The increase in the partial pressure of CO2 has resulted in more dissolved CO2 in the world’s oceans. When CO2 reacts with water, is interacts with a delicate balance of acids and bases in the water. CO2 and water come together to create bicarbonate, a base. However, to maintain a steady pH (a measure of acidity with 7.0 being neutral) in the water, bicarbonate will separate to create carbonic acid and free hydrogen ions. The more hydrogen ions in a solution, the lower the pH and the more acidic the water is (Hillis et al., 2010). This is precisely what is happening in the world’s oceans today.
The acidification of the world’s oceans poses a great problem for the animals and plants living in them. Shellfish are most affected by the acidic oceans because they have external skeletons. These exoskeletons are made of ingredients that create a strong, protective shell for the animal. These animals (clams, lobsters, shrimp, mussels, etc.) have a small space between their shell and the outside water called the calcifying space (Madin, 2010). In this space, the shellfish can combine calcium and carbonate to create calcium carbonate, the crystal that makes the shell. The problem arises when there are too many hydrogen ions in the water, because carbonate binds to them too (Madin, 2010).
The result: shellfish have to use more energy pumping extra hydrogen ions out of the calcification space so that they can build their shells (Madin, 2010). Shellfish that do not have strong enough pumps to get rid of the hydrogen are faced with the deterioration of their shells due to acid erosion and the inability to build faster than (or as fast as) it loses its shell.
The three results of this problem in clams, which have trouble building their shells fast enough, are smaller clams, less clams and clams with brittle shells. Clams have started to grow smaller because they expend a lot more energy in acidic oceans trying to pump out hydrogen ions. Their energy resources are tied up in trying to maximize the production of calcium carbonate so they do not grow as large.
They also cannot produce large shells because of the ocean's increased acidity. Ocean acidification also results in fewer clams because many simply don’t survive. However, there are some that may be more efficient in pumping out the hydrogen and those clams would flourish with less competition, but that would also result in less diversity.
Finally, their shells are brittle because the acidity of the ocean weakens and dissolves them, and most clams are unable to build their shells as fast as they lose them. This is a result in lower levels of calcium carbonate (aragonite) in the oceans that the shellfish need to make their shells. These levels are significantly reduced from years past, especially pre-Industrial Era and from 2010; the majority of the aragonite has been lost (Hoegh-Guldberg et al., 2007).
Though clams, scallops, and snails are suffering due to ocean acidification, the future for shrimp, lobster, and mussels does not look quite as dim. A recent study conducted by Justin Ries, Anne Cohen and Dan McCorkle of the Woods Hole Oceanographic Institution tested many crustaceans (lobsters and shrimp), mussels, snails and other shellfish in different levels of acidity due to CO2 levels. The results were shocking: animals with more protective covering on their shells grew stronger and larger shells rather than deteriorating (Madin, 2010). A proposed theory behind this result is that these animals and plants (crustaceans, temperate urchins, mussels, and some age) have stronger pumps to push out hydrogen and can make their shells faster than they lose them. It turns out that more CO2 actually makes those organisms grow larger.
Ecologists agree that the acidification of the world's oceans is a threat to the stability of the Earth as a whole. Such a large drop in calcifying organisms will undoubtedly have a detrimental effect on the fragile oceanic ecosystem and many other major ecosystems. Economically, the hit on the fishing industry that coastal areas rely so heavily upon will cause them to suffer greatly.