Showing papers on "Oyster published in 1992"

The Trophic Consequences of Oyster Stock Rehabilitation in Chesapeake Bay

Abstract: There is mounting speculation that overharvesting of oyster stocks (Crassostrea virginica) in Chesapeake Bay may be a factor contributing to the decline in water quality and shifts in the dominance of species inhabiting the estuary. The trophic consequences of increasing the oyster population may be addressed using a simple quasi-equilibrium, mass action model of the exchanges transpiring in the Chesapeake mesohaline ecosystem. According to output from the model, increasing oyster abundance would decrease phytoplankton productivity as well as stocks of pelagic microbes, ctenophores, medusae, and particulate organic carbon. Recently acquired field data on phytoplankton productivity, bacterioplankton, and labile organic carbon in the vicinity of rafted oyster aquaculture support model predictions. The model also indicates that more oysters should increase benthic primary production, fish stocks, and mesozooplankton densities. Hence, augmenting the oyster community by restoring beds or introducing raft culture represents a potentially significant adjunct to the goal of mitigating eutrophication through curtailment of nutrient inputs. *** DIRECT SUPPORT *** A01BY059 00005

Natural Sources and Properties of Chemical Inducers Mediating Settlement of Oyster Larvae: A Re-examination.

Abstract: Live adult oysters and biofilms were separated experimentally as potential sources of waterborne chem- ical inducers of settlement in oyster larvae (Crassostrea virginica). Bacteria films growing on external shell surfaces were removed by mechanical agitation and chemical ox- idation. This technique removed >99% of the viable bac- teria without disrupting the normal production of metab- olites by the oysters, measured as the weight-specific pro- duction, of ammonium and dissolved organic carbon (DOC). In comparison to the external biofilms, microfloral abundances in oyster tissues and on internal shell surfaces were numerically insignificant (~0.1% of total). Biofilms growing on aged shell material without the living oyster served as a source of bacteria metabolites. Metabolites released in particle-free, artificial seawater (ASW) medium by biofilms and by adult oysters (lacking biofilms) were tested for effects on larval behavior, relative to ASW (con- trol). The larvae were exposed to solutions in a Plexiglas@ microcosm (30 ml capacity). Locomotor-y responses were video recorded under infrared illumination, then subjected to computer-video motion analysis. Oyster larvae re- sponded similarly to waterborne substances released both from adult conspecifics and from biofilms. The responses included: larvae rapidly swimming vertically downward in the water column; their horizontal swimming speed then slowed while their rate of turning increased, which

Persistence of Vibrio vulnificus in tissues of Gulf Coast oysters, Crassostrea virginica, exposed to seawater disinfected with UV light.

Abstract: Vibrio vulnificus is an estuarine bacterium which can cause opportunistic infections in humans consuming raw Gulf Coast oysters, Crassostrea virginica. Although V. vulnificus is known as a ubiquitous organism in the Gulf of Mexico, its ecological relationship with C. virginica has not been adequately defined. The objective of the present study was to test the hypothesis that V. vulnificus is a persistent microbial flora of oysters and unamenable to traditional methods of controlled purification, such as UV light depuration. Experimental depuration systems consisted of aquaria containing temperature-controlled seawater treated with UV light and 0.2-microns-pore-size filtration. V. vulnificus was enumerated in seawater, oyster shell biofilms, homogenates of whole oyster meats, and tissues including the hemolymph, digestive region, gills, mantle, and adductor muscle. Results showed that depuration systems conducted at temperatures greater than 23 degrees C caused V. vulnificus counts to increase in oysters, especially in the hemolymph, adductor muscle, and mantle. Throughout the process, depuration water contained high concentrations of V. vulnificus, indicating that the disinfection properties of UV radiation and 0.2-microns-pore-size filtration were less than the rate at which V. vulnificus was released into seawater. Approximately 10(5) to 10(6) V. vulnificus organisms were released from each oyster per hour, with 0.05 to 35% originating from shell surfaces. These surfaces contained greater than 10(3) V. vulnificus organisms per cm2. In contrast, when depuration seawater was maintained at 15 degrees C, V. vulnificus was not detected in seawater and multiplication in oyster tissues was inhibited.

Seasonal incidence of Vibrio vulnificus in the Great Bay estuary of New Hampshire and Maine.

Abstract: Vibrio vulnificus, a normal bacterial inhabitant of estuaries, is of concern because it can be a potent human pathogen, causing septicemia, wound infections, and gastrointestinal disease in susceptible hosts. From May 1989 through December 1990, oysters and/or water were obtained from six areas in the Great Bay estuary of New Hampshire and Maine. Water was also sampled from three freshwater sites that lead into these areas. V. vulnificus was first detected in the estuary in early July and remained present through September. V. vulnificus was isolated routinely during this period from oysters and water of the Squamscott, Piscataqua, and Oyster Rivers but was only isolated twice from the oysters or water of the Great Bay itself. This study determined that there was a strong correlation (by analysis of variance) between temperature, salinity, and the presence of V. vulnificus in water and oysters. However, other unidentified factors appear to influence its presence in certain areas of the estuary.

Associations between freshwater inflows and oyster productivity in Apalachicola Bay, Florida

Abstract: Increased and varied demands for consumptive water uses on the Apalachicola-Chattahoochee-Flint River system threaten to reduce freshwater inflows to the Apalachicola estuary and thus may affect estuarine productivity. To investigate how freshwater inflows are associated with productive estuarine conditions, Apalachicola Bay oyster data from 1960–84 and river flows were analysed with linear regression models. Lag periods were incorporated into the analyses to examine the potential effects of various flow magnitudes and durations on different oyster life history stage. Oysters reach a harvestable size in 2 years in this region. Low flows were positively correlated with oyster catch per unit effort (C.P.U.E.) 2 years later, i.e. years with lower minimum flows were followed 2 years later by poor oyster productivity. A possible mechanism behind this association is that lower minimum flows result in higher estuarine salinities, permitting predation by marine species on newly settled spat, and thus reducing harvestable oyster population sizes 2 years later. High flows of short duration (⩽ 30 days) were not significantly correlated with oyster C.P.U.E. for the same year or any time lag period. Oyster landings were low, however, in those years in which flows exceeded 30 000 cfs for 100 days or more, suggesting sustained high flows were detrimental to the same year's harvestable oyster population. Experiments that investigate possible mechanistic causes of these associations are needed to more fully understand the potential impacts of future water allocation decisions.

Seasonal variations in condition, reproductive activity and biochemical composition of the flat oyster, Ostrea edulis, from San Cibran (Galicia, Spain)

Abstract: The influence of environmental parameters (temperature, salinity and available food) on the condition, reproductive activity and biochemical composition of a native population of Ostrea edulis L. in San Cibran (Galicia, Spain) was studied between September 1988 and December 1989. Histological preparations of gonads showed that gametogenesis started when temperature was at its lowest in winter. The water temperature in San Cibran never fell low enough to interrupt it. Gametogenesis proceeded slowly and spawning took place in May–June, although the predicted time of ripening was early March. Salinity in San Cibran was relatively stable throughout the year; it did not seem to have any influence on gametogenesis. Available food appeared to be a very important factor in controlling gonad growth, once gametogenesis was initiated. The major concentration of suspended organic particulate matter was present in the spring at the time of rapid gonadal maturation. Only one spawning period was observed. Larvae were released when the food in the water was high. Seasonal changes in the main biochemical components of this oyster were determined for a standard individual. Lipids and carbohydrates presented a similar time-course whereas proteins were constant. When food was abundant, energy reserves were built up. Spawning produced a decrease in biochemical constituent levels, and recovery coincided with the phytoplankton bloom. The stored reserves, mainly lipids, were used to overcome a state of energy imbalance in late autumn associated with low food availability. Results show this oyster to be an opportunist organism which concentrates its reproductive effort during a short period of favourable conditions and which is directly dependent on nutritive availability in the environment.

Agglutinin activity in Pacific oyster (Crassostrea gigas) hemolymph following in vivo Vibrio anguillarum challenge

Abstract: Hemolymph from the Pacific oyster (Crassostrea gigas) contains lectins that agglutinate horse (Gigalin E) and human (Gigalin H) erythrocytes. The gigalins also agglutinate bacteria, including Vibrio anguillarum, and were adsorbed from oyster hemolymph at different temperatures by living, heat-killed, and freeze-dried V. anguillarum cells. Baseline activities of the two gigalins were established by measuring their activities in oyster hemolymph over a period of 4 years. A normal distribution of Gigalin H activity (mean titer 139) was found, whereas the distribution of Gigalin E activity in the same samples was skew (mean titer 512). No covariance was observed between the two agglutinin activities. Increased lectin activity above this baseline was found in oysters exposed for varying time intervals to V. anguillarum at different seasons and temperatures over a period of 2 years. Such exposure resulted in an increase in activity (titer) of four- to nine-fold for Gigalin E and three- to seven-fold for Gigalin H when compared with controls, and in augmentation in the hemolymph of a protein with the same electrophoretic mobility as affinity-purified oyster lectins (gigalins). Challenge with either living or heat-killed bacteria resulted in a significant increase of Gigalin E activity, whereas results for Gigalin H were variable. Oysters challenged with bacteria were observed to filter normally with open shells during the experiments. Also, no increase was found in hemolymph calcium that could indicate anoxia following bacterial challenge (0.49 +/- 0.004 mg mL-1) compared to unexposed oysters (0.50 +/- 0.001 mg mL-1). Increase in the concentration of free amino acids in oyster hemolymph was observed following exposure to bacteria (15.05 mM) and anaerobiosis (13.51 mM) compared to controls (9.06 mM), and changes (in mol %) of individual amino acids differed considerably between hemolymph from animals challenged with bacteria and animals kept anaerobic. The augmented lectin activity in oyster hemolymph, following in vivo exposure to increased bacteria in the seawater, suggests their involvement in enhancing bacterial clearance and defense in the oyster.

Effects of temporary starvation on the survival, and on subsequent feeding and growth, of oyster (Crassostrea gigas) larvae

Abstract: Larvae of oysters, Crassostrea gigas, were maintained without food for 1 to 8 d after fertilization, and fed daily thereafter. There was little difference in survival and growth between controls and larvae kept without food for 2 or 3 d. Survival and growth rates were depressed in larvae starved for 4 or 5 d. For larvae starved for 6 to 8 d, survival was negligible or nil; even those larvae which survived the starvation period died later in the presence of food, apparently because of impaired digestion. Therefore, food availability in the first few days after spawning appears to be of paramount importance to the successful recruitment of Pacific oysters.

Alterations in cytometric characteristics of hemocytes from the American oyster Crassostrea virginica exposed to a polycyclic aromatic hydrocarbon (PAH) contaminated environment

Abstract: The effects of residing in a polycyclic aromatic hydrocarbon (PAH) contaminated environment on the cytometric characteristics of hemocytes from the American oyster Crassostrea virginica (collected from the Rappahannock River, Virginia, USA in Spring 1991) were analyzed using a multichannel Coulter counter (10000 hemocytes oyster-1). The percentage and relative volume of small-sized hemocytes (>2.5 to 5.1 μm) was higher (P 6.2 to 10 μm) was observed in the HP-oysters. Maintaining the RR-oysters at the HP site for 8 wk induced statistically significant increases in the number and relative volume contribution of the >2.5 to 5.1 μm hemocytes and sharp decreases in the occurrence and relative volume of >6.2 to 13 μm cells (P 2.5 to 5.1 μm) showed a significant decrease over time as compared to the baseline values. On the other hand, the relative number of >6.2 to 13 μm hemocytes increased sharply within 8 wk (P<0.001). This indicates that these changes are both inducible and reversible and, at least in part, due to exposure to the ER-sediment. Based on these studies, oyster hemocyte cytometric characteristics could be developed as a sensitive biomarker of exposure to PAH.

A comparison of methods for calculating condition index in eastern oysters Crassostrea virginica (Gmelin, 1791)

Abstract: A number of techniques have been reported to estimate condition index in oysters and other bivalve molluscs. We report and compare condition index, estimated by three different methods, for oysters collected from a single reef in the James River, Virginia over a four week period in the summer of 1987. Two indices express condition as a ratio of dry meat weight to shell cavity volume, but differ in methods of estimating shell cavity volume. A third method expresses condition as a ratio of dry meat weight to dry shell weight. Within the size range 36-96 mm length there is no effect of size on index values. We suggest that indices based on both shell cavity vqlume and shell weight have utility in reflecting biochemical or nutritive status; however, intercalibration is difficult and comparisons of data from different authors and locations limited in scope.

Different salinity tolerance mechanisms in Atlantic and Chesapeake Bay conspecific oysters : glycine betaine and amino acid pool variations

Abstract: Crassostrea virginica (Gmelin) collected in 1989 from several sites within the Chesapeake Bay have narrower salinity tolerances than conspecific oysters collected in 1989 from several Atlantic coast sites (Georgia to Cape Cod). The basis of this physiological difference appears to be the biochemical mechanisms that control cellular osmolality following salinity stress. When adapted to the same salinity, the amino acid pools of both gill and adductor muscles of Atlantic oysters are larger than those of Bay oysters and different in composition. The Atlantic oyster tissues rely primarily on taurine for salinity tolerance, while the Bay oyster tissues have relatively less taurine, depending instead upon alanine, glycine and proline to adapt to high salinity. In addition, Atlantic oyster gill and adductor have 10 to 25 times the glycine betaine concentrations of these tissues from Bay oysters, depending upor the salinity of acclimation. The betaine concentration varies with salinity in Atlantic oysters, but does not change in Bay oysters. The results suggest that these biochemical differences are the basis of the narrower salinity tolerance in Bay oysters. The biochemical differences may reflect genetic differences between Bay and Atlantic oysters.

Recruitment and growth of the Eastern oyster, Crassostrea virginica, in North Carolina

Abstract: The effects of location, salinity, and depth on recruitment and growth of the eastern oyster Crassostrea virginica in Pamlico and Core sounds, North Carolina, were investigated from 1988 to 1990. We measured length and density of spat settling on oyster cultch deployed at deep (∼3 m) and shallow (∼1 m) depths at six sites in areas with low salinity and six sites in areas with high salinity. These data were compared with similar data taken at some of these sites by the North Carolina Division of Marine Fisheries since 1981 as part of their cultch planting program. Recruitment was generally greater in the high salinity sites, compared to the low salinity sites. Recruitment was less at shallow depths compared to deeper depths. In all three years the highest recruitment occurred in August and September, corresponding to the months of maximum water temperature. Recruitment was highly variable in space and time, but appeared to diminish from 1988 to 1990. Recruitment was reduced by sedimentation and a variety of sessile organisms. All sites appeared to have a similar potential for growth.

Evidence for Ammonia as a Natural Cue for Recruitment of Oyster Larvae to Oyster Beds in a Georgia Salt Marsh

Abstract: Competent veliger larvae of the oysters Crassostrea virginica and C. gigas exhibited settlement behavior when exposed to ammonia (NH3). The threshold for this response decreased with increasing larval age. The response of veligers to adult-conditioned seawater was correlated with the concentration of NH3 in the seawater. Although the concentrations of NH3 found in marsh water flowing over oyster beds on Sapelo Island, Georgia, were never high enough to elicit settlement behavior from oyster larvae, the concentrations found near the substrate were sufficient to induce settlement behavior in older larvae of C. virginica. In addition, dilution occurs during sampling in the field and may lead one to underestimate, by a factor of 1.7 to 3.5, the actual concentration of NH3 associated with surfaces. In conclusion, NH3 may be an important environmental cue triggering settlement behavior of larval oysters, which, along with other substrate cues, leads to cementation and metamorphosis.

Effects of temperature abuse on survival of Vibrio vulnificus in oysters.

Abstract: Opaque and translucent morphotypes of a TnphoA-containing strain of Vibrio vulnificus were fed to oysters, which were subsequently stored at temperatures ranging from 0.5 to 22 degrees C for 10 days. Samples of oysters were homogenized and plated at intervals to determine the cell density of V. vulnificus and total aerobic population of bacteria present. At all temperatures, the numbers of V. vulnificus (both morphotypes) declined over the 10-day study period. The same observation was made with a lower inoculum of V. vulnificus. Identical experiments with shucked oysters showed a more rapid decrease in V. vulnificus. Identical experiments with shucked oysters showed a more rapid decrease in V. vulnificus to levels below limits of detection. Little change in the total bacterial counts was observed in shellstock oysters at any of the test temperatures, whereas incubation at the higher temperatures (17 and 22 degrees C) resulted in large increases in total counts in shucked oysters. These data suggest that temperature abuse of oysters may not be a factor in increasing the public health risk of V. vulnificus through raw oyster consumption. However, the data also suggest that even with proper storage, indigenous levels of V. vulnificus may remain sufficiently higher in shellstock oysters to produce infection in compromised hosts.

Localisation and characterization of acid phosphate activity in Bonamia ostreae (Ascetospora), an intrahemocytic protozoan parasite of the flat oyster Ostrea edulis (Bivalvia)

Abstract: Acid phosphatase activity was cytochemically detected at the ultrastructural level in the protozoan Bonamia ostreae, an intrahemocytic parasite of the flat oyster Ostrea edulis. Lead nitrate was used as capture agent for phosphate liberated during the hydrolysis of the subtrate (cytidine 5' monophosphate). Lead phosphate precipiation, indicative of enzyme activity, was located in membrane-bound organelles corresponding to the cytoplasmic inclusions known as dense bodies . Acid phosphatase activity level and sodium L-tartrate inhibition were measured spectrophotometrically from a purified parasite suspension. The possible involvement of this enzyme in intracellular survival of B. ostrea is discussed.

Ecology of Vibrio vulnificus in Galveston Bay oysters, suspended particulate matter, sediment and seawater: detection by monoclonal antibody - immunoassay - most probable number procedures.

Abstract: Oysters, suspended particulate matter (SPM), sediment and seawater samples were collected from West Galveston Bay, Texas over a 16-month period and analyzed for the presence ofVibrio vulnificus, a naturally-occurring human marine pathogen. Detection and enumeration ofV. vulnificus was performed using a species-specific monoclonal antibody (mAb FRBT37) in an enzyme immunoassay (EIA)-most probable number (MPN) procedure capable of detecting as few as 2000 target organisms.V. vulnificus was not detected in seawater, oyster or SPM samples during the cold weather months, but was detected at low levels in several sediment samples during this time period. Increased levels of the organism were first observed in early spring in the sediment, and then in SPM and oysters. The major increase inV. vulnificus occurred only after the seawater temperature had increased above 20°C and the winter-spring rainfall had lowered the salinity below 16‰. The highestV. vulnificus levels at each site were associated with suspended particulate matter. These results are consistent with the hypothesis that (1)V. vulnificus over-winters in a floc zone present at the sediment-water interface, (2) is resuspended into the water column in early spring following changes in climatic conditions, (3) colonizes the surfaces of zooplankton which are also blooming during early spring and (4) are ingested by oysters during their normal feeding process.