Crassostrea Ariakensis Research Articles

Susceptibility of Crassostrea ariakensis (Fujita 1913) to Bonamia and Perkinsus spp. Infections: Potential for Disease Transmission Between Oyster Species

Using PCR-based methodologies, we surveyed triploid Crassostrea ariakensis (Fujita 1913), introduced in experimental trials in the Chesapeake Bay, for parasites endemic to the native oyster and for Bonamia ostreae. Perkinsus sp. was detected in all in C. ariakensis samples analyzed, reaching prevalences equivalent to or higher than in the native oyster. Bonamia sp. was detected in a small number of C. ariakensis individuals (2.7%) from the York River, and analysis of amplicon sequences revealed novel Bonamia-related sequences as well as those close to previously described Bonamia spp. (B. ostreae, B. exitiosa, and B. perspora). Bonamia ostreae cross-infection experiments based on cohabitation of B. ostreae-infected Ostrea edulis (Linnaeus 1758) with uninfected C. ariakensis revealed no evidence of B. ostreae transmission after four weeks. Although these results may appear inconsistent with the identification of Bonamia-infected oysters obtained from the York River, the relatively short duration of this cross-infection experiment may account for the lack of parasite transmission. In contrast, Perkinsus sp. infected C. ariakensis efficiently transmitted the parasite to uninfected Crassostrea virginica (Gmelin 1791) within two weeks, under similar cohabitation conditions.

Economic Benefits of a Restored Oyster Fishery in Chesapeake Bay

Abstract A simple reduced form inverse demand model is used to determine the price flexibility of Chesapeake Bay oyster production when other producing regions of the United States have their oyster production held at average levels for 2002 to 2006. With the current reduced state of oyster demand compared with earlier periods, a restored Chesapeake oyster fishery that could sustain annual harvests of 4.9 million bushels would result in a predicted price that is significantly lower than the minimum observed from 1950 to 2006 and presumed to be unprofitable. A survey of oyster industry participants suggests that an equilibrium price is more likely to be around $20.06 per bushel. Using the inverse demand model, the predicted level of production is about 3.2 million bushels. Industry members believe that a restored industry, based on Crassostrea ariakensis, would have a greater percentage of oysters going to the shucked market compared with Crassostrea virginica.

Effects of Salinity on Bonamia sp. Survival in the Asian Oyster Crassostrea ariakensis

Abstract A novel Bonamia sp. discovered in Bogue Sound, NC, has recently emerged as a parasitic threat to the Asian oyster Crassostrea ariakensis. Because this oyster is being considered for introduction to the mid-Atlantic region, more data are needed to better evaluate the risks associated with this parasite. Field observations collected from North Carolina and information on other Bonamia spp. suggest an affinity for higher salinities, and direct transmissibility; in the absence of explicit experimental tests, however, this is largely hypothetical. Consequently, we used laboratory trials to test the direct transmissibility and the persistence of Bonamia sp. in infected triploid C. ariakensis transferred to and maintained at three salinities, 10, 20, and 30 psu for at least 15 wk. Under these experimental conditions, there was no evidence of direct Bonamia sp. transmission. Average parasite intensity in infected oysters transferred to and maintained at 10 and 20 psu decreased compared with oysters place...

Comparative Microbial Dynamics in Crassostrea virginica (Gmelin 1791) and Crassostrea ariakensis (Fujita 1913)

Abstract The proposed introduction of Crassostrea ariakensis along the mid-Atlantic Coast of the United States has sparked controversy regarding ecological, economic, and human health consequences. Previous research has focused primarily on the ecological and socioeconomic implications of this initiative, yet few studies have assessed the potential impacts on public health. This study compares rates of bioaccumulation, depuration, and post-harvest decay of Escherichia coli and Vibrio sp. between Crassostrea virginica and C. ariakensis. Our results suggest that (1) bioaccumulation rates of E. coli in C. ariakensis were significantly lower than those for C. virginica, (2) depuration of E. coli was variable between the two species, and (3) C. ariakensis post-harvest decay rates of E. coli were significantly lower than in C. virginica. This research provides a first comparison between C. ariakensis and C. virginica with regards to bacterial dynamics, an important consideration when determining appropriate she...

Identification of Crassostrea ariakensis and Related Oysters by Multiplex Species-Specific PCR

Genetic markers are needed for rapid and reliable identification of oysters. In this study, we developed multiplex genus- and species-specific PCR markers for the identification of oysters from China. We used the mitochondrial cytochrome oxidase I (COI) and nuclear 28S ribosomal RNA genes for marker development. DNA sequences from different species were obtained from GenBank or by direct sequencing. Sequences were aligned, and genus- and species-specific nucleotides were identified. Primers were designed for genus/species-specific amplification to generate fragments of different sizes. A multiplex set of genus- and species-specific primers from the 28S gene was able to separate C. ariakensis and C. hongkongensis from other species and assign oysters to four genera. A set of species-specific COI primers provided positive identification of all five Crassostrea species from China, C. ariakensis, C. hongkongensis, C. angulata, C. gigas, and C. sikamea in a single PCR. The multiplex PCR assays do not require fluorescence-labeling or post-PCR enzyme digestion, providing a simple, fast and reliable method for the identification of oysters from China.

Responses of Crassostrea virginica (Gmelin) and C. ariakensis (Fujita) To Bloom-Forming Phytoplankton Including Ichthyotoxic Karlodinium veneficum (Ballantine)

In the last several decades, the Eastern oyster (Crassostrea virginica) fishery in Chesapeake Bay has collapsed, largely because of overfishing and disease. As a consequence, there is increasing interest in the introduction of the Suminoe oyster Crassostrea ariakensis, which initial experiments suggest grows more rapidly and is more disease tolerant than the native oyster. In the present study, growth and clearance rates of the two oyster species at two different ages were compared for bloom-forming algae typical of the Chesapeake Bay, the ichthyotoxic Karlodinium veneficum and the spring blooming Prorocentrum minimum. Growth rates of 3–14 day-old spat of both species fed K. veneficum were severely depressed compared with growth rates for spat fed P. minimum or a hatchery phytoplankton mixture (Reed Mariculture Formula). Growth in C. ariakensis was more negatively affected by the toxic dinoflagellate than the native oyster. The ichthyotoxic dinoflagellate also appeared to reduce organ development in the developing spat even though clearance rates (pg C μm−1 h−1) for spat from both oyster species were similar for all food sources. When older juveniles (1–2 cm) were placed in bloom densities of Karlodinium (∼3 × 104 cells mL−1) for 6 h each day for 5 days, clearance rates were severely depressed for both oysters compared with rates noted for Tetraselmis, with clearance rates being reduced almost a hundred-fold for C. ariakensis. A nontoxic strain of K. veneficum was cleared at similar rates to Tetraselmis. These results suggest that the increasingly more common blooms of the ichthyotoxic dinoflagellate Karlodinium veneficum may preferentially impact the nonnative oyster more than the native after first set as well as later as it matures. If feeding on this Chesapeake Bay toxic dinoflagellate extends the period of time that new settled individuals remain small in size, the population structure of oyster reefs (e.g., through elevated losses to predation or siltation) may be ultimately altered.

Fertilization Interference Between Crassostrea ariakensis and Crassostrea virginica: A Gamete Sink

Published data indicate that spawning seasons for the Asian oyster Crassostrea ariakensis and the eastern oyster C. virginica overlap. Hybrids can form, but the larvae are not viable. If C. ariakensis is introduced into Chesapeake Bay and synchronous spawning occurs with native C. virginica, hybridization could reduce the production of viable larvae (=gamete sink). We examined the effects of gamete age, sperm concentration, and ratios of heterospecific gametes on fertilization rates and hybridization between the two species. Interspecific fertilization rates were consistently lower than intraspecific rates. Fertilization rates decayed linearly with gamete age, though intraspecific fertilization rates remained above 50% for 4–6 h, indicating that long dispersal of viable gametes is possible. Fertilization rates decayed in a log-linear manner with decreasing sperm density for intra and interspecific crosses. Fertilization rates declined significantly when sperm were (1) given a choice of eggs from each species to fertilize or (2) required to compete to fertilize eggs from a single species. Hence, a gamete sink will likely occur if these two species spawn synchronously. The magnitude of the gamete sink will depend on both gamete concentrations and the relative proportion of interspecific gametes in the water column. Furthermore, genetic analysis of individual 2-day old larvae indicated that C. virginica sperm was more likely to fertilize C. ariakensis eggs than any other interspecific cross. All else being equal, the removal of C. ariakensis eggs through this mechanism may provide C. virginica with a competitive edge.

Identification of outer membrane protein ompR from rickettsia-like organism and induction of immune response in Crassostrea ariakensis

Rickettsia-like organism (RLO) caused mass mortality of oysters, but little is known about the protective immune response to this microorganism. The present study was undertaken to identify a gene, ompR, encoding an outer membrane protein of rickettsia-like organism from oyster Crassostrea ariakensis. The role of this protein in promoting immune responses was characterized through analyzing the interaction between RLO and oyster. The results indicated: (i) full-length DNA of ompR is 531 bp and encodes 176 amino acid residues. Theoretical isoelectric point and molecular weight for the ompR protein are 9.76 and 19.76 kDa, respectively; (ii) the recombinant ompR was successfully expressed in Escherichia coli BL21 (DE3) cells, and the titre of anti- ompR antibody raised against rabbits was about 1:4100. A specific immunoreactive band was detected when anti- ompR antibody was opposed to the total outer membrane proteins of RLO; (iii) the expression level of TNF-α (tumor necrosis factor-alpha) and Myd88 (myeloid differentiation factor 88) in hemocytes was induced by ompR, whereas TGF-β (transforming growth factor-beta) was not; (iv) in hemocytes monolayers, a rapid and persistent increase in the level of phosphorylated P38 and a large decrease in the level of phosphorylated JNK were induced by ompR, whereas the level of phosphorylated ERK did not change with ompR incubation; (v) the DNA binding activity of NF-κB (nuclear factor κB) in hemocytes increased after ompR stimulation.

The Kumamoto Oyster Crassostrea sikamea is Neither Rare nor Threatened by Hybridization in the Northern Ariake Sea, Japan

The status of the Kumamoto oyster Crassostrea sikamea in its native Japan is uncertain because of a lack of information about its abundance and distribution and a suggestion that C. sikamea and the Pacific oyster C. gigas hybridize in the northern Ariake Sea. Furthermore, broodstock populations on the United States Pacific coast have been hybridized with C. gigas in the past and may suffer inbreeding depression from multiple generations of hatchery-propagation. As a result, Japanese conservationists and United States oyster growers share an interest in the status of this species in the wild. We collected wild oysters from three sites in Saga Prefecture located in the northern portion of the Ariake Sea, Kyushu, Japan, in September 2006 and used molecular methods (species-specific PCR of the mitochondrial COI gene and PCR-RFLP of the nuclear ribosomal ITS1 gene) to assign 628 sampled oysters to one of three species found in this region. C. sikamea proved to be the dominant organism on artificial hard substrates, comprising 91% of the oysters sampled and typed. Many individuals confirmed as C. sikamea by diagnostic DNA markers had C. gigas-like phenotypes, such as striped shells. Crassostrea ariakensis was present (8% of typed oysters) but only at the lowest intertidal levels, and C. gigas was rare (1%) at these sites. We found no evidence of hybridization between any of the species and were unable to repeat a previous study, which suggested hybridization between C. sikamea and C. gigas based on sharing of a calmodulin allele. We conducted gamete compatibility tests among all combinations of Japanese (Ariake Sea) and United States C. sikamea and C. gigas broodstocks and found strong one-way gamete incompatibility (male C. sikamea × female C. gigas) between species of Japanese stocks, supporting the molecular diagnosis of C. sikamea. However, this one-way incompatibility was less evident in United States stocks, indicating lower barriers to potential hybridization in commercially cultured stocks.

Identification of Korean Suminoe Oyster (Crassostrea ariakensis) by RFLP Analysis

The Suminoe oyster, Crassostrea ariakensis, occurs in estuaries where rivers meet seawater. In Korea, it is one of the most popular fisheries resources in the Nam River and Sumjin River. However, the genetic identification of this species has been questioned, because specimens are often mis-identified as other species. To identify the species, we conducted polymerase chain reaction (PCR) amplification of the internal transcribed spacer-1 (ITS-1) region, followed by digestion with the restriction enzyme HaeIII. Restriction profiles for oysters collected from Korea, Japan, and China (north and south) were determined by comparing the PCR-restriction fragment length polymorphism (RFLP) patterns of the ITS-1 regions. Our study verified that the oysters collected from Korea were C. ariakensis based on the PCR-RFLP patterns. These results emphasize the value of molecular markers for identifying morphologically uncertain species.

Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis

The proposition to introduce the Asian oyster Crassostrea ariakensis to the mid-Atlantic region of the USA is being considered with caution, particularly after the discovery of a novel microcell haplosporidian parasite, Bonamia sp., in North Carolina. Although this parasite was found to be pathogenic in C. ariakensis under warm euhaline conditions, its persistence in C. ariakensis exposed to various temperature and salinity combinations remained unresolved. In this laboratory experiment, we tested the influence of temperature in combination with a wide range of salinities (10, 20 and 30 psu) on Bonamia sp. Temperature was either changed from warm (>20 °C) to cold (6 °C for 6 weeks) and back to warm or maintained constant and warm. Warm temperature was associated with higher host mortality than cold temperature, suggesting that temperature influenced Bonamia sp. pathogenicity. The effect of salinity was revealed under warm temperature with highest mortality levels observed in infected C. ariakensis exposed to 30 psu. When temperature was increased following low-temperature exposure, Bonamia sp. was not detected; however sub-optimal experimental conditions may have contributed to this result, making it difficult to draw conclusions regarding the reemergence of the parasite after low-temperature exposure. Although the overwintering of Bonamia sp. in C. ariakensis will need to be further investigated, the results presented here suggest that Bonamia sp. may be able to persist in C. ariakensis under a combination of low temperature and meso- to euhaline salinities.

Strong seasonality of Bonamia sp. infection and induced Crassostrea ariakensis mortality in Bogue and Masonboro Sounds, North Carolina, USA

Asian oyster Crassostrea ariakensis is being considered for introduction to Atlantic coastal waters of the USA. Successful aquaculture of this species will depend partly on mitigating impacts by Bonamia sp., a parasite that has caused high C. ariakensis mortality south of Virginia. To better understand the biology of this parasite and identify strategies for management, we evaluated its seasonal pattern of infection in C. ariakensis at two North Carolina, USA, locations in 2005. Small (<50 mm) triploid C. ariakensis were deployed to upwellers on Bogue Sound in late spring (May), summer (July), early fall (September), late fall (November), and early winter (December) 2005; and two field sites on Masonboro Sound in September 2005. Oyster growth and mortality were evaluated biweekly at Bogue Sound, and weekly at Masonboro, with Bonamia sp. prevalence evaluated using parasite-specific PCR. We used histology to confirm infections in PCR-positive oysters. Bonamia sp. appeared in the late spring Bogue Sound deployment when temperatures approached 25 °C, six weeks post-deployment. Summer- and early fall-deployed oysters displayed Bonamia sp. infections after 3–4 weeks. Bonamia sp. prevalences were ⩾75% in Bogue Sound, and 60% in Masonboro. While oyster mortality reached 100% in late spring and summer deployments, early fall deployments showed reduced (17–82%) mortality. Late fall and early winter deployments, made at temperatures <20 °C, developed no Bonamia sp. infections at all. Seasonal Bonamia sp. cycling, therefore, is influenced greatly by temperature. Avoiding peak seasonal Bonamia sp. activity will be essential for culturing C. ariakensis in Bonamia sp.-enzootic waters.

Description of Perkinsus beihaiensis n. sp., a new Perkinsus sp. Parasite in Oysters of Southern China

Oysters were collected from coastal locations in China from 1999-2006 for parasite analyses by molecular, culture, and histological techniques. Polymerase chain reaction-based assays targeting the internal transcribed spacer (ITS) region of the ribosomal RNA gene complex were performed to detect the presence of Perkinsus species. Sequencing and phylogenetic analysis of amplified Perkinsus sp. DNAs indicated that a novel Perkinsus sp. infects Crassostrea hongkongensis, Crassostrea ariakensis, and other bivalve hosts from Fujian to Guangxi provinces in southern China. Prevalence of this Perkinsus sp. reaches as high as 60% in affected oyster populations. Analyses of nucleotide sequences of the rRNA ITS region and of large subunit rRNA and actin genes, consistently confirmed the genus affiliation of this Perkinsus sp., but distinguished it from currently accepted Perkinsus species. Parasite cell types, such as signet ring trophozoites of 2-8 microm diameter, were observed by histology, and application of both genus Perkinsus and Perkinsus species-specific in situ hybridization probes consistently labelled the same Perkinsus sp. cells in histological sections from infected oyster tissues. Combined phylogenetic and histological results support the identity of a new parasite species, Perkinsus beihaiensis n. sp.

Characterization and function of CREB homologue from Crassostrea ariakensis stimulated by rickettsia-like organism

The cAMP response element-binding protein (CREB) is a transcription factor that plays important roles in cellular growth, proliferation and survival. Here, we report that a homologue of CREB transcription factor, Ca-CREB, was identified and functionally characterized in oyster, Crassostrea ariakensis. The full-length cDNA consists of 1397bp with an ORF encoding a 39.3kDa protein. Amino acid sequence analysis revealed that Ca-CREB shares conserved signature motifs with other CREB proteins. Ca-CREB was ubiquitously and constitutively expressed in oyster, and the expression level in hemocytes was higher than that in other tissues. The expression level of Ca-CREB was not modified after RLO stimulation, while tumor necrosis factor-alpha (TNF-alpha) expression was increased obviously, which was revealed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Electrophoretic mobility shift assay (EMSA) and Western blotting showed that recombinant CREB proteins specifically bind the consensus CREB binding site, and DNA-binding activity and phosphorylation of Ca-CREB were induced by RLO. These results suggest that Ca-CREB is a CREB homologue and may be involved in immune responses against RLO.

Effects of Salinity on Bonamia sp. Survival in the Asian Oyster Crassostrea ariakensis

Effects of Salinity on Bonamia sp. Survival in the Asian Oyster Crassostrea ariakensis

COMPARISON OF GROWTH RATES BETWEEN DIPLOID DEBY EASTERN OYSTERS (CRASSOSTREA VIRGINICA, GMELIN 1791), TRIPLOID EASTERN OYSTERS, AND TRIPLOID SUMINOE OYSTERS (C. ariakensis, FUGITA 1913)

Abstract Oyster size and morphology affect individual oyster physiology, reproductive biology, and habitat production as well as population ecological services and availability for commercial harvest. Options for oyster restoration and fishery facilitation for eastern oyster (Crassostrea virginica) populations in the Chesapeake Bay include the use of disease resistant diploid eastern oysters (DEBY strain), triploid eastern oysters, and triploid Suminoe oysters (Crassostrea ariakensis) with the objective of providing a marketable product in a reasonable time frame. Shell height-at-age, growth in shell height in relation to environmental conditions, ontogenetic changes in morphology, and changes in biomass for groups of triploid Suminoe, triploid eastern, and diploid DEBY eastern oysters held at identical grow out conditions for the first two years of their lives were evaluated. Triploid Suminoe oysters reached shell heights of 76 mm (market size in Virginia of 3 in) at 1.1 y with triploid eastern oysters a...

Molecular phylogenies help resolve taxonomic confusion with Asian Crassostrea oyster species

Identification of oyster species is still largely based on phenotypic characters that are highly plastic. Prompted by the proposed introduction of the Asian oyster species Crassostrea ariakensis into the Chesapeake Bay region of the U.S.A., this study uses molecular genetic information to understand the taxonomic framework surrounding C. ariakensis and to confidently distinguish among various sympatric oyster species. Putative samples of C. ariakensis and other species of cupped oysters from across Asia were collected and phylogenetic analyses were conducted on DNA sequences of both nuclear (ITS-1) and mitochondrial (COI) regions. Trees generated based on the two independent molecular datasets were highly congruent, and indicate that many oysters collected for this study as C. ariakensis were originally misidentified. Results also indicate that C. ariakensis, C. hongkongensis and C. nippona are distinct, but closely related species. There is strong support in both analyses for a close relationship between C. gigas and C. sikamea, as well as between C. belcheri and C. gryphoides, and between C. iredalei and C. madrasensis. The parsimony analyses based on these DNA markers, however, did not provide evidence to support C. angulata as a distinct species from C. gigas. Overall, the results emphasize the need for rigorous species identification, and additional extensive and intensive sampling to more accurately determine relationships among Crassostrea species, define their geographic distributions, and establish existing sympatry patterns.

Pathogens in Crassostrea ariakensis and other Asian oyster species: implications for non-native oyster introduction to Chesapeake Bay

With the drastic decline of eastern oyster Crassostrea virginica populations in the Chesapeake Bay due to over-fishing, diseases and habitat destruction, there is interest in Maryland and Virginia in utilizing the non-native oyster species Crassostrea ariakensis for aquaculture, fishery resource enhancement, and ecological restoration. The International Council for the Exploration of the Sea (ICES) recommends that non-native species be examined for ecological, genetic and disease relationships in the native range prior to a deliberate introduction to a new region. Therefore, a pathogen survey of C. ariakensis and other sympatric oyster species was conducted on samples collected in the PR China, Japan and Korea using molecular diagnostics and histopathology. Molecular assays focused on 2 types of pathogens: protistan parasites in the genus Perkinsus and herpesviruses, both with known impacts on commercially important molluscan species around the world, including Asia. PCR amplification and DNA sequence data from the internal transcribed spacer region of the rRNA gene complex revealed the presence of 2 Perkinsus species not currently found in USA waters: P. olseni and an undescribed species. In addition, 3 genetic strains of molluscan herpesviruses were detected in oysters from several potential C. ariakensis broodstock acquisition sites in Asia. Viral gametocytic hypertrophy, Chlamydia-like organisms, a Steinhausia-like microsporidian, Perkinsus sp., Nematopsis sp., ciliates, and cestodes were also detected by histopathology.

Comparative vulnerability to predators, and induced defense responses, of eastern oysters Crassostrea virginica and non-native Crassostrea ariakensis oysters in Chesapeake Bay

Management agencies are considering introducing the Suminoe oyster Crassostrea ariakensis into Chesapeake Bay, USA. It is unknown if the growth of feral populations of this non-native oyster would be regulated by the same predators that once controlled the abundance of the native eastern oyster C. virginica. In laboratory studies, we compared the relative susceptibility of juvenile diploids (shell height < 25 mm) of both oyster species to invertebrate predators of eastern oyster juveniles. Predators included four species of mud crabs [Rhithropanopeus harrisii (carapace width 7–11 mm), Eurypanopeus depressus (6–21 mm), Dyspanopeus sayi (8–20 mm), and Panopeus herbstii (9–29 mm)], the blue crab Callinectes sapidus (35–65 mm), and two sizes of polyclad flatworms (Stylochus ellipticus and possibly Euplana gracilis; planar area ≲5 mm2 and ∼14 to 88 mm2). All four species of mud crab and the blue crab preyed significantly (ANOVA, P ≤ 0.05) more on C. ariakensis than on C. virginica, but predation by flatworms of both sizes did not differ significantly between oyster species. The greater susceptibility of C. ariakensis to crab predation was likely due to its shell compression strength being 64% lower than that of C. virginica (P = 0.005). To test for predator-induced enhancement of shell strength, we held oysters of both species for 54 days in the presence of, but protected from, C. sapidus and R. harrisii. Crabs were fed congeneric oysters twice weekly within each aquarium. Compared to controls, shell strength of C. virginica exposed to R. harrisii increased significantly (P < 0.043), as did shell strength of both oyster species exposed to C. sapidus (P < 0.01). Despite the changes in shell strength by both oyster species in the presence of C. sapidus, the shell of C. ariakensis remained 57% weaker than C. virginica. We conclude that, because C. ariakensis exposed to predators continued to have a weaker shell relative to C. virginica, the natural suite of crab and flatworm predators in Chesapeake Bay will likely serve to control the abundance of feral C. ariakensis. We caution that the situation in the natural environment may be sufficiently different in some locations that C. ariakensis may be able to compensate for its greater vulnerability to crab predation and hence become a nuisance species.

Complications of a non-native oyster introduction: facilitation of a local parasite

Among the risks of introducing non-native species to novel environments is the possibil- ity that the non-native might serve as a reservoir for enzootic pathogens formerly at low abundance. The recent identification of Bonamia sp. in previously uninfected non-native Suminoe oysters deployed to Bogue Sound, Morehead City, North Carolina, USA, raises serious concerns about the oyster's ability to act as a reservoir for the parasite, not formerly known along the east coast of the USA. To assess the current distribution of the Bonamia sp. parasite and its environmental tolerances, non-reproductive triploid Suminoe oysters, certified as uninfected, were deployed at 5 high salinity sites across North Carolina, chosen because of their similarity to the Bogue Sound site, and along a salinity gradient radiating from Morehead City Port, at which the parasite is known to occur. Screen- ing of 2 oyster cohorts failed to detect the Bonamia sp. parasite beyond the immediate vicinity of Morehead City port. At the port, infection was almost entirely confined to small (<40 mm shell height) oysters. These results suggest that the parasite, which is genetically similar to Australasian species, is a recent ballast water introduction through Morehead City Port and that its spread may be dependent on the availability of suitable hosts in high salinity environments. Clearly, the proposed introduction of the Suminoe oyster to the mid-Atlantic coast of the USA represents considerable economic and ecological risk and should not proceed without further study to obtain better estimates of likely effects.