Abstract Despite increasing research on warming and biodiversity, knowledge on how temperature shapes community size structure remains limited, which is one of the main challenges in assessing the consequences of climate change. This gap is evident in vulnerable ecosystems like ponds, crucial for aquatic biodiversity but highly sensitive to temperature increases due to their small size. This study assessed the main climatic and local drivers influencing zooplankton community size structure in 141 ponds across four European countries and Uruguay, covering a wide latitudinal and trophic gradient with standardized sampling. Using linear mixed models, results revealed that local factors, such as trophic status and morphometric pond characteristics, were more consistently associated with size‐spectrum parameters than climatic variables. The normalized size spectrum slopes (ordinary least square regression, OLS) became steeper with higher chlorophyll a (Chl a ) concentrations, reflecting dominance of small zooplankton, suggesting reduced energy transfer efficiency to higher trophic levels, and possibly weaker top‐down phytoplankton control. Conversely, ponds with lower Chl a showed flatter slopes, indicating more large zooplankton and possibly greater top‐down control. The overall intercept was higher in deeper ponds with abundant aquatic vegetation, suggesting greater overall abundance across size classes. Size spectrum metrics did not vary significantly along climatic gradients. These results suggest that zooplankton community size structure in ponds appears to be more closely related to local environmental conditions than large‐scale climatic gradients. This highlights the key role of local habitat characteristics in shaping zooplankton size structure and energy transfer dynamics.

Aim: Species diversity patterns and their drivers are critical pieces of ecological knowledge needed to mitigate the threats faced by freshwater ecosystems globally. We used information on lake glacial history and environmental conditions to identify factors driving fish biodiversity patterns in Ontario and European lakes. Location: 9350 lakes across Ontario; 1824 lakes across northern and western Europe. Methods: Log-log linear mixed-effects models (LMM) and generalised linear mixed-effects models (GLMM) with a Poisson distribution were used to identify associations between fish species richness and climatic, geographic, physical, and historical variables. Local variation in fish diversity patterns was identified by applying beta diversity analysis and nested 'temperature' analysis to local richness data defined by sub-basins identified in the global watershed database HydroBASINS. Results: Lake area was the most important predictor of species richness in both regions. Other drivers evident in both regions were: local and regional measures of lake elevation, lake morphometry, lake age, and longitude. Results from our LMM models were similar to those from our GLMM models. In both Ontario and Europe, the error structure of these models was shaped by the HydroBASINS watershed sub-basin structure defined for each landscape. At all spatial scales, beta diversity was > 0.9, with species turnover being more important than nestedness. Nestedness contributed no more than 22% to total beta diversity. Matrix 'temperature' covered a similar range on both continents (similar to 4 degrees to similar to 40 degrees). Main Conclusions: Similar physical, geographic, and historical predictors influenced lake fish species richness in Ontario and northern and western Europe. The spatial structure of the watershed sub-basins in each region played a similar role in shaping the optimal error structure included in our richness models. By identifying variables that influence biodiversity generally and by mapping local variation in biodiversity in both regions, we provide new information that can inform landscape level conservation management strategies for lakes in both Ontario and Europe.

Mountain ponds are particularly sensitive ecosystems facing significant impacts from ongoing climate change, combined with other pronounced anthropogenic pressures including pollution, introduction of species, and overexploitation of water resources. Implementing mountain ponds as nature-based solutions (NbS) can strengthen their integral role as providers of nature's contributions to people (NCP). This review synthesises knowledge on mountain pond management in Europe from 61 selected publications, offering practical recommendations for conservation, management, and creation. Our literature search provides insights into organismal groups studied and identifies pressures on mountain ponds and geographical biases, highlighting knowledge gaps in either aspect. We link management recommendations with outcomes of NCP targets and highlight which pressures can be addressed by implementing these actions. Additionally, we outline key aspects of the implementation of mountain pond NbS, including the policy framework, stakeholder involvement, target NCPs, and funding acquisition. Effective decision making for successful NbS implementation requires profound ecological understanding, complemented by strategically planned adaptive management approaches, including high local stakeholder engagement. Concluding remarks showcase specific points of action to protect and develop mountain ponds as multifunctional tools in the landscape, safeguarding threatened biodiversity and the provision of valuable NCPs for society.

Despite the crucial importance of pond landscapes for biodiversity conservation, they are less studied, especially in terms of their impacts on people and society. This paper presents the results of a survey carried out on the perceptions of inhabitants and stakeholders across 17 pond landscapes in six countries in Europe, as well as T & uuml;rkiye and Uruguay. We collected 117 and 590 answers from stakeholders and local inhabitants, respectively, through questionnaires, including questions about their perceptions and preferences. Our results show that pondscapes are widely valued for their benefit to the quality of life and biodiversity. Three Nature's Contributions to People are considered important by both groups: 'creation and maintenance of habitats', 'physical and psychological experiences' and 'maintenance of options' (i.e. potential opportunities offered by nature to ensure resilience). Similar perceived threats related to 'climate change' and 'pollution' have been identified by stakeholders and inhabitants in all countries and have a direct impact on the maintenance of the most important contributions. The perceptions of potential solutions to identify threats are quite similar for most pondscapes, with conservation and maintenance actions being the most important for enhancing ecosystems and societal resilience to climate change and other societal challenges.

Body size is a fundamental trait influencing ecological functions, trophic dynamics, and organismal fitness across ecosystems. However, the environmental drivers shaping body size patterns in pond ecosystems across broad spatial scales remain poorly defined. In this study, we assessed the main determinants of body size in cladocerans and copepods, key crustacean zooplankton groups, across 168 ponds including regions in Europe, Asia, and South America. We assess how temperature and latitudinal variation, food availability, and predation influence mean and maximum crustacean body sizes in zooplankton taxa. Using linear mixed models, we identified annual temperature and predation pressure as the strongest predictors of body sizes. Body size increased with lower temperature for both taxa, supporting the temperature-size rule. Fish presence was associated with smaller body sizes for both taxa, while copepod size metrics were additionally influenced by pond morphometry, showing a negative relationship with depth and a positive association with area. These findings suggest temperature and predation pressure act as major selective forces shaping crustacean body size in pond ecosystems. Understanding these patterns is essential for predicting how crustacean communities and processes they mediate may respond to ongoing climate warming, particularly in small-shallow freshwater ecosystems highly sensitive to environmental change.

Pond ecosystems play an important role in the global carbon cycle with the potential to act as both sinks and sources of CO2. However, CO2 emissions during the dry phases of ponds remain underrepresented in global studies, despite growing evidence that climate change-driven shifts in temperature and precipitation are likely to increase the frequency and duration of these dry periods. Here we assess CO2 fluxes from dry pond sediments in relation to climatic region, seasonal changes, and hydroperiod duration. Specifically, we aimed to identify the key environmental drivers shaping CO2 fluxes during the dry phase. We measured CO2 fluxes from bare air-exposed sediments using closed static chambers equipped with internal mini-loggers in 30 ponds across Mediterranean and Temperate regions. Ponds acted as sources of CO2 during dry phases, with emissions ranging from 127 to 4889 mgCm-2d-1 (mean +/- SD=1398 +/- 1201). Although mean emissions did not differ significantly between climate regions, hydroperiod length interacted with climate and season, showing a significant effect in summer, particularly in Mediterranean ponds, where longer hydroperiods led to higher emissions. Emissions were considerably higher in summer than in autumn, primarily driven by the interaction between sediment temperature and water content. The highest fluxes occurred at approximately 27 degrees C and sediment water content between 27 % and 44 %. Additionally, ponds in better conservation status and with lower carbonate content emitted more CO2. Our findings improve understanding of CO2 emissions during increasingly common dry phases and highlight how climate modulates local sediment conditions, thereby influencing the magnitude of these emissions. This underscores the need for comprehensive assessments of carbon fluxes that incorporate dry-phase emissions, accounting for climate, hydroperiod, and both direct and indirect effects of local environmental drivers.

Mediterranean temporary ponds are ecologically vital ecosystems that support numerous endemic and rare species. These shallow ponds undergo unpredictable inter-annual fluctuations, with flooding and dry phase cycles driven largely by meteorological conditions. This study investigates how changes in the physical and chemical environment, resource availability (bottom-up), and predation (top-down) throughout the hydroperiod influence the structure and dynamics of planktonic communities. We analyzed the size spectrum (i.e., the relationship between individual body size and abundance) including phytoplankton and zooplankton communities in three freshwater temporary ponds in NE Spain, sampled monthly over four consecutive hydrologic cycles (2016–2020). Hydroperiod ranged from 2 to 8 months, allowing us to assess whether hydroperiod duration modulates the relative influence of environmental, bottom-up, and top-down controls. Results indicate that macroinvertebrate predation was the main driver of a declining size spectrum intercept, suggesting a general reduction in abundance across all planktonic size classes. Longer hydroperiods intensified top-down effects, also steepening the slope of the spectrum. In contrast, environmental fluctuations across the hydroperiod did not significantly influence the size spectrum shape, regardless of hydroperiod length. These findings highlight size spectra as useful indicators of the temporal changes in the trophic structure and biomass transfer in ephemeral aquatic systems.

This study investigates how pondscapes, networks of ponds, and their surrounding environments contribute to supporting identities across diverse cultural contexts. Supporting identities is a non-material Nature’s Contribution to People referring to people’s sense of place, belonging and connection to nature. We draw on data on landscape features from 17 pondscapes across eight countries in Europe and South America, along with over 700 questionnaire responses. We assessed whether certain landscape features are associated with the perceived delivery of supporting identities and examined how personal characteristics, individual perspectives, and engagement in different activities shape people’s perceptions. Our findings indicate that the perceived delivery of supporting identities emerges from a combination of social and ecological factors rather than from landscape features alone. Although pondscape characteristics showed weak direct effects, pondscapes in warmer climates and with a higher proportion of natural land cover might be associated with a stronger sense of identity. In addition, a strong personal connection to nature and engagement in nature-based activities (wildlife watching, picnicking, hunting), were key pathways shaping perceptions, highlighting that identity-related benefits are context dependent and socially mediated. By integrating ecological and social dimensions, our study highlights the importance of incorporating non-material values into conservation and landscape management strategies.

Nature-based Solutions are strategies inspired by nature that address major societal challenges, such as climate change and food security, by providing several socio-economic and environmental contributions. Despite widespread adoption, evaluating their impacts poses challenges within the field of environmental economics. In this study, we develop a framework for the comprehensive assessment of ponds as Nature-based Solutions. These water systems contribute to carbon storage, provide habitats for biodiversity, as well as leisure, business, and cultural opportunities. We assess them in terms of both effectiveness, which refers to their capacity to deliver benefits according to stakeholder expectations, and eco-efficiency, measuring input-output performance in environmental economic terms. First, we successfully reduce the heterogeneity of pond-specific contributions into comparable composite indicators with a novel application of the Benefit-of-the-Doubt method. Next, we combine Multi-Criteria Decision Analysis with stakeholder preferences to calculate ponds' effectiveness. The results show that these can be viable strategies for the delivery of locally relevant Ecosystem Services. Then, we investigate ponds' technical as well as ecological efficiencies by Data Envelopment Analysis, demonstrating that they can provide both socio-economic and environmental contributions in an efficient manner. Finally, we compare these complementary metrics and confirm the hypothesis that effective ponds can also provide eco-efficient Nature-based Solutions. Furthermore, we elaborate on the potential extensions of our analytical method to other strategies, highlighting how it could support decision makers taking context-specific, informed decisions on the best measures to implement.

Amphibians are commonly occurring inhabitants of most lentic freshwater ecosystems, yet their global populations are in alarming decline. Ponds in particular play a crucial role in supporting amphibian biodiversity. In this study, we identified the main drivers influencing amphibian species richness by conducting a comprehensive ecological characterization in 201 ponds across seven European countries spanning a large latitudinal and longitudinal gradient. The amphibian species richness in each of these ponds was assessed using environmental DNA metabarcoding on water samples. The relative influence of climatic, local abiotic and biotic, and land use variables on variation in species richness across ponds was quantified using boosted regression trees. Our results suggest that local factors, particularly chlorophyll-a concentration, but also pond area and depth, are the main drivers of amphibian richness, together with climatic variables such as annual mean precipitation and temperature. The highest richness was observed in low-nutrient, fishless, intermediate-sized, shallow ponds, located in warmer regions with higher precipitation rates. These potential drivers of amphibian richness should be considered in the planning and implementation of amphibian conservation and management actions.

Background: Ghana’s marine artisanal fisheries, particularly the small pelagic fisheries, are in a state of crisis. The decline in the number of small pelagic fish are attributable to overfishing, climate variability and unsustainable fishing methods. Similarly, in the wake of climate change, shellfishes (particularly oysters, scallops and mussels) are highly vulnerable. Methods: A total of 55 years’ worth of data from Ghana’s marine artisanal fisheries were studied in relation to climate indices. The primary objective was to develop a simple linear regression model for predicting shellfish catch in Ghana. Key informant interviews were employed in soliciting data on changes in climate along the coastline and trends in marine artisanal shell fish catch. Results: The predictor variable that significantly explained shellfish production was temperature. Hence, the model is a valuable tool to predict future trends in the shellfish catch in marine artisanal fisheries. Conclusions: Increases in sea surface temperature will adversely affect shellfish production. It is therefore important that the Ministry of Fisheries and Aquaculture Development and other stakeholders should, in their decision-making processes, ensure the formulation of climate smart policies and management strategies for sustainable use of the resource.

Most amphibians found in Europe inhabit ponds, small aquatic ecosystems commonly threatened by habitat degradation and destruction. Despite this situation, ponds are rarely considered in conservation policies. Thus, their effective management may present a significant opportunity to alleviate the ongoing decline of amphibian populations. In this study, we assessed if the favourable condition of a pond and its conservation status promotes its amphibian species richness, which was determined by using environmental DNA metabarcoding. For this, we investigated the condition of 154 ponds across six European countries, considered through measurements of their conservation status (Shallow Lentic Ecosystem Conservation Status index, ECELS), water quality and trophic state, and physical characteristics. By utilising Generalised Linear Mixed Models, we determined that a higher amphibian species richness, and a higher number of protected ones, are found in shallow ponds with a better pond condition, meaning a higher conservation status and a better water quality. Specifically, we observed that non-eutrophic ponds characterized by permeable and shallow basins with smooth slopes, and without weirs, foster a higher amphibian diversity. Conservation efforts targeting the preservation of natural pond hydrological processes and mitigating nutrient pollution are critical for safeguarding amphibian biodiversity in Europe and contributing to broader freshwater conservation goals.

Ponds and pondscapes are crucial habitats for biodiversity and provide significant ecosystem services and socio-cultural benefits. However, effective management of these habitats requires an in-depth evaluation of how stakeholders perceive them and interact with them. This study aims to explore stakeholder relationships with their local ponds and pondscapes to better understand their interactions, expectations, concerns, and perspectives, ultimately informing more effective conservation and management strategies. Using stakeholder storylines and the Nature Futures Framework (NFF), we analyzed data gathered from participatory workshops in eight countries (United Kingdom, Belgium, Germany, Denmark, Spain, Switzerland, Turkey, and Uruguay). Thematic analysis was performed to identify key themes regarding stakeholders’ interactions, conservation expectations, climate change concerns, and management preferences related to local ponds and pondscapes across different countries. In addition, descriptive analysis was used to assess the different values that stakeholders assigned to ponds, including their ecological, cultural, and socio-economic significance. Our findings reveal a multifaceted relationship between stakeholders and pondscapes, deeply influenced by local socio-ecological contexts, including cultural heritage, biodiversity, recreation, and climate change concerns. Despite regional differences, stakeholders universally acknowledged the urgent need for sustainable conservation practices, envisioning future pondscapes that are resilient to climate change, rich in biodiversity, and capable of supporting diverse ecological and societal functions. Our study underscores the importance of integrating diverse stakeholder perspectives into pondscape management to foster more context-sensitive and sustainable conservation efforts that safeguard these vital habitats worldwide.

According to differences in life history and species niches, community assembly processes are predicted to differ between common and rare species. While neutral processes, in particular dispersal, should contribute strongly to assembly of rare species, environmental filtering (species sorting) should dominate the community assembly of common species. We analysed commonness and rarity by occurrence, abundance and geographic range among 82 fish species in 1871 European lakes and reservoirs. The common 25% (21 species) were excluded, and structure and assembly processes of the 75% rare (61 species) species occurring in 348 lakes were evaluated. General linear latent variable models indicated that environmental variables related to lake type (lakes vs. reservoirs), climate and ecosystem size predicted a large proportion of variance for both rare species presence/absence and abundance models, while spatial variables (co-occurrence in watersheds) contributed little to the models. To link community structure with assembly processes, the contribution of seven fish traits related to life history, feeding and habitat preference to predicting the geographic range of the rare species was analysed by boosted regression trees. Intermediate average fecundity and high maximum body length of species predicted smaller geographic range and hence a higher level of rarity, but the response curves of the variables were mostly non-linear and difficult to interpret. In contrast to our assumption, the results of the dominant assembly processes and predictors for rare species were very similar to those predicted for the common fish species in lakes at the continental scale.

Ponds are key habitats for regional freshwater biodiversity and play a fundamental role in enhancing connectivity between aquatic ecosystems. Despite their importance, ponds are one of the most neglected water ecosystems due to their small size and are particularly affected by climate change and anthropogenic activities. Zooplankton communities serve as sensitive indicators of environmental stressors, such as changes in trophic state, hydroperiod variability, and habitat degradation. Therefore, understanding the drivers of biodiversity and the size structure of the zooplankton community in Mediterranean ponds is important, as it provides valuable insights into how different stressors may impact this community and ecosystems, and provides valuable insights for making appropriate decisions for its conservation. Here, we evaluated the taxonomic and size structure of the zooplankton community and its relationship with trophic status, the presence of fish, macrophyte abundance, morphometry, hydroperiod variability, and land use by conducting a comprehensive ecological characterisation of 30 Mediterranean freshwater ponds. Our results suggest that size metrics are affected by factors related to the trophic status of ponds. Eutrophic ponds, with the highest chlorophyll-a concentration, oxygen supersaturation, presence of fish, and low habitat complexity (i.e., fewer macrophytes), were dominated by small-size zooplankton, and the community was less size diverse (i.e., steeper slope of the size spectra and lower size diversity values). Also, ponds with a high habitat complexity and lower surface area had higher zooplankton biomass (i.e., higher intercept of the size spectra). In contrast, zooplankton richness was only positively influenced by pond surface area. Our results showed that size metrics reflected changes in the zooplankton community along the trophic status and biotic gradients, whereas the taxonomic metrics were more related to the morphometry of ponds. Size-related variables can be effective tools to evaluate the drivers of change of pond communities in the Mediterranean region and possibly others, particularly when taxonomic metrics do not show a significant response. From a management perspective, the results demonstrate the potential of size-based metrics for assessing the ecological status of Mediterranean ponds.

Ponds are key freshwater habitats supporting biodiversity and ecosystem services, yet they remain understudied in the context of land use and climate change. We examined 240 ponds across eight countries (seven in Europe and Uruguay) to assess how internal pond characteristics, surrounding land cover and livestock intensity, seasonal climatic variation, and climate influence nutrient concentrations across spatial and temporal scales. Nutrient concentrations were strongly associated with internal features: shallow ponds and short hydroperiods had higher total nitrogen (TN) and total phosphorus (TP) concentrations, while thermal stratification, typically found in deeper ponds, was associated with higher TN, indicating enhanced internal nutrient recycling. Land use also played a significant role with agricultural intensity increasing nutrient concentration (both TN and TP), whereas forest cover reduced TP. Seasonal variation modulated these patterns, with higher TP concentrations observed in summer, and with dilution effects during wetter and cooler periods, particularly for TN in semi-permanent ponds. These findings underscore the combined influence of physical characteristics, landscape context, and climate variability on nutrient concentrations in ponds and highlight the need for integrated, multi-scale approaches to anticipate the impacts of global climate change effects on these ecologically valuable ecosystems.

Unlocking the full potential of ponds (small water bodies) and pondscapes (network of ponds) as Nature-based Solutions (NbS) is critical pursuit for enhancing ecosystems and societal resilience to climate change and other societal challenges. Despite scattered initiatives for pond/pondscape creation, restoration and management—each considered here a distinct NbS—there is a significant knowledge gap in utilising ponds/pondscapes as effective NbS. We aimed to assess these NbS in terms of their objectives, outcomes, effectiveness, multifunctionality, delivery of potentially conflicting effects, and the implementation process while considering their Nature's Contributions to People (NCPs, i.e., benefits to society). We compiled data on 183 NbS actions implemented across 93 ponds/pondscapes from 24 countries, predominantly from Europe, via a questionnaire distributed to experienced stakeholders implementing NbS in ponds/pondscapes. One single pond/pondscape may imply more than one NbS action. Two-thirds were in rural areas, and one-third in urban settings. Our analysis revealed that Creation of habitat for biodiversity was a primary delivery objective (targeted NCP) in the implementation of most NbS in ponds/pondscapes, often also combined with other NCPs such as Learning and inspiration, Regulation of water quantity, and Physical and psychological experiences, showcasing their intended multifunctionality. Implemented NbS primarily focused on climate change adaptation (especially Regulation of hazards and extreme events, and water quantity) rather than mitigation, with less emphasis on measures like direct greenhouse gas emissions reduction or enhancing carbon sinks. The costs associated with pond's NbS varied significantly depending on factors such as project scope, objectives, location, socio-economic-cultural system, and specific implementation requirements. The creation of ponds/pondscapes often entailed the highest financial investment, much more than their restoration or their management. In conclusion, our study underscores the multifunctionality of ponds/pondscapes and provides insights about their significant potential as cost-effective NbS for enhancing ecosystem and societal resilience to climate change and biodiversity. It underscores the importance of further research to fully understand and measure the diverse range of NbS they offer, particularly in the context of climate change mitigation. Standardised measurements of the NCP provided by these NbS in ponds/pondscapes are essential for validating managers' claims and exploring their role in addressing climate change.