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how reefs protect the land
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it really sucks being a tuna
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city vs village fishing
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the acid ocean
   home/sustainability on coral reefs/the acid ocean

The microdocs in this section focus on the coral reef ecosystem to explore factors influencing ecological sustainability.

The Acid Ocean
  • The ocean is becoming more acidic due to increasing carbon dioxide levels in the atmosphere
  • Increasing ocean acidity is harmful to many marine organisms

Estimates indicate that industrial sources pump 1,000 tons of carbon dioxide into the atmosphere every second; 1/3rd of this CO2 is absorbed into the ocean. This extra CO2 is making seawater more acidic. Increased ocean acidity can reduce marine organisms’ growth and fecundity.

 Acidic oceans

When carbon dioxide dissolves in water some of it turns into carbonic acid. Industrial activities are adding to the natural level of CO2 into the ocean and making the seas more acidic.

Seawater has changed from pH 8.3 to 8.1 since the start of the industrial revolution in the mid-1800s. This may not seem like much, but because the pH scale is logarithmic this means that the sea has become 30% more acidic.

Ocean acidification impacts the lives of marine organisms in 3 main areas:

  • Physiology
  • Reproduction
  • Calcification

Altering the pH of the ocean may interfere with the physiological processes of marine organisms. For example, a more acidic ocean may decrease the amount of oxygen that can be carried in the blood of water breathing organisms.

An acidifying ocean may interfere with the reproductive ability of marine organisms, and may impair sperm mobility, egg production and/or hatching success. Also, the larvae of some marine species may be malformed.

Marine organisms need more energy to form calcium carbonate shells as the ocean becomes more acidic. These shells are created more slowly and may be less dense and/or poorly formed.

 Marine resources and the acidifying ocean

An acidifying ocean is less productive and produces fewer resources. For example, coral polyp skeletons are less dense in an acidifying ocean. Coral reefs are damaged more easily and recover slowly under these conditions. This makes this ecosystem less resilient and productive. Millions of people rely on coral reefs and their resources, and ocean acidification threatens the continued sustainability of these resources.


Anthony, K. et al. (2008, November 6). Ocean acidification causes bleaching and productivity loss in coral reef builders. PNAS 105 (45): 17442-17446

Carnegie Institution for science. (2009, March 11). Coral reefs may start dissolving when atmospheric CO2 doubles. Carnegie institution for science. Retrieved on 23 July 2008 from http://www.ciw.edu/news/coral_reefs_may_start_dissolving_when_atmospheric_co2_doubles

Doney, S. (2009, August 28). Ocean Acidification: The Other CO2 Problem. Annual review of Marine Science 1:169–92.

Earth System Research Laboratory.  (2009). Trends in Atmospheric Carbon Dioxide - Mauna Loa. National Oceanic and Atmospheric Administration Global Monitoring Division. Retrieved 29 July 2009 from http://www.esrl.noaa.gov/gmd/ccgg/trends/index.html#global

Henderson, C. (2006, August 5). Ocean acidification: the other CO2 problem. NewScientist.com. Retrieved on 17 July 2008 from http://environment.newscientist.com/article/mg19125631.200.

Hoegh-Guldberg, O et al. (2007, December 17). Coral reefs under rapid climate change and ocean acidification. Science 318: 1737-1742. PDF retrieved on 23 July 2008 from http://www.eeb.cornell.edu/harvell/Site/2007__files/HoeghGulberg07.pdf

Kleypas, J. et al. (2006). Impacts of ocean acidification on coral reefs and other marine calcifiers: A guide for future research, report of a workshop held 18–20 April 2005, St. Petersburg, FL, sponsored by NSF, NOAA, and the U.S. Geological Survey, 88 pp.

Milligan, K. (2009, June 19). Ocean acidification. The Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO).  Retrieved on 23 July 2008 from http://www.piscoweb.org/topics/climate-change/ocean-acidification

Orr, J. et al. (2005, September 29). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437: 681-686. Retrieved on 23 July 2008 from http://www.nature.com/nature/journal/v437/n7059/full/nature04095.html

Pandolfi, J. et al. (2005, March 18). Are U.S. coral reefs on the slippery slope to slime? Science. Retrieved on 23 July 2008 from http://www.sciencemag.org/cgi/content/full/307/5716/1725.

Royal Society. (2005, June). Ocean acidification due to increasing atmospheric carbon dioxide. The Royal Society. PDF retrieved 29 July 2009 from http://royalsociety.org/displaypagedoc.asp?id=13539

ScienceDaily. (Nov. 26, 2008). Ocean growing more acidic faster than once thought; Increasing acidity threatens sea life. ScienceDaily. Retrieved on 23 July 2008 from http://www.sciencedaily.com/releases/2008/11/081124141053.htm

Wikipedia. (2008, July14). Ocean acidification. Wikipedia. Retrieved on 17 July 2008 from http://en.wikipedia.org/wiki/Ocean_acidification.

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