Marine organisms such as coral and shellfish have carbon in their bodies in what forms?

Marine organisms such as coral and shellfish have carbon in their bodies in the form of calcium carbonate, which makes up their shells and skeletons. Additionally, they also contain carbon in organic molecules such as proteins, lipids, and carbohydrates that are essential for their growth and metabolism. The carbon in these organisms ultimately comes from carbon dioxide in the surrounding seawater, which they assimilate through processes like photosynthesis and feeding.