These productive intertidal or subtidal biogenic ecosystems are formed and dominated by sessile molluscs like mussels or oysters, around temperate or tropical coasts and estuaries globally. They filter plankton from the water column, acting as carbon sinks and modifying local physical environments by changing currents and dampening wave action. Distribution is limited by available rocky substrates on low-energy coastlines, as well as requirements for high water quality and oxygen availability. Many organisms are adapted to the extreme range of conditions typical of the intertidal zone (e.g. shellfish closing valves to avoid adverse desiccation).