Impact of hypoxia on glucose metabolism and hypoxia signaling pathways in juvenile horseshoe crabs Tachypleus tridentatus.

Marine hypoxia poses a significant challenge in the contemporary marine environment. The horseshoe crab, an ancient benthic marine organism, is confronted with the potential threat of species extinction due to hypoxia, making it an ideal candidate for studying hypoxia tolerance mechanisms. In this experiment, juvenile Tachypleus tridentatus were subjected to a 21-day trial at DO:2 mg/L (hypoxia) and DO:6 mg/L conditions. The experimental timeline included a 14-day exposure phase followed by a 7-day recovery period. Sampling occurred on days 0, 7, 14, and 21, where the period from day 14 to day 21 corresponds to seven days of recuperation. Several enzymatic activities of important proteins throughout this investigation were evaluated, such as succinate dehydrogenase (SDH), phosphofructokinase (PFK), hexokinase (HK), lactate dehydrogenase (LDH), and pyruvate kinase (PK). Concurrently, the relative expression of hexokinase-1 (HK), hypoxia-inducible factor 1-alpha inhibitor (FIH), and hypoxia-inducible factor 1-alpha (HIF-1α), pyruvate dehydrogenase phosphatase (PDH), succinate dehydrogenase assembly factor 4 (SDH), and Glucose-6-phosphatase (G6Pase) were also investigated. These analyses aimed to elucidate alterations in the hypoxia signaling pathway and respiratory energy metabolism. It is revealed that juvenile T. tridentatus initiated the HIF pathway under hypoxic conditions, resulting in an upregulation of HIF-1α and FIH-1 gene expression, which in turn, influenced a shift in metabolic patterns. Particularly, the activity of glycolysis-related enzymes was promoted significantly, including PK, HK, PKF, LDH, and the related HK gene. In contrast, enzymes linked to aerobic respiration, PDH, and SDH, as well as the related PDH and SDH genes, displayed down-regulation, signifying a transition from aerobic to anaerobic metabolism. Additionally, the activity of gluconeogenesis-related enzymes such as PK and G6Pase gene expression were significantly elevated, indicating the activation of gluconeogenesis and glycogenolysis pathways. Consequently, juvenile T. tridentatus demonstrated an adaptive response to hypoxic conditions, marked by changes in respiratory energy metabolism modes and the activation of hypoxia signaling pathways.

Perfluorooctanoate and nano titanium dioxide impair the byssus performance of the mussel Mytilus coruscus.

Perfluorooctanoate (PFOA) is widely used as a surfactant and has metabolic, immunologic, developmental, and genetic toxicity on marine organisms. However, the effects of PFOA on individual defense functions in mussels in the presence of titanium dioxide nanoparticles (nano-TiO2) are poorly understood. To investigate the defense strategies and regulatory mechanisms of mussels under combined stressors, the thick-shell mussels Mytilus coruscus were exposed to different PFOA concentrations (0, 2 and 200 µg/L) and nano-TiO2 (0 and 0.1 mg /L, size: 25 nm) for 14 days. The results showed that, compared to the control group, PFOA and nano-TiO2 significantly reduced the number of byssal threads (NBT), byssal threads length (BTL), diameter of proximal threads (DPB), diameter of middle threads (DMB), diameter of distal byssal threads (DDB), adhesive plaque area (BPA), and breaking force of byssal threads (N). Under the influence of PFOA and nano-TiO2, the morphological surface smoothness of the fractured byssal threads surface increased, concurrently inducing an increased surface roughness in the adhesive plaques. Additionally, under the presence of PFOA and nano-TiO2, the foot displayed dispersed tissue organization and damaged villi, accompanied by an increased incidence of cellular apoptosis and an upregulation of the apoptosis gene caspase-8. Expression of the adhesion gene mfp-3 and byssal threads strength genes (preCOL-D, preCOL-NG) was upregulated. An interactive effect on the performance of byssal threads is observed under the combined influence of PFOA and nano-TiO2. Under co-exposure to PFOA and nano-TiO2, the performance of the byssal threads deteriorates, the foot structure is impaired, and the genes mRNA expression of byssal thread secretory proteins have compensated for the adhesion and byssal threads strength by up-regulation. Within marine ecosystems, organic and particulate contaminants exert a pronounced effect on the essential life processes of individual organisms, thereby jeopardizing their ecological niche within community assemblages and perturbing the dynamic equilibrium of the overarching ecosystem. ENVIRONMENTAL IMPLICATION: Perfluorooctanoic acid (PFOA) is prone to accumulate in marine organisms. TiO2 nanoparticles (nano-TiO2) are emerging environmental pollutants frequently found in marine environment. The effects of PFOA and nano-TiO2 on marine mussels are not well understood, and their toxic mechanisms remain largely unknown. We investigated the impacts of PFOA and nano-TiO2 on mussel byssus defense mechanisms. By assessing byssus performance indicators, morphological structures of the byssus, subcellular localization, and changes in byssal secretion-related genes, we revealed the combined effects and mechanisms through which these two types of pollutants may affect the functional capabilities and survival of mussels in the complex marine ecosystem.

Effects of nano-TiO2 and pentachlorophenol on the bioenergetics of mussels under predatory stress.

Organic and nanoparticle pollutants are the main environmental problems affecting marine species, which have received great attention. However, the combined effect of pollutants on marine life in the presence of predators needs to be clarified. In this study, the effects of pentachlorophenol (PCP) and titanium dioxide nanoparticles (nano-TiO2) on the energy metabolism of mussels (Mytilus coruscus) in the presence of predators were assessed through cellular energy allocation (CEA) approach. Mussels were exposed to PCP (0, 1, and 10 µg/L), nano-TiO2 (1 mg/L, 25 and 100 nm), and predators (Portunus trituberculatus presence/absence) for 14 days. Exposure to high concentrations of PCP (10 µg/L) with small particle size nano-TiO2 (25 nm) decreased cellular energy stores (carbohydrates, lipids, and proteins) and increased cellular energy demand (measured as the activity of the mitochondrial electron transport system, ETS). During the first 7 days, energy was supplied mainly through the consumption of carbohydrates, while lipids are mobilized to participate after 7 days. The presence of predators caused a further decrease in energy stores. These findings demonstrate that PCP, nano-TiO2 and predators have a negative impact on energy metabolism at the cellular level. Carbohydrates are not able to meet the metabolic demand, lipids need to be consumed, and energy metabolism was also mediated by the involvement of proteins. Overall, our results suggest that PCP, nano-TiO2 and predators disrupt the cellular energy metabolism of mussels through reduced cellular energy allocation, small particles and predators drive mussels to exert energetic metabolic adjustments for detoxification reactions when toxic contaminants are present.

Effects of elevated temperature and different crystal structures of TiO2 nanoparticles on the gut microbiota of mussel Mytilus coruscus.

Coastal habitats are exposed to increasing pressure of nanopollutants commonly combined with warming due to the seasonal temperature cycles and global climate change. To investigate the toxicological effects of TiO2 nanoparticles (TiO2 NPs) and elevated temperature on the intestinal health of the mussels (Mytilus coruscus), the mussels were exposed to 0.1 mg/L TiO2 NPs with different crystal structures for 14 days at 20 °C and 28 °C, respectively. Compared to 20 °C, the agglomeration of TiO2 NPs was more serious at 28 °C. Exposure to TiO2 NPs led to elevated mortality of M. coruscus and modified the intestinal microbial community as shown by 16S rRNA sequence analysis. Exposure to TiO2 NPs changed the relative abundance of Bacteroidetes, Proteobacteria and Firmicutes. The relative abundances of putative mutualistic symbionts Tenericutes and Fusobacteria increased in the gut of M. coruscus exposed to anatase, which have contributed to the lower mortality in this group. LEfSe showed the combined stress of warming and TiO2 NPs increased the risk of M. coruscus being infected with potential pathogenic bacteria. This study emphasizes the toxicity differences between crystal structures of TiO2 NPs, and will provides an important reference for analyzing the physiological and ecological effects of nanomaterial pollution on bivalves under the background of global climate change.

Size-dependent effects of plastic particles on antioxidant and immune responses of the thick-shelled mussel Mytilus coruscus.

Micro-/nano-plastic particles (MNPs) are present in the ocean with potential detrimental impacts on marine ecosystems. Bivalves are often used as marine bioindicators and are ideal to evaluate the threat posed by various-sized MNPs. We exposed the mussel Mytilus coruscus to MNPs with different particle sizes (70 and 500 nm, 5, 10 and 100 µm) for 3, 72 h and 30 days. The antioxidant responses in digestive gland and the hemolymph were then evaluated. The time of exposure played a strong modulating role in the biological response. A 3-hour exposure had no significant impact on the digestive gland. After 72 h, an increase in oxidative stress was observed in the digestive gland, including increased hydrogen peroxide (H2O2) level, catalase (CAT), glutathione peroxidase (GPx) activities and malondialdehyde (MDA) production. After a 30-day exposure, the oxidative stress decreased while lipid peroxidation increased. A 30-day exposure increased hemocyte mortality (HM) and reactive oxygen species (ROS) levels in the hemolymph, while phagocytosis (PA), lysosome content (LC), mitochondrial number (MN) and mitochondrial membrane potential (MMP) significantly decreased. Longer-term exposure to MNPs caused oxidative stress in the digestive gland as well as impaired viability and immunity of hemocytes. Particle size also influenced the response with smaller particles having more severe effects. A depuration for 7 days was enough to reverse the negative effects observed on the digestive gland and hemolymph. This study provides new insights on the effects of small-sized MNPs, especially nanoplastic particles (NPs), on aquatic organisms, and provides a solid theoretical knowledge background for future studies on toxic effects of MNPs.

The combined effects of phenanthrene and micro-/nanoplastics mixtures on the cellular stress responses of the thick-shell mussel Mytilus coruscus.

Pollution with complex mixtures of contaminants including micro- and nano-plastics (MNPs) and organic pollutants like polycyclic aromatic hydrocarbons (PAH) poses a major threat to coastal marine ecosystems. Toxic mechanisms of contaminant mixtures are not well understood in marine organisms. We studied the effects of single and combined exposures to polycyclic aromatic hydrocarbon phenanthrene (Phe) and MNPs mixture with sizes of 70 nm, 5 µm and 100 µm on the immune health and oxidative stress parameters in the thick-shell mussel Mytilus coruscus. Immune cells (hemocytes) were more sensitive to the pollutant-induced oxidative stress than the gills. In hemocytes of co-exposed mussels, elevated mortality, lower lysosomal content, high production of reactive oxygen species (ROS) and decrease mitochondrial were found. Disparate responses of antioxidant enzymes in the hemolymph (e.g. increased superoxide dismutase (SOD) activity without a corresponding increase in catalase (CAT) in Phe exposures and an increase in CAT without a change in SOD in MNPs exposures) suggests misbalance of the antioxidant defense in the pollutant-exposed mussels. Gill lacked pronounced oxidative stress response showing a decline in ROS and antioxidant levels. Tissue-specific single and combined effects of Phe and MNPs suggest variation in bioavailability and/or different sensitivity to these pollutants in the studied tissues. Notably, the combined effects of MNPs and Phe were additive or antagonistic, showing that MNPs do not enhance and occasionally mitigate the toxic effects of Phe on the hemocytes and the gills of the mussels. Overall, our study sheds light on the impact of long-term exposure to MNPs and Phe mixtures on mussels, showing high sensitivity of the immune system and modulation of the Phe toxicity by MNPs co-exposure. These findings that may have implications for understanding the impacts of combined PAH and MNPs pollution on the health of mussel populations from polluted coastal habitats.

Combined effects of microfibers and polychlorinated biphenyls on the immune function of hemocytes in the mussel Mytilus coruscus.

Numerous studies have shown that microplastics can interact with other pollutants in the environment to produce synergistic effects, leading to more serious impacts. To date, there is little consensus on the combined effects of microfibers (MFs) and polychlorinated biphenyls (PCBs, Aroclor 1254), two legacy and alarming environmental pollutants. There is an urgent need to assess the impact of combined exposures on bivalve immune defences. In this study, we assessed the immune response of the mussels (Mytilus coruscus) hemocyte to MFs and PCBs alone and in combination by using flow cytometry. M. coruscus were exposed to MFs (1000 pieces/L) and PCBs (PCBs) (100 ng/L and 1000 ng/L) alone or in combination for 14 consecutive days and recovered for 7 days. The hemocyte of M. coruscus was collected on day 7, 14 and 21. MF exposure alone had no effect on the hemocyte. The total hemocyte count (THC), esterase (EA), lysosomal contents (LC), mitochondrial number (MN) and mitochondrial membrane potential (MMP) of mussels showed a decreasing trend with increasing PCB concentrations, both individually and in combination; The decreases in EA, MN and MMP were associated with the induction of reactive oxygen species (ROS). Hemocyte mortality (HM) was associated with a decrease in THC. Combined exposure to MFs and PCBs would exacerbate the effects on hemocyte immunity. These new findings improve our understanding of the toxic effects of MFs and organic chemical pollutants, and demonstrate the potential mechanism of PCBs to bivalves through changes in hemolymph immunity-related indicators.

Effects of diel-cycling hypoxia and salinity on lipid metabolism and fatty acid composition of the oyster Crassostrea hongkongensis.

For marine animals living in estuarine, coastal, and intertidal areas, salinity changes and periodic hypoxia are typical stressors; however, how the varying salinity and dissolved oxygen affect the quality and nutrition of marine aquaculture species, such as oysters remains unknown. In this study, we evaluated the diel-cycling hypoxia under different salinities on fatty acid composition and lipid metabolism in oyster Crassostrea hongkongensis digestive glands. After 28 days of exposure, both hypoxia and elevated salinity caused a decrease in the saturated fatty acid (SFA)/polyunsaturated fatty acid (PUFA) ratio of C. hongkongensis, salinity mainly causes changes in C17:0, C17:1, C18:1n9, C20:1n9, C20:4n6, C21:5n3, C22:5n3, with high salinity being more damaging to the fatty acid fractions. Also, Hypoxia accelerates the synthesis of C18:1n9 and C20:4n6. Fatty acid synthase (FAS) synthesis is increased by reduced salinity or hypoxia, but Acetyl CoA carboxylase (ACC) only weakly promotes fatty acid synthesis. Under hypoxic conditions, the activity of both hepatic lipase (HL) and lipoprotein lipase activity (LPL) decreases, which is contrary to the results for dissolved oxygen. The increase in salinity under dissolved oxygen leads to a decrease in LPL activity and an increase in HL activity. Our findings highlighted that exposure to a combination of salinity and hypoxia stressors, can disrupt the protective mechanisms of the oyster and affect the function of its lipid metabolism. Therefore, long-term exposure to periodic hypoxia with salinity changes poses a risk to the nutritional quality of C. hongkongensis, affecting oyster aquaculture and the coastal ecosystem.

Response of moulting genes and gut microbiome to nano-plastics and copper in juvenile horseshoe crab Tachypleus tridentatus.

Nanoplastics (NPs) and heavy metals are typical marine pollutants, affecting the gut microbiota composition and molting rate of marine organisms. Currently, there is a lack of research on the toxicological effects of combined exposure to horseshoe crabs. In this study, we investigated the effects of NPs and copper on the expression of molt-related genes and gut microbiome in juvenile tri-spine horseshoe crabs Tachypleus tridentatus by exposing them to NPs (100 nm, 104 particles L-1) and/or Cu2+ (10 µgL-1) in seawater for 21 days. Compared with the control group, the relative mRNA expression of ecdysone receptor (EcR), retinoid x receptor (RXR), calmodulin-A-like isoform X1 (CaM X1), and heat shock 70 kDa protein (Hsp70) were significantly increased under the combined stress of NPs and Cu2+. There were no significant differences in the diversity and abundance indices of the gut microbial population of horseshoe crabs between the NPs and/or Cu2+ groups and the control group. According to linear discriminant analysis, Oleobacillus was the most abundant microorganism in the NPs and Cu2+ stress groups. These results indicate that exposure to either NPs stress alone or combined NPs and Cu2+ stress can promote the expression levels of juvenile molting genes. NPs exposure has a greater impact on the gut microbial community structure of juvenile horseshoe crabs compared to Cu2+ exposure. This study is helpful for predicting the growth and development of horseshoe crabs under complex environmental pollution.

Nano-TiO2 aggravates the adverse effect of pentachlorophenol on antioxidant and immune response in anti-predatory mussels.

Nano-TiO2 can act as a vector to organic compounds, such as pentachlorophenol (PCP) posing a potential threat to the marine ecosystems. Studies showed that nano pollutant toxicity can be modulated by abiotic factors, but little is known about the potential influence of biotic stressors (such as predators) on the physiological responses to pollutants in marine organisms. We explored the effects of n-TiO2 and PCP on the mussel Mytilus coruscus in the presence of its natural predator, the swimming crab Portunus trituberculatus. Exposure to n-TiO2, PCP, and predation risk showed interactive effects on antioxidant and immune parameters of the mussels. Elevated activities of catalase (CAT), glutathione peroxidase (GPX), acid phosphatase (ACP) and alkaline phosphatase (AKP), suppressed activity of superoxide dismutase (SOD), lower levels of glutathione (GSH) and increased malondialdehyde (MDA) levels indicated dysregulation of the antioxidant system and immune stress induced by single PCP or n-TiO2 exposure. Integrated biomarker (IBR) response values showed the effect of PCP was concentration dependent. Of the two used n-TiO2 sizes (25 and 100 nm), larger particles induced higher antioxidant and immune disturbances indicating higher toxicity possibly due to higher bioavailability. Compared to single PCP exposure, the combination of n-TiO2 and PCP enhanced the imbalance of SOD/CAT and GSH/GPX and led to elevated oxidative lesions and activation of immune-related enzymes. Overall, the combined impacts of pollutants and biotic stress exhibited a greater magnitude of adverse effects on antioxidant defense and immune parameters in mussels. The toxicological effects of PCP were exacerbated in the presence of n-TiO2, and the deleterious impact of these stressors was further amplified under predator-induced risk after prolonged (28 days) exposure. However, the underlying physiological regulatory mechanisms governing the interplay of these stressors and predatory cues on mussels remain elusive, warranting further investigation.

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

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.

Sex-specific digestive performance of mussels exposed to warming and starvation.

As global climate change has dramatically impacted the ocean, severe temperature elevation and a decline in primary productivity has frequently occurred, which has affected the structure of coastal biomes. In this study, the sex-specific responses to temperature change and food availability in mussels were determined in terms of digestive performance. The thick-shelled mussels Mytilus coruscus (male and female) were exposed to different temperature and nutritional conditions for 30 days. The results showed that the digestive enzymes of mussels were significantly affected by temperature, food, sex, and their interactions. High temperature (30°C) and starvation significantly decreased amylase, lysozyme, and pepsase activities of female mussels, while trypsin and trehalase did not change significantly at the experimental end. The activity of amylase, trypsin, and trehalase was significantly reduced in males at high temperature (30°C) under starvation treatment, but high temperature (30°C) elevated pepsase. Unsurprisingly, starvation caused the reduction of lysozyme and pepsase under 25°C in males. Amylase, lipase, and trehalase were higher in female mussels compared with males, while the enzymatic activities of lysozyme, pepsase, and trypsin were higher in male mussels than females. Principal component analysis showed that different enzyme activity indexes were separated in male and female mussels, indicating that male and female mussels exhibited significantly different digestive abilities under temperature and food condition change. The study clarified sex-specific response difference in mussel digestive enzymes under warming and starvation and provided guidance for the development of mussel aquaculture (high temperature management and feeding strategy) under changing marine environments.

Microplastics and food shortage impair the byssal attachment of thick-shelled mussel Mytilus coruscus.

Microplastics (MPs) have become a ubiquitous emerging pollutant in the global marine environment. The potential toxic effects of MPs and interactions of MP pollution with other stressors such as food limitation on marine organisms' health are not yet well understood. This study investigated the effects of three-week exposure to different MPs and food shortage on the physical defense mechanisms (byssus production and properties) of Mytilus coruscus. Starvation significantly reduced the number of byssus threads, and combined exposure to MPs and food shortage suppressed the adhesion ability and condition index of mussels. The length of the byssus threads was not affected by all experimental exposures. Transcript levels of genes encoding key proteins involved in byssus formation (the mussel foot proteins mfp-1, -2, -3, -4, -5 and -6, and prepolymerized collagen proteins preCOL-D, -P and -NG) were altered by interactions between the MPs and food shortage. These findings show that insufficient food supply can exacerbate the adverse effects of MPs on mussel defense which might have implications for survival and fitness of mussels under food limited conditions (e.g. in winter) in polluted coastal habitats.

Ocean acidification but not hypoxia alters the gonad performance in the thick shell mussel Mytilus coruscus.

Ocean acidification and hypoxia have become increasingly severe in coastal areas, and their co-occurrence poses emerging threats to coastal ecosystems. Here, we investigated the combined effects of ocean acidification and hypoxia on the reproductive capacity of the thick-shelled mussel Mytilus coruscus. Our results demonstrated low pH but not low oxygen induced decreased gonadosomatic index (GSI) in mussels. Male mussels had a lower level of sex steroids (estradiol, testosterone, and progesterone) when kept at low pH. Expression of genes related to reproduction were also impacted by low pH with a downregulation of genes involved in gonad development in males (ß-catenin and Wnt-7b involved in males) and an upregulation of testosterone synthesis inhibition-related gene (Wnt-4) in females. Overall, our results suggest that ocean acidification has an impact on the gonadal development through an alternation of gene expression and level of steroids while hypoxia had no significant effect.

Antioxidant responses of the mussel Mytilus coruscus co-exposed to ocean acidification, hypoxia and warming.

In the present study, the combined effects of pH, dissolved oxygen (DO) and temperature levels on the antioxidant responses of the mussel Mytilus coruscus were evaluated. Mussels were exposed to two pH (8.1, 7.7-acidification), two DO (6 mg L-1, 2 mg L-1-hypoxia) and two temperature levels (20 °C, 30 °C-warming) for 30 days. SOD, CAT, MDA, GPx, GSH, GST, TAOC, AKP, ACP, GPT, AST levels were measured in the gills of mussels. All tested biochemical parameters were altered by these three environmental stressors. Values for all the test parameters except GSH first increased and then decreased at various experimental treatments during days 15 and 30 as a result of acidification, hypoxia and warming. GSH content always increased with decreased pH, decreased DO and increased temperature. PCA showed a positive correlation among all the measured biochemical indexes. IBR results showed that M. coruscus were adversely affected by reduced pH, low DO and elevated temperature.

Ingestion of nano/micro plastic particles by the mussel Mytilus coruscus is size dependent.

Plastic particles are thought to accumulate in aquatic organisms and cause potential physiological effects. The uneven sizes of plastic particles may affect the ingestion by marine filter feeding bivalves and may lead to differential further physiological effects. To tackle this scientific question, we investigated the size dependent ingestion and dynamic accumulation of nano/micro plastic particles with different diameters (0.07, 0.5, 5, 10 and 100 µm) in the thick shell mussel Mytilus coruscus. The accumulation of particles in gill, digestive tract and mantle of mussels was measured after 3, 15, 87 h exposure and following 87 h depuration. The results showed that particle ingestion was negatively size dependant and positively related to time in digestive tract. In mantle, particles accumulated over the depuration time with a delay, indicating the translocation of particles. Moreover, our results showed that gill was not a target tissue for steady particle accumulation but the digestive tract was. This study showed size dependent and dynamic ingestion of nano/micro particles in mussels which are one of the main marine organisms for accumulating microplastics.

Short-term exposure to norfloxacin induces oxidative stress, neurotoxicity and microbiota alteration in juvenile large yellow croaker Pseudosciaena crocea.

In recent years, antibiotics have been widely detected in coastal waters of China, which raising concerns for coastal biodiversity and aquaculture. This study evaluated the effects of short-term exposure of norfloxacin (NOR) on oxidative stress and intestinal health of the large yellow croaker Pseudosciaena crocea. Juvenile fish were exposed to four concentrations of NOR (0.1, 10, 100 and 1000 µg/L) for 14 days. The results showed that NOR inhibited growth and threatened the survival of juveniles. According to the changes of intestinal microbiota, we found that NOR led to a significant decrease in intestinal microbiota diversity, with the decreased relative abundance of Proteobacteria, but the increased Tenericutes. From the perspective of microbial function, NOR inhibited metabolism, cellular defence mechanism and information transduction process. In terms of biochemical indicators, NOR caused an increase in malondialdehyde (MDA) level and inhibited superoxide dismutase (SOD) and acetyl cholinesterase (AChE) activities. Catalase (CAT) activity was activated at low concentration but significantly inhibited at high concentration of NOR. Moreover, there was a high correlation between change in biochemical indicators and change in the microbial community. Overall, environmentally relevant concentrations (0.1 µg/L) and high concentrations (10, 100 and 1000 µg/L) of NOR have negative effects on the defence function and intestinal health of large yellow croaker juveniles.

Ocean acidification, hypoxia and warming impair digestive parameters of marine mussels.

Global change and anthropogenic activities have driven marine environment changes dramatically during the past century, and hypoxia, acidification and warming have received much attention recently. Yet, the interactive effects among these stressors on marine organisms are extremely complex and not accurately clarified. Here, we evaluated the combined effects of low dissolved oxygen (DO), low pH and warming on the digestive enzyme activities of the mussel Mytilus coruscus. In this experiment, mussels were exposed to eight treatments, including two degrees of pH (8.1, 7.7), DO (6, 2 mg/l) and temperature (30 °C and 20 °C) for 30 days. Amylase (AMS), lipase (LPS), trypsin (TRY), trehalase (TREH) and lysozyme (LZM) activities were measured in the digestive glands of mussels. All the tested stress conditions showed significant effects on the enzymatic activities. AMS, LPS, TRY, TREH showed throughout decreased trend in their activities due to low pH, low DO, increased temperature and different combinations of these three stressors with time but LZM showed increased and then decreased trend in their activities. Hypoxia and warming showed almost similar effects on the enzymatic activities. PCA showed a positive correlation among all measured biochemical parameters. Therefore, the fitness of mussel is likely impaired by such marine environmental changes and their population may be affected under the global change scenarios.

Microplastics aggravate the adverse effects of BDE-47 on physiological and defense performance in mussels.

The highly hydrophobic surfaces make microplastics a potential carrier of organic pollutants in the marine environment. In order to explore the toxic effects of polybrominated diphenyl ethers (BDE-47) combined with microplastics on marine organisms, we exposed the marine mussel Mytilus coruscus to micro-PS combined with BDE-47 for 21 days to determine the immune defense, oxidative stress and energy metabolism of the mussels. The results showed that the clearance rate (CR) of mussels exposed to single micro-PS, single BDE-47 or both was lower than control group. In general, compared to single BDE-47 exposure, the combination of micro-PS and BDE-47 significantly increased respiration rate (RR), activities of acid phosphatase (ACP) and alkaline phosphatase (ALP), reactive oxygen species (ROS) production and malondialdehyde (MDA) concentrations, but significantly decreased lactate dehydrogenase (LDH) activity and the relative expression of heat shock protein (Hsp70 and 90). Overall, combined stress has more adverse effects on defense performance and energy metabolism in mussels and micro-PS seem to exacerbate the toxicological effects of BDE-47. As microplastics pollution may deteriorate in the future, the health of mussels may be threatened in organically polluted environment, which eventually change the stability of the structure and function of intertidal ecosystem.

Diel-cycling seawater acidification and hypoxia impair the physiological and growth performance of marine mussels.

Ocean acidification and hypoxia are concurrent in some coastal waters due to anthropogenic activities in the past decades. In the natural environment, pH and dissolved oxygen (DO) may fluctuate and follow diel-cycling patterns, but such effects on marine animals have not been comprehensively studied compared to their constant effects. In order to study the effects of diel-cycling seawater acidification and hypoxia on the fitness of marine bivalves, the thick shell mussels Mytilus coruscus were exposed to two constant levels of dissolved oxygen (2 mg/L, 8 mg/L) under two pH treatments (7.3, 8.1), as well as single diel fluctuating pH or DO, and the combined diel fluctuating of pH and DO for three weeks. The experimental results showed that constant acidification and hypoxia significantly reduced the extracellular pH (pHe) and condition index (CI) of mussels, and significantly increased HCO3-, pCO2 and standard metabolic rate (SMR). Diel fluctuating hypoxia and acidification also significantly reduced the pHe and CI, and significantly increased pCO2 and SMR, but had no significant effects on HCO3-. However, the diel-cycling acidification and hypoxia resulted in a higher CI compared to continuous exposure. In general, continuous and intermittent stress negatively impact the hemolymph and growth performance of mussels. However, mussels possess a little stronger resistance to diel-cycling seawater acidification and hypoxia than sustained stress.