The effect of polypropylene on the formation of byssal threads produced by Dreissena polymorpha (zebra mussels)

The presence of microfibers and microplastics in the environment is an ever-growing ecological concern. Accumulation of microplastics (plastic particles smaller than 5 mm) in aquatic environments and the subsequent exposure of these particles to organisms have been shown to have negative effects on aquatic biota. As an invasive, filter-feeding bivalve found across Indiana freshwater ecosystems, the zebra mussel (Dreissena polymorpha) serves as a good model organism for studying microplastics’ effects on physiological and behavioral functions of affected organisms. We have studied the impacts of microplastic exposure on a freshwater mollusk, the zebra mussel. We collected zebra mussels from Stone Lake, Indiana, in late fall of 2019. Individual zebra mussels were exposed to polypropylene rope fibers (concentration of rope fibers in the environment of one zebra mussel was ~400 microfibers per L) for 24-hour trials and assessed the effects by production of byssal threads, which are produced by the zebra mussel for anchorage and in response to predation threats. Results from a comparison between unexposed control mussels (n=70) and mussels exposed to rope fibers (n=70) revealed no significant difference in motility nor the number of byssal threads produced. Despite using microplastic concentrations that were higher than that found in the Great Lakes, a 24 hour exposure time may still not have been enough to significantly impact the animals. Continued research on the attachment strength of Dreissena polymorpha exposed to rope fibers will provide clearer evidence of any direct effect of these microplastics on the ecologically important mussel species.