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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. [ABSTRACT FROM AUTHOR]

We present the first record of two nonnative Bivalvia species originally from North America, Mercenaria mercenaria and Ensis directus, in the waters of the Iberian Peninsula (southwest of the Bay of Biscay). This constitutes the southernmost distribution for these species in the northeast Atlantic to date. We provide notes on the relative abundance, depth range, and substrate preferences of the species in their new habitat. The bivalve E. directus has became the dominant Ensis species along the Cantabric sandy shores it has colonized. [ABSTRACT FROM AUTHOR]

Three selected aquaculture Strains of the commonly used hard clam, Mercenaria mercenaria (Linnacus, 1758)—Massachusetts (MA), New Jersey (NJ), and South Carolina (SC)—were reared in a single hatchery. They were planted in replicate plots in Barnstable Harbor, MA, and Dry Bay, NJ, in spring 2008 and grown to market size. Growth, survival, and QPX (quahog parasite unknown) prevalence and severity were measured in fall 2008, spring 2009, and fall 2009. Growth was similar at both sites for the first summer, but during the second year growth was better in Massachusetts. Overall survival was better for all strains in New Jersey when compared with Massachusetts. Survival of strains in New Jersey was 53.4% and 34.8% for NJ and MA, respectively, closely followed by those in Massachusetts (41.8% and 26.2% for NJ and MA, respectively). Strains from SC seed had the highest prevalence and severity of QPX and the lowest survival (36% and 6.6% in New Jersey and Massachusetts, respectively), Infections with QPX were low at both sites, but this study confirms earlier work indicating that QPX infection rates appear to be strain specific, with strains of southern origin being more susceptible than those of northern origin. Our study also supported anecdotal reports that QPX disease is more severe in Massachusetts than in more southern sites where it has been found. As in most previous field studies, we found that although mortality was correlated with QPX levels, it was considerably higher than infection prevalence would indicate, which suggests that strain interactions with stressful environmental conditions or unidentified factors may be also involved in mortality. [ABSTRACT FROM AUTHOR]

Twenty-two large shells (>90 mm shell height) from a sample of live collected hard shell clams, Mercenaria mercenaria, from Buzzards Bay, Woods Hole, Cape Cod, MA, were subjected to sclerochronological analysis. Annually resolved growth lines in the hinge region and margin of the shell were identified and counted; the age of the oldest clam shell was determined to be at least 106 y. This age represents a considerable increase in the known maximum life span for M. inercenaria, more than doubling the maximum recorded life span of the species (46 y). More than 85% of the clam shells aged had more than 46 annual increments, the previous known maximum life span for the species. In this article we present growth rate and growth performance indicators (the overall growth performance and phi prime) for this record-breaking population of M. ,nercenaria. Recently discovered models of aging require accurate age records and growth parameters for bivalve populations if they are lobe utilized to theiir full potential. [ABSTRACT FROM AUTHOR]

Clam aquaculturists have suspected low water flow over clam grow-out areas as a principal explanation for decreased growth and yield of bivalves; however, empirical data from field studies to support these observations are rare and in some cases contradictory. I conducted two experiments in Back Sound, NC, to examine the effects of water flow and juvenile density on hard clam survivorship and growth. The first experiment assessed differences in early growth and survivorship of juvenile seed clams under three manipulated water flows (enhanced [0-32cm sec-1], reduced [0-12 cm sec-1], and ambient tidal flows [0-22cm sec-1) and three initial stocking density (250, 500, or 1000 m²) of juvenile clams (shell length ISLI = 9mm). The second set experiment examined the effects of two different water flow regimes (ambient [0-22cm sec-1] and low [0-11 cm sec-1]), and three stocking densities (250, 500, or 1000 m²) on growth of seed clams (SL = 12 mm) to market size. Unlike the first experiment, in which no effort was made to exclude predators to examine survivorship, the second experiment mimicked aquaculture operations and used bottom netting to cover seed clams. Neither planting density nor flow regime affected growth or survivorship of juvenile seed clams in the first experiment. Overall survivorship was high (>75%) and clams grew to an average SL of 24 mm during the 4 months of grow-out. In the second experiment, clam growth and, consequently, time to marketable size was affected by water flow; however, differences in clam growth were relatively small (<4 mm SL). After 12 mo, 69% of clams were of harvestable size in the ambient flow (0-22cm sec-1) compared with 42% in the low flow (0-12cm sec-1). Planting density did not affect this relationship; no interaction between planting density and flow regime was evident in either experiment. This result suggests the positive effect of water flow on clam growth increases with individual clam size, but is not density dependent on the square meter scale of our experiments. [ABSTRACT FROM AUTHOR]

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

Bivalve larvae in mixed samples collected from the field have traditionally been identified through morphological differences among species. It is difficult, however, to use this method accurately because of overlapping size ranges and similar shapes of the larvae of many species. We used the molecular technique developed by Hare et al. (2000) to test the accuracy of morphological identification of Mercenaria mercenaria (L.) larvae from plankton samples collected from the Great South Bay and Coecles Harbor on Long Island, New York. We found that morphology is unreliable as the only means of identification for bivalve larvae in a mixed field sample, and a very high false positive rate of identification of M. mercenaria (100% of 71 larvae were misidentified). Morphological characteristics may be used to eliminate larvae from a field plankton sample, as the false negative rate for M. mercenaria was only 1.4% (n = 140). To determine larval bivalve densities accurately, other techniques in addition to those based on morphological characteristics. such as the molecular technique used in this study, must be used. [ABSTRACT FROM AUTHOR]

A numerical bioenergetics simulation mode! based on the physiological processes affecting individual clams across a range of phenotypes describing a cohort has been developed and applied to the conditions in Great South Bay, New York. The clam population is relatively sensitive to food and to a lesser extent to temperature within this system. The timing of temperature and food in the spring, and more importantly in the fall, can increase population sensitivity beyond the effects of one factor operating alone. The effects of fishing on the stocks in proportion to the size structure present, and as directed fisheries on various size classes (littleneck, cherrystone, chowder) was simulated. Recruitment overfishing was responsible for the stock decline in the 1970s and 1980s, but the continued decline into the late 1990s and 2000s cannot be attributed to fishing alone. Recruit-per-adult declined after the mid 1990s. Modeled stock recovery times under constant environmental conditions are on order of 10-15 or more years depending on the exploitation rate. Under base conditions a proportional fishery that removes approximately 25% of the stock, or a littleneck fishery that removes approximately 37.5% of that size class annually would provide the best economic returns under constant average environmental conditions. Slightly less harvest would be desirable to avoid overfishing in years of less than optimal environmental conditions. [ABSTRACT FROM AUTHOR]

To determine if population density in areas closed to fishing in Narragansett Bay is causing differences in the reproductive potential of the organisms, this study used two approaches to determine the reproductive condition of the animals. The first approach consisted in employing a gravimetric condition index (Cl) to evaluate the general condition of quahogs from nine different sites, 3 sites open conditionally for fishing (conditional areas) and 6 sites closed to fishing. The second approach was a determination of gonadal index (GI) of a subset of the sample sites, by histological observation of gonadal tissue sections. Initial sampling included determination of Cl only, and lasted from March 25 to Sep. 22, 2005. The subset of six of the Sites was sampled the next year (2006), every three weeks from April 15 until Sep. 28 to determine Cl and the gonadal index (GI). Results show that there is a significant difference between the Cl of northern quahogs from conditional areas and quahogs from closed areas (P < 0.001). There is a significant difference in GI between sites at (P < 0.10). The Cl in conditional areas was consistently higher than in closed sites indicating that maturation and reproductive stages are more prevalent in conditional areas than in closed sites. When sites were separated into three categories: conditional fishing sites; coves; and Providence River sites, the GI and Cl of the conditional areas were always higher than the Cl and GI of all the other sites. The coves had intermediate indices, and the Providence River sites always had the lowest indices. The results indicate that the populations of quahogs in the closed sites sampled are not completing the gonadal cycle as expected and that the reproductive capability of the quahogs in conditional areas is higher than those in closed areas. Possible explanations to this condition include lower water quality in the closed areas, low dissolved oxygen concentration especially during the summer, poor bottom conditions and high population density. Although, not one single characteristic of the environment is solely responsible for the reproductive condition of the quahog population, density appears to have significant effect. [ABSTRACT FROM AUTHOR]

Protein metabolism is a,1 expensive cellular process that can generally account for one third of basal metabolism in animals. Shifts in the stability of proteins under increased environmental temperatures could potentially alter the energy budget of an organism. However, studying the thermal stability kinetics of individual proteins is tedious and ultimately, difficult to relate to changes in the fitness of an organism. Yet understanding how organisms inhabiting extreme environments (polar seas, hydrothermal vents, and deep ocean basins) are able to maintain or limit the rate of protein turnover in the total cellular protein pool is crucial for our understanding of the total metabolic costs associated with survival in these habitats. To assess protein stability in field collected organisms at a proteome scale, we developed a high-throughput assay for protein denaturation profiles of total tissue extracts in bivalves. These profiles are quantitative and reveal unique compositional features of different tissues. Heat stress experiments in the clam Mercenaria mercenaria reveal that the protein pool of mantle and digestive mass tissues are more thermally stable after a short exposure to 35°C. This increase in stability could have large implications for the energy budget of M. mercenaria when exposed to high summer water temperatures. This methodology could readily be used to assess the stability and/or turnover potential of a variety of organisms experiencing extremes of both temperature and pressure. [ABSTRACT FROM AUTHOR]

The power of sclerochronology as a tool for interpreting the life history of aquatic organisms and the marine environment they inhabited lies in the occurrence of periodic and repeating structures within the skeletal parts of these organisms. Previous work examining the internal growth patterns of northern quahog (=hard clams), Mercenaria mercenaria (L.), along the Atlantic Coast has established their periodicity; however, the two existing descriptions of the annual growth pattern for hard clams from Narragansett Bay, RI are not consistent with one another. One study identified a translucent slow growth band in the summer and the winter, whereas the other study identified a translucent slow growth band only in the winter. To facilitate future sclerochronological analyses using Narragansett Bay hard clams, variations in the existing descriptions of the annual growth pattern were clarified. We found high variability in the annual growth pattern of M. mercenaria collected during the summers of 2005 and 2006. In approximately half the mature individuals observed, the winter growth breaks were separated by three bands, an opaque band of rapid growth in the spring, a translucent slow growth band in the summer, and a second opaque band of rapid growth in the fall. As these individuals approached senility, the pattern became compressed into two seasonal bands, a single opaque band of rapid growth in the spring and a single translucent band of slow growth encompassing both summer and fall. Growth in the remainder of the samples exhibited only two seasonal bands throughout the mature and senile period, an opaque band of rapid spring growth and a translucent band of slow growth throughout the summer and fall. To confirm the patterns observed, we analyzed δ18O from a subsample of shells. After placing the earlier descriptions and the current description of growth in Narragansett Bay hard clams in chronological order, it appears as though the changing environment of Narragansett Bay was reflected in the growth pattern of these clams. This study emphasizes the importance of validating annual growth patterns even in a region where the periodicity of the species has been confirmed. Changes in the marine environment may alter the patterns in the skeletal structures of aquatic organisms as well as their growth rates. [ABSTRACT FROM AUTHOR]

Quahog Parasite Unknown (QPX) disease has significantly impacted cultured and wild hard clam, Mercenaria mercenaria, populations in the Northeastern United States and is the first formidable disease issue concerning near market sized clams for the industry. Most of what is known about this protistan infection comes from diagnostic reports of mortality events and some preliminary field investigations. Disease dynamics and details of parasite pathobiology are somewhat of an obscurity. This study fostered a laboratory approach towards the experimental induction of infection to confirm direct transmissibility of the disease and to verify trends, observed in the field, of varied host susceptibility based on hard clam stock origin. Evidence of QPX as a directly infective pathogen was achieved, through the utilization of laboratory maintained QPX isolate cultures, as injection of QPX cells into hard clam tissue resulted in infection and subsequent mortalities in matter of a few months. Laboratory conditions did not promote transmission in a trial that aimed to mimic `natural' methods of infection by the cohabitation of infected adult hard clams, obtained from the field, with naïve seed clams. Histopathology of the adult hard clams, at the end of the cohabitation trial, displayed a significant amount of dead and degrading QPX cells, which suggests that laboratory conditions may have promoted healing and resistance of the host. This study has established an experimental infection method that can be used for future investigations concerning crucial aspects of the QPX/hard clam disease system. Laboratory conditions that led to the healing of field infected animals require more investigations and may promote a better understanding of factors affecting disease development. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Field surveys in southeastern Raritan Bay and laboratory studies from 1999 to 2005 were conducted to compare the characteristics of mud and sand habitats in relation to the abundance of the northern quahog (Mercenaria mercenaria). In 2000, the population density of quahogs was about 15 times higher in the mud habitat than in the sand habitat. In addition, the mud habitat also had a dense population of the amphipod Ampelisca abdita (about 24,000 m-2) associated with it. This species produces mats of tubes over the bottom. The sediment surface of the mud was comprised mostly of fecal pellets, the majority of which was produced by A. abdita. In contrast, the sand habitat did not have A. abdita tubes or much erect surface structure; its sediments were comprised of medium grain sand (Φ = 1.17-1.4). In southeastern Raritan Bay, the principal quahog predators are the longwrist hermit crab (Pa gurus Ion gicarpus), Atlantic oyster drill (Urosalpinx cinerea), and xanthid mud crabs. Collectively, they were >7 times more abundant in the sand habitat than in the mud habitat. We suggest that quahogs are abundant in the mud habitat because the presence of the tube mats probably reduces water siltation, encourages settlement of larval quahogs and deters predation on the quahogs. [ABSTRACT FROM AUTHOR]

The most commonly used methods for measuring the amount of seston removed from the water column (uptake) by populations of suspension-feeding bivalve molluscs involve taking discrete water samples followed by laboratory analyses. Here we describe a new method based on in situ fluorometry that provides rapid measurement of seston removal rates. The new system is comprised of two identical units, each consisting of an in situ fluorometer, data logger and peristaltic pump with plastic tube attached to a deployment device. The deployment device allows precise placement of the fluorometer probe and intake end of the plastic tube so that in situ fluorescence (chlorophyll a) can be measured and water can be sampled for seston analyses in the laboratory from the same height. The typical setup involves placing one unit upstream and the other downstream of the study area and sampling the water at periodic intervals. Changes in seston concentration are revealed in the field by the fluorometers, and the sampled water can be analyzed in the laboratory for various seston parameters. Comparisons of the in situ data with data from laboratory analyses of pumped water samples were made for three species at four study sites: the eastern oyster (Crassostrea virginica), hard clam (Mercenaria mercenaria), and blue mussel (Mytilus edulis). Comparisons of measured upstream versus downstream seston concentrations indicated significant (t-tests, P < 0.05) differences (uptake) for six of eight trials based on in situ fluorometry, but only marginally significant (P < 0.10) differences at two of the four trials using laboratory chlorophyll a measurements. These data demonstrate that compared with sampling methods requiring laboratory analyses, the new in situ method provides much more rapid quantitative assessments and may provide more accurate estimates. [ABSTRACT FROM AUTHOR]

Studies were undertaken to determine the relationship between size of northern quahogs Mercenaria mercenaria and the rate at which they transport aspartic acid. Quahogs ranging from 25 to 103 mm valve length were collected in Narragansett Bay and placed in seawater aquaria (27 ppt, 20 °C) and allowed to pump water actively. Uptake experiments were carried out using 1 μmol/L C14 radiolabeled aspartic acid. Aspartate transport rates in μmol/h can be related to valve length by the allometric equation with a = 24.32 and b = 0.905 when valve length is in mm. In May 1990, near-bottom samples of seawater were taken from five locations in Narragansett Bay for analysis of dissolved free amino acids (DFAA) by high-pressure liquid chromatography (HPLC). Results showed that the mean total DFAA concentration was 667.6 nmol/L ± 167.3 SD, with the top five being serine, alanine, aspartic acid, glutamic acid, and glycine. A simple spreadsheet model was used to assess the relative importance of the uptake of DFAA vis-à-vis the filtration of particulate organic matter by M. mercenaria. In the model, environmental DFAA concentrations and uptake rates by quahogs determined in this study are compared with literature values for particulate organic nitrogen concentrations and filtration rates by quahogs. On an annual basis, uptake of DFAA can account for about 14% of the total organic nitrogen uptake by quahogs. Uptake of DFAA by these benthic filter feeders may be a pathway of benthic-pelagic nutrient coupling that is often overlooked in coastal ecosystem analyses. [ABSTRACT FROM AUTHOR]