Great Barrier Reef

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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.