Ocean Acidification Research Paper

Discussion Section-1
November 17, 2011
The other CO₂ Problem

Todays oceans are not the same as they once were prior to the industrial revolution. The ocean serves as a reservoir for the worlds green house gasses. The increase in anthropogenic CO₂ has also resulted in an increase in the uptake by the ocean of CO₂. As a result of this uptake, the ocean is becoming progressively more and more acidic. This acidification of the ocean is expected to have great impacts on marine ecosystems. Coral reefs are among the most recognized ecosystems threatened by ocean acidification. It has been found that the lower pH of the ocean hinders calcification of many reef organisms. Ocean acidification affects coral growth in primary polyps, and has also
been found to affect the dynamics of the competitive relationship between corals and macroalgae.

Introduction Coral reefs are one of the most productive and biologically diverse ecosystems on earth (Moberg and Folke,1999). However, despite their beauty and biological significance, coral reefs have been facing massive threats. As of 2011, The Global Coral Reef Monitoring Network (GCRMN) has estimated that 20% of the world’s coral reefs have been effectively destroyed and show no immediate prospects of recovery. The GCRMN has also estimated that 60% of the words coral reefs may be lost by 2030. These observed losses are direct consequence of both human impacts and global climate change (Moberg and Folke, 1999). At the global scale, global warming and ocean acidification have posed the greatest threats to coral reef ecosystems (Wei et al., 2009). Elevated sea water temperatures have been responsible for much of the observed reef damage through coral bleaching. It has not been until recent that ocean acidification has loomed as a serious threat to coral reef ecosystems (Vernon et al., 2009). Ocean acidification is a consequence of rising anthropogenic CO₂ levels in the atmosphere. CO₂ concentrations are currently approaching 390 ppm, and are continuing to increase at an accelerated rate of > 2ppm/yr (Wei et al., 2009). Nearly 30% of this anthropogenic CO₂ is taken up by the ocean, and as a result, causes changes in seawater chemistry (Kleypas et al., 2006). Hence, there is a direct correlation between atmospheric CO₂ concentrations and the amount of CO₂ the ocean uptakes. This phenomena is a result of the way in which CO₂ and sea water chemically react. When carbon dioxide is dissolved in seawater, carbonic acid is formed. The presence of carbonic acid reduces the pH of the seawater, and as a result, causes alterations in the fundamental chemical processes occurring in the oceanic environment ( Atkinson and Cuet, 2008). The pH of the ocean has profound effects on inhabiting organisms. Many organisms have an optimal pH in which they function. Any variation in pH will have a significant affects on their ability to perform the necessary biological functions required for them to live and thrive. The demise of these organisms will be felt thorough out their entire ecosystem. Among all the world ecosystems, coral reefs are the most widely recognized ecosystem threatened by ocean acidification ( Kleypas and Yates , 2009). Coral reefs make up only 0.2% in area of the marine environment (Vernon et. al, 2009). In spite of their relatively low abundance, coral reefs are of great importance to the marine ecosystem. Coral reefs are among the most productive and biodiverse ecosystem in the ocean, and it is estimated that they harbor around one- third of marine species (Moberg and Folke, 1999). The benefits of coral reefs extend beyond the habitat that they provide other organisms. The coral reef structure acts as a defensive wall for coastlines against wave erosion, currents, and storms. Thus with the degradation of coral reef structure, these shorelines will experience greater stresses from currents, waves and storms, resulting in a loss of land through erosion (Moberg and Folke 1999). In addition to the defensive benefits coral reefs provide coastlines, the reef community provides numerous valuable resources for many costal communities. More than 100 countries have coastlines with coral reefs, and nearly 500 million people live within 100km of coral reefs and depend on their resources (Vernon et al. 2009). Thus, the degradation of coral reefs will not only have severe environmental impacts, but will also have great economic impacts, and as a result, effect the quality of life of many people. The economic benefits provided by coral reefs are not restricted to costal communities. Coral reef also provided significant benefits to national economies. Key economic and social benefits associated with healthy coral reefs include: high fishery yields, high tourism-related incomes, and good nutrition for costal communities (Moberg and Folke, 1999). The biodiversity of life that coral reefs permit, has additionally encouraged exploration for bioactive compounds for pharmaceuticals.( Moberg and Folke 1999) The economic and biological losses associate with coral reef degradation are severe making the factors that contribute to their degradation a important area of study. Prior to the industrial revolution, the absorption and release of CO₂ by the ocean was approximately in equilibrium.
During this time the concentration of carbon dioxide in the ocean was relatively constant. Since then carbon dioxide concentrations have been increasing rapidly from year to year at a rate of > 2ppm/yr (Wei et al. 2009). Prior to the industrial revolution atmospheric carbon dioxide was at the level of ~280ppm ( Vernon et al., 2009), and has risen to today level of ~388.92ppm (as measured by the Scripps Institution of Oceanography as of November 4, 2011). The fact that the ocean is progressively getting more acidic with the increasing atmospheric CO₂ concentration cannot be argued. There is much debate, however, as to how and to what extent decreasing pH has and will effect marine ecosystems. The role that ocean acidification plays in the degradation of coral reefs is an area of constant debate. The purpose of this paper is examine the effects of ocean acidification on coral reefs at multiple levels. These levels include: the calcification rates of the coral reef community, the competitive interaction among corals and macroalgae, and the development and settlement of coral primary polyps. For the purpose of this paper, a review of various scientific studies will be conducted to formulate a conclusion as to how each of these different factors are affected by the current pH of the ocean. and will be affected at the low predicted pH of the
future.

Calcification and the Changes in Carbonate Chemistry Calcification is a major process that enables coral reefs to thrive in tropical shallow waters ( Leclercq et al., 2000). It is not surprising then, that calcification is one of the many processes that has been affected by ocean acidification. As a result of increasing atmospheric CO₂, and thus ocean acidification, there is a significant reduction in the carbonate ion in ocean waters. This carbonate ion, ionically bonds to calcium to form a calcium carbonate mineral that is required for many marine organisms to function (Orr et al., 2005). A decrease in the carbonate ion in the ocean, is followed by a decreases in concentration of calcium carbonate minerals. This decrease has a direct effect on the saturation state of seawater with respect to calcium carbonate minerals. The calcium carbonate saturation state is denoted by the symbol Ω arag. The subscript “arag” stands for aragonite, which is another name for calcium carbonate. When Ω arag. > 1.0, the formation of calcium carbonate is thermodynamically favorable. And in contrast, when Ω arag.