Juvenile Oysters Research Articles

Molecular mechanisms affecting the difference in salinity adaptability between juvenile and adult Hong Kong oysters

The Hong Kong oyster (Crassostrea hongkongensis) lives in the brackish waters of estuaries in the intertidal zone and has a high resistance to low levels of salinity, but low resistance to higher levels. Juveniles are more sensitive to high levels of salinity than adults. To better understand the mechanisms underlying these differences, we performed a high-salinity stress analysis of juvenile and adult Hong Kong oysters. Trait analysis between groups showed that Na+-K+-ATPase activity, T-AOC, betaine, taurine and glycogen content of the high-salinity group were almost all higher than that of the control group at 8 h under high-salt stress, but lower than that of the control group at 96 h. The differences are more significant in Adult population. The results indicate that these indexes are related to the salinity adaptability of oysters. Enrichment analysis and protein-protein interaction (PPI) network analysis of the differentially expressed genes (DEGs) screened from transcriptomic data showed that their functions were mainly related to the oxidation-reduction process, immune response, protein ubiquitination and ATP synthesis. Furthermore, a weighted gene co-expression network analysis (WGCNA) of all samples showed that the hub gene functions were mainly associated with the oxidation-reduction process and immune response. These results indicate that immune response-related and antioxidant genes play key roles in the adaptability of Hong Kong oysters to high salinity. This study provides new insights and enriches our current understanding of the salinity adaptation mechanisms in oysters.

Feeding response and dynamic of intoxication and detoxification in two populations of the flat oyster Ostrea chilensis exposed to paralytic shellfish toxins (PST)

Juvenile oysters (Ostrea chilensis) from two populations (Quempillén estuary and Pullinque bay) were exposed to a toxic diet containing paralytic shellfish toxins (PST), produced by Alexandrium catenella, followed by a detoxification period. Feeding behaviour, toxin profile, dynamics of intoxication/detoxification, and survival were evaluated over the entire experimental period. Both populations reduced their feeding rates during the 30-day exposure to the toxic diet. This negative effect was reversible when the diet was switched to the non-toxic one. Oysters from the estuary accumulated PST more rapidly than the population from the bay, suggesting their increased ability to cope with more adverse conditions. Both populations showed low detoxification capacity. Survival was significantly higher in oysters from the estuary, compared to those from the bay. Due to the increasing frequency and intensity of A. catenella blooms in southern Chile, it is necessary to better understand the responses of O. chilensis in different environments. This is important not only because of the ecological and commercial relevance of the bivalve, but also in consideration of expected climate change scenarios, where the new environmental conditions could favour the frequency and intensity of harmful algal bloom events.

Eelgrass beds can mitigate local acidification and reduce oyster malformation risk in a subarctic lagoon, Japan: A three-dimensional ecosystem model study

It is well known that ocean acidification (OA) inhibits growth of marine calcifying organisms. Therefore, the adverse effects of acidification on marine ecosystems and aquaculture, such as oyster farming, are of concern. Since eelgrass beds in neritic areas have a high potential for carbon assimilation, this study focuses on local scale mitigation of OA effects. Using a three-dimensional lower-trophic system ecosystem model, we modeled nitrogen and carbon cycles, and the dynamics of carbonate parameters in a subarctic shallow lagoon and bay, where nitrogen availability limits the photosynthesis of primary producers. Simulation of the present conditions allowed reproduction of spatiotemporal variations in water quality and, by assuming future environmental changes quantitatively, revealed that the progress of OA significantly elevated the probability of shell malformation in juvenile oysters. The results represent the spatiotemporal variations in carbonate parameters inside and outside eelgrass beds and enable the evaluation of the alleviation effect on local acidification by the presence of a dense eelgrass bed. Our study shows that in the absence of the eelgrass bed scenario, the effect of OA on oysters became more remarkable. The simulations revealed that maintaining eelgrass beds is essential to mitigate the effects of acidification on oysters.

Marking the shells of juvenile and adult eastern oysters, Crassostrea virginica, with the fluorochrome dye calcein and measuring growth and mortality after marking

ABSTRACT Techniques for positive re-identification of finfish are well developed and are used to estimate vital rates, migration patterns and stock structure. Fluorochrome dyes, like nontoxic calcein, have been used with success to mark hard parts of fish and the shells of some molluscs. Yet, despite the commercial and ecological importance of the eastern oyster Crassostrea virginica, a systematic evaluation of the effectiveness of calcein for marking this species does not exist. In this study, methods that have been used for marking freshwater mussels with calcein were tested on 2-week- and 2-month-old juvenile C. virginica and on 3-year-old adult C. virginica. Individuals were immersed in 250 mg l−1 of calcein for 24 h either once (single treatment) or three times (triple treatment), and then observed to determine whether marks were visible, how long they remained visible and whether calcein influenced growth and mortality of the different age classes. Results indicated that all marked individuals were recognizable under blue light, that multiple distinct marks were possible on juveniles and that marks on juveniles could remain visible for 3.75 years. Growth of juveniles and adults treated with calcein was not significantly different from controls after 11 months. Survivorship did not differ between treated and control individuals for all treatments and ages, except the 2-month-old juvenile oysters that were immersed three times. Results indicate that calcein is an effective and safe marking technique for juvenile oysters from robust cohorts, and could be used to enhance studies of growth, mortality, larval transport and settlement in situ.

Revisiting tolerance to ocean acidification: Insights from a new framework combining physiological and molecular tipping points of Pacific oyster.

Studies on the impact of ocean acidification on marine organisms involve exposing organisms to future acidification scenarios, which has limited relevance for coastal calcifiers living in a mosaic of habitats. Identification of tipping points beyond which detrimental effects are observed is a widely generalizable proxy of acidification susceptibility at the population level. This approach is limited to a handful of studies that focus on only a few macro-physiological traits, thus overlooking the whole organism response. Here we develop a framework to analyze the broad macro-physiological and molecular responses over a wide pH range in juvenile oyster. We identify low tipping points for physiological traits at pH 7.3-6.9 that coincide with a major reshuffling in membrane lipids and transcriptome. In contrast, a drop in pH affects shell parameters above tipping points, likely impacting animal fitness. These findings were made possible by the development of an innovative methodology to synthesize and identify the main patterns of variations in large -omic data sets, fitting them to pH and identifying molecular tipping points. We propose the broad application of our framework to the assessment of effects of global change on other organisms.

Benthic-pelagic coupling under juvenile oyster influence in a French Mediterranean coastal lagoon (Thau Lagoon)

The aim of the present work was to test the influence of juvenile oyster culture on benthic-pelagic coupling in the French Mediterranean Thau Lagoon. Although the period of juvenile growth induces the introduction of millions of juvenile oysters in the lagoon over a short duration, the effects on the water-column and on the benthic ecosystem are poorly known. Using a multiple ecological approach, water column parameters, sedimentation rates, sediment characteristics and benthic fluxes were monitored on three occasions during the oyster pre-growth period, from October to December, at two sites inside the farming area and two sites outside the farming area that served as reference. In the water column, results showed a significant lower ratio between total phytoplankton biomass (chlorophyll-a) and degraded pigments (pheopigment), a significant increase in the contribution of phytoplankton containing chlorophyll-b (ie chlorophytes) to total phytoplankton biomass and a significant decrease in the contribution of phytoplankton containing chlorophyll-c (mainly diatoms) to the total phytoplankton biomass at farm sites, attributed to the grazing pressure caused by juvenile oysters on large particles, as described for adult oysters. No significant effect was observed at the benthic interface during this period, due to the dispersion of the small quantities of biodeposit produced by juveniles in the low water temperature conditions. A multivariate approach supported the effect of juvenile oysters on the water column and revealed a trend in benthic conditions with farm sites being distinct from the reference ones. The long farming history of the lagoon could have shaped sediment properties such that farming areas maintain different benthic conditions.

Toxicity of innovative antifouling additives on an early life stage of the oyster Crassostrea gigas: short- and long-term exposure effects.

Recent advances in nanotechnology have allowed the encapsulation of hazardous antifouling (AF) biocides in silica mesoporous nanocapsules (SiNC) reducing their short-term toxicity. However, the chronic effects of such novel nanoadditives remain understudied. The present study aimed to assess short- and long-term sub-lethal effects of soluble forms (DCOIT and Ag) and nanostructured forms (SiNC-DCOIT and SiNC-DCOIT-Ag) of two AF biocides and the "empty" nanocapsule (SiNC) on juveniles of Crassostrea gigas after 96h and 14days of exposure. Juvenile oysters exposed for a short period to free DCOIT and AgNO3 presented worse physiological status comparing with those exposed to the nanostructured forms. The long-term exposure to DCOIT and Ag+ caused an extensive biochemical impairment comparing with the tested nanomaterials, which included oxidative damage, activation of the antioxidant defense system, and neurotransmission impairment. Despite the negative effects mostly observed on the health condition index and AChE, the encapsulation of the abovementioned AF biocides into SiNC seems to be a technological advantage towards the development of AF nanoadditives with lower long-term toxicity comparing with the soluble forms of such biocides.

Synergistic effects of salinity and temperature on the eastern oyster Crassostrea virginica throughout the lifespan

The eastern oyster Crassostrea virginica has a wide salinity tolerance, but all life stages are vulnerable to environmental extremes, and elevated temperatures can truncate the expected salinity tolerance. The rising water temperatures and more intense and variable storm events predicted to accompany global climate change therefore raise concerns for habitat suitability for ecologically important species such as the eastern oyster. To better understand environmental limitations, oysters of all life stages were exposed to a range of salinities (0-40) and temperatures (25 and 30°C) to test physiological tolerance to the combined effects of osmotic and thermal stresses. Elevated temperatures (30°C) amplified negative effects during exposure to salinity extremes at all life stages; however, tolerance to extremes increased with developmental stage (gametes < embryos < larvae < spat < adult). Gradual changes allow for a wider tolerance in juvenile oysters (spat) compared to acute changes, and short-term reprieves during low salinity exposure improved survival rates for adults. Overall, the present study found a threshold salinity of 15 for polyhaline oyster populations and highlights the importance of both rate of change and temperature as critical components of salinity tolerance. Additionally, salinities <10 during the summer months could result in negative population effects, especially if extreme low salinity occurs during peak reproduction when pelagic gametes, embryos, and larvae are most vulnerable to environmental stresses. This work will benefit population models and inform resource management decisions regarding the timing of controlled freshwater releases.

Symbiotic microbiome and metabolism profiles reveal the effects of induction by oysters on the metamorphosis of the carnivorous gastropod Rapana venosa

Most marine mollusks have a pelagic larval phase, and they need to undergo metamorphosis to develop into adults. Metamorphosis is affected by many factors, including abiotic factors such as temperature, salinity and illumination as well as biological factors such as food and microorganisms. In our previous study, we found that the metamorphosis of Rapana venosa requires induction by juvenile oysters, which are the food source of R. venosa. However, the regulatory mechanism of this induction is largely unknown. In the present study, we evaluated the impacts of induction by juvenile oysters on competent larvae of R. venosa. Competent larvae were experimentally divided into two pools, and scallop shells without juvenile oysters and scallop shells with juvenile oysters were added for 2 h and 12 h to monitor alterations in critical gene expression, symbiotic microbiota and metabolomic responses. The carboxypeptidase gene was increased while the cellulase gene was decreased, which may mean that the food habit transition was induced by juvenile oysters. Meanwhile, critical genes in the neuroendocrine system were also significantly altered in juvenile oysters. Furthermore, dramatic changes in the symbiotic microbiota and metabolism profiles were observed, with many of them associated with the digestive system and neuroendocrine system. In conclusion, juveniles as food resources may induce metamorphosis in R. venosa by regulating the neuroendocrine system and promoting the development of the digestive system and changes in digestive enzymes. This study may provide evidence that induction by juvenile oysters can promote food habit transition and metamorphosis in R. venosa by regulating the metabolome and microbiome and further altering the digestive and neuroendocrine systems of R. venosa, which expands our understanding of the regulatory mechanism of metamorphosis in R. venosa. However, further studies are needed to explore the specific substance inducing metamorphosis released by juvenile oysters.

Microplastics impact shell and pearl biomineralization of the pearl oyster Pinctada fucata

Microplastics are extremely widespread aquatic pollutants that severely detriment marine life. In this study, the influence of microplastics on biomineralization was investigated. For the first time, multiple forms and types of microplastics were detected and isolated from the shells and pearls of Pinctada fucata. According to the present study, the abundance of microplastics in shells and pearls was estimated at 1.95 ± 1.43 items/g and 0.53 ± 0.37 items/g respectively. Interestingly, microplastics were less abundant in high-quality round pearls. Microplastics may hinder the growth of calcite and aragonite crystals, which are crucial components required for shell formation. During the process of biomineralization microplastics became embedded in shells, suggesting the existence of a novel pathway by which microplastics accumulate in bivalves. After a 96-h exposure to microplastics, the expression level of typical biomineralization-related genes increased, including amorphous calcium carbonate binding protein (ACCBP) gene which experienced a significant increase. ACCBP promotes the formation of amorphous calcium carbonate (ACC), which is the pivotal precursor of shell formation-related biominerals. ACCBP is highly expressed during the developmental stage of juvenile oysters and the shell-damage repair process. The increased expression of ACCBP suggests biomineralization is enhanced as a result of microplastics exposure. These results provide important evidence that microplastics exposure may impact the appearance of biominerals and the expression of biomineralization-related genes, posing a new potential threat to aquatic organisms.

Taxonomy, palaeoecology and palaeobiogeography of upper Cenomanian (Upper Cretaceous) oysters and plicatulids from southern Algeria

ABSTRACT Palaeontological investigation of four lithostratigraphic sections documenting the upper Cenomanian shallow marine carbonates of three palaeogeographic domains of southern Algeria (western Saharan Atlas, Guir Basin and Tinrhert Hamada) has produced a comprehensive collection of large bivalve assemblages for taxonomic purposes. A first inventory list of late Cenomanian oysters and plicatulids from southern Algeria is now available and consists of 15 taxa as follows: Lopha syphax, Ostreidae gen. et sp. indet., Curvostrea rouvillei, Flemingostreidae gen. et sp. indet., Costagyra olisiponensis, Amphidonta obliquata, Ceratostreon flabellatum, Ilymatogyra africana, Rhynchostreon suborbiculatum, Gyrostrea delettrei, Gyrostrea sp. indet., Pycnodonte (Phygraea) vesicularis vesiculosa, Plicatula (Plicatula.) auressensis, Plicatula (Plicatula) batnensis, and Chondrodonta? sp. indet. These taxa build five distinctive oyster-facies patterns, all purportedly recognisable in the field for stratigraphic assignment and regional correlation. Scarce sclerobiontic assemblage (borings: Entobia, Gastrochaenolites and Oichnus; and epibionts: juvenile oysters, serpulid tubes and Berenicean-type bryozoa) observed within these oyster shell assemblages is also identified, briefly described and adressed. This first taxonomic analysis highlights three main palaeogeographic components within these oyster- and plicatuloid-assemblages: endemic Mediterranean, Tethyan-Atlantic and cosmopolitan taxa. Moreover, the present study on these late Cenomanian oyster assemblages provides a first inventory list and stratigraphical baseline data towards further datation and correlation at the regional scale.

Upper Pliocene bivalve shell concentrations from the Lower Chelif basin (NW Algeria): Systematics, sedimentologic and taphonomic framework

Sedimentologic and palaeontological investigation of the Upper Pliocene Slama Formation in the Lower Chelif Basin (NW Algeria) led us to collect important bivalve assemblages for taxonomic and taphonomic purposes. A rather comprehensive inventory list of Upper Pliocene bivalves from northwestern Algeria is now available and consists of 30 species, 17 of which are extinct ones. Four principal taphonomic attributes were analysed: bioerosion, encrustation, fragmentation, and abrasion. Physical and biogenic sedimentary structures are used for palaeoenvironmental interpretations. The taphonomic, sedimentologic and ichnological characteristics of most of the deposits suggests they originated from discontinuous processes of winnowing and bypassing of sediments, probably due to the action of storms in shallow waters, mainly in the shoreface depositional environment. The bivalve assemblage is dominated by disarticulated valves and displays significant taphonomic alteration in the shells. Sclerobionts traces in shells particulary affect the oyster shells. Bioerosion traces are predominately those of clionid sponges (Entobia isp.), polychaetes (Maeandropolydora isp. and Caulostrepsis isp.), bivalves (Gastrochaenolites isp.), and of predatory gastropods (Oichnus isp.). Among the sclerobionts, the identified encrusters were juvenile oyster recruits, barnacles, polychaetes (serpulid tubeworms), bryozoans (Microporella sp. and Acanthodesia sp.), and vermetid gastropods (Petaloconchus intortus).

Mass mortality of pearl oyster (Pinctada fucata (Gould)) in Japan in 2019 and 2020 is caused by an unidentified infectious agent.

Mass mortality of 0-year-old pearl oysters, Pinctada fucata (Gould), and anomalies in adults were observed in Japan’s major pearl farming areas in the summer of 2019 and 2020. Although adult oyster mortality was low, both adult and juvenile oysters underwent atrophy of the soft body, detachment of the mantle from nacre (the shiny inner surface of the valves), deposition of brownish material on the nacre, and loss of nacre luster. Infection trials were conducted to verify the involvement of pathogens in this phenomenon. Healthy adult pearl oysters were obtained from areas where this disease had not occurred to use as the recipients. The sources of infection were either affected adult oysters with atrophied soft bodies or batches of juveniles in which mortality had reached conspicuous levels. Transmission of the disease to the healthy oysters were tested either by cohabitation with affected oysters or by injections of the hemolymph of affected animals. The injection infection test examined the effects of filtration and chloroform exposure on the pathogen. Occurrence of the disease was confirmed by the appearance of brown deposits on the nacre and loss of nacre luster. The abnormalities of nacre were clearly reproduced in recipient shells in three out of four cohabitation trials with affected oysters. The disease was also reproduced in six out of six injection trails either with hemolymph filtered through 100 nm filter or with hemolymph treated with chloroform. In a serial passage with hemolymph injections, the disease was successfully transmitted through eight passages. These results suggest that the etiology of the disease is a non-enveloped virus with a diameter ≤100 nm.

Effects of flood-associated stressors on growth and survival of early life stage oysters (Crassostrea virginica)

Oyster reefs provide essential ecosystem services but are severely degraded worldwide. Extreme flooding events, which can be intensified by water management decisions, reduce water quality in estuaries and further threaten oyster populations. Restoration and conservation of oysters is dependent on the success of early oyster life stages. This study examined the effect of water quality stressors associated with flooding events on the growth and survival of larval and juvenile oysters (Crassostrea virginica). In 96-h assays, we exposed D-stage larvae to a range of dissolved oxygen, microcystin-LR, pH, and salinity concentrations. These conditions were selected based on water quality data from the Mississippi Sound during a 2019 freshwater flooding event caused by the Bonnet Carré Spillway opening. There was no negative effect of microcystin-LR or pH on early veligers at the concentrations tested, but low salinity significantly reduced shell growth, and hypoxia (< 2 mg L−1 O2) decreased both larval growth and survival. Post-metamorphosis juvenile oysters were exposed to the same water quality stressors for 24 days in the lab. Low DO, pH, and salinity treatments reduced juvenile change in wet weight and shell growth rates, but had no effects on survival. These laboratory-exposed juveniles were subsequently deployed into the field to assess the ability of juveniles to recover from short-term exposure to simulated flooding-associated stressors. After deployment to natural conditions in the Mississippi Sound, juvenile oysters were able to compensate for reduced growth during the lab exposure, even though survival was reduced for juveniles previously exposed to low pH during the first two weeks in the field. In general, early oyster life stages were relatively tolerant of the duration and stressor concentrations tested, but negative sublethal impacts of flood-associated stressors must be considered in the face of increasing frequency and duration of flooding events due to climate change.

Growth and survival of the native oyster Crassostrea gasar cultured under different stocking densities in two grow-out systems in tropical climate

ABSTRACT Survival and growth of the native oyster Crassostrea gasar along the juvenile and adult phases were evaluated in three different stocking densities [low (D), medium (2D) and high (3D)] and in two grow-out systems (fixed and floating system). The fixed system consisted of a rack made with PVC, fixed from the bottom with wood sticks. The floating system consisted of floating bags suspended by a rack made with PVC and maintained submerged from the seawater surface by eight floats. Survival and shell height of oysters cultured after 30, 60 and 90 days were registered in each phase and in each grow-out system. Results showed that the grow-out system did not affect survival and growth of C. gasar in the juvenile and adult phases. The tested densities affected the survival of oysters cultured over time in both phases but did not affect oyster growth. At times analyzed, it was observed positive growth in juvenile oysters grow after 90 days of culture. However, in the adult phase, no growth was observed after 90 days of culture. Oyster yield was higher in the density 3D, in both juvenile and adult phases. These findings contributed to the development of the oyster C. gasar culture.

Subchronic exposure to high-density polyethylene microplastics alone or in combination with chlortoluron significantly affected valve activity and daily growth of the Pacific oyster, Crassostrea gigas.

Nowadays, pesticides and microplastics (MPs) are commonly found in coastal waters worldwide. Due to their widespread use, their persistence and toxicity, they may induce adverse effects on physiology and behaviour of marine organisms such as the Pacific oyster (Crassostrea gigas). This study explored the growth and valve activity of juvenile oysters exposed for 24 days to two frequently detected pollutants in the Pertuis Charentais (South West, France): a herbicide (chlortoluron, 85 µg.L-1) and high-density polyethylene microparticles (HDPE 20-25 µm, 112 MP.mL-1) alone or in combination (cocktail condition; 97 µg.L-1 of chlortoluron+108 MP. mL-1). The valve activity of juvenile oysters recorded by using a High Frequency and Non-Invasive valvometer (HFNI) was characterized by three parameters: the number of valve micro-closures (VMC), the Valve Opening Amplitude (VOA), and the Valve Opening Duration (VOD). Additionally, daily shell growth and the oyster daily rhythm were assessed. The exposure to MPs of oysters led to a significant increase of VMC and a decrease of VOD and shell growth. The exposure to chlortoluron showed a significant increase of VOA and a decrease of VMC. In combination with MPs, chlortoluron still increased VOA and decreased VMC but also reduced the shell growth. Chronobiological analysis did not reveal any effects on the daily rhythm of both contaminants. This work highlighted significant effects of high environmental concentrations of MPs and Chlortoluron on the behaviour and growth of the Pacific oyster.

Skewed sex ratio and gametogenesis gene expression in eastern oysters (Crassostrea virginica) exposed to plastic pollution

Plastic pollution is ubiquitous in the oceans, and numerous studies have documented the dangers from entanglement, ingestion, or exposure to individual xenoestrogenic plastic additives. Plastic degradation in seawater poses a complex threat through sorption of harmful organic pollutants, release of complex chemical ingredients that compose plastics, and fragmentation of plastic pieces. Therefore, a more holistic approach is needed to understand the impact of plastic exposure on marine organisms. The eastern oyster (Crassostrea virginica) is a keystone species that serves as an ecosystem engineer in western Atlantic estuaries. Individuals undergo annual gametogenesis and are able to change sex from one year to the next, typically from male to female. A 1:1 sex ratio is maintained at the population level by younger/smaller oysters that are mostly male and older/larger oysters that are mostly female. As sessile bivalves, oysters are susceptible to damaging effects from plastic that settle on the seafloor. The objective of this study was to quantify changes in survival, growth, sex ratio, and gene expression of eastern oysters in response to polyethylene terephthalate (PET) plastic exposure. Hatchery-produced larvae settled onto either oyster shell or PET plastic and metamorphosed into juveniles. One set of juvenile oysters was reared in an aquaculture facility for three months, and a second set was placed on natural reefs in the St. Mary's River of the Chesapeake Bay for ten months. Juvenile oysters grown on PET showed significantly higher mortality rates and reduced growth than those grown on shell after three months. After ten months of growth and maturation in natural waters, oysters grown on shell were 82% male while oysters grown on plastic had a significantly lower proportion of males (56% male). We measured differential gene expression of eight candidate genes involved in gametogenesis. In general, expression patterns followed expectations based on putative roles in either spermatogenesis or oogenesis. Exposure to plastic did not have a significant impact on gene expression. Small sample sizes limited statistical power to detect small effect sizes. Although not significant, females on plastic had higher median and mean expression than those on shell for all genes, except for the mean expression level of vitellogenin-6 (vit-6). Our findings suggest that plastic exposure alters the sex ratio of first-year oysters, resulting in more females than expected. Additional research into the expression of underlying genes that impact gamete differentiation and therefore sex determination is warranted.

A Small Regulatory RNA Generated from the malK 5' Untranslated Region Targets Gluconeogenesis in Vibrio Species.

ABSTRACTVsr217 is a small RNA from Vibrio tasmaniensis LGP32, a pathogen associated with mortality events affecting juvenile oysters. The vsr217 gene is located within the 5′ untranslated region (UTR) of malK, encoding the ATPase component of the maltose importer, and is conserved within the genus Vibrio. In the presence of maltose, vsr217 is regulated by MalT, the positive regulator of the maltose regulon. vsr217 is required in cis for the full expression of malK. In addition, Vsr217 acts in trans to downregulate the expression of fbp encoding fructose-1,6-bisphosphatase, an enzyme involved in gluconeogenesis. Thus, in the presence of maltose, the induction of Vsr217 is expected to promote glycolysis by negatively regulating the expression of a key enzyme of gluconeogenesis.IMPORTANCE Juvenile pacific oysters have been subject in recent years to summer mortality episodes with deep economic consequences. The pathogen Vibrio tasmaniensis has been associated with such mortality events. For bacterial pathogens, survival within the host requires profound metabolic adaptations according to available resources. All kinds of regulatory elements, including noncoding RNAs, orchestrate this response. Oysters are rich in glycogen, a precursor of maltose, and we previously reported that V. tasmaniensis maltose-regulated genes are strongly induced during oyster infection. Here, we report the dual mechanism by which a small regulatory RNA, generated from the 5′ untranslated region of a gene belonging to the maltose regulon, acts both in cis and trans. In cis, it stimulates growth on maltose, and in trans, it downregulates the expression of a gene associated with gluconeogenesis, thus coordinating maltose utilization with central carbon metabolism.

Pharmaceuticals and alkylphenols in transplanted Pacific oysters (Crassostrea gigas): Spatial variation and growth effects

Pharmaceuticals and personal care products in wastewater discharge can be stressors to estuarine species. We transplanted juvenile Pacific oysters at varying distances within sites near wastewater treatment plant outfalls or oyster aquaculture control sites to assess small scale spatial variation in contaminant uptake and oyster condition. Oysters were transplanted to sites in Coos and Netarts Bays, Oregon and Grays Harbor, Washington, then collected after 9 and 12 months. Two pharmaceuticals (miconazole and virginiamycin M1) were detected in spring samples and four alkylphenols (NP1EO, NP2EO, NP and OP) were detected in summer samples, with more frequent detections at wastewater sites. Contaminant concentrations were similar across site types, indicating that even in sparsely populated coastal areas (<25,000 in the watershed), shellfish are exposed to and uptake wastewater contaminants. Additionally, oyster condition was lower at wastewater sites compared to aquaculture sites, indicating a need to better understand whether contaminant exposure affects oyster condition.

The first detection of a novel OsHV-1 microvariant in San Diego, California, USA

The spread, emergence, and adaptation of pathogens causing marine disease has been problematic to fisheries and aquaculture industries for the last several decades creating the need for strategic management and biosecurity practices. The Pacific oyster (Crassostrea gigas), a highly productive species globally, has been a target of disease and mortality caused by a viral pathogen, the Ostreid herpesvirus 1 (OsHV-1) and its microvariants (OsHV-1 µvars). During routine surveillance to establish health history at a shellfish aquaculture nursery system in San Diego, California, the presence of OsHV-1 in Pacific oyster juveniles was detected. Quantification of OsHV-1 in tissues of oysters revealed OsHV-1 viral loads > 106 copies/mg. We characterized and identified the OsHV-1 variant by sequencing of ORFs 4 (C2/C6) and 43 (IA1/IA2), which demonstrated that this variant is a novel OsHV-1 microvariant: OsHV-1 µvar SD. A pilot transmission study indicates that OsHV-1 µvar SD is infectious with high viral loads ~ 7.57 × 106 copies/mg detected in dead individuals. The detection of OsHV-1 µvar SD in a large port mirrors previous studies conducted in Australia where aquaculture farms and feral populations near port locations may be at a higher risk of OsHV-1 emergence. Further research is needed to understand the impacts of OsHV-1 µvar SD, such as transmission studies focusing on potential vectors and characterization of virulence as compared to other OsHV-1 µvars. To increase biosecurity of the global aquaculture industry, active and passive surveillance may be necessary to reduce spread of pathogens and make appropriate management decisions.