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.

In an effort to develop genetic markers for oyster identification, we studied length polymorphism in internal transcribed spacers (ITS) between major ribosomal RNA genes in 12 common species of Ostreidae: Crassostrea virginica, C. rhizophorae, C. gigas, C. angulata, C. sikamea, C. ariakensis, C. hongkongensis, Saccostrea echinata, S. glomerata, Ostrea angasi, O. edulis, and O. conchaphila. We designed two pairs of primers and optimized PCR conditions for simultaneous amplification of ITS1 and ITS2 in a single PCR. Amplification was successful in all 12 species, and PCR products were visualized on high-resolution agarose gels. ITS2 was longer than ITS1 in all Crassostrea and Saccostrea species, whereas they were about the same size in the three Ostrea species. No intraspecific variation in ITS length was detected. Among species, the length of ITS1 and ITS2 was polymorphic and provided unique identification of 8 species or species pairs: C. ariakensis, C. hongkongensis, C. sikamea, O. conchaphila, C. virginica/C. rhizophorae, C. gigas/C. angulata, S. echinata/S. glomerata, and O. angasi/O. edulis. The ITS assay provides simple, rapid and effective identification of C. ariakensis and several other oyster species. Because the primer sequences are conserved, the ITS assay may be useful in the identification of other bivalve species.

Oysters are commonly found on rocky shores along China's northern coast, although there is considerable confusion as to what species they are. To determine the taxonomic status of these oysters, we collected specimens from nine locations north of the Yangtze River and conducted genetic identification using DNA sequences. Fragments from three genes, mitochondrial 16S rRNA, mitochondrial cytochrome oxidase I (COI), and nuclear 28S rRNA, were sequenced in six oysters from each of the nine sites. Phylogenetic analysis of all three gene fragments clearly demonstrated that the small oysters commonly found on intertidal rocks in north China are Crassostrea gigas (Thunberg, 1793), not C. plicatula (the zhe oyster) as widely assumed. Their small size and irregular shell characteristics are reflections of the stressful intertidal environment they live in and not reliable characters for classification. Our study confirms that the oysters from Weifang, referred to as Jinjiang oysters or C. rivularis (Gould, 1861), are C. ariakensis (Wakiya, 1929). We found no evidence for the existence of C. talienwhanensis (Crosse, 1862) and other Crassostrea species in north China. Our study highlights the need for reclassifying oysters of China with molecular data.

The Suminoe oyster Crassostrea ariakensis is considered a potential aquaculture species in Korea, potentially supplementing or supplanting culture of the Pacific oyster Crassostrea gigas, currently the focus of commercial production and research. Production of cultured Suminoe oysters in Korea is limited, in part because of limited information on its biology and ecology. Commercial production is presently restricted to two rivers (Seomjin and Kawha). Here we describe the current status of C. ariakensis in Korea, focusing on its ecology and factors affecting development of aquaculture for this species. Preliminary investigations suggest that the Suminoe oyster shows excellent potential for expanded cultivation. A comprehensive monitoring program is needed to detect natural and anthropogenic ecosystem changes affecting production of the Suminoe oyster.

In April 2004, triploid native (Crassostrea virginica) and nonnative (Crassostrea ariakensis) oysters were deployed in cages at four sites along a salinity gradient in Chesapeake Bay. In Maryland, the lowest salinity site was located in the Severn River and two low to mid-salinity sites were located in the Choptank and Patuxent Rivers. The highest salinity site was located in the York River in Virginia. Growth, disease acquisition, and mortality were measured in the deployed oysters through August 2006. Although ANOVA revealed that the nonnative oysters were significantly larger at the end of the experiment than the native oysters at all sites, the differences were much greater at the Virginia site (59 mm) than in Maryland waters (9–23 mm). With the exception of C. ariakensis in the Severn River, Perkinsus marinus infected both species at all sites. Prevalences and weighted prevalences in both species remained relatively low throughout the experiment, but native oysters consistently acquired higher prevalences and weighted prevalences than C. ariakensis by August 2006. With the exception of several mortality-inducing events including winter freezing and hypoxic exposure, mortality was generally low in both species. No disease-related mortality was suspected in either species given the low weighted prevalences observed. In the York River, where a substantial natural spatfall occurred in 2004, more native spat were found on C. ariakensis than on C. virginica. To our knowledge, this is the first comparison of triploid C. ariakensis to triploid C. virginica conducted in the field. Because we did not observe substantial disease-related mortality, it is too soon to draw conclusions regarding the disease tolerance of C. ariakensis in the field or its viability as a replacement for the native species.

Since 1978, the Maryland Department of Natural Resources has investigated the uptake and depuration by C. virginica of radionuclides released by the Calvert Cliffs Nuclear Power Plant (CCNPP), which is located on the western shore of Chesapeake Bay in southern Maryland. This ongoing program presented a unique opportunity to compare radionuclide transfer dynamics and other parameters such as growth, mortality, disease status, and meat condition for Crassostrea virginica and C. ariakensis in a side-by-side, in-situ environmental setting. Introducing the Asian oyster, C. ariakensis, into Chesapeake Bay has been proposed to help restore an oyster population to historical levels, to enhance the Bay ecosystem, and to contribute to the revival of the commercial oyster fishery. The population of the indigenous C. virginica has declined dramatically throughout the bay in part as a result of infection by two non-native protozoan parasites that cause MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus) diseases. Other factors including habitat loss, reduced water quality, and overfishing have also reduced population size. Crassostrea ariakensis is known to be more tolerant to these diseases and thus may have greater potential for survival and growth in Chesapeake Bay than the native oyster. Triploid C. ariakensis and diploid C. virginica were immersed in cages in the vicinity of the CCNPP discharge for two exposure periods between July and December 2004. After retrieval, oysters were analyzed for radionuclide concentrations, growth rate, mortality, disease status, and meat condition. Fouling of oysters and cages was also observed. Quantities of radionuclides released by the CCNPP for both exposure periods were insufficient to produce detectable concentrations in either C. virginica or C. ariakensis, precluding a comparison of uptake of Co58, Co60, or Ag-110 m, radionuclides that have been detectable historically. Shell lengths were not significantly different between the two species for the two sampling periods, despite the fact that there were considerable age differences between them, but C. ariakensis did show a greater rate of growth. Meat weights and condition indices for C. ariakensis were significantly greater than for C. virginica (P < 0.01). Mortality and Dermo prevalence and intensity were also significantly greater for C. virginica than for C. ariakensis (P < 0.01). Although quantities of radionuclides were insufficient to produce detectable concentrations in either species, this study provided a unique opportunity to examine C. ariakensis in an area of the Maryland Chesapeake Bay where C. ariakensis has not previously been observed.

In an effort to restore the ecological role of oysters in Chesapeake Bay and the economic benefits of a commercial fishery, the states of Maryland and Virginia are considering introducing the nonnative Asian oyster (Crassostrea ariakensis) into the Bay. As part of an ecological risk assessment (ERA) to evaluate the proposed action and alternatives, demographic modeling is being used to project the change in populations of both the Asian and the native eastern oyster (C. virginica) in the Bay across space and time. Annual mortality rates are vital input to the demographic model. We present two approaches for parameterizing mortality rates for C. virginica by salinity ranges and disease-intensity categories and discuss how these rates could be applied to project population growth for the Asian oyster. We estimated mortality rates from empirical data collected during annual dredge surveys of oyster beds in Maryland. We compared counts of recent boxes (dead oysters without fouling or sedimentation on the inner valve surfaces, including “gapers” of one or two weeks old with tissue remaining in the shell), old boxes (dead oysters without tissue remnants but with fouling, sedimentation or both on the inner valve surfaces), and live oysters in market-size and small classes. Our mortality estimates based on counts of recent boxes consistently differentiated between years with high disease intensity and those with low disease intensity, between wet and dry years, and between salinity zones. In contrast, traditional estimates of yearly mortality based on total box counts often were out of phase with measured levels of disease intensity and weather (dry or wet). To model populations of C. ariakensis, we propose to adjust the mortality rates for C. virginica based on research results that provide estimates of differences between the two species' resistance to MSX and dermo and to other mortality factors, such as predation.

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 placed at 30 psu. At the same time, host mortality was significantly reduced at salinities below 30 psu. These experimental results suggest that the survival of Bonamia sp. in C. ariakensis may be limited in mesohaline areas. The persistence, pathogenicity, and transmission of Bonamia sp. under polyhaline conditions will need to be further evaluated to better describe the geographic areas at risk in the event of C. ariakensis introduction.

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.

The drastic decline of the eastern oyster (Crassostrea virginica) in Chesapeake Bay and other estuarine areas along the Atlantic coast of the United States has prompted officials to consider the possibility of introducing the Suminoe oyster Crassostrea ariakensis into these waters. However, the introduction of an exotic oyster species may have unforeseen and potentially harmful effects on the Bay's ecosystem. An important question to be addressed is the potential for the nonnative oyster to become a reservoir for human, fish, and shellfish bacterial pathogens. The purpose of this study is to establish and optimize methodology, and carry out a preliminary screen of C. ariakensis and C. virginica from Chesapeake Bay for the presence of Vibrio parahaemolyticus, V. vulnificus, mycobacteria, and enterobacteria, using cultivation on semiselective media and PCR. In spite of the high prevalence of Vibrio spp. in soft tissues and the shell surface of both oyster species, V. parahaemolyticus and V. vulnificus were absent. Coliform enterobacteria were detected in tissues from both oyster species by cultivation in a semiselective medium. In contrast, mycobacteria were not detected in oyster soft tissues by both cultivation and PCR, but they were abundant on the shell surface. Although oysters have been reported to harbor V. cholerae and other Vibrio species as shell biofilm-associated bacteria, this report provides the first direct evidence for the presence of mycobacteria in oyster shell-associated biofilms. Further, this preliminary study revealed no substantial differences between C. virginica from coastal Maine and C. ariakensis from Chesapeake Bay waters concerning selected components of their associated microbial flora.

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 shellfish management strategies.

The Asian oyster, Crassostrea ariakensis, is being evaluated for its potential success in the restoration of oyster populations in Chesapeake Bay. Critical to an understanding of its potential success is knowledge of the impacts of common harmful algae in its diet; blooms of such algae are common in Chesapeake Bay. In these experiments, C. ariakensis were exposed to a standard algal diet, Isochrysis sp., alone, and in combination with the harmful dinoflagallates Prorocentrum minimum and Karlodinium veneficum and the raphidophytes Heterosigma akashiwo and Chattonella subsalsa. Two experiments were run, with varying proportions of Isochrysis to the test algal species. Feces and pseudofeces were examined microscopically and by high-performance liquid chromatography for changes in diagnostic pigments relative to the initial diet and for production of degradation pigments of chlorophyll. All species were cleared from suspension to varying degrees by the oysters. In the Isochrysis control and in the Isochrysis P. minimum treatment, intact, solid feces were produced, and the highest proportion of chlorophyll degradation pigments were found in the Isochrysis control diet suggesting algal digestion. Thin, “ropey” feces and pseudo-feces were observed in the K. veneficum Isochrysis treatment. Virtually no degradation pigments were found for oysters fed a diet containing K. veneficum, suggesting lack of digestion and assimilation of algal food. With the raphidophytes, reduced production of feces and pseudofeces was evident, and these contained a lower proportion of recognizable harmful algal cells, and higher proportion of degradation pigments than found with the other test species. Amorphous and cellular material that appears to be partly derived from the oyster digestive system was evident in the feces of oysters exposed to K. veneficum, H. akashiwo, and C. subsalsa; this was particularly pronounced in oysters exposed to H. akashiwo and suggests damage to the oyster gut. The impact of the presence of harmful algae in the diet of the oysters thus varied by algal species, but in all cases oyster digestion was altered relative to the control diet.

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.

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.

The Suminoe oyster (Crassostrea ariakensis) is being considered for introduction into the Chesapeake Bay. However, our current understanding of the biology and ecology of C. ariakensis is insufficient to predict whether an introduction will be successful, provide desired benefits, or have adverse impacts. Behavior of native Eastern oyster (C. virginica) pediveligers has been studied for many years and it is well established that they use a variety of habitat characteristics when selecting a site for colonization. Perhaps the most important of these are chemical cues emitted by adult conspecifics, which can lead to gregarious larval settlement and dense, persistent reef communities. Conversely, almost nothing is known about the mechanisms that regulate larval settlement and metamorphosis for C. ariakensis or how pediveligers might respond to conditions found in Chesapeake Bay. In a comparative study with C. virginica, we examined how environmental factors such as substrate type, natural biofilms, sediment and waterborne chemical cues influence larval settlement for two C. ariakensis strains (“south China” and “west coast”). Our results demonstrate many similarities but also potentially important differences. Both species and strains of larvae greatly prefer natural substrates (e.g., shell) covered with biofilms for colonization but the west coast strain of C. ariakensis exhibited greater attachment onto manmade substrates (e.g., fiberglass) than C. virginica. Waterborne chemical cues emitted by adult oysters were also found to enhance substrate attachment for all larval forms but cues do not appear to be species specific. These results provide critical insight to the ability of C. ariakensis larvae to identify and colonize suitable substrates in the Chesapeake Bay, which will have a large impact on recruitment success and their ability to establish self-sustaining populations.

In high salinity habitats along the Middle and South Atlantic coasts of the United States the Eastern oyster, Crassostrea virginica occupies an intertidal refuge from predation, facilitated by its tolerance of aerial exposure and associated desiccation and temperature stress. Observations of the Suminoe oyster, C. ariakensis in its native environments in Asia reveal that this species is most commonly found subtidally or in the very low intertidal zone, suggesting that it may be less tolerant of aerial exposure. With serious consideration being given to introducing C. ariakensis to the mid-Atlantic region, it is important to understand the ability of this non-native species to invade and become established in the intertidal zone. We conducted experiments in an outdoor quarantined facility to compare the tolerances of C. virginica and C. ariakensis to varying levels of aerial exposure. Diploid C. virginica and C. ariakensis were set on 10 cm × 10 cm PVC tiles, held in a flow-though quarantine system exposed to ambient weather conditions, and subjected for eight weeks to four simulated tidal emersion regimes—(1) high intertidal (3.5 h emersion), (2) mid intertidal (2 h emersion), (3) low intertidal (1 h emersion), and (4) subtidal (constant immersion)—and four exposure orientations—(1,2) vertical north- and south-facing, and (3,4) horizontal up- and down-facing. Complete mortality of both species occurred in the high intertidal treatment by the end of week 1. No C. ariakensis had survived in the mid intertidal treatment by week 2 and very few remained alive in the low intertidal treatment. By the end of week 5, only 1.25% of the C. ariakensis had survived in the low intertidal treatment, whereas survival of C. ariakensis in the subtidal treatment was 36.88%. Significantly, C. virginica survival was 80.63% in the subtidal treatment and 67.50% and 28.13% on the vertically-oriented tiles (north- and south-facing treatments combined) in the low intertidal and mid intertidal treatments, respectively. Growth rates of C. virginica across tidal treatments were greatest in the subtidal treatment and C. ariakensis grew faster in the subtidal treatment than C. virginica. These results indicate that even with modest aerial exposure, under climatic conditions characteristic of summers in the mid-Atlantic region of the United States, C. ariakensis would suffer high rates of early post-settlement mortality, effectively restricting this non-native oyster species to subtidal environments if introduced to the region.

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.