The generation of marine litter in Mediterranean island beaches as an effect of tourism and its mitigation

Marine litter, defined as any persistent manufactured or processed solid material discarded in marine and coastal environments, has drawn increasing attention since the late 1960s, with global initiatives such as the International Coastal Cleanup and a growing focus on microplastics. The Mediterranean Sea experiences multiple anthropogenic pressures: a dense coastal population (~150 million), major river inputs, intense shipping (15–30% of global activity), and it attracts about one third of global tourism annually. Its semi-enclosed nature and anti-estuarine circulation make it an accumulation zone for marine litter, with floating plastic concentrations comparable to subtropical gyres. Beaches are key land-based sources for marine litter through inadequate waste management, littering, and illegal dumping, and in the Mediterranean, summer tourism intensifies pressures on coastal municipalities and beach cleanliness—an important driver of tourist choices and local economies. In this context, the study aims to understand the seasonal dynamics of beach-generated waste on Mediterranean islands to design effective mitigation solutions. The authors monitored 24 beaches (remote to highly touristic) across eight islands in both low and high seasons (2017) and compared results to targeted pilot mitigation actions implemented at 11 sites in 2019.

The paper situates the work within decades of marine litter research and management efforts, including prevention, mitigation, removal, and behavior-change strategies. Prior work identifies the Mediterranean as a hotspot for marine litter due to population density, shipping, hydrodynamics, and tourism. Beach cleanliness influences tourist behavior and return intentions, linking environmental quality to socio-economic outcomes. Previous beach litter studies in the Mediterranean report high dominance of artificial polymers and identify tourism and shoreline activities as major sources. Few studies report accumulation rates (ARs); those that do, often on remote islands (Aleutians, Hawaiian archipelago, sub-Antarctic), show ARs orders of magnitude lower than in developed/touristed areas, underscoring the role of local human pressures. Existing indices (e.g., Clean Coast Index) provide snapshots of cleanliness, but there is a need for dynamic metrics capturing accumulation processes, motivating the Accumulation Index (AI) introduced here.

Study area and design: In 2017, 147 surveys were conducted on 24 beaches across eight Mediterranean islands (Mallorca, Sicily, Rab, Malta, Crete, Mykonos, Rhodes, Cyprus). For each island, three beaches were selected: tourist-dominated (Tbeach), locally used (Lbeach), and remote (Rbeach). A fixed 100 m beach segment from waterline to back-beach was monitored per site, following OSPAR guidelines, adapted to include small plastics. Surveys occurred monthly during high season (May–September) and once before (Feb–Apr) and after (Oct–Nov). Items were collected, classified, and disposed properly. Small plastics: Mesoplastics (MePs, 0.5–2.5 cm), large microplastics (MPs, 0.1–0.5 cm), and pellets were collected at the surface by designated surveyors; subsequently sorted into macroplastics (>2.5 cm), MePs, MPs, and pellets. Distance and area: Start/end GPS coordinates defined the segment; when length D ≠ 100 m, counts were normalized to 100 m for reporting collected items per 100 m. Beach area (S) was measured via Google Earth polygons from waterline to back-beach. Accumulation rates (AR): AR (items/1000 m²/day) = (Ncol / S / T) × 1000, where Ncol is uncorrected item count, S is m² of monitored area, and T is days since last cleaning by authorities (or days since previous survey if no cleaning). For MPs and pellets, T was always the interval between surveys (mechanical cleaning assumed ineffective for these sizes). For the first survey, MPs/pellets AR used days since Jan 1, 2017. Average T during high season: 6.2 days (Tbeach), 13.2 (Lbeach), 27.8 (Rbeach); low season: 61.2, 79.0, 105.3 days respectively. One Rbeach (Malta) was excluded due to atypically high ARs and proximity to a harbor. Sources and categorization: Items grouped into nine MSFD categories; shoreline/tourism (ST) category captured likely visitor-derived items (e.g., cigarette butts, caps/lids, cutlery/trays/straws, snack wrappers, metal caps). MePs/MPs assigned as non-sourced; pellets to shipping. Accumulation Index (AI): AI = log10(AR × 1000), categorized into seven grades from extremely low to extremely high to assess dynamics at monthly/seasonal scales for total or specific items. 2019 pilot actions: On 11 beaches (T and L in Sicily, Malta, Crete, Rhodes, Cyprus; T in Mallorca), pilot actions during high season included awareness campaigns (flyers/posters, on-site representatives), provision of ashtrays (6 beaches), improved/added bins with bilingual signage (5 beaches). One survey per site in Aug/Sep 2019 occurred 6.7 days (T) and 35.1 days (L) after last cleaning; ARs for MPs/pellets could not be computed in 2019 due to single surveys. Extrapolation to all Mediterranean islands: Coastline lengths from CCM database and beach extents via Google Earth were used to estimate total beach length (mean 6466.5 ± 2268.0 km; beaches ~34% ± 11.9% of coastlines). Peak-season ARs per 100 m/day for T, L, R were combined to estimate total visitor-derived accumulation region-wide.

• Survey effort and composition: 162,320 items collected in 2017; average 1197.6 ± 2978.0 items per 100 m survey (526.9 ± 794.2 excluding plastic fragments <2.5 cm). Artificial polymers dominated (94.2%).
• Collected items per 100 m by beach type (2017): Lbeach 2157.2 ± 4680.2 (n=49), Tbeach 899.9 ± 858.8 (n=49), Rbeach 425.4 ± 1319.9 (n=42). Raw counts did not show higher totals in high vs low season.
• Accumulation rates (AR) reveal strong seasonality: • Tbeach: High season 329.6 ± 444.9 items/1000 m²/day (n=33), Low season 69.8 ± 110.1 (n=16), +471.9%. • Lbeach: High season 177.2 ± 265.3 (n=33), Low season 51.2 ± 101.2 (n=16), +346.0%. • Rbeach: High season 13.7 ± 32.2 (n=28), Low season 20.3 ± 59.7 (n=14); low-season ARs elevated in Oct–Nov likely due to weather-driven beaching.
• Most frequent items after distance correction: MePs (35.3%), cigarette butts (12.4%), MPs (11.2%), pellets (9.5%), macroplastics >2.5 cm (8.3%). In ST category, top items: cigarette butts (12.4%), plastic caps/lids (3.5%), cutlery/trays/straws (1.6%), crisp/sweet packets and lolly sticks (1.4%), metal bottle caps (0.7%).
• ST category ARs during high season were highest across beach types; cigarette butts ARs reached 173.5 (T), 41.3 (L), and 1.6 (R) items/1000 m²/day.
• Strong correlations suggest on-beach fragmentation contributes to small plastics: AR(MePs) vs AR(ST) R²=0.72 (n=116, p<0.001); AR(MPs) vs AR(MePs) R²=0.48 (n=87, p<0.001).
• Seasonal composition: During high season months, ST items constituted on average 65.7% ± 2.8% (T), 39.8% ± 17.9% (L), 35.5% ± 28.7% (R) of accumulated items; including MePs and MPs increases these to 79.2% ± 4.5% (T), 77.9% ± 9.4% (L), 58.8% ± 19.1% (R).
• Accumulation Index (AI) was consistently higher in high season for all islands and beach types, indicating dynamic seasonal accumulation.
• 2019 pilot actions (high season) reduced ARs of ST items substantially: • Tbeach (6 sites): from 340.3 ± 410.7 to 178.1 ± 200.2 items/1000 m²/day (−47.7%). Concomitant decreases in MePs (−31.3%) and remaining litter (−43.6%, excluding MPs/pellets). • Lbeach (4 sites excluding Sicily outlier): from 60.8 ± 94.1 to 30.3 ± 40.7 (−50.1%). MePs increased (+26.0%) and remaining litter increased (+106.7%), likely influenced by longer intervals since cleaning. • Overall average reduction across tested beaches: 52.5% ± 20.8% for ST items. • Cigarette butts ARs dropped by 54.5% ± 12.0% where ashtrays were provided (6 beaches) and by 57.8% ± 28.2% where they were not; no significant difference between groups. • The only increase occurred at the Lbeach of Sicily (6× in ST; 8× in cigarette butts) where no representative or ashtrays were provided.
• Quantification of visitor-driven loads at peak (Jul–Aug): per 100 m per day, visitors left on average 844.5 items (T) and 295.2 items (L) from ST category; including MePs/MPs totals 1028.4 (T) and 798.3 (L). Rbeach: 57.7 items/100 m/day attributable to tourism.
• Regional extrapolation (Mediterranean islands, beaches ≈ 6466.5 ± 2268.0 km): visitor-derived accumulation estimated at 40.6 million ± 11.5 million items/day during peak; equivalent to ~2500 ± 709 items/km/day if all reached the sea.
• Economic aspect: Estimated average cost of pilot actions extrapolated over May–September high season is ~€111.6k per km of beach.

The study demonstrates that tourism drives a pronounced seasonal increase in marine litter accumulation on Mediterranean island beaches, which is not apparent from raw item counts but becomes clear when accounting for time since last cleaning and monitored area through accumulation rates. The highest impacts occur on tourist and local-use beaches, with remote beaches far less affected by visitor activities. The strong correlations between ST-category accumulation and MePs/MPs suggest that on-site fragmentation of larger plastic items, enhanced by summer conditions and high visitor activity, contributes significantly to small plastic debris on beaches. The Accumulation Index provides a practical dynamic indicator for municipalities to identify periods and sites of highest pressure, prioritize resources, and track effectiveness of interventions. Pilot awareness and infrastructure actions effectively reduced accumulation of visitor-derived items by about half on average, including large reductions in common items like cigarette butts, caps/lids, and cutlery/straws, indicating behavior-change and improved waste disposal can yield rapid benefits. Differences between T and L beaches, and seasonal/weather-driven increases at remote sites in autumn, highlight the role of cleaning frequency and environmental conditions. These findings underscore the need for integrated coastal waste management and sustainable tourism practices to mitigate marine litter generation at the source.

This work quantifies the seasonal influence of tourism on marine litter accumulation across Mediterranean island beaches and introduces a dynamic Accumulation Index to assess and compare site-specific pressures. Accumulation rates increase up to 4.7-fold during high season, with visitor-derived items comprising the majority of accumulated litter on popular beaches. Pilot awareness and infrastructure interventions reduced visitor-derived accumulation by ~50%, demonstrating actionable pathways for mitigation. Extrapolated to all Mediterranean island beaches, peak-season visitor activity is associated with tens of millions of items accumulating per day. The study calls for urgent implementation of efficient, sustainable tourism models, continued public awareness, and targeted waste management infrastructure. Future work should refine understanding of litter beaching processes and seasonality, quantify the on-beach fragmentation pathways to micro/mesoplastics, evaluate long-term effectiveness and cost-efficiency of interventions, and expand monitoring to more sites and seasons to support policy and management.

• In 2019, only one survey per site was conducted, preventing calculation of ARs for MPs and pellets post-intervention.
• One remote beach (Malta) was excluded due to atypically high ARs and nearby harbor influence, reducing representation of that island’s remote conditions.
• Cleaning frequency and variable time since last cleaning differed among sites and seasons, influencing AR estimates and complicating cross-site comparisons.
• Monitored surface varied slightly between surveys due to practical constraints (GPS accuracy, beach access, crowding), though area measurements were used in AR calculations.
• Environmental variability (e.g., autumn storms) likely affects natural beaching and may mask or amplify seasonal patterns, particularly on remote beaches.
• Regional extrapolations rely on estimated beach lengths and average ARs, introducing uncertainty into the total items/day calculation.
• Observed increases in certain categories at some L beaches post-intervention (excluding Sicily outlier) could not be fully explained by the available data and may reflect local/regional differences or cleaning schedules.