An estimated 4.25 x 10 8 Abarenicola pacifica populate the tidal flats of Boundary Bay on the southern flank of the Fraser Delta, British Columbia, and annually rework about 10 6 m 3 of sand. In tidal pools, where Abarenicola attain densities of 200 ind. m (super -2) , the worms completely rework the substrate they live in to a depth of 10 cm in 100 days. In the laboratory, Abarenicola can separate a sand/montmorillonite mixture (90% sand, 10% montmorillonite) by floating the clay out in suspension in the head shaft irrigation current. The clay then settles as a biogenically formed lamina, which is subsequently buried and reworked by the worm. In the natural intertidal environment, the clay would be carried away by tidal currents, and by using this process Abarenicola could "clean" fines out of a loose, muddy sand creating a better sorted sediment.