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The endemic mulberry whelk (Tenguella marginalba) is a common predator on Australian intertidal rocky shores. The introduced Pacific oyster (Crassostrea gigas), found within the natural range of T. marginalba, is potential prey for the whelk. In experiments designed to increase our understanding of predatory behaviour by the whelk on oysters, we found that adult T. marginalba detected C. gigas and increased movement in the presence of oyster prey. Tenguella marginalba showed a preference for smaller C. gigas, but consumed oysters up to 60 mm in shell height. To access oyster flesh, whelks used their radula to drill holes in the oyster’s shell. These holes were on average 0.68 ± 0.09 mm in diameter, most frequently located central to the pericardial cavity on the right (upper) valve. Predation was greatest when predator and prey were both submerged, but was unaffected by a diurnal light cycle. When offered a choice among the native Sydney rock oysters (Saccostrea glomerata), mussels (Trichomya hirsuta) or the invasive C. gigas, whelks displayed no preference among prey. We conclude that the invasive oyster C. gigas represents a viable food source for T. marginalba, which may help to slow the spread of this invasive oyster throughout eastern Australia. [ABSTRACT FROM AUTHOR]

Bacterial contamination on seafood resulting from unhygienic food-handling practices causes foodborne diseases and significant revenue losses. Moreover, control measures are complicated by a high prevalence of antibiotic-resistant bacteria. Alternative measures such as the phage therapy, therefore, is considered as an environmental and consumer-friendly biological control strategy for controlling such bacterial contamination. In this study, we determined the effectiveness of a bacteriophage cocktail in controlling E. coli strains [JM 109, ATCC 13706 and the, extended spectrum beta-lactamase resistant strain (ATCC BAA 196)] and S. enterica subsp. enterica (ATCC 13311) as single and combined contaminants of the edible oysters. Five different E. coli-specific phages (belonging to the Siphoviridae family) and a Salmonella phage (belonging to the Tectiviridae family) were successfully isolated from sewage water samples taken from a local sewage treatment plan in the Sunshine Coast region of Australia. Phage treatments applied to the pathogens when they were presented on the oysters as either single or combined hosts, resulted in significant decrease of the number of these bacteria on edible oysters. Results obtained indicated that bacteriophages could have beneficial applications in oyster-processing plants in controlling pathogenic bacterial infestations. This study thus contributes towards ongoing international efforts into the effective use of bacteriophages for biological control purposes. [ABSTRACT FROM AUTHOR]

Whether sex determination of marine organisms can be altered by ocean acidification and warming during this century remains a significant, unanswered question. Here, we show that exposure of the protandric hermaphrodite oyster, Saccostrea glomerata to ocean acidification, but not warming, alters sex determination resulting in changes in sex ratios. After just one reproductive cycle there were 16% more females than males. The rate of gametogenesis, gonad area, fecundity, shell length, extracellular pH and survival decreased in response to ocean acidification.Warming as a sole stressor slightly increased the rate of gametogenesis, gonad area and fecundity, but this increase was masked by the impact of ocean acidification at a level predicted for this century. Alterations to sex determination, sex ratios and reproductive capacity will have flowon effects to reduce larval supply and population size of oysters and potentially other marine organisms. [ABSTRACT FROM AUTHOR]

Following the discovery of potential chronic perfluoroalkyl substances (PFAS) contamination of Tilligerry Creek, Port Stephens (New South Wales Australia), sampling was undertaken to confirm the presence, extent and levels of contamination in commercial oyster crops of Sydney Rock Oyster ( Saccostrea glomerata ) and Pacific Oyster ( Crassostrea gigas ) grown within the estuary. Among a range of PFAS tested, only perfluorooctane sulfonate (PFOS) was detected. Concentrations of PFOS in oyster tissues for S. glomerata ranged from 1.6 μg kg − 1 ww (wet weight) to below the limit of reporting of 0.3 μg kg − 1 ww, with concentrations generally decreasing toward the lower reaches of the estuary. The sample of C. gigas tested had a PFOS concentration of 0.71 μg kg − 1 ww that was consistent with concentrations observed in nearby S. glomerata . For harvest size (50–60 g) S. glomerata , both holding contaminated oysters in a depuration system, and relocation to a non-contaminated area, saw significant reductions in the tissue PFOS concentrations. For oysters held in a depuration system, PFOS depurated at a rate of 0.008 h − 1 (0.004–0.019 h − 1 ; 90% CI), which corresponded with a depuration half-life of 87 h (35–155 h; 90%). A more conservative model (fitted to data that assumed concentrations < LOR were equal 0.5·LOR) predicted a depuration half-life of 131 h. PFOS concentrations had fallen to below detectable limits within 162 h. Similar decreases were observed in relocated oysters. [ABSTRACT FROM AUTHOR]

Coastal and estuarine environments are characterised by acute changes in temperature and salinity. Organisms living within these environments are adapted to withstand such changes, yet near-future ocean acidification (OA) may challenge their physiological capacity to respond. We tested the impact of CO 2 -induced OA on the acute thermal and salinity tolerance, energy metabolism and acid-base regulation capacity of the oyster Saccostrea glomerata . Adult S. glomerata were acclimated to three CO 2 levels (ambient 380 μatm, moderate 856 μatm, high 1500 μatm) for 5 weeks (24 °C, salinity 34.6) before being exposed to a series of acute temperature (15–33 °C) and salinity (34.2–20) treatments. Oysters acclimated to elevated CO 2 showed a significant metabolic depression and extracellular acidosis with acute exposure to elevated temperature and reduced salinity, especially at the highest CO 2 of 1500 μatm. Our results suggest that the acute thermal and salinity tolerance of S. glomerata and thus its distribution will reduce as OA continues to worsen. [ABSTRACT FROM AUTHOR]

Vitellogenin (Vtg) is a well-established biomarker of estrogenic exposure in aquatic animals. In vertebrates, Vtg gene transcription is controlled by the estrogen receptors (ERs). Although an ER ortholog is present in molluscs, its role as a transcriptional regulator remains elusive. Here, we tested the hypothesis that in the Sydney rock oyster, Saccostrea glomerata , the ER ortholog activates Vtg gene transcription through specific interaction with its promoter. Luciferase reporter assays indicated that sgER activated both a minimal promoter containing the consensus estrogen-responsive elements (EREs) and the sgVtg promoter in an estrogen-independent manner. The sgVtg promoter-luciferase activation was significantly reduced when any of three putative ERE half sites (½EREs) in the promoter were mutated. Electrophoretic mobility shift assay (EMSA) confirmed that sgER binds specifically to a 68-bp promoter sequence where these ½EREs reside. Overall, the results suggest that sgER is a constitutively active transcription factor that binds and activates the sgVtg promoter. [ABSTRACT FROM AUTHOR]

Sessile marine molluscs living in the intertidal zone experience periods of internal acidosis when exposed to air (emersion) during low tide. Relative to other marine organisms, molluscs have been identified as vulnerable to future ocean acidification; however, paradoxically it has also been shown that molluscs exposed to high CO2 environments are more resilient compared with those molluscs naive to CO2 exposure. Two competing hypotheses were tested using a novel experimental design incorporating tidal simulations to predict the future intertidal limit of oysters in a high-CO2 world; either high-shore oysters will be more tolerant of elevated ... because of their regular acidosis, or elevated ... will cause high-shore oysters to reach their limit. Sydney rock oysters, Saccostrea glomerata, were collected from the high-intertidal and subtidal areas of the shore and exposed in an orthogonal design to either an intertidal or a subtidal treatment at ambient or elevated ..., and physiological variables were measured. The combined treatment of tidal emersion and elevated ... interacted synergistically to reduce the haemolymph pH (pHe) of oysters, and increase the ... in the haemolymph (...) and standard metabolic rate. Oysters in the intertidal treatment also had lower condition and growth. Oysters showed a high degree of plasticity, and little evidence was found that intertidal oysters were more resilient than subtidal oysters. It is concluded that in a high-CO2 world the upper vertical limit of oyster distribution on the shore may be reduced. These results suggest that previous studies on intertidal organisms that lacked tidal simulations may have underestimated the effects of elevated .... [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously detected in the water column, associated with particulate matter or in the tissue of marine organisms such as molluscs. PAH exposure and their resultant bioaccumulation in molluscs can cause a range of serious physiological effects in the affected animals. To examine the molecular response of these xenobiotics in bivalves, Sydney rock oysters ( Saccostrea glomerata ) were exposed to pyrene and fluoranthene for seven days. Chemical analysis of the soft-tissue of PAH stressed S. glomerata confirmed that pyrene and fluoranthene could be bioaccumulated by these oysters. RNA-Seq analysis of PAH-exposed S. glomerata showed a total of 765 transcripts differentially expressed between control and PAH-stressed oysters. Closer examination of the transcripts revealed a range genes encoding enzymes involved in PAH detoxification ( e.g. cytochrome P450 ), innate immune responses ( e.g. pathogen recognition, phagocytosis) and protein synthesis. Overall, pyrene and fluoranthene exposure appears to have resulted in a suppression of pathogen recognition and some protein synthesis processes, whereas transcripts of genes encoding proteins involved in clearance of cell debris and some transcripts of genes involved in PAH detoxification were induced in response to the stressors. Pyrene and fluoranthene exposure thus invoked a complex molecular response in S. glomerata , with results suggesting that oysters focus on removing the stressors from their system and dealing with the downstream effects of PAH exposure, potentially at the exclusion of other, less immediate concerns ( e.g. protection from infection). [ABSTRACT FROM AUTHOR]

Background: Oysters have important ecological functions in their natural environment, acting as global carbon sinks and improving water quality by removing excess nutrients from the water column. During their life-time oysters are exposed to a variety of pathogens that can cause severe mortality in a range of oyster species. Environmental stressors encountered in their habitat can increase the susceptibility of oysters to these pathogens and in general have been shown to impact on oyster immunity, making immune parameters expressed in these marine animals an important research topic. Results: Paired-end Illumina high throughput sequencing of six S. glomerata tissues exposed to different environmental stressors resulted in a total of 484,121,702 paired-end reads. When reads and assembled transcripts were compared to the C. gigas genome, an overall low level of similarity at the nucleotide level, but a relatively high similarity at the protein level was observed. Examination of the tissue expression pattern showed that some transcripts coding for cathepsins, heat shock proteins and antioxidant proteins were exclusively expressed in the haemolymph of S. glomerata, suggesting a role in innate immunity. Furthermore, analysis of the S. glomerata ORFs showed a wide range of genes potentially involved in innate immunity, from pattern recognition receptors, components of the Toll-like signalling and apoptosis pathways to a complex antioxidant defence mechanism. Conclusions: This is the first large scale RNA-Seq study carried out in S. glomerata, showing the complex network of innate immune components that exist in this species. The results confirmed that many of the innate immune system components observed in mammals are also conserved in oysters; however, some, such as the TLR adaptors MAL, TRIF and TRAM are either missing or have been modified significantly. The components identified in this study could help explain the oysters’ natural resilience against pathogenic microorganisms encountered in their natural environment. [ABSTRACT FROM AUTHOR]

This study assesses the genetic diversity of four different hatchery bred lines of Sydney rock oyster, Saccosstrea glomerata (SRO) after three, five and seven generations of mass selection using microsatellite DNA markers and mitochondrial cytochrome C oxidase subunit 1 sequences (COX1). This was achieved using seven newly developed microsatellite markers, along with three published loci. Considering the same number of samples in each line, the number of different alleles in each of the four hatchery lines ranged from 49 to 70 alleles from 10 loci, which was approximate 50% less than the 120 alleles found in the samples from the wild population. However, if we pool all our four hatchery lines together, then their total number of alleles was not significantly different from the wild population. Similar to the patterns found for the DNA microsatellite alleles, mtDNA haplotype numbers were considerably lower in each of the hatchery lines than in the samples from the wild population. Again, pooling the hatchery lines gave a total haplotype number not statistically significantly different from that in the samples from the wild. Considering together the DNA microsatellite alleles and the mtDNA haplotypes, we conclude that there was a substantial loss of genetic diversity within all lines separately over generations of mass selection, and that such mass selection was not sustainable in the long term. However, importantly, these data indicate that for oysters, if multiple independent mass selection lines are kept, then their combined genetic diversity may approach that of the ancestral line or wild population even after many generations of mass selection. These results for oysters, finding preservation of diversity among lines yet loss within them, are similar to recent findings for multiple banana shrimp lines; considering both species together it suggests that one relatively simple option suitable for some farms and industry to maintain genetic diversity during mass selection over many generations of selection is to subdivide their breeding nucleus and keep multiple different and independent lines over generations. It remains to be tested if this approach is general across many aquaculture species and circumstances. Statement of relevance This paper attempts to falsify the published hypothesis set out by Knibb et al., 2014 that “the use of multiple lines under some circumstances may be a hedge against loss of diversity” using a second independent example, namely Sydney rock oysters. The data of this paper do not refute the generality of the above hypothesis of Knibb et al., 2014 that splitting mass selection lines into multiple sublines preserves genetic variation. [ABSTRACT FROM AUTHOR]

Species of Alexandrium produce potent neurotoxins termed paralytic shellfish toxins and are expanding their ranges worldwide, concurrent with increases in sea surface temperature. The metabolism of molluscs is temperature dependent, and increases in ocean temperature may influence both the abundance and distribution of Alexandrium and the dynamics of toxin uptake and depuration in shellfish. Here, we conducted a large-scale study of the effect of temperature on the uptake and depuration of paralytic shellfish toxins in three commercial oysters (Saccostrea glomerata and diploid and triploid Crassostrea gigas, n = 252 per species/ploidy level). Oysters were acclimated to two constant temperatures, reflecting current and predicted climate scenarios (22 and 27 °C), and fed a diet including the paralytic shellfish toxin-producing species Alexandrium minutum. While the oysters fed on A. minutum in similar quantities, concentrations of the toxin analogue GTX1,4 were significantly lower in warm-acclimated S. glomerata and diploid C. gigas after 12 days. Following exposure to A. minutum, toxicity of triploid C. gigas was not affected by temperature. Generally, detoxification rates were reduced in warm-acclimated oysters. The routine metabolism of the oysters was not affected by the toxins, but a significant effect was found at a cellular level in diploid C. gigas. The increasing incidences of Alexandrium blooms worldwide are a challenge for shellfish food safety regulation. Our findings indicate that rising ocean temperatures may reduce paralytic shellfish toxin accumulation in two of the three oyster types; however, they may persist for longer periods in oyster tissue. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is predicted to have widespread implications for marine organisms, yet the capacity for species to acclimate or adapt over this century remains unknown. Recent transgenerational studies have shown that for some marine species, exposure of adults to OA can facilitate positive carryover effects to their larval and juvenile offspring that help them to survive in acidifying oceanic conditions. But whether these positive carryover effects can persist into adulthood or the next generation is unknown. Here we tested whether positive carryover effects found in larvae of the oyster, Saccostrea glomerata following transgenerational exposure to elevated CO2, could persist into adulthood and whether subsequent transgenerational exposure of adults to elevated CO2 would facilitate similar adaptive responses in the next generation of larvae and juveniles. Following our previous transgenerational exposure of parental adults and first generation (F1) larvae to ambient (385 μatm) and elevated (856 μatm) CO2, newly settled F1 juveniles were transferred to the field at ambient CO2 for 14 months, until they reached reproductive maturity. At this time, the F1 adults were returned to the laboratory and the previous transgenerational CO2 exposure was repeated to produce F2 offspring. We found that the capacity of adults to regulate extracellular pH at elevated CO2 was improved if they had a prior history of transgenerational exposure to elevated CO2. In addition, subsequent transgenerational exposure of these adults led to an increase in the resilience of their larval and juvenile offspring. Offspring with a history of transgenerational exposure to elevated CO2 had a lower percentage abnormality, faster development rate, faster shell growth and increased heart rate at elevated CO2 compared with F2 offspring with no prior history of exposure to elevated CO2. Our results suggest that positive carryover effects originating during parental and larval exposure will be important in mediating some of the impacts of OA for later life-history stages and generations. [ABSTRACT FROM AUTHOR]

Abstract: Since 1990, Industry and Investment New South Wales'' (NSW) Sydney rock oyster (SRO) breeding programme has successfully used selective breeding to improve oyster growth rates. But, some oyster growers have observed that selected oysters condition at a different rate and to a different extent compared to naturally caught oysters grown under similar conditions. The condition index, sex, gametogenic stage and gonad area of fifth generation SROs selectively bred for fast growth were investigated by collecting monthly samples at a northern, mid and southern site in NSW between June 2005 and July 2006. Non-selected oysters farmed under the same conditions were also sampled at the same time. Overall, selected and non-selected oysters developed and spawned at each site synchronously, however, selectively bred oysters, in most instances, had a lower condition index, different meat conditioning cycle and reduced gonad area than their non-selected counterparts. Although selective breeding for fast growth hasn''t changed reproductive timing, the variation in meat condition is consistent with oyster grower''s observations and has encouraged further research to better understand the environmental responses of selected oysters and improve reproductive condition in SRO through breeding. [Copyright &y& Elsevier]

QX disease causes mass mortalities among Sydney rock oysters ( Saccostrea glomerata). To overcome commercial production losses, Industry & Investment NSW has been developing mass selected QX disease-resistant breeding lines since 1997. This breeding programme has significantly reduced QX-associated mortality in the Lime Kiln Bar (LKB) breeding line relative to non-selected, wild-type (WT) oysters. The current study assessed mortality in families produced by single-pair mating between LKB and WT oysters. When these families were grown in a QX disease-prone area, the progeny of LKB × LKB crosses had significantly lower mortality compared with LKB × WT or WT × WT families. Mortality in the different crosses was associated with infection by sporulating Marteilia sydneyi, the parasite responsible for QX disease. Overall, the study identified a strong association between parentage and mortality resulting from QX disease. [ABSTRACT FROM AUTHOR]

idifying oceans are predicted to fundamentally alter marine ecosystems. Over the next century, acute studies suggest that the impacts of climate change on marine organisms and ecosystems may be catastrophic. To date, however, little is known about whether the response of marine organisms varies within a species and whether this provides a potential 'adaptive capacity'. Here, we show that selectively bred lines of the ecologically and economically important estuarine mollusc, the Sydney rock oyster Saccostrea glomerata, are more resilient to ocean acidification than the wild populations. When reared at elevated pCO, we found a 25% reduction in shell growth of the selectively bred population of the Sydney rock oyster, Saccostrea glomerata, compared to a 64% reduction in shell growth of wild populations. This study shows that there are significantly different sensitivities to ocean acidification even within the same species, providing preliminary evidence that selective breeding may be a solution for important aquaculture industries to overcome the future effects of ocean acidification. [ABSTRACT FROM AUTHOR]

This study compared the synergistic effects of elevated pCO and temperature on the early life history stages of two ecologically and economically important oysters: the Sydney rock oyster, Saccostrea glomerata and the Pacific oyster, Crassostrea gigas. Gametes, embryos, larvae and spat were exposed to four pCO (375, 600, 750, 1,000 µatm) and four temperature (18, 22, 26, 30°C) levels. At elevated pCO and suboptimal temperatures, there was a reduction in the fertilization success of gametes, a reduction in the development of embryos and size of larvae and spat and an increase in abnormal morphology of larvae. These effects varied between species and fertilization treatments with S. glomerata having greater sensitivity than C. gigas. In the absence of adaptation, C. gigas may become the more dominant species along the south-eastern coast of Australia, recruiting into estuaries currently dominated by the native S. glomerata. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to develop a molecular tool to detect the vitellogenin gene expression in Sydney rock oyster (SRO) Saccostrea glomerata. It mentions that the endocrine disruption on the Sunshine Coast was investigated to determine the usability of the tool in detecting environmental oestrogens in waterways. It reveals that the domestic, agricultural and horticultural practices cause the oestrogenic chemicals like fertilisers to enter the environment.

This study investigated the synergistic effects of ocean acidification (caused by elevations in the partial pressure of carbon dioxide pCO2) and temperature on the fertilization and embryonic development of the economically and ecologically important Sydney rock oyster, Saccostrea glomerata (Gould 1850). As pCO2 increased, fertilization significantly decreased. The temperature of 26 °C was the optimum temperature for fertilization, as temperature increased and decreased from this optimum, fertilization decreased. There was also an effect of pCO2 and temperature on embryonic development. Generally as pCO2 increased, the percentage and size of D-veligers decreased and the percentage of D-veligers that were abnormal increased. The optimum temperature was 26 °C and embryonic development decreased at temperatures that were above and below this temperature. Abnormality of D-veligers was greatest at 1000 ppm and 18 and 30 °C (≥90%) and least at 375 ppm and 26 °C (≤4%). Finally prolonged exposure of elevated pCO2 and temperature across early developmental stages led to fewer D-veligers, more abnormality and smaller sizes in elevated CO2 environments and may lead to lethal effects at suboptimal temperatures. Embryos that were exposed to the pCO2 and temperature treatments for fertilization and embryonic development had fewer D-veligers, greater percentage of abnormality and reduced size than embryos that were exposed to the treatments for embryonic development only. Further at the elevated temperature of 30 °C and 750–1000 ppm, there was no embryonic development. The results of this study suggest that predicted changes in ocean acidification and temperature over the next century may have severe implications for the distribution and abundance of S. glomerata as well as possible implications for the reproduction and development of other marine invertebrates. [ABSTRACT FROM AUTHOR]

The Sydney rock oyster Saccostrea glomerata (Gould, 1850) industry acquired hatchery-produced spat selected for faster growth for the first time in January 2004. Selectively bred and non-selected (Control) spat produced concurrently were used to compare performance when grown under commercial conditions. Spat were distributed to farmers in seven estuaries in New South Wales. Individual farmers cultivated these oysters using their own techniques and growth and mortality were recorded quarterly. At each site, the two oyster types were cultivated using the same culture method, location and density. Growth was compared when oysters were 27 months of age. At this time, selectively bred oysters were significantly larger and heavier than Control oysters. The same result was obtained when oysters were compared at the point in time when selectively bred oysters had reached 50 g at each site. No significant difference was found for cumulative mortality between the selectively bred oysters and Control oysters across all sites. However, the seven sites had significantly different levels of cumulative mortality. Overall, the performance of selectively bred oysters was superior to the Control oysters and selectively bred oysters reached the 50 g bench mark within 29.3 months when averaged across all sites. [ABSTRACT FROM AUTHOR]

Very little is currently known regarding the effects of estrogenic endocrine disrupting chemicals on embryonic and larval development in molluscs, nor the potential effects of parental (F 0) exposure on resultant F 1 offspring. In this study, we assessed the embryotoxic impacts of exposure to environmentally relevant concentrations of the synthetic estrogen, 17α-ethinylestradiol (EE2), to male and female parents (50 ng/L) and their offspring (5 and 50 ng/L) in the native Australian Sydney rock oyster, Saccostrea glomerata. There were no detectable effects of parental exposure on fertilisation success, proportions of early larval (F 1) morphs and unfertilised eggs. Offspring impacts were evidenced in terms of developmental delays, with decreased percentages of D-veligers retained by 45 μm mesh, along with a reduction of swimming capabilities of larvae at 2 days post-fertilisation (dpf) when both parents had been exposed to 50 ng/L EE2. Although no significant parental effects were found on the survival of F 1 larvae at 9 dpf, retardation of shell growth was observed on F 1 larvae in treatments where both parents had been exposed to 50 ng/L EE2. Subsequent larval exposure from 2 to 9 dpf caused declines in survival and reduction of shell length in F 1 larvae at both 5 and 50 ng/L EE2 across all parental exposure treatments. Collectively, parental EE2 imparts effects on offspring in terms of retardation of larval development, and subsequent offspring exposure to EE2 further exacerbates impacts to development. Future research should aim to understand the potential mechanisms of EE2 induced toxicity and its transmission resulting in altered phenotypes of the F 1 generation. Image 1 • We assessed larval developmental effects of parental and offspring EE2 exposure. • No parental exposure effects were observed for F 1 fertilisation success. • No parental exposure effects were found on percentage of early larval morphs. • Offspring developmental delays were evidenced when both parents were exposed. • Subsequent larval exposure resulted in declines in survival and shell length. Parental exposure to EE2 causes developmental delays in F 1 offspring of the Sydney rock oyster. [ABSTRACT FROM AUTHOR]

Understanding mechanisms of intraspecific variation in resilience to environmental drivers is key to predict species' adaptive potential. Recent studies show a higher CO 2 resilience of Sydney rock oysters selectively bred for increased growth and disease resistance (‘selected oysters’) compared to the wild population. We tested whether the higher resilience of selected oysters correlates with an increased ability to compensate for CO 2 -induced acid-base disturbances. After 7 weeks of exposure to elevated seawater P CO 2 (1100 μatm), wild oysters had a lower extracellular pH (pH e = 7.54 ± 0.02 (control) vs. 7.40 ± 0.03 (elevated P CO 2 )) and increased hemolymph P CO 2 whereas extracellular acid-base status of selected oysters remained unaffected. However, differing pH e values between oyster types were not linked to altered metabolic costs of major ion regulators (Na + /K + -ATPase, H + -ATPase and Na + /H + -exchanger) in gill and mantle tissues. Our findings suggest that selected oysters possess an increased systemic capacity to eliminate metabolic CO 2 , possibly through higher and energetically more efficient filtration rates and associated gas exchange. Thus, effective filtration and CO 2 resilience might be positively correlated traits in oysters. [ABSTRACT FROM AUTHOR]

We aimed to determine if offspring of oysters from contaminated locations were more tolerant to metals, and whether this tolerance could be attributed to acclimation. Oysters from 10 estuaries were sampled, representing a gradient in metal contamination. Tolerance to metals of the F 1 offspring from adults residing in these estuaries was assessed. Then, adults from these estuaries were translocated to a single estuary and their offspring tolerance reassessed. No linear relationship was found between the Cu concentrations of adults and their offspring's tolerance to Cu. A positive linear relationship was found between the Zn concentration of adults and the Zn EC 50 's of their offspring. Zn tolerance was lost after translocation. Zn EC 50 values of offspring from transplanted adults bore no relation to the Zn EC 50 's of their location of origin. Thus the initial tolerance observed could be attributed to acclimation transferred to the F 1 generation. [ABSTRACT FROM AUTHOR]

The Sydney Rock Oyster, Saccostrea glomerata, is a socioeconomically important species in Australia, yet little is known about the molecular mechanism that regulates its reproduction. To address this gap, we have performed a combination of high throughput transcriptomic and peptidomic analysis, to identify genes and neuropeptides that are expressed in the key regulatory tissues of S. glomerata ; the visceral ganglia and gonads. Neuropeptides are known to encompass a diverse class of peptide messengers that play functional roles in many aspects of an animal’s life, including reproduction. Approximately 28 neuropeptide genes were identified, primarily within the visceral ganglia transcriptome, that encode precursor proteins containing numerous neuropeptides; some were confirmed through mass spectral peptidomics analysis of the visceral ganglia. Of those, 28 bioactive neuropeptides were synthesized, and then tested for their capacity to induce gonad development and spawning in S. glomerata . Egg laying hormone, gonadotropin-releasing hormone, APGWamide, buccalin, CCAP and LFRFamide were neuropeptides found to trigger spawning in ripe animals. Additional testing of APGWa and buccalin demonstrated their capacity to advance conditioning and gonadal maturation. In summary, our analysis of S. glomerata has identified neuropeptides that can influence the reproductive cycle of this species, specifically by accelerating gonadal maturation and triggering spawning. Other molluscan neuropeptides identified in this study will enable further research into understanding the neuroendocrinology of oysters, which may benefit their cultivation. [ABSTRACT FROM AUTHOR]

Abstract: Introduced species that alter the physical structure of marine habitats can have large impacts on biodiversity. We assessed whether in south-eastern Australia the invasive Pacific oyster, Crassostrea gigas, differs from the native Sydney rock oyster, Saccostrea glomerata, in the biogenic habitat that it provides to epibiotic communities. We also assessed how within a species (S. glomerata), genotype influences habitat provision. First, we conducted a field experiment in which we compared recruitment of epibiota to concrete plates with either C. gigas, wild-stock S. glomerata, selectively bred S. glomerata or glue (control). Second, we assessed whether within wild S. glomerata populations invaded by C. gigas, communities of epibenthos are correlated to the ratio of non-native to native oysters. On experimental plates C. gigas grew larger, and experienced higher mortality than both selectively-bred and wild-stock S. glomerata at each of two heights on the shore. The two genotypes of S. glomerata, by contrast, displayed similar rates of growth and mortality. The differing growth patterns among oyster types had not, however, translated to consistent differences in the composition of associated benthic communities by 12months following establishment of experimental treatments. Within established wild oyster assemblages, C. gigas were typically much larger than on our experimental plates, and the non-native influenced the abundance of several epibiotic taxa, although not the identity of species present. Where impacts of C. gigas on the abundance of associated benthic species occurred, they were generally negative. Overall, our results indicate that while differences in the population size-structure of C. gigas and S. glomerata may be evident from small-scale experiments, the detection of flow-on effects to associated epibenthic communities may require approaches that incorporate much larger spatio-temporal scales. Nevertheless, the observation that wild C. gigas primarily influenced the abundance rather than the identity of associated epifauna suggests a certain degree of redundancy between the two species in their provision of habitat to epibiota. [Copyright &y& Elsevier]

Abstract: The effects of starvation on various factors related to immunological defence in Sydney rock oysters (Saccostrea glomerata) were tested in controlled laboratory experiments. A range of parameters was assessed, including total haemocyte counts, and phenoloxidase (PO), superoxide, acid phosphatase and peroxidase activities. Condition indices were also monitored as an indicator of oyster fitness. We found that the frequency of haemocytes and phenoloxidase activity decreased by 25% and 14% respectively when oysters were fed half-satiation rations for three weeks. These decreases became statistically significant when oysters were starved for three weeks. Superoxide and peroxidase activities also decreased significantly when oysters were starved for two to four weeks, while phenoloxidase and acid phosphatase activities were significantly inhibited after oysters had been starved for at least three weeks. All of the immunological parameters returned to at least their original levels after starved oysters were fed to satiation for six days. Phenoloxidase activities over-compensated during the recovery response, so that levels post-recovery were substantially higher than those evident before starvation. There were no significant changes in condition indices during any of the starvation treatments. These data indicate that starvation compromises immunological activity, and that the duration and intensity of starvation differentially affect immune responses. [Copyright &y& Elsevier]

In vertebrates, estrogens and estrogen mimicking chemicals modulate gene expression mainly through a genomic pathway mediated by the estrogen receptors (ERs). Although the existence of an ER orthologue in the mollusc genome has been known for some time, its role in estrogen signalling has yet to be deciphered. This is largely due to its constitutive (ligand-independent) activation and a limited mechanistic understanding of its regulation. To fill this knowledge gap, we cloned and characterised an ER cDNA ( sgER ) and the 5 ′ -flanking region of the gene from the Sydney rock oyster Saccostrea glomerata . The sgER cDNA is predicted to encode a 477-amino acid protein that contains a DNA-binding domain (DBD) and a ligand-binding domain (LBD) typically conserved among both vertebrate and invertebrate ERs. A comparison of the sgER LBD sequence with those of other ligand-dependent ERs revealed that the sgER LBD is variable at several conserved residues known to be critical for ligand binding and receptor activation. Ligand binding assays using fluorescent-labelled E2 and purified sgER protein confirmed that sgER is devoid of estrogen binding. In silico analysis of the sgER 5 ′ -flanking sequence indicated the presence of three putative estrogen responsive element (ERE) half-sites and several putative sites for ER-interacting transcription factors, suggesting that the sgER promoter may be autoregulated by its own gene product. sgER mRNA is ubiquitously expressed in adult oyster tissues, with the highest expression found in the ovary. Ovarian expression of sgER mRNA was significantly upregulated following in vitro and in vivo exposure to 17β-estradiol (E2). Notably, the activation of sgER expression by E2 in vitro was abolished by the specific ER antagonist ICI 182, 780. To determine whether sgER expression is epigenetically regulated, the in vivo DNA methylation status of the putative proximal promoter in ovarian tissues was assessed using bisulfite genomic sequencing. The results showed that the promoter is predominantly hypomethylated (with 0–3.3% methylcytosines) regardless of sgER mRNA levels. Overall, our investigations suggest that the estrogen responsiveness of sgER is regulated by a novel ligand-dependent receptor, presumably via a non-genomic pathway(s) of estrogen signalling. [ABSTRACT FROM AUTHOR]

Marine molluscs, such as oysters, respond to estrogenic compounds with the induction of the egg yolk protein precursor, vitellogenin (Vtg), availing a biomarker for estrogenic pollution. Despite this application, the precise molecular mechanism through which estrogens exert their action to induce molluscan vitellogenesis is unknown. As a first step to address this question, we cloned a gene encoding Vtg from the Sydney rock oyster Saccostrea glomerata ( sgVtg ). Using primers designed from a partial sgVtg cDNA sequence available in Genbank, a full-length sgVtg cDNA of 8498 bp was obtained by 5′- and 3′-RACE. The open reading frame (ORF) of sgVtg was determined to be 7980 bp, which is substantially longer than the orthologs of other oyster species. Its deduced protein sequence shares the highest homology at the N- and C-terminal regions with other molluscan Vtgs. The full-length genomic DNA sequence of sgVtg was obtained by genomic PCR and genome walking targeting the gene body and flanking regions, respectively. The genomic sequence spans 20 kb and consists of 30 exons and 29 introns. Computer analysis identified three closely spaced half-estrogen responsive elements (EREs) in the promoter region and a 210-bp CpG island 62 bp downstream of the transcription start site. Upregulation of sgVtg mRNA expression was observed in the ovaries following in vitro (explants) and in vivo (tank) exposure to 17β-estradiol (E2). Notably, treatment with an estrogen receptor (ER) antagonist in vitro abolished the upregulation, suggesting a requirement for an estrogen-dependent receptor for transcriptional activation. DNA methylation of the 5′ CpG island was analysed using bisulfite genomic sequencing of the in vivo exposed ovaries. The CpG island was found to be hypomethylated (with 0–3% methylcytosines) in both control and E2-exposed oysters. However, no significant differential methylation or any correlation between methylation and sgVtg expression levels was observed. Overall, the results support the possible involvement of an ERE-containing promoter and an estrogen-activated receptor in estrogen signalling in marine molluscs. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the muscle relaxant magnesium chloride (MgCl2) were monitored in the Sydney rock oyster, Saccostrea glomerata, under laboratory conditions. The relaxant was first tested for efficiency and then for potential deleterious effects on immunological and spawning activity. A range of immunological parameters were tested including, total haemocyte frequencies, acid phosphatase, superoxide and phenoloxidase activities in the haemolymph, as well as total haemolymph protein levels. All of the oysters exposed to MgCl2 demonstrated total relaxation within 6h of the initial exposure. Total haemocyte frequencies, acid phosphatase activity and superoxide activity all increased significantly during the first 48h after exposure to the relaxant but declined later. Phenoloxidase activity increased immediately after relaxation but then decreased consistently until 48h after exposure. Overall, the data indicate that MgCl2 is an effective relaxant for use on S. glomerata, and that any potentially deleterious effects of the relaxant do not persist for more than 96h. [Copyright &y& Elsevier]

Queensland unknown (QX) disease is a significant cause of economic loss for the Sydney rock oyster (SRO) aquaculture industry. Evidence is emerging that QX disease is multi-factorial in nature, with a number of environmental and host factors contributing to disease dynamics. Efforts to mitigate the impacts of QX disease are primarily focused on breeding for disease resistance however, the mechanisms that drive disease resistance are poorly understood. One potential factor influencing disease resistance is the microbiota. To determine the influence of location, season and disease resistance on the SRO microbiota, we used 16S rRNA (V1 – V3 region) amplicon sequencing. The microbiota of six SRO families with two categorised as QX-resistant and four as QX-susceptible, deployed to two different locations (Port Stephens and Wallis Lake, NSW, Australia) and over two seasons (Austral summer and winter), were characterised. As expected, the SRO microbiota was distinct to the microbial community found in seawater. Further, the SRO microbiota was significantly influenced by location and season, with operational taxonomic units (OTUs) assigned to the Candidatus Hepatoplasma and Endozoicomonas genera identified as significant drivers of microbiota dissimilarity between locations and seasons. Disease resistance also significantly influenced the SRO microbiota but only at the winter time point which is before the typical QX disease period. Overall, OTUs assigned to the Mycoplasma , Borrelia and Endozoicomonas genera were over-represented in QX-resistant SRO microbiota, whereas members of the Pseudoalteromonas , Vibrio , and Candidatus Hepatoplasma genera were over-represented in QX-sensitive microbiota. These findings confirm the influencing role of location and season on the microbiota structure as evidenced in other molluscan species, but also provide preliminary evidence that the microbiota assemblage before the QX disease period may be important for resistance to disease and may provide new avenues for managing SRO aquaculture in the future. • The Sydney rock oyster microbiota is influenced by location and season. • QX disease-resistance influences the Sydney rock oyster microbiota in winter. • A shifting microbiota before the QX disease period could contribute to QX disease dynamics. [ABSTRACT FROM AUTHOR]

Improving risk assessment and remediation rests on better understanding of contaminant bioavailability. Despite their strong toxicological attributes, little is known about the partitioning behaviour and bioavailability of polar polycyclic aromatic hydrocarbons (PAHs) in aquatic environments. The present study provides an insight into the bioavailable fractions of polar PAHs and their parent analogues in the tissues of the Sydney rock oyster, Saccostrea glomerata, a model aquatic bio-indicator organism. The concentration and distribution patterns of parent and polar PAHs including oxygenated PAHs (oxyPAHs), nitrated PAHs (NPAHs) and heterocyclic PAHs (HPAHs) were determined in water, sediment and oysters from an ecologically and economically important estuary of New South Wales, Australia. Total concentrations of PAHs, oxyPAHs, NPAHs and HPAHs were higher in sediments compared to oyster tissue and water. For most polar PAHs, total concentrations for water, sediment and oyster samples were <1 μg/g (μg/l for water) while parent PAH concentrations were several orders of magnitude higher. Computed biota-sediment accumulation factors (BSAFs) on lipid-normalized oyster concentrations revealed that while ∑oxyPAHs and ∑HPAHs exhibited low accumulation from sediment to oyster tissues (BSAF <1), ∑PAHs and ∑NPAH were found to be accumulated at high levels (BSAF >1). BSAF individual computation showed that bioaccumulation of nine investigated HPAHs in oyster tissues were relatively low and only 2-EAQ (oxyPAH) and 1N-NAP (NPAH) showed high levels of accumulation in oyster tissues, similar to parent PAHs. To the best of our knowledge, this is the first known study on the bioavailability of polar and non-polar PAHs in an Australian aquatic environment. The outcome of this study might be a useful indicator of the potential risks of polar PAHs to humans and other living organisms. Unlabelled Image • First study on the fate of polar PAHs in an Australian aquatic environment • Parent PAHs exhibited the highest levels of bioaccumulation in oyster tissues. • NPAHs were the only polar PAHs that highly bioaccumulated in oyster tissues. • HPAHs and most oxyPAHs showed relatively low levels of bioaccumulation. [ABSTRACT FROM AUTHOR]

The metal-binding protein metallothionein (MT) is widely used as a biomarker of metal contamination. In this study, we cloned a MT gene (sgMT) from the Sydney rock oyster Saccostrea glomerata. The gene encodes a MT-I protein with a classical αβ domain structure and is expressed as two transcripts resulting from alternative polyadenylation. The gene promoter contains two putative metal-responsive elements (MREs) which are known to be required for metal-inducible transcription. A specific and efficient qPCR assay was developed to quantify sgMT mRNA expression. Further, we assessed whether prior metal exposure history influences sgMT mRNA expression upon subsequent metal exposure. Oysters with varying prior metal exposure histories (contaminated and reference) were exposed to Cu, Cd and Zn. Expression of sgMT generally increased with metal dose, and oysters with an elevated past metal exposure history exhibited higher sgMT expression under Cd and Zn stress, representing a potential acclimatory response to prior metal exposure. • The first MT gene was cloned and characterised in the Sydney rock oyster. • Oysters with varying metal exposure histories were subsequently exposed to metals. • sgMT gene expression generally increased with metal dose for both populations. • Elevated past exposure oysters exhibited higher sgMT mRNA under Cd and Zn stress. [ABSTRACT FROM AUTHOR]