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International audience; The Gulf of Mexico, including the southwest Florida coast, USA, experience recurrent blooms of the brevetoxin (PbTx)-producing dinoflagellate, Karenia brevis. Northern quahogs (hard clams) Mercenaria mercenaria, are an important commercial species in this region. This study examined the effects of field and laboratory exposure of adult clams to K. brevis during their reproductive period, and effects on their subsequently produced offspring. Ripe adult clams were collected from a site which had been exposed to an eight-month natural bloom of K. brevis and an unaffected reference site. Ripe adult clams were also exposed to bloom concentrations of K. brevis for 10 days in the laboratory. Clams exposed to K. brevis accumulated PbTx at concentrations of 1508 (field exposure), 1444 (1000 cells mL−1 laboratory treatment) and 5229 ng g−1 PbTx-3 eq (5000 cells mL−1 laboratory treatment). Field-exposed clams showed histopathological effects: a significantly higher prevalence of mucus in the stomach/ intestine (23.3%), edema in gill tissues (30%) and presence of the cestode parasite, Tylocephalum spp. in whole tissue (40%), compared to non-exposed clams (0, 3.3 and 6.7% respectively). These clams also showed reduced gonadal allocation (23% gonadal area) and a higher prevalence of clams of undetermined sex (20%) compared to those sampled from the non-exposed site (43% and 0%, respectively). It is hypothesized that less energy may be channeled into reproduction as more is allocated for homeostasis or tissue repair. The fertilization success of gametes obtained from both field and laboratory-exposed adults was significantly lower in clams that had been exposed to K. brevis and development of these offspring was negatively affected at Days 1 and 4 post-fertilization (in field- and laboratory-exposed clams at the higher K. brevis concentration and in laboratory-exposed clams at the higher K. brevis concentration, respectively). Negative effects may be due to toxin accumulation in the gametes of field-exposed clams (244 ± 50 ng PbTx g−1 and 470 ± 82 ng g−1 wet weight in oocytes and sperm, respectively). Adverse effects in M. mercenaria are compared to those previously reported in oysters, Crassostrea virginica, under similar conditions of exposure. This study provides further evidence of the impacts of K. brevis and its associated toxins on the adults and offspring of exposed shellfish. Site-selection for the collection of broodstock and aquaculture grow-out efforts should therefore consider the local occurrence of K. brevis blooms.

Molluscs mineralize carbon as calcium carbonate in shells within a protein matrix that is a small portion of the total shell mass. In parts of Florida, the northern quahog Mercenaria mercenaria is cultured in mesh bags in shallow coastal marine habitats. These habitats were selected by the State of Florida for their pre-existing lack of large molluscan populations, so most of the shell material harvested by aquaculture operations would not otherwise exist. The carbonate content of shell material was quantified by coulometry, and shell production was estimated per harvested clam, and per unit area per year. The majority of the shell material harvested (about 91%) was M. mercenaria, and the remainder came from other species of molluscs that grew in or on the mesh bags. Of the non-Mercenaria shell material, most (8.5% of total percentage) came from oysters (Crassostrea virginica and Ostrea stentina), and the rest from at least 37 other species of molluscs and other shelled taxa. Each harvested market-size clam represented approximately 2.93 g of mineralized carbon, including shell material that was not part of the marketed clams. Clam leases in full production produced about 1.0 × 103 g of mineralized carbon per square meter per year, including nonclam shell material, and the Florida northern quahog industry produced about 534 metric tons of mineralized carbon in 2008. This mineralization resulted in an estimated atmospheric efflux of 374 tons of metabolic-independent carbon in the form of carbon dioxide, from the Florida northern quahog industry in 2008.

Bivalves serve an important ecosystem function in delivering organic matter from pelagic to benthic zones and are important in mediating eutrophication. However, the fate of this organic matter (i.e., biodeposits) is an important consideration when assessing the ecological roles of these organisms in coastal ecosystems. In addition to environmental conditions, the processing of biodeposits is dependent on its composition and the metabolic capacity of the associated microbial community. The objectives of this study were to compare the biological reactivity, potential denitrification rates, and microbial communities of biodeposits sourced from different bivalve species: hard clam (Mercenaria mercenaria), eastern oyster (Crassostrea virginica), and ribbed mussel (Geukensia demissa). To our knowledge, this is the first study to investigate and compare the microbiome of bivalve biodeposits using high-throughput sequencing and provide important insight into the mechanisms by which bivalves may alter sediment microbial communities and benthic biogeochemical cycles. We show that clam biodeposits had significantly higher bioreactivity compared to mussel and oyster biodeposits, as reflected in higher dissolved inorganic carbon and ammonium production rates in controlled incubations. Potential denitrification rates were also significantly higher for clam biodeposits compared to oyster and mussel biodeposits. The microbial communities associated with the biodeposits were significantly different across bivalve species, with significantly greater abundances of Alteromonadales, Chitinophagales, Rhodobacterales, and Thiotrichales associated with the clam biodeposits. These bioreactivity and microbial differences across bivalve species are likely due to differences in bivalve physiology and feeding behavior and should be considered when evaluating the effects of bivalves on water quality and ecosystem function.

Background Quahog Parasite Unknown (QPX) is an opportunistic protistan pathogen of the clam Mercenaria mercenaria. Infections with QPX have caused significant economic losses in the Northeastern United States. Previous research demonstrated a geographic gradient for disease prevalence and intensity, but little information is available on the genetic diversity of the parasite throughout its distribution range. Also, QPX virulence factors are not well understood. This study addresses the occurrence of QPX genetic variants with a particular focus on functions involved in virulence and adaptation to environmental conditions. Results Analyses were performed using transcriptome-wide single-nucleotide polymorphism (SNP) of four QPX isolates cultured from infected clams collected from disparate locations along the Northeastern United States. For contig assembly and mapping, two different genome builds and four transcriptomes of the parasite were examined. Genomic variants appeared at a differential rate relative to sequenced transcripts at 20.18 and 22.55% occurrence under 1000 base pairs upstream and downstream protein domains respectively and at 57.26% rate in protein domain coding sequences. QPX strains shared 30.50% of the mutations and exhibited a preferential nucleotide substitution towards thymine. Sequence identity suggested relatedness between different QPX strains, with the parasite being possibly introduced to Virginia from the Massachusetts region during clam trading, while QPX could have been naturally present in New York. Diversity in virulence, temperature, and salinity domains suggested a common variability between strains, but with a preferential higher variation in local adaptation genes. This could explain differences in disease prevalence noted in different regions. Overall, the results supported views that this opportunistic parasite might be able to adapt to varying environmental conditions. Conclusion Relatedness and mutations between the four QPX strains suggested that variability in environmental-related functions favors parasite survival, potentially promoting resilience against stressful conditions. These findings are in agreement with the widespread presence of QPX in the environment. Although QPX levels are enzootic in most areas, an increase in disease outbreaks were often associated with seasonal changes in environmental conditions. A selection mediated by the parasitic life of QPX remains possible, but the effect of the environment on the biology of the parasite appears more obvious. Electronic supplementary material The online version of this article (10.1186/s12864-018-4866-8) contains supplementary material, which is available to authorized users.

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In six of seven experiments, exposure to elevated pCO2 levels (∼1700 µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions, whereas rates were significantly higher in the presence of Ulva in all experiments. In many cases, the co-exposure to elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification-only treatment. Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates, and growth rates of bivalves were significantly correlated with Ω in six of seven experiments. Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Ventricles isolated from clams (Mercenaria mercenaria) that had been acclimated to 1000 mOsm seawater (SW) release amino acids when incubated in 500 mOsm SW. Taurine, glycine, and alanine account for nearly all of the released amino acids, and total about 37 μmol/g dry tissue weight during a 2-h incubation. The release of amino acids is increased to 69 μmol/g by the addition of 10-6 M 5-hydroxytryptamine (5HT) to the hypoosmotic SW, and to 83 μmol/g by the addition of 10-6 M FMRFamide to the medium. The potentiation of the release by 5HT is blocked by methysergide. The amino acid release is increased by two phorbol esters--phorbol 12,13-diacetate and phorbol 12-acetate, 13-myristate--to 97 and 83 μmol/g, respectively. Forskolin and other cyclic 3',5' adenosine monophosphate agonists have no effect on the release of amino acids in hypoosmotic SW. Phorbol esters, 5HT, and FMRFamide have no effect on the release of amino acids from ventricles incubated in 1000 mOsm SW. Ventricles, first isolated from clams acclimated to 1000 mOsm SW, and then transferred to 500 mOsm SW, increase in wet weight by 20-25%. The increase is maintained for 30 min, and the tissues return their original weight in the ensuing 30 min. The addition of 5HT, FMRFamide, or phorbol esters to the hypoosmotic SW decreases the time necessary for the tissues to return to pre-transfer weights. These results implicate protein kinase C in the responses of bivalve tissues to hypoosmotic media, and suggest that these responses may be modified by neuronal or neurohumoral control.

The "brown tide" alga, Aureococcus anophagefferens, had no effect on the activity of the lateral cilia of isolated gills of the bivalve mollusks Argopecten irradians, Geukensia demissa, and Mya arenaria. A. anophagefferens caused a significant decrease in the activity of lateral cilia of five other bivalve mollusks, Crassostrea virginica, Ostrea edulis, Mercenaria mercenaria, Modiolus modiolus, and Mytilus edulis. Exposure of isolated gills of M. edulis to the water from which A. anophagefferens had been removed, or to polystyrene beads at the same concentration as A. anophagefferens, had no effect upon the activity of the lateral cilia. Thus, the inhibition of the lateral cilia is not caused by a compound excreted into the water, nor is it the result of the high density of cells. The response of lateral cilia to dopamine was identical to the response to A. anophagefferens; lateral cilia that were inhibited by dopamine were also inhibited by A. anophagefferens. Pretreatment of the gills of M. edulis with the dopamine antagonist ergometrine blocked the inhibition of the lateral cilia by both dopamine and A. anophagefferens. A water-soluble inhibitory compound was released from A. anophagefferens by exposing the cells to amylase, and then removing the cells by filtration. The effect of this inhibitory compound was also blocked by ergometrine. We propose that the isolated gills are digesting the extracellular coat of A. anophagefferens releasing a water soluble dopamine-mimetic compound that causes inhibition of lateral cilia.

The SCPs3 are a small peptide family, characterized in gastropods, and implicated in the control of the cardiovascular system and the muscles involved in feeding and gut motility. We aimed to determine the manifestation of this peptide family in the class Bivalvia. Acetone extracts of whole bivalves were fractionated by high pressure liquid chromatography (HPLC), and reactive peaks were identified by radioimmunoassay (RIA). After purification, sequencing, and analysis by mass spectroscopy, three peptides were identified in the clam Mercenaria mercenaria: IAMSFYFPRMamide, AMSFYFPRMamide, and YFAFPRQamide4. SCP-related peptides from two other species were also sequenced: APKYFYFPRMamide and SAFYFPRMamide from an oyster, Crassostrea virginica; and AMSFYFPRMamide (identical to one of the clam peptides) from a cockle, Dinocardium robustum. The tissue distribution and pharmacological actions of the clam SCPs were determined in M. mercenaria, as follows. The levels of peptide in extracts of 12 tissues were estimated by RIA. The largest concentrations of SCP occur in the palps and the visceral ganglia; the levels in the cerebral and pedal ganglia, the rectum, intestinal typhlosole, and gills were substantially lower; and the smallest amounts were found in the heart and the style sac typhlosoles. Immunohistochemistry revealed many cell bodies in the periphery of the ganglia and fibers in the neuropil. Immunoreactive, varicose fibers also occur in the typhlosoles of the intestine and style sac, and in the rectum, gill, and palps. The atrioventricular valves, but not the atria or ventricle proper, contain immunoreactive fibers. Synthetic clam SCPs were assayed on the rectum, the typhlosoles of the intestine and style sac, and the ventricle, all isolated in an organ bath. At low to moderate doses, the SCPs relaxed the muscles of the rectum; higher doses had biphasic actions. The muscles of the intestinal and style sac typhlosoles were relaxed, and spontaneous rhythmicity was slowed by the SCPs. Most ventricles were unresponsive. We conclude that the SCPs isolated in bivalves--though distinctive--are true homologs of those in gastropods. Moreover, the bivalve peptides also serve similar roles, controlling feeding and digestion, and perhaps even cardioactivity.

The hard clam (Mercenaria mercenaria) is an important economic and ecological bivalve. In this study, the mitochondrial genome was sequenced. The sequenced genome size was 18,360 bp. The nucleotide composition was asymmetric with a AT bias. Mitogenome contained 13 protein-coding genes (PCGs), 2 rRNA genes, and 22 tRNA genes. Of 13 PCGs, 3 genes (cox3, nad3, and cox2) had incomplete stop codons. Furthermore, phylogenetic analysis using 12 PCGs (except atp8) figured out that M. mercenaria was closely related to genus Dosinia. The complete mitogenome of M. mercenaria provides essential information for further phylogenetic and evolutionary analysis in Veneridae.

In marine sediments, many of the processes associated with high post-settlement mortality of infauna have similar effects on the sediment surface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments reported here tested the ability of new juvenile infauna to discriminate between undisturbed and recently disturbed sediment surfaces (i.e., subsurface sediment exposed). Recently settled juveniles of two polychaete species (Nereis vexillosa and Arenicola cristata) and one bivalve species (Mercenaria mercenaria) were exposed to simulated erosional and mixing events as well as to fresh feces, burrow tailings, and feeding tracks. Where the disturbance buried or removed several millimeters of the sediment surface, the time to initiate burrowing or the percentage of individuals failing to burrow increased significantly over times and percentages for juveniles on undisturbed surfaces. In all cases the results were consistent with the hypothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old. For example, 51% of nereid juveniles did not burrow when placed on subsurface sediments, whereas 100% burrowed into surface sediments; their average burrowing time on surface sediments was 29.3 s compared with 109.7 s on fecal mounds of arenicolid polychaetes or 106.1 s on burrow tailings of thalassinid crustaceans. Individuals that did not indicate acceptance of a sediment surface by burrowing were all rapidly eroded from the surface in the presence of flow. Erosion of nonburrowing individuals occurred within 90 s of initiation of flow. Burrowing individuals were not eroded. The decision as to the acceptability of a sediment was made within 30 s. These data imply that the new juveniles are utilizing cues associated with a process, the disturbance of surface sediments, in addition to the species-specific cues described elsewhere.

Motivated by experimental findings, a computational fluid dynamics (CFD) model was used to investigate whether the clam Mercenaria mercenaria may alter its cue downstream variability by an exhalant random pumping behavior. This behavior was hypothesized to occur in the presence of predator chemical signals in order to prevent successful tracking by the predator. Simulated downstream flow and mixing conditions derived from the random nature of the clam exhalant jet in a crossflow were analyzed by computing an intermittency factor, determining the field of finite-time Lyapunov exponents (FTLEs) and identifying the resulting Lagrangian coherent structures (LCSs). Numerical simulations illustrate that the effectiveness of a fluctuating exhalant jet to prevent downstream tracking by a crab, depends on the ratio of the exhalant jet to the crossflow. Specifically, the clam could effectively enhance the downstream dispersion to prevent tracking, but only in the range of parameters where LCSs are generated (jet-to-crossflow ratio ≥ 1). Then, the probability of detection is reduced with respect to the case of a less fluctuating exhalant jet.

Insights into oceanographic environmental conditions such as paleoproductivity, deep-water temperatures, salinity, ice volumes, and nutrient cycling have all been obtained from geochemical analyses of biomineralized carbonate of marine organisms. However, we cannot fully understand geochemical proxy incorporation and the fidelity of such in species until we better understand fundamental aspects of their ecology such as where and when these (micro)organisms calcify. Here, we present an innovative method using osmotic pumps and the fluorescent marker calcein to help identify where and when calcareous meiofauna calcify in situ. Method development initially involved juvenile quahogs (Mercenaria mercenaria); subsequent method refinement involved a neritic benthic foraminiferal community. Future applications of this method will allow determining the in situ growth rate in calcareous organisms and provide insights about microhabitats where paleoceanographically relevant benthic foraminifera actually calcify.

Drillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecological studies because they provide direct, preservable evidence of predation. The muricidEcphorais common in many Neogene Atlantic Coastal Plain assemblages in the United States, but is frequently ignored in studies of naticid predation. We used a combination of Pliocene fossil, modern beach, and experimentally derived samples to evaluate the hypothesis thatEcphorawas an important source of drillholes in infaunal bivalve prey shared with naticids. We focused on the large, thick-shelled venerid,Mercenaria,which is commonly drilled by naticids today. Laboratory experiments, modern beach samples, and the published literature confirm that naticids preferentially drill near the umbo (significant clumping of holes), show a significant correlation between prey size and predator size (estimated by outer borehole diameter), and preferMercenariaEcphora(with or without other large muricids) show no drillhole site stereotypy (no significant clumping, greater variability in placement), no significant predator: prey size correlation, drilled prey shells larger than the largest modern naticids could produce in an experimental setting, and drillholes larger in diameter than those estimated for the largest Pliocene naticids, thus supporting our hypothesis. Substantial overlap in the placement of holes drilled by naticids and muricids, however, made identifying predators from drillhole position problematic. The lack of overlapping ranges of prey shell thickness between fossil and other samples precluded the use of drillhole morphology to establish predator identity (e.g., ratio of inner borehole diameter to outer borehole diameter, drillhole angle). Whereas the difficulty in determining predator identity from drillholes limits the types of analyses that can be reliably performed in mixed-predator assemblages, recognizingEcphoraas a prominent drilling predator creates the opportunity to investigate previously unrecognized questions.

Elevated CO2 levels reduce seawater pH and may affect bioavailability of trace metals in estuaries. We studied the interactive effects of common metal pollutants (50 μg l(-1) Cd or Cu) and PCO2 (~395, 800 and 2000 μatm) on metal levels, intracellular pH, expression of metal binding proteins and stress biomarkers in estuarine bivalves Crassostrea virginica (oysters) and Mercenaria mercenaria (hard clams). Cd (but not Cu or hypercapnia) exposure affected the acid-base balance of hemocytes resulting in elevated intracellular pH. Cd and Cu exposure led to the increase in the tissue metal burdens, and metal accumulation was reduced by elevated PCO2 in the mantle but not hemocytes. No change was found in the intracellular free Cd(2+), Cu(2+) or Fe(2+) during Cu or Cd exposure indicating that these metals are bound to intracellular ligands. Free Zn(2+) content in oyster hemocytes was suppressed by Cd and Cu exposure and below the detection limits in clam hemocytes, which went hand-in-hand with the elevated mRNA expression of metallothioneins and ferritin in Cd- and Cu-exposed bivalves, enhanced by hypercapnia. The metal-binding and antioxidant mechanisms of oysters and clams were sufficient to effectively maintain intracellular redox status, even though metal exposure combined with moderate hypercapnia (~800 μatm PCO2) led to the elevated production of reactive oxygen species in hemocytes. Overall, while hypercapnia modulates metal accumulation, binding capacity and oxidative stress in estuarine bivalves, the physiological effects of elevated CO2 are mild compared to the effects of other common stressors.

The northern hard clam Mercenaria mercenaria is one of the most commercially important bivalve species produced via aquaculture in the eastern United States. Breeding practices associated with large-scale hatchery production of hard clamseedmayresultinunintended,potentiallynegativeconsequencesincludinginbreedingandreducedlevelsofgeneticdiversity. Seven microsatellite markers were used to compare levels of genetic diversity in six hatchery stocks and four wild stocks from the state of Florida. Wild stocks of M. mercenaria had slightly higher levels of allelic richness and similar observed heterozygosity (wild ¼Ar ¼3.61,Ho ¼0.448;hatchery ¼Ar ¼3.46,Ho ¼0.452);however,thesedifferenceswerenotstatisticallysignificant(Ar:P ¼ 0.145; Ho: P ¼ 0.931). Differentiation was highest between hatchery stocks (GST ¼ 0.03, SD ¼ 0.007; P < 0.001) but minimal among hatchery-by-wild comparisons. In contrast, wild stocks were not differentiated (GST ¼ -0.002, SD ¼ 0.004; P � 0.58) and Bayesian comparisons of competing gene flow models (panmixia, stepping stone, and full-migration) suggested that wild stocks were effectively panmictic at this scale. Together, these results indicate that some genetic drift has occurred within hatchery populations, possibly as a result of broodstock selection and spawning practices. The genetic divergence between wild and hatchery stocks observed in this study are not as pronounced as seen in other aquaculture bivalve species. Given the large scale of hard clam production in Florida we argue that hatchery practices should incorporate long-term genetic goals (i.e., avoidance of inbreeding) to maintain the integrity of hatchery stocks. A secondary objective of this study was to amplify a congeneric species, Mercenaria campechiensis, using the same suite of microsatellite markers to assess their utility for detecting interspecific hybridization. Amplification success was poor and failed for four of the seven loci. The identification of microsatellite loci for different species of Mercenaria should be identified de novo in the future.

This study aimed to evaluate the potential impacts of an introduced clam Mercenaria mercenaria on estuarine ecosystem, and implications for the niche competition with a native clam Meretrix meretrix. The biodeposition, respiration, and excretion rates of M. mercenaria were determined seasonally using a sediment trap and a closed respirator in field. The biodeposition rates of M. mercenaria were 0.06–0.37 g/ (ind.·d), and the respiration rates were 0.31–14.66 mg/(ind.·d). The ammonia and phosphate excretion rates were 0.18–36.70 and 1.44–14.87 μg/(ind.·d), respectively. The hard clam M. mercenaria may discharge dry deposits up to 2.1×105 t, contribute 18.3 t ammonia and 9.0 t phosphate to culture ponds, and consume 7.9×103 t O2 from ponds annually. It suggested that the hard clam M. mercenaria might play an important role in pelagic-benthic coupling in pond ecosystem through biodeposition and excretion. A comparison of the key physiological parameters of the introduced clam M. mercenaria and the native clam Meretrix meretrix suggested that M. mercenaria had a niche similar to that of Meretrix meretrix in Shuangtaizi estuary and might have a potential competition with Meretrix meretrix for habitat and food if M. mercenaria species escaped from the culture pond or artificially released in estuarine ecosystem.

Monitoring of persistent QPX infections in clams of Raritan Bay (New York) shows certain areas of the estuary have remained without any significant disease prevalence. This study was conducted to investigate the potential to mitigate QPX disease by relocating infected hard clams, Mercenaria mercenaria (Linnaeus), from enzootic areas to nearby sites with prevailing environmental conditions suggested to deter infection and favour remission and healing. Clams were collected from a location with consistent disease prevalence in central Raritan Bay and brought to near shore habitats subject to lower salinities and higher summer temperatures. A reduced host density treatment was included in the study to examine the common observation of high clam density in the most persistently infected locales. An additional treatment retained clams above the sediment, since sediments are suspected to represent a QPX reservoir. At the end of the 4-month study all treatments displayed less QPX disease than the control group and the greatest contrast was provided by the disappearance of infections in a tidal creek.

To counteract the effects of cold on the pace of membrane bound metabolic processes, winter active ectotherms decrease saturated fatty acids (SFAs) and/or increase highly unsaturated fatty acids (HUFAs) esterified to phospholipids. Whereas it has been shown that winter dormant species do not undergo this cold counteracting lipid remodeling, no studies have investigated winter facultative quiescent species. The northern quahog (Mercenaria mercenaria) enters quiescence conditional to temperature decreasing below 6–7 °C. Previous studies have shown that the species can operate a cold counteracting lipid remodeling with temperatures decreasing from 22 to 8 °C, but there is no evidence that further adjustments are made at lower temperatures during quiescence. This study was designed to precisely investigate if cold counteracting lipid remodeling is further operated by M. mercenaria after entrance into quiescence. Individuals were cultured together with two evolutionarily- related (veneroid) cold-tolerant species (Spisula solidissima and Arctica islandica), and exposed to a natural annual temperature change between 12 °C and 2 °C. Individuals of M. mercenaria were sampled in December (beginning of the 2 °C winter temperature plateau), and all three species were sampled in April (end of 2 °C plateau), and again in August (end of 12 °C summer plateau). Gill membrane carbon chain composition (fatty acids + alkenyl chains) was analyzed separately (GC-MS + GC-FID) for mitochondria and other sources of membranes (non-mitochondrial). Valve opening was monitored visually in all species, and markers of lipoxidation (lipid hydroperoxides and TBARS) were measured during winter in M. mercenaria to investigate possible signs of stress. Below 6–7 °C, individuals of M. mercenaria maintained valves closed, and markers of lipoxidation increased. Changes in membrane lipids were observed for this species; however, these were opposite to what would counteract the effects of cold. The chain fluidity index and mol% HUFA were higher in August (12 °C) instead of April (2 °C). In contrast, both cold tolerant species maintained filter-feeding activity during winter and operated a cold counteracting lipid remodeling of mitochondrial membranes. In April, chain fluidity index was higher for S. solidissima and mol% HUFA was higher for A. islandica as compared to August. Our results show that M. mercenaria do not further attempt at counteracting the effects of cold on membranes after entrance into quiescence. Adjusting the pace of membrane processes to that of the whole organisms through conditional cold counteracting lipid remodeling may benefit facultative active ectotherms.

Overwinter mortality of juvenile northern quahogs, Mercenaria mercenaria, is a major impediment to the aquaculture industry from the mid-Atlantic US through Atlantic Canada. Mortality occurs during prolonged exposures to low temperatures and/or during the winter–spring transition when water temperatures are rising. Recent efforts to overwinter juveniles of M. mercenaria produced from native Maine (ME, USA) broodstock in eastern ME have found high survival while using a newly adopted methodology (i.e. cages in the water column rather than the standard practice of bottom planting) for overwintering. The current study aimed to determine if the high survivorship was a result of the culture methodology or if the ME genetic stock is better adapted for overwinter survival. Field studies were performed across two consecutive winters in ME, New York (NY) and New Jersey (NJ, USA) to compare survivorship of two size classes of juvenile M. mercenaria using the new methodology to the standard practice of bottom planting, and to compare the survival and physiological condition of the ME stock vs. the NY and NJ stocks across a latitudinal gradient. The ME stock had greater survival than the NY and NJ stock at all sites and in both study years. Both of the ME size classes exhibited lower mortality ( M. mercenaria in eastern Maine cannot be applied effectively to more southern locations. However, the results suggest that selective breeding programs may be able to develop aquaculture stocks that are better adapted to overwintering conditions.

Brevetoxins in clams (Mercenaria sp.) exposed to recurring blooms of Karenia brevis in Sarasota Bay, FL, were studied over a three-year period. Brevetoxin profiles in toxic clams were generated by ELISA and LC-MS. Several brevetoxin metabolites, as identified by LC-MS, were major contributors to the composite brevetoxin response of ELISA. These were S-desoxyBTX-B2 (m/z 1018), BTX-B2 (m/z 1034), BTX-B5 (m/z 911), open A-ring BTX-B5 (m/z 929), and BTX-B1 (m/z 1018). Summed values of these metabolites were highly correlated (R2 = 0.9) with composite B-type brevetoxin measurements by ELISA. S-desoxyBTX-B2, BTX-B2, and BTX-B1 were the most persistent and detectable in shellfish for several months after dissipation of blooms. These metabolites were selected as LC-MS biomarkers of brevetoxin exposure and reflective of composite B-type brevetoxins in hard clam. ELISA and LC-MS values were moderately correlated with toxicity of the shellfish by mouse bioassay. ELISA and LC-MS methods offer rapid screening and confirmatory determination of brevetoxins, respectively, as well as toxicity assessment in clams exposed to K. brevis blooms.

Changes in the molar percentage of two omega-3 fatty acids, 20:5n-3 (EPA) and 22:6n-3 (DHA), occur in juvenile northern quahogs, Mercenaria mercenaria, as descending autumn temperatures approach winter lows in the temperate zone. Incorporation of these highly unsaturated fatty acids compensates for the effect of low temperature on cell membrane viscosity by lowering the phase transition of membrane phospholipids. Prior studies have demonstrated that the ability of bivalve mollusks, like M. mercenaria, to manufacture these compounds de novo does not exist or may be limited at best. Insufficient exogenous supply of EPA and DHA, therefore, may restrict their ability to overcome the inhibiting effect of high viscosity on cell membrane phospholipids during this interval. In the present study, a matrix of cultured algae containing various quantities of these compounds was administered to four groups of juvenile M. mercenaria as they adapted to low temperature. Each group displayed a unique response to diet in relative fatty acid profile and mortality. The group receiving abundant EPA adapted well during the early-phase temperature decline, and the one receiving abundant DHA adapted well to the late-phase temperature decline. The group receiving abundant DHA also enjoyed best overall survival following a severe 5-day drop in temperature. The strain native to the local region suffered between 31 and 117 % higher mortality than the notata strain during the 72-day period of temperature decline from 18 to 6 °C.

Vibriosis is a leading cause of seafood-associated morbidity and mortality in the United States. Typically associated with consumption of raw or undercooked oysters, vibriosis associated with clam consumption is increasingly being reported. However, little is known about the prevalence of Vibrio spp. in clams. The objective of this study was to compare the levels of Vibrio cholerae , Vibrio vulnificus , and Vibrio parahaemolyticus in oysters and clams harvested concurrently from Long Island Sound (LIS). Most probable number (MPN)–real-time PCR methods were used for enumeration of total V. cholerae , V. vulnificus , V. parahaemolyticus , and pathogenic ( tdh + and/or trh + ) V. parahaemolyticus . V. cholerae was detected in 8.8% and 3.3% of oyster ( n = 68) and clam ( n = 30) samples, with levels up to 1.48 and 0.48 log MPN/g in oysters and clams, respectively. V. vulnificus was detected in 97% and 90% of oyster and clam samples, with median levels of 0.97 and −0.08 log MPN/g, respectively. V. parahaemolyticus was detected in all samples, with median levels of 1.88 and 1.07 log MPN/g for oysters and clams, respectively. The differences between V. vulnificus and total and pathogenic V. parahaemolyticus levels in the two shellfish species were statistically significant ( P < 0.001). These data indicate that V. vulnificus and total and pathogenic V. parahaemolyticus are more prevalent and are present at higher levels in oysters than in hard clams. Additionally, the data suggest differences in vibrio populations between shellfish harvested from different growing area waters within LIS. These results can be used to evaluate and refine illness mitigation strategies employed by risk managers and shellfish control authorities.

International audience; The brevetoxin-producing dinoflagellate, Karenia brevis, adversely affects many shellfish species including the commercially and ecologically important bivalve molluscs, the northern quahog (=hard clam) Mercenaria mercenaria and eastern oyster Crassostrea virginica, in the Gulf of Mexico, USA. This study assessed the effects of exposure of these bivalves to K. brevis during their early development. In separate experiments, embryos of 2-4 cell stage of M. mercenaria and C. virginica were exposed to both whole and lysed K. brevis cells isolated from Manasota Key, Florida. Low bloom concentrations of 500 to 3000 cellsmL(-1) were simulated for 96h. Shell length, percent abnormality (and normality), and percent mortality of resulting larvae were measured. Percentages were recorded after 6, 24, and 96h of exposure; larval shell length was measured at 24 and 96h. For both quahogs and oysters, the effects of exposing embryos to K. brevis on all larval responses were generally dose- and time-dependent. Percent mortalities and abnormalities of both clam and oyster embryos increased significantly after only 6h of exposure to whole cells of K. brevis. For clams, these parameters were significantly higher in whole and lysed treatments (at 3000 cellsmL(-1)) than in controls. Percent mortalities of oysters were significantly higher in the whole-cell treatment (3000 cellsmL(-1)) than under control conditions. After 24h of exposure, mean larval shell length of both bivalve species was significantly reduced relative to controls. This was evident for clam larvae in both the lysed treatment at 1500 cellsmL(-1) and in whole and lysed treatments at 3000 cellsmL(-1), and for oyster larvae in the lysed treatment at 3000 cellsmL(-1). After 96h, both species exposed to the lysed cell treatment at 3000 cellsmL(-1) had significantly smaller larvae compared to those in the control. Overall, lysed cells of K. brevis had a more pronounced effect on shell length, percent abnormality, and mortality in both clams and oysters than did whole cells. Given the fact that blooms of K. brevis overlap with the spawning periods of these two bivalves, and that cells of this naked dinoflagellate are readily lysed by wave action, these results suggest that exposure to K. brevis during the early life history stages of clams and oysters could adversely affect their population recruitment. Further, the presence of whole or lysed cells of K. brevis in hatcheries could have a major negative impact on production.

Hypercapnia (elevated CO

The importance of chemical signals as foraging and orientation cues has been demonstrated for many marine organisms. It is still unclear whether sea stars use chemical signals during orientation and whether chemoreception occurs in the absence of macroscale flow. To determine whether the sea star Asterias forbesi can perceive chemical signals in the absence of flow and what role such signals play in orientation and foraging behavior, we tested the orientation behavior of sea stars to prey and nonprey items under conditions of nondirectional flow. Prey items were whole and broken clams (Mercenaria mercenaria) and mussels (Mytilus edulis); the nonprey item was squid flesh. Asterias forbesi showed the ability to successfully locate odor sources irrespective of the type of odor. Only in trials with the broken clam did the animals reveal an initial directional choice towards the odor source. There were significant changes in the movement rates and heading angles during orientation for all three stimuli. In addition, orientation paths were different for each of the chemical stimuli tested. From these results, we conclude that sea stars can detect and respond to chemicals in the absence of macroscale flow. Orientation paths appear to be more of a taxis, in which heading is directly guided by the stimulus field.

More widespread use of metallothionein (MT) as a biomarker for trace metal pollution continues to be partly dependent on obtaining reliable baseline concentrations and identifying increased induction of the enzyme with only modest increases in metal concentrations. In this study, new data on metals and MT levels in whole clams tissue, gills, and digestive glands from field samples and in sediments are presented. Concentrations of Cd, Cu, Fe, and Zn in depurated (24 h) clam samples of digestive glands, gills, and the whole clam Merceneria merceneria from the Indian River Lagoon, Florida, varied with location and showed moderate to strong correlations among Zn, Cu, and Fe. Concentrations of metallothionein (dry wt.) ranged from 34─270 μg/g in gills and 150–440 μg/g in digestive glands and showed moderate to strong correlations between organs and with metal concentrations in those organs. Observed trends support increased synthesis of metallothionein with only moderate increases in metal values and in response to statistically higher sediment metal concentrations.

The cockle Cerastoderma edule fishery has traditionally been the most important shellfish species in terms of biomass in Galicia (NW Spain). In the course of a survey of the histopathological conditions affecting this species in the Ria of Arousa, a haplosporidan parasite that had not been observed in Galicia was detected in one of the most productive cockle beds of Galicia. Uni- and binucleate cells and multinucleate plasmodia were observed in the connective tissue mainly in the digestive area, gills and gonad. The parasite showed low prevalence, and it was not associated with abnormal cockle mortality. Molecular identification showed that this parasite was closely related to the haplosporidan Minchinia mercenariae that had been reported infecting hard clams Mercenaria mercenaria from the Atlantic coast of the United States. The molecular characterization of its SSU rDNA region allowed obtaining a fragment of 1,796 bp showing 98% homology with M. mercenariae parasite. Phylogenetic analysis supported this identification as this parasite was clustered in the same clade as M. mercenariae from the United States and other M. mercenariae-like sequences from the UK, with bootstrap value of 99%. The occurrence of M. mercenariae-like parasites infecting molluscs outside the United States is confirmed.

As bivalve aquaculture expands globally, an understanding of how it alters nitrogen is important to minimize impacts. This study investigated nitrogen cycling associated with clam aquaculture in the Sacca di Goro, Italy ( Ruditapes philipinarum ) and the Eastern Shore, USA ( Mercenaria mercenaria ). Ammonium and dissolved oxygen fluxes were positively correlated with clam biomass; R. philippinarum consumed ~ 6 times more oxygen and excreted ~ 5 times more NH 4 + than M. mercenaria . There was no direct effect of clams on denitrification or dissimilatory nitrate reduction to ammonium (DNRA); rather, nitrate availability controlled the competition between these microbial pathways. Highest denitrification rates were measured at sites where both water column nitrate and nitrification were elevated due to high densities of a burrowing amphipod ( Corophium sp.). DNRA exceeded denitrification where water column nitrate was low and nitrification was suppressed in highly reduced sediment, potentially due to low hydrologic flow and high clam densities.

Diurnal variations in pH and dissolved oxygen (DO) concentrations are common seasonal phenomena in many eutrophic estuaries, yet few studies have investigated the concurrent effects of low pH and low DO on marine organisms inhabiting these coastal systems. Here, we assess the effects of diurnal variations in pH and DO on the early-life history of two bivalve species native to Northeast US estuaries, the bay scallop (Argopecten irradians) and hard clam (Mercenaria mercenaria). In one set of experiments, larval- and juvenile-life stage bivalves were exposed to ambient conditions (pHT ~ 7.9), two continuously-low pH levels (pHT ~ 7.3 and 7.6), and diurnal fluctuations between the ambient and low conditions yielding mean pH levels equal to the intermediate pH levels. In a second set of experiments, larval bivalves were exposed to ambient conditions (pHT ~ 7.9, DO ~ 7 mg L−1), two levels of low pH and DO (pHT ~ 7.2, DO ~1 mg L−1; pHT ~ 7.4, DO ~ 4 mg L−1) and diurnal fluctuations of both pH and DO between the ambient and low pH/DO levels that resulted in mean pH and DO levels equal to the intermediate pH and DO levels. Diurnal acidification treatments with ambient DO levels yielded survival rates for both species at both life stages that were consistent with the survival of individuals exposed to the same mean level of chronic pH with juveniles being more resistant to acidification than larvae. In contrast, when both pH and DO varied diurnally, the survival rates of larval bivalves were significantly lower than the survival of individuals chronically exposed to the same mean levels of pH and DO, an indication that bivalves were physiologically more vulnerable to concurrent fluctuations of both parameters compared to acidification alone. While both species displayed sensitivities to diurnal fluctuations in pH and DO, scallops were relatively more susceptible than hard clams. Since many shallow eutrophic estuaries presently experience diurnal cycles of both pH and DO when early-life stages of bivalves are present in estuaries, the populations of the bivalves studied are likely impacted by these conditions which are likely to intensify with climate change.

Locomotion of infaunal bivalve mollusks primarily consists of vertical movements related to burrowing; horizontal movements have only been reported for a few species. Here, we characterize hard clam walking: active horizontal locomotion of adults (up to 118 mm shell length, SL) of the commercially important species, Mercenaria mercenaria, at the sediment surface—a behavior only briefly noted in the literature. We opportunistically observed walking over a 10-yr period, at 9 different sites in the Peconic Bays, New York, USA, and tested several hypotheses for the underlying cause of this behavior through quantitative field sampling and reproductive analyses. Hard clam walking was exhibited by males and females at equal frequency, predominantly during June/July and October, when clams were in peak spawning condition. Extensive walking behavior appears to be cued by a minimum population density; we suggest it may be mediated by unidentified pheromone(s), infaunal pressure waves and/or other unidentified factors. There was no directionality exhibited by walking clams, but individuals in an area of extensive walking were highly aggregated and walking clams were significantly more likely to move toward a member of the opposite sex. Thus, we conclude that hard clam walking serves to aggregate mature individuals prior to spawning, thereby facilitating greater fertilization success. In the process of investigating this behavior, however, we apparently oversampled one population and reduced clam densities below the estimated minimum threshold density and, in so doing, suppressed extensive walking for a period of >3 years running. This not only reinforces the importance of detailed field investigations of species biology and ecology, even for those that are considered to be well studied, but also highlights the need for greater awareness of the potential for research activities to affect focal species behavior.

A before-after-control-impact (BACI) experiment was conducted to examine the effects of hydraulic clam dredging on sediment biogeochemistry of a leased shellfish bed of Mercenaria mercenaria, northern quahog, over the course of an entire growing season. Six study plots (0.67 ha each), three dredged and three not dredged, off of Milford, Connecticut, in Long Island Sound, were sampled from May to October 2009 for porewater fluxes of total ammonia, oxygen, and hydrogen. Particulate samples were also analyzed for grain size, total nitrogen, total carbon, total sulfur, and organic carbon. Statistical analysis indicated no significant difference between dredged and not dredged sites. Grain size and oxygen flux explained 22% of the variation in the total benthic species assemblages; grain size and either total carbon or organic nitrogen explained 18% of the variation in molluscan abundance. Our study demonstrates that one-time hydraulic shellfish harvesting had minor effects on the sediment chemistry of a leased clam bed.

article i nfo Article history: We examined the effects of hydraulic dredging on the benthicecology and sediment biogeochemistry of a leased shellfish bed in Long Island Sound near Milford, Connecticut, where Northern quahog or hard clam, Mercenaria mercenaria (Linnaeus 1758), aquaculture is conducted. Six 1 ha plots were sampled at 1-2 week intervals from June through October of 2010. One-time hydraulic dredging to harvest hard clams was conducted on 3 dredged treatment plots in mid-June, while 3 control plots remained not dredged. Repeated measures analysis indicated no significant differences between dredged and not dredged plots for any of the ecological indices or sediment chemistrymeasurements. Numbers of newlysettledhardclams weresignificantlyhigher ondredgedplots. Clus- ter analysis indicated a strong seasonal influence on benthic community structure distinguishing between early andlate season assemblages.HydraulicshellfishharvestingasconductedonleasedbedsinLongIslandSounddid not appear to significantly impact benthic assemblages or sediment biogeochemistry, while sediment grain size and sampling date had a greater influence on benthic community structure. Published by Elsevier B.V.

The susceptibility of membrane lipids to peroxidation (peroxidation index [PI]) increases with the double bond content of fatty acids and is inversely correlated to longevity in mammals, birds, and bivalve molluscs. In molluscs, membrane polyunsaturated fatty acids content can be affected by temperature, nutrition, and the individual's age. In this study, we evaluated how these three parameters may alter correlations between PI and longevity. We determined the fatty acid and dimethyl acetal compositions of phospholipids from gill mitochondrial and nonmitochondrial preparations from the short-lived Spisula solidissima (maximum longevity = 37 years) and the long-lived Arctica islandica (maximum longevity = 507 years) exposed to diet abundance and temperature (season) treatments. We also evaluated the effect of individual age on PI in S. solidissima (from 6 to 23 years). The temperature increase from winter to summer (2 to 12°C) coincided with decreases in values of PI, proportions of eicosapentaenoic acid, and dimethyl acetals. Higher microalgae supplementation increased polyunsaturated fatty acids and PI and decreased dimethyl acetals; age did not affect the PI in S. solidissima. Our finding that the PI of A. islandica remained significantly lower than that of S. solidissima in corresponding fractions throughout treatments suggests that longevity-related differences in PI are resilient to environmental conditions.

Increased anthropogenic emission of CO2 changes the carbonate chemistry and decreases the pH of the ocean. This can affect the speciation and the bioavailability of metals in polluted habitats such as estuaries. However, the effects of acidification on metal accumulation and stress response in estuarine organisms including bivalves are poorly understood. We studied the interactive effects of CO2 and two common metal pollutants, copper (Cu) and cadmium (Cd), on metal accumulation, intracellular ATP/ubiquitin-dependent protein degradation, stress response and energy metabolism in two common estuarine bivalves—Crassostrea virginica (eastern oyster) and Mercenaria mercenaria (hard shell clam). Bivalves were exposed for 4–5 weeks to clean seawater (control) and to either 50 μg L−1 Cu or 50 μg L−1 Cd at one of three partial pressures of CO2 (PCO2PCO2 ∼395, ∼800 and ∼1500 μatm) representative of the present-day conditions and projections of the Intergovernmental Panel for Climate Change (IPCC) for the years 2100 and 2250, respectively. Clams accumulated lower metal burdens than oysters, and elevated PCO2PCO2 enhanced the Cd and Cu accumulation in mantle tissues in both species. Higher Cd and Cu burdens were associated with elevated mRNA expression of metal binding proteins metallothionein and ferritin. In the absence of added metals, proteasome activities of clams and oysters were robust to elevated PCO2PCO2, but PCO2PCO2 modulated the proteasome response to metals. Cd exposure stimulated the chymotrypsin-like activity of the oyster proteasome at all CO2 levels. In contrast, trypsin- and caspase-like activities of the oyster proteasome were slightly inhibited by Cd exposure in normocapnia but this inhibition was reversed at elevated PCO2PCO2. Cu exposure inhibited the chymotrypsin-like activity of the oyster proteasome regardless of the exposure PCO2PCO2. The effects of metal exposure on the proteasome activity were less pronounced in clams, likely due to the lower metal accumulation. However, the general trends (i.e. an increase during Cd exposure, inhibition during exposure to Cu, and overall stimulatory effects of elevated PCO2PCO2) were similar to those found in oysters. Levels of mRNA for ubiquitin and tumor suppressor p53 were suppressed by metal exposures in normocapnia in both species but this effect was alleviated or reversed at elevated PCO2PCO2. Cellular energy status of oysters was maintained at all metal and CO2 exposures, while in clams the simultaneous exposure to Cu and moderate hypercapnia (∼800 μatm PCO2PCO2) led to a decline in glycogen, ATP and ADP levels and an increase in AMP indicating energy deficiency. These data suggest that environmental CO2 levels can modulate accumulation and physiological effects of metals in bivalves in a species-specific manner which can affect their fitness and survival during the global change in estuaries.