Calcifying organisms are living beings that have the ability to produce and deposit calcium carbonate in their bodies. This process helps them build protective structures like shells or skeletons. Full definition
The effect of ocean acidification on calcifying organisms in marine ecosystems: an organism - to - ecosystem perspective (rstb.royalsocietypublishing.org)
Depends on what scenerio is used — and on the rate of dissolution of calcifying organisms as they sink to the ocean floor. (judithcurry.com)
(There is much less uncertainty in what will happen to ocean chemistry: the pH will drop, with serious consequences for calcifying organisms from coccolithophores to corals to crabs to clams.) (dotearth.blogs.nytimes.com)