From monitoring to management: a standardized indicator-based assessment of long-term dredge disposal impact across three benthic habitats for macrobenthos, epibenthos and fish

Dredging of harbours and navigation channels and the associated disposal of dredged material in designated areas may impact the marine environment. Disposal at sea is regulated by the OSPAR convention and several EU environmental regulations. To comply with these regulations, managers need a simple presentation of potential environmental impacts, based on standardized assessments of available monitoring data. This long-term observational study (2005–2019) provides a standardized indicator-based assessment of dredge disposal effects on three ecosystem components (macrobenthos, epibenthos and demersal fish) in three benthic soft-sediment habitats in the Belgian part of the North Sea. Ecosystem impact was determined by a Benthic Ecosystem Quality Indicator (BEQI) analysis. This approach measures differences in species composition, species richness, density and biomass between an affected and a non-affected set of samples. The relationship between amount of dumping (pressure), benthic habitat type, and ecosystem impact (BEQI) was investigated using linear mixed-effects models. Environmental impact differed slightly among benthic habitats, but increased with increasing pressure in all three habitats, with the strongest effects observed for the macrobenthos ecosystem component due to their restricted mobility. Our findings demonstrate the added value of a standardized indicator-based approach to assess dredge disposal impact across benthic habitats and ecosystem components in soft sediments. It provides managers with a standardized environmental evaluation tool and a simplified traffic light representation of potential dredge disposal impact. The results based on long-term observational monitoring data confirm the importance of contiguous periodic monitoring, with a focus on the macrobenthos community.