Posts Tagged 'oxygen'

Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia

The severity of carbonate chemistry changes from ocean acidification is predicted to increase greatly in the coming decades, with serious consequences for marine species-­ especially those reliant on calcium carbonate for structure and function (Fabry et al. 2008). The Northern California Current Ecosystem off the coast of US West Coast experiences seasonal variations in upwelling and downwelling patterns creating natural episodes of hypoxia and calcite/aragonite undersaturation, exacerbating global trends of increasing ocean acidification and hypoxia (OAH) (Chan et al. 2008) (Gruber et al. 2012). The goal of these experiments was to identify thresholds of tolerance and attempt to quantify a point at which variance in responses to stress collapses. This study focuses on two species: Cancer magister (Dungeness crab) and Haliotis rufescens (red abalone). These species were selected for this study based on their economic and ecological value, as well as their taxonomic differences. Respirometry was used as a proxy for metabolic activity at four different scenarios mimicking preindustrial, upwelling, contemporary upwelling, and distant future conditions by manipulating dissolved oxygen and inorganic carbon (DIC) concentrations. Both species showed a decrease in mean respiration rate as OAH stressors increase, including an effect in contemporary upwelling conditions. These results suggest that current exposure to ocean acidification (OA) and hypoxia do not confer resilience to these stressors for either taxa. In teasing apart the effects of OAH as multiple stressors, it was found that Dungeness crab response was more strongly driven by concentration of dissolved oxygen, while red abalone data suggested a strong interactive effect between OA and hypoxia. Not only did these two different taxa exhibit different responses to a multiple stressors, but the fact that the Dungeness crab were secondarily impacted by acidification could suggest that current management concerns may need to be focus more strongly on deoxygenation.

Continue reading ‘Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia’

Predator avoidance in the European Seabass after recovery from short-term hypoxia and different CO2 conditions

Short-term hypoxia that lasts just a few days or even hours is a major threat for the marine ecosystems. The single effect of the human-induced levels of hypoxia and other anthropogenic impacts such as elevated pCO2 can reduce the ability of preys to detect their predators across taxa. Moreover, both processes, hypoxia and elevated pCO2, are expected to co-occur in certain habitats, but the synergic consequences of both processes and the ability of fish to recover remain unknown. To provide empirical evidence to this synergy, we experimentally evaluated the risk-taking behavior in juveniles of the European seabass (Dicentrachus labrax), an important commercial fisheries species after recovering from short-term hypoxia and different pH scenarios. The behavior of seabass juveniles was monitored in an experimental arena before and after the exposure to a simulated predator and contrasted to control fish (BACI design) (current levels of hypoxia and elevated pCO2) using a mechanistic function-valued modeling trait approach. Results revealed that fish recovering from elevated pCO2, alone or combined with hypoxia, presented less avoidance behavior in failing to seek refuge when a simulated predator was present in the arena compared to those exposed to control pCO2 levels. Our results show that recovery from short-term exposure to acidification and hypoxia was not synergistic and suggest that recovery from acidification takes longer than from short-term hypoxia treatment through a potential effect on the sensorial and hence behavioral capacities of fish.

Continue reading ‘Predator avoidance in the European Seabass after recovery from short-term hypoxia and different CO2 conditions’

Interactive effects of acidification, hypoxia, and thermal stress on growth, respiration, and survival of four North Atlantic bivalves

We investigated the individual and interactive effects of coastal and climate change stressors (elevated temperatures, acidification, and hypoxia) on the growth, survival, and respiration rates of 4 commercially and ecologically important North Atlantic bivalves: bay scallops Argopecten irradians, Eastern oysters Crassostrea virginica, blue mussels Mytilus edulis, and hard clams Mercenaria mercenaria. Month-long experiments were performed on multiple cohorts of post-set juveniles using conditions commonly found during summer months within eutrophied, shallow, temperate, coastal environments (24-31°C; 2-7 mg O2 l-1; pHT, total scale, 7.2-8.0). Elevated temperatures most consistently altered the performance of the bivalves, with both positive and negative physiological consequences. Low levels of dissolved oxygen (DO) and pH individually reduced the survival, shell growth, and/or tissue weight of each bivalve, with A. irradians being the most vulnerable species. Low DO also significantly increased respiration rates of A. irradians and M. mercenaria, evidencing a compensatory physiological response to hypoxia. M. edulis and M. mercenaria both displayed size-dependent vulnerability to acidification, with smaller individuals being more susceptible. The combination of low DO and low pH often interacted antagonistically to yield growth rates higher than would be predicted from either individual stressor, potentially suggesting that some anaerobic metabolic pathways may function optimally under hypercapnia. Elevated temperature and low pH interacted both antagonistically and synergistically, producing outcomes that could not be predicted from the responses to individual stressors. Collectively, this study revealed species- and size-specific vulnerabilities of bivalves to coastal stressors along with unpredicted interactions among those stressors.

Continue reading ‘Interactive effects of acidification, hypoxia, and thermal stress on growth, respiration, and survival of four North Atlantic bivalves’

A strain gauge monitor (SGM) for continuous valve gape measurements in bivalve molluscs in response to laboratory induced diel-cycling hypoxia and pH

An inexpensive, laboratory-based, strain gauge valve gape monitor (SGM) was developed to monitor the valve gape behavior of bivalve molluscs in response to diel-cycling hypoxia. A Wheatstone bridge was connected to strain gauges that were attached to the shells of oysters (Crassostrea virginica). The recorded signals allowed for the opening and closing of the bivalves to be recorded continuously over two-day periods of experimentally-induced diel-cycling hypoxia and diel-cycling changes in pH. Here, we describe a protocol for developing an inexpensive strain gauge monitor and describe, in an example laboratory experiment, how we used it to measure the valve gape behavior of Eastern oysters (C. virginica), in response to diel-cycling hypoxia and cyclical changes in pH. Valve gape was measured on oysters subjected to cyclical severe hypoxic (0.6 mg/L) dissolved oxygen conditions with and without cyclical changes in pH, cyclical mild hypoxic (1.7 mg/L) conditions and normoxic (7.3 mg/L) conditions. We demonstrate that when oysters encounter repeated diel cycles, they rapidly close their shells in response to severe hypoxia and close with a time lag to mild hypoxia. When normoxia is restored, they rapidly open again. Oysters did not respond to cyclical pH conditions superimposed on diel cycling severe hypoxia. At reduced oxygen conditions, more than one third of the oysters closed simultaneously. We demonstrate that oysters respond to diel-cycling hypoxia, which must be considered when assessing the behavior of bivalves to dissolved oxygen. The valve SGM can be used to assess responses of bivalve molluscs to changes in dissolved oxygen or contaminants. Sealing techniques to better seal the valve gape strain gauges from sea water need further improvement to increase the longevity of the sensors.

Continue reading ‘A strain gauge monitor (SGM) for continuous valve gape measurements in bivalve molluscs in response to laboratory induced diel-cycling hypoxia and pH’

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

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 or low oxygen and low or high CO2; varying pCO2 of 450 and 1300 µatm and O2 concentrations of 2–3.5 and 9–10 mg L−1) and respiration measured after 3 and 6 days, respectively. This allowed us to evaluate respiration responses of species of contrasting habitats to single and multiple stressors. Results show that respiratory responses 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 result 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 (update)’

Juvenile rockfish show resilience to CO2-acidification and hypoxia across multiple biological scales

California’s coastal ecosystems are forecasted to undergo shifting ocean conditions due to climate change, some of which may negatively impact recreational and commercial fish populations. To understand if fish populations have the capacity to respond to multiple stressors, it is critical to examine interactive effects across multiple biological scales, from cellular metabolism to species interactions. This study examined the effects of CO2-acidification and hypoxia on two naturally co-occurring species, juvenile rockfish (genus Sebastes) and a known predator, cabezon (Scorpaenichthys marmoratus). Fishes were exposed to two PCO2 levels at two dissolved oxygen (DO) levels: ~600 (ambient) and ~1600 (high) μatm PCO2 and 8.0 (normoxic) and 4.5 mg l−1 DO (hypoxic) and assessments of cellular metabolism, prey behavior and predation mortality rates were quantified after 1 and 3 weeks. Physiologically, rockfish showed acute alterations in cellular metabolic enzyme activity after 1 week of acclimation to elevated PCO2 and hypoxia that were not evident in cabezon. Alterations in rockfish energy metabolism were driven by increases in anaerobic LDH activity, and adjustments in enzyme activity ratios of cytochrome c oxidase and citrate synthase and LDH:CS. Correlated changes in rockfish behavior were also apparent after 1 week of acclimation to elevated PCO2 and hypoxia. Exploration behavior increased in rockfish exposed to elevated PCO2 and spatial analysis of activity indicated short-term interference with anti-predator responses. Predation rate after 1 week increased with elevated PCO2; however, no mortality was observed under the multiple-stressor treatment suggesting negative effects on cabezon predators. Most noteworthy, metabolic and behavioral changes were moderately compensated after 3 weeks of acclimation, and predation mortality rates also decreased suggesting that these rockfish may be resilient to changes in environmental stressors predicted by climate models. Linking physiological and behavioral responses to multiple stressors is vital to understand impacts on populations and community dynamics.

Continue reading ‘Juvenile rockfish show resilience to CO2-acidification and hypoxia across multiple biological scales’

The effects of ocean acidification and reduced oxygen on the behavior and physiology of juvenile rockfish

As climate change progresses, the frequency and duration of upwelling events that bring low pH, low dissolved oxygen (DO) water to nearshore habitats are expected to increase. In addition, long-term global changes in ocean pH and DO are expected to occur within the next few decades to centuries. Locally, there have been documented reductions in near-shore pH along with the expansion of oxygen minimum zones within the California Current System. However, very few studies have investigated the potential interactive effect of these stressors on temperate reef fish. For this thesis, two sets of laboratory experiments were conducted to determine the independent and interactive effects of reduced pH and DO on the behavior and physiology of juvenile rockfish (Sebastes caurinus and Sebastes melanops). Behavioral studies examined fish boldness using an escape trial and brain lateralization by testing the consistency of individual fishes’ turning preference. Physiological studies measured critical swimming speed (Ucrit), ventilation rate, standard metabolic rate (SMR), maximum metabolic rate (MMR), critical oxygen tension (Pcrit), aerobic scope, and growth rate. Over the range of conditions examined, DO proved to have a much stronger effect on rockfish physiology than pH, suggesting that low-oxygen events may be more detrimental to individual fitness than ocean acidification. Significant effects of reduced DO on rockfish physiology include impaired swimming performance in S. caurinus and increased ventilation rate in S. melanops, but substantive responses in metabolic rates (e.g. SMR, MMR, aerobic scope, Pcrit) were not observed. Juveniles of both species appear to be behaviorally resilient to exposure to reduced pH and DO. Together, these experiments address important questions regarding how temperate reef fish will respond to both the independent and interactive effect of these oceanographic stressors. Finally, they set the framework for studying species-specific susceptibility to pH and DO stressors.

Continue reading ‘The effects of ocean acidification and reduced oxygen on the behavior and physiology of juvenile rockfish’

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Ocean acidification in the IPCC AR5 WG II

OUP book