Intertidal sediments of the Minas Basin support an estimated 24 x 10 9 Macoma balthica . Excreta occurs as either loose coils or strings of pseudofeces, or as small cylindrical fecal pellets, both of which are easily transported. Fecal pellets are picked up with fine sand and settle out of suspension with coarse silt. Some pellets last at least one tidal cycle before breaking down into sand grains and mucus-bound aggregates of mud and silt. Each clam produces about 0.5 g (dry weight)/day of excreta, most of which is resuspended by tidal currents. In the areas of highest recorded population densities (3.500/m 2 ), feeding would remove about one foot of sediment (28 cm) per year. Total daily contribution of excreta to the Minas Basin by the 24 billion Macoma amounts to about 6 x 10 9 g (dry weight) of sediment or about 10,000 m 3 of wet excreta. This material is likely a valuable food source and is distributed throughout the Minas Basin by tidal currents.