Physical and biological impact of marine aggregate extraction along the French coast of the Eastern English Channel: short- and long-term post-dredging restoration

Sediment and associated macrofauna of an industrial extraction site off Dieppe have been monitored during a 10-year period. The original heterogeneous substrate of the shingle bank, characterized by gravels and coarse sands, was progressively dominated by fine sands deposited in dredging tracks. The maximum impact on benthic macrofauna was a reduction by 80% for species richness and 90% for both abundance and biomass. The structure of the community changed from one of coarse sands with Branchiostoma lanceolatum to one of fine sands with Ophelia borealis, Nephtys cirrosa, and Spiophanes bombyx, with local dominance of the opportunistic, sessile Pomatoceros triqueter on bare shingles. Impact of overflowing sands on benthic macrofauna in the surrounding deposition area proved equally large as in the dredged area. Early stages of recolonization were studied from 1995 to 1997 after cessation of dredging. Species richness has been fully restored after 16 months, while densities and biomass were still 40% and 25%, respectively, lower than in reference stations after 28 months. Nevertheless, community structure differed from the initial one corresponding to the new type of sediment. Impact within and around the dredging site was classified according to three levels. Exploration of a former experimental site (CNEXO) dredged in the 1970s provided an example of long-term restoration.