koralleja

Korallit (corals) are marine invertebrates within the phylum Cnidaria and class Anthozoa. Most corals are colonial organisms composed of many genetically identical polyps that secrete calcium carbonate skeletons, forming reef structures in suitable shallow, warm seas.

Two major groups are hard corals (Scleractinia), which build coral reefs, and soft corals (Octocorallia), such as sea fans and sea whips. Many corals harbor symbiotic dinoflagellates called zooxanthellae, which perform photosynthesis and supply energy, contributing to reef growth and color. Some species are azooxanthellate and rely on capturing plankton.

Corals are found primarily in the warm, shallow waters of tropical and subtropical oceans, where light and stable temperatures support photosynthesis and calcification. Coral reefs are biodiversity hotspots, supporting countless fish and invertebrate species, providing coastal protection and resources for human communities.

Reproduction occurs both sexually and asexually. Sexually, many corals release eggs and sperm in synchronized spawning events. Asexually, colonies grow by budding and repair themselves through fragmentation. Larvae (planulae) disperse before settling to establish new colonies.

Threats include climate change, which causes bleaching by expelling zooxanthellae, and ocean acidification that weakens calcium carbonate skeletons. Local stressors such as overfishing, pollution, and sedimentation also damage reefs. Conservation efforts include marine protected areas, restoration projects, sustainable tourism, and reducing greenhouse gas emissions.

Notable examples of large reef systems include the Great Barrier Reef and parts of the Coral Triangle.