How have people impacted the ecosystem?
Humans have had a vast impact on the health of the Great Barrier Reef ecosystem. Farming and mining practices have caused inflows of sediment, fertilizers and pesticides. When these nutrients are introduced to marine ecosystems, algal blooms grow because of the increased levels of nitrogen and phosphorus (4). Clear waters are essential for the survival of coral reefs, and these algal blooms make the waters murky, disrupting the path of sunlight to the dependent ecosystem beneath the surface. Furthermore, due to global warming, and the human contributions associated with these climate patterns, sea temperatures in the South Pacific are rising. This fact and increasing oceanic acidity, due to absorption of CO2 (which changes into carbonic acid when it dissolves) into the ocean, is decreasing the rate of calcification, a necessary process for the growth of coral and causes coral bleaching. These impacts are intensified because of coastal development which strips the land of plants that normally serve as a natural barrier to runoff.
The impacts of runoff have wider implications than simply water pollution, however. Scientists believe that agricultural runoff is one of the major causes of what scientists refer to as the Crown of Thorns outbreak. This name refers to the booming population of a certain species of starfish called the Crown of Thorns
The Australian government has been fighting different occurrences of this epidemic since the 1960’s. The nutrients from agricultural runoff inflate plankton populations, which increase the cells sizes of the coral populations (2). This particular breed of starfish, which feed on coral populations, finds these to be perfect feeding conditions. Booms in the Crown of Thorns Starfish population have occurred again since 2009. These booms pose a great threat for the reef. There are several reasons for this. When the starfish populations boom, we tend to see sharp drops in rare species of coral, usually tubular coral (as pictured below). This is because the Crown of Thorns prefer less abundant forms of coral (3).
This trend poses a great threat to the biodiversity of the Great Barrier Reef. More importantly, the Crown of Thorns depresses the coral cover on the reef. Over 40% of coral cover loss over the last decade is due to the Crown of thorns starfish (2). Many scientists argue that this is the biggest treat to the Great Barrier Reef today.
Fishing, shipping and tourism industries have also had a vast impact on the Great Barrier Reef ecosystems. Fishing practices have steadily decreased the population sizes of predator species native to the Great Barrier Reef including dugong and sharks as well as certain species of sea cucumbers and sea turtles.
- "About the Great Barrier Reef." Australia's Great Natural Wonder: The Great Barrier Reef. Great Barrier Reef Organization. Web. 22 Nov 2013. <http://www.greatbarrierreef.org/about.php>.
- McCultcheon, Peter. "Fears Crown of Thorns Star Fish Plague with Wreak Havoc on the Great Barrier Reef." ABC News. (2013): n. page. Print. <http://www.abc.net.au/news/2013-11-06/barrier-reef-under-threat-from-new-starfish-tsunami/5074118>.
- Moran, P.J. "Factors Affecting the of the Crown of Thorns Starfish in the Great Barrier Reef; Feeding Habits."Journal of Experimental Marine Biology and Ecology. 220.1 (1998): 107/126. Web. 22 Nov. 2013. <http://www.sciencedirect.com/science/article/pii/S0022098197001007>. (academic journal)
- Fabricius, Katharina. "Changes in Algal, Coral and Fish Assemblages Along Water Quality Gradients on the Inshore Great Barrier Reef." Marine Pollution Bulletin. 51.1-4 (2005): 384-398. Print. <http://www.sciencedirect.com/science/article/pii/S0025326X04003923>. (academic journal)
http://www.newscientist.com/article/dn22473-coral-autopsy-reveals-great-barrier-reef-collapse.html#.UpADpmRDuFd
http://www.bbc.co.uk/nature/life/Crown-of-thorns_starfish
http://www.corbisimages.com/stock-photo/rights-managed/SP014472/pink-tubular-coral-tubastria-aurea
Written by Sydney Young