Young mussels exposed to high levels of plastic microfibers show restricted growth according to a new study by scientists at Plymouth Marine Laboratory, University of East Anglia and the University of Plymouth, England. 

“As microfibers are so prevalent in the marine environment, it is vital we try to understand their impact on different indicator organisms, such as the blue mussel which is a key marine species important for global food security,” says Christopher Walkinshaw, PhD student at Plymouth Marine Laboratory and the University of East Anglia and lead author of the study. 

Fibers are one of the most common forms of microplastic identified in environmental studies, accounting for up to 91% of the total identified microplastics in some studies. The findings could have negative effects on the marine ecosystem and potentially lead to commercial implications. 

For the “first time,” a study has demonstrated the effect of exposing juvenile mussels to polyester and cotton microfibers at environmentally relevant concentrations over a prolonged timescale. 

Mussel exposure 
The experiment was conducted within a controlled temperature laboratory with night and day cycles using microfibers of 10–500 µm (0.01 mm – 0.5 mm) in size. 

Mussels were exposed to polyester microfibers at two concentrations, eight and 80 microfibers per liter and to cotton microfibers at 80 microfibers per liter. 

Mussels exposed to 80 polyester microfibers per liter were significantly smaller than the control mussels after 32 days of exposure, and their growth rate was, on average, 36% lower than the control mussels. Mussels exposed to cotton microfibers did not show a statistically significant decrease in growth in this experiment.

“Reduced growth rates could alter the energetics of food webs, as smaller mussels are less nutritionally valuable, both to their predators in the natural environment and to us as consumers of seafood,” asserts Walkinshaw. 

“Microfibers and other microplastics expose marine animals, such as mussels, to an additional risk in an environment already at risk from other challenges such as climate change.”

The team hypothesizes that the observed reductions in mussel growth in response to microfibers could stem from a shift in their energetic budget. These changes could be caused by individuals either altering their feeding behaviors to avoid consuming microplastics, diverting energy away from growth into processing ingested microfibers or repairing damage caused by these microfibers.

Microfibers 
Additionally, other toxicity studies show that microplastics can cause adverse health effects at the molecular and cellular level in adult mussels and therefore, energy may be diverted away from growth and reproduction to compensate.

Studies suggest that as much as 4.8 to 12.7 million metric tons of plastic enters the global ocean every year. This number is expected to rise as plastic manufacturing rates are forecast to increase. 

Fibers that are less than 5mm are deemed microfibers and are predominantly generated from the fragmentation of textiles, stemming from the day-to-day use and washing of clothes and from the weathering and abrasion of marine infrastructure, such as netting and rope.

Microfibers are typically composed of polyester, PP or nylon. However, numerous studies also report the presence of naturally derived and semi-synthetic microfibers (e.g., cotton or bioplastic) in environmental samples, which have received relatively little attention compared to their plastic counterparts, highlights the research.

The impact on marine life

Last year, researchers at Flinders University, Australia, found microplastics in variable concentrations in blue mussels and water within the intertidal zone at some of southern Australia’s most popular and more remote beaches.

The researchers warned that the findings mean microplastics are now finding their way into human food supplies – including wild-caught and ocean-farmed fish and seafood sourced from the Southern Ocean and gulf waters of South Australia. 

Meanwhile, the amount of microplastics collected on ocean floors tripled in the past 20 years at the same rate of social plastic consumption, according to research by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona, Spain and the Department of the Built Environment of Aalborg University, Denmark.

The study showed that microplastics remain unaltered in marine sediments and that the amount of microplastic sequestered in the seafloor mimics the rate of global plastic production from 1965 to 2016. 

The results of the recent UK study highlight the importance of conducting longer experiments when considering the impacts of microplastic on marine life. 

While the impact of microplastics on certain aspects of biological function can become evident over short timescales, the impact of environmentally-relevant concentrations of microplastics on growth, reproduction and survival, which have the greatest relevance to populations and communities, require longer observation periods, say the scientists. 

“Future research aims are to conduct a combined experiment investigating energy budgets and subcellular toxicity of microfibers over a similar exposure time to study the reason behind the inhibited growth,” concludes Walkinshaw.