Red abalone, how are their shells made?

Red abalone have shells that grow in bands. As carbonate is deposited on the shell, for the abalone, these bands are deposited in a spiral outward. Ocean acidification is severely impacting the availability of carbonate in the ocean. As the ocean acidifies carbonate is less readily available to marine species who need it (e.g., mussels, abalone, coral, foraminifera).