Marine debris has become a major form of pollution and a serious ecosystem health concern. The present study evaluates the accumulation, origin, and fate of debris in intertidal coral habitats of Mumbai-one of the world's highly populated coastal cities on the west coast of India. Predominantly, seven hermatypic coral species belonging to seven genera and five families were identified and mainly represented by Pseudosidastrea, Porites, and Bernardpora. In terms of number, the mean density of marine debris was 1.60 ± 0.13 SE items/m², which is higher than the global average. The mean density of plastic debris was 1.46 ± 0.14 SE items/m². Approximately 9% of total coral colonies were in physical contact with debris, and 22% of these colonies showed visible signs of partial bleaching. Single use plastic bags and wrappers were dominant plastic debris. The study area was characterized as ‘very poor cleanliness’ according to the Beach Quality Indexes, which include the Clean Coast Index, General Index, and Hazardous Items Index. The numerical model indicates the influence of river discharge and probable areas of plastic accumulation with high tidal currents in this region, maneuvering the spatial advection of litter in the nearshore areas. Combined analysis of ground-truthing and model simulation implies that the possible contributing sources of litter were representatives of land-based and sea-originated. The overall results point to increasing anthropogenic stressors threatening coastal coral communities, including marine debris pollution. It is advocated to adopt an integrated coastal zone management approach supported by coordinated policy frameworks could guide the mitigation of the debris footprint in coastal environments.

The accumulation of human-derived debris in the oceans is a global concern and a serious threat to marine wildlife. There is a volume of evidence that points to deleterious effects of marine debris (MD) on cetaceans in terms of both entanglement and ingestion. This review suggests that about 68% of cetacean species are affected by interacting with MD with an increase in the number of species reported to have interacted with it over the past decades. Despite the growing body of evidence, there is an ongoing debate on the actual effects of plastics on cetaceans and, in particular, with reference to the ingestion of microplastics and their potential toxicological and pathogenic effects. Current knowledge suggests that the observed differences in the rate and nature of interactions with plastics are the result of substantial differences in species-specific diving and feeding strategies. Existing projections on the production, use and disposal of plastics suggest a further increase of marine plastic pollution. In this context, the contribution of the ongoing COVID-19 pandemic to marine plastic pollution appears to be substantial, with potentially serious consequences for marine life including cetaceans. Additionally, the COVID-19 pandemic offers an opportunity to investigate the direct links between industry, human behaviours and the effects of MD on cetaceans. This could help inform management, prevention efforts, describe knowledge gaps and guide advancements in research efforts. This review highlights the lack of assessments of population-level effects related to MD and suggests that these could be rather immediate for small populations already under pressure from other anthropogenic activities. Finally, we suggest that MD is not only a pollution, economic and social issue, but also a welfare concern for the species and populations involved.

Marine debris is now a ubiquitous component of the Anthropocene global ocean. Plastic ingestion by marine wildlife was first reported in the 1960s and since that time, roughly one thousand marine species have been reported to consume this debris. This study focuses on plastic ingestion by marine invertebrates and vertebrates in the North Pacific Ocean. Specifically, we reviewed the scientific literature to assess the scope of the problem, identified key bioindicator species, and proposed guidelines for future monitoring of plastic debris in North Pacific marine ecosystems. Our meta-analysis confirmed that the North Pacific is among the most polluted ocean regions globally; roughly half of all fish and seabird specimens and more than three-quarters of sea turtles and bivalve specimens examined in this region had consumed plastic. While there are not enough standardized data to assess if these ingestion rates are changing, sampling standardization and reporting of methods are improving over time. Using a rubric-evaluation approach, we evaluated 352 species for their potential to serve as bioindicators of the prevalence of plastic pollution in the North Pacific. This analysis revealed a suite of 12 bioindicator species candidates which sample a variety of ecosystem components and cover a wide range of plastic size classes. Thus, we contend that these bioindicator candidates provide a key foundation for developing a comprehensive plastic monitoring program in the region. To enhance the utility of these bioindicators, we developed a framework for standardized data collection to minimize methodological variability across different studies and to facilitate the assessment of temporal trends over space and time. Tracking plastic ingestion by these bioindicators will help to assess the effectiveness of mitigation actions in the region, a critical step to evaluate progress towards sustainability and improved ocean health in the 21st century.

Monitoring beach plastic contamination across space and time is necessary for understanding its sources and ecological effects, and for guiding mitigation. This is logistically and financially challenging, especially for microplastics. Citizen science represents an option for sampling accessible sites to support long term monitoring, but challenges persist around data validation. Here we test a simple citizen science methodology to monitor visible microplastic contamination on sandy beaches using a standard quadrat unit (50 cm × 50 cm x 5 cm depth) sieved to 1 mm, to support the analysis of microplastic on two islands within the marine protected area of the Galápagos Archipelago, Ecuador (San Cristóbal and Santa Cruz islands). High school and university students undertook supervised sampling of two beaches in 2019–2020 collecting over 7000 particles. A sub-sample of the suspected microplastics collected (n = 2,213, ∼30% total) were analysed using FTIR spectrometry, confirming 93% of particles >1 mm visually identified by students were microplastics or rubber, validating this method as a crowd-sourced indicator for microplastic contamination. These data provide important insights into the plastic contamination of Galápagos, revealing plastic abundances of 0–2524 particles m⁻² over the two beaches (the highest reported in Galápagos). Strong accumulation gradients were measured parallel to the waterline at Punta Pitt (San Cristobal island) and perpendicular to the waterline at Tortuga Bay (Santa Cruz island), where four-fold higher concentrations were recorded at the sea turtle nesting habitat on the back-beach dune. No significant seasonal trends were measured during one year. These results demonstrate the value of citizen science in filling spatiotemporal knowledge gaps of beach contamination to support intervention design and conservation.

Plastic pollution is one of several anthropogenic stressors putting pressure on ecosystems of the Caribbean Large Marine Ecosystem (CLME). A ‘Clean Ocean’ is one of the ambitious goals of the United Nations (UN) Decade of Ocean Science for Sustainable Development. If this is to be realized, it is imperative to build upon the work of the previous decades (1980–2020). The objectives of the present study were to assess the state of knowledge about: (i) the distribution, quantification, sources, transport and fate of marine debris/litter and microplastics in the coastal/marine environment of the CLME and, (ii) the effects of plastics on biodiversity. Snapshots, i.e., peer-reviewed studies and multi-year (1991–2020) marine debris data from International Coastal Cleanup (ICC) events, indicated that plastic debris was a persistent issue in multiple ecosystems and environmental compartments of the CLME. Collectively, a suite of approaches (debris categorization, remote sensing, particle tracking) indicated that plastic debris originated from a combination of land and marine-based sources, with the former more significant than the latter. Rivers were identified as an important means of transporting mismanaged land-based waste to the marine environment. Oceanic currents were important to the transport of plastic debris into, within and out of the region. Plastic debris posed a threat to the biodiversity of the CLME, with specific biological, physical, ecological and chemical effects being identified. Existing data can be used to inform interventions to mitigate the leakage of plastic waste to the marine environment. Given the persistent and transboundary nature of the issue, further elucidation of the problem, its causes and effects must be prioritized, while simultaneously harmonizing regional and international approaches.

While the increasing accumulation of anthropogenic litter in the marine environment has received considerable attention over the last decade, litter occurrence and distribution in rivers, the main source of marine litter, have been comparatively less investigated. Moreover, little information is available about the amount and typology of Riverine Anthropogenic Macro-litter (RAM) entering marine environments from intermittent rivers in low populated areas of the Mediterranean basin. To provide insights on this issue, we investigated density and composition of RAM accumulated over a total of 133 riverbanks, belonging to 37 river basins in the Sardinia Island (Mediterranean Sea). We report here that plastics, especially single-use items, represent the most frequent and abundant RAM category in all investigated basins. Statistical modelling revealed that occurrence of lightweight RAM (especially plastic) is mostly explained by levels of urban (12.3% of the relative contribution) and agricultural (12%) land use of the territory, whereas the proximity of bridges to the sampling point (21%) and the local population density (19.8%) are best predictors of heavy weighted RAM items (i.e., large metal items, appliances) occurrence. Our results confirm that plastics represent an important component of RAM and pinpoint that, beside plastic reduction policies and better waste management, actions aimed at abating and monitoring litter contamination should be localized on the proximity of bridges, whatever the local population density. Finally, to fill existing knowledge gaps in understanding the severity of litter discharge and accumulation in the Mediterranean Sea, land-to-sea systematic monitoring campaigns at appropriate spatial and temporal scales should be put in place.

Increased organized monitoring is key to improving our understanding of marine debris on shorelines. Shorelines are demonstrated sinks for marine debris but efforts to quantify debris often fail to capture and report core variables and survey design techniques necessary to ensure study repeatability, comparability and to provide meaningful results. Here, we systematically review the available literature regarding marine debris distribution and abundance on shorelines of countries bordering the North Pacific Ocean (NPO), which are demonstrated to have unusually high marine debris abundance and diversity both at the ocean surface and stranded on shorelines. The majority of the 81 papers documenting shoreline debris in the NPO were studies that took place for less than one year (76.5%). Additionally, most sampling sites were visited only once (57.3%). Precise site locations (GPS coordinates) were provided in only 44.4% of the evaluated studies. Debris quantities were reported using nine different measurement units, with item counts per area and item counts per mass being most commonly reported for macro- and microplastics, respectively. Taken together, most of the reviewed studies could not be repeated by others given the information provided. We propose a series of guidelines with regard to marine debris shoreline sampling metrics, indicators, methods, and target goals in the NPO in order to improve comparability and repeatability. These follow the basic tenets of environmental survey design, which when not accounted for, can limit the applicability and value of large-scale shoreline monitoring efforts.

Through a literature survey and meta-data analysis, monitoring methods and contamination levels of marine micro- and macroplastics in seawater were compared between the North Pacific and the world's other ocean basins. The minimum cut-off size in sampling and/or analysis of microplastics was crucial to the comparison of monitoring data. The North Pacific was most actively monitored for microplastics and showed comparatively high levels in the global context, while the Mediterranean Sea was most frequently monitored for macroplastics. Of the 65 extracted mean abundances of microplastics in seawater from the North Pacific, two (3.1%) exceeded the lowest predicted no-effect concentration (PNEC) proposed thus far. However, in the context of business-as-usual conditions, the PNEC exceedance probability may be expected to reach 27.7% in the North Pacific in 2100. The abundance of marine plastics in seawater, which reflects the current pollution status and marine organisms' waterborne exposure levels, is a useful indicator for marine plastic pollution. For regional and global assessments of pollution status across space and time, as well as assessment of ecological risk, two microplastic monitoring approaches are recommended along with their key aspects. Although microplastic pollution is closely linked with macroplastics, the monitoring data available for floating macroplastics and more extent to mesoplastics in most ocean basins are limited. A more specific framework for visual macroplastic survey (e.g. fixed minimum cut-off size, along with survey transect width and length according to survey vessel class) is required to facilitate data comparison. With the implementation of standardised methods, increased efforts are required to gather monitoring data for microplastics and—more importantly—floating macroplastics in seawater worldwide.

Plastic debris are accumulating in the marine environment and aggregate microorganisms that form a new ecosystem called the plastisphere. Better understanding the plastisphere is crucial as it has self-sufficient organization and carries pathogens or organisms that may be involved in the pollutant adsorption and/or plastic degradation. To date, the plastisphere is mainly described at the taxonomic level and the functioning of its microbial communities still remains poorly documented. In this work, metagenomic and metaproteomic analyzes were performed on the plastisphere of polypropylene and polyethylene plastic debris sampled on a pebble beach from the Mediterranean Sea. Our results confirmed that the plastisphere was organized as self-sufficient ecosystems containing highly active primary producers, heterotrophs and predators such as nematode. Interestingly, the chemical composition of the polymer did not impact the structure of the microbial communities but rather influenced the functions expressed. Despite the fact that the presence of hydrocarbon-degrading bacteria was observed in the metagenomes, polymer degradation metabolisms were not detected at the protein level. Finally, hydrocarbon degrader (i.e., Alcanivorax) and pathogenic bacteria (i.e., Vibrionaceae) were observed in the plastispheres but were not very active as no proteins involved in polymer degradation or pathogeny were detected. This work brings new insights into the functioning of the microbial plastisphere developed on plastic marine debris.

The Black Sea is a semi-enclosed basin subject to major anthropogenic pressures, including marine litter and plastic pollution. Due to numerous large rivers draining into the basin and a population settled along the coast, the region could accumulate significant amounts of floating litter over time. Until now, only limited field data were available, and litter quantities and distribution remained unknown. In this study, floating marine macro litter (FMML) was assessed at the regional Black Sea scale for the first time, showing relatively high litter densities across the basin that reached a weighted mean of 81.5 items/km². Monitoring data revealed an accumulation of floating items offshore in the eastern part of the basin, resembling on a small scale a ‘garbage patch’, where litter items were trapped, showing elevated densities in comparison to their surrounding areas. Most of these items were made of plastic materials (ca. 96%) and included large numbers of plastic and polystyrene fragments of small size ranges (2.5–10 cm). Harmonised field data collection through consistent and regular monitoring programmes across the region is essential to establish baselines and thresholds for large scale assessment at international level.