Pacific Oyster Crassostrea Gigas Research Articles

A novel DM9-containing protein 7 involved in regulating the expression of CgMyD88 and CgIL-17 in oyster Crassostrea gigas

The DM9-containing proteins have been identified as pattern recognition receptors (PRRs) to recognize invading pathogens and subsequently mediate downstream signal pathways, playing essential roles in innate immune responses of molluscs. In the present study, a novel DM9-containing protein (named as CgDM9CP-7) was identified from Pacific oyster Crassostrea gigas, which contained two tandem DM9 repeats similar to the previously identified CgDM9CPs. The mRNA transcripts of CgDM9CP-7 were found to be constitutively expressed in all the tested tissues including haemolymph, gill, hepatopancreas, mantle, adductor muscle and labial palp. The expression level of CgDM9CP-7 mRNA in haemocytes significantly up-regulated at 3 and 6 h after Vibrio splendidus stimulation, which was 5.67-fold (p < 0.01) and 4.71-fold (p < 0.05) of that in the control group, respectively, and it also increased significantly at 6 h (3.08-fold, p < 0.01) post lipopolysaccharide (LPS) stimulation. The protein of CgDM9CP-7 was mainly detected in membrane and cytoplasm of oyster haemocytes after V. splendidus stimulation. The recombinant CgDM9CP-7 protein (rCgDM9CP-7) displayed binding activities to MAN, LPS, PGN, Poly (I:C) as well as gram-negative bacteria (V. splendidus and Escherichia coli), gram-positive bacteria (Staphylococcus aureus and Micrococcus luteus) and fungi (Pichia pastoris and Yarrowia lipolytica). rCgDM9CP-7 was able to agglutinate Bacillus subtilis, V. splendidus, E. coli and S. aureus, inhibit their growth, and bind the recombinant protein CgMyd88-2 (KD = 5.98 × 10−6 M) and CgMyd88s (KD = 8.5 × 10−7 M) in vitro as well. The transcripts of CgIL17-1 (0.45-fold of the control group, p < 0.01), CgIL17-2 (0.19-fold, p < 0.05), CgIL17-3 (0.54-fold, p < 0.05), CgIL17-5 (0.36-fold, p < 0.05) and CgIL17-6 (0.24-fold, p < 0.01) in CgDM9CP-7-siRNA oysters decreased significantly at 6 h after V. splendidus stimulation. These results collectively indicated that CgDM9CP-7 was involved in the regulation of CgMyD88 and CgIL-17 expression in the immune response of oyster.

Mannose oligosaccharide recognition of CGL1, a mannose-specific lectin containing DM9 motifs from Crassostrea gigas, revealed by X-ray crystallographic analysis.

CGL1 is a mannose-specific lectin isolated from the Pacific oyster Crassostrea gigas, and it belongs to the DM9 domain protein family. Each subunit of the CGL1 dimer consists of a tandem repeat of DM9 motifs, which were originally found in the Drosophila melanogaster genome. The CGL1 protomer contains two carbohydrate-binding sites: a high-affinity site A and a low-affinity site B. An assay using dendrimers containing oligomannose from yeast (Saccharomyces cerevisiae) revealed that CGL1 exhibited significantly higher affinity for mannotetraose (Man4) compared to mannobiose (Man2) and mannotriose (Man3). To investigate its oligomannose-recognition mechanism, X-ray crystallographic analyses of CGL1/oligomannose complexes were performed. In the CGL1/Man2 and CGL1/Man3 complexes, Manα1-2Man and Manα1-2Manα1-2Man, respectively, were primarily bound to site A, interacting with the non-reducing mannose residue. On the other hand, in the CGL1/Man4 crystal, Man4 (Manα1-2Manα1-2Manα1-6Man) was bound at both site A and site B at the non-reducing and reducing ends, thus linking adjacent CGL1 molecules with crystallographic symmetry. These findings suggest that CGL1 can recognize both the non-reducing and reducing mannose residues of mannose oligosaccharides at its two distinct carbohydrate-binding sites. This enables efficient complex formation, making CGL1 a pattern-recognition molecule capable of recognizing diverse structures of mannose-containing carbohydrate chains.

Effects of liquid nitrogen freezing at different temperatures on the quality and flavor of Pacific oyster (Crassostrea gigas).

This study aimed to evaluate the effects of different liquid nitrogen freezing (LNF) temperatures (-20, -40, -60, -80, and -100°C) on the water holding capacity, texture, microstructure, and flavor of Crassostrea gigas (C. gigas). The results showed that -40°C LNF, -60°C LNF, and -80°C LNF improved the water holding capacity of C. gigas (P<0.05); -60°C LNF and -80°C LNF could effectively maintain the hardness of the body trunk and adductor muscles. Compared with -20°C refrigerator freezing (RF), the LNF group could form smaller ice crystals and thus reduce the damage to the muscle cell structure damage, especially LNF at -80°C. Gas chromatography-ion mobility spectrometry (GC-IMS) and e-nose results indicated that -80°C LNF maintained the flavor profile of few aldehydes and alcohols compared to other freezing groups. Therefore, -80°C LNF effectively improved the quality and maintain the flavor characteristics of frozen C. gigas.

Plankton and marine aggregates as transmission vectors for V. aestuarianus 02/041 infecting the pacific oyster Crassostrea gigas.

Vibrio aestuarianus is a bacterium related to mass mortality outbreaks of the Pacific oyster, Crassostrea gigas in Europe. In this study, the role of different planktonic substrates (phytoplankton cells, marine aggregates and chitin fragments) in mediating V. aestuarianus 02/041 infection of oysters was evaluated by controlled infection experiments. It was shown that phytoplankton cells and, to a greater extent, marine aggregates, significantly promote V. aestuarianus 02/041 intake by C. gigas maintained under stressful conditions in the laboratory. Such intake is associated with higher concentration of the pathogen in the bivalve hemolymph and compromised health status of infected oysters. In contrast, chitin particles do not play a significant role as transmission vector for V. aestuarianus 02/041 infecting its bivalve host. Interestingly, incorporation into marine aggregates foster extracellular proteases (ECPs) activity and a higher expression of bacterial virulence genes, that are potentially involved in bivalve infection. Results from this study contribute to elucidate transmission patterns of V. aestuarianus 02/041 to C. gigas that may be useful for the development of efficient measures to prevent and control oyster disease outbreaks.

Vibrio parahaemolyticus: Predicting effects of storage temperature on growth in Crassostrea gigas harvested in New Zealand

The frequency of gastroenteritis outbreaks caused by Vibrio parahaemolyticus has been increasing in many parts of the world including New Zealand. Some outbreaks in New Zealand have occurred at times when V. parahaemolyticus concentrations in shellfish in growing waters are low. V. parahaemolyticus is mesophilic, so is not expected to grow under refrigeration. Therefore, one possible explanation for the outbreaks is that the organism was able to grow to hazardous concentrations (e. g. >10,000/g) because of inadequate post-harvest refrigeration. To model the response of growth rates to temperature, we collected Pacific oysters (Crassostrea gigas) containing natural populations of V. parahaemolyticus over three consecutive summers, stored them for various times at 5, 10, 15, 20, 25 and 30 °C and determined V. parahaemolyticus concentrations. A simple log-linear fit was best to determine the growth rates at each temperature for each season. Applying a square root model (√growth rate (MPN/h) = b x (Temperature (°C) - T0) to all the growth rates gave a good fit (R2 = 0.84, RMSE = 0.0178) with b = 0.0096 and T0 = 8.44 °C. Fitted growth rates were considerably lower than previously reported, but the hypothetical minimal growth temperature was also lower. Thus, concentrations of V. parahaemolyticus are likely to increase more slowly in New Zealand oysters than was previously thought, but the organism may also be able to grow at lower temperatures. Both models suggest that the recommended minimum storage temperature of 7 °C in current New Zealand and US regulatory schemes is adequate. This information will be useful for evaluating food safety risks from storing Pacific oysters at different temperatures for different times. It will also assist in formulating time-temperature recommendations for safe handling of Pacific oysters.

Investigating comprehensive effects of depuration salinity and duration on posterior anhydrous living-preservation of Pacific oyster (Crassostrea gigas)

Depuration and anhydrous living-preservation are two important and consecutive steps during the circulation of Pacific oyster (Crassostrea gigas), and two main factors in depuration, salinity and duration, are pivotal to posterior anhydrous living-preservation of C. gigas. In this work, the comprehensive effects of depuration salinity (26–38 g/L) and duration (0–72 h) on anhydrous living-preservation at 4 °C for 7 days were investigated in regard of mortality, biochemical indexes (fatty acids profile analysis, glycogen) and proteome changes as well. The results showed that the mortality of C. gigas increased obviously with 72 h depuration and especially with 20 % salinity fluctuation, concomitantly accompanying metabolism disorder. Furthermore, alterations in salinity and duration resulted in 381 different expression proteins (DEPs), which were gotten more involved in the pathways related to amino acid metabolism. Taken together, it was suggested that duration < 48 h and salinity fluctuations lower than 10 % were the preferred conditions for anhydrous living-preservation.

A galectin-9 involved in the microbial recognition and haemocyte autophagy in the Pacific oyster Crassostrea gigas

Galectin-9 is a tandem-repeat type member of galectin family participating in various immune responses, such as cell agglutination, phagocytosis, and autophagy. In the present study, a tandem repeat galectin-9 (defined as CgGal-9) was identified from Pacific oyster Crassostrea gigas, which consisted of two conserved carbohydrate recognition domains (CRDs) joined by a linker peptide. CgGal-9 was closely clustered with CaGal-9 from C. angulata, and they were assigned into the branch of invertebrate galectin-9s in the phylogenetic tree. The mRNA transcripts of CgGal-9 were detected in all the tested tissues, with the highest expression level in haemocytes. The mRNA expressions of CgGal-9 in haemocytes increased significantly after lipopolysaccharide (LPS) and Vibrio splendidus stimulation. The recombinant CgGal-9 was able to bind all the examined pathogen-associated molecular patterns (LPS, peptidoglycan, and mannose) and microbes (V. splendidus, Escherichia coli, Micrococcus luteus, Staphylococcus aureus, Bacillus subtilis, and Pichia pastoris), and agglutinated most of them in the presence of Ca2+. In CgGal-9-RNAi oysters, the mRNA expressions of autophagy related genes (CgBeclin1, CgATG5, CgP62 and CgLC3) in haemocytes decreased significantly while that of CgmTOR increased significantly at 3 h after V. splendidus stimulation. The autophagy level and mRNA expressions of autophagy related genes decreased in haemocytes after CgGal-9 was blocked by the corresponding antibody. These results revealed that CgGal-9 was able to bind different microbes and might be involved in haemocyte autophagy in the immune response of oyster.

Immune Priming of Pacific Oysters (Crassostrea gigas) to Induce Resistance to Ostreid herpesvirus 1: Comparison of Infectious and Inactivated OsHV-1 with Poly I:C.

Pacific oyster mortality syndrome (POMS), which is caused by Ostreid herpesvirus 1 (OsHV-1), causes economic losses in Pacific oyster (Crassostrea gigas) aquaculture in many countries. Reducing the mortality in disease outbreaks requires changing the host, pathogen and environment interactions to favor the host. Survivors of natural exposure to OsHV-1 are able to survive subsequent outbreaks. This has been replicated under laboratory conditions, suggesting the existence of an immune response. The aim of the present study is to compare the effects of prior exposure to infectious OsHV-1, heat-inactivated OsHV-1 and the chemical anti-viral immune stimulant poly I:C on mortality following exposure to virulent OsHV-1. All treatments were administered by intramuscular injection. Oysters were maintained at 18 °C for 14 days; then, the temperature was increased to 22 °C and the oysters were challenged with virulent OsHV-1. Heat-inactivated OsHV-1, infectious OsHV-1 and poly I:C all induced significant protection against mortality, with the hazard of death being 0.41, 0.18 and 0.02, respectively, compared to the controls, which had no immune priming. The replication of OsHV-1 on first exposure was not required to induce a protective response. While the underlying mechanisms for protection remain to be elucidated, conditioning for resistance to POMS by prior exposure to inactivated or infectious OsHV-1 may have practical applications in oyster farming but requires further development to optimize the dose and delivery mechanism and evaluate the duration of protection.

The dynamic change of flavor characteristics in Pacific oyster (Crassostrea gigas) during depuration uncovered by mass spectrometry-based metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS)

The flavor of Pacific oyster (Crassostrea gigas) significantly changed during the depuration process. This work aimed to explore the mechanism of flavor changes during the 72 h depuration by metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS). The metabolomics analysis indicated that carbohydrate metabolism was more affected in the early stage of depuration, including the citrate cycle, glyoxylae and dicarboxylate metabolism, etc. After 72 h depuration, it affected mainly the metabolism of global and overview maps and nucleoside metabolism, etc. The equivalent umami concentration (EUC) value was calculated and exhibited a gradual increase following a 48 h depuration. The GC–MS results revealed that the content of furans was the highest, and the content of aldehydes, ketones, and alcohols was the lowest after 48 h depuration, while the content of aldehydes, ketones, and alcohols increased after 72 h depuration. All these results suggested the depuration period was recommended to be controlled within 48 h.

Intertidal limits shape covariation between metabolic plasticity, oxidative stress and telomere dynamics in Pacific oyster (Crassostrea gigas)

In intertidal zones, species such as sessile shellfish exhibit extended phenotypic plasticity to face rapid environmental changes, but whether frequent exposure to intertidal limits of the distribution range impose physiological costs for the animal remains elusive. Here, we explored how phenotypic plasticity varied along foreshore range at multiple organization levels, from molecular to cellular and whole organism acclimatization, in the Pacific oyster (Crassostrea gigas). We exposed 7-month-old individuals for up to 16 months to three foreshore levels covering the vertical range for this species, representing 20, 50 and 80% of the time spent submerged monthly. Individuals at the upper range limit produced energy more efficiently, as seen by steeper metabolic reactive norms and unaltered ATP levels despite reduced mitochondrial density. By spending most of their time emerged, oysters mounted an antioxidant shielding concomitant with lower levels of pro-oxidant proteins and postponed age-related telomere attrition. Instead, individuals exposed at the lower limit range near subtidal conditions showed lower energy efficiencies, greater oxidative stress and shorter telomere length. These results unraveled the extended acclimatization strategies and the physiological costs of living too fast in subtidal conditions for an intertidal species.

The oxidative stress of the Pacific oyster Crassostrea gigas under high-temperature stress

Oxidative stress always occurs in the Pacific oyster Crassostrea gigas when they are exposed to high temperature, which will eventually lead to serious summer mortalities. In the present study, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), the total antioxidant capacity (T-AOC), as well as the content of malondialdehyde (MDA) and glutathione (GSH) in gill were employed as the oxidative stress indexes (OSIs) in oxidative stress process, and they were measured under indoor high temperature and during outdoor aquaculture period to investigate the induction of oxidative stress by high temperature. Two evaluation formulas were established to determine the oxidative stress level (represented by oxidative stress score, OSS) in oysters based on the data matrix of OSIs. In the indoor experiment at 12 h under different temperatures (18 °C, 20 °C, 22 °C, 24 °C, 26 °C, 28 °C, 30 °C, 32 °C, and 34 °C) with 16 °C as control group, the GSH content, activities of SOD, CAT and POD reached the bottom at 28 °C in the high-temperature treated groups, which were 1.15-fold, 0.61-fold, 0.68-fold and 0.26-fold of those in the control group, respectively. MDA content increased to 19.95 nmol/mgprot at 30 °C, which was significantly higher than that in the control group (p < 0.05). The mRNA expression levels of CgNrf2 and CgKeap1 reached the bottom at 30 °C, which were 0.78-fold and 0.63-fold of those in the control group, respectively. The indoor OSS (OSSin) sharply decreased to 22.97 at 28 °C and then rebounded to 48.73 at 30 °C. In the outdoor aquaculture period from April to August, the temperature increased from 8.3 °C to 23.9 °C, which was significantly negatively correlated with MDA content (r = −0.743, p < 0.001). MDA content decreased significantly (p < 0.05) from 7.94 nmol/mgprot in April to the lowest value of 3.41 nmol/mgprot in August. The outdoor OSS (OSSout) increased and peaked in June (32.05) and decreased to the lowest value in September (21.64). OSSout of the replicated samples in July and August exhibited a significant larger range of variation compared with the other months, ranging from 22.70 to 41.00 and 20.73 to 37.00, respectively. An average high mortality rate of 33.93% was observed in the period from July to August, but not in the other months. Collectively, it is suggested that oxidative stress occurred around 28 °C after the treatment with indoor high temperature of 12 h, and in July and August 2021 during outdoor aquaculture period. These findings will be helpful to further understand and evaluate the oxidative stress in Pacific oyster exposed to high temperature.

Response to selection for growth in an inbred strain of the Pacific oyster Crassostrea gigas

Response to selection for growth in an inbred strain of the Pacific oyster Crassostrea gigas

Contribution of HIF-1α to Heat Shock Response by Transcriptional Regulation of HSF1/HSP70 Signaling Pathway in Pacific Oyster, Crassostrea gigas.

Ocean temperature rising drastically threatens the adaptation and survival of marine organisms, causing serious ecological impacts and economic losses. It is crucial to understand the adaptive mechanisms of marine organisms in response to high temperature. In this study, a novel regulatory mechanism that is mediated by hypoxia-inducible factor-1α (HIF-1α) was revealed in Pacific oyster (Crassostrea gigas) in response to heat stress. We identified a total of six HIF-1α genes in the C. gigas genome, of which HIF-1α and HIF-1α-like5 were highly induced under heat stress. We found that the HIF-1α and HIF-1α-like5 genes played critical roles in the heat shock response (HSR) through upregulating the expression of heat shock protein (HSP). Knocking down of HIF-1α via RNA interference (RNAi) inhibited the expression of heat shock factor 1 (HSF1) and HSP70 genes in C. gigas under heat stress. Both HIF-1α and HIF-1α-like5 promoted the transcriptional activity of HSF1 by binding to hypoxia response elements (HREs) within the promoter region. Furthermore, the survival of C. gigas under heat stress was significantly decreased after knocking down of HIF-1α. This work for the first time revealed the involvement of HIF-1α/HSF1/HSP70 pathway in response to heat stress in the oyster and provided an insight into adaptive mechanism of bivalves in the face of ocean warming.

Development of Nanopore sequencing-based full-length transcriptome database toward functional genome annotation of the Pacific oyster, Crassostrea gigas

The Pacific oyster (Crassostrea gigas) is a widely cultivated shellfish in the world, while its transcriptome diversity remains less unexplored due to the limitation of short reads. In this study, we used Oxford Nanopore sequencing to develop the full-length transcriptome database of C. gigas. We identified 77,920 full-length transcripts from 21,523 genes, and uncovered 9668 alternative splicing events and 87,468 alternative polyadenylation sites. Notably, a total of 16,721 novel transcripts were annotated in this work. Furthermore, integrative analysis of 25 publicly available RNA-seq datasets revealed the transcriptome diversity involved in post-transcriptional regulation in C. gigas. We further developed a Drupal based webserver, Cgtdb, which can be used for transcriptome visualization, sequence alignment, and functional genome annotation analyses. This work provides valuable resources and a useful tool for integrative analysis of various transcriptome datasets in C. gigas, which will serve as an essential reference for functional annotation of the oyster genome.

The Resistance to Lethal Challenge with Ostreid herpesvirus-1 of Pacific Oysters (Crassostrea gigas) Previously Exposed to This Virus.

Pacific oyster (Crassostrea gigas) aquaculture has been economically impacted in many countries by Pacific oyster mortality syndrome (POMS), a disease initiated by Ostreid herpesvirus 1. The objectives of this study were to determine whether naturally exposed, adult C. gigas could act as reservoirs for OsHV-1 and explain the recurrent seasonal outbreaks of POMS and to test whether or not they were resistant to OsHV-1. In a laboratory infection experiment using thermal shock, OsHV-1 replication was not reactivated within the tissues of such oysters and the virus was not transmitted to naïve cohabitating spat. The adult oysters were resistant to intramuscular injection with a lethal dose of OsHV-1 and had 118 times lower risk of mortality than naïve oysters. Considered together with the results of other studies in C. gigas, natural exposure or laboratory exposure to OsHV-1 may result in immunity during subsequent exposure events, either in the natural environment or the laboratory. While adult C. gigas can carry OsHV-1 infection for lengthy periods, reactivation of viral replication leading to mortality and transmission of the virus to naïve oysters may require specific conditions that were not present in the current experiment. Further investigation is required to evaluate the mechanisms responsible for resistance to disease in oysters previously exposed to OsHV-1, whether immunity can be exploited commercially to prevent POMS outbreaks and to determine the source of the virus for recurrent seasonal outbreaks.

A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification

Bone morphogenetic proteins (BMPs) are key factors controlling osteoblast differentiation, which have been proved to be involved in the hard tissue formation of marine mollusks. In the present study, a member of BMPs gene (CgBMP7) was identified from Pacific oyster Crassostrea gigas (C. gigas) with the aim to understand its possible role in the regulation of shell formation under ocean acidification (OA) conditions. The open reading frame (ORF) of CgBMP7 was of 1254 bp encoding a polypeptide of 417 amino acids. The deduced amino acid sequence of CgBMP7 was comprised of one signal peptide, one prodomain and one TGF-β domain, which shared 21.69%-61.10% identities with those from other species. The mRNA transcript of CgBMP7 was ubiquitously expressed in all the tested tissues of adult oysters with a higher expression level in mantle, notably highest in the middle fold (MF) of the three folds of mantle. The expression level of bone morphogenetic protein type I receptor (CgBMPR1B) mRNA was also highest in the MF and up-regulated dramatically post recombinant BMP7 protein (rCgBMP7) stimulation. After the blockage of BMPR1B with inhibitor LDN193189 (LDN), the mRNA expression level and phosphorylation level of CgSmad1/5/8 in mantle were decreased, and the mRNA expression levels of CgCaM and Cgengrailed-1 were down-regulated significantly. During the oysters were exposed to acidified seawater for weeks, the expression levels of CgBMP7, CgBMPR1B and CgSmad1/5/8 in the MF decreased significantly (p < 0.01) at the 4th week, and CgCaM and Cgengrailed-1 also exhibited the same variable expression patterns as CgBMP7. In addition, the growth of shell in the treatment group (pH 7.8) was slower than that in the control group (pH 8.1). These results collectively indicated that BMP7 was able to trigger the BMPR-Smad signaling pathway and involved in controlling the formation of oyster calcified shell under OA conditions.

Starvation-induced changes in sex ratio involve alterations in sex-related gene expression and methylation in Pacific oyster Crassostrea gigas.

Aquatic animals are subject to varying degrees of starvation stress in their natural habitats due to food limitations. Consequently, starvation is a crucial environmental factor for sex determination in many species; however, limited research has been conducted on the effects of starvation on sex determination in shellfish. Here, four full sibling families of Pacific oysters were established and subjected to starvation stress. The results demonstrated that starvation caused the sex ratio (female to male) to change from 1:0.78 to 1:1.44 and resulted in a delay in gonadal development. Further studies revealed that the expression levels of DNA methylation-related genes Dnmt1 (DNA methyltransferase 1), Dnmt3a/b (DNA methyltransferase 3a/b) and Tet3 (tet methylcytosine dioxygenase 3) decreased under starvation stress. Conversely, the upregulation of Dmrt1 (doublesex and mab-3 related transcription factor 1), a gene typically associated with males, in females suggests that the increased proportion of males may be linked to starvation-induced high expression of this particular gene. In addition, the gene Dgkd (diacylglycerol kinase delta), which is involved in the regulation of second messenger protein kinase C, was differentially methylated between males and females, with the methylation level of this gene gradually increasing with male development, while the methylation level of this gene decreased under starvation stress. Correlation analysis of Dgkd methylation levels with expression levels showed a negative correlation between DNA methylation and gene expression. Finally dual fluorescence reporter experiments confirmed that DNA methylation suppressed Dgkd expression in vitro. In summary, the results suggest that starvation may regulate Dgkd gene expression through DNA methylation and thus affect Dmrt1 expression, thereby causing sex reversal in the Pacific oyster. The outcomes resolved how environmental factors are involved in sex reversal from an epigenetic perspective and provided a theoretical basis for sex control breeding in the Pacific oyster.

Pacific oysters do not compensate growth retardation following extreme acidification events.

Ocean acidification caused by anthropogenic carbon dioxide emissions alters the growth of marine calcifiers. Although the immediate effects of acidification from global ocean models have been well studied on calcifiers, their recovery capacity over a wide range of pH has never been evaluated. This aspect is crucial because acidification events that arise in coastal areas can far exceed global ocean predictions. However, such acidification events could occur transiently, allowing for recovery periods during which the effects on growth would be compensated, maintained or amplified. Here we evaluated the recovery capacity of a model calcifier, the Pacific oyster Crassostrea gigas. We exposed juveniles to 15 pH conditions between 6.4 and 7.8 for 14 days. Oyster growth was retarded below pH 7.1 while shells were corroded at pH 6.5. We then placed the oysters under ambient pH > 7.8 for 42 days. Growth retardation persisted at pH levels below pH 7.1 even after the stress was removed. However, despite persistent retardation, growth has resumed rapidly suggesting that the oysters can recover from extreme acidification. Yet we found that the differences in individual weight between pH conditions below 7.1 increased over time, and thus the growth retardation cannot be compensated and may affect the fitness of the bivalves.

PPCPs in coastal wastewater treatment plant effluent and uptake by Pacific oysters (Crassostrea gigas): Findings from a laboratory experiment

Municipal wastewater treatment plant (WWTP) effluent is a primary source of pharmaceuticals and personal care products (PPCPs) to the marine environment, as most of these compounds are not fully removed during the treatment process. Continual discharge from WWTPs into coastal areas may act as a stressor by continually exposing organisms to a suite of PPCPs. To quantify organismal exposure to PPCP mixtures, we conducted a 12-week lab experiment that exposed Pacific oysters to effluent from two Oregon coastal WWTPs of different discharge capacities (permitted as <1 million gallons/day and >1 million gallons/day; or < or >3.785 million liters/day) at a dilution of 25 %. Composite samples of weekly collected effluent and a subset of freeze-dried oysters from experiment week 12 were analyzed for PPCPs. Though challenges with food availability inhibited our ability to confidently identify effects of the contaminants on growth and fitness, the experiment allowed us to examine uptake of contaminants from effluent into an estuarine bivalve of commercial importance. We detected 30 PPCPs and three alkylphenols in effluent and 13 PPCPs and four alkylphenols in oyster tissue, indicating high rates of release from secondary treatment and significant potential for marine organism exposure to and uptake of PPCPs in rural coastal areas.

Triploid Pacific oysters exhibit stress response dysregulation and elevated mortality following heatwaves.

Polyploidy has been suggested to negatively impact environmental stress tolerance, resulting in increased susceptibility to extreme climate events. In this study, we compared the genomic and physiological response of diploid (2n) and triploid (3n) Pacific oysters (Crassostrea gigas) to conditions present during an atmospheric heatwave that impacted the Pacific Northwestern region of the United States in the summer of 2021. Climate stressors were applied either singly (single stressor; elevated seawater temperature, 30°C) or in succession (multiple stressor; elevated seawater temperature followed by aerial emersion at 44°C), replicating conditions present within the intertidal over a tidal cycle during the event. Oyster mortality rate was elevated within stress treatments with respect to the control and was significantly higher in triploids than diploids following multiple stress exposure (36.4% vs. 14.8%). Triploids within the multiple stressor treatment exhibited signs of energetic limitation, including metabolic depression, a significant reduction in ctenidium Na+ /K+ ATPase activity, and the dysregulated expression of genes associated with stress response, innate immunity, glucose metabolism, and mitochondrial function. Functional enrichment analysis of ploidy-specific gene sets identified that biological processes associated with metabolism, stress tolerance, and immune function were overrepresented within triploids across stress treatments. Our results suggest that triploidy impacts the transcriptional regulation of key processes that underly the stress response of Pacific oysters, resulting in downstream shifts in physiological tolerance limits that may increase susceptibility to extreme climate events that present multiple environmental stressors. The impact of chromosome set manipulation on the climate resilience of marine organisms has important implications for domestic food security within future climate scenarios, especially as triploidy induction becomes an increasingly popular tool to elicit reproductive control across a wide range of species used within marine aquaculture.