Posts Tagged 'respiration'

Varying conditions in intertidal pools: high resolution pH dynamics and primary production

Most studies designed to assess the effects of ocean acidification take place in coastal and intertidal environments, which are characterized by a great variability of its physical and chemical parameters. However, a great number of these studies use fixed pH levels predicted for the future, disregarding natural pH oscillations. In this work we studied the pH oscillations and primary productivity of intertidal rockpools in two rocky shore areas. To provide high resolution continuous pH data we used an autonomous pH measuring system which consisted of a pH sensor, a data logger and a battery encased in a waterproof container. Oxygen concentration and primary production from phytoplankton and macro- phytobentos were also measured. We found a range of pH variation in the pools of 0.07 pH units/day when water dynamics was high and of 0.26 pH units/day when conditions were more stable. Carbonate systems parameters, temperature and oxygen concentration were related and they responded to the day / night cycle and hydrodynamic conditions. We suggest that these natural oscillations in pH and temperature must be taken into account in ocean acidifications studies in order to obtain more accurate results.

Continue reading ‘Varying conditions in intertidal pools: high resolution pH dynamics and primary production’

Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation

Change in the nutritional quality of phytoplankton is a key mechanism through which ocean acidification can affect the function of marine ecosystems. Copepods play an important role transferring energy from phytoplankton to higher trophic levels, including fatty acids (FA)—essential macronutrients synthesized by primary producers that can limit zooplankton and fisheries production. We investigated the direct effects of pCO2 on phytoplankton and copepods in the laboratory, as well as the trophic transfer of effects of pCO2 on food quality. The marine cryptophyte Rhodomonas salina was cultured at 400, 800, and 1200 μatm pCO2 and fed to adult Acartia hudsonica acclimated to the same pCO2 levels. We examined changes in phytoplankton growth rate, cell size, carbon content, and FA content, and copepod FA content, grazing, respiration, egg production, hatching, and naupliar development. This single-factor experiment was repeated at 12°C and at 17°C. At 17°C, the FA content of R. salina responded non-linearly to elevated pCO2 with the greatest FA content at intermediate levels, which was mirrored in A. hudsonica; however, differences in ingestion rate indicate that copepods accumulated FA less efficiently at elevated pCO2. A. hudsonica nauplii developed faster at elevated pCO2 at 12°C in the absence of strong food quality effects, but not at 17°C when food quality varied among treatments. Our results demonstrate that changes to the nutritional quality of phytoplankton are not directly translated to their grazers, and that studies that include trophic links are key to unraveling how ocean acidification will drive changes in marine food webs.

Continue reading ‘Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation’

The physiological response of marine diatoms to ocean acidification: differential roles of seawater pCO2 and pH

Although increasing the pCO2 for diatoms will presumably down‐regulate the CO2‐concentrating mechanism (CCM) to save energy for growth, different species have been reported to respond differently to ocean acidification (OA). To better understand their growth responses to OA, we acclimated the diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Chaetoceros muelleri to ambient (pCO2 400 μatm, pH 8.1), carbonated (pCO2 800 μatm, pH 8.1), acidified (pCO2 400 μatm, pH 7.8), and OA (pCO2 800 μatm, pH 7.8) conditions and investigated how seawater pCO2 and pH affect their CCMs, photosynthesis, and respiration both individually and jointly. In all three diatoms, carbonation down‐regulated the CCMs, while acidification increased both the photosynthetic carbon fixation rate and the fraction of CO2 as the inorganic carbon source. The positive OA effect on photosynthetic carbon fixation was more pronounced in C. muelleri, which had a relatively lower photosynthetic affinity for CO2, than in either T. pseudonana or P. tricornutum. In response to OA, T. pseudonana increased respiration for active disposal of H+ to maintain its intracellular pH, whereas P. tricornutum and C. muelleri retained their respiration rate but lowered the intracellular pH to maintain the cross‐membrane electrochemical gradient for H+ efflux. As the net result of changes in photosynthesis and respiration, growth enhancement to OA of the three diatoms followed the order of C. muelleri > P. tricornutum > T. pseudonana. This study demonstrates that elucidating the separate and joint impacts of increased pCO2 and decreased pH aids the mechanistic understanding of OA effects on diatoms in the future, acidified oceans.

Continue reading ‘The physiological response of marine diatoms to ocean acidification: differential roles of seawater pCO2 and pH’

Ocean warming drives decline in coral metabolism while acidification highlights species-specific responses

Ocean warming and acidification can have negative implications on coral reefs. This mechanistic study aims to evaluate the proximal causes of the observed negative response of Hawaiian corals to climate change scenarios. Net calcification (Gnet), gross photosynthesis, and dark respiration were measured in three species of Hawaiian corals across a range of temperature and acidification regimes using endpoint incubations. Calcification rates showed a curvilinear response with temperature, with the highest calcification rates observed at 26°C. Coral response to ocean acidification (OA) was species dependent and highly variable. OA enhanced calcification rates by 45% in the perforate coral, Montipora capitata, but had no short-term effect on the calcification or photosynthetic rates of imperforate corals, Pocillopora damicornis or Leptastrea purpurea. Further investigations revealed M. capitata to effectively dissipate protons (H+) while increasing uptake of bicarbonate (HCO−3), therefore maintaining high rates of Gnet under acute OA stress. This study demonstrates the first experimental evidence of the ability of a coral species to take advantage of increased dissolved inorganic carbon and overcome an increasing proton gradient in the boundary layer under OA conditions. These observed differences in coral metabolism may underlie the species-specific responses to climate change.

Continue reading ‘Ocean warming drives decline in coral metabolism while acidification highlights species-specific responses’

Contrasting responses of photosynthesis and photochemical efficiency to ocean acidification under different light environments in a calcifying alga

Ocean acidification (OA) is predicted to enhance photosynthesis in many marine taxa. However, photophysiology has multiple components that OA may affect differently, especially under different light environments, with potentially contrasting consequences for photosynthetic performance. Furthermore, because photosynthesis affects energetic budgets and internal acid-base dynamics, changes in it due to OA or light could mediate the sensitivity of other biological processes to OA (e.g. respiration and calcification). To better understand these effects, we conducted experiments on Porolithon onkodes, a common crustose coralline alga in Pacific coral reefs, crossing pCO2 and light treatments. Results indicate OA inhibited some aspects of photophysiology (maximum photochemical efficiency), facilitated others (α, the responsiveness of photosynthesis to sub-saturating light), and had no effect on others (maximum gross photosynthesis), with the first two effects depending on treatment light level. Light also exacerbated the increase in dark-adapted respiration under OA, but did not alter the decline in calcification. Light-adapted respiration did not respond to OA, potentially due to indirect effects of photosynthesis. Combined, results indicate OA will interact with light to alter energetic budgets and potentially resource allocation among photosynthetic processes in P. onkodes, likely shifting its light tolerance, and constraining it to a narrower range of light environments.

Continue reading ‘Contrasting responses of photosynthesis and photochemical efficiency to ocean acidification under different light environments in a calcifying alga’

Seawater acidification increases copper toxicity: a multi-biomarker approach with a key marine invertebrate, the Pacific Oyster Crassostrea gigas

Highlights

• Cu concentration was elevated in Cu-exposed oysters under OA.
• Seawater acidification could exacerbate the toxicity caused by Cu in oysters.
• Disturbed physiological functions were observed in oysters under Cu and/or OA.
• IBR results suggested that co-exposure was the most stressful condition.

Abstract

Ocean acidification (OA) has been found to increase the release of free Cu2+ in seawater. However, only a handful of studies have investigated the influence of OA on Cu accumulation and cellular toxicity in bivalve species. In this study, Pacific oysters, Crassostrea gigas, were exposed to 25 μg/L Cu2+ at three pH levels (8.1, 7.8 and 7.6) for 14 and 28 days. Physiological and histopathological parameters [(clearance rate (CR), respiration rate (RR), histopathological damage and condition index (CI)), oxidative stress and neurotoxicity biomarkers [superoxide dismutase (SOD) and glutathione transferase (GST) activities, lipid peroxidation (LPO) and acetylcholinesterase (AChE) activity], combined with glycolytic enzyme activities [pyruvate kinase (PK) and hexokinase (HK)] were investigated in C. gigas. The bioconcentration of Cu was increased in soft tissues of Cu-exposed oysters under OA. Our results suggest that both OA and Cu could lead to physiological disturbance, oxidative stress, cellular damage, disturbance in energy metabolism and neurotoxicity in oysters. The inhibited CR, increased glycolytic enzymes activities and decreased CI suggested that the energy metabolism strategy adopted by oysters was not sustainable in the long term. Furthermore, integrated biomarker response (IBR) results found that OA and Cu exposure lead to severe stress to oysters, and co-exposure was the most stressful condition. Results from this study highlight the need to include OA in future environmental assessments of pollutants and hazardous materials to better elucidate the risks of those environmental perturbations.

Continue reading ‘Seawater acidification increases copper toxicity: a multi-biomarker approach with a key marine invertebrate, the Pacific Oyster Crassostrea gigas’

Future ocean warming may prove beneficial for the northern population of European seabass, but ocean acidification does not

The world’s oceans are acidifying and warming due to increasing amounts of atmospheric CO2. Thermal tolerance of fish much depends on the cardiovascular ability to supply the tissues with oxygen. The heart itself is highly dependent on oxygen and heart mitochondria thus might play a key role in shaping an organism’s tolerance to temperature. The present study aimed to investigate the effects of acute and chronic warming on respiratory capacities of European sea bass (Dicentrarchus labrax L.) heart mitochondria. We hypothesized that acute warming would impair mitochondrial respiratory capacities, but be compensated after long-term. Increasing PCO2 may cause intracellular changes, likely further constricting cellular energy metabolism. We found increased leak respiration rates in acutely warmed heart mitochondria of cold-conditioned fish in comparison to measurements at their rearing temperature, suggesting a lower aerobic capacity to synthesize ATP. However, thermal acclimation led to increased mitochondrial functionality, e.g. higher RCRo in heart mitochondria of warm-conditioned compared to cold-conditioned fish. Exposure to high PCO2 synergistically amplified the effects of acute and long-term warming, but did not result in changes by itself. We explained the high ability to maintain mitochondrial function under OA with the fact that seabass are moving between various environmental conditions. Improved mitochondrial capacities after warm conditioning could be due to the origin of this species in the warm waters of the Mediterranean. Our results also indicate that seabass are not yet fully adapted to the colder temperatures in their northern distribution range and might benefit from warmer temperatures.

Continue reading ‘Future ocean warming may prove beneficial for the northern population of European seabass, but ocean acidification does not’


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