Great Barrier Reef

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.