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Microplastic represents a rising proportion of marine litter and is widely distributed throughout a range of marine habitats. Correspondingly, the number of reports of species containing microplastics increases annually. Nephrops norvegicus in the Firth of Clyde have previously been shown to retain large aggregations of microplastic fibres. The potential for N. norvegicus to retain plastic over an extended time period increases the likelihood of any associated negative impacts to the individual. This study represents the longest observation of the impacts of microplastic retention in invertebrates. We exposed N. norvegicus to plastic over eight months to determine the impacts of extended exposure. Over this period we compared the feeding rate, body mass, and nutritional state of plastic-fed N. norvegicus to that of fed and starved control groups. Following the experimental period, the plastic-fed langoustine contained microplastic aggregations comparable to those of small individuals from the Clyde Sea Area. Comparisons between fed, unfed and plastic-fed individuals indicated a reduction in feeding rate, body mass, and metabolic rate as well as catabolism of stored lipids in plastic contaminated animals. We conclude that N. norvegicus exposed to high levels of environmental microplastic pollution may experience reduced nutrient availability. This can result in reduced population stability and may affect the viability of local fisheries.

Over the past twenty years microplastic pollution has been recorded in all major marine habitats, and is now considered to be of high environmental concern. Correspondingly, the number of reports of microplastic ingestion by marine species is increasing. Despite this, there are still relatively few studies which address the uptake and retention of microplastic in wild populations. Langoustine, Nephrops norvegicus, sampled from the Clyde Sea Area, have previously been seen to contain large aggregations of microplastic fibres. The large proportion of contaminated individuals and size of the microplastic aggregations observed suggests that Nephrops are at high risk of microplastic ingestion. In this study the levels of ingested microplastic in populations of N. norvegicus from the Clyde Sea Area, North Minch and North Sea are examined. Animals in the near-shore, Clyde Sea population showed both a higher percentage of microplastic containing individuals and much greater weights of microplastic retained in the gut. N. norvegicus revealed that only a small percentage of individuals from the North Sea and Minch contained microplastic, predominantly single strands. An expanded sample from the Clyde Sea Area was examined to identify the factors influencing microplastic retention. This revealed that males, larger individuals, and animals that had recently moulted contained lower levels of microplastic. The presence of identified food items in the gut was not seen to correlate with microplastic loads. Observations of microplastic in the shed stomach lining of recently moulted individuals and the lack of aggregations in wild-caught individuals suggests that ecdysis is the primary route of microplastic loss by N. norvegicus. Therefore the large aggregations observed in wild-caught animals are believed to build up over extended periods as a result of the complex gut structure of N. norvegicus.

Contamination by microplastic particles and fibres has been observed in sediment and animals sampled from the Firth of Clyde, West Scotland. In addition to microplastics released during clothes washing, a probable source is polymer ropes in abandoned, lost and discarded fishing and recreational sailing gear. The fragmentation of polypropylene, polyethylene, and nylon exposed to benthic conditions at 10m depth over 12months was monitored using changes in weight and tensile properties. Water temperature and light levels were continuously monitored. The degree of biofouling was measured using chlorophyll a, the weight of attached macroalgae, and colonising fauna. Results indicate microplastic fibres and particles may be formed in benthic environments despite reduced photodegradation. Polypropylene, Nylon, and polyethylene lost an average of 0.39%, 1.02%, and 0.45% of their mass per month respectively. Microscope images of the rope surface revealed notable surface roughening believed to be caused by abrasion by substrate and the action of fouling organisms.

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