Fish Disappearing In The Ripples Of Reflecting Light. Stock Photography

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.Artificial reefs sometimes have a role in enhancing the physical complexity of featureless sand bottoms, in order to attract a diverse assemblage of organisms, especially algae and fish.