Possible consequences on marine organisms

The dissolution of carbon dioxide in sea water not only provokes an increase in hydrogen ions and thus a decline in pH, but also a decreasein a very important form of inorganic carbon: the carbonate ion (CO32-). Numerous marine organisms such as corals, mollusks, crustaceans and seaurchins rely on carbonate ions to form their calcareous shells or skeletons in a process known as calcification. The concentration of carbonate ions in the ocean largely determines whether there is dissolution or precipitation of aragonite and calcite, the two natural polymorphs of calcium carbonate (CaCO3), secreted in the form of shells or skeletons by these organisms. Today, surface waters are super saturated with respect to aragonite and calcite, meaning that carbonate ions are abundant. This super saturation is essential, not only for calcifying organisms to produce their skeletons or shells, but also to keep these structures intact. Existing shells and skeletons might dissolve if pH reach lower values, and the oceans turn corrosive for these organisms. Consequently, the results ofthe decrease in carbonate ions might be catastrophic for calcifying organisms which play an important role in the food chain and form diverse habitats helping the maintenance of biodiversity.


The magnitude of ocean acidification can be predicted with a high level of confidence since the ocean chemistry is well known. But the impacts of the acidification on marine organisms and their ecosystems is much less predictable. Not only calcifying organisms are potentially affected by ocean acidification. Other main physiological processes such as reproduction, growth and photosynthesis are susceptible to be impacted, possibly resulting in an important loss in marine biodiversity. But it is also possible that some species, like seagrasses that uses CO2 for photosynthesis, are positively influenced by ocean acidification. Ocean acidification research is still in its infancy and more studies are required to answer the numerous questions related to its biological and biogeochemical consequences.