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list of species from which glochidia were tested (Amblema plicata, Fusconaia mitchelli, Lampsilis bracteata, Lampsilis hydiana, Lampsilis satura, Lampsilis teres, Obovaria arkansasensis, and Cyclonaias necki), the collection date and river from which gravid mussels were collected, and the viability of glochidia at the onset of the thermal trials
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Understanding the temperature tolerances of organisms is critical because the thermal regimes of freshwater ecosystems are changing globally. Native freshwater mussels are sensitive to increasing water temperatures because of their physiology and unique life history. Detailed knowledge on lethal temperatures for mussels has been limited to less tha...
Contexts in source publication
Context 1
... tolerances were evaluated for the glochidia of eight species Table 1). Three of these species (A. ...Context 2
... female mussels were collected from the Guadalupe, San Antonio, Colorado, and Neches river basins from April 2017 to April 2018 (Table 1). Following collection, mussels were transported in insulated coolers to the Texas A&M AgriLife Extension and Research Center in Dallas, Texas. ...Context 3
... glochidia isolated from female mussels with ≥80% viability were thermally tested (Ingersoll et al., 2006), except for the ESA candidate species C. necki (77.5 ± 7%) and L. bracteate, from the Llano (64.3 ± 5%) and San Saba rivers (79.6 ± 6%; Table 1). Because of the difficulty in locating gravid females of these rare species, smaller sample sizes (n < 3 gravid females) and lower initial viabilities (~70-80%) were used in order to provide information on the thermal tolerance of glochidia before listing. ...Context 4
... also varied across species ( Figure S1; Table S1). Fusconaia mitchelli, collected during the spring from the Lower Guadalupe, had the highest 12-h LT50 value (36.1 ± 0.4°C), followed by L. hydiana, which was collected during the spring from Cibolo Creek (34.1 ± 0.2°C), and finally L. bracteata, which was collected from the upper Guadalupe (33.9 ± 0.3°C) and Cherokee Creek (33.9 ± 0.2°C). ...Similar publications
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Freshwater mussels (Lamellidens marginalis) are very important components of aquatic ecosystems. The study was undertaken to know population ecology of Lamellidens marginalis. The pearl growing freshwater mussels were cultured in two earthen ponds and one cemented tank was studied for a period of five months (November 2015 to March 2016) in freshwa...
Freshwater mussels are considered the most imperiled group of organisms in North America and systematics research has played an integral role in the development and implementation of their conservation. Despite the importance of systemat-ics in conservation planning, the evolutionary relationships between many mussel taxa remain poorly explored, cl...
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Functional traits are characteristics of an organism that represents how it interacts with its environment and can influence the structure and function of ecosystems. Ecological stoichiometry provides a framework to understand ecosystem structure and function by modeling the coupled flow of elements (e.g. carbon [C], nitrogen [N], phosphorus [P]) b...
Citations
... These considerations have spurred recent interest in the effects of temperature and flow changes on freshwater mussels [25][26][27][28][29]. Laboratory experiments have generated basic thermal tolerance thresholds for mussels [25,[29][30][31][32][33], and mussel assemblage changes in relation to temperature and flow have been empirically observed [11,34,35]. Information relating the current thermal environment of mussels to their thermal tolerances is expanding, however, little empirical field temperature research has been conducted in mussel habitats [36,37]. ...
Freshwater mussels fulfill an important ecological role in aquatic ecosystems, but they currently face many threats, including thermal regime alteration. Thermal transformation of the aquatic environment is associated with climate change, land use alteration, and other pervasive anthropogenic global changes. To enhance our understanding of ecological thermal impacts, we combined extensive field measurements of temperature in the stream water column and substrate depths (5 and 15 cm) at sites where mussels occur, measures of abundance and species richness for mussels and fish, and thermal tolerance knowledge for mussels and fish to generate a comprehensive assessment of the potential threats mussels face as temperatures continue to rise as a result of global change. Mean summer (June-August 2010-2012) temperatures at mussel-occupied sites in the upper Tar River basin of North Carolina, USA, ranged from 16.2 to 34.7 C. The mean temperature from the hottest 96 h at each site ranged from 23.5 to 31.5 C. At 80% of sites, a period of moderate drought coincided with the hottest 96 h period. Temperature threshold exceedance durations indicated that chronic, combined chronic/acute, and acute freshwater mussel thermal tolerance thresholds (i.e., 28 C, 30 C, and 33 C, respectively) based on laboratory exposures of glochidia (larvae) and juveniles were commonly exceeded. Water temperatures exceeded 28 C for at least 24 h at 55% of sites and for at least 96 h at 35% of sites, and they exceeded 30 C for at least 24 h at 15% of sites. We quantified a thermal buffering effect of the substrate that may be protective of mussels. There was a mean difference of 0.5 C between the water column and the upper substrate (5 cm) and a mean difference of 0.9 C between the water column and the lower substrate (15 cm). Maximum differences of up to 5.5 C between the water column and the upper substrate and 11.5 C between the water column and the lower substrate were observed. Our models estimating the relation between the water column and substrate temperatures more realistically characterize ambient temperature exposures and have widespread implications for mussel conservation and climate change risk assessment in similar streams. Freshwater mussels currently exist on the edge of their thermal limits, but their abundance and species richness cannot be explained by temperature patterns alone. Fish species richness was related to the thermal regime, indicating that species interactions may be an important driver of freshwater mussel responses to global change.
... Upper thermal tolerances (LT 05/50 ) of glochidia and juveniles were determined following the methods described by Khan et al. (2019) and Khan et al. (2020). Trials were conducted by placing approximately 250 viable glochidia in a non-aerated 100-mL beaker containing 80 mL of reconstituted hard water with a salinity of 0.34 ppt (±0.05 ppt) (ASTM International, 2006). ...
... The cumulative frequencies (%) of temperature exceedance events were plotted on the x-axis against the duration of events (days) plotted on the y-axis, creating a UCAT curve (Castelli, Parasiewicz & Rogers, 2012). To identify inflection points on the UCAT curves, three-segment piecewise linear regressions were conducted using the lm() function in base R. Exceedance events above F I G U R E 2 Experimental design, following Khan et al. (2019), showing acclimation and experimental temperatures plus nonacclimated (20 C) and acclimated (27 C) controls for Popenaias popeii glochidia (24 h) and juveniles (96 h) in the Black River. Each treatment and control contained three replicates. ...
... including Lampsilis bracteata (Texas fatmucket), which had variations of up to 3 C in the 24-h glochidial LT 50 values across populations (Khan et al., 2019;Goldsmith et al., 2021). The present study suggests that the thermal tolerance of P. popeii is conserved across populations, although with some minor variation. ...
Freshwater mussels are globally imperilled, which is attributed to their sensitivity to changes in streamflow and temperature. The Black River in south‐eastern New Mexico, USA, harbours a stronghold population of the federally endangered unionid Popenaias popeii (Texas hornshell). Decreasing discharge and elevated water temperatures are considered the primary factors responsible for the species’ decline. However, the impact of these factors has not been quantified directly, which may hinder conservation efforts.
The upper thermal tolerances (LT 05 and LT 50 ) of Black River P. popeii larvae (glochidia) and newly transformed juveniles were evaluated. Individuals were acclimated to 27°C and then immersed at five experimental temperatures (28, 30, 32, 34 and 36°C) for 24 h (glochidia) or 96 h (juveniles). The thermal tolerances of P. popeii and its presumed host fishes were then overlain onto in situ water temperature and discharge data to determine thermal exceedances in the past 15 years. Temperature was hindcast back to 2007 using machine learning (random forest model) and coupled with discharge.
For glochidia, LT 05 was exceeded frequently (41%) and LT 50 was exceeded occasionally (13%) during spring and summer periods, whereas juvenile thresholds were never exceeded. Upper continuous duration above threshold (UCAT) analysis revealed periods of catastrophic high temperature, which were used to determine discharge bottlenecks.
This study demonstrates how laboratory‐derived physiological thresholds can be used in conjunction with environmental data to evaluate the hydrological needs of aquatic organisms, which is useful in efforts to maintain flow regimes that protect native ecosystems.
... While some studies note that knowledge of lethal temperatures is limited to 5% of known North American mussel species (Khan et al. 2019), other studies indicate that L. bracteata is more sensitive to dry conditions and desiccation than other species (Mitchell et al. 2019). ...
Riverine ecosystems are dependent in large part on the climate of the region, and climate change is expected to alter climatic factors of interest, such as precipitation, temperature, and evapotranspiration. In central Texas, precipitation is expected to decrease while temperature increases as the climate changes. Drought and flooding events are also expected to increase in the region, which will also effect streamflow and stream temperature in riverine ecosystems. Numerous studies have assessed the potential impacts of climate change on riverine species. This study examines the projected climate changes, determines potential changes in streamflow and stream temperature for river basins in central Texas, and assesses the appropriate uses of climate projections for riverine species impact assessments, using the Texas fatmucket ( Lampsilis bracteata ) as a case study. Previously established regression methods were used to produce projections of streamflow and stream temperature. This study finds that streamflow is projected to decrease and stream temperature is projected to increase. Using thermal tolerance thresholds previously determined for the Lampsilis bracteata , this study also finds that the lethal temperature events for the Lampsilis bracteata will increase. Finally, this study makes several recommendations on the use of downscaled climate projections for impact assessments for riverine species such as the Lampsilis bracteata .
... glochidia compared to 0 and 10 °C. Unfortunately, little is known about mussel thermal tolerance, though this has started to change [23][24][25] . ...
... The upper thermal limits (LT05 and LT50) of glochidia and juveniles were estimated by adapting methods presented in Khan et al. 24,40 Specifically, glochidia were acclimated to 27 °C from room temperature (20 ± 1 °C) by increments of 1 °C per hour in a refrigerated incubator. Once 27 °C was reached, glochidia were held at this temperature for two hours prior to testing as per ASTM International guidelines 41 . ...
... Lethal temperatures resulting in 5% and 50% mortality (LT05 and LT50, respectively) were determined for glochidia and juveniles by fitting survival data to a logistic regression model (n = 3). Because initial glochidial viability was under 100%, survival values were adjusted following methods described in Wang et al. 43 and Khan et al. 24 by dividing treatment viability (assessed after 12-h or 24-h) by initial viability. Only LT50 was determined for juveniles since there were only three experimental temperatures, and therefore LT05 could not be reliably calculated. ...
Freshwater mussels are particularly sensitive to hydrologic changes, including streamflow and temperature, resulting in global decline. The Devils River in south-central Texas harbors the endangered freshwater mussel Popenaias popeii (Unionidae; Texas hornshell). There is concern that water withdrawals from the underlying aquifer may be negatively impacting this species. To assess this risk, we evaluated upper thermal tolerances (LT05 and LT50) of larvae (glochidia) and juveniles from two sites. After being acclimated to 27 °C, glochidia were subjected to five experimental temperatures (30, 32, 34, 36, and 38 °C) and non-acclimated control (20 °C) for 12-h and 24-h while juveniles were subjected to three experimental temperatures (30, 32, and 36 °C) and non-acclimated control (20 °C) for 96-h. We overlaid tolerance estimates against in situ water temperature and
discharge data to evaluate thermal exceedances. Additionally, we reviewed upper thermal tolerances of P. popeii’s presumed host fish (Carpiodes carpio, Cyprinellas lutrensis, and Moxostoma congestum) and their congeners. Stream temperatures only occasionally exceeded mussel LT05/50 and fish CLMax/LTMax, likely due to the Devils River’s large spring input, highlighting the importance of protecting spring flows. We provide a practical framework for assessing hydrological needs of aquatic ectotherms, including the parasite-host relationship, which can be used to optimize environmental management.
... However, during low flow conditions, spring temperature can rise to approximately 26 • C (data from the Edward Aquifer Authority in Appendix B). Average water temperatures in non-spring influenced riverine ecosystems in central Texas can range from 28 to 30 • C in July to 11-13 • C in January (SWQM, 2017;Khan et al., 2019). In the present study, we conducted several experiments examining the effects of exposure to increasing water temperatures on the four aforementioned species that differ in their habitat associations (i.e., surface water streams-versus spring-associated). ...
Organisms living in environmentally stable ecosystems are hypothesized to exhibit narrow environmental tolerance ranges; however, previous experiments testing this prediction with invertebrates in spring habitats are equivocal. Here we examined the effects of elevated temperatures on four riffle beetle species (family: Elmidae) native to central and west Texas, USA. Two of these, Heterelmis comalensis and Heterelmis cf. glabra are known to occupy habitats immediately adjacent to spring openings and are thought to have stenothermal tolerance profiles. The other two, Heterelmis vulnerata and Microcylloepus pusillus are surface stream species with more cosmopolitan distributions and are assumed to be less sensitive to variation in environmental conditions. We examined performance and survival of elmids in response to increasing temperatures using dynamic and static assays. Additionally, changes in metabolic rate in response to thermal stress were assessed for all four species. Our results indicated that spring-associated H. comalensis is most sensitive while the more cosmopolitan elmid M. pusillus is least sensitive to thermal stress. However, there were differences in temperature tolerances among the two spring-associated species: H. comalensis had relatively narrow thermal tolerance in comparison to H. cf. glabra. This could be due to differences in the climatic and hydrological conditions in the geographical regions which the respective riffle beetle populations reside. However, despite these differences, H. comalensis and H. cf. glabra showed a dramatic increase in their metabolic rates with increasing temperatures indicating that these species are indeed spring specialists and likely have a stenothermal profile.
... Thermal sensitivity is a functional trait that integrates a mussel species' behavioural and metabolic responses to increasing temperatures (Galbraith, Blakeslee & Lellis, 2012;Khan et al., 2019;Galbraith et al., 2020). Southern North American mussel species can generally be placed in two guilds based on their physiological tolerance to high water temperatures: thermally sensitive species that suffer decreased body condition and thermally tolerant species that continue to grow (Spooner & Vaughn, 2008). ...
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.
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.
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.
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.
... Information gathered from this type of research can result in a better understanding of the functional relationships between mussels and their environments across a range of spatial and temporal scales, which in turn, can aid in efforts to manage and protect them. For example, (Khan et al., 2019) measured significant differences in the upper thermal tolerances of glochidia across populations of Lampsilis bracteata within the San Saba and Llano rivers in Texas. The authors showed differences in climate and hydrology between the rivers and hypothesized these differences could be driving localized adaptation. ...
Aim
Biogeography seeks to identify and explain the spatial distributions of species and has become an important tool used by conservationists to protect and manage aquatic organisms. Texas, located in the southwestern United States, is home to 52 species of freshwater mussels, 9 of which are endemic to Texas and 7 that are endemic to Texas and neighboring states or countries. There have been two major attempts to classify this fauna into biogeographical provinces; however, both efforts relied on limited distribution information and outdated taxonomy. To address both issues, we set out to delineate biogeographic provinces for freshwater mussels in Texas by using a comprehensive distributional dataset of >28,000 records and molecular information.
Location
Southwestern United States.
Methods
We compiled community and molecular data for 48 of the 52 freshwater mussel species that occur in Texas. We performed algorithmic hierarchal cluster analysis (HCA) and nonmetric multidimensional scaling (NMDS) based on Euclidean distance to identify biogeographic groupings. We conducted a similar analysis using molecular sequence data for our target species.
Results
Based on the results from community and molecular data, we identified seven biogeographic provinces for freshwater mussels in Texas: Great Plains, Mississippi Embayment, Sabine‐Neches, Trinity‐San Jacinto, Central Texas, Rio Grande and Coastal. However, the Coastal and Great Plains provinces were not included in our analysis and were recognized based on previous work.
Main conclusions
Our approach integrating community and molecular datasets provides a comprehensive assessment of the biogeography of freshwater mussels in Texas, which serves as a model for future biogeographic studies. Our findings also shed light on the ecological, evolutionary and geologic processes shaping freshwater mussel communities in Texas, which is important for the conservation of remaining biodiversity in the state.
... This relationship likely illustrates the effect of low flows on mussels during thermally stressing events such as periods of low precipitation. It is well known that elevated water temperatures can affect mussel survival (Khan et al., 2019(Khan et al., , 2020Pandolfo et al., 2010), and these effects often occur during periods of reduced flow (Archambault et al., 2014). Reduced flows are inherent to a rivers flow regime and are biologically important (Biggs et al., 2005;Bovee, 1986;Poff et al., 2006), but they can become problematic during periods of reduced precipitation and/or overuse by humans (Golladay et al., 2004;Randklev et al., 2018). ...
Species distribution models (SDMs) are an increasingly important tool for conservation particularly for difficult-to-study locations and with understudied fauna. Our aims were to (1) use SDMs and ensemble SDMs to predict the distribution of freshwater mussels in the Pánuco River Basin in Central México; (2) determine habitat factors shaping freshwater mussel occurrence; and (3) use predicted occupancy across a range of taxa to identify freshwater mussel biodiversity hotspots to guide conservation and management. In the Pánuco River Basin, we modeled the distributions of 11 freshwater mussel species using an ensemble approach, wherein multiple SDM meth-odologies were combined to create a single ensemble map of predicted occupancy. A total of 621 species-specific observations at 87 sites were used to create species-specific ensembles. These predictive species ensembles were then combined to create local diversity hotspot maps. Precipitation during the warmest quarter, elevation, and mean temperature were consistently the most important discriminatory environmental variables among species, whereas land use had limited influence across all taxa. To the best of our knowledge, our study is the first freshwater mussel-focused research to use an ensemble approach to determine species distribution and predict biodiversity hotspots. Our study can be used to guide not only current conservation efforts but also prioritize areas for future conservation and study. K E Y W O R D S climate, conservation, habitat, maxent, mycetopodidae, random forest, species distribution model, unionidae
... Growth is an anabolic process: thermally sensitive species cannot grow when temperatures are high. Many freshwater mussels probably live close to their thermal maximum during the summer, which seasonally affects their role as ecosystem engineers (Khan et al., 2019;Spooner & Vaughn, 2008). As such, thermally sensitive species should reach a smaller potential maximum size at lower latitudes due to thermal stress during growing seasons. ...
As body size often predicts energetic requirements and fecundity, understanding the drivers behind size variation is important. Neo‐Bergmann's rule states that larger individuals are found at higher latitudes and this size variation is attributable to temperature gradients. In ectotherms, this macroecological pattern has mixed support within the literature—both the direction and mechanism of size correlation with latitude varies.
We asked if two species of freshwater mussels with different thermal niche preferences, Amblema plicata and Lampsilis cardium , follow neo‐Bergmann's rule and what mechanisms might drive that latitudinal variation. Lampsilis cardium is a thermally sensitive species intolerant of high temperatures, and A. plicata is more tolerant of a wide range of temperatures. We predicted that the thermally sensitive species at southern latitudes would have stunted growth in the summer and that this stunting would produce a steeper relationship with latitude than in the thermally tolerant species. We collected and thin‐sectioned 113 A. plicata shells from 23 sites and 85 Lampsilis cardium shells from 12 sites across a latitudinal gradient in the eastern U.S.A. We used back‐calculated size‐at‐age data to determine logistic growth parameters for each taxon across this gradient. We used Bayesian model selection to evaluate how environmental information correlated with potential maximum size.
We found that both mussel species reached a larger potential maximum size at higher latitudes, with the thermally sensitive species having the larger increase in potential maximum size across the gradient when compared to the thermally tolerant species. Average annual water temperature explained mussel potential maximum size better than annual catchment precipitation, annual minimum flow ratio, and species identity. Both increased average water temperature and annual catchment precipitation, two predicted outcomes of climate change, were associated with smaller potential maximum size.
Reductions in mussel maximum size due to climate change induced shifts in temperature regimes and precipitation patterns could lead to reduced reproductive output of this threatened guild and subsequent changes in ecosystem function and services, such as decreased biofiltration.
As climate change alters precipitation patterns and stream productivity, and increases water temperature, understanding size variation and its cause in aquatic organisms will be important for managing these vulnerable populations.
... Recent estimates have shown that global freshwater species populations have declined by as much as 83%, which appears to be correlated with changes in water temperature and flow regimes (World Wildlife Fund, 2018). It is well known that the distribution and ecology of aquatic organisms is mediated by their physiology and life history, both of which are tightly coupled with temperature and flow (Vannote & Sweeney, 1980;Ward & Stanford, 1982;Olden & Naiman, 2010;Khan et al., 2019). For example, Matthews & Berg (1997) examined how rainbow trout (Oncorhynchus mykiss) respond to changes in water temperature and found that increases above 25 C caused O. mykiss to seek thermal refugia. ...
... Freshwater mussels are one of the most imperilled groups of aquatic species, and in the USA, where they reach their greatest diversity, it is estimated that 70% of the species are extinct or imperilled, compared with 16.5% of mammalian species and 14.6% of bird species (Williams et al., 1993;Strayer et al., 2004;Haag, 2012;Randklev et al., 2018). These declines have been attributed to inherent biological characteristics that make them sensitive to anthropogenic changes such as increases in water temperature and changes in flow (Randklev et al., 2018;Khan et al., 2019). Specifically, mussels are ectotherms which means that survival, growth and reproduction are regulated by external water temperature. ...
... Climate within the basin is characterized as semi-arid to sub-humid with long, hot summers and cool winters (Larkin & Bomar, 1983;Blum, Toomey & Valastro, 1994;Randklev et al., 2018). Mean monthly water temperatures range from 7-9 C (January) to 28-29 C (July) (Surface Water Quality Monitoring, 2017; Khan et al., 2019). Mean annual rainfall ranges from 559 to 864 mm (Griffith et al., 2007) with the wettest seasons occurring in early autumn and late spring (Larkin & Bomar, 1983;Blum, Toomey & Valastro, 1994;Randklev et al., 2018). ...
• Overexploitation of freshwater resources coupled with climate change can affect the flow and temperature regimes in rivers, which can be catastrophic for aquatic biota. The San Saba and Llano rivers, located in central Texas, are experiencing low flows and stream dewatering owing to over-allocation. Both systems harbour imperilled species, including Lampsilis bracteata, Texas fatmucket, which has been proposed for listing under the US Endangered Species Act. It is suspected that elevated water temperatures are a contributing factor in its decline.
• The upper thermal tolerances of glochidia and juvenile life stages were evaluated within each river. Mussels were acclimated to 27°C and tested across a range of temperatures (30–39°C) in 24 h (glochidia) and 96 h (juveniles) laboratory tests. The resulting tolerances were related to in situ water temperature and discharge using a uniform continuous above-threshold analysis.
• In the Llano, the 24 h LT50 (lethal temperature resulting in 50% mortality) was 31.8°C (95% CI 31.5–32.1°C), whereas the 96 h LT50 was 32.4°C (95% CI 32.1–32.7°C). In the San Saba, the 24 h LT50 was 34.7°C (95% CI 34.5–35.0°C), whereas the 96 h LT50 was 32.5°C (95% CI 32.2–32.9°C). LT50 thresholds were not exceeded for L. bracteata within the San Saba, but LT05 (lethal temperature resulting in 5% mortality) thresholds were exceeded. Water temperature loggers were lost in the Llano River as a result of a large flood; however, samples reported by the Texas Commission on Environmental Quality show that the LT05 and LT50 for both glochidia and juveniles were exceeded.
• Findings from this study indicate that thermal tolerances of L. bracteata vary by population and that low flows may be contributing to its decline. Our approach is non-species and region specific, which means that the methods presented should help managers and conservationists evaluate whether reduced water quantity and elevated temperatures are exerting impacts on aquatic species within their region.
