Ocean absorption of CO2 has helped alleviate some of the potential effects of increasing atmospheric CO2 levels, but in doing so has changed the chemistry of the seawater. The chemical reaction from CO2 absorption decreases the water’s pH levels, making the water more acidic. Since the Industrial Revolution, the pH has dropped .1 units and is expected to drop another .3 units if CO2 emissions continue the way they are now. It is uncertain how marine organisms are going to adapt to increased acidity, making the potential threat of ocean acidification alarming. One of the main processes seriously affected by the change is calcification, which enables organisms to produce their shells or skeletons. Increased levels of CO2 in the ocean will shift the carbonate system equilibrium towards higher concentrations of CO2 and lower carbonate ion concentrations. Carbonate ions are essential in order to produce calcium carbonate, which is needed to develop the shells of oysters and mussels.

The change in pH, affecting coral reefs and other calcifying organism, particularly imperils oysters and mussels. Studies have shown that the calcification rates of the edible mussel and Pacific oyster are strongly correlated with increasing concentrations of CO2.If the pH levels continue to decrease as projected, the ability of these mussels and oysters to produce shell material will decrease by 25% and 10% respectively by the year 2100. Oysters are less sensitive to increased levels of CO2, due to their differing shell composition. Mussel shells are composed of mostly calcite, while oyster shells contain a large amount of aragonite. Currently, calcium carbonate is readily available to these organisms so that they can create their shells, but soon it will become harder, requiring greater expenditures of energy, for these organisms to produce shells.

Mussels and oysters are an integral part of the fishing economy and the predicted decrease in calcification due to ocean acidification will lead to significant economic losses. Global shellfish production has had an annual increase of 7.9% over the last 30 years, which corresponds to a commercial value of 10.5 billion US dollars. The Pacific oyster was the most cultivated species in 2002 and represented 10.8% of the total world aquaculture production, while mussels represented 3.6% of total production. There are fishermen whose livelihoods depend on the sale of shellfish. Although a much more sudden example, many fishermen were put out of work and incapable of providing for their families after the oil spill in the Gulf of Mexico. A similar thing could happen if ocean acidification continues to make calcification increasingly difficult. Any decline in these species will cause considerable damage to the fishing market as well as have major consequences for coastal biodiversity.

Mussels and oysters serve an important purpose in coastal ecosystems. They both regulate energy and nutrient flow, as well as provide habitats for other species. If the population of mussels and oysters diminishes because of their inability to calcify and make shells, there will be huge repercussions for biodiversity and the function of the ecosystem.

Websites:

http://en.wikipedia.org/wiki/Ocean_acidification#Calcification

http://oregonstate.academia.edu/GeorgeWaldbusser/Papers/646403/Biocalcification_in_the_eastern_oyster_Crassostrea_virginica_in_relation_to_long-term_trends_in_Chesapeake_Bay_pH

http://ec.europa.eu/environment/integration/research/newsalert/pdf/63na1.pdf