THE EFFECTS OF MARINE GRAVEL EXTRACTION ON THE MACROBENTHOS - RESULTS2 YEARS POST-DREDGING

An offshore experimental dredging study was initiated off North Norfol k (UK) in 1992 to investigate the impacts of marine gravel extraction on the macrofauna. A dredged 'treatment' and a non-dredged 'reference' site were selected to evaluate the initial impacts and subsequent pro cesses of recolonization. A survey of the benthos was conducted prior to the removal of 50000 t of marine aggregate from the treatment site. Thereafter annual monitoring surveys were conducted commencing immedi ately after the dredging episode. Results indicated that whilst the do minant species recolonized quickly following dredging many rarer speci es did not. Evidence from side-scan sonar records and underwater camer as indicated a considerable amount of sediment transport during the fi rst two winters following dredging and the once well-defined dredge tr acks have now become infilled with sand and gravel. The substantially reduced biomass at the treatment site some 24 months after dredging is thought to be due to a local increase in sediment disturbance caused by tide and wave action over the winter period. Finally, the biologica l findings of this study are discussed in relation to their wider envi ronmental significance. Crown copyright (C) 1996 Published by Elsevier Science Ltd