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Why are mussels losing their grip?

Weakening may be linked to food deprivation caused by microplastic pollution.

February 2 2019, Blue Hill, Maine – Microplastic fibers have been found in every ocean, from shorelines to the very depths of the Mariana Trench, at sizes minuscule enough to be mistaken for food by all marine life. As efficient filter feeders, mussels function as valuable proxies for coastal ecosystems by providing insights into pollution levels.

A recent study conducted by the Shaw Institute and the Bigelow Laboratory for Ocean Sciences found that blue mussels ingest plastic fibers as food at predictable rates under laboratory conditions (1). A surprise finding indicated mussels expelled as much as 70% of the microplastic fibers both before and after ingesting them.

“While our microplastic concentrations were higher than environmental levels, our study shows that mussels are actively rejecting microplastics while filtering,” said Madelyn Woods, Shaw Institute scientist and lead study author.

Although this new information appears to have positive implications, the ingestion and expulsion of microplastics resulted in an alarming  50% reduction in intake of algae, the mussel’s primary food source. This limited feeding ability could result in nutritional deprivation and a weakened condition over time. The authors speculate that a compromised nutritional state could affect mussels’ ability to grip their surroundings, a trend recently identified by scientists at Anglia Ruskin University (2).

“The UK study shows that exposed mussels are unable to produce byssal threads, the fibers that enable them to cling to the substrate of a rocky coast,” said Dr. Susan Shaw, Shaw Institute CEO/Founder and study co-author. “Although not proven, it is certainly plausible that nutrition-deprived mussels could lose their tenacity, causing them to drift and collapse.”

At first glance, the suggestion that mussels expel the majority of ingested microplastic fibers has engendered optimism in the commercial seafood industry, implying a means to control contamination in mussels marketed for human consumption (3). But Shaw Institute scientists caution that mussels retain a significant amount of plastics and associated chemicals in their tissues, which carries potential health risks for both mussels and their consumers.

“On the Maine coast, we are seeing widespread attrition in wild mussels,” said Dr. Shaw. “Mussels have long been important ecologically and commercially, but we now have a problem – they are ingesting microplastics, they are unable to feed normally, and they are disappearing. We urgently need to understand how microplastic pollution may be affecting their resilience and their safety as human food.”

1. Madelyn N. Woods, Margaret E. Stack, David M. Fields, Susan D. Shaw, Patricia A. Matrai. Microplastic fiber uptake, ingestion, and egestion rates in the blue mussel (Mytilus edulis). Marine Pollution Bulletin, 2018
2.Dannielle S. Green, Thomas J. Colgan, Richard C. Thompson, James C. Carolan. Exposure to microplastics reduces attachment strength and alters the
haemolymph proteome of blue mussels (Mytilus edulis). Environmental Pollution, 2019
3. https://www.postandcourier.com/news/shellfish-avoid-ingesting-most-microplastics-new-research-finds/article_59c504a0-1429-11e9-9333-2b0b7eda9e1b.html