Acidic ocean water decreases the ability of aquatic organisms to form shells or exoskeletons, while also dissolving shells and coral that have already been formed.

David Littschwager/National Geographic Creative

An experiment by Orr et al. showed the increased rate of dissolution (dissolving) of pteropod shells in water with less calcium carbonate. In this test, shells were exposed to water containing the lower levels of calcium carbonate we expect to see in 2100 if we continue to use fossil fuels at the same rate that we now do. (At lower pHs, there will be less calcium carbonate in the ocean.)