Posts Tagged 'oxygen'

Defense responses to short-term hypoxia and seawater acidification in the thick shell mussel Mytilus coruscus

The rising anthropogenic atmospheric CO2 results in the reduction of seawater pH, namely ocean acidification (OA). In East China Sea, the largest coastal hypoxic zone was observed in the world. This region is also strongly impacted by ocean acidification as receiving much nutrient from Changjiang and Qiantangjiang, and organisms can experience great short-term natural variability of DO and pH in this area. In order to evaluate the defense responses of marine mussels under this scenario, the thick shell mussel Mytilus coruscus were exposed to three pH/pCO2 levels (7.3/2800 μatm, 7.7/1020 μatm, 8.1/376 μatm) at two dissolved oxygen concentrations (DO, 2.0, 6.0 mg L−1) for 72 h. Results showed that byssus thread parameters, such as the number, diameter, attachment strength and plaque area were reduced by low DO, and shell-closing strength was significantly weaker under both hypoxia and low pH conditions. Expression patterns of genes related to mussel byssus protein (MBP) were affected by hypoxia. Generally, hypoxia reduced MBP1 and MBP7 expressions, but increased MBP13 expression. In conclusion, both hypoxia and low pH induced negative effects on mussel defense responses, with hypoxia being the main driver of change. In addition, significant interactive effects between pH and DO were observed on shell-closing strength. Therefore, the adverse effects induced by hypoxia on the defense of mussels may be aggravated by low pH in the natural environments.

Continue reading ‘Defense responses to short-term hypoxia and seawater acidification in the thick shell mussel Mytilus coruscus’

The adaptive potential of early life-stage Fucus vesiculosus under multifactorial environmental change

Multiple global and local stressors threaten populations of the bladderwrack Fucus vesiculosus (Phaeophyceae). Baltic F. vesiculosus populations presumably have a lower genetic diversity compared to other populations. I investigated the adaptive potential under multifactorial environmental change in F. vesiculosus germlings. Effects of warming and acidification were crossed during one year at the two levels “present” and “future” (according to the year 2110) at the “Kiel Outdoor Benthocosms” by applying delta-treatments. Effects of warming varied with season while acidification showed generally weak effects. The two factors “ocean acidification and warming” (OAW) and nutrients were crossed showing that nutrient enrichment mitigated heat stress. Germlings previously treated under the OAW x nutrient experiment were subsequently exposed to a simulated hypoxic upwelling. Sensitivity to hypoxia was enhanced by the previous OAW conditions. Difference in the performance of genetically different sibling groups and diversity level were observed indicating an increased adaptive potential at higher genetic diversity. Different sibling groups were analysed under multiple factors to test correlations of genotypic sensitivities. Sensitivity towards warming, acidification and nutrient enrichment correlated positively while sensitivities towards OAW and hypoxia showed a negative correlation demonstrating that genotypes previously selected under OAW are sensitive to hypoxic upwelling. In a literature review, responses of marine organisms to climate change were analysed through different levels of biological organisation showing that climate change has different effects on each single level of biological organisation. This study highlights that global change research requires an upscaling approach with regard to multiple factors, seasons, natural fluctuations, different developmental stages and levels of biological organisation in the light of the adaptive potential.

Continue reading ‘The adaptive potential of early life-stage Fucus vesiculosus under multifactorial environmental change’

Diurnal fluctuations in acidification and hypoxia reduce the growth and survival of larval and juvenile bay scallops (Argopecten irradians) and hard clams (Mercenaria mercenaria)

Diurnal variations in pH and dissolved oxygen (DO) concentrations are common seasonal phenomena in many eutrophic estuaries, yet few studies have investigated the concurrent effects of low pH and low DO on marine organisms inhabiting these coastal systems. Here, we assess the effects of diurnal variations in pH and DO on the early-life history of two bivalve species native to Northeast US estuaries, the bay scallop (Argopecten irradians) and hard clam (Mercenaria mercenaria). In one set of experiments, larval- and juvenile-life stage bivalves were exposed to ambient conditions (pHT ~ 7.9), two continuously-low pH levels (pHT ~ 7.3 and 7.6), and diurnal fluctuations between the ambient and low conditions yielding mean pH levels equal to the intermediate pH levels. In a second set of experiments, larval bivalves were exposed to ambient conditions (pHT ~7.9, DO ~ 7 mg L-1), two levels of low pH and DO (pHT ~ 7.2, DO ~1 mg L-1; pHT ~7.4, DO ~ 4 mg L-1) and diurnal fluctuations of both pH and DO between the ambient and low pH/DO levels that resulted in mean pH and DO levels equal to the intermediate pH and DO levels. Diurnal acidification treatments with ambient DO levels yielded survival rates for both species at both life stages that were consistent with the survival of individuals exposed to the same mean level of chronic pH with juveniles being more resistant to acidification than larvae. In contrast, when both pH and DO varied diurnally, the survival rates of larval bivalves were significantly lower than the survival of individuals chronically exposed to the same mean levels of pH and DO, an indication that bivalves were physiologically more vulnerable to concurrent fluctuations of both parameters compared to acidification alone. While both species displayed sensitivities to diurnal fluctuations in pH and DO, scallops were relatively more susceptible than hard clams. Since many shallow eutrophic estuaries presently experience diurnal cycles of both pH and DO when early-life stages of bivalves are present in estuaries, the populations of the bivalves studied are likely impacted by these conditions which are likely to intensify with climate change.

Continue reading ‘Diurnal fluctuations in acidification and hypoxia reduce the growth and survival of larval and juvenile bay scallops (Argopecten irradians) and hard clams (Mercenaria mercenaria)’

Development of embryonic market squid, Doryteuthis opalescens, under chronic exposure to low environmental pH and [O2]

The market squid, Doryteuthis opalescens, is an important forage species for the inshore ecosystems of the California Current System. Due to increased upwelling and expansion of the oxygen minimum zone in the California Current Ecosystem, the inshore environment is expected to experience lower pH and [O2] conditions in the future, potentially impacting the development of seafloor-attached encapsulated embryos. To understand the consequences of this co-occurring environmental pH and [O2] stress for D. opalescens encapsulated embryos, we performed two laboratory experiments. In Experiment 1, embryo capsules were chronically exposed to a treatment of higher (normal) pH (7.93) and [O2] (242 μM) or a treatment of low pH (7.57) and [O2] (80 μM), characteristic of upwelling events and/or La Niña conditions. The low pH and low [O2] treatment extended embryo development duration by 5–7 days; embryos remained at less developed stages more often and had 54.7% smaller statolith area at a given embryo size. Importantly, the embryos that did develop to mature embryonic stages grew to sizes that were similar (non-distinct) to those exposed to the high pH and high [O2] treatment. In Experiment 2, we exposed encapsulated embryos to a single stressor, low pH (7.56) or low [O2] (85 μM), to understand the importance of environmental pH and [O2] rising and falling together for squid embryogenesis. Embryos in the low pH only treatment had smaller yolk reserves and bigger statoliths compared to those in low [O2] only treatment. These results suggest that D. opalescens developmental duration and statolith size are impacted by exposure to environmental [O2] and pH (pCO2) and provide insight into embryo resilience to these effects.

Continue reading ‘Development of embryonic market squid, Doryteuthis opalescens, under chronic exposure to low environmental pH and [O2]’

Antioxidant response of the hard shelled mussel Mytilus coruscus exposed to reduced pH and oxygen concentration

Ocean acidification (OA) and hypoxic events are increasing worldwide problems, their interactive effects have not been well clarified, although their co-occurrence is prevalent. The East China Sea (the Yangtze River estuary area) suffers from not only coastal hypoxia but also pH fluctuation, representing an ideal study site to explore the combined effect of OA and hypoxia on marine bivalves. We experimentally evaluated the antioxidant response of the mussel Mytilus coruscus exposed to three pH levels (8.1, 7.7 and 7.3) at two dissolved oxygen (DO) levels (2.0mgL-1 and 6.0mgL-1) for 72h. Activities of superoxide dismutase, catalase, glutathione peroxidase, acid phosphatase, and alkaline phosphatase and levels of malondialdehyde were measured in gills and hemolymph. All enzymatic activities in hemolymph and gills followed a similar pattern throughout the experiment duration. Generally, low DO showed greater effects on enzyme activities than elevated CO2. Significant interactions between DO, pH and time were only observed at superoxide dismutase and catalase in both tissues. PCA revealed positive relationships between most enzyme activities in both gills and hemolymph with the exception of alkaline phosphatase activity and the level of malondialdehyde in the hemolymph. Overall, our results suggested that decreased pH and low DO induced similar antioxidant responses in the hard shelled mussel, and showed an additive effect on most enzyme activities. The evaluation of multiple environmental stressors, a more realistic scenario than single ones, is crucial to predict the effect of future global changes on coastal species and our results supply some insights on the potential combined effects of reduced pH and DO on marine bivalves.

Continue reading ‘Antioxidant response of the hard shelled mussel Mytilus coruscus exposed to reduced pH and oxygen concentration’

The metabolic response of thecosome pteropods from the North Atlantic and North Pacific oceans to high CO2 and low O2 (update)

As anthropogenic activities directly and indirectly increase carbon dioxide (CO2) and decrease oxygen (O2) concentrations in the ocean system, it becomes important to understand how different populations of marine animals will respond. Water that is naturally low in pH, with a high concentration of carbon dioxide (hypercapnia) and a low concentration of oxygen, occurs at shallow depths (200–500 m) in the North Pacific Ocean, whereas similar conditions are absent throughout the upper water column in the North Atlantic. This contrasting hydrography provides a natural experiment to explore whether differences in environment cause populations of cosmopolitan pelagic calcifiers, specifically the aragonitic-shelled pteropods, to have a different physiological response when exposed to hypercapnia and low O2. Using closed-chamber end-point respiration experiments, eight species of pteropods from the two ocean basins were exposed to high CO2 ( ∼  800 µatm) while six species were also exposed to moderately low O2 (48 % saturated, or  ∼  130 µmol kg−1) and a combined treatment of low O2/high CO2. None of the species tested showed a change in metabolic rate in response to high CO2 alone. Of those species tested for an effect of O2, only Limacina retroversa from the Atlantic showed a response to the combined treatment, resulting in a reduction in metabolic rate. Our results suggest that pteropods have mechanisms for coping with short-term CO2 exposure and that there can be interactive effects between stressors on the physiology of these open ocean organisms that correlate with natural exposure to low O2 and high CO2. These are considerations that should be taken into account in projections of organismal sensitivity to future ocean conditions.

Continue reading ‘The metabolic response of thecosome pteropods from the North Atlantic and North Pacific oceans to high CO2 and low O2 (update)’

Diurnal fluctuations in CO2 and dissolved oxygen concentrations do not provide a refuge from hypoxia and acidification for early-life-stage bivalves

This study assessed the effects of constant and diurnally fluctuating acidification and hypoxia on the survival, growth, and development of larval stages of 3 bivalves indigenous to the east coast of North America: bay scallops Argopecten irradians, hard clams Mercenaria mercenaria, and eastern oysters Crassostrea virginica. Bivalves were exposed to ideal (pH = ~7.9, dissolved oxygen [DO] = ~7 mg l-1), acidified (pH = ~7.2, DO = ~7 mg l-1), hypoxic (pH = ~7.9, DO = ~2 mg l-1), and acidified and hypoxic (pH = ~7.2, DO = ~2 mg l-1) conditions, as well as treatments that fluctuated between ideal conditions by day and acidified, hypoxic, or acidified and hypoxic conditions by night. Continuously acidified conditions reduced survival of larvae of all 3 species, slowed growth of larval bay scallops and eastern oysters, and delayed the development of bay scallop larvae. Continuously hypoxic conditions reduced the survival, growth, and development of larval bay scallops and slowed the development of larval hard clams. Simultaneous exposure to continuously low pH and DO yielded more negative effects than each factor independently. Diurnal exposure to low pH and/or low DO rarely altered, and never fully mitigated, the negative effects of hypoxia and/or acidification despite significantly higher mean pH and DO levels. This suggests that pH and DO fluctuations were too intense, and/or the durations of normoxic and normcapnic conditions were not long enough for bivalve larvae to overcome the physiological stress of hypoxia and acidification. Therefore, the diurnal fluctuations of pH and DO in this study did not provide a temporal refuge from hypoxia and acidification for North Atlantic bivalve larvae, suggesting that such fluctuations in an ecosystem setting can be a significant threat to these larvae.

Continue reading ‘Diurnal fluctuations in CO2 and dissolved oxygen concentrations do not provide a refuge from hypoxia and acidification for early-life-stage bivalves’


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Ocean acidification in the IPCC AR5 WG II

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