Benthic suspension feeders depend on the fluid medium for their supply of edible particles. The horizontal flux of organic seston is a function of the interaction of particles of varying densities with the near-bed velocity field. Analytical and numerical models of this process predict that the shape of the flux profile varies with flow rate, bottom roughness and particle settling velocity. Bulk horizontal particle flux may either decrease or increase with height above the bed. Flume experiments with natural sediments from Eastern Passage, Nova Scotia confirmed the trends predicted by the model. In a complex suspension, denser, inorganic particles have flux maxima closer to the bed than lighter, organic seston, so suspension feeders must reach several centimeters above bed level to maximize the organic composition of their ration. The feeding ecology and diet of a passive suspension feeder, the polychaete, Spio setosa, were examined in light of the modelled seston dynamics and suggested that S. setosa is adapted to feed at 4 to 5 centimeters above the bed and specializes on suspended macrophyte detritus and flocculated organic-mineral aggregates. The influx of this organic seston at Eastern Passage is periodic and coincident with the local seiche period, showing that the hydrodynamic control of seston transport is an important factor in benthic trophic interactions.