SEDIMENT REWORKING BY THE POLYCHAETE HETEROMASTUS-FILIFORMIS ON A TIDAL FLAT IN THE DUTCH WADDEN SEA

Sediment reworking by Heteromastus filiformis was studied in the field for several years. Heteromastus feeds 10 to 20 cm below the sediment surface and deposits its oval faecal pellets on the sediment surface. The pellets are relatively resistent against bacterial and mechanical breakdown. Numerical density of Heteromastus varied both during the seasons and from year to year. The size distributions of the faecal pellets produced by the population could be used as a measure of the population structure. Recruitment did not occur every year on the locality studied. Numerical densities largely controlled the amount of sediment reworked. On average the Heteromastus population amounted to 500 m-2 and the amount of sediment brought to the surface to ca 100 ml·m-2 ·d-1 corresponding with a sediment layer of 4 cm annually. A heavy settlement in summer and autumn 1978 resulted in densities up to 9000 m-2 and a sediment reworking rate of 2.51·m-2·d-1, corresponding with a sediment layer of 200 1·m-2, or 20 cm in total in the period August to November inclusive 1978. © 1979.