What is the term for coral that builds reefs?

The term for coral that builds reefs is hermatypic coral. These corals create reef structure by depositing hard calcium-carbonate skeletons, which accumulate over generations into the framework of a reef.

Most familiar shallow-water reef builders are stony corals in the order Scleractinia. Many contain photosynthetic algae called zooxanthellae, which help supply energy and allow corals to thrive in sunlit, nutrient-poor tropical waters. However, “hermatypic” describes reef-building ability, not simply the presence of algae.

That distinction matters because some corals with zooxanthellae do not build substantial reefs, while certain deep-water hermatypic corals can form reefs without relying on sunlight or these symbiotic algae. Corals that do not contribute to reef development are called ahermatypic, or non-reef-building, corals.

“Stony coral” is a common near-answer, but it is broader and describes a hard-skeleton group rather than the specific ecological role. Soft corals generally do not create the rigid limestone framework associated with major barrier reefs, although they can be important members of reef communities.