Climate Change and Ocean Acidification Killing Coral Reefs

Lucas McCann

Student ID: 0716782

Over the past few decades, the number of threats towards coral reef survival has increased; with the main threat to coral reef survival being climate change. As the ever steady increase in atmospheric CO₂ is the main driving force for this problem. As atmospheric CO₂ concentrations increase, the pH of the oceans decrease (more acidic) and the available carbonate ions required to make coral skeletons decreases. Another reason climate change is having such a huge impact is that it affects much more than just atmospheric carbon dioxide concentrations. It also increases local threats such as: water quality, coastal development, deforestation and over fishing, and these threats can have just as a significant impact on reef communities as ocean acidification and CO₂ concentration increase do. This study is so interesting because it takes into account what affects coral reef ecosystems, and how the continued deterioration of these ecosystems will negatively affect biodiversity and economies around the world.

This study is based off of climate scenarios as well as observations of the coral reefs themselves. These climate scenarios are mostly centered on carbon dioxide concentrations and how varying concentrations in the atmosphere will affect the oceans and coral reef ecosystems. The reason that carbon dioxide concentration is the main focal point of these studies and scenarios is that it directly and indirectly impacts the other factors affecting the coral reefs. The three main scenarios that are shown are CRS-A, CRS-B and CRS-C, and these represent different coral reef scenarios based on different levels of carbon dioxide in the atmosphere (Hoegh-Guldberg et al 2007).

Figure 1: represents coral bleaching, which is a very real possibility if the increase in atmospheric [CO₂] continues at its current rate.

Coral reef scenario A is used if the concentration of carbon dioxide in the atmosphere were to stabilize at today’s levels; which happens to be 390ppm. At this level, the coral reefs will continue to change however they will stay coral dominated, and will most likely not reach their tipping point (Hoegh-Guldberg et al 2007). The reef will not die, but it will not be the same as it once was for a long time. If the concentration of carbon dioxide were to stabilize at 380ppm, than it would be more appropriate to try and manage local factors such as water quality (toxins, nutrients) and fishing levels. As the concentration of CO₂ continues to increase than the CRS-A scenario becomes less likely. As the concentration increases, the types of coral in the reef communities will change to more thermally adept coral such as the massive Porites. Coral reef scenario B involves carbon dioxide concentration levels between 450-500ppm and at these levels the coral reef ecosystems will have trouble surviving. This is due to the fact that at these levels carbonate-ion concentration will drop below 200µmol kg^- and reef erosion will exceed the reefs ability to calcify (Hoegh-Guldberg et al 2007). Basically the coral in the reef ecosystems will not be able to re-build themselves faster than they are degrading. This essentially means the loss of coral in reef communities, as well as the loss of biodiversity due to habitat simplification. Coral reef scenario C is used to describe what could happen if CO₂ concentration exceeds 500ppm; and this simply shows that the survival and stabilisation of reefs may not occur for hundreds of years and that the ability of coral to migrate and grow will be impeded. Once the concentration of carbon dioxide in the atmosphere reaches those of CRS-B and CRS-C, more than just the reef ecosystems will become affected; at this point the communities that rely on the reefs will become affected.

Coral reef ecosystem are a major economic resource that bring in large portions income to some countries (in some cases billions of dollars a year), most of them developing countries. Some of these nations are already poor, if coral reef ecosystems deteriorate beyond repair than these nations will take a large hit to their GDP and ultimately making poor nations even poorer. Coral reef ecosystems are also responsible for providing food to billions of people. So as coral reef ecosystems decrease, the amount of food that is available to these people decreases, placing more stress on these people as well as other sources of food that now have to feed a lot more people. Another important function of coral reefs is coastal protection; these ecosystems take a lot of punishment during hurricanes and other storms, ultimately reducing the impact these storms can have on shore. The deterioration of coral reefs due to climate change can have a doubly negative affect; as the deterioration of the reefs increases the damage done to shorelines, and climate change also causes stronger storms and higher sea levels. This could greatly increase the damage that some storms cause.

The deterioration of coral reef ecosystems due to climate change and ocean acidification is a major issue that if not seriously addressed can impact billions of people across the world. Coral reefs provide us with food, money and protection; if coral reefs are gone than all those previously mentioned will be negatively affected. This study showed that the destruction of coral reefs is directly related to the concentration of CO₂ in the atmosphere; so if we want to save the reefs and ourselves we should do what is necessary to limit the amount of CO­₂ that is emitted into the atmosphere.

Reference:

Hoegh-Guldberg, O., P.J Mumby, A.J Hooten, R.S Steneck, P. Greenfield, E. Gomez, C.D Harvell, P.F Sale, A.J Edwards, K. Knwlton, C.M Eakin, R. Iglesias-Prieto, N. Muthiga, R.H Bradbury, A. Dubi, and M.E Hatziolos. "Coral Reefs Under Rapid Climate Change and Ocean Acidification." Science 318 (2007): 1737-742. Science Mag. 14 Dec. 2007. Web. 8 Oct. 2010. .