Especially calcium carbonate skeleton building organisms are affected by the rapidly dwindling seawater pH and carbonate saturation state. (bitsofscience.org)
Soft corals are colonial animals and some do have calcium carbonate skeletons of a sort. (AmbergrisCaye.com)
Sea creatures with calcium carbonate skeletons eventually die and some of mineral matter in their skeletons is buried in the sea bed. (ramblingsdc.net)