Shellfish Hatcheries Research Articles

Hatchery capacity needed to support large‐scale Atlantic surfclam fishery enhancement

AbstractFishery enhancement methods are being explored globally to sustain commercial and recreational fisheries through improving the productivity and management of marine populations impacted by anthropogenic stressors. It is expected that access to important Atlantic surfclam fishing grounds will be limited or lost due to growing overlap with offshore wind energy development. This study explores the economic viability of large‐scale hatchery production to improve fishery access and potentially offset additional costs, reduced revenues and potential job losses associated with the displacement of the fishing fleet. Reports and primary literature were used to understand the growth and survival of Atlantic surfclams in hatchery and nursery settings to calculate the scale of hatchery efforts needed to support one million (1M) bushels of fishery‐sized clams (>120 mm). Data on labour, energy, construction and material inputs and costs for hatchery and nursery production were gathered by analysing available literature and information provided by hatchery managers, researchers and others knowledgeable about shellfish hatchery production. A techno‐economic cost model and Monte Carlo analyses were employed to explore average costs and their variability. This study suggests that 374M–2.1B Atlantic surfclams are needed at the end of the hatchery stage to produce 1M bushels of market‐sized product. Total production costs range from $3.7 to $15.1M, including $2.9–$13.3M in hatchery costs and $800K–$1.9M in nursery costs. Under current market conditions, where Atlantic surfclams regularly sell for $14–$17/bushel, this analysis suggests that hatchery production could be considered a viable fishery enhancement method that supports human access to the fishery, though several additional questions remain.

Relative importance of phenotypic plasticity and carryover effects in response to small salinity shifts during oyster aquaculture production

Variability of water conditions in coastal environments could affect oyster aquaculture production through three main environmental-tolerance mechanisms: phenotypic plasticity, within-generation carryover effects, and selective mortality. Aquaculture production of eastern oyster, Crassostrea virginica, larvae occurs on weekly timescales in Virginia, with variations in salinity experienced by subsequent larval cohorts. The present study examined the relative importance of within-generation carryover effects – phenotypic changes during a previous life stage that impact a later stage – and phenotypic plasticity in shaping the performance of juvenile oysters after an experience of small differences in salinity (< 2 salinity units) during the larval stage. Genetic diversity was also assessed to rule out large shifts in allele frequencies, or loss of diversity, that would suggest observed effects were the result of selective mortality rather than carryover effects or phenotypic plasticity. Larval oysters were reared through settlement and metamorphosis under two salinities (thirteen and fifteen) that represent small differences between consecutive spawns in a hatchery. Juveniles were then raised in situ in two Virginia tributaries of the lower Chesapeake Bay, the York and Rappahannock rivers. Oyster production occurs within these two tributaries under distinct salinity conditions, with the Rappahannock tending to be of lower salinity. Metrics of survival, growth, oxidative stress, and condition index were compared to assess phenotypic plasticity and within-generation carryover effects. Juvenile oyster survival and physiology correlated with in situ environmental conditions rather than previous larval salinity experience. Specifically, juvenile oysters raised in the Rappahannock River had greater survival (13%), shell length (14%), condition index (38%), and dry tissue weight (78%) than those raised in the York River, regardless of larval salinity. Rappahannock River oysters also had 20% lower total antioxidant capacity than York River oysters. Genetic diversity remained high with no large shifts in allelic frequencies that would suggest non-random loss of alleles attributable to selection. Our results suggest that small salinity differences experienced in shellfish hatcheries 48 h after fertilization likely do not impact juvenile oyster performance during grow-out; rather, phenotypic plasticity likely underpins juvenile oyster performance during the transition from hatchery to farms. The importance of phenotypic plasticity presents another reason why farm site selection is critical to the performance and success of aquaculture product. Future studies are needed to further identify whether larval responses to salinity conditions are dependent on additional environmentally relevant conditions like temperature or the timing of exposure post-fertilization to better understand the relative importance of phenotypic plasticity, within-generation carryover effects, and selective mortality within oyster aquaculture.

Genomic diversity of wild and cultured Yesso scallop Mizuhopecten yessoensis from Japan and Canada.

The Yesso scallop Mizuhopecten yessoensis is an important aquaculture species that was introduced to Western Canada from Japan to establish an economically viable scallop farming industry. This highly fecund species has been propagated in Canadian aquaculture hatcheries for the past 40 years, raising questions about genetic diversity and genetic differences among hatchery stocks. In this study, we compare cultured Canadian and wild Japanese populations of Yesso scallop using double-digest restriction site-associated DNA (ddRAD) sequencing to genotype 21,048 variants in 71 wild-caught scallops from Japan, 65 scallops from the Vancouver Island University breeding population, and 37 scallops obtained from a commercial farm off Vancouver Island, British Columbia. The wild scallops are largely comprised of equally unrelated individuals, whereas cultured scallops are comprised of multiple families of related individuals. The polymorphism rate estimated in wild scallops was 1.7%, whereas in the cultured strains, it ranged between 1.35 and 1.07%. Interestingly, heterozygosity rates were highest in the cultured populations, which is likely due to shellfish hatchery practices of crossing divergent strains to gain benefits of heterosis and to avoid inbreeding. Evidence of founder effects and drift was observed in the cultured strains, including high genetic differentiation between cultured populations and between cultured populations and the wild population. Cultured populations had effective population sizes ranging from 9 to 26 individuals whereas the wild population was estimated at 25,048-56,291 individuals. Further, a depletion of low-frequency variants was observed in the cultured populations. These results indicate significant genetic diversity losses in cultured scallops in Canadian breeding programs.

Physical and Biological Controls on the Annual CO2 Cycle in Agua Hedionda Lagoon, Carlsbad, CA

Agua Hedionda Lagoon (AHL), a tidal estuary located on the southern California coast, supports a diverse ecosystem while serving numerous recreation activities, a marine fish hatchery, a shellfish hatchery, and the largest desalination plant in the western hemisphere. In this work, a 1-year time series of carbon dioxide data is used to establish baseline average dissolved inorganic carbon conditions in AHL. Based on a mass balance model of the outer basin of the lagoon, we propose that AHL is a source of inorganic carbon to the adjacent ocean, through advective export, at a rate of 5.9 × 106 mol C year−1, and a source of CO2 to the atmosphere of 0.21 × 106 mol C year−1 (1 mol C m−2 year−1), implying a net heterotrophic system on the order of 6.0 × 106 mol C year−1 (30 mol C m−2 year−1). Although variable with a range throughout the year of 80% about the mean, the ecosystem remained persistently heterotrophic, reaching peak rates during the summer season. Using results from the mass balance, the annual cycle of selected properties of the aqueous CO2 system (pH, pCO2, and CaCO3 saturation state) were mathematically decomposed in order to examine the relative contribution of drivers including advection, ecosystem metabolism, and temperature that act to balance their observed annual cycle. Important findings of this study include the identification of advection as a prime driver of biogeochemical variability and the establishment of a data-based estimate of mean flushing time for AHL.

Development and evaluation of a formulation of probiont Phaeobacter inhibens S4 for the management of vibriosis in bivalve hatcheries

AbstractLarval eastern oysters (Crassostrea virginica) grown in shellfish hatcheries are susceptible to bacterial diseases, particularly vibriosis. Probiotics are microbes that confer health benefits to the host and have been identified as promising tools to manage diseases in aquaculture. The marine bacterium Phaeobacter inhibens S4 (S4) protects larval eastern oysters against challenge with the bacterial pathogen Vibrio coralliilyticus RE22 (RE22). A concentrated liquid formulation of probiont S4 that maintained high cell viability after long‐term storage was developed for commercial use in shellfish hatcheries. The safety and efficacy of the formulation were tested in six different trials in two hatcheries. The S4 formulation was added to C. virginica larvae culture tanks daily at 104 colony forming units (CFU)/mL from Day 1 post fertilisation until Day 6, 12 or 14, depending on the trial. Treatment of larvae in the hatchery with the S4 formulation did not significantly affect the survival and growth of the larvae. Formulated probiont S4 treatment in the hatchery led to a significant increase in relative percent survival (RPS) when larvae were subsequently challenged with the pathogen RE22 (105 CFU/mL) for 24 h in a laboratory challenge as compared to probiotic‐untreated RE22‐challenged larvae (RPS increase of 46%–74%, p &lt; 0.05). These results suggest that this novel S4 formulation is a safe, easy‐to‐use and effective tool in preventing larval losses due to vibriosis in hatcheries.

A Rapid Assessment of Microalgal Concentration Using Turbidity Measurement for Shellfish Hatchery Seed Production

The goal of this study was to develop a rapid assessment of microalgal concentration using a turbidity meter to serve commercial shellfish hatcheries for feeding shellfish larvae and broodstock. We used four commonly used algal species, Tetraselmis suecica, Isochrysis galbana, Chaetoceros calcitrans, and Chaetoceros gracilis, generating serial dilutions of each and measuring cell concentrations and turbidity of each sample. We identified linear correlations between cell concentration and turbidity and established standard equations between cell concentration and turbidity for each species. We sampled and quantified algae from a shellfish hatchery using these equations and compared hemocytometer counts. No differences were found (P ≥ 0.174), indicating the accuracy of the equations. We expect that this method can provide a quick, accurate, easy method for shellfish hatcheries to quantify algal concentration and avoid either over- or underfeeding larvae and broodstock.

D-amino acid peptides as antimicrobial agents against vibrio-associated diseases in aquaculture

Vibriosis is one of the most usual infection diseases in bivalve mollusks, particularly affecting seeds and larvae, which are more susceptible than adults to these bacterial infections. The devastating effect of vibriosis in shellfish hatcheries is aggravated by the increasing resistance of many Vibrio species to traditional antibiotics, highlighting the need to find new antimicrobial agents. Antimicrobial peptides (AMPs) are a promising alternative, however, their low stability can be a handicap for their practical application. In this study, the 3D structure and the stability of a synthetic all-D-amino acid peptide (D-Caerin) to proteases and extreme pH conditions have been analyzed and compared with its corresponding natural L-enantiomer peptide, Caerin 1.1. Moreover, the antimicrobial activity of D-Caerin has been tested in vitro against the control bacteria Micrococcus luteus CECT 245; and four Vibrio species: Vibrio aestuarianus CECT 625 T, Vibrio anguillarum CECT 522 T, Vibrio harveyi CECT 525 T and Vibrio tapetis CECT 4600 T, which are among the most representative causative agents of vibriosis in aquaculture. Our results demonstrate that D-Caerin contains two left-handed alpha helices, and is more stable and effective against the bacterial species tested than its corresponding natural L- counterpart. The bioactivity of D-Caerin has also been tested in vivo, in clam seeds infected with a mixed inoculum of these vibrio species. These preliminary assays show that D-Caerin-treated specimens exhibit higher survival rates after infection, demonstrating the superior stability of D-Caerin and its effectiveness against vibriosis-causative agents.

Characterization of Vibrio mediterranei Isolates as Causative Agents of Vibriosis in Marine Bivalves.

Marine bivalves include species important globally for aquaculture and estuary ecology. However, epizootics of variable etiologies often pose a threat to the marine fishery industry and ecosystem by causing significant mortalities in related species. One of such diseases is larval vibriosis caused by bacteria of the genus Vibrio, which frequently occurs and causes mass mortalities in bivalve larvae and juveniles in hatcheries. During a mass mortality of razor clam, Sinonovacula constricta, juveniles in a shellfish hatchery in 2019, Vibrio mediterranei was identified as a dominant bacterial species in diseased animals and their rearing water. In this study, we selected and characterized 11 V. mediterranei isolates and studied their pathogenicity to the larvae and juveniles of S. constricta and Crossostrea sikamea. We found that V. mediterranei isolates showed various degrees of pathogenicity to the experimental animals by immersion. Injection of the extracellular products (ECPs) of the strains into clam juveniles resulted in similar pathogenicity with strain immersion. Furthermore, the measurements of enzyme activity suggested the existence of virulence factors in the ECPs of disease-causing V. mediterranei strains. Additionally, proteomic analysis revealed that more than 700 differentially expressed proteins were detected in the ECPs among V. mediterranei strains with different levels of virulence, and the higher expressed proteins in the ECPs of highly virulent strains were involved mainly in the virulence-related pathways. This research represented the first characterization of the V. mediterranei strains as causative agents for larval bivalve vibriosis. The mechanisms underlying the pathogenicity and related strain variability are under further study. IMPORTANCE In the marine environment, Vibrio members have a significant impact on aquatic organisms. Larval vibriosis, caused by bacteria of the genus Vibrio, often poses a threat to the marine fishery industry and ecosystem by causing the mortality of bivalves. However, the emerging pathogens of larval vibriosis in bivalves have not been explored fully. Vibrio mediterranei, the dominant bacterium isolated from moribund clam juveniles in a mortality event, may be responsible for the massive mortality of bivalve juveniles and vibriosis occurrence. Thus, it is necessary to study the pathogenic mechanisms of V. mediterranei to bivalve larvae. We found that V. mediterranei was the pathogen of larval bivalve vibriosis, and its extracellular products contributed a critical role for virulence in juveniles. This research is the first report of V. mediterranei as a causative agent for vibriosis in bivalve juveniles. Our results provide valuable information for understanding the pathogenic mechanism of V. mediterranei to bivalve larvae.

Changes in Bacterial Communities of Kumamoto Oyster Larvae During Their Early Development and Following Vibrio Infection Resulting in a Mass Mortality Event.

Vibrio and Ostreid herpesvirus 1 are responsible for mass mortalities of oyster larvae in hatcheries. Relevant works have focused on their relationships with the disease when larval mortality occurs. On the contrary, little is known about how the resident microbiota in oyster larvae responds to Vibrio-infected disease causing mortality as the disease progressed, whereas this knowledge is fundamental to unveil the etiology of the disease. Here, we analyzed the temporal succession of the microbiome of Kumamoto oyster (Crassostrea sikamea) larvae during their early development, accompanied by a Vibrio-caused mortality event that occurred at the post D-stage of larval development in a shellfish hatchery in Ningbo, China, on June 2020. The main causative agent of larval mortality was attributable to Vibrio infection, which was confirmed by linearly increased Vibrio abundance over disease progression. Larval bacterial communities dramatically changed over host development and disease progression, as highlighted by reduced α-diversity and less diverse core taxa when the disease occurred. Null model and phylogenetic-based mean nearest taxon distance analyses showed that the relative importance of deterministic processes governing larval bacterial assembly initially increased over host development, whereas this dominance was depleted over disease progression. Furthermore, we screened the disease-discriminatory taxa with a significant change in their relative abundances, which could be indicative of disease progression. In addition, network analysis revealed that disease occurrence remodeled the co-occurrence patterns and niche characteristics of larval microbiota. Our findings demonstrate that the dysbiosis of resident bacterial communities and the shift of microecological mechanisms in the larval microbiome may contribute to mortality during oyster early development.

Metatranscriptomics reveals a shift in microbial community composition and function during summer months in a coastal marine environment

AbstractTemperate coastal marine waters are often thermally stratified from spring through fall but can be dynamic and disrupted by tidal currents and wind‐driven upwelling. These mixing events introduce deeper, cooler water with a higher partial pressure of CO2 (pCO2) and its associated microbial communities to the surface. Anecdotally, these events impact shellfish hatcheries and farms, warranting improved understanding of changes in composition and activity of marine microbial communities in relation to environmental processes. To characterize both compositional and functional changes associated with abiotic factors, here, we generate a reference metatranscriptome from the Strait of Georgia over representative seasons and analyze metatranscriptomic profiles of the microorganisms present within intake water containing different pCO2 levels at a shellfish hatchery in British Columbia from June through October. Abiotic factors studied include pH, temperature, alkalinity, aragonite, calcite, and pCO2. Community composition changes were observed to occur at broad taxonomic levels and most notably to vary with temperature and pCO2. Functional gene expression profiles indicated a strong difference between early (June–July) and late summer (August–October) associated with viral activity. The taxonomic data suggest this could be due to the termination of cyanobacteria and phytoplankton blooms by viral lysis in the late season. Functional analysis indicated fewer differentially expressed transcripts associated with abiotic variables (e.g., pCO2) than with the temporal effect. Microbial composition and activity in these waters vary with both short‐term effects observed alongside abiotic variation and long‐term effects observed across seasons. The analysis of both taxonomy and functional gene expression simultaneously in the same samples by environmental RNA (eRNA metatranscriptomics) provided a more comprehensive view for monitoring water bodies than either would in isolation.

Detection of toxins and harmful algal bloom cells in shellfish hatcheries and efforts toward removal

As the start of the supply chain for the aquaculture industry, hatcheries are a crucial component in the success of oyster and northern quahog (hard clam) aquaculture on the East Coast of the US. Intermittent failures in hatchery production slow industry growth and reduce profits. To begin investigations into the possible role of algal toxins in hatchery production failure, post-treatment hatchery water from one research and four commercial hatcheries in lower Chesapeake Bay, USA, was sampled for (1) toxin presence and (2) harmful algal bloom (HAB) cell enumeration. Overall, seven toxin classes, likely produced by six different HAB species, were detected in post-treatment hatchery water, despite a lack of visually identifiable HAB cells within the facility. Toxins detected include pectenotoxin-2, goniodomin A, karlotoxin-1 and karlotoxin-3, okadaic acid and dinophysistoxin-1, azaspiracid-1 and azaspiracid-2, brevetoxin-2, and microcystin-LR. In a second, more targeted study, two batches of source water were followed and sampled at each step of a water-treatment process in the VIMS Aquaculture Genetics and Breeding Technology Center research hatchery in Gloucester Point, Virginia, USA. Two treatment steps showed particular promise for decreasing the concentrations of the three toxins detected in the source water, 24-h circulation through sand filters and activated charcoal filtration. Toxin concentrations of pectenotoxin-2, 3.53 ± 0.56 pg mL−1, okadaic acid, 6.14 ± 0.69 pg mL−1, and dinophysistoxin-1, 1.88 ± 0.0 pg mL−1, were low in the source water. The sand filtration step decreased these concentrations by 49–62%. Activated charcoal filtration subsequently brought the concentrations down to <0.5 pg mL−1, successfully removing another 87–99% of toxins from incoming water. With toxin breakthrough now documented in commercial hatchery facilities during non-bloom conditions, future studies are needed to investigate breakthrough and water-treatment options during more-intense bloom conditions, as well as the potential interactions of algal toxins with other stressors in a potentially multifactorial etiology underlying hatchery production failures.

Biodegradable, metal-chelating compounds as alternatives to EDTA for cultivation of marine microalgae

Iron (Fe) is an essential nutrient for microalgal metabolism. The low solubility of Fe in oxic aquatic environments can be a growth-limiting factor for phytoplankton. Synthetic chelating agents, such as ethylenediaminetetraacetic acid (EDTA), are used widely to maintain Fe in solution for microalgal cultivation. The non-biodegradable nature of EDTA, combined with sub-optimal bioavailability of Fe-EDTA complexes to microalgae, indicates opportunity to improve microalgal cultivation practices that amplify production efficiency and environmental compatibility. In the present study, the effects of four organic chelating ligands known to form readily bioavailable organic complexes with Fe in natural aquatic environments were investigated in relation to growth and biochemical composition of two marine microalgae grown as live feeds in shellfish hatcheries (Chaetoceros calcitrans and Tisochrysis lutea). Three saccharides, alginic acid (ALG), glucuronic acid (GLU), and dextran (DEX), as well as the siderophore desferrioxamine B (DFB), were compared to EDTA. Organic ligands characterized by weaker binding capacity for cationic metals (i.e., ALG, GLU, DEX) significantly improved microalgal growth and yields in laboratory-scale static batch cultures or bubbled photobioreactors. Maximal microalgal growth enhancement relative to the control (e.g., EDTA) was recorded for GLU, followed by ALG, with 20–35% increase in specific growth rate in the early stages of culture development of C. calcitrans and T. lutea. Substitution of EDTA with GLU resulted in a 27% increase in cellular omega 3-polyunsaturetd fatty acid content of C. calcitrans and doubled final cell yields. Enhanced microalgal culture performance is likely associated with increased intracellular Fe uptake efficiency combined with heterotrophic growth stimulated by the organic ligands. Based upon these results, we propose that replacement of EDTA with one of these organic metal-chelating ligands is an effective and easily implementable strategy to enhance the environmental compatibility of microalgal cultivation practices while also maximizing algal growth and enhancing the nutritional quality of marine microalgal species commonly cultured for live-feed applications in aquaculture.

Hatchery crashes among shellfish research hatcheries along the Atlantic coast of the United States: A case study of production analysis at Horn Point Laboratory

Shellfish hatcheries have become an increasingly important component of aquaculture production in the United States. Although the industry has been advancing technologically over time to stabilize production and supply, many hatcheries suffer regularly from bouts of stalled or failed production, termed crashes. Crashes are widely acknowledged to occur and are considered a persistent problem in the industry but also an understudied phenomenon in the field of shellfish aquaculture that warrants greater investigation. Furthermore, there are few thorough reports on production variability from established hatcheries. To help fill the data gap and initiate a broader discussion on the causes of hatchery crashes, we provide testimonials from research hatchery managers across the Atlantic Coast about their experiences with crashes. As a case study, we report on long-term production trends (2011−2020) at Horn Point Laboratory's oyster hatchery, which included persistent production failure during the 2019 season. During the 2019 season, larval assays were conducted to determine drivers of production failure; however, no clear culprits were identified. Machine learning was used to help characterize production variability and hindcast the specific conditions when the hatchery's production was most efficient. Microbial community structure of larval associated microorganisms was shown to differ between a crash and non-crash time-point. We highlight the ubiquity of hatchery crashes along the Atlantic Coast of the US, the range of severity at which crashes can occur, and the difficulty of identifying the underlying causes of crashes, even at world-class research facilities. Collectively, we conclude that more research, data sharing, and cross-institution collaboration are needed to prevent crashes, and to develop mitigation strategies to maintain high levels of consistent shellfish aquaculture production.

Coupled microbiome analyses highlights relative functional roles of bacteria in a bivalve hatchery

BackgroundMicrobial communities are ubiquitous throughout ecosystems and are commensal with hosts across taxonomic boundaries. Environmental and species-specific microbiomes are instrumental in maintaining ecosystem and host health, respectively. The introduction of pathogenic microbes that shift microbiome community structure can lead to illness and death. Understanding the dynamics of microbiomes across a diversity of environments and hosts will help us to better understand which taxa forecast survival and which forecast mortality events.ResultsWe characterized the bacterial community microbiome in the water of a commercial shellfish hatchery in Washington state, USA, where the hatchery has been plagued by recurring and unexplained larval mortality events. By applying the complementary methods of metagenomics and metaproteomics we were able to more fully characterize the bacterial taxa in the hatchery at high (pH 8.2) and low (pH 7.1) pH that were metabolically active versus present but not contributing metabolically. There were shifts in the taxonomy and functional profile of the microbiome between pH and over time. Based on detected metagenomic reads and metaproteomic peptide spectral matches, some taxa were more metabolically active than expected based on presence alone (Deltaproteobacteria, Alphaproteobacteria) and some were less metabolically active than expected (e.g., Betaproteobacteria, Cytophagia). There was little correlation between potential and realized metabolic function based on Gene Ontology analysis of detected genes and peptides.ConclusionThe complementary methods of metagenomics and metaproteomics contribute to a more full characterization of bacterial taxa that are potentially active versus truly metabolically active and thus impact water quality and inter-trophic relationships.

Bacteriophages against Vibrio coralliilyticus and Vibrio tubiashii: Isolation, Characterization, and Remediation of Larval Oyster Mortalities.

Vibrio coralliilyticus and Vibrio tubiashii are pathogens responsible for high larval oyster mortality rates in shellfish hatcheries. Bacteriophage therapy was evaluated to determine its potential to remediate these mortalities. Sixteen phages against V. coralliilyticus and V. tubiashii were isolated and characterized from Hawaiian seawater. Fourteen isolates were members of the Myoviridae family, and two were members of the Siphoviridae In proof-of-principle trials, a cocktail of five phages reduced mortalities of larval Eastern oysters (Crassostrea virginica) and Pacific oysters (Crassostrea gigas) by up to 91% 6 days after challenge with lethal doses of V. coralliilyticus Larval survival depended on the oyster species, the quantities of phages and vibrios applied, and the species and strain of Vibrio A later-generation cocktail, designated VCP300, was formulated with three lytic phages subsequently named Vibrio phages vB_VcorM-GR7B, vB_VcorM-GR11A, and vB_VcorM-GR28A (abbreviated 7B, 11A, and 28A, respectively). Together, these three phages displayed host specificity toward eight V. coralliilyticus strains and a V. tubiashii strain. Larval C. gigas mortalities from V. coralliilyticus strains RE98 and OCN008 were significantly reduced by >90% (P < 0.0001) over 6 days with phage treatment compared to those of untreated controls. Genomic sequencing of phages 7B, 11A, and 28A revealed 207,758-, 194,800-, and 154,046-bp linear DNA genomes, respectively, with the latter showing 92% similarity to V. coralliilyticus phage YC, a strain from the Great Barrier Reef, Australia. Phage 7B and 11A genomes showed little similarity to phages in the NCBI database. This study demonstrates the promising potential for phage therapy to reduce larval oyster mortalities in oyster hatcheries.IMPORTANCE Shellfish hatcheries encounter episodic outbreaks of larval oyster mortalities, jeopardizing the economic stability of hatcheries and the commercial shellfish industry. Shellfish pathogens like Vibrio coralliilyticus and Vibrio tubiashii have been recognized as major contributors of larval oyster mortalities in U.S. East and West Coast hatcheries for many years. This study isolated, identified, and characterized bacteriophages against these Vibrio species and demonstrated their ability to reduce mortalities from V. coralliilyticus in larval Pacific oysters and from both V. coralliilyticus and V. tubiashii in larval Eastern oysters. Phage therapy offers a promising approach for stimulating hatchery production to ensure the well-being of hatcheries and the commercial oyster trade.

Use of anionic polymer-coated magnetic beads to pre-concentrate Ostreid Herpesvirus 1 from seawater: Application to a UV disinfection treatment

Ostreid Herpesvirus 1 (OsHV-1) represents a serious threat to shellfish aquaculture worldwide. To minimise its impact, early warning systems able to detect the virus in seawater prior to infection of oysters are of utmost importance. However, monitoring OsHV-1 in seawater is challenging because of its presence at very low concentrations. Thus, a rapid and simple method to pre-concentrate the virus is needed to enable detection. Herein, magnetic beads (MBs) coated with an anionic polymer were used to pre-concentrate OsHV-1 from biological matrices including oyster homogenate and seawater samples. Following virus capture, OsHV-1 DNA detection was performed by quantitative PCR (qPCR). The MB-based approach combined with qPCR attained a limit of detection (LOD) as low as 0.1 viral copy/μL, which was 100 times lower than that of the qPCR alone. This approach was applied to the analysis of OsHV-1 in seawater from an Enhanced Hydro-Optic UV (HOD-UV) disinfection experiment operating at a UV dose of 1360 J/m2 in an open flow system. Our approach enabled detection of the virus in non-treated seawater and not in UV-treated seawater, discrimination that was not possible using qPCR alone. Moreover, the strategy provided data on the pattern of kinetics of the release of the virus in seawater. The approach could find applications in shellfish hatcheries and depuration plants to ensure biosecurity requirements.

First description outside Europe of the emergent pathogen Vibrio europaeus in shellfish aquaculture

Vibrio europaeus is an emergent pathogen affecting the most important bivalve species reared in Spanish and French hatcheries. Using a genomic approach, we identified V. europaeus outside Europe for the first time from massive larval mortalities of scallop (Argopecten purpuratus) in Chile and from seawater near a shellfish hatchery in the US West Coast. Results show the worldwide spreading and potential impact of V. europaeus for aquaculture; these four countries are among the 10 major producers of mollusks. Pathogenicity of V. europaeus was demonstrated for the first time towards scallop, the second most important species for Chilean mariculture.

High-Resolution Carbonate System Dynamics of Netarts Bay, OR From 2014 to 2019

Netarts Bay is a shallow, temperate, tidal lagoon located on the northern coast of Oregon and the site of the Whiskey Creek Shellfish Hatchery (WCSH). Data collected with an autonomous continuous flow-through system installed at WCSH capable of high-resolution (1 Hz) partial pressure of aqueous CO2 (pCO2) and hourly total dissolved inorganic carbon (TCO2) measurements, with combined measurement uncertainties of &amp;lt; 2.0% and 0.5%, respectively, is analyzed over the 2014–2019 interval. Summer upwelling, wintertime downwelling, and in situ bay biogeochemistry represent significant modes of the observed variability in carbonate system dynamics. Summer upwelling is associated with large amplitude diel pCO2 variability, elevated TCO2 and alkalinity, but weak variability in salinity. Wintertime downwelling is associated with bay freshening by both local and remote sources, a strong tidal signature in salinity, TCO2, and alkalinity, with diel pCO2 variability much less amplified when compared to summer. Further, analysis of alkalinity-salinity relationships suggests multiple water masses inhabiting the bay during 1 year: mixing of end-members associated with direct precipitation, coastal rivers, southward displacement of the Columbia River plume, California Current surface and deep upwelled waters. The importance of in-bay processes such as net community metabolism during intervals of high productivity are apparent. These direct measurements of pCO2 and TCO2 have been useful to local hatchery owners who have monitored intake waters following historic seed-production failures related to high-CO2 conditions exacerbated by ocean acidification.

Comparative genomic analysis of Vibrios yields insights into genes associated with virulence towards C. gigas larvae

BackgroundVibriosis has been implicated in major losses of larvae at shellfish hatcheries. However, the species of Vibrio responsible for disease in aquaculture settings and their associated virulence genes are often variable or undefined. Knowledge of the specific nature of these factors is essential to developing a better understanding of the environmental and biological conditions that lead to larvae mortality events in hatcheries. We tested the virulence of 51 Vibrio strains towards Pacific Oyster (Crassostreae gigas) larvae and sequenced draft genomes of 42 hatchery-associated vibrios to determine groups of orthologous genes associated with virulence and to determine the phylogenetic relationships among pathogens and non-pathogens of C. gigas larvae.ResultsV. coralliilyticus strains were the most prevalent pathogenic isolates. A phylogenetic logistic regression model identified over 500 protein-coding genes correlated with pathogenicity. Many of these genes had straightforward links to disease mechanisms, including predicted hemolysins, proteases, and multiple Type 3 Secretion System genes, while others appear to have possible indirect roles in pathogenesis and may be more important for general survival in the host environment. Multiple metabolism and nutrient acquisition genes were also identified to correlate with pathogenicity, highlighting specific features that may enable pathogen survival within C. gigas larvae.ConclusionsThese findings have important implications on the range of pathogenic Vibrio spp. found in oyster-rearing environments and the genetic determinants of virulence in these populations.

Dynamic response in the larval geoduck (Panopea generosa) proteome to elevated pCO2.

Pacific geoducks (Panopea generosa) are clams found along the northeast Pacific coast where they are important components of coastal and estuarine ecosystems and a major aquaculture product. The Pacific coastline, however, is also experiencing rapidly changing ocean habitat, including significant reductions in pH. To better understand the physiological impact of ocean acidification on geoduck clams, we characterized for the first time the proteomic profile of this bivalve during larval development and compared it to that of larvae exposed to low pH conditions. Geoduck larvae were reared at pH 7.5 (ambient) or pH 7.1 in a commercial shellfish hatchery from day 6 to day 19 postfertilization and sampled at six time points for an in‐depth proteomics analysis using high‐resolution data‐dependent analysis. Larvae reared at low pH were smaller than those reared at ambient pH, especially in the prodissoconch II phase of development, and displayed a delay in their competency for settlement. Proteomic profiles revealed that metabolic, cell cycle, and protein turnover pathways differed between the two pH and suggested that differing phenotypic outcomes between pH 7.5 and 7.1 are likely due to environmental disruptions to the timing of physiological events. In summary, ocean acidification results in elevated energetic demand on geoduck larvae, resulting in delayed development and disruptions to normal molecular developmental pathways, such as carbohydrate metabolism, cell growth, and protein synthesis.