Current Human Impacts

          Although the World Heritage listed The Great Barrier Reef as a “dynamic system” where the coral populations naturally increases and decreases, human activities have significantly accelerated the death of coral reefs, leaving little room for them to recover (Phillips, 2012). The rise in ocean temperature and acidification has led to the death of the organisms residing inside the coral skeleton, also known as coral bleaching, accounting for 10 percent of coral reef decline (Phillips, 2012). Global warming models show how higher water temperatures are also leading to more severe cyclones, which accounts for 48 percent of coral die off (Phillips, 2012). Coastal development and agricultural runoff has led to a significant increase in the amount of sediments, nutrients, and pesticides entering the ocean, causing algal blooms (Hoegh-Guldberg et al. 2004:32). This intensification of nutrients from runoff leads to the rise in crown of thorn starfish larvae survival due to the abundance of algae that the larvae consume (Phillips, 2012). Although the crown of thorn starfish is a natural predator of coral reefs, they are multiplying so quickly that the reef does not have enough time to recover from damage (Phillips, 2012). The crown of thorn starfish outbreak accounts for 42 percent of The Great Barrier Reef coral wipeout. In the past 27 years, over 50 percent of The Great Barrier Reef coral has been wiped out and if nothing is done in the next ten years only 25 perfect of the coral reef will remain (Phillips, 2012).

This is a chart taken from an article in The Age, an Australian daily broadcast newspaper.
http://www.theage.com.au/environment/conservation/great-reef-catastrophe-20121002-26vzq.html

An image of a thorn starfish outbreak eating coral. Credit: Katharina Fabricius, Australian Institute of Marine Science
http://www.livescience.com/23611-image-gallery-great-barrier-reef-through-time.html

          In addition to the destruction of coral, wildlife populations have also been significantly damaged due to unsustainable fishing methods and marine based pollution (Hoegh-Guldberg et al. 2004:32). Destructive fishing methods such as trawling for prawns is allowed in over one third of the Great Barrier Reef and leads to bycatch and seafloor destruction (WWF, 2012) Other destructive fishing methods such as cyanide and dynamite fishing also destroy the coral and reef wildlife (Hoegh-Guldberg et al. 2004:32). Overexploitation of fish has led to an imbalance in the ecosystem. The fish are key predators and prey in the coral reef food chain and when their population is significantly reduced, the population of the organisms they fed on drastically increase while the organisms that fed on the fish dramatically decrease (Hoegh-Guldberg et al. 2004:32). Coastal developments have led to an increase in pollution and chemicals that are dumped into the ocean, which then accumulate and poison corals and organisms (Hoegh-Guldberg et al. 2004:32). The disposal of plastic bags in the ocean not only suffocates marine wildlife but also prohibits photosynthesis by blocking the sun (Hoegh-Guldberg et al. 2004:32). The dangerous fishing and disposal practices from human exploitation of these coral reefs have serious affects on not only the coral but also the marine life. 

This is an illustration of the destructive effects of ecosystem overfishing. Credit: John Michael Yanson
Source: Adapted from Pauley et al., 1998; Goni, 2000
http://see-the-sea.org/topics/commerce/overfishing.htm

This image of the horseshoe reef shows the destruction of the reef by crown of thorn starfish. The left side of the image is the before the outbreak and the right side is an image after the destruction.
Credit: AIMS Long-Term Monitoring Team
http://www.pbs.org/newshour/multimedia/before-after-aims/2.html

This image of the MacDonald reef shows the before (left) and after (right) a tropical cycle damaged the coral reef.
Credit: AIMS Long-Term Monitoring Team
http://www.pbs.org/newshour/multimedia/before-after-aims/index.html

Sources:

1. "Great Barrier Reef." WWF Australia. WWF, 2012. Web. 30 Nov 2012. <http://www.wwf.org.au/our_work/saving_the_natural_world/oceans_and_marine/priority_ocean_places/great_barrier_reef/>.

2. Hoegh-Guldberg, Hans, and Ove Hoegh-Guldberg. " Implications of Climate Change for the Australia’s Great Barrier Reef.” WWF Australia. (2004): 32. Web. 30 Nov. 2012. <http://awsassets.wwf.org.au/downloads/cl029_great_barrier_reef_2050_the_implications_of_climate_change_1fev04.pdf>.

3. Phillips, Nicky. "Great reef catastrophe." Age [Melbourne, Australia] 2 10 2012, Web. 30 Nov. 2012. <http://www.theage.com.au/environment/conservation/great-reef-catastrophe-20121002-26vzq.html>.