Oyster Growth Research Articles

Assessing the spatial variability of cage movement and velocity attenuation of an off-bottom oyster farm and its influence on eastern oyster (Crassostrea virginica) growth performance

The global shellfish aquaculture industry has expanded over the last seven decades. Similarly, the size of individual shellfish farming operations has grown in some states. Circulation processes in natural water bodies are dynamic and vary across multiple temporal and spatial scales. How gear installation affects the circulation of currents and waves, and subsequent phytoplankton delivery to crops within farms, is largely unknown. Documenting and understanding variability in wave and current energy within an individual farm could help optimize production. Our study sought to understand the variability in oyster growth attributable to hydrodynamic and atmospheric forcing across an active commercial shellfish aquaculture lease in the Patuxent River, Maryland. We observed a 17 % reduction in water flow downstream of the farm (rho = −0.673, p = 0.002, Spearman rank test), suggesting the bottom cages attenuated downstream current velocity during flood tides. Differences in flow speed and the movement of cages and oysters throughout the farm correlated with variances in oyster shell morphology and oyster survival while in bottom cages. Our results demonstrate the occurrence of variability in production within an individual farm location. Further, our findings suggest that insight into the spatial growth patterns across a lease can be practical for forecasting growth and quality of cultured oysters and may enable growers to strategically place oysters within their farm to improve yield and product consistency.

Nutritional value of a novel EMS-induced cell wall-defective strain of Saccharomyces cerevisiae yeast for Pacific oyster (Magallana gigas) juveniles

The difficulties and high costs of live microalgae production have driven the search for alternative diets in bivalve aquaculture. The baker's yeast (Saccharomyces cerevisiae) represents a promising, cost-effective, high-quality protein for aquaculture. However, its application is restricted by poor digestibility due to its thick, rigid cell wall. Previously, we observed that the deletion of mnn9 gene in S. cerevisiae, leading to defective mannan synthesis and increased β-glucan exposure, enhances growth and immune response in Magallana gigas oysters. Nevertheless, using ∆mnn9 in aquaculture is not feasible due to restrictions on genetically modified organisms (GMO) containing antibiotic-resistance genes. This study aimed to create a non-GMO cell-wall defective yeast mutant (JH40) via ethyl methanesulfonate (EMS) mutagenesis and evaluate its nutritional value for M. gigas juveniles. Phenotypical differences between wild-type S. cerevisiae (WT), ∆mnn9, and JH40 were characterized using fluorescein isothiocyanate (FITC)-labeled lectin analysis, microscopy, cell diameter measurements, growth curves, and osmosensitivity tests. The nutritional value of a microalgae-based diet (Chaetoceros muelleri:Tisochrysis lutea, 50:50 based on dry weight) and its 50% substitution with JH40 or WT was assessed over 21 days in M. gigas juveniles. A complementary test also explored higher substitution levels (63%, 75%, and 100%) of the based diet with JH40 and the addition of extra JH40 (+25 %) in the 63% and 75% replacement diets. Results indicated that JH40 forms clumps, grows slower than the WT, has a larger cell diameter, higher binding affinity to WGA and LEL lectins than the WT, and is highly sensitive to hypo-osmotic stress, which are characteristics of cell-wall defective yeasts. Oysters fed a diet with 50% JH40 substitution showed significantly higher growth compared to those fed the WT-containing diet. JH40 could replace 50% of the algal diet without significantly affecting oyster growth and survival. However, higher inclusion levels of JH40 (62 %, 75 %, and 100 %) did not achieve the oyster growth observed with the algae-based diet, even with additional yeast. These findings are attributed to the limited polyunsaturated fatty acid content in yeast cells. Further research on dosing and administration frequencies is needed to evaluate the immunostimulatory potential of JH40.

Dual benefits of biofouling reduction in non-fed aquaculture: On-site heat treatment enhances oyster production and mitigates local environmental impacts

We experimentally evaluated the biofouling reduction by on-site heat treatment in enhancing oyster aquaculture production and mitigating its environmental impacts. Specifically, we compared oyster growth, settling flux of particulate organic matter (POM), and its oxygen consumption rate (OCR) between heat-treated (HT) and non-treated (N) sections within suspension oyster farms in a temperate bay. HT demonstrated a substantial reduction of 81–99% in fouling mussel biomass and approximately 20–30% increases in cultivated oysters’ growth and condition index. The settling flux of POM was 10–57% smaller in HT mainly due to the reduction in biodeposition from fouling mussels. However, OCR of settling POM at a unit mass was 6–62% higher in HT than in N; overall, the short-term oxygen consumption by settling POM did not significantly differ between HT and N. The increase in OCR of settling POM in HT may be attributable to the decrease in biodeposits from fouling organisms and increase in the relative contribution of fresh POM entering from unfarmed areas. Meanwhile, from the longer-term perspective, the substantial reduction in settling POM by the heat treatment lower the potential for oxygen consumption in the bottom layers over the half-year farming operation by 31%. In conclusion, on-site heat treatment is a simple tactic for controlling nutrient and POM flows at production sites, simultaneously enhancing oyster production and mitigating the local environmental impact of non-fed oyster aquaculture. Furthermore, this approach exemplifies an effective tactic to enhance the sustainability of primary food production processes.

Pertumbuhan tiram mutiara (Pinctada maxima) menggunakan metode karambah apung dan longline

Pearl oyster cultivation is a growing industry in various countries. The growth and quality of pearls produced by oysters is greatly influenced by the cultivation method used. This research aims to compare the growth of pearl oysters (Pinctada maxima) cultivated using the floating cage and longline methods. Different cultivation methods can influence the growth of pearl oysters and the surrounding environmental conditions. Statistical analysis was conducted on sample size, mean values, standard deviation, and standard error of the mean for both cultivation methods. The results indicate no significant difference in the growth of pearl oysters between the floating cage and longline methods. However, biofouling and other disrupting organisms can affect the growth of pearl oysters in the floating cage method. The study also highlights the importance of environmental factors such as water quality, temperature, and food availability in influencing the growth of pearl oysters. Thus, this research provides valuable insights for the pearl oyster cultivation industry in selecting the optimal cultivation method to enhance productivity and the quality of the pearls produced.

A novel application of sclerochronology: Assessing the paleoenvironment of a marine transgressed Archaic Period archaeological site in the Gulf of Mexico

Sequential oxygen (δ18O) and carbon (δ13C) isotope analysis were performed on eight eastern oyster (Crassostrea virginica) valves excavated from a marine transgressed archaeological site on the southwest coast of Florida, USA. The oysters were attached to Archaic Period human skeletal material and serve as a marker of mid-Holocene sea level rise at this once-inland mortuary pond. Data were analyzed to— (1) determine if a sample of oysters excavated from the site represent one or more inundation episodes, (2) assess past water parameters as the pond was transgressed, and (3) determine how long the oysters grew on exposed human skeletal material. Results of sclerochronological analysis and radiocarbon dating demonstrate there were two distinct environments at the time of oyster growth, each representing separate time periods and water parameters, with the earlier oyster group indicating fresher water parameters. Oysters were between one and three years old, suggesting human skeletal material was exposed for at least that long. This is the first instance in which oysters attached to Archaic Period skeletal material were used to draw wider conclusions about past marine transgression and environmental change, and results show that oysters contain valuable information for investigation at drowned archaeological sites. This research clarified methodologies that could be employed to better understand sea level rise's effects on archaeological sites on drowned portions of continental shelves.

Stochastic modeling of eastern oyster (Crassostrea virginica) production in a Mexican tropical coastal lagoon using alternative stocking density management schemes

A stochastic model was developed to analyze Crassostrea virginica production when cultivated at three stocking densities, defined as the area occupation (50, 75, and 100%) in Nestier-type trays, using juvenile oysters with an initial size (height) of 29.40 ± 0.18 mm. A 25-week grow-out was first conducted in the Rio Lagartos lagoon, showing that final oyster size was inversely related to density (P < 0.05), ranging from 61.87 mm (100% density) to 68.00 mm (50% density). At the same time, mortality was negligible (lower than 1.0%). The environmental conditions in the lagoon were stable, and the oyster growth rate positively correlated with water temperature and pH. Low pH was associated with slow oyster growth, possibly as an adverse effect of acidic conditions on the oyster shell formation. The model indicated that, for an initial 100,000 oyster population, the maximum production (oyster dozens) is obtained after 20 weeks (8310 at 50% density) and 25 weeks (8250 at 75%, and 6670 at 100% density). There was a 100% probability of oysters reaching a minimum commercial size (MCS) of 60.00 mm when using the 50 and 75% densities and 80.6% when using 100%. The model estimated that, for the maximum density, extending the grow-out up to 32 weeks would allow reaching MCS with 100% probability, although this should be experimentally confirmed. The random variability of oyster production in 50 and 75% densities was minimal, while at 100% density, it was extremely high. A sensitivity analysis indicated that for 50 and 75% densities, the main stochastic elements influencing production, are related to oyster mortality, while at 100% density, they are related to oyster growth.

Hydrodynamics of artificial and oyster-populated breakwaters: A laboratory study with scaled-down oyster castles under unidirectional flow

Oyster populations within the Chesapeake Bay have been drastically reduced over the last century mainly due to unregulated human activities and diseases. Regulations and restoration efforts have focused on restoring oyster populations while also considering their ability to provide ecosystem services, such as coastal protection and water quality improvement, among others. To promote oyster growth and the settlement of new populations, a recent technique adopted along the east coast of the US is the use of oyster castles (OCs). OCs have proven effective in recruiting and retaining oysters and in promoting both vertical growth and horizontal expansion of oyster habitats. OCs are widely used in coastal protection as greener alternative to common engineering solutions. We quantified hydrodynamic differences that occur around these OCs during their early stage (i.e. castles without oysters), and with fully developed oysters covering the surface of the castles through a series of laboratory experiments. The experiments were conducted in a recirculating Odell-Kovasznay type channel at the Ecohydraulics and Ecomorphodynamics Laboratory (EEL) at the University of Illinois. OCs (both with and without oysters) were 3D printed at 1:7 scale to fit the canal, and Particle Image Velocimetry (PIV) was used for 2D flow characterization. Data showed noticeable differences in flow acceleration atop the castles when covered with oysters, as well as an increase in the generation and distribution of turbulent kinetic energy atop and around the oyster-covered castles. Magnitudes and spatial distribution of Reynolds stresses were also affected by the presence of oysters in both submerged and near-emergent conditions. Challenges associated with the estimation of the drag coefficient for both gray and oyster-covered OCs highlighted the need for more data besides the centerline 2D PIV output. Further research involving the whole three-dimensional structure of the flow, in both unidirectional and oscillatory conditions, will allow us to provide relevant guidelines on the design and use of oyster-populated breakwaters as a viable nature-based solution for coastal protection within low-energy environments.

Exploring high intertidal refugia as an approach for the restoration of an intertidal oyster

Marine organisms frequently inhabit intertidal zones that serve as refuges from predation and competition but are not optimal physiologically. Restoration practitioners working with intertidal species may similarly have to consider whether restoration success will be greater where conditions are more benign (usually lower in the intertidal) or where negative biotic interactions are reduced (usually higher in the intertidal). In cases where a target species has greater desiccation tolerance than its enemies, restoration may be more successful higher in the intertidal zone, despite potential performance trade-offs. In many US West Coast estuaries, non-native drill species can decimate native oyster populations, posing a challenge to restoration. Given that native Olympia oysters Ostrea lurida should be better able to withstand tidal emersion than the non-native Atlantic oyster drill Urosalpinx cinerea, we explored using the high intertidal as a refuge from predation as a potential restoration technique. Using surveys and a field experiment, we investigated the recruitment, growth, and survival of oysters as well as drill abundance and predation over 3 tidal elevations. Oysters recruited and survived equally well at +0.1, +0.5, and +0.8 m mean lower low water, but juvenile oyster growth decreased with increasing elevation. In our experiment, predation on oysters was lower at the highest elevation than at low and mid elevations, but in natural populations there was a near complete absence of O. lurida at any elevation where U. cinerea was present. This suggests that a higher tidal elevation refuge is not a viable approach for oyster restoration in our study area.

Site selection for farming the oyster Saccostrea cucullata in a tropical coastal lagoon

This study investigates the influence of variable environmental conditions on the growth of the natural rock oyster (hooded oyster) Saccostrea cucullata in the river-fed Ambinanibe coastal lagoon (Madagascar), with the objective to establish sites with optimal growth conditions for aquaculture purposes. Specimen marked with manganese were placed in cages over an approximately one-year period. The cages were installed at four sites i.e. one at the river mouth, two sites within the main lagoon and one site in an adjacent connected lagoon, which is out of river influence and considered as the control site. Multiple mark and recapture experiments were used to investigate the variations in growth rate and condition index (tissue weight/shell weight). The results show that the species overall exhibits a fast growth rate at a young age, with a gradual growth reduction with age. The hinge growth rate shows important spatial and seasonal variations in the lagoon. Oysters from the site located at the river mouth have the highest hinge growth rate (20.5 ± 13.6 µm d−1) and condition index (4.5 ± 2.8 %) while those from the control site out of river and ocean influences exhibit the lowest hinge growth rate (7.7 ± 4.2 µm d−1) and condition index (0.7 ± 0.6 %), suggesting that river freshwater inflow provides suitable environmental conditions for oyster growth and a profitable oyster farming is thus feasible. River inflow is an important external source of nutrients, providing thus a significant food source (phytoplankton), as well as suitable temperature and salinity conditions for S. cucullata in this lagoon. Overall, our results show that oyster market size (shell length: 40 mm) in Madagascar can be reached faster at the river-influenced site (in 8 months) in comparison with the other sites (in 1 – 1.2 years), indicating that the river-impacted site is well suitable for oyster farming.

Marine aquaculture spatial planning on market orientation for Pacific oyster in Shandong, China

Accessing the production value is essential to the selection of suitable sites for aquaculture farms. This study employed a Dynamic Energy Budget (DEB) model and used market-oriented indicators, including shell length, flesh weight, condition index and minimum farming duration, to analyze the suitability for Pacific oyster aquaculture in offshore Shandong, China. Chlorophyll a (Chl-a) concentration, Total Suspended Sediment (TSS) concentration, and Sea Surface Temperature (SST) were extracted by remote sensing and used as forcing variables in the bioenergetic model. Four market-oriented indicators and five zones in the study area were chosen to develop a Suitable Market-Aquaculture site-selection model (SMASM) and estimate the oyster farming suitability. The results demonstrated that Sanggou Bay exhibits high potential for Pacific oyster year-round aquaculture. Eastern Laizhou Bay is suitable for the autumn-spring fattening culture of adult oysters. Laoshan Bay and Changshan Islands are suitable for promoting rapid growth in juvenile oysters. The results of our model were consistent with the oyster production value in Shandong, showing an overall increasing trend except for the anomalous value observed in 2019. Sudden drops in water temperature, red tides, and significant increases in turbidity can exert detrimental effects on oyster production, which has been evidenced to be influenced by Super Typhoon Lekima in 2019. Although this study concentrated on a specific geographical region, the model could be applied to other regions to develop market-oriented suitability management for species and environments worldwide.

Location and reef size drive oyster reef restoration success

Optimizing habitat restoration success requires understanding how restoration location and design enhance the persistence and function of a restored habitat. Particular attention to the configuration of structure and its interaction with landscape‐scale processes is critical for enhancing the habitat value of restored areas. We monitored six subtidal restored oyster reefs in Pamlico Sound, North Carolina, United States, to identify how oyster demographics responded to initial habitat characteristics (e.g. reef area, volume, vertical relief, and perimeter‐to‐area ratio) and how changes in habitat characteristics over time altered suitability for oysters. Changes in reef habitat were measured by repeated mapping using bathymetric and side‐scanning sonar systems. A 2‐year time series of oyster demographic data quantified oyster response to habitat changes over time. All reefs provided habitat for the settlement and growth of oysters. Within 2 years of restoration, relative differences in oyster recruitment and survival emerged and were related to variations in reef location and two‐dimensional habitat characteristics among reefs, namely reef area and perimeter‐to‐area ratio. Larger reefs that were less fragmented resisted burial from sedimentation and enhanced oyster densities and biomass relative to smaller, more fragmented reefs that became heavily sedimented and failed to support oyster recruitment and survival. Positive feedback mechanisms between habitat characteristics and oyster recruitment success were established within 1 year of restoration and were likely driven by landscape‐scale processes such as sediment dynamics and larval supply. To improve restoration success, we recommend creating larger reef surfaces with low perimeter‐to‐area ratios in areas that promote habitat persistence.

Contribution of the TGFβ signaling pathway to growth of Pacific oyster (Crassostrea gigas)

Growth mediated by the transforming growth factor β (TGFβ) signaling pathway is a key trait in understanding environmental adaptability and species stability. The aim of the present study was to identify the TGFβ signaling pathway members and their expression patterns in different sized Pacific oysters (Crassostrea gigas). Nine oysters were selected for each of two groups: group L (shell height 77.57 ± 7.55 mm, shell length 49.96 ± 4.79 mm) and group B (shell height 43.58 ± 2.74 mm, shell length 33.25 ± 2.78 mm). Using a bioinformatics approach, 37 protein sequences of TGFβ signaling pathway members were classified in C. gigas, including 19 species for this species, nine ligands, five receptors, and five Smads. The mRNA expression levels of TGFβ pathway members in oysters of different sizes showed that both the TGFβ/activin/Nodal and BMP/GDF/MIS subfamilies are involved in the growth regulation of C. gigas. In the first subfamily, there was one possible signaling pathway: INHBA - TGFBR1/BMPR1B/ACVR1 - BMPR2 - Smad3/Smad1, 5, 8. In the second subfamily, there were three possible signaling pathways: BMP2 - BMPR1B - BMPR2 - Smad1, 5, 8; BMP4 - BMPR1B - BMPR2 - Smad1, 5, 8; and BMP7 - ACVR1/BMPR1B - BMPR2 - Smad1, 5, 8. Principle components analysis identified Bmp3, I-Smad, Bmp4, INHBA, and Smad3 as biomarkers of growth in the TGFβ signaling pathway of C. gigas, implicating the TGFβ pathway in the growth of C. gigas.

Recruitment of a threatened foundation oyster species varies with large and small spatial scales.

Understanding how habitat attributes (e.g., patch area and sizes, connectivity) control recruitment and how this is modified by processes operating at larger spatial scales is fundamental to understanding population sustainability and developing successful long-term restoration strategies for marine foundation species-including for globally threatened reef-forming oysters. In two experiments, we assessed the recruitment and energy reserves of oyster recruits onto remnant reefs of the oyster Saccostrea glomerata in estuaries spanning 550 km of coastline in southeastern Australia. In the first experiment, we determined whether recruitment of oysters to settlement plates in three estuaries was correlated with reef attributes within patches (distances to patch edges and surface elevation), whole-patch attributes (shape and size of patches), and landscape attributes (connectivity). We also determined whether environmental factors (e.g., sedimentation and water temperature) explained the differences among recruitment plates. We also tested whether differences in energy reserves of recruits could explain the differences between two of the estuaries (one high- and one low-sedimentation estuary). In the second experiment, across six estuaries (three with nominally high and three with nominally low sedimentation rates), we tested the hypothesis that, at the estuary scale, recruitment and survival were negatively correlated to sedimentation. Overall, total oyster recruitment varied mostly at the scale of estuaries rather than with reef attributes and was negatively correlated with sedimentation. Percentage recruit survival was, however, similar among estuaries, although energy reserves and condition of recruits were lower at a high- compared to a low-sediment estuary. Within each estuary, total oyster recruitment increased with patch area and decreased with increasing tidal height. Our results showed that differences among estuaries have the largest influence on oyster recruitment and recruit health and this may be explained by environmental processes operating at the same scale. While survival was high across all estuaries, growth and reproduction of oysters on remnant reefs may be affected by sublethal effects on the health of recruits in high-sediment estuaries. Thus, restoration programs should consider lethal and sublethal effects of whole-estuary environmental processes when selecting sites and include environmental mitigation actions to maximize recruitment success.

Determination of optimal temperature, salinity, and stocking density combinations for larval growth and survival of diploid, triploid, and tetraploid Fujian oyster (Crassostrea angulata)

For nurseries, thriving larvae mean higher incomes. Three factors - temperature, salinity and stocking density - are critical to the success of larval rearing. However, the effects of these three factors on the performance of diploid, triploid and tetraploid Crassostrea angulata larvae have not yet been comprehensively investigated. In this study, the combined effects of temperature (T, 12.0–35.0 °C), salinity (S, 10.0–38.0 psu) and stocking density (D, 0.5–10.0 ind. ml−1) on the accumulated growth rate (AGR) and survival rate (SR) of diploids (DD), triploids (DT) and tetraploids (TT) C. angulata larvae were comprehensively assessed using a central composite design and response surface methodology. The results revealed that suitable temperature-salinity-stocking density combinations significantly increased the AGR and SR of larvae from all three groups, while unsuitable environments (e.g., ultra-high temperature - extra-high salinity -high stocking density combinations or ultra-high temperature - extra-low salinity - high stocking density combinations) significantly reduced the AGR and SR of the larvae, albeit to different magnitudes. The optimal temperature-salinity-stocking density combinations were obtained by model optimization. The maximum AGR and SR of DT reached at 23.6 °C, 26.5 psu and 0.5 ind. ml−1 combinations with values of 17.13 μm day−1 and 64.81%, respectively. The combinations of 24.0 °C - 25.89 psu - 1.99 ind. ml−1 and 25.9 °C - 25.96 psu - 0.5 ind. ml−1 were the optimal breeding conditions for DD and TT (DD: AGR = 13.10 μm day−1, SR = 63.55%; TT: AGR = 10.11 μm day−1, SR = 25.89%). In addition, validation experiments were carried out under the obtained optimum conditions. The AGR and SR of DD, DT and TT obtained from the validation experiments were basically in conformity with the maximum AGR and SR obtained under the theoretically predicted conditions. Moreover, the growth and survival of tetraploids remained lower than those of diploid and triploid counterparts, even under optimal breeding conditions. This means that more attention should be paid to the tetraploids so as to safeguard the succession of this fragile population. The application of the findings of this study will help to improve the breeding efficiency of C. angulata with different ploidies in larval culture.

Growth and survival of milkfish (Chanos chanos), tiger prawns (Panaeus monodon), and oysters (Crassostrea sp.) in integrated multi-trophic aquaculture (IMTA) system with varying stocking densities

Integrated Multitrophic Aquaculture System (IMTA) is a sustainable approach to aquaculture, utilizing ecosystem dynamics by integrating various species. This study examined the growth and survival of milkfish (Chanos chanos), tiger shrimp (Penaeus monodon), and oysters (Crassostrea spp.) in IMTA systems with different stocking densities. A 30-day experiment using a nonfactorial-completely randomized design with four treatments and three replications was conducted. The results showed that the implementation of IMTA had no significant impact on the survival rate of milkfish, tiger prawns or oysters in all treatments. However, important variations in growth parameters were observed. Milkfish and tiger prawns showed the highest weight and length gain in treatment B, followed by treatments A, C, and D. Similarly, oysters showed optimal growth in treatment B, followed by A, C, and D, based on weight gain, length, width, and shell thickness. Throughout the study, the physicochemical parameters of the water remained within acceptable ranges, thus supporting ideal growth conditions for the cultured species. These findings underscore the potential of IMTA to increase aquaculture productivity while upholding the principles of environmental sustainability. By optimizing stocking density and encouraging species diversity, IMTA presents a promising avenue for advancing integrated aquaculture practices, in line with the FAO's blue economy concept and ecosystem approach to aquaculture. Future research should concentrate on refining the IMTA system and evaluating its long-term ecological and economic consequences.

Efficacy and effects of three desiccation intervals on biofouling and Eastern oysters (Crassostrea virginica) at three commercial oyster farms in the Chesapeake Bay, MD

Oyster aquaculture is a growing industry both globally and nationally. Productive coastal waters support high-density containerized culture of oysters, but also sustain many other macrofaunal species which can settle on oysters and cage materials (biofouling), causing problems for oyster farms. Desiccation, or periodic air drying, of farm infrastructure and oysters has been used to control colonization and growth of biofouling organisms on oyster farms worldwide, but the minimum necessary interval of desiccation has yet to be thoroughly assessed. Given the known stresses to oysters associated with periods of emersion, an understanding of the effects of different weekly desiccation intervals is needed. This study investigated the use of desiccation in controlling biofouling and the associated impacts to oyster growth and mortality at three oyster farms within Maryland's portion of the Chesapeake Bay, including one low salinity site in an upper Chesapeake Bay tributary and two sites in the middle portion of the Chesapeake Bay. Three desiccation treatments were applied at each site: control (no desiccation), 8 consecutive hours of desiccation per week, and 24 consecutive hours of desiccation per week. Oysters were deployed between July–December 2018 and the percent valve coverage by individual biofouling species was monitored, along with worm abundance, oyster growth, and oyster mortality. Total biofouling was significantly greater on non-desiccated oysters but minimal differences in biofouling coverage were observed among oysters desiccated for 8 or 24 h weekly. Seven biofouling species were observed among the sites, and all except for a single macroalgal species (Ulva intestinalis) were controlled by the 8- and 24-h desiccation treatments. No clear treatment-derived differences in oyster growth or mortality were observed. Overall, results suggest desiccating weekly for either 8 or 24 consecutive hours may be a suitable biofouling management strategy for gross biofouling reduction on oyster farms.

The Identification of a Cell Cycle Regulation Gene Cyclin E from Hong Kong Oysters (Crassostrea hongkongensis) and Its Protein Expression in Response to Salinity Stress

Hong Kong oysters (Crassostrea hongkongensis) are an important marine bivalve with nutritional and commercial value. The expanded off-bottom farming scale in recent years makes the oysters more susceptible to exposure to abiotic stresses, such as salinity stress, an important environmental factor that has been proven to have significant effects on oyster growth and development. However, the molecular mechanism is still unclear. Cyclin E is an important protein in the process of cell cycle regulation that is indispensable for propelling G1/S phase transition in a dose-dependent manner. In order to investigate whether the salinity stress affects cyclin E expression in oysters, the cDNA sequence of C. hongkongensis cyclin E (Ch-CCNE) was isolated from a gill cDNA library, and the 2.8 kbp length cDNA fragment contained a complete open reading frame (ORF) encoding 440 amino acid residues. Ch-CCNE mRNA was highly expressed in the gonad and low in the adductor mussel, mantle, gill, labial palp, and digestive gland. The recombinant CCNE protein was expressed and purified in a pET32a(+)-CCNE/Escherichia coli BL21(DE3) system via IPTG induction and was used for generating mice anti-Ch-CCNE antiserums. Western blot analysis showed that the CCNE protein in the gill was maintained at low expression levels under either hypo- (5 ppt) or hyper- (35 ppt) salinity, and could be produced at high levels under appropriate salinity during a 10-day exposure period. The immuno-localization indicated that the Ch-CCNE protein was distributed in the nucleus. These results suggested that either hypo- or hyper-salinity stress could inhibit the CCNE expression of Hong Kong oysters and their negative impact on cell division and proliferation.

Abundance of Vibrio aestuarianus, water temperature, and stocking density are associated with summer mortality of Pacific oysters in suspended culture

High mortality rates of cultured Pacific oysters (Crassostrea gigas) during the summer months have regularly occurred on oyster farms in British Columbia, Canada over the last 10 years, but little is known about the microbial and environmental conditions that contribute to such mortality events. The objective of the study was to determine correlative factors associated with the onset of a summer mortality event in oysters (mean ± SD shell height: 14.2 ± 0.5 mm) grown in suspended culture at four stocking densities (150, 300, 450, 600 oysters tray−1) from May 11 to September 17, 2018. Variables examined included both biotic (oyster growth, mortality, reproductive development, and microbiome (approximately every week); Vibrio and harmful algal species abundance) and abiotic (temperature, salinity, turbidity, dissolved oxygen, pCO2, pH, and aragonite saturation) ones. Both the absolute abundance of V. aestuarianus and the relative abundance of Vibrio spp. increased with observed oyster mortality and declining health. Mortality was highest on August 12 and associated with a prior period of elevated temperatures (i.e., increasing temperatures from early July to early August) and increased oyster growth/reproductive development. At that time, systemic mixed microbial infections and necrotic gill tissue in histological cross sections were observed in 19% of oysters that appeared healthy macroscopically. Cumulative percent mortalities per tray ranged from 34 to 75%, the highest-density trays having significantly less mortality and smaller shell width, shell length, and gonad length than lower-density trays. This study demonstrates the significant impact of summer mortality on Pacific oysters and highlights the biotic (host growth, reproductive development, and microbiome composition as well as Vibrio spp. abundance) and abiotic (water temperature) factors associated with the observed mortality in this region.

Growth of Oyster (Crassostrea virginica) Larvae in Small-Scale Systems Using an Algae Concentrate Food Source

Replicated studies are advantageous for optimizing larval rearing of the Eastern oyster (Crassostrea virginica) and increasing the availability of high-quality seed for the continued expansion of the U.S. oyster aquaculture industry. Although small-scale systems using live algal feeds have been used successfully, rearing larvae on algae concentrate presents additional challenges. To determine the feasibility of rearing oyster larvae in small-scale systems using algae concentrate, oyster larvae were raised for 2 weeks in replicate control (1,000 L) and microcosm (17 L) tanks. Five aeration strategies were tested in the microcosms in two separate trials. Results of this study indicate similar survival in small systems compared to controls through the appearance of eyed larvae. Accumulated algae and pink biofilm formation in microcosms using polyvinyl chloride (PVC) airlifts suggest that this aeration strategy is undesirable. One- and 5-mL air injectors maintained higher overnight oxygen levels than controls. The recovery of more eyed larvae after 14 dpf in control systems may be the result of significant temperature fluctuations in microcosms. Overall, this study demonstrates that algae concentrate can be used to rear oyster larvae in small-scale systems, providing a live feed alternative that saves space and labor in replicated studies.

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

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