Crepidula dilatata (Lamark, 1822) and Crepidula fecunda (Gallardo, 1979) are sympatric species in southern Chile. Separating them by species is difficult because they are morphologically similar; an important character, which separates them is their comparative larval development. C. dilatata includes nutritive eggs within its egg capsules that are consumed by larvae in the capsule during their intracapsular development. Metamorphosis occurs in the capsule, followed by the hatching of crawling juveniles. The C. fecunda intracapsular development leads to the release of planktotrophic veliger larvae that persist in the water column for about 15 days prior to settlement and metamorphosis. These two contrasting reproductive strategies (direct and indirect development) may influence the capabilities of these species for dispersal, which could influence their comparative gene flow and population genetics. Newly developing molecular genetic techniques, such as RAPD used in the present study, were useful in identification of the two species studied and provided some initial data on their comparative population genetics. Greater gene flow and interpopulational gene diversity were found in C. fecunda (pelagic larva) compared with C. dilatata (direct development), with the latter showing populations to be the more genetically heterogeneous within the geographic range studied. It was thus evident that the pattern of larval development (direct or planktonic) influenced the comparative population genetic structure between these two species.

Among the Thais species, the broad consensus has long been that Thais clavigera (Kuster) is the most noxious predator of cultured oysters in Taiwan. Recently, two new Thais species (i.e., T. rufotincta Tan & Sigurdsson 1996 and T. keluo Tan & Liu 2001) have been identified and named in Taiwanese waters yet their impact on oyster culture is unknown. In this study, the overall impact of the three species on the oyster industry was estimated on the basis of their distribution in the field, their feeding rate and their temperature preference based on laboratory tests. The proportion of T. clavigera varied monthly from 24% to 100%, whereas the percentage of T. keluo was negatively correlated with low tide levels (P < 0.01). Thais clavigera occurred widely in the intertidal zone and T. keluo and T. rufotincta near the subtidal, this distribution pattern was consistent with their specific-preferred temperatures in the upper-limits. As shown in the laboratory, T. clavigera, T. rufotincta and T. keluo preferred 36°C, 32C° and 30°C water, respectively. In the field, the respective average feeding rate of T. clavigera, T. rufotincta and T. keluo was significantly different at 0.054, 0.010 and 0.038 oysters snail⁻¹ day⁻¹ (P < 0.05). Based on the abundance of the three Thais species at oyster cultural sites (Liu 2002) and their feeding rates, when oyster predation was made up of T. clavigera, T. rufotincta and T. keluo, predation was respectively 87%, 11% and 2%. The most destructive Thais species in the oyster industry remains T. clavigera, and it accounts for 87% to 100% of all intertidal losses in Taiwan. To the other one-third subtidal culture industry, owing to the use of off-bottom raft or longline method, the distribution of snails extended to subtidal may be limited and the reported major predator is the flatworm of Stylochus orientalis.

This study evaluates the effects of three diets, at 3 different temperatures (15°, 18° and 22°C), on the energy budget of one-year-old abalone. The organisms were fed either an experimental diet based on fishmeal, a commercial abalone diet or fresh seaweed as control. The energy budget was estimated by measuring ingestion, egestion, somatic growth, reproductive investment, respiration, excretion and pedal mucus production. All variables were assessed in female abalone of 16.36 ± 0.17 mm length and 0.24 ± 0.03 g dry weight. Animals fed the formulated diets and cultured at 18°C and 22°C showed better growth than those fed the natural seaweed diet. However, abalone reared at 18°C and fed the formulated diets used 94% of the total energy consumed, with most of this energy allocated to growth, respiration and reproduction. Individuals cultured at 22°C channeled 22% less energy into growth and almost 2.5 times more energy into reproduction than those cultured at 18°C. Hence, diet and temperature were factors that combined to influence growth rates and gonad development in one-year-old Haliotis tuberculata.

Results are presented on the histology of the hypobranchial gland of the marine muricid Plicopurpura pansa (Gould 1853). The general structure and secretory features were investigated using light microscopy and histochemical methods for the determination of tryptophan/indol. The hypobranchial gland of P. pansa is an antero-posteriorly elongated organ located on the internal surface area of the mantle, that folds on its posterior side near the rectum, right of the ctenidia and anterior to the kidney. In dead animals it is easily distinguishable by the purple color that develops after removing the shell. Parallel to the hypobranchial gland, in the same position, can be found a black-pigmented structure, presumably the anal gland. The secretory epithelium, which forms the hypobranchial gland consists of at least six different and very long (156.7 μm) cell types. It was impossible to distinguish clearly the different histological regions of the hypobranchial gland, because the different cell types were uniformly distributed throughout the gland, with the exception of the rectal area. The number of acidophilic granular cells differed markedly between animals, probably because of different levels of secretion. In the mantle cavity was always found a large quantity of mucus and only occasionally acidophilic granulated secretory products. Only the two cell types with acidophilic granules in the hypobranchial gland showed histochemically strong positive reactions for tryptophan, indicating in these cells high concentrations of the precursors for “Tyrian Purple.”

Marked, sized and sex determined purple snails Plicopurpura pansa, (Gould, 1853) were distributed randomly among other snails in crevices of an intertidal rocky island splashed during high tides by high impact waves. After 89 days 18%, after 117 days 12%, after 145 days 8% and after 183 days only 3% of the marked snails could be recovered. There was no statistically significant difference between size and sex and the recovery rate. In the laboratory we determined the time needed for reattachment to the surface under different situations. Snails placed with the aperture down on a wet surface or in water reattached themselves after about 20 min, snails placed in water on their backs; in about 40 min, and snails left on a wet surface on their backs after 2 hours. After 4 hours only 50% of the snails placed on their backs in a wet surface were found to be reattached. Great differences were noticed in the period needed for reattachment among individual snails. The time needed for the snails to overcome the stress of being detached from the surface and to reattach themselves again can be blamed for the loss of animals during the increasing incoming tides combined with the high impact wave actions. The prohibition of “milking” P. pansa to obtain “Tyrian Purple” and to collect the snails as a bait for fishery or as a special food for foreigners should be enforced and should be extended to the removal the snails from the crevices of intertidal rocks.

Although studies of this species have focused on its reproductive cycle, there is no literature available on the ultra-structure of its germ cells. This study consequently aims to describe the latter cells as well as the shape of the acrosome, a character that may be of help in the taxonomic allocation of species of this family or other bivalve families. Results indicate spermatogonia have a central, spherical nucleus as well as scattered heterochromatin granules throughout the nucleoplasm. Rough endoplasmic reticulum is scarce, but the cytoplasm is rich in mitochondria and disperse glycogen granules. In primary spermatocytes, heterochromatin is more highly condensed and there is a reduction in the amount of cytoplasm and number of mitochondria as compared with spermatogonia. In secondary spermatocytes, heterochromatin is present in peripheral areas of the nucleus, forming occasional projections towards its center. In spermatids chromatin is fully condensed, taking up the entire nucleus. Mitochondria increase in size and migrate to the basal pole, giving rise, along with the centriole, to the spermatozoon neck. In spermatozoa, the nucleus is ovoid, the acrosome is round and the centriole is surrounded by four mitochondria, unlike other bivalves, like Anadara tuberculosa, in which the nucleus is reported to be round, the acrosome is pyramidal and there are five mitochondria.

Because the accumulation of inbreeding within hatchery-propagated stocks of the hard clam, Mercenaria mercenaria (Linnaeus, 1758), could result in reduced growth and survival, we studied the potential for improving performance through out-crossing among existing hatchery strains. We produced all 10 possible out-crossed combinations among 5 strains of clams as well as all 5 pure parental strains simultaneously in the hatchery and measured their size at the time of metamorphosis (the spat stage) and at the end of a nursery period in mesh bags at a single field site (the seed stage). We then planted replicate plots of all fifteen strains at five field sites in Virginia, USA encompassing the range of salinity conditions used by commercial growers, and monitored growth and survival for two growing seasons. We found significant phenotypic differences among strains at the spat and seed stage, but different strains performed best at each stage. In the field we found significant site effects, strain effects and strain-by-site interactions, but there was no evidence of negative correlations in performance among sites indicating strong trade-offs that would be problematic for selective breeding. Three different linear contrasts designed to compare out-crossed and pure strains for each parental stock, test for nonadditive genetic effects within each pairing of different parental strains, and estimate the general combining ability of parental strains reveal a complex pattern. We found both inbreeding and out-breeding depression depending on the developmental stage of the clams and the parental strain examined. Within strain crosses generally produced larger spat but smaller seed. Out-crossed progeny were generally smaller at the spat stage than the average of their parental lines but larger at the seed stage. The two best performing parental strains had significant, positive, general combining abilities, whereas this measure was negative for the two worst parental strains. In the field, inbreeding depression was restricted to lines that showed poor pure strain performance, and these strains also showed poor general combining ability, whereas strains with good pure line performance showed out-breeding depression and good general combining ability. Only the poorest performing pure parental lines showed non-additive effects when we compared each out-crossed strain to the mean of its parental strains, suggesting that heterotic effects are unlikely to be useful for selective breeding. Finally, there were significant correlations between seed measurements and field performance indicating that it may be possible, in the context of selective breeding programs, to weed out inferior strains or families early in the life cycle.

An individual-based model was developed to simulate growth of the hard clam, Mercenaria mercenaria, in response to temperature, salinity and food supply conditions. Unique characteristics of the model are that: (1) length and tissue weight are related only by condition index, so that weight, up to a point, can vary independently of length, and (2) age is decoupled from length. Tissue weight changes result from the difference in assimilation and respiration. Changes in hard clam condition are determined from a standard length-weight relationship for average hard clam growth. Changes in hard clam length (growth) occur only when condition index is greater than zero, which happens when excess weight for a given length is attained. No change in length occurs if condition index is zero (mean case) or negative (less weight than expected at a given length). This model structure resolves limitations that accompany models used to simulate the growth and development of shellfish populations. The length-frequency distribution for a cohort was developed from the individual-based model through simulation of a suite of genotypes with varying physiological capabilities. Hard clam populations were then formed by the yearly concatenation of cohorts with partially independent trajectories that are produced by cohort- and population-based processes. Development and verification of the hard clam model was done using long-term data sets from Great South Bay, New York that have been collected by the Town of Islip, New York. The ability to separately track length and age in the simulations allowed derivation of a general mathematical relationship for describing age-length relationships in hard clam populations. The mathematical relationship, which is based on a twisted bivariate Gaussian distribution, reproduces the features of age-length distributions observed for hard clam populations. The parameters obtained from fitting the twisted bivariate Gaussian to simulated hard clam length-frequency distributions obtained for varying conditions yield insight into the growth and mortality processes and population-dependent processes, compensatory and otherwise, that structured the population. This in turn provides a basis for development of theoretical models of population age-length compositions. The twisted bivariate Gaussian also offers the possibility of rapidly and inexpensively developing age-length keys, used to convert length-based data to age-based data, by permitting a relatively few known age-length pairs to be expanded into the full age- and length-frequency structure of the population.

An age-structured projection model was used to study the impacts of alternative exploitation intensities on geoduck populations, based on a large accumulation of survey data, age composition data and published estimates of natural mortality. Data were analyzed and results presented by geographic region. Historic recruitment patterns were back calculated using an age-structured model. Trends in recruitment were independent of the value of M used, although rates were higher when M of 0.036 was applied compared with M of 0.016. Historic recruitment rates were found to be highly variable in the prefishery state: rates generally increased from the early 1930s to 1950, decreased until early 1960, increased to another peak in the mid 1960s, declined until the mid 1980s and have been increasing to present. Future recruitment was simulated from the estimated historic pattern. The fishing patterns examined were combinations of different mortality rates (0.016 or 0.036) and different periods of historical recruitment (beginning in 1940 or 1960). For each simulation year, in each set of 1,000 runs, the ratio of current biomass to virgin biomass was calculated and compared with the management objective of not exceeding 50% of virgin biomass within 50 y of harvest. An exploitation rate of 1.2% and 1.8% of estimated current biomass is recommended for the west coast of Vancouver Island and the rest of the coast respectively.

The aim of this study is to determine the proximate composition, biometrical measurements and heavy metal content differences of marine bivalve Ruditapes philippinarum (Venice, Italy) and Ruditapes philippinarum (Izmir, Turkey. No statistical (P < 0.05) difference was observed in the values of crude lipid, moisture, ash and carbohydrate but statistical differences occurred in their crude protein values. They were 0.98 ± 0.169%; 83.98 ± 0.16%; 3.3 ± 0.424%; 1.14 ± 0.02%; 9.56 ± 0.06% for Ruditapes decussatus, respectively. They were 0.78 ± 0.16%; 85.91 ± 1.22%; 3.1 ± 0.232%; 1.10 ± 0.02%; 8.71 ± 0.18%, for Ruditapes phillippinarum, respectively. Each of the clam was determined as fresh and in perfect quality according to their TVB-N values but in the comparison of color values statistical difference was observed(P > 0.05).Trace metal levels were below the legal limits set by national standards of Turkish governments.

A series of intertidal field experiments was conducted from 1986–2003 in eastern Maine to examine biotic and abiotic factors influencing the growth and survival of wild and cultured individuals of the softshell clam, Mya arenaria L. Separate experiments examined: (1) the efficacy of transferring sublegal wild clams (<50.8 mm SL) from areas near the high intertidal zone where shell growth was slow to areas where growth was predicted to be faster; (2) effects of tidal height on wild and cultured clam growth; (3) effects of spatial variation on cultured clam growth; (4) dispersion and growth of cultured juveniles in small experimental units; (5) effects of the naticid gastropod, Euspira heros Say, predation on survival of wild and cultured clams and (6) the species composition of large, crustacean predators that forage intertidally during periods of tidal inundation. Protective netting (4.2 mm aperture) increased recovery rate of transferred clams by 120% and resulted in a 3-fold enhancement of wild recruits. Effects of tidal height on wild clam growth revealed complex behaviors in >0 y-class individuals. Clams growing near the upper intertidal take >8 y to attain a legal size of 50.8 mm SL, whereas animals near the mid intertidal generally take 4.5–6.5 y. Unexpectedly, clams initially 38–54 mm SL and growing near the extreme low tide mark at a mud flat in Eastport, Maine, added, on average, <2 mm of new shell in a year, which was 8–10 mm SL less than animals at higher shore levels. It is hypothesized that biological disturbance by moon snails, that consumed >90% of clams at the low shore levels, contributed to this slow growth. In another field trial from 1986–1987, moon snails and other consumers were allowed access to clams ranging in size from 15–51 mm. E. heros preyed on clams over the entire size range and attacked clams between 31–40 mm at a rate that was nearly double what had been expected. Mean snail size was estimated to range from 10–52 mm shell height (SH), based on a laboratory study that yielded information about the linear relationship between snail size and its borehole diameter. In an experiment from June to September 1993, moon snails consumed >70% of juvenile clams (ca. 10 mm SL) within a month after planting at each of three tidal heights. Snail sizes ranged from 15–20 mm SD with larger individuals occurring near the upper intertidal zone. Green crabs, Carcinus maenas (L.) also prey heavily on softshell clam populations, but most studies that use shell damage to assign a predator have assumed that all crushing and chipping predation is because of this invasive species. An intertidal trapping study demonstrated that both green crabs and rock crabs, Cancer irroratus Say, are present during periods of tidal inundation, with the latter species accounting for ca. 40% of large crustacean numbers.

The soft-shell clam, Mya arenaria (L. 1758), has the highest landed value of Maine bivalves. Landings have been variable over the last century with current landings one third of their historical highs caused by low harvests in Eastern Maine. Diminished clam populations have been subjected to constant fishing pressure and heavy predation by green crabs apparently unchecked by winterkill. Clam stocks previously closed to harvesting because of pollution are now dug. Reduced breeding populations are tasked to produce a sufficient set to overcome offshore dispersal of larvae to repopulate flats on the coast of Maine. On-bottom and off-bottom sampling found few clam larvae in Eastern Maine. Recovery of the fishery will require reestablishment of breeding stocks.

Surfclam (Spisula solidissima Dillwyn) larval settlement and the initial growth of recruits were studied on the inner shelf of New Jersey. Initial recruitment was measured by taking weekly benthic core samples during the summer settling season, and larval supply was characterized using meroplankton samples taken every four hours in July. The temporal variation in recruitment at two inshore stations (12-m depth) was linked to larval supply from the water column, and spatial differences (inshore vs. offshore) in recruitment also appeared to be related to larval supply. Spatial and temporal variation in larval concentrations was associated with wind-driven cross-shelf circulation. Contrasting recruitment patterns between the two inshore stations could not be explained by larval supply alone and were likely affected by near-bottom flows. Growth rates of initial surfclam recruits (with initial shell lengths <360 μm) were estimated to be 10–20 μm d⁻¹, and the growth rates of individuals >360 μm shell length were 25–50 μm d⁻¹. This study provides realistic field estimates of early growth rates of surfclams and further evidence of the relationship between upwelling/downwelling events and surfclam larval supply and initial recruitment on the inner continental shelf.

Bay scallops, Argopecten irradians, sustained a valuable commercial and recreational fishery in Florida during the middle part of the last century. In 1994, after decades of declining stocks, state managers closed this fishery to commercial harvest and severely limited the recreational harvest. In Florida, most bay scallops reproduce only once, generally during the fall at an age of roughly 12. The current 10-week recreational harvest season, July 1 through September 10, occurs at a time when somatic and reproductive tissues are changing rapidly in preparation for the fall spawning season. This study describes changes in tissue weights (reproductive, somatic, visceral) during the 2002 harvest season in scallops collected from six subpopulations along Florida's Gulf of Mexico coast. We observed tissue-specific patterns of weight change during the 7-month study and also noted regional differences. In three Panhandle sites (St. Joseph Bay, Lanark Village, and St. Marks), a shift from somatic growth to reproductive growth occurred later in the year and was more intense than in peninsular sites (Steinhatchee, Homosassa and Anclote). We also monitored recruitment of juvenile scallops at three of the sites from July of 2001 through June of 2003. There were protracted fall and winter peaks within a background of constant, low-level recruitment. The harvest limits allow each person to collect two gallons (7.55 L) of whole scallops or one pint (0.47 L) of adductor muscle meat each day. In June, just prior to the harvest season, the number of whole scallops that would be collected varied significantly between sites (range 55–203), as did the equivalent yield of adductor muscles (range 143–342). Muscle size peaked in August or September, depending on location. The allowable number of scallops collected within the volume-based limits had decreased (41–112 whole scallops or 84–116 shucked scallops) and between-site variability in the numerical harvest was lower.

The gametogenic cycle and breeding season of the calico scallop, Argopecten gibbus was examined in Bermuda using quantitative and qualitative methods. Gonadal index varied seasonally, a rapid increase occurring in the winter months from January to March, and reaching maximum values in March and April. Greatest gonad growth and spawning were associated with low seawater temperature and low food levels. Variations in muscle indices implied a partial reliance on muscle reserves during the early stages of oogenesis. The later stages of ovarian growth (vitellogenesis and oocyte maturation) seemed to show a direct dependence on food supply. Histological analysis indicated the initiation of gamete development in early fall, when cell differentiation was first observed; oocyte ripening took place in late fall and early winter, reflected in increased oocyte diameters and gonadal indices. The lack of spawning activity during the hot summer months was seen histologically by the high proportion of spent cells in the gonads and a reduction in oocyte size, resulting in a minimal gonadal index. Individuals with gonad indices above 2 and mean oocyte diameters exceeding 50 μm were induced to spawn with thermal shocks, exceeding 70% response rate in oocyte release in all trials. The present study extends our limited knowledge of the reproductive cycle in this subtropical scallop while providing a useful index to evaluate spawning readiness in cultured broodstock for routine hatchery purposes.

Assortative mating and reduced hybrid fitness are typically invoked to explain the stability of hybrid zones and the specification of two closely related taxa. Such examples of mate preferences in nature, especially for broadcast free-spawning marine invertebrates, and the understanding of the underlying mechanisms responsible for this positive selection are still lacking. This study documents another example of assortative fertilization by genome in situ hybridization in reciprocal crosses of scallops Chlamys farreri and Patinopecten yessoensis. Females produced eggs selected sperm nonrandomly but showed significant gamete preference of conspecifics over heterospecifics, with Chlamys farrei females using average 89.1% of conspecific sperms and the Patinopecten yessoensis using average 94.3% in natural spawning conditions (temperature 17°C, salinity 31.5‰). This conspecific gamete advantage may be related to the coordinated communication between interacting gametes, and the conspecific bindin genotype selection during the communicational process may also be involved. Two environmental factors, temperature and salinity were also tested to determinate to what extent they affect the patterns of assortative fertilization between these two species. The result showed that temperature seemed to have more influence on assortative fertilization than salinity did. At the temperatures of 11°C, 17°C, 22°C and 26°C, the average conspecific sperms preference of Chlamys farreri eggs was 80.0%, 89.1%, 95.1% and 95.5% respectively, whereas at the salinity of 24‰, 28‰, 31.5‰ and 35.5‰, the average mating preference was 97.2%, 91.2%, 89.1% and 99.5% respectively. These results may have some bearings on the condition dependent alteration in the inter gamete recognition system. Alternatively, it may be simply the byproduct of different sperm tolerance ability under different conditions. The implication it may provide to hybrid production was also discussed.

A reciprocal mussel seed transfer experiment was conducted involving two farm sites (Charles Arm and Thwart Island) whose seedstocks differed significantly in their respective compositions of Mytilus edulis L., M. trossulus Gould and hybrids. Electrophoretic variation at the mannose phosphate isomerase (Mpi) enzyme locus was used to classify the two species and their hybrids. Survival and growth in shell length, wet weight, shell weight and flesh weight were monitored over a 14-mo period. Both stock groups originating from Thwart Island seed (TI reared on its native site and the transferred TI-X stock) and the transferred stock group originating from Charles Arm seed (CA-X) showed no evidence of genotype-dependent variability in survival whereas, in the Charles Arm seed reared on its native site (CA), the proportion of M. edulis declined in relation to M. trossulus. There was no evidence of either a survival advantage or disadvantage in hybrids. After 14 mo, both transferred stocks (CA-X and TI-X) had comparatively higher frequencies of M. edulis and hybrids and lower frequencies of M. trossulus than did their respective nontransferred stocks (CA and TI) indicating a significant genotype x site interaction effect on survival. Significant species, stock, stock × time, species × time and stock × species × time effects on shell length, wet weight, shell weight and flesh weight occurred. Intrastock growth rates of M. trossulus were lower than M. edulis and hybrids for shell length (3 of 4 stocks), and for the 3 weight variables, wet weight, shell weight and flesh weight (4 of 4 stocks). These results support the conclusion that growth is genotype-dependent in rope-cultured mussel populations and that these differences in weight growth favoring M. edulis are maintained when such stocks are transferred to other sites. Mussel biomass (kg m⁻¹) was similar for the CA, CA-X and TI-X stock groups and lower for the TI stock group. Rates of production (wet weight) over the 14-mo growout period were similar for the CA, CA-X and TI stock groups and significantly higher for the TI-X stock group. In both stock groups originating from Thwart Island seed (TI reared on its native site and the transferred TI-X stock), the intrastock rates of production of M. edulis and hybrids were significantly greater than sympatric M. trossulus. However, in the transferred Charles Arm stock (CA-X), the rates of production were similar in M. edulis and M. trossulus and significantly greater in hybrids. In the Charles Arm stock reared on its native site (CA), the rate of production of M. trossulus was significantly greater than either M. edulis or hybrids. We conclude M. edulis and hybrids have intrinsically greater rates of weight growth, but not necessarily length growth, than does M. trossulus. Neither M. edulis nor M. trossulus nor hybrids have consistently greater rates of survival or production in suspended rope culture. These results are discussed in the context of a directed seed-stocking program involving the transfer of M. edulis seedstocks to sites whose native stocks have a high M. trossulus component as a means to enhance commercial mussel production within the