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 transport 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 comparison 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.

Spatial and temporal variability in juvenile bivalve dispersal: effects of sediment transport and flow regime

“…This suggests that dispersal of these species of juvenile bivalves (of which Gemma gemma are the most abundant) is primarily initiated by sediment erosion and occurs as bedload transport. Other studies also have found strong relationships between sediment transport and bivalve transport in the field (Emerson & Grant 1991, Commito et al 1995a, b, Hunt & Mullineaux 2002 and the laboratory (Hunt 2005). This type of relationship occurs in other groups of macrofauna (e.g.…”

“…Rates of transport were low at Sites 2 and 4, where the sediment was covered with tubes created by the amphipod Ampelisca abdita. In the laboratory, Hunt (2005) found that erosion of juvenile Mya arenaria and sediment collected from the 4 sites used in the present study varied strongly among sites at a common shear velocity, likely due to an effect of the amphipod mats on sediment erosion. Mats created by this amphipod may impact bivalves significantly.…”

“…Laboratory experiments with sediments from the Navesink estuary (Hunt 2005) suggested that dispersal of juvenile bivalves in the field would be linked to sediment transport and that dispersal would be considerably greater at Sites 1 and 3 than at Sites 2 and 4. This field study confirms this hypothesis, with the exception of low bivalve dispersal at Site 3 in 2003, likely due to lower rates of sediment transport at this site in that year but possibly also to low ambient densities of bivalves.…”

“…This study is a component of a project (Hunt 2005 and authors' unpubl. data) examining the magnitude and scale of transport of juvenile bivalves in the Navesink River estuary.…”

Larval responses to turbulence and temperature in a tidal inlet: Habitat selection by dispersing gastropods?

“…Invertebrate biomass at Barnstable Harbor is dominated by direct-developing gem clams (Gemma gemma), two polychaetes with short-lived demersal larvae (Clymenella torquata and Glycera dibranchiata), and perhaps paradoxically, intertidal mud snails (Nassarius obsoletus) with planktonic larvae (Sanders et al, 1962). Juveniles and larvae of the first three species have never been observed to venture into the water column except by resuspension (e.g., Hunt, 2005) and would have limited transport in the harbor. In contrast, mud snail larvae spend 2-4 weeks in the plankton before they become competent to metamorphose (Scheltema, 1967).…”