Calcium. An element that we and billions and billions of organisms cannot live without. All vertebrates, with their vertebral columns and many other bones and teeth need calcium. All shelled mollusks and barnacles require calcium. You don’t find many barnacles, if any, in freshwater environments. Calcium is found in a host of other animals where it serves a variety of vital functions. Plants don’t metabolize calcium per se, but the calcium in lime or limestone neutralizes acid soils, which inhibits the growth of many plant species, including grasses, forbs, shrubs, and trees.