About half of the carbon dioxide produced by burning fossil fuels is absorbed by the oceans. However, increases in the amount of carbon dioxide being absorbed is changing the basic chemistry of the oceans. Once in seawater carbon dioxide undergoes a chemical transformation to carbonic acid. This phenomenon, known as "ocean acidification,"decreases the availability of chemical building blocks needed by organisms that produce shells and skeletons made of the calcium carbonate.
Sadly, scientists have found that almost all marine life that build calcium carbonate shells and skeletons that have been studied have shown deterioration due to increasing carbon dioxide levels in sea water. For example, acidification has been shown to significantly reduce the ability of reef-building corals to produce their skeletons. Known as "ocean acidification," over time this phenomenon is having major negative impacts on corals and other marine life. This has affected the growth of individual corals and made reefs more vulnerable to erosion. It is predicted that by the middle of the 21st century coral reefs may well erode faster than they can be rebuilt.
Other species, such as sea urchins, starfish, lobsters ad bivalves (oysters, clams, mussels, and scallops) that construct shells or skeletons could also be jeopardized. Some higher marine life forms, including some fish, may be affected by acidification through a process called acidosis - carbonic acid buildup in body fluids. Acidosis can lead to lowered immune response, metabolic decline and reproductive respiratory difficulties.
In short, the impacts of ocean acidification on shelled organisms and higher marine life forms could negatively affect marine food webs, and when combined with other aspects of climatic change, could substantially alter the number, variety and health of ocean wildlife and the human community's dependent upon them.