Coral Reefs
Factors associated with global change, such as elevated atmospheric carbon dioxide levels, can reduce the growth rate of corals. Increased atmospheric carbon dioxide concentrations would lead to increased dissolution of carbon dioxide into seawater, which in turn would decrease surface ocean pH (acidify the surface ocean). By lowering surface ocean pH, some investigators believe that the ability of corals to grow would be retarded and in some cases the corals might begin to dissolve. Reducing coral growth rates would further aggravate the effects of elevated sea-surface temperatures on the ability of coral reefs to keep up with sea level rise and subsequently protect shorelines from storm surge and wave action.
Click here to read an in-depth report on ocean acidification.
Below are results of a study on the impact that the rise in future atmospheric carbon dioxide levels until 2069 will have on the aragonite saturation state (click here for description of staturation state) of seawater in the Pacific Ocean basin. Aragonite (CaCO3), made of calcium (Ca) and carbonate ions (CO3), is the mineral which coral polyps precipitate to form their skeleton and thus reef structure. The saturation state of the ocean water with respect to aragonite indicates whether aragonite will precipitate or will dissolve. Among other things, the aragonite saturation state is a function of the amount of dissolved carbon dioxide in the water and temperature of the water. Figure 25 shows the negative impacts of future projected atmospheric carbon dioxide levels on aragonite saturation state in the Pacific Ocean basin. Generally speaking, from present day to 2069, the area of optimal and adequate saturation states contracts from high to low latitudes and from the ocean basin margins toward the center of the basin. By the year 2069, there is almost a complete absence of adequate areas of aragonite saturation state in the Pacific Basin. The reefs of Hawaii produce an estimated total annual economic benefit of $363 million dollars that future changes in surface ocean aragonite saturation state could negatively impact.
Figure 25. Pacific Basin aragonite (a form of the mineral calcium carbonate, CaCO3, which serves as the physical structure that reef building organisms use to construct coral reefs) saturation state: (a) Calculated preindustrial (1870) values; Atmospheric carbon dioxide = 280 parts per million; (b) Projected values for 2020-2029; Atmospheric carbon dioxide = 465 parts per million; (c) Projected values for 2060-2069; Atmospheric carbon dioxide = 517 parts per million.
