Posts Tagged 'oxygen'

Interactive effects of ocean acidification with other environmental drivers on marine plankton

Planktonic organisms form the base of the marine food web and may be impacted by environmental change in many ways. The interactive effects of multiple, simultaneous climate-driven changes on these organisms are not well understood. This dissertation examined the impacts of ocean acidification in combination with other environmental stressors on marine plankton and determined spatial patterns of one of these potential interactive drivers. Chapter 2 investigated the synergistic effects of ocean acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae. Findings indicated that empirical studies may be crucial to accurately predict organismal responses to multi-stressors. Results also suggested that photorespiration may serve a previously unrecognized role in dinoflagellate metabolism. Chapter 3 examined the combined effects of ocean acidification and lithogenic trace metals on the growth of another harmful dinoflagellate, Cochlodinium polykrikoides. Results indicated that high suspended sediment loads may deliver toxic concentrations of trace elements to marine phytoplankton in acidified coastal ecosystems. Chapter 4 examined the interactive effects of ocean acidification and bacteria on the severity and extent of dissolution in the shells of larval gastropods and the adult pteropod Limacina helicina. Research findings indicated that microbial communities on the shell surfaces of some planktonic molluscs may mediate certain types of shell dissolution in acidified, upwelled waters. Chapter 5 explored the use of thorium isotope fluxes as a proxy for dust and lithogenic iron in the Indian Ocean. Results suggested that the gradient of dust fluxes in the region could impose thresholds for biological productivity. Together, these interdisciplinary studies demonstrate coupled biological and chemical changes in marine ecosystems as a result of increased anthropogenic environmental change.

Continue reading ‘Interactive effects of ocean acidification with other environmental drivers on marine plankton’

Functional spatial contextualisation of the effects of multiple stressors in marine bivalves

Many recent studies have revealed that the majority of environmental stressors experienced by marine organisms (ocean acidification, global warming, hypoxia etc.) occur at the same time and place, and that their interaction may complexly affect a number of ecological processes. Here, we experimentally investigated the effects of pH and hypoxia on the functional and behavioural traits of the mussel Mytilus galloprovincialis, we then simulated the potential effects on growth and reproduction dynamics trough a Dynamic Energy Budget (DEB) model under a multiple stressor scenario. Our simulations showed that hypercapnia had a remarkable effect by reducing the maximal habitat size and reproductive output differentially as a function of the trophic conditions, where modelling was spatially contextualized. This study showed the major threat represented by the hypercapnia and hypoxia phenomena for the growth, reproduction and fitness of mussels under the current climate change context, and that a mechanistic approach based on DEB modelling can illustrate complex and site-specific effects of environmental change, producing that kind of information useful for management purposes, at larger temporal and spatial scales.

Continue reading ‘Functional spatial contextualisation of the effects of multiple stressors in marine bivalves’

Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments

Eutrophication-induced hypoxia is one of the primary anthropogenic threats to coastal ecosystems. Under hypoxic conditions, a deficit of O2 and a surplus of CO2 will concurrently decrease pH, yet studies of hypoxia have seldom considered the potential interactions with elevated pCO2 (reduced pH). Previous studies on gelatinous organisms concluded that they are fairly robust to low oxygen and reduced pH conditions individually, yet the combination of stressors has only been examined for ephyrae. The goals of this study were to determine the individual and interactive effects of hypoxia and elevated pCO2 on the asexual reproduction and aerobic respiration rates of polyps of the scyphozoan Aurelia aurita during a manipulative experiment that ran for 36 d. pCO2 and pO2 were varied on a diel basis to closely mimic the diel conditions observed in the field. Exposure to low dissolved oxygen (DO) reduced asexual budding of polyps by ~50% relative to control conditions. Under hypoxic conditions, rates of respiration were elevated during an initial acclimation period (until Day 8), but respiration rates did not differ between DO levels under prolonged exposure. There was no significant effect of increased pCO2 on either asexual reproduction or aerobic respiration, suggesting that elevated pCO2 (reduced pH) did not exacerbate the negative reproductive effects of hypoxia on A. aurita polyps.

Continue reading ‘Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments’

Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios

Coastal hypoxia is a problem that is predicted to increase rapidly in the future. At the same time we are facing rising atmospheric CO2 concentrations, which are increasing the pCO2 and acidity of coastal waters. These two drivers are well studied in isolation however; the coupling of low O2 and pH is likely to provide a more significant respiratory challenge for slow moving and sessile invertebrates than is currently predicted. The Gullmar Fjord in Sweden is home to a range of habitats such as sand and mud flats, seagrass beds, exposed and protected shorelines, and rocky bottoms. Moreover, it has a history of both natural and anthropogenically enhanced hypoxia as well as North Sea upwelling, where salty water reaches the surface towards the end of summer and early autumn. A total of 11 species (Crustacean, Chordate, Echinoderm and Mollusc) of these ecosystems were exposed to four different treatments (high/low oxygen and low/high CO2; varying pCO2 of 450 and 1300 ppm and O2 concentrations of 2–3.5 and 9–10 mg L−1) and respiration measured after 3 and 6 days, respectively. This allows us to evaluate respiration responses of species of contrasting habitats and life-history strategies to single and multiple stressors. Results show that the responses of the respiration were highly species specific as we observed both synergetic as well as antagonistic responses, and neither phylum nor habitat explained trends in respiratory responses. Management plans should avoid the generalized assumption that combined stressors will results in multiplicative effects and focus attention on alleviating hypoxia in the region.
Continue reading ‘Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios’

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’


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Ocean acidification in the IPCC AR5 WG II

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