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Low streamflows can increase vulnerability to warming, impacting coldwater fish. Water managers need tools to quantify these impacts and predict future water temperatures. Contrary to most statistical models' assumptions, many seasonally changing factors (e.g., water sources and solar radiation) cause relationships between flow and water temperature to vary throughout the year. Using 21 yr of air temperature and flow data, we modeled daily water temperatures in California's snowmelt‐driven Scott River where agricultural diversions consume most summer surface flows. We used generalized additive models to test time‐varying and nonlinear effects of flow on water temperatures. Models that represented seasonally varying flow effects with intermediate complexity outperformed simpler models assuming constant relationships between water temperature and flow. Cross‐validation error of the selected model was ≤1.2°C. Flow variation had stronger effects on water temperatures in April–July than in other months. We applied the model to predict effects of instream flow scenarios proposed by regulatory agencies. Relative to historic conditions, the higher instream flow scenario would reduce annual maximum temperature from 25.2° to 24.1°C, reduce annual exceedances of 22°C (a cumulative thermal stress metric) from 106 to 51 degree‐days, and delay onset of water temperatures >22°C during some drought years. Testing the same modeling approach at nine additional sites showed similar accuracy and flow effects. These methods can be applied to streams with long‐term flow and water temperature records to fill data gaps, identify periods of flow influence, and predict temperatures under flow management scenarios. Plain Language Summary: Warm water temperatures threaten culturally and economically important salmon in Pacific Northwest Rivers, causing chronic stress and direct mortality. Climate change and agricultural water use have reduced summer river flows in recent decades, intensifying water scarcity. Years with deep mountain snowpack and resulting high groundwater levels extend the high flow season and keep water temperatures cool through the end of July, whereas in drought years the river warms sooner. We used 21 yr of river flow and air temperature data from the Scott River, California, to create computer models that simulate water temperatures. Our models allow the effect of flow on water temperatures to vary by season (i.e., stronger cooling effects in spring and summer), improving accuracy of the simulated temperatures. We used the Scott River model to simulate water temperatures under two alternative flow scenarios considered in local water management plans. Our simulations indicate that relative to current conditions, the higher flow scenario would lower the summers' highest temperatures and decrease the number of days that river temperatures exceed a biological threshold. Testing the same modeling approach at nine additional Klamath Basin sites showed similar accuracy and flow effects. Our model is freely available for public use. Key Points: In this snowmelt and groundwater‐influenced river, water temperatures stayed cool later into summer in high‐flow years than low‐flow yearsStatistical water temperature model predictions became more accurate when the influence of river flow was allowed to vary seasonallyThese accessible models can be applied to other rivers or streams with daily, long‐term flow and water temperature records [ABSTRACT FROM AUTHOR]

Accurately predicting the effects of future warming on aquatic ectotherms requires an understanding how thermal history, including average temperature and variation, affects populations of the same species. However, many laboratory studies simplify the thermal environment to focus on specific organismal responses and sacrifice environmental realism. Here, we paired laboratory-based transcriptomic RNA-seq analysis to identify thermally responsive genes with NanoString analysis of a subset of those genes to characterize natural field-based variation in thermal physiology among populations. We tested gene expression responses of three populations of field-acclimatized larval caddisflies (Dicosmoecus gilvipes) from streams in different eco-regions (mountain, valley, and coast) following exposure to current and future summertime temperatures. We hypothesized that distinct thermal histories across eco-regions could differentiate populations at baseline "control" levels of gene expression, as well as gene expression changes in response to dailywarming and heat shock. Population-specific patterns of gene expression were apparent under the control and daily warming conditions suggesting that local acclimatization or local adaptation may differentiate populations, while responses to extreme temperatures were similar across populations, indicating that response to thermal stress is canalized. Underlying gene co-expression patterns in the daily warming and heat shock treatments were different, demonstrating the distinct physiological mechanisms involved with thermal acclimatization and response to thermal stress. These results highlight the importance and limitations of studies of the thermal biology of wild-caught organisms in their natural environment, and provide an important resource for researchers of caddisflies and aquatic insects in general. [ABSTRACT FROM AUTHOR]

Hybridization between native and non‐native species is an ongoing global conservation threat. Hybrids that exhibit traits and tolerances that surpass parental values are of particular concern, given their potential to outperform native species. Effective management of hybrid populations requires an understanding of both physiological performance and the underlying mechanisms that drive transgressive hybrid traits. Here, we explore several aspects of the hybridization between the endangered California tiger salamander (Ambystoma californiense; CTS) and the introduced barred tiger salamander (Ambystoma mavortium; BTS). We assayed critical thermal maximum (CTMax) to compare the ability of CTS, BTS and F1 hybrids to tolerate acute thermal stress, and found that hybrids exhibit a wide range of CTMax values, with 33% (4/12) able to tolerate temperatures greater than either parent. We then quantified the genomic response, measured at the RNA transcript level, of each salamander, to explore the mechanisms underlying thermal tolerance strategies. We found that CTS and BTS have strikingly different values and tissue‐specific patterns of overall gene expression, with hybrids expressing intermediate values. F1 hybrids display abundant and variable degrees of allele‐specific expression (ASE), likely arising from extensive compensatory evolution in gene regulatory mechanisms between CTS and BTS. We found evidence that the proportion of genes with allelic imbalance in individual hybrids correlates with their CTMax, suggesting a link between ASE and expanded thermal tolerance that may contribute to the success of hybrid salamanders in California. Future climate change may further complicate management of CTS if hybrid salamanders are better equipped to deal with rising temperatures. [ABSTRACT FROM AUTHOR]

As rivers warm, cold‐water fish species may alleviate thermal stress by moving into localized thermal refuges such as cold‐water plumes created by cool tributary inflows. We quantified use of two tributary confluence plumes by juvenile steelhead, Oncorhynchus mykiss, throughout the summer, including how trout positioned themselves in relation to temperature within confluence plumes. At two confluences, Cedar and Elder creeks, along the South Fork Eel River, California, USA, we monitored temperatures using in situ logger grids throughout summer 2016. Fish were counted within confluences via snorkel surveys five times a day on 5 days at each site. We found diel and seasonal dependence on confluence use by steelhead, especially at the Cedar Creek confluence, where mainstem temperatures exceeded 28°C. At this site, fish moved into the confluence on the warmest days and warmest times of the day. Fish observed within the Cedar Creek confluence plume were most common in locations between 20–22°C, rather than the coldest locations (14.5°C). At Elder Creek, where mainstem temperatures remained below 24°C, there was little relationship between mainstem temperature and steelhead presence in the confluence plume. At both sites, steelhead distribution within plumes was influenced by spatial variation of temperature and mean temperature in surveyed grid cells. Our results show that cool tributaries flowing into warmer mainstem reaches (over 24°C) likely create important thermal refuges for juvenile steelhead. As mainstem rivers warm with climate change, cool‐water tributary inputs may become more important for sustaining cold‐water salmonids near the southern end of their range. [ABSTRACT FROM AUTHOR]

Marine habitat‐forming species often play critical roles on rocky shores by ameliorating stressful conditions for associated organisms. Such ecosystem engineers provide structure and shelter, for example, by creating refuges from thermal and desiccation stresses at low tide. Less explored is the potential for habitat formers to alter interstitial seawater chemistry during their submergence. Here, we quantify the capacity for dense assemblages of the California mussel, Mytilus californianus, to change seawater chemistry (dissolved O2, pH, and total alkalinity) within the interiors of mussel beds at high tide via respiration and calcification. We established a living mussel bed within a laboratory flow tank and measured vertical pH and oxygen gradients within and above the mussel bed over a range of water velocities. We documented decreases of up to 0.1 pH and 25 μmol O2 kg−1 internal to the bed, along with declines of 100 μmol kg−1 in alkalinity, when external flows were < 0.05 m s−1. Although California mussels often live in habitats subjected to much faster velocities, sizeable populations also inhabit bays and estuaries where such moderate flow speeds can occur > 95% of the time. Reductions in pH and O2 inside mussel beds may negatively impact resident organisms and exacerbate parallel human‐induced perturbations to ocean chemistry while potentially selecting for improved tolerance to altered chemistry conditions. [ABSTRACT FROM AUTHOR]

Rock environments both underground and on Earth's surface show indications of energetic macroscale fracture. In tunnels and excavations, these manifest as rockbursts—energetic explosions of rock that can damage engineering projects, and may pose ongoing financial and safety risk as rock stresses adjust during post-failure relaxation. In natural settings at the surface, evidence for rockbursts exist in the form of tent-like structures of ruptured exfoliation sheets, but few direct observations of such events exist, precluding the analysis of how natural rock formations may evolve after rupture. Here we investigate the post-failure evolution of a granitic rock dome following rapid fracture events (i.e., surficial rockbursts) that occurred in California, USA during 2014–2016. Building upon previous work that showed a thermal stress origin for the observed fracturing, we investigate the return to background stress conditions (i.e., stress relaxation) observed in both short- (week, month) and long-term (multi-year) rock deformation trends. Acoustic emissions, deformation, and environmental monitoring data indicate that partially detached rock sheets forming the surface of the dome undergo fracture aperture closing during cooling periods, concurrent with reduction of rock stress by the source of forcing (i.e., thermal stress). However, with sufficient critical and/or subcritical fracture, our observations also show that rock sheets can become decoupled from the source of stress, resulting in a long-term return to background stress conditions. Our results provide insight into the cyclic and likely ephemeral nature of rock fracture in surficial rock domes, as well as in underground rockburst environments. [ABSTRACT FROM AUTHOR]

Intertidal communities of wave-swept rocky shores have served as a powerful model system for experiments in ecology, and mussels (the dominant competitor for space in the mid-intertidal zone) play a central role in determining community structure in this physically stressful habitat. Consequently, the ability to account for mussels' physiological responses to thermal stress affects ecologists' capacity to predict the impacts of a warming climate on this ecosystem. Here, we examined the effect of heating rate on cardiac thermal tolerance in the ribbed mussel, Mytilus californianus, comparing populations from high and low sites in the intertidal zone where emersion duration leads to different mean daily heating rates. Two temperature-related cardiac variables were examined: (1) the critical temperature (Tcrit) at which heart rate (HR) precipitously declines, and (2) flatline temperature (FLT) where HR reaches zero. Mussels were heated in air at slow, moderate and fast rates, and HR was measured via an infrared sensor affixed to the shell. Faster heating rates significantly increased Tcrit in high- but not low-zone mussels, and Tcrit was higher in high- versus low-zone mussels, especially at the fastest heating rate. By contrast, FLT did not differ between zones, and was minimally affected by heating rate. As heating rate significantly impacted high- but not low-zone mussels' cardiac thermal tolerance, realistic zone-specific heating rates must be used in laboratory tests if those tests are to provide accurate information for ecological models attempting to predict the effects of increasing temperature on intertidal communities. [ABSTRACT FROM AUTHOR]

Responses of marine ectotherms to variable environmental temperature often entails maintanence of cellular homeostasis and physiological function through temperature compensation and physiological changes. We investigated the physiological response to thermal stress by examining proteomic changes in the marine kelp forest gastropod and emerging fisheries species Kellet's whelk (Kelletia kelletii) across a naturally-existing thermal gradient that ranges from a warmer-water site inside the species' native range and extends to the northern, cold-water edge of the range. We hypothesized that abundance of cellular stress response and energy metabolism proteins would increase with decreasing temperature in support of cold-compensation. Our exploratory proteomic analysis of whelk gill tissue (N = 6 whelks) from each of the four California Channel Island sites revealed protein abundance changes related to the cytoskeleton, energy metabolism/oxidative stress, and cell signaling. The changes did not correlate consistently with temperature. Nonetheless, whelks from the coldest island site showed increased abundance of energy metabolism and oxidative stress proteins, possibly suggesting oxidative damage of lipid membranes that is ameliorated by antioxidants and may aid in their cold stress response. Similarly, our exploratory analysis revealed abundances of cell signaling proteins that were higher at the coldest site compared to the warmest site, possibly indicating an importance for cell signaling regulation in relatively cooler environments. This study provides protein targets for future studies related to thermal effects in marine animals and may contribute to understanding the physiological response of marine organisms to future ocean conditions. • Whelks (Kelletia kelletii) have expanded their range northward into cooler habitats. • We used proteomics to investigate the cost of environmental thermal variability. • Proteomics suggest whelks respond to thermal changes with metabolic compensation. • Changes in antioxidant proteins revealed possible oxidative damage to membranes. • This is the first proteomic analysis of whelks responding to thermal variability. [ABSTRACT FROM AUTHOR]

Rock domes, with their onion-skin layers of exfoliation sheets, are among the most captivating landforms on Earth. Long recognized as integral in shaping domes, the exact mechanism(s) by which exfoliation occurs remains enigmatic, mainly due to the lack of direct observations of natural events. In August 2014, during the hottest days of summer, a granitic dome in California, USA, spontaneously exfoliated; witnesses observed extensive cracking, including a ~8000 kg sheet popping into the air. Subsequent exfoliation episodes during the following two summers were recorded by instrumentation that captured—for the first time—exfoliation deformation and stress conditions. Here we show that thermal cycling and cumulative dome surface heating can induce subcritical cracking that culminates in seemingly spontaneous exfoliation. Our results indicate that thermal stresses—largely discounted in dome formation literature—can play a key role in triggering exfoliation and therefore may be an important control for shaping domes worldwide. [ABSTRACT FROM AUTHOR]

• Mechanism of 2012 Brawley swarm is explored via numerical simulation • Simulation result (flow rate, pressure, surface deformation) reproduces observation • Surface deformation is primarily driven by normal fault slip • Stress transfer via aseismic normal faulting triggered the deeper Brawley swarm Surface deformation and earthquake swarms are correlated in space and time with operations at the Brawley geothermal field in southern California. The seismicity culminated in 2012, about 2 years after the onset of geothermal activity, with a M5.4 earthquake. These earthquakes occurred at a >5km depth, much larger than the ∼1km reach of the geothermal wells, raising questions about the triggering mechanism. Surface deformation shows that aseismic slip on a normal fault intersecting the geothermal reservoir preceded the swarm and possibly triggered it. In this study, we resort to geomechanical modeling to investigate how the sequence of aseismic and seismic slip unfolded. The modeling accounts for thermo- and poro-elastic stress changes induced by the geothermal operations and allows for inelastic deformation and faulting of the reservoir and surrounding medium. The simulation successfully reproduces the flow rates and well-head pressures reported by the operator as well as the measured surface subsidence. By varying the model parameters, we show that the surface subsidence is due to thermal contraction and normal faulting. The fault reactivation is driven by pressure changes and thermal unclamping. The pressure-driven reactivation is rapid and influences a larger area, while the temperature-driven reactivation is more gradual and more localized near the injection wells. In our simulation, aseismic normal faulting driven by the geothermal operation leads to elastic stress release via yielding and faulting within the reservoir volume and, conversely, to stress build-up beneath the reservoir, where the 2012 swarm developed. Such a stress transfer provides a plausible explanation for the 2012 Brawley swarm. Our study shows how a geothermal operation can, in principle, contribute to seismic hazard mitigation through the aseismic release of tectonic stresses within a geothermal field but points to the difficulty of mitigating the hazard posed by stress transfers in the surrounding area. [ABSTRACT FROM AUTHOR]

This study compared the heat-shock response and metabolic energy status in hatchery-raised and two groups of wild-caught steelhead trout parr collected from the Navarro River watershed, California. Wild parr were from coastal and inland sites with different thermal regimes. Fish were exposed in the laboratory to 25 ± 0.2°C for 2-h and the heat-shock response was assessed in muscle tissue via induction of heat-shock proteins (hsps) 63, 72, 78, and 89. Metabolic measurements included muscle phosphocreatine (PCr), ATP, ADP, and AMP, and hepatic glycogen. Inland and coastal fish overlapped considerably with regard to their hsp responses and energetic endpoints, but hatchery fish were distinct in the biochemical patterns they exhibited. Hsp expression levels after temperature shock were significantly lower in hatchery than in wild fish. Hatchery fish also had significantly lower hepatic glycogen and higher muscle ADP, ATP, and PCr concentrations than wild fish. Coastal and inland steelhead did not differ significantly with regard to peak hsp72 and hsp89 levels or to concentrations of energy metabolites. However, fish from the warm-water, inland site expressed significantly less hsp63, maintained higher basal levels of hsp72, and induced hsp89 more slowly than fish from the cold-water, coastal site. Discriminant function analysis revealed that hatchery fish can be distinguished from wild Navarro River fish with 84.9% certainty using the following function: f( x) = - 43.6 + 0.14(Gly) + 4.1(PCr) + 186.4(AMP) + 80.8(ADP) - 0.14(hsp63) + 0.005(hsp72). This study demonstrates that within a single species, rearing conditions or genetic variation can influence an organism's disposition and cellular response to thermal stress. Extrapolation of results from laboratory studies on hatchery fish to wild fish may therefore not be possible, and caution must be used when interpreting hsp data obtained for wild fish with different thermal histories. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the first results obtained in a facility constructed at the University of California, Los Angeles to study the interaction of ceramic breeder pebble beds with structural materials in conditions relevant to fusion energy power plant blanket operations. The experiments study the thermo-mechanical performance of lithium meta-titanate oxide (Li2TiO3) pebbles and silicon carbide clad constrained by a low thermal expansion alloy in vacuum and He atmosphere. The results show that large deformations due to induced thermal stresses are present during the first heat cycle but afterward are accommodated by a combination of pebble re-arrangement within the bed and thermally induced creep deformation. Initial results of a numerical simulation of the experiments using a finite element code that includes creep deformation is also presented. Planned operation of the UCLA thermo-mechanics test facility is summarized to conclude the paper. [Copyright &y& Elsevier]

Presents abstracts of studies on temperature regulation and fluid balance, presented at the Experimental Biology/International Union of Physiological Sciences 2005 congress held in San Diego, California. "Plasma Cytokine Response During Heat Strain Recovery in Mice," by Lisa R. Leon and Michael Blaha; "Effects of Thermal Stress on Vascular Pressures in Humans," by Craig G. Crandall, Carsten Tollund et al.; "Role of Depolarizing TRP Currents in Hypothalamic Neuronal Warm Sensitivity," by Yanmei Zhao and Jack A. Boulant.

Thermal microrefugia, sites within a landscape which are relatively protected from temperature extremes and warming trends, may be necessary for the conservation of animal species as climates warm. In freshwater environments, cold water fish species such as Pacific salmonids already rely on thermal microrefugia to persist in the southern extent of their range. Identifying sites that can provide such thermal microrefugia is essential to inform conservation and management decisions. At present, however, there is no consensus on appropriate ways to identify such sites, and multiple approaches are presented in the literature. Here, we use high resolution thermal data from two cold‐water zones created at the confluence of tributaries with a warm main channel of the South Fork Eel River in Northern California to demonstrate that the characteristics of cold zones identified as thermal microrefugia are not robust to the choice of microrefugium definition. Common definitions disagree on the existence, volume, seasonal temporal trends, and diurnal variations in microrefugia at the two confluences. The disagreements arise from the complex interaction between the confluence mixing regime with diurnal/seasonal warming patterns and how this shapes the distribution of water temperature at the confluences, and how it is classified by each definition. The disagreements cannot be resolved by simple bias correction approaches. Given that all existing definitions rely on simplifications that negate the nuanced way fish use cold water zones and respond to thermal stress, alternative observation and classification approaches may be needed to characterize cold zones in rivers as thermal microrefugia. [ABSTRACT FROM AUTHOR]