps and hydrocorals bounded together by the soft remains of coralline algae and microorganisms.

The Great Barrier Reef is over 1,250 mi (2,000 km) long and is 80,000 mi2 (207,000 km2) in surface area , which is larger than the island of Great Britain. It snakes along the coast of the continent of Australia, roughly paralleling the coast of the State of Queensland, at distances ranging 10100 mi (16160 km) from the shore. The reef is so prominent a feature on Earth that it has been photographed from satellites. The reef is located on the continental shelf that forms the perimeter of the Australian landmass where the ocean water is warm and clear. At the edge of the continental shelf and the reef, the shelf becomes a range of steep cliffs that plunge to great depths with much colder water. The coral polyps require a temperature of at least 70°F (21°C), and the water temperature often reaches 100°F (38°C).

The tiny coral polyps began building their great reef in the Miocene Epoch that began 23.7 million years ago and ended 5.3 million years ago. The continental shelf has subsided almost continually since the Miocene Epoch. In response, the reef has grown upward with living additions in the shallow, warm water near the surface; live coral cannot survive below a depth of about 25 fathoms (150 ft, or 46 m) and also depend on the salt content in seawater. As the hydro-corals and polyps died and became cemented together by algae, the spaces between the skeletons were filled in by wave action that forced in other debris called infill to create a relatively solid mass at depth. The upper reaches of the reef are more open and are riddled with grottoes, canyons, caves, holes bored by mollusks, and many other cavities that provide natural homes and breeding grounds for thousands of other species of sea life. The Great Barrier Reef is, in reality, a string of 2,900 reefs, cays, inlets, 900 islands, lagoons, and shoals, some with beaches of sand made of pulverized coral.

The reef is the product of over 350 species of coral and red and green algae. The number of coral species in the northern section of the reef exceeds the number (65) of coral species found in the entire Atlantic Ocean. Polyps are the live organisms inside the coral, and most are less than 0.3 in (8 mm) in diameter. They feed at night by extending frond-like fingers to wave zooplankton toward their mouths. In 1981, marine biologists discovered that the coral polyps spawn at the same time on one or two nights in November. Their eggs and sperm form an orange and pink cloud that coats hundreds of square miles of the ocean surface. As the polyps attach to the reef, they secrete lime around themselves to build secure turrets or cups that protect the living organisms. The daisy- or feather-like polyps leave limestone skeletons when they die. The creation of a 1 in (2.5 cm) thick layer of coral takes five years.

The coral is a laboratory of the living and once-living; scientists have found that coral grows in bands that can be read much like the rings in trees or the icecaps in polar regions. By drilling cores 25 ft (7.6 m) down into the coral, 1,000 years of lifestyles among the coral can be interpreted from the density, skeleton size, band thickness, and chemical makeup of the formation. The drilling program also proved that the reef has died and revived at least a dozen times during its 25-million-year history, but it should be understood that this resiliency predated human activities. The reef as we know it is about 8,000 years old and rests on its ancestors. In the early 1990s, study of the coral cores has yielded data about temperature ranges, rainfall, and other climate changes; in fact, rainfall data for design of a dam were extracted from the wealth of information collected from analysis of the coral formation.

Animal life forms flourish on and along the reef, but plants are rare. The Great Barrier Reef has a distinctive purple fringe that is made of the coralline or encrusting algae Lithothamnion (also called stony seaweed), and the green algae Halimeda discodea that has a creeping form and excretes lime. The algae are microscopic and give the coral its many colors; this is a symbiotic relationship in which both partners, the coral and the algae, benefit. Scientists have found that variations in water temperature stress the coral causing them to evict the resident algae. The loss of color is called coral bleaching, and it may be indicative of global warming or other effects like El Niño.

This biodiversity makes the reef a unique ecosystem. Fish shelter in the reef's intricacies, find their food there, and spawn there. Other marine life experience the same benefits. The coastline is protected from waves and the battering of storms, so life on the shore also thrives.

See also El Niño and La Niña phenomena; Greenhouse gases and greenhouse effect; Tropical cyclone

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Great Barrier Reef

Great Barrier Reef, largest complex of coral reef in the world, c.1,250 mi (2,000 km) long, in the Coral Sea, forming a natural breakwater for the coast of Queensland, NE Australia. Composed of more than 2,800 individual reefs, the Great Barrier Reef is separated from the mainland by a shallow lagoon from 10 to 100 mi (16–161 km) wide. In some places it is more than 400 ft (122 m) thick. The coral in the reef is threatened, however, by predation by the crown-of-thorns starfish, by damage caused by cyclones (hurricanes), and by coral bleaching, the effect of climate change. Although the Australian government declared the reef a marine sanctuary in 1975, a 2012 study estimated that half of the coral had disappeared since 1985, with losses much greater in some areas than others.

A major tourist attraction, the reef has many islets, coral gardens, and unusual marine life. The Great Barrier Reef Marine Park, more than 130,000 sq mi (340,000 sq km), encompasses most of the reefs and interreefal areas as well as the neighboring lagoon and a large section of the continental shelf. It is the largest UNESCO World Heritage Area. Known to Australian aborigines for thousands of years, the reef was discovered by the Western world when Capt. James Cook's ship ran aground there in 1770; it was explored in the 19th cent. by Matthew Flinders and Charles Darwin.

See R. Endean, Australia's Great Barrier Reef (1983); I. McCalman, The Reef: A Passionate History (2014).

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Great Barrier Reef

Great Barrier Reef World's largest coral reef, in the Coral Sea off the ne coast of Queensland, Australia. It was first explored by James Cook in 1770. It forms a natural breakwater and is up to 800m (2600ft) wide. The reef is separated from the mainland by a shallow lagoon, 11–24km (7–15mi) wide. It is a world heritage site. Length: 2000km (1250mi). Area: c.207,000sq km (80,000sq mi).

http://www.reefed.edu.au; http://www.gbrmpa.gov.au

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Great Barrier Reef

Great Barrier Reef

Location and extent

Formation

Discovery and exploration

Biology

Tourism and environmental hazards

Resources

The Great Barrier Reef, which lies off the northeastern coast of Australia, has been described as the most complex and perhaps the most productive biological system in the world. The Great Barrier Reef is the largest structure ever made by living organisms, including human beings. It consists of the skeletons of coral polyps and hydrocorals bounded together by the soft remains of coralline algae and microorganisms.

Location and extent

The Great Barrier Reef is over 1,250 mi (2,000 km) long and occupies 80,000 sq mi (207,000 sq km) of surface area, which is larger than the island of Great Britain. It lies off Australia, roughly parallel to the coast of the State of Queensland, at distances ranging from 10100 mi (16160 km) offshore. The reef is located on the continental shelf that forms the perimeter of the Australian landmass, where the ocean water is warm and clear. At the edge of the continental shelf and the reef, the shelf becomes a range of steep cliffs that plunge to great depths and colder water. The coral polyps require a temperature of at least 70°F (21°C), and the water temperature around the reef often reaches 100°F (38°C).

Formation

The Great Barrier Reef is, in reality, a string of 2,900 reefs, cays, inlets, 900 islands, lagoons, and shoals, some with beaches of sand made of pulverized coral. Coral polyps began building the reef in the Miocene epoch, which began 23.7 million years ago and ended 5.3 million years ago. The continental shelf has subsided almost continually since the Miocene Epoch, so the reef has grown upward with the living additions to the reef in the shallow, warm water near the surface. Coral cannot live below a depth of about 25 fathoms (150 ft or 46 m) and is also sensitive the salt content in seawater. As the hydrocorals and polyps died and became cemented together by algae, the spaces between the skeletons were filled in by wave action that forced in other debris, called infill, to create a nearly solid mass at depth. The upper reaches of the reef are open and are riddled with grottoes, canyons, caves, holes bored by molluscs, and other cavities that provide natural homes and breeding grounds for thousands of other species of sea life.

Discovery and exploration

The Aborigines (the native people of Australia) undoubtedly were the first discoverers of the Great Barrier Reef. The Chinese probably explored it about 2,000 years ago while searching for marine creatures like the sea cucumber, which are believed to have medicinal properties. During his voyage across the Pacific Ocean in 1520, Ferdinand Magellan (14801520) missed Australia and its reef. Captain James Cook (17281779), the British explorer credited with discovering Australia, discovered the Great Barrier Reef by accident when his ship, the Endeavour, ran aground on the reef on June 11, 1770. Cooks crew unloaded ballast (including cannon now imprisoned in the coral growth) and waited for a high tide that dislodged the ship from the reef. After extensive repairs, it took Cook and his crew three months to navigate through the mazelike construction of the Great Barrier Reef. These obstacles did not discourage Cook from exploring and charting the extent of the reef and its cays, passages, and other intricacies on this first of three expeditions of discovery he undertook to the Reef.

In 1835, Charles Darwins (18091882), voyage of scientific discovery on the British ship the Beagle included extensive study of the reef. Mapping continued throughout the nineteenth century, and, in 1928, the Great Barrier Reef Expedition began as a scientific study of coral lifestyles, reef construction, and reef ecology. The Expeditions work concluded in 1929, but a permanent marine laboratory on Heron Island within the reef was founded for scientific explorations and environmental monitoring. The reef is also the final resting place of a number of ships that sank during World War II (19391945).

Biology

The Reef is the product of over 350 species of coral and red and green algae. The number of coral species in the northern section of the Reef exceeds the number (65) of coral species found in the entire Atlantic Ocean. Polyps are the live organisms inside the coral, and most are less than 0.3 in (8 mm) in diameter. They feed at night by extending frond-like fingers to wave zooplankton toward their mouths. In 1981, marine biologists discovered that the coral polyps spawn at the same time on one or two nights in November. Their eggs and sperm form an orange and pink cloud that coats hundreds of square miles of the ocean surface. As the polyps attach to the Reef, they secrete calcium carbonate around themselves to build secure turrets or cups that protect the living organisms. The daisy-or feather-like polyps leave limestone skeletons when they die. The creation of a 1 in (2.5 cm)-thick layer of coral takes five years.

The coral is a laboratory of the living and once-living. Scientists have found that coral grows in bands that can be read much like the rings in trees or the icecaps in polar regions. By drilling cores 25 ft (7.6 m) down into the coral, 1,000 years of coral history can be interpreted from the density, skeleton size, band thickness, and chemical makeup of the formation. The drilling program also proved that the reef has died and revived at least a dozen times during its 25-million-year history (although it must be understood that this resiliency predated human activities). The reef as we know it is about 8,000 years old and rests on its ancestors. In the early 1990s, study of the coral cores yielded data about temperature ranges, rainfall, and other climate changes in sufficient detail to use long-term rainfall data for design of a dam.

Coral also shows considerable promise in the field of medicine. Corals produce chemicals that block ultraviolet rays from the sun, and the Australian Institute has applied for a patent to copy these chemicals as potential cancer inhibitors. Chemicals in the coral may also yield analgesics (pain relievers) and anti-AIDS medications.

KEY TERMS

Aborigines The native people of the continent of Australia.

Algae A group of aquatic plants (including seaweed and pond scum) with chlorophyll and colored pigments.

Biodiversity The biological diversity of an area as measured by the total number of plant and animal species.

Cay A low-lying reef of sand or coral.

Continental shelf A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.

Ecotourism Ecology-based tourism, focused primarily on natural or cultural resources.

El Nino The phase of the Southern Oscillation characterized by increased sea water temperatures and rainfall in the eastern Pacific, with weakening trade winds and decreased rain along the western Pacific.

Phytoplankton Minute plant life that lives in water.

Polyp The living organism in coral with an attached end and an open end with a mouth and fine tentacles.

Symbiosis A biological relationship between two or more organisms that is mutually beneficial. The relationship is obligate, meaning that the partners cannot successfully live apart in nature.

Zooplankton Minute animal life that lives in water.

Animal life flourishes on and along the reef, but plants are rare. The Great Barrier Reef has a distinctive purple fringe that is made of the coralline or encrusting algae Lithothamnion (also called stony seaweed), and the green algae Halimeda discodea that has a creeping form and excretes lime. The algae are microscopic and give the coral its many colors; this is a symbiotic relationship in which both partners, the coral and the algae, benefit. Scientists have found that variations in water temperature stress the coral causing them to evict the resident algae. The loss of color is called coral bleaching, and it may be indicate global warming or other effects such as El Nino.

Other animal life includes worms, crabs, prawns, crayfish, lobsters, anemones, sea cucumbers, starfish, gastropods, sharks, 22 species of whales, dolphins, eels, sea snakes, octopus, squid, dugongs (sea cows), 1,500 species of fish including the largest black marlin in the world, and birds such as the shearwater, which migrates from Siberia to lay its eggs in the hot coral sand. The starfish Acanthaster planci, nicknamed the crown-of-thorns, is destructive to the reef because it eats live coral. The starfish ravages the coral during periodic infestations then all but vanishes for nearly twenty years at a time. The crown-of-thorns has lived on the Great Barrier Reef for ages (again according to the history shown in the drilling cores), but scientists are concerned that human activities may be making the plague-like infestations worse. Giant clams that grow to more than 4 ft (1.2 m) across and 500 lb (187 kg) in weight are the largest molluscs in the world. Of the seven species of sea turtles in the world, six nest on Raine Island within the Reef and lay over 11,000 eggs in a single reproductive night.

This biodiversity makes the reef a unique ecosystem. Fish shelter in the reefs intricacies, find their food there, and spawn there. Other marine life experience the same benefits. The coastline is protected from waves and the battering of storms, so life on the shore also thrives.

Tourism and environmental hazards

In 1990, Conservation, Education, Diving, Archaeology, and Museums International (CEDAM International) gathered the opinions of marine experts and selected seven underwater wonders of the world including the Great Barrier Reef. The idea was inspired by the seven wonders of the ancient world, which were all manmade and of which only the Great Pyramid survives.

Education is essential if the Great Barrier Reef is to survive. More than 1.5 million visitors per year visit the area, and development along the Australian coast to accommodate the tourists was largely uncontrolled until 1990. In the 1980s, the island resort of Hamilton was built following the dredging of harbors, leveling of hills, construction of hotels and an airport, and the creation of artificial beaches. About 25 resorts like this dot the Reef. Fishing has also decimated local fish populations; fish that are prized include not only those for food, but also tropical fish for home aquariums. Fishing nets, boat anchors, and waste from fishing and pleasure boats all do damage. Prospectors have mined the coral because it can be reduced to lime for the manufacture of cement and for soil improvement in the sugar cane fields.

Environmental hazards such as oil spills have seriously threatened the reef. The maze of reefs includes a narrow, shallow shipping channel that is used by oil and chemical tankers and that has a high accident rate. Lagoons have collected waste runoff from towns, agriculture, and tourist development; and the waste has allowed algae (beyond the natural population) to flourish and strangle the live coral. Pesticides and fertilizers also change the balance between the coral and algae and zoo- and phyto-plankton, and the coral serves as an indicator of chemical damage by accumulating PCBs, metals, and other contaminants. Sediment also washes off the land from agricultural activities and development; it clouds the water and limits photosynthesis. Periodic burning off of the sugar cane fields fills the air with smoke that settles on reef waters, overfishing of particular species of fish shifts the balance of power in the undersea world, and shells and coral are harvested (both within and beyond legal limits) and sold to tourists.

The Government of Australia has declared the Great Barrier Reef a national park, and activities like explorations for gold and oil and spearfishing were permanently banned with the Reefs new status. The United Nations Educational, Scientific, and Cultural Organization (UNESCO) has named it a world heritage site in attempts to encourage awareness and protect the area.

Resources

BOOKS

Aronson, R.B. (editor). Geological Approaches to Coral Reef Ecology. Berlin: Springer, 2006.

Cote, I.M. and J.D. Reynold, eds. Coral Reef Conservation. Cambridge: Cambridge University Press, 2006.

Gillian S. Holmes

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Great Barrier Reef

Great Barrier Reef


The Great Barrier Reef, located in the Coral Sea off the eastern coast of Queensland in northeastern Australia , consists of more than 2,800 reefs that range in size from 1 hectare to over 10,000 hectares in area. As the largest reef in the world, the Great Barrier Reef is 1,250 mi (2,011 km) in length, extending from a point near McKay, Queensland in the south to the Torres Strait in the north, which lies between Australia and New Guinea. The Reef is 45 mi (72 km) across at its widest point, with a total area of more than 300,000 square kilometers. Approximately 20% of the reefs are submerged reefs or shoals, while about 26% are fringing reefs around continental islands or along the mainland coast. The remaining reefs are shelf reef platforms. Water depths range from 65.698 ft (2030 m) in lagoonal areas to 131197 ft (4060 m) between the reefs on the outer shelf. Starting in the south near the Tropic of Capricorn, the Great Barrier Reef is a wide scattering of reefs about 186 mi (300 km) out from the coast; moving north the Reef becomes more continuous and is within 1012 mi (1619 km) of the coast, with a few individual reefs in the inner lagoon (the area between the reef and the coast). North of Cairns the reef is almost a continuous barrier between the coast and the Coral Sea. Drilling has indicated that in places the reef is over 1,640.5 ft (500 m) thick.

At the end of the last ice age , about 20,000 years ago, the sea level was about 394 ft (120 m) lower than it is today, and dry land extended from the present day coast to the location of today's outer Barrier Reef. As the ice melted, the sea rose, and by 13,000 years ago the coastal plain had become a submerged continental shelf. Corals and reefs grow best where there is water movement, so the reefs tended to form on submerged hills in the flooding coastal plain. By 6000 to 7000 years ago, the sea had reached its present level, and the reef began to assume its present shape. The Spanish mariner Luis Vaáez de Torres was the first European known to have sailed the northern reef, but the Spanish kept the route a secret to protect their route between Europe and the Orient. The Reef was explored and charted by Captain James Cook, whose ship in 1770 ran aground on the reef that now is called the Endeavor, after the name of his ship.

The Great Barrier Reef provides homes and shelter for a wide diversity of life. The Great Barrier Reef is home to corals, which form the reefs, dolphins and whales , six species of sea turtles , more than 1,500 species of fish, 4,000 types of mollusks, 500 species of seaweed, and more than 200 species of birds. The corals that make up the Reef consist of individual living coral polyps, which as they divide in a process called budding, form colonies in fan, antler, brain, and plate shapes. Each polyp, which is a tiny jelly-like, sack-like animal with a mouth surrounded by tentacles, lives inside a shell of aragonite, a type of calcium carbonate that is the hard shell typically recognized as coral. The polyps are joined together to form a colony. Coral polyps obtain food by catching plankton in their tentacles as well as deriving nutrients from symbiotic algae, the zooxanthellae, that live within their tissues. These zooxanthellae produce nutrients through photosynthesis , which are then available for use by the coral. Association with the algae allow corals to build skeletons three times faster in the light than in the dark, and faster than storms and waves can break it down. Coral bleaching occurs when stressed corals expel the zooxanthellae and turn white, or bleached. If the zooxanthellae do not return to the coral, the coral will die.

Every year about one-third of the 350 species of coral reproduce sexually during a mass spawning event. Spawning occurs in most of the inner reefs around November and in the outer reefs in December. The spawning occurs at night, up to six days after the full moon. Eggs and sperm are released into the water, where they combine to form a free-swimming larval stage.

The Great Barrier Reef is completely within the tropics. The climate of the Reef is a typical monsoon weather pattern, which consists of strong south-easterly winds dominating during the dry winter months and weaker variable winds occurring during the summer wet season. Both air and sea temperatures exhibit seasonal variations. Mean sea temperatures in inshore areas exhibit a range of temperatures of 69.8°F (21°C) in July and August to 86°F (30°C) in January and February. Temperatures on offshore reefs exhibit less seasonal difference, varying from 73.4°F (23°C) in winter to 82°F (28°C) in summer.

There are two types of islands along the Great Barrier Reef. The larger islands, such as those of the Whitsunday group, are the tops of submerged mountains that at one time were high points of a range running along the coast. These islands have vegetation similar to the mainland. Some of these islands that have fertile soils and are affected by heavy monsoonal rains are covered with rain forests. Other islands are isolated low-lying coral cays. Cays are formed when coral grow to levels that are higher than sea level, even at low tide. Coral can only survive a few hours out of water. The dead coral on the cays is worn down and broken off by waves and storm action. Eventually the coral debris is ground into sand. Through time the sand stabilizes, seabirds start to nest, and hardy vegetation begins to grow. Decomposing plant materials and bird droppings change the sand into a more developed soil , providing an environment for a wider diversity of plant life. Cays are found more frequently on inner reefs in the Great Barrier Reef, where waves and currents are less strong than on reefs further away from the coastline. However, vegetated cays are not sufficiently stable to withstand severe weather, such as storms and cyclones.

Comprehensive protection of the Great Barrier Reef was accomplished in 1975 by the formation of the Great
Barrier Reef Marine Park, administered by the Great Barrier Reef Marine Park Authority (GBRMPA). Over 98% of the area, with the exception of a few coastal areas, is now included within the Marine Park. Drilling and mining for minerals within all areas of the Marine Park is forbidden. In 1981, in recognition of its outstanding natural heritage value, most of the Great Barrier Reef area was added to the World Heritage List by the United Nations Education, Scientific, & Cultural Organization (UNESCO ). The Great Barrier Reef World Heritage Area is the largest of the world's over 550 World Heritage Areas. In addition to the coral reef area, the Great Barrier Reef World Heritage Area also contains the continental slope, the inter-reefal areas, and the Great Barrier Reef lagoon.

The Great Barrier Reef Marine Park has been classified into 70 bioregions, which are areas of differing marine biodiversity with plant and animal communities that, together with physical features, are significantly different than the surrounding areas and the rest of the Marine Park. Based on these bioregions, the GBRMPA has divided the Marine Park into six zones: (1) the Preservation Zone, which includes areas that are intended to be kept completely untouched; (2) the Scientific Research Zone, which includes areas set aside exclusively for scientific research; (3) the Marine National Park A Zone, which includes areas where recreational use (i.e., fishing with one line and one hook) is permitted, but commercial fishing is not permitted; (4) the General Use B Zone, where reasonable recreational and commercial uses are permitted, but trawling and shipping are prohibited; and (5) the General Use A Zone, where all reasonable uses are permitted, including trawling and shipping, but mining, oil drilling , commercial spear fishing and fishing with scuba equipment are not permitted.

More than two million people a year visit the reef, generating more than $AU1 billion in tourism dollars. Tourists visit the reef using private charter boats, regular scheduled daily cruises, seaplanes, air charter, and helicopter flights. They view the reefs through reef walks, glass bottom or semi-submersible boats, snorkeling, or scuba diving.

The Great Barrier Reef is sensitive to climate changes and to changes in patterns of water movement. In 1998 scientists announced that about 60% of the reef had been affected by coral bleaching due to increasing sea temperatures and fresh water flooding.

The Reef is also susceptible to physical damage. Human damage to the Great Barrier Reef has been occurring due to carelessness, where people walk on the reefs, drop anchors onto them, drag diving gear over them, break them into pieces to take as souvenirs, and knock into and ground boats onto them.

Since the 1960s, during periodic outbreaks, the Crown of Thorns starfish has been destroying corals that make up the reef. The Crown of Thorns is a large, thorny, brown-colored starfish. The starfish eats coral by turning its stomach out through its mouth, in a process called stomach eversion, wraps the stomach around a coral, and secretes an enzyme to digest the living coral polyps. When the stomach is drawn back in, all that is left is the limestone coral skeleton. This skeleton becomes covered with green algae and other types of encrusting plants and animals, which give the coral skeleton a dull, gray appearance. Some types of corals become infested with boring organisms. During periods of rough weather (e.g., during a cyclone ), the dead colony and the newly attached organisms may collapse. Some scientists feel that outbreaks of the Crown of Thorns starfish may be a natural part of the lifecycle of the reef. By feeding on fast-growing species of corals, the starfish may act to preserve coral diversity, for fast-growing populations, if left unchecked, could dominate the reef.

Water quality has been identified by the Great Barrier Reef Marine Park Authority as a critical management issue, as pollution by sediments, toxic metal and organic contaminants, oil spills , and pesticides, can potentially harm the Reef. Sewage discharge is regulated in the Marine Park area, with tertiary treatment (i.e., nutrient reduction) required before marine discharge; alternatively secondary or tertiary treated wastewater can be land applied with minimal marine discharge. However, the primary water quality concern is nutrient loading from inshore ecosystems. Programs are being developed to reduce nutrient inputs through regulation of discharges, integrated catchment management, improved land management practices, and wetland protection.

[Judith L. Sims ]


RESOURCES

BOOKS

Cates, Alison. The Great Barrier Reef: Australia's Tropical Paradise. Sydney: New Holland/Struik, 1998.

Doubilet, David. Great Barrier Reef. Washington, DC: National Geographic Society, 2002.

Lawrence, David, et al. The Great Barrier Reef: Managing an Ecosystem. Melbourne: Melbourne University Press, 2002.

Smith, Fay. Australia's Great Barrier Reef. Seven Hills, Australia: Cimino Publishing Group, 1998.

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Great Barrier Reef

Great Barrier Reef

Introduction

The Great Barrier Reef, which lies off the northeastern coast of Australia, has been described as “the most complex and perhaps the most productive biological system in the world.” The Great Barrier Reef is the largest structure ever made by living organisms, including human beings. It consists of the skeletons of coral polyps and hydrocorals bounded together by the soft remains of coral line algae and microorganisms.

Historical Background and Scientific Foundations

The Great Barrier Reef is over 1,250 mi (2,000 km) long and occupies 80,000 sq mi (207,000 sq km) of surface area, which is larger than the island of Great Britain. It lies off Australia, roughly parallel to the coast of the state of Queensland, at distances ranging from 10–100 mi (16– 160 km) offshore. The reef is located on the continental shelf that forms the perimeter of the Australian landmass,

where the ocean water is warm and clear. At the edge of the continental shelf and the reef, the shelf becomes a range of steep cliffs that plunge to great depths and colder water. The coral polyps require a temperature of at least 70°F (21°C), and the water temperature around the reef often reaches 100°F (38°C).

The Great Barrier Reef is, in reality, a string of 2,900 reefs, cays, inlets, 900 islands, lagoons, and shoals, some with beaches of sand made of pulverized coral. Coral polyps began building the reef in the Miocene Epoch, which began 23.7 million years ago and ended 5.3 million years ago. The continental shelf has subsided almost continually since the Miocene Epoch, so the reef has grown upward with the living additions to the reef in the shallow, warm water near the surface. Coral cannot live below a depth of about 25 fathoms (150 ft or 46 m) and is also sensitive to the salt content in seawater. As the hydrocorals and polyps died and became cemented together by algae, the spaces between the skeletons were filled in by wave action that forced in other debris, called infill, to create a nearly solid mass at depth. The upper reaches of the reef are open and are riddled with grottoes, canyons, caves, holes bored by mollusks, and other cavities that provide natural homes and breeding grounds for thousands of other species of sea life.

Discovery and Exploration

The Aborigines (the native people of Australia) undoubtedly were the first discoverers of the Great Barrier Reef. The Chinese probably explored it about 2,000 years ago while searching for marine creatures like the sea cucumber, which are believed to have medicinal properties. During his voyage across the Pacific Ocean in 1520, Farin and Magellan (1480–1521) missed Australia and its reef. Captain James Cook (1728–1779), the British explorer credited with discovering Australia, discovered the Great Barrier Reef by accident when his ship, the Endeavour, ran aground on the reef on June 11, 1770. Cook's crew unloaded ballast (including cannon now imprisoned in the coral growth) and waited for a high tide that dislodged the ship from the reef. After extensive repairs, it took Cook and his crew three months to navigate through the mazelike construction of the Great Barrier Reef. These obstacles did not discourage Cook from exploring and charting the extent of the reef and its cays, passages, and other intricacies on this first of three expeditions of discovery he undertook to the reef.

In 1835, Charles Darwin's voyage of scientific discovery on the British ship the Beagle included extensive study of the reef. Mapping continued throughout the nineteenth century, and, in 1928, the Great Barrier Reef Expedition began as a scientific study of coral lifestyles, reef construction, and reef ecology. The Expedition's work concluded in 1929, but a permanent marine laboratory on Heron Island within the reef was founded for scientific explorations and environmental monitoring. The reef is also the final resting place of a number of ships that sank during World War II (1939–1945).

WORDS TO KNOW

ABORIGINES: Native peoples or indigenous peoples: the cultural or racial group that are the oldest inhabitants of a region.

ALGAE: Single–celled or multicellular plants or plantlike organisms that contain chlorophyll, thus making their own food by photosynthesis. Algae grow mainly in water.

BIODIVERSITY: Literally, “life diversity”: the number of different kinds of living things. The wide range of organisms— plants and animals—that exist within any given geographical region.

CAY: A low-lying reef of sand or coral.

CONTINENTAL SHELF: A gently sloping, submerged ledge of a continent.

EL NIÑO: Regularly-recurring warming of the surface waters of the eastern Pacific that has affects on global climate; part of the El Nin˜o–Southern Oscillation Cycle (ENSO). In some contexts, “El Nin˜o” refers to the entire ENSO cycle.

PHYTOPLANKTON: Microscopic marine organisms (mostly algae and diatoms) that are responsible for most of the photosynthetic activity in the oceans.

SYMBIOSIS: A pattern in which two or more organisms live in close connection with each other, often to the benefit of both or all organisms.

ZOOPLANKTON: Animal plankton. Small herbivores that float or drift near the surface of aquatic systems and that feed on plant plankton (phytoplankton and nanoplankton).

Biology

The reef is the product of over 350 species of coral and red and green algae. The number of coral species in the northern section of the reef exceeds the number (65) of coral species found in the entire Atlantic Ocean. Polyps are the live organisms inside the coral, and most are less than 0.3 in (8 mm) in diameter. They feed at night by extending frond-like fingers to wave zooplankton toward their mouths. In 1981, marine biologists discovered that the coral polyps spawn at the same time on one or two nights in November. Their eggs and sperm form an orange and pink cloud that coats hundreds of square miles of the ocean surface. As the polyps attach to the reef, they secrete calcium carbonate around themselves to build secure turrets or cups that protect the living organisms. The daisy- or feather-like polyps leave limestone skeletons when they die. The creation of a 1 in (2.5 cm) thick layer of coral takes five years.

Animal life flourishes on and along the reef, but plants are rare. The Great Barrier Reef has a distinctive purple fringe that is made of the coral line or encrusting algae Lithothamnion (also called stony seaweed) and the green algae Halimeda discodea that has a creeping form and excretes lime. The algae are microscopic and give the coral its many colors; this is a symbiotic relationship in which both partners, the coral and the algae, benefit.

Other animal life includes worms, crabs, prawns, crayfish, lobsters, anemones, sea cucumbers, starfish, gastropods, sharks, 22 species of whales, dolphins, eels, sea snakes, octopus, squid, dugongs (sea cows), 1,500 species of fish including the largest black marlin in the world, and birds such as the shearwater, which migrates from Siberia to lay its eggs in the hot coral sand. The starfish Acanthaster planci, nicknamed the crown-of-thorns, is destructive to the reef because it eats live coral. The starfish ravages the coral during periodic infestations then all but vanishes for nearly twenty years at a time. The crown-of-thorns has lived on the Great Barrier Reef for ages (again according to the history shown in the drilling cores), but scientists are concerned that human activities may be making the plague-like infestations worse. Giant clams that grow to more than 4 ft (1.2 m) across and 500 lb (187 kg) in weight are the largest molluscs in the world. Of the seven species of sea turtles in the world, six nest on Raine Island within the reef and lay over 11,000 eggs in a single reproductive night.

This biodiversity makes the reef a unique ecosystem. Fish shelter in the reef's intricacies, find their food there, and spawn there. Other marine life experience the same benefits. The coastline is protected from waves and the battering of storms, so life on the shore also thrives.

Impacts and Issues

Scientists have found that variations in water temperature stress the coral causing them to evict the resident algae. The loss of color is called coral bleaching, and it may indicate global warming or other effects such as El Niño.

The coral is a laboratory of the living and once-living. Scientists have found that coral grows in bands that can be read much like the rings in trees or the icecaps in polar regions. By drilling cores 25 ft (7.6 m) down into the coral, 1,000 years of coral history can be interpreted from the density, skeleton size, band thickness, and chemical makeup of the formation. The drilling program also proved that the reef has died and revived at least a dozen times during its 25-million-year history (although it must be understood that this resiliency predated human activities). The reef as we know it is about 8,000 years old and rests on its ancestors. In the early 1990s, study of the coral cores yielded data about temperature ranges, rainfall, and other climate changes in sufficient detail to use long-term rainfall data for design of a dam.

IN CONTEXT: REEFS IN PERIL

Evidence is growing that coral destruction is a sensitive indicator of global warming. Although there are vigorous scientific and political arguments about assigning proportions of blame to global warming, pollution, or other more direct forms of danger and destruction, recent data indicate that at the present rate of destruction, Australia's Great Barrier Reef could be doomed by mid-century. According to researchers at the Queensland University Center for Marine Studies, the reef may be in greater and more imminent peril than previously assumed. The study, titled “Implications of Climate Change for Australia's Great Barrier Reef,” was commissioned by the Worldwide Fund for Nature. If the reef reaches a critical stage of destruction, it could take hundreds of years to recover if and when environmental conditions improve.

The stress experienced by corals comprising the Great Barrier Reef reflects a global pattern of damage and destruction.

Studies on more than 300 reefs in the Atlantic, Caribbean, and Indo-Pacific regions reveal similar evidence of damage to corals and/or associated indicators of ecological stress such as the absence of lobsters, eels, sea urchins, and declining populations of native fish species.

Estimates peg the worldwide loss of coral reefs at approximately 10% over the last five to seven years. Some interpretations of data, however, assert that the global loss was sudden and due to widespread bleaching of corals in 1997 and 1998, and that corals in some areas are on the rebound. Severely stressed corals lose their symbiotic algae (zooxanthellae) and appear white or “bleached.”

U.S. National Oceanic and Atmospheric Administration (NOAA) officials acknowledge that corals have experienced a recent worldwide decline, but that making accurate assessments is difficult because of a lack of baseline data that can tell scientists how far the observed changes deviate from normal cyclic patterns (i.e., how much of the damage is due to stress from human (anthropogenic) activity.

Coral also shows considerable promise in the field of medicine. Corals produce chemicals that block ultraviolet rays from the sun, and the Australian Institute has applied for a patent to copy these chemicals as potential cancer inhibitors. Chemicals in the coral may also yield analgesics (pain relievers) and anti-AIDS medications.

More than 1.5 million visitors per year visit the area, and development along the Australian coast to accommodate the tourists was largely uncontrolled until 1990. In the 1980s, the island resort of Hamilton was built following the dredging of harbors, leveling of hills, construction of hotels and an airport, and the creation of artificial beaches. About 25 resorts like this dot the reef. Fishing has also decimated local fish populations; fish that are prized include not only those for food, but also tropical fish for home aquariums. Fishing nets, boat anchors, and waste from fishing and pleasure boats all do damage. Prospectors have mined the coral because it can be reduced to lime for the manufacture of cement and for soil improvement in the sugar cane fields.

Environmental hazards such as oil spills have seriously threatened the reef. The maze of reefs includes a narrow, shallow shipping channel that is used by oil and chemical tankers and that has a high accident rate. Lagoons have collected waste runoff from towns, agriculture, and tourist development; and the waste has allowed algae (beyond the natural population) to flourish and strangle the live coral. Pesticides and fertilizers also change the balance between the coral and algae and zoo- and phyto-plankton, and the coral serves as an indicator of chemical damage by accumulating PCBs, metals, and other contaminants. Sediment also washes off the land from agricultural activities and development; it clouds the water and limits photosynthesis. Periodic burning off of the sugar cane fields fills the air with smoke that settles on reef waters, overfishing of particular species of fish shifts the balance of power in the undersea world, and shells and coral are harvested (both within and beyond legal limits) and sold to tourists.

The government of Australia has declared the Great Barrier Reef a national park, and activities like explorations for gold and oil and spearfishing were permanently banned with the reef's new status. The United Nations Educational, Scientific, and Cultural Organization (UNESCO) has named it a world heritage site in attempts to encourage awareness and protect the area.

See Also El Niño and La Niña; Environmental Pollution; Ocean Circulation and Currents; Oceans and Seas.

BIBLIOGRAPHY

Books

Aronson, R. B., ed. Geological Approaches to Coral Reef Ecology. Berlin: Springer, 2006.

Cote, I. M., and J. D. Reynold, eds. Coral Reef Conservation. Cambridge: Cambridge University Press, 2006.

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Great Barrier Reef

Great Barrier Reef

The Great Barrier Reef lies off the northeastern coast of Australia and is both a scientific wonder and an increasingly popular tourist attraction. It has been described as "the most complex and perhaps the most productive biological system in the world." The Great Barrier Reef is the largest structure ever made by living organisms including human beings, consisting of the skeletons of tiny coral polyps and hydrocorals bounded together by the soft remains of coralline algae and microorganisms .


Location and extent

The Great Barrier Reef is over 1,250 mi (2,000 km) long and is 80,000 sq mi (207,000 sq km) in surface area, which is larger than the island of Great Britain. It snakes along the coast of the continent of Australia, roughly paralleling the coast of the State of Queensland, at distances ranging from 10-100 mi (16-160 km) from the shore. The Reef is so prominent a feature on Earth that it has been photographed from satellites. The Reef is located on the continental shelf that forms the perimeter of the Australian land mass where the ocean water is warm and clear. At the edge of the continental shelf and the Reef, the shelf becomes a range of steep cliffs that plunge to great depths with much colder water. The coral polyps require a temperature of at least 70°F (21°C), and the water temperature often reaches 100°F (38°C).


Formation

The tiny coral polyps began building their great Reef in the Miocene Epoch which began 23.7 million years ago and ended 5.3 million years ago. The continental shelf has subsided almost continually since the Miocene Epoch so the Reef has grown upward with the living additions to the Reef in the shallow, warm water near the surface; live coral cannot survive below a depth of about 25 fathoms (150 ft or 46 m) and also depend on the salt content in sea water. As the hydrocorals and polyps died and became cemented together by algae, the spaces between the skeletons were filled in by wave action that forced in other debris called infill to create a relatively solid mass at depth. The upper reaches of the Reef are more open and are riddled with grottoes, canyons, caves, holes bored by molluscs, and many other cavities that provide natural homes and breeding grounds for thousands of other species of sea life. The Great Barrier Reef is, in reality, a string of 2,900 reefs, cays, inlets, 900 islands, lagoons, and shoals, some with beaches of sand made of pulverized coral.


Discovery and exploration

The aborigines (the native people of Australia) undoubtedly were the first discoverers of the Great Barrier Reef. The Chinese probably explored it about 2,000 years ago while searching for marine creatures like the sea cucumber that are believed to have medicinal properties. During his voyage across the Pacific Ocean in 1520, Ferdinand Magellan missed Australia and its Reef. Captain James Cook, the British explorer credited with discovering Australia, also found the Great Barrier Reef by sudden impact. His ship, the Endeavour, ran aground on the Reef on June 11, 1770. Cook's crew unloaded ballast (including cannon now imprisoned in the coral growth) and, luckily, caught a high tide that dislodged the ship from the Reef. After extensive repairs, it took Cook and his crew three months to navigate through the maze-like construction of the Great Barrier Reef. These obstacles did not discourage Cook from exploring and charting the extent of the Reef and its cays, passages, and other intricacies on this first of three expeditions of discovery he undertook to the Reef.

In 1835, Charles Darwin's voyage of scientific discovery on the British ship the Beagle included extensive study of the Reef. Mapping the natural wonder continued throughout the nineteenth century, and, in 1928, the Great Barrier Reef Expedition was begun as a scientific study of coral lifestyles, Reef construction, and the ecology of the Reef. The Expedition's work concluded in 1929, but a permanent marine laboratory on Heron Island within the Reef was founded for scientific explorations and environmental monitoring. The Reef is also the final resting place of a number of ships that sank during World War II.


Biology

The Reef is the product of over 350 species of coral and red and green algae. The number of coral species in the northern section of the Reef exceeds the number (65) of coral species found in the entire Atlantic Ocean. Polyps are the live organisms inside the coral, and most are less than 0.3 in (8 mm) in diameter. They feed at night by extending frond-like fingers to wave zooplankton toward their mouths. In 1981, marine biologists discovered that the coral polyps spawn at the same time on one or two nights in November. Their eggs and sperm form an orange and pink cloud that coats hundreds of square miles of the ocean surface. As the polyps attach to the Reef, they secrete lime around themselves to build secure turrets or cups that protect the living organisms. The daisy-or feather-like polyps leave limestone skeletons when they die. The creation of a 1 in (2.5 cm)-thick layer of coral takes five years.

The coral is a laboratory of the living and once-living; scientists have found that coral grows in bands that can be read much like the rings in trees or the icecaps in polar regions. By drilling cores 25 ft (7.6 m) down into the coral, 1,000 years of lifestyles among the coral can be interpreted from the density , skeleton size, band thickness, and chemical makeup of the formation. The drilling program also proved that the Reef has died and revived at least a dozen times during its 25-million-year history, but it should be understood that this resiliency predated human activities. The Reef as we know it is about 8,000 years old and rests on its ancestors. In the early 1990s, study of the coral cores has yielded data about temperature ranges, rainfall, and other climate changes; in fact, rainfall data for design of a dam were extracted from the wealth of information collected from analysis of the coral formation.

Coral also shows considerable promise in the field of medicine. Corals produce chemicals that block ultraviolet rays from the sun , and the Australian Institute has applied for a patent to copy these chemicals as potential cancer inhibitors. Chemicals in the coral may also yield analgesics (pain relievers) and anti-AIDS medications.

Animal life forms flourish on and along the Reef, but plants are rare. The Great Barrier Reef has a distinctive purple fringe that is made of the coralline or encrusting algae Lithothamnion (also called stony seaweed), and the green algae Halimeda discodea that has a creeping form and excretes lime. The algae are microscopic and give the coral its many colors; this is a symbiotic relationship in which both partners, the coral and the algae, benefit. Scientists have found that variations in water temperature stress the coral causing them to evict the resident algae. The loss of color is called coral bleaching, and it may be indicate global warming or other effects like El Niño.

Other animal life includes worms, crabs , prawns, crayfish , lobsters , anemones, sea cucumbers , starfish , gastropods, sharks , 22 species of whales, dolphins, eels, sea snakes, octopus , squid , dugongs (sea cows), 1,500 species of fish including the largest black marlin in the world, and birds like the shearwater that migrates from Siberia to lay its eggs in the hot coral sand. The starfish Acanthaster planci, nicknamed the crown-of-thorns, is destructive to the Reef because it eats the live coral. The starfish ravages the coral during periodic infestations then all but vanishes for nearly 20 years at a time. The crown-of-thorns has lived on the Great Barrier Reef for ages (again according to the history shown in the drilling cores), but scientists are concerned that human activities may be making the plague-like infestations worse. Giant clams that grow to more than 4 ft (1.2 m) across and 500 lb (187 kg) in weight are the largest molluscs in the world. Of the seven species of sea turtles in the world, six nest on Raine Island within the Reef and lay over 11,000 eggs in a single reproductive night.

This biodiversity makes the Reef a unique ecosystem . Fish shelter in the Reef's intricacies, find their food there, and spawn there. Other marine life experience the same benefits. The coastline is protected from waves and the battering of storms, so life on the shore also thrives.

Tourism and environmental hazards

In 1990, Conservation, Education, Diving, Archaeology, and Museums International (CEDAM International) gathered the opinions of the world's most respected marine experts and selected "seven underwater wonders of the world" including the Great Barrier Reef. Of course, the idea was inspired by the seven wonders of the ancient world, which were all manmade and of which only the Great Pyramid survives. The underwater wonders give people points of interest and focus for preserving our planet's vast oceans.

Education of the public is needed if the Great Barrier Reef is to survive. Over 1.5 million visitors per year visit the tropical paradise, and development along the Australian coast to accommodate the tourists was largely uncontrolled until 1990. In the 1980s, the island resort of Hamilton was built following the dredging of harbors, leveling of hills, construction of hotels and an airport, and the creation of artificial beaches. About 25 resorts like this dot the Reef. Fishing has also decimated local fish populations; fish that are prized include not only those for food but tropical fish for home aquariums. Fishing nets, boat anchors, and waste from fishing and pleasure boats all do their own damage. Greedy prospectors have mined the coral itself because it can be reduced to lime for manufacture of cement and for soil improvement in the sugar cane fields. Reefs in other parts of the world are near collapse, thanks to such irresponsibility.

Environmental hazards like oil spills have seriously threatened the Reef. The maze of reefs includes a narrow, shallow shipping channel that is used by oil and chemical tankers and that has a high accident rate . Over 2,000 ships per year navigate the channel, and the environmental organization Greenpeace is campaigning to ban the oil traffic through this vulnerable channel. Lagoons have collected waste runoff from towns, agriculture, and tourist development; and the waste has allowed algae (beyond the natural population) to flourish and strangle the live coral. Pesticides and fertilizers also change the balance between the coral and algae and zooand phyto-plankton, and the coral serves as an indicator of chemical damage by accumulating PCBs, metals, and other contaminants. Sediment also washes off the land from agricultural activities and development; it clouds the water and limits photosynthesis . A thousand other hazards inflict unknown damage on the Reef. Periodic burning off of the sugar cane fields fills the air with smoke that settles on Reef waters, overfishing of particular species of fish shifts the balance of power in the undersea world, and shells and coral are harvested (both within and beyond legal limits) and sold to tourists.

The Government of Australia has declared the Great Barrier Reef a national park, and activities like explorations for gold and oil and spearfishing were permanently banned with the Reef's new status. The United Nations Educational, Scientific, and Cultural Organization (UNESCO) has named it a world heritage site in attempts to encourage awareness and protect the area. Despite many threats, the marine park is one of the best protected in the world, thanks to citizens who recognize the worth of this treasure and visitors who are willing to practice ecotourism , and thanks to an extensive body of protective laws.

Resources

books

Care, Patricia. The Struggle for the Great Barrier Reef. New York: Walker and Company, 1971.

McGregor, Craig. The Great Barrier Reef. Amsterdam: Time-Life Books, 1975.

Reader's Digest Guide to the Great Barrier Reef. Sydney, Australia: Reader's Digest, 1988.

periodicals

Belleville, Bill, and David Doubilet. "The Reef Keepers." Sea Frontiers (Mar-Apr. 1993): 50+.

Drogin, Bob. "Trouble Down Under." Los Angeles Times Magazine (Sept. 19, 1993):16+.

FitzGerald, Lisa M. "Seven Underwater Wonders of the World." Sea Frontiers (Dec. 1990): 8-21.

organizations

Great Barrier Reef Marine Park Authority [cited April 2003]. <www.gbrmpa.gov.au>.

other

National Gerographic Society. "Virtual World: Great Barrier Reef" [cited April 2003]. <http://www.nationalgeographic.com/earthpulse/reef/reef1_flash.html>.


Gillian S. Holmes

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aborigines

—The native people of the continent of Australia.

Algae

—A group of aquatic plants (including seaweed and pond scum) with chlorophyll and colored pigments.

Biodiversity

—The biological diversity of an area as measured by the total number of plant and animal species.

Cay

—A low-lying reef of sand or coral.

Continental shelf

—A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.

Ecotourism

—Ecology-based tourism, focused primarily on natural or cultural resources.

El Niño

—The phase of the Southern Oscillation characterized by increased sea water temperatures and rainfall in the eastern Pacific, with weakening trade winds and decreased rain along the western Pacific.

Phytoplankton

—Minute plant life that lives in water.

Polyp

—The living organism in coral with an attached end and an open end with a mouth and fine tentacles.

Symbiosis

—A biological relationship between two or more organisms that is mutually beneficial. The relationship is obligate, meaning that the partners cannot successfully live apart in nature.

Zooplankton

—Minute animal life that lives in water.

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