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Suspension-feeding bivalve molluscs have evolved a highly effective mechanism for particle discrimination, which allows them to process efficiently the material to which they are exposed. The mechanisms controlling this preingestive sorting process have been described as either passive or active. Evidence of a passive selection mechanism has been demonstrated in several species of suspension-feeding bivalves. In contrast, to date there has been no evidence that active selection mechanisms underlay particle selection in bivalves, although the possibility of such mechanisms has been hypothesized numerous times. The present study was designed to examine active selection on the gill of the eastern oyster Crassostrea virginica. The gill was chosen for study because in oysters this organ is involved in particle selection. Two in vivo assays were designed in which the gill was exposed to dissolved cell exudate or extracts from the microalga Tetraselmis chuii, and the transport of polystyrene microspheres (25 µm) by the frontal cilia of the ordinary filament quantified by means of video endoscopy. Results demonstrated that the addition of exudates or extracts of T. chuii cells had no significant effect on the percentage of particles being transported dorsally (likely ingested) or ventrally (more likely rejected), and no differences in the number of particles in the ventral groove between control and experimental treatments. Results of follow-up experiments using covalently bound neoglycoproteins commonly found on cell surfaces of microalgal species demonstrated differences in transport of captured microspheres (10 µm, carboxylated) depending on the sugar type. Although chemoreception cannot be completely ruled out, these findings further indicate that physicochemical properties of particles, and not an active behavioral or physiological response (i.e., chemoreception of dissolved metabolites) by the animal, mediate particle selection in oysters.

Oysters are one of the most important groups in terms of production by fisheries and aquaculture in developed countries of temperate areas. In subtropical and tropical regions, oyster species are economic important resources but many are exploited in an artisanal way and without a legal framework, what can result in overexploitation. One alternative is aquaculture but biological information and development of techniques for local species are required. Therefore, this review organizes information on subtropical and tropical oysters from the American Pacific addressing on their fisheries, cultivation, management, and conservation. The study focuses on two native species Striostrea prismatica and Crassostrea corteziensis and two introduced species Crassostrea gigas and Crassostrea sikamea having more information and technological development. Fisheries and their problems are analyzed and some alternatives are proposed to improve their organization and preservation. The most important aquaculture technological aspects are described including the processes for the production of spat in hatcheries and the techniques used for field cultivation. Biological, physiological, and ecological studies as well as the implementation of legal measures are required to administrate, restore, and recover fisheries. The aquaculture of C. corteziensis and S. prismatica presents great advances but the other native species require the development of technologies to progress in many aspects. The production of C. sikamea is concentrated in one region without expecting further expansion, and the cultivation of C. gigas can be recreated on various sites and expanded to estuaries in tropical areas.

Stock–recruitment relationships (SRR) are used by many resource managers as a metric to evaluate stock reproductive potential and rebuilding capacity when harvested. This relationship is more evident in traditional finfish stock assessment models where larvae are frequently limited by the abundance of spawning adults, whereas invertebrate resources are much more confounding and often do not express a clear spawning SRR. Oysters in particular appear to be limited more strongly by post-settlement mortality as larvae are regularly demonstrated to be present in high abundance in response to timely shell plants; yet unexpectedly, a brood SRR appears to be present. Because of the unique life history of oysters which provide their own habitat through reef accretion, a posit is that the quantity and quality of such habitat are crucial determinants of recruitment to the stock, and habitat quality acts as a surrogate for brood stock in the stock–recruit relationship. An extensive dataset from Delaware Bay with a 65-y time series was analyzed to assess the relationship between available Crassostrea virginica natural reef materials and subsequent spat (

The eastern oyster Crassostrea virginica contributes important ecological and structural elements to estuarine ecosystems worldwide. Oyster reef persistence requires regular recruitment as well as growth by existing individuals. Saltmarsh tidal creek oyster population age structure and growth rates directly influence local benthic–pelagic coupling and biogenic habitat formation. Recruitment monitoring, substrate deployments (2017–2020), and field surveys (2018) were conducted in North Inlet Estuary, SC, to quantitatively describe oyster age–shell height relationships, population age structure, daily growth rates, and survivorship. Multiple recruitment events resulted in three to four cohorts each year. Oysters exhibited rapid shell growth but most died by the end of their second growth season after attaining shell heights of less than 100 mm. Daily growth rates immediately after recruitment (approximately 0.07–0.29 mm day–1) and within the first 2 y (0.1–0.4 mm day–1) allow maximum shell heights of 50–55 mm after to 6–8 mo, 80 mm within 1 y, and 140 mm within 1.6 y. Recruitment timing strongly influenced shell heights after 1 y, with July recruits approximately 33% larger than May recruits within the same year. The North Inlet oyster population age structure was dominated by oysters in their first (55%) or second (45%) growth season, with individuals less than 100 mm shell height composing approximately 99% of the population. Oyster survivorship beyond 2 y appears to be unusual. The opportunistic life history strategy used by North Inlet oysters incorporates multiple large recruitment events each year and rapid growth rates to offset short life spans so as to maintain reef populations and related ecosystem services.

Attempts to decipher the life cycle of Haplosporidium nelsoni began almost immediately after it was identified as the pathogen causing MSX disease in eastern oysters, Crassostrea virginica. But transmission experiments failed and the spore stage, characteristic of haplosporidans, was extremely rare. Researchers concluded that another host was involved: an intermediate host in which part of the life cycle was produced, or—if the oyster was an accidental host—an alternate host that produces infective elements. A later finding that spores were found more often in spat (

Eosinophilic Rickettsia-like organisms (E-RLO) were found for the first time in sick oysters of the species Crassostrea gigas, grown in Laguna de San Ignacio, Baja California Sur, Mexico, in August 2014. This work presents the histological description of development of bacteria in parasitophorous vacuoles of infected cells. Confirmative diagnosis was performed by polymerase chain reaction and in situ hybridization. Bacterial growth started with eosinophilic granules (colonial), followed by the formation and growth of intracytoplasmic inclusions. The presence of E-RLO was detected in the gill epithelium, mantle, labial palps, digestive tract, and both male and female gametes. This work describes for the first time an E-RLO in C. gigas with potential vertical transmission.

Microcystins (MC) produced by several cyanobacteria are potent hepatotoxins, whereas the toxicokinetics and subsequent detrimental effects ofMCare not fully understood in marine bivalves. In this study, the accumulation and depuration pattern of MC-Leucine-Arginine (MC-LR) along with the antioxidant response were investigated in the gill tissue of Pacific oyster Crassostrea gigas and blue mussel Mytilus edulis exposed to 0.1, 1, 10, and 20 µg L-1 MC-LR for 7 days. Time- and concentration-dependent accumulation and depuration of MC-LR were observed in the gill tissue during the exposure and depuration phases. The values for maximum accumulation of MC-LR and malondialdehyde content were statistically significant (P < 0.05) at the end of exposure (day 7) to 20 µg L-1 MC-LR for both the bivalves, and at the beginning of the depuration period when M. edulis and C. gigas were exposed to 10 and 20 µg L-1, respectively. A significant level of glutathione (GSH) was detected in M. edulis in response to 20 ...

Despite nearly a century of exploitation and scientific study, predicting growth and mortality rates of the eastern oyster (Crassostrea virginica) as a means to inform local harvest and management activities remains difficult. Ensuring that models reflect local population responses to varying salinity and temperature combinations requires locally appropriate models. Using long-term (1988 to 2015) monitoring data from Louisiana's public oyster reefs, we develop regionally specific models of temperature- and salinity-driven mortality (sack oysters only) and growth for spat ( 75 mm) oyster size classes. The results demonstrate that the optimal combination of temperature and salinity where Louisiana oysters experience reduced mortality and fast growth rates is skewed toward lower salinities and higher water temperatures than previous models have suggested. Outside of that optimal range, oysters are commonly exposed to combinations of temperature and salinity that are correlated with high mortality and reduced growth. How these combinations affect growth, and to a lesser degree mortality, appears to be size class dependent. Given current climate predictions for the region and ongoing large-scale restoration activities in coastal Louisiana, the growth and mortality models are a critical step toward ensuring sustainable oyster reefs for long-term harvest and continued delivery of the ecological services in a changing environment.

Mortality of two size classes ( 35 mm) of eastern oysters Crassostrea virginica when exposed to combinations of low salinity (1, 2, 3, and 4) for extended periods (up to 30 days) at summer water temperatures typical of the Virginia Chesapeake Bay subestuaries was examined. A critical salinity-temperature combination of less than two at greater than 28°C for more than 1 wk exposure for oyster mortality is suggested. A review of limited historical salinity-temperature tolerance data suggest selection of local populations of oysters having differing salinity tolerances. Such selection may prove critical to persistence of low-salinity populations in the Chesapeake Bay subestuaries with projected climate change.

To improve the accuracy and reproducibility of the previous near infrared reflectance spectroscopy (NIRS) model for glycogen in the oyster species Crassostrea virginica, a new model using freeze-dried samples was developed. The NIRS glycogen calibration model was developed using 380 individual oyster samples collected between 2014 and 2016 from several locations in the Chesapeake Bay. Homogenized freeze-dried samples were scanned in the near infrared region between 1,000 and 2,500 nm. In parallel, glycogen concentration (GC), measured as percent dry weight, was determined using laboratory-based methods. The two sets of data allowed us to build a NIRS model based on freeze-dried oyster meats, and the model gave a strong prediction of GC [coefficient of determination for validation (R2val) = 0.96 and residual predictive deviation (RPD) = 5.2]. The second part of the study applied the model to determine GC among 39 diploid and 40 triploid C. virginica and determined the strength of the relationship between the GC of tissues excised for histological sampling to the remaining tissue (corpus) to verify assumptions made throughout the literature. There was an estimated R2 = 0.99 between the GC in the corpus and the tissues of whole oyster meat. Among the samples, two factors, ploidy and size (shell height), had a significant effect on GC.

To examine the role of substratum concavity in determining oyster [Crassostrea virginica (Gmelin, 1791)] settlement success, laboratory settlement was examined on natural and artificial substrata of various concavities, defined by width-to-depth (W:D) ratio. Experiments were conducted in 204-l capacity laboratory flumes. Concavities tested include W:D ratios of 2, 5, and 16, plus a flat surface for control comparisons. Active settlement, passive settlement, and flow around these concavity treatments were examined. In addition, settlement on oyster shell cultch presented in different surface orientations, and either zip-tied to open mats, or packed in mesh bags, was examined. Results indicate that concavity can affect settlement success (W:D ratio of 5 resulted in the highest settlement success under this study's conditions). Examination of flow rates and patterns suggests that water movement over W:D 5 treatments delivers larvae to the settlement surface, but active attachment behavior is required to explain W:D 5's higher settlement densities relative to W:D 2. The highest settlement occurred with open mats on surfaces oriented horizontally and facing downward. Comparisons of mat, bag, and orientation results suggest that optimal current range for settlement is between 0.3 and 2.0 cm/sec. Too little flow results in supply failure, while flow exceeding 2 cm/sec inhibits searching and attachment behaviors.

A 2007 study of Suminoe (Crassostrea ariakensis) and eastern (Crassostrea virginica) oysters exposed to Indian River Lagoon (IRL), Florida waters revealed the presence of Bonamia spp. in exposed oysters. In 2010, a survey of oysters and other bivalves (n = 721, 18 species) was conducted in the southern IRL (10 sites) and in the more southerly Lake Worth Lagoon (LWL, 3 sites). Polymerase chain reaction (PCR) was used to assess the prevalence of three oyster parasites, Bonamia spp., Perkinsus marinus, and Haplosporidium nelsoni, in collected samples. Histology, fluorescent in situ hybridization (FISH) and standard H&E staining, was used to confirm PCR-positive Bonamia results. Bonamia spp. was detected in eight species (Brachidontes exustus, Crassostrea virginica, Geukensia demissa, Ischadium recurvum, Isognomon alatus, Isognomon bicolor, Mercenaria campechiensis, and Ostrea stentina). The prevalence was 17.3% in the IRL and 9.9% in LWL with 66% of PCR-positive samples subsequently identified as either Bonamia exitiosa or Bonamia perspora. The presence of Bonamia spp. was confirmed by FISH in C. virginica, O. stentina, I. alatus, I. bicolor, and G. demissa, although only C. virginica and O. stentina showed evidence of infection. The presence of P. marinus was detected in eight species (Atrina rigida, B. exustus, C. virginica, G. demissa, I. recurvum, I. alatus, I. bicolor, and O. stentina). The prevalence was 12.4% in the IRL and 7.7% in LWL. The presence of MSX was not detected in any of the collected bivalves. This study confirms the presence of Bonamia spp. and P. marinus in Florida east coast waters and widens the described geographic range for Bonamia spp., and provides further evidence that MSX is unlikely to be found in Florida waters

Oyster classification is problematic because of variations in shell morphology, and the use of molecular data may help to confirm species identity and clarify taxonomic confusion. Two ostreid oysters were collected from Peru and identified as Undulostrea megodon (Hanley, 1846) and Talonostrea talonata (Li & Qi, 1994), based on shell morphology. To confirm their taxonomic status, fragments of mitochondrial cytochrome oxidase I and 16S rRNA genes were sequenced. Phylogenetic analyses of both sequences do not support the validity of the two genera that were solely founded on these two species. Oyster U. megodon is clearly a member of Ostrea and T. talonata a member of Crassostrea. Thus, U. megodon should retake its original name of Ostrea megodon (Hanley, 1846), and T. talonata should be renamed as Crassostrea talonata (Li & Qi, 1994). Oyster C. talonata is a described species of China, and its occurrence in western Pacific is unusual and probably because of human facilitated introductions.

Studies that carefully monitor and attempt to explain causes of massive oyster mortalities are urgently needed. The objective of the present study was to assess the effects of seeding dates on the mortality and reproductive cycle of the oyster Crassostrea gigas. Seeds of two sizes (3.5–4 mm and 1.5–2 mm) were planted during three seasons: early summer, early autumn, and late autumn. The experimental period was 6 mo. Mortalities of C. gigas at culture phase nursery lantern-nets, intermediate lantern-nets, and final lantern-nets were recorded. The reproductive cycle of the oysters grown from 3.5 to 4 mm seeds planted in each season was closely monitored (bimonthly) during the experimental period. In addition, seawater parameters [temperature (daily) and salinity (weekly)] were monitored throughout the experimental period. Results of this study demonstrated that the planting season affected C. gigas mortality after the nursery phase. Lower cumulative mortality was observed for 3.5–4 mm seeds than fo...

This work was undertaken to assess the effects that different environmental conditions of tropical and temperate aquaculture sites have on growth, survival, and reproduction of diploid and triploid Pacific oyster Crassostrea gigas. Diploid and triploid oysters were evaluated with the purpose of determining if the triploid condition results in any advantage on growth and survival that can be exploited for aquaculture of this species in tropical environments. The evaluations were performed by comparing three sites: two tropical sites in the Gulf of California and one temperate site in the Pacific Coast of the Baja California Peninsula, Mexico. When comparing tropical versus temperate sites, C. gigas growth and survival were less at the tropical sites regardless of ploidy. This can be attributed to environmental conditions, that is, high temperatures causing low productivity, in addition to an earlier-onset and sustained reproductive condition in the tropical sites when compared with the temperate site regardless of ploidy. Analyses of gonad maturation stages and number of oocytes among triploids indicated that a larger reproductive effort occurs at the tropical sites than at the temperate site. Regardless of the lower performance of both ploidy groups in the tropical environmental conditions, triploids grew significantly better than diploids in both tropical sites, and survival was the same for both ploidy groups. This contrasts with the marginal differences observed in growth between ploidies at the temperate site, where triploids showed lower survival than diploids. Possible causes for the lower triploid survival at this site are discussed.

The eastern oyster Crassostrea virginica once supported one of the largest fisheries in the eastern United States. Oyster populations and the reefs they form have suffered chronic long-term decline throughout the species' range, including in northwest Florida's Pensacola Bay estuary system (PBS). To guide efforts to rebuild oyster populations in the PBS, connectivity patterns were evaluated among historic and extant reef locations using an integrated biophysical numerical model. Water quality parameters and oyster recruitment were monitored in May 2007 and then monthly from July 2007 through July 2008. Resultant salinity data were used to calibrate an Estuarine Coastal Ocean Model—based numerical circulation model of Pensacola Bay, which was then coupled to an existing, individual-based, oyster larvae routine to predict ontogenetic larval distribution. Threedimensional Lagrangian transport algorithms were used to simulate transport of modeled larvae during four 20-day time periods during those su...

Tagging methods used in bivalve research can be broadly categorized into two groups: internal and external. External tagging methods are more commonly used; however, the legibility of external tags tends to decline over time, and tag recovery rates are often low due to the abrasion or biofouling of shells, particularly during long-term studies. The aim of the current study was to compare two external identification methods placed on or in the shells of adult Crassostrea gigas: (1) a plasticlaminated glue-on tag and (2) novel use of a t-bar anchor tag inserted into the upper shell, to determine the optimal methodology to use in longitudinal studies of greater than 1-y duration. Over a 15-mo period, 100% of glue-on numbered tags were lost or became overgrown and could not be read, whereas 91.5% of t-bar anchor tags were retained and remained legible. The results of this study suggest that t-bar anchor tags are a better choice for long-term longitudinal studies of adult C. gigas in temperate marine ...

In the summer of 2010, the Damariscotta River Estuary, ME, experienced the first large multinucleate sphere X disease (Haplosporidium nelsoni) outbreak in commercial stocks of the eastern oyster (Crassostrea virginica). In 2012, biofouling organisms were sampled in and around the commercial oyster operations with the intent of looking for the presence of the parasite to see which, if any, biofouling species may be acting as a reservoir host and harboring the parasite. Organisms collected included tunicates, gastropods, polychaetes, and arthropods, as well as plankton samples from the surrounding water column. A quantitative polymerase chain reaction assay for H. nelsoni using a TaqMan minor groove binder probe, which was originally developed for detection of the parasiteDNAin oysters, was applied to biofouling species. The protozoan parasite H. nelsoniDNA was present in up to 70% of tunicate samples and about 30% of plankton samples. The highest parasite DNA copies (averaging 4 × 104 copies) were...

Spatial and temporal genetic structure of the eastern oyster Crassostrea virginica was examined along the coast of North Carolina (NC); utilizing a fragment of the mitochondrial large (16S) ribosomal subunit gene sequence known to distinguish three regional haplotypes in C. virginica—North Atlantic, South Atlantic, and Gulf of Mexico. Significant geographic genetic structure was identified among all populations studied, with little temporal genetic variation observed over the 9-y sampling period. The results are consistent with those of previous studies analyzing geographic variation in mitochondrial DNA16S sequence data, which revealed a genetic discontinuity between North and South Atlantic oyster assemblages along the NC Coast. The increased geographic resolution and duration of sampling in this study revealed a sustained significant shift in genetic composition between Pamlico Sound populations and southern NC populations of C. virginica. These results suggest that a prolonged or persistent b...

Bacterial pathogens are a major cause of mortality in bivalve hatcheries, and outbreaks can result in shortages of seed supply to the grow-out industry. The use of probiotic bacteria is a potential preventative measure to limit the impact of bacterial diseases. Previous research showed that the marine bacteria Phaeobacter inhibens S4 (S4) and Bacillus pumilus RI06—95 (RI) protect larval eastern oysters (Crassostrea virginica) when challenged with the pathogens Vibrio tubiashii RE22 (now Vibrio coralliilyticus RE22) and Roseovarius crassostreae CV919-312T. In this study, these probiotic bacteria were tested under hatchery conditions. Daily addition of S4 and RI (104 colony forming units (CFU)/ml) to 100-l culture tanks resulted in a significant decrease in the levels of total Vibrios in water and tank surfaces (P < 0.05), but not in oysters. Larval growth and survival was unaffected by the probiotic treatments. Larvae treated with probiotics in the hatchery showed significantly less mortality than...

Hatcheries providing seed for bivalve mollusc aquaculture can suffer from disease outbreaks resulting in high losses of larvae. Previous research demonstrated the effectiveness of candidate probiotics Phaeobacter inhibens S4 (S4) and Bacillus pumilus RI06-95 (RI) in protecting the larvae of eastern oysters Crassostrea virginica, against bacterial challenge. In this study, the ability of this probionts in protecting larvae of other bivalve species, including northern quahog Mercenaria mercenaria, bay scallops Argopecten irradians, blue mussels Mytilus edulis, and razor clams Ensis directus, was investigated. Pretreatment of larvae with 106 colony forming units /ml probiotic S4 and a mixture of S4 and RI protected bay scallop larvae [relative percent survival (RPS): 69% ± 4%]. In pilot-scale hatchery trials, daily additions of candidate probiotics to the water of static tanks containing northern quahog or bay scallop larvae had no significant impact on larval growth and survival. Daily treatment of...

Understanding the population dynamics and complete life cycle of bivalves is important for effective management of these commercially and ecologically important organisms. Most of the literature and research on bivalves to date has focused on juvenile and adult bivalves, but much less is known about larvae. The larval stage has been difficult to study due to the lack of a rapid automated approach for identifying the species. A new technique, called ShellBi, utilizes color patterns on the larval shell under polarized light to identify bivalve larvae. The objective of our research was to review the scientific basis for ShellBi and to apply it to bivalve larvae from the Choptank River in mesohaline Chesapeake Bay, with the goal of distinguishing larvae of the eastern oyster (Crassostrea virginica) from seven other species that spawn at the same time. A digital camera and polarized light microscope was used to capture images of the larval shells of the eight species under standard and cross-polarized light. Images of C. virginica were distinguishable from those of other species based on color patterns, especially at later stages of development. These images could serve as a visual guide to distinguish larvae of C. virginica from other bivalves inhabiting mesohaline tributaries of Chesapeake Bay.

The utility of shell overlays to oyster (Crassostrea virginica) plantings as a cownose ray (Rhinoptera bonasus) predator deterrence mechanism was examined. Typical industry practice of oyster seed planting was followed in an experimental design employing treatment areas of 0.5–1.0 acre (0.2–0.4 hectare). Areas were prepared in the Lower Machodoc Creek, Virginia, by the initial application of shell to insure a stable substrate under planted seed oysters. Seed oysters were planted using standard industry methods. Experimental areas were located, two upstream and two downstream, of a constriction in the Lower Machodoc that dictated differing physical environments in the respective locations with downstream locations being more exposed to northeast wind-driven stresses and, historically, a greater incidence of ray predation. Once oysters were planted, two of the areas, one upstream and one downstream of the aforementioned constriction, were additionally treated with a shell overlay as a predation det...

14 páginas, 1 figura, 3 tablas.-- Simone Sühnel ... et al., The protozoans Perkinsus marinus, Perkinsus olseni, Bonamia ostreae, Bonamia exitiosa, and Marteilia refringens are responsible for some of the most detrimental diseases in the production of cultivated shellfish worldwide and are classified as notifiable diseases by the World Organization for Animal Health (OIE). This study examined the general health status of wild and cultured bivalves from southern Brazil and included diagnostic tests for the presence of Perkinsus sp., Bonamia sp., andMarteilia sp. Cultured bivalves included the mangrove oyster Crassostrea gasar (syn. Crassostrea brasiliana), the brown mussel Perna perna, the lion's paw scallop Nodipecten nodosus, andwing pearl oyster Pteria hirundo. Themangrove oyster Crassostrea rhizophorae and the carib pointed venus clam Anomalocardia brasiliana (syn. Anomalocardia flexuosa) were collected from wild populations. A variety of parasitic or commensal organisms were detected by histology including Ancistrocoma-like and Spenophrya-like organisms; Bucephalus genus, Nematopsis sp., Steinhausia sp., and Tylocephalum sp.; unidentified trematode; unknown protozoan and metazoans; and an amoeba parasite. Hemocytic infiltration was most commonly associated with parasitized animals. Histological, culture and molecular diagnostic tests did not find any evidence of the presence of OIE-listed pathogens or related species in this study. Although the current survey did not identify any pathogens or diseases of concern, it provides baseline health assessment data for these species against which any future disease developments or significant changes in population health can be compared. These data are also valuable with respect to the development and implementation of public policies related to aquatic animal health, We would like to thank to the Ministry of Fisheries and Aquaculture, Brazil, for the research support provided to the Fundaçao de Amparo à Pesquisa do Estado de Santa Catarina (FAPESC), Brazil; the National Council of Technological and ScientificDevelopment, Brazil (CNPq-558222/2008-0), for supporting themacro- andmicroscopical analysis and for providing a grant (CNPq-301072/2007-8); the Coordenaçao de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES), Brazil, for post-doctoral scholarship support for SS; the Pacific Biologic Station and Vancouver Island University (VIU) in Canada for supporting the molecular studies

International audience; The Deepwater Horizon (DWH) oil spill in 2010 resulted in the release of millions of liters of oil into the Gulf of Mexico. Dispersants such as Corexit 9500A were used to disperse oil both at the well-head and at the surface. Polycyclic aromatic hydrocarbons and dispersants have been shown to deleteriously affect early life stages of organisms including oysters. This study examined the impacts of chemically enhanced water-accommodated fractions [CEWAF; 1.29–26.14 µg/l tPAH50 (a sum of 50 different polycyclic aromatic hydrocarbons)], high-energy water-accommodated fractions (HEWAF; 16.53–248.89 µg/l tPAH50), and dispersants (0.625–10 mg/l) on the cellular functions (viability, mitochondrial membrane potential (MMP), reactive oxygen species production (ROS), and acrosomal integrity) and resulting fertilization success of eastern oyster Crassostrea virginica spermatozoa. While viability of spermatozoa was not affected by CEWAF and HEWAF at concentrations tested, dispersant exposure caused significant decrease in viability at the highest concentration tested. Fertilization success as well as MMP and ROS production were significantly decreased upon exposure to CEWAF, HEWAF, and dispersants. Also, although not affected by HEWAF exposure, acrosomal integrity decreased upon exposure to CEWAF and dispersants at concentrations tested. The results of this study suggest that impaired fertilization and reduced viability observed after exposure to DWH oil spill contaminants may result, at least partially, from alterations of cellular functions of spermatozoa and contribute to negative effects on oyster populations, and thus the ecology and economy of the Gulf of Mexico.

The production of toxic secondary metabolites by marine phytoplankton and their accumulation in molluscs and fish has ecosystem-wide and human health impacts. The potent neurotoxin saxitoxin and its analogs, which can cause paralytic shellfish poisoning, are produced by species of the dinoflagellate genus Alexandrium. These toxins can accumulate in filter-feeding molluscs, including commercially grown species of shellfish. A feeding experiment was designed to assess the use of quantitative polymerase chain reaction to detect a gene involved in saxitoxin biosynthesis (sxtA) in two commercial oyster stocks. Both diploid and triploid Crassostrea gigas were fed with toxic cultures of Alexandrium minutum over a period of 12 days to allow toxin accumulation. A barcoding gene specific to Alexandrium (ITS 5.8s rRNA) and the sxtA gene, domain 4, which is specific to the saxitoxin synthesis pathway, were assayed. Both targets were detected in oysters collected after 6 and 12 days feeding with A. minutum, a...

Stable carbon and nitrogen isotope analyses were used to evaluate the influence of microalgal diet on growth and survival of hatchery-reared Pacific oysterCrassostrea gigas larvae.D-veliger larvae were fedmonospecific diets of Pavlova lutheri (P), Tahitian Isochrysis aff. galbana (T), and Chaetoceros calcitrans (C), and a standard hatchery trispecific diet of 25P:25T:50C (PTC). The dietary effects on nutrient assimilation, isotopic turnover rates, and discrimination factors were assessed using exponential models. Of the four dietary treatments evaluated over the 15-day feeding trial, larvae fed C. calcitrans and PTC had the best growth and high survival. Larvae in all dietary treatments had relatively high isotopic turnover rates (0.075–0.327/day), although some discrimination factors found in this study were out of the normal range for aquatic invertebrates (Δ13C: 0.4‰–4.1‰ and δ15N: 0.1‰–5.3‰). Overall, the turnover rates and discrimination factors for δ13C and δ15N indicated that C. gigas larv...

The World Register of Marine Species (WoRMS) currently registers all Pacific cupped oysters that were formerly members of the genus Crassostrea in a new genus, Magallana. Magallana gigas is designated as an ‘‘accepted name,’’ whereas a search for Crassostrea gigas results in the message ‘‘no matching results found.’’ This has caused dismay among many biologists, aquaculturists, and other stakeholders with an interest in the Pacific and other oysters. This note, which is authored by 27 interested scientists, presents a dissenting view and a rebuttal of the proposed change of genus.

Neurotoxic shellfish poisoning caused by the ingestion of shellfish contaminated with brevetoxins threatens human health and economies reliant on the Gulf of Mexico. In the United States, the only federally approved method to test shellfish for brevetoxins is a mouse bioassay. Although effective in protecting public health, this assay has considerable shortcomings, including low throughput, lack of sensitivity and specificity, and reliance on live animal testing. Here, a commercially available enzyme-linked immunosorbent assay (ELISA) (MARBIONC) was validated, and results of field samples tested using ELISA and the mouse bioassay were compared. In this validation of the ELISA method for eastern oysters Crassostrea virginica and clams (Mercenaria spp. and sunray venus Macrocallista nimbosa), ELISA demonstrated strong recoveries, specificity, and ruggedness. Quantitative results were obtained for more than 90% of the 526 field samples tested by ELISA compared with only 26% of the samples tested by mouse bioassay. When quantitative data were available for both assays, significant correlations across methods were found. Based on this work, in 2017, the Interstate Shellfish Sanitation Conference approved the limited use of the MARBIONC ELISA in neurotoxic shellfish poisoning management.

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure.