A reef is a rock, sandbar, or other feature lying beneath the surface of the water (80 meters or less beneath low water). Many reefs result from abiotic processes - deposition of sand, wave erosion planing down rock outcrops, and other natural processes - but the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae. Artificial reefs such as shipwrecks are sometimes created to enhance physical complexity on generally featureless sand bottoms in order to attract a diverse assemblage of organisms, especially fish. Read more ...
Animals built reefs 550 million years ago, fossil study finds Science Daily - June 26, 2014
It is a remarkable survivor of an ancient aquatic world -- now a new study sheds light on how one of Earth's oldest reefs was formed. Researchers have discovered that one of these reefs -- now located on dry land in Namibia -- was built almost 550 million years ago, by the first animals to have hard shells.
Scientists say it was at this point that tiny aquatic creatures developed the ability to construct hard protective coats and build reefs to shelter and protect them in an increasingly dangerous world. They were the first animals to build structures similar to non-living reefs, which are created through the natural processes of erosion and sediment deposition. The study reveals that the animals attached themselves to fixed surfaces -- and to each other -- by producing natural cement composed of calcium carbonate, to form rigid structures.
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