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Australia's Great Barrier REEF.

Coral reefs are the "rainforests of the sea"--the second richest ecosystem, or interdependent environment, on Earth after tropical forests. Reefs are made up of billions of tiny animals called coral polyps. The Great Barrier Reef off Australia's northeast coast is the world's longest coral reef chain and the largest single structure ever created by living creatures--so huge it's visible from space. Yet the Great Reef remains largely unexplored by marine biologists, scientists who study sea life.

Like all reefs, it provides food, shelter, and protection for thousands of ocean plants and Animals. But coral reefs are in grave peril, explains David Gilliam, a research scientist at Florida's National Coral Reef Institute. Last year, 10 percent of the world's coral reefs died from water temperatures rising as a result of global warming, Earth's heating temperatures due to increased trapped gases in the atmosphere. "Without protection, nearly three quarters of the world's reefs could die within 50 years," says Gilliam.


Great Barrier Reef

Length: 2,027 km (1,260 ml)

Width: up to 150 km (93 ml)

Fish Species: over 1,400

Total Marine Species (such as eels and octopuses): over 2,000

Estimated Coral Species: about 400

Reefs in Danger: up to 60%

World Reefs

* cover 0.2% of the ocean floor and less than 0.1% (580,000 sq km) of Earth's surface

* support 2,500 species of coral

* consist of two types of coral: hard (reef-building) coral and soft coral

* can be between 5,000 and 10,000 years old

* contain about 25% of the world's ocean species, including 5,000 species of reef fish

* serve as nurseries for growing fish

* supply a source of protein (seafood) in human diets

* provide food, shelter, and protection to many marine species

How the Reef Formed

Scientists believe the Great Barrier Reef formed 30 million years ago during an ice age, when frozen polar ice caps kept Pacific Ocean water levels much lower than today. Colonies of corals grew upward and outward from the Australian continental shelf, the land that slopes into the sea. Barrier reefs are separated from land by wide deep lagoons. The Great Barrier Reef acts as a sturdy wall that protects Australia's coastline against crashing Pacific Ocean waves.

Coral Bleaching

Coral grows only in clear tropical waters between 20 [degrees] and 28 [degrees] C (68 [degrees] to 82 [degrees] F). Earth's warming ocean temperatures cause coral bleaching. How? Coral polyps share their protective limestone shell with a type of alga (plant, usually aquatic, without stems, roots, or leaves). Coral provides the algae with a home; in turn, algae supplement the coral's diet with needed sugars. When warm water stresses coral, polyps expel algae--which drains coral of color--and the polyps die, leaving behind only their skeletons.

Tourist Damage

Coral reefs are under attack from a host of sources. Tourists and scuba divers damage reefs by touching fragile coral, killing them. Pollution from sewage, industrial chemicals, and pesticides dumped into the ocean, suffocate living coral. Overfishing disrupts a reef's complex environmental balance

Coral Life

Coral polyps--some the size of your hand, others as tiny as a pinhead--collect the chemical calcium carbonate (limestone) from seawater and secrete it around their soft, tube-shaped bodies. The limestone hardens into a protective shell around each polyp and cements it to the reef. As polyps die, a new generation "builds" atop their skeletons and the reef grows larger.

Cross-Curricular Connection

Geography: Locate the world's reef systems on a map. Where are most reefs located?

Did You Know?

* A report by Greenpeace, an environmental organization, estimates that most of the Great Barrier Reef will be dead in 30 years unless projected levels of climate change are mitigated.

* Reef destruction is also caused by natural events such as hurricanes and outbreaks of predators, like sea stars and other coral-eating animals.

* There are two additional types of reefs besides barrier reefs: Fringing reefs are submerged coral platforms that extend out from the shore. Atolls are rings of coral islands above the sea surface that surround a lagoon.

National Science Education Standards

Grades 5-8: structure and function in living systems * diversity and adaptation of organisms * population, resources, and environments

Grades 9-12: interdependence of organisms * matter, energy, and organization in living systems * environmental quality * natural and human-induced hazards


The Great Barrier Reef--A Treasure in the Sea, by Alice Gilbreth, (Dillon Press, 1996) General information on coral reefs: Reefs at Risk:

Australia's Great Barrier Reef

1.e 2. d 3. a 4. b 5. c

Australia's Great Barrier Reef

Directions: Match the words in the left column with the correct phrase on the right.
-- 1. coral bleaching a. type of plant

-- 2. calcium carbonate b. interdependent environment

-- 3. algae c. Earth's heating temperatures

-- 4. ecosystem d. limestone

-- 5. global warming e. caused by global warming
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Publication:Science World
Date:Sep 4, 2000
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