Ecological Consequences of Sand Nourishment: Sediment Dynamics and Meiofauna Community Shifts Revealed by Metabarcoding

Beach nourishment is a widely used coastal protection measure that affects beach morphology, sedimentology, and ecology. In Ahrenshoop (Baltic Sea), sand nourishments are applied approximately every five years to widen a 4 km stretch of the tourist beach. From September 2021 to March 2023, we monitored changes in beach width, sediment composition, and the reaction of meiofauna communities. To assess the impact of nourishment, we determined water line shifts, analysed sediment grain size and shape, and used DNA metabarcoding to characterise the meiofauna communities at the beach–water line. Following the nourishment, the sediment composition had shifted towards finer sand, but it returned to the coarser pre-impact state one year later. By this time, the artificial widening of the beach had almost eroded. Meiofauna communities collected before and after the nourishment differed significantly and were associated with fine and coarse sand, respectively. Grain shape parameters correlated with shifts in meiofauna communities, albeit to a lesser extent than grain size. The differences in community composition were primarily driven by operational taxonomic units belonging to Acari, Annelida, and Platyhelminthes. We recommend the establishment of curated genetic reference barcode libraries for future beach nourishment monitoring studies.