Rising water temperatures in rivers due to climate change are already having observable impacts on river ecosystems. Warming water has both direct and indirect impacts on aquatic life, and further aggravates pervasive issues such as eutrophication, pollution, and the spread of disease. Animals can survive higher temperatures through physiological and/or genetic acclimation, behavioral and phenological change, and range shifts to more suitable locations. As such, those animals that are adapted to cool‐water regions typically found in high altitudes and latitudes where there are fewer dispersal opportunities are most at risk of future extinction. However, sub‐lethal impacts on animal physiology and phenology, body‐size, and trophic interactions could have significant population‐level effects elsewhere. Rivers are vulnerable to warming because historic management has typically left them exposed to solar radiation through the removal of riparian shade, and hydrologically disconnected longitudinally, laterally, and vertically. The resilience of riverine ecosystems is also limited by anthropogenic simplification of habitats, with implications for the dispersal and resource use of resident organisms. Due to the complex indirect impacts of warming on ecosystems, and the species‐specific physiological and behavioral response of organisms to warming, predicting how river ecosystems will change in the future is challenging. Restoring rivers to provide connectivity and heterogeneity of conditions would provide resilience to a range of expected co‐occurring pressures, including warming, and should be considered a priority as part of global strategies for climate adaptation and mitigation.This article is categorized under: Science of Water > Water and Environmental Change Water and Life > Nature of Freshwater Ecosystems Water and Life > Stresses and Pressures on Ecosystems

Restoration of degraded freshwater ecosystems has gained considerable attention in the USA over the past decades. However, most projects focus almost entirely on the restoration of physical habitat or specific water quality parameters, while ignoring critical ecological processes related to food web re-establishment. In this study, we investigate the impact of riparian habitat in different stages of restoration on food availability for fish in four streams in Pennsylvania, USA. The riparian buffer habitats ranged from open meadow to mature forest and included new to long-term restoration sites. We quantified abundance and community composition of aquatic macroinvertebrates and riparian arthropods with aerial and ground-dwelling life history strategies. We found that riparian habitat and water temperature exert a strong influence over potential food resources for fish, with the open meadow habitat having highest abundance of terrestrial and aquatic insects, lowest taxa richness, and possible multivoltine aquatic insect life-history. Our results provide insight into the importance of riparian buffer habitat and water temperature on the composition of food availability for fish species of concern such as brook trout. The significant differences emphasize the need to include food web dynamics into riparian habitat restoration design to guide future rehabilitation projects focusing on fish conservation.

Animals that burrow, forage, or produce physical structures can have substantial impacts on transport processes related to erosion. However, the influence of behavior and body size on regulating the magnitude of engineering effects by animals is not well understood. For example, crayfish are common and abundant freshwater organisms that disturb sediments in ways that influence gravel transport, fine sediment suspension, and bank stability. Animals such as crayfish also display complex territorial and aggressive behaviors, often related to body size, which might influence their ability to influence sediment transport dynamics. We conducted an experiment with spiny-cheek crayfish (Faxonius limosus) to investigate the influence of behavior and body size on substrate disturbance. The experiment included 4 enclosure (0.31-m long × 0.21-m wide × 0.17-m deep) treatments that differed in the body size of individual crayfish and the amount of biomass: 1) 2 small young-of-the-year (YOY) crayfish of 15-mm ca...

Crayfish are one of the most prolific freshwater invaders, yet the role of crayfish as ecosystem engineers that structure benthic substrates in their nonnative habitat is rarely studied. We used an in situ experimental manipulation to document changes in sediment dynamics and macroinvertebrate density and richness caused by the presence or absence of invasive rusty crayfish (Orconectes rusticus). Rusty crayfish reduced fine-sediment accumulation and increased pit and mound structures in the river bed by moving gravels at the bed surface. We predicted that this omnivorous species would directly reduce macroinvertebrate density and richness, but we found that macroinvertebrate density was higher in treatments with rusty crayfish present and that macroinvertebrate richness did not differ between treatments with and without crayfish. Our findings suggest that rusty crayfish, which are spreading throughout the northeast USA, are probably important engineers of physical habitat structure in stream ecosystems. Rusty crayfish may also have unexpected, facilitative consequences for other benthic species by reducing fine-sediment accumulation in streams that are sediment impaired. Our study illustrates that biological forces can influence benthic gravel-size distributions and topography and suggests that crayfish may be important drivers of substrate-sorting dynamics and disturbance regimes, with consequences for community structure in streams where they are invasive.