Posts Tagged 'mollusks'



Stress responses in Crassostrea gasar exposed to combined effects of acute pH changes and phenanthrene

Highlights

• Acidification is capable to unbalance transcription of biotransformation genes.

• CYP2AU1, CYP2-like2 and GSTΩ genes were upregulated at pH 6.5.

• Water acidification increases gill’s susceptibility to oxidative stress.

• PHE activated enzymatic antioxidant system after 96 h exposure.

• Oysters can protect against with oxidative stress.

Abstract

Ocean acidification is a result of the decrease in the pH of in marine water, caused mainly by the increase in CO2 released in the atmosphere and its consequent dissolution in seawater. These changes can be dramatic for marine organisms especially for oysters Crassostrea gasar if other stressors such as xenobiotics are present. The effect of pH changes (6.5, 7.0 and 8.2) was assessed on the transcript levels of biotransformation [cytochromes P450 (CYP2AU1, CYP2-like2) and glutathione S-transferase (GSTΩ-like)] and antioxidant [superoxide dismutase (SOD-like), catalase (CAT-like) and glutathione peroxidase (GPx-like)] genes, as well as enzyme activities [superoxide dismutase, (SOD), catalase (CAT), glutathione reductase (GR), glutathione-S-transferases (GST) and glucose-6-phosphate dehydrogenase (G6PDH)] and lipid peroxidation (MDA) in the gills of Crassostrea gasar exposed to 100 μg·L−1 of phenanthrene (PHE) for 24 and 96 h. Likewise, the PHE burdens was evaluated in whole soft tissues of exposed oysters. The accumulation of PHE in oysters was independent of pH. However, acidification promoted a significant decrease in the transcript levels of some protective genes (24 h exposure: CYP2AU1 and GSTΩ-like –; 96 h exposure: CAT-like and GPx-like), which was not observed in the presence of PHE. Activities of GST, CAT and SOD enzymes increased in the oysters exposed to PHE at the control pH (8.2), but at a lower pH values, this activation was suppressed, and no changes were observed in the G6PDH activity and MDA levels. Biotransformation genes showed better responses after 24 h, and antioxidant-coding genes after 96 h, along with the activities of antioxidant enzymes (SOD, CAT), probably because biotransformation of PHE increases the generation of reactive oxygen species. The lack of change in MDA levels suggests that antioxidant modulation efficiently prevented oxidative stress. The effect of pH on the responses to PHE exposure should be taken into account before using these and any other genes as potential molecular biomarkers for PHE exposure.

Continue reading ‘Stress responses in Crassostrea gasar exposed to combined effects of acute pH changes and phenanthrene’

Legacy of multiple stressors: responses of gastropod larvae and juveniles to ocean acidification and nutrition

Ocean acidification poses a significant threat to calcifying invertebrates by negatively influencing shell deposition and growth. An organism’s performance under ocean acidification is not determined by the susceptibility of one single life-history stage, nor is it solely controlled by the direct physical consequences of ocean acidification. Shell development by one life-history stage is sometimes a function of the pH or pCO2 levels experienced during earlier developmental stages. Furthermore, environmental factors such as access to nutrition can buffer organismal responses of calcifying invertebrates to ocean acidification, or they can function as a co-occurring stressor when access is low. We reared larvae and juveniles of the planktotrophic marine gastropod Crepidula fornicata through combined treatments of nutritional stress and low pH, and we monitored how multiple stressors endured during the larval stage affected juvenile performance. Shell growth responded non-linearly to decreasing pH, significantly declining between pH 7.6 and pH 7.5 in larvae and juveniles. Larval rearing at pH 7.5 reduced juvenile growth as a carryover effect. Larval rearing at pH 7.6 reduced subsequent juvenile growth despite the absence of a negative impact on larval growth, demonstrating a latent effect. Low larval pH magnified the impact of larval nutritional stress on competence for metamorphosis and increased carryover effects of larval nutrition on juvenile growth. Trans-life-cycle effects of larval nutrition were thus modulated by larval exposure to ocean acidification.

Continue reading ‘Legacy of multiple stressors: responses of gastropod larvae and juveniles to ocean acidification and nutrition’

Characterization of Pacific oyster Crassostrea gigas proteomic response to natural environmental differences

Global climate change is rapidly altering coastal marine ecosystems that are important for food production. A comprehensive understanding of how organisms will respond to these complex environmental changes can come only from observing and studying species within their natural environment. To this end, the effects of environmental drivers—pH, dissolved oxygen content, salinity, and temperature—on Pacific oyster Crassostrea gigas physiology were evaluated in an outplant experiment. Sibling juvenile oysters were outplanted to eelgrass and unvegetated habitat at 5 different estuarine sites within the Acidification Nearshore Monitoring Network in Washington State, USA, to evaluate how regional environmental drivers influence molecular physiology. Within each site, we also determined if eelgrass presence, which buffered pH conditions, changed the oysters’ expressed proteome. A novel, 2-step, gel-free proteomic approach was used to identify differences in protein abundance in C. gigas ctenidia tissue after a 29 d outplant by (1) identifying proteins in a data-independent acquisition survey step and (2) comparing relative quantities of targeted environmental response proteins using selected reaction monitoring. While there was no difference in protein abundance detected between habitats or among sites within Puget Sound, C. gigas outplanted at Willapa Bay had significantly higher abundances of antioxidant enzymes and molecular chaperones. Environmental factors at Willapa Bay, such as higher average temperature, may have driven this protein abundance pattern. These findings generate a suite of new hypotheses for lab and field experiments to compare the effects of regional conditions on physiological responses of marine invertebrates.

Continue reading ‘Characterization of Pacific oyster Crassostrea gigas proteomic response to natural environmental differences’

Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida

Epigenetic analyses constitute an emerging approach for better understanding of the mechanisms underlying environmental responses and their role during acclimatization and adaptation across diverse ecosystems. The expansion of environmental epigenetic studies to a broader range of ecologically and environmentally relevant organisms will enhance the capability to forecast ecological and evolutionary processes, as well as to facilitate a retrospective assessment of stress exposures in biomonitor organisms through “epigenetic footprinting” analyses. With such purpose, the present study monitored spatial and temporal variation in abiotic parameters (temperature, salinity, pH, and horizontal visibility) over a 2-y period in a mangrove ecosystem located in North Biscayne Bay (North Miami, FL). The obtained data were subsequently compared with epigenetic modifications (global genome-wide DNA methylation levels) in the flat tree oyster Isognomon alatus, used as a sentinel model organism across experimental sites. The obtained results revealed a certain level of seasonality in temporal DNA methylation patterns, which seem to be primarily associated with changes in temperature and horizontal visibility. These results constitute the first long-term study combining spatial and temporal epigenetic analyses in a marine organism in its natural environment, laying the initial groundwork to assess the biomonitoring potential of environmental epigenetic analyses.

Continue reading ‘Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida’

The dynamic ocean acidification manipulation experimental system: Separating carbonate variables and simulating natural variability in laboratory flow‐through experiments

Carbonate chemistry variables such as PCO2, pH, and mineral saturation state (Ω) are commonly thought of as covarying in open‐ocean settings but have decoupled over geologic time‐scales and among modern dynamic coastal margins and estuaries. Predicting responses of vulnerable coastal organisms to past, present, and future ocean acidification (OA) scenarios requires the empirical identification of organismal sensitivity thresholds to individual carbonate chemistry parameters. Conversely, most OA experiments involve chemistry manipulations that result in covariance of carbonate system variables. We developed the Dynamic Ocean Acidification Manipulation Experimental System (DOAMES)—a feed‐forward, flow‐through carbonate chemistry control system capable of decoupling PCO2, pH, or Ω by independently manipulating total alkalinity (TAlk) and total inorganic carbon (TCO2). DOAMES proof‐of‐concept can manipulate source seawater with stable or variable carbonate chemistry and produce experimental treatments with constant and dynamic carbonate chemistry regimes. The combination of dynamic input and output allows for offset treatments that impose a ΔPCO2 on naturally variable conditions. After overcoming several operational challenges, DOAMES is capable of simultaneously generating three different experimental treatments within 1% ± 1% of TCO2 and TAlk targets. The achieved precision and accuracy resulted in the successful decoupling of pH and ΩAr in five trials. We tested the viability of sensitive bivalve embryos raised in DOAMES‐manipulated seawater and found no difference in development when compared to the control, demonstrating DOAMES suitability for organismal studies. DOAMES provides a novel tool to evaluate organismal effects of exposure to decoupled carbonate system variables and to past, current, and future carbonate chemistry scenarios.

Continue reading ‘The dynamic ocean acidification manipulation experimental system: Separating carbonate variables and simulating natural variability in laboratory flow‐through experiments’

Multiple stressor effects on macrobenthic communities in Corpus Christi Bay, Texas, U.S.A.

At any moment in nature, organisms are likely being exposed to multiple stressors, the effects of which are difficult to separate. Often, however, environmental stressors are considered on an individual basis. In southeastern Corpus Christi Bay, TX, declines in benthic macrofaunal community abundance, biomass, diversity, species richness, and species evenness have largely been attributed to the occurrence of hypoxia, a condition of low dissolved oxygen (DO). This study proposes that multiple stressors contribute to these observed benthic macrofaunal declines in southeastern Corpus Christi Bay. Therefore, a 30-year time series of water quality data (salinity, temperature, DO, pH, phosphate, ammonium, nitrite+nitrate, sulfate) and benthic community data (abundance, biomass, species richness, species evenness) was analyzed to describe 1) water quality dynamics of the region and 2) relationships between water quality dynamics and benthic macrofaunal response. Principal component analysis indicated that a large variability in the water quality dataset (63%) could be summarized by three principal components representing a multiple stressor index, a nutrient index, and an acidification index. Seasonality was found to be confounded with the multiple stressor index but not the nutrient or acidification indexes. Spearman rank-order correlations indicated both the multiple stressor and acidification indexes were inversely related to benthic macrofaunal community abundance, biomass, and species richness. A stepwise multiple linear regression analysis on individual water quality variables specified DO, and possibly temperature, to be leading explanatory variables for predicting benthic abundance. Temperature, pH, and nitrite+nitrate were indicated as leading explanatory variables for predicting benthic biomass. Temperature was indicated to be the only leading explanatory variable for predicting species richness. Results demonstrate that multiple stressors, including high temperature, high salinity, and low DO concentrations, are collectively acting on benthic communities in southeastern Corpus Christi Bay.

Continue reading ‘Multiple stressor effects on macrobenthic communities in Corpus Christi Bay, Texas, U.S.A.’

Dose-dependence and small-scale variability in responses to ocean acidification during squid, Doryteuthis pealeii, development

Coastal squids lay their eggs on the benthos, leaving them to develop in a dynamic system that is undergoing rapid acidification due to human influence. Prior studies have broadly investigated the impacts of ocean acidification on embryonic squid, but have not addressed the thresholds at which these responses occur or their potential variability. We raised squid, Doryteuthis pealeii (captured in Vineyard Sound, Massachusetts, USA: 41°23.370’N 70°46.418′W), eggs in three trials across the breeding season (May–September, 2013) in a total of six chronic pCO2 exposures (400, 550, 850, 1300, 1900, and 2200 ppm). Hatchlings were counted and subsampled for mantle length, yolk volume, hatching time, hatching success, and statolith morphology. New methods for analysis of statolith shape, rugosity, and surface degradation were developed and are presented (with code). Responses to acidification (e.g., reduced mantle lengths, delayed hatching, and smaller, more degraded statoliths) were evident at ~ 1300 ppm CO2. However, patterns of physiological response and energy management, based on comparisons of yolk consumption and growth, varied among trials. Interactions between pCO2 and hatching day indicated a potential influence of exposure time on responses, while interactions with culture vessel highlighted the substantive natural variability within a clutch of eggs. While this study is consistent with, and expands upon, previous findings of sensitivity of the early life stages to acidification, it also highlights the plasticity and potential for resilience in this population of squid.

Continue reading ‘Dose-dependence and small-scale variability in responses to ocean acidification during squid, Doryteuthis pealeii, development’


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Ocean acidification in the IPCC AR5 WG II

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