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Identifying the most important factors affecting population growth in animal life cycles is an important tool of species conservation. Delta Smelt (Hypomesus transpacificus), an annual fish endemic to the San Francisco Estuary in California (USA), has been provided legal protection since 1993 but 30 years later exists in a conservation‐reliant state on the brink of extinction. Despite considerable controversies about what factors are most responsible for the species' decline, no population growth rate sensitivity comparisons between the most important factors regulating growth have been done. Nor has anyone attempted to quantitatively identify habitat conditions needed to support positive population growth. We developed a set of stage‐structured population models to link habitat indices regulating recruitment of new generations of fish as they metamorphosed into juveniles and the subsequent survival of those fish over several seasons until they reached adulthood. These models are used to quantify drivers of growth rate variation over 30 years. Several complimentary sensitivity analyses indicated freshwater outflow to the estuary during summer had the largest potential to change population growth. Multiple habitat metrics (e.g., food availability, temperature) influencing recruitment and life stage specific survival rates across different seasons interacted in nonlinear ways to determine habitat conditions and water management targets associated with positive population growth. We discuss the implications for freshwater management, Delta Smelt conservation, and the challenges climate change poses for co‐implementation of these two societal priorities. [ABSTRACT FROM AUTHOR]

The impacts of climate change are widespread and threaten natural systems globally. Yet, within regions, heterogeneous physical landscapes can differentially filter climate, leading to local response diversity. For example, it is possible that while freshwater lakes are sensitive to climate change, they may exhibit a diversity of thermal responses owing to their unique morphology, which in turn can differentially affect the growth and survival of vulnerable biota such as fishes. In particular, salmonids are cold‐water fishes with complex life histories shaped by diverse freshwater habitats that are sensitive to warming temperatures. Here we examine the influence of habitat on the growth of sockeye salmon (Oncorhynchus nerka) in nursery lakes of Canada's Skeena River watershed over a century of change in regional temperature and intraspecific competition. We found that freshwater growth has generally increased over the last century. While growth tended to be higher in years with relatively higher summer air temperatures (a proxy for lake temperature), long‐term increases in growth appear largely influenced by reduced competition. However, habitat played an important role in modulating the effect of high temperature. Specifically, growth was positively associated with rising temperatures in relatively deep (>50 m) nursery lakes, whereas warmer temperatures were not associated with a change in growth for fish among shallow lakes. The influence of temperature on growth also was modulated by glacier extent whereby the growth of fish from lakes situated in watersheds with little (i.e., <5%) glacier cover increased with rising temperatures, but decreased with rising temperatures for fish in lakes within more glaciated watersheds. Maintaining the integrity of an array of freshwater habitats—and the processes that generate and maintain them—will help foster a diverse climate‐response portfolio for important fish species, which in turn can ensure that salmon watersheds are resilient to future environmental change. [ABSTRACT FROM AUTHOR]

The number of invasive species threatening freshwater habitats are increasing globally, and can be accelerated by climate change. Thus, risk assessments of potential invasive species are required for establishing prevention measures, in which quantitative risk assessments provide results objectively. In this study, the invasion risk of largemouth bass (Micropterus salmoides) in four major river basins (the Han, Nakdong, Geum, and Yeongsan) in South Korea was evaluated using an ensemble of species distribution models (SDMs). A weighted ensemble of the SDMs was developed to predict the probability of largemouth bass occurrence in the present (2011–2015) and two future periods: 2050 (2046–2055) and 2080 (2076–2085). The invasion risk of largemouth bass was evaluated using two approaches: relative and absolute risk assessments. Both approaches predicted an increase in Tier 1 (the highest risk) areas under representative concentration pathway (RCP) 4.5; however, a decrease in the areas of concern under RCP 8.5. In particular, the upper streams of the Nakdong and Han river basins are expected to be at risk in the future. In addition, Tier 1 risk areas are predicted to shift northward under both RCP 4.5 and 8.5 scenarios, especially in the Nakdong River Basin. This study provides a quantitative risk assessment tool based on the SDMs for the management of largemouth bass invasion under climate change. [ABSTRACT FROM AUTHOR]

This document is a summary of a journal article titled "Impacts of Human Activities and Climate Change on Freshwater Fish—Volume II." The article explores the threats faced by freshwater fish due to human activities and climate change, including changes in land and water use, pollution, invasive species, and climate change. It presents case studies from different regions, covering topics such as the importance of macrophytes for fish diversity, the presence of microplastics in fish gastrointestinal tracts, the effects of atrazine exposure on fish behavior, genetic and morphological variations in barbel species, heat tolerance of Thai river fish species, trophic structure of fish communities in subtropical lakes, habitat suitability of native fish species in Central Anatolia, and factors influencing fish beta diversity and size diversity. The article provides valuable insights into the impacts of human-induced changes on freshwater fish and offers potential solutions for conservation efforts. Additionally, the article discusses a study on the ecology of balitorid fish in Thailand, which found that high ammonia levels and river temperatures negatively affected the occurrence and diversity of balitorid fish, while dissolved silica had a positive influence. The study concluded that balitorid fish are vulnerable to climate change and pollution, and recommended reducing anthropogenic pressure to preserve their freshwater habitat. [Extracted from the article]

The Gulf of Maine hosts the southernmost remaining population of North American Atlantic salmon. Despite extensive hatchery supplementation since the late 1800s, and more recent riverine habitat restoration efforts and fishing restrictions, US-origin Atlantic salmon populations continue to decline and have remained at low abundance over recent decades. Climate change has been identified as a critical threat to the future of US Atlantic salmon. In this study, we synthesized available information on how habitats used by Atlantic salmon across all their life stages will be affected by climate change as well as the suitability of future conditions for salmon's persistence in the region. Maintaining sufficient cool water refugia during increasing summer temperatures in riverine habitats is required for sustaining salmon in the future. Changes in groundwater quantity and temperature, which will depend on future precipitation and temperature, will be critical factors for river temperatures, as will land use and land cover. While Atlantic salmon's freshwater life stages are heavily documented, the marine phase is relatively less studied. Climate models predict basin-scale changes over the next century, but impacts to salmon are difficult to predict. Furthermore, disparate drivers and differential rates of change between freshwater and marine habitats could present an obstacle to the transition between phases in the future. We have a general understanding of migration patterns and prey preferences but lack a clear picture of how salmon respond to habitat and ecosystem-level changes associated with climate change progression. More research to understand freshwater habitat changes and salmon's marine spatiotemporal distribution responses will enhance capacities to evaluate future risks and predict impacts of climate change to US-origin Atlantic salmon. [ABSTRACT FROM AUTHOR]

Climate change is affecting freshwater habitats worldwide through multiple, interacting pressures that influence the survival, distribution, and persistence of freshwater organisms. Temporary freshwater habitats, or those that dry seasonally, can exhibit wide‐ranging variability in temperature and drying regimes. Aquatic organisms with complex life cycles (e.g., aquatic and terrestrial life stages) often rely on temporary freshwaters to complete their life cycles and have specific adaptations to cope with these dynamic environments. However, climate change is altering the temperature and drying regime of many temporary freshwater habitats worldwide, often resulting in warmer habitats available for shorter durations of time. The ways in which climate‐mediated changes to temporary freshwaters affect development and life history of aquatic organisms, particularly those with complex life cycles, remains poorly understood.We investigated larval development, growth, survival, and relationships among them for two amphibian species, wood frogs (Lithobates sylvaticus) and spring peepers (Pseudacris crucifer), in response to warming and drying in a mesocosm experiment. Over 13 weeks in the spring and summer of 2019, we manipulated temperature and water levels in 48 outdoor pond mesocosms to produce four treatments: control (ambient conditions), drying alone, warming alone, and drying + warming. We predicted reduced survival, body size, and time to metamorphosis for both species in response to warming and drying, with the effect being stronger on wood frogs due to their more specialised habitat use and shorter breeding period.Warming treatments were on average 2°C higher than controls, and drying treatments decreased water depth by 2.5 cm each week. We found that warming temperature shortened larval time to metamorphosis, and drying decreased body size at metamorphosis. Surprisingly, we also found that, across all treatment groups, individuals with early metamorphosis tended to be larger in size and from mesocosms with generally higher survival.Our study indicates that warming and drying may act independently on different developmental responses for amphibians. Our results echo recent calls for a better understanding of the nuanced, often unpredictable, relationships among climate‐mediated environmental pressures and the developmental traits they influence, particularly for organisms with complex life cycles that depend upon dynamic habitat for growth and survival. Understanding these relationships and the mechanisms that drive them will be key to predicting the response of freshwater organisms to climate change. [ABSTRACT FROM AUTHOR]

Thermal refuges are becoming increasingly influential for dictating the population status and spatial distribution of cold-water stenotherm salmonids in the mid- to southern extent of their range. The global climate is predicted to continue to warm, and therefore, the overall thermal suitability of freshwater habitats for stream salmonids is predicted to decline in concert. However, stream and river thermal heterogeneity will offer considerable resiliency for these populations. Thermal refuges are formed by many physical processes; common natural refuges include cold tributary plumes, groundwater springs, alcoves, and hyporheic upwellings. However, many anthropogenically formed refuges (such as stratified reservoirs or cold-water tailrace outflows) also exist in hydropower-regulated rivers. The significance of these refuges to stream salmonids depends on their size and temperature differential, but also other habitat characteristics such as their depth, flow velocity, Froude number, and many biotic factors within the refuges. Modern technologies such as drone-mounted thermal infrared cameras and other remote sensing techniques allow for the efficient identification of such refuges, and inexpensive options include the identification of refuges during ice cover using orthophotographs. Behavioural thermoregulation, i.e., salmonids aggregating in cold-water refuges, can be either facultative or obligate and the timing of these events is governed by life stage, species, and population-specific physiologically regulated cumulative thresholds that are inherently related to the recent thermal history, or hysteresis, of each individual. Salmonids appear to have an excellent spatial cognition for locating and relocating cold-water refuges, and their spatial distribution is largely affected by the availability of the cold-water refuges during the warm-water period in many thermally stressed rivers. Gregarious behaviour is the norm for salmonid fishes within the thermal refuges; however, the size/microhabitat hierarchy appears to dictate the within-refuge distribution at the micro-scale. There continues to be a great impetus for protecting—and in carefully determined cases creating—cold-water refuges in the future. A thorough understanding of what a "goldilocks" refuge is for various salmonids and their different life stages will be imperative as cold-water restoration is gaining popularity. Finally, disentangling the roles of the climate-induced and landscape activity-induced warming potential of fluvial freshwater will be important to ensure continued environmentally responsible landscape activities in future waterscapes. [ABSTRACT FROM AUTHOR]

Long, S.A.; Mango-Mutiti, C.; Mutiti, S., and Weese, D.A., 2023. Investigating the effects of increasing water salinity on an endemic crayfish. Journal of Coastal Research, 39(5), 816–822. Charlotte (North Carolina), ISSN 0749-0208. The greatest diversity of freshwater crayfish is found in the southeastern United States, home to nearly 75% of the world's known crayfish species. Many of the freshwater habitats for these crayfish are threatened by human activities and face degradation from multiple fronts, one being climate-related sea-level rise. This threat is significant for island populations that are unable to disperse to favorable locations. The goal of this study was to investigate the salinity tolerance of Procambarus lunzi (Hobbs 1940b), a species endemic to a small coastal region in the southeastern United States, to predict how sea-level rise might affect vulnerable coastal populations. A total of 171 crayfish was collected from a barrier island in Georgia and exposed to three treatments: freshwater, a slow salinity increase (salinity raised by 1.5‰ weekly), and a fast salinity increase (salinity raised by 3‰ weekly). Weekly mortalities were recorded and used to compute percent survivorship. Individual body masses were also monitored weekly and the average change in body mass between treatment groups was compared using one-way analysis of variance. Regression analysis was used to assess the relationship between initial body mass and the salinity level tolerated before mortality occurred. There was no significant difference in body mass change between the control group and the salinity treatment groups. The salinity level tolerated before mortality occurred was not correlated with individuals' body mass at the start of the treatments. The first mortality occurred at 30‰ salinity and 50% mortality occurred when salinity was >39‰. These results indicate a high tolerance to salinity that was unexpected for a freshwater species. The implication is that P. lunzi may be able to withstand habitat degradation due to sea-level rise given its relatively high tolerance to increases in salinity. [ABSTRACT FROM AUTHOR]

As the global climate is changing, average water temperatures and the supply of CO2 to water bodies are increasing. To determine how the effects of these changes on freshwater communities interact, we ran a month‐long factorial mesocosm experiment, in which we manipulated water temperature (heated, ambient) and pCO2 (preindustrial, ambient, future). We found that the total phytoplankton biomass responded positively to the pCO2 and temperature treatments but no interactive effects were detected. Green algae were positively affected by temperature and, over the course of the experiment, responded to pCO2 first positively, then negatively. Heterokonts, on the other hand, were unaffected by temperature but responded positively to pCO2. pCO2 enrichment also led to increases in seston C : N stoichiometry, although the experiment ended before we could observe any effects of pCO2 on the zooplankton community composition. Warming caused shifts in zooplankton community composition, primarily through higher abundances of the cladoceran Bosmina longirostris and the rotifer Conochilus unicornis, and lower abundances of the rotifer Polyarthra vulgaris. We found that, in contrast to the effects of temperature, which can be explained by temperature‐dependent plankton growth curves, the responses of algal groups to pCO2 enrichment were difficult to anticipate, despite the availability of priors from previous pCO2 enrichment experiments in the same lake mesocosms. We conclude that climate change‐induced increases in aquatic pCO2 and temperatures are likely to affect pelagic ecosystems, though further research in freshwater systems is needed before generalized claims regarding the simple and interactive effects of pCO2 can be made. [ABSTRACT FROM AUTHOR]

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Waterbirds depend on a dispersed network of wetlands for their annual life cycle during migration. Climate and land use changes raise new concerns about the sustainability of these habitat networks, as water scarcity triggers ecological and socioeconomic impacts threatening wetland availability and quality. During the migration period, birds can be present in large enough numbers to influence water quality themselves linking them and water management in efforts to conserve habitats for endangered populations. Despite this, the guidelines within laws do not properly account for the annual change of water quality due to natural factors such as the migration periods of birds. Principal component analysis and principal component regression was used to analyze the correlations between the presence of a multitude of migratory waterbird communities and water quality metrics based on a dataset collected over four years in the Dumbrăvița section of the Homoród stream in Transylvania. The results reveal a correlation between the presence and numbers of various bird species and the seasonal changes in water quality. Piscivorous birds tended to increase the phosphorus load, herbivorous waterbirds the nitrogen load, while benthivorous duck species influenced a variety of parameters. The established PCR water quality prediction model showed accurate prediction capabilities for the water quality index of the observed region. For the tested data set, the method provided an R2 value of 0.81 and a mean squared prediction error of 0.17. [ABSTRACT FROM AUTHOR]

Simple Summary: Long-term research tends to fall short in the fast-track "publish or perish" research era, even in ecology where it is proven time and time again that natural community variability is sometimes hard to distinguish from the community's response to environmental stressors. In this research, we present how unimpacted freshwater habitats and the dipteran communities therein deal with changing climate and discharge conditions with regard to community structure. Distinguishing "normal" from "extreme" events and taxa indicative of these periods was made possible only after analyzing long-term data. This research presents how freshwater indicator taxa and local dipteran diversity change significantly with regard to extremes in discharge regimes. Most ecologists have used climate change, as an omnipresent pressure, to support their findings in researching the vulnerability of specific taxa, communities, or ecosystems. However, there is a widespread lack of long-term biological, biocoenological, or community data of periods longer than several years to ascertain patterns as to how climate change affects communities. Since the 1950s, southern Europe has faced an ongoing trend of drying and loss of precipitation. A 13-year research program in the Dinaric karst ecoregion of Croatia aimed to comprehensively track emergence patterns of freshwater insects (true flies: Diptera) in a pristine aquatic environment. Three sites, spring, upper, and lower tufa barriers (calcium carbonate barriers on a barrage lake system that act as natural damns), were sampled monthly over 154 months. This coincided with a severe drought event in 2011/2012. This was the most significant drought (very low precipitation rates for an extended period of time) in the Croatian Dinaric ecoregion since the start of detailed records in the early 20th century. Significant shifts in dipteran taxa occurrence were determined using indicator species analysis. Patterns of seasonal and yearly dynamics were presented as Euclidian distance metrics of similarity in true fly community composition compared at increasing time intervals, to ascertain the degree of temporal variability of similarity within the community of a specific site and to define patterns of similarity change over time. Analyses detected significant shifts in community structure linked to changes in discharge regimes, especially to the drought period. [ABSTRACT FROM AUTHOR]

Intensive human exploitation of the Antarctic fur seal (Arctocephalus gazella) in its primary population centre on sub-Antarctic South Georgia, as well as on other sub-Antarctic islands and parts of the South Shetland Islands, in the eighteenth and nineteenth centuries rapidly brought populations to the brink of extinction. The species has now recovered throughout its original distribution. Non-breeding and yearling seals, almost entirely males, from the South Georgia population now disperse in the summer months far more widely and in higher numbers than there is evidence for taking place in the pre-exploitation era. Large numbers now haul out in coastal terrestrial habitats in the South Orkney Islands and also along the north-east and west coast of the Antarctic Peninsula to at least Marguerite Bay. In these previously less- or non-visited areas, the seals cause levels of damage likely never to have been experienced previously to fragile terrestrial habitats through trampling and over-fertilisation, as well as eutrophication of sensitive freshwater ecosystems. This increased area of summer impact is likely to have further synergies with aspects of regional climate change, including reduction in extent and duration of sea ice permitting seals access farther south, and changes in krill abundance and distribution. The extent and conservation value of terrestrial habitats and biodiversity now threatened by fur seal distribution expansion, and the multiple anthropogenic factors acting in synergy both historically and to the present day, present a new and as yet unaddressed challenge to the agencies charged with ensuring the protection and conservation of Antarctica's unique ecosystems. [ABSTRACT FROM AUTHOR]

It has been well documented that periphyton communities play a key role in primary productivity, nutrient cycling, and food web interactions. However, a worldwide overview of research on the key themes, current situation, and major trends within the field is lacking. In this study, we applied the machine learning technique (latent Dirichlet allocation, LDA) to analyze the abstracts of 6690 publications related to periphyton from 1991 to 2020 based on the Web of Science database. The relative frequency of classical and basic research on periphyton related to colonization, biomass, growth rate, and habitats has been clearly decreasing. The increasing trends of research on periphyton are embodied in the periphyton function in freshwater ecosystems (e.g., application as ecological indicators, function in the removal of nutrients, and application in paleolimnology), the research at macroscales (e.g., spatial–temporal variation, and functional and taxonomic diversity), and the anthropogenic themes (e.g., climate warming, response to multiple stressors, and land use type). The keyword and title analysis showed that the periphyton studies are concentrated mainly on diatom aspects, especially with respect to streams relative to lakes. The thematic space based on non-metric multidimensional scaling (NMDS) showed that the classical themes such as growth rate, colonization, and environmental factors (e.g., multiple stressors and climate warming) were most linked to other research themes. We proposed that future trends in the periphyton should focus on the function of periphyton in lakes and their response to multiple environmental pressures with the increasingly extensive eutrophication in lakes and the increasingly significant change in the climate. [ABSTRACT FROM AUTHOR]

As part of the world's largest coordinated network of protected areas, Natura 2000, European Union member states designate special areas of conservation (SACs) to maintain or achieve favourable conservation status for imperilled aquatic species listed under Annex II of the Habitats Directive. Long‐term suitability of SAC habitats is potentially challenged by continuing climate change.To examine this emerging threat to aquatic species conservation, the habitat suitability of designated SACs (n = 8,221) for 24 Central European freshwater species (18 teleosts, two lampreys, two crayfish and two bivalves) was assessed under current and projected end‐of‐century climate using environmental niche models calibrated on species occurrences reported under the Habitats Directive (n = 33,995). Potential future conditions included three climate‐change scenarios representing a gradient from effective climate protection measures to a worst‐case warming scenario.Habitat suitability of SACs was consistently calculated as high under present climate but projected to decline severely for two‐thirds of the species under future climate conditions, with the magnitude of decline generally paralleling that of projected climate change. Under high emission scenarios, one third to more than half of the species were predicted to face unsuitable conditions in ≥75% of SACs. Predicted change in habitat suitability varied across biogeographical regions, with Alpine SACs often undergoing lower or no decline in predicted suitability.Given the discrepancy between the location of currently designated SACs and predicted areas of suitable habitat under projected end‐of‐century climate, climate change can be expected to undermine the long‐term effectiveness of currently protected areas. Fostering climate resilience of freshwater habitats within SACs, restoring stream connectivity among SACs, assisted migration to newly suitable SACs where natural dispersal is not possible, as well as designation of new protected areas within climate refugia represent key actions to overcome this potential future conservation gap. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are exceptionally vulnerable to biological invasions. The introduction of non-native species of fish to Europe has been a common practice, including the introduction of the North American pumpkinseed, Lepomis gibbosus. The range expansion of this species has continued across the continent, with new areas occupied in Ukraine. Using a species distribution modelling approach, predictions are made of the geographic range of the fish based on presence records and environmental variables from the Near-global environmental information for freshwater ecosystems database likely to be associated with habitat suitability and important for the possible further expansion of L. gibbosus. Results show the current widespread distribution of L. gibbosus in Ukraine and prospects for future expansion of the species into Belarus and the Baltic countries. In Latvia, at the potential range edge of L. gibbosus, chances for a spontaneous invasion are relatively low. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Image," published in the journal Ecology, features a photograph of dragonfly nymphs, specifically the rainpool glider nymph (Pantala spp.), which are known for preying on mosquito larvae in various freshwater habitats. The study conducted by Davidson et al. explores the impact of warmer conditions on the predation of mosquito larvae by dragonfly nymphs. Through a combination of theoretical modeling and field data collected from riverine rock pools along the James River in Richmond, Virginia, the study suggests that a changing climate may result in weaker predation of mosquito larvae by dragonfly nymphs. This could potentially lead to a decrease in the effectiveness of predators in controlling populations of prey with distinct life stages, such as mosquitoes. The photo credit goes to Andrew T. Davidson. [Extracted from the article]

Climate change threatens biodiversity through global alteration of habitats, but efficient conservation responses are often hindered by imprecise downscaling of impacts. Besides thermal effects, warming also drives important ancillary environmental changes, such as when river hydrology evolves in response to climate forcing. Earlier snowmelt runoff and summer flow declines are broadly manifested in snow‐dependent regions and relevant to socioeconomically important cold‐water fishes. Here, we mechanistically quantify how climate‐induced summer flow declines during historical and future periods cause complex local changes in Chinook salmon (Oncorhynchus tshawytscha) habitats for juveniles and spawning adults. Changes consisted of large reductions in useable habitat area and connectivity between the main channel and adjacent off‐channel habitats. These reductions decrease the capacity of freshwater habitats to support historical salmon abundances and could pose risks to population persistence in some areas. Plain Language Summary: The large majority of climate change research for aquatic organisms has focused on stream water temperature and discounted the importance of flow changes associated with evolving precipitation regimes. Using a high‐resolution stream topographic map that supported a series of linked flow and fish habitat quality models, our research describes how observed historical flow reductions and projected future reductions affect local habitat quality, distributions, and connectivity for a salmon population. We demonstrated that as climate change continues to change flow regimes in snow‐dependent regions, it will cause fragmentation and reduce the overall volume of available habitats in headwater streams where salmon and other cold‐water fish species spawn and grow during early life stages. Key Points: Warming from climate change accelerates runoff and decreases streamflow during low flow periods in many snow dependent regionsExtended summer low flows reduce and fragment the capacity of freshwater habitats to support historical salmon abundancesClimate adaptation actions for salmon should consider hydrologic changes and floodplain connectivity besides increasing water temperatures [ABSTRACT FROM AUTHOR]

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p < 0.05). However, the habitat degradation for Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish. [ABSTRACT FROM AUTHOR]

Estuaries, acting as transitional habitats receiving species introductions from both freshwater and marine sources, undergo significant impacts from global climate changes. Planktonic microorganisms contribute significantly to estuarine biodiversity and ecological stability. These microorganisms primarily fall into three groups: eukaryotic plankton, particle-associated bacteria, and free-living bacteria. Understanding the structural characteristics and interactions within these subcommunities is crucial for comprehending estuarine dynamics. We collected samples from three distinct locations (< 0.1 PSU, 6.6 PSU, and 19 PSU) within the Yangtze River estuary. Samples underwent analysis for physicochemical indicators, while microbial communities were subjected to 16S/18S rRNA amplicon sequencing. Additionally, simulated mixing experiments were conducted using samples of varying salinities. Estuary samples, combined with simulated experiments, were employed to collectively examine the structural characteristics and assembly processes of estuarine microbes. Our research highlights the considerable impact of phylogenetic classification on prokaryotic behavior in these communities. We observed a transition in assembly processes from primarily stochastic for particle-associated bacteria to a predominant influence of homogeneous selection as salinity increased. Particle-associated bacterial communities exhibited a greater influence of stochastic processes compared to free-living bacteria, showcasing higher stability in diversity. The variations in composition and structure of estuarine microbial subcommunities were influenced by diverse environmental factors. Particle-associated bacteria displayed elevated network characterization values and established closer interactions with eukaryotic plankton. Structural equation modeling (SEM) analysis revealed that free-living bacteria displayed a heightened sensitivity to environmental factors and exerted a more significant influence on assembly processes and network characteristics. Simulated mixing in these environments resulted in the loss of species with similar microbial taxonomic relationships. The functioning of bacterioplankton is influenced by salinity and the processes governing their assembly, particularly in relation to different living states. These findings significantly contribute to our understanding of the intricate interplay between prokaryotic and eukaryotic plankton microorganisms in highly dynamic environments, laying a robust foundation for further exploration into the ecological mechanisms governing microbial dynamics in estuaries. • Differences in assembly processes among estuarine sub-communities. • Sourcetracking analysis reveals community response to water mixing of estuary. • Bacterial lifestyles (Free-living & particle-associated) alter community interactions and functions. [ABSTRACT FROM AUTHOR]

Climate change and pollution are affecting remote mountain ecosystems that have traditionally been described as pristine. Due to the environmental stress factors present in mountain freshwater systems, their organisms may be more sensitive to change. The damage caused to them will also have repercussions downstream. Michael Gross reports. Climate change and pollution are affecting remote mountain ecosystems that have traditionally been described as pristine. Due to the environmental stress factors present in mountain freshwater systems, their organisms may be more sensitive to change. The damage caused to them will also have repercussions downstream. [ABSTRACT FROM AUTHOR]

The widespread salinisation of freshwater ecosystems poses a major threat to the biodiversity, functioning, and services that they provide. Human activities promote freshwater salinisation through multiple drivers (e.g., agriculture, resource extraction, urbanisation) that are amplified by climate change. Due to its complexity, we are still far from fully understanding the ecological and evolutionary consequences of freshwater salinisation. Here, we assess current research gaps and present a research agenda to guide future studies. We identified different gaps in taxonomic groups, levels of biological organisation, and geographic regions. We suggest focusing on global- and landscape-scale processes, functional approaches, genetic and molecular levels, and eco-evolutionary dynamics as key future avenues to predict the consequences of freshwater salinisation for ecosystems and human societies. The global acceleration of freshwater salinisation due to human activities such as agriculture, resource extraction, and urbanisation and its amplification by climate change is unequivocal. Although research in this field is growing, there are key aspects at the ecological and evolutionary levels that remain unaddressed. Increasing salinisation is a problem as it can increase the stress or mortality of freshwater organisms, leading to a loss of diversity and/or functionality of freshwater ecosystems but also the services and benefits to human societies that they provide. We identify the main gaps of recent research and suggest a research agenda to facilitate future research efforts in order to achieve a more comprehensive understanding on freshwater salinisation. [ABSTRACT FROM AUTHOR]

The Asian potamid subfamily Potamiscinae is the most species‐rich group of primary freshwater crabs in the world, and a large number of these (318 species in 52 genera) are found in China where they exhibit a remarkably high rate of endemism. However, the evolutionary history and phylogenetic relationships of this subfamily is still poorly understood and the hypothesis that the Chinese potamids originated in the Indochina Peninsula has yet to be tested using a modern phylogeographic reconstruction and molecular dating methods. Here we analyze the phylogenetic relationships and biogeographic history of the Chinese potamiscines based on whole mitogenomes of 72 species of Asian freshwater crabs representing 65% of the potamiscine genera found in China, including new mitogenome sequences for 57 species. The mitogenomic phylogeny generated four separate clades: Southwest China (SWC), Indochina‐Southwest China (ISWC), Central China (CC), and South China‐adjacent Islands (SCI). Our results suggest that the Chinese potamiscine fauna most likely originated in Indochina during the Eocene. The establishment of the East Asian monsoon during the Eocene/Oligocene resulted in major climate changes that coincide with the local diversification of the CC and SCI clades. In addition, diversification of two other clades (ISWC and SWC) may have been driven by past large scale environmental changes taking place at that time such as increased local precipitation and expanding freshwater habitats associated with the uplifting of the Hengduan Mountains. In addition, our phylogenies did not support monophyly for six currently recognized potamiscine genera, highlighting the need for further taxonomic revisions of this fauna. The broad taxonomic sampling and well‐supported molecular phylogenies used here allow for the updating of our understanding of the evolutionary origins and diversification of the potamiscine freshwater crabs in China. [ABSTRACT FROM AUTHOR]

Indigenous Peoples in the Arctic have for millennia relied on freshwaters for drinking water and freshwater species that comprise important subsistence harvests, which promotes a strong connection to the land and unique understanding of organisms and ecosystem processes and changes. Despite the importance of freshwater biodiversity and ecosystem services to Arctic Indigenous communities, there have been limited attempts to summarise available Indigenous Knowledge (IK) regarding Arctic freshwater systems and to understand how conservation can benefit from this knowledge base.This paper presents a systematic review of literature documenting circumpolar Arctic IK with a focus on freshwater biodiversity in Canada, Greenland, Fennoscandia (Norway, Sweden, and Finland), Russia, and the U.S.A. (Alaska). Standardised search terms and methodologies were used to locate relevant documents using Google Scholar and Google Advanced search engines. Thematic coding was used to identify freshwater biodiversity themes within the identified documents.Documented IK of freshwater biodiversity was found from all five geographic regions and included data on both species presence and habitat changes with potential to affect biodiversity. Canada had the highest number of relevant documents (n = 127), followed by the U.S.A. (Alaska; n = 116), Fennoscandia (n = 38), Russia (n = 27), and Greenland (n = 5). The number of relevant documents with IK published per year was highest in most recent years, from 2010 onwards, in all geographic regions.Fish represented the highest number of faunal observations with 59 species observed, approximately half of which were Salmonidae (29 species). Local‐scale assessment of fish diversity found observations of the highest number of species (11–25) in Alaska, and individual observations of 6–10 species were found throughout Alaska, mainland areas of Canada, and the Kola Peninsula in Russia. Documented IK also contributed new information on historical fish diversity and indicated local‐scale loss or gain of species. Such information is of vital importance to provide long‐term records of fish composition and abundance, especially when this information does not exist in other knowledge bases such as western science datasets.Indigenous Knowledge included observations of changes in freshwater and terrestrial habitat associated with a warming climate, such as: decreasing water levels and more draining/drying of lakes and rivers, a shorter period of ice cover (late freeze and early break‐up), decreasing ice thickness, and increasing occurrence of permafrost thaw and eroding banks. Such observations by those who actively rely on Arctic freshwater ecosystem services are important because they signify that change is occurring and that action is needed to mitigate the impacts on freshwater habitats and the biodiversity therein.This study demonstrates that previously documented IK provides valuable information towards determining freshwater biodiversity baselines and patterns of change in the circumpolar Arctic. However, these results do not sufficiently cover the depth and breadth of IK on freshwater biodiversity and ecology held by Indigenous communities. Further work incorporating Indigenous worldviews around freshwater ecology would provide context to the knowledge collected and a deeper understanding of Arctic circumpolar freshwater environments. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is increasingly threatening biodiversity on a global scale. Rich spots of biodiversity, regions with exceptionally high endemism and/or number of species, are a top priority for nature conservation. Terrestrial studies have hypothesized that rich spots occur in places where long-term climate change was dampened relative to other regions. Here we tested whether biodiversity rich spots are likely to provide refugia for organisms during anthropogenic climate change. We assessed the spatial distribution of both historic (absolute temperature change and climate change velocities) and projected climate change in terrestrial, freshwater, and marine rich spots. Our analyses confirm the general consensus that global warming will impact almost all rich spots of all three realms and suggest that their characteristic biota is expected to witness similar forcing to other areas, including range shifts and elevated risk of extinction. Marine rich spots seem to be particularly sensitive to global warming: they have warmed more, have higher climate velocities, and are projected to experience higher future warming than non-rich-spot areas. However, our results also suggest that terrestrial and freshwater rich spots will be somewhat less affected than other areas. These findings emphasize the urgency of protecting a comprehensive and representative network of biodiversity-rich areas that accommodate species range shifts under climate change. [ABSTRACT FROM AUTHOR]

Climate change increasingly threatens alpine natural areas and notably aquatic systems. Alpine waterbodies, such as ponds, are particularly vulnerable to changes in temperature. Their biodiversity faces rising threats, especially for cold stenothermal species. Located at high elevation (>2600 m a.s.l.), the aquatic network of the Macun catchment (35 ponds and several streams) was put under a strict protection framework in 2000 ("Swiss National Park") to mitigate threats to alpine biodiversity. The pond network has been regularly monitored as a sentinel of change, through aquatic macroinvertebrate sampling and physico-chemical measurements. Monitoring shows an alarmingly sharp increase in summer water temperature, rising by 4 °C between 2005 and 2020 (2.7 °C per decade). In contrast, nutrient concentrations have remained low and stable over these 15 years. The aquatic macroinvertebrate species richness has also been mostly stable between 2002 and 2021, with no negative impacts on the monitored cold stenotherms. Indeed, as the ponds are located at high elevation, these cold stenotherms are still living within their thermal range. Some cold stenothermal species have colonised the ponds from lower elevations, so the Macun pondscape acts as a refuge for these migrating taxa. In synthesis, our investigation highlights the alarming abiotic condition of the high-elevation freshwater biodiversity habitats, including a sharp temperature increase. It also provides evidence that their high elevation allows theses waterbodies to remain refuges for cold stenotherms, for now. In the longer term, however, a tipping point is likely to be reached, with a potential collapse of cold stenothermal biodiversity. This demonstrates the critical need to continue longer-term monitoring of high-elevation ecosystems to assess the magnitude of the impairment and to implement suitable conservation strategies, such as enhanced protection or the creation of new suitable habitats. [Display omitted] • Water temperature increased sharply in high-elevation ponds in the last 15 years. • Warming has not yet impaired macroinvertebrate communities in high-elevation ponds. • High-elevation pondscapes (>2600 m) act today as refuges for cold-specialist species. • Protection and monitoring are required to conserve these unique alpine habitats. [ABSTRACT FROM AUTHOR]

Anadromous Atlantic salmon (Salmo salar) populations have declined across their Southern distributions in North America. While river temperature has been identified as a central factor influencing migration behavior and over‐winter survival, little research has addressed the prevalence of infectious agents in wild Atlantic salmon populations. Further, current understanding of how temperature may interact with fish condition to influence infection outcomes in the wild is limited.The objective of this research was to characterize the change in individual condition and pathogen dynamics as salmon acclimatized to the freshwater environment during the spawning migration. Serial individual sampling (non‐lethal gill biopsy and microwave fatmeter readings) was accomplished by repeated capture and release of 27 marked individuals, which revealed how lipid content, infectious agent prevalence and relative loads, and stress and osmoregulatory transcripts changed during the initial month of their annual spawning migration.Relative infection burden (a composite metric representing the overall pathogen profile) and transcription profiles were modeled with freshwater residency, river temperature, and lipid content. Infectious agents Tetracapsuloides bryosalmonae, Candidatus Branchiomonas cysticola, Flavobacterium psychrophilum, Paranucleospora theridion, and Piscichylamidia salmonis were detected in the population. Relative infection burden and microbial pathogen species richness increased over the course of the study.Water temperature and time since fresh water entry were related to salmon transcriptional response, but not relative infection burden, highlighting the metabolic cost associated with warming temperatures and dynamic nature of pathogen infection profiles in migratory fish species.This work is the first to provide a comprehensive screening of microbial pathogen species in wild Atlantic salmon in the region, and the first to employ a unique study design that facilitates serial sampling without imposing holding stress. The high prevalence and relative load of T. bryosalmonae observed may demonstrate increased exposure to transmission pathways as a result of migratory barriers or elevated susceptibility to infection during spawning migrations in anadromous species. [ABSTRACT FROM AUTHOR]

Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. We demonstrate that climate changes and deforestation can drive recurrent microbial blooms, inhibiting the recovery of freshwater ecosystems for hundreds of millennia. From the stratigraphic successions of the Sydney Basin, Australia, our fossil, sedimentary and geochemical data reveal bloom events following forest ecosystem collapse during the most severe mass extinction in Earth's history, the end-Permian event (EPE; c. 252.2 Ma). Microbial communities proliferated in lowland fresh and brackish waterbodies, with algal concentrations typical of modern blooms. These initiated before any trace of post-extinction recovery vegetation but recurred episodically for >100 kyrs. During the following 3 Myrs, algae and bacteria thrived within short-lived, poorly-oxygenated, and likely toxic lakes and rivers. Comparisons to global deep-time records indicate that microbial blooms are persistent freshwater ecological stressors during warming-driven extinction events. Harmful algal and bacterial blooms are increasingly frequent in lakes and rivers. From the Sydney Basin, Australia, this study uses fossil, sedimentary and geochemical data to reveal bloom events following forest ecosystem collapse during the end-Permian event and that blooms have consistently followed warming-related extinction events, inhibiting the recovery of freshwater ecosystems for millennia. [ABSTRACT FROM AUTHOR]

Aim: Shaped by climate change and sea‐level rise, tidal salt marshes represent ephemeral systems that are home to only a few species. The dynamic ecological histories of these habitats, however, render it challenging to reconstruct the complete biogeographical histories of their endemic taxa. To better understand the evolutionary history of tidal marsh endemic sparrows, we employ genomic data to evaluate the timing and direction of tidal marsh colonization events and leverage these data to test a series of models describing the biogeographical history of our study taxa. Location: North America. Taxon: Ammospiza Sparrows. Methods: We sampled 54 individuals from the Ammospiza clade from freshwater and saltwater habitats. We sequenced whole genomes and generated a dataset containing 21 million SNPs. Detailed phylogenomic analyses were conducted to identify relationships between tidal marsh and freshwater species. These phylogenies were then used to date divergence times and reconstruct the biogeographical history of the clade as well as identify historic signals of introgression. Results: Phylogenies based on several million SNPs supported well‐resolved clades that correspond to all previous species designations. Demographic modelling within A. nelsoni provided further resolution into the subspecies topology. Phylogenetic and biogeographical reconstructions support a series of saltwater to freshwater colonization events, with some endemic taxa exhibiting associations with tidal marsh habitat over longer evolutionary time‐scales and some habitat transitions occurring as recently as 5,000 years ago. Main Conclusions: Biogeographical and phylogenomic reconstructions support an original freshwater origin of the Ammospiza sparrows currently inhabiting tidal marshes in North America. We also found strong evidence for a saltwater to freshwater transition in A. n. subvirgatus as opposed to the long hypothesized freshwater origin of this group. We conclude that the increased resolution from genomic data paired with an integrative framework of phylogenomic, demographic and biogeographical reconstructions is important for resolving evolutionary histories in complex and ephemeral environments. [ABSTRACT FROM AUTHOR]

Inland fisheries and their freshwater habitats face intensifying effects from multiple natural and anthropogenic pressures. Fish harvest and biodiversity data remain largely disparate and severely deficient in many areas, which makes assessing and managing inland fisheries difficult. Expert knowledge is increasingly used to improve and inform biological or vulnerability assessments, especially in data-poor areas. Integrating expert knowledge on the distribution, intensity, and relative influence of human activities can guide natural resource management strategies and institutional resource allocation and prioritization. This paper introduces a dataset summarizing the expert-perceived state of inland fisheries at the basin (fishery) level. An electronic survey distributed to professional networks (June-September 2020) captured expert perceptions (n = 536) of threats, successes, and adaptive capacity to fisheries across 93 hydrological basins, 79 countries, and all major freshwater habitat types. This dataset can be used to address research questions with conservation relevance, including: demographic influences on perceptions of threat, adaptive capacities for climate change, external factors driving multi-stressor interactions, and geospatial threat assessments. Measurement(s) Perception • Threats • Adaptive capacity Technology Type(s) Survey Factor Type(s) Fishery location • Demographics Sample Characteristic - Organism Homo sapiens • fish Sample Characteristic - Environment freshwater environment • lake • stream • wetland ecosystem Sample Characteristic - Location Europe • Asia • Oceania • Africa • South America • North America • Australia Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.14749161 [ABSTRACT FROM AUTHOR]

The last 85,000 years were characterized by high climate and environmental variability on the Yucatán Peninsula. Heinrich stadials are examples of abrupt climate transitions that involved shifts in regional temperatures and moisture availability. Thus, they serve as natural experiments to evaluate the contrasting responses of aquatic and terrestrial ecosystems. We used ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6, ~85 ka) recovered from Lake Petén Itzá, Guatemala, to assess the magnitude and velocity of community responses. Ostracodes are sensitive to changes in water temperature and conductivity. Vegetation responds to shifts in temperature and the ratio of evaporation to precipitation. Ostracodes display larger and more rapid community changes than does vegetation. Heinrich Stadial 5-1 (HS5-1) was cold and dry and is associated with lower ostracode and vegetation species richness and diversity. In contrast, the slightly warmer and dry conditions during HS6 and HS5a are reflected in higher ostracode species richness and diversity. Our paleoecological study revealed the greatest ecological turnover for ostracodes occurred from 62.5 to 51.0 ka; for pollen, it was at the Pleistocene/Holocene transition. Future studies should use various climate and environmental indicators from lake and marine sediment records to further explore late glacial paleoclimate causes and effects in the northern neotropics. [ABSTRACT FROM AUTHOR]

Grasslands contribute greatly to biodiversity and human livelihoods; they support 70% of the world's agricultural area, but are heavily degraded by human land use. Grassland restoration research and management receives less attention than forests or freshwater habitats, although grasslands are critical for sustaining ecosystems multifunctionality and capacity to support biodiversity. In this article, we introduce a Special Issue which considers major trends and prospects in grassland restoration. We identified three key topics: First, restoration must confront widespread seed and site limitations, and new monitoring methods, including remote sensing techniques, are critical for restoration projects. Second, we highlight that restored grasslands typically require ongoing disturbance management and that research is required to determine optimal approaches for implementing this management during restoration. Third, global and regional restoration agendas should be harmonized with site‐level goals, and syntheses of current knowledge and research needs must guide grassland restoration across scales. We also identify research gaps to be filled, and challenges which grasslands face in the future: (1) a need for careful target vegetation selection and climate‐adaptive restoration; (2) lack of knowledge in dynamics and restoration of several regions and grassland types, including drylands and (sub)tropical regions; (3) increased importance of species arrival sequence, and high stochasticity of species establishment; and finally (4) issues of post‐restoration management to guarantee long‐term sustainability of restored sites. A new generation of research and restoration projects to bridge these gaps is necessary to mitigate environmental challenges spanning localities to the globe as we commence the UN Decade on Ecosystem Restoration. [ABSTRACT FROM AUTHOR]

Many freshwater ecosystems are in decline because of anthropogenic disturbance including climate change, yet our understanding of ecological vulnerability to future conditions including climatic variation is limited. Understanding climate risks to freshwater ecosystems requires combining hydrological and ecological knowledge. While there have been significant advances in ecohydrological approaches when applied within the large array of methods available for undertaking impact assessments, the ecological and hydrological elements are often not well‐integrated. This results in a mismatch in their ability to accommodate the inherent uncertainty in both impacts and responses. We examine published literature that assesses climate change impacts on freshwater ecosystems using both hydrological and ecological models to better understand method choices. We identify four fundamentally distinct modeling approaches used to assess climate change risk. We discuss which approaches are less useful for predicting ecological impacts under climate change, and highlight approaches of comparable complexity that can maximize the utility of dynamic, process‐based modeling while capturing the effects of climate uncertainty and variability. Using an illustrative case study of riparian vegetation health under climate change, we show how the four alternate modeling approaches feature different degrees of information in their outcomes and inferences about future risk. Most current studies that examine climate change risks to freshwater ecosystems use simplified methods or inadequately combine key elements. However, unless the interactions between changing hydrologic variability and ecological responses are explicitly captured in scale‐sensitive modeling methods, the risks of climate change to freshwater ecosystems will likely be substantially misrepresented, with negative consequences for effective management responses. Capturing these interactions requires combining ecological and hydrological methods of comparable complexity. This article is categorized under:Climate, Ecology, and Conservation > Modeling Species and Community Interactions [ABSTRACT FROM AUTHOR]

Abiotic conditions are important considerations in the species sorting process, which ultimately determines the distribution and abundance of species. Freshwater ecosystems will be impacted by ongoing temperature rise and other anthropogenically induced changes, such as nutrient enrichment and eutrophication. Changing characteristics of freshwater habitats will likely impact organisms in numerous ways, including through effects on colonization dynamics. Species are expected to colonize habitat patches where fitness will be the highest for themselves and their offspring, and how habitat selection interacts with changing environments remains an important question. We conducted a warming experiment to test the habitat selection preferences of aquatic beetles and hemipterans between habitat patches (mesocosms) of varying temperatures (via heaters), nutrient addition, and their interaction. Overall, insect abundance and richness were higher in unheated patches, with taxon‐specific variation in response to heating. Although nutrients had limited effects on environmental conditions in mesocosms, their addition had no significant effects on insects. Insect assemblages had unique structures across heating treatments, with lower beta diversity and higher effective numbers of species in the warmest mesocosms. Our data support the importance of spatial variation in abiotic factors during the habitat selection process, and in determining species distributions and abundances as shallow lentic ecosystems are impacted by rising global temperatures. [ABSTRACT FROM AUTHOR]

Understanding how the movement and habitat use of fishes are influenced by flow regimes is important in sustainably managing river ecosystems, particularly in regions undergoing drying due to climate change. Here, we aimed to determine how the movement of a freshwater fish from refuge pools is influenced by discharge and environmental variables in south‐western Australia, a region that has suffered an ~50% reduction in surface flows since the 1970s. We quantified the movement patterns of the freshwater plotosid Tandanus bostocki using acoustic telemetry in two rivers that had different flow regimes and habitat characteristics. We hypothesized that its movements would be positively influenced by discharge and it would also display a high degree of site fidelity. Fifty fish were tagged and monitored across both rivers for a 1‐year period. There was an overall significant positive relationship between daily movements from the monitored refuge pools with both discharge and solar irradiation in both rivers. However, there was a greater probability of movement at a lower magnitude of discharge in the regulated Harvey River, which was attributed to the influence of river gradient and prevalence of instream barriers moderating the effect of flow on movements in the Brunswick River. The species demonstrated a considerable degree of site fidelity and also displayed homing behaviour. The study suggests that the maintenance of key refuge pools during baseflow, and ensuring river connectivity during the key movement periods, would help maintain the viability of the species as river discharge continues to decline due to climate change. [ABSTRACT FROM AUTHOR]

Recent climate-driven, physico-chemical changes documented in aquatic systems throughout the world are expected to intensify in the future. Specifically, changes in key environmental attributes of aquatic systems, such as water quantity, clarity, temperatures, ice cover, seasonal flow regimes, external loading, and oxygen content, will undoubtedly have a broad set of direct and indirect ecological consequences. Some anticipated impacts may be similar across different aquatic ecosystems, while others may be system-specific. Here, we review the potential effects of climatic changes for different freshwater habitats within the state of Indiana, USA, a Midwestern state with diverse land and water features. Given this heterogeneity and that the state is among the southernmost states of the US Midwest, evaluation of freshwater habitats of Indiana provides a useful perspective on potential impacts of climate change. In our study, we first review expected or anticipated changes to physico-chemical and habitat conditions in wetlands, lotic systems, small glacial lakes and Lake Michigan. We then highlight anticipated responses of select aquatic biota to these changes. We describe how climatic changes may interact with other anthropogenic stressors affecting freshwater habitats and consider the potential for evolutionary adaptation of freshwater aquatic organisms to mediate any responses. Given anticipated changes, we suggest aquatic ecosystem managers take a precautionary approach broadly applicable in temperate regions to (a) conserve a diversity of aquatic habitats, (b) enhance species diversity and both inter- and intra-population genetic variation, and (c) limit stressors which may exacerbate the risk of decline for aquatic biota. [ABSTRACT FROM AUTHOR]

Diadromous fish species have a complex life cycle during which they migrate between marine and freshwater habitats. They experience multiple human-induced pressures in both environments, likely exacerbated by climate change, leading to dramatic population declines across their distribution ranges. Currently Species Distribution Models (SDMs) have been applied separately in both their continental and marine habitats to improve our understanding of their lifecycles and help with species management. Integrating the freshwater-sea continuum into the decisions would now be a step further in improving their management. With this objective, we developed a decision tree that links marine and freshwater SDM outputs with current observations of population functionality and suggested management guidance options for the viability of these species. Potential effects of climate change were included through future SDM projections to guide integrative and long-term management. Several criteria were proposed to assess the SDM validity considering the main sources of SDM uncertainties and local expert knowledge on habitat and population status. The framework was applied to approximately one hundred catchments from southern Portugal to southern Scandinavia for four diadromous species. At the European level, management guidance options differed between the two anadromous and two catadromous species. Platichthys flesus and Chelon ramada European populations seemed in better state than those of Alosa alosa and A. fallax. Finally, with the help of national diadromous species experts, we focused on four catchments distributed along the European latitudinal gradient to test the proposed methodology and demonstrate local management challenges in terms of freshwater-sea continuity. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are threatened worldwide, with 1/3 of freshwater species being under extinction risk. Yet, systematic conservation planning has received little attention as a means to prioritize freshwater conservation areas. Here, we develop a comprehensive approach to spatially delineate key areas for freshwater conservation across Europe, considering directed-connectivity, climate change and human-related disturbances. We assess the adequacy of the current reserve network in protecting European freshwater ecosystems and provide guidelines for expansion. We conducted 13 prioritization scenarios for 18,300 sub-basins across Europe, accounting for the distribution of 1,668 freshwater species. Connectivity properties, metrics of climatic stability and human induced pressures were incorporated into the spatial prioritization framework. We highlight the critical importance of specific regions in Central and Southern Europe, the Mediterranean Basin, and parts of the Balkan Peninsula for future freshwater conservation efforts. However, our analysis also reveals the complete inadequacy of the current reserve network, as protected sub-basins only cover 4 % of the study area and encompass on average only 3 % of freshwater species distributions. In contrast, expanding current reserves to cover the top 17 % of high priority areas across Europe could substantially improve the overall coverage of species distributions, reaching an average of 61.5 % for all freshwater species and even exceeding 93.1 % for species of conservation interest (critically endangered, endangered and vulnerable species). The priority freshwater conservation network derived from the analysis provides specific spatial recommendations to help achieve conservation goals if the current reserve network is appropriately expanded. • Freshwater species are at risk worldwide and conservation planning is overlooked. • A new comprehensive approach prioritizes key areas for European freshwaters. • Critical regions for conservation exist in Central Europe and the Mediterranean. • Current reserves are inadequate covering only 4 % of Europe's freshwater ecosystems. • Expanding reserves can result in a 20-fold increase in species coverage within PAs. [ABSTRACT FROM AUTHOR]

• Parasite infections often peak in certain seasons in aquatic ecosystems. • Meta-analysis of 693 seasonal infection contrasts reveals no universal pattern. • Taxon-specific patterns rule among winter-summer and wet-dry season infection dynamics. • The same parasite taxa show contrasting patterns between freshwater and marine habitats. • Sensitivity to abiotic conditions therefore varies widely among host-parasite systems. Seasonal infection dynamics characterise many host-parasite interactions, as abiotic conditions drive fundamental biological processes in both hosts and parasites. The extent to which seasonal cycles in parasite abundance are universal, and whether the same underlying mechanisms are responsible for seasonality across different host-parasite associations, have received little attention to date. Here, global patterns of seasonal infection dynamics are tested using a meta-analysis of 693 seasonal contrasts in the local abundance of metazoan parasites in aquatic vertebrates, representing 343 parasite species and 148 host species. These include both contrasts between winter and summer in temperate systems, and between wet and dry seasons in tropical systems. Overall, the analysis found no evidence that seasonal infection dynamics are universal, nor that they are controlled by the same factors. More specifically, the results indicate no overall effect of the magnitude of local seasonal differences in abiotic conditions (temperature or precipitation), type of host (amphibian or fish), habitat (freshwater, coastal marine or deep-sea), host body length, or mode of transmission (skin contact or trophic) on the extent of seasonal differences in parasite infections. Instead, the results revealed many clear taxon-specific or habitat-specific patterns of seasonal infection dynamics, with some parasite or host taxa generally showing distinct peaks in infections in summer or dry seasons, and others showing no seasonal changes. The present findings serve to identify empirically which host-parasite associations are most likely to respond to changing climatic conditions, and thus provide useful information for fisheries and aquaculture. [ABSTRACT FROM AUTHOR]

Today, aquatic biodiversity suffers from many pressures linked to human activities, including climate change, which particularly affects alpine areas. Many alpine freshwater species have shifted their geographical distribution to colder areas, but a reduced availability of suitable habitats is also forecasted. New artificial water bodies could provide habitat enhancement opportunities, including small mountain reservoirs built to overcome a lack of snow during winter.To investigate the role of reservoirs as a habitat for freshwater invertebrates, a case study was conducted on eight reservoirs in the Swiss Alps. The study aimed to compare the water quality and freshwater biodiversity of the reservoirs with those of 39 natural and newly excavated ponds. Data were collected on physico‐chemistry, freshwater habitat structure, and aquatic insects (dragonflies and aquatic beetles).The study showed that the mountain reservoirs investigated did not differ from natural ponds in terms of surface area, conductivity, and trophic level. Similarly to natural ponds, reservoirs showed signs of impairment owing to surface run‐off carrying pollutants linked to ski tourism. They presented a low diversity of mesohabitats, and in particular lacked vegetation. Compared with natural ponds, the species richness in reservoirs was lower for dragonflies but not for beetles. At the regional scale, the community from the reservoirs was a subset of the natural ponds community, supporting 38% of the regional species richness for these two insect groups.The results suggest that mountain reservoirs are likely to be important for biodiversity in alpine areas, both as habitats and as stepping stones for species shifting their geographical range. These water bodies can be enhanced further by some nature‐friendly measures to maximize benefits for biodiversity, including margin revegetation or the creation of adjacent ponds. Ecological engineering needs to be innovative and promote freshwater biodiversity in artificial reservoirs. [ABSTRACT FROM AUTHOR]

Formation of diatom frustules depends on the process of silicification. In many planktonic species of algae, ambient temperature and nutrients are already known to affect growth and morphology, making them suitable bioindicators. In this study, a similar indicator function of benthic diatoms is proposed based on the principle that cell wall thickness is inversely proportional to temperature and nutrients. Therefore, higher turnover rates at warmer temperatures are hypothesized to favour smaller and lighter diatoms due to their shorter regeneration time. Accordingly, benthic diatom species were classified into seven categories according to their intensity of silicification, referred to as 'Silicification Value'. For each diatom assemblage, an abundance-weighted average silicification value was calculated and tested for its applicability to assess global change impact on mountain lakes in the northern calcareous Alps of Europe. Surface sediment diatom samples and morphometric and ecological parameters of 41 lakes from a wide altitudinal range in the Bavarian and Tyrolian Alps were collected and analysed. Statistical tests revealed that temperature conditions in a lake and its altitude were the most decisive proxies related to the 'Silicification Value'. Moreover, trophic status and the presence of macrophytes had some influence. This supported the hypothesis that lakes, which are warmer and richer in nutrients, show a weaker average silicification in diatom assemblages. A dependence of silicification on valve size could be shown but appears to be negligible in climatological issues. In particular, the correlation with temperature makes the silicification value an applicable palaeoecological proxy to assess climate change impact in freshwater lakes. [ABSTRACT FROM AUTHOR]

Extreme climatic events, such as heat waves, may induce changes in nutrient acquisition by omnivorous ectotherms. Likely modulated by the intensity, frequency and duration of these events, dietary shifts during heat waves may threaten the stability of freshwaters. We investigated the effects of heat wave duration on diet assimilation and life-history traits of the freshwater gastropod Radix balthica. We compared the magnitude of the effects of a short (1 week) and a long heat wave (7 weeks) on the assimilation of animal- and plant-based diets, measuring performance in terms of growth rate and reproduction. We hypothesized that heat waves should increase the proportion of plant material assimilated on the mixed diet and change the performance of snails on the animal and plant-based diets. Both heat waves increased the assimilation of plant material on the mixed diet and growth rate, with minor negative effects on reproduction. However, responses were disproportional to heat wave duration, as the short heat wave elicited swift and relatively stronger responses. Our findings showcase the role of phenotypic plasticity in aiding ectotherms to cope with increased thermal stress and acclimate. Temporarily changing the strength of trophic interactions, heat waves may alter community dynamics in freshwater habitats. [ABSTRACT FROM AUTHOR]

Biological invasions are a primary threat to global biodiversity, supporting mounting calls for the development of early‐warning systems to manage existing and emerging invaders. Here, we evaluated the geographical pattern of invasion risks of currently established and potentially emerging nonnative freshwater fishes in China by jointly considering the threats of introduction and establishment under climate change. Introduction threats were estimated according to proxies of human activities and propagule pressure for two primary pathways (aquaculture or ornamental). Establishment threats for 51 current and 64 potential invaders (based on whether having established or not self‐sustaining populations) were assessed using an ensemble of species distribution models under current (1960–1990) and future [2041–2060 (2050s) and 2061–2080 (2070s)] climate scenarios. Geographical patterns of invasion risk were then assessed by overlaying the threats of introduction and establishment for each species group both in present‐day and in the future. We found that eastern China displayed the highest threat of introduction. By contrast, southeastern and northwestern regions were identified as the most suitable for the establishment of both current and potential invaders. Under a changing climate, 83 out of 115 species displayed an increase in habitat suitability, resulting in an overall increase of 4.8% by 2050s and 7.1% by 2070s in the extent of suitable habitat for nonnative freshwater fishes. Taken together, invasion risk was found to be highest in southeastern China and lowest in the Tibet Plateau. Our research highlights the importance of assessing invasion risk by integrating the threats associated with the introduction and establishment stages. In particular, our findings revealed convergent patterns of invasion risk between current and potential nonnative freshwater fishes under climate change. Geographic patterns in hotspots of existing and emerging invasions provide critical insights to guide the allocation of resources to monitor and control existing and emerging invasions in China. [ABSTRACT FROM AUTHOR]

One of the main constraints affecting invertebrate diversity in many freshwater lentic habitats is the presence of a dry phase which forces aquatic organisms to avoid this period through the migration to other water bodies or the production of resting stages. Field studies show contradictory results when comparing invertebrate diversity in permanent (PW) and temporary lentic waters (TW).Our objective was to test how diversity is influenced by the permanence of water in lentic habitats, and which factors affect the magnitude and direction of this difference, including sampling design. Through a systematic review, 66 publications were selected and classified according to the sampling design (spatial, temporal, and spatio‐temporal datasets).Meta‐analysis of the spatial dataset, which included 70% of the studies, revealed that diversity in PW was higher than in TW, and this difference was not influenced by annual precipitation, dispersal mode, habitat type or level of anthropogenic impact (proximity to urban or agricultural areas).We found a significantly higher effect size (PW greater than TW) when considering species richness rather than cumulative richness or Shannon diversity index, disconnected water bodies (hindering the exchange of individuals through water connection), organisms with passive dispersal (which cannot actively avoid the dry period), and study sites with high anthropogenic impact (where temporary habitats could undergo impacts; e.g. concentration of pollutants and eutrophication).We also found that the differences in diversity between PW and TW may decrease with increasing sampling effort. This result may be attributable to high species turnover due to the higher temporal environmental variation in TW relative to PW. Also, it indicates that sampling effort should be comparatively higher in TW to properly characterize the biodiversity in these environments in order to compare with PW.As global climate continues to change, our results suggest that loss in aquatic invertebrate diversity of TW will be likely to occur in regions where the frequency of drying events increases. [ABSTRACT FROM AUTHOR]

Climatic scenarios for the Mediterranean predict an increase in drought and erratic precipitation, which may affect waterbirds breeding in freshwater habitats. Artificial wetlands may provide an alternative for these species when conditions in natural habitats deteriorate. We studied Little Ringed Plovers Charadrius dubius nesting in natural streams and agricultural ponds in southern Portugal. Based on 24 nests and 31 colour-ringed adults, we describe nest-site characteristics, breeding parameters and site fidelity. In streams, nests (n = 17) were in sites with more abundant and coarser gravel, while in ponds there was more vegetation around the nest (n = 7). In both habitats, nests were close and at similar distances to water, but this was unrelated to nest outcome (success of 30.8% across habitats). Nest failure in natural streams was mostly attributable to flooding after heavy rains, while in agricultural ponds cattle trampling was the main cause of failure. Based on their renesting capacity and relatively high breeding site fidelity (25%-36% return rate to same area), we suggest that Little Ringed Plovers may trade-off the overall better conditions of natural streams (i.e. higher availability of nesting substrate, food resources and lower disturbance from cattle) against the stochastic risk of floods. Nevertheless, under current predictions of climate change, agricultural ponds can provide more stable and reliable nesting conditions for this and other species, as unpredictable changes in Mediterranean streams' flooding regimen may become more frequent. Despite the limitations of our dataset, we provide novel information on the breeding biology of this understudied species and highlight its potential for future research. [ABSTRACT FROM AUTHOR]

With increasing advances in telemetry technology, prospecting behaviour was identified in many seabirds; mostly in immatures, but also in adults – during pre-breeding and post-breeding periods and among failed breeders. However, prospecting has not yet been documented among active breeders. We equipped 17 Common terns Sterna hirundo with GPS-UHF data-loggers and tracked their movements during late incubation and chick rearing in continental Croatia. We monitored the fate of their clutches until chicks left the nest. Birds of both sexes visited other breeding colonies within relatively short distances, while they still had active nests. These results confirm for the first time the presence of prospecting trips during incubation and chick-rearing in active breeders. Such behaviour probably developed because quick and unpredictable changes in their freshwater habitats can cause failure of whole colonies, forcing them to renest at other sites during the same breeding season. Prospecting during the first breeding attempt might shorten the renesting interval, and increase renesting success when multiple breeding sites are available on an easily accessible area. With increasing vulnerability of colony sites due to climate change, studies of scattered colonies are needed to better understand renesting and adult prospecting strategies. [ABSTRACT FROM AUTHOR]

Hydrological extremes have negative impacts on natural, agricultural, and urban landscapes and place substantial ecological pressure on freshwater habitats. However, the role of artificial freshwater habitats during hydrological drought is poorly understood. Insects make up much of total aquatic fauna and lend themselves to understanding how drought impacts freshwater ecosystems.Using the Greater Cape Floristic Region as an example of a drought‐prone area, we determined the effects of a severe drought on a subset of insects occupying lentic habitats in terms of their species richness, diversity, and assemblage composition. Here, we: (1) calculated the percentage change in average precipitation between a record dry season and the last consistently wet decade; (2) identified the environmental variables driving aquatic insect species richness, diversity and composition; (3) identified the environmental differences between natural ponds and artificial reservoirs; (4) determined whether artificial reservoirs act as suitable habitats for focal taxa during drought; and (5) compared these results to other, pre‐drought studies.Environmental variables related to water chemistry and physical characteristics were drivers of species richness, diversity, and composition, yet vegetation cover remained a major driver. In terms of marginal vegetation cover, most artificial reservoirs did not resemble natural ponds, yet overall 38.4% of sampled aquatic insect species were shared between natural ponds and artificial reservoirs. We found some rare endemic species in artificial reservoirs that had never before been recorded in this habitat during wet years. When our drought findings were compared to earlier, wet years, species richness did not change significantly, although abundance was much lower during the drought year.We postulate that historically, these aquatic insects, which have been through many ecological filters such as drought, must have sought low‐quality habitats to survive water stress periods. Artificial reservoirs, being novel landscape features, cannot fully replace natural ponds, but enable some aquatic insects to survive drought. Artificial reservoirs can be attractive habitats to aquatic insects when they resemble natural ponds, with specific reference to their marginal vegetation characteristics. [ABSTRACT FROM AUTHOR]

Island nations such as New Zealand provide valuable insights into conservation challenges posed by strongly connected and recently developed or exploited freshwater and marine ecosystems.The narrow land mass, high rainfall, and steep terrain of New Zealand, like many other island nations, mean that land‐based stressors are rapidly transferred to freshwater habitats and propagated downstream to coastal environments via short, fast‐flowing river systems.Freshwater and marine environments are linked through faunal life histories; for example, diadromous fishes, many of which are considered threatened or at risk of extinction, and require cross‐ecosystem conservation to ensure survival of critical life stages and persistence of source populations.Recent invasions of marine and freshwater environments by non‐indigenous species reveal rapid impacts on a naïve biota and highlight conservation conundrums caused by management aimed at enhancing native biodiversity by improving habitat connectivity.Understanding and managing interconnected freshwater and marine ecosystems is a key concept for local indigenous communities, and highlights socio‐cultural connectivity and sustainable local harvesting of traditional resources as key elements of contemporary marine and freshwater conservation planning in New Zealand. [ABSTRACT FROM AUTHOR]

Worldwide, tidal barriers (e.g. barrages, dikes, tide gates) are constructed in the lower reaches and estuaries of rivers to limit saltwater incursion into upstream freshwater reserves, facilitate water diversion and abstraction, limit flooding, reclaim land and generate electricity. While performing these functions, tidal barriers also affect fish through: 1) reduced connectivity; 2) loss of tidal flux; 3) conversion of upstream estuarine habitats to freshwater; and 4) diminished freshwater discharge, which compresses the spatio-temporal salinity regime of downstream estuarine habitats. As such, tidal barriers commonly cause declines of diadromous and estuarine associated fish species, with a subsequent loss of ecosystem services. These impacts will be exacerbated as climate change promotes sea-level rise and alters freshwater flow regimes and will be amplified by increasing demands for freshwater by a growing human population. As a result, more tidal barriers are likely. Nevertheless, in estuaries with tidal barriers, management that promotes connectivity and more natural ecosystem function is increasing but remains complex from ecological, economic and engineering perspectives. We present case studies from the Netherlands, southeastern United States and southern Australia to characterise impacts on fishes in different biogeographical regions and document contemporary approaches to restoring ecosystem function and fish populations in systems with tidal barriers. To meet these goals, we suggest three key considerations for future research and management are provision of fish passage, reinstating tidal flux and delivering environmental flows. • Tidal barriers fragment habitats and alter hydrodynamics to the detriment of fishes. • Global case studies are used to demonstrate impacts on fishes and approaches to remediation. • Key areas for research and remediation are: fish passage, restoration of tidal flux and environmental flows. • Remediation should consider predicted changes to river hydrology and sea level rise. [ABSTRACT FROM AUTHOR]