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O-2-flux into sediments attributed to the pumping behaviour of two macrofauna species, Callianassa subterranea (Decapoda) and Lanice conchilega (Polychaeta) was investigated, Samples were obtained from the North Sea near Helgoland in 1989 and 1990.The two species were found to transport roughly similar amounts (3 mmol m(-2) d(-1)) of oxygen into the sediment although they displayed markedly different pumping behaviours.Irrigation by C.subterranea was intermittent and characterized by regularly recurring breathing currents which lasted 2.6 min and were separated by 40-min pauses.In addition to this regular intermittent irrigation, an irregular mode was observed.C.subterranea constructed a complex burrow system.At least half of the burrow wall was not in contact with oxygenated water, however, and thus not effective as additional interface for O-2-exchange.Sediment expelled from the burrow increased the total oxygen uptake (TOU) relative to the surrounding sediment surface.L.conchilega moved water much more frequently (every 4 min) than C.subterranea.We suggest that L.conchilega acted as a piston when moving in its tube, exchanging burrow water with the overlying water.This mechanism, termed 'piston-pumping', is also potentially important in other smaller tube dwelling organisms.At a shallow water station in the southern North Sea 21 ind of C.subterranea constructed 1.6 m(2) burrow surface per m(2).L.conchilega (300 ind m(-2)) created only 0.37 m(2) m(-2) tube surface.On the basis of the abundance and oxygen transport associated with pumping activity, it is calculated that the two species increase TOU by 85% compared to O-2-flux across the sediment-water interface.