Mussel population shifts over a century in an urbanizing watershed

Urban, agricultural, and industrial development is increasing in many parts of the central and eastern United States and these changes can lead to population shifts in long-lived, sessile species like freshwater mussels. We examined over 150 years of freshwater mussel data from the Fox River watershed to determine whether community assemblages are shifting with land-use change. The Fox River flows from southeastern Wisconsin into north-central Illinois and over 30 species of freshwater mussels have been recorded from this basin. Most early survey and conservation efforts were focused on the mainstem Fox River, which has been dammed and industrialized over the past century. We compiled species richness data, identified areas with unique assemblages, and located habitat or existing locales of rare, endangered species. We sampled ~75 sites in 2020-2022, and confirmed presence of 24 live species in the watershed. Rare or imperiled species such as Snuffbox (Epioblasma triquetra) and Purple Wartyback (Cyclonaias tuberculata) remain extirpated, but we documented diverse, abundant mussel populations in many major tributaries. These data will be used to update the focus of conservation efforts in the watershed, which includes augmentation of state-endangered Rainbow (Cambarunio iris) in Wisconsin. Documenting comprehensive changes in freshwater mussel communities is necessary to understand species shifts and adaptations in a changing environment.