Posts Tagged 'molecular biology'

Corals adapted to extreme and fluctuating seawater pH increase calcification rates and have unique symbiont communities

Ocean acidification (OA) is a severe threat to coral reefs mainly by reducing their calcification rate. Identifying the resilience factors of corals to decreasing seawater pH is of paramount importance to predict the survivability of coral reefs in the future. This study compared corals adapted to variable pH (i.e., 7.23-8.06 pH units) from the semi-enclosed lagoon of Bouraké, New Caledonia, to corals adapted to more stable seawater pH (i.e., 7.90-8.18 pH units). In a 100-day aquarium experiment, we examined the physiological response and genetic diversity of Symbiodiniaceae from three coral species ( Acropora tenuis , Montipora digitata and Porites sp.) from both sites under three stable pH conditions (i.e., 8.11, 7.76, 7.54 pH units) and fluctuating pH conditions (i.e., between 7.56 and 8.07 pH units). Bouraké corals consistently exhibited higher growth rates than corals from the stable pH environment, with specific ITS2 intragenomic variant profiles. While OA generally decreased coral calcification by ca. 16%, Bouraké coralsshowed higher growth rates (21 to 93% increase, depending on species with all pH conditions pooled) than those from the stable pH environment. This superior performance coincided with divergent ITS2-like profiles with better consistency for both variable and low pH conditions. This response was not gained by corals from the more stable environment exposed to variable pH during the four-month experiment, suggesting that such a kind of plasticity is time dependent. Future long-term experiments should address the exposure duration required to confer fitness benefits for sustained calcification, hopefully fast enough to cope with the ongoing rapid OA.

Continue reading ‘Corals adapted to extreme and fluctuating seawater pH increase calcification rates and have unique symbiont communities’

Molecular features associated with resilience to ocean acidification in the northern quahog, Mercenaria mercenaria

The increasing concentration of CO2 in the atmosphere and resulting flux into the oceans will further exacerbate acidification already threatening coastal marine ecosystems. The subsequent alterations in carbonate chemistry can have deleterious impacts on many economically and ecologically important species including the northern quahog (Mercenaria mercenaria). The accelerated pace of these changes requires an understanding of how or if species and populations will be able to acclimate or adapt to such swift environmental alterations. Thus far, studies have primarily focused on the physiological effects of ocean acidification (OA) on M. mercenaria, including reductions in growth and survival. However, the molecular mechanisms of resilience to OA in this species remains unclear. Clam gametes were fertilized under normal pCO2 and reared under acidified (pH ~ 7.5, pCO2 ~ 1200 ppm) or control (pH ~ 7.9, pCO2 ~ 600 ppm) conditions before sampled at 2 days (larvae), 32 days (postsets), 5 and 10 months (juveniles) and submitted to RNA and DNA sequencing to evaluate alterations in gene expression and genetic variations. Results showed significant shift in gene expression profiles among clams reared in acidified conditions as compared to their respective controls. At 10 months of exposure, significant shifts in allele frequency of single nucleotide polymorphisms (SNPs) were identified. Both approaches highlighted genes coding for proteins related to shell formation, bicarbonate transport, cytoskeleton, immunity/stress, and metabolism, illustrating the role these pathways play in resilience to OA.

Continue reading ‘Molecular features associated with resilience to ocean acidification in the northern quahog, Mercenaria mercenaria’

Transcriptome analysis of hepatopancreas in penaeus monodon under acute low pH stress

The decrease of seawater pH can affect the metabolism, acid-base balance, immune response and immunoprotease activity of aquatic animals, leading to aquatic animal stress, impairing the immune system of aquatic animals and weakening disease resistance, etc. In this study, we performed high-throughput sequencing analysis of the hepatopancreas transcriptome library of low pH stress penaeus monodon, and after sequencing quality control, a total of 43488612–56271828 Clean Reads were obtained, and GO annotation and KEGG pathway enrichment analysis were performed on the obtained Clean Reads, and a total of 395 DEGs were identified. we mined 10 differentially expressed and found that they were significantly enriched in the Metabolic pathways (ko01100), Biosynthesis of secondary metabolites (ko01110), Nitrogen metabolism (ko00910) pathways, such as PIGA, DGAT1, DGAT2, UBE2E on Metabolic pathways; UGT, GLT1, TIM genes on Biosynthesis of secondary metabolites; CA, CA2, CA4 genes on Nitrogen metabolism, are involved in lipid metabolism, induction of oxidative stress and inflammation in the muscular body of spot prawns. These genes play an important role in lipid metabolism, induction of oxidative stress and inflammatory response in the muscle of the shrimp. In summary, these genes provide valuable reference information for future breeding of low pH-tolerant shrimp.

Continue reading ‘Transcriptome analysis of hepatopancreas in penaeus monodon under acute low pH stress’

Unraveling cellular and molecular mechanisms of acid stress tolerance and resistance in marine species: new frontiers in the study of adaptation to ocean acidification

Graphical abstract

Highlights

  • OA poses a threat to marine life, although some taxa can tolerate low seawater pH.
  • Different responses at cellular and molecular level observed in marine organisms
  • Role of ABC transporter proteins towards acid stress tolerance and resistance
  • Understanding cellular mechanisms of acid stress tolerance to unravel OA impacts

Abstract

Since the industrial revolution, fossil fuel combustion has led to a 30 %-increase of the atmospheric CO2 concentration, also increasing the ocean partial CO2 pressure. The consequent lowered surface seawater pH is termed ocean acidification (OA) and severely affects marine life on a global scale. Cellular and molecular responses of marine species to lowered seawater pH have been studied but information on the mechanisms driving the tolerance of adapted species to comparatively low seawater pH is limited. Such information may be obtained from species inhabiting sites with naturally low water pH that have evolved remarkable abilities to tolerate such conditions. This review gathers information on current knowledge about species naturally facing low water pH conditions and on cellular and molecular adaptive mechanisms enabling the species to survive under, and even benefit from, adverse pH conditions. Evidences derived from case studies on naturally acidified systems and on resistance mechanisms will guide predictions on the consequences of future adverse OA scenarios for marine biodiversity.

Continue reading ‘Unraveling cellular and molecular mechanisms of acid stress tolerance and resistance in marine species: new frontiers in the study of adaptation to ocean acidification’

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.

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

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.

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

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.

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

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.

Continue reading ‘Calmodulin regulates the calcium homeostasis in mantle of Crassostrea gigas under ocean acidification’

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.

Continue reading ‘Transcriptomic stability or lability explains sensitivity to climate stressors in coralline algae’

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.

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

Intestinal microbiota perturbations in the gastropod Trochus niloticus concurrently exposed to ocean acidification and environmentally relevant concentrations of sulfamethoxazole

Graphical abstract.

Highlights

  • Exposure to OA leads to the microbiota dysbiosis in the intestine of T. niloticus.
  • Exposure to SMX barely affected the intestinal microbiota of T. niloticus.
  • Exposure to SMX accelerated spread of sulfonamide ARGs.

Abstract

Ocean acidification (OA) and antibiotic pollution pose severe threats to the fitness of keystone species in marine ecosystems. However, the combined effects of OA and antibiotic pollution on the intestinal microbiota of marine organisms are still not well known. In this study, we exposed the herbivorous gastropod Trochus niloticus, a keystone species to maintains the stability of coral reef ecosystems, to acidic seawater (pH 7.6) and/or sulfamethoxazole (SMX, 100 ng/L, 1000 ng/L) for 28 days and determined their impacts on (1) the accumulation of SMX in the intestine of T. niloticus; (2) the characteristics of the intestinal microbiota in T. niloticus; (3) the relative abundances of sulfonamide resistance genes (i.e., sul1 and sul2) and intI1 in the intestinal microbiota of T. niloticus. Our results show that OA exposure leads to dramatic microbiota dysbiosis in the intestine of T. niloticus, including changes in bacterial community diversity and structure, decreased abundances of dominant species, existences of characteristic taxa, and altered functional predictions. In addition, SMX exposure at environmentally relevant concentrations had little effect on the intestinal microbiota of T. niloticus, whether in isolation or in combination with OA. However, after exposure to the higher SMX concentration (1000 ng/L), the accumulation of SMX in the intestine of T. niloticus could induce an increase in the copies of sul2 in the intestinal microbiota. These results suggest that the intestinal health of T. niloticus might be affected by OA and SMX, which might lead to fitness loss of the keystone species in coral reef ecosystems.

Continue reading ‘Intestinal microbiota perturbations in the gastropod Trochus niloticus concurrently exposed to ocean acidification and environmentally relevant concentrations of sulfamethoxazole’

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.

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

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.

Continue reading ‘Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium’

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.

Continue reading ‘Epigenetic-associated phenotypic plasticity of the ocean acidification-acclimated edible oyster in the mariculture environment’

Ocean acidification alters the acute stress response of a marine fish

Graphical abstract.

Highlights

  • Ocean acidification (OA) impacts the physiological stress response of European sea bass.
  • Post-stress return to basal plasma cortisol and glucose levels is delayed under OA.
  • This delay is associated to alteration of hypothalamic neurotransmitters pattern.
  • Motor activity is reduced during recovery from stress in fish under OA conditions.

Abstract

The absorption of anthropogenic carbon dioxide from the atmosphere by oceans generates rapid changes in seawater carbonate system and pH, a process termed ocean acidification. Exposure to acidified water can impact the allostatic load of marine organism as the acclimation to suboptimal environments requires physiological adaptive responses that are energetically costly. As a consequence, fish facing ocean acidification may experience alterations of their stress response and a compromised ability to cope with additional stress, which may impact individuals’ life traits and ultimately their fitness. In this context, we carried out an integrative study investigating the impact of ocean acidification on the physiological and behavioral stress responses to an acute stress in juvenile European sea bass. Fish were long term (11 months) exposed to present day pH/CO2 condition or acidified water as predicted by IPCC “business as usual” (RCP8.5) scenario for 2100 and subjected to netting stress (fish transfer and confinement test). Fish acclimated to acidified condition showed slower post stress return to plasma basal concentrations of cortisol and glucose. We found no clear indication of regulation in the central and interrenal tissues of the expression levels of gluco- and mineralocorticoid receptors and corticoid releasing factor. At 120 min post stress, sea bass acclimated to acidified water had divergent neurotransmitters concentrations pattern in the hypothalamus (higher serotonin levels and lower GABA and dopamine levels) and a reduction in motor activity. Our experimental data indicate that ocean acidification alters the physiological response to acute stress in European sea bass via the neuroendocrine regulation of the corticotropic axis, a response associated to an alteration of the motor behavioral profile. Overall, this study suggests that behavioral and physiological adaptive response to climate changes related constraints may impact fish resilience to further stressful events.

Continue reading ‘Ocean acidification alters the acute stress response of a marine fish’

The differential ability of two species of seagrass to use carbon dioxide and bicarbonate and their modelled response to rising concentrations of inorganic carbon

Seagrass meadows are one of the most productive ecosystems on the planet, but their photosynthesis rate may be limited by carbon dioxide but mitigated by exploiting the high concentration of bicarbonate in the ocean using different active processes. Seagrasses are declining worldwide at an accelerating rate because of numerous anthropogenic pressures. However, rising ocean concentrations of dissolved inorganic carbon, caused by increases in atmospheric carbon dioxide, may benefit seagrass photosynthesis. Here we compare the ability of two seagrass from the Mediterranean Sea, Posidonia oceanica (L.) Delile and Zostera marina L., to use carbon dioxide and bicarbonate at light saturation, and model how increasing concentrations of inorganic carbon affect their photosynthesis rate. pH-drift measurements confirmed that both species were able to use bicarbonate in addition to carbon dioxide, but that Z. marina was more effective than P. oceanica. Kinetic experiments showed that, compared to Z. marinaP. oceanica had a seven-fold higher affinity for carbon dioxide and a 1.6-fold higher affinity for bicarbonate. However, the maximal rate of bicarbonate uptake in Z. marina was 2.1-fold higher than in P. oceanica. In equilibrium with 410 ppm carbon dioxide in the atmosphere, the modelled rates of photosynthesis by Z. marina were slightly higher than P. oceanica, less carbon limited and depended on bicarbonate to a greater extent. This greater reliance by Z. marina is consistent with its less depleted 13C content compared to P. oceanica. Modelled photosynthesis suggests that both species would depend on bicarbonate alone at an atmospheric carbon dioxide partial pressure of 280 ppm. P. oceanica was projected to benefit more than Z. marina with increasing atmospheric carbon dioxide partial pressures, and at the highest carbon dioxide scenario of 1135 ppm, would have higher rates of photosynthesis and be more saturated by inorganic carbon than Z. marina. In both species, the proportional reliance on bicarbonate declined markedly as carbon dioxide concentrations increased and in P. oceanica carbon dioxide would become the major source of inorganic carbon.

Continue reading ‘The differential ability of two species of seagrass to use carbon dioxide and bicarbonate and their modelled response to rising concentrations of inorganic carbon’

Genetic architecture of behavioural resilience to ocean acidification

Genetic variation is essential for adaptation to rapid environmental changes. Identifying genetic variation associated with climate-change related phenotypes is therefore the necessary first step towards predictive models of genomic vulnerability.

Here we used a whole-genome scan to identify candidate genetic variants associated with differences in behavioural resilience to ocean acidification in a coral reef fish. We identified three genomic regions that differ between individuals that are behaviourally tolerant compared with behaviourally sensitive to elevated CO2. These include a dopamine receptor (drd4rs), cadherin related family member 5-like (cdhr5l), Synapse-associated protein 1 (syap1), and GRB2 Associated Regulator of MAPK1 Subtype 2 (garem2), which have previously been found to modify behaviour related to boldness, novelty seeking, and learning in other species, and differ between behaviourally tolerant and sensitive individuals.

Consequently, the identified genes are promising candidates in the search of the genetic underpinnings and adaptive potential of behavioural resilience to ocean acidification in fishes.

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Transcriptomic analysis reveals distinct mechanisms of adaptation of a polar picophytoplankter under ocean acidification conditions

Graphical abstract.

Highlights

  • Increase of carbon dioxide emission to the atmosphere acidifies the ocean.
  • Ocean acidification drives the growth of a small green phytoplankter (picochlorophyte).
  • Picochlorophytes exhibit distinct metabolism compared to other polar phytoplankton.
  • Genes related to ribosomal proteins, amino acid synthesis, RNA post-transcriptional modification, nitrogen assimilation, molecular chaperones, light harvesting complexes, pigment synthesis, were found to be differentially expressed under future predicted CO2 levels.

Abstract

Human emissions of carbon dioxide are causing irreversible changes in our oceans and impacting marine phytoplankton, including a group of small green algae known as picochlorophytes. Picochlorophytes grown in natural phytoplankton communities under future predicted levels of carbon dioxide have been demonstrated to thrive, along with redistribution of the cellular metabolome that enhances growth rate and photosynthesis. Here, using next-generation sequencing technology, we measured levels of transcripts in a picochlorophyte Chlorella, isolated from the sub-Antarctic and acclimated under high and current ambient CO2 levels, to better understand the molecular mechanisms involved with its ability to acclimate to elevated CO2. Compared to other phytoplankton taxa that induce broad transcriptomic responses involving multiple parts of their cellular metabolism, the changes observed in Chlorella focused on activating gene regulation involved in different sets of pathways such as light harvesting complex binding proteins, amino acid synthesis and RNA modification, while carbon metabolism was largely unaffected. Triggering a specific set of genes could be a unique strategy of small green phytoplankton under high CO2 in polar oceans.

Continue reading ‘Transcriptomic analysis reveals distinct mechanisms of adaptation of a polar picophytoplankter under ocean acidification conditions’

Effects of ocean acidification and tralopyril on bivalve biomineralization and carbon cycling: a study of the Pacific Oyster (Crassostrea gigas)

Graphical abstract.

Highlights

  • The toxicity of combined exposure fell in between tralopyril and OA alone.
  • Tralopyril and/or OA activates stress defense and interferes with energy metabolism.
  • Tralopyril and/or OA affects bivalve biomineralization and marine carbon cycling.

Abstract

The combined effects of emerging pollutants and ocean acidification (OA) on marine organisms and marine ecosystems have attracted increasing attention. However, the combined effects of tralopyril and OA on marine organisms and marine ecosystems remain unclear. In this study, Crassostrea gigas (C. gigas) were exposed to tralopyril (1 μg/L) and/or OA (PH = 7.7) for 21 days and a 14-day recovery acclimation. To investigate the stress response and potential molecular mechanisms of C. gigas to OA and tralopyril exposure alone or in combination, as well as the effects of OA and/or tralopyril on bivalve biomineralization and marine carbon cycling. The results showed that the combined toxicity was between that of acidification and tralopyril alone. Single or combined exposure activated the general stress defense responses of C. gigas mantle, affected energy metabolism and biomineralization of the organism and the carbon cycle of the marine ecosystem. Moreover, acidification-induced and tralopyril-induced toxicity showed potential recoverability at molecular and biochemical levels. This study provides a new perspective on the molecular mechanisms of tralopyril toxicity to bivalve shellfish and reveals the potential role of tralopyril and OA on marine carbon cycling.

Continue reading ‘Effects of ocean acidification and tralopyril on bivalve biomineralization and carbon cycling: a study of the Pacific Oyster (Crassostrea gigas)’

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