organismscorals

Corals are marine invertebrate animals belonging to the phylum Cnidaria. Most corals live in colonies composed of many genetically identical individuals called polyps. These colonies secrete calcium carbonate skeletons that, over time, form reef structures. Hard corals, or scleractinian corals, are the primary reef builders, while soft corals do not produce the same rigid skeletons.

Many reef-building corals host symbiotic photosynthetic algae, zooxanthellae, within their tissues. The algae provide the corals with energy through photosynthesis, while the corals supply nutrients and protection. This mutualism typically confines corals to sunlit, warm, shallow waters and contributes to rapid growth in tropical regions. Corals also feed on plankton captured by their tentacles.

Reproduction occurs both sexually and asexually. Sexually, corals release eggs and sperm in spawning events, producing free-swimming larvae that settle to form new colonies. Asexually, colonies grow by budding and fragmentation. These strategies help corals spread and recover from disturbance.

Ecologically, coral reefs support high biodiversity and provide services such as coastal protection from waves, habitat for many marine species, and resources for fisheries and tourism. They are vulnerable to rising sea temperatures, ocean acidification, pollution, sedimentation, overfishing, and disease. Coral bleaching occurs when stress causes corals to expel their zooxanthellae, leading to loss of color and energy supply.

Protection and management include marine protected areas, sustainable tourism, reef restoration projects, and efforts to reduce greenhouse gas emissions and local stressors. As organisms, corals are living animals rather than plants or algae, though their health and distribution are tightly linked to the presence of their symbiotic algae.