Water temperature drives variability in salmonfly abundance, emergence timing, and body size

Abstract

Freshwater organisms are disproportionately impacted by climate change and human disturbance, resulting in shifts in species' distributions and life histories. We coupled contemporary and historical datasets documenting physical and ecological variables over four decades to quantify changes in the abundance, emergence timing, and body size of salmonflies (Pteronarcys californica) in the Madison River in southwest Montana. In contemporary surveys, water temperature was the main driver of salmonfly abundance, emergence timing, and body size. Salmonfly densities were negatively correlated with summer water temperature, which explained 60% of variation in larval density among sites, whereas substrate type played a negligible role. Emergence occurred 20 days earlier, and male and female exuvia length were 13.8% and 11.3% shorter, respectively, at the warmest site relative to the coolest site (4°C difference). These patterns were supported by historical data. For example, a 1.2°C increase in mean annual water temperature in the Madison River between 1977 and 2017 coincided with evidence for upstream range contraction. Between 1973 and 2017, emergence timing varied widely among years, occurring up to 41 days earlier in years when spring water temperatures were relatively warm. As climate change progresses,we predict that salmonflies could be extirpated from an additional 28 km of currently occupied habitat, representing a 22.6% reduction in suitable habitat along the Madison River. This study provides evidence of long-term biological change of an aquatic insect and highlights the importance of combining spatial and historical datasets to better understand species' responses to environmental stressors across both space and time.

Thermal Regimes of Perennial Rivers and Streams in the Western United States

“…Previous research in the West has used similar geospatial scenarios of mean August stream temperature, also developed from the NorWeST database and closely allied with PC1, to begin addressing at least some thermal ecology questions. These include predicting where in river networks species invasions, range contractions from climate warming, and hybridization zones may occur near thermally mediated boundaries (Al‐Chokhachy et al 2016; Young et al 2016; Rubenson and Olden 2019); understanding phenological cues for aquatic insects (Anderson et al 2019), developing accurate species distribution models to estimate the effect of temperature relative to other environmental covariates (Isaak et al 2017b; Wilcox et al 2018), assessments of migration success and interspecific competition (Westley et al 2015; Myrvold and Kennedy 2017; Rinnan 2018); and precise identification of climate refuge streams throughout the ranges of species of conservation concern (Isaak et al 2015; Palmer 2017; Young et al 2018). None of these early applications have relied on datasets derived from simultaneous collection of temperature and biological datasets, but instead as Hill and Hawkins (2014) also demonstrate, simply referenced existing biological survey information from separate sources against accurate stream temperature scenario maps.…”

Quantifying the habitat preferences of the stoneflyPteronarcys californicain Colorado

“…There are many biotic and abiotic factors that affect the distribution and abundance of invertebrate species and more research is needed to investigate other factors that influence salmonfly density. Water temperature is an abiotic factor recently reported to influence salmonfly abundance in the Madison River in Montana (Anderson et al, 2019). We purposely restricted our sampling sites to river reaches well within the known range of P. californica to achieve our objective of exploring physical habitat characteristics within a stream reach where temperature (and other environmental factors) was not likely to limit distribution.…”

“…Due to a recent paper suggesting that temperature affects salmonfly density (Anderson et al, 2019), a post hoc analysis was conducted to evaluate if our sites were similar enough in temperature regime to accomplish our objectives of comparing only physical habitat variables. To evaluate stream temperature variability at our sites we used modelled stream temperatures from NorWeST, a western United States stream temperature model (Isaak et al, 2017).…”

“…While found in high abundance at some sites, the salmonfly has relatively specific environmental requirements and is classified a sensitive species in bioassessment protocols (Barbour, Gerritsen, Snyder, & Stribling, 1999; Bryce, Lomnicky, & Kaufmann, 2010; Fore, Karr, & Wisseman, 1996). The sensitivity of P. californica to disturbance and habitat alteration has led to declines in range and numbers in several rivers of the Intermountain West (Anderson, Albertson, & Walters, 2019), including the Logan and Provo rivers in Utah (Birrell, Meek, & Nelson, 2019; Elder & Gaufin, 1973), and several rivers in Montana (Anderson et al, 2019; Stagliano, 2010). In Colorado, the range of salmonflies has declined in both the upper Gunnison and Colorado rivers, primarily due to changes in habitat quality and flow alterations associated with river impoundments (Elder & Gaufin, 1973; Nehring et al, 2011).…”

Thermal variability drives synchronicity of an aquatic insect resource pulse

“…On the Madison River in particular, a 44‐yr record demonstrates that salmonfly emergence date is strongly correlated with spring water temperature over time, with emergence occurring earlier in years when spring water temperatures are relatively warm (Anderson et al. ).…”