Potential Function of 3,5-Dihydroxy-4-Methoxybenzyl Alcohol from Pacific Oyster (Crassostrea gigas) in Brain of Old Mice.

SCOPE: 3,5-Dihydroxy-4-methoxybenzyl alcohol (DHMBA) is found in oyster extracts in recent years and is reported to have antioxidant activity. Although it has been reported to be protective in various models of oxidative stress, the therapeutic effect of DHMBA on neurological damage caused by aging remains to be demonstrated. METHODS AND RESULTS: The present study investigates the potential functions of DHMBA in brain of old C57BL/6J mice and aging cell model. Administration of DHMBA improves working memory, reduces anxiety behavior, decreases the expression levels of cell cycle proteins, cycin-dependent kinase inhibitor 1(P21) and peptidase inhibitor 16(P16)  and inhibits neuronal loss in old mice. The data obtained from the aging cell model are consistent with those from the old mice. The interaction between DHMBA and Kelch-like ECH-associated protein 1 (Keap1) is predicted by molecular docking assay, and then it is verified by co-immunopricipitation (CoIP) that factor red lineage 2-related factor 2 (Nrf2)-Keap1 protein-protein interaction is inhibited by DHMBA. Protein levels of Nrf2 and its target genes, such as glutathione peroxidase 4(GPX4) and heme oxygenase 1 (HO-1), are detected in old mice and aging cell model. CONCLUSION: This study provides new evidence that explores the antioxidant mechanism of DHMBA and implies a potential role of DHMBA on antiaging in brain.

Susceptibility of shellfish aquaculture species in the Chesapeake Bay and Maryland coastal bays to ostreid herpesvirus 1 microvariants.

Ostreid herpesvirus 1 (OsHV-1) and its microvariants (µVars) cause economically devastating mass mortalities of oysters and pose a threat to the shellfish aquaculture industry globally. OsHV-1 outbreaks can cause up to 100% mortality in the Pacific oyster Crassostrea gigas. However, OsHV-1 and its variants have a broad host range and can infect at least 7 bivalve species, including bay scallops Argopecten irradians and eastern oysters C. virginica. Determining the susceptibility of economically and ecologically important bivalve species to OsHV-1 is critical for improving biosecurity and disease management to protect the aquaculture industry. Surveys of eastern oysters were conducted in June to August 2021 in the Maryland portion of the Chesapeake Bay to determine the prevalence and viral load of OsHV-1 at 5 aquaculture farms. Using quantitative PCR, OsHV-1 was not detected at any sites. Experiments examined the susceptibility of single stocks of eastern oysters and hard clams Mercenaria mercenaria to the virus and their ability to horizontally transmit it using OsHV-1 µVar SD (San Diego, California) and OsHV-1 µVar FRA (Marennes-Olreon, France). Results showed that OsHV-1 µVars did not cause mortality or symptomatic infection in the single stocks of eastern oysters and hard clams used in these experiments using natural infection pathways. However, the eastern oyster stock, when injected with OsHV-1, did transmit the virus to naïve Pacific oysters. Further experimentation using additional stocks and lines and establishment of surveillance programs along the east and Gulf coasts of the USA are necessary to prepare for the potential spread and impact of OsHV-1 related disease.

Emerging and legacy contaminants on the Brazilian southern coast (Santa Catarina): A multi-biomarker approach in oysters Crassostrea gasar (Adanson, 1757).

Coastal environments, such as those in the Santa Catarina State (SC, Brazil), are considered the primary receptors of anthropogenic pollutants. In this study, our objective was to evaluate the levels of emerging contaminants (ECs) and persistent organic pollutants (POPs) in indigenous Crassostrea gasar oysters from different regions of SC coast in the summer season (March 2022). Field collections were conducted in the São Francisco do Sul, Itajaí, Florianópolis and Laguna coastal zones. We analyzed the bioaccumulation levels of 75 compounds, including antibiotics (AB), endocrine disruptors (ED), non-steroidal anti-inflammatory drugs (NSAIDs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and pesticides. Furthermore, we assessed biomarker responses related to biotransformation, antioxidant defense, heat shock protection and oxidative damage in oysters' gills. Prevalence of ECs was observed in the central and southern regions, while the highest concentrations of POPs were detected in the central-northern regions of SC. Oysters exhibited an induction in biotransformation systems (cyp2au1 and cyp356a1, sult and GST activity) and antioxidant enzymes activities (SOD, CAT and GPx). Higher susceptibility to lipid peroxidation was observed in the animals from Florianópolis compared to other regions. Correlation analyses indicated possible associations between contaminants and environmental variables in the biomarker responses, serving as a warning related to climate change. Our results highlight the influence of anthropogenic activities on SC, serving as baseline of ECs and POPs levels in the coastal areas of Santa Catarina, indicating more critical zones for extensive monitoring, aiming to conserve coastal regions.

Cross-talk and mutual shaping between the immune system and the microbiota during an oyster's life.

The Pacific oyster Crassostrea gigas lives in microbe-rich marine coastal systems subjected to rapid environmental changes. It harbours a diversified and fluctuating microbiota that cohabits with immune cells expressing a diversified immune gene repertoire. In the early stages of oyster development, just after fertilization, the microbiota plays a key role in educating the immune system. Exposure to a rich microbial environment at the larval stage leads to an increase in immune competence throughout the life of the oyster, conferring a better protection against pathogenic infections at later juvenile/adult stages. This beneficial effect, which is intergenerational, is associated with epigenetic remodelling. At juvenile stages, the educated immune system participates in the control of the homeostasis. In particular, the microbiota is fine-tuned by oyster antimicrobial peptides acting through specific and synergistic effects. However, this balance is fragile, as illustrated by the Pacific Oyster Mortality Syndrome, a disease causing mass mortalities in oysters worldwide. In this disease, the weakening of oyster immune defences by OsHV-1 µVar virus induces a dysbiosis leading to fatal sepsis. This review illustrates the continuous interaction between the highly diversified oyster immune system and its dynamic microbiota throughout its life, and the importance of this cross-talk for oyster health. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach.

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Inorganic osmolytes and enzymatic biomarkers from the manabi oyster (Crassostrea cf. corteziensis) in response to saline stress.

Abrupt drops in salinity that occur in tropical estuaries during the equatorial rainy season led to hyposaline conditions which may reduce the populational density of oysters. To assess the effect of saline stress on physiological and metabolic responses of the Manabi oyster (Crassostrea cf. corteziensis) was exposed to 35, 30, 20,10 and 5‰ concentrations during 96 h. Inorganic osmolytes, pH, salinity, haemocyanin and protein concentration in the plasma as well as the number of oysters with closed valves were recorded. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and catalase (CAT) activity were analysed. Inorganic osmolytes and internal salinity were elevated in oysters exposed to 35, 10 and 5‰. A significant number of oysters with valve closure was observed in 10 and 5‰, which coincided with a decline in physiological pH and changes in haemocyanin concentrations. AST activity and AST/ALT ratio were reduced under 35, 10 and 5‰, and CAT increased in oysters exposed to 35‰; but protein concentration, LDH and ALP did not show significant variations. Metabolic adjustment and behavior of the Manabi oyster could explain tolerance and survival (at least for a short term) to hyposaline stress in tropical estuarine ecosystems.

Ingestion and depuration of polyester microfibers by Crassostrea gasar (Adanson, 1757).

The study aimed to obtain environmentally relevant microfibers (MFs) from polyester fabric and assess their impact on the oyster Crassostrea gasar. MFs were obtained by grinding the fabric, and their accumulation in oysters gills and digestive glands was analyzed after exposure to 0.5 mg/L for 2 and 24 h. Additionally, a 48 h depuration was conducted on the oysters exposed for 24 h. Sublethal effects were assessed in oysters exposed for 24 h and depurated for 48 h, using biomarkers like Catalase (CAT), Glutathione S-transferase (GST), and Glutathione Peroxidase (GPx), along with histological analyses. Polyester fabric grinding produced significant MFs (average length: 570 µm) with degraded surface and increased malleability. Oysters showed increased MF accumulation in digestive glands post-exposure, with no impact on antioxidant enzymes. Depuration decreased MFs accumulation. Histological analysis revealed accumulation in the stomach and brown cells, possibly indicating inflammation. This raises concerns about MFs bioaccumulation in marine organisms, impacting the food chain and safety.

Effects of ambient UVB light on Pacific oyster Crassostrea gigas mantle tissue based on multivariate data.

Ambient ultraviolet radiation (UVB) from solar and artificial light presents serious environmental risks to aquatic ecosystems. The Pacific oyster, Crassostrea gigas, perceives changes in the external environment primarily through its mantle tissue, which contains many nerve fibers and tentacles. Changes within the mantles can typically illustrate the injury of ambient UVB. In this study, a comprehensive analysis of phenotypic, behavioral, and physiological changes demonstrated that extreme UVB radiation (10 W/m²) directly suppressed the behavioral activities of C. gigas. Conversely, under ambient UVB radiation (5 W/m²), various physiological processes exhibited significant alterations in C. gigas, despite the behavior remaining relatively unaffected. Using mathematical model analysis, the integrated analysis of the full-length transcriptome, proteome, and metabolome showed that ambient UVB significantly affected the metabolic processes (saccharide, lipid, and protein metabolism) and cellular biology processes (autophagy, apoptosis, oxidative stress) of the C. gigas mantle. Subsequently, using Procrustes analysis and Pearson correlation analysis, the association between multi-omics data and physiological changes, as well as their biomarkers, revealed the effect of UVB on three crucial biological processes: activation of autophagy signaling (key factors: Ca2+, LC3B, BECN1, caspase-7), response to oxidative stress (reactive oxygen species, heat shock 70, cytochrome c oxidase), and recalibration of energy metabolism (saccharide, succinic acid, translation initiation factor IF-2). These findings offer a fresh perspective on the integration of multi-data from non-model animals in ambient UVB risk assessment.

Exploring the Potential of Crassostrea nippona Hydrolysates as Dietary Supplements for Mitigating Dexamethasone-Induced Muscle Atrophy in C2C12 Cells.

Muscle atrophy is a detrimental and injurious condition that leads to reduced skeletal muscle mass and disruption of protein metabolism. Oyster (Crassostrea nippona) is a famous and commonly consumed shellfish in East Asia and has become a popular dietary choice worldwide. The current investigation evaluated the efficacy of C. nippona against muscle atrophy, which has become a severe health issue. Mammalian skeletal muscles are primarily responsible for efficient metabolism, energy consumption, and body movements. The proteins that regulate muscle hypertrophy and atrophy are involved in muscle growth. C. nippona extracts were enzymatically hydrolyzed using alcalase (AOH), flavourzyme (FOH), and protamex (POH) to evaluate their efficacy in mitigating dexamethasone-induced muscle damage in C2C12 cells in vitro. AOH exhibited notable cell proliferative abilities, promoting dose-dependent myotube formation. These results were further solidified by protein expression analysis. Western blot and gene expression analysis via RT-qPCR demonstrated that AOH downregulated MuRF-1, Atrogin, Smad 2/3, and Foxo-3a, while upregulating myogenin, MyoD, myosin heavy chain expression, and mTOR, key components of the ubiquitin-proteasome and mTOR signaling pathways. Finally, this study suggests that AOH holds promise for alleviating dexamethasone-induced muscle atrophy in C2C12 cells in vitro, offering insights for developing functional foods targeting conditions akin to sarcopenia.

A Comparative Study of Mercury Bioaccumulation in Bivalve Molluscs from a Shallow Estuarine Embayment.

In estuarine food webs, bivalve molluscs transfer nutrients and pollutants to higher trophic levels. Mercury (Hg) pollution is ubiquitous, but it is especially elevated in estuaries historically impacted by industrial activities, such as those in the U.S. Northeast. Monomethylmercury (MeHg), the organic form of Hg, is highly bioaccumulative and transferable in the food web resulting in the highest concentrations in the largest and oldest marine predators. Patterns of Hg concentrations in marine bivalve molluscs, however, are poorly understood. In this study, inorganic Hg (iHg), MeHg, and the total Hg (THg) in soft tissues of the northern quahogs (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), and ribbed mussels (Geukensia demissa) from eastern Long Island sound, a temperate estuary of the western North Atlantic Ocean was investigated. In all three species, concentrations of THg remained similar between the four sampling months (May, June, July, and September), and were mostly independent of animal size. In quahogs, MeHg and iHg displayed significant (p < 0.05) positive (iHg in May and June) and negative (MeHg in July and September) changes with shell height. Variability in concentrations of THg, MeHg, and iHg, both inter- and intra-specifically was high and greater in quahogs and oysters (THg: 37, 39%, MeHg: 28, 39%, respectively) than in mussels (THg: 13%, MeHg: 20%). The percentage of THg that was MeHg (%MeHg) was also highly variable in the three species (range: 10-80%), highlighting the importance of measuring MeHg and not only THg in molluscs.

The prokaryotic and eukaryotic microbiome of Pacific oyster spat is shaped by ocean warming but not acidification.

Pacific oysters (Magallana gigas, a.k.a. Crassostrea gigas), the most widely farmed oysters, are under threat from climate change and emerging pathogens. In part, their resilience may be affected by their microbiome, which, in turn, may be influenced by ocean warming and acidification. To understand these impacts, we exposed early-development Pacific oyster spat to different temperatures (18°C and 24°C) and pCO2 levels (800, 1,600, and 2,800 µatm) in a fully crossed design for 3 weeks. Under all conditions, the microbiome changed over time, with a large decrease in the relative abundance of potentially pathogenic ciliates (Uronema marinum) in all treatments with time. The microbiome composition differed significantly with temperature, but not acidification, indicating that Pacific oyster spat microbiomes can be altered by ocean warming but is resilient to ocean acidification in our experiments. Microbial taxa differed in relative abundance with temperature, implying different adaptive strategies and ecological specializations among microorganisms. Additionally, a small proportion (~0.2% of the total taxa) of the relatively abundant microbial taxa were core constituents (>50% occurrence among samples) across different temperatures, pCO2 levels, or time. Some taxa, including A4b bacteria and members of the family Saprospiraceae in the phyla Chloroflexi (syn. Chloroflexota) and Bacteroidetes (syn. Bacteroidota), respectively, as well as protists in the genera Labyrinthula and Aplanochytrium in the class Labyrinthulomycetes, and Pseudoperkinsus tapetis in the class Ichthyosporea were core constituents across temperatures, pCO2 levels, and time, suggesting that they play an important, albeit unknown, role in maintaining the structural and functional stability of the Pacific oyster spat microbiome in response to ocean warming and acidification. These findings highlight the flexibility of the spat microbiome to environmental changes.IMPORTANCEPacific oysters are the most economically important and widely farmed species of oyster, and their production depends on healthy oyster spat. In turn, spat health and productivity are affected by the associated microbiota; yet, studies have not scrutinized the effects of temperature and pCO2 on the prokaryotic and eukaryotic microbiomes of spat. Here, we show that both the prokaryotic and, for the first time, eukaryotic microbiome of Pacific oyster spat are surprisingly resilient to changes in acidification, but sensitive to ocean warming. The findings have potential implications for oyster survival amid climate change and underscore the need to understand temperature and pCO2 effects on the microbiome and the cascading effects on oyster health and productivity.

An LPS-induced TNF-α factor involved in immune response of oyster Crassostrea gigas by regulating haemocytes apoptosis.

LPS induced TNF-α Factor (LITAF) is a transcription factor widely involving in activation of Tumor Necrosis Factor (TNF) and other cytokines in the inflammatory response. In the present study, a homologue of LITAF with a conserved LITAF domain was identified from the Pacific oyster Crassostrea gigas. The transcripts of CgLITAF were detected in all examined tissues with highest expression in hepatopancrease. The immunofluorescence assay and Western blot showed that LPS stimulation induced an obvious nucleus translocation of CgLITAF protein in haemocytes. While the mRNA level of CgLITAF changed slightly after LPS stimulation. When the siRNA of CgLITAF was injected to inhibit its expression, the apoptotic level of haemocytes decreased observably after LPS stimulation. Consistently, the transcripts of CgTNF3 and CgTNF4 (LOC105343080, LOC105341146), the apoptotic-related molecules including CgBax, CgCytochrome c, CgCaspase9 and CgCaspase3, were significantly suppressed in the CgLITAF-RNAi oysters. While the mRNA expression level of CgBcl was enhanced significantly in the CgLITAF-RNAi oysters. These results indicated that CgLITAF promoted haemocyte apoptosis by regulating the expression of apoptotic-related factors, suggesting its important role in the immune response of oysters.

Human health risk attributed to consumption of seafood and recreation swimming in Negombo Lagoon, Sri Lanka: An assessment on lagoon water and inhabitant oysters (Crassostrea cucullata Born, 1778).

The Negombo Lagoon is a coastal lagoon influenced by local communities that introduce waste into its ecosystem. This study examined seven sewage entry points, out of which five sites were chosen for oyster sampling based on availability. Physicochemical and microbiological parameters of water (measured in triplicate at each site, n = 84) and oyster samples (total length, TL > 6 cm, n = 30) were assessed. Variation in regional coliform contamination was analyzed employing a one-way analysis of variance (ANOVA). Results indicated that the northern part of the lagoon exceeded recommended coliform thresholds for swimming (total coliform concentration (TCC) < 126 most probable number (MPN)) and seafood consumption (TCC < 100 MPN/g), indicating the presence of Escherichia coli. Water quality indices affirmed fecal pollution, except in the southern part of the lagoon. Furthermore, the study found high oyster consumption (76.7 %), elucidating that oysters from the northern part of Negombo Lagoon pose health risks.

Impact of nano- and micro-sized polystyrene beads on larval survival and growth of the Pacific oyster Crassostrea gigas.

This study successionally monitored how nano- and micro-sized polystyrene beads (MNPs) influence larval mortality, growth, and attachment behavior of the Pacific oyster Crassostrea gigas related to MNP diameter and concentration. D-shaped larvae were sequentially exposed to three-diameter MNPs (0.55, 3.00, 6.00 µm) at five concentrations (0, 0.1, 1.0, 10, 20 µg/mL), and their mortality, growth stages and attachment were observed daily until they die. In addition, MNP intake and accumulation in larvae at each growth stage were determined using fluorescent beads. Deterioration in larval growth and survival was observed under all the exposure conditions, while significant negative effects on the growth parameters were defined with smaller MNPs at lower concentrations. Fluorescent signals were detected in larval digestive tracts at all except D-shaped larval stage, and on the mantle and foot in pediveligers. Therefore, MNP intake adversely affects larval physiological conditions by the synchronal effects of MNP size and concentration. Our findings highlight the implications of MNP characteristics on Pacific oyster larvae, emphasizing the interplay between size, concentration, and physiological responses, crucial for mitigating nanoparticle pollution in marine ecosystems.

Entanglement and ingestion of microfibers by the oyster pea crab Zaops ostreum, an endosymbiont of the eastern oyster Crassostrea virginica.

The kleptoparasitic pea crab Zaops ostreum lives within the gills of bivalves, including the economically important eastern oyster Crassostrea virginica. Previous research along the east coast of central Florida has found an average of 2.3 pieces of plastic per oyster. The goals of our research were to determine if filter-feeding oysters transfer microfibers to Z. ostreum via the crab: 1) actively consuming plastic particles, or 2) passively becoming entangled in microfibers. Our results show that both occur. While only 11.6 % of Z. ostreum (total n = 122) consumed microfibers, those that did had up to 14 pieces in their soft tissues. Similarly, only 7.4 % of Z. ostreum had microfibers entangled around their appendages. Mean lengths of consumed and entangled fibers were similar, 1.9 and 2.7 mm, respectively. Additional research is needed to understand the positive and negative impacts of microfibers associated with pea crabs on both species.

Biochemical responses in Pacific oysters Magallana gigas (Thunberg, 1793): Tools to evaluate the environmental quality of aquaculture areas.

The discharge of sanitary sewage into the bays of the Florianópolis Metropolitan Area (Southern Brazil), has led to the contamination of oyster farms. Consequently, linear alkylbenzenes (LABs) were quantified in the sediment, and the biochemical responses in gills and digestive gland of oysters from six farms were assessed. Our findings revealed elevated levels of LABs in the sediment of the Imaruim and Serraria farms. Additionally, alterations were observed in the antioxidant enzymes: catalase, glutathione peroxidase and superoxide dismutase in both oyster tissue from the Serraria, Santo Antonio de Lisboa and Sambaqui farms. Furthermore, correlation analyses indicated strong and moderate associations between biochemical responses, organic contaminants, and certain physicochemical parameters. Consequently, our results demonstrated the activation of the antioxidant system in oysters, representing a protective response to the presence of sanitary sewage and other contaminants. Therefore, we propose the utilization of biochemical biomarkers for monitoring the environmental quality of farms.

Understanding the variable metal concentrations in estuarine oysters Crassostrea hongkongensis: A biokinetic analysis.

Understanding the metal concentrations in oysters is important because of its relevance to human health and biomonitoring. However, metal concentrations in oysters are highly variable in nature and not well explained by metal exposure. This study examined the metal contamination in farm oysters Crassostrea hongkongensis grown in Qinzhou Bay, south China. Cadmium (Cd), zinc (Zn), nickel (Ni), and copper (Cu) concentrations in the oysters varied between 7.9 and 72.2, 282-17003, 0.37-47.7 and 37-4012 µg g-1, respectively, showing large metal variability among different individuals. Oyster metal concentrations decreased with increasing body size and significantly higher levels were observed in wet season. Low salinity and slower oyster growth due to inferior growth conditions could be responsible for the elevated metal concentrations in the wet season. Biokinetic modeling showed that the coupling of ingestion rate and growth can cause 2.8-4.2 folds differences in the oyster Cd and Zn concentrations, respectively, suggesting the significant role of oyster bioenergetics in contributing to the metal variability. Modeling data revealed that Cd and Zn concentrations in oyster tissues reach maximum levels when oysters have their lowest growth efficiency. This suggests that any factors influencing the energy budget in oysters could simultaneously alter their metal concentrations, which might be the reason why oyster metal concentrations are so variable in the natural environment.

Inactivation of two oyster pathogens by photocatalysis and monitoring of changes in the microbiota of seawater: A case study on Ostreid herpes virus 1 µVar and Vibrio harveyi.

The pollution of seawater by both biotic (bacteria, viruses) and abiotic contaminants (biocides, pharmaceutical residues) frequently leads to economic losses in aquaculture activities mostly mortality events caused by microbial infection. Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis allow the removal of all organic contaminants present in water and therefore could reduce production losses in land-based farms. Oysters in land-based farms such as hatcheries and nurseries suffer from a large number of mortality events, resulting in significant losses. If photocatalysis has been widely studied for the decontamination, its application for disinfection is still overlooked, especially on seawater for viruses. We therefore studied seawater disinfection using the photocatalysis (UV365/TiO2) method in the context of Pacific oyster mortality syndrome (POMS). POMS has been defined as a polymicrobial disease involving an initial viral infection with Ostreid Herpes Virus 1, accompanied by multiple bacterial infections. We investigated the impact of treatment on Vibrio harveyi, a unique opportunistic pathogenic bacterium, and on a complex microbial community reflecting a natural POMS event. Viral inactivation was monitored using experimental infections to determine whether viral particles were still infectious after. Changes in the total bacterial community in seawater were studied by comparing UV365/TiO2 treatment with UV365-irradiated seawater and untreated seawater. In the case of OsHV-1, a 2-h photocatalytic treatment prevents POMS disease and oyster mortality. The same treatment also inactivates 80% of viable Vibrio harveyi culture (c.a. 1.5 log). Since OsHV-1 and Vibrio harveyi are effectively inactivated without long-term destabilization of the total bacterial microbiota in the seawater, photocatalysis appears to be a relevant alternative for disinfecting seawater in land-based oyster beds.

Immunotoxicity of microplastics and polychlorinated biphenyls alone or in combination to Crassostrea gigas.

Microplastics (MPs) and polychlorinated biphenyls (PCBs) are pervasive pollutants in the marine environment, exerting adverse effects on marine organisms. While it is suggested that their exposure may compromise the immune responses of marine organisms, the cumulative immunotoxic effects remain uncertain. Additionally, the intricate mechanisms underlying the immunotoxicity of PCBs and MPs in marine organisms are not yet fully comprehended. To illuminate their combined biological impacts, Crassostrea gigas were exposed to 50 µg/L MPs (30-µm porous) alone, as well as 10 or 100 ng/L PCBs individually or in combination with 50 µg/L of MPs for 28 days. Our data demonstrated that oysters treated with the pollutants examined led to decreased total haemocyte count, inhibited phagocytosis of haemocytes, enhanced the intracellular contents of reactive oxygen species, lipid peroxidation and DNA damage, reduced lysozyme concentration and activity, gave rise to superoxide dismutase. Catalaseand glutathione S-transferaseactivity. The expression of three immune-related genes (NF-κB, TNF-α, TLR-6) was drastically suppressed by the PCBs and MPs treatment, while the apoptosis pathway-related genes (BAX and Caspase-3) showed a significant increase. In addition, compared to oysters treated with a single type of pollutant, coexposure to MPs and PCBs exerted more severe adverse impacts on all the parameters investigated, indicating a significant synergistic effect. Therefore, the risk of MPs and PCBs chemicals on marine organisms should be paid more attention.

Geographical distribution and ecological niche dynamics of Crassostrea sikamea (Amemiya, 1928) in China's coastal regions under climate change.

Global climate change drives species redistribution, threatening biodiversity and ecosystem heterogeneity. The Kumamoto oyster, Crassostrea sikamea (Amemiya, 1928), one of the most promising aquaculture species because of its delayed reproductive timing, was once prevalent in southern China. In this study, an ensemble species distribution model was employed to analyze the distribution range shift and ecological niche dynamics of C. sikamea along China's coastline under the current and future climate scenarios (RCP 2.6-8.5 covering 2050 s and 2100 s). The model results indicated that the current habitat distribution for C. sikamea consists of a continuous stretch extending from the coastlines of Hainan Province to the northern shores of Jiangsu Province. By the 2050 s, the distribution range will stabilize at its southern end along the coast of Hainan Province, while expanding northward to cover the coastal areas of Shandong Province, showing a more dramatic trend of contraction in the south and invasion in the north by the 2100 s. In RCP8.5, the southern end retracts to the coasts of Guangdong, whereas the northern end covers all of China's coastal areas north of 34°N. C. sikamea can maintain relatively stable ecological niche characteristics, while it may occupy different ecological niche spaces under future climate conditions. Significant niche expansion will occur in lower temperature. We concluded C. sikamea habitats are susceptible to climate change. The rapid northward expansion of C. sikamea may open new possibilities for oyster farming in China, but it will also have important consequences for the ecological balance and biodiversity of receiving areas. It's imperative that we closely examine and strategize to address these repercussions for a win-win situation.