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From Core to Front: Microplastic Loads Along a Signal Crayfish ( Pacifastacus leniusculus ) Invasion Gradient
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Even remote, protected mountain rivers in Portugal aren't safe from plastic pollution—researchers found microplastics (mostly tiny fibers from things like plastic bottles and packaging) in the guts of invasive crayfish, with the highest amounts at the invasion's leading edge. This matters because it shows plastic contamination is working its way into wildlife even in pristine-seeming environments, and since these crayfish are eaten by other animals (and sometimes humans), the plastic particles they ingest could move up the food chain.
Plastic pollution is one of the most persistent threats to aquatic ecosystems, yet studies in low-disturbed mountain aquatic environments remain scarce. This study examined the presence of macro- and microplastics in three rivers in the Montesinho Natural Park and adjacent areas, Portugal. It investigated how intrapopulational ecological traits of the signal crayfish (Pacifastacus leniusculus), a non-native species widely distributed across Europe, may influence contaminant accumulation. Sampling was conducted at five sites along an invasion gradient (front-core), where macroplastics along the margins and signal crayfish were collected, followed by laboratory analyses for the morphological and polymeric characterization of the plastics. Chemical identification was performed using Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and Raman spectroscopy. Behavioural assays of boldness and aggressiveness were carried out on 100 captured signal crayfish individuals. Macroplastics were detected in all sampling sites. Microplastic abundance was higher at the invasion front, and the digestive tract contained significantly more particles than the gills, suggesting that the digestive tract is the primary route of exposure. No differences were detected between sex or individual size. Fibers were the dominant form, mainly in blue and black colors, and polymers such as polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) prevailed. Although personality traits differed between the invasion front and the core, with generally bolder and more aggressive individuals at the front, behavioural responses also showed sex-related patterns, with females tending to leave the shelter faster and males showing higher aggressiveness. However, no statistically significant correlations were found between animal personality and microplastic accumulation. Overall, our results indicate that plastic contamination depends on multiple factors arising from interactions between local environmental factors, including hydromorphological processes, and intrapopulational ecological traits (i.e., diet). This study highlights the importance of integrating behavioural analyses to better understand differential exposure to contaminants and their potential environmental implications for non-native species and possible legacy for native communities.
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Microplastic burden in invasive signal crayfish (Pacifastacus leniusculus) increases along a stream urbanization gradient
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Researchers found microplastics in the digestive tracts of invasive signal crayfish at every site along a stream gradient from rural to urban, with concentrations rising as more of the upstream area was developed — and detected microplastics in crayfish tail muscle tissue for the first time. Because crayfish are important prey for many species, their accumulation of microplastics in both gut and tissue suggests these pollutants can move through freshwater food chains more broadly than previously recognized.
Plastic Debris in the Stomach of the Invasive Signal Crayfish Pacifastacus leniusculus from a Baltic Coastal River
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Researchers examined the stomach contents of invasive signal crayfish (Pacifastacus leniusculus) for plastic debris, finding ingested plastic fragments and fibres in a proportion of sampled individuals. The study identifies signal crayfish as accumulators of microplastics in freshwater food webs, with potential implications for predators that consume crayfish in affected river systems.
Microplastic Presence and Frequency in Crayfish within Urban and Rural Streams
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Researchers compared the presence and frequency of microplastics found in crayfish living in urban versus rural streams, aiming to understand how human development influences microplastic ingestion in freshwater animals. Crayfish serve as useful environmental indicators because they feed at the bottom of streams where microplastics tend to settle.
Impact of a recent invader on a freshwater top predator exposure to microplastics and flame retardants
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Scientists studying rivers in Portugal found that an invasive crayfish species may be helping spread microplastics and toxic flame retardant chemicals up the food chain to otters, top predators that eat the crayfish. This matters beyond otters because it shows how invasive species can act as a hidden "delivery system" for pollutants that build up in animals we eat, like fish and shellfish — a reminder that plastic and chemical pollution in waterways doesn't stay contained, and invasive species could make human exposure through seafood worse than expected.
Microplastic burden in native (Cambarus appalachiensis) and non-native (Faxonius cristavarius) crayfish along semi-rural and urban streams in southwest Virginia, USA
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Researchers conducted the first comparative study of microplastic contamination in native and non-native crayfish species along semi-rural and urban streams in southwest Virginia. They found significantly higher microplastic concentrations in urban surface water compared to semi-rural areas, and the non-native crayfish species showed greater microplastic body burden than the native species. The findings suggest that urbanization influences microplastic exposure in freshwater organisms and that invasive species may accumulate plastics differently than native ones.
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