Showing papers on "Oyster published in 1988"

In situ measurement of respiratory metabolism and nitrogen fluxes at the interface of oyster beds

Abstract: Nitrogen and oxygen fluxes were measured in situ during monthly dark enclosure experiments on oyster beds. The incubations were performed on undisturbed sediment with its endofauna, on 10 oysters Crassostrea gigas isolated from the substratum, and on 10 oysters associated with the sediment, to assess the impact of oyster farming on the environment. Ammonia was released by the sediment following a seasonal pattern, s ammonia excretion increased in spring (3.21 pm01 g-' h-') and autumn (2.5 to 6.7 pm01 g-' h-'), compared to low winter values (0.28 pm01 g-' h-'), in accordance with changes in temperature and oxygen consumption (0.14 and 1.3 mg O2 g-' h-' in winter and summer respectively). Some nitrate production was observed, suggesting occasional nitrification. Primary amine exchanges were rather erratic, whereas urea seems to play an important role seasonally as a nitrogenous end-product, in relation to a lower condition index at the end of the winter A sirnp!e budge? sf sediment-water exchanges, calculated on a m-' basis (e. g. 2 kg oysters m-'), indicates that over the year the oysters' contribution to the fluxes averages 37 and 40 % for ammonia and urea release respectively, and 26 O/ O for oxygen uptake. However, the actual contribution of oysters to the exchanges at the water-sediment interface rarely fits the expected values from potential estimates. Oxygen consumption, ammonia release and nitrate absorption of the association of oysters with sediment are mainly depressed, except durlng winter and early spring when respiration is stimulated.

Field validation of a habitat suitability index model for the American oyster

Abstract: A habitat suitability index (HSI) model, developed for the American oyster,Crassostrea virginica, along the Gulf of Mexico, was field tested on 38 0.1-ha reef and nonreef sites in Galveston Bay, Texas. The HSI depends upon six (HSI1) or, optionally, eight (HSI2) variables. The six variables are percent of bottom covered with suitable cultch (V1), mean summer water salinity (V2), mean abundance of living oysters (V3) (a gregarious settling factor), historic mean water salinity (V4), frequency of killing floods (V5), and substrate firmness (V6). The optional variables are the abundance of the southern oyster drillThais haemostoma (V7), and the intensity of the oyster pathogenPerkinsus marinus (V8). The HSI values were lowest at high and low salinity sites and highest at intermediate-salinity sites. To validate the model, the hypothesis that the output of the HSI model was correlated with oyster density was therefore tested. A significant correlation was found between HSI1 and oyster density (Kendall Tau Beta correlation coefficient, τ=0.674, p<0.001, n=38); however, a statistical independence problem exists with the above test, that is, oyster density is both the independent standard for the test and a variable in the model. A regression model was constructed to test the relationship between log-transformed oyster density values (dependent variable) and the other variables of the model (independent variables). Most variation (r2=0.72, r=0.85) in the log-transformed density values were explained by a regression model that contained V2, V4, V5, V6, V7, and V8 as independent variables. The regression model was useful in constructing a modified HSI model (MHSI). A significant correlation (τ=0.674, p<0.05, n=10) was found between MHSI1 values and oyster densities from reefs closed to harvesting. The MHSI improves upon the original model by (i) simplifying the model structure, (ii) removing the requirement to measure V3, (iii) accounting better for the negative effects of high salinity, disease, and parasitism upon oysters, and (iv) eliminating the statistical independence problem by dropping V3 from the model. The MHSI should be tested against a new, independently-collected data set.

Combined effects of temperature and salinity on fed and starved larvae of the European flat oyster Ostrea edulis

Abstract: Combined effects of temperature, salinity and nutrition on larval survival and growth of the European oyster Ostrea edulis L. were studied over a period of seven days in the laboratory. Larvae were obtained in August 1985 from oysters reared under field conditions on the Mediterranean coast. Four temperatures (15°, 20°, 25°, 30°C), four salinities (20, 25, 30, 35‰ S) and two levels of nutrition (fed or unfed) were used in the experimental design; the fed larvae received a mixed algal diet of Isochrysis galbana and Chaetoceros calcitrans forma pumilum at a concentration of 100 cells per microlitre. Larvae survived over a wide range of temperature and salinity; statistical analysis indicated that nutrition had the greatest effect on the development of O. edulis larvae, explaining 85 to 88% of the variance in growth. Compared with temperature, the effect of salinity was very slight, usually statistically insignificant. The combined effects of temperature and nutrition produced the only significant interaction. Growth of starved larvae seems to be independent of both temperature and salinity within the range of levels tested.

The geomorphic development of wreck shoal, a subtidal oyster reef of the James River, Virginia

Abstract: Wreck Shoal is a subtidal oyster reef located in the James River estuary, Virginia. This estuary has moved upstream and landward in response to rising sea level. The recent geomorphic history of Wreck Shoal is analyzed based on bathymetric records from the 1850’s to the 1980’s. The data indicate that the shallow oyster reef areas have lost elevation in the last 130 yr. This is attributed to intense harvesting activity during the last century. The late Holocene evolution of Wreck Shoal is developed based on the results of sub-bottom profiles and coring data. These suggest that the Wreck Shoal oyster reef has developed on the ridge and swale topography of a point-bar formed during the late Pleistocene epoch. Contemporary biodeposition processes on Wreck Shoal are evaluated. The results indicate that sediments of biogenic origin (fecal and shell material) potentially accumulate at rates in excess of 50 cm 100 years−1. A model for subtidal oyster reef development is proposed that accounts for sea level rise, biodeposition, and the harvesting activity of man. The model is verified with field observations of reef elevation and radiocarbon dates of oyster shell material. The implications of these results are that oyster reefs should be considered a renewable natural resource, and therefore managed accordingly in concert with the oysters.

Bonamiasis: A Model Study of Diseases in Marine Molluscs

Abstract: Research on bonamiasis, an epizootic disease of the edible oyster Ostrea edu/is caused by the protozoan Bonamia ostreae, is discussed in relation to oyster fanning, research technology, epizootiology, and management. Morphological and infectious characteristics of the parasite are described. Recent progress in isolation and purification of the parasite have permitted investigations into host defense mechanisms, parasite infectivity, and the development of a mol1usc-pathogen mode!.

A LONG~ERM STUDY OF "MICROCELL" DISEASE IN OYSTERS WITH A DESCRIPTION OF A NEW GENUS, MIKROCYTOS (Go No), AND TWO NEW SPECIES, MIKROCYTOS MACKINI (SP. No) AND MIKROCYTOS ROUGHLEYI (SP. No)

Abstract: ABSTRACf Continuing long-tenn studies of oyster disease problems have been carried out over the past 26 years using field monitoring, gross, histologic, and ultrastructural pathologic methods. A microorganism of uncertain taxonomy was discovered in 1963 by J. G. Mackin in association with lesions and mortalities of Japanese oysters, Crassostrea gigas, from Denman Island, Britisll Columbia, Canada. Mackin coined the tenn "microcell" for this organism and described the parasite as 1-3,.m cells with small nuclei which occurred within vesicular connective tissue cells adjacent to characteristic abscesses. We are describing this organism as Mikrot:ytos mac1cini sp. n. in his honor. Similar appearing organisms were seen by the senior author in flat oysters, Ostrea edulis, from Milford, Connecticut, on three different occasions: 1) in oysters transferred from Milford. Connecticut, to Chincoteague Bay. Virginia; 2) in oysters transferred from Milford to Elkhorn Slough, California; and 3) in oysters trans­ ferred from Milford to Oxford, Maryland, and held in recirculated sea water. The causative organism in these three episodes has been sIlown by electron microscopy to be Bonamiaostreae, the parasite that was implicated in recent mortalities in flat oysters in Europe. Similar organisms have also been seen in Olympia oysters, Ostrea lurida, from Oregon and in the Sydney rock oyster, Saccostrea commercialis, from Australia. Presence of the organism in the latter species is associsted with the winter mortalities originally described by T. C. Roughley, and the pathogen is here described as Mikrot:ytos roughleyi (sp. n.) in his honor. "Microcell" type parasites of oysters are associated with a complex of diseases that occur in Japanese oyster, Crassostrea gigas; Sydney rock oyster, Sac­ costrea commercialis; flat oyster, Ostrea edulis; and Olympia oyster, O. lunda, in North America, Europe, and Australia. Severity of disease varies from an acute, highly lethal form to a chronic, seasonally recurring disease that does not produce massive mortalities. The etiologic agents are small, morphologically simple, and very difficult to com­ pare and characterize taxonomically at light micro­ scope levels of resolution. Associated lesions vary according to species affected and provide some of the differences that may be used to distinguish the agents involved. The complexity of this group and the difficulties involved in achieving an understand­ ing regarding whether we are dealing with one or a group of organisms and how they were transferred to new locations, the long time span involved in

Environmental Influence on Activities and Foreign-Particle Binding by Hemocytes of American Oysters, Crassostrea virginica

Abstract: American oysters (Crassostrea virginia) from an estuarine and an oceanic habitat were held in the laboratory under various temperature and salinity regimes. After a month, their hemocytes were withdrawn from the adductor muscle and measured in vitro for time to spreading (TTS), time to spreading after an acute salinity increase (TTS + 12), rate of locomotion (ROL), and binding of fluorescent microspheres (beads). Bead binding was compared with binding of bacteria (Vibrio parahemolyticus). TTS and TTS + 12 measurements were negatively correlated with temperature whereas ROL and bead binding measurements were positively correlated with temperature. An acute rise in salinity (TTS + 12) increased the time required for hemocyte spreading. Spreading was faster, however, at higher salinities for acclimated oysters from both habitats. This finding contradicted previous results for estuarine oyster hemocytes and emphasized the role of environmental history and/or seasonality on hemocyte responses. Oceanic oysters ...

Rehabilitation Of The Troubled Oyster Industry Of The Lower Chesapeake Bay

Abstract: After 1885 Virginia's lower Chesapeake Bay system produced more oysters per year than any other area in the United States and remained predominant until 1960. Since then she has surrendered supremacy as annual harvests of her troubled oyster industry have steadily declined. Numerous factors were responsible for the tremendous productivity of the lower Bay's oyster beds; a number have been involved in its decline. Natural events, such as the catastrophic epizootics of the early 1960's, continuing disease and predation, increased salinities of drought years and great freshets of tropical storms have contributed significantly to the reduction. Pollution and other man-related alterations have been involved also. Additionally, high costs of money and operations, risk-reduction efforts, loss of competitive position and markets, and, in some problem areas, lack of certain important scientific knowledge have contributed. Persistent overfishing by public harvesters, lack of application of best-management practices and recent technological advances, reduction of planting efforts by private growers, and resistance to remedial improvements by industry and public managers are the major factors causing the continuing decline! Nevertheless, restoration of oyster production in Virginia (and Maryland) waters can be accomplished by applying a combination of currently available scientific knowledge and technological skills and by making or enabling sociological, economic and political improvements.

A habitat suitability index model for suspended tray culture of the Pacific oyster, Crassostrea gigas Thunberg

Abstract: . A habitat suitability index (HSI) model for suspended tray culture of the Pacific oyster, Crassostrea gigas Thunberg, was constructed from existing information in the literature on oyster-environment relationships. In the model, biophysical data are used to rate aquaculture potential of coastal areas on a scale from 0.0 to 1·0. where 1·0 represents optimal conditions for growth and survival and 0·0 represents totally unsuitable habitat conditions. The model was tested with environmental, growth (increase in shell height) and secondary production (g· 100 oysters−1 day−1) data collected over a 14-month period for two age-classes of oysters transplanted to 10 locations along the coast of British Columbia. Canada. Regressions of HSI values calculated from entire study environmental data against oyster growth and secondary production were highly significant for both age-classes. Environmental data subsets representing short sampling programmers (1–3 months) resulted in HSI values significantly correlated to oyster growth, provided that some sampling occurred during periods of high food availability. HSI modeling techniques have potential application in site selection and coastal management of aquaculture.

Unusually high intake and fecal output of cadmium, and fecal output of other trace elements in New Zealand adults consuming dredge oysters. [Tiostrea lutaria]

Abstract: The concentration of cadmium in New Zealand dredge oyster Tiostrea lutaria (commonly known as a Bluff oyster) is sufficiently high so that the ingestion of just one oyster can more than double a normal daily intake of cadmium for a New Zealand adult. A survey of 75 adults associated with the oyster fishing industry was carried out before and at the end of the oyster season. Preseason intakes (from dietary history questionnaires and from 3-day fecal collections) of cadmium, selenium, zinc, copper, and manganese were normal for a New Zealand adult not consuming Bluff oysters. The subjects were classified according to their reported average oyster consumption during the 6 months of the oyster fishing season; the subjects who consumed more oysters were more likely to smoke cigarettes. The end-season fecal output of cadmium confirmed the reported average oyster intakes: Category I (0-5 oysters/week): 15 +/- 8 (mean +/- SD) ..mu..g Cd/day; Category II (6-23 oysters/week): 84 +/- 134 ..mu..g Cd/day; Category III (24-71 oysters/week): 129 +/- 144 ..mu..g Cd/day; Category IV (72 + oysters/week): 233 +/- 185 ..mu..g Cd/day. The fecal output of selenium as well was increased by the consumption of many oysters but the fecal outputs of zinc,more » copper, manganese were not. Using fecal cadmium excretion to predict dietary cadmium intake, 8-15% of the subjects in this study were identified as having an intake of cadmium which has been associated with an increased prevalence of tubular proteinuria.« less

Effect of parasitism by the pyramidellid gastropod Boonea impressa on the net productivity of oysters (Crassostrea virginica).

Abstract: The effect of an ectoparasitic gastropod, Boonea (= Odostomia) impressa , on the energy bidget of its host, the American oyster, Crassostrea virginica , was examined. A model was developed from laboratory and field data, as well as from equations developed by Powell and Stanton (1985) . The model predicted that net productivity by large (7 cm length) oysters parasitized by 10 and 30 large (6 mm length) snails would be reduced by 21% and 63%, respectively. In contrast, net productivity in small (3 cm length) oysters would be reduced 25% by only 3 snails. Small oysters would have a negative energy balance when parasitized by 10 snails. The predicted reduction in growth was compared with measured growth in small and large oysters parasitized at abundances typical of Texas oyster reefs. Control oysters (no parasites) gained more shell weight than parasitized oysters. In four-week experiments conducted during the spring and fall, small control oysters gained 86% and 75% more weight than highly parasitized oysters. Large control oysters had 29% and 88% more shell deposition. Snail parasitism produced 75% mortality in small, highly parasitized oysters in the summer. In typical field populations in Texas bays, a minimal estimate of 4–12% of the energy otherwise available to the oyster for growth and reproduction is consumed by Boonea impressa .

Speciation of butyltin compounds in oyster samples

Abstract: Experimental instrumentation for the speciation of butyltin compounds by hydride generation and gas chromatography-quartz furnace atomic absorption spectrometry is described. Evaluation of a number of extraction methods revealed that simple acid leaching of oyster samples gave adequate recoveries. The levels of each butyltin species in oyster flesh and gill are reported together with the tentative identification of a mixed methylbutyltin compound.

Invitro binding of parasites (Bonamia ostreae) and latex particles by hemocytes of susceptible and insusceptible oysters

Abstract: Bonamia ostreae is a protozoan parasite that has caused severe losses in the flat oyster (Ostrea edulis) industry in Europe The cupped oyster (Crassostrea gigas), recently introduced and cultured in Europe, is not infected by the disease In vitro tests were conducted to determine whether there was a difference in the ability of hemocytes from each species to recognize and bind inert foreign particles (fluorescent latex beads) and purified, infective B ostreae The results indicated no difference in their ability to bind latex beads, but C gigas were able to bind more B ostreae than were O edulis The relative inability of the O edulis hemocytes to recognize the parasite is discussed as a possible factor in flat oyster susceptibility