Interactive Effects Of Temperature Research Articles

The combined effects of temperature and salinity on the digestion and respiration metabolism of Pinctada fucata

The combined effects of temperature and salinity on the digestion and respiration metabolism of Pinctada fucata were evaluated via response surface methodology and box-benhnken design under laboratory condition. Results indicated that the primary and secondary effects of salinity and temperature had significant effects on amylase (AMS) of P. fucata (P < 0.05)., The digestive enzyme reached the maximum activity when temperature was 26 °C. The AMS and trypsin (TRYP) increased at first, and then decreased with increasing temperature. The Lipase (LPS) was positively correlated with either salinity or temperature. Salinity had no significant effect on TRYP as a primary effect (P > 0.05), but had a significant effect on TRYP as a secondary effect (P < 0.01). These effects were completely opposite to the effect of temperature on pepsin (PEP) as primary and secondary effects. The combined effects of salinity and temperature on AMS, TRYP and PEP were significant (P < 0.01), but had no significant effect on LPS (P > 0.05). The primary, secondary and interaction effects of salinity had significant effects on NKA (Na+-K+-ATPase) of P. fucata (P < 0.05), and NKA presented a U-shaped distribution with increasing salinity. The quadratic and interactive effects of temperature had a significant effect on AKP (P < 0.05), and AKP showed a U-shaped distribution with increasing temperature. Lactate dehydrogenase (LDH) activity decreased at first, and then increased when temperature and salinity changed from 20 to 30 °C and 23–33 ‰, respectively. The expression of GPX gene affected by temperature in gills may be delayed compared with that in hepatopancreas, and its expression is tissue-specific. The appropriate digestion and respiratory metabolism index models were established under the combined temperature and salinity conditions. The optimization results showed that the optimal combination of temperature and salinity was 26.288 °C/28.272‰. The desirability was 0.832. Results from the present study will provide a theoretical reference for shellfish culture affected by environmental interactions and the establishment of related index models.

Speed it up: How temperature drives toxicokinetics of organic contaminants in freshwater amphipods.

The acceleration of global climate change draws increasing attention towards interactive effects of temperature and organic contaminants. Many studies reported a higher sensitivity of aquatic invertebrates towards contaminant exposure with increasing or fluctuating temperatures. The hypothesis of this study was that the higher sensitivity of invertebrates is associated with the changes of toxicokinetic processes that determine internal concentrations of contaminants and consequently toxic effects. Therefore, the influence of temperature on toxicokinetic processes and the underlying mechanisms were studied in two key amphipod species (Gammarus pulex and Hyalella azteca). Bioconcentration experiments were carried out at four different temperatures with a mixture of 12 exposure relevant polar organic contaminants. Tissue and medium samples were taken in regular intervals and analysed by online solid-phase extraction liquid chromatography high-resolution tandem mass spectrometry. Subsequently, toxicokinetic rates were modelled and analysed in dependence of the exposure temperature using the Arrhenius equation. An exponential relationship between toxicokinetic rates versus temperature was observed and could be well depicted by applying the Arrhenius equation. Due to a similar Arrhenius temperature of uptake and elimination rates, the bioconcentration factors of the contaminants were generally constant across the temperature range. Furthermore, the Arrhenius temperature of the toxicokinetic rates and respiration was mostly similar. However, in some cases (citalopram, cyprodinil), the bioconcentration factor appeared to be temperature dependent, which could potentially be explained by the influence of temperature on active uptake mechanisms or biotransformation. The observed temperature effects on toxicokinetics may be particularly relevant in non-equilibrated systems, such as exposure peaks in summer as exemplified by the exposure modelling of a field measured pesticide peak where the internal concentrations increased by up to fourfold along the temperature gradient. The results provide novel insights into the mechanisms of chemical uptake, biotransformation and elimination in different climate scenarios and can improve environmental risk assessment.

A positive temperature‐dependent effect of elevated CO2 on growth and lipid accumulation in the planktonic copepod, Calanus finmarchicus

AbstractCalanus finmarchicus were reared from eggs to adults at 12°C and 16°C with non‐limiting food in combination with ambient (600 μatm) and high (1100 μatm) pCO2. These conditions are likely to be encountered by the species at the southern margins of its biogeographical range by the end of the century. Dry weight (DW), carbon (C) and nitrogen (N) mass, oil‐sac volume (OSV), fatty acid composition (FA), and oxygen consumption rates (OCR) were measured on newly molted stage CV copepodites and recently molted adult females. By focusing our measurements on these precise events in the life cycle, we were able to obtain a more accurate comparison of growth and respiration across treatments. Copepods raised at 12°C had a significantly greater DW, OSV, and C and N mass than those raised at 16°C High pCO2, independent of temperature, was associated with a further increase in the DW and C content of the copepods. Interactive effects of temperature and pCO2 resulted in a larger OSV at low temperature and high pCO2. Mass‐specific respiration rates were significantly lower at lower temperatures and elevated pCO2 suggesting that the increase in mass (DW, C, and OSV) resulted from reduced metabolic cost. The composition of fatty acids in the copepods varied mainly with temperature. Two fatty acids varied with pCO2: 16:0 tended to decrease with higher pCO2 and 18:3n−3 tended to increase with higher pCO2. These observations suggest that elevated pCO2/lower pH in future oceans may have a beneficial effect on C. finmarchicus.

Modeling the behavior of Celtis mildbraedii sawdust and polyethylene terephthalate co-pyrolysis for syngas production

The co-pyrolysis behavior of Celtis mildbraedii sawdust (CMS) and polyethylene terephthalate (PET) waste for syngas production was investigated using a response surface methodology (RSM) based on Box-Behnken design (BBD). The production parameters were examined at a temperature, feedstock concentration (CMS/PET ratio), and nitrogen (N2) gas flow rate range of 600–800 °C, 50/50–80/20%, and 2–10 normal liters per minute (NL/min), respectively. A second-order regression model was used to predict the response with the outcomes analyzed using Minitab statistical software (version 19) at a 95% confidence interval. Results showed that CMS can be used solely and/or in a mixture with PET for pyrolysis. The syngas yield was influenced by the interactive effects of temperature and N2 gas flow rate with a significant p-value of less than 0.05. It was observed that temperature was the most influencing factor due to its high F-value of 355.06. The optimum yield of syngas was attained at a temperature of 800 °C, N2 gas flow rate of 6 NL/min, and feedstock concentration of a mixture of 50 wt.% of sawdust and 50 wt.% of plastic. At these conditions, the obtained syngas yield was 68.1 wt.%. In conclusion, the current study proves that co-pyrolysis has the potential to convert biomass and plastics to fuels and other green chemicals.

Natural history and ecological effects on the establishment and fate of Florida carpenter ant cadavers infected by the parasitic manipulator Ophiocordyceps camponoti‐floridani

Abstract Ophiocordyceps fungi manipulate the behaviour of their ant hosts to produce a summit disease phenotype, thereby establishing infected ant cadavers onto vegetation at elevated positions suitable for fungal growth and transmission. Multiple environmental and ecological factors have been proposed to shape the timing, positioning and outcome of these manipulations. We conducted a long‐term field study of Ophiocordyceps camponoti‐floridani infections of Camponotus floridanus ants—the Florida zombie ants. We propose and refine hypotheses on the factors that shape infection outcomes by tracking the occurrence of and fungal growth from hundreds of ant cadavers. We modelled and report these data in relation to weather, light, vegetation and attack by hyperparasites. We investigated environmental factors that could affect the occurrence and location of newly manipulated ant cadavers. New cadaver occurrence was preferentially biased towards epiphytic Tillandsia bromeliads, canopy openness and summer weather conditions (an interactive effect of temperature, humidity and precipitation). Furthermore, we suggest that incident light at the individual cadaver level reflects microhabitat choice by manipulated ants or selective pressure on cadaver maintenance for conditions that improve fungal survival. We also asked which environmental conditions affect fungal fitness. Continued fungal development of reproductive structures and putative transmission increased with moist weather conditions (interaction of humidity and precipitation) and canopy openness, while being reduced by hyperparasitic mycoparasite infections. Moreover, under the most open canopy conditions, we found an atypical Ophiocordyceps growth morphology that could represent a plastic response to conditions influenced by high light levels. Taken together, we explore general trends and the effects of various ecological conditions on host and parasite disease outcomes in the Florida zombie ant system. These insights from the field can be used to inform experimental laboratory setups that directly test the effects of biotic and abiotic factors on fungus–ant interactions or aim to uncover underlying molecular mechanisms. Read the free Plain Language Summary for this article on the Journal blog.

Assessment of nitrogen interaction with temperature on the growth and toxin production of mat-forming toxin-producing Anagnostidinema carotinosum.

Global warming and eutrophication contribute to the severity of cyanobacteria blooms. However, it is unclear how these factors influence the growth and toxin production of Anagnostidinema carotinosum. Based on morphological and molecular analysis, this is the first time A. carotinosum was identified in South Korea. The interactive effect of temperature (25, 30 or 34°C) and nitrogen (2.5, 3.5 or 4.5mg NO3 -N l-1 ) on A. carotinosum growth and toxin production was studied. Increasing nitrogen limitation reflects reduced growth and chlorophyll-a content at all temperatures. However, the growth was effective under nitrogen limitation when temperatures exceeded 25°C. The maximum growth was found at 30°C, followed by 34°C under higher nitrate levels (3.5 and 4.5mg l-1 ). In addition, the cell microcystin and anatoxin-a quota increased significantly at 25°C with increasing nitrate limitation, decreasing considerably at 30°C in the same nitrate gradient. These results suggested temperatures stimulate A. carotinosum growth at 30 and 34°C and cellular toxin quota at 25 and 34°C with increasing NO3 -N levels. These findings imply that limiting nitrogen input alone can effectively reduce biomass; however, controlling A. carotinosum and its toxins at higher temperatures under nitrate limitation is necessary for water quality.

Interactive effects of temperature and nitrogen source on the elemental stoichiometry of a polar diatom

AbstractA recent study hypothesized that the near‐zero temperatures that generally prevail in Arctic waters negate the influence that different nitrogen (N) sources can otherwise have on the growth and elemental stoichiometry of marine micro‐algae. Here we test this hypothesis experimentally by evaluating how temperature (0–9°C) affects the growth and elemental stoichiometry of an ecologically relevant Arctic diatom Chaetoceros gelidus growing on different N sources (ammonium, nitrate, urea) at saturating irradiance. Following an initial acclimation period in which steady growth rates were achieved under each experimental treatment, changes in cellular concentrations of chlorophyll a and particulate carbon (C), nitrogen (N), phosphorus (P), and biogenic silica (Si) were monitored. While N source effects on growth rate became manifest as temperature rose above 0°C, the estimated optimal growth temperature was similar in all cases (Topt = 8.3°C). A positive effect of temperature on the N : P ratio occurred only at 6°C. Above this temperature, the N : P ratio decreased to values close to those observed at 0°C and 3°C. By contrast, the C : N ratio remained nearly invariant between 0°C and 6°C but increased substantially at 9°C. Overall, the results suggest that the presently widespread and successful diatom C. gelidus possesses the ability to remain competitive despite ongoing environmental changes and that its responses to warming and the availability of different N sources may impact elemental fluxes in the future.

Low temperatures lead to higher toxicity of the fungicide folpet to larval stages of Rana temporaria and Bufotes viridis.

Pesticides are one of the main drivers of the worldwide amphibian decline. Their actual toxicity depends on a number of factors, like the species in focus or the developmental stage of exposed individuals. As ectothermic species, the metabolism of amphibians is influenced by ambient temperature. Therefore, temperature also affects metabolic rates and thus processes that might enhance or reduce toxic effects. Studies about the interactive effect of temperature and toxicity on amphibians are rare and deliver contrasting results. To investigate the temperature-dependent pesticide sensitivity of larvae of two European species we conducted acute toxicity tests for the viticultural fungicide Folpan® 500 SC with the active ingredient folpet at different temperatures (6°C, 11°C, 16°C, 21°C, 26°C). Sensitivity of Rana temporaria and Bufotes viridis was highly affected by temperature: early larvae (Gosner stage 20) were about twice more sensitive to Folpan® 500 SC at 6°C compared to 21°C. Next to temperature, species and developmental stage of larvae had an effect on sensitivity. The most sensitive individuals (early stages of R. temporaria at 6°C) were 14.5 times more sensitive than the least sensitive ones (early stages of B. viridis at 26°C). Our results raise concerns about typical ecotoxicological studies with amphibians that are often conducted at temperatures between 15°C and 20°C. We suggest that future test designs should be performed at temperatures that reflect the temperature range amphibians are exposed to in their natural habitats. Variations in the sensitivity due to temperature should also be considered as an uncertainty factor in upcoming environmental risk assessments for amphibians.

Interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga Saccharina japonica (Laminariales) from Hokkaido, Japan

The interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga, Saccharina japonica (var. japonica, Laminariales) from Hokkaido, Japan were examined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Assessment of maximum quantum yields (in darkness) and effective quantum yields (at 50 μmol photons m−2 s−1) at nine temperatures (4–36 °C, four increments) during 3-d culture indicated a temperature threshold at 24 °C, with early decline of maximum quantum yields at such temperature, which could probably be due to exhaustion of carbohydrate reserves by respiration in prolonged darkness. Unlike maximum quantum yields that was relatively stable through 4–20 °C, effective quantum yields under 50 μmol photons m−2 s−1 gradually declined at low temperatures, revealing light sensitivity under chilling temperatures. Chronic 6-h exposures under 200 (low) and 1000 (high) μmol photons m−2 s−1 at 4, 16, and 24 °C generated a significant decline in effective quantum yields at 4 °C under both irradiances; however, only treatments under low irradiance fully recovered after a subsequent 12-h dim light treatment. Moreover, post-dim light acclimation effective quantum yields of treatments at 16 and 24 °C under high irradiance returned to initial levels, suggesting accelerated photoinhibition at low temperature. Photosynthesis–irradiance responses at 16 °C under blue (450 nm), green (525 nm), red (660 nm), and white light (metal halide lamp) showed that the maximum photosynthetic output occurred under blue and white lights. The photoinhibitory sensitivity to chilling-light stress and the enhanced photosynthesis under blue light of S. japonica presented additional evidence of their physiological adaptation to cold-temperate subtidal waters.

OPTIMIZATION AND KINETICS STUDIES OF THE DISSOLUTION OF DOLOMITE IN SULPHURIC ACID (H2SO4) VIA BOX-BEHNKEN EXPERIMENTAL DESIGN

Background: The recovery of any valuable component from dolomite as a double carbonate mineral depends on its dissolution efficiency. Aim: This study aimed to optimize and provide a simplified novel approach to the kinetics of dolomite dissolution in sulphuric acid solution using the Box-Behnken experimental design. Methods: The dolomite sample was dissolved in a sulphuric acid solution at seventeen different experimental conditions. The residue containing impurities was removed via filtration, while precipitation was carried out at the optimum conditions. Results and Discussion: The relationship between the independent and dependent variables best fits into the two-factor interaction model with a coefficient of determination of 0.9492, adjusted R² of 0.9187, and predicted R² of 0.7514. The total residual sum of 3x10-13 and adequate precision of 18.769 show that the predicted dissolution efficiency is much closer to the experimental values. The analysis of variance revealed that the individual effect of acid concentration, temperature, and dissolution time all positively contribute to the dissolution. The interactive effect of acid concentration with temperature and the interactive effect of temperature with dissolution time also positively influences the dissolution efficiency. Following the dissolution of dolomite in sulphuric acid, a white precipitate was formed at room temperature, which dissolved back at a temperature of 70 oC, agitation speed of 900 revolutions per minute, and within 10 minutes. A predictive approach using a two-factor interactive model was applied to generate the kinetic data. Conclusions: The established model equation is suitable for predicting dolomite dissolution in sulphuric acid. The application of the shrinking core model to the generated data shows that the reaction between dolomite and sulphuric acid is film diffusion control with a first-order reaction (0.6587) and activation energy of 27.5 KJmol-1k-1.

Optimization of parameters in biomethanization process with co-digested poultry wastes and palm oil mill effluents

Poultry wastes (PW) and palm oil mill effluents (POME) are thought to be promising starting materials for biogas production. In the present study, the optimization of biomethanization process from co-digested (PW) and POME was investigated. To assist digestion, samples were sun-dried, ground, and mixed with water to form slurry. The central composite design was used in the experimental design, while the desirability function was applied in the process optimization of the co-digestion process. The interactive effects of temperature, pH, and hydraulic retention time were equally studied. The results showed a high co-efficient of determination (R2) value of 0.9920. Also, the predicted and experimental values obtained were 4377.71 ml and 4379.01 respectively, while the optimum conditions obtained were 45 °C, 8.00 and 15 days for temperature, pH, and hydraulic retention time, respectively. This finding shows that the proposed technique is effective and robust in predicting biomethane generation from co-digested POME and PW.

Warmer temperature decreases the maximum length of six species of marine fishes, crustacean, and squid in New Zealand

As global oceans continue to warm and deoxygenate, it is expected that marine ectotherms will reduce in body size resulting from the interactive effects of temperature and dissolved oxygen availability. A temperature-size response describes how wild populations of ectothermic species grow faster and reach a smaller size within warmer temperatures. While temperature-size responses are well observed in marine ectotherms, the mechanisms underpinning such a reduction in body size remain debated. Here, we analyse the relative influence of temperature, dissolved oxygen concentration, and geographic location (which encompasses multiple latent variables), on the maximum body length of four fish, one crustacean, and one squid species, which inhabit shallow to deep sea (1000 m) New Zealand waters across a temperature gradient of 1.5 to 18 °C. We found that all study species displayed a temperature-size response, with the strongest response exhibited by the largest species, hoki (Macruronus novaezelandiae). We also found that temperature was more important than dissolved oxygen concentration in determining maximum body length, as dissolved oxygen levels were at or near saturation in the study area. Our results suggest that larger-bodied species may experience the strongest temperature-size responses, and support expectations from the gill-oxygen limitation theory (GOLT) and the oxygen and capacity limited thermal tolerance (OCLTT) concept that increases in oxygen demand may be size- and temperature-dependent, thus driving a reduction in maximum body length of marine ectotherms with warming.

Coral calcification mechanisms in a warming ocean and the interactive effects of temperature and light

Ocean warming is transforming the world’s coral reefs, which are governed by the growth of marine calcifiers, most notably branching corals. Critical to skeletal growth is the corals’ regulation of their internal chemistry to promote calcification. Here we investigate the effects of temperature and light on the calcifying fluid chemistry (using boron isotope systematics), calcification rates, metabolic rates and photo-physiology of Acropora nasuta during two mesocosm experiments simulating seasonal and static temperature and light regimes. Under the seasonal regime, coral calcification rates, calcifying fluid carbonate chemistry, photo-physiology and metabolic productivity responded to both changes in temperature and light. However, under static conditions the artificially prolonged exposure to summer temperatures resulted in heat stress and a heightened sensitivity to light. Our results indicate that temperature and light effects on coral physiology and calcification mechanisms are interactive and context-specific, making it essential to conduct realistic multi-variate dynamic experiments in order to predict how coral calcification will respond to ocean warming.

Interactive effect of temperature and plant species on nitrogen cycling and treatment in stormwater biofiltration systems

Stormwater biofiltration systems (also known as biofilters, bioretention, rain gardens) are engineered nature-based solutions, which help mitigate aquatic nitrogen pollution arising from storm runoff. These systems are being increasingly used in a range of climates across the world. A decline in treatment performance is frequently observed in cold weather conditions. While plant species comprise an important design factor influencing system performance, the effect of temperature on the fate of dissolved nitrogen forms, namely ammonium (NH4+) and nitrate (NO3−), in the presence of different plant species in these systems remains unclear. A large scale laboratory experiment was undertaken that measured potential rates of nitrification, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) as well as the microbial community structure to investigate nitrogen fate and hence removal under two different temperature conditions (2 °C and 15 °C) in the presence of four distinct plant species. The results indicate that lower nitrification rates (reduced by a factor of 4) coupled with potential media NH4+ desorption could be contributing to reduced NH4+ removal during cold conditions. Planting with species exhibiting good nutrient uptake capacity can reduce the extent of this performance decline. While NO3− reduction generally remains problematic during cold weather (<0 to 55% reduction), which may not be significantly different from warmer periods, the study demonstrated that the denitrification potential and gene abundance (nap, nar, NirS, norB, nosZ) to be higher than those of nitrification (amoA). Denitrification may not proceeding at optimal rates due to lack of conducive environmental conditions. Nitrogen transformation via DNRA was found to be relatively insignificant. Future studies should investigate the potential of employing cold-resilient plant species to maintain both NH4+ and NO3− removal in cold weather conditions.

The interactive effects of temperature and food consumption on growth of larval Arctic cod (Boreogadus saida)

Understanding larval growth, mediated by the interaction of early life traits and environmental conditions, is crucial to elucidate population dynamics. We used a bioenergetic model as an integrative tool to simulate the growth of Arctic cod (Boreogadus saida) larvae and to test the sensitivity of modeled growth to temperature and food quantity and quality. The growth was computed as the energy gained through food consumption minus the energy lost through respiration and other metabolic processes. We extended a previously published bioenergetic model to cover the full range of larval length and used a simplified feeding module. This simplification allowed us to build a predictive tool that can be applied to larval Arctic cod at a large spatial scale. Our model suggested that with subzero temperatures in the High Arctic, larvae need to increase food consumption in order to reach the observed length-at-age in late summer. The modeled growth agreed well with the field observations in the High Arctic but was 2–3 times higher than the laboratory-derived growth rate, probably due to differences in food type and selective mortality. Our study reveals important knowledge gaps in our understanding of larval cod growth in the High Arctic, including the lack of empirical estimations of daily ration and respiration for larvae under the natural habitat temperatures.

The interactive effects of temperature and nutrients on a spring phytoplankton community

AbstractA complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold‐adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6°C and chlorophyll &gt; 9 μg L−1. Water was incubated in triplicate at −0.5°C, 2.6°C, and 6°C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature–nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature–nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

APPLICATION OF BOX-WILSON CENTRAL COMPOSITE EXPERIMENTAL DESIGN TO OPTIMIZE THE PROTEOLYTIC ACTIVITY IN MILK BY LACTOCOCCUS LACTIS LCL STRAIN

In this work, the individual and interactive effects of temperature and pH on the proteolytic activity of Lactococcus lactis LCL strain in milk were studied by quadratic Response Surface Methodology. The effects of the selected variables have been analysed using a Central Composite Design and the maximum response (proteolysis rate) under the optimum values of variables and of a satisfactory fit model was realized. The mathematical relationship of the proteolytic activity on the two significant independent variables can be approximated by a nonlinear polynomial model. Predicted values were found to be in a good agreement with experimental values (R2 = 0.937) demonstrating the good significance of the model. The result of optimization predicted by the model has shown that the maximal result for the proteolysis rate revolved around of 43.7 ± 1.4 % at the optimal condition (30°C and pH 7).

Will Climate Change Enhance Algal Blooms? The Individual and Interactive Effects of Temperature and Rain on the Macroalgae Ulva

Will Climate Change Enhance Algal Blooms? The Individual and Interactive Effects of Temperature and Rain on the Macroalgae Ulva

The Combined Effects of Warming and Body Size on the Stability of Predator-Prey Interactions

Environmental temperature and body size are two prominent drivers of predation. Despite the ample evidence of their independent effects, the combined impact of temperature and predator-prey body size ratio on the strength and stability of trophic interactions is not fully understood. We experimentally tested how water temperature alters the functional response and population stability of dragonfly nymphs (Cordulegaster boltonii) feeding on freshwater amphipods (Gammarus pulex) across a gradient of their body size ratios. Attack coefficients were highest for small predators feeding on small prey at low temperatures, but shifted toward the largest predators feeding on larger prey in warmer environments. Handling time appeared to decrease with increasing predator and prey body size in the cold environment, but increase at higher temperatures. These findings indicate interactive effects of temperature and body size on functional responses. There was also a negative effect of warming on the stability of predator and prey populations, but this was counteracted by a larger predator-prey body size ratio at higher temperatures. Here, a greater Hill exponent reduced feeding at low prey densities when predators were much larger than their prey, enhancing the persistence of both predator and prey populations in the warmer environment. These experimental findings provide new mechanistic insights into the destabilizing effect of warming on trophic interactions and the key role of predator-prey body size ratios in mitigating these effects.

Interactive effects of temperature and salinity on the growth and cytotoxicity of the fish-killing microalgal species Heterosigma akashiwo and Pseudochattonella verruculosa

Fish-killing blooms of Heterosigma akashiwo and Pseudochattonella verruculosa have been devastating for the farmed salmon industry, but in Southern Chile the conditions that promote the growth and toxicity of these microalgae are poorly understood. This study examined the effects of different combinations of temperature (12, 15, 18 °C) and salinity (10, 20, 30 psu) on the growth of Chilean strains of these two species. The results showed that the optimal growth conditions for H. akashiwo and P. verruculosa differed, with a maximum rate of 0.99 day−1 obtained at 15 °C and a salinity of 20 psu for H. akashiwo, and a maximum rate of 1.06 day−1 obtained at 18 °C and a salinity of 30 psu for P. verruculosa. Cytotoxic assays (2 × 101 – 2 × 105 cell mL−1; cells, filtrates, and cell lysates) performed at salinities of 20 and 30 psu showed a 100% reduction in the viability of embryonic fish cells exposed to intact cells of H. akashiwo and a 39% reduction following exposure to culture filtrates of P. verruculosa. Differences in the fish-killing mechanisms (direct cell contact vs. extracellular substances) and physiological traits of H. akashiwo and P. verruculosa explain the recent occurrence of very large blooms under contrasting (cold-brackish vs. hot-salty) extreme climate conditions in Chile.