Posts Tagged 'oxygen'

Ocean acidification and hypoxia alter organic carbon fluxes in marine soft sediments

Anthropogenic stressors can alter the structure and functioning of infaunal communities, which are key drivers of the carbon cycle in marine soft sediments. Nonetheless, the compounded effects of anthropogenic stressors on carbon fluxes in soft benthic systems remain largely unknown. Here, we investigated the cumulative effects of ocean acidification (OA) and hypoxia on the organic carbon fate in marine sediments, through a mesocosm experiment. Isotopically labelled macroalgal detritus (13C) was used as a tracer to assess carbon incorporation in faunal tissue and in sediments under different experimental conditions. In addition, labelled macroalgae (13C), previously exposed to elevated CO2, were also used to assess the organic carbon uptake by fauna and sediments, when both sources and consumers were exposed to elevated CO2. At elevated CO2, infauna increased the uptake of carbon, likely as compensatory response to the higher energetic costs faced under adverse environmental conditions. By contrast, there was no increase in carbon uptake by fauna exposed to both stressors in combination, indicating that even a short‐term hypoxic event may weaken the ability of marine invertebrates to withstand elevated CO2 conditions. In addition, both hypoxia and elevated CO2 increased organic carbon burial in the sediment, potentially affecting sediment biogeochemical processes. Since hypoxia and OA are predicted to increase in the face of climate change, our results suggest that local reduction of hypoxic events may mitigate the impacts of global climate change on marine soft‐sediment systems.

Continue reading ‘Ocean acidification and hypoxia alter organic carbon fluxes in marine soft sediments’

Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)

Highlights

  • Marine fishes will be exposed to multiple stressors under climate change.
  • Hypoxia and high pCO2 are both expected to cause shifts in energy metabolism.
  • No signs of energetic shifts were observed at transcriptomic or enzymatic levels.
  • Multiple stressor transcriptomes are not predictable based on responses to single stressors.
  • Blue rockfish may be relatively tolerant to intensified upwelling conditions.

Abstract

Global climate change is predicted to increase the co-occurrence of high pCO2 and hypoxia in upwelling zones worldwide. Yet, few studies have examined the effects of these stressors on economically and ecologically important fishes. Here, we investigated short-term responses of juvenile blue rockfish (Sebastes mystinus) to independent and combined high pCO2 and hypoxia at the molecular level, using changes in gene expression and metabolic enzymatic activity to investigate potential shifts in energy metabolism. Fish were experimentally exposed to conditions associated with intensified upwelling under climate change: high pCO2 (1200 μatm, pH~7.6), hypoxia (4.0 mg O2/L), and a combined high pCO2/hypoxia treatment for 12 h, 24 h or two weeks. Muscle transcriptome profiles varied significantly among the three treatments, with limited overlap among genes responsive to both the single and combined stressors. Under elevated pCO2, blue rockfish increased expression of genes encoding proteins involved in the electron transport chain and muscle contraction. Under hypoxia, blue rockfish up-regulated genes involved in oxygen and ion transport and down-regulated transcriptional machinery. Under combined high pCO2 and hypoxia, blue rockfish induced a unique set of ionoregulatory and hypoxia-responsive genes not expressed under the single stressors. Thus, high pCO2 and hypoxia exposure appears to induce a non-additive transcriptomic response that cannot be predicted from single stressor exposures alone, further highlighting the need for multiple stressor studies at the molecular level. Overall, lack of a major shift in cellular energetics indicates that blue rockfish may be relatively resistant to intensified upwelling conditions in the short term.

Continue reading ‘Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)’

Hypoxia aggravates the effects of ocean acidification on the physiological energetics of the blue mussel Mytilus edulis

Highlights

• Combined effects of ocean acidification and hypoxia are investigated in mussels.

• Physiological activities of mussels are inhibited by low pH and hypoxia.

• OA and hypoxia exert additive effects on the physiological metabolism of mussels.

Abstract

Apart from ocean acidification, hypoxia is another stressor to marine organisms, especially those in coastal waters. Their interactive effects of elevated CO2 and hypoxia on the physiological energetics in mussel Mytilus edulis were evaluated. Mussels were exposed to three pH levels (8.1, 7.7, 7.3) at two dissolved oxygen levels (6 and 2 mg L−1) and clearance rate, absorption efficiency, respiration rate, excretion rate, scope for growth and O: N ratio were measured during a14-day exposure. After exposure, all parameters (except excretion rate) were significantly reduced under low pH and hypoxic conditions, whereas excretion rate was significantly increased. Additive effects of low pH and hypoxia were evident for all parameters and low pH appeared to elicit a stronger effect than hypoxia (2.0 mg L−1). Overall, hypoxia can aggravate the effects of acidification on the physiological energetics of mussels, and their populations may be diminished by these stressors.

Continue reading ‘Hypoxia aggravates the effects of ocean acidification on the physiological energetics of the blue mussel Mytilus edulis’

Growth of the estuarine fish Fundulus heteroclitus in response to diel-cycling hypoxia and acidification: interaction with temperature

Growth rate of Fundulus heteroclitus was examined at 25 and 30 °C in nine treatments of diel-cycling dissolved oxygen (DO) and pH. Extreme diel-cycling DO (1–11 mg O2·L−1) negatively impacted growth during 10 days at 30 °C, but not at 25 °C. Moderate DO cycles (3–9 mg O2·L−1) had no direct growth impact at either temperature. Fish did not appear to acclimate, during days 10–30, to the initial growth-limiting effects of extreme diel DO cycles at 30 °C. Diel-cycling DO interacts synergistically with temperature to impact growth. There was no evidence of an independent growth effect of either moderate pH cycles (7.2–7.8) or extreme pH cycles (6.8–8.1) at either temperature. Mean low pCO2 levels in extreme cycles were ∼32 000 and ∼47 000 μatm at 25 and 30 °C, respectively. It is noteworthy that these high mean nightly pCO2 levels are more than an order of magnitude higher than the chronic mean oceanic pCO2 of ∼1000 μatm projected by the year 2100.

Continue reading ‘Growth of the estuarine fish Fundulus heteroclitus in response to diel-cycling hypoxia and acidification: interaction with temperature’

Uncovering mechanisms of global ocean change effects on the Dungeness crab (Cancer magister) through metabolomics analysis

The Dungeness crab is an economically and ecologically important species distributed along the North American Pacific coast. To predict how Dungeness crab may physiologically respond to future global ocean change on a molecular level, we performed untargeted metabolomic approaches on individual Dungeness crab juveniles reared in treatments that mimicked current and projected future pH and dissolved oxygen conditions. We found 94 metabolites and 127 lipids responded in a condition-specific manner, with a greater number of known compounds more strongly responding to low oxygen than low pH exposure. Pathway analysis of these compounds revealed that juveniles may respond to low oxygen through evolutionarily conserved processes including downregulating glutathione biosynthesis and upregulating glycogen storage, and may respond to low pH by increasing ATP production. Most interestingly, we found that the response of juveniles to combined low pH and low oxygen exposure was most similar to the low oxygen exposure response, indicating low oxygen may drive the physiology of juvenile crabs more than pH. Our study elucidates metabolic dynamics that expand our overall understanding of how the species might respond to future ocean conditions and provides a comprehensive dataset that could be used in future ocean acidification response studies.

Continue reading ‘Uncovering mechanisms of global ocean change effects on the Dungeness crab (Cancer magister) through metabolomics analysis’

De novo transcriptome assembly and gene expression profile of thermally challenged green abalone (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia

Highlights

• Abalone gene expression under warming, hypoxia, and hypercapnia, individually and combined.

• The response reflects enhanced damage control at the expense of energy metabolism.

• Gene networks of gill and muscle conform with different levels of thermal sensitivity.

• Warming combined with hypercapnia and hypoxia enhanced mitochondrial capacity.

Abstract

Transcriptional regulation constitutes a rapid response of marine organisms facing stressful environmental conditions, such as the concomitant exposure to warming, ocean acidification and hypoxia under climate change. In previous studies, we investigated whole-organism physiological patterns and cellular metabolism in gill and muscle of the marine gastropod Haliotis fulgens in response to increasing temperature (18 °C to 32 °C at +3 °C per day) under hypoxia (50% air saturation), hypercapnia (1000 μatm pCO2) and both factors combined. Here, we report investigations of the molecular responses of H. fulgens to temperature and identify mechanisms concomitantly affected by hypoxia and hypercapnia. A de novo transcriptome assembly with subsequent quantitative PCR and correlation network analysis of genes involved in the molecular response were used to unravel the correlations between gene expression patterns under the different experimental conditions. The correlation networks identified a shift from the expression of genes involved in energy metabolism (down-regulated) to the up-regulation of Hsp70 during warming under all experimental conditions in gill and muscle, indicating a strong up-regulation of damage prevention and repair systems at sustained cellular energy production. However, a higher capacity for anaerobic succinate production was evicted in gill, matching with observations from our previous studies indicating succinate accumulation in gill but not in muscle. Additionally, warming under hypoxia and hypercapnia kept mRNA levels of citrate synthase in both tissues unchanged following a similar pattern as muscle enzyme capacity from a previous study, suggesting an emphasis on maintaining rather than down-regulating mitochondrial activity.

Continue reading ‘De novo transcriptome assembly and gene expression profile of thermally challenged green abalone (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia’

An experimental evaluation of the sensitivity of coastal marine fishes to acidification, hypoxia, and warming

Ocean acidification (OA) during the coming century will impact marine ecosystems in profound ways. Laboratory studies have played a pioneering role in identifying biological vulnerabilities and have documented deleterious effects in taxonomically diverse fauna. The early life-stages of marine fish may be particularly sensitive to OA, thereby constituting a global threat to some of the world’s most important marine resources. Despite the rapid accumulation of experimental evidence, considerable uncertainty remains in estimating the scope of OA impacts. To date, most studies have relied on relatively short-term exposures to estimate effects of elevated pCO, while few have considered longer term OA effect across multiple life-stages. Additionally, while single-factor CO2 experiments are a necessary first step in identifying OA sensitivities, there is a growing understanding that OA will proceed concurrently with warming and deoxygenation, yet multi-stressor factorial experiments remain rare. Furthermore, meta-analyses of existing research have highlighted the large, and thus far unexplained variability in OA responses among taxa and populations. One promising mechanism which could explain this variability involves the role of local adaptation to existing pCO2fluctuations that characterizes marine habitats to different degrees. This framework remains untested in fish. The primary goal of this dissertation was to apply state-of-the-art experimental techniques to address the aforementioned knowledge gaps. By using two ecological important forage species, the Atlantic silverside (Menidia menidia) and Northern sand lance (Ammodytes dubius) with contrasting life-history characteristics, this dissertation provides novel insights into potential near-future climate impacts on fish. Chapter 1 summarizes a long-term OA experiment on M. menidia finding that elevated pCO2 exposure resulted in small but significant reductions in offspring size and condition factor. Chapter 2 tested CO2 × temperature effects in M. menidia offspring and found complex growth and survival responses. Chapter 3 reports on CO2 × temperature trials on offspring of A. dubius and documented precipitous reductions to survival and growth. Chapter 4 describes two CO2 × dissolved oxygen trials on M. menidia offspring that demonstrated a negative synergistic effect on embryonic survival. Together, this dissertation provides much needed baseline data and novel insights into climate effects in forage fish.

Continue reading ‘An experimental evaluation of the sensitivity of coastal marine fishes to acidification, hypoxia, and warming’


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Ocean acidification in the IPCC AR5 WG II

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