Impacts of dredged material disposal on a tropical soft-bottom benthic assemblage

The soft-bottom benthic macrofauna in a spoil-ground of dredged material in Cleveland Bay, North Queensland, Australia, was studied to detect possible impacts of the disposal of sediments. The spatial distribution of the assemblage was studied in relation to the source of the impact at 28 stations on four occasions during 1998 and 1999. Additionally, environmental variables were measured on each occasion at each station. Macrobenthic assemblages inside the spoil-ground were different from assemblages outside the spoil ground only immediately after (15 days) the disposal of dredged material. Given the decrease in the abundance of organisms and number of species, it is suggested that this effect was due to direct burial of the macrobenthic assemblage inside the spoil-ground. Macrobenthic assemblages inside the spoil ground were not different from assemblages outside the spoil ground 3 months after dumping. These results suggest that the soft-bottom macrobenthic assemblages may respond quickly to the disturbance associated with the dumping of dredged material.