Final answer:
Marine organisms such as mollusks, vertebrates, and plankton like pteropods, in addition to shells, need carbon and calcium to form their shells and skeletons made up of calcium carbonate (CaCO3). However, ocean acidification can make it difficult for these organisms to absorb calcium and carbonate ions, leading to the dissolution of their shells.
Step-by-step explanation:
Marine organisms that need carbon and calcium include not only shells, but also other organisms such as mollusks, vertebrates, and plankton like pteropods. These organisms rely on the equilibrium between carbon dioxide and bicarbonate ions to mobilize the molecules needed to form their shells and skeletons, which are made up of calcium carbonate (CaCO3). However, ocean acidification, caused by increased carbon dioxide levels in the ocean, can make it difficult for these organisms to absorb calcium and carbonate ions and form calcium carbonate, leading to the dissolution of their shells while they are still alive.