Which underwater ecosystem is made of calcium carbonate structures? tide pools coral reefs kelp forests salt marshes

Coral reefs

A coral reef is a deep underwater ecosystem exhibiting walls or reefs build by corals. Reefs are formed by the colonies of organisms called as polyps, which are held together by calcium carbonate. The coral reefs are build in order to form stony corals, because of clustering of the polyps. These provide shelter to small marine organisms like fishes.  

answer; i believe the answer is hydraulic action;