Burial survival of benthic macrofauna following deposition of simulated dredged material

In many coastal regions, the disposal of dredged material constitutes the largest (albeit often localised) anthropogenic disturbance to the seabed. Impacts can be minimised by reducing the amount of sediment overburden on the bed at any one time allowing short-term recovery to proceed via the vertical migration of resident species. However, there is currently a limited understanding of the ability of such species to successfully vertically migrate. This study presents the findings of a field experiment to investigate the vertical migratory capability of temperate macroinvertebrate species following the placement of simulated dredged material. The relationships between vertical migration success with sediment characteristics (organic carbon and sand content) and placement depth were explicitly examined. While the polychaete worms Tharyx sp. A. and Streblospio shrubsolii showed poor vertical migration with only 6 cm of sediment overburden, the oligochaete Tubificoides benedii showed some recovery while the gastropod mollusc Hydrobia ulvae exhibited good migratory success, even with 16 cm of sediment overburden. While increases in sand content from 16% to 38% had no noticeable effect on vertical migration, increased sediment organic content from 0.8% to 3.3% detrimentally affected vertical migratory activity. The results support the theory that species' survival following sediment burial is trophic group-related. The relevance of these findings with respect to dredged material disposal management is discussed.