Posts Tagged 'laboratory'

Reanalysis shows there is not an extreme decline effect in fish ocean acidification studies

Clements and colleagues [1] claim there is an extreme decline effect in studies published between 2009 and 2019 on the impacts of ocean acidification (OA) on fish behaviour, with the modelled average effect size declining from >5 in 2009 to 2010 to <0.5 after 2015. Here, I show that the extreme decline effect reported by Clements and colleagues is a statistical artifact caused by the way they corrected for zero values in percentage data, which was more common in the earliest experiments compared with later studies. Furthermore, selective choices for excluding or including data, along with data compilation errors and missing studies with strong effects, weakened the effect sizes reported for papers after 2010, further exacerbating the decline effect reported by Clements and colleagues. When the data is reanalysed using appropriate corrections for zeros in percentage and proportional data and using a complete, corrected, and properly screened data set, the extreme decline effect reported by Clements and colleagues no longer exists (Fig 1A and 1B). Instead, there is a more gentle and consistent decline in effect size magnitude through time, from a modelled average <3 in 2009 to 2010 (Fig 1C) and remaining well above zero in 2018 to 2019 (Fig 1D).

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Ocean acidification affects the bioenergetics of marine mussels as revealed by high-coverage quantitative metabolomics

Graphical abstract.

Highlights

  • The metabolic response of mussels to acidification was evaluated.
  • Acidification decreased energy storage and increased energy demands.
  • Acidification affected amino acid metabolism and biosynthesis.
  • Carry-over effects of acidification on cellular energy allocation were observed.

Abstract

Ocean acidification has become a major ecological and environmental problem in the world, whereas the impact mechanism of ocean acidification in marine bivalves is not fully understood. Cellular energy allocation (CEA) approach and high-coverage metabolomic techniques were used to investigate the acidification effects on the energy metabolism of mussels. The thick shell mussels Mytilus coruscus were exposed to seawater pH 8.1 (control) and pH 7.7 (acidification) for 14 days and allowed to recover at pH 8.1 for 7 days. The levels of carbohydrates, lipids and proteins significantly decreased in the digestive glands of the mussels exposed to acidification. The 14-day acidification exposure increased the energy demands of mussels, resulting in increased electron transport system (ETS) activity and decreased cellular energy allocation (CEA). Significant carry-over effects were observed on all cellular energy parameters except the concentration of carbohydrates and cellular energy demand (Ec) after 7 days of recovery. Metabolomic analysis showed that acidification affected the phenylalanine, tyrosine and tryptophan biosynthesis, taurine and hypotaurine metabolism, and glycine, serine and threonine metabolism. Correlation analysis showed that mussel cell energy parameters (carbohydrates, lipids, proteins, CEA) were negatively/positively correlated with certain differentially abundant metabolites. Overall, the integrated biochemical and metabolomics analyses demonstrated the negative effects of acidification on energy metabolism at the cellular level and implicated the alteration of biosynthesis and metabolism of amino acids as a mechanism of metabolic perturbation caused by acidification in mussels.

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Sex and gametogenesis stage are strong drivers of gene expression in Mytilus edulis exposed to environmentally relevant plasticiser levels and pH 7.7

Plastic pollution and changes in oceanic pH are both pressing environmental issues. Little emphasis, however, has been placed on the influence of sex and gametogenesis stage when investigating the effects of such stressors. Here, we examined histology and molecular biomarkers of blue mussels Mytilus edulis exposed for 7 days to a pH 7.7 scenario (− 0.4 units) in combination with environmentally relevant concentrations (0, 0.5 and 50 µg/L) of the endocrine disrupting plasticiser di-2-ethylhexyl phthalate (DEHP). Through a factorial design, we investigated the gametogenesis cycle and sex-related expression of genes involved in pH homeostasis, stress response and oestrogen receptor-like pathways after the exposure to the two environmental stressors. As expected, we found sex-related differences in the proportion of developing, mature and spawning gonads in histological sections. Male gonads also showed higher levels of the acid–base regulator CA2, but females had a higher expression of stress response-related genes (i.e. sodcathsp70). We found a significant effect of DEHP on stress response-related gene expression that was dependent on the gametogenesis stage, but there was only a trend towards downregulation of CA2 in response to pH 7.7. In addition, differences in gene expression between males and females were most pronounced in experimental conditions containing DEHP and/or acidified pH but never the control, indicating that it is important to consider sex and gametogenesis stage when studying the response of mussels to diverse stressors.

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Transcriptomic analysis of large yellow croaker (Larimichthys crocea) during early development under hypoxia and acidification stress

Simple Summary

The large yellow croaker is one of the most economically important fish in China. In recent years, the deterioration of the water environment and unregulated aquaculture have caused great economic losses to the large yellow croaker breeding industry. The aim of this study was to analyze the effects of hypoxia and acidification stress on large yellow croaker. This study revealed that hypoxia and acidification stress suppressed the growth of the large yellow croaker. Transcriptome analysis revealed that genes of the collagen family play an important role in the response of large yellow croaker to hypoxia and acidification stress. The study elucidates the mechanism underlying the response of large yellow croaker to hypoxia–acidification stress during early development and provides a basic understanding of the potential combined effects of reduced pH and dissolved oxygen on Sciaenidae fishes.

Abstract

Fishes live in aquatic environments and several aquatic environmental factors have undergone recent alterations. The molecular mechanisms underlying fish responses to hypoxia and acidification stress have become a serious concern in recent years. This study revealed that hypoxia and acidification stress suppressed the growth of body length and height of the large yellow croaker (Larimichthys crocea). Subsequent transcriptome analyses of L. crocea juveniles under hypoxia, acidification, and hypoxia–acidification stress led to the identification of 5897 differentially expressed genes (DEGs) in the five groups. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that several DEGs were enriched in the ‘protein digestion and absorption’ pathway. Enrichment analysis revealed that this pathway was closely related to hypoxia and acidification stress in the five groups, and we found that genes of the collagen family may play a key role in this pathway. The zf-C2H2 transcription factor may play an important role in the hypoxia and acidification stress response, and novel genes were additionally identified. The results provide new clues for further research on the molecular mechanisms underlying hypoxia–acidification tolerance in L. crocea and provides a basic understanding of the potential combined effects of reduced pH and dissolved oxygen on Sciaenidae fishes.

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Community context and pCO2 impact the transcriptome of the “helper” bacterium Alteromonas in co-culture with picocyanobacteria

Many microbial photoautotrophs depend on heterotrophic bacteria for accomplishing essential functions. Environmental changes, however, could alter or eliminate such interactions. We investigated the effects of changing pCO2 on gene transcription in co-cultures of 3 strains of picocyanobacteria (Synechococcus strains CC9311 and WH8102 and Prochlorococcus strain MIT9312) paired with the ‘helper’ bacterium Alteromonas macleodii EZ55. Co-culture with cyanobacteria resulted in a much higher number of up- and down-regulated genes in EZ55 than pCO2 by itself. Pathway analysis revealed significantly different transcription of genes involved in carbohydrate metabolism, stress response, and chemotaxis, with different patterns of up- or down-regulation in co-culture with different cyanobacterial strains. Gene transcription patterns of organic and inorganic nutrient transporter and catabolism genes in EZ55 suggested resources available in the culture media were altered under elevated (800 ppm) pCO2 conditions. Altogether, changing transcription patterns were consistent with the possibility that the composition of cyanobacterial excretions changed under the two pCO2 regimes, causing extensive ecophysiological changes in both members of the co-cultures. Additionally, significant downregulation of oxidative stress genes in MIT9312/EZ55 cocultures at 800 ppm pCO2 were consistent with a link between the predicted reduced availability of photorespiratory byproducts (i.e., glycolate/2PG) under this condition and observed reductions in internal oxidative stress loads for EZ55, providing a possible explanation for the previously observed lack of “help” provided by EZ55 to MIT9312 under elevated pCO2. If similar broad alterations in microbial ecophysiology occur in the ocean as atmospheric pCO2 increases, they could lead to substantially altered ecosystem functioning and community composition.

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Effect of temperature and CO2 concentration on the morphogenesis of sagittal otoliths in Atlantic herring (Clupea harengus) larvae

Otoliths are very useful biomarkers especially for fish growth. Climate change with the associated global changes in warming and acidification could affect the calcification and the shape of otoliths during the crucial larval period in teleost fish. To evaluate this predicted combined effect of temperature and CO2, Atlantic herring (Clupea harengus) embryos and larvae were reared from hatching to respectively 47 and 60 days post-hatching (dph), under present day conditions and a scenario predicted for the year 2100 (IPCC RCP8.5). Otolith morphogenesis was tracked by analyzing area and normalized Elliptical Fourier coefficients. We found that otolith area for fish of similar size increased under the predicted 2100 climate change scenario compared to the present day. Climate change does not, however, seem to directly affect the otolith shape. Finally, the onset of otolith morphogenesis is hardwired, but the relationship between otolith and fish size is environment-dependent.

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Calmodulin regulates the calcium homeostasis in mantle of Crassostrea gigas under ocean acidification

The biosynthesis of shell is a complicated calcification process in the marine bivalve, which can be severely impacted by ocean acidification (OA). Calmodulin (CaM) is a pivotal calcium regulator and thought to be crucial for calcification. In the present study, a CaM (designated CgCaM) with calcium-binding activity was identified from the Pacific oyster Crassostrea gigas with the objective to understand its possible role in the regulation of calcium homeostasis under acidification treatment. The open reading frame (ORF) of CgCaM was of 474 bp encoding a 17.5 kDa protein with four continuous EF-hand domains. CgCaM shared high similarity with CaMs from other invertebrates and vertebrates. The mRNA transcript of CgCaM was constitutively expressed in all detected tissues with the higher expression level in mantle, especially highest in the middle fold of the three folds of mantle. CgCaM was found to be mainly distributed in the mantle epithelium. When the oysters were exposed to acidified seawater, the expression level of CgCaM in the middle fold of mantle and the content of Ca2+ in this fold both decreased significantly. These results collectively suggested that CgCaM was involved in the regulation of calcium homeostasis in the middle fold of mantle under acidification treatment.

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A story of resilience: Arctic diatom Chaetoceros gelidus exhibited high physiological plasticity to changing CO2 and light levels

Arctic phytoplankton are experiencing multifaceted stresses due to climate warming, ocean acidification, retreating sea ice, and associated changes in light availability, and that may have large ecological consequences. Multiple stressor studies on Arctic phytoplankton, particularly on the bloom-forming species, may help understand their fitness in response to future climate change, however, such studies are scarce. In the present study, a laboratory experiment was conducted on the bloom-forming Arctic diatom Chaetoceros gelidus (earlier C. socialis) under variable CO2 (240 and 900 µatm) and light (50 and 100 µmol photons m-2 s-1) levels. The growth response was documented using the pre-acclimatized culture at 2°C in a closed batch system over 12 days until the dissolved inorganic nitrogen was depleted. Particulate organic carbon and nitrogen (POC and PON), pigments, cell density, and the maximum quantum yield of photosystem II (Fv/Fm) were measured on day 4 (D4), 6 (D6), 10 (D10), and 12 (D12). The overall growth response suggested that C. gelidus maintained a steady-state carboxylation rate with subsequent conversion to macromolecules as reflected in the per-cell POC contents under variable CO2 and light levels. A substantial amount of POC buildup at the low CO2 level (comparable to the high CO2 treatment) indicated the possibility of existing carbon dioxide concentration mechanisms (CCMs) that needs further investigation. Pigment signatures revealed a high level of adaptability to variable irradiance in this species without any major CO2 effect. PON contents per cell increased initially but decreased irrespective of CO2 levels when nitrogen was limited (D6 onward) possibly to recycle intracellular nitrogen resources resulting in enhanced C: N ratios. On D12 the decreased dissolved organic nitrogen levels could be attributed to consumption under nitrogen starvation. Such physiological plasticity could make C. gelidus “ecologically resilient” in the future Arctic.

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Photorespiration in eelgrass (Zostera marina L.): a photoprotection mechanism for survival in a CO2-limited world

Photorespiration, commonly viewed as a loss in photosynthetic productivity of C3 plants, is expected to decline with increasing atmospheric CO2, even though photorespiration plays an important role in the oxidative stress responses. This study aimed to quantify the role of photorespiration and alternative photoprotection mechanisms in Zostera marina L. (eelgrass), a carbon-limited marine C3 plant, in response to ocean acidification. Plants were grown in controlled outdoor aquaria at different [CO2]aq ranging from ~55 (ambient) to ~2121 μM for 13 months and compared for differences in leaf photochemistry by simultaneous measurements of O2 flux and variable fluorescence. At ambient [CO2], photosynthesis was carbon limited and the excess photon absorption was diverted both to photorespiration and non-photochemical quenching (NPQ). The dynamic range of NPQ regulation in ambient grown plants, in response to instantaneous changes in [CO2]aq, suggested considerable tolerance for fluctuating environmental conditions. However, 60 to 80% of maximum photosynthetic capacity of ambient plants was diverted to photorespiration resulting in limited carbon fixation. The photosynthesis to respiration ratio (PE: RD) of ambient grown plants increased 6-fold when measured under high CO2 because photorespiration was virtually suppressed. Plants acclimated to high CO2 maintained 4-fold higher PE: RD than ambient grown plants as a result of a 60% reduction in photorespiration. The O2 production efficiency per unit chlorophyll was not affected by the CO2 environment in which the plants were grown. Yet, CO2 enrichment decreased the light level to initiate NPQ activity and downregulated the biomass specific pigment content by 50% and area specific pigment content by 30%. Thus, phenotypic acclimation to ocean carbonation in eelgrass, indicating the coupling between the regulation of photosynthetic structure and metabolic carbon demands, involved the downregulation of light harvesting by the photosynthetic apparatus, a reduction in the role of photorespiration and an increase in the role of NPQ in photoprotection. The quasi-mechanistic model developed in this study permits integration of photosynthetic and morphological acclimation to ocean carbonation into seagrass productivity models, by adjusting the limits of the photosynthetic parameters based on substrate availability and physiological capacity.

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Effects of ocean acidification and hypoxia on stress and growth hormone responses in juvenile blue rockfish (Sebastes mystinus)

Global climate change is causing increasing ocean acidification (OA) and deoxygenation (hypoxia) of coastal oceans. Along the coast of California, where upwelling is a dominant seasonal physical process, these environmental stressors often co-occur and are intensified in nearshore ecosystems. For juvenile nearshore fishes, who spend a crucial developmental life stage in coastal kelp forests during the upwelling season, these stressors are experienced concurrently and may have large implications for fitness. Environmental stress can set off an endocrine response, which impacts physiology, energy allocation, growth, and behavior. To test the effects of climate change on juvenile blue rockfish, I measured the endocrine response to single and combined stressors of OA and hypoxia after one week of exposure. Assays of cortisol and IGF-1 hormone responses, served as proxies for stress and growth, respectively. Full organismal effects of environmental stressors were evaluated using a scototaxis (i.e., light/dark anxiety) behavior test, and measures of physiological changes in maximum metabolic rate (MMR) and body condition (i.e., Fulton’s K condition index). I found that peak (~1 hour) cortisol levels were highest in the single stressor low pH (7.3 pH), followed by the combined stressor (7.3 pH and 2.0 mg/L O2) and then the single stressor hypoxic treatment (2.0 mg/l O2). This high peak cortisol associated with low pH may indicate the role of cortisol in acid-base regulation. Only the low DO (dissolved oxygen) group did not exhibit a recovery of cortisol levels by the end of one week. There was no observable difference in IGF-1 in juvenile blue rockfish after a week of exposure to any of the pH or DO stressors. When cortisol levels were high, the same fish had low levels of IGF-1, and when cortisol levels were lower, the same fish had highly variable levels of IGF-1. At one-week of exposure, cortisol exhibited a positive relationship with MMR, such that higher stress levels were associated with greater oxygen consumption by the fish. MMR values themselves were highest in the low DO fish, which subsequently also had slightly higher cortisol levels at one-week. Juvenile blue rockfish were largely robust to any behavioral changes associated with stress across treatments. Hypoxic treatment fish had significantly lower body condition than fish from treatments with ambient DO levels after one week. Overall, the results indicated that pH levels influenced hormonal stress physiology, while DO levels contributed to observed differences in metabolism, body condition, and behavioral anxiety in juvenile blue rockfish. I was unable to tease apart and classify whether OA and hypoxia work in an additive, antagonistic, or synergistic way. Continued research should include more experimental stressor treatment levels of varying intensity of both individual and combined treatments as well as upwelling/relaxation fluctuating treatment levels. Elucidating the effects of climate change on fish endocrine response and physiology is important for fish population management and can help inform stock assessment models of blue rockfish in a rapidly changing ocean.

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Transcriptomic stability or lability explains sensitivity to climate stressors in coralline algae

Background

Crustose coralline algae (CCA) are calcifying red macroalgae that play important ecological roles including stabilisation of reef frameworks and provision of settlement cues for a range of marine invertebrates. Previous research into the responses of CCA to ocean warming (OW) and ocean acidification (OA) have found magnitude of effect to be species-specific. Response to OW and OA could be linked to divergent underlying molecular processes across species.

Results

Here we show Sporolithon durum, a species that exhibits low sensitivity to climate stressors, had little change in metabolic performance and did not significantly alter the expression of any genes when exposed to temperature and pH perturbations. In contrast, Porolithon onkodes, a major coral reef builder, reduced photosynthetic rates and had a labile transcriptomic response with over 400 significantly differentially expressed genes, with differential regulation of genes relating to physiological processes such as carbon acquisition and metabolism. The differential gene expression detected in P. onkodes implicates possible key metabolic pathways, including the pentose phosphate pathway, in the stress response of this species.

Conclusions

We suggest S. durum is more resistant to OW and OA than P. onkodes, which demonstrated a high sensitivity to climate stressors and may have limited ability for acclimatisation. Understanding changes in gene expression in relation to physiological processes of CCA could help us understand and predict how different species will respond to, and persist in, future ocean conditions predicted for 2100.

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Ocean warming and acidification affect the transitional element and macromolecular accumulation in harmful raphidophyte Heterosigma akashiwo

Despite ocean warming and acidification being expected to increase the harmful algal species worldwide, the raphidophyte Heterosigma akashiwo is reported to have decreased. However, it is unknown on the transitional scale how this species physically and metabolically modifies its elements, and macromolecular accumulation leads to such condition. With 1st,10th, and 20th culture generation under present (21℃; pCO2 400ppm [LTLC]) and projected (25℃; pCO2 1000ppm [HTHC]) ocean conditions we examined these elemental and macromolecular changes along with transcriptome sequencing. Results showed that compared to HTHC (1st generation), the (20th generation) cells showed large decreases in carbon (QC:40%), nitrogen (QN:36%), and phosphorus-quotas (QP:43%), reflected in their reduction of overall DNA and RNA quantity. Decreased metabolic pathways in photosynthesis, carbon fixation, and lipid accumulation were coincident with changes in photosynthetic efficiency, carbon, and lipid quantity with long-term (20th generation) exposure to HTHC conditions. We observed that these variations of internal metabolic changes are caused by external changes in temperature by activating the (Ca+) signaling pathway and external changes in pCO2 by altering the (proton exchange) pathways. Our results suggest that H. akashiwo in the future ocean will undergo severe changes in its elemental and macromolecular properties, leading to programmed cell death.

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Evaluation of growth, primary productivity, nutritional composition, redox state, and antimicrobial activity of red seaweeds Gracilaria debilis and Gracilaria foliifera under pCO2-induced seawater acidification

Graphical abstract.

Highlights

  • Seawater acidification improved primary productivity, pigments, and carbon storage.
  • No sign of oxidative stress under acidification
  • Improved antimicrobial activities in acidified samples
  • Possible benefits in the future high pCO2 conditions

Abstract

The genus Gracilaria is an economically important group of seaweeds as several species are utilized for various products such as agar, used in medicines, human diets, and poultry feed. Hence, it is imperative to understand their response to predicted ocean acidification conditions. In the present work, we have evaluated the response of Gracilaria foliifera and Gracilaria debilis to carbon dioxide (pCO2) induced seawater acidification (pH 7.7) for two weeks in a controlled laboratory conditions. As a response variable, we have measured growth, productivity, redox state, primary and secondary metabolites, and mineral compositions. We found a general increase in the daily growth rate, primary productivity, and tissue chemical composition (such as pigments, soluble and insoluble sugars, amino acids, and fatty acids), but a decrease in the mineral contents under the acidified condition. Under acidification, there was a decrease in malondialdehyde. However, there were no significant changes in the total antioxidant capacity and a majority of enzymatic and non-enzymatic antioxidants, except for an increase in tocopherols, ascorbate and glutathione-s-transferase in G. foliifera. These results indicate that elevated pCO2 will benefit the growth of the studied species. No sign of oxidative stress markers indicating the acclimatory response of these seaweeds towards lowered pH conditions. Besides, we also found increased antimicrobial activities of acidified samples against several of the tested food pathogens. Based on these observations, we suggest that Gracilaria spp. will be benefitted from the predicted future acidified ocean.

Continue reading ‘Evaluation of growth, primary productivity, nutritional composition, redox state, and antimicrobial activity of red seaweeds Gracilaria debilis and Gracilaria foliifera under pCO2-induced seawater acidification’

Impacts of seawater pH buffering on the larval microbiome and carry-over effects on later-life disease susceptibility in Pacific oysters

Ocean acidification upwelling events and the resulting lowered aragonite saturation state of seawater have been linked to high mortality of marine bivalve larvae in hatcheries. Major oyster seed producers along North America’s west coast have mitigated impacts via seawater pH buffering (e.g., addition of soda ash). However, little consideration has been given to whether such practice may impact the larval microbiome, with potential carry-over effects on immune competency and disease susceptibility in later-life stages. To investigate possible impacts, Pacific oysters (Crassostrea gigas) were reared under soda ash pH buffered or ambient pH seawater conditions for the first 24 h of development. Both treatment groups were then reared under ambient pH conditions for the remainder of the developmental period. Larval microbiome, immune status (via gene expression), growth, and survival were assessed throughout the developmental period. Juveniles and adults arising from the larval run were then subjected to laboratory-based disease challenges to investigate carry-over effects. Larvae reared under buffered conditions showed an altered microbiome, which was still evident in juvenile animals. Moreover, reduced survival was observed in both juveniles and adults of the buffered group under a simulated marine heatwave and Vibrio exposure compared with those reared under ambient conditions. Results suggest that soda ash pH buffering during early development may compromise later-life stages under stressor conditions, and illustrate the importance of a long-view approach with regard to hatchery husbandry practices and climate change mitigation.

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Could acidified environments intensify illicit drug effects on the reproduction of marine mussels?

The increasing oceanic uptake is a direct response to the increasing atmospheric burden of CO2. Oceans are experiencing both physical and biogeochemical changes. This increase in CO2 hosts in oceans promotes changes in pH and seawater chemistry that can modify the speciation of compounds, largely due to dependent element speciation on physicochemical parameters (salinity, pH, and redox potential). So, ocean acidification can trigger enhanced toxicity of illicit drugs to non-target marine organisms due to the combined effects of crack cocaine and low pH (from 8.3 to 7.0 pH values) on the reproduction of the marine mussel Perna perna. Fertilization rate and embryo–larval development were used as endpoints to assess the effects of crack-cocaine concentrations (6.25, 12.5, 25, 50, and 100 mg L−1) and its association with pH values variation (8.3, 8.0, 7.5, and 7.0). The IC50 was calculated from the results of an embryo–larval assay in different methods of acidification (CO2 and HCl), which evidenced that HCl treatment was more toxic than CO2 treatment for the same drug concentrations. Results showed that the gametes of P. perna react to acidification when exposed to crack-cocaine concentration and pH reductions.

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Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium

Growth of the prominent nitrogen-fixing cyanobacterium Trichodesmium is often limited by phosphorus availability in the ocean. How nitrogen fixation by phosphorus-limited Trichodesmium may respond to ocean acidification remains poorly understood. Here, we use phosphate-limited chemostat experiments to show that acidification enhanced phosphorus demands and decreased phosphorus-specific nitrogen fixation rates in Trichodesmium. The increased phosphorus requirements were attributed primarily to elevated cellular polyphosphate contents, likely for maintaining cytosolic pH homeostasis in response to acidification. Alongside the accumulation of polyphosphate, decreased NADP(H):NAD(H) ratios and impaired chlorophyll synthesis and energy production were observed under acidified conditions. Consequently, the negative effects of acidification were amplified compared to those demonstrated previously under phosphorus sufficiency. Estimating the potential implications of this finding, using outputs from the Community Earth System Model, predicts that acidification and dissolved inorganic and organic phosphorus stress could synergistically cause an appreciable decrease in global Trichodesmium nitrogen fixation by 2100.

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Effects of hypoxia and acidification on Calanus pacificus: behavioral changes in response to stressful environments

Copepods, which play major roles in marine food webs and biogeochemical cycling, frequently undergo diel vertical migration (DVM), swimming downwards during the day to avoid visual predation and upwards at night to feed. Natural water columns that are stratified with chemical stressors at depth, such as hypoxia and acidification, are increasing with climate change. Understanding behavioral responses of copepods to these stresses—in particular, whether copepods alter their natural migration—is important to anticipating impacts of climate change on marine ecosystems. We conducted laboratory experiments using stratified water columns to measure the effects of bottom water hypoxia and pH on mortality, distribution, and swimming behaviors of the calanoid copepod Calanus pacificus. When exposed to hypoxic (0.65 mg O2 l-1) bottom waters, the height of C. pacificus from the bottom increased 20% within hypoxic columns, and swimming speed decreased 46% at the bottom of hypoxic columns and increased 12% above hypoxic waters. When exposed to low pH (7.48) bottom waters, swimming speeds decreased by 8 and 9% at the base of the tanks and above acidic waters, respectively. Additionally, we found a 118% increase in ‘moribund’ (immobile on the bottom) copepods when exposed to hypoxic, but not acidic, bottom waters. Some swimming statistics differed between copepods collected from sites with versus without historical hypoxia and acidity. Observed responses suggest potential mechanisms underlying in situ changes in copepod population distributions when exposed to chemical stressors at depth.

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pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: metal accumulation, antioxidant defenses and biodetoxification in livers

Graphical abstract.

Highlights

  • SA and Cu interact during hepatic antioxidant defenses and biodetoxification.
  • Moderate SA helps alleviate Cu exposure-induced LPO, but extreme SA exacerbates it.
  • Thiols respond actively to cope with Cu toxicity in acidified seawater.
  • SOD, CAT, EROD and GST sensitively respond to SA and Cu coexposure.
  • Pearson’s correlation coefficient and PCA usefully integrate biomarker responses.

Abstract

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO2-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L−1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO2 ∼1353.89 μatm; extreme SA: pH 7.30, pCO2 ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and biodetoxification in response to coexposure. Hepatic Cu accumulation (30.22–184.90 mg kg−1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and biodetoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

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Do global environmental drivers’ ocean acidification and warming exacerbate the effects of oil pollution on the physiological energetics of Scylla serrata?

Global climate change–induced ocean warming and acidification have complex reverberations on the physiological functioning of marine ectotherms. The Sundarbans estuarine system has been under threat for the past few decades due to natural and anthropogenic disturbances. In recent years, petroleum products’ transportation and their usage have increased manifold, which causes accidental oil spills. The mud crab (Scylla serrata) is one of the most commercially exploited species in the Sundarbans. The key objective of this study was to delineate whether rearing under global environmental drivers (ocean acidification and warming) exacerbates the effect of a local driver (oil pollution) on the physiological energetics of mud crab (Scylla serrata) from the Sundarbans estuarine system. Animals were reared separately for 30 days under (a) the current climatic scenario (pH 8.1, 28°C) and (b) the predicted climate change scenario (pH 7.7, 34°C). After rearing for 30 days, 50% of the animals from each treatment were exposed to 5 mg L−1 of marine diesel oil for the next 24 h. Physiological energetics (ingestion rate, absorption rate, respiration rate, excretion rate, and scope for growth), thermal performance, thermal critical maxima (CTmax), acclimation response ratio (ARR), Arrhenius activation energy (AAE), temperature coefficient (Q10), warming tolerance (WT), and thermal safety margin (TSM) were evaluated. Ingestion and absorption rates were significantly reduced, whereas respiration and ammonia excretion rates significantly increased in stressful treatments, resulting in a significantly lower scope for growth. A profound impact on thermal performance was also noticed, leading to a downward shift in CTmax value for stress-acclimated treatment. The present results clearly highlighted the detrimental combined effect of global climatic stressors and pollution on the physiological energetics of crabs that might potentially reduce their population and affect coastal aquaculture in forthcoming years.

Continue reading ‘Do global environmental drivers’ ocean acidification and warming exacerbate the effects of oil pollution on the physiological energetics of Scylla serrata?’

Epigenetic-associated phenotypic plasticity of the ocean acidification-acclimated edible oyster in the mariculture environment

For marine invertebrates with pelagic-benthic life cycle, larval exposure to ocean acidification (OA) can affect adult performance in response to another environmental stressor. This carry-over effect has the potential to alter phenotypic traits. However, molecular mechanisms that mediate “OA” triggered carry-over effects have not been explored despite such information being key to improve species fitness and management strategies for aquafarming. This study integrated genome-wide DNA methylome and transcriptome to examine epigenetic modification-mediated carry-over OA impacts on phenotypic traits of the ecologically and commercially important oyster species Crassostrea hongkongensis under field conditions. Larvae of C. hongkongensis were exposed to control pH8.0 and low pH7.4 conditions mimicking OA scenario before being outplanted as post-metamorphic juveniles at two mariculture field sites with contrasting environmental stressors for nine months. The larval carry-over OA effect was found to have persistent impacts on the growth and survival trade-off traits on the outplanted juveniles, although the beneficial or adverse effect depended on the environmental conditions at the outplanted sites. The site-specific plasticity was demonstrated with a diverse DNA methylation-associated gene expression profile, with signal transduction and endocrine system being the most common and highly enriched functions. The highly methylated exons prevailed in the key genes related to general metabolic and endocytic responses and these genes are evolutionarily conserved in various marine invertebrates in response to OA. These results suggest that oysters with prior larval exposure history to OA had the capability to trigger rapid local adaptive responses via epigenetic modification to cope with multiple stressors in field.

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