These deep, lightless ecosystems are centred on major geomorphic features of deep ocean floors. These elevated features interrupt lateral ocean currents and generate upwelling of nutrients. This promotes productivity in surface waters, which returns to depths as detritus. The input of these resources, combined with varied rocky micohabitats, unlike the sand and mud around them, supports diverse communities of immobile filter feeders (e.g. sponges), mobile benthic organisms (e.g. molluscs and starfish), and large aggregations of fish, especially around seamounts.