Survival and growth of triploid Crassostrea virginica and triploid C. ariakensis were investigated at four sites surrounding Chesapeake Bay, United States, that varied in salinity, tidal regime, water depth, predation intensity and disease pressure. Four experimental treatments were established at each site: C. virginica; C. ariakensis; 50:50 of C. virginica: C. ariakensis; and shell only. Oysters were deployed at mean shell heights of 12.80 mm and 13.85 mm (C. virginica and C. ariakensis, respectively), at an overall density of 347.5 oysters m-². Oyster survival and growth varied significantly with site and species. Survival was significantly higher in C. virginica than C. ariakensis at the intertidal site, and significantly higher in C. ariakensis than C. virginica at the highest salinity, subtidal site. Survival did not differ significantly between species at the mid and low salinity, subtidal sites. For both species, survival differed significantly between sites, with lowest survival in both species occurring at the intertidal site. Among the subtidal sites, C. virginica survival varied inversely with salinity, whereas C. ariakensis had the lowest survival at the mid salinity site. Eight months after deployment C. ariakensis were significantly larger than C. virginica at all sites. This difference generally persisted throughout the experiment, though the size differences between oyster species at the lowest salinity site were small (< 10%). Shell heights within single-species treatments differed significantly between sites; highest growth rates were observed at the high salinity, subtidal site, whereas lowest growth rates were observed at the high salinity, intertidal site. At low and mid salinity subtidal sites, C. ariakensis shell heights were significantly greater in the single-species treatment compared with the mixed-species treatment. Perkinsus marinus infections occurred in both species at all sites, with prevalences varying between sites. In C. virginica, moderate and high intensity infections were only common at the two higher salinity sites, whereas infections in C. ariakensis were generally low to rare. Haplosporidium nelsoni infections in C. virginica were only observed at the two higher salinity sites and prevalences were generally low. Two out of 53 C. ariakensis tested at the high salinity, subtidal site had rare H. nelsoni infections. Bonamia spp. infections were never observed. Our study supports previous laboratory findings and observations from its native range that C. ariakensis survives poorly in intertidal habitats. In subtidal habitats, however, C. ariakensis displayed broad environmental tolerances, often exceeding native oyster survival and growth rates. Post-introduction C. ariakensis populations would be shaped by the survival and growth patterns described here, but also by their reproductive success, larval survival, predator-prey interactions and prevailing disease dynamics.

Increases in the frequency and duration of hypoxia and the loss of biogenic reefs are two of the most prominent environmental insults to estuaries. We investigated the interaction between moderate hypoxia and habitat restoration activities on estuarine ecosystems by measuring population growth and somatic growth for newly settled Eastern oysters (Crassostrea virginica). Experiments were conducted at a site that historically experiences moderate hypoxia (2.0 mg l^-1 < [O₂] < 4.0 mg l^-1) (Whitehouse Reef) and at a site that experiences normoxia (Dauphin Island). Panels with known starting densities of oyster spat were deployed at the surface, 1.25 m above the bottom, and 0.5 m above the bottom at both sites. Population growth at the bottom and the 1.25 m panels at Whitehouse Reef was -1% to 0% individuals day^-1 caused by periods of moderate hypoxia; however, as oxygen conditions improved in September, population growth increased to approximately 1 to 3% individuals day^-1. For these two panels, total population growth averaged 1% over the experiment duration. For the surface panel at Whitehouse Reef and all three depths at Dauphin Island, population growth remained positive with population growth of between 2% to 17% individuals day^-1. Somatic growth indicated significant location and depth specific differences with somatic growth being negatively correlated with depth. Marginal water quality caused by moderate hypoxia may limit oyster population growth to a much greater extent than predicted by previous laboratory experiments. Additionally, we demonstrate that low-cost experiments prior to the initiation of restoration activities can help ensure success by providing critical in situ information on design and location.

We describe oyster population trends in the James River, VA from 1993 through 2006 using quantitative fishery independent survey data collected using a stratified random design. The 23 reefs contained in the study area cover a total of 2.41 × 107 m² and vary in individual size from 1.26 × 10⁴ m² to 4.98 × 10⁶ m². There is a marked pattern in density of oysters among the reefs: during the study period a small group of reefs comprising 5.4% of the total area consistently contained between 25.7 and 55.5% by number and 35.8 and 54.8% by biomass of the total oyster population. The highest density reefs exhibit, with very few exceptions, mean densities well in excess of 200 oysters m^-2, typically between 300 and 500 m^-2, with a single maximum value of 773 oysters m^-2 in 2002 coincident with the highest annual recruitment observed during the study period. Recruitment events were usually followed by very high mortality with very small percentages of the population reaching ages ≥3 y of age. A strong stockrecruit relationship is absent; rather population demographics appear to be dominated by periodic high recruitment events. Biomass maxima tended to lag one to two years after recruitment maxima. Standing stock for the total system varied between 1.07 × 10⁸ g and 3.31 × 10⁸ g (107 and 331 metric tonnes) in 2003 and 2005, respectively as the 2002 recruits grew and suffered mortality. Age-at-length relationships were estimated from demographics: using a July 1 birth date and a November 1 survey date giving lengths of 37.3 mm at 0.33 y, 58.9 mm at 1.33 y, 80.5 mm at 2.33 y, 102.1 mm at 3.33 y and 123.7 mm at 4.33 y Length demographics were recast as age demographics to estimate annual proportional mortality. Mean proportional mortality values for age 1 oysters range from a low of 0.2–0.4 to a high in excess of 0.7. Age 2 mean proportional mortality values range from a low of 0.41 to a high exceeding 0.75. The proportional mortality for age 3 and 4 y olds generally exceeded mean values of 0.6 with highest values approaching 0.95. In all cases, these values exceeded mortality estimates calculated using traditional box count methods by a considerable margin. The ability to accurately estimate age specific mortality allows the construction of shell (habitat) budgets for the individual reef systems. Shell half-life loss rate estimates in the most productive reefs is between 2 and 3 y, and the population is maintained by the continual and extraordinary recruitment in the face of high mortality - the latter driven by disease (predominantly Perkinsus marinus) epizootics. The shell resource, even on the most productive reefs, is modest, equivalent to little more than a monolayer several centimeters thick. Individual reefs demonstrate remarkable stability as either high shell density high population density associations (high:high) or low shell density - low population density associations (low:low), even in the face of temporal population and demographic fluctuations associated with disease related mortality. The probability of manipulating either shell and/or live oyster density to effect the transition of a low:low reef to a high:high reef is considered bleak in the face of extant recruitment and mortality patterns. The primary impediment to population expansion or rebuilding is high and uncontrolled mortality rather than a lack of recruitment. Given the large numbers of oysters in low salinity refugia that have the ability to continually contribute to the larval pool, active selection against disease susceptible oysters on a system wide basis is unlikely.

Scrippsiella spp. resting cysts, unlike many other dinoflagellate cysts, possess an outer layer of calcite beneath which is a thin sporopollenin wall. This feature may affect cyst survival through the digestive tract of benthic organisms, when they consume the cysts. The extent of digestibility is related to the degree to which grazing by benthic organisms could influence a benthic cyst population. To test consumption and digestion of a representative Scrippsiella cyst by one benthic grazer, the eastern oyster (Crassostrea virginica) was fed culture-produced resting cysts of the dinoflagellate Scrippsiella lachrymosa under controlled conditions. Cyst recovery from no-oyster, control containers was 97%; therefore, digestive destruction of cysts could be quantified as the difference between cysts added to experimental containers containing oysters and the number of intact cysts recovered after a period of oyster feeding. In each treatment, 18% of the cysts were destroyed after being ingested at a cell density of 43.4 cysts/mL and 11% were digested at a higher cell density (263.2 cysts/mL). Cysts were observed to become rounded and turn yellow after first losing the outer, calcareous wall as a first step in digestion. In fecal-pellet samples, contents from broken cysts could be found as well as intact cysts and rounded yellow cysts. Viability of ingested cysts was not evaluated, but it seems that Scrippsiella cysts are relatively resistant to digestion by oysters.

Large numbers of genetic markers are needed for genomic analyses in the eastern oyster (Crassostrea virginica). We previously identified 53 simple sequence repeat (SSR) markers from an expressed sequence tag (EST) database using a high selection standard. We mined the same EST database again using a lower threshold (>5 di-nucleotide and 4 other repeats) and identified 330 new SSR-containing ESTs. Primers were designed for 201 suitable sequences, and PCR was successful for 137. The screening of 113 primer pairs that produced fragments shorter than 800 bp produced 66 polymorphic SSR markers, which were characterized in 30 oysters from three populations and a full-sib family. The SSRs had an average of 5.4 alleles per locus, ranging from 2–12. Thirty-four loci segregated in the family, with seven showing significant deviation from Mendelian ratios after Bonferroni correction. Nullalleles were observed at 17 loci. The EST-derived SSRs are part of expressed genes, and most of them should be useful for gene and genome mapping. This study shows that more SSR markers can be developed from ESTs using lower selection standards.

A program for restoration of the public oyster grounds at the mouth of the Rappahannock River was initiated by the Commonwealth of Virginia in 2000. Responding to pressure from harvesters, the state developed a management strategy that allows commercial harvest from some of these grounds while maintaining the development of a potentially disease tolerant broodstock population in nonharvested sanctuaries. To assess this management plan, a STELLA model of the oyster fishery that links the biological system, the state management program and harvest effort was developed. The model portrays one area open to harvest once every three years. One sector of the model shows the effects of the state's program of enhancing natural productivity by shelling and maintaining sanctuaries of broodstock oysters. High natural mortality rates caused by disease and predation are shown to severely reduce the number of juveniles that reach maturity in the population growth sector. In the harvest sector, one half of the mature oysters are taken during the open season as tends to be the case in this fishery. Whereas revenue net of harvester costs is found to be positive in some scenarios, including management policies such as restricting the number of vessels, limiting the season, revenue net of state costs and revenue net of both costs are always negative. The management program is not justified by purely monetary returns. Recovery of the public oyster grounds using the native species is thus of doubtful value without a truly disease tolerant strain or the presence of some nonmonetary benefits of native oyster population increase.

Oyster (Crassostrea virginica) aquaculture has a long history and tradition in Long Island Sound (Connecticut, USA). Although most of the producers practice traditional on-bottom aquaculture, there are a growing number of individuals utilizing bottom gear for cultivation and depuration. The use of this gear presents a potential conflict in eastern Long Island Sound where the last remaining populations of eelgrass (Zostera marina L.) exist. Shellfish aquaculture activity has been identified as a potential source for negative impacts to eelgrass populations. However, bivalve aquaculture has also been shown to provide an equivalent or greater degree of ecosystem services as submerged aquatic vegetation. The effects of short-term oyster depuration activity were gauged by comparing eelgrass reference sites and experimental plots (eelgrass areas containing oyster depuration cages with and without oysters) in triplicate. Changes in sheath length of the eelgrass 1 m from the cages were used as a proxy for growth rate. The aquaculture gear had no effect on this measure of growth rate of eelgrass in any of the deployments. Sediment characteristics (sediment chlorophyll, sediment % organics) in the cage footprint and 1m from the cages also failed to show an effect of the depuration cages on the local environment. Video monitoring of the footprints and local area indicated little physical damage to the eelgrass beds as a result of the short deployment of the aquaculture gear. The water column at all three sites was vertically well mixed and no effect of the cages on water column light and other characteristics was detectable. The results of this study indicated that at the current level of activity, short-term depuration of oysters has minimal effect on eelgrass growth, water quality and the sediment characteristics measured. However, if depuration activity expands in terms of the amount of gear and/or individual operations, it may result in measurable effects. Understanding the interactions between shellfish aquaculture activity and the marine environment is necessary for sustainable growth of the industry.

The presence of bivalves and bivalve aquaculture can have positive and negative impacts on seagrass and associated benthic communities. Some oyster (Crassostrea gigas) aquaculture methods recently have been restricted to reduce benthic disturbance and protect native eelgrass (Zostera manna) in West coast (USA) estuaries. We argue that aquaculture, like all food production systems, involves tradeoffs with natural systems, but that the magnitude of those tradeoffs depends on the ecological details of the production system. Capitalizing on oyster aquaculture farms as large scale “manipulations” in Willapa Bay, WA (USA), we explored three different oyster aquaculture methods (mechanical harvest or “dredged” on-bottom, hand-picked on-bottom and long line off-bottom). We found that both the biological (oyster-eelgrass interactions) and physical (disturbance or structure) components of aquaculture led to changes in the eelgrass population. Eelgrass density declined with oyster density in all aquaculture areas, likely as a result of direct competition for space. Eelgrass relative growth rate, plant size, and production did not change with oyster density. However, all eelgrass measures were affected by aquaculture, and the type and magnitude of impacts varied among eelgrass measures and aquaculture methods. Throughout the bay, eelgrass in long line areas occurred at densities indistinguishable from nearby uncultivated areas, but in 2004, eelgrass in long line areas was smaller (32%) and had lower production per area (70%). Cultivating oysters in dredged or hand picked beds increased eelgrass growth rates slightly, but led to lower eelgrass density (70% and 30%, respectively), plant size (32%, both cases), and production (70%, both cases). In a large scale simulated mechanical harvest experiment, the temporal response of eelgrass density varied dramatically by site, ranging from 1 to >4 y. If eelgrass impact reduction, rather than avoidance, is identified as the management goal, the degree of tradeoff between eelgrass habitat and oyster production can be minimized by managing aquaculture methods or oyster planting densities, depending on the eelgrass measure of interest. Explicit management goals and appropriate eelgrass habitat indicators must be developed before our findings can be used to suggest best management practices for intertidal aquaculture in the Pacific Northwest.

Shellfish Quality Assurance programs rely on the use of bacteriological fecal pollution indicators as a routine monitoring tool for risk assessment and management in shellfish growing areas. Internationally, shellfish programs vary in detail but are typically based on either the United States model, as in Australia, which relies on the enumeration of indicator bacteria in water as a measure of fecal pollution, or the European Union model, which assesses the exposure of production sites to fecal pollution by determining indicator bacteria present in shellfish flesh. The equivalency of these approaches for delivering the same level of public health protection is not immediately apparent Both indicator tests are used in combination in a very conservative approach adopted in the Australian state of New South Wales (NSW) by the Shellfish Program for the oyster (predominately Sydney rock oyster) fishery, the country's oldest and the state's most productive fishery. This study reports on the analysis of a large data set of these two indicators taken at multiple sites within three NSW estuaries between 2000 and 2005. We report on performance measures used routinely in epidemiological studies to compare the two tests. These measures demonstrate poor agreement between the two tests. When the harvest area is deemed closed by the water test the odds of a negative test based on shellfish flesh is approximately one in four. Conversely, the odds of a positive test based on shellfish flesh occurring during extended periods of dry weather when the water test is clear exceed one in five and are seemingly random in occurrence. We are able to demonstrate a highly significant statistical relationship between the water test and environmental covariates of rainfall, salinity, and water temperature. We use k-fold cross validation methods to develop predictive models using these environmental covariates that can account for over 90% of the variation in water test readings. In contrast we are unable to demonstrate a valid predictive model for the oyster flesh test using these covariate. We discuss the results of these analyses and suggest that there are significant issues with the efficacy of the shellfish flesh test and, in particular, the unexplained systematic error that occurs at a high rate in the current program. The dual use of these tests in harvest management results in routine uncertainty that must create significant unpredictability and costs in trade. In turn, this uncertainty and the costs of testing result in levels of commercial risk that could prove unsustainable. The study highlights the need for the performance of tests to be rigorously appraised in shellfish quality assurance programs. In so doing it may be possible to maintain public health standards while minimizing unnecessary disruptions and costs in the trade of fresh oysters.

In 2000, the northern quahog (= hard clams) Mercenaria mercenaria population was surveyed in Raritan Bay with the purpose of determining sustainable harvest levels. To complement this population survey, we determined the size-at-age structure and experimentally determined mortality rate and size specific growth of adult clams. Clams of a range of sizes, obtained from the sampling program, were measured, cleaned, and aged by counting growth rings in sectioned shells. Experimental plots were established in the low intertidal zone at two sites in the Raritan/Sandy Hook Bay system. Marked clams of five sizes were planted in three seasons and harvested quarterly. Experimental estimates of mortality and survival were based on collected live and dead individuals and are thus conservative because they do not address the numbers missing. Some of the clams from both sites were removed from the area by predators. Estimated mortality for individuals >25 mm by instantaneous rate yielded a mean of 0.0176. Integrating the size specific information with the size-frequency distribution from field survey yielded an average instantaneous mortality rate of 0.0187. Growth, based on the difference between the mean size planted and the mean size of the same size class retrieved was analyzed with a general ANOVA, and exhibited typical seasonal growth. The smallest size individuals grew faster than larger individuals. Survey data indicated an increasing clam population and increasing harvests. The survey mortality estimates, based on box counts, seem to overestimate losses. Our experimental work suggests adult mortality rates of nearly 2%, but loss of individuals from the plots made computation of exact mortality rates difficult, and 2% probably underestimates adult natural mortality rates. The results indicate that current levels of fishing mortality are sustainable with 3% natural adult mortality, but a natural adult mortality rate just above 5% would reduce the population growth to near zero. This information is important, because there has been interest in establishing additional depuration facilities to take advantage of the clam population and put more people to work. To sustain current levels of harvest, it will be essential to increase population level monitoring activities over time to assure the population is not being over harvested because of slight changes in recruitment or mortality rates.

We evaluated the technique of measuring the exhalant siphon area (ESA) as an indicator of feeding activity in the blue mussel, Mytilus edulis. To accomplish this, we established the relationships between ESA measured using video and image analysis and clearance rate (CR) measured simultaneously in mussels exposed to various concentrations of microalgae as a food source in the laboratory. Two size classes of mussels (30 and 60 mm shell length) were fed 6 and 7 concentrations of the unicellular alga Isochrysis galbana., respectively (0, 0.6, 1.2, 1.8, 2.4, 3.0, 6.0 mg L^-1). ESA and the variation in feeding activity associated with individual mussels significantly influenced CR in 60mm mussels, whereas effects of algal concentration were not significant within the range tested. Individual variation in feeding activity significantly influenced CR in 30 mm mussels. However, unlike the 60 mm mussels, ESA did not significantly influence CR, whereas algal concentration did have a significant effect in 30 mm mussels. We did observe significant relationships between ESA and CR in some groups of mussels suggesting it may be a useful indicator of feeding activity under certain circumstances. However, the high degree of variation observed in our laboratory-based experiments on the relationship between CR and ESA leads us to conclude that measurements of ESA may be better used as an estimate of general behavior trends in feeding rather than a quantitative measure of clearance rate.

Crabs and sea stars are known to preferentially select mussels with morphological traits that diminish the predators' searching or handling times. I compared two distinct morphotype of mussels (Mytilus trossulus; Gould, 1850) from Howe Sound, British Columbia, Canada, by dissection and measurement. Then, I experimentally offered mussels of the two morphotypes on the same patch to crabs (Cancer productus; Randall, 1839) and sea stars (Pisaster ochraceus; Brandt, 1835) to quantify the extent to which these predators select prey based on morphological features. Sea stars preferentially consumed mussels with gaps in shell closures, although these mussels also had larger adductor muscles compared with mussels rejected. Gaps at the shell margin presumably allowed sea stars easier access between shell valves to insert their stomachs and begin digestion. Small crabs preferentially consumed mussels with thin shells, which are easier to crush, whereas, large crabs consumed more thick-shelled mussels, possibly because these mussels were larger and offered greater energetic return. However, overall, crabs and sea stars did not exhibit strong preferences for smaller or larger mussel prey. These findings indicate that morphological features of mussels are important in prey selection by crab and sea star predators. Predator selectivity could cause a trade-off in defense strategies in mussels, and ultimately mediate indirect effects between these predators in the rocky intertidal community.

The effect of diet quality on reproduction and energy storage in bivalves has not been widely investigated. Food quality and quantity influences reproductive success in many bivalve species, and the timing and rate of reproductive maturation is a dominant influence on natural population dynamics, whereas understanding and controlling reproduction is vital for the reliable production of juvenile mussels for aquaculture. In this study, adult mussels were fed for six weeks on 1 of 4 diets: (1) raw seawater; and raw seawater plus equivalent dry weights of (2) Chaetoceros calcitrans, (3) Pavlova lutheri, and (4) a 1:1 combination of the 2 species. Chaetoceros calcitrans has a higher proportion of simple sugars and sterols compared with P. lutheri, whereas P. lutheri has greater proportions of DHA. Diet composition had a significant effect on the glycogen concentration and reproductive indicators at the end of six weeks. The combined C. calcitrans and P. lutheri supplement showed no change in glycogen stores after 6 wk, however a greater percentage of animals spawned, and a greater proportion of vitellogenic and atretic mussels were produced. Mussels supplemented with C. calcitrans increased glycogen stores and produced greater proportions of mussels with vitellogenic oocytes. Those supplemented with P. lutheri produced a greater proportion of mussels with atretic oocytes, and a lower proportion of D-veliger larvae produced from the eggs. Mussels fed with raw seawater produced a greater proportion of resting mussels, and a lower percentage of mussels spawned at the end of the conditioning period. Oocyte diameter and fecundity showed no significant difference among diets. These results show that diet quality directly influences the allocation of energy to glycogen storage and gametogenesis, however, the mechanism by which this occurs is unclear. Investigation into the allocation of individual biochemical components to each of these processes would further illuminate the process by which diet quality influences the allocation of energy to glycogen storage versus gametogenesis.

This paper presents the results from an experiment, where uptake and elimination of diarrhetic shellfish toxins (DST) of the okadaic acid (OA) and pectenotoxin (PTX) groups were compared between blue mussels (Mytilus edulis) and European oysters (Ostrea edulis). Caged mussels and oysters were suspended in the water column and exposed to a dense bloom of Dinophysis acuta (500–2000 cells L^-1) for 4 wk, which was followed by detoxification in the laboratory during 7 wk. Weekly sampling and analysis of OA-group toxins including fatty acid esters (‘DTX-3’) as well as PTX in individual shellfish and plankton samples were performed. The results showed that mussels rapidly accumulated OA-group toxins to levels about 10 times above the regulation limit (160 µg OA kg^-1 mussel) whereas concentrations never reached this limit in oysters during the field exposure. Overall, levels were 10–50 times greater in mussels. The OA-group toxins were mainly in the form of esters (>90%) in oysters, whereas in mussels, the esters constituted only a minor proportion of total OA toxin levels. Reduction rates were estimated for each OA toxin to evaluate if faster elimination could explain the lower toxin retention in oysters. However, no consistent species-specific difference in reduction rates were observed, but esters of OA appeared to be reduced at a faster rate in oysters (t_1/2 = 23 days) compared with mussels (t_1/2 = 35 days). In both species, the free form of OA was eliminated at a faster rate (t_1/2=15–17 days) compared with free DTX1 (t_1/2 = 23–31 days) and DTX2 (t_1/2 = 28–33 days). Slightly slower elimination rates were estimated for the ester forms (t_1/2 = 23–42 days). Regarding PTX, PTX2 seco acid (PTX2 SA) was the major PTX detected in both species, but small amounts of PTX2, PTX12 and PTX12 SA were also found. As for the OA-group toxins, oysters generally contained lower total amounts of PTX compared with mussels, but the difference was much less apparent. Estimation of reduction rates of the different PTX compounds showed that these toxins were rapidly eliminated in both oysters and mussels (t_1/2 = 6–13 days). We propose that differential rates of gut assimilation and/or biotransformation of the OA-group and PTX explain some of the observed differences in retention and toxin profiles between the bivalves, rather than differences in elimination rates. However, models related to differences in feeding rates, particle selection and behavioural response to toxic algae should be tested in future experiments to evaluate the importance of preingestive mechanisms to the differential toxin retention in these bivalves.From the industrial perspective, our results suggest that O. edulis may be regarded as a low-risk species for DST contamination, which should be taken into consideration by regulatory authorities in charge of sampling frequencies and monitoring programs for shellfish toxins.

Scallop aquaculture has a 20-y-old history in Coquimbo, Chile. At the beginning develop and introduce on industrial level the culture techniques was the main goal, but in recent years research to improve the broodstock quality has been introduced. Development of non destructive procedures to determine gonadal ripeness were necessary. The use of magnetic resonance imaging proved to be an interesting tool to view the internal anatomy of the Chilean scallop Argopecten purpuratus (Lamarck 1819) without any harmful side effect. A central groove located in the middle of the adductor muscle, became visible using MRI, and could possibly be related to the haemolymphatic circulation system.

We evaluated indicators of quality for female gonads (ovary and oocytes), male gonads (testis and seminal tubules), and selected somatic tissues (fiber packages in the adductor muscle and adenomeres in the digestive gland) that participate in reproduction of the pearl oyster Pinctada mazatlanica. The goal was to identify timing of optimal broodstock condition for larval rearing practices. Tissue samples were collected seasonally and processed with a combination of histochemistry and digital image analysis to develop a gonad tissue index, a lipid index, and a glycogen index. Seasonal changes in these indicators were correlated with changes in water temperature and chlorophyll a in the water. P. mazatlanica uses a combination of stored reserves and food supply (conservative vs. opportunistic strategy) to regulate reproduction, but the way energy is acquired and allocated varies between sexes. Female gonads contained higher lipid contents during spring. We suggest energy allocation from digestive gland, because this tissue showed lower lipid contents in the same season (conservative strategy). Within oocytes, the accumulation of lipids occurred from nutrients obtained from food supply during winter (19.6°C and ∼650 ng/L) (opportunistic strategy). Male gonads contained higher glycogen contents in spring. A decreasing trend in the glycogen content of the adductor muscle was also detected in spring. This suggests that sperm build-up occurs partly at the expense of the glycogen stored in this tissue (conservative strategy). In seminal tubules, no correlation with the glycogen content of adductor muscle was detected, suggesting that these reserves were obtained from food supply in spring (22°C and ∼400 ng/L) (opportunistic strategy). Optimal broodstock condition occurs mainly in spring and secondly in early winter.

This study describes the seasonal reproductive cycle, gonad structure, and sex ratio of the Anodonta gabillotia pseudodopsis. A total of 300 individuals was collected in monthly samples from September 2005 to August 2006 in Göolbaşi Lake, Turkey. Calculation of the gonadosomatic index and histological examination of the gonads showed that gametogenesis began in winter and spawning occurred in summer and early autumn. Although, sex ratios of Anodonta gabillotia pseudodopsis were not significantly different from the expected 1:1 ratio (P > 0.05), slightly female biased sex ration were recorded. Although mature oocytes and spermatozoa were present for almost the entire year, gonadal activity seemed lowest in October and December, when gonad recovery and reorganization were more evident than gametogenesis. Both sexes displayed greatest gonad activity during the summer months of the year. Three types of gonads were identified, which varied according to the proportion of gametogenic tissue. According to our morphologic and histologic observation, Anodonta gabillotia pseudodopsis were classified as accidental or abnormal hermaphrodite (typically in dioecious species) species. The hermaphroditic specimens of A. pseudodopsis had gonads composed predominately of tissue of only female. These results suggest that under certain environmental conditions females may become hermaphrodites and self-fertilization occur.

Evolutionary convergence and plasticity of shell characters creates great confusion in freshwater mussel systematics and complicates field census efforts. Genetic identification offers a powerful alternative. But methods involving DNA sequencing are expensive and require tissue sampling, whose effects on survival and health of animals from natural populations have seldom been assessed. We used hemolymph sampling as a nonlethal source of tissue for DNA extraction, and developed genetic identification methods using Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis as an alternative for field surveys. We focused on two morphologically similar endemic species in Lake Waccamaw, North Carolina: the abundant Elliptio waccamawensis and the less common Lampsilis fullerkati. These served as models for surveyors who are often faced with conducting accurate census of cryptic rare species that co-occur with more common forms. Hemolymph-sampled and control individuals of these two species and Leptodea ochracea were caged together in enclosures in Lake Waccamaw. Eight-week survival was 100% and we detected no significant effect of hemolymph extraction on shell growth. PCR-RFLP analysis of the 16s rRNA gene reliably identified species and detected cases of morphological misidentification, both in these collections and from belt transects in the lake. We also developed PCR-RFLP markers that distinguished pairs of cryptic taxa from surveys of streams in southeastern North Carolina. Our results show how nonlethal tissue sampling and PCR-RFLP assays designed for a regional fauna can be useful tools in freshwater mussel conservation programs.

Brown Muscle Disease (BMD) affects Manila clam Ruditapes philippinarum. It was described for the first time in 2005 in Arcachon Bay, France. The pathology consists in a progressive necrosis of the posterior adductor muscle, valve gaping, clam migration to the sediment surface, and death. This study aims to quantify the prevalence of BMD in the bay and to evaluate the effect of BMD on Manila clam dynamics. The prevalence was assessed on 50 stations spread within Arcachon Bay. About 62% of Manila clam habitat surface was infected by BMD. A survey of buried and surface clams was conducted from November 2006 to March 2008 in Lanton, a site infected by BMD. Modal progression analysis separated confidently cohorts from 2003 to 2005 recruitments. This pathology only affected adult clams (>25 mm, >2 years). For both buried and surface individuals, shell length was significantly correlated with BMD infection. Surface clams had prevalence (67%) higher than buried clams (23%) and showed greater mortality rate after 15 d in running water: 82% against 12% for buried individuals. The final disease index (FDI) and the condition index (CI) were monthly evaluated on 50 clams located at each position in the sediment. CI displayed a significant decrease after BMD's infection from light to severe disease stages. Length data analysis through Bhattacharya's method (FISAT II software) allowed identifying four cohorts. The 2003s cohort enabled to calculate mortality rate that was 39% for 5 months and to estimate that BMD was responsible of 95% of that mortality. The temperature was certainly an important factor in BMD transmission, because cohort dynamics results argued that BMD developed during spring and summer.

Veined rapa whelks (Rapana venosa), carnivorous marine gastropods experienced significant mortality during an Alexandrium monilatum bloom in the lower York River, VA in September 2007. Rapa whelks stopped feeding as dissolved oxygen and chlorophyll concentrations increased with the development of the bloom. Whelk mortality was preceded by external signs of stress including reduced ventilation, inability to attach to hard substrates, periodic pumping of the opercular plate, and increased mucus production over a period of 24–48 h prior to death. High concentrations (2–7 µg g^-1 tissue) of goniodimum A, a toxin produced by A. monilatum, were observed in bivalves attached to the shells of rapa whelks. Concentrations of goniodimum A in whelk foot tissue ranged from 0.02–8.39 µg g^-1. Mortality of rapa whelks was 100%. Mortality of oysters (Crassostrea virginica) and northern quahogs (Mercenaria mercenaria) in the same flow through system was 0%. The symptoms displayed by the rapa whelks in the 24–48 h prior to death were indicative of paralysis and followed a similar time course documented for other molluscs exposed to toxic A. monilatum.

Six micro satellite DNA markers were used to investigate the levels of genetic diversity and to determine parentage in a South African hatchery of the abalone Haliotis midae. Samples examined from the farm consisted of three broodstock groups and their respective F1 offspring. Additional wild samples were collected at sites on the East and West coast of South Africa from where the broodstock samples were originally collected. All samples showed significant departures from HWE over all loci. Observed heterozygosity, H_o, for the broodstock samples ranged from 0.5366–0.6121 and from 0.5105–0.6179 for the F1's. The overall number of observed alleles, n_a, for the broodstock samples ranged from 11–12 and for the F1's from 6–10, the allelic richness, A, for the broodstocks ranged from 9.9–10.1 and for the F1's from 5.3–8.9. No loss of heterozygosity was observed between wild and broodstock samples or between broodstock and F1 samples. Only one of the three cohorts showed a significant loss in average number of alleles where a 63% reduction was observed between the F1 and its corresponding broodstock. Only three out of six markers were suitable for parental assignment, with a combined exclusion probability of 88% for the first and 97% for the second parent. Eight percent of the F1 individuals remained unassigned. The results obtained warn of the cumulative effect of differential parental contributions and possible selection pressures negatively influencing the genetic diversity within farm populations. The data would assist in designing management strategies, selection programs, as well as reseeding programs.

Juveniles and adults hitch-hiking in fishing gear, recreational vessels, and fisheries and aquaculture products are believed to be important vectors of local dispersal of invasive European green crab (Carcinus maenus L.). Assessing the distance green crab might spread by hitch hiking requires an estimate of survival time under typical transport conditions. An exposure experiment (stocking density 62 crabs/m²) was conducted in fish crates containing: just crabs (no water, no cover), dry rope, damp eelgrass (Zostera marina L.), seawater (1.5 cm deep), rope seawater, or eelgrass seawater. At mean air temperature of 24°C, almost no crabs died during the first 48 h, 50% of crabs stocked alone or with dry rope survived 68 h (none survived five days), 50% of crabs in eelgrass or eelgrass seawater survived 90–100 h, and > 80% of crabs in sea water or rope seawater survived the full five days. The second experiment (just crabs, sea water, and rope seawater) used three stocking levels (84, 168, and 251 crabs/m²) and ran for seven days. Stocking density did not have a significant effect on survival. At mean air temperature of 29°C, 50% of crabs fully exposed to air survived 60 h (almost none survived seven days), whereas about 60% of crabs survived to seven days when seawater or seawater rope were present. The survival of green crab for several days out of water under severe summer conditions would allow them to be carried on boats to any point in Atlantic Canada, or almost anywhere on the eastern seaboard on trailered boats. This could result in further northward dispersal and the introduction of “northern” genetic material into previously colonized southern portions of the range, potentially increasing over wintering survival.

This study examined how the purple sea urchin, Anthocidaris crassispina, responded to food limitation and hyposalinity, two common stressors it may experience in the field. Young adults were reared under a combination of two food (adlibitum feeding vs. fed once biweekly) and two salinity (31.5‰ to 33.5‰ natural seawater versus 25‰ diluted seawater) levels in a laboratory for 24 wk. Within the ranges examined, both stressors had a significant negative effect on test diameter, total weight, test weight, gonad weight, and gonad index. Food limitation led to marked urchin mortality (20.9% to 37.5%), but had no significant affect on lantern weight, demipyramid length, or lantern index. Hyposalinity alone did not alter urchin survival, lantern weight, or demipyramid length, but it had a significant negative effect on total weight, test weight, gonad weight, and gonad index, whereas it had a significant positive effect on lantern index. Our results indicate that this sea urchin has substantial adaptability to food limitation and hyposalinity, and such adaptation can have important consequences in resource allocation and body allometry. In response to food limitation, this sea urchin appears to allocate energy to body maintenance, rather than to increasing the relative size of the lantern (a strategy different from many other sea urchins). In response to hyposalinity, it reduces test weight, thereby increasing the relative weight of the lantern.

Strongylocentrotus intermedius is a widespread sea urchin species in Asian waters and experiences a large seasonal variation in temperature. It is essential to understand how temperature affects utilization of nutrients and production. Large (5 cm test diameter) S. intermedius were maintained in the laboratory and fed a formulated feed from 28 February when the gonads were small (gonad index, GI, ∼10) and sea water temperature was low (7°C) until 27 June when sea water temperature was high (24°C) under five temperature treatments (environmental temperature, 7, 12, 17 and 22°C. Temperature had little effect on rate of consumption of food or absorption efficiency and little effect on assimilation efficiency except for a significant decrease at 22°C. The gonad index was consistently least at 22°C. Organic matter production in the gonads was greatest and earliest (April) at 12 and 17°C. Strongylocentrotus intermedius acclimated to temperature <22°C during the season of gonad production. These data indicate temperature should not be a great concern in land aquaculture. Under the conditions of this experiment, S. intermedius in culture produced gonads of marketable size (gonad index >15) within one month.

The movement of the sea urchin Paracentrotus lividus from a rocky habitat to patches of Posidonia oceanica was investigated with respect to the size of the sea urchins and their location from the edge of the patch. With this aim, a manipulative experiment was conducted (4 times) at a location where several P. oceanica patches were interspersed on rocky platforms. Each time, after an accurate removal of the sea urchins populating them, 15 of these patches were randomly assigned in sets of 3 to 5 different urchin addition treatments, using groups of 10 large or small P. lividus specimens (test diameter >50 and <30 mm, respectively) positioned at close and far distances (25 and 100 cm, respectively) from the edges of the patches as follows: large-close, large-far, small-close, small-far, and control patches where no urchins were added. The abundance of sea urchins inside the patches was counted after 24 h. Results highlighted significant variability because of the distance from the patches, whereas no significant effect was observed for sea urchin size. These results suggested that: P. lividus specimens close to P. oceanica patches might have a greater probability of reaching them, and that the chance to reach the patch does not depend on the size of sea urchins. In fact, a comparable ability to move towards the patches was evident for different-sized specimens, indicating that migration from one habitat to the other is possible even for small-sized individuals.

The unresolved status of the proximate cause for sexual size dimorphism in horseshoe crabs has practical consequence, because harvest recommendations rely on assumptions about sex-specific growth and maturity. We propose and evaluate competing hypotheses for the proximate cause of sexual size dimorphism in horseshoe crabs (Limulus polyphemus) by comparing size and estimated age frequencies from spring-captured juveniles (n = 9,075) and adults (n = 36,274) to predictions from the competing hypotheses. We found that the number of identifiable juvenile size distributions was greater for females than males and the probability of remaining a juvenile was higher for females than males among older juveniles. These findings are consistent with males maturing earlier than females. Molt increments and mean sizes were similar for male and female juveniles, which is not consistent with differential growth. Among adults, one size distribution accounted for ≥90% of females regardless of carapace wear. Also, size ratio of adult females to males was 1.26, and size ratio of the largest adult to largest juvenile female was 1.28. These observations are not consistent with females continuing to molt as adults. Differential-maturity is the most parsimonious explanation for sexual size dimorphism in Delaware Bay horseshoe crabs. In addition, because of a low frequency of juvenile females >195 mm relative to adult females and male-biased sex ratios starting at 105 mm, we hypothesize that females, more than males, migrate as older juveniles and mature in the ocean. Management implications include that (1) minimum size limits, as previously suggested, would not allocate harvest to older adults as intended because size does not indicate age among adult horseshoe crabs in the Delaware Bay population, and (2) the Shuster Horseshoe Crab Reserve, which has reduced harvest on the continental shelf, could be protecting older juveniles and newly mature females from harvest prior to their first spawn.

Molluscan shells may display a variety of colors, which formation, inheritance, and evolutionary significance are not well understood. Here we report a new variant of the Pacific abalone Haliotis discus hannai that displays a novel orange shell coloration (O-type) that is clearly distinguishable from the wild green-shelled abalone (G-type). Controlled mating experiments between O- and G-type abalones demonstrated apparent Mendelian segregations (1:1 or 3:1) in shell colors in F₂ families, which support the notion that the O- and G-types are under strict genetic control at a single locus with a recessive o (for orange shell) allele and a dominant G (for green shell) allele. Feeding with different diets caused modifications of shell color within each genotype, ranging from orange to yellow for O-type and green to dark-brown for the G-type, without affecting the distinction between genotypes. A previously described bluish-purple (B-type) shell color was found in one of the putative oo × oG crosses, suggesting that the B-type may be a recessive allele belonging to the same locus. The new O-type variant had no effect on the growth of Pacific abalone on the early seed-stage. This study demonstrates that shell color in Pacific abalone is subject to genetic control as well as dietary modification, and the latter probably offers selective advantages in camouflage and predator avoidance.