coralreef

A coral reef is a diverse underwater ecosystem built by colonies of coral polyps that secrete calcium carbonate skeletons. Most reefs form in warm, shallow marine waters, typically less than 70 meters deep, where sunlight supports photosynthesis by symbiotic algae living in coral tissues. Coral reefs are among the planet's most productive and biodiverse ecosystems, hosting thousands of species of fish, invertebrates, and other marine organisms.

Biology and formation: Many reef-building corals (hermatypic corals) maintain a mutualistic relationship with photosynthetic algae called zooxanthellae, which provide energy through photosynthesis. In return, corals offer nutrients and a protected habitat. Growth occurs as corals deposit calcium carbonate skeletons, gradually building complex habitats with crevices, ledges, and lagoons. Elevated water temperatures can cause corals to expel their algae, a phenomenon known as bleaching; repeated or prolonged bleaching weakens corals and can lead to die-offs.

Structure and distribution: Reefs occur in a variety of forms, including fringing reefs along coastlines, barrier reefs separated from the shore by lagoons, and atolls that encircle central lagoons. They are concentrated in tropical and subtropical regions, with notable systems in the Indo-Pacific and western Atlantic.

Ecology and services: Reefs provide habitat for countless species, nurture fisheries, and attract tourism. They also offer coastal protection by reducing wave energy and contribute to nutrient cycling in associated ecosystems. Their calcium carbonate framework stores carbon and supports diverse microhabitats.

Threats and conservation: Coral reefs face climate change, ocean warming and acidification, pollution, sedimentation, overfishing, and destructive practices. Conservation approaches include establishing marine protected areas, sustainable fisheries, reef restoration and transplantation, improving water quality, and reducing greenhouse gas emissions. Ongoing monitoring and research inform management and resilience-building efforts.