Adding climate change to the mix: responses of aquatic ectotherms to the combined effects of eutrophication and warming

A microfluidic approach to study variations in Chlamydomonas reinhardtii alkaline phosphatase activity in response to phosphate availability

Algal growth depends strongly on phosphorus (P) as a key nutrient, underscoring the significance of monitoring P levels. Algal species display a sensitive response to fluctuations in P availability, notably through the expression of alkaline phosphatase (AP) when challenged with P-depletion. As such, alkaline phosphatase activity (APA) serves as a valuable metric for P availability, offering insights into how algae utilize and fix available P resources. However, current APA quantification methods lack single cell resolution, while also being time- and reagent consuming. Microfluidics offers a promising cost-effective solution to these limitations, providing a platform for precise single-cell analysis. In this study, a trap-based microfluidic device was integrated with a commercially available AP live stain to study the single cell APA response of a model algae strain, Chlamydomonas reinhardtii, when exposed to different exogenous P levels. A three-step culture-starve-spike process was used to induce APA in cells cultured under two different basal P levels (1 and 21 mM). When challenged with different spiked P levels (ranging from 0.1-41 mM), C. reinhardtii cells demonstrated a highly heterogeneous APA response. Two-way ANOVA confirmed that this response is influenced by both spiked and basal P levels. Utilizing an unsupervised machine learning approach (HDBSCAN), distinct subpopulations of C. reinhardtii cells were identified exhibiting varying levels of APA at the single-cell level. These subpopulations encompass significant groups of individual cells with either notably high or low APA, contributing to the overall behavior of the cohorts. Considerable intrapopulation differences in APA were observed across cohorts with similar average behavior. For instance, while some cohorts exhibited a concentrated distribution around the overall average APA, others displayed subpopulations dispersed across a wider range of APA levels. This underscores the potential bias introduced by analyzing a small number of cells in bulk, which may skew results by overrepresenting extreme behavioral subpopulations. The findings if this study highlight the need for analytical approaches that account for single cell heterogeneity in APA and demonstrate the utility of microfluidics as a well-suited means for such investigations. This study illuminates the complexities of APA regulation at the single cell level, providing crucial insights that advance our understanding of algal phosphorus metabolism and environmental responses.

Coping with environmental degradation: Physiological and morphological adjustments of wild mangrove fish to decades of aquaculture-induced nutrient enrichment

The impact of eutrophication on wild fish individuals is rarely reported. We compared physiological and morphological traits of Siganus lineatus chronically exposed to aquaculture-induced eutrophication in the wild with individuals living at a control site. Eutrophication at the impacted site was confirmed by elevated organic matter (up to 150 % higher), phytoplankton (up to 7 times higher), and reduced oxygen (up to 60 % lower). Physiological and morphological traits of S. lineatus differed significantly between the two sites. Fish from the impacted site exhibited elevated hypoxia tolerance, increased gill surface area, shorter oxygen diffusion distances, and altered blood oxygen-carrying capacity. Elevated blood lactate and scope for anaerobic ATP production were observed, suggesting enhanced survival below critical oxygen levels. A significant 8.5 % increase in metabolic costs and altered allometric scaling, related to environmental degradation, were recorded. Our study underscores eutrophication's profound impact at the organism-level and the importance to mitigate it.

The interaction between warming and enrichment accelerates food-web simplification in freshwater systems

Nutrient enrichment and climate warming threaten freshwater systems. Metabolic theory and the paradox of enrichment predict that both stressors independently can lead to simpler food-webs having fewer nodes, shorter food-chains and lower connectance, but cancel each other's effects when simultaneously present. Yet, these theoretical predictions remain untested in complex natural systems. We inferred the food-web structure of 256 lakes and 373 streams from standardized fish community samplings in France. Contrary to theoretical predictions, we found that warming shortens fish food-chain length and that this effect was magnified in enriched streams and lakes. Additionally, lakes experiencing enrichment exhibit lower connectance in their fish food-webs. Our study suggests that warming and enrichment interact to magnify food-web simplification in nature, raising further concerns about the fate of freshwater systems as climate change effects will dramatically increase in the coming decades.

Feeding on stressed algae exerts important effects on life history traits of Daphnia magna in a multi-stressor environment

Freshwater ecosystems are increasingly exposed to anthropogenic eutrophication, including high nitrogen. In addition, climate change is leading to more intense and frequent heatwaves, which have enormous impacts on all trophic levels of the ecosystem. Any change in the lower trophic levels, e.g., the phytoplankton, also introduces stress to higher trophic levels e.g., the zooplankton crustacean Daphnia. Individual effects of heatwaves, high nitrate, and changing feed quality have been studied in daphnia, but less is known about their interactive effects. This study used a 3 × 3 × 2 factorial design in which daphnia were exposed to combinations of ecologically relevant nitrate concentrations (0, 50, or 200 mg/L) and different heatwave scenarios (no, short-moderate, or long-intense) in which individuals were either fed with microalgae (P. subcapitata and C. reinhardtii) grown at 20 °C and 50 mg/L nitrate (control feed) or the same conditions as daphnia was exposed to (experimental feed). Throughout the experiment, the interactive effects of high nitrate, heatwave, and feed on mortality, maturation, offspring, and body size were evaluated. In general, heatwaves shorten the lifespan of daphnia. Exposing daphnia to a long-intense heatwave combined with high nitrate resulted in poor performance. In the nitrate-limited condition, however, the restricted proliferation of microalgae reduced feed availability, which also had a major impact on daphnia's life history traits. Daphnia cultured in high nitrate and fed control feed performed better than when fed experimental feed, suggesting that in a high nitrate condition, the microalgae grown under the same experimental conditions was either unable to meet energy requirements or introduced extra stress for the daphnia. Most importantly, the effect of nitrate and heatwave as stressors on the availability and quality of the feed had a greater impact on daphnia than its direct impact. Interestingly, a transgenerational adaptation to nitrate was observed which may help to maintain ecological balance in the long run.

Spatial and Seasonal Changes in Microbial Community of Hynobius amjiensis Breeding Pools in a Sphagnum-Dominated Peatland

Peatlands deliver a variety of beneficial ecosystem services, particularly serving as habitats for a diverse array of species. Hynobius amjiensis is a critically endangered amphibian initially discovered in a Sphagnum-dominated peatland in Anji, China. The unique habitat requirements of H. amjiensis make it highly vulnerable to environmental changes. Here, we investigated the different breeding pools of H. amjiensis in the Sphagnum-dominated peatland (the type locality) for a one-year period to evaluate the interactions among the egg sacs present, water quality, and microbial communities (16S and 18S rRNA gene amplicon). The numbers of egg sacs were higher in the breeding pools located at the marginal area than those at the core area of the peatland. Similarly, the α-diversity of bacteria, fungi, and protists were lower in the core region compared to those at the edge of the peatland, perhaps due to water eutrophication. The microbial communities and water quality differed significantly among breeding pools and sampling months. The simpler microbial networks of the breeding pools in the core wetland may impact the numbers and health of the egg sacs. This study contributes to a better understanding of the effect of water quality on biodiversity in peatlands, and it can also guide regulations for wetland conservation and the protection of endangered species.

Cyanobacteria in the Anthropocene: Synanthropism forged in an era of global change

The Anthropocene has driven a transformative era where human activities exert unprecedented influence on Earth's biosphere. Consequently, synanthropic organisms, adept at thriving in human-modified environments, have emerged. While well studied in terrestrial ecosystems, the presence and ecological importance of synanthropic species in aquatic ecosystems, specifically among cyanobacteria, are less understood. Cyanobacteria blooms, notorious for their detrimental effects on ecosystems and human health, are increasing in frequency and intensity globally. In this perspective, we explore the evidence supporting this rise of cyanobacteria blooms, emphasizing the roles of human-induced eutrophication and climate change on select cyanobacteria genera. Cyanobacteria are not a monolith, with certain genera showing an observable increase within anthropogenically modified environments. We propose the establishment of a new sub-branch of phycology that explicitly investigates the ecology and physiology of synanthropic cyanobacteria. Understanding the intricate interactions between synanthropic species and human populations is imperative for managing human-altered ecosystems and conserving freshwater resources, particularly in the face of increasing global water insecurity. PRACTITIONER POINTS: The rise in cyanobacteria blooms is driven by a small subset of human-adapted genera-synanthropic cyanobacteria. Research is needed to characterize synanthropic cyanobacteria, which will aid in developing tailored management approaches. A paradigm shift from domesticating to "rewilding" landscapes and modifying behaviors to facilitate cohabitation are solutions to reducing risks.

TP or Not TP? Successful Comparison of Two Independent Methods Validates Total Phosphorus Inference for Long-Term Eutrophication Studies

Validating paleo total phosphorus (TP) inference methods over long time scales is essential for understanding historic changes in lake P supply and the processes leading up to the present-day global lake eutrophication crisis. Monitored lake water TP time series have enabled us to identify the drivers of eutrophication over recent decades. However, over longer time scales, the lack of reliable TP inference means our understanding of drivers is speculative. Validation of lake water TP reconstruction, therefore, remains the "ultimate aim" of eutrophication studies. Here, we present the first critical comparison of two fully independent paleo TP inference approaches: the well-established diatom method (DI-TP) and a recently developed sediment geochemical method (SI-TP). Using lake sediment records from a small eutrophic U.K. lake (Crose Mere), we find a statistically significant agreement between the two inferred TP records with greater than 60% shared variance. Both records show identical timings, with a 19th century acceleration in TP concentration and subsequent declines following a peak in 1930. This significant agreement establishes the validity of long-term paleo TP inference for the first time. With this, we can now test assumptions and paradigms that underpin understanding of catchment P sources and pathways over longer time scales.

Productivity declines threaten East African soda lakes and the iconic Lesser Flamingo

Soda lakes are some of the most productive aquatic ecosystems.1 Their alkaline-saline waters sustain unique phytoplankton communities2,3 and provide vital habitats for highly specialized biodiversity including invertebrates, endemic fish species, and Lesser Flamingos (Phoeniconaias minor).1,4 More than three-quarters of Lesser Flamingos inhabit the soda lakes of East Africa5; however, populations are in decline.6 Declines could be attributed to their highly specialized diet of cyanobacteria7 and dependence on a network of soda lake feeding habitats that are highly sensitive to climate fluctuations and catchment degradation.8,9,10,11,12 However, changing habitat availability has not been assessed due to a lack of in situ water quality and hydrology data and the irregular monitoring of these waterbodies.13 Here, we combine satellite Earth observations and Lesser Flamingo abundance observations to quantify spatial and temporal trends in productivity and ecosystem health over multiple decades at 22 soda lakes across East Africa. We found that Lesser Flamingo distributions are best explained by phytoplankton biomass, an indicator of food availability. However, timeseries analyses revealed significant declines in phytoplankton biomass from 1999 to 2022, most likely driven by substantial rises in lake water levels. Declining productivity has reduced the availability of healthy soda lake ecosystems, most notably in equatorial Kenya and northern Tanzania. Our results highlight the increasing vulnerability of Lesser Flamingos and other soda lake biodiversity in East Africa, particularly with increased rainfall predicted under climate change.14,15,16 Without improved lake monitoring and catchment management practices, soda lake ecosystems could be pushed beyond their environmental tolerances. VIDEO ABSTRACT.

Young-of-the-year fish as bioindicators of eutrophication and temperature regime of water bodies

Young-of-the-year fish communities are widely used as bioindicators of various environmental disturbances. This study was conducted from 1997 to 2015 and aims to develop fish trait-based indices of changes in the temperature regime and eutrophication of water bodies in the Dnipro River basin. We identified fish traits that significantly correlate with both temperature and chlorophyll-a concentration optimum: reproduction habitat, oxygen tolerance, and toxicity tolerance. Compared to other ecological groups, lithophilic species exhibited the lowest degree of thermal and eutrophication optimum, indicating this species' greater vulnerability to environmental alteration. Fish species that are intolerant to water quality and low oxygen concentration were the most sensitive to changes in temperature regime and eutrophication level. Salinity preferences and water quality tolerance emerged as reliable predictors of temperature optimum. Freshwater fish had an average temperature optimum that was 4.5% higher than that of freshwater-brackish and freshwater-brackish-marine fish. Species tolerance to the temperature factors and nutrient loads correlated only with rheophily, with rheophilic species having an average 13.8% higher temperature tolerance than other fish species and a 10.4% higher chlorophyll-a concentration tolerance. The fish temperature index increased over time during the study period in all the studied water bodies, consistent with ongoing warming affecting all sites. In contrast, the Fish Eutrophication Index showed greater temporal heterogeneity in studied water bodies, indicating various adaptative potentials of fish communities to eutrophication. These indices can be relevant for assessing disturbed situations caused by changes in climatic and anthropogenic impacts on water bodies.

Influence of EE2 exposure, age and sex on telomere length in European long-snouted seahorse (Hippocampus guttulatus)

After a Telomere Lengthening in juvenile stage, a progressive telomere shortening occurs with age despite higher telomerase level. Telomere Length (TL) may also reflect past physiological state such as a chronic chemical stress. Several studies have revealed a correlation between TL, ageing and/or sex in vertebrates, including teleosts; however, the patterns of telomere dynamics with telomerase mRNA expression, sex, lifespan or chemical stress in teleosts are unclear. The first aim of this study is to verify if telomere length is age and sex-dependent. The second aim is to consider if TL is a useful indicator of stress response in European long-snouted seahorse, Hippocampus guttulatus, an ectothermic and non-model system. We showed that after telomere lengthening during the juvenile stage, a telomeric attrition became significant in sexually mature individuals (p = 0.042). TL decreased in older seahorses despite the presence of somatic telomerase mRNA expression at all life stages studied. There was no difference in TL between males and females, but telomerase mRNA expression was consistently higher in females than males. Exposure to EE2 had no effect on TL in young seahorses, but was correlated with a significant increase in telomerase mRNA expression and various physiological disruptions. Here, a growth retardation of -10 % for body length (p = 0.016) and approximately -45 % for mass (p = 0.001) compared to healthy juvenile seahorses was observed. Our data suggest that telomere dynamics alone should not be used as a marker of EE2 exposure in juvenile seahorses.

Modelling based study on the occurrence characteristics and influencing factors of the typical antibiotics in Bohai Bay

Previous studies have demonstrated that antibiotics have the potential impacts to ecosystems and human health. However, due to their various classes and distinct characteristics, creating comprehensive, integrated and dynamic simulations has proven to be a challenging task. In this study, a 3D hydrodynamic-contaminant model was developed to gain a better understanding of the transportation and prevalence of antibiotics in the Bohai Bay. Specifically, we focused on four types of antibiotics as examples. To accurately capture the dynamic distribution of antibiotics, both transport and biochemical processes were taken into account. Based on this model, the antibiotics' spatial and temporal distribution was examined, the potential impact of the future antibiotics consumption and climate change was also analyzed. The study found that human activity has a greater impact on the presence of antibiotics in Bohai Bay than temperature rise. Based on the current consumption rate, the total amount of antibiotics in Bohai Bay may increase by 10 ng/L and affect nearly one third of the study area within the next 20-30 years. The significant impact of human activity on water contamination in coastal areas may also have implications for other coastal regions. This finding can provide a valuable framework for pollution prevention and control.

Body size and trophic position determine the outcomes of species invasions along temperature and productivity gradients

Species invasions are predicted to increase in frequency with global change, but quantitative predictions of how environmental filters and species traits influence the success and consequences of invasions for local communities are lacking. Here we investigate how invaders alter the structure, diversity and stability regime of simple communities across environmental gradients (habitat productivity, temperature) and community size structure. We simulate all three-species trophic modules (apparent and exploitative competition, trophic chain and intraguild predation). We predict that invasions most often succeed in warm and productive habitats and that successful invaders include smaller competitors, intraguild predators and comparatively small top predators. This suggests that species invasions and global change may facilitate the downsizing of food webs. Furthermore, we show that successful invasions leading to species substitutions rarely alter system stability, while invasions leading to increased diversity can destabilize or stabilize community dynamics depending on the environmental conditions and invader's trophic position.

Warmer temperature overrides the effects of antidepressants on amphibian metamorphosis and behavior

Climate change can exacerbate the effects of environmental pollutants on aquatic organisms. Pollutants such as human antidepressants released from wastewater treatment plants have been shown to impact life-history traits of amphibians. We exposed tadpoles of the wood frog Lithobates sylvaticus to two temperatures (20 °C and 25 °C) and two antidepressants (fluoxetine and venlafaxine), and measured timing of metamorphosis, mass at metamorphosis, and two behaviors (startle response and percent motionless). Antidepressants significantly shortened time to metamorphosis at 20 °C, but not at 25 °C. At 25 °C, tadpoles metamorphosed significantly faster than those at 20 °C independent of antidepressant exposure. Venlafaxine reduced body mass at 25 °C, but not at 20 °C. Temperature and antidepressant exposure affected the percent of tadpoles showing a startle response. Tadpoles at 20 °C displayed significantly more responses than at 25 °C. Exposure to fluoxetine also increased the percent of tadpoles showing a startle response. Venlafaxine reduced the percent of motionless tadpoles at 25 °C but not at 20 °C. While our results showed that antidepressants can affect the timing of metamorphosis in tadpoles, warmer temperatures overrode these effects and caused a reduction in an important reaction behavior (startle response). Future studies should address how warmer global temperatures may exacerbate or negate the effects of environmental pollutants.

Environmental transcriptomics under heat stress: Can environmental RNA reveal changes in gene expression of aquatic organisms?

To safeguard biodiversity in a changing climate, taxonomic information about species turnover and insights into the health of organisms are required. Environmental DNA approaches are increasingly used for species identification, but cannot provide functional insights. Transcriptomic methods reveal the physiological states of macroorganisms, but are currently species-specific and require tissue sampling or animal sacrifice, making community-wide assessments challenging. Here, we test whether broad functional information (expression level of the transcribed genes) can be harnessed from environmental RNA (eRNA), which includes extra-organismal RNA from macroorganisms along with whole microorganisms. We exposed Daphnia pulex as well as phytoplankton prey and microorganism colonizers to control (20°C) and heat stress (28°C) conditions for 7 days. We sequenced eRNA from tank water (after complete removal of Daphnia) as well as RNA from Daphnia tissue, enabling comparisons of extra-organismal and organismal RNA-based gene expression profiles. Both RNA types detected similar heat stress responses of Daphnia. Using eRNA, we identified 32 Daphnia genes to be differentially expressed following heat stress. Of these, 17 were also differentially expressed and exhibited similar levels of relative expression in organismal RNA. In addition to the extra-organismal Daphnia response, eRNA detected community-wide heat stress responses consisting of distinct functional profiles and 121 differentially expressed genes across eight taxa. Our study demonstrates that environmental transcriptomics based on extra-organismal eRNA can noninvasively reveal gene expression responses of macroorganisms following environmental changes, with broad potential implications for the biomonitoring of health across the trophic chain.

Deteriorating waterways: The effect of nitrate pollution on the development and physiology of the endangered southern bell frog (Litoria raniformis)

Nitrogen-based fertilizers can increase agricultural yields and crop quality, but this comes at the risk of contaminating nearby waterways. Nitrate is the most stable and abundant form of inorganic nitrogen in the environment and chronic exposure can impair performance and fitness in aquatically respiring species. But it remains unknown if these impairments are linked to disruptions in energy homeostasis. Here, we investigated the energetic cost of living in nitrate contaminated waters during early, energy-limited, larval life stages in the endangered southern bell frog (Litoria raniformis). We hypothesised that chronic nitrate exposure during development would increase energetic costs, evidenced by reductions in growth rates and body sizes, and elevations in routine heart rate (RHR) and routine metabolic rate (RMR). Following hatching, larvae were exposed to one of three nitrate treatments (0, 25 and 50 mg NO3-L-1) for 12 weeks, and survival, growth, RHR, and RMR were measured. Survival rates were similar across all treatments. Nitrate exposure caused a reduction in growth rates, resulting in larvae with significantly smaller body sizes. Compared to controls, nitrate-exposed larvae were 12% and 18% smaller in total length in the 25 and 50 mgNO3-L-1 treatments, respectively. However, RHR and RMR were independent of nitrate exposure, indicating that the 'cost of living' was similar across treatments. Observed growth reductions were therefore independent of RHR and RMR, suggesting other mechanisms were involved. Taken together, these results highlight the vulnerability of L. raniformis to nitrate during early life and suggest that the application of nitrogen-based fertilizers near critical aquatic habitats will be harmful.

Climate change amplifies the risk of potentially toxigenic cyanobacteria

Cyanobacterial blooms pose a significant threat to water security, with anthropogenic forcing being implicated as a key driver behind the recent upsurge and global expansion of cyanobacteria in modern times. The potential effects of land-use alterations and climate change can lead to complicated, less-predictable scenarios in cyanobacterial management, especially when forecasting cyanobacterial toxin risks. There is a growing need for further investigations into the specific stressors that stimulate cyanobacterial toxins, as well as resolving the uncertainty surrounding the historical or contemporary nature of cyanobacterial-associated risks. To address this gap, we employed a paleolimnological approach to reconstruct cyanobacterial abundance and microcystin-producing potential in temperate lakes situated along a human impact gradient. We identified breakpoints (i.e., points of abrupt change) in these time series and examined the impact of landscape and climatic properties on their occurrence. Our findings indicate that lakes subject to greater human influence exhibited an earlier onset of cyanobacterial biomass by 40 years compared to less-impacted lakes, with land-use change emerging as the dominant predictor. Moreover, microcystin-producing potential increased in both high- and low-impact lakes around the 1980s, with climate warming being the primary driver. Our findings chronicle the importance of climate change in increasing the risk of toxigenic cyanobacteria in freshwater resources.

Niche-Specific Restructuring of Bacterial Communities Associated with Submerged Macrophyte under Ammonium Stress

Submerged macrophytes and their epiphytic microbes form a "holobiont" that plays crucial roles in regulating the biogeochemical cycles of aquatic ecosystems but is sensitive to environmental disturbances such as ammonium loadings. Increasingly more studies suggest that plants may actively seek help from surrounding microbial communities whereby conferring benefits in responding to particular abiotic stresses. However, empirical evidence is scarce regarding how aquatic plants reconstruct their microbiomes as a "cry-for-help" against acute ammonium stress. Here, we investigated the temporal dynamics of the phyllosphere and rhizosphere bacterial communities of Vallisneria natans following ammonium stress and recovery periods. The bacterial community diversity of different plant niches exhibited opposite patterns with ammonium stress, that is, decreasing in the phyllosphere while increasing in the rhizosphere. Furthermore, both phyllosphere and rhizosphere bacterial communities underwent large compositional changes at the end of ammonium stress, significantly enriching of several nitrifiers and denitrifiers. Meanwhile, bacterial legacies wrought by ammonium stress were detected for weeks; some plant growth-promoting and stress-relieving bacteria remained enriched even after stress disappeared. Structural equation model analysis showed that the reshaped bacterial communities in plant niches collectively had a positive effect on maintaining plant biomass. Additionally, we applied an age-prediction model to predict the bacterial community's successional trajectory, and the results revealed a persistent change in bacterial community development under ammonium treatment. Our findings highlight the importance of plant-microbe interactions in mitigating plant stress and fostering a better understanding of the assembly of plant-beneficial microbes under ammonium stress in aquatic ecosystems. IMPORTANCE Increasing anthropogenic input of ammonium is accelerating the decline of submerged macrophytes in aquatic ecosystems. Finding efficient ways to release submerged macrophytes from ammonium stress is crucial to maintain their ecological benefits. Microbial symbioses can alleviate abiotic stress in plants, but harnessing these beneficial interactions requires a detailed understanding of plant microbiome responses to ammonium stress, especially over a continuous time course. Here, we tracked the temporal changes in bacterial communities associated with the phyllosphere and rhizosphere of Vallisneria natans during ammonium stress and recovery periods. Our results showed that severe ammonium stress triggers a plant-driven timely reshaping of the associated bacterial community in a niche-specific strategy. The reassembled bacterial communities could potentially benefit the plant by positively contributing to nitrogen transformation and plant growth promotion. These findings provide empirical evidence regarding the adaptive strategy of aquatic plants whereby they recruit beneficial microbes against ammonium stress.

Can the establishment of a protected area improve the lacustrine environment? A case study of Lake Chaohu, China

Eutrophication of lacustrine environments with frequent cyanobacterial blooms has become a serious problem. Overpopulation and runoff into groundwater and lakes from fertilizers with too much nitrogen and phosphorous have caused most of the problems. Here, we first devised a land use and cover classification system based on the local characteristics of the first-level protected area of Lake Chaohu (FPALC). Lake Chaohu is the fifth largest freshwater lake in China. The land use and cover change (LUCC) products were produced using sub-meter resolution satellite data from 2019 to 2021 in the FPALC. This study presents an evaluation of the effectiveness of the established protected areas. The results show the most impactful type was the reduction in cropland with an area that declined from 7446.4 hm² to 6433.3 hm² from 2019 to 2021. Most of the reduced cropland was converted into wetlands, with 460.2 hm² and 152.0 hm² of cropland restored to wetlands from 2019 to 2020 and 2020-2021, respectively. The area of cyanobacterial blooms in Lake Chaohu showed a downward trend, and the lacustrine environment was greatly improved after the establishment of the FPALC. These quantified data can inform decision-making related to Lake Chaohu conservation and provide a reference for managing the aquatic environment in other watersheds.

Gill surface area allometry does not constrain the body mass scaling of maximum oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus

The gill oxygen limitation hypothesis (GOLH) suggests that hypometric scaling of metabolic rate in fishes is a consequence of oxygen supply constraints imposed by the mismatched growth rates of gill surface area (a two-dimensional surface) and body mass (a three-dimensional volume). GOLH may, therefore, explain the size-dependent spatial distribution of fish in temperature- and oxygen-variable environments through size-dependent respiratory capacity, but this question is unstudied. We tested GOLH in the tidepool sculpin, Oligocottus maculosus, a species in which body mass decreases with increasing temperature- and oxygen-variability in the intertidal, a pattern consistent with GOLH. We statistically evaluated support for GOLH versus distributed control of [Formula: see text] allometry by comparing scaling coefficients for gill surface area, standard and maximum [Formula: see text] ([Formula: see text]_,Standard and [Formula: see text]_,Max, respectively), ventricle mass, hematocrit, and metabolic enzyme activities in white muscle. To empirically evaluate whether there is a proximate constraint on oxygen supply capacity with increasing body mass, we measured [Formula: see text]_,Max across a range of Po₂s from normoxia to P_crit, calculated the regulation value (R), a measure of oxyregulatory capacity, and analyzed the R-body mass relationship. In contrast with GOLH, gill surface area scaling either matched or was more than sufficient to meet [Formula: see text] demands with increasing body mass and R did not change with body mass. Ventricle mass (b = 1.22) scaled similarly to [Formula: see text]_,Max (b = 1.18) suggesting a possible role for the heart in the scaling of [Formula: see text]_,Max. Together our results do not support GOLH as a mechanism structuring the distribution of O. maculosus and suggest distributed control of oxyregulatory capacity.

Are Mediterranean marine threatened species at high risk by climate change?

Rapid anthropogenic climate change is driving threatened biodiversity one step closer to extinction. Effects on native biodiversity are determined by an interplay between species' exposure to climate change and their specific ecological and life-history characteristics that render them even more susceptible. Impacts on biodiversity have already been reported, however, a systematic risk evaluation of threatened marine populations is lacking. Here, we employ a trait-based approach to assess the risk of 90 threatened marine Mediterranean species to climate change, combining species' exposure to increased sea temperature and intrinsic vulnerability. One-quarter of the threatened marine biodiversity of the Mediterranean Sea is predicted to be under elevated levels of climate risk, with various traits identified as key vulnerability traits. High-risk taxa including sea turtles, marine mammals, Anthozoa and Chondrichthyes are highlighted. Climate risk, vulnerability and exposure hotspots are distributed along the Western Mediterranean, Alboran, Aegean, and Adriatic Seas. At each Mediterranean marine ecoregion, 21%-31% of their threatened species have high climate risk. All Mediterranean marine protected areas host threatened species with high risk to climate change, with 90% having a minimum of 4 up to 19 species of high climate risk, making the objective of a climate-smart conservation strategy a crucial task for immediate planning and action. Our findings aspire to offer new insights for systematic, spatially strategic planning and prioritization of vulnerable marine life in the face of accelerating climate change.

Seasonal Variation and Vertical Distribution of Inorganic Nutrients in a Small Artificial Lake, Lake Bulan, in Mongolia

This is the first seasonal observation study on nutrient dynamics undertaken in a small freshwater lake with eutrophication in Mongolia. The vertical profile and seasonal fluctuation of nutrients are crucial to understanding the biogeochemical cycles in aquatic systems. In this study, field research was carried out at a small and shallow lake, Lake Bulan, in the lower Kharaa River basin. The area has been receiving increased nutrient loads from the water catchment area for the last 20 years. Water samples were collected seasonally from the lake from 2019–2022 and analyzed for nutrients, major cations, trace metals, and dissolved organic carbon. The average concentration of dissolved inorganic nitrogen (DIN) in the surface lake water had a wide seasonal variation from 0.26 ± 0.11 mg N/L in August to 1.44 ± 0.08 mg N/L in January. Seasonal differences were also observed in the vertical profiles. Concentrations were relatively similar at the various water depths in April and September at turnover time. Thermal stratification was observed when the lake was covered in ice, with the maximum concentrations being observed in the bottom layer in the months of January and August. The phosphate concentration showed a similar variation trend. These results indicate that both the summer and winter stratifications are important for regeneration of nutrients in the bottom layer, biochemical cycling, and mitigating impacts of global warming on small and shallow lakes in Mongolia.

Fire and rain: A systematic review of the impacts of wildfire and associated runoff on aquatic fauna

Climate and land-use changes are expected to increase the future occurrence of wildfires, with potentially devastating consequences for freshwater species and ecosystems. Wildfires that burn in close proximity to freshwater systems can significantly alter the physicochemical properties of water. Following wildfires and heavy rain, freshwater species must contend with complex combinations of wildfire ash components (nutrients, polycyclic aromatic hydrocarbons, and metals), altered light and thermal regimes, and periods of low oxygen that together can lead to mass mortality events. However, the responses of aquatic fauna to wildfire disturbances are poorly understood. Here we provide a systematic review of available evidence on how aquatic animals respond to and recover from wildfire disturbance. Two databases (Web of Science and Scopus) were used to identify key literature. A total of 83 studies from across 11 countries were identified to have assessed the risk of wildfires on aquatic animals. We provide a summary of the main ecosystem-level changes associated with wildfires and the main responses of aquatic fauna to such disturbances. We pay special focus to physiological tools and biomarkers used to assess how wildfires impact aquatic animals. We conclude by providing an overview of how physiological biomarkers can further our understanding of wildfire-related impacts on aquatic fauna, and how different physiological tools can be incorporated into management and conservation plans and serve as early warning signs of wildfire disturbances.