Posts Tagged 'oxygen'

Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming

Ocean chemistry is changing as a result of human activities. Atmospheric carbon dioxide (CO2) concentrations are increasing, causing an increase in oceanic pCO2 that drives a decrease in oceanic pH, a process called ocean acidification (OA). Higher CO2 concentrations are also linked to rising global temperatures that can result in more stratified surface waters, reducing the exchange between surface and deep waters; this stronger stratification, along with nutrient pollution, contributes to an expansion of oxygen-depleted zones (so called hypoxia or deoxygenation). Determining the response of marine organisms to environmental changes is important for assessments of future ecosystem functioning. While many studies have assessed the impact of individual or paired stressors, fewer studies have assessed the combined impact of pCO2, O2, and temperature. A long-term experiment (∼10 months) with different treatments of these three stressors was conducted to determine their sole or combined impact on the abundance and survival of a benthic foraminiferal community collected from a continental-shelf site. Foraminifera are well suited to such study because of their small size, relatively rapid growth, varied mineralogies and physiologies. Inoculation materials were collected from a ∼77-m deep site south of Woods Hole, MA. Very fine sediments (<53 μm) were used as inoculum, to allow the entire community to respond. Thirty-eight morphologically identified taxa grew during the experiment. Multivariate statistical analysis indicates that hypoxia was the major driving factor distinguishing the yields, while warming was secondary. Species responses were not consistent, with different species being most abundant in different treatments. Some taxa grew in all of the triple-stressor samples. Results from the experiment suggest that foraminiferal species’ responses will vary considerably, with some being negatively impacted by predicted environmental changes, while other taxa will tolerate, and perhaps even benefit, from deoxygenation, warming and OA.

Continue reading ‘Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming’

Ocean acidification but not hypoxia alters the gonad performance in the thick shell mussel Mytilus coruscus

Highlights

  • Ocean acidification adversely affects the gonadal performance of mussels.
  • Hypoxia does not have effects on fecundity of mussels.
  • Steroids and Wnt/β-catenin gene expressions have weak correlations with fecundity in mussels.

Abstract

Ocean acidification and hypoxia have become increasingly severe in coastal areas, and their co-occurrence poses emerging threats to coastal ecosystems. Here, we investigated the combined effects of ocean acidification and hypoxia on the reproductive capacity of the thick-shelled mussel Mytilus coruscus. Our results demonstrated low pH but not low oxygen induced decreased gonadosomatic index (GSI) in mussels. Male mussels had a lower level of sex steroids (estradiol, testosterone, and progesterone) when kept at low pH. Expression of genes related to reproduction were also impacted by low pH with a downregulation of genes involved in gonad development in males (β-catenin and Wnt-7b involved in males) and an upregulation of testosterone synthesis inhibition-related gene (Wnt-4) in females. Overall, our results suggest that ocean acidification has an impact on the gonadal development through an alternation of gene expression and level of steroids while hypoxia had no significant effect.

Continue reading ‘Ocean acidification but not hypoxia alters the gonad performance in the thick shell mussel Mytilus coruscus’

An integrated field-laboratory investigation of the effects of low oxygen and pH on North Pacific krill (Euphausia pacifica)

Krill are abundant and ecologically important zooplankton that inhabit dynamic environments characterized by strong natural variability, but global ocean change is shifting the range of conditions that they experience. Laboratory tests reveal that krill are sensitive to ocean acidification despite residing in naturally low pH areas, showing the importance of modulating factors for determining their responses. This study combines laboratory manipulations with field observations across a strong natural water chemistry gradient in Puget Sound, Washington, USA to investigate the effects of pH and oxygen on adult female North Pacific krill, Euphausia pacifica. Enzyme activities of the Electron Transport System (ETS) and aminoacyl-tRNA synthetases (AARS) were used as indices of zooplankton metabolism and growth, respectively, and were paired with traditional incubation methods. Acclimation to pH and oxygen conditions in the laboratory did not reveal effects on respiration rate, ETS, or AARS activity of krill. However, field observations showed that respiratory potential, as estimated by ETS activity, decreased with decreasing oxygen, declining 9% (95% confidence interval 2.5–15%) over the range of conditions we observed (3.9–8.1 mg O2 L−1). This reduction would depress the metabolic potential of krill in areas of stressful conditions (concurrent low pH), though krill also displayed a high degree of inter-individual variability. Although differences in age structure suggest different patterns of recruitment between E. pacifica populations in areas with stressful conditions and those without, populations persist at stressful sites. Lower temperature of waters with low oxygen and pH, as well as high food concentrations, may contribute to these populations’ success.

Continue reading ‘An integrated field-laboratory investigation of the effects of low oxygen and pH on North Pacific krill (Euphausia pacifica)’

Gene expression responses of larval gopher (Sebastes carnatus) and blue (S. mystinus) rockfish to ocean acidification and hypoxia

Global climate change is driving shifts in ocean chemistry, which combined with intensification of coastal upwelling, reduces ocean pH and dissolved oxygen (DO) content in the nearshore habitats of the California Current System. Physiological plasticity, within and across generations, might be especially important for long-lived, late-to-mature species, like rockfishes (genus Sebastes), that may be unable to keep pace with climate change via genetic adaptation. Rockfishes exhibit matrotrophic viviparity and may be able to buffer their offspring from environmental stress through early developmental exposure or transgenerational plasticity (non-genetic inheritance of phenotypes). In this study, mature female gopher (S. carnatus) and blue (S. mystinus) rockfish were pre-exposed to one of four treatments; 1) control conditions, 2) low pH, 3) low DO, or 4) combined low pH/DO stressors during embryonic growth (i.e. fertilization and gestation), followed by a 5-day larval exposure after birth in either the same or a different treatment received by mothers. I used RNA sequencing to determine how the maternal environment affected larval rockfish gene expression (GE) at birth, after the 5-day larval exposure in either the same maternal treatment or a novel pH/DO environment, and between larvae sampled at birth and after the 5-day larval exposure within each treatment. For both species, I found that the maternal exposure drove larval GE patterns regardless of sampling time point or treatment. Furthermore, the maternal environment continued to strongly influence larval GE for at least the first five days after birth. In gopher rockfish, larvae differentially expressed fewer genes at birth between the control and hypoxic groups than larvae that gestated in and remained in the same treatment and were sampled after the 5-day larval exposure. Gene functions also shifted; at day 5, there was an increase in differentially expressed genes that were related to metabolic pathways, implying that the larvae in the hypoxic treatment are responding to the stressor. In both species, I found that larvae which experienced a pH and/or hypoxic stressor during the maternal exposure had fewer differentially expressed genes across time compared to larvae that experienced control conditions. This pattern remained consistent, even if the larvae were placed into control conditions for the 5-day larval exposure, indicating that exposure to low pH/DO stressors might cause a delay in development. These data suggest that rockfish may not be able to buffer their offspring from environmental stressors, highlighting the important role of the maternal environment during gestation. Between the two species, however, blue rockfish may in fact fare better in future conditions as their reproductive season occurs before the onset of strong spring upwelling, when more hypoxic and low pH water intrudes the nearshore. However, if future climate models are correct, shifts in the timing and intensity of upwelling season may overlap with the reproductive season in blue rockfish. Elucidating the critical role of the maternal environment on offspring physiology can help us better understand how economically and ecologically important species will fare in the face of climate change.

Continue reading ‘Gene expression responses of larval gopher (Sebastes carnatus) and blue (S. mystinus) rockfish to ocean acidification and hypoxia’

Multi-stressor extremes found on a tropical coral reef impair performance

Global change has resulted in oceans that are warmer, more acidic, and lower in oxygen. Individually any one of these stressors can have numerous negative impacts on marine organisms, and in combination they are likely to be particularly detrimental. Understanding the interactions between these factors is important as they often covary, with warming promoting hypoxia, and hypoxia co-occurring with acidification. Few studies have examined how all three factors interact to affect organismal performance, and information is particularly sparse for tropical organisms. Here we documented a strong relationship between high temperatures, low dissolved oxygen (DO), and low pH in and around a tropical bay. We used these field values to inform two multi-stressor experiments. Each experimental factor had two levels, one representing current average conditions and the other representing current extreme conditions experienced in the area. We used sea urchin righting response as a measure of organismal performance for an important reef herbivore. In the first experiment 2-h exposures to a fully factorial combination of temperature, DO, and pH showed that righting success was significantly depressed under low oxygen. To more fully understand the impacts of pH, we acclimated sea urchins to control and low pH for 7 days and subsequently exposed them to the same experimental conditions. Sea urchins acclimated to control pH had significantly reduced righting success compared to animals acclimated to low pH, and righting success was significantly depressed under hypoxia and high temperature, compared to normoxia and ambient temperature. These results show that short, 2 h exposures to the temperature and DO extremes that are already experienced periodically by these animals have measurable detrimental effects on their performance. The positive impact of reduced pH is evident only over longer, 7 days durations, which are not currently experienced in this area.

Continue reading ‘Multi-stressor extremes found on a tropical coral reef impair performance’

Antioxidant responses of the mussel Mytilus coruscus co-exposed to ocean acidification, hypoxia and warming

Highlights

  • Low pH, low DO and high temperature have adverse effects on the antioxidant parameters.
  • Exposure time of stressors has significant effects on the antioxidant parameters.
  • Combined stressors exert more severe effects on the antioxidant indicators than single ones.

Abstract

In the present study, the combined effects of pH, dissolved oxygen (DO) and temperature levels on the antioxidant responses of the mussel Mytilus coruscus were evaluated. Mussels were exposed to two pH (8.1, 7.7-acidification), two DO (6 mg L−1, 2 mg L−1-hypoxia) and two temperature levels (20 °C, 30 °C-warming) for 30 days. SOD, CAT, MDA, GPx, GSH, GST, TAOC, AKP, ACP, GPT, AST levels were measured in the gills of mussels. All tested biochemical parameters were altered by these three environmental stressors. Values for all the test parameters except GSH first increased and then decreased at various experimental treatments during days 15 and 30 as a result of acidification, hypoxia and warming. GSH content always increased with decreased pH, decreased DO and increased temperature. PCA showed a positive correlation among all the measured biochemical indexes. IBR results showed that M. coruscus were adversely affected by reduced pH, low DO and elevated temperature.

Continue reading ‘Antioxidant responses of the mussel Mytilus coruscus co-exposed to ocean acidification, hypoxia and warming’

Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)

Highlights

  • Deoxygenation enhanced the survival of the creeping polyps of Alatina alata.

  • More creeping polyps settled under low pH and low dissolved O2 (DO) treatments than under normal pH and DO conditions.

  • Exposure to low pH and DO did not influence the number of tentacles, mobility or movement velocity of the creeping polyps.

  • The Irukandji jellyfish may persist in coastal areas with coastal deoxygenation and acidification.

Abstract

Deoxygenation and acidification co-occur in many coastal ecosystems because nutrient enrichment produces excess organic matter that intensifies aerobic respiration during decomposition, thereby depleting O2, increasing CO2 and lowering pH. Despite this link between coastal deoxygenation (CD) and acidification (CA), and evidence that both stressors pose a risk to marine fauna, few studies have examined the effects of these drivers in combination on marine animals including invertebrates. Here, we studied the individual and combined effects of CD (∼1.5 mg L−1 O2) and CA (∼7.7 pH) on the survival, number of tentacles, settlement and movement behaviours of creeping polyps of the Irukandji jellyfish, Alatina alata. Low DO increased the survival rate (17% more) of the creeping polyps. 12% more creeping polyps settled in low pH than ambient pH and 16.7% more settled in low DO than ambient DO treatment. Exposure to CA and CD did not influence the number of tentacles, mobility or movement velocity of the creeping polyps, but after 4 h exposure to the treatments, they moved approximately half as fast. Our results indicate that CD can enhance survival and settlement success, but CA does not intensify these outcomes on A. alata creeping polyps.

Continue reading ‘Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)’

Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)

The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 (pCO2) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m−2 · s−1, respectively, of visible light), low and high pCO2 (400 and 1,000 μatm, respectively), nutrient limitation (nitrate‐limited and nutrient‐replete conditions), and temperatures of 10–32°C. Under nutrient‐replete conditions, there was no adverse effect of high pCO2 on growth rates at temperatures of 10–25°C. The response of the cells to high pCO2 was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO2 depressed growth rates at both low and high irradiance. Under nitrate‐limited conditions, cells were grown at 38 ± 2.4% of their nutrient‐saturated rates at the same temperature, irradiance, and pCO2. Dark respiration rates consistently removed a higher percentage of production under nitrate‐limited versus nutrient‐replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate‐limited conditions, but there was no analogous correlation under nutrient‐replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO2 (lower pH).

Continue reading ‘Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)’

Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta

Acidification and deoxygenation are two consequences of climate change that also co-occur in eutrophied coastal zones and can have deleterious effects on marine life. While the effects of hypoxia on marine herbivores have been well-studied, how ocean acidification combined with hypoxia affects herbivory is poorly understood. This study examined how herbivory and survival by the gastropod Lacuna vincta grazing on the macroalgae Ulva rigida was influenced by hypoxia and ocean acidification, alone and in combination, with and without food limitation. Experiments exposed L. vincta to a range of environmentally realistic dissolved oxygen (0.7 – 8 mg L–1) and pH (7.3 – 8.0 total scale) conditions for 3 – 72 h, with and without a starvation period and quantified herbivory and survival. While acidified conditions (pH < 7.4) reduced herbivory when combined with food limitation, low oxygen conditions (< 4 mg L–1) reduced herbivory and survival regardless of food supply. When L. vincta were starved and grazed in acidified conditions herbivory was additively reduced, whereas starvation and hypoxia synergistically reduced grazing rates. Overall, low oxygen had a more inhibitory effect on herbivory than low pH. Shorter exposure times (9, 6, and 3 h) were required to reduce grazing at lower DO levels (∼2.4, ∼1.6, and ∼0.7 mg L–1, respectively). Herbivory ceased entirely following a three-hour exposure to DO of 0.7 mg L–1 suggesting that episodes of diurnal hypoxia disrupt grazing by these gastropods. The suppression of herbivory in response to acidified and hypoxic conditions could create a positive feedback loop that promotes ‘green tides’ whereby reduced grazing facilitates the overgrowth of macroalgae that cause nocturnal acidification and hypoxia, further disrupting herbivory and promoting the growth of macroalgae. Such feedback loops could have broad implications for estuarine ecosystems where L. vincta is a dominant macroalgal grazer and will intensify as climate change accelerates.

Continue reading ‘Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta’

Physiological resilience of pink salmon to naturally occurring ocean acidification

Pacific salmon stocks are in decline with climate change named as a contributing factor. The North Pacific coast of British Columbia is characterized by strong temporal and spatial heterogeneity in ocean conditions with upwelling events elevating CO2 levels up to 10-fold those of pre-industrial global averages. Early life stages of pink salmon have been shown to be affected by these CO2 levels, and juveniles naturally migrate through regions of high CO2 during the energetically costly phase of smoltification. To investigate the physiological response of out-migrating wild juvenile pink salmon to these naturally occurring elevated CO2 levels, we captured fish in Georgia Strait, British Columbia and transported them to a marine lab (Hakai Institute, Quadra Island) where fish were exposed to one of three CO2 levels (850, 1500 and 2000 μatm CO2) for 2 weeks. At ½, 1 and 2 weeks of exposure, we measured their weight and length to calculate condition factor (Fulton’s K), as well as haematocrit and plasma [Cl]. At each of these times, two additional stressors were imposed (hypoxia and temperature) to provide further insight into their physiological condition. Juvenile pink salmon were largely robust to elevated CO2 concentrations up to 2000 μatm CO2, with no mortality or change in condition factor over the 2-week exposure duration. After 1 week of exposure, temperature and hypoxia tolerance were significantly reduced in high CO2, an effect that did not persist to 2 weeks of exposure. Haematocrit was increased by 20% after 2 weeks in the CO2 treatments relative to the initial measurements, while plasma [Cl] was not significantly different. Taken together, these data indicate that juvenile pink salmon are quite resilient to naturally occurring high CO2 levels during their ocean outmigration.

Continue reading ‘Physiological resilience of pink salmon to naturally occurring ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

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