Red gorgonian fan with brittle star, Ha'apai, Tonga

Coral reefs are the most diverse and beautiful of all marine habitats. Large wave resistant structures have accumulated from the slow growth of corals. The development of these structures is aided by algae that are symbiotic with reef-building corals. Coralline algae, sponges, and other organisms, combined with a number of cementation processes also contribute to reef growth.