Long-term impact of dredging and beach nourishment works on benthic communities

Dredging and rainbowing techniques are commonly used to replenish sandy beaches and protect the coast against erosion. Since 2003, such operations have been conducted every other year on Pyla Beach, Arcachon Bay (French Atlantic Coast). The evolution of macrobenthic communities subjected to regular disturbance was analyzed once in springtime at dredging and disposal sites, as well as in a control area, over 21 years. The overall benthic community was dominated by the same few species. The dredged area harbors a benthic community whose characteristics suggest the maintenance of a disturbed status, compared to the control area, whose community follows a trajectory possibly influenced by the general decrease of organic matter in the sediment. Regarding the disposal site, species richness is slowly declining. In both disturbed areas, the community was dominated by species able to recolonize rapidly (polychaetes, peracarid crustaceans), while the control area rather favored bivalves. • Sea level rise, coastal erosion and beach management challenge stakeholders. • Over 21 years, benthic communities evolved differently in dredged and disposal areas. • Regularly replenished beach undergoes a decrease of benthic diversity. • Benthic communities in a regularly dredged area remain in a stable, disturbed state.