Impacts of aggregate dredging on sediment composition and associated benthic fauna at an offshore dredge site in the southern North Sea

Dredging and associated screening at a dredge site in the southern North Sea (Area 408) is associated with areas of well-sorted fine sand that extend for up to 3 km to the south-east of the dredged area and overlay sediments with a more variable particle size composition. This well-sorted fine sand may reflect deposition and transport of material mobilised by the dredging and screening processes at the dredge site. Multivariate analysis of the benthic community structure suggests that marine aggregate dredging, at the level of intensity employed in the study area prior to sample collection, has had a limited impact on benthic community composition compared with that reported from studies elsewhere. This is ascribed to the likely rapid rates of recolonisation by the mobile opportunistic polychaetes and crustaceans that dominate the macrofauna of the sandy gravel deposits at this particular dredge site. Analysis of variance showed, however, that significant differences existed between the sample treatments in terms of species evenness (Pielou's J). Dredged samples were found to have the lowest mean species evenness (0.71) when compared to controls (0.77). The present study highlights the inherent difficulties in the application of general impact/recovery predictions to dredged sites with varying environmental characteristics.