Assessing the effects of the sand engine on essential nursery habitat conditions for juvenile placie and sole

Sand nourishment is a widely applied strategy for coastal protection in the Netherlands. The Sand Engine nourishment project is a counter measure for anticipated coastal erosion due to sea level rise for the next 20 to 40 years. This mega nourishment project 9ffers the chance to identify potential effects of nourishments on juvenile flatfish that use the coastal zone as a nursery area. Temporal and spatial variations in essential nursery habitat conditions were investigated in relation to juvenile plaice Pleuronectes platessa and sole Solea solea abundance. Their opportunistic prey take advantage of the initial death by burial of the benthic community. Prey biomass for juvenile flatfish increased in the first years after construct ion of the Sand Engine and re-established after 3 to 4 years. This peak could offer a temporary advantage for juvenile flatfish growth. Local patches of high benthic biomass showed an increased abundance of both fish species. We conclude that food availability is the driving factor for juvenile f ish abundance. Sediment grain size is additionally important for the abundance of sole and plaice. Their abundance is lower when grain size becomes coarser. The observed coarsening around the Sand Engine showed a more prominent effect on juvenile plaice abundance than on sole. Cumulative effects of repeated sand nourishments can potentially affect the nursery habitat of flatfish with repercussions on their adult population size. A progressive coarsening of sediment grain size along the coast has already been observed. Therefore, any habitat alterations should be carefully monitored. Future nourishments should consider the recovery of the benthic community and the applied sediment type. It is recommended to design a nourishment strategy that maintains nursery habitat quality and minimizes the effects on benthic abundance and recovery.