Adult Oysters Research Articles

Secretory and transcriptomic responses of mantle cells to low pH in the Pacific oyster (Crassostrea gigas)

Since the Industrial Revolution, the concentration of atmospheric carbon dioxide (CO2) due to anthropogenic activities has increased at unprecedented rates. One-third of the atmospheric anthropogenic CO2 emissions are dissolved in the oceans affecting the chemical equilibrium of seawater, which in turn leads to a decrease in pH and carbonate ion (CO32-) concentration, a phenomenon known as ocean acidification (OA). This chemical disequilibrium can be detrimental to marine organisms (e.g., mollusks) that fabricate mineralized structures based on calcium carbonate (CaCO3). Most studies on the effect of reduced pH in seawater have been conducted on the early developmental stages of shell-building invertebrates, given less attention to how adult individuals face OA stress. Here, we evaluate histological, secretory, and transcriptional changes in the mantle of adult oysters (Crassostrea gigas) exposure to ambient (8.0 ± 0.2) and reduced (7.6 ± 0.2) pH during 20 days. Most histological observations did not show differences in terms of mantle cell morphology. However, Alcian Blue/PAS staining revealed significant differences in the number of Alcian Blue positive cells in the mantle edge, suggesting a decrease in the secretory activity in this morphogenetic zone. Transcriptomic analysis revealed 172 differentially expressed genes (DEGs) between mantle tissues from adult oysters kept in normal and reduced pH conditions. Almost 18% of the DEGs encode secreted proteins that are likely to be contributing to shell fabrication and patterning. 17 of 31 DEGs encoding secreted proteins correspond to oyster-specific genes, highlighting the fact that molluscan shell formation is underpinned by a rapidly evolving secretome. The GO analysis of DEGs encoding secreted proteins showed that they are involved in the cellular response to stimulus, response to stress, protein binding, and ion binding, suggesting these biological processes and molecular functions are altered by OA. This study demonstrates that histology and gene expression profiling can advance our understanding of the cellular and molecular mechanisms underlying adult oyster tolerance to low pH conditions.

Early gonadal differentiation is associated with the antagonistic action of Foxl2 and Dmrt1l in the Pacific oyster.

As the second largest phylum in the zoological kingdom next to arthropods, the mechanism of gonadal differentiation in mollusca is quite complex. Currently, although much has been carried out on gonadal differentiation in the Pacific oyster, there is still unknown information that needs to be further explored. Here, analysis of the Foxl2 and Dmrt1l expression in samples at different development periods of male and female gonads as well as in annual gonad samples revealed that Log10 (Foxl2/Dmrt1l) values were an effective method for sex identification in oysters. In differentiated gonadal tissue, Log10 (Foxl2/Dmrt1l) values greater than 2 were females and less than 1 for males. Subsequent sequential sampling of the same individuals verified that Log10 (Foxl2/Dmrt1l) values greater than 2 for resting gonads would develop as females and less than 1 would develop as males in the future. Relative expression analysis of Foxl2 and Dmrt1l in the annual samples revealed a negative correlation between Log10 (Foxl2) and Log10 (Dmrt1l). Double fluorescence reporter validation results showed that DMRT1L protein was able to bind the Foxl2 promoter and repress its activity with a weak dosage effect. Antagonism between Dmrt1l and Foxl2 is therefore not restricted to vertebrates, and the competing regulatory networks are of great significance in the maintenance of gonadal sex in oysters after sexual differentiation. This study provides novel ideas and insights into the study of early gonadal differentiation in the adult oyster.

Emergence and clonal expansion of Vibrio aestuarianus lineages pathogenic for oysters in Europe.

Crassostrea gigas oysters represent a significant global food source with 4.7 million tons harvested per year. In 2001, the bacterium Vibrio aestuarianus subsp. francensis emerged as a pathogen that causes adult oyster mortality in France and Ireland. Its impact on oyster aquaculture has increased in Europe since its re-emergence in 2012. To better understand the evolutionary mechanisms leading to the emergence and persistence over time of this pathogen, we conducted a survey of mollusc diseases through national reference laboratories across Europe. We analysed 54 new genomes of Vibrio aestuarianus (Va) isolated from multiple environmental compartments since 2001, in areas with and without bivalve mortalities. We used a combination of comparative genomics and population genetics approaches and show that Va has a classical epidemic population structure from which the pathogenic Va francensis subspecies emerged and clonally expanded. Furthermore, we identified a specific cus-cop-containing island conferring copper resistance to Va francensis whose acquisition may have favoured the emergence of pathogenic lineages adapted and specialized to oysters.

Gametogenic Cycle of the Oysters Pinctada capensis (Sowerby III, 1890) and Saccostrea cucullata (Born, 1778) (Class Bivalvia) in Inhaca Island, Southern Mozambique: A Subsidy for Bivalve Culture in the Region

This study describes reproductive aspects of the Pinctada capensis (pearl oyster) and Saccostrea cucullata (rocky shore oyster) in Inhaca Island, southern Mozambique (Western Indian Ocean). Adult oysters were collected monthly over two years within seagrass banks for P. capensis and rocky shore habitats for S. cucullata. The animals were evaluated using biometric and histological analyses of the gonads. Of the total population, females were predominant among larger individuals (>55 mm) and males were more dominant among smaller individuals (<55 mm) for both species. The sex ratio was (1 M–1.5 F) for Pinctada capensis and (1 M–1.6 F) for Saccostrea cucullata. Five gonad maturation stages were identified: indifferent, developing I, developing II, ripe and spent. The size at first maturity was mm and 26.2 mm for pearl oysters females and males, respectively, whereas for rocky shore oysters was 32.8 and 28.3 mm for females and males, respectively. We conclude that the reproduction of S. cucullata and P. capensis occurs mainly in summer, with a short resting period in winter, when many oysters are in the indifferent stage. These results provide valuable information to fisheries for management of both species in the area.

A conserved RNAi molecule Ago2 involved in antiviral immunity of oyster Crassostrea gigas

Argonaute (Ago) is the core component of RNA-induced silencing complex to play a crucial role in the antiviral immunity, which always cooperates with Dicer in RNA interference (RNAi) to silence the target genes. In the present study, an Ago homologue (CgAgo2) was identified in the Pacific oyster Crassostrea gigas. There were four classical functional domains in the predicted CgAgo2 protein, including an N-terminal domain, a PAZ domain, a Mid domain, and a PIWI domain. The deduced amino acid sequence of CgAgo2 shared 63.52%–84.27% identity with other Agos. Transcriptome analysis showed that CgAgo2 was highly expressed in embryonic period and gradually decreased from blastula to gastrula. The transcripts of CgAgo2 were detectable in all the examined tissues of adult oysters, with the highest expression in haemocytes (36.61-fold of that in adductor muscle, p < 0.001). The expression level of CgAgo2 mRNA in haemocytes increased significantly at 12 h after poly (I:C) and dsRNA stimulation, which were 2.71-fold (p < 0.05) and 58.00-fold (p < 0.001) of that in the control group respectively. Immunocytochemistry assay revealed that CgAgo2 proteins were mainly distributed in the cytoplasm and nucleus of haemocytes. The interaction between the recombinant CgAgo2 protein (rCgAgo2) and cleavage protein rCgDicer was observed in vitro by BLI and pull-down assays. These results indicated that CgAgo2 participated in the antiviral immunity of oyster by functioning as a component of RNA-induced silencing complex in RNAi.

Reproductive Phenology of the Eastern Oyster, Crassostrea virginica (Gmelin, 1791), Along a Temperate Estuarine Salinity Gradient

Low salinity can negatively affect reproduction in estuarine bivalves. The spatial and temporal extents of these effects are important to inform models of population dynamics, environmental risk assessments, restoration efforts, and predictions of climate change effects. A hypothesis of delayed gametogenesis for oysters at low salinity sites was tested relative to their higher salinity counterparts in downstream experimental cages. In 2018, the timing of gametogenesis and spawning was observed June–August for 2-year-old oysters from three distinct ancestries (native, hatchery, aquaculture), outplanted at age 1 month along the salinity gradient (3–30 psu) of a temperate estuary. A second season of data was collected in 2019 from a 3-year-old aquaculture line and mixed-age native adult oysters dredged and transplanted 1 year prior. Dermo was tested in 2019 and prevalence was 1.3% (n = 240). Gametogenesis and spawning were retarded for all ancestries at low salinity relative to higher salinity sites during July and August. The reverse pattern was found in June, with low salinity sites having more advanced gonad index than at a high salinity site. This difference in average gonad index was 2.65 vs 1.46, respectively, for the native line and 2.62 vs 2.08 for aquaculture. Low salinity seemed to not only induce earlier gametogenesis in June, but also extended the reproductive season relative to higher salinity sites. Among oyster ancestries, the aquaculture line stood out as having 30–48% lower gametogenic synchrony within sites, but only in 2018. Because the native oysters used in this study have been restricted to low salinity conditions for many generations, demonstration of their reproductive plasticity across salinities is notable and broadens the range of potential future restoration strategies.

Spatiotemporal spatfall dynamics and prevailing estuarine conditions for optimal oyster (Crassostrea tulipa) spat availability in selected Gulf of Guinea brackish systems

Uncertainties associated with wild harvests of seed and adult oysters due to unknown oceanographic oscillations are a major challenge in oyster fisheries and aquaculture development. In contribution to addressing this challenge, we proffer clarity on the spatiotemporal variations in spatfall (number of spat/m2) of the mangrove oyster Crassostrea tulipa (Lamarck, 1819) in four estuaries along the Gulf of Guinea coast. By monthly deployment of artificial substrates affixed to bamboo racks over 12 months, we find significant differences in spatfall among and within the brackish systems, and across months and seasons. Spatfall regimes were unique in each ecosystem albeit with an overall preponderance of dry season availability of spat. Locations with reef oysters had superior spatfall to mangrove root-adapted-oyster areas. Narkwa, a relatively small lagoon with reef oysters had the highest annual mean spatfall, which was 1.3, 2.5, and 9.8 folds the spatfall in Densu Delta, Benya Lagoon and Whin Estuary, respectively. Spatfall varied significantly by depth as the more frequently exposed top collectors harvested much less spat than submerged collectors. There was a year-round availability of spat, confirming continuous spawning in C. tulipa. Spatfall variability was significantly driven by fluctuations in prevailing dissolved oxygen and salinity. Prevailing dissolved oxygen and salinity levels in the estuaries for optimal spat settlement were 1.68 – 3.40 mg L-1 and 11.00 – 29.33 ppt (parts per thousand), respectively. The findings of this study are recommended as empirical reference points for sustainable seed procurement for aquaculture production and management of C. tulipa fishery in the region of the study.

Bonamia-free flat oyster (Ostrea edulis L.) seed for restoration projects: non-destructive screening of broodstock, hatchery production and test for Bonamia-tolerance

Native (flat) oyster (Ostrea edulis) beds, once a major component of the North Sea, largely disappeared from the region in the late 19th century. Flat oyster restoration is taking place at a number of locations in the North Sea. When flat oyster beds are restored in areas where O. edulis is functionally extinct it is advised to treat these as disease-free areas. Adult oysters were collected in the Dutch Delta area which is infected with the pathogenic parasite Bonamia ostreae. The aim of this research was to obtain Bonamia-free seed from parents collected in a Bonamia-infected area. In addition, the oysters were analysed to identify candidate genomic regions related to bonamiosis tolerance and exposed to Bonamia in the field to assess survival compared to a naïve control group. With the aid of a non-destructive screening method, Bonamia-free broodstock were selected. These oysters produced Bonamia-free larvae and seed. For comparison, broodstock oysters were collected in the Dutch Wadden Sea, an area free of Bonamia. These oysters also produced Bonamia-free larvae and seed. To study if the Delta area oysters had developed a degree of resistance to the disease, while the naïve Wadden Sea oysters had not, seed of both groups was challenged in Lake Grevelingen where Bonamia occurs. Survival of the pre-selected Bonamia-free oysters was significantly higher than the naïve group. Samples of seed were analysed for association of candidate genetic markers related to bonamiosis tolerance. A higher percentage of individuals with tolerance-associated marker genotypes was found in the screened group compared to the naïve one. However, mortality of the naïve group could not be related to Bonamia presence. Further challenge tests are needed before firm conclusions regarding the genetic markers can be made. The results show that hatchery production of Bonamia-free and potentially Bonamia-tolerant flat oysters is possible.

Experimental estimation of ladder dredge efficiency for capture of European flat oysters over mixed sediment

Fishing gear-based landings or survey methods are often used to make assessments of species stock abundance. In order to convert catch into abundance values, estimates or assumptions are made on the catch efficiency of the gear-based method. This is the case in areas where flat oysters, Ostrea edulis, are surveyed for fisheries and conservation objectives in a range of projects across Europe. Flat oyster dredge efficiency assumptions vary widely from 5–30% in published studies and uncertainty in what is an appropriate efficiency estimate has led some survey teams to switch to Catch-per-unit-effort (CPUE), where CPUE is also of concern should catch efficiency change with shellfish density, ground type or some other unmeasured variable such as shellfish distribution. We undertook an experimental approach to estimate dredge efficiency in a standard ladder dredge used to harvest and survey adult flat oysters in the UK and Ireland. The dredge efficiency trials assessed how efficiency was influenced by oyster density (between 1 and 2.2 oysters m2), distribution (clumped vs uniform) and ground types across a gradient of more hard to more soft surface sediments. Dredge efficiency was significantly affected by oyster distribution, but also density and ground hardness as well as their interactions. While a median value between 7 and 10% seems an appropriate universal ladder dredge efficiency to adopt, ground type and distribution had such an effect that local conditions may effect this considerably. Catch efficiency was negatively density-dependent, this makes CPUE methods challenging where oyster densities are likely to vary. Practitioners, regulators and researchers conducting surveys can improve CPUE approaches through standard techniques and knowledge of how catch efficiency varies as we have presented here.

Transgenerational transfer of the microbiome is altered by ocean acidification in oyster larvae

Ocean acidification will affect marine molluscs, however, transgenerational plasticity (TGP) can ameliorate some effects. Marine molluscs acquire members of their microbiome via the egg, yet we know little about how the microbiome can be influenced by transgenerational exposure to ocean acidification. We exposed adult Sydney Rock oysters (Saccostrea glomerata) from four genotypes to elevated and ambient PCO2 for nine weeks. Larvae were then raised in the same ambient and elevated PCO2 conditions. The relative abundance of bacteria in eggs and larvae were characterised using 16S RNA amplicon sequencing. Parental exposure to elevated PCO2 significantly altered the bacterial community composition of both eggs and larvae, but this was dependent on genotype. Parental exposure to elevated PCO2 caused five core Rhodobacteraceae ASVs to increase in relative abundance, and three Rhodobacteraceae ASVs to decrease in relative abundance. These findings show transfer of maternal microbiomes to larvae is altered by exposure to ocean acidification and this may play a role in TGP.

Life‐stage‐dependent effects of multiple flood‐associated stressors on a coastal foundational species

AbstractGlobal changes in precipitation patterns have increased the frequency and duration of flooding events. Freshwater inflows into estuaries reduce salinity levels and increase nutrient inputs, which can lead to eutrophication and impaired water quality. Oysters are important ecosystem engineers in coastal environments that are vulnerable to co‐occurring environmental stressors associated with freshwater flooding events. Successful recruitment is necessary to maintain adult oyster populations, but early life stage responses to multiple stressors are not well understood. Flood‐associated stressor conditions were observed near oyster habitats at multiple locations across the northern Gulf of Mexico during peak recruitment months in the spring and summer of 2021. In the laboratory, we examined the interactive effects of acidification, hypoxia, and low salinity on larval and juvenile life stages of the eastern oyster (Crassostrea virginica) to better understand the impact of flooding events on oyster development and survival. Salinity stress in isolation reduced larval growth and settlement, and decreased survival and growth at the juvenile stage. Hypoxia was more stressful to oyster larvae than to juveniles, whereas low pH had negative effects on juvenile growth. There were no synergistic effects of multiple flood‐associated stressors on early oyster life stages and effects were either additive or predicted by the salinity stress response. The negative impacts of flooding disturbances on recruitment processes in benthic populations need to be considered in restoration planning and flood control mitigation strategies as the frequency and intensity of extreme freshwater events continue to rise worldwide.

Role of the Vibrio community, reproductive effort, and environmental parameters in intertidal Pacific oyster summer mortality in British Columbia, Canada

In recent years, mortality of cultured Pacific oysters (Crassostrea gigas) during July and August has regularly exceeded 50% in many oyster farms in Baynes Sound, British Columbia (BC), Canada. However, little is known about the bacterial diversity and environmental/biological conditions that may be contributing to such mortality events in the region. A study of Pacific oysters in intertidal culture trays was conducted during the summer of 2017 in Baynes Sound to monitor the occurrence of oyster mortality, while identifying potentially pathogenic bacteria present in the oysters, examining oyster reproductive development, and recording various environmental parameters (temperature, salinity, dissolved oxygen, chlorophyll a, carbon chemistry, phytoplankton species/abundance, zooplankton species/abundance) at three farm sites in Buckley Bay, Fanny Bay, and Ship's Point. Continuous mortality was observed throughout July and August, cumulative mortalities ranging from 16.5 to 35.1% at the three sites. Mortality over time was examined with a binomial generalized linear mixed-effects regression model, which demonstrated a correlation with date, tides, temperature, gonad somatic index, and gonad developmental phase (Rc2 = 0.598). Average cumulative mortality per module was highly correlated with average oyster gonad length and the proportion of female oysters in a multiple linear-regression model (p = 0.002, R2 = 0.824). A total of 158 bacterial isolates were cultured and identified based on sequencing of the recA gene. Among those isolates, Vibrio aestuarianus and V. harveyi, with 27 and three isolates, respectively, are well-documented pathogens of Pacific oysters in other regions. This study is the first to concurrently evaluate a broad array of factors potentially associated with Pacific oyster summer mortality in BC. We provide evidence that summer mortality of Pacific oysters in Baynes Sound is occurring with an etiology similar to summer mortalities of adult Pacific oysters reported in other countries.

Life-history traits in the Pacific oysterCrassostrea gigasare robust to ocean acidification under two thermal regimes

AbstractOcean acidification and warming (OAW) are pressing contemporary issues affecting marine life and specifically calcifying organisms. Here, we investigated the direct effects of OAW on life-history traits of the Pacific oyster Crassostrea gigas, the most cultivated bivalve species worldwide. We also tested whether parental conditioning history shaped the phenotypic characters of their progenies (intergenerational carryover effects). Adult oysters and their offspring were exposed to two temperatures (18°C, +3°C) under ambient pH conditions or under an end-of-century acidification scenario (−0.33 pH unit). In adults, we monitored standard biometric and reproductive parameters, stress response by quantifying neuroendocrine metabolites and gamete quality. In larvae, we measured hatching rate, size, biochemical quality, and behavior. We found that reducing pH reduced growth rate and activated the serotonin system, but increasing temperature attenuated these effects. There was no effect of pH on reproduction at either temperature, and no intergenerational carryover effects. Larval characteristics were similar between treatments, regardless of parental conditioning history. Thus, the Pacific oyster seems robust to changes in pH, and increasing temperature is not an aggravating factor. We emphasize that the use of neuroendocrine indicators holds promise for revealing sublethal impacts of environmental changes.

A novel antibody-based biosensor method for the rapid measurement of PAH contamination in oysters.

Conventional PAH analytical methods are time-consuming and expensive, limiting their utility in time sensitive events (i.e. oil spills and floods) or for widespread environmental monitoring. Unreliable and inefficient screening methods intended to prioritize samples for more extensive analyses exacerbate the issue. Antibody-based biosensor technology was implemented as a quantitative screening method to measure total PAH concentration in adult oysters (Crassostrea virginica) - a well-known bioindicator species with ecological and commercial significance. Individual oysters were analyzed throughout the historically polluted Elizabeth River watershed (Virginia, USA). Significant positive association was observed between biosensor and GC-MS measurements that persisted when the method was calibrated for different regulatory subsets of PAHs. Mapping of PAH concentrations in oysters throughout the watershed demonstrates the utility of this technology for environmental monitoring. Through a novel extension of equilibrium partitioning, biosensor technology shows promise as a cost-effective analysis to rapidly predict whole animal exposure to better assess human health risk as well as improve monitoring efforts.

Detection of the protistan parasite, Haplosporidium costale in Crassostrea gigas oysters from the French coast: A retrospective study

The parasite Haplosporidium costale is known to infect and cause mortality in the oyster Crassostrea virginica in the USA. Decades after its first description in the 1960s, this parasite was detected in Crassostrea gigas in the USA and China. However, it presented a low prevalence and no mortality was associated with it. More recently, in 2019, H. costale was detected in France in a batch of moribund oysters. In order to observe how long this parasite has been present on French coasts, from Normandy to Thau lagoon, a retrospective investigation was conducted on 871 adult and spat oyster batches from 2004 to 2020. To allow rapid detection on a large panel of samples, a real-time PCR for the H. costale actin gene was developed. This method allowed the detection of H. costale DNA in adults from 2005 and in spat from 2008. The H. costale prevalence in spat appeared higher than in adults over the years studied, 14.59 % compared to 6.50 %, respectively. All samples presenting positive results were then sequenced on two targets, H. costale rRNA and actin genes. The actin gene sequencing highlighted the presence of two H. costale strains. Adult C. gigas as well as spat batches coming from hatcheries and DNA controls from C. virginica all presented with the Profile 1 H. costale strain. The Profile 2 H. costale strain was detected only in C. gigas spat coming from natural sources. These observations suggest a correlation between the origin of oysters and H. costale strains which may have been caused by commercial imports between Japan, USA and France back to the 1970s. Over the positive samples studied, only few batches (n = 3) suffered mortalities which could be hypothesized to be caused by H. costale, all presenting the Profile 1 H. costale strain.

Transcriptome analysis and pattern recognition receptors (PRRs) identification in different tissues of adult Pacific oysters infected with Vibrio parahaemolyticus

Contamination of V. parahaemolyticus in raw product and culture areas of Crassostrea gigas has been a concern in food hygiene and infectious diseases in the shellfish aquaculture industry for decades. Although numerous researchers have presently objective of decreasing pathogen microorganism contaminated load in raw oysters or genetics improvement for prevention, the in-depth information at the molecular level of host-pathogen interaction in terms of immune-related genes, primarily pattern recognition receptors (PRRs) still has poor understanding. Hence, this study was focused on the biological process and differential expression of immune-related genes in PRRs against V. parahaemolyticus infection via transcriptomic analysis in the digestive gland and mantle tissues. As a result, differential gene expressions (DEGs) of transcriptomic profiling indicated that the digestive gland and mantle tissues had expressed differently in response to immune mechanisms and immune gene-related against post-infection. GO and KEGG enrichment analysis revealed up-regulated genes expressed in digestive gland tissues that demonstrated the reaction of the immune mechanism in Gram-negative bacterial adhesion against epithelium host cells and phagocytosis. In contrast, mantle tissue showed significantly oxidative stress and peroxidase reaction response against infection. Underline with up-regulated gene expression data sets in bacterial infection pathway from KEGG enrichment analysis. The result indicated that seven genes related to PRRs consisted of CgPGRP-SC2X2 (peptidoglycan recognition proteins), CgC-type-lectin, Cgperlucin-like, CgMCR1 (macrophage mannose receptor 1), CgGal-9 (galectin-9), CgLBP (lipopolysaccharide-binding protein), and CgGBP (β-1,3-glucan-binding protein) have induced at 12–24 h post-infection. In contrast, down-regulated genes expressed datasets have similarly provided gene-related expression with cell-based movement on the cytoskeleton in both digestive gland and mantle tissues. The protein binding function was studied on four successful recombinant protein expressions via an immunofluorescent assay to better understand. The result revealed that rCgGal-9 and rCgMCR1 contained carbohydrate-binding domains (CBDs), demonstrated strongly in binding functions with the outer layer of V. parahaemolyticus, clinical separation, and ATCC 17800 strains, more than rCgβGBP and rCgPGRP-SC2X2. In summary, all these results suggest, at 12–24 h post-infection, immune genes related to PRRs function were induced by V. parahaemolyticus, and the most highly up-regulated gene expression and strongly binding in bacterial infection pathways indicated to C-type lectins family and carbohydrate-binding protein domains, which play a critical role in defense mechanism. Moreover, the information from this study points out a list of interesting genes and biological mechanisms in C. gigas against V. parahaemolyticus infection and produces lists of novel relevant candidate genes for further studies.

Meta-analysis of ecosystem services associated with oyster restoration.

Restoration of foundation species promises to reverse environmental degradation and return lost ecosystem services, but a lack of standardized evaluation across projects limits understanding of recovery, especially in marine systems. Oyster reefs are restored to reverse massive global declines and reclaim valuable ecosystem services, but the success of these projects has not been systematically and comprehensively quantified. We synthesized data on ecosystem services associated with oyster restoration from 245 pairs of restored and degraded reefs and 136 pairs of restored and reference reefs across 3500km of U.S. Gulf of Mexico and Atlantic coastlines. On average, restoration was associated with a 21-fold increase in oyster production (mean log response ratio=3.08 [95% confidence interval: 2.58-3.58]), 34-97% enhancement of habitat provisioning (mean community abundance=0.51 [0.41-0.61], mean richness=0.29 [0.19-0.39], and mean biomass=0.69 [0.39-0.99]), 54% more nitrogen removal (mean=0.43 [0.13-0.73]), and 89-95% greater sediment nutrients (mean=0.67 [0.27-1.07]) and organic matter (mean=0.64 [0.44-0.84]) relative to degraded habitats. Moreover, restored reefs matched reference reefs for these ecosystem services. Our results support the continued and expanded use of oyster restoration to enhance ecosystem services of degraded coastal systems and match many functions provided by reference reefs.

An ecological assessment of Australia's first community oyster gardens

SummaryOyster gardening is a community‐driven activity where oysters are grown in cages hanging off docks or other coastal infrastructure. Besides the provision of adult oysters for restoration programmes, oyster gardening may also support other ecosystem services such as providing habitat for fishes and invertebrates as well as encouraging community involvement and citizen science. Australia's first oyster gardening programme was undertaken in a canal estate on Bribie Island in Moreton Bay, Queensland between October 2016 and November 2017. Oyster gardens consisting of plastic mesh cages were deployed with either three species of bivalves (polyculture), or exclusively Sydney Rock Oysters (monoculture) to investigate whether the habitat value differed between the two garden types. After one year of growth, polyculture cages supported higher abundances and species richness of both invertebrates and fish compared to the monoculture gardens. Our study showed that oyster gardening can provide habitat for a range of invertebrate and fish species in the highly modified coastal environment of a canal estate. Further studies are needed to discern whether these oyster gardens would also support larger and mobile fauna, such as species with commercial and recreational importance.

The expression profile of a multi-stress inducible transient receptor potential vanilloid 4 (TRPV4) in Pacific oyster Crassostrea gigas

Transient receptor potential vanilloid 4 (TRPV4) is one of the major non-selective cation channel proteins, which plays a crucial role in sensing biotic and abiotic stresses, such as pathogen infection, temperature, mechanical pressure and osmotic pressure changes by regulating Ca2+ homeostasis. In the present study, a TRPV4 homologue was identified in Pacific oyster Crassostrea gigas, designated as CgTRPV4. The open reading frame (ORF) of CgTRPV4 was of 2298 bp encoding a putative polypeptide of 765 amino acid residues with three typical ankyrin domains and six conserved transmembrane domains of TRPV4 subfamily proteins, as well as multiple N-glycosylation sites, cAMP- and cGMP-dependent protein kinase phosphorylation sites, protein kinase C phosphorylation sites, casein kinase II phosphorylation sites, and prokaryotic membrane lipoprotein lipid attachment site. The deduced amino acid sequence of CgTRPV4 shared 20.5%-26.2% similarity with TRPV4s from other species. During the early ontogenesis stages of oyster, the mRNA transcripts of CgTRPV4 were detectable in all the stages with the highest expression level in fertilized eggs and the lowest in D-hinged larvae. In adult oyster, the CgTRPV4 mRNA could be detected in all the examined tissues, including gill, hepatopancreas, adductor muscle, labial palp, mantle and haemocyte, with the highest expression level in gill (45.08-fold of that in hepatopancreas, p < 0.05). In immunocytochemical assay, the CgTRPV4 positive signals were distributed in both endoplasmic reticulum and cytoplasmic membrane of oyster haemocytes. The mRNA expression of CgTRPV4 in gill was significantly up-regulated after high temperature stress at 30°C (p < 0.05) and after Vibrio splendidus stimulation (p < 0.05). These results indicated that CgTRPV4 was a classical member of TRPV4 family in oyster, which was induced by either biotic or abiotic stimulations and involved in mediating the stress response of oysters.

Are We Falling Short on Restoring Oysters at a Regional Scale?

Across coastal areas of the northern Gulf of Mexico, the Deepwater Horizon oil spill resulted in significant ecological injury, and over 8 billion USD directed to restoration activities. Oyster restoration projects were implemented with regional goals of restoring oyster abundance, spawning stock, and population resilience. Measuring regional or large-scale ecosystem restoration outcomes challenges traditional project-specific monitoring and outcome reporting. We examine the outcomes of oyster restoration at the project-level and discuss potential pathways to measure progress toward region-level goals. An estimated 15 km2 of oyster habitat was restored across 11 different estuaries with 62 individual reef footprints created, ranging in size from ~0.2 to 1.45 km2. Individual sites were distributed across the salinity gradient, and all reefs were subtidal. One-year post-restoration, mean total oyster density across all sites was 53.0 ± 60.7 ind m-2 of which 38.4 ± 42.2 ind m-2 were adult (>25 mm shell height) oysters. Recent data (2018/2019) available for all sites indicates reduced densities of total oysters (44.6 ± 70.9 ind m-2) and adult oysters (14.6 ± 21.6 ind m-2). These data provide insight into project specific outcomes, suggesting an overall enhancement in oyster abundance compared to pre-restoration, but fall short of informing outcomes at the regional-level that incorporate cumulative effects on adjacent and connected reef populations, or inform overall resiliency of the regional oyster resource. Developing regional outcome benchmarks that enable assessment of cumulative and synergistic impacts of individual projects may benefit from broader spatial and temporal monitoring requirements that can better inform development of regional tools or models. Such tools would enable cumulative effects analyses examining net resource change, resilience and assess impacts of restoration activities on regional resource status.