The main chemical composition of the oceans affected by atmospheric CO2 is largely understood and can be accurately calculated. However, there is much uncertainty about the biological effects caused by ocean acidification and how they will vary among organisms; some may cope better than others. Although research on ocean acidification is still very young, there is already evidence of biological impacts due to changes in ocean chemistry. The greatest evidence of the impacts of ocean acidification on marine ecosystems can be seen in experiments on calcifying organisms. When seawater is acidified to varying levels, the formation and dissolution of calcium carbonate shells and skeletons in marine organisms such as reef-building corals, oysters and mussels, as well as phytoplankton and zooplankton which constitute the basis of marine food webs (“Ocean Acidification: A National Strategy…”,