Reefs are formed by calcium carbonate produced by the coral polyps. As a single polyp dies, its soft tissue decays, but the calcium carbonate cup remains.Other polyps build on top of the cup, and when they die, other polyps will build on their cups. Over time, this process creates larger and larger coral reefs.While corals are the chief architects of the reef structure, they are not the only builders. Corallin algae cement various corals together with compounds of calcium, and other organisms such as tube worms andmollusks donate their hard skeletons to the construction.
