Welladsen, H. M., Southgate, P. C. & Heimann, K., 2010. The effects of exposure to near-future levels of ocean acidification on shell characteristics of Pinctada fucata (Bivalvia: Pteriidae). Molluscan Research 30(3): 125-130.

Pearl Oysters of species Pinctada fucata produce pearls through building up nacre deposits between the shell and mantle of the oyster. Normally, these deposits are isolated from their surroundings, but it has been suggested that ocean acidification breaks down the protective shells and removes the isolation of the system.
The study serves to show that this breakdown of the oyster shell occurs, and has negative effects upon the nacre formations. The Pinctada fucata were exposed to water of pH 7.8 and 7.6 for 28 days, which resulted in shells 25.9% and 26.8% weaker, respectively, than the controls. As a result, the nacre formations showed signs of malformation and dissolution in comparison to the controls, as shown through scanning electron microscopy.
This degradation of shell strength and nacre formation could have serious effects on the cultured pearl industry, which relies heavily on the natural production of pearls within Pinctada fucata.

http://www.mapress.com/mr/content/v30/2010f/n3p130.pdf