Posts Tagged 'oxygen'



Metabolic response and thermal tolerance of green abalone juveniles (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia

Highlights

  • Assessment of the impacts of hypoxia and hypercapnia on thermal tolerance
  • Hypoxia induced a downshift in critical temperature.
  • Hypercapnia did not affect thermal tolerance.
  • Both drivers combined prompted a stronger narrowing of thermal tolerance.
  • Warming stress induced protein degradation under all experimental conditions.


Abstract

With ongoing climate change, rising ocean temperature is usually accompanied by falling oxygen levels (hypoxia) and increasing CO2 concentration (hypercapnia). Both drivers may impose constraints on physiological mechanisms that define thermal limits resulting in increased vulnerability towards warming in marine ectotherms. The present study aimed to detect differences in thermal tolerance by investigating the underlying metabolic responses in the green abalone (Haliotis fulgens) under conditions of hypoxia and hypercapnia. Juvenile abalones were exposed to a temperature ramp (+ 3 °C day− 1) under hypoxia (50% air saturation) and hypercapnia (~ 1000 μatm pCO2), both individually and in combination. Impacts on energy metabolism were assessed by analyzing whole animal respiration rates and metabolic profiles of gills and hepatopancreas via 1H NMR spectroscopy. While hypercapnia had a minor impact on the results of the temperature treatment, hypoxia strongly increased the vulnerability to warming, indicated by respiration rates falling below values expected from an exponential increase and by the onset of anaerobic metabolism suggesting a downward shift of the upper critical temperature. Warming under combined hypoxia and hypercapnia elicited a severe change in metabolism involving a strong accumulation of amino acids, osmolytes and anaerobic end products at intermediate temperatures, followed by declining concentrations at warmer temperatures. This matched the limited capacity to increase metabolic rate, loss of attachment and mortality observed under these conditions suggesting a strong narrowing of the thermal window. In all cases, the accumulation of free amino acids identified proteins as a significant energy source during warming stress.

Continue reading ‘Metabolic response and thermal tolerance of green abalone juveniles (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia’

Potential transgenerational effects of ocean acidification and hypoxia on the Olympia oyster Ostrea iurida: a three-part experimental study

Ocean acidification (OA) is decreasing the pH of surface waters in Puget Sound, Washington, an area already prone to low pH from natural processes such as upwelling, freshwater inputs, and high respiration/decomposition rates. High rates of production and long residence times in Puget Sound can also lead to low dissolved oxygen (DO) levels (hypoxia) in some areas. Studies have shown the negative effects of these stressors on marine organisms, particularly calcifiers. I examined how changes in pH and oxygen in seawater affect adult fecundity and larval survival of the native Olympia oyster (Ostrea lurida). Through three discrete trials, I observed the following trends: Adult oysters conditioned at ~400 µatm released significantly more larvae than those conditioned at higher pCO2 levels ranging from 1000 to 2475 µatm pCO2. Larval survival decreased in two multi-stressor treatments when challenged with varying combinations of pCO2 and DO. Offspring of parents conditioned under high pCO2 experienced reduced survival when exposed to both high pCO2 and low DO (14.7% survival). In addition, progeny of adults conditioned under low pCO2 died when exposed to high pCO2 and high DO (22% survival). Our results suggest that elevated pCO2 negatively affects fecundity in O. lurida but that the synergistic effects of high CO2 and low DO on larval survival is more complicated than previously reported. Multigenerational, multi-stressor studies such as this are important in determining how species will respond to an environmental change in the ocean.

Continue reading ‘Potential transgenerational effects of ocean acidification and hypoxia on the Olympia oyster Ostrea iurida: a three-part experimental study’

Effects of diel-cycling hypoxia and acidification on juvenile weakfish Cynoscion regalis growth, survival, and activity

During summertime, dissolved oxygen (DO) and pH/pCO2 cycle daily in shallow estuarine waters used by young fishes as nursery habitat. Laboratory experiments on juvenile weakfish Cynoscion regalis examined individual and interactive impacts of present-day levels of diel-cycling hypoxia and acidification on growth and activity. Fish were exposed to 3 DO treatments (extreme cycling DO, 1-11 mg O2 l-1; moderate cycling DO, 3-9 mg O2 l-1; and constant normoxia, 7.5 mg O2 l-1) and 3 pH treatments (extreme cycling pH, 6.8-8.1; moderate cycling pH, 7.2-7.8; and constant pH, 7.5) for 20 d in a 3 × 3 factorial design. Growth was not impacted by moderate diel cycles of DO and acidification with mean daily lows of 3.0-3.3 mg O2 l-1 and mean daily highs of 7.8-9.5 mg O2 l-1 (mean daily low pH 7.03-7.47 and high pCO2 ~16000-5000 µatm). However, 100% mortality occurred within ~10 d at extreme diel-cycling hypoxia during which DO cycled between mean daily lows of 1.5-2.1 mg O2 l-1, mean daily low pH 6.99-7.44, and associated high pCO2 of ~16500-5500 µatm. We found no clear independent or interactive effect of pH/pCO2 on growth or survival despite pH being as low as 6.86 and pCO2 as high as ~20000 µatm. Furthermore, fish that survived as much as 10 d exposure to extreme and moderate diel cycles of DO and acidification experienced no residual negative impact on growth following return to normoxia and static pH. Our results suggest that juvenile weakfish have substantial tolerance of diel cycles of oxygenation and acidification encountered in shallow estuarine nursery habitat.

Continue reading ‘Effects of diel-cycling hypoxia and acidification on juvenile weakfish Cynoscion regalis growth, survival, and activity’

Effects of hypoxia and ocean acidification on the upper thermal niche boundaries of coral reef fishes

Rising ocean temperatures are predicted to cause a poleward shift in the distribution of marine fishes occupying the extent of latitudes tolerable within their thermal range boundaries. A prevailing theory suggests that the upper thermal limits of fishes are constrained by hypoxia and ocean acidification. However, some eurythermal fish species do not conform to this theory, and maintain their upper thermal limits in hypoxia. Here we determine if the same is true for stenothermal species. In three coral reef fish species we tested the effect of hypoxia on upper thermal limits, measured as critical thermal maximum (CTmax). In one of these species we also quantified the effect of hypoxia on oxygen supply capacity, measured as aerobic scope (AS). In this species we also tested the effect of elevated CO2 (simulated ocean acidification) on the hypoxia sensitivity of CTmax. We found that CTmax was unaffected by progressive hypoxia down to approximately 35 mmHg, despite a substantial hypoxia-induced reduction in AS. Below approximately 35 mmHg, CTmax declined sharply with water oxygen tension (PwO2). Furthermore, the hypoxia sensitivity of CTmax was unaffected by elevated CO2. Our findings show that moderate hypoxia and ocean acidification do not constrain the upper thermal limits of these tropical, stenothermal fishes.

Continue reading ‘Effects of hypoxia and ocean acidification on the upper thermal niche boundaries of coral reef fishes’

Combined impacts of ocean acidification and dysoxia on survival and growth of four agglutinating foraminifera

Agglutinated foraminifera create a shell by assembling particles from the sediment and comprise a significant part of the foraminiferal fauna. Despite their high abundance and diversity, their response to environmental perturbations and climate change is relatively poorly studied. Here we present results from a culture experiment with four different species of agglutinating foraminifera incubated in artificial substrate and exposed to different pCO2 conditions, in either dysoxic or oxic settings. We observed species-specific reactions (i.e., reduced or increased chamber formation rates) to dysoxia and/or acidification. While chamber addition and/or survival rates of Miliammina fusca and Trochammina inflata were negatively impacted by either dysoxia or acidification, respectively, Textularia tenuissima and Spiroplectammina biformis had the highest survivorship and chamber addition rates with combined high pCO2 (2000 ppm) and low O2 (0.7 ml/l) conditions. The differential response of these species indicates that not all agglutinating foraminifera are well-adapted to conditions induced by predicted climate change, which may result in a shift in foraminiferal community composition.

Continue reading ‘Combined impacts of ocean acidification and dysoxia on survival and growth of four agglutinating foraminifera’

Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean-based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) ($60 and 180 mm. kg SW) and temperature (9, 13, and 18 C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 C—upwelling) to average (13 C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 C) often associated with El Nino Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real-world consequences of changing ocean conditions.

Continue reading ‘Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)’

Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival

Diel fluctuations in dissolved oxygen (DO) and pH create hypoxic conditions that alter the quality of shallow estuarine nursery habitats for juvenile fishes. Understanding how different species in these environments mitigate stress associated with intermittent hypoxia through compensatory behaviors, such as aquatic surface respiration (ASR), is important in determining the effect of these stressors on estuarine ecosystems. Behavioral responses of Atlantic silversides (Menidia menidia), striped killifish (Fundulus majalis), mummichog (Fundulus heteroclitus), and juvenile striped bass (Morone saxatilis) were independently observed during exposure to two levels of diel-cycling DO (3–9 mg O2 l− 1 and 1–11 mg O2 l− 1) each tested with both the corresponding pH cycle (7.2–7.8 and 6.8–8.1, respectively) and static pH (7.5) under controlled laboratory conditions. In treatments in which DO declined to ~ 3 mg O2 l− 1, none of the species examined exhibited ASR behavior either with or without the associated pH decline. However, ASR was observed during both 4-hour and extended 16-hour exposure where DO declined to ~ 1.0–1.6 mg O2 l− 1 in M. menidia and both Fundulus species. M. saxatilis did not exhibit ASR and no mortalities occurred during 4-hour low DO/pH treatments or during 16 hour exposure to 1.5 mg O2 l− 1. During extended 16-hour treatments, DO thresholds for ASR were not found to be different between F. majalis and F. heteroclitus, but both differed significantly from M. menidia. Across both 4-hour and 16-hour treatments, the onset of ASR was observed in M. menidia at or near lethal levels (1.31–1.62 mg O2 l− 1). No evidence of a pH (pCO2) effect on ASR or survival was found in any species in response to naturally co-varying DO and pH swings, despite pH as low as 6.8 and high pCO2 levels of >~12,000 μatm. These results suggest that utilization of ASR is a species-specific response influenced by the magnitude and duration of hypoxic exposure. ASR may serve as a last-ditch strategy by M. menidia to prolong survival for minutes to hours, but function as a means for F. heteroclitus to mitigate or reduce negative effects of hypoxia on a scale of days to weeks, with F. majalis exhibiting an intermediate response.

Continue reading ‘Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival’


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Ocean acidification in the IPCC AR5 WG II

OUP book