Multi-endpoint ecophysiological indicators to assess freshwater mussel translocation success

Freshwater mussels are considered keystone fauna of aquatic ecosystems and globally declining. Translocation of mussels has been used as a conservation tool, but there is a lack of indicators for the success of such measures. This study investigated ecophysiological responses of three native mussel species ( Anodonta anatina, A. cygnea, Unio pictorum ) after translocations into different substitute habitats, hypothesizing that the response patterns can be used as ecological indicators for translocation success. Over 47,000 mussels were relocated from a drained reservoir to three replacement habitats: a fishpond, the pre-dam and a slow-flowing section of the river inflow of the reservoir (river Schwarzach). Mortality, growth and macromolecules (glycogen, glucose, protein, lipids) in the mussel foot tissue were measured in PIT-tagged mussels over three years. Survival rates greatly varied between habitats (0% in the Schwarzach, 38% in the fishpond, 66% in the pre-dam area). Shell growth was higher in the fishpond than in the pre-dam, and concentrations of storage compounds varied over time and between habitats. The results highlight that the combined assessment of multiple biological endpoints comprising mortality, growth and biochemical markers provides a valuable ecological indicator for assessing mussel translocation success which is crucial for improving conservation efforts. They also stress the critical importance of considering temporal patterns in assessing ecophysiological responses to stress, and the need for risk mitigation and careful habitat selection for successful translocation of freshwater mussels.