Ingestion of marine debris by Wedge-tailed Shearwaters (Ardenna pacifica) on Lord Howe Island, Australia during 2005-2018

A review of methods for modeling microplastic transport in the marine environments

Microplastic (MP) pollution is ubiquitous in the oceans and poses serious threats to the marine ecosystems. Nowadays numerical modeling has become one of the widely used tools for monitoring and predicting the transport and fate of MP in marine environments. Despite the growing body of research on numerical modeling of marine MP, the advantages and disadvantages of various modeling methods have not received systematic evaluation in published works. Important aspects such as parameterization schemes for MP behaviors, factors influencing MP transport, and proper configuration in beaching are essential for guiding researchers to choose proper methods in their work. For this purpose, we comprehensively reviewed the current knowledge on factors influencing MP transport, classified modeling approaches according to the governing equations, and summarized up-to-date parameterization schemes for MP behaviors. Critical factors such as vertical velocity, biofouling, degradation, fragmentation, beaching, and washing-off were reviewed in the frame of MP transport processes.

Assessing human and physical drivers of macro-plastic debris spatially across Queensland, Australia

Plastic pollution poses environmental and socio-economic risks, requiring policy and management interventions. The evidence-base for informing management and evaluation of their effectiveness is limited. Partnerships with citizen scientists provide opportunities to increase the spatio-temporal scale of monitoring programs, where training and standardised protocols provides opportunities for the use of data in addressing multiple hypotheses. Here, we provide a baseline of debris trends and infer debris drivers of abundance across 18° of latitude, using 168 surveys from 17 beaches across Queensland, Australia through the ReefClean project. Plastics were the dominant material (87% of total debris, with hard, soft and foam plastics aggregated), although linking recovered debris to sources was limited, as 67% of items were fragmented. We tested potential drivers of specific debris types (i.e., plastics, commercial fishing items, items dumped at-sea, and single-use items) and identified significant relationships between debris accumulation with distance from the nearest population centre and site characteristics (modal beach state, beach orientation and across-beach section). Management efforts should consider beach type and orientation within site selection, as an opportunity to maximise the amount recovered, alongside other criteria such as the risks posed by debris on environmental, economic, and social values. This study demonstrates the utility of citizen science to provide baselines and infer drivers of debris, through data gathered at scales that are infeasible to most formal monitoring programs. The identified drivers of debris may also differ from regional and global studies, where monitoring at relevant scales is needed for effective management.

Can the mass of plastic ingested by seabirds be predicted by the number of ingested items?

Plastics pollution has been documented for decades, yet repeatable methods for evaluating quantities are lacking. For wildlife, the mass and number of ingested plastics are widely reported, but these are not without their challenges, especially in field settings. Rapid methods for estimating the mass of ingested plastic could therefore be useful, but the relationship with the number of ingested pieces has not been explored. Using a dataset covering 1278 individuals of 11 Procellariiform species, we investigated this relationship to determine if counts could act as a proxy for the mass of ingested plastic by seabirds. Larger species ingested larger pieces of plastic, and birds that consumed more pieces also ingested items that are physically larger. Across species, sample size significantly influenced the slope of the relationship between the mass and number of ingested plastics. The mass-number relationship is species-specific, highly driven by sample size, and varies temporally.

New Methods for the Quantification of Ingested Nano- and Ultrafine Plastics in Seabirds

Plastic ingestion has been documented in a plethora of taxa. However, there is a significant gap in the detection of nano- and ultrafine particles due to size limitations of commonly used techniques. Using two Australian seabird species as case studies, the flesh-footed shearwater (FFSH) Ardenna carneipes and short-tailed shearwater (STSH) A. tenuirostris, we tested a novel approach of flow cytometry to quantify ingested particles <70 μm in the fecal precursor (guano; colon and cloacal contents) of both species. This method provided the first baseline data set for these species for plastics in the 200 nm-70 μm particle size ranges and detected a mean of 553.50 ± 91.21 and 350.70 ± 52.08 plastics (count/mg fecal precursor, wet mass) in STSH and FFSH, respectively, whereas Fourier transform infrared spectroscopy (FT-IR) provided accurate measurements of polymer compositions and quantities in the size range above 5.5 × 5.5 μm². The abundance of nano- and ultrafine particles in the guano (count/mg) was not significantly different between species (p-value = 0.051), suggesting that foraging distribution or prey items, but not species, may contribute to the consumption of small plastics. In addition, there was no correlation between macroplastics in the stomach compared to the fecal precursor, indicating that small particles are likely bioaccumulating (e.g., through shedding and digestive fragmentation) and/or being directly ingested. Combining flow cytometry with FT-IR provides a powerful quantitative and qualitative analysis tool for detecting particles orders of magnitude smaller than that are currently explored with wider applications across taxa and marine environments.

Continental patterns in marine debris revealed by a decade of citizen science

Anthropogenic marine debris is a persistent threat to oceans, imposing risks to ecosystems and the communities they support. Whilst an understanding of marine debris risks is steadily advancing, monitoring at spatial and temporal scales relevant to management remains limited. Citizen science projects address this shortcoming but are often critiqued on data accuracy and potential bias in sampling efforts. Here we present 10-years of Australia's largest marine debris database - the Australian Marine Debris Initiative (AMDI), in which we perform systematic data filtering, test for differences between collecting groups, and report patterns in marine debris. We defined five stages of data filtering to address issues in data quality and to limit inference to ocean-facing sandy beaches. Significant differences were observed in the average accumulation of items between filtered and remaining data. Further, differences in sampling were compared between collecting groups at the same site (e.g., government, NGOs, and schools), where no significant differences were observed. The filtering process removed 21% of events due to data quality issues and a further 42% of events to restrict analyses to ocean-facing sandy beaches. The remaining 7275 events across 852 sites allowed for an assessment of debris patterns at an unprecedented spatial and temporal resolution. Hard plastics were the most common material found on beaches both nationally and regionally, consisting of up to 75% of total debris. Nationally, land and sea-sourced items accounted for 48% and 7% of debris, respectively, with most debris found on the east coast of Australia. This study demonstrates the value of citizen science datasets with broad spatial and temporal coverage, and the importance of data filtering to improve data quality. The citizen science presented provides an understanding of debris patterns on Australia's ocean beaches and can serve as a foundation for future source reduction plans.

Birds of a feather eat plastic together: high levels of plastic ingestion in Great Shearwater adults and juveniles across their annual migratory cycle

Limited work to date has examined plastic ingestion in highly migratory seabirds like Great Shearwaters (Ardenna gravis) across the their entire migratory range, although this species is prone to ingest plastic as a wide-ranging procellariiform. We examined 217 Great Shearwaters obtained from 2008-2019 at multiple locations spanning their yearly migration cycle across the Northwest and South Atlantic to assess accumulation of ingested plastic as well as trends over time and between locations. A total of 2,328 plastic fragments were documented in the ventriculus portion of the gastrointestinal tract, with an average of 9 plastic fragments per bird. The mass, count, and frequency of plastic occurrence (FO) varied by location, with higher plastic burdens but lower FO in South Atlantic individuals from the breeding colonies. No fragments of the same size or morphology were found in the primary forage fish prey, the sand lance, (Ammodytes spp., n = 202) that supports Great Shearwaters in Massachusetts Bay, USA, suggesting the birds directly ingest the bulk of their plastic loads rather than accumulating via trophic transfer. Fourier-transform infrared spectroscopy indicated that low- and high-density polyethylene were the most common polymers ingested, within all years and locations. Individuals from the South Atlantic contained a higher proportion of larger plastic items and fragments compared to juveniles and non-breeding adults from the NW Atlantic, possibly due to increased use of remote, pelagic areas subject to reduced inputs of smaller, more diverse, and potentially less buoyant plastics found adjacent to coastal margins. Different signatures of polymer type, size, and category between similar life stages at different locations suggests rapid turnover of ingested plastics commensurate with migratory stage and location, though more empirical evidence is needed to ground-truth this hypothesis. This work is the first to comprehensively measure the accumulation of ingested plastics by Great Shearwaters over the last decade and across multiple locations spanning their yearly trans-equatorial migration cycle, and underscores their utility as sentinels of plastic pollution in Atlantic ecosystems.

Temporal trends and interannual variation in plastic ingestion by Flesh-footed Shearwaters (Ardenna carneipes) using different sampling strategies

The world's oceans are under increasing pressure from anthropogenic activities, including significant and rapidly increasing inputs of plastic pollution. Seabirds have long been considered sentinels of ocean health, providing data on physical and chemical pollutants in their marine habitats. However, long-term data that can elucidate important patterns and changes in seabird exposure to marine pollutants are relatively limited but are urgently needed to identify and support effective policy measures to reduce plastic waste. Using up to 12 years of data, we examined the benefits and challenges of different approaches to monitoring plastic in seabirds, and the relationship between plastic and body size parameters. We found the mass and number of ingested plastics per bird varied by sample type, with lavage and road-kill birds containing less plastic (9.17-9.33 pieces/bird) than beach-washed or otherwise dead birds (27.62-32.22 pieces/bird). Beached birds therefore provide data for only a particular subset of the population, mostly individuals in poorer body condition, including those severely impacted by plastics. In addition, the mass and number of plastics in beached birds were more variable, therefore the sample sizes required to detect a change in plastic over time were significantly larger than for lavaged birds. The use of lavaged birds is rare in studies of plastic ingestion due to ethical and methodological implications, and we recommend future work on ingested plastics should focus on sampling this group to ensure data are more representative of a population's overall exposure to plastics.

Plastics in regurgitated Flesh-footed Shearwater (Ardenna carneipes) boluses as a monitoring tool

Plastic production and pollution of the environment with plastic items is rising rapidly and outpacing current mitigation measures. Success of mitigation actions can only be determined if progress can be measured reliably through incorporation of specific, measurable targets. Here we evaluate temporal changes in the amount and composition of plastic in boluses from Flesh-footed Shearwaters during 2002-2020 and assess their suitability for measuring progress against national and international commitments to reduce plastic pollution. Plastic in the shearwater boluses showed a generally decreasing pattern from 2002 to 2015 and increasing again to 2020. The colour and type of plastics in boluses was comparable to items recovered from live and necropsied birds, but a much smaller sample size (~35 boluses/year) was required to detect changes in plastic number and mass over time. We therefore suggest shearwater boluses are a low-effort, high-statistical power monitoring tool for quantifying progress against environmental policies in Australia.

Latex balloons do not degrade uniformly in freshwater, marine and composting environments

Latex balloons are a poorly-studied aspect of anthropogenic pollution that affects wildlife survival, aesthetic value of waterways, and may adsorb and leach chemicals. Pure latex needs to be vulcanised with sulphur and requires many additional compounds to manufacture high quality balloons. Yet, balloons are often marketed as "biodegradable", which is confusing to consumers. Due to the persistence of latex balloons in the environment and the lethal, documented threat to wildlife, degradation behaviours of latex balloons were quantified in freshwater, saltwater and industrial compost. Using the metrics mass change, ultimate tensile strength (UTS) and superficial composition via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), latex balloon degradation was documented for 16 weeks. Overall, latex balloons retained their original shape and size. Composted balloons lost 1-2% mass, but some balloons in freshwater gained mass, likely due to osmotic processes. Balloons' UTS decreased from 30.7 ± 10.8-9.5 ± 4.1 Newtons in water, but remained constant (34.3 ± 13.4 N) in compost. ATR-FTIR spectra illustrated compositional and temporal differences between treatments. Taken together, latex balloons did not meaningfully degrade in freshwater, saltwater, or compost indicating that when released into the environment, they will continue to contribute to anthropogenic litter and pose a threat to wildlife that ingest them.

A critical review of harm associated with plastic ingestion on vertebrates

Studies documenting plastic ingestion in animals have increased in recent years. Many do not describe the less conspicuous, sub-lethal impacts of plastic ingestion, such as reduced body condition or physiological changes. This means the severity of this global problem may have been underestimated. We conducted a critical review on the sub-lethal impacts of plastic ingestion on marine vertebrates (excluding fish). We found 34 papers which tried to measure plastics' impact using a variety of tools, and less than half of these detected any impact. The most common tools used were visual observations and body condition indices. Tools that explore animal physiology, such as histopathology, are a promising future approach to uncover the sub-lethal impacts of plastic ingestion in vertebrates. We encourage exploring impacts on species beyond the marine environment, using multiple tools or approaches, and continued research to discern the hidden impacts of plastic on global wildlife.

Seasonal ingestion of anthropogenic debris in an urban population of gulls

Gulls are generalist seabirds, increasingly drawn to urban environments where many species take advantage of abundant food sources, such as landfill sites. Despite this, data on items ingested at these locations, including human refuse, is limited. Here we investigate ingestion of prey and anthropogenic debris items in boluses (regurgitated pellets) from Pacific Gulls (Larus pacificus). A total of 374 boluses were collected between 2018 and 2020 in Tasmania. Debris was present in 92.51% of boluses (n = 346), with plastic (86.63%, n = 324) and glass (64.71%, n = 242) being the most prominent types. An abundance of intact, household items (e.g., dental floss, food wrappers) suggest the gulls regularly feed at landfill sites. In addition, the boluses are deposited at a roosting site located within an important wetland, thus we propose that the gulls may be functioning as a previously unrecognised vector of anthropogenic debris from urban centres to aquatic environments.

Ingested plastic and trace element concentrations in Short-tailed Shearwaters (Ardenna tenuirostris)

Pollution of marine environments is concerning for complex trophic systems. Two anthropogenic stresses associated with marine pollution are the introduction of marine plastic and their associated chemicals (e.g., trace elements) which, when ingested, may cause harm to wildlife. Here we explore the relationship between plastic ingestion and trace element burden in the breast muscle of Short-tailed Shearwaters (Ardenna tenuirostris). We found no relationship between the amount of plastic ingested and trace element concentration in the birds' tissues. Though the mass and number of plastic items ingested by birds during 1969-2017 did not change significantly, trace element concentrations of some elements (Cu, Zn, As, Rb, Sr and Cd), appeared to have increased in birds sampled in 2017 compared to limited data from prior studies. We encourage policy which considers the data gleaned from this sentinel species to monitor the anthropogenic alteration of the marine environment.

Albatrosses and petrels at South Georgia as sentinels of marine debris input from vessels in the southwest Atlantic Ocean

Increasing amounts of anthropogenic debris enter the ocean because of mismanagement in coastal communities and, despite a global ban on deliberate dumping, also from vessels, endangering wildlife. Assessing marine plastic pollution directly is challenging, and an alternative is to use seabirds as bioindicators. Our analyses of long time-series (26-years) revealed substantial variation in the amount, characteristics and origin of marine debris (mainly macroplastics and mesoplastics, and excluding fishing gear) associated with seabirds at South Georgia, and, for two species, long-term increases in incidence since 1994. Annual debris recovery rates (items per capita) were 14 × higher in wandering albatrosses Diomedea exulans, and 6 × higher in grey-headed albatrosses Thalassarche chrysostoma and giant petrels Macronectes spp., than in black-browed albatrosses T. melanophris, partly related to differences in egestion (regurgitation), which clears items from the proventriculus. Although some debris types were common in all species, wandering albatrosses and giant petrels ingested higher proportions that were food-related or generic wrapping, gloves, clear or mixed colour, and packaged in South America. This was highly likely to originate from vessels, including the large South American fishing fleets with which they overlap. Debris associated with the two smaller albatrosses was more commonly shorter, rigid (miscellaneous plastic and bottle/tube caps), and packaged in East Asia. Grey-headed albatrosses are exposed to large and increasing amounts of user plastics transported from coastal South America in the Subantarctic Current, or discarded from vessels and circulating in the South Atlantic Gyre, whereas the lower debris ingestion by black-browed albatrosses suggests that plastic pollution in Antarctic waters remains relatively low. Current plastic loads in our study species seem unlikely to have an impact at the population level, but the results nevertheless affirm that marine plastics are a major, trans-boundary animal-welfare and environmental issue that needs to be addressed by much-improved waste-management practices and compliance-monitoring both on land and on vessels in the south Atlantic.

Plastic ingestion by seabirds in New Caledonia, South Pacific

The accumulation of plastic pollutants in marine environments has many adverse effects on wildlife. In particular, marine predators are often exposed to accidental plastic ingestion, that may negatively affect survival due to the concentration of debris in the digestive tract. Among the species most vulnerable to plastic ingestion, seabirds are of major interest for conservation because of their wide foraging areas, long generation time and extended lifespan. We analysed stomach contents of 90 seabird specimens from 12 different species collected in New Caledonia to assess the local prevalence of plastic ingestion. Overall, we found plastic debris in 14.4% of sampled individuals, exclusively in procellariids: Gould's Petrel (41.2%, highest incidence), Tahiti Petrel (33.3%) and Wedge-tailed Shearwater (7.7%). To our knowledge, this study is the first characterization of plastic ingestion in seabirds from New Caledonia and our results show an overall lower ingestion prevalence compared to other assessments in the tropical Pacific.

Mobilization and bioaccessibility of cadmium in coastal sediment contaminated by microplastics

Cadmium has had a number of historical applications in plastics but is now highly regulated. In this study, plastics containing pigmented or recycled Cd at concentrations up to 16,300 μg g^-1 were processed into microplastic-sized fragments and added to clean estuarine sediment. Plastic-sediment mixtures (mass ratio = 1:100) were subsequently exposed to fluids simulating the digestive conditions encountered in marine deposit-feeding invertebrates prepared from a protein and a bile acid surfactant in seawater and the mobilization of Cd measured as a function of time. Kinetic profiles over a six-hour period were complex, with some fitted using a diffusion model and others exhibiting evidence of Cd interactions between the plastic and sediment surface. The maximum concentration of Cd released from plastic-sediment mixtures was about 0.8 μg g^-1 and orders of magnitude greater than Cd mobilization from sediment alone. It is predicted that large communities of deposit-feeders could mobilize significant quantities of Cd from historical microplastics.

Clinical Pathology of Plastic Ingestion in Marine Birds and Relationships with Blood Chemistry

Pollution of the environment with plastic debris is a significant and rapidly expanding threat to biodiversity due to its abundance, durability, and persistence. Current knowledge of the negative effects of debris on wildlife is largely based on consequences that are readily observed, such as entanglement or starvation. Many interactions with debris, however, result in less visible and poorly documented sublethal effects, and as a consequence, the true impact of plastic is underestimated. We investigated the sublethal effects of ingested plastic in Flesh-footed Shearwaters (Ardenna carneipes) using blood chemistry parameters as a measure of bird health. The presence of plastic had a significant negative effect on bird morphometrics and blood calcium levels and a positive relationship with the concentration of uric acid, cholesterol, and amylase. That we found blood chemistry parameters being related to plastic pollution is one of the few examples to date of the sublethal effects of marine debris and highlights that superficially healthy individuals may still experience the negative consequences of ingesting plastic debris. Moving beyond crude measures, such as reduced body mass, to physiological parameters will provide much needed insight into the nuanced and less visible effects of plastic.

Is plastic ingestion in birds as toxic as we think? Insights from a plastic feeding experiment

Plastic pollution is a modern tragedy of the commons, with hundreds of species affected by society's waste. Birds in particular mistake plastic for prey, and millions of wild birds carry small plastic loads in their stomach and are exposed to potential toxicological effects. It is currently unknown how severely the toxicological and endocrine disrupting chemicals in plastic affect avian development, reproduction and endocrine function. To address this question, we conducted multi-generational plastic feeding experiments to test the toxicological consequences of plastic ingestion at environmentally relevant loads in Japanese quail, Coturnix japonica, investigating parental and two filial generations. Contrary to expectations, we found no evidence of lasting toxicological effects on mortality, adult body weight, organ histology, hormone levels, fertility, hatch rates and eggshell strength in birds experimentally fed plastic. However, we found plastic ingestion causes higher frequencies of male reproductive cysts and minor delays in chick growth and sexual maturity, though without affecting ultimate survival or reproductive output. We report that although plastic ingestion causes detectable endocrine effects in our model species, our lack of finding mortality, morbidity and adverse reproductive outcomes may challenge the common hypothesis of severe toxicological harm and population-level effects when environmentally relevant loads of plastic are ingested.

Plastic ingestion in seabirds of the western Indian Ocean

We investigated seabird plastic ingestion in the western Indian Ocean by analyzing the stomach contents of 222 individuals belonging to nine seabird species (including two endangered species endemics to Reunion Island). The most affected species were tropical shearwaters (79%) and Barau's petrels (59%). The average number of plastic particles per contaminated bird was higher in Barau's petrels (6.10 ± 1.29) than in tropical shearwaters (3.84 ± 0.59). All other studied species also showed plastic presence in their stomach contents. The mass of plastic particles was significantly higher both in juvenile's Barau's petrels and tropical shearwaters than in adults. These results demonstrate the foraging areas of seabirds of the western Indian Ocean have a high level of plastic pollution. In Reunion Island, hundreds of tropical shearwaters and Barau's petrels are attracted by urban lights and die each year. We suggest taking advantage of this situation by using these species as long-term indicators of plastic marine pollution in the region.

Seabird plastic ingestion differs among collection methods: Examples from the short-tailed shearwater

Despite the increase of literature on seabird plastic ingestion in recent years, few studies have assessed how plastic loads vary according to different sampling methods. Most studies use necropsies of seabirds with a natural cause of death, e.g. beached or predated, to determine plastic loads and monitor marine debris. Sampling naturally dead seabirds may be biased as they have perished because of their intrinsic factors, e.g. poor body condition, high parasite loads, sickness or predation, affecting estimates of plastic loads. However, seabirds killed accidentally may be more representative of the population. Here, we used the short-tailed shearwater Ardenna tenuirostris to test different sampling methods: naturally beached fledglings and accidentally road-killed fledglings after being attracted and grounded by artificial lights. We compared plastic load, body condition, and feeding strategies (through using feathers' δ¹³C and δ¹⁵N isotope niche) between beached and road-killed fledglings. Beached birds showed higher plastic loads, poorer body condition and reduced isotopic variability, suggesting that this group is not a representative subsample of the whole cohort of the fledgling population. Our results might have implications for long-term monitoring programs of seabird plastic ingestion. Monitoring plastic debris through beached birds could overestimate plastic ingestion by the entire population. We encourage the establishment of refined monitoring programs using fledglings grounded by light pollution if available. These samples focus on known cohorts from the same population. The fledgling plastic loads are transferred from parents during parental feeding, accumulating during the chick-rearing period. Thus, these fledglings provide a higher and valuable temporal resolution, which is more useful and informative than unknown life history of beached birds.