Long‐term monitoring shows that drought sensitivity and riparian land use change coincide with freshwater mussel declines

Abstract

1. Freshwater mussels (Bivalvia: Unionoida) are globally imperilled and are the subjects of wide-ranging conservation initiatives. This study combined traditional species-monitoring surveys with a novel functional trait classification scheme and publicly available environmental data to assess potential environmental drivers of declining mussel abundance and species richness. 2. Surveys to document mussel abundance and assemblage composition in south-east Oklahoma, United States were conducted on the Glover, Mountain Fork and upper Little rivers. Present day survey results (2015-2021) were compared with those from previous studies (1993-1999, 2010) to document long-term changes in the species and functional composition of mussel assemblages and concurrent changes in climate and land use. 3. Mussel catch per unit effort declined by 71.5% between historical and present day surveys. Species richness declined by 44.4% over this same period. Using a novel classification of mussel drought sensitivity, it was found that the declines were associated with a disproportionate loss of drought-sensitive taxa (67.0% decline)those classified as drought-tolerant did not decline in abundance. Mussel declines coincided with the loss of open surface waters (such as streams, ponds and lakes) and riparian wetlands, increased local air temperatures and longer and more intense hydrological drought. 4. These findings indicate that for a complete understanding of the causes and consequences of mussel declines, conservation biologists must not only monitor the species composition and abundance of threatened organisms, but also consider functional traits. The results further underscore the importance of long-term monitoring for long-lived organisms owing to the decadal time scales over which climate and land use change occur.

How low can you go? Widespread challenges in measuring low stream discharge and a path forward

“…Low-flow conditions (Mauger et al 2021), which we define as streams or rivers with little downstream surface water flow caused by small volumes or very low downstream velocities (i.e., slackwater), are increasingly prevalent and thus necessitate greater focus on quantification approaches. Streamflow is the underlying physical template structuring biotic and abiotic processes, biogeochemical cycling, and ecological communities in river systems; thus, inaccurate low-flow measurements can propagate to and hinder diverse analyses requiring accurate low-flow data, ranging from drought characterization (Hammond et al 2022), environmental flow allocations (Neachell and Petts 2019), ecological function assessments (Leigh and Datry 2017), species conservation plans (Lopez et al 2022), and streamflow forecasting (Forzieri et al 2014).…”

When rivers run dry: Perennial pools as ecological refuges for freshwater mussels during drought

“…Severe drought conditions can lead to mass mortality events for mussel populations (e.g., DuBose et al, 2019;Gagnon et al, 2004), as well as community-wide declines (Golladay et al, 2004;Haag & Warren, 2008;Mitchell et al, 2019;Tarter et al, 2022) and shifts towards more tolerant species (Lopez et al, 2022).…”

“…However, most mussel species are unable to withstand desiccation for even relatively short time periods (Fogelman et al., 2023; Galbraith et al., 2012; Mitchell et al., 2018). Severe drought conditions can lead to mass mortality events for mussel populations (e.g., DuBose et al., 2019; Gagnon et al., 2004), as well as community‐wide declines (Golladay et al., 2004; Haag & Warren, 2008; Mitchell et al., 2019; Tarter et al., 2022) and shifts towards more tolerant species (Lopez et al., 2022).…”

Influence of Bed Roughness on Flow and Turbulence Structure Around a Partially‐Buried, Isolated Freshwater Mussel

“…Freshwater mussels are among the world's most imperiled fauna (Ferreira‐Rodríguez et al., 2019; Lydeard et al., 2004; Strayer et al., 2004). The survival of the mussel is strongly dependent on the aquatic environment in which they live (Lopez et al., 2022). Together with the chemical and biological characteristics of the habitat (e.g., availability of nutrients, water pH and temperature), flow hydrodynamics plays an important role for mollusk conservation efforts as it influences habitat conditions.…”