Effects of sediment source and flow regime on clam and sediment transport

Abstract

Erosion and transport of juvenile benthic invertebrates, including bivalves, has the potential to alter patterns of distribution and abundance during the early postsettlement period. Field observations indicate that there is often great spatial variability in rates of transport of juvenile bivalves. Differences in transport among sites may arise from both physical and biological causes, including variation in water flow, sediment grain size, and the local biological community. In this study, an experiment was conducted in a laboratory flume to examine the effect of sediment source (4 subtidal sites in the Navesink River estuary, New Jersey, USA) and flow velocity on rates of trans- port of juvenile Mya arenaria and Gemma gemma. Rates of erosion of M. arenaria were significantly related to sediment volume eroded, suggesting that dispersal at high flow speeds is linked to bedload transport. Sediment erosion and clam transport was lower for sediment cores from the 2 sites where the sediment was covered by a mat of amphipod Ampelisca abdita tubes. Reduction of the tube mat resulted in a small but significant increase in sediment erosion. The results of this study and compar- ison of shear velocities between the laboratory and the field suggest that both the presence of an amphipod mat and low shear velocities will result in low rates of transport of sediment and juvenile clams in the field.