Coralli

Coralli, commonly referred to as corals, are marine cnidarians that build calcium carbonate skeletons. They include hard corals, or scleractinians, which form reef frameworks, and soft corals, or octocorals, that have flexible, internal skeletons. Corals live in colonies composed of many genetically related polyps that connect through tissue and share resources.

A defining feature of many reef-building corals is their symbiosis with photosynthetic algae called zooxanthellae (dinoflagellates). The algae reside within coral tissues and provide a large portion of the coral’s energy through photosynthesis, while the coral offers the algae a protected environment and nutrients. Corals also capture plankton and organic particles with their tentacles and cnidocytes. The combination of autotrophic and heterotrophic feeding supports rapid growth in suitable conditions.

Most corals inhabit sunlit, shallow tropical and subtropical waters, typically within 30 meters of the surface, though some species live at greater depths or in temperate zones. Coral reefs form complex three‑dimensional habitats that support high biodiversity, protect coastlines from erosion, and provide resources for fisheries and tourism.

Reproduction occurs sexually, via broadcast spawning or brooding, and asexually, through budding or fragmentation. Corals are sensitive to environmental stress; prolonged heat waves can cause bleaching, where symbiotic algae are expelled. Ocean acidification, pollution, overfishing, and destructive practices threaten reef health and resilience.

Fossil records show corals have existed for hundreds of millions of years, with modern reef-building corals arising in the Paleozoic–Mesozoic era. Today they remain central to marine ecosystems and global biodiversity, but face severe conservation challenges.