A strategy for producing juvenile Pecten maximus to a suitable size for final culture (≈20–60 mm shell-height) within a year is suggested. Effects of stocking density, fouling on cages and shells, and handling frequency (every 1, 2, or 3 mo) on scallop growth and survival were investigated. Small juveniles (16.8 ± 3.0 mm) were initially stocked in August at densities of 24, 36, and 48 scallops quarter⁻¹ (17% to 34% coverage), and 35.5 ± 5.1 mm scallops were restocked in January to 6, 12, 18, and 24 quarter⁻¹ (18% to 73%). Survival was neither affected by stocking density nor handling, and was 98% the first period and from 93.2% to 96.9% between January and July. Shell-growth was mainly affected by stocking density and less affected by handling frequency. Growth slowed down during the winter months, and stocking density influenced growth during all seasons. Juveniles kept at the lowest densities obtained highest growth. Final mean shell-height was 54.8–67.2 mm and coverage 22% to 165%. Scallops handled monthly and bimonthly had significantly larger sizes than scallops handled every three months. Fouling on the cages increased with rising sea temperature, whereas high stocking density significantly reduced fouling on cages. Effective production during intermediate secondary culture in Galicia should include high initial stocking density in August, restocking to low density in January, and changes or cleaning of cages every second month.

The scallop Argopecten ventricosus (Sowerby II 1842) supported an important fishery in the Gulf of Panama (Pacific Panama) during 1981–1990, but the fishery essentially collapsed in 1991. To determine if the A. ventricosus population in one major fishing ground, Las Perlas Archipelago, has recovered almost 15 years after that collapse, we interviewed fishermen, reviewed historical data about scallop export markets and fishing grounds, and assessed the state of the scallop population using traditional local trawling methods. During four expeditions (2000–2004), we intensively surveyed 183 trawling stations, which included the major shallow fishery sites as well as other deeper areas within the archipelago. We collected hundreds of relic adult and juvenile scallop shells, but we retrieved only 30 live individuals. This suggests that minimal recruitment has occurred in the archipelago and that the fishery remains collapsed. We argue that this population's failure to recover may be because of a lack of suitable available habitats for juveniles, predation and variation in local oceanographic conditions, as previously suggested. Further studies are needed to fully determine why the scallop population has failed to recover. Application of mariculture techniques may be required to restore the stock and repopulate A. ventricosus natural banks in Las Perlas Archipelago.

We investigated the relationship between physiological properties, swimming performance, shell fluctuating asymmetry, and heterozygosity at allozyme loci in the Iceland scallop, Chlamys islandica, in an attempt to describe potential physiological mechanisms for the negative relationship between shell fluctuating asymmetry and survival of this species in pearl nets (Fréchette & Daigle 2002). No clear relationship was observed between shell fluctuating asymmetry and the different physiological and genetic parameters, although the maximum number of contractions in a series during escape tests and the specific activity of arginine kinase in the adductor muscle were linked with shell asymmetry before the application of corrections for multiple comparisons. Pyruvate kinase activity in soft tissues was higher in animals that were heterozygous at 2 loci compared with those that were heterozygous at 4 loci. Although our exploratory study suggests that shell asymmetry may reflect bioenergetic difficulties, further study is required to confirm such links.

Current knowledge of the evolutionary relationships among scallop species (Mollusca: Bivalvia: Pectinidae) in the Indo-Pacific region is rather scanty. To enhance the understanding of the relationships within this group, phylogenies of nine species of scallops with the majority from coastal regions of Thailand, were reconstructed by maximum parsimony, maximum likelihood, and Bayesian methods using sequences of the 16S rRNA of the mitochondrial genome, and a fragment containing the ITS1, 5.8S and ITS2 genes of the nuclear DNA. The trees that resulted from the three methods of analysis were topologically identical, however, gained different levels of support at some nodes. Nine species were clustered into two major clades, corresponding to two subfamilies (Pectininae and Chlamydinae) of the three currently recognized subfamilies within Pectinidae. Overall, the relationships reported herein are mostly in accordance with the previous molecular studies that used sequences of the mtDNA cytochrome oxidase subunit I, and the classification system based on microsculpture of shell features and morphological characteristics of juveniles. Levels of divergences were different among genes (i.e., the 5.8S gene showed the lowest levels of nucleotide divergence at all levels, whereas the 16S rRNA showed the highest level of variation within species, and ITS2 gene revealed the highest level of divergence at higher levels).

The life history strategy of the veined rapa whelk Rapana venosa, a temperate marine gastropod, includes generation times of 1 y, individual longevity of >10 y, annual production of egg cases, and an adult size range of 40 to >160 mm shell length (SL). This life history combined with the animal's generalist ecological preferences and broad physiological tolerances makes rapa whelks well suited for ecological success along a gradient of habitat and community types. Ballast water transport of veliger larvae across traditional zoogeographic boundaries has resulted in the establishment of invasive rapa whelk populations in Chesapeake Bay, USA, as well as European habitats. Although the need for a quantitative understanding of rapa whelk reproductive biology in terms of annual embryo production or fecundity is acknowledged as a necessary step in assessing the biological and ecological consequences of such an invasion, rapa whelk fecundity in relation to size for the entire adult size range (40–>160 mm SL) has not previously been quantified. The relationships between rapa whelk female size and egg case height, number of embryos egg case⁻¹, number of egg cases produced female whelk⁻¹ yr⁻¹ and fecundity, and the number of embryos female⁻¹ yr⁻¹, are described for a size range of individuals from Chesapeake Bay. In 2001 and 2003, egg laying began in mid to late May at water temperatures of approximately 18°C and salinities 14–20 ppt and continued for 11–12 wk. The smallest rapa whelk observed (45 mm SL, 5.8 g wet tissue weight) laid egg cases with heights of approximately 7 mm. The largest whelk (163 mm SL, 220 g) laid egg cases with heights 30–33 mm. The number of embryos observed in egg cases produced by Chesapeake Bay rapa whelks ranged from 123 embryos in a 7.4 mm high egg case to 3,673 embryos in a 33.5 mm high egg case. Rapa whelk fecundity (number of embryos female⁻¹yr⁻¹) increased with female size. Egg case production was observed in rapa whelks that had hatched from egg cases and recruited within the previous year (<1 y old). Small (<80 mm SL, <28 g wet tissue weight) rapa whelks have relatively lower annual fecundities (1 × 10⁵ embryos female⁻¹ yr⁻¹) than large (>80 mm SL, >28 g wet tissue weight) rapa whelks that may produce between 1 × 10⁶ and 4 × 10⁶ embryos female⁻¹ yr⁻¹. Estimates of rapa whelk fecundity, even for small rapa whelks, are at least an order of magnitude greater than similar estimates for native United States Atlantic coast gastropods.

Different stains are used to internally mark calcified structures of mollusc shells in growth experiments. Because of interspecific variations in marking success, an assessment of suitability for each species is necessary. The potential of calcein, alizarin red, and strontium chloride hexahydrate (strontium chloride) was investigated for the Chilean abalone Concholepas concholepasr and the surf clam Mesodesma donacium, two molluscs of commercial importance in Chile. Wild specimens from Northern Chile were marked using different concentrations and immersion periods of the three stains. Animals were reared for 20 days to allow growth, mortality, body condition index (BCI), and growth rate was measured to assess the effects of the treatments. To detect marks, individuals were culled and shell sections analyzed using scanning electron microscopy for strontium chloride and fluorescence microscopy for calcein and alizarin red, respectively. Strontium chloride produced narrow bright bands only at concentrations of 2,880 mg·l⁻¹ and 24 h exposure. Calcein markings produced fluorescent bands detectable in all treatments (50 and 100 mg·l⁻¹, 3 and 6 h) whereas alizarin red only yielded irregular bands with 50–100 mg·l⁻¹ and 6 h exposure. Our results show that growth rates of C. concholepas are significantly affected by the stains factor: Strontium chloride showed the lowest growth rates whereas that of alizarin red and calcein was similar to the control group. High concentrations of strontium chloride negatively affected (P < 0.05) the body condition of the gastropod. Although no statistical differences were found, BCI of M. donacium followed the same trend as observed for C. concholepas. In conclusion, calcein was the best growth marker for both species because it produced bright, long-lasting bands even at low concentrations and immersion times without detectable lethal or sublethal effects.

A 152-day growth experiment was conducted in a recirculated water system to investigate the interaction between vitamins A (retinol) and D (cholecalciferol) on growth and metabolic responses in abalone Haliotis discus hannai Ino. Triplicate groups of juvenile abalone (initial weight: 0.35 ± 0.03 g; initial shell length: 11.31 ± 0.25 mm) were fed to satiation one of 16 semipurified diets containing 0, 1 × 10³, 1 × 10⁵, 1 × 10⁶ IU/kg vitamin A and 0, 500, 1 × 10³, 5 × 10³ IU/kg vitamin D in a 4 ×4 factorial design. Abalone were weighed and shell-length measured on the 76th day and the 152nd day, respectively. The total specific growth rate (SGR) during the 152 days, neither the SGR in the first 76 days nor in the second 76 days, was significantly influenced by the interaction between vitamins A and D. Dietary vitamins A and D significantly stimulated viscera 25-hydroxyvitamin D₃ [25(OH)D₃] and 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃] contents in a cooperative fashion. Dietary vitamin A generally increased the alkaline phosphatase (AKP) activity in viscera except the excessive supplement (1 × 10⁶ IU/kg), which significantly decreased AKP activity. Dietary vitamin D significantly increased AKP activity. Contents of P, not Ca and Mg, in soft body increased with dietary vitamin D supplement. Dietary vitamin A significantly improved contents of lipid and retinol in soft body and viscera, respectively. Meanwhile, dietary vitamin D significantly increased contents of ash and cholecalciferol in soft body and viscera, respectively. Based on these results, interaction between vitamins A and D was expressed in various manners as different indicators were considered, though there was potential antagonism mechanism at molecular level between the two fat-soluble vitamins.

Distribution and abundance of Strombus gigas (Linné 1758) larvae were studied in Alacranes reef to identify if this marine protected area could be a basin site for recruitment of this species. Duplicate samples were collected every month from November 1999 to October 2000. Plankton tows were made with a conical net of 302-μm mesh-size. During the sample period, 1,864 veligers were collected. Larvae were more abundant during June through August, with 1,288 larvae (69.10%), September through February with 367 larvae (19.69%), and 209 larvae were counted in March through May (11.21%). Larval density varied from 0.31 veligers · 10 m⁻³ in March to 5.24 veligers · 10 m⁻³ in June; 86.42% of larvae were less than 350 μm, and 2.35% were between 450 and 950 μm. A high abundance of small sizes suggests that Alacranes reef is a very important basin site for the recruitment of Strombus gigas larvae. Moreover surface marine current in Alacranes reef is northeast and crossing the lagoon reef, thus Alacranes could supply S. gigas larvae to Florida.

Larval and juvenile development were studied in the volcano keyhole limpet Fissurella volcano over 77 days under laboratory conditions at temperatures ranging from 18°C to 20°C. Larvae obtained by spontaneous spawning were fed a mixture of the microalgae Nannochloropsis oculata and Phaeodactylum tricornutum. Elapsed time from fertilization to veliger larva was 22.5 h. Veliger release occurred on day 3. Formation of the fissure giving rise to the keyhole began after day 16. On days 28 through 33, the keyhole reached its final position and juveniles exhibited adult-like morphological characteristics.

The ultrastructures of germ cells and follicle cells during oogenesis, the reproductive cycle, and the size at sexual maturity in female Meretrix lusoria were investigated for clams collected from Simpo, Korea by cytological, histological, and morphometric analysis. Vitellogenesis occurred through a process of autosynthesis, involving the combined activity of the Golgi complex, mitochondria and rough endoplasmic reticulum, and a process of heterosynthesis, in which extraovarian precursors were incorporated into oocytes by endocytotic activity at the basal region of the oolemma of the early vitellogenic oocytes. The follicle cells appeared to play an integral role in vitellogenesis and oocyte degeneration: the functions of the follicle cells are phagocytosis and intracellular digestion of products originating from the degeneration of oocytes. During the period of oocyte degeneration, follicle cells of this species probably have a lysosomal system for breakdown, and resorb various phagosomes in the cytoplasm for nutrient storage, as seen in other bivalves. The reproductive cycle in females can be classified into five successive stages: early active stage (January to March), late active stage (February to May), ripe stage (April to August), partially spawned stage (June to September), and spent/inactive stage (September to February). The spawning period continues from June to September, with a peak between July and August when the seawater temperature exceeds 22°C. The percentage of individual female clams 40.0–45.0 mm in shell length that were at first sexual maturity was over 56.3%, and for clams over 50.0 mm in shell length, it was 100%. Shell length at 50% of sexual maturity (rate of sexual maturity, RM₅₀) was 41.0 mm. Thus, female clams were determined to be sexually mature at two years of age. Because harvesting clams <40.1 mm in shell length could potentially cause a drastic reduction in recruitment, a measure indicating a prohibitory fishing size should be taken for adequate fisheries management.

The reproductive cycle and the energy content of soft parts of Tawera gayi were studied monthly from August 2001 to July 2002 in Ushuaia Bay, Beagle Channel. The degree of sexual maturity was determined histologically. The sex ratio was significantly different of 1:1 (896 females, 796 males, χ²-test, P < 0.05). First sexual maturity occurred at 12 mm shell height in both sexes. In males the reproductive cycle was determined analyzing the monthly percentage of gonadal stages. High percentages (85%–100%) were mature (ripe stage) during a large part of the year (March to September) and in October the 100% of individuals were partially spawned with recovery. An image analyzer was used to determine quantitatively female reproductive cycle. The percentage of gonadal area covered by oocytes was lower in December. The mean number of mature oocytes (diameter >40 μm) by gonadal area and the mean diameter of oocytes reached the lower values during October, November, and December, indicating a spawning peak. This more intensive spawning activity coincides with the phytoplankton bloom in spring. The energy content of soft parts was measured using a microbomb calorimeter in monthly samples during a year. The mean energy content in both sexes was significantly different reaching 20.95 kJ/g AFDW for females and 21.39 kJ/g AFDW for males. The relative condition index attained the lower values in August, September, and October. The monthly values of the energy content did not show significant differences in both sexes. Results of this study indicate that notwithstanding T. gayi lives in a markedly seasonal environment as Subantarctic waters of Beagle Channel shows a protracted gamete production with a principal spawning episode and small pulses of evacuation during the rest of the year.

Degradation of coastal habitats can result in loss or depletion of valued vegetation, fish, and shellfish stocks. Consequently, there are many initiatives to protect and restore these areas or populations to their previous state. Here we describe a study designed to provide necessary information on dispersal, mortality and growth rates of transplanted adult (25–32-mm shell length) cockles, Austrovenus stutchburyi (Gray) with which to evaluate the density of transplants and need for predation protection that should be used in larger-scale projects. Marked Austrovenus were transplanted at high (75 ind) and low (20 ind) densities, at two sites on an intertidal sandflat. To distinguish between epibenthic predator-associated mortality, other mortality and natural dispersal, caged and uncaged plots (30 × 30 cm) were used. Around 30% of the adult Austrovenus transplanted remained in the plots 12 mo later, and abundances were enhanced relative to pretransplant ambient densities. Death rates increased in later months and were significantly higher for Austrovenus kept at high densities in cages. There was no effect of caging on plot sediment characteristics, no obvious targeting of the plots by predators and no size-dependency of the deaths. However, being caged at high densities appeared to act as a stressor that rendered Austrovenus less able to cope with the extreme environmental conditions that occurred in later months. Growth rates were low over the 12-mo trial (<0.2 cm mo⁻¹), did not differ significantly with site, transplant density, or the presence/absence of cages. Results indicate adult Austrovenus should be transplanted at densities intermediate between those used here and that caging is unnecessary. Our observations of dispersal of cockles out of the uncaged plots suggest that future trials should investigate transplanting cockles in patches within larger areas than the plots used here.

Northern quahogs Mercenaria mercenaria were grown in trays suspended in the York River, Virginia from November 1954 (4 months old) to December 1970 (16 years old). Measurements of shell length (mm) were made at least once a year from 1954 to 1970 and measurements of shell width (mm) were made in November 1962 and August 1965 and then once per year from 1967 through 1970. Quahog densities within the trays ranged from 1500 m⁻² (November 1954 to October 1955) to 269 m⁻² (November 1955 to December 1970). Quahog shell length (mm) increased with age (yr) and was described with a Von Bertalanffy growth model (coefficient of determination = 0.93). Most of the growth in shell length occurred in the first 6 years with clams reaching shell lengths of 58 mm by November 1960 and maximum shell lengths of 77–84 mm by 1963 (age 9). Shell length:shell width relationships were similar for tray held and wild quahogs collected from the York River during 1967 to 1970. The observed annual shell length growth increment decreased exponentially with quahog age. Standardized shell length growth index (SGI) values for 11 of the 15 years for which data are available describe better than expected quahog growth trends although there was no clear relationship between SGI and average annual surface temperature or average growth period (water temperature >7°C, typically March to November) surface temperature in the York River between 1955 and 1967.

QPX (Quahog Parasite Unknown) a protistan pathogen of northern quahogs (=hard clams), Mercenaria mercenaria, has caused disease outbreaks in maritime Canada, and in Massachusetts, New York, New Jersey, and Virginia, USA. Although epizootics have occurred in wild hard clam populations, the parasite has most seriously affected cultured hard clams, suggesting that aquaculture practices may promote or predispose clams to the disease. In this investigation the influence of clam genetic origin and the geographic location at where they are grown on QPX disease susceptibility was examined in a common garden experiment. Aquaculture stocks were acquired from hatcheries in Massachusetts, New Jersey, Virginia, South Carolina, and Florida and spawned at a single hatchery in Virginia. All stocks were originally, although not exclusively, derived from wild hard clam populations from each state. The seed clams were deployed at two sites, New Jersey and Virginia, and evaluated during the subsequent 2.5 y for growth, survival, and QPX disease. At both sites, South Carolina- and Florida-derived clam stocks exhibited significantly higher QPX prevalence and lower survival than New Jersey and Massachusetts clam stocks. Levels in the Virginia stock were intermediate. In Virginia, mortality at the termination of the experiment was 78%, 52%, 36%, 33%, and 20% in the Florida, South Carolina, Virginia, Massachusetts, and New Jersey hard clam stocks, respectively. Mortality was significantly correlated with QPX prevalence. Maximum QPX prevalence in the South Carolina and Florida stocks ranged from 19% to 21% and 27% to 29%, respectively, whereas in the Virginia, New Jersey, and Massachusetts stocks prevalence was 10% or less. Similar trends were observed in New Jersey where mortality at the termination of the experiment was estimated to be 53%, 40%, 20%, 6%, and 4% in the Florida, South Carolina, Virginia, Massachusetts, and New Jersey clam stocks, respectively. QPX prevalence peaked at 18% in the Florida stock, 38% in the South Carolina, 18% in the Virginia, and 5% in the New Jersey and Massachusetts stocks. These results suggest that host genotype is an important determinant in susceptibility to QPX disease. As such, hard clam culturist should consider the genetic origin of clam seed stocks an important component of their QPX disease avoidance/management strategies.

To obtain basic ecological information on declining Tokyo Bay stocks of the Manila clam Ruditapes philippinarum, life history (including spawning, larval transport and settlement, and growth and survival of benthic clams) was investigated in local habitats, mainly in Sanbanse and Kisarazu. Spawning-stage adult clams were histologically detected from May to October at both sites, with two peak periods in summer and autumn. From May to November, between 13 and 23 larval cohorts appeared annually in each site, even during periods when spawning-stage adults were not detected. Spawning over many months plus larval transport from other habitats may contribute to the continuous appearance of larvae at both sites. This confirms the hypothesis that the clam population is maintained and supported by the reproduction of local populations. High density cohorts of newly settled clams, which later formed adult populations, may originate from larval cohorts spawned during peak spawning periods. A number of summer cohorts of benthic juveniles disappeared within 3–4 mo after settlement, whereas autumn cohorts maintained a relatively high density through the following spring, and subsequently they formed adult populations. Severe mortality resulting from extreme environmental factors may have affected the summer cohorts during summer and autumn. The recent decline of the adult stocks may be related to the unstable recruitment of summer cohorts, which was one of the two major seasonal components contributing to recruitment.

Species of Hematodinium are endoparasitic dinoflagellates of crustaceans. Certain stages of the parasites can be very difficult to detect in the hemolymph of their hosts, because the trophic stages resemble hemocytes, and they can occur at relatively low densities, making diagnosis by microscopy difficult. We developed a polymerase chain reaction (PCR) assay to detect the Hematodinium sp. infecting the blue crab, Callinectes sapidus, based on the amplification of the parasite's first internal transcribed spacer region (ITS1) of the ribosomal RNA (rRNA) gene complex. The PCR assay was combined with a restriction endonucleases digestion (Bsg I) of the amplification products to differentiate between different forms of Hematodinium from different hosts. The assay had a limit of detection equivalent to 0.3 parasites per 100-μL hemolymph. In addition, two oligonucleotide DNA probes were designed to target the 18S rRNA gene sequence of the parasite, facilitating detection in situ in crustacean tissues. These probes appear to target several, if not all species within the genus, because they labeled all isolates of Hematodinium tested in this study, whereas they were not hybridizing to other parasite species. The PCR-RFLP assay will be invaluable for future studies investigating parasite prevalence, the existence of secondary hosts or environmental reservoirs, and modes of transmission, whereas the DNA probes will be useful for confirming and localizing Hematodinium parasites in crustacean tissues.

A 4×4 factorial experiment was conducted to determine the effects of salinity (0.2‰, 11‰, 21‰, and 31‰) and temperature (20°C, 24°C, 28°C, and 32°C) on survival, growth, and energy budget of juvenile Litopenaeus vannamei with the initial wet body weight of 0.274–0.283 g. The experiment lasted for 5 wk. The results showed that all shrimp survived at 11‰, 21‰, and 31‰, irrespective of temperature; at 0.2‰, survival decreased with increasing temperature from 20°C to 28°C, then plateaued at 32°C. At all levels of temperature with increases of salinity within the range tested, specific growth rate or food consumption gradually increased, reaching the maximum value and thereafter declined. At 0.2‰, specific growth rate, food consumption, or apparent digestibility coefficient exhibited an increasing trend from 22°C, reaching the maximum value at 28°C, then showed a decline up to 32°C with increasing temperature, whereas at salinities of 11‰, 21‰, and 31‰; specific growth rate, food consumption, or apparent digestibility coefficient exhibited an increasing trend. By contrast, feed efficiency generally decreased in response to increasing temperature within the salinity range tested.

The experimental material for the investigations was collected from the deep zones of the Gulf of Gdañsk. The experiments were performed at salinities of 3.0 PSU (96.87 mmol/kg), 7.3 PSU (235.73 mmol/kg), 15 practical salinity unit (PSU) (484.39 mmol/kg) and 25 PSU (807.32 mmol/kg) in conditions of hypoxia (saturation = 15% O₂), anoxia (saturation <1% O₂) and control conditions in aerated water (saturation = 100% O₂), at a constant temperature of 10°C. Hypoxia (saturation = 15% O₂) had no statistically significant effect (P > 0.05) on the osmoregulation of S. entomon in comparison with the control samples. Anoxia (saturation <1% O₂) decreased the osmotic concentration of hemolymph in S.entomon. After 6 h only at salinity 3 PSU there was a statistically significant difference between the anoxic and control samples (P < 0.05). After 96 h there was a statistically significant tendency (P < 0.05) for the osmotic concentrations to decrease in anoxic conditions at all the salinities tested except 25 PSU. A tendency was observed for the Na concentrations in the hemolymph to decrease in anoxic conditions, which was statistically significant at salinity 7.3 PSU (P < 0.05) after 96 h but not statistically significant at the other salinities tested. The results show a low concentration of K in the hemolymph of S. entomon and slight fluctuations of K concentrations, but at environmental salinities the K concentration decreases under anoxic conditions but not to a statistically significant extent (P > 0.05).

Mussel cultivation involves collecting mussel spat or transplanting mussels that typically harbor complex assemblages of associated species, into more favorable growing sites. The biodiversity associated with cultivated mussel assemblages thus depends partly on the source of the mussels and on the new habitat created by the method of cultivation. The aim of the current study was to make a quantitative comparison of the macrofaunal communities associated with natural intertidal seed beds and with cultivated mussels grown either on the seabed or on ropes, particularly in relation to the structure of the mussel populations. Core samples (79 cm²) were collected from rope-grown and subtidal bottom-cultured populations and from natural intertidal mussel beds using a nested ANOVA design. The size distribution, biomass and density of the mussel populations and the macrofauna associated with each type of population were quantified. The biomass of macrofauna associated with mussels was significantly greater within rope-grown mussel assemblages than on mussel beds. There were significantly fewer individuals among bottom-cultured mussels than either rope-grown or naturally occurring intertidal mussels. Positive correlations between mussel biomass and associated faunal biomass existed at certain sites but not others. There was a shift from oligochaete to polychaete dominated worm communities caused by mussel cultivation. Sessile polychaetes were most abundant among rope-grown mussels whereas highly motile polychaetes were most abundant at the bottom-culture sites. Fewer amphipod crustaceans were found under both types of cultivation. To maintain or enhance the abundance and biomass of mussel-associated fauna relative to the intertidal beds, suspended culture is preferable to on-bottom cultivation. Positive mussel and associated-macrofaunal biomass correlations are species dependent; cultivation sites could thus be selected to minimize detrimental impacts of mussel farming or even increase the biomass of mussel-associated macrofauna.

Summer seed mortality (SSM) has occurred yearly in Tomales Bay, California since 1993. SSM has resulted in up to 90% cumulative losses, and has been associated with extreme temperature, phytoplankton blooms, and an oyster herpesvirus. In this study, three stocks of Pacific oysters were planted at three sites in California (Inner Tomales Bay, Outer Tomales Bay, and Bodega Harbor) in October of 2000 (Fall) and April of 2001 (Spring) and monitored for mortality, growth, and health status. In April of 2001, a similar study was conducted in Totten Inlet, WA state using cohorts of oysters planted in California; animals were monitored for mortality and growth. Temperature data were collected at all sites; phytoplankton abundance data were collected at the California sites. Mortality occurred only at the Inner Tomales Bay site where losses were correlated with maximum temperatures (r = 0.949) and preferentially affected faster growing oysters (r = 0.916). Significant differences in cumulative mortality were identified among oysters stocks and two of the three oysters stocks planted in the fall outperformed their cohorts planted in the spring (P < 0.0001). Microscopic changes in connective tissue and digestive tubules are consistent with previous observations of herpesvirus infections in oysters including: diffuse to multifocal pertibular hemocyte infiltration, diapedesis, dilation of the digestive tubules, nuclear hypertrophy, and chromatin margination. Nuclear hypertrophy and chromatin margination, in particular, are suggestive of herpesvirus infections; these histological changes were rare indicating the need to use multiple diagnostic methods when oyster herpesviruses are suspected to cause SSM. Temperature maxima (∼25°C) experienced at the Inner Tomales Bay site are not considered extreme for Pacific oyster survival; the association between oyster herpesviruses and temperature in Tomales Bay, California is discussed.

This study investigated the influence of age and tissue weight on cadmium (Cd) levels in Pacific oysters (Crassostrea gigas). Oysters from 4 different age groups (1, 2, 3, and 4 y) were collected at an oyster farm in Willapa Bay, Washington. To examine the effects of age, 60 oysters from each group were sorted into 3 composites of 20, and Cd analysis was carried out on all composite samples. To study the effects of tissue weights, 25 oysters from each of the 4 age groups were collected and analyzed individually for Cd. All oyster Cd concentrations were below the 3.7 ppm (μg/g) wet wt Food and Drug Administration (FDA) level of concern and the 2 ppm wet wt Hong Kong limit. There was a moderate correlation between Cd concentration and age (R² = 0.60). The 1-y-old oysters had significantly lower Cd concentrations than the 2–4-y-old oysters. Tissue weight also influenced Cd concentration (R² = 0.31). The effect of tissue weight was found to vary with age, with a stronger correlation to Cd levels in the 1- and 2-y-olds and a weaker correlation among the 3- and 4-y-olds. The results indicate that oysters accumulate the majority of their Cd during the first two years of their lives, after which point they become saturated and show only incremental additions of Cd in later years.

The decline of the eastern oyster (Crassostrea virginica) as an estuarine resource is well documented for many estuaries on the United States east coast. This decline is often associated with a decline in the shell resource and ultimately the disappearance of the shell bed. We develop a model that expressly and conjointly evaluates oyster abundance and surficial shell quantity and examine whether stability in the stock and the habitat can be simultaneously achieved. Simulations suggest that a steady-state shell content exists for any set of recruitment and natural mortality rates and that the amount of shell present at steady state varies over a wide range as recruitment and natural mortality vary. Shell mass is maximized at a natural mortality rate near the rate observed in unfished populations unimpacted by disease. A species dependent on the maintenance of hard substrate for survival, as is the oyster, might have a life span adapted to maximize the accretion of carbonate; thereby sustaining the substrate on which it depends. Relatively small changes in the recruitment rate produce large changes in abundance and consequently shell mass and the scale of variation dwarfs that of natural mortality or fishing. Only variations in the rate of shell loss or the average size of animals at death produce equivalent excursions in shell mass. In comparison, the ambit of natural mortality imposed by the disease process fortuitously occurs in a range that restrains the change in carbonate mass, probably because increased mortality reduces abundance but also increases the death rate, thus adding more shell. Simulations covering a range of fishing rates indicate that no fishing rate exists that is likely to be sustainable of the shell resource over the long term. Fishing will always abet the taphonomic and depositional processes conspiring to debilitate the oyster bed. Successful management of the oyster shell resource is obstructed by the simple fact that no additional mortality, whether imposed by disease or through fishing, can occur that will not result in habitat loss at some rate. The shell resource is maximized when the population is at predisease natural mortality rates and unfished. Thus, if fishing is to be permitted or if disease has increased persistently the natural mortality rate, the only recourse of the manager is the perpetual addition of shell in compensation to the loss or the acceptance of the degradation of the shell bed.

The known range of the oyster pathogen Haplosporidium nelsoni Haskin, Stauber, and Mackin (MSX) extends along the North American Atlantic coast from Nova Scotia to Florida. Our study demonstrates that H. nelsoni is also present throughout the Gulf of Mexico. Thirty of 41 oysters (73%) sampled from sites ranging from Florida to as far south as Venezuela were positive for MSX by PCR amplification of the ribosomal rRNA gene complex. DNA sequences cloned from oysters positive for H. nelsoni were ≥99% identical to H. nelsoni and clearly divergent (<89% identical) from known haplosporidian congeners, including Haplosporidium costalei Wood and Andrews (SSO). The absence of MSX epizootics in the Gulf of Mexico, despite the wide distribution of H. nelsoni infections, raises questions about pathogenicity and the host-parasite relationship in subtropical latitudes.

In artificial incubation of astacid crayfish eggs, stage 2 juveniles must be removed by hand from incubators and a significant decrease in survival rates has been recorded between hatching (stage 1) and the first moult (stage 2). To reduce these losses, eggs of Pacifastacus leniusculus were incubated at a density of 6.6 cm⁻² and different removal frequencies of stage 2 juveniles from the incubators were tested: every 5, 4, 3, and 2 days, daily and only once at the end of incubation. Formaldehyde was used to control growth of fungi. The best final survival rate (88.6%) was obtained when stage 2 juveniles were removed daily from the incubators. There were no significant differences nor between removals every 2 and 3 days (79.6% and 76.5%, respectively) neither between 4 and 5 days (72.6% and 69.8%, respectively). Considering all treatments, final survival rates decreased as juvenile removal was delayed up to only one removal at the end of incubation.

We contrast ecological and life history traits of the well studied freshwater invader, the zebra mussel (Dreissena polymorpha), with the lesser known invasive golden mussel (Limnoperna fortunei) to compare salient biological traits and environmental limits, and to predict the potential spread and ecosystem impacts of L. fortunei in areas where it is introduced. Both species are sessile, byssate bivalves with a planktonic larval stage and extremely high reproductive capacity. For both species adults attain much higher biomass in waterbodies they invade than all of the native invertebrates combined, and they create substrate complexity otherwise not found in freshwater systems. Both are very active suspension feeders, greatly enhance benthic-pelagic coupling, and act as effective ecosystem engineers. Although taxonomically unrelated, their ecosystem impacts are surprisingly similar and follow from the novel ecological niche they share, rather than being species specific. The golden mussel has broader environmental tolerances and therefore may be a much more successful invader than D. polymorpha in regions dominated by acidic, soft and contaminated waters. In the near future L. fortunei may colonize the southern and central parts of North America, much farther north than has been previously predicted. Although to date the zebra mussel is considered the most aggressive freshwater invader, soon many waterbodies may receive another, even more aggressive invader.

Shell damage, if properly recognized, can provide information about biotic interactions between molluscs and their predators. However, it can be difficult to distinguish predatory damage from mechanical breakage, thus making interpretation of damaged modern and fossil shells problematic. To establish a clear-cut distinction between antemortem predatory crab damage and ante- and postmortem mechanical damage in Mytilus trossulus shells, a combined field and experimental approach was used. Mussels were exposed to predation by crabs, tumbled-live, tumbled-dead, and trampled. After 100 h of tumbling, live-collected mussel shells were abraded and disarticulated but not otherwise damaged. Eight percent of the dead-collected shells were broken during tumbling. There was a proportional (length, width, and thickness) size reduction in both tumbled-live and tumbled-dead shells after 100 h. Breakage caused by crab predation under laboratory conditions was ∼19% of the prey offered. Three types of diagnostic damage were inflicted by crab predation: nibbles, nibbles and chips, and peels. Trampling and tumbling yielded three diagnostic breakage patterns: crescentic chips, angular chips, and slivered chips. Crushed shells and shells with fractured margins were caused by predation and trampling. Only twenty percent of the trampled-shells could be mistaken for preyed-upon shells. Only twenty-seven percent of the preyed-on shells could be mistaken for mechanically-damaged shells. Overall, the source of damage could be correctly identified in 74% of the shells. Proper identification of crab predation in dead shells of this commercially important resource may prove valuable in studies of trophic interactions in modern environments. Inferring levels of crab predation, based on damage in fossil specimens, can be reliable if such analyses are calibrated by experimental studies of living representatives or analogs.

Hermit crabs select shells based on size, weight, species of gastropod, and shell condition. However, in many environments, empty, undamaged gastropod shells are in short supply and this shortage may influence hermit crab shell selection behavior. In this study, the effects of isolation, competition, and predation on shell selection behaviors were investigated using Pagurus granosimanus (Stimpson), a hermit crab from San Juan Island, WA. The hermit crabs were provided with a choice between undamaged, slightly damaged, or very damaged Nucella lamellosa (Gmelin) gastropod shells and were subjected to either isolation (control treatment), water infused with the chemical cues of conspecific hermit crabs (competition treatment) or water infused with both predator (Cancer magister, Dana), and dead conspecific chemical cues (predation treatment). In all 3 experimental treatments, after a trial duration of 20 min, hermit crabs preferentially selected the undamaged shell. However, the frequency of shell switches varied significantly between the three experimental conditions. Hermit crabs in the control treatment switched between shells most frequently and hermit crabs in the competition group switched least frequently. Additionally, larger hermit crabs switched shells more frequently than smaller hermit crabs in all experimental conditions. In settings where competition is the primary environmental stress, such as in the San Juan Islands, the reduced frequency of shell switching may have a long-term effect on hermit crab defense against predation, in turn reducing the reproductive success and population size of hermit crabs.

Biotic interactions between brachiopods and spionid polychaete worms, collected around San Juan Islands (USA), were documented using observations from live-collected individuals and traces of bioerosion found in dead brachiopod shells. Specimens of Terebratalia tranversa (Sowerby), Terebratulina unguicula (Carpenter), Laqueus californianus (Koch), and Hemithiris psittacea (Gmelin) were collected from rocky and muddy substrates, from sites ranging from 14.7–93.3 m in depth. Out of 1,131 specimens, 91 shells showed traces of bioerosion represented by horizontal tubes. Tubes are U-shaped, straight or slightly curved, sometimes branched, with both tube openings communicating externally. On internal surfaces of infested shells, blisters are observed. All brachiopod species yielded tubes, except for H. psittacea. Tubes are significantly more frequent on live specimens, and occur preferentially on larger, ventral valves. This pattern suggests selectivity by the infester rather than a taphonomic bias. Given the mode of life of studied brachiopods (epifaunal, sessile, attached to the substrate, lying on dorsal valve), ventral valves of living specimens should offer the most advantageous location for suspension-feeding infesters. Frequent infestation of brachiopods by parasitic spionids is ecologically and commercially noteworthy because farmed molluscs are also commonly infested by parasitic polychaetes. In addition, brachiopod shells are among the most common marine macroscopic fossils found in the Phanerozoic fossil record. From a paleontological perspective, spionid-infested brachiopod shells may be a prime target for studying parasite-host interactions over evolutionary time scales.

One hundred one individuals of Protothaca staminea were live-collected from Argyle Lagoon (sand/mud substrate) and Argyle Creek (gravel/sand substrate), San Juan Island, Washington and examined for trace-producing parasite infestation. Eighty-six percent of individuals contained at least one parasite-induced trace. Trematode-induced pits and blisters were identified on 62% of individual clams. Spionid-induced mudblisters and u-shaped borings were identified on 50% and 29% of individuals, respectively. Trematode and spionid parasites were not selective between the left and right valve when infesting the host. Epifaunal clams from Argyle Creek were significantly smaller than their infaunal counterparts from Argyle Lagoon. This size discrepancy between environments may be related to the reduction of growth rates triggered by environmental stress or parasitism, increased susceptibility to durophagous predators, differences in hydrodynamics, or the comparison of different cohorts. Spionid mudblister-infested clams from Argyle Creek are significantly smaller than noninfested clams from the same environment. This suggests that substrate-induced epifaunality and parasite-induced shell weakening reduced the bivalves’ defenses against durophagous predators. These results suggest that parasites may negatively affect the survival of infested bivalves. The frequent occurrence of trematode and spionid trace-producing parasites in modern bivalve populations suggests that these traces are common in the fossil record, making the systems amenable to study in deep time.

Spines are frequently considered to be an important physical defense against predators. This experiment shows that spines do not always function successfully as physical protection. Using natural predators and prey (the drilling muricid gastropod Nucella lamellosa (Gmelin 1791) and the mussel Mytilus trossulus (Gould 1850)) this experiment used artificial spines in different configurations and densities to try to assess the role of spines as predatory defense. The presence of spines did not inhibit the predator from choosing ornamented prey. Greater spine density did not improve the probability of surviving a predator encounter. Although mean handling time increased to some extent with higher spine density, the outcome of the encounter was the same. Presence or density of spines did not deter predators from attacking prey, and experimental prey with greater spine-density experienced greater mortality than did specimens with fewer spines. Drillhole dimensions differed slightly between the treatments, probably as a consequence of difficulties for the gastropod to maneuver its accessory boring organ (ABO) in between the spines.

In the summer of 2004, seven Nucella lamellosa snails from the rocky intertidal zone were found to have detached from their shells after collection. The snails continued to live and function normally for several weeks after discovery. The loss of the shell may have been a reaction to stressful environmental stimuli.

Modern ecological studies suggest that avian predation has a significant impact on intertidal mollusc-dominated communities and can potentially bias the fossil record by altering the composition and probability of preservation of shelly fauna in coastal habitats. To assess if bird predation can be detected indirectly using surficial shell assemblages, fourteen samples from an area known for bird predation were compared with an expected model derived from observational studies on bird feeding behavior in the literature. The model predicts: (1) minimal bioerosion and physical decay of mollusc shells; (2) high degree of shell fragmentation; (3) ubiquity of distinct fracture patterns; and (4) shell assemblages dominated by a few species. This model was evaluated using 3 distinct habitats of Argyle Bay (San Juan Island, WA); lagoon, bay, and gravel bar. On the gravel bar, where avian delivery of prey items is observed to be high shell assemblages displayed high fragmentation (>75% of valve missing), dominance of pristine shells, frequent presence (68%) of specimens still retaining ligaments, dominance (72%) of valve fractures that cut straight across growth lines, and nearly monospecific composition. In contrast, shells from the bay and lagoon, where avian export of prey items would be high but processing negligible, have a low proportion (30%) of highly fragmented shells, a dull to chalky appearance, lower frequency (44%) of ligament–preserving specimens, and much more variable fracture patterns. Fidelity analysis, a comparison of species diversity and abundance between the sympatric life and death assemblages, indicates low death fidelity and in all three habitats death and life assemblages differ significantly from one another. However, the gravel bar death assemblage is more similar in taxonomic composition to the life assemblages than to the other two death assemblages, suggesting that the gravel bar approximates the present day composition of the local mollusc fauna ecosystem more closely than either the bay or lagoonal death assemblages. The bar deposit, with a combination of highly fragmented but pristine shells, dominant fracture patterns, and monospecific composition, suggests that supratidal deposits resulting from bird predation can be identified using indirect methods based on damage patterns in shell assemblages. These results offer a promise for applying unique taphonomic and taxonomic signatures of shell accumulations generated by molluscivorous birds to study avian predation from historical, ecological, and paleoecological perspectives.