A unionid mussel biodiversity hotspot experiencing unexplained declines: Evaluating the influence of chemical stressors using caged juveniles
Unionid mussels in the Clinch River, Virginia, have declined sharply, but the causes remain unclear. Using juvenile Villosa iris and Lampsilis fasciola deployed in cages and silos, researchers measured trace elements, PAHs and nitrogen isotopes in mussel tissues, shells and surrounding environmental media. Elevated concentrations of As, Cu, Fe, Mn, Ni, Sr and PAHs—especially in tributaries such as Dumps Creek and Guest River—identified a distinct zone of decline. Several contaminants correlated with bioaccumulation patterns, and metals including Co, Cu, Fe and V were negatively associated with mussel growth. PAH accumulation also aligned with lower resident mussel densities. Results highlight contaminant exposure as a key factor in the decline and underscore the need for targeted watershed management.
Subject Tags
- Rivers
- Biodiversity
- Wildlife
Abstract
Unionid mussel populations in a section of the Clinch River in Virginia, USA, has declined substantially, but the causes of the decline remain unknown. To investigate this zone of decline (ZOD), we deployed juvenile freshwater mussels (Villosa iris in 2012 and Lampsilis fasciola in 2013) in both cages and silos at sites within the Clinch River System. We analyzed mussel tissues for trace element and organic contaminant concentrations, shells for trace elements, and environmental media (total water, dissolved water, particulate sediment and bedload sediment) for both inorganic and organic contaminants. We found a few differences between mussels deployed in cages and those deployed in silos: survival was slightly lower in cages due to periodic sedimentation. Our results identified the ZOD based on the accumulation of trace elements (notably As, Cu, Fe, Mn, Ni, and Sr), polycyclic aromatic hydrocarbons (PAHs) and δ15N enrichment, with especially high concentrations found in the human-impacted tributaries, Dumps Creek and Guest River. Some correlations were found between environmental media and both mussel tissues and shells. In particular, PAHs and Mn had several significant relationships between bioaccumulated concentrations and environmental concentrations. Finally, Co, Cu, Fe, and V in soft tissues negatively correlated with mussel growth, whereas bioaccumulated PAH concentrations correlated negatively with resident mussel densities.
Citation
Wilson, W. A., Bergeron, C., Archambault, J., Unrine, J., Jones, J., Beaty, B., ... & Cope, W. G. (2025). A Unionid Mussel Biodiversity Hotspot Experiencing Unexplained Declines: Evaluating the Influence of Chemical Stressors Using Caged Juveniles. Diversity, 17(8), 503. https://doi.org/10.3390/d17080503
TNC Authors
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Braven Beaty
Stewardship Ecologist Clinch Valley, Virginia
The Nature Conservancy
Email: bbeaty@tnc.org