The Ecological Impacts of the Joint U.S.-Russian Benthic Impact Experiment

The Benthic Impact Experiment (BIE) is designed to address the effects of sediment redeposition prior to the commencement of commercial mining in the deep sea. Sediment resuspension and subsequent redeposition during manganese-nodule mining is predicted to be the primary impact on benthic communities living on the abyssal seafloor. Sediment redeposition could adversely affect abyssal benthic communities through entombment, spatio-temporal changes in recruitment patterns, or through starvation caused by food dilution and obstructed feeding. NOAA started the BIE with baseline studies in July 1993 with the deployment of a transponder net and current meters, and by conducting side scan sonar/camera surveys, and benthic sampling. Following the baseline activities the study area was blanketed with varying thicknesses of sediment using the Disturber. In the BIE, the Disturber was towed 49 times through a l50-m-x-3,000-m tow zone resuspending 4,000 m³ of wet sediment. The bulk of the resuspended material was transported north of the tow 7-one by northerly currents at the time of disturbance. The majority of the discharged sediment settled quickly as a sediment-laden fluid flow. After towing, samples were randomly collected in the area of heaviest resedimentation to determine the impacts on macro- and Meiofauna immediately after towing and one year later in 1994. Meiofaunal analyses indicate that nematodes exhibit a significant decrease in abundance in the sediment redeposition area 9 months after the initiation of the BIE. Macrofaunal data analysis conducted at the family level indicated that only Sabellid polychaetes and Macrostylid isopods exhibit a significant treatment affect that could be attributed to sediment redeposition. Multivariate community similarity analysis reveals that the glycerid polychaete Glycera sp. A was positively associated with samples collected from the sediment redeposition zone immediately following the initiation of the experiment. However, overall species diversity remained unaffected by sediment redeposition.