Coral Reef Acidification

My first blog is a follow up on a previous class presentation, on the effects of high atmospheric CO2 levels on coral reefs. Currently, environmentalists are concerned about the bleaching and productivity loss of reef builders due to rising CO2 levels. Coral bleaching and calcification (used for reef building) are two aspects taken into account  when looking at the effects of CO2 on coral reefs. High levels of CO2 can cause corals to start bleaching and die, while high temperatures can enhance the effects of bleaching and calcification rates. Studies have shown that bleaching occurs as a result of CO2's impact on photoprotective mechanisms of the photosystems ( Anthony, K.R. 2008). These results are part of an 8 week study done to compare bleaching, productivity, and calcification responses of crutose coralline algae (CCA) and branching ( Acropora) and massive (Porites) coral species in response to acidification and warming. In this study, 30 tanks were set up with alternating CO2 levels for the three different types of corals.

      The results of the experiment show that high CO2 levels resulted in 40-50% bleaching for CCA and Acropora after the 8 weeks. Effects of CO2 dosing on bleaching was stronger than the effect of temperature on bleaching as well. The high-CO2 dosing led to a two to three fold increase in bleaching relative to the control, whereas high temperatures led to only a 20% increase in bleaching for those species. The Porite species showed a less sensitive reaction and bleached to a max of 20% in high-CO2 dosing/ high-temperature. High temperature, however, enhanced bleaching by 10-20% in CCA and Acropora, but up to 50% in Porites.
      Below is a picture of a coral reef structure before, and after being effected by coral bleaching.

     The picture above shows calcium carbonate concentrations in the years 1765 and 1995, as well as predicted concentrations in 2040 and 2100. Image credit: Quirolo, C.


      The above image show concentrations of calcium carbonate in the years 1765 and 1995, as well as the predicted concentrations in 2040 and 2100. Image credit: Kleypas et al., (2006).

   Results of the tests of CO2 levels on reef builing (calcification) showed much more astonishing results. CCA response to high-CO2 dosing was very sensitive and showed a 130-190% reduction in calcification rate realtive to control at low and high temperatures. The Acropora calcification rate was supressed significantly by warming only when high-CO2 dosing, and Porites did not show a clear response to warming.
     The results of this experiment are very conclusive and prove that a rise in CO2 concentration in the environment will have a severely negative impact on the well-being of coral reefs around the world. While rising temperatures alone don't have a serious effect, when combined with the effects of increased CO2 concentrations, it can lead to even more reef destruction. It is clear that prolonged exposure to CO2 causes bleaching, and low calcification rates. As a result of this experiment, people should take more into consideration when studying the effects of warming and CO2 on corals. It is clear that these processes pose a threat to our environment, and that more studies need to be done to explore these issues. People should also start taking extra precautions when taking part in air pollution, but all types of pollution as well.

                                                                References

Anthony K.R. et al., (2008). "Ocean acidification causes bleaching and productivity loss in coral reef builders. Proceedings of the National Academy of Sciences. Vol 105 (issue 45) p. 17442-17446. Retrieved from http://www.ncbi.nlm.nih.gov/m/pubmed/18988740/

Quirolo, C (2010). "Reef relief/ Marine Photo bank." Climate, Carbon and Coral Reefs. http://www.wmo.int/pages/prog/wcp/agm/publications/documents/Climate_Carbon_CoralReefs.pdf 

Kleypas et al., (2012). "Impact of Ocean Acodification on Coral Reefs and other Marine Calcifiers: 
A Guide to Future Research. Retrieved from http://www.reefbase.org/resource_center/publication/pub_25651.aspx