Seasonal data on phytoplankton composition of seston and stomach contents of the mussel (Mytilus edulis Linnaeus, 1758) from two contrasting sites, an estuarine mud flat and a rocky open shore, were compared to ascertain: (a) the extent to which differential characteristics of both sites affect this composition and (b) the degree of similarity between stomach contents and microalgal composition of seston of these sites as an index reflecting the complex processes of selection taking place within the feeding-digestive system of mussels. Individuals and water samples were collected monthly from November 2001 to December 2002, when salinity, temperature, and total and organic particulate matter concentration were also recorded in the water column. Preserved samples of seston and stomach contents were analyzed by inverted microscopy according to the Utermöhl method. Phytoplankton cells were counted and the different species grouped, taxonomically and, according to the habitat, into pelagic and tychopelagic. These data served to compute abundance (total cell count) and frequency index. Relative abundances of each group were compared for similarity between sampling sites and stomach and water samples in each site. Similarity analyses were performed using the index of Bray-Curtis, significant differences between samples being determined by the non parametric test of ANOSIM. Results of this test for the comparison between water and stomach contents resulted in significant differences: R = 0.68 in the estuary and R = 0.75 in the open shore area. Stomach contents presented a reduced average number of species (n = 6 in mussels from both sites) and a greater proportion of tychopelagic forms for comparison with the water samples (n = 20 and 24 in the estuary and open shore, respectively). Maximum phytoplankton density in water samples occurred in the May to October period, the group responsible for this increment being the diatoms. The stomach contents of marine mussels displayed two peaks of phytoplankton concentration in May (caused by the dinoflagellate Ensiculifera sp.) and in July (caused by the diatoms Pseudo-nitzschia pungens and Licmophora sp.). In the case of stomach contents of estuarine mussels, a single peak of abundance was recorded in the month of May and was mainly produced by Ensiculifera sp. To conclude, the main result coming from these comparisons is the increased abundance of dinoflagellates in the stomach contents relative to the corresponding seawater samples in the estuarine and open shore media. This result is discussed in the light of previous data concerning the differential utilization of species of phytoplankton by bivalve molluscs.

Seawater velocity, meat content, food availability, and algae toxins were measured in a commercial long-line (200 × 15 m) mussel farm (Mytilus edulis [L]) in Lysefjorden, in southern Norway. The mean current speed decreased rapidly within the farm area during the 4 days current measurements. The current speed 30 m inside the farm was reduced to less than 30% compared with the current speed outside the farm. The reduction was a consequence of friction from the mussels and farm structures. More than 50% of the incoming phytoplankton biomass (chlorophyll a) was depleted within the first 30 m in the mid section of the farm. After this decrease the chlorophyll a concentrations stabilized at approximately 0.6 mg m⁻³ throughout the farm. The reduction in current speed led to food depletion and lower meat content within the farm. The concentration of diarrhetic shellfish toxins (DST) was inversely related to the meat content of the mussels. This relationship can be used to optimize monitoring programs for shellfish toxins. The range of DST in mussels varied from 0.40 to 1.60 mg kg⁻¹ steamed meat within the farm. It is suggested that depuration of DST was faster in areas with high food availability.

Previous investigations of the bivalve Mya truncata in the Southern North Sea revealed the absence of the 1987 to 2001 y classes. Because the species' southern-most distribution limit is the southern North Sea, at the Frisian Front, we examined if M. truncata was reproductively active in this region. Histologic sections of reproductive tissues from individuals collected between June and April 2002 revealed synchronous gametogenesis with low numbers of vitellogenic oocytes. The low number of ripe oocytes may be one explanation for repeated recruitment failures of this species at this site.

Sudden salinity drops in Gulf Coast clam growing areas in Florida have been suggested as a cause of seed (juvenile) clam mortality. Laboratory experiments were used to assess short-term impacts of rapid salinity drops on hatchery-produced juvenile northern quahog (=hard clam), Mercenaria mercenaria, in two separate trials. Mortality and condition index (CI) were measured as response parameters. In Trial I, clams were exposed to a salinity drop of 5 ppt, 15 ppt, or 24 ppt over a span of 24 h, and the duration of this exposure was either 3 or 6 days. In Trial II, clams were either immediately immersed or dry-stored for 24 h prior to immersion, representing common treatment patterns by clam growers. In this trial, clams were exposed to acute salinity drops of either 10 ppt or 20 ppt for up to 7 days. Both trials were conducted at ambient seasonal temperatures.

Juvenile hard clams were surprisingly robust and resilient to changes in salinity, experiencing less than 5% mortality after relatively abrupt reductions in salinity of 10 to 15 ppt. Nonetheless, salinity declines of the magnitude occasionally observed at clam culture sites, up to 24 ppt, resulted in significant mortality; 17% (Trial I) and 100% (Trial II). Condition index (CI) was an insensitive response parameter. Dry storage of clams did not appear to have an effect on their ability to withstand changes in salinity; storage decreased final survival by <2.5%. Our results suggest that the salinity declines typically experienced at the Gulf Coast aquaculture sites are not of a magnitude or speed to account for the particular seed clam mortality events that spurred this research. However, long-term effects of salinity changes remain to be tested. In addition, reduced salinity may be indicative of a variety of other stressors, such as increased temperature and turbidity, or decreased phytoplankton concentration, which compound the effects of salinity on clam health and survival.

The northern coquina clam, Donax fossor, is often found in association with the hydroid Lovenella gracilis in the intertidal zone of exposed sandy beaches of southern New Jersey. Although previous workers have suggested that the Donax-Lovenella relationship is one of commensalism, this assumption rarely has been quantified or experimentally investigated. Our objectives are: (1) to eliminate the possibility that the association is a recent occurrence, (2) to quantify whether the hydroid has any affect on predation rates of the clam, (3) to quantify the effect of the hydroid on the ability of the clam to swash-ride, and (4) to document seasonal variation in the association. Monthly field samples collected at two sites over a 2-y period revealed that D. fossor and L. gracilis are seasonal in occurrence. The proportion of the D. fossor population with an epibiotic hydroid varied among season, clam size, and field site. Hydroid abundance also varied between years, among seasons, and between field sites. Overall, larger clams were more likely to support a hydroid colony than smaller clams. Predation by the moonsnail Neverita duplicata on D. fossor was affected by the presence of L. gracilis. Clams without a hydroid colony were drilled more frequently than clams with a hydroid colony, suggesting that D. fossor benefits from the hydroid by way of predator deterrence. The results of this study indicate that the Donax-Lovenella association is quite common during the summer months although it has been overlooked for decades. The evidence to date implies that the Donax-Lovenella relationship is a candidate for a case of mutualism because of the reduced predation rates by moonsnails on clams with a hydroid colony.

Innovative Fishery Products Inc. (IFP) has managed a 1682-ha northern quahog (Mercenaria mercenaria) lease in St. Mary's Bay, Nova Scotia, Canada, since 1997. This study describes the commercial harvest and age structure of the northern quahog population from St. Mary's Bay and provides estimates of total mortality and exploitation rates for the lease area. Overall, mean densities ranged from 48.3–88.4 individuals/m² for surveys conducted in June 2001 and 2002, and in May 2003. Catch and effort in the fishery increased from 1999 to 2001. The mean age to market was 7 y. Recruitment of spat (SL < 5 mm) was variable and age frequencies suggested immigration of juvenile quahogs (3–6 y old) onto the intertidal portion of the lease area. The abundance of large quahogs (SL > 60 mm or >8 y old) was low. Catch curve analyses resulted in a high estimate of total mortality (Z) for quahogs of ages 7–10. Commercial exploitation only represented 5% to 10% of the estimated standing stock of commercial size quahogs, which suggests that natural mortality may be high. However, field experiments conducted during 2003 suggested that summer survival (May to October) was high ranging from 93.8 ± 1.54 to 97.6 ± 2.14%. Causes of apparent high total mortality of adult quahogs are unclear, but winter-kill due to ice abrasion or scouring, predation, and the movement of quahogs from the lease area may be responsible.

Genome size (the C-value) is known to vary considerably among organisms, but is relatively constant among individuals of the same species. To determine the genome size in the Northern Chilean scallop Argopecten purpuratus, two populations were analyzed by measuring the fluorescence signal in hemocyte nuclei stained with DAPI. The fluorescence intensity was measured during a fluorescence-fading period by image analysis (fluorescence fading method). The area under the curve during a fading period was associated with the genome size, thus we determined the C-value in the Arica population as 1.057 ± 0.057 pg of DNA and 1.139 ± 0.066 pg of DNA for the Tongoy population. The interindividual variation was smaller that 6% for both populations. Variance analysis was performed to detect the effects of organisms and population in the genome size of A. purpuratus. Significant differences were detected between Arica and Tongoy populations (P = 0.0011). The genome size of Tongoy population was larger statistically compared with the Arica population. Several hypotheses are discussed about genome size variation.

A technique for growing small P. maximus spat in suspension culture from rafts is described. Hatchery produced spat of initial size 3.0- and 4.3-mm shell height were transferred to a sea-based primary nursery system in May. Scallop spat (3.0 mm) grew to 16.8 ± 3.0 mm during 85 days. Survival was 70.0 ± 8.1%, but decreased due to presence of predators in 33.4% of the sampling units, to between 0 and 37.4%. Important predators were the crabs Atelecyclus undecimlineatus, Liocarcinus arcuatus, and Necora puber and the starfish Asterias rubens. A significant negative correlation was found between Asterias rubens arm length and survival of scallops. Initial shell height affected growth and survival significantly whereas stocking density (50–400 spat quarter⁻¹ and initial coverage of 1% to 17%) had significant effect on growth. Spat of 4.3 mm initial size were significantly bigger than the spat of 3.0 mm after 34 and 57 days, whereas survival was 96.4 ± 4.4% versus 71.4 ± 12.8% after 37 days. No mortality occurred during the second sampling period, but growth was negatively correlated to increased density of spat. The results give important information regarding development of economic production of scallops and showed promising opportunities for optimizing stocking density in intermediate primary culture. The choice of production methods in the next production step (secondary nursery stage) can be based on the results obtained.

The gametogenic cycle of the ponderous ark, Noetia ponderosa (Say, 1822), was studied in a Cedar Key, Florida population between March 2001 and January 2003. Ponderous arks are dioecious, and no hermaphrodites were found in this study (n = 592). The sex ratio of females to males was 0.84:1.00, but was not significantly different from parity. On the Gulf coast of Florida, the ponderous ark dribble spawns over most of the year, peaking in the summer and fall months and with the least spawning activity occurring during the spring when gametes are maturing. A small percentage (5.2%) was found infested with an undescribed digenetic trematode. The Cedar Key area has an important commercial hard clam (Mercenaria mercenaria) aquaculture industry, and the implications of these findings on the potential for its diversification based on this species are discussed.

Microhabitat selection and diurnal and nocturnal movement patterns in two tropical littoral gastropods (Nerita versicolor and Tectarius antonii) were compared in relation to shore position allowing for an assessment of the influence of physical stressors (heat and desiccation) on their behaviors and vertical distributions. Monitoring of individually marked specimens indicated that movement, and presumably feeding activities of tropical littoral gastropods, is initiated during periods of decreased desiccation and thermal stress. Near continuous movement was observed in snails inhabiting moist eulittoral (midshore) habitats. In contrast, snails inhabiting the upper eulittoral fringe (high-shore) exhibited movement only during periods of rain or when shores were moistened by increased wave action. Twenty-four hour surveys indicated a preference for nocturnal activity in mid- and high-shore habitats. The propensity for increased activity during conditions of reduced desiccation stress was also supported by an experiment in which wetting of the substrate (simulating inundation) encouraged activity in mid- and high-shore species. Mid- and high-shore species exhibited a preference for sheltered microhabitat and avoided exposed surfaces.

Most marine snails of the families Muricidae and Thaididae produce in their hypobranchial gland (mucus gland) a colorless secretion containing minute amounts of chromogens, which develop under the influence of light and oxygen into a pigment known as “Tyrian Purple.” The hypobranchial gland of Plicopurpura pansa (Gould, 1853) is an exception among the muricids, because it is so active the snails can be stimulated periodically to expulse the secretion without harming the animals. In view of reported drastic declines of the populations of P. pansa because of the Tyrian Purple exploitation, in this laboratory study the effect of periodically “milking” of P. pansa on the frequency of expulsion and on the mortality of the snails was determined. At the beginning of the experiment using 110 animals (55 males and 55 females) only 30% expelled secretion. No relation was found between the occurrence of expulsion and the size or sex of the animals. In contrast to the laboratory snails the proportion of expulsions from free-living animals was 56%. Also here no differences were found between the occurrence of expulsion and the size or sex of the animals. For a period of 98 days it was tried in the laboratory to obtain daily secretions from 46 snails (23 males and 23 females). The frequency of expulsion declined drastically and at the end of the experiment no expulsions at all could be obtained. No difference could be noted between the sex and size of the snails and the decline of secretions, however, the total number of secretions during the test period was nearly double with the females, than with the males. The survival rate of the male snails was 83, of the females 87%. Handling mistakes during cleaning and feeding were the main reason for the mortalities. The attempt to milk the snails weekly caused, as during the daily milking experiment, a decline in the frequency of expulsion, and after 13 wk only 13% of the animals expulsed. To milk the animals every 2 wk caused a decline in the number of snails that expulsed, and only 18% of the animals secreted. No decline in the rate of expulsions was found by milking the animals every 3 and every 4 wk, and all animals survived. Frequent attempts to milk the animals has no impact on the survival rate, however, it affects the occurrence of expulsions. From the results reported here the decline of natural snail populations after milking could be explained by the environmental conditions of the intertidal zone. After milking, the animals don't adhere fast enough to the rocks and they are washed away to unsuitable areas by the high wave action. For this reason, P. pansa should never be removed from the rocks, and the collection of the secretion should be allowed only in exceptional cases.

The acute and subchronic toxicity of lead was determined in the spotted babylon, Babylonia areolata. The 96-h static bioassay was conducted to estimate the median lethal concentration (LC₅₀). The snails were exposed to lead nitrate (Pb[NO₃]₂). The LC₅₀ values for 24, 48, 72, and 96 h were 29.31, 14.64, 12.44, and 10.50 mg Pb/L, respectively. In the subchronic experiment, the snails were exposed to 0.5 mg Pb/L (10% MATC, the maximum acceptable toxicant concentration) of lead nitrate for 3 mo. Lead accumulation was found in different organs with the greatest accumulation in the stomach and lesser in the esophagus, gill, rectum, digestive gland, proboscis, and foot. The histopathologic alterations in the digestive system and gills of B. areolata were studied by light microscopy. The general tissue alterations were decrease in length of cilia, decrease in acidophilic granules, slight distension of nuclei, and the loss of heterochromation. There were increases of mucous vacuoles, damaged ciliated cells, and enlargement of vacuoles.

A feeding trial of 5 dietary protein levels (12%, 22%, 32%, 42%, and 52%) and 2 dietary energy levels (3.3 and 3.9 kcal/g diet) factorial design with three replicates was conducted to investigate the proper dietary protein and energy levels for the growth of the snail (Semisulcospira gottschei). Snails, initial averaging 37 mg, were fed the experimental diets for 12 wk. Survival of each group was all above 80% and no significant difference among treatments. Mean weight gain of the snails was improved with increasing dietary protein level up to 22% and 32% at 3.3 and 3.9 kcal/g diets (P < 0.05), respectively, and reached a plateau above these levels (P > 0.05). Mean weight gain of snails fed the 22% protein diets with 3.3 kcal/g diet was not significantly (P > 0.05) different from that of snails fed the 32% to 52% protein diets with both energy levels. Lipid content of snails fed the 3.9 kcal/g diets showed higher values than that of the 3.3 kcal/g diet at the same protein level. Snails fed the 3.9 kcal/g diets showed a tendency toward to higher in 18:1n-9, 18:2n-6, 18:3n-3, and 22:6n-3 and lower in 20:4n-6 and 22:1n-9 than those of snails fed the 3.3 kcal/g diets energy diets. The results of this study indicate that a diet containing 22% protein and 3.3 kcal/g diet with P/E ratio of 69 mg protein/kcal was recommended for snail growth.

The eastern oyster, Crassostrea virginica Gmelin, is a common inhabitant of estuarine and coastal waters from maritime Canada through the Gulf of Mexico. Because mitochondrial DNA haplotypes exhibit a distinct genetic break between Atlantic and Gulf oysters at Cape Canaveral, Florida, the degree of divergence between Atlantic and Gulf oysters in nuclear genes is less well known. We examined patterns of variation in four nuclear loci using restriction fragment analysis of amplified DNA (PCR-RFLP) in oysters (n = 317) from 16 locations spanning the geographic range of C. virginica. Marked differentiation was observed between Atlantic and Gulf populations, with smaller differences detected between North Atlantic and South Atlantic populations. Intermediate populations were observed in both eastern and northwest Florida. Regional population structure was also evident in the Gulf Coast, with Texas oysters highly divergent from all other populations.

This study was designed to evaluate whether the addition of peat moss particles to an algal diet influenced the physiology, biochemical composition, reproductive development, and survival of the Eastern oyster (Crassostrea virginica) under laboratory conditions. In two consecutive 5-wk trials (13°C to 15°C), 70-mm oysters were fed a mixed algal diet (25 μg Chl L⁻¹ or 2.3 mg TPM L⁻¹) supplemented with 3 concentrations of peat particles (2.7, 11.2, or 31.2 mg TPM L⁻¹). The proportion of organic matter (POM:TPM) in the various diets increased from 79% for the algal control to 96% for the highest peat concentration. Following a 5-d acclimation period, oysters in the various treatments exhibited similar clearance rates calculated either on the basis of chlorophyll (2.3 L h⁻¹g⁻¹) or particle removal (2.8 L h⁻¹g⁻¹). Chlorophyll filtration rates were similar among treatments (63 μg Chl h⁻¹g⁻¹), whereas particle filtration rates increased with peat concentration in the diet (9–58 mg TPM h⁻¹ g⁻¹). Although pseudofeces production rates increased with peat concentration (2–30 mg TPM h⁻¹g⁻¹), estimates of particle ingestion rate also increased (7–28 mg TPM h⁻¹g⁻¹). Fecal production rates were similar for the various treatments (2 mg TPM h⁻¹g⁻¹) as were respiration rates (0.32 ml O₂ h⁻¹g⁻¹). Oysters sampled after 3-wk and 5-wk exposure to the four diet treatments exhibited no significant differences in biochemical composition, gonad maturation rate or survival. In general, this study suggested that the presence of peat particles in an excess algal diet had no impact on oyster performance. However, the results of these laboratory trials may not be directly applicable to oysters subjected to similar peat concentrations under field conditions.

The condition index (CI) is a tool that has been used to estimate the effect that different environmental factors have on oyster meat quality. The CI of oysters in five beds in Sapelo Island and the Doboy Sound (Georgia, United States) were calculated using three different methodologies. Values from each site were used to: (1) compare two sites located in relatively large systems (river/sound) and three sites in a small creek to test for differences due to system size and related nutrient availability; (2) determine the effect of a parasite, the pea crab (Pinnotheres spp.), on oyster CI; and (3) determine the effect of differential position of oysters on a bed, with respect to CI (oysters were collected from areas of the bed that are permanently submerged and areas with the longest dry periods between tidal cycles). With respect to the three analyses mentioned earlier, it was found that oyster CIs for sites in larger systems (river and sound sites) were significantly higher than those in sites with lower flux and width (creek sites) and that the presence of pea crabs as parasites can reduce CI by ~50%. In addition, no difference in CI was found between oysters collected from different positions in the oyster bed, indicating that the CI was not altered within a site from effects of exposure. This relatively unusual finding is discussed but suggests the robustness of CI as an intersite analysis tool. Not all differences found in the comparisons were significant for all CIs used, but qualitative results among them were consistent. These variations in significance and the adequacy of each method for analysis are briefly discussed.

To gauge the influence of salinity on the habitat value of oyster reefs, spatial and seasonal patterns of the presence of reef-resident fishes and decapods were assessed in the Caloosahatchee, Estero, and Faka-Union estuaries of Southwest Florida. Lift nets (1 m²) containing 5 L of oyster clusters were deployed on intertidal reefs at three sites along the salinity gradient of each estuary. Nets were deployed during three seasonally dry and three seasonally wet months for a period of 30 d. Oyster densities were estimated at each site and a number of community metrics were calculated as a measure of habitat use (e.g., organism density, biomass, diversity, dominance, richness). Several metrics increased downstream in one or more systems (e.g., organism density, biomass, diversity) and in general appeared to be more related to salinity than to the density of living oysters present. Although organism density was higher during the wet season for all three systems, biomass was higher during the dry season in the Caloosahatchee. In the Caloosahatchee and the Estero, measures of biodiversity tended to be higher during the dry season. These results suggest that the salinity requirements of the organisms that inhabit oyster reefs should be considered in the planning of oyster-reef restoration or enhancement projects or in the management or alteration of freshwater inflow into estuaries.

Anecdotal reports have long indicated that oysters, Crassostrea virginica (Gmelin), in the Chesapeake Bay once grew in large 3-dimensional reef structures. However, hard evidence of widespread 3-dimensional oyster reefs in the Chesapeake Bay has been scarce. This study uses data collected from historic charts of the James River, one of the most productive oyster producing tributaries of the Chesapeake Bay, to examine the natural occurrence of these reefs as well as their destruction. An early series of charts from the 1870s clearly documents widespread emergent oyster reefs in the James River from Burwell's Bay to Newport News Point. They were long, fairly wide, and shoal-like and oriented at right angles to the current. A 1940s series of charts indicates that by this time nearly all of these reefs had become submerged. Paired t-tests indicate a significant decrease in reef height and volume but not in reef area. This suggests that oysters and shell have been physically removed from the reefs. This likely had a major impact on water circulation patterns over and around the reefs, which may also have further adversely affected oyster populations.

To determine if natural populations of the eastern oyster possess resistance to Perkinsus marinus, progeny representing several oyster stocks from the Chesapeake Bay and the Gulf of Mexico were deployed at two sites within the Chesapeake Bay. Mortality, P. marinus infection (prevalence and intensity), shell height, condition index, and energy reserves (glycogen, protein, and lipid) were compared between these stocks. Oyster stocks from the Chesapeake Bay had higher intensities of Dermo infection than Louisiana stocks, with differences among individual stocks. Throughout the 2-y study, a natural Dermo-resistant stock from Tangier Sound (CTS), was identified. Despite infection intensities approaching those of a susceptible Rappahannock River stock (CRB) and higher than a Gulf of Mexico stock (LOB), CTS consistently had lower mortality for the 2-y grow out, and was comparable to a hatchery disease-resistant strain (XB). At a site (Port Kinsale) where the significant parasite was P. marinus, the LOB stock grew to the largest shell heights and had significantly lower intensities of infection. However, the performance of the LOB stock was comparatively poorer at the other deployment site (Regent Point) where MSX was present. Shell heights were highest overall in the CRB stock at Regent Point, despite high susceptibility to disease. Condition index varied between stocks, although not necessarily along trends of disease resistance since condition was highest in the CRB and XB stocks. Variations in energy reserves were strongly influenced by season, but not disease, or stock origin. The present study shows that differences between stocks contain an underlying genetic component. Differences seen between deployed stocks in mortality, growth, and condition have strong implications for development of selective criteria for an aquaculture-based industry.

A survey was conducted to characterize the status of water quality (salinity, dissolved oxygen, pH, and temperature), eastern oyster (Crassostrea virginica) reproduction, and eastern oyster health in the St. Lucie Estuary (SLE), located near Stuart, Florida. The SLE receives water from an intensively drained watershed through a variety of interconnected swales, ditches, and canals. Specific indicators of oyster health and recruitment included condition index, gonadal index, spat settlement, and infection intensity of Perkinsus marinus. Water pH, salinity, DO, and temperature varied among locations and throughout the seasons. Temperatures were highest (31°C) from June through August and lowest (13°C) in January. Salinity, the most variable parameter, ranged from <1–30 ppt. Significant depressions in salinity were apparent during Lake Okeechobee discharge events through Canal-44 (C-44) and when long-duration rainfall events occurred within the immediate watershed and the Canal-23 (C-23) and Canal-24 (C-24) drainage basins. Measured DO was generally >2 mg L⁻¹ and pH ranged from 7–8.5. Spat settlement was always lower in the SLE as compared with reference sites in the Indian River Lagoon. The majority of spat settlement in the SLE occurred from April through June. Gonadal stage of oysters and condition index varied throughout the seasons. This survey will serve as a useful benchmark for measuring the success of future projects directed towards management of water quality and enhancement of oyster habitat in the SLE.

Eastern oysters (Crassostrea virginica) inhabit highly variable environments and are exposed to large seasonal shifts in temperature. Prevalence and intensity of oyster diseases, particularly Perkinsus marinus (Dermo), increase during thermally stressful periods, thus posing additional stress on the oyster host. Heat shock proteins (hsps) are important in protecting organisms from thermal and overall environmental stress. Additionally, hsps may play protective roles for both the host and parasite during infection. The interactive effects of temperature and disease on heat shock protein expression in oysters, however, are unknown. In this study, using slot and western blotting assays, seasonal and intraspecific variation in heat shock protein 70 (hsp70) expression was compared among stocks of C. virginica known to be resistant or susceptible to Dermo at two sites in the Chesapeake Bay. Mortalities, shell heights, condition, and P. marinus infections were also compared among stocks to examine relationships between hsp70 and these variables. Hsp70 was analyzed at 4 seasonal samplings (fall, winter, spring, and summer months), while all other variables were measured bimonthly. Patterns and amounts of hsp70 expression varied significantly across different seasons, but did not correspond with seasonal temperature. Total amounts of hsp70 were significantly highest in the fall. Seasonal variation in specific isoforms of hsp 70 (69 kDa and 72 kDa) was observed. Highest amounts of each were expressed in the spring and fall, respectively, and they were inversely proportional to each other. Differential expression was observed during the winter and spring, with several individuals expressing only hsp72 in the winter and only hsp69 in the spring. Although hsp72 changed concurrently with seasonal changes in infection, both hsp72 and hsp69 did not vary significantly between stocks or with levels of P. marinus infection. This study reveals that measuring total levels of hsp70 do not sufficiently describe the effect of seasonal temperatures on hsp70 expression. Stock mortalities were consistent with the patterns of disease resistance exhibited by their stock parentage, implying existence of a strong genetic component to resistance to Dermo disease. Differences in shell heights, condition index, and P. marinus infection differences showed significant associations among stock, site, and time. Variation in hsp70 did not reflect differences in infection among oyster stocks, indicating that hsp70 may not be a useful indicator to distinguish the effects of pathogenic stress between resistant and susceptible oyster stocks. Differences in expression between hsp69 and hsp72 suggest that seasonal patterns of specific hsp70 isoforms must be understood to determine the role of hsp70 proteins in stress and disease resistance in oysters.

Oyster culture, which is a large part of the North American aquaculture industry, is greatly hindered by the parasite Perkinsus marinus. The different oyster defense mechanisms and how the parasite seems to evade them are not fully understood, and the role of apoptosis as an oyster defense mechanism remains unclear. Apoptosis of eastern oyster (Crassostrea virginica) hemocyte subpopulations (granulocytes and hyalinocytes) was quantified at the single cell level using flow cytometric Annexin-V and TUNEL assays. The influences of habitat salinity (540 mOsm [18.9‰] and 910 mOsm [31.9‰] for oysters and 488 mOsm [17.1‰] and 810 mOsm [28.4‰] for P. marinus) and temperature (14.5°C and 25°C for oysters, 14.4°C and 22.5°C for P. marinus) on apoptosis frequencies were evaluated experimentally on the host hemocytes and the parasite. Apoptosis frequency was higher in granulocytes than hyalinocytes, regardless of temperature or salinity. Salinity affected apoptosis of granulocytes and hyalinocytes, with more apoptosis at 910 mOsm than at 540 mOsm (at 14.5°C and 25°C). Parasite apoptosis frequency was significantly higher on culture at the low salinity (488 mOsm) at both low and high temperatures (14.5°C and 22.5°C). Temperature did not significantly affect either hemocyte or parasite apoptosis frequencies. Investigation of apoptosis as an oyster defense mechanism and how temperature and salinity affect C. virginica and P. marinus apoptosis may lead to a better understanding of host/parasite interactions and the mechanisms leading to disease susceptibility or resistance. Such information could lead to better management strategies that may result in reduced disease morbidity and mortality for oyster producers.

Hyotissa hyotis specimens were collected at Espíritu Santo Island, Gulf of California, from March 1998 to March 1999. Water temperature was recorded, gut-content samples were obtained, phytoplankton abundance was estimated, and the reproductive status was inferred through the gonadic index. Gut content included phytoplankton, mostly diatoms (86.5%) and dinoflagellates (13.5%). The highest phytoplankton frequency in gut contents occurred from March to May, along with a growing phytoplankton abundance in seawater, matching the period of gonad development and the seasonal rise in temperature. Phytoplankton comprised diatoms (73.3%), dinoflagellates (10.4%), nannoplankton (18.8%), cyanobacteria (3.3%), and silicoflagellates (2.2%). The gonadic index suggests that this population has an annual reproductive pattern. Gonad development takes place from March to April, with the population ripening between April and July, matching the seasonal temperature rise from 22 °C to 27 °C, and spawning from July to September when temperatures reach a peak between 27 °C to 29 °C. From October onwards the population enters a postspawning and reproductive-inactivity phase.

Brooding pattern and fertility of the puelche oyster (Ostrea puelchana) were investigated in a native population from the San Matías Gulf (40°48′S; 65°05′W, Northern Patagonia, Argentina). Monthly samples of 100 oysters were randomly collected at the oyster ground during the period November 1999 to January 2000, and weekly in the 2000 to 2001 reproductive season. Complementary data were obtained from the literature (1976 to 1978) and samplings performed during the periods 1980 to1984 and 1987 and 1998. The date at which oysters begin larval brooding may be placed somewhere within the period November 18 to January 11. In most seasons (77%), brooding starts within the period November 18 to December 5. The number of brooders is low at the debut (7.5% in 1999, 4% in 2000), peaking at the end of spring (20%), and gradually decreasing until reaching nearly 1% by middle February. Total number of larvae brooded on each sampling date showed a high correlation with brooding percentages (r² = 0.85). Mean fertility showed no correlation with the percentage of oysters brooding larvae (r² = 0.12). The highest value of mean fertility (2.7 million) was recorded at the beginning of the season when 4% of the oysters were brooding larvae. Mean fertility ranged from 900,000 to 2,700,000 larvae. Brood size ranges from 447,500 to 3,790,000 larvae (mean = 1,868,212; s = 813,808; n = 121). Individual fertility showed no correlation with neither size (total height) nor with internal volume of oysters within a size range of 60–115 mm. O. puelchana shows the highest fertility recorded in Ostrea species, a feature that seems consistent with its short incubation period, small egg size, long planktonic life, and small size of pediveligers.

The purpose of this study is to investigate summer mortality of the cupped oyster, Crassostrea gigas, in relation to culture practices in the traditional oyster production region of Marennes-Oléron (France). Four oyster rearing conditions, varying culture location (“on-“ or “off-bottom”), and site depth (65% to 80% daily immersion termed “deep” or 45% to 65%, termed “shallow”) were studied to compare biologic performance and maturation status of oysters, in relation to sediment and water column parameters. The most severe mortality occurred in June to July in “on-bottom” reared oysters (25%), as compared with 10% mortality in “off-bottom” cultured oysters. Oysters (shell and meat) grew significantly better when reared “off-bottom” than “on-bottom.” Reproductive effort was almost double in “off-bottom” reared oysters, compared with those “on-bottom”; thus, reproduction cannot be directly related to mortality in this summer mortality event. Low glycogen content recorded for both “on” and “off-bottom” reared oysters in summer, confirmed the probable lack of food and/or the overstocking in the Marennes-Oléron Bay, but did not discriminated among culture conditions. Whatever the immersion depth (“deep” or “shallow” conditions), “on-bottom” cultured oysters were adversely affected in growth, reproductive effort, and survival suggesting a direct effect of the mud (the so called “mud effect”) on the biologic performance of oysters cultured on the bottom. Data from monitoring of sediment redox potential, organic content, and ammonium release did not support hypotheses that these parameters were alone responsible for the observed differences in mortality events.

To investigate the polycyclic aromatic hydrocarbon (PAH) effect on fertilization of the Pacific oyster, Crassostrea gigas, we exposed the adult brood stocks to PAHs (200 ppb) for 30 days as the treated (E group) with a nonexposed group as the control (C group). In addition, each subset of the gametes from both groups was further exposed to graded level of PAHs (0, 50, 100, and 200 ppb). Motile sperm and linearity were significantly affected by parental exposure, whereas straight line velocity (VSL) and curvilinear velocity (VCL) were affected by both of parental and larval exposure to PAHs. Fertilization and larval development were also affected by parental exposure. Our result suggests that fertilization capability and larval development are adversely affected by parental exposure whereas sperm movement was more vulnerable to larval exposure. In the brood stock contaminated by PAHs, larval development was also vulnerable to larval exposure to PAHs.

We evaluated experimental collection of Pinctada mazatlanica spat on substrates of different textures and colors placed at different depths within settlement tanks. When larvae reached the pediveliger stage (day 25), black-colored spat collectors (“envelope” type) composed of the following materials were offered as settlement substrates: onion bag, mosquito net, fishing net, and 63% shade-cloth. Spat collectors measured 30 × 30 cm and were composed of an outer bag and inner substrate made of the same material. The influence of the color of spat collector material on recruitment was investigated using a second type of spat collector composed of onion bags as the outer bag and inner substrate (“bag” type). Bags were prepared in 3 different outer/inner (O/I) color combinations of green/green, green/black, and red/black (O/I). Both types of collectors were deployed at different depths within settlement tanks. Approximately 2.7% of the initial larval population survived, resulting in 35,583 spat. Of these, 71.3% recruited to bag type collectors, 21.9% to envelope type collectors, and 6.8% to the surfaces of the culture tanks. Spat recruitment was significantly affected by collector material (P < 0.01), with fishing net and shade-cloth yielding highest and lowest density of spat, respectively. Similarly, spat collector color combination significantly influenced spat collection (P < 0.01), with higher recruitment to red and green substrates. For both spat collector types, there was significantly greater (P < 0.01) recruitment of spat to collectors in the middle of the water column (60–90-cm depth). This study showed that both the type and color of material used for spat collectors, as well as depth of deployment, influenced recruitment of P. mazatlanica spat. These results will help fine-tune current hatchery techniques for this species.

To investigate the occurrence of thermal adaptation in the zebra mussel, Dreissena polymorpha, inhabiting the lower reaches of the Mississippi River, we compared lethal heat-tolerance among three populations (mussels collected at Lake Pepin, MN; Alton, IL; and Baton Rouge, LA). We determined time-to-death at 32°C for 160 individuals per site, for mussels collected at a water temperature of 15°C and then maintained in the laboratory for about 8 wk under uniform conditions. Both shell length and condition index significantly affected survival time and were included as covariates in the analysis for interpopulation differences in heat-tolerance. Zebra mussels from our southernmost location had a higher heat-tolerance than those from the two northern locations. This difference in heat-tolerance among sites may indicate adaptation to local temperature regimes. In addition, in a comparison of heat tolerance within populations, we separated mussels into size classes (where larger mussels have been exposed to local conditions longer) and calculated an adjusted mean time-to-death (TTD). We found a different TTD/size relationship depending on sampling location. Minnesota mussels had decreasing heat tolerance as size increased, where Louisiana mussels had the opposite relationship. These patterns of heat-tolerance within populations indicate a selection pressure for increased heat-tolerance at Louisiana. However, even if the selection pressure is strong at the Louisiana site, it has not (at least not yet) resulted in an adaptation, as high heat-tolerance is not ubiquitous within this population. Zebra mussels may have insufficient genetic variation for heat-tolerance or gene flow may have been too strong for genetic adaptation to occur in the short amount of time that zebra mussels have occurred in the lower Mississippi River.

Dioxins, furans, and trace metals were evaluated in shellfish and sediments from St. Louis Bay, Mississippi and adjacent waters of Mississippi Sound. Highest concentrations and the most toxic dioxin congener were found in St. Louis Bay sediments in closest proximity to the effluent outfall from the titanium dioxide refinery on the northern shore of the bay. Using conservative assumptions, we estimated the dioxin and furan burden of 17 measured congeners in St. Louis Bay sediments to be between 3.72 and 6.16 kg. Comparison of lipid-adjusted dioxins and furans in oysters (Crassostrea virginica) from this study with those collected from seafood markets and grocery stores in southern Mississippi in 1997 shows dioxin and furan contamination about 1.7 to 8 times higher in the samples from this study, depending on collection location. Oysters from St. Louis Bay and adjacent marine waters may accumulate higher concentrations of dioxins and furans than measured here, at other times during the year, due to the low lipid content of oysters in this single-season study. At other times, with typical higher oyster lipid levels, the dioxin content of oysters could increase by a factor of 8.5 to 12.7 times, commensurate with the expected increase in oyster lipids, although the rate of uptake of these contaminants is not known. Certain trace metals have increased markedly in St. Louis Bay shellfish since a 1978 baseline study that was conducted prior to the operation of the titanium dioxide refinery that produces large quantities of soluble waste metals such as chromium, nickel, and lead. In 2004, the percent value of chromium in oysters in St. Louis Bay was at least 1,167% greater than the 1978 values, and the percent value for nickel in oysters in the bay was at least 467% greater than the 1978 value. The percent value for chromium in 2004 from oysters outside the bay was between 7,700% and 11,300% greater than the 1978 reported in bay values. Rangia clams (Rangia cuneata) from St. Louis Bay tended to have greater increases than did oysters for all metals measured above detection limits in both studies, except for zinc, which declined in both shellfish species. Metals also increased in sediments, but soluble metals which are produced by, and apparently released from, the titanium dioxide refinery may be flushed out of the bay to higher salinity seawater before becoming adsorbed on fine silt and clay-size particles which are consumed by shellfish and/or deposited in sediments. Oysters from waters near the mouth of St. Louis Bay were also contaminated with dioxins, furans, and heavy metals. Based on widely published estimated safe and adequate daily dietary intake for chromium and nickel (the latter standard for hypersensitive individuals) the values recorded in this study indicate that less than one oyster per day should be consumed from the open harvest site sampled in adjacent Mississippi Sound. An evaluation of other regional sources of dioxin and dioxin-like compounds and heavy metals was conducted using data reported to the United States Environmental Protection Agency. Because of the lack of other identifiable large sources of these contaminants, the transport dynamics of soluble metals and the occurrence of highest dioxin and dioxin-like compound concentrations near the titanium dioxide refinery outfall, we conclude that the refinery is the most likely and most significant source of the measured dioxins, dioxin-like compounds, chromium, and nickel contamination found in St. Louis Bay and adjacent marine waters of Mississippi Sound.

Methanol: water (1:1), methanol: dichloromethane (1:1) and acetone extracts of molluscs comprising 77 whole body, four inks, four opercula, 10 egg masses, and 10 digestive glands were screened for antimicrobial activity on marine biofilm bacteria. The methanol: water (1:1) whole body extracts of Nerita albicilla and Nerita oryzarum showed broad spectral inhibitory activity against 93% and 95% of the 40 biofilm bacteria. The egg masses from 10 gastropods showed activity against more than a quarter of the biofilm bacteria. The methanolic extract of Chicoreus virgineus, Chicoreus ramosus egg masses, and acetone extract of the egg mass of Rapana rapiformis showed broad-spectrum antibacterial activity against all the 40 biofilm bacterial strains. The activity in gastropod egg masses was localized to their internal matrix. Overall screening showed activity in 38.1% of the methanolic extracts followed by 13.3% of methanol: water, 12.4% of methanol: dichloromethane, and 3.8% of acetone extracts. Gastropods showed good activity when compared with bivalves and cephalopods.

Although seagrass in the lower segments of estuaries provides good nursery habitat for blue crabs, the role of alternative inshore habitats for early blue crab recruitment is not well-known. Using suction sampling, we examined the recruitment dynamics of early blue crabs (Callinectes spp.) over a 10-wk study period at 7 sites representing potential nursery habitats, including 2 marsh edge sites, 2 subtidal unvegetated sites adjacent to salt marsh, 2 subtidal unvegetated sites adjacent to developed marsh, and 1 upestuary subtidal vegetated site. Abundances of small (<6.0 mm CW) and large (≥6.0 mm) juvenile crabs varied over the study period, mainly reflecting two monthly pulses of small crabs coinciding with the new moon phase. Early crabs were significantly more abundant from structured habitats than from subtidal unvegetated habitat; although small crabs were moderately abundant at subtidal unvegetated sites situated lower in the estuary. Large crabs were not abundant from subtidal unvegetated sites; whereas large crabs were abundant from sites with structured habitat. Subtidal unvegetated sites were characterized by crab size-distributions with single modes representing postsettlement crabs and with few large crabs; whereas structured habitats contained relatively more large crabs. However, crab size-distributions varied among structured habitats. Spatio-temporal variation in the early recruitment dynamics of blue crabs reflected temporal changes, such as lunar periodicity; landscape effects, such as proximity to currents; and habitat effects.

Recent studies have shown that zoea larvae of brachyuran crabs often occur in patches that are formed at spawning and persist on time scales ranging from days to at least a week. In the present work we investigated the spatial distribution of the megalopal stage of 2 taxa of brachyurans (Callinectes sapidus and Uca spp.) in Delaware Bay on the east coast of North America (ca. 38.6°N, 75.2°W). We used a combination of high-frequency plankton sampling and data from a moored current meter to characterize the length scale of patches of megalopae at a single station in the mouth of the bay. The study consisted of 12 separate sampling periods during the late summers of 2001 and 2002. During each period, plankton were collected every 10 min over a single flood-tidal phase. Current-velocity data were collected simultaneously via an S-4 current meter moored at the station. Subsequent analysis demonstrated the transport of patches of megalopae past the station during five of the sampling periods. The radius of the patches was determined through autocorrelation analysis. The radii of patches of C. sapidus megalopae ranged from approximately 500–2,000 m, whereas the radii for Uca patches was typically smaller with values around 500 m. This patchy distribution has important consequences for transport and settlement of the megalopae in juvenile habitat.

The Delaware Bay stock of blue crabs supports a bistate fishery in New Jersey and Delaware, with annual landings climbing through the 1980s and 1990s to almost 11 × 10⁶ pounds (4,390 metric tons) in 1995 and then declining to a recent average of 7 × 10⁶ pounds (2,796 metric tons) over the last 5 y. In Delaware, this fishery ranks as number one in value. Landings declines in 1996 spurred efforts to conduct a stock assessment, which is now updated annually. This assessment was based on: (1) a biomass-based minimum recruitment threshold from a Ricker stock-recruitment model fit to indices of relative abundance from a research trawl survey and (2) a catch-survey model incorporating observation and process error that produced annual estimates of absolute abundance, biomass, and fishing mortality rates from 1979 through 2002. Adult blue crab abundance estimates showed a positive trend over the period, ranging from 20 × 10⁶ in 1979 up to 146 × 10⁶ in 1993, with recent estimates between 70 × 10⁶ and 97 × 10⁶. Estimated average exploitable stock biomass over the period was 23.43 × 10⁶ pounds (9,357 metric tons). Recruit abundance was highly variable, ranging from 34 × 10⁶ up to 631 × 10⁶. Use of the log survival ratio to estimate Z showed no trend in Z, although estimates were highly variable. Estimation of the exploitable stock size was problematic due to high density-dependent recruit mortality. Because of this fact, we developed upper and lower bounds of the exploitation rate, then estimated upper and lower bounds of F from Baranov catch equation, F = μ/(1 − e^−Z)*Z. We also estimated the Collie & Kruse (1998) harvest rate and extended it to estimate F. The upper bound of F ranged from 0.13 up to 0.77 and averaged 0.44. The upper bound on F and the Collie-Kruse F showed a positive linear or curvilinear trend. Annual M estimates from Z - F, conditioned on an original model input value of constant M = 1.0, were erratic and showed no trend but were correlated with recruitment, supporting the hypothesis of compensatory density dependence. The relatively low estimate of F versus M and the overcompensatory and resilient stock-recruitment relationship suggest that overfishing is not occurring on this stock.

One of the most damaging viral diseases affecting the shrimp aquaculture industry is white spot disease (WSD) caused by white spot virus (WSSV), which causes high morbidity and mortality rates in penaeid shrimp and other crustaceans. The rapid spread of WSSV within wild and cultured stocks of shrimp may be caused by unregulated processing, disposal of infected imported shrimp, or the use of contaminated broodstock. The risk of introducing this virus to cultured and wild shrimp and other native species of crustaceans in the United States warrants investigation. The aim of this study is to determine the prevalence of WSSV in frozen commodity shrimp sold at four stores in the Boston area belonging to different supermarket chains. Samples from two size classes were collected in two different batches a month apart. Polymerase chain reaction was used to amplify a portion of the WSSV genome using a commercial PCR kit (ShrimpCare, DiagXotics). WSSV positive samples were visualized by electrophoresis and amplified product of selected samples was sequenced. Results showed a range of 0% to 38.7% for WSSV prevalence rate in the test populations, with an overall prevalence of 4.7%. Significant (P < 0.001) differences in WSSV prevalence were observed between shrimp from the two batches purchased a month apart, the two size classes, and the four test stores. Country of origin seemed to dominate the results. Sequence analysis confirmed the presence of WSSV genome in PCR-positive samples. Results provide preliminary evidence that an appreciable proportion of the shrimp sold in Massachusetts' supermarkets are carrying WSSV, and this constitutes a substantial risk of importation of this virus into the local environment. Further investigation is necessary to determine the risk of release of this virus into native fresh and marine water environments in Massachusetts and throughout the United States.

A population of humpback shrimp inhabiting Drury Inlet, British Columbia, was surveyed in November 2001 and March 2002 with trawl and trap fishing gear. Trawl catches were more representative of the shrimp population than trap catches in terms of age-structure and sex-stage proportions. Shrimp, as much as 81.4 tons, lived on a variety of benthic habitats, including deeper trawlable muddy and shallower untrawlable rocky areas. The shrimp population was comprised mainly of small age 1 shrimp (58% to 66%); the proportion that would be targeted by commercial fishers (i.e., larger older shrimp) was small (3% to 8%). Individual shrimp in the Drury Inlet population were generally smaller than shrimp reported from other areas of the BC coast. Females had not released their eggs in mid November and most (75%) were egg-bearing in mid March. Many more shrimp were in the transitional stage in March (24.9%) compared with November (0.4%). Shrimp numbers declined in trap catches at depths greater than 60 m. In trawlable areas, shrimp were abundant at depths 31 to 40 m and in rocky areas between 21 and 40 m. Egg-bearing females tended to be shallower in March just prior to egg hatch compared with when they were not carrying eggs in November. Males were collected from a broad depth range (11 to 80 m). Shrimp in the transitional stage were collected between 11 and 70 m, with more individuals being collected in shallower areas (11 to 20 m). The natural mortality rate of the population was high (mean M = 2.0). Mean fecundity was 905 ± 377 eggs per individual. We used a curvilinear model to describe the relationship between female size and fecundity. Shrimp with microsporidia infections were found in low prevalence (0.24%) in the sampled population. Humpback shrimp may experience competition for food resources from spiny pink shrimp, prawns, crangons, and eualids. Herring and shiner perch may prey on larval shrimp. Other species that may prey on juvenile and adult shrimp include eelpouts, english sole, sand sole, pricklebacks, giant wrymouths, staghorn sculpins, great sculpins, red rock crabs, and graceful crabs.

The effect of varying levels of fiber, protein, and lipid feed component levels on gut passage time (GPT) and gut passage rate (GPR) of Farfantepenaeus aztecus (Pérez Farfante & Kensley 1997), Litopenaeus setiferus (Pérez Farfante & Kensley 1997), and Litopenaeus vannamei (Pérez Farfante & Kensley 1997), was examined in field feeding trials in a tidal creek and shrimp culture pond. Feeding trials were conducted in flow-through enclosures and feeds were thoroughly mixed with inert fluorescent latex beads to facilitate observation of the feed location within the guts of the shrimp. Rather than being able to continuously view feed passage through the shrimp guts (as is possible in the laboratory), we developed indirect methods that allowed us to obtain periodic “snapshots” of feed movement through shrimp guts at 10-min intervals, which were then used to calculate GPT and GPR. We expected to observe differences in GPTs because invertebrates are known to adjust their gut passage dynamics and GPTs should change as a function of food quality. Surprisingly, very large variations in feed component levels, whether fiber, protein, or lipid, did not cause any large differences is GPT within any of the three species. Mean GPTs ranged from 65.7–90.5 min in F. aztecus and L. setiferus and from 48.3–66.6 min in L. vannamei. GPRs were not constant, ranging from 5–16 mm/min when GPTs were short and from 0.1–2 mm/min for longer GPTs. Finding little change in GPTs with large changes in food quality was consistent with previous studies using other methods.

No Abstract available.