Dynamics of plastic resin pellets deposition on a microtidal sandy beach: Informative variables and potential integration into sandy beach studies

The study addressed temporal dynamics of plastic resin pellets input on a Mediterranean beach, paired with standard environmental variables known to be relevant to sandy beach ecology. Time-related component of the study were related to two levels: 1) weekly sampling along one year, and 2) allocation of beached pellets to categories “old” and “new” as proxy of the time spent in the environment. Pellets were collected by sieving along a fixed transect perpendicular to the shoreline. In correspondence of each sampling were measured beach width and beach face slope. Weekly records of main wind direction and strength, and seasonal substrate mean grain size estimates were added to the dataset. Both density of total pellets and density of “new” pellets were modelled with quantile regression analysis, and best models were selected by Akaike Information Criterion. Data indicate a constant input of pellets ashore, with about 50% evenly represented by “new” items. Beach width resulted the only variable significant to pellets' density, whether total or “new”, with increasing densities of pellets related to narrower beach widths, best explained by a logarithmic fashion. Results hence point to plastic resin pellets as a pressure impact, rather than a spill-related, time-limited one. A list of simple and cost-effective measurements of sandy beach features is provided as a guidance to couple basic ecological information with a possible range of research (including citizen science) addressing beached anthropogenic litter -including plastic pellets. This would ideally enhance the relevance of both research on beached plastics and sandy beach biota, so far running along parallel paths.