How climate change could make the problems of plastic waste worse.

Both anthropogenic climate change and plastic waste are considered to be significant threats to the global environment, which have arisen largely since the beginning of the twentieth century, and which are driven by the consumption of fossil fuels. Rising global temperatures are already having a profound affect on life across the globe, leading to  intense droughts, wildfires, rising sea levels, melting polar ice and catastrophic storms that are causing widespread ecological and socioeconomic harm and impacting Human health. The plastics industry generates large amounts of highly persistent waste, which is accumulating in both managed and natural environments, and which place significant stresses on both ecosystems and individual organisms. These have generally been treated as separate problems, but are clearly linked in many ways, sharing a common origin and because the negative outputs they generate are likely to amplify one-another, and because the magnitude of problems they cause has the potential to push the Earth over the boundaries described in the Planetary Boundaries Framework.

The evolution of the planetary boundaries framework. Stockholm Resilience Centre.

Previous research on the relationship between plastics and climate change has largely concentrated on how plastics contribute to climate change. More than 98% of plastics are made from fossil hydrocarbons, and the plastics industry represents about 12% of global oil consumption. Every stage of the plastics cycle causes emissions of greenhouse gasses, from the extraction of oil and transportation process, through the manufacturing process, to the production of breakdown products from discarded plastics. About 90% of the greenhouse gas emissions associated with plastics come from the production phases (which include the extraction and 'cracking' of oil), with about 10% coming from the end of life processes (70% of this from the incineration of plastics, the remainder from its breakdown in landfill sites and the environment). The plastics industry is thought to be responsible for about 3.7% of greenhouse gas emissions, more than many countries.

Polyethylene is the biggest emitter of greenhouse gasses, producing methane and ethylene as it weathers and breaks down. Unfortunately, it is also the most widely produced and discarded synthetic polymer.

A limited amount of research has been carried out into the climatic impact of airborne microplastic particles. This can be complicated for particulate matter; particles such as rock dust and sulphates are known to have a localised cooling effect, whereas black carbon particles contribute to atmospheric warming. So far, it appears that small fragments and fibres of undyed plastics at a concentration of about one particle per cubic metre have a slight cooling effect, but these are very preliminary results, and may vary at other geographical locations, or when the particles are at different altitudes in the atmosphere, as well as the addition of pigments or other additives to the plastic. Since microplastic particles are present at levels of hundreds or even thousands of particles per square metre in the atmosphere in some urban environments, airborne microplastics may already be influencing the local climate in some areas. 

How a warming climate is likely to impact plastic waste is less clear, although some research is starting to be done in this area. In a paper published in the journal Frontiers in Science on 27 November 2025, Frank Kelly and Stephanie Wright of the Environmental Research Group at the Medical Research Council, Guy Woodward of the Georgina Mace Centre for the Living Planet at Imperial College London, and Julia Fussell, also of the Environmental Research Group at the Medical Research Council, present a review of research ti date on how a warming climate is likely to impact plastic waste.

Comparison of global mean temperature (orange), carbon dioxide emissions (blue) and plastic production (turquoise). Kelly et al. (2025).

Plastics are complex heterogeneous synthetic materials built around carbon polymer backbones. These typically comprise large numbers of a carbon monomer molecule stitched together with covalent bonds, and often with the addition of other elements, which give them colour, flexibility, stability, water repellence, flame retardation, and ultraviolet resistance. Many of these additives are highly toxic, often being carcinogens, neurotoxicants and endocrine disruptors. However, plastics are remarkably versatile substances, being strong, light, easily mouldable, resistant to water, and, above all, cheap, making them potentially the most widely used materials in the modern world. Plastics can be substituted for a wide range of other materials, including glass, wood, metals, and a variety of natural fibres, which has enabled significant technical advances in areas such as  construction, vehicle parts, electronics, aerospace, and medicine. Consequently, plastics have become a ubiquitous part of modern lives, and an essential component of both our technology and our economy. Notably, the lightweight nature of plastics and their usefulness in making air tight packaging which prevents the spoiling of foods and medicines, have made them an important part of our efforts to reduce greenhouse gas emissions. 

Total global annual production of plastics in 1950 was below two million tons. By 2023, the world was producing more than 400 million tons of plastic each year. More than half of the plastics ever produced have been manufactured since 2002. About 35% of plastics produced are single use, with single use plastics being the most rapidly growing portion of the plastics manufacturing sector. Part of the reason so much plastic is produced is because plastic is not a single substance, but a group of highly versatile artificial polymers. The most commonly produced plastic is polypropylene, but this only accounts for about 16% of the total, with fibres such as polyester and nylon forming another 13%, high density polythene 12%, low density polythene another 12%. Global plastic production is predicted to triple by 2060, with annual production reaching 1231 million tons per year.

Methods of disposing of plastic include controlled and uncontrolled landfill sites, burning, thermal conversion into new plastics, fuels, or lubricants, and, in the case of high-income countries, exporting it to lower income countries. A 'reduce, reuse, recycle' approach to waste management has proven highly effective for substances such as aluminium, glass, and paper, where respective recycling rates of 76%, 68%, and 32% have been achieved. The recycling of aluminium and glass results in no loss of quality, meaning that these materials can effectively be recycled indefinitely, while paper can be recycled 5-7 times. In all these cases, recycling requires less energy than new production. Plastics, however, are difficult to recycle, they tend to degrade in quality rapidly, and recycling processes tend to require more energy than simply making new plastics. This has resulted in plastic recycling rates as low as 9%, with about 22 million tons of waste plastic being produced annually, much of it single-use plastic. Furthermore, plastics tend to accumulate within the environment, with about 6 billion tons of plastic waste thought to have built up within the global environment since 1950. This environmental waste is broken down over time into progressively smaller particles, which become more mobile and potentially more biologically harmful. 

Plastic waste at the Thilafushi Waste Disposal site in the Maldives. Mohamed Abdulraheem/The World Bank.

Plastic pollution can arise from litter deposited into urban and natural environments, much of which could potentially be recycled if it could be removed quickly, or not dropped in the first place. Similarly, much of the plastic entering landfill sites has at least a theoretical potential to be recycled. Even where recycling does not occur, landfill sites vary in the quality of their management, and plastic waste has less chance of entering the environment if it is buried at depth and sites are sealed properly after use. However, once plastic has entered the environment and begun to degrade, it becomes much more problematic, breaking down into ever smaller particles which are increasingly hard to remove, and which have increasing potential to cause harm.

Plastics can be weathered by both biotic and abiotic chemical processes, both of which accelerate at higher temperatures, as well as mechanical degradation, which increases during extreme weather events such as storms. Plastic waste has the potential to remain in the environment for long periods of time, with its persistence determined by factors such as the chemistry of the base polymer, the size of the particles, and the presence of stabilisers, as well as the local environmental conditions. Physical weathering of plastics typically results in cracking and flaking, resulting in smaller pieces with larger relative surface areas. Chemical weathering tends to break the long polymer chains of the plastic by hydrolysis or oxidation, resulting in the formation of shorter polymers with more polar functional groups, such as carboxyls and carbonyls, leading to decreased resilience to water penetration. Thus each weathering process increases the vulnerability of the plastic to further weathering. These processes not only produce products from the breakdown of the base polymer, but also release any additives used during the chemical manufacturing process. 

Many plastic products begin to fragment while still in use, particularly fibre products used in clothing, and car tyres. Recycling processes typically involve mechanical breaking up of the plastic waste, which can lead to fragments escaping into the environment, as can the degradation of plastics within landfill sites. These processes produce microplastics, particles smaller than 5 mm, which over time degrade into nanoplastics, particles smaller than 1 μm. In addition, there are primary micro- and nanoplastics, which are intentionally manufactured at these scales. These small particles are notoriously hard to remove from the environment, and often form mixed assemblages, comprising particles with many different morphologies and compositions. These particles are often invisible to the Human eye, but can be harmful to a range of organisms, and are a significant pollutant in many environments. 

About 2.7 million tons of microplastics are thought to enter the environment every year. This derives from a range of sources, including road transportation, about 700 000 tons per year from tyre fragments,100 000 tons per year from break pads, and 200 000 per year from wear to road markings, about 800 000 tons of dust from the abrasion of shoe soles, paint wear, construction and demolition activities, and household textiles, and a further 800 000 derived from wastewater sludge, including particles from products such as cosmetic exfoliants and liquid detergents. The small size of such particles makes it very easy for them to become mobilised within the environment, and easily carried for long distances by rivers, ocean currents, winds, and even sea spray.

Plastic beads on a beach in Aquitaine, France, in March 2011. Wikimedia Commons.

The variable nature of microplasics makes it hard to understand their environmental impact. It is known that their small size makes it easy for many organisms to ingest, and that having entered the food chain they can leach a range of toxins, such as monomers, plasticisers, flame retardants, and UV stabilisers. However, to what extent these are bioavailable in the environment is unclear, as most laboratory studies are based upon laboratory-grade pristine, homogeneous particles, quite unlike the waste-derived particles found in the environment.

Studies in the environment have shown that microplastics can alter soil composition and plant ecology, and that animals which ingest microplastics can suffer physical injuries, compromised immune responses, impaired physiologies, stunted growth, and trouble feeding and reproducing.

As with climate change, there are concerns that the impacts of plastic pollution will persist for a long time, even should the cause of the problem be eliminated. This is particularly concerning as we do not really yet know what the long term results of plastic pollution are likely to be, nor how they are likely to interact with the effects of global warming.

The presence of large amounts of plastic in the environment creates a 'global toxicity debt', as plastic becomes more toxic over time as it fragments and chemically degrades, likely producing health and environmental outcomes which we do not yet foresee. 

Workers at a plastic recycling plant near Bangkok, Thailand. Diego Azubel/EPA.

Like climate change is a global environmental problem present across all environmental systems. Its effects experienced as both incremental change (i.e. rising global temperatures, ocean acidification) and pulsed effects, such as wildfires, droughts, floods, and storms. There is significant opportunity for interactions between plastic pollution and climate change, not just because of the greenhouse gasses generated by the plastics industry, but because global warming will inevitably influence the way in which plastics in the environment break down, and how the breakdown chemicals produced will interact with biological systems.

Climate change is leading not just to increased temperatures, but also increased atmospheric moisture, and higher levels of ultraviolet radiation reaching the Earth's surface. All of which are known to accelerate the degradation of plastic polymers, leading to a faster breakdown of plastics, and the creation of more microplastics. A 10°C increase in temperatures is known to double the rate at which most plastics break down, even without the added effects of moisture and ultraviolet radiation. 

Droughts and heatwaves are predicted to become much more frequent and longer lasting with rising global temperatures, and are also likely to increase the release of toxic compounds from plastic waste. This is likely to be more severe in urban areas, where plastic waste tends to be concentrated. Urban centres are also often located on floodplains, increasing the opportunity for plastic waste and toxic breakdown products to enter rivers and thence the ocean.

Storms and floods can dramatically increase the rate at which plastics and plastic-derived pollutants are redistributed, generally into the oceans and aquatic ecosystems. They also increase the rate at which plastic waste is broken into smaller particles by mechanical wear. More extreme storm events have a greater capacity to do all these things, and are becoming more common as a result of global warming. For example, beach sediments in Hong Kong have been shown to suffer almost fortyfold increases in their plastic concentrations after typhoons. 

Plastics on a beach in Hong Kong. Ocean Recovery Alliance.

Flood events also have the ability to remobilise plastics trapped in coastal sediments, as potentially does long term sealevel rise. The majority of used plastics end up in landfill sites and open dumps, where there is also potential for them to be re-exposed by extreme floods or storm events, particularly as site sites tend to be located in low value, low lying areas, close to urban centres (often areas which have probably been spared urban development because they are vulnerable to floods or other problems). It has been estimated in the UK that the failure of one landfill waste cell could release up to 3860 tons of plastic waste into the Themes Estuary. 

Global warming is also predicted to lead to consistently stronger ocean winds, as well as profound changes in marine currents, altering the way in which microplastic particles are moved within the oceans. Higher winds lead to greater wave action, increasing the mixing of plastics within the water column, and increasing the likelihood of buried plastics in coastal sediments being remobilised. 

Sea ice is known to scavenge plastics from the ocean, creating a significant marine plastic sink. With the loss of sea ice due to global warming, it is likely that these environments will become net producers of plastic waste, as previously frozen waste is released, although the potential scale of this is far from clear.

The likely impacts of an increased amount of plastics in the oceans is unclear, but there is a clear potential for this to interfere with biological and ecological processes. Should this include in any way inhibiting the ability of marine phytoplankton to lock away atmospheric carbon through photosynthesis, then it could seriously hamper efforts to bring global warming under control. Worryingly, there is already evidence that leachates from plastic waste can impair photosynthesis by some marine micoalgae. Plastic waste in the oceans can also potentially interfere with carbon cycling in other ways, such as interacting with microbes in the lipid-rich uppermost layer of the sea in ways which reduce the ability of the sea to absorb carbon dioxide from the atmosphere, or by making Fish faecal pellets more buoyant, thereby reducing the rate at which carbon is moved from the surface waters into the ocean depths. Since all of these effects are dependent on the concentration of plastics in the water, it is likely that these problems will get worse, or manifest in different and unexpected ways, in the future.

Plastic waste within the ocean. Flora & Fauna International (2022).

Global warming has the potential to place a great deal of stress on living organisms, potentially in a lot of ways in which we do not understand. A considerable amount of research has been done on the potential impacts of higher temperatures on individual organisms, and one trend which has consistently emerged from this is that larger organisms, and those which live in aquatic ecosystems are particularly vulnerable to rising temperatures. Unfortunately, these are also the organisms thought to be most at risk from the hazards associated with plastic waste.

How the effects of global warming and plastic pollution will interact are not well understood. The outcomes of interactions between different phenomena are seldom as simple as adding the outcomes of each on their own together. Global warming is likely to effect the way in which plastics weather, bioaccumulate, leach breakdown products, and move through the environment. 

Both heat stress and the presence of microplastics are known to inhibit nitrogen cycling and therefore impact crop yields. The heatwaves combined with the presence of microplastics in the soil have been shown to reduce both the quantity and quality of rice yields, while rice plants have also been shown to lose their ability to absorb nitrogen when raised carbon dioxide levels were combined with the presence of microplastics. The presence of microplastics in soils has also been shown to reduce the ability of a variety of Fungal strains to produce water-stable aggregates at higher temperatures, thus inhibiting growth under conditions which would otherwise lead to growth acceleration. Microplastics have also been shown to affect the health of Maize plants, although increasing the temperature did not seem to increase this. The presence of microplastics appear to influence the ability of temperate grasslands to cope with droughts, nor the above ground biomass of Onions.

Freshwater ecosystems are thought to be particularly vulnerable to the combined impact of plastic pollution and global warming. Both warmer temperatures and leachates from tyres have been demonstrated to enhance the growth of Duckweeds, Lemnoidea, and their associated microbes, both on their own and in combination. However, at the same time they disrupt the mutualistic relationship between these organisms. The presence of nanoplastics has been shown to inhibit the growth of the common freshwater Algae Scenedesmus obliquus, with this becoming worse at higher temperatures and carbon dioxide concentrations. Conversely, the marine diatom, Phaeodactylum tricornutum, shows enhanced growth and nitrogen uptake when exposed to both increased temperatures and microplastic pollution.

The effect of microplastics on zooplankton were more distinct, with the combination of increased heat and plastic pollution proving toxic to Water Flees, Daphnia magna, and other studies showing that this combination had an adverse impact on Midge larvae and Freshwater Mussels. Since the negative impacts of both microplastics and raised temperatures are known to be more harmful to larger organisms, it is predicted that these negative impacts will increase further up the food chain. The Nile Tilapia, Oreochromis niloticus, has been shown both to ingest more microplastics at higher temperatures, and to be more adversely impacted by their toxicity.

Marine ecosystems resemble freshwater ecosystems in many ways, but also have some important differences, largely due to the size of the oceans. This size means that the oceans have far greater thermal inertia than any freshwater system (i.e. it takes a lot more energy to warm the oceans), and that both nutrients, and pollutants become much more diluted. Marine environments also tend to have much longer food chains, with the largest organisms being much larger. Oceans also have major current systems unlike anything present in freshwater systems, and contain a much wider range of ecosystems, from the highly productive biodiverse shallow marine environments such as Coral reefs to the 'marine deserts' of the deep ocean floors.

Again, the combination of increased heat and microplastic pollution appears to be harmful to many marine organisms, particularly those towards the top of the food chain, although this is not a simple or predictable relationship, with closely related and apparently similar species often reacting quite differently to these stressors. For example, some species of Coral found it harder to eject ingested microplastics under warmer conditions, particularly following bleaching events (the loss of symbiotic Algae), but other species seemed unaffected. Some species of Sea Anemones appeared to suffer similar a similar inability to eject ingested plastics at higher temperatures, but again not all. Populations of marine Fish living around Coral reefs have been shown to suffer population declines in response to both bleaching events and the presence of microplastics, but do not appear to be affected more adversely when these are combined.

In cooler waters, Pteropod Sea Snails have been shown to be more vulnerable to the effects of ocean acidification when microplastics are present. Sea Urchins exposed to warmer conditions and more acidic seawater were more prone to buildups of microplastics within their bodies, leading in turn to suppressed growth. 

Mussels are reef building Bivalves found in estuaries and nearshore environments in temperate seas. They are extremely efficient at filtering particulate matter from the water column, making them significant environmental regulators in these environments. The combination of microplastics and ocean acidification has been shown to inhibit the production of digestive enzymes by Mussels, leading to their digestive tracts becoming clogged, slowing their metabolic rates, and suppressing their immune systems.

Gobies have been shown to suffer mortality events when exposed to microplastics, with increasing heat making this worse. A 5°C increase in temperature has been shown to quadruple the rate at which Gobies died when exposed to microplasrics. Predatory Cod, which typically feed on small Fish such as Gobies, reacted to reduced marine oxygen levels (an outcome of warming, as warmer water is not able to retain as much dissolved oxygen) by switching to feeding on benthic invertebrates, which in turn lead to the amounts of microplastics in their guts more than doubling, showing that plastics were being passed up the food chain, and biomagnification (increasing concentrations of a substance at higher trophic levels) was occurring. 

Thus estuarine and marine ecosystems, which play a significant role in the cycling of carbon, nitrogen, phosphorus, and other key nutrients, can be severely disrupted by the presence of plastic pollution. The presence of plastics has also been shown to slow the decomposition of coastal Kelp and Eelgrass detritus, although this effect disappeared at higher temperatures.

Plastic waste on a beach in the Thames Estuary in Kent, England. Getty Images/BBC.

While research to date on the interaction potential interactions between plastic waste and global warming has been limited, it is clear that in at least some ecosystems, and for at least some organisms, the two have the potential to exacerbate one-another. This appears to be particularly true for larger, long-lived organisms at the top of aquatic food chains, which are vulnerable to the bioconcentration, bioaccumulation, and biomagnification of toxins, as well as extreme weather events caused by global warming. 

Feeding in aquatic environments is often determined by the gape-size of organisms, but this evolutionary advantage places organisms at greater risk of ingesting micro- and nanoplastics. Filter feeding organisms such as Bivalves are good at concentrating toxins, and then passing them up the food chain. Furthermore, Bivalves, like top predators, tend to be ecosystem engineers, which shape their habitats, and therefore the way other species interact with one-another, even if those species do not directly interact with Bivalves. This means that threats to Bivalves have the potential to affect marine ecosystems in unpredictable ways. At the other end of the food chain, the largest marine predators, such as Whales and Sharks, which may be the most vulnerable organisms on the planet to the combination of global warming and plastic pollution, are wide ranging animals, interacting with many different marine environments, with the upshot that their loss could have consequences in many different and apparently unrelated ecosystems.

The effects of plastic pollution and global warming on the microbial activity that drives most ecosystems is less clear. On the whole, warmer temperatures tend to increase the metabolic and growth rates of microbial organisms, whereas chemicals leached from plastics have the potential to suppress them. This could lead to a masking effect, whereby no change is perceived.

The majority of studies into the potential effects of plastic pollution carried out to date have concentrated on aquatic ecosystems, as these were where the problem was first identified. Plastic waste has often undergone significant breaking down by the time it reaches these environments, increasing the speed with which plastic-derived toxins enter the food chain. However, plastics originate in terrestrial environments, and over time are both accumulating and breaking down into smaller particles on land, where the potential long term consequences of their presence are still less well understood.

Because terrestrial ecosystems are typically more complex than aquatic ones, the long-term outcomes of the both climate change and plastic pollution are far harder to predict, particularly in modified environments such as urban centres and agricultural land.

Plastic at a waste dump in Malaysia. Greenpeace (2021).

Anthropogenic global warming and plastic pollution are potentially the largest of the many stressors to which Humans are currently subjecting the natural environment. Because these phenomena have the ability to interact and in some cases amplify one-another, their potential impacts on both geophysical and biological systems probably go far beyond those we have seen to date. While we do not yet fully understand these processes, studies to date have given us some insight into the potential effects of these hazards acting in concert.

The logical response to the potential hazards presented by widespread plastic pollution would be to rapidly reduce production. However, this would require some significant changes in the way many social, economic, and commercial systems are organised. There is widespread consensus that plastic pollution is both a serious problem, and an avoidable one; at least with regard to the accumulation of waste plastics. Reducing plastic waste would require a coordinated international effort, involving manufacturers, consumers, waste management services, environmental organisations, activists, regulatory authorities, governments, world leaders, investors, and the research community. There is already significant action being taken towards this goal, including grass roots organisations in many parts of the world, multinational environmental organisations, national legislatures, and waste processing organisations. However, effective action to bring plastic waste under control will almost certainly involve a global treaty, and negotiations in Geneva in August 2025 failed to produce such a treaty, following disagreements about capping plastic production and regulating toxic additives. 

Key stakeholders in the transformation of the way plastics are produced, consumed and disposed of. Kelly et al. (2025).

Reducing the amount of plastic waste being produced is likely to require a similar level of enthusiasm and commitment to that which has gone into creating the problem in the first place. In particular, this will require the more-or-less total elimination of single use plastics, as well as setting strict limits on total plastic production. However, such efforts are unlikely to be achieved without overcoming significant opposition, particularly as the world's major oil companies have been shifting investment towards greater production of plastic base polymers in response to the falling demand for petrochemicals caused by the transition to green energy.

Given the deep political commitment to protecting the petrochemical industry, which may stymie efforts to prevent or reduce plastic production, efforts should also be made to eliminate hazardous additives from the plastic production process, and to ensure that plastic products are genuinely recyclable, and to prevent plastic waste from entering the environment. However, any major shift in the way plastic is produced, used, and processed at the end of its life should be based upon vigorous scientific research, in order to  evaluate any negative impact they may have on economies, social justice, the environment and human health. For example, burning of waste plastics to produce energy, despite reducing the amount of plastic waste in the environment, produces greenhouse gasses, and can produce toxic emissions with direct adverse effects on Human health. Any new materials introduced as an alternative to plastics would need to be evaluated for their contribution to greenhouse gas production, and how they can be disposed of at the end of their lives.

The widespread awareness of the problems associated with plastics in the environment has led to the development of a range of technologies which aim to either recover environmental plastics or prevent plastics from entering the environment at all. These include household wastewater filters and laundry balls, large-scale booms, receptacles, and watercraft vehicles. However, efforts to remove or contain environmental plastics tend to be concentrated around pollution hotspots such as harbours and beaches, and questions have been raised about the environmental impact of such collection efforts, as well as the ultimate fate of the plastics collected. There is no evidence that cleaning up plastic is more beneficial than curtailing the amount of plastic entering the environment, something which has led some to view such efforts as a form of greenwashing.

Bioremediation, the use of microbes such as Bacteria or Fungi to break down plastic waste, is another solution which has been suggested as a way to tackle the situation. Typically, such microbes break down the long chain base molecules in plastics to form monomers that can be further metabolised or mineralised into carbon dioxide, nitrogen, methane, water molecules, or other compounds. A variety of bioremediation methods have been developed, however, none is currently practical as a process which could be scaled up to significantly reduce the plastic pollution problem, as such processes are typically slow, and will only work on specific base polymers, which are often hard to identify in large volumes of mixed plastic waste. 

The ability of natural environments to cope with the presence of large volumes of microplastics is unclear, but it is possible that in some sensitive environments they are already starting to exceed natural tolerances. Our understanding of the impacts of microplastics on the environment is hampered by the variable chemical nature of these pollutants, and a limited understanding of how they interact with other phenomena. Because microplastics are largely produced by the breakdown of larger plastic items, which are also a significant presence in many environments, it is likely that even were all plastic production to stop immediately, microplastics would continue to build up in the environment for some time. 

Some degree of climate change due to the build up of greenhouse gasses in the atmosphere is now likewise inevitable. This makes it imperative to understand how microplastics are likely to behave in a warming climate. Some research has already been done into this topic, but this is limited in scope, with most laboratory work involving pristine beads made from a single form of plastic. It is far from clear how closely results obtained with such materials reflect potential outcomes in the natural world where microplastics comprise a mixture of particle compositions and shapes. Laboratory-based experiments are also naturally short term in nature, and cannot reproduce the long term effects of plastic particles breaking down over many years in a changing natural environment.

Increasing public understanding of the problem presented by plastic waste is a key part of preventing plastic waste from entering the environment. Studies of public attitudes have suggested that most people would like to reduce the amount of plastic being used, and have some idea that plastic waste is harmful to the environment. Unlike global warming, plastic waste is immediately identifiable as of Human origin, and is both clearly visible and considered by most people to be unsightly. Thus plastic waste is viewed as detracting from people's quality of life, and tends to heighten concerns about potential exposure to harmful chemicals. Hence nobody really denies the existence of plastic pollution in the way that people deny anthropogenic climate change is real.

Despite this, the general public is probably less aware of the hazards associated with effects of a warming climate on the abundance, distribution, exposure, or the hazards of plastics in the environment, along with the potential for delayed ecotoxicological effects due to weathering-related degradation. 

Kelly et al.'s review aims to provoke a wider understanding of these issues, although the authors do not claim an understanding alone will enable the public to resolve these problems. They do, however, believe that citizen science activities, combined with outreach and education projects will make people better equipped to deal with the long term consequences of plastic pollution, and that public participation can greatly improve the collection of data on microplastics.

See also...

Cleanup operation under way after millions of plastic beads wash up on English beach.

Volunteers from a range of organisations and the general public are struggling to clean up millions of plastic beads which have washed up on the beach at Camber Sands, a popular tourist destination on the south coast of England. The beads, which cover about 2.5 km of the 5 km-long beach first appeared on Thursday 6 November 2025, and have been identified as biobeads, a type of plastic pellet used in wastewater treatment plants.

Volunteers cleaning up plastic beads from Camber Sands Beach in East Sussex, England. Strandliners.

Biobeads are typically about 5 mm in diameter, and have a rough surface to promote the growth of Bacteria, which aid the water treatment process. Typically wastewater is passed through large tanks containing millions of such beads, allowing the Bacteria growing on them to filter out nutrients. However, when released into the environment, this large surface are also serves as an ideal growing space for marine Algae, which makes the beads resemble a food item to many marine Animals, according to environmental campaign group Strandliners. Once such beads are ingested, they are more-or-less impossible for most Animals to expel, blocking the consumers digestive tract and killing them. 

Plastic biobeads covering a beach at Camber Sands. Rother District Council.

While the source of the beads is unclear, local MP Helena Dollimore, who has been taking part in the cleanup efforts, has contacted  Southern Water, the company responsible for water treatment in the area (and who have been repeatedly fined for discharging untreated sewage), requesting an explanation for the event. Southern Water has stated that it is cooperating with an investigation by the Environment Agency and Rother District Council, and that its own investigations have found that water quality at Camber Sands has been unaffected by the presence of the beads.

Plastic biobeads on the beach at Camber Sands. Strandliners.

See also...

Searching for suspended and Salp-ingested microplastic debris in the North Pacific, using epifluorescence microscopy.

Marine debris is a worldwide ocean pollution problem, with plastics found in virtually all aquatic environments. The majority of marine debris analyzed to date has been microplastic, plastic particles less than 5 mm in size. However, findings suggest even smaller plastics (less than 333 μm) are both under-sampled due to the inappropriate mesh size of common sampling nets and far more numerous because plastic particles physically degrade over time into progressively smaller pieces. Such small debris can be consumed by, and deleterious to, suspension-feeding marine organisms, including Salps. Salps are pelagic Tunicates that possess the highest per-individual filtration rates among marine zooplankton, ingesting particles from under 1.0 μm to about 1.0 mm in size. They primarily feed in the upper water column, where microplastics are abundant. Once plastics are ingested by zooplankton, they have the potential to bioaccumulate in the food web into larger organisms, along with adsorbed persistent organic pollutants and harmful chemical additives, with unknown physiological consequences.

In a paper published in the journal Limnology and Oceanography Letters on 27 November 2019, Jennifer Brandon of the Scripps Institution of Oceanography at the University of California San Diego, Alexandra Freibott, also of the Scripps Institution of Oceanography, and of the Pacific Northwest Research Station of the United States Forest Service, and Linsey Sala, again of the Scripps Institution of Oceanography, present the results of a study which aimed to isolate, identify, and quantify microplastics 5–333 μm in size, a subgroup of microplastics which they termed mini-microplastics, from surface seawater samples and salp specimens collected from the North Pacific.

Although many zooplankton species consume microplasticc in a laboratory setting, the ecologically significant question lies in whether they are ingesting such particles in situ. Although the measured abundance of surface seawater microplastics is high, it is 1–3 orders of magnitude below model predictions of plastic inputs. In 2014 a considerable influx of both salp tunics and fecal pellets to about 4000 m depth following a bloom of Salpa spp. in the northeast Pacific. Thus, Salps could be a key link explaining the discrepancy between modeled and measured abundances of buoyant plastics, because fast sinking Salp fecal pellets and carcasses may be a vector moving ingested surface microplastics to the deep sea.

A Salp (plural Salps) is a barrel-shaped, planktic Tunicate. It moves by contracting, thus pumping water through its gelatinous body, one of the most efficient examples of jet propulsion in the Animal Kingdom. The Salp strains the pumped water through its internal feeding filters, feeding on phytoplankton. Wikipedia/Oregon Department of Fish and Wildlife.

Isolating, identifying, and quantifying microplastics 5–333 μm in size is a difficult task in the ocean due to their small size and irregularity. Brandon et al. took advantage of the well-documented autofluorescence of many plastics, and modified an epifluorescence microscopy approach normally used to enumerate planktonic microorganisms, to quantify oceanic mini-microplastics in surface seawater and Salp gut contents. Specifically, they asked: What are the distribution and abundances of these mini-microplastics in surface seawater? Are Salps ingesting mini-microplastics in situ? And, does the size distribution of ingested particles reflect that of available plastic particles?

Surface seawater samples and salp specimens used in this analysis came from the following cruises: SEAPLEX (02–21 August 2009), R/V Falkor (21–30 October 2013), SKrillEx I (26–31 July 2014), and SKrillEx II (11–17 June 2015). Surface seawater samples (1–2 m) were collected in metal buckets, immediately filtered onto 5 μm pore polycarbonate filters, and frozen. Brandon et al. sorted Salps from sodium borate-buffered 1.8% formaldehyde preserved plankton samples. These were collected via a 202 μm mesh bongo net at a tow depth of approximately 200 m or a surface-dwelling 333 μm mesh manta net. They tested for airborne plastic contamination during sample collection on a separate cruise in January 2017 by separately filtering both surface seawater samples and ultra-filtered Milli-Q water.

Maps of sampling locations, for testing of microplastics both in surface seawater and in Salp gut contents via epifluorescence microscopy. Surface seawater samples were taken via bucket tow in the open ocean (A) on the R/V Falkor (yellow, California Current; purple, transition region; mint green, North Pacific Subtropical Gyre; grey, SKrillEx sites), in 2013 and the nearshore (B) on SKrillEx I in July 2014 (blue) and SKrillEx II (green) in June 2015. Salp samples were taken via manta tow in the open ocean (A), on SEAPLEX (red), in August 2009, and in the nearshore environment (C), on SKrillEx I in July 2014. In (C) the bright green dots indicate stations with 10 Salps present, dark green indicate less than ten Salps present, and grey indicate no Salps in the sample. Brandon et al. (2019).

Brandon et al. sorted, measured, and identified Salp species and life history stage from preserved specimens from each sampling location, located in three open ocean regions: North Pacific Subtropical Gyre, California Current, the transition region, and a nearshore region. Life history stage was designated as blastozooid, the sexual chain-forming generation, or oozooid, the asexual solitary generation. Salp guts were dissected; however, any existing mucous nets and gill bars were not analyzed to avoid artifacts of net feeding.

Traditional epifluorescence microscopy techniques add fluorochromes to stain the DNA and proteins of plankton so that identifying features appear under different reflected wavelengths of light. Because Brandon et al.'s target was identification of plastics, not living organisms, they did not add any fluorochromes. Brandon et al. left prepared slides at room temperature for at least 24 hours to diminish chlorophyll a autofluorescence of plankton before visualization. This ensured the most fluorescent particles on microscopy images were likely microplastics, bacteria, or transparent exopolymeric particles. Brandon et al.tested multiple plastic and nonplastic reference materials, such as cotton and wool, under the four light excitation channels of our microscope to determine their autofluorescence. Filtered surface seawater samples and Salp gut contents were prepared for microscopy using an all-glass filtration apparatus.

Brandon et al. created a decision tree to determine if a particle was plastic. Generally, plastics appeared as long, thin fibers or flat fragments with sharp edges. Plastic particles fluoresced uniformly and did not have inner striations, coloration patterns, or features suggestive of biological particles, such as spines, nuclei, or organelles. Not all plastics fluoresce, so this was not used as a diagnostic feature Particles that were invisible under transmitted light but fluoresced under another light channel were determined to be transparent exopolymeric particles. Particles identified as likely diatom frustules, including chain-formers and pennates like Pseudo-nitzschia, were not counted as plastics. When in doubt, particles were not counted as plastic, so Brandon et al.'s estimates are conservative and most likely underestimate total mini-microplastic abundance.

Decision tree for enumerating plastic microdebris on slides, used to determine which particles were plastic and which were biota or other detritus. Brandon et al. (2019).

Particles were categorized as short or long fibers and fragments. The lengths, widths, areas, and fluorescence were recorded for every fragment and short fiber (under 300 μm) in automated images. Long fibers (at least 300 μm) were enumerated in separate, manual visual transects at lesser magnification to eliminate the possibility of double-counting single large fibers that were not visualized in their totality in automated images. Fibers under 200 μm in length were not counted in manual transects; however, there may be some overlap between the short fibers counted in automated images and long fibers counted in manual transects, due to the 200–300 μm overlap. Brandon et al. recorded long fiber color, length, and width with an ocular micrometer.

Brandon et al. analyzed plastic particles in filtered salp gut contents via epifluorescence microscopy. Because Salp gut walls and ingested biogenic material can fluoresce, fluorescence was considered a secondary characteristic of ingested plastic over particle shape and reflectivity under transmitted light. However, fluorescence was checked to visualize inner striations or patterns characteristic of diatom chains. When in doubt, particles were not counted as plastic. The thick gut walls of Salps and ingested biogenic material most likely occluded some plastic, so our data underestimate total plastic ingestion.

To calculate salp ingestion rates of plastic, mini-microplastic counts were divided by gut clearance times for each species identified, which ranged from 2.5 to 6.25 hours.

Brandon et al. found different patterns of fluorescence between plastic and biological materials, and when in doubt, particles were not counted as plastic. Using a controlled test, they determined that the vast majority of mini-microplastic materials in these filtered seawater samples were not from contamination during processing.

Transmitted light and epifluorescence images of microplastics from surface seawater, including a plastic fragment (A), thick and thin short plastic fibers (B), a long fiber and transparent exopolymer particles (C). Column (1) transmitted light; Column (2) Excitation 450-490 nm, Emission greater than 515 nm; Column (3) Excitation 340-380 nm, Emission 435-485 nm; Column (4) Excitation 465-495 nm, Emission 635-685 nm. Brandon et al. (2019).

Brandon et al. detected no significant spatial heterogeneity in seawater plastic concentrations across the Falkor transect (at 12 h intervals) for three open ocean regions: North Pacific Subtropical Gyre, California Current, the transition region. Nearshore samples from SKrillEx I and II were collected at approximate 15 km intervals, and showed no significant spatial heterogeneity possibly due to small sample sizes. Mean open ocean mini-microplastic concentrations compared to nearshore demonstrated significant heterogeneity between regions. Nearshore mini-microplastic concentrations differed from all other regions

Open ocean mini-microplastic concentrations were on the order of 10-100 per litre for short fibers and fragments with lower long fiber concentrations (1-10 per litre). In contrast, the fluorescent long fibers were 3.5–6.5 times more abundant than mean concentrations of nearshore short fibers and fragments on SKrillEx I, and almost eight times more abundant on SKrillEx II.

Almost every open ocean fragment and short fiber was below 333 μm in length and would have been missed by previous studies using larger mesh nets. Long fibers were usually over 333 μm, but thin enough to easily slip through 333 μm mesh. The minimum lengths of fragments and short fibers were between 14 and 50 μm for all locations, approaching the 5-μm pore size of the filters. For long fibers, both surface area and length were significantly different among regions, with significantly shorter fibers in the transition region. Similarly, in the nearshore samples (SKrillEx I and II), every measured fragment and short fiber length was under 333 μm

Individual particle surface area ranged from 0.0 003 to 0.71 mm², compared to earleir studies using a 333 μm net, which detected particles 0.01–565 mm². These earlier studies found plastic particle lengths ranging from 0.34 to 65.7 mm, while Brandon et al found lengths from 0.01 to 16.27 mm (including long fibers). Ultimately, the most pronounced difference between Brandon et al.'s findings and those of earlier studies was not the size range of particles, but rather their concentrations. Mini-microplastics in this study were five orders of magnitude more abundant than the over 333 μm microplastics of earlier studies. However, when concentration was multiplied by surface area Brandon et al. found that the over 333 μm microplastics had significantly higher areal concentrations than the under 333 μm mini-microplastics.

Salps have a very interesting life cycle, known as alternation of generations.  Salps have two different life stages: a solitary asexual stage and a colonial sexual stage.  The solitary stage of Salps (also referred to as the oozooid stage) has a special structure called a stolon.  This stolon develops into chains of the colonial stage.  When a chain of the aggregate stage has grown large enough within the solitary organism the chain will be released.  The chain is the sexual stage of the Salp (also referred to as the blastozooid stage).  In many species, the colonial stage (chain) looks very different from the solitary stage, and in fact when scientists first discovered Salps they often thought that the colonial and solitary stages of the same species were actually different species.  Chains of the colonial stage can extend for several meters in the water, and include hundreds of individuals.  The chains start off as females, and are fertilized by the sperm from older chains.  Once the eggs within a chain are fertilized, an embryo (of the solitary stage) will grow within each individual of the colonial stage.  The colonial stage will then give live birth to the solitary (asexual) stage so that the process can repeat itself.  As the chains matures it will switch from a female to a male. FSU Zooplankton Ecology and Biogeochemistry Lab.

Every single Salp gut analyzed contained plastic. Blastozooids had higher ingestion rates than oozooids. In general, nearshore Salps were larger than open ocean Salps  The California Current Salps were the smallest and had the lowest plastic ingestion rates. Excepting the North Pacific Subtropical Gyre and transition region oozooids, there was no detectable relationship between body length and plastic ingestion rate for dissected Salps. Although Brandon et al found regional differences in mini-microplastic concentrations in the water column, there was no significant effect of region on Salp plastic ingestion rate. Fibers made up 91% of the total ingested particles. The surface area and lengths of fibers and fragments differed significantly between most regions.

Brandon et al. compared the size of ingested mini-microplastics with that of ambient mini-microplastics in surface seawater, both from their data and from earlier studies Most of the net-collected particles from earlier studies fell within the size range of potential Salp food particles. At all sample locations, the average size of particles consumed by Salps was significantly smaller than the size of ambient seawater plastic.

Brandon et al. successfully used epifluorescence microscopy to identify mini-microplastic particles in natural seawater samples and Salp gut contents. This method required careful judgment and expertise to distinguish biotic from plastic materials. Furthermore, autofluorescence of Salp gut walls and biogenic materials made ingested plastic fluorescence only a secondary identification characteristic. This method allowed us to distinguish plastic from nonplastic particles and fluorescent from nonfluorescent plastic, but not to identify specific plastic types. Isolating plastic-type autofluorescence patterns under specific emission wavelengths may permit such differentiation in future work. However, our ultimate goal was to use standard epifluorescence microscopy techniques to differentiate plastics from nonplastic particles in order to obtain accurate bulk measurements of plastics under 333 μm, which the method accomplished.

This study may be one of the first to estimate the abundance of the smallest mini-microplastics in surface seawater, which are consistently under-sampled. Brandon et al. found a mean plastic concentration across all locations of 8277 particles per litre (8 277 000 particles per m³). Their particle concentrations averaged 5–7 orders ofmagnitude higher than previous studies. This highlights the previously unquantified significance ofmini-microplastics inmarine debris counts.

Nearshore samples had higher plastic concentrations than open ocean samples. This agrees with published findings that have recorded similar spikes in plastic concentrations nearshore, close to populated areas, with a decline in plastic moving offshore. The difference in plastic concentrations between SKrillEx I and II may be explained by annual differences in rainfall and watershed input to these nearshore waters.

Many estimates of macro- and microdebris, including modeled debris trajectories agree that the highest concentrations of open ocean marine debris occur in convergence zones of subtropical gyres. However, Brandon et al. did not detect a significant increase in mini-microplastic concentration in the North Pacific Subtropical Gyre and their open ocean samples were not significantly different across regions. Many possible sinks of mini-microplastics could account for this. Plastic below 5 μm in size presumably degrade beyond the detection limit of Brandon et al.'s method. Plastics can also be biofouled and sink out of surface water, or ingested and removed from the water. As plastic accumulates in the North Pacific Subtropical Gyre and breaks down into progressively smaller pieces, Brandon et al.'s data suggest that plastic under 333 μm is removed from the gyre through biofouling, ingestion, or degradation at the same rate it is being supplied. In the nearshore zone, however, mini-microplastics, especially long fibers (in the 200 μm–17 mm range), likely have a higher rate of input than loss. All of these sources and sinks require further research to be better parameterized.

Earlier studies sampled almost no particles smaller than 0.333 mm × 0.333 mm (0.11 mm²), due to the mesh size of the sample collection net, while Brandon et al. detected many particles below that limit (minimum size 0.000 3 mm²). Their results show the majority of plastic concentrations occur between under 333 μm and 0.11 mm². Although the mini-microplastics they measured were more numerically abundant, they did not comprise the majority of the plastic surface area in the water. Organisms that colonize surface substrates in the ocean are more likely to find surface area on micro- and macroplastics rather than mini-microplastics, despite the numerical abundance of mini-microplastics.

This is the first record of Salp ingestion of microplastic in situ. Every Salp dissected had plastic in its gut, regardless of species, life history stage, or region of the ocean sampled. Salp gut clearance times are on the order of 2–7 hours, so Brandon et al. are confident that by only analyzing the gut, they avoided artifacts of net feeding or other contamination. Airborne contamination is a major concern in modern microplastic work, especially when samples are dominated by fibers, as in this study (91% of the Salp-ingested particles). However, our processes of seawater filtration, slide preparation, and salp dissection limited contamination. Compared to filtered control samples, most of the plastics in Brandon et al.'s surface seawater samples were not contamination.

Brandon et al. detected no regional differences in plastic ingestion by Salps, excluding the much lower values of the California Current Salps. This finding is likely attributable to the very small body size of those salps. The California Current Salps had the lowest ingestion rate of any region, whereas for surface seawater, concentrations of mini-microplastics in the nearshore environment were significantly higher than the entire open ocean. Overall, however, both Salp ingestion and surface seawater plastic concentrations had limited regional differences.

Salps are predominantly generalist suspension feeders with ingestion based primarily on particle size, typically from less than 1 μm to 1 mm. All seawater mini-microplastic measured, and almost all the plastic in earlier studies, fall within their possible ingestion range. Yet, the Salps sampled by Brandon et al. ate significantly smaller pieces of plastic than were available in the ambient surface water. This may be explained by the fact that Salps can efficiently collect down to submicron particles and feed throughout a greater area of the water column than the surface, where larger,more buoyant plastic is retained.

Salps are of ecological importance due to several factors: their notoriously rapid growth and opportunistic reproductive rates that can lead to extremely high population densities or 'blooms', higher filtration rates per individual than any other zooplankton grazer, and production of dense fecal pellets that can result in high vertical fluxes of this material to deeper depths. The large fecal pellets of Salps have proven to possess rapid sinking and slow decomposition rates such that they can reach the deep ocean relatively intact, transporting organic carbon and potential microplastics with them. Brandon et al.'s evidence for the widespread and universal consumption of microplastics by Salps leads Brandon et al. to believe that Salps may be an important vector of marine debris transport from the surface ocean to deep-sea communities. The transport of microplastics via Salps may be critical to incorporate into microplastic export calculations as an overlooked output from surface waters.

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Assessing the impact of plastic waste on Hermit Crabs on remote Pacific Islands.

Plastics are designed to be light-weight, convenient, and durable; several characteristics that make them suitable packaging alternatives compared to other materials such as wood, glass or metal, but also makes them problematic in marine and terrestrial environments. Low manufacturing costs have contributed to huge demand for new plastic materials, with global production increasing by 6–8% per annum. Globally, less than 10% of the 348 million tonnes of plastic produced annually is ever recycled, with approximately 40% of plastic waste comprised of single-use packaging. The significant increase in disposal rates in the last half century, combined with inadequate or ineffective waste management, has led to huge quantities of plastic polluting ecosystems worldwide. Once in the ocean, plastic items can either sink or float, becoming dispersed over long distances via tides and currents Significant quantities of plastic are now recorded in all aquatic ecosystems, accounting for more than 95% of all debris items observed at-sea, on beaches, and along river banks. These synthetic materials persist for decades in the environment, posing a considerable threat to aquatic flora and fauna Mortality of wildlife from plastic debris can occur directly (e.g. through entanglement) or indirectly through exposure to plastic-associated toxins, which may contribute to reduced body condition or survival in some species. While evidence of harmful effects on individual organisms is increasing, there is currently little knowledge or agreement regarding whether plastic debris poses an ecologically relevant threat, affecting wildlife at the population level and contributing to an overall decline in species’ abundance. Establishing a clear link between debris interactions and population persistence is crucial, as loss of biodiversity contributes to the degradation of ecosystems and the valuable services they provide. While much of the focus of plastic impacts has understandably been on the marine ecosystem, increasing quantities of debris accumulating on beaches and adjacent vegetated areas has the potential to disrupt terrestrial species and ecosystems. In tropical ecosystems, Crabs, Malacostraca, play a crucial role in forest growth and development through aeration of soils and creation of carbon-rich soil microhabitats, therefore reductions in Crab abundance may impact plant recruitment.

In a paper published in the Journal of Hazardous Materials on 16 November 2019, Jennifer Lavers of the Institute for Marine and Antarctic Studies at the University of Tasmania, Paul Sharp and Silke Stuckenbrock of the Two Hands Project, and Alexander Bond of the Bird Group at the Natural History Museum, describe the results of a study into the effects of plastic waste on Hermit Crabs on two remote Pacific locations, the Cocos Islands and Henderson Island.

In order to understand the potential impact accumulating plastic may have on coastal crab populations, Lavers et al. recorded the number and frequency of Strawberry Hermit Crabs, Coenobita perlatus, entrapped in beach debris on individual beaches within the Cocos Islands and on Henderson Island, in the Pitcairn group, two remote areas where significant quantities of debris accumulate. We then estimate entrapment rates across both islands to provide an estimate of population-level impact of plastic beach debris on Crab populations.

The Cocos Islands are two small, mid-oceanic atolls (total land area 14 km²) located approximately 2760 km north-west of Perth, Western Australia. The southern atoll consists of a horseshoe chain of 26 islands around a shallow, central lagoon. The northern atoll (North Keeling, administered as Pulu Keeling National Park) is a relatively pristine, uninhabited island. Most of the Human population (around 600 people) reside on Home and West Islands. A range of marine resources are fished for food and tourism, including Crabs and other Crustaceans which are consumed or used for bait. Henderson Island is a raised coral atoll and UNESCO World Heritage Site (total land area 43 km²), administered as part of the Pitcairn Islands (UK). It is extremely remote, uninhabited, and located on the western boundary of the South Pacific Gyre, a known plastic-accumulation zone. Both Henderson and Cocos are very polluted, with about 38 million (239 items/m²) and 414 million debris items (713items/m²) deposited on beaches and throughout the beach-back vegetation, respectively.

Map of the study sites (blue circles): Cocos Islands (top; North Keeling not shown on inset map) and Henderson Island (bottom) with sampling regions shown in red. Lavers et al. (2019).

Lavers et al. recorded visible macro-debris located on the surface within randomly-placed quadrats. In the beach-back, significant quantities of debris accumulate amongst the vegetation, creating an obvious hazard for Crabs. On Cocos, four quadrats were established on Direction Island and four on West Island from 20 to 29 March 2017, one on Pulu Blan Madar, and two on Home Island, from 1 to 2 September 2019, and 20 quadrats along the East Beach of Henderson Island during 12 to 16 June 2019. The boundary of each quadrat was located along the top edge of the beach and extended into the vegetation towards the centre of the island. On Cocos, the dimensions of each quadrat were 5 × 3 m (2017) or 6 × 4 m (2019), and on Henderson 6 × 6 m, reflecting differences in accessibility at each site. The size was reduced slightly for some quadrats (2/8 on Cocos in 2017 and 2/20 on Henderson) to enable navigation through thick forest and to protect sensitive habitats.

(A) Accumulated plastic debris creates an obstacle for crabs on the beaches of the Cocos Islands. (B) A Hermit Crab inside a green bucket along the high tide of South Island. (C) Accumulated plastic debris in the beach-back vegetation on West Island. (D) Crabs that became trapped and died inside a plastic drink bottle that washed up on Cocos. (2019). Lavers et al. (2019).

The location of the beach-back quadrats and timing of surveys overlapped periods when a range of Crab size classes were present on both islands and encompassed a diversity of habitats (e.g., areas dominated by Velvetleaf Soldierbush, Heliotropium foertherianum, or Small-leaved Mangrove, Pemphis acidula). However, the density of Crabs within these habitats was not recorded and no attempt was made to survey across seasons due to the remote nature of each site and limited access.

Within each quadrat, all intact plastic containers (e.g., drink, commercial, and industrial bottles) were recorded. Containers were then assessed for whether they posed a potential entrapment hazard to crabs based on meeting both of these criteria: (1) The lid was missing or the container was damaged such that it allowed Crabs access to the inside of the container, and (2) the container was positioned with the opening facing an upward angle, such that a Crab would have difficulty exiting and would therefore become entrapped. Lavers et al. then counted the number of Crabs (dead or alive) that had become entrapped in each container.

Lavers et al.used the density of bottles available to entrap Crabs across the eight quadrats on Cocos, 20 quadrats in the beach-back vegetation of Henderson, and four transects along Henderson’s East Beach (totalling 1139 m) to extrapolate the total number across the archipelago by resampling the values, with replacement, 10,000 times and scaling this to the area of beach-back vegetation (defined as the length of the vegetation line and extending 10 m inland). Beach length and beach-back dimensions were obtained using Google Earth Pro (version 7.3.2) and satellite imagery from 2016 to 2018 for beaches that were ocean-facing. Beaches that faced into the lagoon on Cocos (e.g., away from prevailing currents, sheltered by other islands) or small unnamed and potentially ephemeral sand bars were excluded as they do not likely accumulate significant quantities of plastic debris.

The estimated mean number of bottles on each beach was then used to predict the total entrapment using the probability and intensity values.

On Cocos we recorded 218 bottles that could potentially entrap Crabs across eight quadrats. Of these, 190 (87%) contained no Crabs, and the probability of entrapment was 0.128 (i.e. 12.8% of bottles contained Crabs). Of bottles that contained Crabs, the mean entrapment intensity was 7.857 Crabs per bottle. The overall entrapment rate was therefore 1.009 Crabs per bottle.

The density of plastic bottles in beach back ranged from 0.13 to 3.67 bottles per m². Across the 454 720 m² of ocean-facing beach back habitat, Lavers et al. estimated there were 562 352 bottles that could potentially entrap Crabs, producing an estimate of 507 938 Crabs entrapped in bottles across the archipelago.

In the beach-back vegetation on Henderson Island, Lavers et al. recorded 77 bottles across 20 quadrats covering 690 m², of which 65 (84%) contained no Crabs, and the probability of entrapment was 0.156 (i.e. 15.5% of bottles contained Crabs). There were 106.25 individuals in those containers with Crabs, resulting in an overall entrapment rate of 16.55 Crabs per bottle.

On East Beach, Crabs were found in 8 of 33 bottles (24%) across 12 762 m² of the beach. The probability of entrapment was 0.242 (i.e. 24.2% of bottles contianed crabs), and the entrapment intensity 60.0 Crabs per bottle. The overall entrapment rate was therefore was 14.55 Crabs per bottle.

The density of bottles ranged from 0.083 to 1.103 bottles per m² in the beach-back, and was 0.035 bottles/m² on East Beach of Henderson Island, resulting in a potential 2046 bottles in 7600 m² of beach-back vegetation and 865 bottles on 24 908 m² of East Beach where Crabs could become entrapped. Combining the entrapment values, Lavers et al. estimate 33 922 Crabs entrapped on the beachback, and 28 003 Crabs on the beach, for a total of 60 961 entrapped Crabs on Henderson Island.

Overall Hermit Crab entrapment rates were extremely high on both Henderson and Cocos, with nearly 61 000 (2.447 Crabs/m²) and 508 000 crabs (1.117 crabs/m²) becoming entrapped, respectively. Though overall mortality on Henderson is lower, the beach area is much smaller than that on Cocos, and both the rate and severity of entrapment and mortality is much higher. These estimates are liberal, as the rate of degradation of Crab carcasses is unknown, therefore some shells may have been present in the bottles for more than 12 months. Furthermore, Lavers et al.'s analysis does not account for temporal patterns, such as localised abundance during the breeding season, which could influence entrapment rates, and must be considered as point estimates rather than a temporal rate (e.g., annual mortality). Such rates should be a research priority on sites that are heavily polluted and can be visited regularly.

At a temperature of 28–29 °C and relative air humidity of 75 % (similar to conditions at both field sites), reported average survival of Hermit Crabs was 5–9 days when the Crabs lacked access to water. Thus, once entrapped in plastic containers, mortality of Hermit Crabs likely occurs over a very brief period, depending on rainfall. Hermit Crabs, including Coenobita perlatus, use the odour of dead conspecifics to locate available shells, increasing shell-acquisition behaviour by up to 10 times, which are a limiting resource and both live and freshly Dead Crabs were occasionally observed together inside plastic containers. This suggests entrapments occur on a regular basis and conspecific attraction, the very mechanism that evolved to ensure Hermit Crabs could replace their shells, has resulted in a lethal lure. Accumulation of more than 20 Crabs in containers suggests a threshold, or dose response, may exist whereby the chemical signals of decaying Crabs act additively or multiplicatively with a maximum of 526 Crabs observed in a single container on Henderson Island.

(A) A Strawberry Hermit Crab navigates through natural and anthropogenic debris on East Beach, Henderson Island. (B) Accumulated debris on East Beach, Henderson Island. (C) 526 Hermit Crabs trapped inside a single container on Henderson Island in June 2019. (D) Some of the 526 Hermit Crab shells from the container shown in panel (C). Lavers et al. (2019).

The significant entrapment rate has the potential to negatively impact Hermit Crab populations. While no population size data exist for any Hermit Crab species on Henderson or Cocos, and estimates of adult or juvenile survival are not available, existing pressure on these Crabs is appreciable on Cocos as small Crabs are used as bait in recreational and artisanal fishing and there are localised depletions of Crabs around populated areas. Concerns have been raised regarding the current recreational fishery bag limit on Cocos, 9 l per day for mixed, small Crabs, and a no-take regulation was considered as part of a Parks Australia review of recreational fishing regulations. Information on longevity of Crabs is sparse, but suggests Anomuran Crabs (the group which includes Hermit Crabs) are long-lived (5–30 years in the wild). Entrapment in debris along beaches, and in the beach back vegetation, therefore presents an additional, significant threat to Crab populations which are already under pressure and likely rely on high survivorship of breeding adults to maintain populations. On Henderson, Crab populations are likely under predation pressure from introduced Pacific Rats, Rattus exulans, which can modify coastal ecosystems greatly.

Significant reductions in crab populations have the potential to harm islands in several ways. On Cocos, tourism is a major source of employment, providing substantial economic and social benefits, and receiving widespread community support. On the main islands of Cocos, Seabirds no longer breed, therefore charismatic species like Hermit Crabs may provide an important opportunity for tourists to observe native wildlife. For example, on Christmas Island, the diversity and abundance of Crabs is a well-known tourist attraction. Cocos and Henderson Island lack native ground predators, therefore Crabs play a critical role in seed dispersal, removing detritus, and provide a range of benefits, such as soil turbation through burrow excavation and collection of leaf litter. Entrapment and mortality of large numbers of Crabs could therefore affect ecosystem function of coastal areas, which would have consequences for other biota as well as for tourism.

The accumulation of plastic debris alters water movement and heat transfer through beach sediments. Accumulated debris can also create a physical barrier, reducing the accessibility of beaches for breeding and hatchling Sea Turtles. Limited information is available for other species, especially invertebrates, however the presence of beach debris smothers benthic communities resulting in fewer Polychaete Worms and reduces the number of burrows constructed by Crabs. Significant annual losses of Crabs could lead to reduced breeding, and consequently lower recruitment. The larval duration and transport distance of most small Decapods, including Hermit Crabs, is relatively short with populations maintained through a combination of allochthonous (long distance) and autochthonous (local) recruitment. However, with the increasing isolation of an island, it becomes difficult for shallow water species to traverse the open ocean and establish a viable population, and Crab species richness on Cocos and Henderson is markedly lower than other island and mainland populations in the region. Similarly, Henderson’s remoteness would significantly impede successful larval dispersal to the island. Successful recruitment of Crabs therefore relies on considerable new individuals being released into the environment. Depleted populations, or those located on smaller, isolated islands therefore have less resilience to acute stressors than mainland ones, since they do not have the diversity of habitats to act as refuge for populations of species under pressure.

The increasing urbanisation and pollution of much of the world’s coasts with plastic debris threatens increasing and irreversible damages to beach ecosystems. Over the last three decades, plastic drink bottles have shown the fastest growth rate of all debris types reported on some remote islands. When such widespread changes are overlaid with the broad distribution of hermit crabs throughout the subtropics and tropics, it becomes clear the negative interactions between Crabs and debris are set to increase. This is of particular concern in areas of high Hermit Crab abundance, diversity, and endemism.

The mortality of Hermit Crabs attributed to beach debris, documented here for the first time, is significant, and likely a key factor contributing to the reported declines in hermit crabs on Cocos. Unfortunately, Cocos and Henderson are not unique, with similarly high concentrations of debris reported on beaches and in coastal vegetation worldwide. Other beaches with high debris load and Hermit Crabs may well experience similar mortality. The global mortality of Hermit Crabs is undocumented, likely to be substantial, and requires urgent investigation.

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