Hemocytes in blue mussel Mytilus edulis adopt different energy supply modes to cope with different BDE-47 exposures.

The energetic response of blue mussel Mytilus edulis when coping with tetrabromodiphenyl ether (BDE-47) exposure was evaluated from the perspective of alterations in energy supply mode, and the possible regulating mechanism was discussed based on a 21-day bioassay. The results showed that the energy supply mode changed with concentration: 0.1 µg/L BDE-47 decreased the activity of isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase and oxidative phosphorylation, suggesting inhibition of the tricarboxylic (TCA) acid cycle and aerobic respiration. The coincident increase in phosphofructokinase and the decrease in lactate dehydrogenase (LDH) indicated that glycolysis and anaerobic respiration were increased. When exposed to 1.0 µg/L BDE-47, M. edulis mainly utilized aerobic respiration, but lowered glucose metabolism as indicated by the decrease in glutamine and l-leucine was suggested to be involved in this process, which was differed from that in the control. The reoccurrence of IDH and SDH inhibition as well as LDH elevation indicated attenuation of aerobic and anaerobic respiration when the concentration increased to 10 µg/L, but severe protein damage was evidenced based on the elevation of amino acids and glutamine. Under the 0.1 µg/L BDE-47, activation of the AMPK-Hif-1a signaling pathway promoted the expression of glut1, which was the potential mechanism for the improvement of anaerobic respiration, and further activated glycolysis and anaerobic respiration. This study shows that the energy supply mode experienced a conversion from aerobic respiration under normal conditions to anaerobic mode in the low BDE-47 treatment and back to aerobic respiration with increasing BDE-47 concentrations, which may represent a potential mechanism for mussel physiological responses when faced with different levels of BDE-47 stress.

Post-ecological effect and risk assessment of using modified clay in harmful algal bloom mitigation: An attempt based on the responses of zooplankton Brachionus plicatilis and bivalve Mytilus edulis.

The modified clay is the only worldwide-accepted practical method for mitigating algal bloom. Is it ecologically safe? To evidence it, a simulative bloom-occurring system of Karenia mikimotoi was set up, and the sentinel organisms of rotifer Brachionus plicatilis in sea surface and blue mussel Mytilus edulis on the benthos were respectively included. The organisms' physiological responses were determined as the indicators to reflect the ecological impacts when clay settled from surface to the bottom during the mimic bloom-mitigating process. Modified clay at a concentration of 0.1 g/L effectively removed the K. mikimotoi at an 81% removal rate, and its addition would not significantly strengthen the negative impacts on population dynamics and reproductive activities of B. plicatilis induced by sole K. mikimotoi within the first 2 h. Even an alleviation was observed at 2 d indicated by the increase of survival rate, egg and larva production after clay addition compared with those of 2 h. When the clay particles settled to benthos, the physical damage to the gills and digestive glands of M. edulis were found via the tissue and SEM observation, especially in higher treatment groups of 0.5 and 1.0 g/L, and filtering rate, digestive enzymes, condition index, water content and mortality were also influenced. However, little impact was found in group of 0.1 g/L. Risk assessment based on the adverse outcome pathway (AOP) model further revealed that the complete key event-key event relationship-adverse outcome pathway was only clearly observed in 0.5 g/L and 1 g/L groups but not in 0.1 g/L group, inferring the small ecological risk of 0.1 g/L. The integrated biomarker response (IBR) based on the mussel's physiological responses further backed up the AOP outcoming. The combined results from rotifer to bivalve emphasized on one conclusion that modified clay at 0.1 g/L was effective and ecologically safe in coastal bloom mitigation.

An Explanation Based on Energy-Related Changes for Blue Mussel Mytilus edulis Coping With Seawater Acidification.

As ocean acidification (OA) is gradually increasing, concerns regarding its ecological impacts on marine organisms are growing. Our previous studies have shown that seawater acidification exerted adverse effects on physiological processes of the blue mussel Mytilus edulis, and the aim of the present study was to obtain energy-related evidence to verify and explain our previous findings. Thus, the same acidification system (pH: 7.7 or 7.1; acidification method: HCl addition or CO2 enrichment; experimental period: 21d) was set up, and the energy-related changes were assessed. The results showed that the energy charge (EC) and the gene expressions of cytochrome C oxidase (COX) reflecting the ATP synthesis rate increased significantly after acidification treatments. What's more, the mussels exposed to acidification allocated more energy to gills and hemocytes. However, the total adenylate pool (TAP) and the final adenosine triphosphate (ATP) in M. edulis decreased significantly, especially in CO2 treatment group at pH 7.1. It was interesting to note that, TAP, ATP, and COXs gene expressions in CO2 treatment groups were all significantly lower than that in HCl treatment groups at the same pH, verifying that CO2-induced acidification exhibited more deleterious impacts on M. edulis, and ions besides H+ produced by CO2 dissolution were possible causes. In conclusion, energy-related changes in M. edulis responded actively to seawater acidification and varied with different acidification conditions, while the constraints they had at higher acidification levels suggest that M. edulis will have a limited tolerance to increasing OA in the future.

Depicting an energetic chain involved in physiological responses of blue mussel Mytilus edulis coping with BDE-47 exposure.

Depiction on an energetic chain in terms of assimilation, allocation and consumption as well as the linkage between energetic alteration and physiological process was performed in blue mussel Mytilus edulis coping with tetrabromodiphenyl ether (BDE-47) based on a 21-day bioassay to shed light on the possible mechanism from energetic perspective. The filtration was hindered along with BDE-47 concentration increment and the influence of digestion was suggested according to the combination of the digestive enzymatic activities' alteration and digestive gland tissue impairment, both of which decided the energy availability reduction. Energy consumption indicated by the electron transport system activity was firstly inhibited while was greatly increased with BDE-47 increment, and the cellular energy allocation and adenylate pool were decreased simultaneously. An energetic chain was thus depicted: it tended to reduce energy absorption, elevate the energy consumption and decrease the energy metabolism with BDE-47 exposure, and M. edulis adopted the energetic strategy with variation regarding to the stressing level, suggesting as the preference switched from protein utilization to lipid utilization with the concentration increment. A consistence was observed in index of growth and survival with the change of energy allocation, inferring the energetic involvement in sustaining the viability of the mussel.

The toxicity, bioaccumulation and debromination of BDE-47 and BDE-209 in Chlorella sp. under multiple exposure modes.

Polybrominated diphenyl ethers (PBDEs) are a series of important persistent organic pollutants (POPs) in marine environments. Microalgae are the start of PBDEs bioaccumulated and bioconcentrated along the marine food web. In order to investigate the variations of PBDEs bioaccumulation by microalgae and its influencing factors, we set up a series of experiments with Chlorella sp. under different BDE-47 or BDE-209 exposure modes to measure their toxicity, bioaccumulation and degradation patterns. The inhibition effect on cell growth was much more obvious in BDE-47 than BDE-209, with the EC50 values at 96 h calculated as 64.7 µg L-1 and 4070 µg L-1, respectively. Microalgal uptake rates showed BDE-209 diffused less into cells than BDE-47, with highest measured uptake rates of 0.145 × 10-7 µg h-1 cell-1 and 0.45 × 10-7 µg h-1 cell-1, respectively. The bioaccumulation amount by unit microalgal cell varied with PBDE concentrations and culture time, which appeared to be related to the changes of extracellular polymeric substances (EPS) and cellular neutral lipids under the toxicity of PBDEs. Finally, we found Chlorella sp. delayed the debromination patterns of BDE-209 compared to seawater. This study linked the toxicity, microalgal bioaccumulation and metabolism of PBDEs, provided new insights in the research of POPs by microalgae and marine food webs.

Title: CO2 and HCl-induced seawater acidification impair the ingestion and digestion of blue mussel Mytilus edulis.

Anthropogenic CO2 emissions lead to seawater acidification that reportedly exerts deleterious impacts on marine organisms, especially on calcifying organisms such as mussels. A 21-day experiment focusing on the impacts of seawater acidification on the blue mussel, Mytilus edulis, was performed in this study, within which two acidifying treatments, CO2 enrichment and HCl addition, were applied. Two acidifying pH values (7.7 and 7.1) and the alteration of the key physiological processes of ingestion and digestion were estimated. To thoroughly investigate the impact of acidification on mussels, a histopathological study approach was adopted. The results showed that: (1) Seawater acidification induced either by CO2 enrichment or HCl addition impaired the gill structure. Transmission electron microscope (TEM) results suggested that the most obvious impacts were inflammatory lesions and edema, while more distinct alterations, including endoplasmic reticulum edema, nuclear condensation and chromatin plate-like condensation, were placed in the CO2-treated groups compared to HCl-treated specimens. The ciliary activity of the CO2 group was significantly inhibited simultaneously, leading to an obstacle in food intake. (2) Seawater acidification prominently damaged the structure of digestive glands, and the enzymatic activities of amylase, protease and lipase significantly decreased, which might indicate that the digestion was suppressed. The negative impacts induced by the CO2 group were more severe than that by the HCl group. The present results suggest that acidification interferes with the processes of ingestion and digestion, which potentially inhibits the energy intake of mussels.

Cooperation Between Photosynthetic and Antioxidant Systems: An Important Factor in the Adaptation of Ulva prolifera to Abiotic Factors on the Sea Surface.

Large-scale green tides have occurred continuously in the Yellow Sea of China from 2007 to 2018, and the causative species of the Yellow Sea green tide (YSGT) is Ulva prolifera. The thalli form floated thallus mats, and the thalli from different layers of the thallus mat suffer significantly different environmental conditions. In the present study, the environmental conditions of the surface layer (SL), middle layer (ML), and lower layer (LL) of the thallus mat from mid-June (Stage I) to mid-July (Stage II) were simulated. Photosynthetic traits and antioxidant systems were measured. The results showed that (1) photoprotective [non-photochemical quenching (NPQ) and cyclic electron transport (CEF)] and antioxidant systems both play important roles in protecting against abiotic factors in U. prolifera. (2) Cooperation between NPQ and CEF was observed in the ML group; CEF and the antioxidant system in the SL group work synergistically to protect the thalli. Furthermore, an inferred spatiotemporal attribute regarding the YSGT is presented: the significant changes in abiotic factors on the sea surface can easily affect the thalli of SL and ML from mid-June to mid-July, and those of LL can be affected in mid-July. This cooperation combined with the spatiotemporal attributes offers an explanation for the annual occurrence of the YSGT. HIGHLIGHTS     -Adaptive mechanisms of Ulva prolifera against abiotic factors.     -Cooperation between photosynthetic and antioxidant systems.     -Spatiotemporal attributes regarding the Yellow Sea green tide are presented.

Is it photosensitization or photodegradation when UV-B irradiation is combined with BDE-47? Evidence from the growth and reproduction changes of rotifer Brachionus plicatilis.

Ecotoxicological methods were applied in the present study, and the marine rotifer Brachionus plicatilis was used as the toxic endpoint to depict what occurred when 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) was combined with solar ultraviolet-B radiation (UV-B). B. plicatilis was exposed to three different combination methods of BDE-47 and UV-B at an equal toxicity ratio, including normal rotifer co-cultured with UV-B-irradiated BDE-47 (known as Method I), UV-B-irradiated rotifer co-cultured with BDE-47 exposure (known as Method II) and normal rotifer co-cultured with the simultaneous addition of BDE-47 and UV-B irradiation (known as Method III). Acute and chronic experiments were preformed to determine the toxicity differentiation according to the growth and reproduction changes in the rotifer. Twenty-four-hour acute experiments showed that the modes of three combined methods changed from antagonism to additive, to synergistic with the concentration/dose increment, and the contribution rates of Method I and Method II to Method III were calculated by approximately 40.4% and 59.6%, respectively. Chronic exposure to either the single stressor or the combination of stressors inhibited the growth and reproduction of the rotifer, demonstrating the inhibition of the population growth rate and the decrease in the larvae production. Three combined groups presented more serious damages compared to groups with single stress exposure, and the ascending sequence of toxicity was Method I

The ROS-mediated pathway coupled with the MAPK-p38 signalling pathway and antioxidant system plays roles in the responses of Mytilus edulis haemocytes induced by BDE-47.

Our previous study found that BDE-47 could change the immune function of haemocytes in Mytilus edulis, and reactive oxygen species (ROS) might be involved in the process of physiological alteration. Here, we aimed to better understand this relationship. To accomplish this, we analysed changes in different ROS as well as various antioxidant system components. Additionally, the expression of MAPK-p38, a signalling protein regulated by ROS that helps to regulate numerous cellular processes, was also analysed. BDE-47 was given at low, medium, and high amounts. The results showed that (1) BDE-47 significantly affected ROS component levels in haemocytes. O2- content was increased under all conditions. H2O2 content was also increased under all conditions, except in the middle concentration group. In contrast, OH content was increased in the low and middle concentration groups and decreased in the high concentration group. (2) Estimations of the antioxidant systems revealed concentration-dependent changes. Catalase activity was increased throughout the experiment, while superoxide dismutase (SOD) exhibited a decreasing trend in the tested groups with an increase of exposure time. On day 21, only the high concentration group showed a slight increase in SOD activity compared to the control. Furthermore, glutathione peroxidase and glutathione reductase activity increased in the low and middle concentration groups but decreased in the high concentration group. The GSH/GSSG ratio increased for all treatments over time, indicating that changes in redox status occurred. (3) MAPK-p38 was activated following BDE-47 exposure. Based on our previous study, we speculate that BDE-47 exposure induces ROS production and affects the ROS-mediated pathway, which may explain the resultant functional damage observed in haemocytes. Furthermore, BDE-47 also affected the antioxidant system and altered redox status, although these changes did not ameliorate the damage caused by ROS.

Seawater acidification induced immune function changes of haemocytes in Mytilus edulis: a comparative study of CO2 and HCl enrichment.

The present study was performed to evaluate the effects of CO2- or HCl-induced seawater acidification (pH 7.7 or 7.1; control: pH 8.1) on haemocytes of Mytilus edulis, and the changes in the structure and immune function were investigated during a 21-day experiment. The results demonstrated that seawater acidification had little effect on the cellular mortality and granulocyte proportion but damaged the granulocyte ultrastructure. Phagocytosis of haemocytes was also significantly inhibited in a clearly concentration-dependent manner, demonstrating that the immune function was affected. Moreover, ROS production was significantly induced in both CO2 and HCl treatments, and four antioxidant components, GSH, GST, GR and GPx, had active responses to the acidification stress. Comparatively, CO2 had more severe destructive effects on haemocytes than HCl at the same pH level, indicating that CO2 stressed cells in other ways beyond the increasing H+ concentration. One possible explanation was that seawater acidification induced ROS overproduction, which damaged the ultrastructure of haemocytes and decreased phagocytosis.

BDE-47 exposure changed the immune function of haemocytes in Mytilus edulis: An explanation based on ROS-mediated pathway.

Brominated Tetra-BDE (BDE-47), is suggested to be widely distributed in marine environments and highly accumulated in marine organisms. Blue mussel Mytilus edulis is a sentinel organism that is commonly used for monitoring chemical contaminants in coastal ecosystems, and its haemocytes play an essential role in immune function. Therefore, we estimated the effects of BDE-47 exposure on the M. edulis haemocytes' immune function under controlled laboratory conditions. The study found the following results: (1) BDE-47 exposure increased the mortality of the haemocytes and decreased the total haemocyte counts. The ultrastructure and microstructure in the haemocytes were significantly changed, and the micronucleus frequency was increased steadily in a concentration-dependent manner, inferring that cellular and molecular damages occur during the exposure. (2) The immune function of the haemocytes was estimated from lysosomal and phagocytic changes. The lysosomal membrane stability was significantly disrupted compared to the control according to neutral red retention time changes, and the phagocytic ability was reduced significantly. Two lysosomal enzymes, acid phosphatases and alkaline phosphatases, presented similar increasing trends during the treatment. (3) BDE-47 exposure significantly induced the overproduction of reactive oxygen species and malondialdehyde in a clear time- and concentration-dependent manner, suggesting the occurrence of oxidative stress. We thus presumed that BDE-47 exposure affected the immune function of the mussel's haemocytes, and an ROS-mediated pathway might be one of the possible explanations for the observation.