Reefs

Reefs are underwater ecosystems, most commonly coral reefs built from the calcium carbonate skeletons of scleractinian corals. Reefs can also form from other organisms or reef-like rock, but coral reefs are the most extensive and diverse.

They form in warm, clear, shallow tropical waters with low sedimentation. Corals rely on symbiotic algae (zooxanthellae) that photosynthesize, providing energy to the corals, which in turn build calcium carbonate structures. Reefs develop as fringing, barrier, or atoll formations.

Ecologically, reefs host high biodiversity and serve as habitats, feeding and nursery grounds for many fish and invertebrates. They also deliver services such as coastal protection from waves, tourism and recreation, fisheries, and cultural value.

Threats include climate change causing thermal stress and bleaching, ocean acidification reducing calcification, pollution, sedimentation, overfishing, and destructive practices. Many reefs have declined in recent decades.

Conservation efforts include marine protected areas, restoration projects, improved water quality, sustainable fisheries, and strategies to reduce greenhouse gas emissions.

Notable reefs include the Great Barrier Reef (Australia) and the Belize Barrier Reef System.