Oyster Mortality Research Articles

Early life microbial exposures shape the Crassostrea gigas immune system for lifelong and intergenerational disease protection

BackgroundThe interaction of organisms with their surrounding microbial communities influences many biological processes, a notable example of which is the shaping of the immune system in early life. In the Pacific oyster, Crassostrea gigas, the role of the environmental microbial community on immune system maturation — and, importantly, protection from infectious disease — is still an open question.ResultsHere, we demonstrate that early life microbial exposure durably improves oyster survival when challenged with the pathogen causing Pacific oyster mortality syndrome (POMS), both in the exposed generation and in the subsequent one. Combining microbiota, transcriptomic, genetic, and epigenetic analyses, we show that the microbial exposure induced changes in epigenetic marks and a reprogramming of immune gene expression leading to long-term and intergenerational immune protection against POMS.ConclusionsWe anticipate that this protection likely extends to additional pathogens and may prove to be an important new strategy for safeguarding oyster aquaculture efforts from infectious disease. tag the videobyte/videoabstract in this section5X1-nepGVFkCxreirqFTHAVideo

Synergistic Interaction of Low Salinity Stress With Vibrio Infection Causes Mass Mortalities in the Oyster by Inducing Host Microflora Imbalance and Immune Dysregulation.

A sudden drop in salinity following extreme precipitation events usually causes mass mortality of oysters exposed to pathogens in ocean environment. While how low salinity stress interacts with pathogens to cause mass mortality remains obscure. In this study, we performed an experiment by low salinity stress and pathogen infection with Vibrio alginolyticus to investigate their synergistic effect on the mortality of the Pacific oyster toward understanding of the interaction among environment, host, and pathogen. We showed that low salinity stress did not significantly affect proliferation and virulence of V. alginolyticus, but significantly altered microbial composition and immune response of infected oysters. Microbial community profiling by 16S rRNA amplicon sequencing revealed disrupted homeostasis of digestive bacterial microbiota with the abundance of several pathogenic bacteria being increased, which may affect the pathogenesis in infected oysters. Transcriptome profiling of infected oysters revealed that a large number of genes associated with apoptosis and inflammation were significantly upregulated under low salinity, suggesting that low salinity stress may have triggered immune dysregulation in infected oysters. Our results suggest that host-pathogen interactions are strongly affected by low salinity stress, which is of great significance for assessing future environmental risk of pathogenic diseases, decoding the interaction among environment, host genetics and commensal microbes, and disease surveillance in the oyster.

Genetic diversity and connectivity of the Ostreid herpesvirus 1 populations in France: A first attempt to phylogeographic inference for a marine mollusc disease.

The genetic diversity of viral populations is a key driver of the spatial and temporal diffusion of viruses; yet, studying the diversity of whole genomes from natural populations still remains a challenge. Phylodynamic approaches are commonly used for RNA viruses harboring small genomes but have only rarely been applied to DNA viruses with larger genomes. Here, we used the Pacific oyster mortality syndrome (a disease that affects oyster farms around the world) as a model to study the genetic diversity of its causative agent, the Ostreid herpesvirus 1 (OsHV-1) in the three main French oyster-farming areas. Using ultra-deep sequencing on individual moribund oysters and an innovative combination of bioinformatics tools, we de novo assembled twenty-one OsHV-1 new genomes. Combining quantification of major and minor genetic variations, phylogenetic analysis, and ancestral state reconstruction of discrete traits approaches, we assessed the connectivity of OsHV-1 viral populations between the three oyster-farming areas. Our results suggest that the Marennes-Oléron Bay represents the main source of OsHV-1 diversity, from where the virus has dispersed to other farming areas, a scenario consistent with current practices of oyster transfers in France. We demonstrate that phylodynamic approaches can be applied to aquatic DNA viruses to determine how epidemiological, immunological, and evolutionary processes act and potentially interact to shape their diversity patterns.

Stomatopod (Gonodactylaceus falcatus) Predation of the Akoya Pearl Oyster (Pinctada fucata) in Ocean Culture

Crustaceans of the family Gonodactylidae (Order Stomatopoda) are potential predators of cultured pearl oysters in ocean-culture systems, yet they have not previously been implicated in contributing to on-farm mortality of culture stock. Improved knowledge of the threat posed by stomatopods to pearl oyster survival in ocean-culture systems, as well as possible influencing factors, is necessary to determine whether stomatopod predation merits concern and for prioritizing efforts to prevent and control predator incursions. The aims of this study were, therefore, to determine if the presence of stomatopods within culture units significantly affects cultured pearl oyster survival in an ocean-culture system, and whether predator or prey size exert influencing effects. Mortality of Akoya pearl oysters (Pinctada fucata) over a 6-wk culture period ranged from zero to 33.3% among individual culture units containing a single stomatopod (Gonodactylaceus falcatus) at the study site in north Queensland, Australia. An interaction between stomatopod size and their time at liberty within culture units, as well as an interaction between stomatopod size and pearl oyster size, explained 84.1% of the variance in pearl oyster survival among culture units. Most prominently, small stomatopods (total length: 37.0 ± 0.9 mm) caused minimal mortality of culture stock (4.6% ± 1.1%), whereas large stomatopods (total length: 69.0 ± 1.1 mm) had a significantly greater impact (20.8% ± 2.1% mortality) over the 6-wk period (P < 0.05). Given the potential for a single G. falcatus to cause up to 33.3% mortality of culture stock within a culture unit, the threat from stomatopod predation during ocean culture of pearl oysters could be significant and collection of site-specific information to assess this threat is recommended.

Bacteriophages improve survival and metamorphosis of larval Pacific oysters (Crassostrea gigas) exposed to Vibrio coralliilyticus strain RE98

The bacterial pathogen Vibrio coralliilyticus has been implicated in severe larval oyster mortality events in U.S. hatcheries. The aims of this study were to determine whether additions of bacteriophages (phages) specific to V. coralliilyticus strain RE98 can lower concentrations of V. coralliilyticus in seawater and consequently enhance survival, growth and metamorphosis of larvae of the Pacific oyster (Crassostrea gigas). Cocktails containing 2 or 3 previously characterized phages in the family Myoviridae (designated 6B, 7B and 11A) were added to cultures of C. gigas larvae together with V. coralliilyticus RE98. Results confirmed that: 1) the addition of a 2-phage cocktail (7B and 11A) significantly reduced concentrations of V. coralliilyticus in autoclaved seawater over a 48-h period in the absence of larvae (p < 0.05); 2) the concentration of a 2-phage cocktail required to significantly reduce mortality of 2-day post fertilization (PF) larvae depended on the initial concentration of V. coralliilyticus added to the seawater; 3) preparation of three-phage cocktails using tangential flow filtration increased the effectiveness of the phages; and 4) a single addition of a cocktail containing 3 phages to 2-day old oyster larval cultures eliminated mortality due to exposure to V. coralliilyticus and significantly improved the proportion of larvae metamorphosing to become spat more than 16 days later. Reductions in V. coralliilyticus-associated larval mortalities by additions of phages were consistent across a range of culture conditions, varying from 1 ml cultures with autoclaved seawater to 10-l cultures supplied with non-sterile, 10-μm filtered seawater.

A Deterministic Model for Understanding Nonlinear Viral Dynamics in Oysters.

ABSTRACTContamination of oysters with a variety of viruses is one key pathway to trigger outbreaks of massive oyster mortality as well as human illnesses, including gastroenteritis and hepatitis. Much effort has gone into examining the fate of viruses in contaminated oysters, yet the current state of knowledge of nonlinear virus-oyster interactions is not comprehensive because most studies have focused on a limited number of processes under a narrow range of experimental conditions. A framework is needed for describing the complex nonlinear virus-oyster interactions. Here, we introduce a mathematical model that includes key processes for viral dynamics in oysters, such as oyster filtration, viral replication, the antiviral immune response, apoptosis, autophagy, and selective accumulation. We evaluate the model performance for two groups of viruses, those that replicate in oysters (e.g., ostreid herpesvirus) and those that do not (e.g., norovirus), and show that this model simulates well the viral dynamics in oysters for both groups. The model analytically explains experimental findings and predicts how changes in different physiological processes and environmental conditions nonlinearly affect in-host viral dynamics, for example, that oysters at higher temperatures may be more resistant to infection by ostreid herpesvirus. It also provides new insight into food treatment for controlling outbreaks, for example, that depuration for reducing norovirus levels is more effective in environments where oyster filtration rates are higher. This study provides the foundation of a modeling framework to guide future experiments and numerical modeling for better prediction and management of outbreaks.IMPORTANCE The fate of viruses in contaminated oysters has received a significant amount of attention in the fields of oyster aquaculture, food quality control, and public health. However, intensive studies through laboratory experiments and in situ observations are often conducted under a narrow range of experimental conditions and for a specific purpose in their respective fields. Given the complex interactions of various processes and nonlinear viral responses to changes in physiological and environmental conditions, a theoretical framework fully describing the viral dynamics in oysters is warranted to guide future studies from a top-down design. Here, we developed a process-based, in-host modeling framework that builds a bridge for better communications between different disciplines studying virus-oyster interactions.

Seaweeds influence oyster microbiota and disease susceptibility.

A growing awareness of role that microbiota can play in mediating the effects of pathogens on hosts has given rise to the concept of the pathobiome. Recently, we demonstrated that the Pacific oyster mortality syndrome affecting Crassostrea gigas oysters is caused by infection with the Ostreid herpesvirus type 1 (OsHV-1) followed by infection with multiple bacterial taxa. Here we extend the concept of this pathobiome beyond the host species and its bacterial microbiota by investigating how seaweed living in association with oysters influences their response to the disease. We hypothesized that by their mere presence in the environment, different species of seaweeds can positively or negatively influence the risk of disease in oysters by shaping their bacterial microbiota and their immune response. Although seaweed and oysters do not have direct ecological interactions, they are connected by seawater and likely share microbes. To test our hypothesis, oysters were acclimated with green, brown or red algae for 2weeks and then challenged with OsHV-1. We monitored host survival and pathogen proliferation and performed bacterial microbiota and transcriptome analyses. We found that seaweeds can alter the bacterial microbiota of the host and its response to the disease. More particularly, green algae belonging to the genus Ulva spp. induced bacterial microbiota dysbiosis in oyster and modification of its transcriptional immune response leading to increased susceptibility to the disease. This work provides a better understanding of a marine disease and highlights the importance of considering both macrobiotic and microbiotic interactions for conservation, management and exploitation of marine ecosystems and resources.

Predicting Oyster Harvests at Maximum Sustained Yield: Application of Cultch and Stock Benchmarks to Depleted Public Oyster Reefs in the Northern Gulf of Mexico

A sustainable fisheries model for the estimation of harvests of oysters, maintenance of cultch, and restoration of reefs has been applied across the northern Gulf of Mexico. Oyster density and size, and cultch density are provided from surveys by State agencies. The model simulates oyster growth and mortality, and cultch loss. Reef shell mass is increased when oysters die in place and diminished when oysters are removed by fishing. Harvest is estimated as sacks of live oysters that can be removed while retaining reef quality (i.e., reef cultch mass, oyster density). Application of oyster density and cultch density standards (OCS) for fishing at maximum sustained yield shows little sustainable harvest on Public Grounds in the northern Gulf of Mexico. Model heuristics focus discovery of negative and positive feedbacks to reef demise or persistence. Oyster reef dynamics are viewed as persistent processes within negative and positive feedback loops, and occasional shifts between them. A negative feedback loop is set up on poor-quality reefs. Lack of cultch and a paucity of adult oysters diminish recruitment and shell replenishment. In the absence of recruitment, natural shell loss ultimately drives the reef to extinction. A positive feedback loop is set up on reefs with adequate cultch and an abundance of oysters. There, oysters set, survive critical early stages in boxes and reef interstices, reproduce, grow to a large size, and die in place. Harvests on high-quality reefs beyond that which maintains reef cultch and spawning stock, and consequential recruitment failure cause a shift from a positive to a negative feedback loop. Likewise, restricting harvests and planting cultch on poor-quality reefs, together with successful recruitment, promotes a shift from a negative to a positive state. Results of no-net loss of cultch (NNL) and OCS simulations suggest two distinct management approaches. The NNL promotes the sustainability of reef shell and assumes that a stable shell bed promotes a stable living resource, whereas OCS explicitly promotes the sustainability of cultch and stock at msy (maximum-sustainable-yield). Furthermore, OCS, which incorporates optimal reef cultch and oyster density standards, provides restoration benchmarks. Achieving sustainability at msy will simultaneously promote habitat restoration, restoration of ecosystem services, and a sustainable oyster fishery.

Evaluation of methods for reducing epibionts during farming of the mangrove oyster Crassostrea gasar (Adanson, 1757).

Due to the competition for food, space, oxygen and due to their role as diseases vector, epibionts can negatively affect oyster farming. We assessed the efficacy of six methods commonly used for the removal of epibionts from oyster shells during farming. The experiment was conducted at an oyster farm on the Paraná coast - South Brazil. Oysters (Crassostrea gasar) were acclimated for 90 d in the cultivation system and later exposed to cleaning treatments: i) freshwater; ii) hypersaline water; iii) sodium hypochlorite solution; iv) quaternary ammonia solution; v) exposure to air; vi) hydroblasting; and vii) no cleaning procedure (control). After treatment, oysters were kept in the cultivation system for 15 and 30 d - when the total incrustation and mortality were measured. Epibionts from nine phyla were identified. The most abundant were Arthropoda (Crustacea) (62.5%), Mollusca (33.8%) and Annelida (3.1%). Freshwater [15 (n = 2263 epibionts) and 30 days (n = 2822 epibionts)] and hydroblasting [15 (n = 1850 epibionts) and 30 days (n = 2389 epibionts)] treatments were the most efficient to reduce epibionts and caused lower rates of oyster mortality [15 (5.0 and 3.33%, respectively) and 30 days (1.67 and 6.67%, respectively)].

Anaesthetic induced relaxation of the winged pearl oyster, Pteria penguin, varies with oyster size and anaesthetic concentration

Stress and mortality of pearl oysters during nucleus implanting for round pearl and mabé pearl production can be reduced using appropriate anaesthetics that allow improved access to nucleus implanting sites. This study evaluated the efficacy of three different concentrations of benzocaine (0.25, 0.50 and 1.20 g L-1) and 1-propylene phenoxetol (2.50, 3.00 and 3.50 mL L-1) when presented to ‘small’ (dorso-ventral height [DVH], 78.7 ± 1.6 mm), ‘medium’ (DVH, 118.2 ± 2.0 mm) and ‘large’ (DVH, 149.3 ± 1.1 mm) cohorts of the winged pearl oyster, Pteria penguin. Results showed the following general trends across treatments with both anaesthetics: (1) greater proportions of large oysters became relaxed compared to small oysters; (2) large oysters required shorter exposure times to become relaxed than small oysters; (3) for each size class of oyster, an increase in anaesthetic concentration resulted in an increased proportion of relaxed oysters; and (4) ‘mantle collapse’ (where the mantle collapses away from the shell) was only recorded in large oysters in treatments with higher concentrations of anaesthetics. The most effective concentration of benzocaine to use with small, medium and large Pt. penguin was the highest level tested in this study (1.20 g L-1). Similarly, the highest concentration of 1-propylene phenoxetol tested (3.5 mL L-1) was also the most effective with all three size classes of Pt. penguin. These treatments caused mantle collapse in large oysters, for which use of lower, less effective anaesthetic concentrations may be considered preferable, to avoid potentially negative impacts of mantle collapse on subsequent mabé pearl production. As well as efficacy, choice of anaesthetic should consider ease of preparation and preparation time. Benzocaine requires dissolving in methyl alcohol and heating to 88–92˚C, while 1-propylene phenoxetol is readily soluble in seawater.

Severe introduced predator impacts despite attempted functional eradication

Established non-native species can have significant impacts on native biodiversity without any possibility of complete eradication. In such cases, one management approach is functional eradication, the reduction of introduced species density below levels that cause unacceptable effects on the native community. Functional eradication may be particularly effective for species with reduced dispersal ability, which may limit rates of reinvasion from distant populations. Here, we evaluate the potential for functional eradication of introduced predatory oyster drills (Urosalpinx cinerea) using a community science approach in San Francisco Bay. We combined observational surveys, targeted removals, and a caging experiment to evaluate the effectiveness of this approach in mitigating the mortality of prey Olympia oysters (Ostrea lurida), a conservation and restoration priority species. Despite the efforts of over 300 volunteers that removed over 30,000 oyster drills, we report limited success. We also found a strong negative relationship between oyster drills and oysters, showing virtually no coexistence across eight sites. At experimental sites, there was no effect of oyster drill removal on oyster survival in a caging experiment, but strong effects of caging treatment on oyster survival (0 and 1.6% survival in open and partial cage treatments, as compared to 89.1% in predator exclusion treatments). We conclude that functional eradication of this species requires significantly greater effort and may not be a viable management strategy in this system. We discuss several possible mechanisms for this result with relevance to management for this and other introduced species. Oyster restoration efforts should not be undertaken where Urosalpinx is established or is likely to invade.

Aquatic pathogens and biofouling: pilot study of ostreid herpesvirus 1 translocation by bivalves

Ostreid herpesvirus 1 (OsHV-1) has caused mass mortalities in Pacific oysters (Crassostrea gigas) in Europe, Australia, and New Zealand. While aquaculture-associated movements of infected Pacific oysters are a well-known cause of OsHV-1 spread once established in a region, translocation via biofouling of aquaculture equipment or vessels needs further investigation to explain the more distant spread of OsHV-1. Laboratory experiments were designed to test for transmission of OsHV-1 between infected and naïve Pacific oysters via a simulated biofouling translocation scenario. Three common biofouling species [Sydney rock oysters (Saccostrea glomerata), Mediterranean mussels (Mytilus galloprovincialis) and Pacific oysters] were tested as intermediaries using a cohabitation challenge with Pacific oysters infected by injection. Transmission occurred, albeit for one of eight replicates when Pacific oysters were the intermediary species. This demonstrated a possible pathway for pathogen spread via biofouling containing Pacific oysters while highlighting the complexity of OsHV-1 transmission. Such complexities require further investigation to inform future risk assessments and management of fouled aquaculture equipment and vessels.

Temperature effects on the nutritional quality in Pacific oysters (Crassostrea gigas) during ultraviolet depuration

Oysters are mainly consumed in the raw form, so it is important to get rid of bacteria and other harmful substances. Ultraviolet (UV) sterilization depuration is a commonly used method and does not produce chemical residues or act directly on shellfish, resulting in minimal adverse effects on flavor. This study simulated the industrial depuration process using UV sterilization to depurate Pacific oysters (Crassostrea gigas). The effects of different temperatures (15, 20, and 25 °C) on the quality and taste components of C. gigas were investigated by measuring changes in physiological and biochemical indexes in C. gigas tissue samples. At the end of depuration, no oyster mortality occurred, but it was up to 55% at 25 °C at 84 h. Glycogen content decreased the most at 25 °C at 48 h. The fatty acid content was higher at 20 and 25 °C. Succinic acid content decreased significantly and was higher at 20 and 25 °C at 48 h with no significant difference. Total free amino acid (FAA) content was significantly higher at 20 °C, however, there were no significant differences in nucleotide content at any temperature at 48 h. Adenylate energy charge (AEC) values decreased, with higher values at 15 and 25 °C, and equivalent umami concentration (EUC) values increased, with higher values at 20 and 25 °C. Considering the changes in flavor substances and mortality rate, 20°C is the appropriate temperature for UV sterilization depuration of C. gigas to produce better edible quality. © 2021 Society of Chemical Industry.

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

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

Stocking density effect on the growth and mortality of juvenile European flat oyster (Ostrea edulis Linnaeus, 1758)

AbstractThe effect of stocking density on the growth and mortality of the European flat oyster (Ostrea edulis Linnaeus, 1758) reared in lantern nets was evaluated, starting from spat up to the end of juvenile phase. Oysters were deployed in a raft on the Basque coast (SE Bay of Biscay) for 18 months. Oysters were divided into four densities ranging from 25% to 100% of surface coverage. At the end of the experiment, oysters from an initial mean height and wet weight of 22.79 ± 3.70 mm and 1.00 ± 0.30 g reached mean values of 55.86 ± 8.21 mm and 19.08 ± 9.66 g, respectively. Although significant differences were detected in the growth of oysters reared at different stocking densities, these differences were not density dependent. On the other hand, mortality increased with time showing relatively high values (27%–38%), but especially at the end of the study when oysters at the highest density showed values up to 50%. In conclusion, stocking density had no effect on the growth, but had a negative effect on the survival at the highest density. A stocking density of 75% is recommended as the optimum for rearing O. edulis in the Basque coast.

Genetic improvement of survival in Pacific oysters to the Tomales Bay strain of OsHV-1 over two cycles of selection

Yearly mass mortalities of Pacific oysters in a major oyster-growing estuary on the West Coast of the United States (Tomales Bay, California) present a constraint to shellfish aquaculture. These mortalities have been associated with the presence of Ostreid herpesvirus 1 (OsHV-1; Tomales Bay strain) and increased seawater temperature in the estuary. In order to develop oyster families that are more tolerant to OsHV-1 than current oyster stocks, one cohort was planted in Tomales Bay per year over a three-year period, two of which were selected based on survival data collected from previous cohorts. Analyzing survival data from 23,590 oysters from 191 biparental families planted in Tomales Bay over three years, we estimated the heritability of survival on the observed and underlying liability scales to be 0.30 and 0.47, respectively. Survival breeding values increased 10.3 and 21.2 percentage points after one and two cycles of selection, respectively, suggesting that genetic selection was highly effective at producing oysters that were more tolerant of OsHV-1. The oyster families developed in this breeding program are the first in the United States specifically bred to be tolerant to OsHV-1 under elevated temperatures and will be valuable to oyster growers as well as researchers studying the genetic basis of OsHV-1 tolerance in Pacific oysters.

The killer within: Endogenous bacteria accelerate oyster mortality during sustained anoxia

AbstractSustained periods of anoxia, driven by eutrophication, threaten coastal marine systems and can lead to mass mortalities of even resilient animals such as bivalves. While mortality rates under anoxia are well‐studied, the specific mechanism(s) of mortality are less clear. We used a suite of complementary techniques (LT50, histology, 16S rRNA amplicon sequencing, and valvometry) to show that the proliferation of anaerobic bacteria within eastern oysters (Crassostrea virginica) accelerates mortality rate under anoxic conditions. Manipulative laboratory experiments revealed that oyster survival under anoxic conditions was halved when bacteria were present compared to when they were excluded by the broad‐spectrum antibiotic chloramphenicol. Histological assessments supported this mechanism and showed infiltration of bacteria in oysters that were not treated with antibiotics compared to a general lack of bacteria when oysters were treated with antibiotics. 16S rRNA amplicon sequencing failed to identify any particular genera of bacteria responsible for mortality, rather a diversity of endogenous anaerobic and/or sulfate‐reducing bacteria were common among oysters. In addition, monitoring of oyster valve gaping behavior in the field revealed that oysters showed remarkable valve closure synchrony when first exposed to anoxia. However, oysters periodically opened throughout anoxia/hypoxia in both the lab and field, suggesting that the infiltration of exogenous bacteria from the environment may also influence mortality rates under natural settings. Coupled with previous studies, we posit that mass mortality events in a wide range of coastal bivalves are likely the result of co‐morbidity from asphyxiation and bacterial processes.

Toxicity of Atrazine to Marine Invertebrates Under Flow-Through Conditions\u2014Eastern Oyster (Crassostrea virginica) and Mysid Shrimp (Americamysis bahia)

The triazine herbicide atrazine is routinely detected in freshwaters, and has also been detected in coastal waters in Europe and the US. Relatively few atrazine studies have been conducted with estuarine/marine invertebrates. This study sought to contribute additional invertebrate atrazine toxicity data using model species, Eastern oyster (Crassostrea virginica) and Mysid shrimp (Americamysis bahia). Specifically, we investigated (1) acute effects on survival and growth of Eastern oyster, and (2) acute and chronic effects on survival, reproduction, and growth of the Mysid shrimp. No oyster mortality was observed following 96-h exposure to up to 17 mg a.i./L, but shell growth was reduced by 0.55% to 16% in 1.0, 9.2, and 17 mg a.i./L treatments, resulting in a 96-h EC50 of > 17 mg a.i./L. In the 96-h Mysid test, mortality rates of 5 to 70% were observed in 1.7, 2.4, 3.6, and 6.4 mg a.i./L treatments, and the 96-h LC50 was 5.4 mg a.i./L. Sub-lethal effects were observed among surviving Mysids exposed to ≥ 2.4 mg a.i./L. After 28 days of exposure to up to 1.1 mg a.i./L, there were no effects on survival or reproduction. The LOEC was 0.50 mg a.i./L, based on reduced body size, and the NOEC was 0.26 mg a.i./L. Overall, the results indicate that atrazine is slightly toxic towards Eastern oyster and moderately toxic to the Mysid shrimp under acute exposure conditions. These data will help to fill a gap in the literature and inform risk assessment of potential effects of atrazine towards estuarine/marine communities.

Immunomodulatory and Antiviral Effects of Macroalgae Sulphated Polysaccharides: Case Studies Extend Knowledge on Their Importance in Enhancing Shellfish Health, and the Control of a Global Viral Pathogen Ostreid Herpesvirus-1 microVar

Macroalgae are the primary source of non-animal sulphated polysaccharides (SPs) in the marine environment with fucoidans derived from brown algae (Phaeophyta) and carrageenans from red algae (Rhodophyta). Much research has been carried out on SP effects on Asian shrimp species (genera Penaeus and Metapenaeus) but their effect on commercially important bivalve mollusc species is limited and in Pacific oyster Crassostrea gigas is unknown. Knowledge of their impact on bivalve pathogens and Palaemon shrimp is unknown. The objectives of this study were to assess the effects of Fucus vesiculosus (Phaeophyta), Mastocarpus stellatus (Rhodophyta) and algal derivatives (fucoidan and κ-carrageenan) on C. gigas performance, and on ostreid herpesvirus-1 microvar (OsHV-1 μVar) and bacteria Vibrio spp. development. Both pathogens have been associated with significant oyster mortalities and economic losses globally. The effects of sulphated galactan from Gracilaria fisheri (Rhodophyta) on European common prawn Palaemon serratus, an important fishery species, was also assessed. Findings indicate a rapid and prolonged increase in total blood cell count, lysozyme (enzyme that destroys pathogens), and a difference in the ratio of blood cell types in treated individuals compared to their control counterparts. A significantly lower OsHV-1 μVar prevalence was observed in treated oysters and κ-carrageenan was found to suppress viral replication (loads), while OsHV-1 μVar was not detected in the fucoidan treated oysters from Day 8 of the 26-day trial. No antibacterial effect was observed however, the oysters did not succumb to vibriosis. These findings contribute further knowledge to macroalgae sulphated polysaccharide biotherapeutic properties, their twofold effect on animal health and viral suppression.

Changes in benthic macrofauna in oyster parks during an OsHV-1 μVar oyster spat mortality outbreak

In intertidal areas, oyster farming creates a crosshatching pattern between oyster tables and aisles. Tables provide a refuge from the current and solar irradiance and the oysters facilitate the accumulation of OM, thereby structuring the spatial organization of the associated macrozoobenthic community at mesoscale. The aim of this study was to describe the quality of the oyster table environment at small scale and the response of the macrozoobenthic community to OsHV-1 μvar oyster mortality. The species assemblage was dominated by Golfingia vulgaris, Tubificoides benedii, Capitella capitata and Scoloplos armiger. The table habitat appeared to be in a bad ecological state throughout the 2-month survey (May and June 2017), whereas in the aisle, eutrophication occurred lately and was clearly related to be due to the massive stranding of dead seaweed at the end of the survey (in early July). So, this disturbance of the species assemblage seemed to occur in two phases: 1) after oyster spat mortality and 2) after seaweed stranding resulted in a bad ecological status, as revealed by macrofaunal indicators. Large quantities of OsHV-1 DNA were also found in some species, including small crabs and amphipods, one week after the mortality crisis, but there is no apparent virus reservoir found in the benthic species.