Underlying geology and climate interactively shape climate change refugia in mountain streams

Abstract

Identifying climate‐change refugia is a key adaptation strategy for reducing global warming impacts. Knowledge of the effects of underlying geology on thermal regime along climate gradients and the ecological responses to the geology‐controlled thermal regime is essential to plan appropriate climate adaptation strategies. In the present study, the dominance of volcanic rocks in the watershed is used as a landscape‐scale surrogate for cold groundwater inputs to clarify the importance of underlying geology in stream ecosystems along climate gradients. First, using hundreds of monitoring stations distributed across multiple catchments, we explored the relationship between watershed geology and the mean summer water temperature of mountain streams along climate gradients in the Japanese archipelago. Mean summer water temperature was explained by the interaction between the watershed geology and climate in addition to independent effects. The cooling effect supported by volcanic rocks reached up to 3.3°C among study regions, which was more pronounced in streams with less summer precipitation or lower air temperatures. Next, we examined the function of volcanic streams as cold refugia under contemporary and future climatic conditions. Community composition analyses revealed that volcanic streams hosted distinct stream communities composed of more cold‐water species compared with nonvolcanic streams. Scenario analyses based on multiple global climate models and Representative Concentration Pathways (RCPs) revealed a geology‐related pattern of thermal habitat loss for cold‐water species. Nonvolcanic streams rapidly declined in thermally suitable habitats for lotic sculpins even under the lowest emission scenario (RCP 2.6). In contrast, most volcanic streams will be sustained below the thermal threshold, especially for low‐ and mid‐level emission scenarios (RCP 2.6, 4.5). However, the distinct stream community in volcanic streams and geology‐dependent habitat loss for lotic sculpins was not uniform and were more pronounced in streams with less summer precipitation or lower air temperatures. These findings highlight that underlying geology, climate variability, and their interaction should be considered simultaneously for the effective management of climate‐change refugia in mountain streams.

Stream groundwater inputs generate fine‐scale variation in brook trout phenology and growth across a warming landscape

“…The warmer incubation temperatures at groundwater-dominated sites can significantly advance brook trout phenology (Crisp, 1981), whereas their cooler temperatures during the summer can provide suitable habitat for juveniles after emergence (Borwick et al, 2006). Similar patterns have been documented in other coldwater fish species (Beacham & Murray, 1990), and recent research suggests that groundwater-dominated streams harbour distinct and more temporally stable ecological communities (Hitt et al, 2023;Ishiyama et al, 2023). Thus, brook trout can serve as a model for understanding the diverse impacts of groundwater on coldwater fish populations.…”

“…Such fine‐scale variation has largely been overlooked in past assessments of brook trout conservation status and climate vulnerability (Fesenmyer et al., 2017; Flebbe et al., 2006; Hudy et al., 2008), so future research should develop tools that enable managers to incorporate stream‐specific thermal regimes into decision‐making. More widespread data collection would facilitate this process, as paired air–stream temperature monitoring (Ishiyama et al., 2023), thermal infrared cameras (Iwasaki et al., 2023; Morgan & O'Sullivan, 2022) and high‐resolution models (e.g., DeWeber & Wagner, 2014) offer promising ways to identify and preserve thermal refuges for many species.…”

“…Stream temperatures often exhibit strong temporal autocorrelation (Johnson et al., 2020), so residual autocorrelation functions were plotted within each stream and all air–stream temperature relationships were re‐estimated with an autoregressive error structure using the nlme package in R (Pinheiro et al., 2022). Finally, precipitation can affect stream temperature positively (Ishiyama et al., 2023) or negatively (Carlson et al., 2019), so residuals from air–stream temperature relationships from March to November were regressed on daily precipitation data from the DayMet database to explore its effects within each stream. This period was selected because precipitation often influences stream temperature most strongly during the warmest months (Carlson et al., 2019), whereas wintertime effects may be unreliable in Cape Race because high winds often limit accumulation of snow.…”

Cold-water habitats, climate refugia, and their utility for conserving salmonid fishes

“…From a broader biodiversity perspective, there are a variety of non-salmonid fishes (Troia et al 2019;Cussac et al 2020;Sharma et al 2021;Ishiyama et al 2023), macroinvertebrates, and amphibian species (Milanovich et al 2010;Hotaling et al 2017) that are restricted to cold headwater streams, considered to be climate sensitive, and could also be good candidates for SDMs to delineate climate refugia. It is unknown how accurately the distributions of these species could be predicted based on the environmental gradients that appear relevant to salmonids, but exploratory analyses would be intriguing and may yield encouraging results.…”

Hot spots in a cold river synchronize temporarily separated salmon runs in their offspring’s development

“…Temperature regime changes are considered extrinsic stressors because many ectotherms, including freshwater species, are characterized by specific thermal adaptations and tolerances (Deutsch et al, 2008; Sunday et al, 2014; Comte et al, 2014). To this end, the identification of thermal heterogeneity and spatially temporally projected population dynamics of concerned species has progressed in recent years, and potentially available adaptive strategies have been proposed in contemporary freshwater research, especially for cold-water fish, including salmonid species (Fullerton et al, 2017; 2018; Morelli et al, 2020; Ishiyama et al, 2023). These relationships are spatially diverse and specific to underlying climates, geology, land use, and the level of hydrological alterations.…”