This study investigates the distribution and concentration of microplastics (MPs) across the littoral profile of a beach, from dune base to offshore sector, including an estuarine channel and Sabellaria alveolata bioconstructions. The research was conducted at Pino di Lenne beach (Taranto, Ionian Sea), a wave-dominated, microtidal littoral system representing a unique natural laboratory with minimal anthropogenic pressure. An eco-friendly extraction protocol was used, combining methods that were already known in the literature. Olive oil proved highly effective in isolating a wide range of MP densities from sediment samples. Statistical analysis identified key accumulation zones, with the highest mean concentrations found in the submerged sandbar (2435 MPs/kg), Sabellaria bioconstructions (2324 MPs/kg), and the base of the dune (2065 MPs/kg). Fibres were the predominant morphology across all sub-environments. Distribution is interpreted as controlled by hydrodynamic processes and biological activity. The submerged beach drives MP transport, with the sandbar and shoreface acting as dynamic sinks. Sabellaria bioconstructions function as biological trap, actively incorporating MPs into their tubular structures. The dune base acts as a sink for wind-blown and storm-deposited plastics. These sub-environments function as critical littoral traps for MPs, essential for developing targeted monitoring and remediation strategies in similar coastal systems.

Beaches are complex and dynamic sedimentary environments in which marine and continental processes continuously interact on various spatial and temporal scales, also influenced by human activities. Beaches provide a wide range of essential ecosystem services for environmental health and human well-being, such as coastal protection, rich biodiversity, cultural, and aesthetic value.Furthermore, from an economic perspective, beaches are important resources. In fact, the growth of coastal tourism has significantly boosted commercial activities making the tourism industry one of the most dynamic and remarkable sectors for local and national economies. A good example is represented by the countries in the southern Mediterranean area, which are among the most popular tourist destinations in the world. Furthermore, demographic, social, and environmental changes currently impacting coastal areas, particularly during the summer seasons, can lead to environmental degradation and undermine the sustainability of this ecosystem. To address the potential issues arising from anthropic coastal exploitation coupled with climate-related variations expected for the next decades, it is important to assess the site-specific beach carrying capacity, generally defined as the relationship between the available beach area and the occupancy level.Since the 1960s, bibliography studies have shown that growing interest in coastal tourism has led to the development of different methods for calculating carrying capacity. Through field surveys and laboratory analysis, this work proposes an integrated geo-environmental characterization of coastal systems, using an index-based approach to determine beaches carrying capacity and so assess the limits beyond which irreversible damage, such as erosion, habitat destruction, or pollution, occurs due to human activities and climate-related processes. To this end, data on various factors that may impact carrying capacity are integrated:Geological factors assessed in terms of sedimentological composition and geomorphological characteristics, which influence the choice and spatial distribution of tourists across the investigated beach sectors; Morphodynamic factors affecting the evolution and the use of the beach environment, in terms of available and usable space. This is evaluated in terms of natural processes such as weather- and marine-related events (e.g., waves or storms) that may cause beach retreat, and anthropogenic processes, which can lead to changes in sediment budget (e.g., the amount of sediment potentially removed by tourists); Waste pollution factors that, in addition to causing environmental problems and health risks, can reduce the scenic value and compromise public use of the beaches. Meteorological factors analyzed through data on rainfall, wind, cloud cover, and temperature, as these elements influence the recreational use of the beaches, affecting bathing activities and the presence of tourists. Based on the surveys, analyses, and evaluations, the proposed method aims to provide a more comprehensive carrying capacity assessment. This tool, useful for supporting sustainable beach management and planning actions, will lead to a more efficient use of coastal resources to protect beaches from geo-environmental degradation.