Reef

Reef refers to a ridge or mound near the surface of the sea, formed by living organisms or by geological processes. In marine biology, the term most often denotes coral reefs, which are biogenic structures built by the calcium carbonate skeletons of corals and other calcifying organisms. Reefs can also describe rocky or sandy structures that provide habitat but are not built by corals.

Coral reefs develop in warm, shallow, clear waters where sunlight can reach corals. Most reef-building corals have a symbiotic relationship with photosynthetic algae called zooxanthellae, which supply energy to the corals through photosynthesis. The corals secrete calcium carbonate, creating a hard framework that accumulates over thousands of years. Reef growth is influenced by water temperature, salinity, wave exposure, and sediment levels.

Common reef types include fringing reefs that hug coastlines, barrier reefs separated from land by a lagoon, atolls that encircle lagoons formed from sinking volcanic islands, and patch reefs that occur within lagoons or on continental shelves. The Great Barrier Reef, the Belize Barrier Reef, and many Red Sea and Caribbean reefs are well-known examples.

Reefs support extraordinary biodiversity and provide ecosystem services such as coastal protection, fisheries, tourism, and cultural value. They are sensitive to disturbances like climate change, ocean acidification, warming, pollution, destructive fishing practices, and sedimentation. Conservation approaches include marine protected areas, sustainable tourism, reef restoration, and targeted reductions in local stressors, alongside ongoing research into resilience and restoration techniques.