Wednesday, June 12, 2013

Ocean Acidification: Will it be the end for benthic biodiversity?

Source: Animal Rights Zone (

Since the start of the industrial revolution the atmospheric concentration of carbon dioxide has risen from 280ppm to 380ppm, that’s a rise of nearly 40% above pre-industrial levels. As the CO2 diffuses into the ocean it is forming carbonic acid. This weak acid dissociates to produce hydrogen and bicarbonate ions. The hydrogen ions that are formed mix with the carbonate ions that are present in the surface waters to create more bicarbonate ions that end up creating a buffer for the ocean and allowing the pH to remain between 8 and 8.3 for the last 25 million years. Because of this researchers thought that the buffering system would keep pH levels in the ocean “normal” despite the rise in CO2 emissions. Decreased pH and increased temperatures could result in an overall loss of diversity and species abundances in these benthic organisms over the next 90 years.

More research showed that ocean surface water pH has fallen .1 pH units when compared to pre-industrial times, which is an increase of 30% in the concentration of hydrogen ions being produced (Widdicombe et al, 2008). Estimates of future CO2 levels show that the pH could fall by up to .4 pH units before 2100 putting our CO2 concentrations at a range of 490-1260 ppm (Hart et al., 2011). As a result of this the temperature of the ocean is predicted to rise by 2-6.7 degrees Celsius by 2099. Studies show that the changes in the seawater pH and temperature can alter not only the diversity of benthic organisms, but also their structure.


So, what does this actually mean for the ocean and its inhabitants since the oceans harbor tremendous biological diversity?    

In a TED talk by Rob Dunbar he discusses the threat of ocean acidification. During this talk he states how the rise of CO2 levels leads to the dissolution of calcium carbonate shells and how organisms have to exude more energy in trying to build and maintain their shells once the decalcification process has begun. If organisms aren’t able to build their shells fast enough or regenerate the calcium carbonate that’s being lost they die. Dunbar also goes on to say that the carbonate producers aren’t the only ones being affected. Ocean acidification is taking its toll on all organisms. It’s creating physiological sensitivities, reducing the intake of oxygen, lowering reproductive success and having a serious impact on diversity.

Similarly, the majority of marine biodiversity is made up of invertebrates either residing in (infaunal) or on (epifaunal) sediments with the benthos containing 98% of all marine species and harboring living representatives of all but one of the 29 non-symbiont animal phyla (Widdicombe et al, 2008). Given the importance of the benthic environment as a reservoir for diversity ocean acidification has the potential to reduce benthic diversity by impacting key biological processes like growth, calcification, activity, metabolic rate and respiration. This decrease could also lead to a reduction in key ecosystem functions like carbon and nitrogen cycling. Since deep sea ecosystems are extremely stable these organisms will be more susceptible to extinction compared with more opportunistic organisms which are adapted to more variable environments as found in the ocean surface waters. According to the University of Bristol it is likely that many benthic marine organisms will be susceptible to extinction due to the effects of ocean acidification in the future; especially in the face of declining carbonate saturation influencing their ability to produce shells and skeletons from calcium carbonate.

According to Hale et al. the changes in seawater pH and temperature can alter the structure and diversity of marine benthic communities at decreased pHs and increased temperatures predicted to occur over the next 90 years and that an overall loss of diversity and a decrease in species abundances is likely. Within the benthic community there are some phyla that are more vulnerable than others, with echinoderms and mollusks being the most vulnerable and arthropods and annelids being the least vulnerable. I believe that the echinoderms and mollusks are the most vulnerable because they are calcifiers while annelids and arthropods are not, so they will not be affected as much.

Organisms may be able to partly compensate for the alterations often caused by exposure to low pH or elevated temperature, but less capable to maintain their homeostatic and growth function when exposed to both conditions (Hart et al., 2011). Based on the research found these organisms will be detrimentally affected by the decrease in ocean pH and elevated temperature once the window of tolerance for each organism is exceeded. Significant impacts for marine organisms include lower net calcification rates, reduced fertilization success, slower developmental rates, smaller larval size, and many physiological changes that are affected by the acid-base imbalance and reduced oxygen transport capacity (Griffith et al., 2011). 

 Source: Ocean Park Wiki.jpeg

 Finally, in my opinion there are many things that we can do to help decrease the amount of CO2 that’s being pumped into the ocean. I understand that the ocean is a natural seep that takes in the excess CO2 in the atmosphere, but if we continue to pump excess amounts of CO2 into the atmosphere and into the ocean eventually it will have no place else to go and will stay in the atmosphere. I’m not sure about anyone else, but I know that I don’t like the idea of breathing in large amounts of CO2. Our oceans don’t seem to get a lot of attention, but they are important. By taking simple steps like riding a bike or walking instead of driving can make a big difference for not only our oceans, but for our own health. We have to be the voices that speak out for the animals of the “Blue Planet” since they can’t speak out for themselves.

Popular Literature
1. Rob Dunbar - The treat of Ocean acidification
2.University of Bristol
Primary Literature
3. Griffith, Gary P., Elizabeth A. Fulton, and Anthony J. Richardson. "Effects of Fishing and Acidification-Related Benthic Mortality on the Southeast Australian Marine Ecosystem." Global Change Biology 17.10 (2011): 3058-3074. Environment Complete. Web. 29 May 2013.
4. R. Hale, et al. "Predicted Levels Of Future Ocean Acidification And Temperature Rise Could Alter Community Structure And Biodiversity In Marine Benthic Communities." Oikos 120.5 (2011): 661-674. Environment Complete. Web. 29 May 2013.
5. S. Widdicombe, et al. "Pedicting the impact of ocean acidification on benthic diversity: What can animal physiology tell us?"Experimental Marine Biology and Ecology 7.24 (2008): 1-11. Environment Complete. Web. 29 May 2013.