Effects of the polychlorinated biphenyl Aroclor® 1254 on the American oyster Crassostrea virginica

Young oysters (Crassostrea virginica) were continuously exposed to Aroclor^® 1254, a polychlorinated biphenyl (PCB), in flowing, unfiltered seawater. Growth rate (height and in-water weight) was significantly reduced (=0.05) in oysters exposed to 5 g/l (ppb) for 24 weeks. Growth rate was not affected in oysters exposed to 1 ppb for 30 weeks. Mortality was not significant in exposed and control groups. In oysters exposed to 5 ppb, greatest PCB residue (whole body) was 425 mg/kg (ppm), 85,000x the concentration in the water, and less than 0.3 ppm was retained after 28 weeks depuration in PCB-free water. In oysters exposed to 1 ppb, greatest residue was 101 ppm, 101,000x the concentration in the water, and less than 0.2 ppm was retained after 12 weeks depuration. Examination of oysters exposed to 5 ppb of this PCB for pathogenesis revealed atrophy of digestive diverticular epithelium and degeneration of vesicular connective tissues concomitant with leukocytic infiltration, but tissue recovery seemed excellent after 12 weeks depuration.Registered trademark, Monsanto Company, St. Louis, Missouri, USA. Mention of commercial products or trade names does not constitute endorsement by the Environmental Protection Agency.Contribution No. 146, Gulf Breeze Laboratory.     

Dietary protein levels and growth of the oyster Crassostrea virginica

The diatom Thalassiosira pseudonana in exponential phase or stationary phase and grown under 3 light regimes was fed to 6 groups of juvenile oysters, Crassostrea virginica Gmelin, for a 10-week period. Oysters fed diets from the stationary phase grew more rapidly and had a higher glycogen content than those fed diets from the exponential phase. The stationary phase, cool white-light diet produced the greatest increase in dry weight, shell height and glycogen content of the 6 diets examined. Oysters grew more rapidly when fed diets richer in carbohydrates than proteins.     

Accumulation and depuration of mercury in the American oyster Crassostrea virginica

To study the kinetics of mercury uptake in oysters, adult Crassostrea virginica (Gmelin) were held in seawater containing 10 g mercury/l (ppb) or 100 g mercury/l (ppb), added in the form of mercuric acetate, for 60 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats, using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 140,000 g mercury/kg tissue (ppb) and 28,000 g mercury/kg tissue (ppb) in the 100 ppb and 10 ppb experimental groups, respectively. After this time, concentrations dropped sharply, probably due to spawning. Clearance of mercury from tissue was studied by exposing treated adults to estuarine water (with no additions) for 30 days (100 ppb group) and 160 days (10 ppb group). Tissue concentrations in the 100 ppb mercury environment group declined from 115,000 to 65,000 ppb, and those of the 10 ppb group declined from 18,000 to 15,000 ppb, in 18 days; there-after, no further decline occurred in either group. Oysters accumulated mercury 1,400 times and 2,800 times above the environmental concentrations of 100 and 10 ppb mercury, respectively. Total self-purification was not achieved over a 6 month cleansing period.     

Ultrastructure of the gonad and gametogenesis in the eastern oyster,Crassostrea virginica. I. Ovary and oogenesis

The ultrastructural features of the ovary and oogenesis are described in the eastern oyster,Crassostrea virginica (Gmelin, 1791). The ovary is a diffuse organ consisting of highly branching acini in which oocytes develop. The acini are surrounded by a matrix of vesicular connective tissue (VCT tells) which serves a nutrient storage function. Each acinus is bathed by fluid within a surrounding connective tissue compartment, the hemocoel, which likely serves as a means of transporting nutrients to the oocytes. Oocytes begin growth while positioned near to the inner acinus wall. As differentiation proceeds and they enter the late stages of vitellogenesis, they become stalle-shaped and project into the acinus lumen. Follicle tells are closely associated with oocytes during the early and middle stages of vitellogenesis but they are largely confined to the basal, stalked region of late-stage oocytes. Vitellogenesis occurs through a process of autosynthesis, involving the combined activity of the Golgi complex and rough endoplasmic reticulum, and heterosynthesis in which extraovarian precursors are incorporated into oocytes via receptor-mediated endocytosis involving the basal surface of the oocytes. It is suggested that the follicle tells play some important role during oogenesis but probably are not the major source of yolk precursors. The VCT celas are probably the main source of nutrients for vitellogenesis.     

Ultrastructure of the gonad and gametogenesis in the eastern oyster,Crassostrea virginica. II. Testis and spermatogenesis

The pelagic harpacticoid copepod, Macrosetella gracilis (A. Scott), is found in association with colonies of the nitrogen-fixing (diazotrophic), bloomforming cyanobacterium Trichodesmium spp. in tropical and subtropical waters. M. gracilis is one of the few direct grazers of these often toxic cyanobacteria. Experiments investigating NH ₊ ⁴ regeneration by M. gracilis were conducted in the Caribbean in September 1992 and the Coral Sea, Australia in November 1994. Rates of M. gracilis ingestion of Trichodesmium thiebautii labelled with ¹⁵N₂ measured in the eastern Caribbean indicated that M. gracilis could consume 33 to 45% of total T. thiebautii colony N d^-1 and >100% of new N fixed d^-1. We also measured the release of NH ₊ ⁴ by M. gracilis feeding on T. thiebautii, as well as by non-feeding copepods, using ¹⁵N isotope dilution methods. In non-feeding copepods, rates of NH ₊ ⁴ release increased as numbers of copepods were increased as both copepod numbers and food availability increased. In the presence of T. thiebautii colonies, M. gracilis had an average rate of NH ₊ ⁴ regeneration of 7.7±1.5 nmol N copepod^-1 h^-1 (±SE), which was significantly higher than when food was absent (1.9±0.7 nmol N copepod^-1 h^-1). Rates of M. gracilis excretion were relatively high based on excretion: ingestion ratios, which could be due to having a high-N food source readily available, to sloppy-feeding effects, or as a response to toxins in the cyanobacterium. Incubations of M. gracilis with and without T. erythraeum resulted in significant increases in [NH ₊ ⁴ ] as a function of copepod density only. Ammonium leakage from the cyanobacterium and/or microheterotroph associates was relatively low. M. gracilis, through excretion and possible mechanical breakage of cells while grazing, appears to provide a direct link between atmospherically derived new nitrogen and regenerated NH ₊ ⁴ in the oligotrophic systems where Trichodesmium spp. are abundant.     

Effects of tidal fluctuations of salinity on pericardial fluid composition of the American oyster Crassostrea virginica

Crassostrea virginica Gmelin were subjected to simulated tidal fluctuations of salinity, and the subsequent effects on osmotic and ionic composition of the pericardial fluid, body water and valve movements were investigated. Ambient salinity fluctuation patterns of 20-10-20, 15-10-15 and 10-5-10 were simulated during 24.8-h periods. An additional 10-5-10 S experiment was performed using a dilution water approximating the ionic composition of Mississippi River water with regard to Mg⁺⁺, Ca⁺⁺ and SO ₄ ⁼ , instead of deionized water. Finally the effects of a 2-week diurnal fluctuation pattern between 20 and 10 S were investigated with respect to pericardial fluid composition. Pericardial fluid osmolality, concentrations of Cl^-, Na⁺, Mg⁺⁺, K⁺, Ca⁺⁺ and ninhydrin-positive substances (NPS) were analyzed periodically throughout all experiments. Pericardial fluid osmolality was slightly hyperosmotic as ambient water salinity decreased during a cycle, and then became slightly hyposmotic as ambient salinity increased. In the 2-week experiment, pericardial fluid osmolality tracked ambient seawater closely through Day 5, but became more intermediate between high and low seawater values as the experiment progressed. Similar patterns during fluctuations of salinity were observed for Na⁺, Cl^-, Mg⁺⁺ and Ca⁺⁺. Pericardial fluid K⁺ levels did not track ambient seawater as closely as did other ions. The ionic composition of dilution water had little effect on the osmotic or ionic response of the oyster's pericardial fluid. Pericardial fluid NPS level varied inversely with salinity during the 20-10-20 cycle. During the longterm fluctuation experiment, NPS values gradually decreased over the 2-week period compared to constant salinity control values. Percent body water also varied inversely with ambient salinity. Solute movement accounted for most of the change in pericardial fluid osmolality during the simulated cycles with water movement responsible for 1 to 11%. Water movement contributed more to the change of pericardial fluid osmolality during the decreasing salinity phase than the increasing phase of a given cycle. During 20-10-20 S cycles, oyster valves remained open 56% of the time (n=23). In contrast, when salinity was abruptly changed from 20 to 10 within 5 min, valve closure occurred in 4.8±0.3 min (n=20). Valves did not reopen for 19.3±1.2 h (n=15).     

Selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston and cultured algae

I investigated selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston from Chesapeake Bay and laboratory-cultured algae of different sizes or chemical content. In 15 of 16 experiments with complex natural suspensions as food, small(<150 m) and large (>150 m) larvae selected most strongly for small (2 to 4 m) food particles, but in the presence of a large (>10 m)-cell dinoflagellate bloom, large larvae strongly selected much larger (22 to 30 m) food material (presumably dinoflagellates). When fed simplified mixtures of four cultured algal species (Synechococcus bacillaris, Isochrysis sp., Dunaliella tertiolecta, and Prorocentrum minimum) ranging in size from 1 to 11 m, small larvae preferred 1 m algae while large larvae preferred 11 m algae. In experiments with algal mixtures, and with suspensions of natural particles and added algae, large larvae preferred algal species harvested from exponential-phase cultures over other species from stationary-phase cultures. Larval ingestion rates of the cultured alga Thalassiosira pseudonana were about three times higher for cells with a low carbon:nitrogen ratio (7.2:1) than for high C:N ratio (16.2:1) cells when these cells were offered separately in suspensions of equal concentration. As a result, more algal cells, algal C, and algal N was ingested by larvae fed low C:N cells. However, larvae did not show a significant preference for either type of cell when they were offered in a 1:1 cell mixture. Feeding patterns of C. virginica larvae in natural food suspensions can vary with the composition of these complex suspensions, and ingestion seems dependent not only on the size, but on the growth rate and chemical quality of food particles.     

Interaction of genotype and salinity in larvae of the oyster Crassostrea virginica

Adult Crassostrea virginica were obtained from 4 populations and spawned in the laboratory. The larvae from the within-population crosses and the hybrid crosses were raised at 4 salinities. There were no significant differences in survival of the larvae between the populations. However, one set of hybrids did show overdominance in survival. There were genetic differences between the populations in growth rate, but the expression of the differences depended upon the salinity, i.e, there was significant genotype-environment interaction. There were expressions of nonadditive genetic effects in the hybrid crosses, but the direction and magnitude was dependent upon the salinity. There was as much difference between populations from the same estuary as there was between populations from geographically isolated populations.     

Genetics of larvae and spat growth rate in the oyster Crassostrea virginica

The heritability of oyster (Crassostrea virginica) larval growth rate was estimated to be in the range of 0.25 to 0.50 and a significant part of this genetic variation is of the additive type. Larval growth rate and spat growth rate were found to be highly correlated. These results suggest that a selection program for faster growing larvae and spat would be successful.     

Latitudinal patterns of shell thickness and metabolism in the eastern oyster Crassostrea virginica along the east coast of North America

The goal of this study was to quantify growth and metabolic responses of oysters to increased temperatures like those that will occur due to global warming. Impact of temperature on eastern oyster (Crassostrea virginica) shell growth and metabolism was investigated by sampling 24 sites along the eastern North American seaboard ranging from New Brunswick, Canada, to Florida, USA, in March and August 2013. There was a positive correlation between oyster shell thickness and site temperature. At southern sites, shells were up to 65 % thicker than at the northernmost site, likely due to higher precipitation of CaCO₃ in warmer water. This was supported by laboratory experiments showing that thicker shells were produced in response to temperatures 2, 4, and 6 °C above ambient seawater temperatures (8–14 °C) in Connecticut, USA. Field experiments with oyster respiration were conducted during winter and summer at 13 sites to compare responses to thermal stress with latitude. Respiration rates were much higher during summer than winter, but the combination of summer and winter data fell along the same exponential curve with respect to temperature. At all sites, temperature-specific metabolic rates at elevated temperatures were lower than predicted, indicating significant seasonal acclimatization by C. virginica.     

Mortality of newly metamorphosed eastern oysters (Crassostrea virginica) in mesohaline Chesapeake Bay

 Stocks of eastern oysters, Crassostrea virginica (Gmelin), in mesohaline Chesapeake Bay, USA, exhibit a high degree of inter-annual and spatial variability in recruitment. We found that cumulative oyster spatfall on off-bottom collector plates, measured throughout the summer in 14 years over a span of three decades, was highly positively correlated (r ² = 0.8) with juvenile oyster recruitment on adjacent oyster bars. Total abundances of juvenile oysters on these bars were, however, generally 99.7% lower than predicted from cumulative seasonal larval settlement on collector plates. We propose that although the number of larvae metamorphosing was the key factor in determining the gross annual pattern of recruitment to these mesohaline oyster bars, the actual magnitude of recruitment was governed by post-settlement processes, such as competition for limited resources and predation. We tested the hypothesis that predation may be partly responsible for high post-settlement juvenile oyster mortality. We performed a series of 3-d field investigations over two summers (1989, 1990) at a mesohaline site, employing cages of various mesh sizes (400, 800, 1500 μm) to protect hatchery-reared spat of 0.5 to 4.0 mm shell height. Mortality rates for spat held for 3 d in the estuary (17.8%) were significantly higher (P = 0.0001) for the smallest spat (0.5 to 2.0 mm) compared with those of 2.01 to 4.0 mm (4.2%). In 1990, but not in 1989, enclosure within 400 and 800 μm mesh cages significantly (P = 0.004) increased survival during 3-d deployments (9.4 and 10.1%, respectively) compared with spat unprotected by mesh cages (21.9%). In a series of laboratory predation studies that used the entire community of invertebrates that could penetrate the cages, microscopic juvenile polyclad flatworms, Stylochus ellipticus, were the only organisms that we observed crawling into living oysters and feeding on oyster tissue. Large flatworms (50 to 200 mm²) are known to be important predators on oysters, but this ability of flatworms that were so small (<ca. 5 mm²) and translucent as to be almost invisible without magnification to feed on immediate post-metamorphic oysters has not been documented previously. Our results suggest that the rate of mortality due to predation in mesohaline Chesapeake Bay is much reduced once spat survive for 2 to 3 weeks post-metamorphosis. Thus, it is likely that predation in the 1 to 2 week period immediately after settlement may be a crucial factor in the structuring of eastern oyster populations. Received: 21 December 1998 / Accepted: 2 December 1999     

Accumulation,release and retention of petroleum hydrocarbons by the oyster Crassostrea virginica

Two Crassostrea virginica populations, differing in fat content, were experimentally exposed to a complex petroleum-hydrocarbon fraction. The hydrocarbons in this mixture were accumulated by both groups of oysters, and their lipid content, as well as the concentration of hydrocarbon in the water, were found to affect the rate and extent of accumulation. Hydrocarbons accumulated were rapidly, although incompletely, discharged when the oysters were transferred to an uncontaminated system. Amounts of hydrocarbons discharged and amounts retained after discharge are probably related to the level of contamination. The data can be interpreted as indicating that equilibration and the occurrence of multiple compartments where hydrocarbons can reside are factors involved in the uptake and retention of nonbiogenic hydrocarbons by oysters. The petroleum hydrocarbons contained in the oysters differed from the contaminating oil by displaying a greater aromatic content. In addition, gas-liquid chromatograms of aliphatic fractions of the hydrocarbons in the oysters rapidly showed a degraded appearance; the possibility that the oysters themselves are modifying the oil cannot be excluded.Contribution No. 3098 from the Woods Hole Oceanographic Institution.     

Inducible defenses in the eastern oyster Crassostrea virginica Gmelin in response to the presence of the predatory oyster drill Urosalpinx cinerea Say in Long Island Sound

The response of the eastern oyster C. virginica to the presence of the oyster drill Urosalpinx cinerea was examined from July to September 2011. Several aspects of oyster growth were measured, including wet weight, shell weight, and dorsal shell area for oysters collected near Groton, Connecticut (41.32036 N, −72.06330 W). Wet weight and shell weight growth were significantly higher in the presence of the predator U. cinerea, while tissue weight showed no difference from the control. The control group showed more shell area growth and a much lower ratio of shell weight growth to shell area growth. Differences in shell weight to area ratio indicated that C. virginica dramatically shifted from lateral shell growth to shell thickening in the presence of U. cinerea. This inducible defense has not been previously shown for C. virginica and could play an important role in the predator–prey interaction between these two species.     

Uptake of Kepone from sediment suspensions and subsequent loss by the oyster Crassostrea virginica

Marine Biology - Oysters in laboratory trays received sediment suspensions prepared with sediments contaminated with Kepone** from the James River, Virginia, USA. Oysters in trays were also exposed...     

Factors affecting the accumulation and removal of mercury from tissues of the American oyster Crassostrea virginica

Adult oysters, Crassostrea virginica (Gmelin) were held in seawater containing 10 or 100 ppb mercury in the form of mercuric acetate for 45 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 91,600 and 12,100 ppb in the 100 and 10 ppb mercury groups, respectively. A slight decline in mercury residues in the 100 ppb group during the accumulation period was attributed to spawning. Clearance of mercury from tissues was studied in a constant temperature regime (25°C±2C^o) for 25 days and in a declining temperature regime (25° to 5°C) for 80 days by exposing treated adults to estuarine water with no mercury added. The biological half-life of mercuric acetate was 16.8 and 9.3 days in the 25°C temperature regime, and 35.4 and 19.9 days in the declining temperature regime, for the 10 and 100 ppb groups, respectively. Smaller oysters (0 to 7 g) consistently accumulated more mercury per gram wet weight than larger oysters (7 to 20 g) in populations exposed to 10 and 100 ppb mercury.     

Predators influence the tidal distribution of oysters (Crassostrea virginica)

Biotic and abiotic conditions can separately and synergistically influence the abundance and distribution of species and create vertical zonation patterns in marine systems. In Corpus Christi Bay, TX, USA, eastern oysters (Crassostrea virginica) are limited to intertidal habitats, while in adjacent estuaries, oysters not only grow subtidally, but thrive in these areas to the extent they are a viable commercial fishery. The purpose of this study was to assess how predators and abiotic conditions affect oyster mortality and growth at different tidal elevations. Anecdotal evidence suggests that abiotic conditions, primarily hypoxia and salinity, as well as oyster disease, limits oysters to intertidal areas. Yet, in Corpus Christi Bay, oysters are absent from subtidal areas where hypoxia is not known to occur. Infection by Perkinsus marinus (Dermo) is common in the study area, but previous work suggests that infection rates do not increase when oysters are transplanted subtidally. We investigated oyster tidal distributions by transplanting newly settled oysters into intertidal and subtidal areas. Predation on oysters was significantly greater in subtidal as compared to intertidal habitats. When protected from predators using cages, oyster survival significantly increased. Further, oysters in subtidal areas allocated significantly more resources to shell growth than did those in intertidal areas, and oysters are known to grow heavier shells in response to predators. Oyster settlement was not statistically different between inter and subtidal areas, and abiotic conditions measured during the study did not exceed known tolerance limits for oysters. Previous studies have shown that abiotic conditions influence oyster mortality and the success of restored oyster reefs. Our findings indicate that predators can also affect oyster distribution, and their effects should be evaluated when developing plans for oyster management and restoration.     

Population genetics of the American oyster Crassostrea virginica along the Atlantic coast and the Gulf of Mexico

An examination by protein-gel electrophoresis of 19 different geographical populations of the American oyster Crassostrea virginica (Gmelin) was conducted along the Atlantic coast and the Gulf of Mexico. Estimates were made of levels of genetic variation and similarity among the populations based on 32 structural loci. The percentage of loci polymorphic ranged from 46.9 to 65.6% along the Atlantic coast while the estimate ranged from 54.8% to 68.8% on the Gulf of Mexico. The percentage of loci heterozygous ranged from 18.6 to 23.6% along the Atlantic coast and from 20.0 to 25.4% in the Gulf of Mexico. The genetic similarities between all contiguous populations from Cape Cod, Massachusetts to Corpus Christi, Texas were estimated as 99%, while the same estimate between Corpus Christi and Brownsville, Texas was computed as 93%, indicating a major transition in genetic structure for the Brownsville population of the Laguna Madre. The study revealed that the migration of planktonic oyster larvae is predominantly in a westerly direction along the Gulf of Mexico and that gene flow appears to be disrupted in the region of the Laguna Madre. Evidence has been presented for single gene selection at the Lap-2 and Pgi loci in the form of macrogeographical clines in allele frequencies with changing environmental conditions.     

The ecological energies of growth,respiration and assimilation in the intertidal American oyster Crassostrea virginica

Seasonal variations in the growth, respiration and assimilation of the intertidal oyster Crassostrea virginica (Gmelin) of different sizes were determined. The instantaneous growth rates for intertidal oysters decreased with increasing size and with lower temperatures. Q₁₀ values computed from instantaneous growth rates were approximately 2 during the warm growing season, but were higher in the colder months. Oxygen consumption increased with temperature and body size. A model was developed to predict oxygen consumption at any environmental temperature from 10° to 30°C for oysters ranging in weight from 0.1 to 100.0 g. Q₁₀ values computed from oxygen-consumption rates decreased with increasing temperature and increasing body size. Intertidal oysters utilize a large proportion of their assimilated energy in growth.Supported by a Belle W. Baruch Fellowship in Marine Ecology.     

Winter quiescence and spring awakening of the Eastern oyster Crassostrea virginica at its northernmost distribution limit

To test the hypothesis that oysters, Crassostrea virginica, from the northernmost part of the species range in the Gulf of St. Lawrence (48°N) open their valves at lower temperatures than those reported for more southern oysters, Hall element sensors were used to monitor their gaping behaviour. These observations were made in a flow-through system and the temperature, salinity and relative fluorescence of unfiltered seawater were monitored. Photoperiod was controlled (15?h dark:9?h light) and light levels were measured but not closely controlled. Gaping behaviour was followed from February to June 2010 (113?days) and from April to May 2011 (34?days) and was classified into three successive phases: quiescent, awakening and active. Although valves were either closed or slightly open during the quiescent phase (maximum gape angle?=?0.49°, SE?=?0.04), they abruptly opened to maximum angles of about 5.88° (SE?=?0.29) during the awakening phase. Moreover, there was noticeable synchrony amongst individuals, since approximately one-half of the monitored population awoke within a 6.6-h period in both study years. Correlative analyses identified temperature as a factor influencing valve movement, and oysters awakened when temperatures were 0.2–4.0?°C (mean?=?2.2, SE?=?0.2). Oysters exerted their maximal gape angle as soon as temperatures reached 2.8–6.6?°C (mean?=?4.8, SE?=?0.2). During the active phase, valves remained open 68.6?% (2010) and 79.7?% (2011) of the time. An unexpected result was the observation of a diurnal rhythm in valve openness whereby the openness was greatest near the end of the afternoon and least in the early morning.