Posts Tagged 'respiration'

Adult Antarctic krill proves resilient in a simulated high CO2 ocean

Antarctic krill (Euphausia superba) have a keystone role in the Southern Ocean, as the primary prey of Antarctic predators. Decreases in krill abundance could result in a major ecological regime shift, but there is limited information on how climate change may affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Here we show that, in the laboratory, adult krill are able to survive, grow, store fat, mature, and maintain respiration rates when exposed to near-future ocean acidification (1000–2000 μatm pCO2) for one year. Despite differences in seawater pCO2 incubation conditions, adult krill are able to actively maintain the acid-base balance of their body fluids in near-future pCO2, which enhances their resilience to ocean acidification.

Continue reading ‘Adult Antarctic krill proves resilient in a simulated high CO2 ocean’

Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO2 rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO2 levels. Under low light conditions, elevated CO2 significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO2 level predicted for the end of the century.

Continue reading ‘Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising’

CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium

We established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol-1 = low-CO2, 380 µmol mol-1 = mid-CO2 and 720 µmol mol-1 = high-CO2). We found that biomass (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five-times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m-2 s-1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon concentrating mechanism (CCM) at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth.

Continue reading ‘CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium’

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’

Impact of ocean acidification on thermal tolerance and acid–base regulation of Mytilus edulis from the White Sea

Ocean warming and acidification are two important environmental drivers affecting marine organisms. Organisms living at high latitudes might be especially threatened in near future, as current environmental changes are larger and occur faster. Therefore, we investigated the effect of hypercapnia on thermal tolerance and physiological performance of sub-Arctic Mytilus edulis from the White Sea. Mussels were exposed (2 weeks) to 390 µatm (control) and 1120 µatm CO2 (year 2100) before respiration rate (MO2), anaerobic metabolite (succinate) level, haemolymph acid–base status and intracellular pH (pHi) were determined during acute warming (10–28 °C, 3 °C over night). In normocapnic mussels, warming induced MO2 to rise exponentially until it levelled off beyond a breakpoint temperature of 20.5 °C. Concurrently, haemolymph PCO2 rose significantly > 19 °C followed by a decrease in PO2 indicating the pejus temperature (TP, onset of thermal limitation). Succinate started to accumulate at 28 °C under normocapnia defining the critical temperature (TC). pHi was maintained during warming until it dropped at 28 °C, in line with the concomitant transition to anaerobiosis. At acclimation temperature, CO2 had only a minor impact. During warming, MO2 was stimulated by CO2 resulting in an elevated breakpoint of 25.8 °C. Nevertheless, alterations in haemolymph gases (> 16 °C) and the concomitant changes of pHi and succinate level (25 °C) occurred at lower temperature under hypercapnia versus normocapnia indicating a downward shift of both thermal limits TP and TC by CO2. Compared to temperate conspecifics, sub-Arctic mussels showed an enhanced thermal sensitivity, exacerbated further by hypercapnia, indicating their potential vulnerability to environmental changes projected for 2100.

Continue reading ‘Impact of ocean acidification on thermal tolerance and acid–base regulation of Mytilus edulis from the White Sea’

Indications of future performance of native and non-native adult oysters under acidification and warming

Highlights

• Acidification and warming negatively impacted the physiology of Magallana gigas.
Ostrea edulis appeared unaffected by the treatment conditions.
• Efforts to promote the restoration of native O. edulis beds should be pursued.
• Efforts to eradicate M. gigas populations may need to be reconsidered.

Abstract

Globally, non-native species (NNS) have been introduced and now often entirely replace native species in captive aquaculture; in part, a result of a perceived greater resilience of NSS to climate change and disease. Here, the effects of ocean acidification and warming on metabolic rate, feeding rate, and somatic growth was assessed using two co-occurring species of oysters – the introduced Pacific oyster Magallana gigas (formerly Crassostrea gigas), and native flat oyster Ostrea edulis. Biological responses to increased temperature and pCO2 combinations were tested, the effects differing between species. Metabolic rates and energetic demands of both species were increased by warming but not by elevated pCO2. While acidification and warming did not affect the clearance rate of O. edulis, M. gigas displayed a 40% decrease at ∼750 ppm pCO2. Similarly, the condition index of O. edulis was unaffected, but that of M. gigas was negatively impacted by warming, likely due to increased energetic demands that were not compensated for by increased feeding. These findings suggest differing stress from anthropogenic CO2 emissions between species and contrary to expectations, this was higher in introduced M. gigas than in the native O. edulis. If these laboratory findings hold true for populations in the wild, then continued CO2 emissions can be expected to adversely affect the functioning and structure of M. gigas populations with significant ecological and economic repercussions, especially for aquaculture. Our findings strengthen arguments in favour of investment in O. edulis restoration in UK waters.

Continue reading ‘Indications of future performance of native and non-native adult oysters under acidification and warming’

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’


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