Eye numbers were quantified on the mantles of sea scallops (Placopecten magellanicus) to determine whether they varied with scallop size (correlated with age), and to compare the numbers of eyes present on the upper (left) and lower (right) mantles. We used Poisson regressions to model eye addition with growth and found that larger scallops had significantly more eyes than their smaller conspecifics, although eye addition occurred only on the upper mantle. Consistent with predictions of an adaptive evolutionary response in eye numbers driven by the need for visualizing objects in the water column, we found scallops had significantly more eyes on the upper mantle than on the lower mantle. This may favor detection of predators, food, or habitat. We also documented significantly greater densities of eyes on the mantles of the smallest scallops, which may indicate vision is especially important in juveniles, which are most vulnerable to predation.

Worldwide, shellfish beds are declining and are threatened by anthropogenic changes. Although the little neck clam Austrovenus stutchburyi supports commercial harvesting, little is known about the population status of this burrowing venerid bivalve in many parts of New Zealand. Populations were sampled seasonally (4 times each year) for 3 y and then during the summer for an additional 4 y within 4 estuarine systems in the Canterbury region of South Island. The aim was to determine population density and class size composition, comparing high-salinity and low-salinity sites with a range of contaminant inputs. The data presented cover pre- and postearthquake events (earthquake sequence commenced on September 4, 2010). Our results show both temporal and spatial variation in population size with irregular recruitment success (0–70 juveniles/m²) across all sites. Density (range, 100–3,500 clams/m²) and mean clam length (range, 17.4–31.6 mm) did not correlate with salinity, sediment trace metal concentration, silt content, nutrient concentration, or anthropogenic land use. A combination of factors and multiple stressors are most likely responsible for determining the population structure and abundance of this species.

For species' dynamics highly influenced by environmental conditions, sustainable management for conservation and/or exploitation purposes requires the ability to segregate natural processes from anthropogenic impacts. In this context, identification of phenotypic variations in morphological patterns, and clarification of the mechanisms involved, constitute useful tools to identify adequate management measures from Europe-wide to local conditions. Although such approaches are already used effectively in the management of fish stocks, they are more recent for bivalve stocks, which are also good candidates for such management tools. The current study examines morphological patterns in the Manila clam (Venerupis philippinarum) through morphometric studies of 4 populations on the French Atlantic coast (Banc du Guer, Morbihan Gulf, Bellevue, and Arcachon Bay). The methodology relies mainly on conventional shape analysis using 8 morphometric ratios involving metrics and weight. In addition, an outline description was created for selected individuals that revealed different forms of the anterior—dorsal valve margin identified for future research. Using supervised classification methods, morphometric—latitudinal trends were revealed between northern and southern populations of V. philippinarum. Relationships between discriminatory morphometric ratios (describing elongation, valve density, and weight related to length) and available environmental conditions (temperature, salinity, and chlorophyll a concentrations) were considered using linear multilevel models. They revealed significant relationships with chlorophyll a concentrations and with 1 ratio with seawater temperature ranging from 12–20°C. Four potential causes were hypothesized to explain the unexpected relationship identified between morphometric characteristics and trophic conditions: (1) a negative effect resulting from high chlorophyll a concentrations, (2) a masked effect of other food resources affecting valve growth, (3) interspecific competition for food among filter-feeding populations, (4) and effects of other environmental parameters such as sediment type. Observed differences in shape may result from a combination of these 4 causes with varying degrees, depending on site-specific environmental conditions. Last, the consequences of morphometric variation on population regulation are addressed.

This study investigated the effects of reduced salinity on the heterotrophic capabilities of juvenile giant clams Tridacna gigas under hatchery conditions. Juvenile T. gigas were selected randomly and exposed to salinity levels of 18,25, and 35 (control)for 14 days. Clearance rate (CR)and absorption efficiency (AE) were determined on days 1,4, 7, 10, 12, and 14.The CR seems to be highly dependent on salinity—highest in the control, followed by salinity 25, and it was considerably reduced at salinity 18. There were significant differences in CR between treatments, except on day 14. Absorption efficiency was generally high, and was significantly different only on day 4. There was a weak negative correlation between AE and salinity, but no correlation between CR and AE. The exposure to reduced salinity resulted in epithelial hyperplasia and hypertrophy in the clam's ctenidial lamellae. Cells were closely packed and exhibited highly granulated nuclei with ruptured nuclear membrane. There were fusions and elongations of the branchial filaments with eroded frontal cilia. These structural changes could reduce feeding. However, an acclimatization response was observed in which increased CR was noted at the end of the exposure, indicating that, to some extent, giant clam juveniles are capable of acclimating to prolonged exposure to reduced salinity.

Sustainability of a fishery is traditionally and typically considered achieved if the exploited population does not decline in numbers or biomass over time as a result of fishing relative to biological reference point goals. Oysters, however, exhibit atypical population dynamics compared with many other commercial species. The population dynamics often display extreme natural interannual variation in numbers and biomass, and oysters create their own habitat—the reef itself. With the worldwide decline of oyster reef habitat and the oyster fisheries dependent thereon, the maintenance of shell has received renewed attention as essential to population sustainability. We apply a shell budget model to estimate the sustainable catch of oysters on public oyster grounds in Louisiana using no net shell loss as a sustainability reference point. Oyster density and size are obtained from an annual stock assessment. The model simulates oyster growth and mortality, and natural shell loss. Shell mass is increased when oysters die in place, and is diminished when oysters are removed by fishing. The shell budget model has practical applications, such as identifying areas for closure, determining total allowable catch, managing shell planting and reef restoration, and achieving product certification for sustainability. The determination of sustainable yield by shell budget modeling should be broadly applicable to the eastern oyster across its entire range.

The eastern oyster (Crassostrea virginica) is a reef-forming organism commonly found in estuaries throughout the Atlantic and Gulf coasts of North America. Eastern oyster reefs provide several ecosystem services, including water filtration, habitat diversity, and storm surge protection, among others. Oyster abundance has declined precipitously during the past century along the Atlantic and Gulf coasts as a result of overfishing, disease and predation, and large-scale human-mediated events. Given the importance of oysters, both ecologically and economically, there have been significant efforts during the past 20 y to reestablish and/or restore oysters to historical levels. Successful reef restoration depends on choosing sites that optimize survival, which requires an understanding of the environmental factors that influence the life stage of an oyster. For most restoration projects, time and budget constraints prevent long-term field studies; therefore, modeling is often used to determine the best locations for restoration. In this study, we developed a spatially explicit, flexible, 4-parameter habitat suitability index model that can be used to determine locations suitable for restoration of eastern oyster reefs throughout the western Atlantic and Gulf coasts. The model captures the minimum environmental parameters required for successful restoration suitability and was applied in 2 studies: (1) Chesapeake Bay, a data rich environment, and (2) northern Gulf of Mexico (western Mississippi Sound), a data poor environment. It illustrates the implications of using data of varying quality when applying the model for identifying restoration potential. In both locations, the model was most sensitive to the presence of appropriate substrate, but not as sensitive to salinity values. This model provides a scientifically based support tool for natural resource managers and project planners, and local conditions may require further consideration.

The efficiency of depuration of the Indian backwater oyster Crassostrea madrasensis (Preston, 1916) using the fill-draw method (static method) with high-loading density was evaluated in this study. Depuration experiments were conducted with cartridge-filtered and UV-treated seawater at a salinity of 30.3‰, a pH of 8.3, and a temperature of 29.5°C. The oysters located in trays on the surface and on the bottom were compared for microbial loads. Samples were taken at 0 h, 8 h, 16 h, 24 h, 36 h, and 48 h of depuration. The results showed that in winter monsoon-sampled nondepurated oysters, the most probable number of fecal coliforms and Escherichia coli were greater than the limits according to NSSP and European Union regulations. The surface held oysters took 24 h to reduce the coliforms and E. coli levels to below safe limits whereas for bottom held oysters it took 48 h. The species Salmonella was never detected in the oysters sampled, whereas Vibrio spp. were present in the nondepurated oysters and were eliminated completely after 8 h of depuration. Variation in depuration of total coliforms, fecal coliforms, E. coli, total plate count, and fecal streptococci in oysters were significant (P < 0.05) between surface and bottom oysters. The study results recommend a loading density of 2 oysters/L water stacked in 1 layer as the optimum loading density for commercial depuration completed within 24 h.

Settlement of pediveligers of the Pacific oyster Crassostrea gigas on nitrocellulose membrane, plaster plate, GF/C filter paper, and glass, both as is and with extract from shells of conspecifics (oyster shell extract [OSE]) added to them, were investigated to select a suitable substrate for settlement assays with OSE. Furthermore, the effects of wheat germ agglutinin (WGA), soybean lectin (SBA), lentil lectin (LCA), and concanavalin A (ConA) on the settlement inducing activities of shell chips (SC) of conspecifics and OSE were investigated. Larvae of C. gigas did not settle on any of the substrates tested. When 50 mg SC equivalent (eq) OSE was added to each of these substrates, larvae settled on all substrates, but greatest settlements were on the GF/C filter papers. Settlement of C. gigas on SC and GF/C filter papers containing 100 mg SC eq OSE (OSE paper) decreased in the presence of WGA (0.5 µg/mL) and SBA (5 µg/mL) for SC, and 0.5 µg/mL for OSE paper, but increasing the concentration of SBA in both cases did not result in less settlement. Treating OSE paper with different concentrations of WGA for 2 h reduced C. gigas settlement on OSE paper, with settlement decreasing with the increase in WGA concentration. Treating larvae with 5 µg/mL WGA for 2 h also reduced larval settlement on OSE paper; but, at 50 µg/mL, larval settlement was not significantly different from the control group. Larval settlement was inhibited in the presence of N-acetyl-D-glucosamine (GlcNAc). Furthermore, larval settlement on OSE paper was not affected when OSE papers were treated with mixtures of 50 µg/mL WGA and GlcNAc. Shell chips and GF/C filter papers with OSE dyed with fluorescein isothiocyanate-conjugated WGA exhibited fluorescence under the UV field. Thus, a WGA-binding sugar chain of the glycoprotein in shells of conspecifics may mediate the settlement of C. gigas larvae on conspecifics.

The aim of this study was to evaluate how Crassostrea corteziensis interacts with its habitat (abiotic factors) and to examine the isotopic variations that may exist over different scales of space and time at a subtropical gradient. This information will contribute to the work required to understand the ecology of this oyster species. We analyzed stable isotopes (δ¹³C and δ¹⁵N) in oyster soft tissue and the concentrations of chlorophyll a, NH₄ , and NO₃^- in the waters of 6 lagoons during the dry and rainy seasons of 2008 and 2009. The mean C:N ratios in soft tissue were generally greater than 3.5 in the different lagoons and during both seasons, indicating a relatively high amount of lipids in the soft tissue related to reproductive activity. The isotopic variability between sites in this study (-25.5 to — 17.1‰ for δ¹³C and 6.5 to 13.7‰ for δ¹⁵N) suggested differences in the composition of suspended organic matter in the diet of this species at different locations, showing an opportunistic behavior that allowed us to detect differences on temporal and spatial scales. On a temporal scale, however, there was no difference in δ¹³C, which was most likely related to the high food availability and the observation that individuals tend to feed on and share the same overabundant prey. In the case of δ¹⁵N, significant temporal differences were evident in only a few lagoons. These differences were related to a differential contribution of NH₄ and NO₃^- as primary sources to the suspended organic matter pool during the 2 seasons. On a spatial scale, some lagoons showed significant differences (P < 0.05) and high δ¹⁵N values (>10‰) in addition to high concentrations of NH₄ . Enriched δ¹⁵N values are often associated with an anthropogenic impact, as human and animal waste nitrate have δ¹⁵N values of approximately 10–20‰.

In support of aquaculture development and sustainable fisheries, survival, condition index, and stable isotope composition of the commercially important bivalve species Arca noae were investigated on individuals suspended in the water column at 2 distances from fish cages and those collected from natural populations. Significant differences were recorded in temperature and chlorophyll a with respect to season, and temperature and salinity values differed significantly with respect to sampling site. Mortality was greatest at the beginning of the experiment, probably as a result of the stress associated with collection of A. noae and the shell-marking process. The relatively small numbers of individuals that survived the experiment did not allow for a detailed statistical analysis of growth rates at the 3 study sites. Condition index showed a pronounced seasonal variation, with greater values recorded between April to July (CI, ∼24) and lesser values noted during November and December (CI, ∼20). Statistically significant intersite differences were detected. Samples collected from the control site in the Pašman Channel had lower condition index values than samples at other sites in 4 of 6 sampling months for which differences between sites were detected. Differences in stable carbon (δ¹³C_VPDB) and nitrogen (δ¹⁵N_air) isotope compositions were recorded with respect to tissue type and season, but no differences with respect to sampling site were noted. Results indicate that A. noae is highly sensitive to manipulation.

Examination of the larval shell (prodissoconch) of molluscs with planktotrophic development can provide valuable information on their planktonic and early benthic life. We examined temporal variability of abundance and size among 11,994 veligers of the blue mussel (Mytilus edulis) in a coastal lagoon during settling periods between 1995 and 2009. Size and date at metamorphosis during the recruitment season were determined for 1,925 postlarvae (shell length, 255–900 µm) with prodissoconch II (PII) measurements. Emphasizing the recurrence of metamorphosis delay in the field, our study reveals a net increase in mean size at metamorphosis through time, with means for PII size ranging from 255–288 µm early in summer (after peak spawning events) to 400–422 µm (PII) during late July to early September. By estimating the “true” settlement date using the amount of dissoconch secreted after metamorphosis, such time-series analyses appropriately recapitulated the temporal pattern of mean pediveliger (competent larvae) size in the plankton. Our results demonstrate that greater settlement success rates were related to small size at metamorphosis—in particular, less than 320 µm. Seasonal increase in mean PII size occurring during the latter part of the settling period may be explained by competent veligers remaining adrift and delayed metamorphosis as a result of the lack of favorable encounters with a suitable substrate or the absence of specific trophic signals, or cues, required for stimulating settlement, thus forcing larvae to continue planktonic growth. The difference between the smallest and largest means for PII size corresponds to 122 µm of larval shell growth, or 47.8%, potentially representing a 322% difference in larval body mass at settlement.

The aim of the current study was to investigate the effect of water current velocities on the clearance rate of Mytilus edulis when different numbers of mussels were used in the experiments. An automatic setup, which controlled and monitored the algal concentration continually, was used to measure the effect of increasing current velocity (0.05–1.4 m/sec) on the M. edulis clearance rate. Clearance rate measurements were performed under constant food concentrations of 3,000 cells/mL of Rhodomonas salina on either 3 mussels or 20 mussels. We found that the clearance rate of 20 mussels was unaffected by current velocities up to 1.4 m/sec, whereas experiments with 3 mussels showed that clearance of the mussels decreased progressively at current velocities greater than 0.2 m/sec, and reached 0 L/h per individual at current velocities greater than 0.6 m/sec. The constant feeding at all current velocities observed in the experiments with 20 mussels was most likely a result of a combination of reduced current velocity within the aggregated mussels, a current velocity-dependent change of siphon orientation, and attachment of the mussels at current velocities less than 1.2 m/sec, whereas in experiments with 3 mussels, mussels were detached at ≥0.4 m/sec and the mussel valves were closed in general. Thus, it is evident that the number of mussels present in the experimental tank affects the results and emphasizes the importance of discriminating between the individual level and the level of mussel aggregations in the study of current velocity effects on clearance, especially when the study is made on a bivalve species that form dense beds in nature, to ensure consistency with field observations.

The processes of gametogenesis, development, and degeneration, together with the gonad fatty acids, of the pen shell Atrina pectinata were studied. The results showed that water temperature is the key factor affecting gonadal development. The gonad started to develop and differentiate at 6–7°C, with fast development of both the visceral mass and the gonad when the temperature increased to 11–12°C. The gonad index peaked at approximately 21°C, which suggested that 6–7°C is the threshold for gonad development and that 21°C is the optimum temperature at which broodstock will mature. The gonad fatty acid 18:1n-9 correlated remarkably with the condition and gonad indices, which might be indicative of the maturity of the gonad of A. pectinata. From the perspective of nutritional composition, Pavlova sp. and Chroococcus sp. were thought to be the most appropriate feed for A. pectinata broodstock cultivation.

The lipid classes and fatty acid profiles of oils extracted from male and female New Zealand Greenshell (Perna canaliculus) mussel samples either raw, or treated with heat or with high-pressure processing were compared. The Bligh and Dyer solvent extraction method was performed for mussel oil extraction. Iatroscan was used for lipid class determination, and gas chromatography—mass spectrometry was used for the fatty acid composition determination. Eight minutes of steaming time was required for the medium-size mussel meat placed as a single layer in a plastic pouch to achieve an internal temperature of at least 75°C. Female mussels had greater oil yield than male mussels on a dry weight basis, and female mussel oil extracts had a greater content of fatty acids than male mussels in general. No significant differences were observed in yield, lipid classes, and fatty acid compositions as a result of different treatments (raw, steamed, and high-pressure processing).

This study demonstrates the daily deposition of increments in Octopus vulgaris beaks for both lateral wall surfaces (LWS) and rostrum sagittal sections (RSS). Forty-nine marked wild animals kept in aquaria (weight range, 158–3,521 g) and 24 captive-reared known-age individuals (paralarvae, 0–98 days old; adults, 200–734 days old) were studied, encompassing for the first time the full age range of the species, including known-age individuals older than 1 mo. The daily deposition of beak increments was validated in the LWS by injection of Calcofluor, and in the RSS by environmental marking (thermal, confinement, capture, and stress of the chemical marking process). A total of 111 successful validations (when beak increments corresponded precisely to days elapsed) were achieved, and the maximum validated periods were 57 days (LWS) and 112 days (RSS). In the pelagic stage and transition to the settlement stage, a new pattern of microincrements that record age was demonstrated in the lateral hood surfaces of upper jaws, where stress checks were observed. In the benthic stage, tip erosion in beak RSS results in some underestimation of age; however, the demonstration that RSS can record environmental stress renders it a potentially useful tool for documenting life events.

Populations of green crab (Carcinus maenas) have expanded within Newfoundland, and this has raised concern from fish harvesters and scientists regarding bivalve predation in coastal areas on species such as juvenile sea scallops (Placopecten magellanicus). We used 2 microcosm experiments to determine (1) the effects of water temperature (5°C and 12°C) on scallop predation; (2) scallop size selection in small and large green crabs and a large indigenous predator, the rock crab (Cancer irroratus); and (3) bivalve prey selection in large green crabs between softshell clams (Mya arenaria), blue mussels (Mytilus edulis), and sea scallops. Overall, green and rock crabs captured 4 times more scallops in warm water (12°C) than cold (5°C). Large green (60–70 mm) and rock (75–90 mm) crabs captured similar numbers of scallops, selected medium-size (30–40 mm) scallops, and avoided small (10–20 mm) scallops. Small green crabs (40–50 mm) captured only small scallops. Large green crabs selected softshell clams and blue mussels over scallops. Overall, our research demonstrated that both green and rock crabs can prey on similar sizes of scallops, and suggests that green crabs may be a new predation threat to the shallow coastal scallop populations in Newfoundland.

Identification of commonly available Indian mud crabs of the genus Scylla was carried out using RAPD and PCR-RFLP to resolve the taxonomic ambiguity of the genus. Samples were collected from western, eastern, and Andaman coastal waters of India. A total of 16 potential species-specific RAPD markers were identified from 179 individuals using 4 arbitrary primers (OPA2, OPA14, UBC122, and UBC456). Three PCR-RFLP markers were developed that could be used to confirm taxonomic status of Indian mud crab species. The species-specific RAPD markers and the digestion pattern of PCR-RFLP analysis indicate conclusively that only 2 species of mud crabs (Scylla serrata and Scylla olivacea) are commonly present in Indian coastal waters.

Effects of dietary carbohydrate (CBH) levels on growth, body composition, and ammonia tolerance of juvenile white shrimp Litopenaeus vannamei at a low salinity of three were evaluated. Six isonitrogenous and isolipid diets containing different CBH levels were formulated and fed to juvenile L. vannamei for 42 days in triplicate for each treatment. Weight gain and survival rate of shrimp fed 20% CBH were the greatest and differed from those fed 5% CBH and 30% CBH. Shrimp whole-body crude protein of the 20% CBH group was significantly greater than that of other treatments. Whole-body crude lipid levels increased with the increase of dietary CBH, and was significantly higher in the 20%, 25%, and 30% CBH groups than in the control. Hepatosomatic index, condition factor, whole-body moisture, and ash contents were not affected by dietary CBH levels. Hepatopancreas soluble protein peaked in shrimp fed 20% CBH, and was significantly greater than in other groups. Hepatopancreas and muscle glycogen showed a similar tendency, but peaked in shrimp fed 15% CBH. Malate dehydrogenase, pyruvate kinase, and glucose-6-phosphate dehydrogenase activities were not affected significantly by dietary CBH levels. An ammonia challenge of 96 h showed that the shrimp in the 20% CBH group had the greatest survival rate, although no significant differences were observed among treatments. This study indicates that 15%–20% dietary CBH is optimal for growth and can improve the ability of L. vannamei to handle stress at low salinities.

The marine waters around Argentina are periodically affected by a range of phytoplankton species that are known producers of paralytic shellfish poisoning (PSP) toxins. The toxic dinoflagellates Alexandrium tamarense and Gymnodinium catenatum have been associated with PSP outbreaks in bivalve molluscs such as mussels. These bivalves are used as a food source by a number of species of carnivorous gastropods, including 2 species of marine snails, Zidona dufresnei and Adelomelon beckii. There is, consequently, a significant risk to consumers of the snails, which can accumulate PSP toxins after predation on the bivalves. Forty-one snail samples of carnivorous snails harvested between 1986 and 2012, representing 2 species (Z. dufresnei and A. beckii), were analyzed for PSP by the reference mouse bioassay (MBA) method and an alternative liquid chromatography with fluorescence detection (LC-FLD) method based on AOAC 2005.06. Sample toxicities determined by the 2 methods correlated well, with no statistical difference in the 2 sets of data. The highest levels of PSP were measured in the viscera of the snails, although PSP was still measured in the edible foot muscle as well above the maximum permitted level in many of the samples. The LC-FLD analysis confirmed the presence of toxins in snail samples returning negative MBA results, therefore showing the advantages of using a more sensitive detection method. The LC-FLD results also enabled the assessment of toxin profiles in each of the snail samples, with data confirming the dominance of saxitoxin (STX) in the majority of snails in comparison with the dominant gonyautoxins quantified in the mussel food source. Conversely, a lower number of Z. dufresnei samples did not exhibit the STX-dominant profile, with a total of 4 different profile clusters determined in the 36 samples analyzed. For A. beckii, these variations were not observed, with a consistent STX-dominant profile measured in each of the samples received. There was no correlation between profile type and the year or season of harvest, although there was some indication that the snails harvested from more southern regions (below 39°S) contained lower relative concentrations of STX on average. Results also confirmed there were no significant differences between the profiles determined in the foot, mucus, and viscera matrices. Overall, the study showed good evidence for another useful confirmatory tool for monitoring levels of PSP in 2 species of carnivorous snails. The generation of toxin profile data has enabled the confirmation of the conversion or selective retention of STX in snail tissues. Whilst the majority of Z. dufresnei samples were found to contain the STX-dominant Although, the remainder of samples were found to contain notably different profiles, the reasons for this remain unknown.

Harmful algal blooms cause serious problems to public health and the economic viability of shellfish industries in Alaska. The most common phycotoxins in this region are saxitoxin and its congeners, collectively referred to as paralytic shellfish toxins, the causative agents of paralytic shellfish poisoning (PSP) in humans. The illness of 26 and death of 2 people in southeast Alaska as a result of PSP in 2010 through 2012 illustrates the need for change in the way paralytic shellfish toxins are monitored and managed in Alaska. The implementation of a scientific monitoring partnership, the Alaska Harmful Algal Bloom monitoring network, designed to provide an early warning of harmful algal blooms—in particular, those that cause PSP—is described. The program includes a tiered sampling approach, and weekly microscopic observation of seawater samples for the presence of the causative toxic dinoflagellate Alexandrium, followed by rapid toxin testing using a high-throughput antibody-based test as a complement to the standard regulatory testing performed by managers at the Alaska Department of Environmental Conservation. Partners in the Alaska Harmful Algal Bloom monitoring network began monitoring in 2008 and thus were able to provide an early warning of a widespread PSP event near Ketchikan in 2011, and the environmental conditions preceding a shellfish closure resulting from paralytic shellfish toxins near Mosman Island in southeast Alaska in 2012. A comprehensive and integrative communication network between Alaska Harmful Algal Bloom monitoring network personnel and state managers, health professionals, shellfish growers, and the general public is proposed to protect human health and promote safe shellfish harvest in Alaska.