The role of dominant macrobenthic communities for the material budget of the Sylt-Romo tidal basin was investigated in the course of the SWAP project by measuringin situ flux rates with the flume technique. Mussel beds, seagrass beds andArenicola flats were found to be sinks for particles, whereas sandy shoals and elevated sands, poor in macrofauna, acted as sources for particles. Dissolved inorganic nitrogen was released by communities which were dominated by macrozoobenthos. Seagrass beds were sinks for nutrients on calm days, but released also dissolved material when storms induced high water turbulence. The total intertidal area of the basin was a sink for particles and a source for dissolved substances. However, the character of the whole ecosystem was determined by the dominating subtidal area which covered 2/3 of the area of the basin. Therefore, the subtidal exchange processes were assessed by extrapolating exchange rates from intertidal communities with comparable sediments and macrobenthic densities. Subtidal benthic communities were sparsely populated compared to the intertidal communities and their material exchange was directed from the bottom to the water column. These release processes were supported by physical forces as strong currents and water turbulence. Mussel beds were counteracting the continuous export of material from the subtidal sea floor to the water. Mussel beds and seagrass beds play an important role for the material budget, which is shown in a scenario in which both communities were excluded from the system. For the Sylt-Romo tidal basin historical changes of benthic communities and water dynamics are reported and a possible interplay between the functioning of benthic communities and physical forces is discussed.