Experiments on the entrainment of surface sediments around polychaete tubes at natural and manipulated densities were conducted in a recirculating seawater flume. Intact cores with either 0 or 8 Diopatra cuprea tubes per 0.01 m* plus associated assemblages were collected in the field. Sediments which contained D. cuprea tubes had natural macrofaunal densities > 5 x those of sediments without tu...