MEPS 281:145-154 (2004)  -  doi:10.3354/meps281145

ABSTRACT: Ecological investigations are increasingly focusing on the activities by which biota structure their ecosystems. Understanding the effects of hyperbenthic organisms on sediment dynamics is expected to provide new insights into estuarine processes. The estuarine mysid Neomysis integer (Leach) occurs in large numbers at the turbidity maximum in the upper reaches of European estuaries, where it feeds from surface sediments. This study assesses the impact of mysid feeding behaviour on sediment stability, and the potential role of N. integer as an ‘ecosystem engineer’. Cores of natural, undisturbed sediment were taken from the upper intertidal area of the Tamar Estuary (UK) and placed in a laboratory-based annular flume. Mysids were placed in the flume and left overnight to feed and to interact with the sediment. The following day, the sediment was subjected to increasing water current velocities (0.05 to 0.45 m s^-1), and suspended particulate matter (SPM) was measured via an optical back-scatter probe. Overnight feeding by mysids increased the amount of SPM: 3000 mysids in the flume (18000 ind. m^-2) caused nearly 150 g sediment m^-2 to be suspended, while 180 ind. m^-2 resuspended 2 g m^-2; on an individual basis, resuspension of sediment was most intensive at a mysid density of 600 ind. m^-2. In control sediments without mysids, resuspension was negligible. Mysid feeding behaviour de-stabilised the surface sediment, enhancing erosion rates. Threshold shear-stress for erosion (τ_e) decreased from 0.15 N m^-2 at 600 mysids m^-2 to 0.05 N m^-2 at 18000 mysids m^-2. These τ_e values are equivalent to current velocities of 0.29 and 0.15 m s^-1, respectively. It seems likely that, besides feeding in the turbidity maximum of estuaries, N. integer actually contributes to the turbidity maximum itself. Furthermore, because N. integer occurs at high densities (90000 mysids m^-3 in the present study), it is predicted to play an important role in sediment dynamics and should be considered in models of sediment transport in upper estuaries.

KEY WORDS: Bioturbation · Neomysis integer · Turbidity · Flume · Sediment dynamics · Swarm