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Showing papers on "Oyster published in 1998"


Journal ArticleDOI
TL;DR: In this paper, a survey of natural reefs in the Neuse River estuary, North Carolina, USA showed that the percentage of oysters found dead during a survey in May 1993 was significantly higher at 6m (92? 10%) than at 3-m (28? 9%) water depth.
Abstract: Oysters are ecosystem engineers that create biogenic reef habitat important to estuarine biodiversity, benthic-pelagic coupling, and fishery production. Prevailing ex- planations for the dramatic decline of eastern oysters (Crassostrea virginica) during the last century overlook ecosystem complexity by ignoring interactions among multiple en- vironmental disturbances. To explain oyster loss, we tested whether (1) mortality of oysters on natural oyster reefs varies with water depth (3 m vs. 6 m), (2) harvesting by oyster dredges reduces the height of oyster reefs, and (3) bottom-water hypoxia/anoxia and re- duction in reef height through fishery disturbance interact to enhance mortality of oysters in the Neuse River estuary, North Carolina, USA. The percentage of oysters found dead (mean ? 1 SD) during a survey of natural reefs in May 1993 was significantly greater at 6-m (92 ? 10%) than at 3-m (28 ? 9%) water depth. Less than one season's worth of oyster dredging reduced the height of restored oyster reefs by -30%. During stratification of the water column in summer, oxygen depletion near the seafloor at 6 m caused mass mortality of oysters, other invertebrates, and fishes on short, deep experimental reefs, while oysters and other reef associates elevated into the surface layer by sufficient reef height or by location in shallow water survived. Highly mobile blue crabs (Callinectes sapidus) abandoned burrows located in hypoxic/anoxic bottom waters but remained alive in shallow water. Our results indicate that interaction of reef habitat degradation (height reduction) through fishery disturbance and extended bottom-water hypoxia/anoxia caused the pattern of oyster mortality observed on natural reefs and influences the abundance and distribution of fish and invertebrate species that utilize this temperate reef habitat. Interactions among environmental disturbances imply a need for the integrative approaches of ecosystem man- agement to restore and sustain estuarine habitat.

435 citations


Journal ArticleDOI
TL;DR: The temperature and salinity parameters associated with waters and oysters linked to food-borne Vibrio vulnificus infections and the findings suggest that the hazard of V. vulnimiasis in Gulf Coast oysters is not limited to brief periods of unusual abundance of the virus or to environmental conditions that are unusual to Gulf Coast estuaries.
Abstract: This study investigated the temperature and salinity parameters associated with waters and oysters linked to food-borne Vibrio vulnificus infections. V. vulnificus was enumerated in oysters collected at three northern Gulf Coast sites and two Atlantic Coast sites from July 1994 through September 1995. Two of these sites, Black Bay, La., and Apalachicola Bay, Fla., are the source of the majority of the oysters implicated in V. vulnificus cases. Oysters in all Gulf Coast sites exhibited a similar seasonal distribution of V. vulnificus: a consistently large number (median concentration, 2,300 organisms [most probable number] per g of oyster meat) from May through October followed by a gradual reduction during November and December to 10(3) per g) were typically found in oysters from intermediate salinities (5 to 25 ppt). Smaller V. vulnificus numbers (< 10(2) per g) were found at salinities above 28 ppt, typical of Atlantic Coast sites. On 11 occasions oysters were sampled at times and locations near the source of oysters implicated in 13 V. vulnificus cases; the V. vulnificus levels and environmental parameters associated with these samples were consistent with those of other study samples collected from the Gulf Coast from April through November. These findings suggest that the hazard of V. vulnificus infection is not limited to brief periods of unusual abundance of V. vulnificus in Gulf Coast oysters or to environmental conditions that are unusual to Gulf Coast estuaries.

278 citations


Journal ArticleDOI
TL;DR: Control measures should focus on the increased risk from oysters harvested from the Gulf of Mexico during warm months as well as education about host susceptibility factors.
Abstract: Vibrio vulnificus infections are highly lethal and associated with consumption of raw shellfish and exposure of wounds to seawater. V. vulnificus infections were reported to the Centers for Disease Control and Prevention from 23 states. For primary septicemia infections, oyster trace-backs were performed and water temperature data obtained at harvesting sites. Between 1988 and 1996, 422 infections were reported; 45% were wound infections, 43% primary septicemia, 5% gastroenteritis, and 7% from undetermined exposure. Eighty-six percent of patients were male, and 96% with primary septicemia consumed raw oysters. Sixty-one percent with primary septicemia died; underlying liver disease was associated with fatal outcome. All trace-backs with complete information implicated oysters harvested in the Gulf of Mexico; 89% were harvested in water >22 degrees C, the mean annual temperature at the harvesting sites (P < .0001). Control measures should focus on the increased risk from oysters harvested from the Gulf of Mexico during warm months as well as education about host susceptibility factors.

258 citations


Journal ArticleDOI
TL;DR: It is demonstrated that an organism's response to habitat patchiness is species-specific, and that for a given species, the response is further modified by animal density and body size, which further highlights the importance of scale-dependent responses by mobile organisms to complex benthic habitats.

198 citations


Journal ArticleDOI
TL;DR: The ability of BLIS-(bacteriocin-like inhibitory substance)-producing Aeromonas media, strain A199, to act as a probiotic was assessed on the host animal, Crassostrea gigas, to prevent death of the oyster larvae when challenged with Vibrio tubiashii.

189 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined water temperatures, rather than air temperatures, for five stations located in areas affected by the recent epizootics and found that increasing winter water temperatures have been important in the recent outbreak of P. marinusin oysters.
Abstract: From its initial discovery in the Gulf of Mexico in the late 1940s until 1990,Perkinsus marinus, the parasite responsible for Dermo disease in the eastern oyster,Crassostrea virginica, was rarely found north of Chesapeake Bay. In 1990–92, an apparent range extension of the parasite led to epizootic outbreaks of the disease over a 500 km range north of Chesapeake Bay. One of the hypotheses for the range extension argues that small, undetected numbers of parasites were already present in northern oysters as the result of repeated historical introductions, and that a sharp warming trend in 1990–92 stimulated the disease outbreak. This argument was based on trends in air temperature. The present study examined this hypothesis by analysing water temperatures, rather than air temperatures, for five stations located in areas affected by the recent epizootics. At all five stations, there was a strong increasing trend in winter sea-surface temperature (SST) between 1986 and 1991. At four of the five stations, there was a smaller increasing trend in winter temperatures after 1960. There were no consistent or obvious trends in summer (August) temperatures. In Delaware Bay, which has a 40 year history of monitoring for oyster diseases, occasional findings ofP. marinusin oysters were correlated with warming episodes that were especially notable in the winter (February) record. Empirical orthogonal function (EOF) analysis showed that winter temperatures varied consistently at the stations examined and were associated with variations inP. marinusprevalence. Associations using EOF analysis with August temperatures were much weaker. The SST record is consistent with the hypothesis that increasing winter water temperatures have been important in the recent outbreak ofP. marinusepizootics in the north-eastern U.S.A.

176 citations


Journal ArticleDOI
TL;DR: Investigation of recurrent outbreaks of a disease leading to mass mortalities in an oyster hatchery located in western Japan found the probability that broodstock could be the source and route of transmission of this pathogen is high, and detection of V. splendidus II from broodstock, especially in the gonad of a few breeders, suggests the probability of this disease being transmitted.
Abstract: Recurrent outbreaks of a disease leading to mass mortalities in an oyster (Crassostrea gigas) hatchery located in western Japan were investigated. The disease occurred regularly in 2- to 8-d-old larvae and has been experimentally controlled in the hatchery by treating the larval rearing water with streptomycin, without ascertaining the etiological agent. The signs of the disease and the course of infection resembled bacillary necrosis reported in oysters and other bivalve molluscs in the USA and Europe. Quantitative and qualitative examinations of the bacterial flora of hatchery samples including source water, broodstock, larval feed and larvae revealed a very high total bacterial load and presumptive vibrios in diseased larvae. Further, the bacterial profile revealed that Vibrio spp. constituted approximately 60 to 95% of the bacteria isolated from infected larvae and most isolates were identified as V. splendidus biovar II and V. harveyi, suggesting their possible role in the disease. However, experimental challenges proved the pathogenicity of V. splendidus II. Several isolates of V. splendidus II from infected larvae were highly pathogenic, producing 100% mortality at levels of 10(5) cfu ml-1 in 24 h, while isolates from other sources demonstrated a low degree of virulence. Detection of V. splendidus II from broodstock, especially in the gonad of a few breeders, suggests the probability that broodstock could be the source and route of transmission of this pathogen.

166 citations


Journal ArticleDOI
TL;DR: Near the island of Sylt in the North Sea, importedCrassostrea gigas are grown on oyster trestles, and strong spatfalls occurred in 1991 and 1994 on natural mussel beds, revealing a survival of 66% in spite of a foregoing severe winter.
Abstract: Near the island of Sylt in the North Sea, importedCrassostrea gigas are grown on oyster trestles. These oysters reproduced successfully, and strong spatfalls occurred in 1991 and 1994 on natural mussel beds. The wild oyster population comprised about one million in summer 1995. Resampling in 1996 revealed a survival of 66% in spite of a foregoing severe winter. Oysters growing on mussel beds attained a length of 20 to 50 mm in their 1st year and 50 to 80 mm in their 2nd. Some of the oysters were larger and presumably much older. Abundance was highest (up to 8 oysters m−2) on exposed mussel beds at low tide level, not covered by algae. It is expected thatC. gigas will become a permanent member of the biotic community in the Wadden Sea. It does not invade the vacated niche of the regionally extincted EuropeanOstrea edulis but lives as an epibiont on densily packed mussels.C. gigas here consitutes an r-selected species invading a crowded community in an undisturbed habitat. Through oyster imports, the culture site served as a gateway for 5 other, inadvertently introduced species into this part of the Wadden Sea.

147 citations


Journal ArticleDOI
01 Dec 1998-PALAIOS
TL;DR: Examining delta 18 O and delta 13 C profiles across ligamental increments found in Crassostrea virginica shells from the recent of Terrebonne Bay, Mississippi Delta, and the Pleistocene of Chesapeake Bay, Virginia demonstrates that stable isotope sclerochronology of oyster shells facilitates the interpretation of past estuarine environments and oyster life histories.
Abstract: Sclerochronology, the study of periodic increments in skeletal organisms, can decipher the life history and environmental records preserved in fossil shells. Two powerful tools used in sclerochronologic studies are oxygen and carbon isotope profiles. Although many studies have applied isotopic analyses to marine shells, few have examined isotope profiles from estuaries. One common inhabitant of estuaries is the crassostreine oyster, which preserves a sclerochronologic record on the ligamental area surface in the form of external convex and concave bands. This study examines delta 18 O and delta 13 C profiles across ligamental increments found in Crassostrea virginica shells from the recent of Terrebonne Bay, Mississippi Delta, and the Pleistocene of Chesapeake Bay, Virginia. Results show that Mississippi Delta oysters calcified their shells close to isotopic equilibrium with respect to their environment. Three skeletal breaks found in one oyster formed from cessation of shell growth when summer temperature exceeded 27 degrees C. delta 18 O profiles show that ligamental increments formed annually from varying growth rates through the year, with convex bands forming from rapid growth during spring and summer, and concave bands forming from slower growth during winter. Chesapeake oysters have well-defined ligamental increments with deep concave bands that formed from slow growth and cessation during winter. Skeletal growth breaks suggest that temperature decreased below 10 degrees C during winter. Estimated Pleistocene delta 18 O water values are similar to published recent delta 18 O water values measured at the mouth of the Chesapeake Bay. Two important factors affecting shell delta 13 C values are metabolic changes and occurrence of phytoplankton blooms. Ranges of shell delta 13 C values are similar to delta 13 C dic values measured from water samples, which indicate that oyster delta 13 C profiles are tracking changes in environmental DIC, such as changes related to phytoplankton blooms and benthic respiration. Summer delta 13 C maxima may be related to recovery from gametogenesis. These results demonstrate that stable isotope sclerochronology of oyster shells facilitates the interpretation of past estuarine environments and oyster life histories.

144 citations


Journal ArticleDOI
TL;DR: Analysis of sex ratios in 86 pair‐mated families of the Pacific oyster, Crassostrea gigas Thunberg, revealed significant paternal effects, which corresponded to two types of sires, so that MF are true males and FF are protandric females that are capable of sex change.
Abstract: A unique feature of sex in Crassostrea oysters is the coexistence of protandric sex change, dioecy, and hermaphroditism. To determine whether such a system is genetically controlled, we analyzed sex ratios in 86 pair-mated families of the Pacific oyster, Crassostrea gigas Thunberg. The overall female ratios of one-, two-, and three-year-old oysters were 37%, 55%, and 75%, respectively, suggesting that a significant proportion of oysters matured first as males and changed to females in later years. Detailed analysis of sex ratios in factorial and nested crosses revealed significant paternal effects, which corresponded to two types of sires. No major maternal effects on sex were observed. Major genetic control of sex was further indicated by the distribution of family sex ratios in two to four apparently discreet groups. These and other data from the literature are compatible with a single-locus model of primary sex determination with a dominant male allele (M) and a protandric female allele (F), so that MF are true males and FF are protandric females that are capable of sex change. The rate of sex change of FF individuals may be influenced by secondary genes and/or environmental factors. Strong maternal and weak paternal effects on sexual maturation or time of spawning were also suggested.

139 citations



Journal ArticleDOI
Yamama Naciri-Graven1, A.-G Martin1, Jean-Pierre Baud1, Tristan Renault1, Andre Gerard1 
TL;DR: Good evidence for additivity of the resistance was provided by both the intermediate behaviour of a cross between S85-G2 and the controls and the rapid improvement that was obtained from the first generations, and the selected strains showed a tendency toward higher weights and higher weight variances when compared to controls.

Journal ArticleDOI
TL;DR: The results indicate that the haemocytes of the European flat oyster Ostrea edulis are most stable at high salinity and intermediate temperature (28‰/15°C), and it is evident that at low salinities the adaptive capacity of the cellular processes is reduced to such an extent that theHaemocytes are unable to respond to favourable temperature regimes.
Abstract: The neutral red retention assay was adapted to assess the effects of a matrix of temperature and salinity combinations on haemocytes of the European flat oyster Ostrea edulis (L.). Oysters were collected from a commercially fished site in the western Solent and were acclimated to different temperature and salinity combinations in the laboratory. The results indicate that the haemocytes are most stable at high salinity and intermediate temperature (28‰/15°C). Furthermore it is evident from the data that at low salinities the adaptive capacity of the cellular processes is reduced to such an extent that the haemocytes are unable to respond to favourable temperature regimes. The use of neutral red as a probe to monitor cellular stability is discussed.

Journal ArticleDOI
TL;DR: Veligers removed from brooding T~ostrea chilens~s (Philippi, 1845) experienced -95% mortalities over 3 to 4 d at 16 to 18°C that appeared to be associated with a herpes-like virus, the fifth ostreid species from which herpesviruses have been reported.
Abstract: Veligers removed from brooding T~ostrea chilens~s (Philippi, 1845) experienced -95% mortalities over 3 to 4 d at 16 to 18°C that appeared to be associated with a herpes-like virus. Ultrastructural observations of post-removal veligers showed the presence of early viral replication or putative latent stages at 4 h, all stages of replication at low levels at 24 h, which increased to high levels at 48 h, followed by mortalities at 72 h onwards. Initially, infected interstitial or epithelia1 cells had an enlarged nucleus with a wavy outline in which heterochromatin was marginated. With continued increase in size, nuclei became smooth in outline with reduction or loss of heterochromatin. Capsids with lucent cores (LCC) and empty capsids appeared in the nucleus, often in association with tubular structures -65 nm in diameter that were composed of subunits in a helical configuration that contained a tubular core -35 nm in diameter. Empty capsids and LCC sometimes occurred in paracrystalline arrays. Partial nucleolar disaggregation and encapsidation of dense fibrillar material preceded envelopment entering and de-envelopment leaving the perinuclear cisterna, tegumentation in cytoplasmic vesicles, and egress. Groups of dense cytoplasmic filaments 30 to 35 nm in diameter occurred in some infected cells. Apparently normal cells with a few intranuclear empty capsids and/or LCC at 4 h postremoval may represent latent infections. Replication was not observed in larvae held at 24 to 27'C. but a few cells had enlarged hypochromatic karyolytic nuclei, and 1 to 2 capsids were observed in them, at 48 h. Viral replication was similar to that of ranid herpesvirus 1 (Lucke tumour) infections. This is the fifth ostreid species from which herpesviruses have been reported.

Journal ArticleDOI
TL;DR: Reduction of cholesterol in serum and body organs was found to be dependent on the amount of dietary oyster mushroom administered, and the highest dose induced a decrease in conjugated diene levels in erythrocytes and an increase in the levels of reduced glutathione in the liver.

Journal ArticleDOI
TL;DR: In this paper, the impact of agricultural activity on oysters in Chesapeake Bay tributaries was assessed using a preliminary assessment of pesticide residues in oyster tissues and water samples.

Journal ArticleDOI
TL;DR: Metamorphosis in the Chilean oyster Ostrea chilensis was complete 36 h after release of the larvae, when 100% of the individuals showed edge growth of the dissoconch.
Abstract: Metamorphosis in the Chilean oyster Ostrea chilensis was complete 36 h after release of the larvae, when 100% of the individuals showed edge growth of the dissoconch. The size of the larval shell did not change during metamorphosis, although the total dry weight of the larva decreased considerably. During this period, when the gill ciliature was undeveloped and the oyster therefore unable to feed, energy demands were met by biochemical reserves retained from the larval phase. Proteins contributed the largest quantity of energy to the metamorphosing oyster, 69.3% of the total expended, whereas lipids supplied 24.3% and carbohydrates only 6.4%. The process of metamorphosis consumed 64.5% of the energy reserves held by the pediveliger at the time of release. When metamorphosis was complete, growth began and tissue reserves were replenished, protein and carbohydrate accumulating rapidly early in the juvenile stage.

01 Jan 1998
TL;DR: A general hypothesis will be proposed to explain mortality occurrence of C. gigas summer mortality rates and the relationship among environmental parameters and mortality rates.
Abstract: A comprehensive research program has been developed since 1995 to focus on C. gigas abnormal mortality rates occurring regularly during the summer period in the Bay of Marennes Oleron (France). Several subprojects were carried out including in-vitro ecophysiological studies to asses l) the relationship between reproductive status, scope for growth and mortality, 2) effects of stress temperature on physiological functions. Meanwhile, field studies concerned monitoring surveys of calibrated oyster populations at various emersion time and geographic sites. A database was developed and incorporated into a geographic information system (GIS) to overlay several layers of information and establish relationship among environmental parameters and mortality rates. Concomitantly, seawater quality monitoring surveys were developed to assess carrying capacity and overall environmental conditions affecting oysters. Temperature probes were deployed at the near vicinity of oysters as weIl as a multiparameter probe to record, temperature, salinity, turbidity, pH and 02 concentration on a continuous basis. Moreover, a valvometer recording continuously the oyster valve cl 0 sure activity was deployed near the previous probe to establish relationship with environmental conditions. C. gigas summer mortality rates will be discussed and a general hypothesis will be proposed to explain mortality occurrence.

Journal ArticleDOI
TL;DR: F+ coliphages and their serotypes are promising indicators of human enteric virus contamination in oysters and their harvest waters.

Journal ArticleDOI
TL;DR: In this article, the authors examined the species-specificity and sensitivity of a polymerase chain reaction (PCR)-based assay for Perkinsus marinus and compared its overall performance with the fluid thioglycollate medium (FTM) assay on oyster hemolymph, mantle, and rectum samples.
Abstract: We examined the species-specificity and sensitivity of a polymerase chain reaction (PCR)-based assay for Perkinsus marinus and compared its overall performance with the fluid thioglycollate medium (FTM) assay on oyster (Crassostrea virginica) hemolymph, mantle, and rectum samples. Our results indicated that the PCR-based methodology is species-specific because Perkinsus olseni, Perkinsus atlanticus, and Perkinsus spp. DNAs were not amplified with the PCR primers developed for P. marinus diagnosis. The sensitivity of the PCR method, as assessed through spike/recovery experiments, was established by the detection of as few as 1 cell of P. marinus in 30 mg of oyster tissue. Tissue samples from naturally infected oysters analyzed both by the FTM and PCR assay suggested that the latter was more sensitive for the diagnosis of P. marinus. Positive results for P. marinus infection ranged from 70% to 83% by FTM and from 92% to 100% by PCR, depending on the tissue examined. Therefore, species-specificity and sensitivity of the NTS-based PCR assay validate its use as a tool for assessment of P. marinus in mollusks.

Journal ArticleDOI
TL;DR: Analysis of CL activity after bacterial inoculation indicated that most of the strains could initiate the respiratory burst, however, the intensity of CL was not related to the virulence of the bacteria.


Journal ArticleDOI
TL;DR: Barnacles recruited at higher rates at coastal sites and oysters at estuarine sites, as predicted by the literature, and densities after one month of colonization were lower on open or partially caged tiles than on caging tiles, supporting the hypothesis that predators, like blue and mud crabs, or southern oyster drills, may regulate barnacle abundance.

Journal Article
TL;DR: Circulation patterns observed are favorable for local retendon of larvae in the system and suggest that the Great Wicomico River is a “trap-type” estuary.
Abstract: Natural oyster populations in the Chesapeake Bay have become severely depleted in recent years due to a combination of overfishing, declining water quality, and diseases. Replenishment programs in the form of artificial reefs are currently in effect throughout most of the Chesapeake bay region. Shell Bar reef built in the Great Wicomico River, Virginia in 1996 was supplemented with reproductively active broodstock oysters from Tangier and Pocomoke Sounds. The Great Wicomico River was historically a high spatfall and seed producing river, but production in the river has decreased in recent years. Oyster larval concenttations (in the form of plankton tows), gonad development, and circulation data were collected in the Great Wicomico River throughout the 1997 reproductive season. The broodstock oysters spawned from mid June through mid August, with a peak occurring from mid June through mid July. Larval concentrations were several orders of magnitude higher than the highest reported in the literature for extant reefs in the James River. Larvae were significantly more abundant on the flood tidal stage, suggesting some vertical migration with change in tidal cycle, thus aiding in their retendon in the system. Setdement of larvae on shellstrings and on bottom substrate, was higher than in recent years. The most abundant setdement occurred near the reef and upriver of the reef. Circulation patterns observed are favorable for local retendon of larvae in the system and suggest that the river is a “trap-type” estuary. Reef building, and subsequent transplants of broodstock onto these artificial reefs, can be an effecdve management option provided the circulation patterns of the system are similar in nature to the Great Wicomico (i.e. larvae are “trapped” in the estuary). OYSTER REEF BROODSTOCK ENHANCEMENT IN THE GREAT WICOMICO RIVER, VIRGINIA

Journal ArticleDOI
TL;DR: Results from this study indicate that a morphologically diverse group of phages which infect V. vulnificus is abundant and widely distributed in oysters from estuaries bordering the northeastern Gulf of Mexico.
Abstract: Phages infecting Vibrio vulnificus were abundant (>104 phages g of oyster tissue−1) throughout the year in oysters (Crassostrea virginica) collected from estuaries adjacent to the Gulf of Mexico (Apalachicola Bay, Fla.; Mobile Bay, Ala.; and Black Bay, La.). Estimates of abundance ranged from 101 to 105 phages g of oyster tissue−1 and were dependent on the bacterial strain used to assay the sample. V. vulnificus was near or below detection limits (<0.3 cell g−1) from January through March and was most abundant (103 to 104 cells g−1) during the summer and fall, when phage abundances also tended to be greatest. The phages isolated were specific to strains of V. vulnificus, except for one isolate that caused lysis in a few strains of V. parahaemolyticus. Based on morphological evidence obtained by transmission electron microscopy, the isolates belonged to the Podoviridae, Styloviridae, and Myoviridae, three families of double-stranded DNA phages. One newly described morphotype belonging to the Podoviridae appears to be ubiquitous in Gulf Coast oysters. Isolates of this morphotype have an elongated capsid (mean, 258 nm; standard deviation, 4 nm; n = 35), with some isolates having a relatively broad host range among strains of V. vulnificus. Results from this study indicate that a morphologically diverse group of phages which infect V. vulnificus is abundant and widely distributed in oysters from estuaries bordering the northeastern Gulf of Mexico.

Journal ArticleDOI
TL;DR: Persistent differences between oyster strains from different origins over several generations support a hypothesis that these estuarine populations have experienced long-term genetically-based population differentiation.
Abstract: We analyzed a data set collected over 15 yr, containing growth data from strains of eastern oysters, Crassostrea virginica (Gmelin, 1791), initiated from parent populations in Long Island Sound, Delaware Bay, and lower Chesapeake Bay. The long-term growth data proved to be a powerful tool for examining patterns of growth differentiation among separated populations of C. virginica. The oyster strains had been grown in a common environment in lower Delaware Bay for up to seven generations. We found that the oyster strains with origins in Long Island Sound were significantly larger over several generations than oyster strains from Delaware Bay and Chesapeake Bay. Chesapeake Bay oyster strains were larger than Delaware Bay oyster strains at 1.5 yr old, but Delaware Bay oysters were larger at 2.5 yr. Year-to-year variation in environmental conditions had a strong significant effect on absolute oyster size and the relative sizes of the oyster strains. Persistent differences between oyster strains from different origins over several generations support a hypothesis that these estuarine populations have experienced long-term genetically-based population differentiation. This result is consistent with hypotheses of population differentiation of oysters based on observations of local reproductive timing.

Journal Article
TL;DR: Seilacher et al. as discussed by the authors classified Rudistmorphotypes of bivalve shells into five classes based on their morphology and morphological properties: variances in the early Cenomanian, the mid-Cenomanians, the late Jurassic, the Late Jurassic, and the early Jurassic.
Abstract: s, 28th Intemational Geological Congress, 70. Washington, D.C. Seilacher, A., Matyja, B.A., & Wierzbowski, A. 1985. Oyster Beds: Morphologic response to changing substrate conditions. In: U. Bayer & A. Seilacher (eds), Sedimentary and Evolutionary Cycles. Lecture Notes in Earth Sciences 1,421435. Skelton,P.W&Gili,E. l99l.Palaeoecologicalclassificationofrudistmorphotypes. In:Proceedingsofthe First Intemational Conference on Rudists (Beograd, 1988) Serbian Geological Society Special P ublications 2. 265-287 . smith,A.B.&Paul,C.R.C.1985.variationintheirregularechinoidDiscoidesduńngtheearlyCenomanian. Special Papers in Palaeontology 33,29-37. Stenzel, H.B. 1971. Oysters. 1n: R.C. Moore & C. Teichert (eds), Treatise on Invertebrate Paleontology (N) Mollusca 6, Bivalvia 3, N953-Nlf24.Unwersity of Kansas Printing Service, Lawrence. Taylor, P.D. 1990. Preservation of soft-bodied and other organisms by bioimmuration a review. Palaeontology 33, I-I7 . Thomson, J.M. 1954. The genera of oysters and the Australian species. Australian Journal Marine and F re shw at e r Re s e arch 5, I3f-I68. Todd, J.A. 1993. The bivalve shell as a preservation trap, as illustrated by the Late Jurassic gryphaeid, Deltoideum delta (Smith). Scripta Geologica, Special Issue 2,417433. Trammer, J. 1981. Morphological variation and relative growth in two Jurassic demosponges. Neues J ahrbuc h fiir G e o lo g i e und P altiont ol o gi e, M onat s heft e 1, 5 M4. Waddington, C.H. 1957.The Strategy of Genes.262pp. Allen & Unwin, London.

Journal ArticleDOI
TL;DR: Polychlorinated biphenyls were analysed in two length classes of the oyster Crassostrea angulata and the clam Ruditapes decussatus collected in Sado estuary and Ria Formosa, respectively and showed no significant differences.

Journal Article
TL;DR: A cohort study undertaken using a postal questionnaire showed that illness was associated with having eaten raw oysters and more work is needed to protect oyster beds from contamination and to identify methods to render oysters safe for consumption.
Abstract: Nine members of a party of 24 people who attended a birthday party fell ill with gastroenteritis between one and three days later. A cohort study undertaken using a postal questionnaire showed that illness was associated with having eaten raw oysters. Six of the cases had their stools examined and two were positive for small round structured virus. The illness was brief and none of the cases had consulted a general practitioner. Had the cases not been part of a party they would not have been identified. The oysters were grown in English coastal waters in grade B oyster beds. They underwent depuration treatment before they were sold for consumption. More work is needed to protect oyster beds from contamination and to identify methods to render oysters safe for consumption.

Journal ArticleDOI
TL;DR: Relatively high P. marinus infection levels that persisted throughout the winter in NY oysters compared with VA oysters could reflect constant high salinity in Long Island Sound which favors parasite activity, and also rapid decline in temperature in the fall that may have prevented epizootic oyster mortalities.
Abstract: Perkinsus marinus infection intensity was measured in eastern oysters Crassostrea virginica collected in October and December 1993, and March, May, and July 1994 from 3 U.S. sites: Apalachicola Bay (FL), Chesapeake Bay (VA), and Oyster Bay (NY). Gill, mantle, digestive gland, adductor muscle, hemolymph, and remaining tissue (including gonadal material and rectum) were dissected from 20 oysters from each site at each collection time. Samples were separately diagnosed for P. marinus infections by incubation in Ray's Fluid Thioglycollate Medium (RFTM) and subsequent microscopic quantification of purified enlarged hypnospores. At all sampling times and sites, average P. marinus infection intensity (g wet wt tissue-1 or ml hemolymph-1) was lowest in hemolymph samples, and generally highest in the digestive gland. Perkinsus marinus prevalence was 100% at both FL and NY sites for each of the 5 collection times, and, for the VA site, was less than 100% in only 1 month (May 1994). Seasonal intensity patterns and mean total body burdens differed among the sites. Average body burden was highest in VA during October and progressively declined to a minimum in May. This decline was probably due to mortality of heavily infected oysters and diminution of parasite activity associated with colder temperatures and reduced salinities. Intensities varied little during the months of October and December at both the FL and NY sites. Minimum average intensities were observed in March in FL oysters and May in NY oysters. Relatively high P. marinus infection levels that persisted throughout the winter in NY oysters compared with VA oysters could reflect constant high salinity in Long Island Sound which favors parasite activity, and also rapid decline in temperature in the fall that may have prevented epizootic oyster mortalities.