Is a seashell an abiotic feature?

Originally landed on: Abiotic Factors of an Open Ocean Ecosystem

The definition of "abiotic" is "non-biological." A seashell is made by a living organism, therefore it is biotic. In the sea, shells come from creatures like clams, oysters, mussels, scallops, whelks, conchs, periwinkles, and other sea snails.

While seashells are biotic, they can significantly influence the abiotic factors of their surroundings, especially the pH of water. Seashells are made of calcium carbonate, which acts as a buffer by dissolving in acidic conditions and causing pH to go up, becoming more basic.

In general, all precipitated calcium carbonate in the sea has a biotic origin. Corals use it to build massive reefs. Many types of creatures of all sizes use it to make protective shells, including microplankton. Old shells become white calcium-carbonate sand, and eventually over geologic timeframes, limestone.

In modern times, an increase in global carbon dioxide has begun to make the oceans more acidic, which makes it much harder for marine organisms to precipitate calcium carbonate for their shells.