Temperature-dependent stress response in oysters, Crassostrea virginica: pollution reduces temperature tolerance in oysters

Mytilus galloprovincialis: A valuable bioindicator species for understanding the effects of diclofenac under warming conditions

Drugs are chemical compounds used to treat and improve organic dysfunctions caused by diseases. These include analgesics, antibiotics, antidepressants, and antineoplastics. They can enter aquatic environments through wastewater streams, where their physico-chemical properties allow metabolites to distribute and accumulate. Current climate change and associated extreme weather events may significantly impact these substances' toxicity and aquatic organisms' sensitivity. Among the chemicals present in aquatic environments is the non-steroidal anti-inflammatory drug diclofenac (DIC), which the EU monitors due to its concentration levels. This study investigated the influence of temperature (control at 17 °C vs. 21 °C) on the effects of DIC (0 μg/L vs. 1 μg/L) in the mussel species Mytilus galloprovincialis. Significant results were observed between 17 and 21 °C. Organisms exposed to the higher temperature showed a decrease in several parameters, including metabolic capacity and detoxification, particularly with prolonged exposure. However, in some parameters, after 21 days, the M. galloprovincialis showed no differences from the control, indicating adaptation to the stress. The results of this study confirm that DIC concentrations in the environment, particularly when combined with increased temperatures, can produce oxidative stress and adversely affect M. galloprovincialis biochemical and physiological performance. This study also validates this species as a bioindicator for assessing environmental contamination with DIC. Beyond its direct impact on aquatic organisms, the presence of pharmaceuticals like DIC in the environment highlights the interconnectedness of human, animal, and ecosystem health, underscoring the One Health approach to understanding and mitigating environmental pollution.

Impacts of elevated temperature, decreased salinity and microfibers on the bioenergetics and oxidative stress in eastern oyster, Crassostrea virginica

Projected increases in temperature and decreases in salinity associated with global climate change will likely have detrimental impacts on eastern oyster, Crassostrea virginica, as these variables can influence physiological processes in these keystone species. We set out to determine how the interactive effects of temperature (20 °C or 27 °C) and/or salinity (27‰ or 17‰) impacted the energetic reserves, aerobic and anaerobic metabolism, and changes to oxidative stress or total antioxidant potential as a consequence of an altered environment over a 21-day exposure. Gill and adductor muscle were used to quantify changes in total glycogen and lipid content, Electron Transport System and Citrate Synthase activities, Malate Dehydrogenase activity, Protein Carbonyl formation, lipid peroxidation, and total antioxidant potential. A second exposure was performed to determine if these environmental factors influenced the ingestion of microfibers, which are now one of the leading forms of marine debris. Elevated temperature and the combination of elevated temperature and decreased salinity led to an overall decline in oyster mass, which was exacerbated by the presence of microfibers. Changes in metabolism and oxidative stress were largely influenced by time, but exposure to elevated temperature, decreased salinity, the combination of these stressors or exposure to microfibers had small impacts on oyster physiology and survival. Overall these studies demonstrate that oyster are fairly resilient to changes in salinity in short-term exposures, and elevations in temperature or temperature combined with salinity result in changes to the oyster energetic response, which can be further impacted by the presence of microfibers.

Metal nanoparticle-induced effects on green toads (Amphibia, Anura) under climate change: conservation implications

The toxicity of aluminum oxide (Al2O3), copper oxide (CuO), iron oxide (Fe3O4), nickel oxide (NiO), zinc oxide (ZnO), and titanium dioxide (TiO2) nanoparticles (NPs) on amphibians and their interaction with high temperatures, remain unknown. In this study, we investigated the survival, developmental, behavioral, and histological reactions of Bufotes viridis embryos and larvae exposed to different NPs for a duration of 10 days, using lethal concentrations (LC25%, LC50%, and LC75% mg/L) under both ambient (AT: 18 °C) and high (HT: 21 °C) temperatures. Based on LC, NiONPs > ZnONPs > CuONPs > Al2O3NPs > TiO2NPs > Fe3O4NPs showed the highest mortality at AT. A similar pattern was observed at HT, although mortality occurred at lower concentrations and Fe3O4NPs were more toxic than TiO2NPs. The results indicated that increasing concentrations of NPs significantly reduced hatching rates, except for TiO2NPs. Survival rates decreased, abnormality rates increased, and developmental processes slowed down, particularly for NiONPs and ZnONPs, under HT conditions. However, exposure to low concentrations of Fe3O4NPs for up to 7 days, CuONPs for up to 72 h, and NiO, ZnONPs, and TiO2NPs for up to 96 h did not have a negative impact on survival compared with the control group under AT. In behavioral tests with larvae, NPs generally induced hypoactivity at AT and hyperactivity at HT. Histological findings revealed liver and internal gill tissue lesions, and an increase in the number of melanomacrophage centers at HT. These results suggest that global warming may exacerbate the toxicity of metal oxide NPs to amphibians, emphasizing the need for further research and conservation efforts in this context.

Redox control of antioxidants, metabolism, immunity, and development at the core of stress adaptation of the oyster Crassostrea gigas to the dynamic intertidal environment

This review uses the marine bivalve Crassostrea gigas to highlight redox reactions and control systems in species living in dynamic intertidal environments. Intertidal species face daily and seasonal environmental variability, including temperature, oxygen, salinity, and nutritional changes. Increasing anthropogenic pressure can bring pollutants and pathogens as additional stressors. Surprisingly, C. gigas demonstrates impressive adaptability to most of these challenges. We explore how ROS production, antioxidant protection, redox signaling, and metabolic adjustments can shed light on how redox biology supports oyster survival in harsh conditions. The review provides (i) a brief summary of shared redox sensing processes in metazoan; (ii) an overview of unique characteristics of the C. gigas intertidal habitat and the suitability of this species as a model organism; (iii) insights into the redox biology of C. gigas, including ROS sources, signaling pathways, ROS-scavenging systems, and thiol-containing proteins; and examples of (iv) hot topics that are underdeveloped in bivalve research linking redox biology with immunometabolism, physioxia, and development. Given its plasticity to environmental changes, C. gigas is a valuable model for studying the role of redox biology in the adaptation to harsh habitats, potentially providing novel insights for basic and applied studies in marine and comparative biochemistry and physiology.

Effects of acute heat stress on haemato-biochemical parameters, oxidative resistance ability, and immune responses of hybrid yellow catfish (pelteobagrus fulvidraco × P. vachelli) juveniles

This study investigated the effect of heat stress on the physiological parameters, oxidation resistance ability and immune responses in juvenile hybrid yellow catfish. Heat stress group exposed to 35 °C and control to 28 °C. Blood and liver were sampled at different hours' post-exposure. Results showed that red blood cell (RBC), white blood cell (WBC) counts, Hemoglobin (HGB) levels and hematocrit (HCT) values increased significantly (P < 0.05) post-exposure to heat stress. This indicates the increase of cell metabolism. Serum alanine aminotransferase (ALT) and aspartate transaminase (AST) activities, total cholesterol (TC), total protein (TP), triglyceride (TG) and glucose increased significantly (P < 0.05) indicating the need to cope with stress and cell damage. Liver TC, TG, COR hormone, C3 complement increased significantly from 24 to 96 h. Heat stress mostly affects the hepatic antioxidant and immune resistance functions, resulting in increments of cortisol levels, lysozyme, superoxide dismutase (SOD), and catalase (CAT) enzyme activities. The increase of Malondialdehyde (MDA), alkaline phosphatase (AKP) indicate stimulation of the immune responses to protect the liver cells from damage. The decrease in Liver TP indicated liver impairment. Decrease in Glycogen content from 6 to 96 h indicated mobilization of more metabolites to cope with increased energy demand. Interestingly, results showed that heat stress trigged costly responses in the experimental fish like accelerated metabolism and deplete energy reserves, which could indirectly affect ability of fish to set up efficient long term defense responses against stress. These results provide insight into prevention and management of stress in juvenile hybrid yellow catfish.

Combined threats of climate change and contaminant exposure through the lens of bioenergetics

Organisms face energetic challenges of climate change in combination with suites of natural and anthropogenic stressors. In particular, chemical contaminant exposure has neurotoxic, endocrine-disrupting, and behavioral effects which may additively or interactively combine with challenges associated with climate change. We used a literature review across animal taxa and contaminant classes, but focused on Arctic endotherms and contaminants important in Arctic ecosystems, to demonstrate potential for interactive effects across five bioenergetic domains: (1) energy supply, (2) energy demand, (3) energy storage, (4) energy allocation tradeoffs, and (5) energy management strategies; and involving four climate change-sensitive environmental stressors: changes in resource availability, temperature, predation risk, and parasitism. Identified examples included relatively equal numbers of synergistic and antagonistic interactions. Synergies are often suggested to be particularly problematic, since they magnify biological effects. However, we emphasize that antagonistic effects on bioenergetic traits can be equally problematic, since they can reflect dampening of beneficial responses and result in negative synergistic effects on fitness. Our review also highlights that empirical demonstrations remain limited, especially in endotherms. Elucidating the nature of climate change-by-contaminant interactive effects on bioenergetic traits will build toward determining overall outcomes for energy balance and fitness. Progressing to determine critical species, life stages, and target areas in which transformative effects arise will aid in forecasting broad-scale bioenergetic outcomes under global change scenarios.

Are the consequences of lithium in marine clams enhanced by climate change?

Coastal areas, such as estuaries and coastal lagoons, are among the most endangered aquatic ecosystems due to the intense anthropogenic activities occurring in their vicinity. These areas are highly threatened by climate change-related factors as well as pollution, especially due to their limited water exchange. Ocean warming and extreme weather events, such as marine heatwaves and rainy periods, are some of the consequences of climate change, inducing alterations in the abiotic parameters of seawater, namely temperature and salinity, which may affect the organisms as well as the behaviour of some pollutants present in water. Lithium (Li) is an element widely used in several industries, especially in the production of batteries for electronic gadgets and electric vehicles. The demand for its exploitation has been growing drastically and is predicted a large increase in the coming years. Inefficient recycling, treatment and disposal results in the release of Li into the aquatic systems, the consequences of which are poorly understood, especially in the context of climate change. Considering that a limited number of studies exist about the impacts of Li on marine species, the present study aimed to assess the effects of temperature rise and salinity changes on the impacts of Li in clams (Venerupis corrugata) collected from the Ria de Aveiro (coastal lagoon, Portugal). Clams were exposed for 14 days to 0 μg/L of Li and 200 μg/L of Li, both conditions under different climate scenarios: 3 different salinities (20, 30 and 40) at 17 °C (control temperature); and 2 different temperatures (17 and 21 °C) at salinity 30 (control salinity). Bioconcentration capacity and biochemical alterations regarding metabolism and oxidative stress were investigated. Salinity variations had a higher impact on biochemical responses than temperature increase, even when combined with Li. The combination of Li with low salinity (20) was the most stressful treatment, provoking increased metabolism and activation of detoxification defences, suggesting possible imbalances in coastal ecosystems in response to Li pollution under extreme weather events. These findings may ultimately contribute to implement environmentally protective actions to mitigate Li contamination and preserve marine life.

Metal Exposure and Sex Shape the Fatty Acid Profile of Midges and Reduce the Aquatic Subsidy to Terrestrial Food Webs

Aquatic micropollutants can be transported to terrestrial systems and their consumers by emergent aquatic insects. However, micropollutants, such as metals, may also affect the flux of physiologically important polyunsaturated fatty acids (PUFAs). As certain PUFAs have been linked to physiological fitness and breeding success of terrestrial consumers, reduced fluxes from aquatic systems could affect terrestrial populations and food webs. We chronically exposed larvae of the aquatic insect Chironomus riparius to a range of environmentally relevant sediment contents of cadmium (Cd) or copper (Cu) in a 28-day microcosm study. Since elevated water temperatures can enhance metals' toxic effects, we used two temperature regimes, control and periodically elevated temperatures (heat waves) reflecting an aspect of climate change. Cd and Cu significantly reduced adult emergence by up to 95% and 45%, respectively, while elevated temperatures had negligible effects. Both metal contents were strongly reduced (∼90%) during metamorphosis. Furthermore, the chironomid FA profile was significantly altered during metamorphosis with the factors sex and metal exposure being relevant predictors. Consequently, fluxes of physiologically important PUFAs by emergent adults were reduced by up to ∼80%. Our results suggest that considering fluxes of physiologically important compounds, such as PUFAs, by emergent aquatic insects is important to understand the implications of aquatic micropollutants on aquatic-terrestrial meta-ecosystems.

Effects of elevated temperature on 8-OHdG expression in the American oyster (Crassostrea virginica): Induction of oxidative stress biomarkers, cellular apoptosis, DNA damage and γH2AX signaling pathways

Global temperature is increasing due to anthropogenic activities and the effects of elevated temperature on DNA lesions are not well documented in marine organisms. The American oyster (Crassostrea virginica, an edible and commercially important marine mollusk) is an ideal shellfish species to study oxidative DNA lesions during heat stress. In this study, we examined the effects of elevated temperatures (24, 28, and 32 °C for one-week exposure) on heat shock protein-70 (HSP70, a biomarker of heat stress), 8‑hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of pro-mutagenic DNA lesion), double-stranded DNA (dsDNA), γ-histone family member X (γH2AX, a molecular biomarker of DNA damage), caspase-3 (CAS-3, a key enzyme of apoptotic pathway) and Bcl-2-associated X (BAX, an apoptosis regulator) protein and/or mRNA expressions in the gills of American oysters. Immunohistochemical and qRT-PCR results showed that HSP70, 8-OHdG, dsDNA, and γH2AX expressions in gills were significantly increased at high temperatures (28 and 32 °C) compared with control (24°C). In situ TUNEL analysis showed that the apoptotic cells in gill tissues were increased in heat-exposed oysters. Interestingly, the enhanced apoptotic cells were associated with increased CAS-3 and BAX mRNA and/or protein expressions, along with 8-OHdG levels in gills after heat exposure. Moreover, the extrapallial (EP) fluid (i.e., extracellular body fluid) protein concentrations were lower; however, the EP glucose levels were higher in heat-exposed oysters. Taken together, these results suggest that heat shock-driven oxidative stress alters extracellular body fluid conditions and induces cellular apoptosis and DNA damage, which may lead to increased 8-OHdG levels in cells/tissues in oysters.

Temperature, salinity and body-size influences depuration of heavy metals in commercially important edible bivalve molluscs of India

The effect of temperature, salinity and body-size on depuration of naturally accumulated heavy metals in clams, mussels and oysters harvested from Ashtamudi and Vembanad estuaries of Kerala, India were investigated using a static depuration system. Before depuration, the concentrations of heavy metals such as Ni, Co, Fe, Mn, Cu, Pb and Zn were analysed and it was found that the Fe, Zn, Cu and Pb contents in all the three bivalve molluscs were above the prescribed limit which poses a significant health risk to bivalve consumers. To protect consumer food safety, depuration experiments were conducted at varying temperatures, salinities and body-sizes. The clams, mussels and oysters depurated under the room temperature depuration system (RTDS) showed a better reduction of heavy metals compared with low-temperature depuration system (LTDS). ANOVA showed clams and mussels depurated at RTDS significantly (p < 0.05) reduced the heavy metals than LTDS. However, there was no significant (p > 0.05) difference in oysters between RTDS and LTDS. Further, clams and mussels depurated at low salinity (15-psμ) showed high resistance against Pb reduction. But, all the heavy metals, particularly, Pb, Fe, Zn and Cu were effectively removed at higher salinity depuration (25-psμ and 35-psμ). Moreover, irrespective of the body-size of clams, mussels and oysters used for depuration, a significant (p < 0.05) reduction in all metals (Ni, Co, Fe, Mn, Zn, Pb and Cu) was observed. Relatively, the medium-size bivalves showed higher reductions compared to small-size bivalves. Based on the experiments conducted, we recommend 48 h depuration using the static system under room temperature (30 ± 1 °C) with a salinity range of (25-35 psμ) using medium-size bivalves (clam>30 mm; mussel >45 mm, and oyster >65 mm length) as optimum conditions for producing safe bivalves for consumption in the tropics.

Drivers of copper sensitivity in copepods: A meta-analysis of LC50s

Copper is both an essential trace element and a potent pesticide. The use of copper as an antifoulant has increased in the last decades in line with the expanding aquaculture and shipping industries. In aquatic environments, it also affects non-target taxa. One of which are copepods, which constitute the central link in the marine food web. Despite their ecological importance, there are no systematic reviews of the lethal concentration range and drivers of copper toxicity in this taxon. Here, we combined literature data from 31 peer-reviewed articles recording the Lethal Concentration 50 (LC50) for copper in copepods and the experiments' respective environmental, developmental, and taxonomic parameters. The LC50 is a traditional endpoint for toxicity testing used in standardized toxicity testing and many ecological studies. In total, we were able to extract 166 LC50 entries. The variability in the metadata allowed for a general analysis of the drivers of copper sensitivity in copepods. Using a generalized additive modeling approach, we find that temperature increases copper toxicity when above approximately 25℃. Counter to our expectations; salinity does not influence copper sensitivity across copepod species. Unsurprisingly, nauplii are more susceptible to copper exposure than adult copepods, and benthos-associated harpacticoids are less sensitive to copper than pelagic calanoids. Our final model can predict sensible specific-specific copper concentrations for future experiments, thus giving an informed analytical approach to range testing in future dose-response experiments. Our model can also potentially improve ecological risk assessment by accounting for environmental differences. The approach can be applied to other toxicants and taxa, which may reveal underlying patterns otherwise obscured by taxonomic and experimental variability.

In-situ microplastic egestion efficiency of the eastern oyster Crassostrea virginica

Microplastics (MP) are a pervasive environmental pollutant that enter coastal water bodies, posing an ingestion risk to marine biota. This study quantified the ability of the Eastern oyster (Crassostrea virginica) to egest MP in-situ in their biodeposits - feces and pseudofeces. Oysters of all sizes were able to egest environmental MP at a mean rate of 1 MP per 1 h through feces, and 1 MP per 2 h through pseudofeces. Smaller C. virginica were more efficient at egesting MP, and efficiency decreased by 0.8% per 1-g increase in tissue weight, with C. virginica of harvestable size being much less efficient. These findings are of relevance to resource managers for C. virginica populations as it further contributes to our understanding of MP accumulation in wild populations and has implications for not just C. virginica but also for their consumers.

Does the environmental history of mussels have an effect on the physiological response to additional stress under experimental conditions?

Expected effects on marine biota of the ongoing elevation of water temperature and high latitudes is of major concern when considering the reliability of coastal ecosystem production. To compare the capacity of coastal organisms to cope with a temperature increase depending on their environmental history, responses of adult blue mussels (Mytilus spp.) taken from two sites differentially exposed to chemical pollution were investigated during an experimental exposure to a thermal stress. Immune parameters were notably altered by extreme warming and transcriptional changes for a broad selection of genes were associated to the temperature increase following a two-step response pattern. Site-specific responses suggested an influence of environmental history and support the possibility of a genetic basis in the physiological response. However no meaningful difference was detected between the response of hybrids and M galloprovincialis. This study brings new information about the capacity of mussels to cope with the ongoing elevation of water temperature in these coastal ecosystems.

Temporal and spatial characteristics of PAHs in oysters from the Pearl River Estuary, China during 2015-2020

Estuary connects the inland freshwater and open seawater, which may become a sink for pollutants from land-derived outflows, especially for persistent organic pollutants (e.g., polycyclic aromatic hydrocarbons, PAHs). Due to complex fluctuation in estuary, it's difficult to achieve a comprehensive assessment of the pollution characteristics by grabbed environmental samples. Oysters serve as efficient biomonitors of pollution status in highly dynamic and anthropogenically impacted estuaries, like the Pearl River Estuary (PRE), South China. Here, we investigated the annual, seasonal, and spatial variations of PAHs in the soft tissues of oysters from the PRE over the last six years (2015-2020) and quantitatively analyzed the influence of environmental factors on PAH occurrence in the oysters. The concentrations of Σ₁₅PAH in oysters ranged from 74 to 1164 (337 ± 218) ng/g dry wt., with a peak occurrence in 2017. Highly seasonal and geographical variations in PAH pollution were documented in the PRE, with higher concentrations in oysters during the wet season than dry season, and in the eastern coast than western coast. Furthermore, geographical variation in PAH levels in the oysters was enhanced during the wet season, indicating a possible contribution of heavy rainfall flushing from the Pearl River. In addition to precipitation, water temperature and salinity also significantly influenced PAH levels in the oysters from the PRE by changing the bioavailability and biokinetics. Long-term biomonitoring using oysters in the current study reflected the pollution status and variation trends of PAHs in the highly dynamic PRE.

A Size-dependent Bioaccumulation of Metal Pollutants, Antibacterial and Antifungal Activities of Telescopium telescopium, Nerita albicilla and Lunella coronata

We assessed metal/metalloid pollutants (through multi-indices) in seawater, sediments, tissues and shells of gastropods using various indices such as contamination degree (modified/unmodified; Cd/mCd; 1875/187.5). From sediment indices; e.g. the potential ecological risk index/enrichment factor (Eri/EF; 3396.8/105.5) indicated the area to be highly contaminated with metal/metalloid pollutants. Indeed, bioaccumulation with these materials was gastropod size dependent. Antimicrobial and percentage activity indices (AMI/PAI) for; T. telescopium was (AMI/PAI; 1.59/159), N. albicilla (1.14/114) and L. coronata (0.95/95) against E. coli. Similarly T. telescopium (1.33/133), N. albicilla (1.19/119) and L. coronata (1.14/114) have AMI/PAI against A. terreus. The total activity index (TAI), for T. telescopium was the highest, while L. coronata has lowest for all pathogens. This study indicates, T. telescopium, N. albicilla and L. coronata, surviving under metal/metalloid stress exhibited altered natural defense to pathogens which was related to the degree of toxin bioaccumulation.

Impact of Polycyclic Aromatic Hydrocarbon Accumulation on Oyster Health

In the past decade, the Deepwater Horizon oil spill triggered a spike in investigatory effort on the effects of crude oil chemicals, most notably polycyclic aromatic hydrocarbons (PAHs), on marine organisms and ecosystems. Oysters, susceptible to both waterborne and sediment-bound contaminants due to their filter-feeding and sessile nature, have become of great interest among scientists as both a bioindicator and model organism for research on environmental stressors. It has been shown in many parts of the world that PAHs readily bioaccumulate in the soft tissues of oysters. Subsequent experiments have highlighted the negative effects associated with exposure to PAHs including the upregulation of antioxidant and detoxifying gene transcripts and enzyme activities such as Superoxide dismutase, Cytochrome P450 enzymes, and Glutathione S-transferase, reduction in DNA integrity, increased infection prevalence, and reduced and abnormal larval growth. Much of these effects could be attributed to either oxidative damage, or a reallocation of energy away from critical biological processes such as reproduction and calcification toward health maintenance. Additional abiotic stressors including increased temperature, reduced salinity, and reduced pH may change how the oyster responds to environmental contaminants and may compound the negative effects of PAH exposure. The negative effects of acidification and longer-term salinity changes appear to add onto that of PAH toxicity, while shorter-term salinity changes may induce mechanisms that reduce PAH exposure. Elevated temperatures, on the other hand, cause such large physiological effects on their own that additional PAH exposure either fails to cause any significant effects or that the effects have little discernable pattern. In this review, the oyster is recognized as a model organism for the study of negative anthropogenic impacts on the environment, and the effects of various environmental stressors on the oyster model are compared, while synergistic effects of these stressors to PAH exposure are considered. Lastly, the understudied effects of PAH photo-toxicity on oysters reveals drastic increases to the toxicity of PAHs via photooxidation and the formation of quinones. The consequences of the interaction between local and global environmental stressors thus provide a glimpse into the differential response to anthropogenic impacts across regions of the world.

Contemporary Oyster Reef Restoration: Responding to a Changing World

Globally, there is growing interest in restoring previously widespread oyster reefs to reinstate key ecosystem services such as shoreline protection, fisheries productivity and water filtration. Yet, since peak expiration of oysters in the 1800s, significant and ongoing environmental change has occurred. Estuaries and coasts are undergoing some of the highest rates of urbanization, warming and ocean acidification on the planet, necessitating novel approaches to restoration. Here, we review key design considerations for oyster reef restoration projects that maximize the probability that they will meet biological and socio-economic goals not only under present-day conditions, but into the future. This includes selection of sites, and where required, substrates and oyster species and genotypes for seeding, not only on the basis of their present and future suitability in supporting oyster survival, growth and reproduction, but also based on their match to specific goals of ecosystem service delivery. Based on this review, we provide a road map of design considerations to maximize the success of future restoration projects.

How efficient is graphene-based nanocomposite to adsorb Hg from seawater. A laboratory assay to assess the toxicological impacts induced by remediated water towards marine bivalves

Advanced investigations on the use of graphene based nanomaterials have highlighted the capacity of these materials for wastewater treatment. Research on this topic revealed the efficiency of the nanocomposite synthetized by graphene oxide functionalized with polyethyleneimine (GO-PEI) to adsorb mercury (Hg) from contaminated seawater. However, information on the environmental risks associated with these approaches are still lacking. The focus of this study was to evaluate the effects of Hg in contaminated seawater and seawater remediated by GO-PEI, using the species Ruditapes philippinarum, maintained at two different warming scenarios: control (17 °C) and increased (22 °C) temperatures. The results obtained showed that organisms exposed to non-contaminated and remediated seawaters at control temperature presented similar biological patterns, with no considerable differences expressed in terms of biochemical and histopathological alterations. Moreover, the present findings revealed increased toxicological effects in clams under remediated seawater at 22 °C in comparison to those subjected to the equivalent treatment at 17 °C. These results confirm the capability of GO-PEI to adsorb Hg from water with no noticeable toxic effects, although temperature could alter the responses of mussels to remediated seawater. These materials seem to be a promise eco-friendly approach to remediate wastewater, with low toxicity evidenced by remediated seawater and high regenerative capacity of this nanomaterial, keeping its high removal performance after successive sorption-desorption cycles.

The Influence of Temperature Increase on the Toxicity of Mercury Remediated Seawater Using the Nanomaterial Graphene Oxide on the Mussel Mytilus galloprovincialis

Mercury (Hg) has been increasing in waters, sediments, soils and air, as a result of natural events and anthropogenic activities. In aquatic environments, especially marine systems (estuaries and lagoons), Hg is easily bioavailable and accumulated by aquatic wildlife, namely bivalves, due to their lifestyle characteristics (sedentary and filter-feeding behavior). In recent years, different approaches have been developed with the objective of removing metal(loid)s from the water, including the employment of nanomaterials. However, coastal systems and marine organisms are not exclusively challenged by pollutants but also by climate changes such as progressive temperature increment. Therefore, the present study aimed to (i) evaluate the toxicity of remediated seawater, previously contaminated by Hg (50 mg/L) and decontaminated by the use of graphene-based nanomaterials (graphene oxide (GO) functionalized with polyethyleneimine, 10 mg/L), towards the mussel Mytilus galloprovincialis; (ii) assess the influence of temperature on the toxicity of decontaminated seawater. For this, alterations observed in mussels’ metabolic capacity, oxidative and neurotoxic status, as well as histopathological injuries in gills and digestive tubules were measured. This study demonstrated that mussels exposed to Hg contaminated seawater presented higher impacts than organisms under remediated seawater. When comparing the impacts at 21 °C (present study) and 17 °C (previously published data), organisms exposed to remediated seawater at a higher temperature presented higher injuries than organisms at 17 °C. These results indicate that predicted warming conditions may negatively affect effective remediation processes, with the increasing of temperature being responsible for changes in organisms’ sensitivity to pollutants or increasing pollutants toxicity.

Does the environmental condition affect the tolerance of the bivalve Anomalocardia flexuosa to different intensities and durations of marine heatwaves?

Populations of the clam Anomalocardia flexuosa, subjected to different pollution conditions, were experimentally exposed to marine heatwaves of actual and future intensities and varying durations. We measured physiological and biochemical biomarkers and survival rates of the species under simulated heatwave events of 7 and 11 days. We observed that both the response of A. flexuosa to heatwaves and its baseline values of biomarkers were distinct between populations, demonstrating that the previous exposure to contaminants negatively interferes with the thermal tolerance of this bivalve. The duration and intensities of heatwaves here tested represent a considerable challenge for the survival of coastal bivalves. Our results suggest that the predicted increase in the ocean's average temperature and the frequency and intensity of marine heatwaves, as well as urbanization and increasing occupation of coastal regions, are factors that synergistically make A. flexuosa increasingly vulnerable over the decades.

Two-sided effects of prolonged hypoxia and sulfide exposure on juvenile ark shells (Anadara broughtonii)

Oxygen deficit and sulfide have been restrictive factors in mariculture zones. However, the adaptive mechanism in aquatic lives is still unclear. The commercial ark shells Anadara broughtonii were selected to test the tolerance and adaptive responses to prolonged and intermittent hypoxia with or without exogenous sulfide (mild, moderate, high) by evaluating their behavior, mortality, oxidative level, antioxidant responses, and the MAPK-mediated apoptosis in gills. The results indicated that the clams were tolerant to hypoxia and sulfide exposure but vulnerable during reoxygenation from the challenges. Even so, sulfide had remarkable effect on attenuating the accumulation of reactive oxygen species (ROS) and lipid peroxides caused by reoxygenation from prolonged hypoxia. The increase of glutathione level was probably as an early and primary protective response to prevent the expected reperfusion injury from reoxygenation. The challenges suppressed the oxidative level with a dose-dependent effect of sulfide, with an exception when exposed to mild sulfide. Synchronously, biphasic effects of exogenous sulfide on apoptotic cascade, which was induced by mild sulfide while it was inhibited by higher sulfide, were also detected in gills. The induced or inhibited apoptosis by hypoxia and sulfide kept to a typical ROS-MAPK-CASPASE cascade, desiderating further investigation.

Exposure to four chemical UV filters through contaminated sediment: impact on survival, hatching success, cardiac frequency, and aerobic metabolic scope in embryo-larval stage of zebrafish

UV filters are widely used in many pharmaceutical and personal care products such as sunscreen and cosmetics to protect from UV irradiation. Due to their hydrophobic properties and relative stability, they have a high capacity to accumulate in sediment. Little information is available on their ecotoxicity on fish. In aquatic ecosystems, fish eggs could be directly affected by UV filters through contact with contaminated sediment. The aim of this study was to investigate the individual toxicity of four UV filters: benzophenone-3 (BP3), butyl methoxydibenzoylmethane (BM), bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), and methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), in embryo-larval stages of zebrafish Danio rerio. Fish eggs were exposed to single UV filters by contact with spiked sediment during 96 h at a concentration of 10 μg g^-1. Among the four UV filters tested, BP3 was the more toxic, reducing cardiac frequency and increasing standard metabolic rate of larvae.

New challenges of marine ecotoxicology in a global change context

Currently, research agenda in marine ecotoxicology is facing new challenges with the emergence of newly and complex synthetized chemicals. The study of the fate and adverse effects of toxicants remains increasingly complicated with global change events. Ecotoxicology had provided for a decades, precious scientific data and knowledge but also technical and management tools for the environmental community. Regarding those, it is necessary to update methodologies dealing with these issues such as combined effect of conventional and emergent stressors and global changes. In this point of view article, we discuss one hand the new challenges of ecotoxicology in this context, and in the other hand, the need of updating agenda and methodologies currently used in monitoring programs and finally recommendations and future research needs. Among recommendations, it could be cited the necessity to perform long-term experiments, the standardization of sentinel species and taking benefit from baseline studies and omics technologies.

Temperature Effects During a Sublethal Chronic Metal Mixture Exposure on Common Carp (Cyprinus carpio)

The aquatic environment is the final sink of various pollutants including metals, which can pose a threat for aquatic organisms. Waterborne metal mixture toxicity might be influenced by environmental parameters such as the temperature. In the present study, common carp were exposed for 27 days to a ternary metal mixture of Cu, Zn, and Cd at two different temperatures, 10 and 20°C. The exposure concentrations represent 10% of the 96 h-LC₅₀ (concentration lethal for the 50% of the population in 96 h) for each metal (nominal metal concentrations of Cu: 0.08 μM; Cd: 0.02 μM and Zn: 3 μM). Metal bioaccumulation and toxicity as well as changes in the gene expression of enzymes responsible for ionoregulation and induction of defensive responses were investigated. Furthermore the hepatosomatic index and condition factor were measured as crude indication of overall health and energy reserves. The obtained results showed a rapid Cu and Cd increase in the gills at both temperatures. Cadmium accumulation was higher at 20°C compared to 10°C, whereas Cu and Zn accumulation was not, suggesting that at 20°C, fish had more efficient depuration processes for Cu and Zn. Electrolyte (Ca, Mg, Na, and K) levels were analyzed in different tissues (gills, liver, brain, muscle) and in the remaining carcasses. However, no major electrolyte losses were observed. The toxic effect of the trace metal ion mixture on major ion uptake mechanisms may have been compensated by ion uptake from the food. Finally, the metal exposure triggered the upregulation of the metallothionein gene in the gills as defensive response for the organism. These results, show the ability of common carp to cope with these metal levels, at least under the condition used in this experiment.

Bioenergetics in environmental adaptation and stress tolerance of aquatic ectotherms: linking physiology and ecology in a multi-stressor landscape

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior and ecology. Metabolic rates define the physiological and life-history performance of an organism, have direct implications for Darwinian fitness, and affect ecologically relevant traits such as the trophic relationships, productivity and ecosystem engineering functions. Natural environmental variability and anthropogenic changes expose aquatic ectotherms to multiple stressors that can strongly affect their energy metabolism and thereby modify the energy fluxes within an organism and in the ecosystem. This Review focuses on the role of bioenergetic disturbances and metabolic adjustments in responses to multiple stressors (especially the general cellular stress response), provides examples of the effects of multiple stressors on energy intake, assimilation, conversion and expenditure, and discusses the conceptual and quantitative approaches to identify and mechanistically explain the energy trade-offs in multiple stressor scenarios, and link the cellular and organismal bioenergetics with fitness, productivity and/or ecological functions of aquatic ectotherms.

Long-term environmental tolerance of the non-indigenous Pacific oyster to expected contemporary climate change conditions

The current global redistribution of biota is often attributed to two main drivers: contemporary climate change (CCC) and non-indigenous species (NIS). Despite evidence of synergetic effects, however, studies assessing long-term effects of CCC conditions on NIS fitness remain rare. We examined the interactive effects of warming, ocean acidification and reduced salinity on the globally distributed marine NIS Magallana gigas (Pacific oyster) over a ten-month period. Growth, clearance and oxygen consumption rates were measured monthly to assess individual fitness. Lower salinity had a significant, permanent effect on M. gigas, reducing and increasing clearance and oxygen consumption rates, respectively. Neither predicted increases in seawater temperature nor reduced pH had a long-term physiological effect, indicating conditions predicted for 2100 will not affect adult physiology and survival. These results suggest that M. gigas will remain a globally successful NIS and predicted CCC will continue to facilitate their competitive dominance in the near future.

Bisphenols alter thermal responses and performance in zebrafish (Danio rerio)

Plastic pollutants are novel environmental stressors that are now persistent components of natural ecosystems. Endocrine disrupting chemicals such as bisphenols that leach out of plastics can modify physiological responses of animals by interfering with hormone signalling. Here, we tested whether three commonly produced bisphenols, bisphenol A (BPA), bisphenol F (BPF) and bisphenol S (BPS), impair thermal acclimation of swimming performance and metabolic enzyme [citrate synthase (CS) and lactate dehydrogenase (LDH)] activities in adult zebrafish (Danio rerio). We found that exposure to 30-μg l-1 BPF and BPS, but not BPA, reduced swimming performance, and no interactions between bisphenol exposure and acclimation (3 weeks to 18°C and 28°C) or acute test (18°C and 28°C) temperatures were found. BPA interacted with acclimation and acute test temperatures to determine CS activity, an indicator of mitochondrial density and aerobic metabolic capacity. BPS reduced CS activity and an interaction (at a one-tailed significance) between acclimation temperature and BPF exposure determined CS activity. LDH activity reflects anaerobic ATP production capacity, and BPA and BPF altered the effects of thermal acclimation and acute test temperatures on LDH activity. Our data show that all bisphenols we tested at ecologically relevant concentrations can disrupt the thermal responses of fish. BPS and BPF are used as environmentally safer alternatives to BPA, but our data show that these bisphenols are also of concern, particularly in thermally variable environments.

Immunological and oxidative stress responses of the bivalve Scrobicularia plana to distinct patterns of heatwaves

As a consequence of global warming, extreme events, such as marine heatwaves (MHW), have been increasing in frequency and intensity with negative effects on aquatic organisms. This innovative study evaluated for the first time, the immunological and physiological response of the estuarine edible bivalve Scrobicularia plana to different heatwaves, with distinct duration and recovery periods. So, extensive immune (total haemocyte count - THC, haemocyte viability, phagocytosis rate, respiratory oxidative burst of haemocytes, total protein, protease activity, nitric oxide and bactericidal activity of plasma) and oxidative stress (lipid peroxidation - LPO, superoxide dismutase - SOD, catalase - CAT and glutathione-S-Transferase - GST) analyses were performed in an experimental study that tested the impact of heatwaves during 25 days. The survival and condition of S. plana were not affected by the exposure to the extreme events. However, our data suggested that longer heatwaves with shorter recovery periods can be more challenging for the species, since THC and phagocytic activity were most affected under the temperature increase conditions. Regarding the oxidative status, the species increased its SOD activity while MDA production slightly declined to the increase of temperature, protecting the organism from cellular damage. These results indicate that S. plana has a great capacity to adapt to environmental temperature changes, however, the expected higher frequency/duration of heatwaves with climate change trends can cause some debility of the species face to other stressors, which can compromise its success in the future.

Warmer temperature increases mercury toxicity in a marine copepod

Marine biota have been co-challenged with ocean warming and mercury (Hg) pollution over many generations because of human activities; however, the molecular mechanisms to explain their combined effects are not well understood. In this study, a marine planktonic copepod Pseudodiaptomus annandalei was acutely exposed to different temperature (22 and 25 °C) and Hg (0 and 118 μg/L) treatments in a 24-h cross-factored experiment. Hg accumulation and its subcellular fractions were determined in the copepods after exposure. The expression of the genes of superoxide dismutase (SOD), glutathione peroxidase (GPx), metallothionein1 (mt1), heat shock protein 70 (hsp70), hsp90, hexokinase (hk), and pyruvate kinase (pk) was also analyzed. Both the Hg treatment alone and the combined exposure of warmer temperature plus Hg pollution remarkably facilitated Hg bioaccumulation in the exposed copepods. Compared with the Hg treatment alone, the combined exposure increased total Hg accumulation and also the amount of Hg stored in the metal-sensitive fractions (MSF), suggesting elevated Hg toxicity in P. annandalei under a warmer environment, given that the MSF is directly related to metal toxicity. The warmer temperature significantly up-regulated the mRNA levels of mt1, hsp70, hsp90, and hk, indicating the copepods suffered from thermal stress. With exposure to Hg, the mRNA level of SOD increased strikingly but the transcript levels of hsp90, hk, and pk decreased significantly, indicating that Hg induced toxic events (e.g., oxidative damage and energy depletion). Particularly, in contrast to the Hg treatment alone, the combined exposure significantly down-regulated the mRNA levels of SOD and GPx but up-regulated the mRNA levels of mt1, hsp70, hsp90, hk, and pk. Collectively, the results of this study indicate that ocean warming will potentially boost Hg toxicity in the marine copepod P. annandalei, which is information that will increase the accuracy of the projections of marine ecosystem responses to the joint effects of climate change stressors and metal pollution on the future ocean.

Metal body burden and tissue oxidative status in the bivalve Venerupis decussata from Tunisian coastal lagoons

Coastal transitional waters are exposed to many anthropogenic threats. This study aims to assess the trace metals' pollution status of transitional waters by evaluating its biological effects in the clam Venerupis decussata. Among the studied sites along the Tunisian littoral, South Tunis and Boughrara were the most impacted, since clams from these two lagoons presented significant differences in: (i) trace metal contents, (ii) in-cell hydrogen peroxide, (iii) enzymatic and non-enzymatic defenses, (iv) damage to lipids and proteins, and (v) protein post-translational modifications. These changes related to evident histopathological traits. PCA showed a clear separation between the digestive gland and gills tissues and illustrated an impact gradient in Tunisian coastal lagoons. Water temperature was revealed as an added natural stressor that, when concurring with high pollution, may jeopardize an ecosystem's health and contribute to the accumulation of hazardous metals in organisms.

Environmental Fate of Multistressors on Carpet Shell Clam Ruditapes decussatus: Carbon Nanoparticles and Temperature Variation

Ruditapes decussatus is a native clam from the Southern Europe and Mediterranean area, relevant to the development of sustainable aquaculture in these regions. As sessile organisms, bivalves are likely to be exposed to chemical contaminations and environmental changes in the aquatic compartment and are widely used as bioindicator species. Carbon-based nanomaterials (CNTs) use is increasing and, consequently, concentrations of these contaminants in aquatic systems will rise. Therefore, it is imperative to assess the potential toxic effects of such compounds and the interactions with environmental factors such as water temperature. For this, we exposed R. decussatus clams to four different water temperatures (10, 15, 20 and 25 °C) in the presence or absence of CNTs for 96 h. Different parameters related with oxidative stress status, aerobic metabolism, energy reserves and neurotoxicity were evaluated. The relationship and differences among water temperatures and contamination were highlighted by principal coordinates analysis (PCO). CNTs exposure increased oxidative damage as protein carbonylation (PC) in exposed clams at 10 °C. Higher temperatures (25 °C) were responsible for the highest redox status (ratio between reduced and oxidized glutathione, GSH/GSSG) observed as well as neurotoxic effects (acetylcholinesterase—AChE activity). Antioxidant defenses were also modulated by the combination of CNTs exposure with water temperatures, with decrease of glutathione peroxidase (GR) activity at 15 °C and of glutathione S-transferases (GSTs) activity at 20 °C, when compared with unexposed clams. Clams energy reserves were not altered, probably due to the short exposure period. Overall, the combined effects of CNTs exposure and increasing water temperatures can impair R. decussatus cellular homeostasis inducing oxidative stress and damage.

Impact of marine heat waves and cold spell events on the bivalve Anomalocardia flexuosa: A seasonal comparison

The effects of increasing or decreasing extreme temperatures on bivalves depend on their physiological and biochemical capacity to respond to changes in ambient temperature. We tested the response of the clam Anomalocardia flexuosa to simulated marine heat waves and cold spells, under summer and winter experimental conditions. We sought information about physiological and biochemical parameters, as well as survival rates during two bioassays of 43 days each. The winter cold spell simulations showed that extreme temperatures acted as a physiological and biochemical stimulus, linked to an increase in metabolic rates, and consequently higher maintenance costs, as acclimatory strategies. On the other hand, the summer heat wave extreme temperatures exceeded the individuals' thermal tolerance limits, resulting in an inability to acclimate and a high mortality. These experiments suggest that A. flexuosa can be considered as a sensitive indicator of heat wave events.

Thermal discharge influences the bioaccumulation and bioavailability of metals in oysters: Implications of ocean warming

Human-induced temperature changes influence coastal regions, both via thermal pollution and ocean warming, which exerts profound effects on the chemistry of metals and the physiology of organisms. However, it remains unknown whether the increased temperature of discharged water or ocean warming, as a result of climate change, lead to an increase of human health risks associated with the consumption of sea foods. In this study, the influence of temperature on metal accumulation by oysters was studied in individuals collected from a coastal area affected by the thermal water discharge of the Houshi Power Plant, China. The bioaccumulation factor (BAF) and oral bioavailability (OBA) of metals in oysters was determined. Elevated temperatures led to an increase in BAF for Cu, Zn, Hg, and Cd (p < 0.05), but no change was observed for As and Pb (p > 0.05). The OBA for Cd, As, and Pb correlated positively to elevated temperatures (p < 0.05). However, for Cu and Zn, OBA was negatively correlated with increasing temperature (p < 0.05). As, Pb, and Cd in the trophically available metal (defined as a sum of heat-stable proteins, heat-denaturable proteins, and organelles) was significantly elevated at the highest temperature seawater site (site A) compared to the lowest seawater site (site B). Thus, the irregular variation of OBA for each metal may be the result of variations in the subcellular distribution of metals and the protein quality influenced by the increased temperature. Moreover, the increased temperature and increased the hazard quotient values of As and Cd (p < 0.05 for As, n = 6, p < 0.05 for Cd, n = 6), which provided an indication of the potential risks of the consumption of oysters or other seafood to future warming under climate change scenarios.

The effects of ZnO nanostructures of different morphology on bioenergetics and stress response biomarkers of the blue mussels Mytilus edulis

Biofouling causes massive economical losses in the maritime sector creating an urgent need for effective and ecologically non-harmful antifouling materials. Zinc oxide (ZnO) nanorod coatings show promise as an antifouling material; however, the toxicity of ZnO nanorods to marine organisms is not known. We compared the toxicity of suspended ZnO nanorods (NR) with that of ZnO nanoparticles (NP) and ionic Zn²⁺ in a marine bivalve Mytilus edulis exposed for two weeks to 10 or 100 μg Zn L^-1 of ZnO NPs, NRs or Zn²⁺, or to immobilized NRs. The multi-biomarker assessment included bioenergetics markers (tissue energy reserves, activity of mitochondrial electron transport system and autophagic enzymes), expression of apoptotic and inflammatory genes, and general stress biomarkers (oxidative lesions, lysosomal membrane stability and metallothionein expression). Exposure to ZnO NPs, NRs and Zn²⁺ caused accumulation of oxidative lesions in proteins and lipids, stimulated autophagy, and led to lysosomal membrane destabilization indicating toxicity. However, these responses were not specific for the form of Zn (NPs, NR or Zn²⁺) and showed no monotonous increase with increasing Zn concentrations in the experimental exposures. No major disturbance of the energy status was found in the mussels exposed to ZnO NPs, NRs, or Zn²⁺. Exposure to ZnO NPs and NRs led to a strong induction of apoptosis- and inflammation-related genes, which was not seen in Zn²⁺ exposures. Based on the integrated biomarker response, the overall toxicity as well as the pro-apoptotic and pro-inflammatory action was stronger in ZnO NPs compared with the NRs. Given the stability of ZnO NR coatings and the relatively low toxicity of suspended ZnO NR, ZnO NR coating might be considered a promising low-toxicity material for antifouling paints.

Do differences in developmental mode shape the potential for local adaptation?

Future climate change is leading to the redistribution of life on Earth as species struggle to cope with rising temperatures. Local adaptation allows species to become locally optimized and persist despite environmental selection, but the extent to which this occurs in nature may be limited by dispersal and gene flow. Congeneric marine gastropod species (Littorina littorea and L. saxatilis) with markedly different developmental modes were collected from across a latitudinal thermal gradient to explore the prevalence of local adaptation to temperature. The acute response of metabolic rate (using oxygen consumption as a proxy) to up-ramping and down-ramping temperature regimes between 6°C and 36°C was quantified for five populations of each species. The highly dispersive L. littorea exhibited minimal evidence of local adaptation to the thermal gradient, with no change in thermal optimum (T_opt ) or thermal breadth (T_br ) and a decline in maximal performance (_max ) with increasing latitude. In contrast, the direct developing L. saxatilis displayed evidence of local optimization, although these varied idiosyncratically with latitude, suggesting a suite of selective pressures may be involved in shaping thermal physiology in this relatively sedentary species. Our results show that the biogeography of thermal traits can differ significantly between related species, and show that interpopulation differences in thermal performance do not necessarily follow simple patterns that may be predicted based on latitudinal changes in environmental temperatures. Further research is clearly required to understand the mechanisms that can lead to the emergence of local adaptation in marine systems better and allow improved predictions of species redistribution in response to climate change.

Effects of a Sudden Drop in Salinity on Immune Response Mechanisms of Anadara kagoshimensis

In this experiment, the effects of a sudden drop of salinity on the immune response mechanisms of the ark shell Anadara kagoshimensis were examined by simulating the sudden drop of salinity that occurs in seawater after a rainstorm. Additionally, the differentially expressed genes (DEGs) were identified using transcriptome sequencing. When the salinity dropped from 30‱ (S30) to 14‱ (S14), the phagocytic activity of blood lymphocytes, the O₂^- levels produced from respiratory burst, the content of reactive oxygen species, and the activities of lysozymes and acid phosphatases increased significantly, whereas the total count of blood lymphocytes did not increase. Total count of blood lymphocytes in 22‱ salinity (S22) was significantly higher than that in any other group. The raw data obtained from sequencing were processed with Trimmomatic (Version 0.36). The expression levels of unigenes were calculated using transcripts per million (TPM) based on the effects of sequencing depth, gene length, and sample on reads. Differential expression analysis was performed using DESeq (Version 1.12.4). Transcriptome sequencing revealed 269 (101 up-regulated, 168 down-regulated), 326 (246 up-regulated, 80 down-regulated), and 185 (132 up-regulated, 53 down-regulated) significant DEGs from comparison of the S14 vs. S22, S22 vs. S30, and S14 vs. S30 groups, respectively. Gene Ontology enrichment analysis of the DEGs in these salinity comparison groups revealed that the cellular amino acid metabolic process, the regulation of protein processing, the regulation of response to stress, and other terms were significantly enriched. Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway (ko04621), apoptosis-multiple species (ko04215), Toll and Imd signaling pathway (ko04624), NF-κB signaling pathway (ko04064), apoptosis (ko04210), and focal adhesion (ko04510) were significantly enriched in all salinity comparison groups. qRT-PCR verification of 12 DEGs in the above six pathways was conducted, and the results were consistent with the transcriptome sequencing results in terms of up-regulation and down-regulation, which illustrates that the transcriptome sequencing data are credible. These results were used to preliminarily explore the effects of a sudden drop of salinity on blood physiological and biochemical indexes and immunoregulatory mechanisms of A. kagoshimensis. They also provide a theoretical basis for the selection of bottom areas optimal for release and proliferation of A. kagoshimensis required to restore the declining populations of this species.

Potential nitrous oxide production by marine shellfish in response to warming and nutrient enrichment

Bivalves facilitate microbial nitrogen cycling, which can produce nitrous oxide (N2O), a potent greenhouse gas. Potential N₂O production by three marine bivalves (Mytilus edulis, Mercenaria mercenaria and Crassostrea virginica) was measured in the laboratory including responses to nitrogen (N) loading and/or warming over short-terms (up to 14 or 28 days). N additions (targeting 100 μM-N ammonium nitrate) or warming (22 °C) individually and in combination were applied with experimental controls (20 μM-N, 19 °C). N₂O production rates were higher with N additions for all species, but warming lacked significant direct effects. Ammonium and nitrate concentrations varied but were consistent with nitrification as a potential N₂O source for all bivalves. Highest N₂O emissions (7.5 nmol N₂O g^-1 h^-1) were from M. edulis under hypoxic conditions coincident with a drop in pH. Macro-epifauna on M. edulis did not significantly alter N₂O production. Thus, under short-term hypoxic conditions, micro-organisms in M. edulis guts may be a particularly significant source of N₂O.

Examining the relationship between metal exposure (Cd and Hg), subcellular accumulation, and physiology of juvenile Crassostrea virginica

To assess the toxicity and accumulation (total and subcellular partitioning) of cadmium (Cd) and mercury (Hg), juvenile eastern oysters, Crassostrea virginica, were exposed for 4 weeks to a range of concentrations (Control, Low (1×), and High (4×)). Despite the 4-fold increase in metal concentrations, oysters from the High-Cd treatment (2.4 μM Cd) attained a body burden that was only 2.4-fold greater than that of the Low-Cd treatment (0.6 μM Cd), while oysters from the High-Hg treatment (0.056 μM Hg) accumulated 8.9-fold more Hg than those from the Low-Hg treatment (0.014 μM Hg). This fold difference in total Cd burdens was, in general, mirrored at the subcellular level, though binding to heat-denatured proteins in the High-Cd treatment was depressed (only 1.6-fold higher than the Low-Cd treatment). Mercury did not appear to appreciably partition to the subcellular fractions examined in this study, with the fold difference in accumulation between the Low- and High-Hg treatments ranging from 1.5-fold (heat-stable proteins) to 4.6-fold (organelles). Differences in toxicological impairments (reductions in condition index, protein content, and ETS activity) exhibited by oysters from the High-Cd treatment may be partially due to the nature of how different metals partition to subcellular components in the oysters, though exact mechanisms will require further examination.

Simulated Marine Heat Wave Alters Abundance and Structure of Vibrio Populations Associated with the Pacific Oyster Resulting in a Mass Mortality Event

Marine heat waves are predicted to become more frequent and intense due to anthropogenically induced climate change, which will impact global production of seafood. Links between rising seawater temperature and disease have been documented for many aquaculture species, including the Pacific oyster Crassostrea gigas. The oyster harbours a diverse microbial community that may act as a source of opportunistic pathogens during temperature stress. We rapidly raised the seawater temperature from 20 °C to 25 °C resulting in an oyster mortality rate of 77.4%. Under the same temperature conditions and with the addition of antibiotics, the mortality rate was only 4.3%, strongly indicating a role for bacteria in temperature-induced mortality. 16S rRNA amplicon sequencing revealed a change in the oyster microbiome when the temperature was increased to 25 °C, with a notable increase in the proportion of Vibrio sequences. This pattern was confirmed by qPCR, which revealed heat stress increased the abundance of Vibrio harveyi and Vibrio fortis by 324-fold and 10-fold, respectively. Our findings indicate that heat stress-induced mortality of C. gigas coincides with an increase in the abundance of putative bacterial pathogens in the oyster microbiome and highlights the negative consequences of marine heat waves on food production from aquaculture.

Bioenergetic responses of freshwater mussels Unio tumidus to the combined effects of nano-ZnO and temperature regime

Bivalves from the cooling reservoirs of electrical power plants (PP) are exposed to the chronic heating and chemical pollution making them a suitable model to study the combined effects of these stressors. We investigated the effect of in situ exposures to chemical and thermal pollution in the PP cooling ponds on the metabolic responses of unionid bivalves (Unio tumidus) to a novel widespread pollutant, ZnO nanoparticles (nZnO). Male U. tumidus from the reservoirs of Dobrotvir and Burshtyn PPs (DPP and BPP) were maintained in clean water at 18 °C, or exposed for 14 days to one of the following conditions: nZnO (3.1 μM) or Zn²⁺ (3.1 μM, a positive control for Zn impacts) at 18 °C, elevated temperature (T, 25 °C), or nZnO at 25 °C (nZnO + T). Baseline levels of glycogen, lipids and ATP were similar in the two studied populations, whereas the levels of proteins, lactate/pyruvate ratio (L/P) and extralysosomal cathepsin D level were higher in the tissues of BPP mussels. The levels of glycogen and glucose declined in most experimental exposures indicating elevated energy demand except for a slight increase in the digestive gland of warming-exposed BPP mussels and in the gills of the nZnO + T-exposed DPP-mussels. Experimental exposures stimulated cathepsin D activity likely reflecting onset of autophagic processes to compensate for stress-induced energy demand. No depletion of ATP in Zn-containing exposures was observed indicating that the cellular metabolic adjustments were sufficient for such compensation. Unexpectedly, experimental warming mitigated most metabolic responses to nZnO in co-exposures. Our data thus indicate that metabolic effects of nZnO strongly depend on the environmental context of the mussels (such as temperature and acclimation history) which must be taken into account for the molecular and cellular biomarker-based assessment of the nanoparticle effects in the field.

The impact of temperature on metal mixture stress: Sublethal effects on the freshwater isopod Asellus aquaticus

Chemical and natural factors have been demonstrated to interact and potentially change the toxicity of the individual stressors. Yet, while there exists a multitude of papers studying the temperature-dependent toxicity of single chemicals, little research exists on the impact of temperature on chemical mixtures. This paper investigates the effect of temperature on environmentally-relevant mixtures of Cd, Cu and Pb. We linked the effects on respiration, growth, feeding rate and activity of Asellus aquaticus to the free ion activities, as a measure for the bioavailability of the metals, and the body concentrations. We observed interactions of temperature and metal body concentrations on all sublethal endpoints, except activity. Mixture effects on accumulation and feeding rate were observed as well and even an interaction between metal body burden, mixture and temperature treatment was revealed for the feeding rate of Pb exposed isopods. This research adds to a growing body of evidence that the current chemical-based monitoring is insufficient to estimate chemical toxicity in aquatic ecosystems and must, therefore, be complemented with effect-based tools.

Bioenergetics-adverse outcome pathway: Linking organismal and suborganismal energetic endpoints to adverse outcomes

Adverse outcome pathways (AOPs) link toxicity across levels of biological organization, and thereby facilitate the development of suborganismal responses predictive of whole-organism toxicity and provide the mechanistic information necessary for science-based extrapolation to population-level effects. Thus far AOPs have characterized various acute and chronic toxicity pathways; however, the potential for AOPs to explicitly characterize indirect, energy-mediated effects from toxicants has yet to be fully explored. Indeed, although exposure to contaminants can alter an organism's energy budget, energetic endpoints are rarely incorporated into ecological risk assessment because there is not an integrative framework for linking energetic effects to organismal endpoints relevant to risk assessment (e.g., survival, reproduction, growth). In the present analysis, we developed a generalized bioenergetics-AOP in an effort to make better use of energetic endpoints in risk assessment, specifically exposure scenarios that generate an energetic burden to organisms. To evaluate empirical support for a bioenergetics-AOP, we analyzed published data for links between energetic endpoints across levels of biological organization. We found correlations between 1) cellular energy allocation and whole-animal growth, and 2) metabolic rate and scope for growth. Moreover, we reviewed literature linking energy availability to nontraditional toxicological endpoints (e.g., locomotor performance), and found evidence that toxicants impair aerobic performance and activity. We conclude by highlighting current knowledge gaps that should be addressed to develop specific bioenergetics-AOPs. Environ Toxicol Chem 2019;38:27-45. © 2018 SETAC.

The impacts of seawater physicochemical parameters and sediment metal contents on trace metal concentrations in mussels-a chemometric approach

The concentrations of Al, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sr, Zn, and Hg were studied in Mytilus galloprovincialis collected from the coastal area of Montenegro. The impact of seawater temperature, salinity, dissolved oxygen, total organic carbon (TOC), and metal content in sediment samples on the metal contents in mussels collected from three locations in four different seasons was analyzed by a Pearson correlation coefficient (r), principal component analysis (PCA), and cluster analysis (CA). These analyses were used to discriminate groups of samples, elements, and seawater parameters, according to similarity of samples chemical composition in different seasons, as well as the impact of seawater parameters and surface sediment composition on the mussels' element concentrations. Synergistic interactions occurred between seawater TOC, Fe, and Al concentrations in mussels. Compared with other studies, which are usually performed under constant laboratory conditions where mussels undergo only one stress at a time, this study was performed in nature. The analyses showed the importance of considering simultaneously acting environmental parameters that make determining of separate impacts of each factor selected very difficult and complex.

Highly polluted life history and acute heat stress, a hazardous mix for blue mussels

Intertidal sessile organisms constitute through their life history unintended stress recorders. This study focuses on the impact of pollution on Mytilus edulis ability to cope with an additional stress. For this purpose, two acclimation stages to different temperatures were conducted before an acute stress exposure in mussels collected from a heavily polluted site. Gill proteomes were analyzed by 2DE and regulated proteins identified. Massive mortality was observed for organisms acclimated to colder temperatures. Despite this major difference, both groups shared a common response with a strong representation of proteoforms corresponding to "folding, sorting and degradation" processes. Nevertheless, surviving mussels exhibit a marked increase in protein degradation consistent with the observed decrease of cell defense proteins. Mussels acclimated to warmer temperature response is essentially characterized by an improved heat shock response. These results show the differential ability of mussels to face both pollution and acute heat stress, particularly for low-acclimated organisms.

Seasonal variations and relationships between environmental parameters and heavy metal concentrations in tissues of Crassostrea species and in its ambience from the tropical estuaries

This study aimed to evaluate the relationship between physicochemical parameters and heavy metal (Cu, Ni, Pb, and Cd) concentrations from sediment, seawater, and its accumulation in tissues of oyster species (Crassostrea madrasensis and C. gryphoides) from the three sites (Chicalim Bay (CB), Nerul Creek (NC), Chapora Bay (ChB)) along the Goa coast (India). Results showed enrichment of Cu and Ni in sediment exceeding the effect range low (ERL) level. The higher concentrations of Cu and Ni in sediments and in suspended particulate matter (SPM) from all the study sites are indicative of severe contamination of estuarine and associated habitats. Moreover, particulate Ni (at all the sites), Cu (at NC and ChB), Pb (at NC), and Cd (at CB and NC) concentrations were recorded more than its total loadings in surface sediment. Concentration of Cu and Cd in oyster tissue was several folds higher than its concentration in ambience. Further, this study showed that the levels of metal in oysters and their ambient environment were higher during the monsoon season. Hence, the consumption of oysters needs to be considered carefully with respect to the health hazards posed by the elevated levels of metal contaminants in certain seasons. The present study concludes that metals associated with the particulate matter in water column are the main source of metal accumulation in oyster. It is also suggested that concentration of metal pollutants in coastal and estuarine water bodies should be monitored regularly to ensure the acceptable limits of metal concentrations.