Posts Tagged 'physiology'

Effects of pH and nitrogen form on Nitzschia closterium growth by linking dynamic with enzyme activity


• The growth of Nitzschia closterium was inhibited by ocean acidification with low growth indication.

• Acidification might induce ROS with the enzyme activities (SOD, CAT) increase under lower pH levels.

• Acidification has a more detrimental effect on the growth of N. closterium under NO3–N than NH4–N.


In this study, Nitzschia closterium was incubated in seawater at different pH values (8.10, 7.71, and 7.45) and using different nitrogen forms (NO3–N and NH4–N) in the laboratory. The results showed that the growth of N. closterium was inhibited by ocean acidification, with individuals under lower pH levels showing lower growth rates and lower nitrogen uptake rates for both nitrogen forms. The Vmax/Ks ratio decreased with decreasing pH, indicating the inhibition of nitrogen uptake, whereas the ratios for NH4–N cultures were higher than those for NO3–N cultures, implying the highly competitive position of NH4–N. Acidification might induce reactive oxygen species based on the result that the maximum enzyme activities of SuperOxide Dismutase (SOD) and CATalase (CAT) increased under lower pH levels. The SOD and CAT activities for the NO3–N cultures were higher than those for NH4–N cultures at the low pH level, indicating that acidification might cause more oxidative stress for NO3–N cultures than for NH4–N cultures. Thus, ocean acidification might have a more detrimental effect on the growth of N. closterium under NO3–N conditions than NH4–N conditions, with a lower ratio (γ) of the maximum growth rate to the maximum nutrient uptake rate, and a drop in nitrate reductase activity under lower pH levels.

Continue reading ‘Effects of pH and nitrogen form on Nitzschia closterium growth by linking dynamic with enzyme activity’

Effects of seawater acidification and cadmium on the antioxidant defense of flounder Paralichthys olivaceus larvae


• Seawater acidification and Cd induced oxidative stress in flounder larvae.

• Two stressors interacted to regulate mRNA expressions of antioxidant-related genes.

• Integrated antioxidant response was promoted with increasing oxidative stress.


Increasing atmospheric carbon dioxide has led to a decrease in the pH of the ocean, which influences the speciation of heavy metals and consequently affects metal toxicity in marine organisms. To investigate the effects of seawater acidification and metals on the antioxidant defenses of marine fishes, the flounder Paralichthys olivaceus, was continuously exposed to cadmium (Cd; control, 0.01 and 0.15 mg L−1) and acidified seawater (control (pH 8.10), 7.70 and 7.30) for 49 days from embryogenesis to settlement. The results demonstrated that both Cd and acidified seawater could induce oxidative stress and consequently cause lipid peroxidation (LPO) in the larvae. Antioxidants (i.e., superoxide dismutase, SOD; catalase, CAT; reduced glutathione, GSH; glutathione S-transferase, GST; glutathione peroxidase, GPx; and glutathione reductase, GR) functioned to defend the larvae against oxidative damage. Overall, Cd induced (SOD, GST and GSH) or inhibited (CAT and GPx) the enzymatic activities or contents of all the selected antioxidants except for GR. The antioxidants responded differently to seawater acidification, depending on their interaction with the metal. Similarly, the mRNA expressions of the antioxidant-related genes were upregulated (sod, gr and gst) or downregulated (cat and gpx) in response to increasing Cd exposure. Seawater acidification did not necessarily affect all of the biomarkers; in some cases (e.g., SOD and sod, GR and gr), Cd stress may have exceeded and masked the stress from seawater acidification in regulating the antioxidant defense of the larvae. The integrated biomarker response (IBR) was enhanced with increasing levels of the stressors. These findings support the hypothesis that seawater acidification not only directly affects the antioxidant defense in flounder larvae but also interacts with Cd to further regulate this defense. This study has ecological significance for assessing the long-term impacts of ocean acidification and metal pollution on the recruitment of fish populations in the wild.

Continue reading ‘Effects of seawater acidification and cadmium on the antioxidant defense of flounder Paralichthys olivaceus larvae’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial, light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 µatm) and future (1000 µatm) pCO2 levels under a constant as well as a dynamic light, simulating more realistic light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its photophysiology for effective light usage during both low- and high-light periods. This photoacclimative response, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla is able to maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, M. pusilla is likely to cope well with future conditions in the Arctic Ocean.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)’

Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification

Microorganisms form the basis of ocean ecosystems yet the effects of perturbations such as decreasing pH on microbial community structure, interactions and functionality remain compared to multicellular organisms. Using an experimental manipulation of Southern Ocean seawater, we subjected bacterioplankton and mycoplankton to artificial pH decreases, which are predicted to occur in the future. We show that acidification led to substantial increases of bacterioplankton diversity, while in contrast it had no effect on mycoplankton diversity. Our analyses revealed a loss of putative keystone taxa and a decrease in predicted community interactions as a response to lower pH levels. Bacterioplankton shifted from generalist to specialist community members, suggesting a specific stress response to unfavourable conditions. In addition, enzyme activities involved in nitrogen acquisition were lower at reduced pH levels, suggesting altered organic matter cycling in a more acidic ocean. Our findings suggest that bacterioplankton and mycoplankton may respond differentially to future ocean acidification, with potentially negative impacts on community structure and biogeochemical cycling in the Southern Ocean.

Continue reading ‘Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification’

Po uptake in microalgae at different seawater pH: an experimental study simulating ocean acidification


• Study provides insight on 210Po concentration and likely uptake by phytoplankton under OA scenarios

• Lower 210Po and 209Po levels in microalgae were observed at low pH conditions

• Differences in 210Po concentrations in microalgae species at different pH were statistically significant after 96-h exposure

• Final seawater 210Po concentration was low at 8.2 compared to 7.5 in all experimental tanks


Climate change effects such as ocean acidification (OA) are known to affect the trace metal distribution. This experimental study provides the first data on 209Po uptake rates and 210Po concentration in five microalgae species under different pH scenarios. The experiment was conducted in replicates at three pH conditions 8.2, 8.0, and 7.5, representing the current and future climate change scenario as per IPCC RCP8.5. The 209Po uptake in the phytoplankton was highest in Thalassiosira weissflogi, i.e. 83% of the 209Po tracer was taken up at 8.2 pH whereas the lowest uptake was observed in Dunaliella salina equivalent to 20% at 7.5 pH. Similar behavior was observed in 210Po concentrations in these microalgae, where 210Po ranged between 3.16 ± 0.03 and 11.6 ± 0.04 Bq kg−1 wet weight (ww), with the highest in the Thalassioria weissflogi at 8.2 pH, and the lowest in Dunaliella salina at 7.5 pH. The difference in 209Po uptake and 210Po concentration was statistically significant (p Tetraselmis suecica > Chaetoceros muelleri > Isochrysis galbana > Dunaliella salina and 8.2 > 8.0 > 7.5. A higher concentration of 209Po in seawater was measured at low pH condition in all the experimental tanks. Though the data clearly show the difference in concentration and uptake of polonium at different pH conditions, it is not known if lower pH is affecting the adsorbed or absorbed fraction. A detailed investigation will be required to understand the process as it can have a significant effect on biomagnification and marine food chain transfer under changing climatic scenarios.

Continue reading ‘Po uptake in microalgae at different seawater pH: an experimental study simulating ocean acidification’

Measurement of feeding rates, respiration, and pH regulatory processes in the light of ocean acidification research

The physiology of marine larvae has received considerable attention in the context of anthropogenic ocean acidification (OA). Many marine larvae including those of echinoderms, hemichordates, and mollusks are characterized by a developmental delay when exposed to reductions in seawater pH with the underlying mechanisms being largely unexplored.

A key task in the frame of OA research lies in the identification of unifying physiological principles that may explain reductions in growth and development. The sea urchin larva has been identified as a good model organism, and energy allocations toward compensatory processes were found to be key factors affecting development. However, physiological approaches to assess the animal’s energy budget, as well as methods to characterize energy consuming processes (e.g., gut pH homeostasis and biomineralization) were scarce. During the last decade, a suite of physiological techniques was developed, to accurately determine the larval energy budget including feeding and metabolic rate measurements. To identify and characterize energy consuming processes, gastroscopic pH measurements in the larval gut and intracellular pH measurements of primary mesenchyme cells were developed.

These techniques helped to understand fundamental processes of gut homeostasis and biomineralization in the developing sea urchin larva and their interaction with the environment. Using the sea urchin larva as a model these methods were successfully transferred to other echinoderm and hemichordate early developmental stages. This chapter explains and provides the methodological basis for the determination of feeding and metabolic rates as well as intracellular and extracellular pH measurements using the sea urchin larva as an example.

Continue reading ‘Measurement of feeding rates, respiration, and pH regulatory processes in the light of ocean acidification research’

Climate change enhances disease processes in crustaceans: case studies in lobsters, crabs, and shrimps

Climate change has resulted in increasing temperature and acidification in marine systems. Rising temperature and acidification act as stressors that negatively affect host barriers to infection, thus enhancing disease processes and influencing the emergence of pathogens in ecologically and commercially important species. Given that crustaceans are ectotherms, changes in temperature dominate their physiological and immunological responses to microbial pathogens and parasites. Because of this, the thermal ranges of several crustacean hosts and their pathogens can be used to project the outcomes of infections. Host factors such as molting, maturation, respiration, and immune function are strongly influenced by temperature, which in turn alter the host’s susceptibility to pathogens, further amplifying morbidity and mortality. Microbial pathogens are also strongly influenced by temperature, arguably more so than their crustacean hosts. Microbial pathogens, with higher thermal optima than their hosts, grow rapidly and overcome host immune defenses, which have been weakened by increased temperatures. Pathogen factors such as metabolic rates, growth rates, virulence factors, and developmental rates are often enhanced by rising temperature, which translates into increased transmission, dispersal, and proliferation at the population level, and ultimately emergence of outbreaks in host populations. Less well known are the effects of acidification and salinity intrusion on host-pathogen processes, but they operate alongside temperature, as multiple stressors, that impose significant metabolic and physiological demands on host homeostasis.

Continue reading ‘Climate change enhances disease processes in crustaceans: case studies in lobsters, crabs, and shrimps’

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Ocean acidification in the IPCC AR5 WG II

OUP book