The Great Barrier Reef is the largest coral reef system in the world. This ecosystem alone represents 10% of all coral reefs. As can be seen in the picture below, it covers two-thirds of the northern eastern coastline of Australia, from Bundaberg to Cape York. The Great Barrier Reef is home to a host of diverse organisms, many of which are endemic. Unfortunately, the Great Barrier Reef is threatened by human activity, and its future is largely determined by our actions.  

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The Great Barrier Reef dates back to as long as 20 million years ago. Because of its old age, this ecosystem has endured and adapted through many cyclical changes in temperature and sea level. The reefs build themselves on top of old reef systems after each ice age, when the sea level rises and floods the low-lying coastal regions. The Great Barrier Reef in its present state is believed to have developed 8,000 years ago. The Aboriginal and Torres Strait Islander people are speculated to be the first people to interact with the reefs, and in the 18th century, the reefs were rediscovered by the Europeans. With increasing rates of human interaction, the Great Barrier Reef’s environment is changing at a faster rate, giving the coral reefs limited time for adaptation. Whenever natural disasters have occurred in the past, the Great Barrier Reef has managed to recover. Unfortunately, whether or not the Great Barrier Reef can survive from these manmade disasters is uncertain.

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Human Impacts

There are three main factors threatening the life of the Great Barrier Reef: global warming, sediment runoff, and pollution. Because of these factors, a fifth of the reefs have been destroyed, a quarter of the reefs are endangered, and another quarter face long-term collapse.

Global warming is causing increased UV radiation, which as a result is preventing the plants and algae from photosynthesizing. This is a problem because coral reefs live in a symbiotic relationship with millions of microscopic algae. These algae foster the growth of corals by aiding in nutrient production. With this increased UV radiation, algae are leaving the coral reef and the coral inevitably dies.

Temperature and chlorophyll concentration in relation to the reefs.
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Sediment runoff is a result of deforestation from farming. Because this sediment was previously used for growing plants, the sediment is filled with fertilizers such as nitrogen and phosphorous. These nutrients cause massive algae growth that leads to a depletion in oxygen. As a result of these algae blooms, crown-of-thorn starfish, which eat coral across the Great Barrier Reef, have been spiking in population. A doubling of chlorophyll in water leads to a tenfold increase in the crown-of-thorn starfish survival rate. Unfortunately, 80% of the land adjacent to the Great Barrier Reef is farmland that supports agricultural production, so an immediate solution to this problem is not possible.

Crown-of-Thorns Starfish are a problem in other reefs besides the Great Barrier Reef as well.
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Pollution in the air inevitably travels to the ocean though rain, which in return, slowly acidifies the water. Greater than 30% of carbon dioxide emitted by human activities goes into the ocean. The acidification of the sea causes two problems to occur: coral bleaching and low calcium carbonate accretion by organisms. 

Increasing acidification and temperature has caused a dramatic decrease in calcification.
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Future Prospects

Over the years, the Great Barrier Reef has adjusted through glacial and interglacial periods. The ecosystem has also survived through many natural disasters. Evidence shows that the Great Barrier Reef is a resilient ecosystem. In the past, live coral cover has decreased about 70% as a result of storm damage, and the Great Barrier Reef was able to restore itself within 10 years. However, due to human impact, the Great Barrier Reef's environment is changing at a faster rate. As a result, the Great Barrier Reef does not have as much time to adjust and regenerate from these changes. Coral bleaching may be increasing at a faster rate than coral growth. One source predicts that 95% of coral will be dead by 2050. Though there are efforts to sustain the reef, these efforts may not be enough to sustain the Great Barrier Reef's current environment.    

Coral bleaching is occurring at a rapid rate.
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Conservation Status

Although the Great Barrier Reef is under threat, there are many organizations in Australia that are fighting for its survival. The most prominent organization is The Great Barrier Reef Marine Park Authority. This organization has allocated different levels of protection to reefs throughout the ecosystem. The three levels are: general use, intermediate levels of access and extraction, and complete preservation. The GBR Marine Park Authority tries its best to create a balance of socioeconomic and ecological priorities. The organization also has won numerous international awards for its innovative and effective eco-initiatives. One is example is the “Eye of the Reef,” which is a partnership with the tourism industry and the reef research community. While selected tourism operators collect biological information at frequently visited reef and island sites, community and reef members help detect large-scale coral bleaching. Besides the efforts of the GBR Marine Park Authority, other organizations are suggesting to budget the amount of nitrogen and phosphorus farmers can use to soften the impact of nutrient runoff. The most important thing to do is to spread awareness about Great Barrier Reef's problems and to support these organizations. The Great Barrier Reef is a leading source of tourism for Australia, and Australia can leverage this power to help save the reef.   

Over the years, the GBR Marine Park Authority has increased protection on the reefs.
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References

Anthony, K. R. N., D. I. Kline, G. Diaz-Pulido, S. Dove, & O. Hoegh-Guldberg. 2008. Ocean Acidification Causes Bleaching and Productivity Loss in Coral Reef Builders. Proceedings of the National Academy of Sciences of the United States of America. Volume 105, no. 45, pp 17442-17446

Butler, Rhett A., Coral Reefs Decimated by 2050, Great Barrier Reef's Coral 95% Dead. mongabay.com

DeVantier, L. M., G. De'Ath, T. J. Done, & E. Turak. 1998. Ecological Assessment of a Complex Natural System: A Case Study from the Great Barrier Reef. Ecological Applications. Volume 8, no. 2, pp 480-496

Halford, A., J. Cheal, D. Ryan, & D. McB. Williams. 2004. Resilience to Large-Scale Disturbance in Coral and Fish Assemblages on the Great Barrier Reef. Ecology. Volum 85, no. 7, pp 1892-1905

Marshall, P.A., & A. H. Baird. 2000. Bleaching of corals on the Great Barrier Reef:
Differential Susceptibilities among Taxa. Springer Berlin / Heidelberg. Volume 19, no. 2, pp 155-163

McCook, L.J. 1999. Macroalgae, Nutrients and Phase Shifts on Coral Reefs: Scientific Issues and Management Consequences for the Great Barrier Reef. Springer Berlin/Heidelberg. Volume 18, no. 4, pp 357-367

Nowak, Rachel. 2003. Is run-off wrecking the reef? New Scientist. Volume 178, no. 2398, pp 8

Southall, Ben. 2011. Conserving Australia's Great Barrier Reef: The Best Expedition in the World. The Ecologist. 

Tchernov, Dan. 2004. Membrane Lipids of Symbiotic Algae are Diagnostic of Sensitivity to Thermal Bleaching in Corals. PNAS. Volume 101, no. 37

Young, Emma. 2004. Farm Run-off Sparks Invasion of Coral Crunchers. New Scientist. Volume 181, no. 2439 pp 1, 17