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Which organisms besides corals help build coral reefs?

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coral reef The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.

While corals provide the primary structural framework for reefs, several other organisms play essential roles in building and maintaining these complex ecosystems.1

Calcareous Algae: Often referred to as stony seaweeds, these organisms are vital for reef construction. In areas with strong surf, such as the central Pacific, they can be even more important than corals in building the reef structure. They also help bind and cement reef components together through sheetlike growth.1
Zooxanthellae: These photosynthetic, single-celled algae live symbiotically within the tissues of corals and many other invertebrates. They significantly aid in the formation of the coral skeleton by accelerating the process of calcium carbonate secretion.23
Shelly and Calcareous Organisms: Mollusks, echinoderms, protozoans, sponges, and sea cucumbers contribute to the reef by providing skeletal fragments and spicules that fill the gaps between corals.1
Sediment-Stabilizing Plants: Mangroves, seagrasses, and blue-green algal mats trap and stabilize sediment, allowing these accumulations to be incorporated into the broader reef complex.4