Elevated Water Temperature Research Articles

Rapid detection of heat stress biomarkers in Atlantic salmon (Salmo salar) liver using targeted proteomics

AbstractMost fish are ectothermic; therefore, their physiology is significantly affected by temperature. Aquaculture fish have limited ability to avoid elevated water temperatures, with impacts increasing as a result of climate change. To date, quantifying gene expression has been proposed to monitor heat stress in salmon liver. This study aimed to establish a faster multiplexed proteomics method to measure the abundance of thermal stress biomarkers in liver of salmon reared at 15°C or 20°C. Moreover, this study aimed to determine the effects that sample pooling, and data normalisation using housekeeping (HK) protein peptides would exert over the statistical significance of these thermal stress markers. A multiple reaction monitoring (MRM) mass spectrometry method, comprised 45 peptides derived from thermal stress markers and 10 peptides from HK proteins, was applied to measure these markers in liver of salmon reared at 15°C or 20°C. When samples were processed individually, 34 peptides were significant between salmon livers at 15°C or 20°C. In pooled samples, this decreased to five significant peptides. Peptides hprt1_HYADDLDR (hypoxanthine phosphoribosyl transferase) and gapdh_VPTPNVSVVDLTVR (glyceraldehyde‐3‐phosphate dehydrogenase) were the most stable and unstable HK protein peptides, respectively. When data was normalised with hprt1_HYADDLDR, 16 peptides were significant in individual samples and 13 in pooled samples. Significant peptides serpinh1a_ADLSNISGK, SerpinH1_TNSILFIGR, ela2_VVGGEDVR and gapdh_VPTPNVSVVDLTVR were common regardless of data strategy. A fast and reliable MRM method was established to validate thermal stress markers in salmon liver, where individual samples yielded better results than pooled samples. Sample pooling was only better when combined with normalisation as it validated twice the number of markers than sample pooling alone. This method could be applied to monitoring stress response in experiments involving feeding additives designed to mitigate thermal stress or in selective breeding programs to help understanding family variance in thermal tolerance.

An automated modular heating solution for experimental flow‐through stream mesocosm systems

AbstractWater temperature is a key environmental variable in stream ecosystems determining species distribution ranges, community composition, and ecological processes. In addition to global warming, direct anthropogenic impacts, for example through the influx of power plant cooling water or due to sun exposure after the removal of riparian vegetation, result in elevated water temperatures. However, temperature effects in stream ecosystems have mostly been tested in recirculating experimental systems, which can neither capture diurnal and seasonal variability in other environmental variables nor allow for entrainment of stream organisms. In contrast, open flow‐through systems, which are constantly supplied with stream water, offer a more realistic setting for stream ecological experiments, yet are difficult to implement. Here, we outline a heating module for the purpose of differential temperature regulation in a flow‐through mesocosm system by automatic control of warm water supply. We validated the functionality of the module in indoor trials as well as in an outdoor ExStream experimental mesocosm system. Furthermore, we tested the implications of different warm water temperatures for the survival of invertebrates drifting through the heating module to derive recommendations for the maximum warm water temperature for mixing with the natural water inflow. The module allows for controlled open flow‐through experiments in the field and the key components are flexible and scalable. Therefore, the module can be easily integrated into existing experimental flow‐through setups.

Feasibility study on cooling scheme design of the concrete shielding for swimming pool-type low-temperature heating reactor

Elevating the operational parameters of Swimming Pool-type Low-Temperature Heating Reactors to augment heating capacity raises concerns about heightened water temperatures within the pool. Elevated water temperatures pose a significant challenge to the integrity and durability of the concrete shielding, necessitating innovative solutions for effective thermal insulation. Existing approaches, such as insulation coatings and static insulation water layers, have shown limitations in maintaining prolonged cooling efficiency under reactor operating conditions. In response to this challenge, our research introduced a novel approach: the implementation of a flowing water layer within the concrete structure. A specialized insulation water layer is integrated within the reactor to efficiently isolate high-temperature pool water from the surrounding concrete shielding. A comprehensive experimental setup is established to assess the insulation effectiveness, yielding insights into the water layer’s insulation performance. Results demonstrate a significant radial temperature difference of up to 14.31 °C between the cold and hot walls of the water layer within the experimental parameters. Investigation into critical experimental variables indicates that inlet positioning minimally affects insulation efficiency. This study not only verifies the viability of the insulation water layer approach but also furnishes crucial experimental data for future research endeavors about the cooling scheme of the Swimming Pool-type Low-Temperature Heating Reactor.

Impacts of Extratropical Cyclone Fiona on a sensitive coastal lagoon ecosystem

AbstractOceanic storms can strongly disturb the physical and biogeochemical conditions of transitional coastal waters. Impacts of extreme oceanic storms on coastal ecosystems have received limited attention worldwide, with no studies at higher latitudes (> 45°) where tropical cyclones have usually abated. This study investigates the combined impacts from marine and atmospheric forcing on a coastal lagoon in Prince Edward Island, Canada, during and after Extratropical Cyclone Fiona in September 2022. Physical (water levels and temperature) and biogeochemical (dissolved oxygen [DO], electrical conductivity, pH, nitrate–nitrogen concentrations, total suspended solids [TSS]) datasets from the lagoon and the watershed's tributaries, groundwater springs, and piezometers were used to assess ecosystem disturbance and recovery timelines following the storm. Fiona resulted in a 1.6 m storm surge into the lagoon that elevated water temperatures by up to 6°C, disturbed the density‐dependent stratification of salinity and temperature, and reduced the diel amplitude of DO, indicating a reduction in plant respiration due to ecosystem disturbance. The freshwater tributaries revealed sharp changes in flow (30‐fold increase), nitrate–nitrogen (NO3‐N) concentrations and loading (70‐fold increase), and TSS loading (40‐fold increase) to the lagoon during and immediately following the storm. The lagoon rapidly recovered (hours) from the hydraulic disturbance of the storm surge, but elevated nutrient levels persisted for months. The intensity and frequency of extratropical cyclones is projected to increase in the Northwest Atlantic, making field‐based studies of cyclone impacts on coastal waters critical for understanding future coastal ecosystem disturbance and recovery periods relative to the timing of future storms.

HOTFLOOR: A benthic chamber system to simulate warming on the seafloor

AbstractThe frequency of abnormally warm water events is increasing not only in surface waters, but also in subsurface layers, with major impacts on benthic ecosystems. Previous insights on heatwave effects have been obtained through field observations or manipulative laboratory experiments. Here, we introduce a system capable of inducing elevated water temperatures in benthic habitats in situ over several days. The system consists of a commercially available electric boiler, usually applied in domestic underfloor heating, and custom‐designed benthic acrylic glass chambers connected to individual thermostats. Furthermore, the chambers are semi‐open, allowing constant water exchange, maintaining otherwise near‐natural conditions, including oxygen concentrations, while the temperature is elevated. The water exchange can be stopped to facilitate incubations measuring changes in benthic fluxes. We conducted a 15‐d trial study in July 2021 on a bare‐sediment habitat at 2.5 m depth, exposing five chambers to water temperatures 5°C above ambient temperatures for 6 d and comparing with five control chambers. In this assessment, we demonstrate that the temperature control and stability were reliable while maintaining natural oxygen conditions. The modular character of the system permits adaptations for various benthic habitats, facilitating the investigation of elevated temperatures in situ for future climate change scenarios.

Thermal tolerance exceedances of an endangered unionid mussel in the Rio Grande Basin, with implications for river management

Abstract Freshwater mussels are globally imperilled, which is attributed to their sensitivity to changes in streamflow and temperature. The Black River in south‐eastern New Mexico, USA, harbours a stronghold population of the federally endangered unionid Popenaias popeii (Texas hornshell). Decreasing discharge and elevated water temperatures are considered the primary factors responsible for the species’ decline. However, the impact of these factors has not been quantified directly, which may hinder conservation efforts. The upper thermal tolerances (LT05 and LT50) of Black River P. popeii larvae (glochidia) and newly transformed juveniles were evaluated. Individuals were acclimated to 27°C and then immersed at five experimental temperatures (28, 30, 32, 34 and 36°C) for 24 h (glochidia) or 96 h (juveniles). The thermal tolerances of P. popeii and its presumed host fishes were then overlain onto in situ water temperature and discharge data to determine thermal exceedances in the past 15 years. Temperature was hindcast back to 2007 using machine learning (random forest model) and coupled with discharge. For glochidia, LT05 was exceeded frequently (41%) and LT50 was exceeded occasionally (13%) during spring and summer periods, whereas juvenile thresholds were never exceeded. Upper continuous duration above threshold (UCAT) analysis revealed periods of catastrophic high temperature, which were used to determine discharge bottlenecks. This study demonstrates how laboratory‐derived physiological thresholds can be used in conjunction with environmental data to evaluate the hydrological needs of aquatic organisms, which is useful in efforts to maintain flow regimes that protect native ecosystems.

Correlational Study of Escherichia coli Concentrations and Coastal Water Temperatures in Metro Vancouver’s Routine Beach Water Quality Reports from 2016-2022

The impact of climate change and the resulting more frequent heatwaves severely affect public health, as seen in the record-breaking 2021 Western North America heat wave. The elevated coastal water temperatures caused by rising ambient temperatures are expected to lead to increased recreational water use, which could contribute to higher levels of Recreational Water Illnesses (RWIs) due to the growth of specific pathogens. This study investigates any potential correlation between Escherichia Coli levels and coastal water temperatures in Routine Beach Water Quality reports from Metro Vancouver from 2016-2022. Furthermore, it aims to create a standardized Bathing Water Quality Index (BWQI) to reduce public exposure to pathogens and prepare for future extreme weather events.

Postprandial metabolism of Australian hybrid abalone (Haliotis laevigata × H. rubra) in relation to temperature and dietary protein manipulation

Understanding the physiological responses of abalone to culture conditions and nutritional inputs is paramount to maintain optimal performance under densely stocked farming conditions. High water temperature (>24 °C) is widely accepted as a key contributor to elevated summer mortality. High crude protein levels in modern abalone diets may interact with elevated water temperature to produce detrimental effects on abalone physiological processes but have received scant attention. This study measured the energy used in the digestion, absorption, and assimilation (i.e., specific dynamic action (SDA)) of hybrid abalone (Haliotis laevigata x H. rubra) after four months of acclimation to three protein levels (32, 38 and 44%) at three culture temperatures (12, 17 and 22 °C). Hybrid abalone exhibited significant stepwise increases in meal size as temperature increased from 12 through to 22 °C, contributing to significantly different SDA between the temperature treatments. Resting (standard) aerobic metabolic rate and peak metabolism (peak ṀO2) during SDA both increased with temperature, while SDA duration was lowest at 17 °C. No effect of dietary protein was observed within the temperature treatments for the SDA metrics. Abalone held at 12 °C exhibited significantly higher rates of gonad maturation, particularly among females. When 22 °C-acclimated abalone were exposed to a simulated summer heatwave up to 26 °C, they exhibited similar mortality and metabolic responses across protein treatment groups and there was a trend of steadily decreasing ṀO2 with sustained 26 °C water temperature, probably due to fasting. These results help to inform best farming practices to ensure optimal diet, growth, metabolic performance, and survival of hybrid abalone in the dynamic farm environment.

A simple model for predicting oxygen depletion in lakes under climate change

ABSTRACT The advent of climate change has placed aquatic ecosystems at risk for potential declines in water quality, including an increase in the number of lakes experiencing substantial dissolved oxygen (O2) depletion. Through its influence on the thermal structure of lakes via elevated water temperatures and alterations in stratification phenology, climate change intensifies biogeochemical and ecological processes involved in O2 consumption, giving rise to conditions like hypoxia/anoxia. However, predicting O2 dynamics is difficult, with in situ O2 depletion rates showing considerable lake-dependent variability, underpinned by distinct underlying mechanisms. Our study attempts to overcome these lake-specific features and targets distilling key components of O2 depletion into a simple and transferable conceptual model applicable across a diverse array of lakes and at large scales. Using O2 depletion rates from literature reflecting variability in trophic state, we quantified the typical O2 depletion rate ranges for oligotrophic, mesotrophic, and eutrophic lakes and assessed their temperature sensitivity for a broader climate impact assessment. Our model gave reasonable estimates for O2 depletion and risks of anoxia through 3 explanatory variables: trophic state, stratification duration, and hypolimnion temperature. We validated our model predictions using data from 5 German lakes and assessed the relative importance of the 3 influencing factors. This easy-to-use approach has potential for lake management to attain rapid assessments of possible future problems with O2 dynamics in a given lake, even in the absence of in situ data. Moreover, it allows scaling of O2 dynamics continentally/globally without lake-specific hydrological or morphological details.

Intermittent shading can moderate coral bleaching on shallow reefs

The health of coral reefs is declining from the effects of human activity and climate change. Mass coral bleaching is often triggered by elevated water temperature and excessive solar irradiance. Shading can reduce coral bleaching risk. Shading-based management interventions, such as whole-of-reef marine fogging, have been proposed as a conservation tool for periods when coral undergoes excessive thermal stress. This study examined the effect of intermittent shade (30% for 0, 4, or 24 h) on two coral species, Duncanopsammia axifuga and Turbinaria reniformis, held at either 26.4°C or 32.4°C for 18 days. Coral fragments were assessed for bleaching (relative mean intensity of grey, chlorophyll a, and symbiont density), photochemistry (PAM fluorometry), and antioxidant biomarkers (SOD and CAT). Shading responses were species-specific, with T. reniformis more responsive to shading than D. axifuga. Thirty per cent shading delayed bleaching up to three-degree heat weeks (DHW), and 24 h shade was more protective than 4 h shade. Shading suppressed catalase activity in T. reniformis. Overall, our results suggest that intermittently shading corals for 4 h can moderate light stress and slow bleaching in some corals and could improve the efficiency of active solar radiation management in marine ecosystems.

Additive multiple predator effects increase prey mortality under experimental warming in a rocky intertidal food web

Climate warming is expected to alter species interactions, which are shaped by components of individual foraging behavior. Yet few studies examine species' behavioral responses to inform predictions about how species interactions will be affected by warming. Multiple predator effects (MPEs) may be mediated by climatic warming, especially in highly diverse coastal ecosystems that are prone to extreme warming events. In a laboratory experiment, we quantified the effects of elevated sea water temperature on mortality rates of mussels (Mytilus californianus, Conrad, 1837), and the behavioral responses of their predators: crabs (Romaleon antennarium, Stimpson, 1856) and sea stars (Pisaster ochraceus, Brandt, 1835), to understand how warming affects MPEs and if predators' behavioral responses to warming are indicative of the outcome of MPEs. Sea star effects on mussel mortality did not vary with temperature, but declined threefold in the presence of crabs, due to behavioral avoidance of physical contact with crabs. In contrast, the effect of crabs on mussel mortality was ten times higher under elevated temperature, but was unaffected by sea stars. In mixed predator treatments, crabs caused significant mussel mortality, but sea stars had weaker impacts, regardless of temperature. Consequently, multiple predators had effects that did not differ from those of the more effective crab predator. Increasing temperature in the eastern North Pacific may create locations where crabs become the dominant predator of mussels, with warming increasing predation risk for mussels in this region. Field studies should examine the effects of warming on crab predation on mussels in this system.

Reproductive Characteristics and Germ Cell Status of Indian Major Carp, <i>Labeo rohita</i> Reared in Elevated Water Temperature Regime

Rearing water temperature and fluctuations in it has a profound effect on survival and gonadal development of fish. Reproduction in fish, compared with other physiological processes, only occurs in a bounded temperature range; therefore, small changes in water temperature could significantly affect this process. Here we analysed the effects of different rearing water temperatures (28 °C, 30 °C, 32 °C, 34 °C and 36 °C) and a cytotoxic drug (busulfan) on germ cell status and maturation in Indian major carp, Labeo rohita. The effectiveness of the treatment was assessed by gonadosomatic index, histology and dye uptake of GC. Thermo-chemical treatments were given either: as elevated water temperature alone (0.69±0.09) or in combination with busulfan that showed a low GSI value (0.49±0.26) as compared to control (0.88±0.009). Gonadal morphology visibly shrunk after the thermochemical treatments. Similarly, the gonadal histology confirmed that the GC depletion took place when the rohu were reared at elevated temperature along with the application of a cytotoxic drug busulfan (40 mg/kg). According to the deteriorating reproductive responses of the fish by temperature fluctuations, it is plausible that changes may affect aquaculture production and affecting future populations of fish, so new strategies for amelioration should be anticipated.

Evaluating Muskellunge catch‐and‐release mortality at elevated summer water temperature

AbstractObjectiveFisheries managers and anglers have expressed concerns regarding warmwater angling mortality, representing a need to evaluate mortality rates at various water temperatures and multiple latitudes. Up to 97% of Muskellunge Esox masquinongy caught by anglers are released, and previous research on catch and release (C&R) for Muskellunge has suggested relatively low mortality rates (0–5%). However, those studies were all conducted within the range of water temperatures that are thermally optimal for Muskellunge and generally at water temperatures less than 25°C. As many Muskellunge populations routinely experience temperatures greater than 25°C during the summer months our objective was to quantify warmwater (>25°C) C&R mortality rates in Muskellunge.MethodsWe collected 102 adult Muskellunge (>760 mm) and stocked them into and identify factors influencing mortality by using experimental ponds. Adult Muskellunge (n = 102) were stocked into eight earthen or plastic‐lined flow‐through ponds (0.06–0.71 ha) at densities less than 16 fish/ha. Muskellunge (n = 50) were angled by utilizing specialized Muskellunge fishing gear at water temperatures of 19.6–32.6°C, with 32 fish being caught at temperatures exceeding 25°C. After being angled, fish were closely monitored for 2 weeks to assess mortality; fish that remained uncaught during the experiment were used as controls (n = 53).ResultMortality was greater for angled fish (30.0%) than for control fish (11.3%). Differences in C&R mortality were compared across a range of temperature regimes using Firth logistic regression. Five‐day cumulative temperature and net time were positively related to the probability of mortality, but size and sex were unrelated to mortality. Increasing C&R mortality with temperature was mitigated somewhat by lower catch rates at higher temperatures. Mortalities per 100 angler‐hours were 0 at <25°C, 4.98 at 25.00–27.49°C, 2.48 at 27.5–30.0°C, and 1.17 at >30°C.ConclusionRecent field studies have identified the importance of thermal refuge in mitigating summer C&R mortality of Muskellunge. This study identified specific temperature conditions responsible for elevated mortality in the absence of refugia. Although increasing temperatures above 25°C led to increasing C&R mortality in our ponds, lower catchability seemingly provided some mitigation. The interactive effects of thermal refugia and catch rates with temperature warrant further investigations into population‐level effects at varying levels of exploitation.

Vibrio cholerae-An emerging pathogen in Austrian bathing waters?

Vibrio cholerae, an important human pathogen, is naturally occurring in specific aquatic ecosystems. With very few exceptions, only the cholera-toxigenic strains belonging to the serogroups O1 and O139 are responsible for severe cholera outbreaks with epidemic or pandemic potential. All other nontoxigenic, non-O1/non-O139 V.cholerae (NTVC) strains may cause various other diseases, such as mild to severe infections of the ears, of the gastrointestinal and urinary tracts as well as wound and bloodstream infections. Older, immunocompromised people and patients with specific preconditions have an elevated risk. In recent years, worldwide reports demonstrated that NTVC infections are on the rise, caused amongst others by elevated water temperatures due to global warming.The aim of this review is to summarize the knowledge gained during the past two decades on V.cholerae infections and its occurrence in bathing waters in Austria, with aspecial focus on the lake Neusiedler See. We investigated whether NTVC infections have increased and which specific environmental conditions favor the occurrence of NTVC. We present an overview of state of the art methods that are currently available for clinical and environmental diagnostics. Apreliminary public health risk assessment concerning NTVC infections related to the Neusiedler See was established. In order to raise awareness of healthcare professionals for NTVC infections, typical symptoms, possible treatment options and the antibiotic resistance status of Austrian NTVC isolates are discussed.

Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana, Phaeophyceae).

Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10-22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10-14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16-18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.

Ceratonova shasta infection in lower Feather River Chinook juveniles and trends in water-borne spore stages

We performed a five-year (2015–2020) survey of juvenile natural Chinook Salmon (Oncorhynchus tshawytscha), adult salmon carcasses, and river water from the lower Feather River to determine infection prevalence, distribution, and spore quantity of the myxozoan parasite Ceratonova shasta. Average prevalence of infection in juvenile salmon collected from the high flow channel ranged from 45–58% depending on assay method. Initial infection of fry and detection of actinospore stage in river water began in late January or early February. Overt disease occurred in March and was lethal. Infection of the gill was detected weeks ahead of intestinal infection. Water-borne spore measurement and fish infection demonstrate an infectious zone beginning at the outlet of the Thermalito Afterbay. This zone is expanding downriver past the confluence of the Yuba River. Adult carcasses produce billions of myxospores annually that move downriver over the winter. C. shasta infection is one of several factors (predation, limited rearing habitat, elevated water temperature, water withdrawal, etc.) limiting natural Chinook Salmon recruitment in the Feather River.

Signaling and crosstalk of rhizobacterial and plant hormones that mediate abiotic stress tolerance in plants.

Agricultural areas exhibiting numerous abiotic stressors, such as elevated water stress, temperatures, and salinity, have grown as a result of climate change. As such, abiotic stresses are some of the most pressing issues in contemporary agricultural production. Understanding plant responses to abiotic stressors is important for global food security, climate change adaptation, and improving crop resilience for sustainable agriculture, Over the decades, explorations have been made concerning plant tolerance to these environmental stresses. Plant growth-promoting rhizobacteria (PGPR) and their phytohormones are some of the players involved in developing resistance to abiotic stress in plants. Several studies have investigated the part of phytohormones in the ability of plants to withstand and adapt to non-living environmental factors, but very few have focused on rhizobacterial hormonal signaling and crosstalk that mediate abiotic stress tolerance in plants. The main objective of this review is to evaluate the functions of PGPR phytohormones in plant abiotic stress tolerance and outline the current research on rhizobacterial hormonal communication and crosstalk that govern plant abiotic stress responses. The review also includes the gene networks and regulation under diverse abiotic stressors. The review is important for understanding plant responses to abiotic stresses using PGPR phytohormones and hormonal signaling. It is envisaged that PGPR offer a useful approach to increasing plant tolerance to various abiotic stresses. However, further studies can reveal the unclear patterns of hormonal interactions between plants and rhizobacteria that mediate abiotic stress tolerance.

Green algae outcompete cyanobacteria in a shallow lake, Longhu Lake

Abstract Green algae are natural competitors of cyanobacteria, but we still do not know why green algae have a competitive advantage in shallow lakes. In this study, we used qPCR to quantify and monitor green algae and cyanobacteria in Longhu Lake. Our results showed that green algae were dominant in Longhu Lake, accounting for 71.80–80.31%. The temporal and spatial dynamics of green algal blooms were consistent with that of total organic nitrogen (TON), indicating that organic nitrogen may be the key trigger of green algal blooms. Nitrogen and phosphorus were excessive, and the peak of ammonia nitrogen occurred during the blooms, implying that ammonia nitrogen may be one of the important factors stimulating green algal blooms. Spearman correlation analysis and RDA analysis showed that green algae and cyanobacteria were positively correlated with water temperature, TON, and ammonia nitrogen, indicating that they have similar favorable growth conditions in Longhu Lake. Our results indicated that the combined effects of elevated water temperature, excessive nitrogen and phosphorus, non-stratification, and short water retention time could favor the competitive dominance of green algae in Longhu Lake. The findings here improve our understanding of the competition between green algae and cyanobacteria in shallow lakes.

Elevated water temperature initially affects reproduction and behavior but not cognitive performance or physiology in Gambusia affinis

Warming temperatures associated with climate change and urbanization affect both terrestrial and aquatic populations with freshwater fish being especially vulnerable. As fish rely on water temperature to regulate their body temperature, elevated temperatures can alter physiology and in turn behavioral and cognitive skills. We examined whether reproduction, physiology, behavior, and cognitive skills were altered by exposure to elevated water temperatures during one reproductive cycle in the live-bearing fish, Gambusia affinis. We found that within four days of exposure to a higher temperature (31°C), females were more likely to drop underdeveloped offspring than females maintained at 25°C. However, females did not show a change in cortisol release rates over time or altered fecundity and reproductive allotment, despite increased growth at the higher temperature. But in the heat treatment fish that started the experiment with higher baseline cortisol dropped their offspring sooner than fish with lower cortisol release rates. We used a detour test to explore behavior and cognitive skills at three time points after exposure to the heat treatments: early, midway, and at the end (day 7, 20 and 34). We found that on day 7, females were less likely to exit the starting chamber when maintained at 31°C but did not differ in their time to exit the starting chamber or in their motivation (reach the clear barrier). Similarly, females did not differ in their time to swim around the barrier to reach a female fish reward (solving skill). Nonetheless, we found a link between behavior and cognition, where females who were slower to exit the start chamber got around the barrier faster, indicating that they learned from prior experience. Together our results indicate that G. affinis is initially affected by elevated water temperatures but may partially cope with higher temperatures by not altering their hypothalamus-interrenal axis (baseline cortisol), and at the same time this might act to buffer their young. Acclimation may reduce costs for this species and potentially explain why they are successful invaders and tolerant species despite climate change.

Susceptibility of DNA damage recognition activities linked to nucleotide excision and mismatch repair in zebrafish (Danio rerio) early and mid-early embryos to 2.5 to 4.5°C heat stress.

Fish at early life stages are sensitive to temperature change because of their narrower temperature tolerance ranges. Initiated by damage detection, DNA mismatch repair (MMR) and nucleotide excision repair (NER) maintain genome integrity respectively by eliminating mismatched nucleotides and helix-distorting DNA lesions. As discharge of heated effluent from power plants may elevate water temperatures to only 2 to 6°C higher than ambient, this study explored if temperatures within this range affected MMR and NER-linked damage detection activities in fish embryos using zebrafish (Danio rerio) embryo as a model organism. Exposure of early embryos at 10h post fertilization (hpf) to a warmer temperature at + 4.5°C for 30min enhanced damage recognition activities targeting UV-induced cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts (6-4PPs) that distorted helical structures. Conversely, photolesions sensing activities were inhibited in 24 hpf mid-early embryos under the same stress conditions. A much higher temperature at + 8.5°C imposed similar effects on UV damage detection. A mild heat stress at + 2.5°C for 30min, however, repressed both CPD and 6-4PP binding activities in 10 and 24 hpf embryos. Inhibition of damage recognition under mild heat stress impeded the overall NER capacity evidenced by a transcription-based repair assay. Warmer water temperatures at + 2.5 and + 4.5°C also inhibited G-T mismatch binding activities in 10 and 24 hpf embryos, but G-T recognition was more sensitive to + 4.5°C stress. Inhibition of G-T binding partially correlated with a downregulation of Sp1 transcription factor activity. Our results showed the potential of water temperature elevation within 2 to 4.5°C to disturb DNA damage repair in fish at embryonic stages.