Acknowledgments

The behavior and activities of a terebellid polychaete, Eupolymnia heterobranchia, in the presence of artificially irrigated tubes and the effects of Eupolymnia and artificial irrigation on silicate removal from sediment pore waters were examined in the laboratory. Eupolymnia built more tubes and longer tubes in sediments containing artificially irrigated tubes relative to unventilated sediments. Morcovcr, worm tubes were located closer to artificially ventilated tubes than expected by chance. Silicate fluxes were positively related to the dry weight ofworms and to the number of tubes in sediments when they consisted of either Eupolymnia tubes or artificially irrigated tubes alone. However when tube types were mixed (Eupolymnia + artificially irrigated tubes), silicate Auxcs were lower than in sediments containing arti-ficially ventilated tubes alone. Thus, worm behavior was altered by the prescncc of artificially irrigated tubes. In addition, interactions between worms and artificially ventilated tubes served to rcducc silicate flux relative to sediments containing artificially ventilated tubes only. In marine benthic environments, the distri-butions of organisms are affected by a suite of physical and biological processes, including currents (e.g. Bckman 1983), internal waves (Shanks and Wright 1987), the physical and chemical properties of substrates (Wethey 1986; Woodin et al. 1993), the supply of larvae to the habitat (Roughgarden et al. 1988), the ability of larvae to establish themselves during settlement and postsettlement events (Wood-in 1986) and biological interactions (e.g. pre-dation, competition) among established mem-bers of the infaunal community (Woodin 198 1; Peterson and Beal 1989). Significant interac