Recent surveys using high-resolution imagery have enabled improved detection of Atlantic sea scallops, Placopecten magellanicus, between 10 mm and 65 mm in shell height, allowing the observation of juvenile scallops in the wild, which was previously difficult. Using these high-resolution images from 2008 and 2009 surveys of Georges Bank and the Mid-Atlantic Bight, the distribution and crowding levels of juvenile and adult scallops were examined. Mean crowding values revealed differences in small-scale distribution of scallops that were undetectable with density estimates. Juveniles on Georges Bank were 2.6–3.9 times more crowded than adults, and 2.9–7.4 times more crowded than juveniles and adults in the Mid-Atlantic Bight. The increased crowding of juvenile scallops on Georges Bank may be the result of differences in substrate, sea star interactions, and abundance of filamentous flora and fauna. The incorporation of high-resolution imagery into optical surveys represents an important development in the advancement of survey techniques because it has the potential (1) to quantify year class strength of 1-y-old scallops more accurately; (2) to improve growth, mortality, and biomass estimates in stock assessments; and (3) to advance our understanding of scallop ecology, including recruitment processes and population dynamics.

Bay scallops (Argopecten irradians Lamarck) are ecologically important in U.S. Atlantic waters off northeastern states and in the Florida Gulf of Mexico, and have been intensely harvested from both of those regions for decades. However, a detailed study comparing their basic population genetic structures using more than a single type of genetic marker has not been conducted. Through such a study, key phylogeographic, taxonomic, and fisheries issues can be addressed. We used variation in allozyme loci and mitochondrial DNA restriction fragment length polymorphisms to evaluate and compare the population genetic structures of bay scallops from those two regions, to propose a new interpretation for the composition of the North Carolina bay scallop population, to resolve the taxonomic quandary of Argopecten irradians taylorae, and to evaluate the apparent and potential genetic effects of the common fishery practice of hatchery-based stock enhancement on the genetic diversity and relatedness of Atlantic bay scallop populations. Atlantic Ocean (North Carolina through New York) bay scallop populations are genetically more distant from each other than are Florida Gulf bay scallop populations, except those in Florida Bay. Each Atlantic population has a different phylogeographic history, is quasi-independent, and should be treated as a genetically unique entity. The North Carolina bay scallop population is composed of Argopecten irradians irradians individuals, but also has genetic input from Argopecten irradians concentricus. Bay scallops occurring in Florida Bay constitute a population of A. i. concentricus that has diverged from other Florida Gulf populations because it has undergone repeated contractions and expansions of varying magnitude and is nearly isolated from other bay scallop populations. For the common practice of hatchery-based stock enhancement in the Atlantic, broodstock bay scallops should be taken from the same genetic population, and all stock enhancement efforts should include comprehensive genetic monitoring programs. In some cases, improving the abundance and density of bay scallop aggregations through habitat improvement may be preferable to stock enhancement for bay scallop restoration, but in other cases genetically conscientious stock supplementation or restoration may be the only alternative.

Hatchery production of shellfish seed is necessary to supplement natural recruitment, which is constrained by various stresses, including habitat loss, pollutant contamination, overfishing, and climate change. Bacterial diseases are considered to be a major cause of mortality in hatchery shellfish larviculture; however, overuse of antimicrobials can result in development of resistant strains of bacterial pathogens. The use of probiotics for disease prevention and improved nutrition in aquaculture is becoming increasingly popular as the demand for environmentally-friendly aquaculture grows. The objective of this study was to isolate and evaluate the efficacy of new probiotic bacteria that, incorporated into functional foods for use in shellfish hatcheries, may significantly improve larval survival. First, 26 probiotic-candidate bacteria were isolated from oysters, scallops, and a mass culture of green algae. Fifteen of these isolates (8 oyster strains and 7 bay scallop strains) inhibited known scallop-pathogen bacterial strains B183 and B122 in disk-diffusion assays. Similar to control (unchallenged) oyster larvae, survival of oyster larvae exposed to these 15 probiotic candidates for 48 h was more than 90%. The probiotic candidates were then reisolated from challenged larvae and characterized by Gram stain, colony morphology on solid agar, and the Biolog Bacterial Identification System, finding only 7 distinct strains. Using 12-well microplate assays, 5-day challenges were performed to confirm positive effects of these 7 probiotic candidates on larval survival when challenged with pathogen B183. Oyster larvae exposed to probiotic candidate OY15 had the highest survival; furthermore, survival of pathogen-challenged larvae was significantly improved by the presence of OY15 compared with pathogen alone. In addition, probiotic candidate OY15 exhibited no toxic effects on the microalgal feed strain Isochrysis sp. (T-ISO) in the range of 10²-10⁴ cfu/mL. Future studies will confirm optimal dosage and positive effects of probiotic candidate OY15 on survival during long-term rearing of oyster larvae.

Environmentally-friendly methods for controlling microbial pathogenesis in aquaculture with probiotic bacteria are becoming increasingly preferred over the use of chemical means, such as disinfectants or antibiotics. Previous research at the Milford Laboratory has shown that naturally-occurring bacteria isolated from the digestive glands of adult oysters (Crassostrea virginica) show promise as potential probiotic additives in oyster larviculture, based on bench-scale experiments. The previous, bench-scale challenge studies reported in the accompanying article (Lim et al. this volume) indicated that 48-h survival of 2-dayold oyster larvae supplemented with Vibrio sp. strain OY15 improved after challenge with pathogenic Vibrio sp. strain B183 compared with the pathogen alone. This study investigated further the effectiveness of probiotic candidate OY15 to improve survival of oyster larvae to metamorphosis under pilot-scale culture conditions, both with and without pathogen B183 challenge. The effective dosage of probiotic candidate OY15 that significantly improved larval survival was determined to be 10³ cfu/mL. The LD₅₀ calculated for pathogen B183 was 9.6 × 10⁴ cfu/mL. Results from these bioassays indicated that addition of probiotic candidate OY15 significantly improved survival of oyster larvae to metamorphosis when challenged with pathogen B183 in pilot-scale trials. These studies can provide the basis for the development of functional foods for use in shellfish larviculture that incorporate a naturally-occurring, probiotic bacterial strain.

The Eastern oyster, Crassostrea virginica, is a sensitive bio-indicator of environmental changes ranging from tidal flux to heavy-metal pollution. Extreme fluctuations in dissolved oxygen levels are well documented in Mobile Bay, AL. Extended periods of low dissolved oxygen occurring during the summer months have been shown to cause oyster mortality. The current study examined the effects of anoxia on tubule morphology of the digestive gland in the Eastern oyster as well as the quantity and quality of whole-body anaerobic bacteria counts. Oysters were exposed to anoxic conditions (<0.1 mg/L O₂) at 28°C in a laboratory setting and sampled at 0 h (preexposure), 24 h, 48 h, and 60 h, and after a 4-wk recovery interval. The whole-body anaerobic bacteria count for test oysters (Mean = 1.11 × 10⁶ cfu/mL) from the 60-h interval was significantly higher than counts for the preexposure oysters, 24-h, and 48-h experimental intervals. The most common bacteria isolated were Clostridium sp. Histological examination of oysters exposed to anoxic conditions indicated stress in the digestive gland. Changes in shape and size of digestive tubule epithelial cells occurred, as well as sloughing of secretory absorptive cells into the digestive tubule lumen. Necrosis and inflammation composed of aggregates of hemocytes along with bacterial infiltration into digestive tissue was noted in oysters exposed to anoxic conditions. Digestive tubule lumen ratios of oysters sampled after a 60-h exposure to anoxia were increased significantly in comparison with preexposure oysters. Digestive tubule lumen ratios returned to preexposure morphology after a 4-wk week recovery period. Oysters have the ability to regenerate digestive gland tissue if environmental conditions return to normal. These findings indicate that anoxia exposure at summer temperatures contributes to digestive gland atrophy and necrosis in C. virginica. The combination of digestive gland atrophy, necrosis, and bacterial infiltration into digestive tissues suggests that oysters may be succumbing to infection during periods of anoxic stress.

In the Eastern oyster (Crassostrea virginica) hemocytes are important effector cells for maintenance of defense against pathogenic microorganisms. Various forms of β-glucans have been suggested for use in shrimp and fish aquaculture because of their potential to enhance disease resistance via hemocyte activation. To gain insight to the effects of these compounds in molluscs, changes in circulating oyster hemocyte numbers, population profiles, and adhesion were quantified after injection of β-1, 3-glucans. These agents included zymosan A or MacroGard, an immune stimulant suggested for aquaculture applications. Results were compared with those from estuarine water-injected control oysters at daily intervals for 3 days. MacroGard produced a rapid (by 1 day) elevation of total circulating hemocytes, which remained significant for 3 days; zymosan A stimulation of this response was not statistically significant. MacroGard administration resulted in a sustained increase in percent granulocytes in circulation. Zymosan A also produced an increment in the numbers of granulocytes that became significant by 3 days. Granulocytes are considered to be the most immunologically active hemocyte subclass. Both β-glucan preparations promoted hemocyte aggregation at days 1–3 after injection. Analysis of avidity of hemocyte aggregation using an index of clump cellular density confirmed this observation. Hemocytic aggregation is thought to be an indicator of cell activation. These results suggest that β-glucans can act to increase the numbers of circulating hemocytes available for defense responses, to promote longterm changes in the hemocyte profile favoring immunologically active cells, and to enhance hemocytic aggregation. Further studies of the physiological consequences of these effects of β-glucans on oyster hemocyte defense parameters are in progress.

We present a particle tracking model that simulates the dispersal of the oyster Ostrea chilensis Philippi in Tasman Bay, New Zealand. The model was calibrated to reproduce observed vertical distributions of larvae, and was verified against an independent data set of such distributions. The seabed in Tasman Bay contains little hard substrate other than shell hash. By comparing simulated and observed settlement, we infer that larvae must either be able to sense shell hash at a distance and orient onto it, such that settlement success is higher than indicated by the 1-km² resolution relative density (square meter of exposed shell per square meter of seabed), or be settling on material other than shell hash. The modeling indicates that only a very small proportion of those larvae that do settle travel more than 1 km from their natal location. There are plans to endeavor to restore the oyster fishery by provision of new shell hash to the bed. Our simulations suggest that these new beds will be colonized rapidly only if the new beds are placed close to the remnant beds, or if they are artificially seeded with mature oysters. Conversely, if the new beds are artificially seeded, our simulations imply that a large fraction of the spawn from these adults may be retained within the new bed, rather than dispersing into the surrounding, unsuitable soft sediments.

Oyster shell is a crucial component of healthy oyster reefs. Shell planting has been a main component of oyster restoration efforts in many habitats and has been carried out on scales from individual and grassroots efforts to multiagency efforts across entire estuaries. However, the cycling and lifetime of the shell that makes up the bulk of an oyster reef has only recently received attention, and most of the work to date has focused on the role of epi- and endobionts on shell degradation. Here we report findings from a laboratory study in which we manipulated pH in a flow-through control system using water from the mesohaline mouth of the Patuxent River to measure dissolution rates of intact oyster shell. Shells from the Eastern oyster (Crassostrea virginica Gmelin 1791) with three different legacies were exposed to 4 levels of pH that encompass a range typical of the mesohaline waters of the Chesapeake Bay (∼7.2–7.9 on the NBS scale). Mass loss over a 2-wk period was used to measure dissolution rate on 3 shell legacies: fresh, weathered, and dredged. We found that pH and shell legacy had significant effects on shell dissolution rate, with lower pH increasing dissolution rate. Fresh shell had the highest dissolution rate, followed by weathered then dredged shell. Dissolution rates were significantly different among all 4 pH treatments, except between the lowest (∼7.2) and the next lowest (∼7.4); however, shells lost mass even under noncorrosive conditions (∼7.9). We discuss the implications of our findings to ongoing efforts to understand shell budgets and cycling in oyster reef habitat, the interaction of biological and geochemical agents of shell degradation, and the complexity associated with shell carbonate cycling in the unique milieu of the oyster reef.

As a result of its historical abundance and ecological significance, the eastern oyster, Crassostrea virginica, has been identified as a primary restoration target for the Hudson River-New York Harbor region. Prior to any large-scale restoration investments, a spatial assessment has been made to characterize the region's potential for hosting restored oyster populations. Using existing geographic data of the physical attributes of the river, a GIS-based restoration suitability index has been developed with the goal of identifying specific areas that hold a greater probability for success in oyster restoration. The results show that much of the river's restoration potential is initially limited by the physical environment, depth, and sediment type, and is reduced further by the salinity distribution. The results from this model should be used as a preliminary guide to focus future restoration efforts within the lower Hudson River and New York Harbor area as well as to investigate possible changes to the restoration potential with changing salinities brought on by regional climate change and hydrodynamic alterations.

Today, populations of eastern oysters, Crassostrea virginica, are commonly limited by disease mortality. Resistance to MSX disease has developed in a number of cases, but the development of resistance to Dermo disease would appear to be limited, despite the high mortality rates and frequency of epizootics. Can aspects of the host's genetics or population dynamics limit the response to the disease despite the apparent opportunity afforded by alleles conferring disease resistance or tolerance? To answer this question, we use a gene-based population dynamics model, configured for C. virginica, to simulate the development of disease resistance using mortality as the agent of selection. Simulated populations were exposed to 4 levels of mortality covering the range in mortality observed in Delaware Bay in the 1990s. In each case, disease resistance increased in the simulated population over time, normally proportional to the increase in mortality rate imposed by the disease. However, simulations show that the population responds even at its most rapid rate on multidecadal to half-century timescales. As the mortality rate declines with increasing disease resistance, the rate of further improvement in disease resistance likewise declines. Thus, disease resistance develops over decadal timescales at a 40%-per-year mortality rate, but, as mortality rate falls to 25% per year, the rate of further development of disease resistance extends to half-century timescales. The discouraging profundity is that a mortality rate of 25% per year, yielding a rate of selection profoundly slow, is still very high. In northern climes, significant decrements in oyster abundance will occur. Evidence from fisheries retrospectives suggests that oysters cannot withstand a constant removal at this scale without compromising population integrity noticeably. So, a mortality rate that grievously limits the development of disease resistance still sorely strains the species' ability to maintain a vibrant population necessary to its long-term survival.

Potential lethal and sublethal effects of oil from the Deepwater Horizon spill to oysters (Crassostrea virginica) in Louisiana east of the Mississippi River were examined along a biophysical gradient of oil pollution, salinity, and disease. Approximately 6 mo after the capping of the Deepwater Horizon wellhead, no polycyclic aromatic hydrocarbons were detected in oysters from oil-exposed sites. Variations in oyster condition and reproductive state, and infection with the oyster parasite Perkinsus marinus are consistent with natural differences along the salinity gradient and not with impacts of polycyclic aromatic hydrocarbon contamination.

A century-long decline of the fishery for the Eastern oyster Crassostrea virginica (Gmelin, 1791) in Maryland and Virginia stimulated numerous efforts by federal, state, and nongovernmental agencies to restore oyster populations, with limited success. To learn from recent efforts, we analyzed records of restoration and monitoring activities undertaken between 1990 and 2007 by 12 such agencies. Of the 1,037 oyster bars (reefs, beds, or grounds) for which we obtained data, 43% experienced both restoration and monitoring, with the remaining experiencing either restoration or monitoring only. Restoration activities involved adding substrate (shell), transplanting hatchery or wild seed (juvenile oysters), bar cleaning, and bagless dredging. Of these, substrate addition and transplanting seed were common actions, with bar cleaning and bagless dredging relatively uncommon. Limited monitoring efforts, a lack of replicated postrestoration sampling, and the effects of harvest on some restored bars hinders evaluations of the effectiveness of restoration activities. Future restoration activities should have clearly articulated objectives and be coordinated among agencies and across bars, which should also be off limits to fishing. To evaluate restoration efforts, experimental designs should include replication, quantitative sampling, and robust sample sizes, supplemented by pre- and postrestoration monitoring.

As an intertidal species, the Pacific oyster (Crassostrea gigas, Thunberg) is very tolerant to varying abiotic conditions. The temperature range for survival has, however, not been fully evaluated. Most notably, information about cold tolerance of the species is missing. As a first step toward acquiring a better understanding of the species' cold tolerance, the aim of this study was to measure mortality of groups of Pacific oysters after exposure to simulated winter conditions (-22°C) for 24, 48, and 72 h. Such conditions are not very different from what can be experienced in nature during wintertime in Scandinavia. The Pacific oyster was found to be very tolerant to low temperatures with, in general, 50% survival after 24 h. Thermal acclimatization and premature adjustment to winter conditions allowing for improved survival after cold treatment were also observed.

Shell growth, survival, and physiology were compared between diploid Suminoe (Crassostrea ariakensis) and eastern oysters (Crassostrea virginica) under conditions simulating a U.S. subtropical estuary. Two age groups (4 mo and 28 mo) of both oyster species were grown for 9 mo (December 2006 through August 2007) in quarantine mesocosms (700 L) supplied with ambient flowing (≥ 10 L/min) water (annual temperature range, 18.6–30.4°C; salinity, 28–37.7). There was no difference in overall rates of shell growth between the 2 oyster species over the 9-mo period. Specific growth rates for C. ariakensis did not differ over time, but they did for C. virginica. The growth rate of C. virginica was slowest in the winter (8.9 × 10^-4 mm²/day) and fastest in the spring (43.5 × 10^-4 mm²/day). Mortality of both species rose abruptly in April 2007, and all (100%) remaining C. ariakensis were dead by the end of the study. Although 28% of the remaining C. virginica died in April 2007, there was little further mortality in this species before the study was terminated in August 2007. Physiological responses of both species of oysters were compared under seasonal temperate euhaline quarantine conditions to understand better how temperature affects these species without the confounding unexplained mortality encountered in the subtropical mesocosms. The clearance rate of C. ariakensis (1.2 L/g/h) was half that of C. virginica (2.2 L/g/h) during the summer (25°C); however, respiration rates for C. ariakensis (2.6 ml O₂/g/h) and C. virginica (2.5 ml O₂ g/h) were similar. The low clearance rate of C. ariakensis during the summer resulted in a negative scope for growth (-36.2 J/g/h) during this season. During the winter, C. ariakensis remained physiologically active when water temperatures were as low as 2°C; C. virginica were quiescent during this time. We conclude that the “Oregon” strain of C. ariakensis tested will not thrive in the warm subtropical waters of the U.S. southeastern coast; however, given its native range in Asia, we do not discount the possibility of an adaptation to warmer temperatures over time.

Although several different U.S. hatchery stocks of the Asian Suminoe oyster Crassostrea ariakensis were used in laboratory and field trials assessing performance, and in comparative studies with the native oyster Crassostrea virginica, the genetic composition of these hatchery stocks has not yet been examined comprehensively. Using eight microsatellite markers we investigated the genetic variability among five hatchery stocks and compared the genetic makeup of these stocks with 8 wild populations from Asia. Results showed significant genetic differentiation among the 5 hatchery stocks that was 6-fold larger than that observed among wild populations. A significant reduction in genetic diversity was observed in hatchery stocks compared with wild source populations, indicating a genetic bottleneck. Two long-established stocks showed significant decreases in both allelic diversity and heterozygosity compared with the wild Japanese source population, whereas three recently established stocks showed less severe reductions in allelic diversity and a nonsignificant change in levels of heterozygosity compared with their source Chinese populations. These microsatellite markers also proved useful for assignment of hatchery individuals back to their source stocks with a high degree of confidence. Although assignment of wild individuals back to their population of origin proved less reliable, approximately 70% of wild individuals could be assigned either to their source population or to geographically proximal populations. Our results suggest that results obtained from experiments that used hatchery animals of a single C. ariakensis stock for biological and ecological studies should be interpreted cautiously, because they may not always accurately reflect the behavior of wild populations or of other hatchery stocks.

The objectives of this study were to determine chemical composition of the siphon and the mantle of commercialsize geoducks clams harvested in Southeast Alaska, and to measure textural differences between the two muscle tissues, comparing them with their frozen counterparts. Live geoducks were processed using standard industry practices and analyzed either fresh or after 90 days of frozen storage. The mantle significantly differed in composition and texture from the siphon. The mantle had significantly higher contents of carbohydrates and lipids, whereas the siphon had a higher moisture content. Protein content was similar between tissues, but soluble protein content in the siphon was significantly higher than in the mantle. Large differences were observed in the electrophoretic profiles of the contractile siphon, which had a greater abundance of higher molecular weight proteins than the mantle. There were also textural differences in hardness and shear energy, with the siphon presenting significantly higher values than the mantle. After freezing, hardness values for the mantle significantly increased, and this finding is in line with Southeast Alaska geoduck processor observations. Overall, the composition and textural differences recorded are commensurate with differences in anatomic functions of the siphon and the mantle in live geoduck clams.

Aquaculture of the geoduck, Panopea generosa Gould, 1850, has increased dramatically during the past decade in southern Puget Sound, WA, and the effects of these intertidal aquaculture geoduck beds on local fauna is mostly unknown. This study examined the species composition, relative abundances, and biodiversity indices of mobile benthic fauna in geoduck farm areas of southern Puget Sound. Surveys of geoduck farms in two different stages of aquaculture production were carried out using a trapping strategy with two types of traps. The site in Eld Inlet had predator protection tubes around the planted geoduck. The site in Nisqually Reach was in grow-out phase with no predator protection. Nearby areas with no aquaculture were used as control sites. Traps yielded 1,161 individuals from 15 species of mobile benthic animals during the course of this study. The graceful crab, Cancer gracilis, accounted for 76.3% of all specimens. The effects of geoduck aquaculture on biodiversity were subtle and not consistent between the two locations. Using Coleman rarefaction analysis, species richness was significantly higher (P < 0.05) in the geoduck farm in Eld Inlet compared with its control site, but no significant difference was observed in species richness between the geoduck farm in Nisqually Reach with its control site. Biodiversity was higher in Nisqually Reach compared with Eld Inlet, and Simpson's biodiversity index for the Nisqually Reach geoduck farm was significantly higher than its control site (0.73 and 0.62, respectively, P = 0.001). Large differences in capture rates were noted between female and male Cancer gracilis crab in Eld Inlet and Nisqually Reach. Possible causes of the observed differences between the sites are discussed.

There have been numerous attempts to create and/or develop harvestable tidal areas where juveniles of the natural Manila clam Ruditapes philippinarum may be abundantly stocked. To prevent erosion and/or promote the colonization of natural juveniles through improving the physical stability of bottom sediment, it is important to understand the mechanisms that regulate dispersal and recolonization of benthic juveniles. The physical transport of bottom sediment is known to have a substantial effect on the spatial distribution patterns of infaunal bivalves in intertidal soft-bottom habitats. During the summers of 2004 and 2005, we conducted field experiments to identify the physical transport mechanisms for newly-settled postlarval Manila clams until growth to a size of 1 mm shell length at the Banzu tidal flat of Tokyo Bay in Japan. We used sediment traps to collect natural and released hatchery-reared juveniles, in parallel to acquiring measurements of seawater flow and observations of the spatial distribution of newly-settled natural juveniles. There was a sharp increase in the number of clams that were collected in the traps placed on the soft-bottom surface when τ_w (wave shear stress) exceeded 0.3 N m^-2. Because the τ_c (advection shear stress) was far lower than τ_w (τ_c/τ_w =1/60–1/130), the initiation of juvenile transport appeared to depend primarily on wave-generated oscillatory flow. The number of trapped juveniles regressed linearly to the weight of the sediment that was simultaneously collected in the trap (R² = 0.99, 0.81), which indicated that clams were transported in a similar way to that of sediment grains, despite juveniles and sand particles exhibiting different physical properties (size and specific gravity). Hence bedload transport may have resulted from the biologically induced adhesion of juvenile clams to sediment grains and/or their burrowing behavior. In the release-recovery experiment of marked juveniles, a larger number of clams were recovered from traps that had been placed downstream of the water current from the release point. A denser distribution of the natural Manila clam population settled in mid-July 2004, and subsequently moved several hundreds of meters inshore within a one month period. The concurrent monitoring of bottom flow during a total 4 wk period in the summer of 2004 indicated that τ_w frequently exceeded the incipient threshold of bedload transport (assumed to be 0.3 N m^-2). Consequently, the bedload movement of Manila clam juveniles in the study area was expected to be initiated at a wave shear stress that was greater than the incipient threshold, and in a downstream direction of the advection current. Because juvenile clams in the summer population appeared to be frequently subjected to hydrodynamic stress, which forces juveniles to move and halt incidentally in the early benthic stages, physical transport is likely to contribute to the changing pattern of juvenile distribution at the Banzu tidal flat of Tokyo Bay in Japan.

Biological and ecological research is seriously handicapped because of difficulties experienced in the reliable detection and quantification of bivalve larvae. This is a critical issue in the case of the Manila clam Ruditapes philippinarum (Adams & Reeve, 1850), a largely invasive and commercially relevant species, with important wild, cultured, and naturalized populations throughout the world. A SYBR Green real-time PCR assay, containing TPHI16S1F and TPHI16S2R primers (specific to R. philippinarum female mtDNA), was designed and tested to provide a rapid and high-throughput PCR-based method for larval quantification. Accurate estimations of larval numbers in spiked plankton samples point to the usefulness of this system. It can be used through a wide range of evaluated variable experimental conditions, such as the presence of closely related bivalve species, stationary-dependent plankton abundance, sampling volumes, and larval size.

The occurrence and spread of brown ring disease (BRD) to several northern Mediterranean coasts is described. We report the results of a 6-y surveillance of BRD in natural populations of carpet shell clams (Ruditapes decussatus) in 14 zones along the Gulf of Gabes in Tunisia (southern Mediterranean Sea). BRD symptoms in adult animals resulting from conchiolin deposits in inner parts of carpet shell were observed in all zones surveyed. Infestation rates within each site ranged from 65–100%, and BRD prevalence varied from 1–58% of clams in winter and from 1–33% in summer. Positive correlations were demonstrated between BRD prevalence and Vibrio spp. concentrations in clams. Vibrio tapetis was not identified among the bacterial organisms, suggesting that other marine Vibrio species are capable of causing BRD-like illness in carpet shell clams.

Three selected aquaculture strains of the commonly used hard clam, Mercenaria mercenaria (Linnaeus, 1758)—Massachusetts (MA), New Jersey (NJ), and South Carolina (SC)—were reared in a single hatchery. They were planted in replicate plots in Barnstable Harbor, MA, and Dry Bay, NJ, in spring 2008 and grown to market size. Growth, survival, and QPX (quahog parasite unknown) prevalence and severity were measured in fall 2008, spring 2009, and fall 2009. Growth was similar at both sites for the first summer, but during the second year growth was better in Massachusetts. Overall survival was better for all strains in New Jersey when compared with Massachusetts. Survival of strains in New Jersey was 53.4% and 34.8% for NJ and MA, respectively, closely followed by those in Massachusetts (41.8% and 26.2% for NJ and MA, respectively). Strains from SC seed had the highest prevalence and severity of QPX and the lowest survival (36% and 6.6% in New Jersey and Massachusetts, respectively). Infections with QPX were low at both sites, but this study confirms earlier work indicating that QPX infection rates appear to be strain specific, with strains of southern origin being more susceptible than those of northern origin. Our study also supported anecdotal reports that QPX disease is more severe in Massachusetts than in more southern sites where it has been found. As in most previous field studies, we found that although mortality was correlated with QPX levels, it was considerably higher than infection prevalence would indicate, which suggests that strain interactions with stressful environmental conditions or unidentified factors may be also involved in mortality.

The recent reduction of catches of common shellfish in southern Spain has pointed out an overexploitation of these resources. For this reason, new shellfish resources have been investigated—among them, the venerid Venus nux Gmelin, 1791. To provide information to managers for a better regulation of this new fishery, we studied the reproductive cycle in the Atlantic (Huelva) and Mediterranean littoral (Malaga) of southern Spain from June 1999 to May 2000 using histology and changes in flesh dry weight. Histological examination of the gonads showed a long and asynchronous reproductive period. Spawning occurred throughout the year in both populations. Two different spawning peaks were observed: April/May for the Mediterranean population and June/July for the Atlantic one. These peaks correspond to the highest percentage of population in spawning stage, together with the greatest loss of tissue weight. During the annual reproductive cycle, new activation of the gonads from postactive stages occurred without passing through a resting period in both populations. The absence of a resting period during the reproductive cycle could be related to mild seawater temperatures (12–16°C) and high levels of chlorophyll a (2.4–4µg/L). Considering these data, we propose that if this fishery continues, and taking into account the low recruitment rate and the monocohort structure of the populations, a closed season from June to July for the Atlantic population and from April to May for the Mediterranean one should be considered for management of this new resource.

Laboratory experiments were carried out to evaluate juvenile and adult mortality in Musculium argentinum over a given period of time. Specimens of M. argentinum were collected in May 2009 from the evacuation channel of the Lautaro fish farm, Araucanía Region, Chile (38°32′ S, 72°27′ W), and a laboratory experiment was carried out consisting of 2 treatments (T1 and T2), with 3 replications of each. In each treatment and replication, a plastic container (15×10×5 cm) was filled with water and dead leaf litter from the channel inhabited by the study species. During T1, the population density of the container was 100 individuals (D100); during T2, the population density was 60 individuals (D60). The individuals were allowed 2 days to adapt to their new environment. Every 7 days during the following 2 mo, the anteroposterior valve length of each specimen in each treatment was measured to an accuracy of 0.1 mm. Adults were measured using digital calipers, and juveniles were measured using a stereomicroscope fitted with a micrometer eyepiece. Mortality was determined by counting and measuring the number of empty left valves of adults and juveniles. The mortality rate (MR, measured as a percentage) was estimated by counting the number and recording the size of live individuals (LI) present at the start of each period, the number of recruits (R) entering the system during the period, and the number of dead individuals (DI) during the same period using the formula MR = (DI/[LI R]) × 100. From the results of the current study, it may be concluded that M. argentinum populations have a mortality rate that varies over time, with juveniles showing a higher mortality rate than adults, and that the population density affects significantly the mortality of both classes of individuals. The results also show that mortality in M. argentinum is density dependent.

In a laboratory study, we investigated the clearance rates (CRs), respiration rates (RRs), total hemocyte count (THC), pathological alterations, and mucocyte densities in the gills of the short-neck clam Ruditapes philippinarum when exposed to the toxic dinoflagellate Heterocapsa circularisquama. Within 2 h of exposure to H. circularisquama at a concentration of 5–10³ cells/mL, both the CRs and the RRs were significantly decreased by 43–52% compared with the control CRs and 43–93% compared with the control RRs, respectively (ANOVA, Newman-Keuls, P < 0.05). Clams exposed to H. circularisquama at 10³ cells/mL for 96 h showed a set of defensive and degenerative pathologies that were absent in control clams. Within 3 h, the gills exhibited cilia matting, followed within 24 h by heavy hemocytic infiltration in the connective tissue of plicae, distortion of filaments, hyperplasia, and fusion of adjacent filaments with matted cilia. Within 48 h, the gill plicae became contracted and showed multifocal epithelial hyperplasia, increased filament fusion, exfoliation of the frontal cilia, epithelial desquamation, and abnormal epithelial masses. After 72 h, the gills presented extensive necrosis of epithelial and connective tissues, atrophy and fusion of the filaments, large masses of gill debris and mucus, and extensive exfoliation and loss of the frontal, laterofrontal, and lateral cilia. After 96 h, the gills of moribund clams exhibited more advanced stages of necrosis and degeneration. Quantitative analysis of the pathological alterations showed that both the prevalence and intensity of the defensive pathologies increased significantly, reaching their maximal values after 24 h of exposure, then decreasing. Meanwhile, the prevalence and intensity of the degenerative pathologies continued to increase throughout the experiments (ANOVA, Newman-Keuls/Fisher's LSD, P < 0.05). In addition, significant decreases in the THC (t-test, P < 0.01) and the total, acid, and mixed mucocyte densities in the gills (ANOVA, Fisher's LSD, P < 0.05) were observed after 48 h of exposure. The current study clearly showed physiological, pathological, and defense alterations induced by H. circularisquama in clams, highlighting the occurrence of cytotoxicity and tissue repair failure. Inhibition of feeding and respiration as well as extensive necrosis in the gills, coupled with depression of defense mechanisms resulting from depletion of hemocytes and mucocytes, ultimately resulted in the death of the clams.

Disseminated neoplasia in cultured Mytilus chilensis (Mytilidae) from the Beagle Channel (Tierra del Fuego Province) in southern Argentina has been detected for the first time. The disease is characterized by the infiltration of neoplastic cells with enlarged nuclei and high nuclear-to-cytoplasmic volume ratios. All specimens with disseminated neoplasia were female and exhibited gonadal atrophy in advanced stages of the disease. The high prevalence reported (13.3%) indicates an epizootic level.

The green-lipped mussel Perna viridis is distributed widely in estuarine and coastal areas of the Indo-Pacific region and is regarded as a cultured mussel or by-product in aquaculture. However, in estuarine and coastal waters where salinity varies with freshwater input and rainfall during the wet season, hypoxia frequently occurs, especially when waters are highly eutrophic. The current study aimed to evaluate the effects of two key environmental factors in estuarine and coastal waters—dissolved oxygen (DO) and salinity—on growth and body composition of juvenile green-lipped mussels P. viridis. Parameters studied included shell length (SL), tissue dry weight (TDW), condition index (CI), specific growth rate (shell length, SGR_L; tissue dry weight, SGR_W), moisture content (MC), crude protein (CP), crude fat (CF), crude carbohydrate (CC), crude ash (CA), and energy content (EC). Mussels were cultured for 6 wk at 4 salinities (15, 20, 25, and 30) and 3 dissolved oxygen concentrations (1.5 ± 0.3, 3.0 ± 0.3, and 6.0 ± 0.3 mg 0₂/L) in a 4 × 3 factorial design. All growth parameters (SL, TDW, CI, SGR_L, and SGR_W) decreased under reduced DO and salinities, but interactive effects between these 2 factors were statistically indistinguishable except for SGR_W. Higher percentages of CF and CP, and lower percentages of CC were obtained at reduced salinities and DO. When changes in biochemical content (weight per individual) were compared, both CP and CC content decreased significantly as salinity or DO decreased, whereas no pattern was observed for CF. EC (calories per gram) was not significantly different among DO treatments, but varied significantly with salinity. Total energy content (calories per individual), however, increased significantly with both DO and salinity, but the interaction between salinity and DO was statistically indistinguishable.

Bivalve production in Greece pertains to a vast extent of mussel farming and a few other species of fishery products. Mussel farming in Greece covers 375.5 ha primarily located in the northern part of the country. About 523 farms have been licensed since 1976, of which 218 are using the single long-line floating technique for a nominal production capacity of about 100 t/ha and a farming area of 1–2 ha on average. The total annual production (gross pergolari weight) increased to 36,000 t in 2008. Currently, there is a trend for further expansion by licensing new farming sites. Eighty percent of the farmed mussels are exported fresh and intact, primarily to Italy. One major problem seems to be the increasing number of harmful algal bloom incidents during the past decade. The future of the industry depends on the industrialization of production methods and the development of scale to suppress the production cost. Support of product branding and development of a quality scheme would further strengthen the sector.

This is the first report on the parasites of blood cockle Anadara granosa from the Straits of Malacca. For a histopathological survey, samples were collected for 13 mo from 3 natural habitats: the west coast of Pulau Aman, Malaysia; the east coast of Banda Acheh; and the east coast of Lhokseumawe, Indonesia. After reviewing histological preparations, Nematopsis sp. was found in the connective tissue, gills, gonad, mantle, digestive glands, and foot; trematode sporocysts were identified in the gonads, stomach epithelium, mantle, digestive glands, and foot; and a turbellarian was observed in the stomach epithelium, gonads, digestive glands, mantle, and gills. Remarkable spatial differences were found in the parasitic communities of A. granosa of the Straits of Malacca; however, no apparent temporal variation in the prevalence of any parasite was evident. Nematopsis sp. infection was very common in A. granosa collected from Pulau Aman, with no clear host tissue damage. Trematode sporocysts were observed at all sites, and the gonads were completely lacking in some individuals as a result of infection. A turbellarian was detected without any evidence of pathological damage to the host. From the survey, only a trematode was detected as a potential threat to the natural stocks of A. granosa along the coasts of the Straits of Malacca. Further study should be carried out to identify the specific taxonomic affiliation of the parasites.

Current low densities of the northern abalone Haliotis kamtschatkana may be affecting the fertilization success of this endangered broadcast spawner, thus preventing its populations from recovering to historical levels. This study attempted to determine whether the northern abalone were significantly aggregated during the period just before spawning because this may compensate in part for their low densities. We used scuba to map the spatial distribution, sex, and spawning condition of tagged abalone within grids at three different sites close to Bamfield Marine Sciences Center on the west coast of Canada. Underwater tagging methods were then used to monitor individuals over a 3-wk period during the 2009 spawning season. We found that the populations at all sites had nearest neighbor R ratios significantly less than 1.0, which indicates an aggregated distribution. Within the range of densities observed for our 3 sites (0.12-0.64 adults/m²), the mean distances to the nearest neighbor (1) of either sex, (2) of the opposite sex, and (3) of the opposite sex with ripe gonads were always less than 1.00 m except in one case. Individual abalone aggregated independently of sex; therefore, the probability of finding both a ripe male and a ripe female within an aggregation increased linearly with density. We estimated that the northern abalone populations observed were sufficiently aggregated to make successful fertilization more likely at low densities. This is the first study to map abalone sex and degree of gonad development that allow the analysis of nearest neighbor measurements with respect to gender and spawning condition.

The current study deals with the critically endangered limpet Patella ferruginea (Gastropoda: Patellidae) endemic to the western Mediterranean. The species has been in decline since the early 20th century and is currently restricted to certain locations on the Iberian Peninsula, Corsica, Sardinia, and the North African coasts of Morocco, Algeria, and Tunisia. Its large size and conspicuous shell often makes the species a target of human collection. We describe the results of temporal monitoring conducted on one of the remaining most important P. ferruginea populations in North Africa, and provide quantitative data on growth rates, natural mortality, and harvesting rates. The maximum collection rates were recorded during the summer months, when fishermen most attend the beach. This type of mortality mostly affected medium and large individuals, and increased natural mortality rates up to 37%. All results and previously available data were implemented for population viability analysis. We determined that the species is clearly overexploited in the study area, and may face local extinction within the next 20 y if harvesting activities are not controlled. Even though more precise predictions could be obtained by using a longer time series, our study is the first attempt to model the future viability of the species, and indicates the urgent need of establishing efficient protection measures.

Channel whelks (Busycotypus canaliculatus) were cultured from hatch through 171 days to describe the early life history and growth rates of juveniles. Whelks began to hatch at water temperatures of 15–18°C. Channel whelks grew quickly from average shell lengths (SL) at hatch of 3.8 mm (SE = 0.1) to an average of 48.4 mm SL (SE = 1.3, n = 42 individuals) at 171 days post-hatch. The largest individual reached 53.2 mm SL, a gain of ∼49.4 mm SL in 171 days, with a growth rate of 0.29 mm/day. Juvenile whelks readily consumed oyster (Crassostrea virginica) and mussel (Geukensia demissa) prey. A linear growth model (SL = 0.21 × [Age (days post-hatch)] 1.6068) was used to describe the channel whelk age-at-length relationship. This is the first published growth curve for juvenile channel whelks. The observed juvenile growth rates for B. canaliculatus (0.21 mm/day) are higher than those previously described for Busycon carica. Whelk mortality was very low (<2%) after whelks reached SLs of ∼10–12 mm.

The New Zealand mudsnail (NZMS) is an invasive first discovered in Olympia, Washington's, Capitol Lake in 2009 and has since been detected in the lake at high densities. In this study, we review salinity tolerances from NZMS investigations conducted in the wild and in the laboratory. Based on the review, we backflushed Capitol Lake with saltwater introduced through a dam that connects the lake to the sea to examine the effect of increasing the lake's salinity on NZMS survival. We present pre- and postbackflush survival rates from 26 sample stations, 8 of which were supplemented with the topical application of salt. Increasing the lake's salinity decreased survival, and the topical application of salt increased the effect. Sample size and location had a significant effect on survival. We subjected pre- and postbackflush NZMSs to laboratory saltwater trials and used the data to construct a generalized linear model to predict survival rates under various salinity exposure regimes. More NZMSs were killed in response to the backflush than was predicted by the generalized linear model. Water temperatures in the lake were lower than those used in the laboratory and this may have decreased NZMS resistance to increased salinities in the lake.

The physicochemical and functional properties of actomyosin from fins of frozen, stored squid caught either by jigging machines (AME1) or by trawling (AME2) were investigated. At time 0 SDS-PAGE, 10% of AMEl and AME2 showed the characteristic polypeptide bands of myofibrillar proteins and two components of 155 kDa and 55 kDa. Both the degradation of the myosin heavy chain and an increase in the 155-kDa component occurred earlier in AME2. Irrespective of the capture method used, no significant changes in protein solubility and a decrease (P < 0.05) in reduced viscosity were observed in both AMEl and AME2. Surface hydrophobicity (SoANS) of AMEl increased (P < 0.05) during the first month of storage and remained unchanged thereafter. The SoANS of AME2 was unchanged. The initial value of SoANS of AME2 was higher than that of AMEl. The emulsion activity index and the emulsion stability of AME2 increased (P < 0.05) during the first month of storage, whereas the emulsion activity index and emulsion stability of AMEl remained unchanged during the frozen storage period. These results indicate that the capture method influences the rate of autolysis and the functional properties of myofibrillar proteins of fin from frozen, stored squid.

Examining congeners can help identify critical differences between species that affect invasion and spread. We examined Dreissenapolymorpha (zebra mussel) and Dreissena rostriformis bugensis (quagga mussel), which are important invaders in freshwater and share general ecological characteristics, to determine whether they had similar rates of invasion at different spatial scales (global, regional, local, and individual water bodies) from the time of first introduction to the present. We also contrasted differences in ecological and population characteristics that could influence speed of spread. Although D. polymorpha and D. r. bugensis are relatives and share a common native habitat, morphology, lifestyle, life history, and dispersal potential, D. polymorpha was found to be a better invader than D. r. bugensis at most spatial scales throughout their invasion history. Spread at the regional scale in North America was the same for both species, but the initial rate of invasion by zebra mussels far outpaced the spread of quagga mussels both in the United States and in Europe. The estimated lag time between initial introduction and maximal population size is 5 times shorter for D. polymorpha than for D. r. bugensis, which may be an important factor affecting the speed with which this species can spread. Differences in population dynamics may facilitate the increased rates of spread of D. polymorpha relative to D. r. bugensis, especially at smaller spatial scales.

The planktonic veligers of the invasive quagga mussel were present year-round from April 2008 to March 2009 in Lake Mead, with high abundance from September to October (>20 veligers/L), whereas the percentage of competent veligers, in terms of the ability to settle, peaked from November 2008 to January 2009 (>60%). The results from this experiment are useful in understanding the life history and population dynamics of quagga mussels in the lower Colorado River Basin.

This study was undertaken using data drawn from 5 sites along the Atlantic shoreline of Galicia (Northwest Spain) for a period of 2 y. The length—weight relationship of Pollicipes pollicipes (Gmelin, 1789) was estimated to observe the way in which individuals of this species gain weight as they increase in size. A classic allometric model was used for the purpose. As an alternative, a more general nonparametric model was also estimated, using local linear kernel smoothers. Comparison of these two models showed that use of the nonparametric model resulted in a better fit of the data. In addition, derivatives were used for estimating a size of capture for this species. For the same purpose, we also estimated this crustacean's mean size at sexual maturation (L₅₀) and the number of broods that it spawns per annum. Individuals' weight gain, a female maturity size of 15.7 mm, and P. pollicipes' estimated 1.73 broods per annum tend to suggest a size of capture based on a rostrocarinal length of 21.50 mm.

We determined the dominance hierarchy in competition for refuges by the xanthid crabs Panopeus simpsoni, Eurypanopeus depressus, Rhithropanopeus harrisii, and juvenile Callinectes sapidus, and used it to predict predation risk from adult blue crabs in laboratory experiments at two salinities. Experiments were first run with pairwise combinations of species with limited refuges. To determine any effects of diffuse competition on dominance and predation risk, all four species were then held together with limited refuges. The same process was then repeated in experiments with a blue crab predator, again with limited refuges. Juvenile C. sapidus and E. depressus were dominant over P. simpsoni and R. harrisii in occupying shelters at both salinities, in both paired- and multiple-species combinations. Dominance in refuge use increased with salinity in C. sapidus, E. depressus, and P. simpsoni, but not in R. harrisii. Because they were more dominant, C. sapidus and E. depressus sustained lower mortality to predation than P. simpsoni, and R. harrisii. Furthermore, field sampling indicated the least dominant species, R. harrisii, was common only in low-salinity areas with few predators. The greater dominance of C. sapidus and E. depressus may thus decrease their predation risk in estuarine waters and explain their broader distribution across salinities.

Recently, infectious diseases have seriously inhibited the aquaculture of mud crab Scylla serrata in southeastern China. A better understanding of the immune molecules and defense mechanisms may be beneficial in reducing the harmful nature of these diseases. Available data show that hemocyanin (HMC) is a copper-containing respiratory protein present in the hemolymph of both mollusc and arthropod, and that it plays multiple roles in immune defense. In the current study, HMC from S. serrata (HMC-C) was isolated, and its hemolytic properties were investigated. The HMC-C shows hemolytic activities against vertebrate erythrocytes. The hemolysis displays dependency on pH, temperature, divalent cation, and HMC-C concentration. Complete hemolysis occurred at a concentration of 0.1 mg/mL, pH 5.0, and temperature of 37^°C in the presence of calcium. Furthermore, all 5 subunits of HMC-C were detected in the solubilized incubation products of erythrocytes with HMC-C, and the hemolysis could be inhibited to different degrees by osmoprotectants of various molecular masses. Together, our data suggest that HMC-C mediates hemolysis by inserting all 5 subunits into the erythrocyte membrane, causing cell rupture through a colloidosmotic mechanism.

The aim of this study was to compare the reproductive performance of the wild shrimp species Farfantepenaeus paulensis and Farfantepenaeus brasiliensis in captivity. The broodstocks were collected in offshore waters in Santa Catarina and transferred to the Marine Station of Aquaculture of the Federal University of Rio Grande. Broodstocks with a similar body weight between the two species were selected to measure reproductive performance. Females with mature ovaries were identified each day to obtain measures of reproductive performance. After spawning, fertilization rates were determined by microscopic examination. In addition, three samples of 100 eggs were collected to determine hatching rates, and three samples of 100 nauplii were collected to evaluate the rate of metamorphosis to protozoa. For males, spermatophores were manually extruded, weighed, and homogenized in 2 mL calcium-free saline solution, and 0.1 mL trypan blue was added. Sperm counts, abnormal cells (malformations of the main body or absence of the spike), and dead cells (blue coloration) were estimated with cell counts, using a hemacytometer under a light microscope. Spermatophore melanization was checked. The larval production of the two species was similar, but F. brasiliensis spawned in less time after unilateral eyestalk ablation. The spermatophore weight and sperm count were higher in the F. brasiliensis males, and none of the shrimp showed melanization.

The current study quantified the relative contribution of dietary carbon and nitrogen supplied by live biomass of the green macroalgae Ulva clathrata and a commercial inert feed to the growth of juvenile shrimp Litopenaeus vannamei. The stable isotope ratios of carbon and nitrogen (δ¹³C and δ¹⁵N) were analyzed in both food sources, whole bodies, and muscle tissue of shrimp reared on co-feeding regimes where 75%, 50%, and 25% of daily consumed macroalgal biomass was substituted by inert feed (regimes 75F/25U, 50F/50U, and 25F/75U, respectively). Higher growth rates were observed in shrimp fed regime 75F/ 25U (k = 0.062), followed by shrimp fed only inert feed (100F, k = 0.060). Animals reared only on U. clathrata (100U) showed minimal growth (k = 0.008) and very high metabolic turnover rates of carbon and nitrogen. Isotopic values measured in inert feed (δ¹³C = -23.0‰, δ¹⁵N = 9.1‰) and macroalgae (δ¹³C = -13.1‰, δ¹⁵N = -3.5‰) were highly contrasting and both had a rapid influence on the isotopic values of shrimp. Animals reached full isotopic equilibrium through growth and fast metabolic turnover in only 2 wk, except shrimp fed macroalgae only. At the end of the experiment, δ¹³C and δ¹⁵N values in shrimp reared on all cofeeding regimes were strongly biased toward the isotopic values of U. clathrata. Total dry matter contributions to growth were estimated using an isotope mixing model, and considered the elemental concentration of both nutritional sources. Results indicated that shrimp in the co-feeding regimes incorporated significantly higher amounts of dietary carbon and nitrogen from the macroalgal biomass. Shrimp in treatment 75F/25U incorporated 52% of carbon from the inert feed and 48% from the macroalgae. Animals under feeding regimes 50F/50U and 25F/75U incorporated higher amounts of dietary carbon from U. clathrata (65–89%) when compared with carbon proportions supplied by both co-feeding regimes (33-70%), and also incorporated the majority of nitrogen from the macroalgae. However, a high incorporation of nitrogen was not reflected in larger growth in the latter treatments because metabolic turnover rates were very high. Estimated turnover rates ranged from 0.049–0.191/day for carbon and from 0.013–0.100/day for nitrogen, and values followed an increasing trend as a function of macroalgae consumption. Nitrogen halftimes in tissue consistently decreased throughout the different treatments from 9.5 days (100F) to 6.4 days (100U). Proportions of incorporated nutrients in muscle tissue followed similar patterns as those observed in whole bodies.

The U.S. Food and Drug Administration (FDA) provides guidance to state shellfish control authorities on establishing prohibitive closure zones in proximity to wastewater treatment plant (WWTP) discharges with the purpose of minimizing the exposure of molluscan shellfish to health hazards posed by bacterial and viral pathogens present in wastewater effluents. For more than 25 years, the FDA has recognized conditional area management as an option to minimize the size of a prohibitive closure zone, and to enlarge the size and productivity of shellfish growing areas. To use this option, the FDA has recommended achieving a 1,000:1 dilution of effluent within the perimeter of the prohibited closure zone. Using newly available analytical methods and hydrographic equipment, the FDA is undertaking studies to determine whether its 1,000:1 dilution recommendation is supported by the findings. From 2007 through 2009, the FDA conducted field investigations to assess the impacts of wastewater effluent from a large municipal WWTP that discharges into Alabama's Mobile Bay. The dilution of the effluent in the bay was ascertained by conducting a hydrographic dye study using rhodamine WT tracer dye. Submersible fluorometers fastened to oyster cages at sentinel stations were used to determine continuously the dilution of the dye-tagged effluent throughout a 4-day study period. In addition, dilution and dispersion of the dye-tagged effluent was tracked throughout Mobile Bay by fluorometric measurements made while conducting boat transects. The microbiological impacts of the wastewater on molluscan shellfish were assessed by testing oysters placed in cages at sentinel stations at various distances along the anticipated path of the effluent. Levels of fecal coliforms, Escherichia coli, male-specific coliphage, and norovirus genogroups I and II were determined. Norovirus genogroup II was detected in oysters that were located as far as 5.74 km from the discharge, an area in close proximity to the calculated 1,000:1 dilution line. Results also showed that the levels of indicator microorganisms and viral pathogens in the shellfish inversely correlated with increased dilutions of the wastewater effluent in Mobile Bay.