Hydraulic requirements of freshwater mussels (Unionidae) and a conceptual framework for how they respond to high flows

Abstract

Spatiotemporal variability in flow determines the physical structures of habitat. During low flows, aquatic organisms can be exposed to reduced dissolved oxygen concentrations, increased water temperature, and desiccation, whereas at high flows, increased velocity and hydraulic forces on the streambed can be equally detrimental. These constraints create a mosaic of habitat that influences the distribution and abundance of aquatic biota. This mosaic can change due to stochastic events or those mediated by humans. Understanding how low and high flow conditions affect aquatic organisms is critical not only for advancing ecological knowledge but also for protecting imperiled aquatic species such as unionid mussels. The overall goal of this project was to examine how substrate and hydrologic conditions affect mussel habitat and to then use the resulting information combined with life‐history traits and shell morphology (i.e., sculpturing) to better understand how flow shapes mussel assemblage structure. Using quantile regression, we found that low values of relative shear stress (RSS), a measure of substrate stability, were associated with high mussel species richness and density. Change point analysis using threshold indicator taxa analysis (TITAN) indicated species‐specific preferences for varying levels of bed stability. These preferences were best explained by life‐history strategy and shell morphology based on the results of a principal component analysis. Using these results, we then present a conceptual model from which to derive expectations concerning taxonomic composition, life‐history strategy, and shell sculpture type based on the degree of substrate mobility using RSS and variability in RSS.

Short‐term responses of freshwater mussels to floods in a southwestern U.S.A. river estimated using mark–recapture sampling

“…At the highest flood magnitude, 4,332 m 3 /s in this study, abundances were reduced 93–95% among three species. These findings, along with site‐ and species‐specific responses reported in other studies (Inoue et al., 2014; Meador et al., 2011; Randklev et al., 2019; Sansom et al., 2018), suggest a complex relationship between mussel abundances and peak flow, which is likely to be influenced by site‐specific substrate and hydraulic conditions.…”

“…There are several factors that, once quantified and replicated, could add robustness to explaining mussel population dynamics and peak flow relationships. These factors include site‐specific attributes, such as basin size, stream geomorphology, substrate type and stability, habitat types, and species‐specific attributes such as shell morphology and burrowing behaviour (Allen & Vaughn, 2010; Gangloff & Feminella, 2007; Meador et al., 2011; Morales et al., 2006; Randklev et al., 2019; Strayer, 1999; Zigler et al., 2008). Observations during this study provide empirical support that substrate and shell morphology influence mussel population response to increased flow.…”

“…An estimated 50,000 mussels, representing 4–8% of the total population, were displaced and stranded, and then died. In other studies, the ability of freshwater mussels to resist floods depends on substrate stability and related hydraulic variables such as shear stress (Allen & Vaughn, 2010; Gangloff & Feminella, 2007; Morales et al., 2006; Randklev et al., 2019; Strayer, 1999; Zigler et al., 2008), habitat type (Meador et al., 2011), channel geomorphology (Gangloff & Feminella, 2007), as well as shell morphology, behaviour, and life‐history strategies (Allen & Vaughn, 2009; Goodding et al., 2019; Randklev et al., 2019). To date, empirical studies that directly assess effects of floods on mussel population dynamics in rivers are lacking, particularly in relation to large floods (e.g.…”

A cautionary tale about translocating mussels and implications for conservation: A case study from two river basins in central Texas

“…Survivorship between these sampling periods remained high (>93%) across species and treatments, probably owing to the physical structure of both sites. Generally, mussels occur in areas along the stream bottom where the potential for bed movement is low during high flows (Gangloff & Feminella, 2007; Stoeckl & Geist, 2016; Randklev et al, 2019). The study sites in the East Fork occurred at riffles characterized by sand substrate overlaid with an armouring layer of gravel and cobble.…”

Establishing conservation units to promote recovery of two threatened freshwater mussel species (Bivalvia: Unionida: Potamilus)

“…To estimate relative abundance and distributional trends of P. amphichaenus and P. streckersoni throughout their known ranges, we compiled available or generated data from freshwater mussel surveys that detected live specimens in the Brazos, Neches, Sabine, and Trinity River drainages (Ford et al, ,2009(Ford et al, , , 2014(Ford et al, , , 2016Randklev et al, 2011Randklev et al, , 2017Randklev et al, , 2020Smith et al, 2019). For select sites where survey effort was reported (e.g., survey time, number of surveyors), we estimated abundance using catch per unit effort (CPUE), which is calculated by dividing the total number of live individuals by the total person-hours.…”