Using 3D printed replicates to assess subadult freshwater mussel mobilization thresholds in a flume

Freshwater mussels are a highly imperiled, mostly sessile, benthic fauna that rely on stable sediments for their habitat. The subadult life stage is most often used in reintroduction efforts but very little is known about their physical habitat requirements. Here, 20-mm and 40-mm 3D printed subadult mussels are developed as a proxy for live subadult mussels for four common mussel species in the southeast United States: Pustulosa pustulosa (pimpleback), Quadrula verrucosa (pistolgrip), Amblema plicata (threeridge), and Lampsilis teres (yellow sandshell). These mussels were used in a flume study to identify the mobilization thresholds and calculate a new metric, the mussel mobilization index (Tm), based on observed mussel shear stress and sediment critical shear stress. A set of live L. teres subadult mussels was used to corroborate the morphometrics and thresholds of printed L. teres mussels, with 20-mm mussels matching well dimensionally. For 20-mm lengths, live mussels had higher mobilization thresholds than similar sized printed mussels. Overall, small sediments provided higher mussel mobilization index values, but larger sediments produced more stable mussels. The 3D printing of mussels provides an opportunity for managers to assess potential habitat without the risk of losing live specimen.