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Some reef algaes, the so-called coralline algaes, are calcified, providing them with protection both from grazers and physical damage by surge. These appear as small pink "trees," or flat, encrusting pink or lavender growths on old chunks of coral. Some of the coralline algaes grow in areas of very high wave action, indeed preferring areas that are too turbulent for even corals to survive.

On reefs facing the open ocean, it is a ridge of coralline red algae that receives the full force of the crashing ocean waves, dissipates their energy, and allows less robust organisms including corals to thrive. Other varieties of coralline algae grow deep on the reef, below the level at which reef-building corals can survive, where they contribute significantly to reef growth and sand production.

One recognizable green macro-alga that can sometimes be seen on shallower reefs is Halimeda, a heavily calcified alga made up of chains of green disks, each the size of a small button. These disks are calcium carbonate, like coral, and in some areas Halimeda rubble is a major component of the reef substrate.