The speciation of carbon is important because carbonate ions are a primary constituent of the outer shells of many marine animals. These animals, including corals, crustaceans and molluscs, often take up carbonate ions to form calcium carbonate (CaCO₃), although occasionally organisms can create calcium carbonate from hydrogen carbonate as well, which is then used to make the tough outer shells characteristic of these sea creatures.

However, the concentration of carbonate ions also decreases as ocean pH decreases. As carbonate becomes less available, it is increasingly difficult for many marine animals to build their shells. This can seriously harm the entire marine ecosystem because many of the animals that rely on carbonate ions to build their shells (such as corals and pteropods) form the base of the marine food web. Damage to marine ecosystems will have detrimental effects on the fishing and tourism industries that provide sustenance and livelihood for many people around the world.