Wild Oysters Research Articles

Spatial patterns in the condition index of the wild Pacific oyster Crassostrea gigas in a macrotidal coastal ecosystem: Influence of tidal processes and beyond

In macrotidal coastal ecosystems, spatial heterogeneity of the water column properties is induced by both oceanic and continental influences. Hydrodynamic processes generate a land-sea gradient of environmental conditions, affecting the biological performances of sedentary organisms. The aim of the present study is to establish an extensive spatial assessment in the reproductive investment of the wild Pacific oyster Crassostrea gigas in Arcachon Bay. This is done by looking for a relationship between the Lawrence and Scott condition index (LSCI) and two tidal processes: the immersion level (IL) and the local oceanic flushing time (LoFt). The LSCI of C. gigas was assessed, just before gamete release, at 68 sampling stations in Arcachon Bay. Oyster performance was overall low and spatially variable. Significant differences in the LSCI were detected between the outer and inner bay. Oyster reefs located toward the mouth of the bay exhibited high LSCI (between 9 and 11), while oyster reefs located in inner bay, especially in south-eastern part around the Eyre River, had low LSCI (below 6). Linear modelling allowed to highlight significant effects of both tidal processes IL and LoFt on the obtained LSCI gradient. IL, LoFt explained 33% of the spatial variability observed on LSCI (IL=3%; LoFt=17%; LoFt+IL: 13%), 6% were attributed to the intra-station variation (ISv). Thus, high IL and rapid LoFt favor a better development of somatic-gonadal volume, probably because of longer feeding time and higher supply of food from the ocean by tide flows. Disentangling the effects of IL and LoFt on LSCI allowed to describe the spatial pattern in 61% of variability not explained by both tidal factors. A residual gradient directed southeast-northwest highlighted that others factors, independent from IL and LoFt seems to hamper inner bay oyster reproductive performance. Consequently, investigating on the ecological functioning (Eyre influences), trophic potential and anthropogenic pressures of this zone seem crucial on the understanding of C. gigas reproductive pattern in Arcachon Bay.

Early Post-Settlement Growth in Wild Eastern Oyster (Crassostrea virginica Gemlin 1791) Populations

Management and restoration of wild oyster populations with the ecosystem services they provide require detailed understanding of oyster population dynamics, including temporally and spatially varying growth. Much of the existing literature documenting growth rates for eastern oysters (Crassostrea virginica) reports growth for large, protected, and/or hatchery-spawned oysters. By following growth of wild oysters set on planted clamshells in Delaware Bay, we document early growth (within the first year) of 21 wild oyster cohorts settling over 8 years and assess the importance of interannual variability in temperature and salinity. In general, oysters follow a linear growth trajectory in the first year of life, interspersed by periods of little to no growth in the colder months. Wild oysters settling in the Delaware Bay mid-salinity region reach a size between 27 and 33 mm in their first year and tend to reach greater shell heights at 1 year of age in higher salinity years and at temperatures averaging 23 °C. Multi-year, population-level estimates of wild growth such as these are important for understanding changes in restored and managed oyster populations, and resulting ecosystem services, under naturally variable conditions.

Current genetic status, temporal stability and structure of the remnant wild European flat oyster populations: conservation and restoring implications

The flat oyster (Ostrea edulis) is one of the most appreciated molluscs in Europe, but natural beds have been greatly reduced due to harvesting and the effects of the parasite Bonamia ostreae. Characterization of current wild populations is required to develop long-term bed restoration programmes by enhancing genetic diversity and tolerance to bonamiosis. Oysters from different locations corresponding to the main natural beds from Denmark, The Netherlands, England, Ireland, France and Spain, including two different cohorts per location were sampled in 2011 and 2013. Sixteen microsatellite loci were used to study temporal and geographical genetic structure. Temporal variation was low, although sometimes significant probably due to high variance in reproductive success among individuals. Conversely, samples from different countries showed much higher genetic divergence, and Ireland and France presented differences among locations within country. Clustering analyses grouped samples into three main geographical regions, associated with oceanic fronts: one group constituted by The Netherlands and Denmark; another by France, Ireland and England; and a third one exclusively by Spain. Effective population sizes (Ne) within regions were high (>1000), which reflects population stability and low levels of genetic drift. The presence of regional genetic structure shows the potential for local adaptation of O. edulis and suggests caution when transplanting individuals, especially between distant geographical regions.

Ecological impacts of non-native Pacific oysters (Crassostrea gigas) and management measures for protected areas in Europe

Pacific oysters are now one of the most ‘globalised’ marine invertebrates. They dominate bivalve aquaculture production in many regions and wild populations are increasingly becoming established, with potential to displace native species and modify habitats and ecosystems. While some fishing communities may benefit from wild populations, there is now a tension between the continued production of Pacific oysters and risk to biodiversity, which is of particular concern within protected sites. The issue of the Pacific oyster therefore locates at the intersection between two policy areas: one concerning the conservation of protected habitats, the other relating to livelihoods and the socio-economics of coastal aquaculture and fishing communities. To help provide an informed basis for management decisions, we first summarise evidence for ecological impacts of wild Pacific oysters in representative coastal habitats. At local scales, it is clear that establishment of Pacific oysters can significantly alter diversity, community structure and ecosystem processes, with effects varying among habitats and locations and with the density of oysters. Less evidence is available to evaluate regional-scale impacts. A range of management measures have been applied to mitigate negative impacts of wild Pacific oysters and we develop recommendations which are consistent with the scientific evidence and believe compatible with multiple interests. We conclude that all stakeholders must engage in regional decision making to help minimise negative environmental impacts, and promote sustainable industry development.

Potential of Abalone Shells as Vectors for Exotic Oyster Species in the Abalone Farming Practice in China

Pacific abalone Haliotis discus hannai (Ino, 1953) aquaculture is a thriving and prosperous industry in China, producing more than 110,000 metric tons in 2013. In recent years, Fujian in the southern region of China has become the chief abalone farming center, accounting for 85% of the total Pacific abalone yield. The practice of transferring abalone to northern regions to oversummer emerged because of challenges in Fujian, such as fouling, high temperature stress, and unexpected extreme weather events. From the view of ecology and conservation biology, however, the potential ecological risks of this practice should be considered as the abalone shells could act as vectors of exotic organisms. In this study, oyster samples from the shells of live, farmed abalones were collected in Fujian in southern and Rongcheng in northern China. The oysters were identified using a recently developed molecular method. In addition, the fouling oysters on Pacific abalone transferred to the northern region were monitored in a field trial. Survivorship and growth performance of the fouling oysters on the transferred abalones were determined through investigation of digital images taken at 2-wk intervals during the oversummering period. Results of the molecular analysis showed that fouling oysters collected from southern and northern regions are Crassostrea angulata and Crassostrea gigas, respectively. The field trial demonstrated that approximately half of the C. angulata, from the southern region, were still alive after a 6-mo oversummering period in the northern region. Findings from this study have important implications for aquaculture, the management and monitoring of cultured populations of Pacific abalone, and the conservation of wild oyster species in China.

Stock assessment for eastern oyster seed production and field grow-out in Louisiana

There is little information on the performance of oyster populations from Louisiana estuaries limiting the ability to choose stocks for hatchery seed production and field grow-out. The objectives of this study were therefore to compare the mortality, growth, dermo (Perkinsus marinus) infection intensity and condition index of the progeny of wild oysters collected from three Louisiana estuaries differing in salinity regime and oysters specifically selected for dermo resistance. Progeny were deployed in cages in the field, along a salinity gradient in coastal Louisiana. Overall, salinity and temperature had major impacts on the mortality, growth, dermo infection intensity and condition index of oysters of all four stocks and a few differences between stocks could be shown at some sites. At the lowest salinity site, the progeny of wild oysters from Sister Lake, a low salinity estuarine lake, had the lowest mortality suggesting enhanced tolerance to low salinity conditions compared to the other stocks. At the highest salinity site, the progeny of wild oysters from Lake Calcasieu, a high salinity estuarine lake, had the lowest mortality during summer concomitant with increasing dermo infection intensities suggesting a better resistance to dermo disease compared to the other wild stocks and confirming an earlier finding. This initial result suggests that the stocks used are genetically differentiated with respect to low salinity tolerance as well as dermo-related mortality at high salinity and that stock selection for aquaculture grow-out or restoration effort will benefit from being site-specific and dependent on the dominant environmental conditions. Statement of relevanceAssessment of eastern oyster stocks in Louisiana or other Gulf of Mexico estuaries for seed production and field grow-out is lacking.

A Parallel Population Genomic and Hydrodynamic Approach to Fishery Management of Highly-Dispersive Marine Invertebrates: The Case of the Fijian Black-Lip Pearl Oyster Pinctada margaritifera.

Fishery management and conservation of marine species increasingly relies on genetic data to delineate biologically relevant stock boundaries. Unfortunately for high gene flow species which may display low, but statistically significant population structure, there is no clear consensus on the level of differentiation required to resolve distinct stocks. The use of fine-scale neutral and adaptive variation, considered together with environmental data can offer additional insights to this problem. Genome-wide genetic data (4,123 SNPs), together with an independent hydrodynamic particle dispersal model were used to inform farm and fishery management in the Fijian black-lip pearl oyster Pinctada margaritifera, where comprehensive fishery management is lacking, and the sustainability of exploitation uncertain. Weak fine-scale patterns of population structure were detected, indicative of broad-scale panmixia among wild oysters, while a hatchery-sourced farmed population exhibited a higher degree of genetic divergence (Fst = 0.0850–0.102). This hatchery-produced population had also experienced a bottleneck (NeLD = 5.1; 95% C.I. = [5.1–5.3]); compared to infinite NeLD estimates for all wild oysters. Simulation of larval transport pathways confirmed the existence of broad-scale mixture by surface ocean currents, correlating well with fine-scale patterns of population structuring. Fst outlier tests failed to detect large numbers of loci supportive of selection, with 2–5 directional outlier SNPs identified (average Fst = 0.116). The lack of biologically significant population genetic structure, absence of evidence for local adaptation and larval dispersal simulation, all indicate the existence of a single genetic stock of P. margaritifera in the Fiji Islands. This approach using independent genomic and oceanographic tools has allowed fundamental insights into stock structure in this species, with transferability to other highly-dispersive marine taxa for their conservation and management.

Ostreid herpesvirus in wild oysters from the Huelva coast (SW Spain).

This is the first report of ostreid herpesvirus 1 microvariant (OsHV-1 µVar) infecting natural oyster beds located in Huelva (SW Spain). The virus was detected in 3 oyster species present in the intertidal zone: Crassostrea gigas (Thunberg, 1793), C. angulata (Lamarck, 1819) and, for the first time, in Ostrea stentina Payraudeau, 1826. Oysters were identified by a specific polymerase chain reaction (PCR) and posterior restriction fragment length polymorphism (RFLP) analysis based on cytochrome oxidase I (COI) mitochondrial DNA. Results confirmed that C. angulata still remains the dominant oyster population in SW Spain despite the introduction of C. gigas for cultivation in the late 1970s, and its subsequent naturalization. C. angulata shows a higher haplotype diversity than C. gigas. OsHV-1 virus was detected by PCR with C2/C6 pair primers. Posterior RFLP analyses with the restriction enzyme MfeI were done in order to reveal the OsHV-1 µVar. Detections were confirmed by DNA sequencing, and infections were evidenced by in situ hybridization in C. gigas, C. angulata and O. stentina samples. The prevalence was similar among the 3 oyster species but varied between sampling locations, being higher in areas with greater harvesting activities. OsHV-1 µVar accounted for 93% of all OsHV-1 detected.

Seasonal variation of sperm quality in Pacific oyster (Crassostrea gigas)

Seasonal changes of sperm quality which can affect sperm biological parameters throughout the breeding period, have been little studied in mollusc species. Controlling gamete quality would aid the management of gametes in hatcheries and the development of selection programs. The aim of the present study was to describe the changes in sperm quality of wild Pacific oysters through the spawning season by comparing sperm parameters at the beginning (May), middle (July) and end (October) of this period using a panel of bio-descriptors. These parameters were studied over the 2014 breeding season based on shed sperm collected after serotonin injection of wild breeders. A significantly higher percentage of motile sperm was observed at the end of the spawning season (+78% relative to the value observed at the beginning) althought a lower total number of spermatozoa was collected (−59%). The mean condition index of oysters, however, was no different between the three sampling dates. For intratesticular sperm, the increase of the percentage of motile sperm and Velocity of the Average Path (VAP) in relation to time post activation was not significantly different among sperm sampling periods, suggesting that the kinetic of the sperm maturation process was similar. Furthermore, the mean VAP observed on shed sperm did not change through the spawning season. The sub-continuous gametogenesis of Pacific oyster can help to explain why only limited consequences of sperm ageing are observed in this species. Furthermore, the effects of sperm ageing may depend on the annual reproductive pattern of Pacific oyster. Statement of relevanceThis study showed the effect of sperm ageing on sperm quality parameters. This knowledge is useful for aquaculture and would support the recent trends of mollusc farming, allowing a better management of the gametes in hatchery.

Responses to thermal and salinity stress in wild and farmed Pacific oysters Crassostrea gigas

The Pacific oyster Crassostrea gigas was introduced from Japan to many countries in the world for oyster farming, resulting in the establishment of wild populations in intertidal zones and resource competition with local faunas. This study examined physiological responses of wild oysters and farmed oysters to thermal (15°C, 25°C, 37°C and 44°C) and salinity stress (39, 50 and 60ppt). The wild oysters produced more 72kDa heat shock proteins when the temperature increased from 15°C to 25°C and 37°C and the salinity increased from 39 to 50 and 60ppt. However, the amount of 69kDa heat shock protein was similar between farmed and wild oysters when the temperature increased from 15°C to the sublethal temperature 37°C, but it was lower in wild oysters than in farmed oysters when the temperature increased from 15°C to the lethal temperature 44°C. In the tissues, wild oysters used more glycogen to promote metabolic activities by increasing the level of AEC (adenylate energy charge). The results suggest that farmed oysters might have limited ability to cope with heat stress due to low energy reserve and glycolysis activity for HSP synthesis. This study provides experimental evidence on differential responses between wild and farmed oysters to temperature and salinity changes, leading to a better understanding on the pattern of distribution for invading oyster species in the marine environment and the adaptation of marine invertebrates to the threat of climate change.

Multiple stressors associated with acid sulfate soil effluent influence mud crab Scylla serrata predation on Sydney rock oysters Saccostrea glomerata

Studies of long-term exposure to multiple stressors on predator–prey interactions are necessary to determine the effect of coastal degradation on organisms that have had generations to adapt and acclimate to change. In New South Wales, Australia, a natural gradient of multiple stressors produced by acid sulfate soil effluent was used to determine the impact of exposure to multiple stressors on predator–prey dynamics between mud crabs Scylla serrata and Sydney rock oysters Saccostrea glomerata. Wild oysters were collected from two polluted and two reference sites that varied in their distance away from a flood gate that acted as a point source of water with low salinity, low pH and low alkalinity. Oysters from sites affected by multiple stressors and those from reference sites were offered to mud crabs in 48-h laboratory no-choice feeding trials. Oysters from affected sites had lower mortality than those from a reference site that was farthest from the source of polluted water. Linear models containing distance from flood gate best explained oyster mortality. Differences in rates of mortality were due to the decreased time crabs spent foraging on affected oysters. Long-term exposure to acid sulfate soil effluent alters trophic dynamics between predators and prey, which may have consequences for coastal food webs.

Ostreid herpesvirus type 1 genomic diversity in wild populations of Pacific oyster Crassostrea gigas from Italian coasts

Ostreid herpesvirus 1 (OsHV-1) is a significant pathogen affecting the young Pacific oyster Crassostrea gigas, worldwide. A new variant, OsHV-1 μVar, has been associated with recurrent mortality events in Europe since 2008. Epidemiological data collection is key for global risk assessment; however little is known about health status and genotypes present in European wild oyster beds. Most studies to date have involved only cultivated individuals during mortality events, and reported low genotype diversity. With this study, conducted along the Italian coasts, we investigated for the first time the presence of OsHV-1 in European natural oyster beds. Analysis of three genomic regions revealed the presence of at least nine different genotypes, including two variants close to the OsHV-1 reference, known since the early 1990s but with no European record reported since 2010, and highlights relevant genotype diversity in natural environment. Phylogenetic analysis distinguished two distinct clusters and geographical distribution of genotypes, with the exception of a variant very closely related to the μVar, which appeared the single genotype present in all the Adriatic sites. Interestingly, these wild symptom free populations could represent, in Europe, an accessible alternative to the import of OsHV-1-resistant oyster strains from the East Pacific, the native area of C. gigas, avoiding the high-risk of non-native marine species and new pathogen introductions.

Restocking Natural Beds with Remote-Set Disease-Resistant Oysters in Connecticut: A Field Trial

ABSTRACT Oyster production in Connecticut historically has had large fluctuations due to two major factors: disease epizootics caused by a protozoan parasite multinucleate sphere X (Haplosporidium nelsoni), and long periods without successful natural sets. A field trial was performed to investigate whether the remote set of oysters can be used to restock natural beds during mortalities caused by disease epizootics and lack of recruitment due to periods without sets. Disease-resistant oysters were remote set in a hatchery and placed either in or without biodegradable nets on a natural bed. Aged, clean cultch was used as the control, and the growth, mortality, predation, fouling, and prevalence of disease were monitored for two growing seasons. The oysters grew to market size (3 inches, 76.2 mm) in 15 mo. Predation, due mainly to Atlantic oyster drills Urosalpinx cinerea, and overgrowth of oysters caused a mortality of 72% in the oyster seed during the first growing season. More abundant wild oysters set bu...

The mismatch of bioaccumulated trace metals (Cu, Pb and Zn) in field and transplanted oysters (Saccostrea glomerata) to ambient surficial sediments and suspended particulate matter in a highly urbanised estuary (Sydney estuary, Australia).

A significant correlation between sedimentary metals, particularly the 'bio-available' fraction, and bioaccumulated metal concentrations in the native Sydney rock oyster (Saccostrea glomerata) tissues has been successfully demonstrated previously for Cu and Zn in a number of estuaries in New South Wales, Australia. However, this relationship has been difficult to establish in a highly modified estuary (Sydney estuary, Australia) where metal contamination is of greatest concern and where a significant relationship would be most useful for environmental monitoring. The use of the Sydney rock oyster as a biomonitoring tool for metal contamination was assessed in the present study by investigating relationships between metals attached to sediments and suspended particulate matter (SPM) to bioaccumulated concentrations in oyster tissues. Surficial sediments (both total and fine-fraction), SPM and wild oysters were collected over 3years from three embayments (Chowder Bay, Mosman Bay and Iron Cove) with each embayment representing a different physiographic region of Sydney estuary. In addition, a transplant experiment of farmed oysters was conducted in the same embayments for 3months. No relationship was observed between sediments or SPM metals (Cu, Pb and Zn) to tissue of wild oysters; however, significant relationship was observed against transplanted oysters. The mismatch between wild and farmed, transplanted oysters is perplexing and indicates that wild oysters are unsuitable to be used as a biomonitoring tool due to the involvement of unknown complex factors while transplanted oysters hold strong potential.

Genetic inviability is a major driver of type III survivorship in experimental families of a highly fecund marine bivalve.

The offspring of most highly fecund marine fish and shellfish suffer substantial mortality early in the life cycle, complicating prediction of recruitment and fisheries management. Early mortality has long been attributed to environmental factors and almost never to genetic sources. Previous work on a variety of marine bivalve species uncovered substantial genetic inviability among the offspring of inbred crosses, suggesting a large load of early-acting deleterious recessive mutations. However, genetic inviability of randomly bred offspring has not been addressed. Here, genome-wide surveys reveal widespread, genotype-dependent mortality in randomly bred, full-sib progenies of wild-caught Pacific oysters (Crassostrea gigas). Using gene-mapping methods, we infer that 11-19 detrimental alleles per family render 97.9-99.8% of progeny inviable. The variable genomic positions of viability loci among families imply a surprisingly large load of partially dominant or additive detrimental mutations in wild adult oysters. Although caution is required in interpreting the relevance of experimental results for natural field environments, we argue that the observed genetic inviability corresponds with type III survivorship, which is characteristic of both hatchery and field environments and that our results, therefore, suggest the need for additional experiments under the near-natural conditions of mesocosms. We explore the population genetic implications of our results, calculating a detrimental mutation rate that is comparable to that estimated for conifers and other highly fecund perennial plants. Genetic inviability ought to be considered as a potential major source of low and variable recruitment in highly fecund marine animals.

Hyperspectral remote sensing of wild oyster reefs

The invasion of the wild oyster Crassostrea gigas along the western European Atlantic coast has generated changes in the structure and functioning of intertidal ecosystems. Considered as an invasive species and a trophic competitor of the cultivated conspecific oyster, it is now seen as a resource by oyster farmers following recurrent mass summer mortalities of oyster spat since 2008. Spatial distribution maps of wild oyster reefs are required by local authorities to help define management strategies. In this work, visible-near infrared (VNIR) hyperspectral and multispectral remote sensing was investigated to map two contrasted intertidal reef structures: clusters of vertical oysters building three-dimensional dense reefs in muddy areas and oysters growing horizontally creating large flat reefs in rocky areas. A spectral library, collected in situ for various conditions with an ASD spectroradiometer, was used to run Spectral Angle Mapper classifications on airborne data obtained with an HySpex sensor (160 spectral bands) and SPOT satellite HRG multispectral data (3 spectral bands). With HySpex spectral/spatial resolution, horizontal oysters in the rocky area were correctly classified but the detection was less efficient for vertical oysters in muddy areas. Poor results were obtained with the multispectral image and from spatially or spectrally degraded HySpex data, it was clear that the spectral resolution was more important than the spatial resolution. In fact, there was a systematic mud deposition on shells of vertical oyster reefs explaining the misclassification of 30% of pixels recognized as mud or microphytobenthos. Spatial distribution maps of oyster reefs were coupled with in situ biomass measurements to illustrate the interest of a remote sensing product to provide stock estimations of wild oyster reefs to be exploited by oyster producers. This work highlights the interest of developing remote sensing techniques for aquaculture applications in coastal areas.

Past and present platinum contamination of a major European fluvial–estuarine system: Insights from river sediments and estuarine oysters

Platinum Group Metals (PGM) are modern, technologically relevant elements for which (i) the anthropogenic cycle has outcompeted the natural cycles and (ii) environmental behavior, fate and impact are still widely unknown. Stripping voltammetry was used for accurate determinations of platinum (Pt) in historical records of river sediments and estuarine oysters from the Gironde fluvial–estuarine continuum (SW France) comprising the Lot River. Sediment cores from the Lot River, dated from 1952 to 2001, showed past Pt contamination due to former industrial (smelter) activities in the Lot River watershed. These samples revealed the phasing-out of a historical Pt contamination with Pt/Th (Thorium) values of 11×10−5±0.79×10−5 for the deepest part of the core which is clearly greater than the regional geochemical background value (Pt/Th ~2.2×10−5±0.68×10−5). Wild oyster samples from the mouth of the Gironde Estuary collected from 1981 to 2013 showed Pt concentrations ranging from 0.80±0.01pmol.g−1 to 3.10±0.14pmol.g−1. Oyster samples have recorded the phasing-out of the smelter-related historical industrial Pt contamination and empirical modeling suggests the recent rise of a new source of Pt to the system. Temporal variations of Pt in oysters attributed to this recent source reflect the exponential increase of Pt demand for car catalytic converters, pointing towards the increasing importance of this emerging source to the aquatic system. Estuarine oysters prove to be suitable bioindicators for Pt contamination providing sensitive monitoring of emission variations over time. Furthermore, oysters may bioconcentrate Pt (bioconcentration factor, BCF ~103) and transfer this metal contamination to the higher food chain. These findings highlight the need for a deeper understanding of environmental Pt contamination, processes and possible adverse effects to biota.

The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France

Zinc stable isotopes measurements by MC-ICP-MS, validated by laboratory intercalibrations, were performed on wild oysters, suspended particles and filtered river/estuarine water samples to provide new constraints for the use of Zn isotopes as environmental tracers. The samples selected were representative of the long range (400km) transport of metal (Zn, Cd, etc.) contamination from former Zn-refining activities at Decazeville (i.e. δ66Zn>1‰) and its phasing out, recorded during 30years in wild oysters from the Gironde Estuary mouth (RNO/ROCCH sample bank). The study also addresses additional anthropogenic sources (urban and viticulture) and focuses on geochemical reactivity of Zn in the turbidity gradient and the maximum turbidity zone (MTZ) of the fluvial Gironde Estuary. In this area, dissolved Zn showed a strong removal onto suspended particulate matter (SPM) and progressive enrichment in heavy isotopes with increasing SPM concentrations varying from δ66Zn=−0.02‰ at 2mg/L to +0.90‰ at 1310mg/L. These signatures were attributed to kinetically driven adsorption due to strongly increasing sorption sites in the turbidity gradient and MTZ of the estuary. Oysters from the estuary mouth, contaminated sediments from the Lot River and SPM entering the estuary showed parallel historical evolutions (1979–2010) for Zn/Cd ratios but not for δ66Zn values. Oysters had signatures varying from δ66Zn=1.43‰ in 1983 to 1.18‰ in 2010 and were offset by δ66Zn=0.6–0.7‰ compared to past (1988) and present SPM from the salinity gradient. Isotopic signatures in river-borne particles entering the Gironde Estuary under contrasting freshwater discharge regimes during 2003–2011 showed similar values (δ66Zn≈0.35±0.03‰; 1SD, n=15), i.e. they were neither related to former metal refining activities at least for the past decade nor clearly affected by other anthropogenic sources. Therefore, the Zn isotopic signatures in Gironde oysters reflect the geochemical reactivity of Zn in the estuary rather than signatures of past metallurgical contaminations in the watershed as recorded in contaminated river sediments. The study also shows that the isotopic composition of Zn is strongly fractionated by its geochemical reactivity in the Gironde Estuary, representative of meso–macrotidal estuarine systems.

Recovery of wild Pacific oyster, Crassostrea gigas in terms of reproduction and gametogenesis two-years after the Hebei Spirit Oil Spill Accident off the West Coast of Korea

The Hebei Spirit oil spill in December 2007 at Taean off the west coast of Korea was the largest oil tanker accident in Korea. However, the impact of the spill on physiology of benthic animals remains largely unknown. Two-years after the accident, we compared reproductive effort and annual gametogenesis of the wild Pacific oyster Crassostrea gigas, residing at oil spill site with a control oyster population in Incheon Bay, North-West coast of Korea. Results showed that the oyster sampled from the oil spill site showed a significantly higher (279.0mgstandard animal−1, P<0.05) growth by tissue dry weight to that of the control population (228.0mgstandard animal−1, P<0.05). Histology revealed that there was no significant difference in the annual gametogenic pattern between the two populations, and most of the females of both populations spawned between August and September. During spawning season, egg mass of oysters determined using enzyme-linked immunosorbant assay (ELISA) in the oil spill area was significantly higher (136.3mgstandard animal−1, P<0.05) than the control population (120.5mgstandard animal−1, P<0.05). The tissue protein level in the oysters at the contaminated area was significantly higher (102.6mgstandard animal−1, P<0.05) than the level measured from the control oysters (81.4mgstandard animal−1, P<0.05). The observed better biological performances of oysters at the contaminated site suggested their recovery of the physiological status to normal level after two years of the oil spill accident.

Survey of Pathologies inCrassostrea gasar(Adanson, 1757) Oysters from Cultured and Wild Populations in the São Francisco Estuary, Sergipe, Northeast Brazil

The production of native oysters Crassostrea rhizophorae and Crassostrea gasar is expanding in northeastern Brazil, where reports of bivalve pathology are scarce. Recently, Perkinsus marinus was detected for the first time infecting C. rhizophorae in the state of Paraiba, in northeastern Brazil. Thus, more information on factors affecting the health of oysters is needed, especially concerning the pathogens listed by the World Organisation for Animal Health (OIE). The current study evaluated the health status of wild and cultured C. gasar mangrove oysters from the estuary of the Rio Sao Francisco, Sergipe state, northeastern Brazil. Results show that C. gasar oysters cultivated in the Rio Sao Francisco estuary had a greater prevalence of diseases and pathogens than oysters from a natural population in the same estuary, including maladie du pied (shell disease), Rickettsia—like organisms in gills, Steinhausia sp. oocyte infections, and Polydora sp. valve infestations. Of the two OIE notifiable diseases investigated, perkinsosis occurred at variable levels of prevalence that were always greater among cultured oysters (50.8%) than wild oysters (25.8%), and the intensity was predominantly low, suggesting low mortality impact. Bonamiosis was not detected.