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Ocean uptake of carbon dioxide (CO2) is causing changes in carbonate chemistry that affect calcification in marine organisms. In coastal areas, this CO2-enriched seawater mixes with waters affected by seasonal degradation of organic material loaded externally from watersheds or produced as a response to nutrient enrichment. As a result, coastal bivalves often experience strong seasonal changes in carbonate chemistry. In some cases, these changes may resemble those experienced by aquacultured bivalves during translocation activities. We mimicked these changes by exposing juvenile hard clams (500 μm, Mercenaria mercenaria) to pCO2 in laboratory upwellers at levels resembling those already reported for northeastern US estuaries (mean upweller pCO2 = 773, 1274, and 1838 μatm) and then transplanting to three grow-out sites along an expected nutrient gradient in Narragansett Bay, RI (154 bags of 100 clams). Prior to the field grow-out, clams exposed to elevated pCO2 exhibited larger shells but lower dry weight per unit volume (dw/V). However, percent increase in dw/V was highest for this group during the 27-day field grow-out, suggesting that individuals with low dw/V after the laboratory treatment accelerated accumulation of dw/V when they were transferred to the bay. Treatments also appeared to affect shell mineral structure and condition of digestive diverticula. Although treatment effects diminished during the field grow-out, clams that were pre-exposed for several weeks to high pCO2 would likely have been temporarily vulnerable to predation or other factors that interact with shell integrity. This would be expected to reduce population recovery from short-term exposures to high pCO2.

As bivalve aquaculture expands worldwide, an understanding of its role in nutrient cycling is necessary to ensure ecological sustainability and determine the potential of using bivalves for nutrient mitigation. Whereas several studies, primarily of epifaunal bivalves, have assessed denitrification, few have considered nutrient regeneration processes such as dissimilatory nitrate reduction to ammonium (DNRA), which competes with denitrification for nitrate and results in nitrogen retention rather than loss. This study compares sediment nitrogen cycling including mineralization, DNRA, and denitrification within U.S. clam aquaculture sediments to nearby uncultivated sediments, seasonally. Clam aquaculture significantly increased sediment ammonium and phosphate effluxes relative to uncultivated sediments. Both DNRA and denitrification were significantly enhanced at clam beds compared to uncultivated sediments in July and November, while in May only DNRA was increased. The ratio of DNRA to denitrification was significantly higher at clam beds compared to uncultivated sediments, demonstrating that DNRA may be favored due to a ready supply of labile organic carbon relative to nitrate and perhaps sulfidic conditions. Functional gene abundances, nrfA (DNRA) and nirS (denitrification) followed similar patterns to nitrate respiration rates with highest nrfA abundances in the clam sediments and similar nirS abundances across seasons and sediment type. Ultimately clam sediments were found to be a significant source of nutrients to the water column whereas uncultivated sediments retained ammonium produced by microbial mineralization. Thus, clam cultivation may promote local eutrophication (i.e., increased primary production) by facilitating nutrient regeneration and retention of ammonium in the sediments.

Acute toxicity tests (48-96-h duration) were conducted with larvae of 2 echinoderm species (Strongylocentrotus purpuratus and Dendraster excentricus) and 4 bivalve mollusk species (Crassostrea virginica, Crassostrea gigas, Mytilus galloprovincialis, and Mercenaria mercenaria). Developing larvae were exposed to water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of fresh and weathered oils collected from the Gulf of Mexico during the Deepwater Horizon incident. The WAFs (oils alone), CEWAFs (oils plus Corexit 9500A dispersant), and WAFs of Corexit alone were prepared using low-energy mixing. The WAFs of weathered oils had no effect on survival and development of echinoderm and bivalve larvae, whereas WAFs of fresh oils showed adverse effects on larval development. Similar toxicities were observed for weathered oil CEWAFs and WAFs prepared with Corexit alone for oyster (C. gigas and C. virginica) larvae, which were the most sensitive of the tested invertebrate species to Corexit. Mean 10% effective concentration values for total polycyclic aromatic hydrocarbons and dipropylene glycol n-butyl ether (a marker for Corexit) in the present study were higher than all concentrations reported in nearshore field samples collected during and after the Deepwater Horizon incident. The results suggest that water-soluble fractions of weathered oils and Corexit dispersant associated with the Deepwater Horizon incident had limited, if any, acute impacts on nearshore larvae of eastern oysters and clams, as well as other organisms with similar sensitivities to those of test species in the present study; however, exposure to sediments and long-term effects were not evaluated. Environ Toxicol Chem 2016;35:2016-2028. © 2016 SETAC.

Prey organisms reduce predation risk by altering their behavior, morphology, or life history. Avoiding or deterring predators often incurs costs, such as reductions in growth or fecundity. Prey minimize costs by limiting predator avoidance or deterrence to situations that pose significant risk of injury or death, requiring them to gather information regarding the relative threat potential predators pose. Chemical cues are often used for risk evaluation, and we investigated morphological responses of oysters (Crassostrea virginica) to chemical cues from injured conspecifics, from heterospecifics, and from predatory blue crabs (Callinectes sapidus) reared on different diets. Previous studies found newly settled oysters reacted to crab predators by growing heavier, stronger shells, but that adult oysters did not. We exposed oysters at two size classes (newly settled oyster spat and juveniles ~2.0 cm) to predation risk cue treatments including predator or injured prey exudates and to seawater controls. Since both of the size classes tested can be eaten by blue crabs, we hypothesized that both would react to crab exudates by producing heavier, stronger shells. Oyster spat grew heavier shells that required significantly more force to break, an effective measure against predatory crabs, when exposed to chemical exudates from blue crabs as compared to controls. When exposed to chemical cues from injured conspecifics or from injured clams (Mercenaria mercenaria), a sympatric bivalve, shell mass and force were intermediate between predator treatments and controls, indicating that oysters react to injured prey cues but not as strongly as to cues released by predators. Juvenile oysters of ~ 2.0 cm did not significantly alter their shell morphology in any of the treatments. Thus, newly settled oysters can differentiate between predatory threats and adjust their responses accordingly, with the strongest responses being to exudates released by predators, but oysters of 2.0 cm and larger do not react morphologically to predatory threats.

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.

Littleneck hard clams (Mercenaria mercenaria) harvested from New Jersey coastal waters in the United States were high-pressure processed (HPP) in their shells using a 10 L high-pressure processing unit. A response surface (RS) methodology approach was used to optimize the pressure and time parameters for microbial inactivation caused by the high-pressure application. The total surviving microbial load in the hard clams was enumerated after processing at each experimental condition. The results indicated that log reduction in total plate count (TPC) due to high-pressure processing of hard clams was primarily a function of pressure. Pressure of at least 480 MPa was needed to achieve 1-log reduction in TPC in hard clams harvested from special restricted waters. In a parallel study, a panel of 60 regular raw clams consumers tasted both raw and processed hard clams that were harvested from approved waters and HPP at 310 MPa for 3 min. The consumers showed equal preference for processed and raw hard clams. Two subgroups of hard clam consumers were revealed; 1 group preferred the plumpness of the HPP clam and the other group preferred aroma of the unprocessed clam. Thus, plumpness and aroma may influence consumer acceptance of HPP hard clams. Practical Application: High-pressure processing has gained momentum as a processing technique that aids in retention of fresh appearance in foods. It holds promise as a method to process premium value food products while retaining quality attributes. Quantification of its impact on safety and consumer acceptance is critical for its acceptance and use in the food industry.

During routine histopathology of 180 juvenile hard clams, Mercenaria mercenaria, from a site in Virginia, USA, in 2007, we discovered a single individual heavily infected with a parasite resembling a haplosporidian, some members of which cause lethal bivalve diseases. Scanning electron microscopy of spores and sequencing of small subunit ribosomal DNA confirmed a new species: Minchinia mercenariae n. sp. Further sampling of clams at the site found prevalences up to 38% using polymerase chain reaction (PCR). No parasites were found in routine histological screening of the same individuals, but re-examination of clams judged positive by in situ hybridization (ISH) revealed very faintly staining plasmodia. No unusual mortalities have occurred among the sampled groups. Analysis of clams from Massachusetts to Florida by PCR failed to detect the parasite, but a haplosporidian found in a clam from New Jersey in 2001 was subsequently identified by ISH as M. mercenariae. No other haplosporidians have been reported in thousands of hard clams from the US east coast examined histologically since the mid-1980s. The discovery underscores critical questions about how to assess the risks associated with parasites in groups known to be lethal, but that themselves are not considered a problem.

We present experiments that examined the metamorphosis, growth, and survivorship of larvae from three species of commercially and ecologically valuable shellfish (Mercenaria mercenaria, Argopecten irradians, and Crassostrea virginica) at the levels of CO2 projected to occur during the 21st century and beyond. Under CO2 concentrations estimated to occur later this century (,66 Pa, 650 ppm), M. mercenaria and A. irradians larvae exhibited dramatic declines (.50%) in survivorship as well as significantly delayed metamorphosis and significantly smaller sizes. Although C. virginica larvae also experienced lowered growth and delayed metamorphosis at ,66 Pa CO2, their survival was only diminished at ,152 Pa CO2. The extreme sensitivity of larval stages of shellfish to enhanced levels of CO2 indicates that current and future increases in pelagic CO2 concentrations may deplete or alter the composition of shellfish populations in coastal ecosystems. The combustion of fossil fuels and the resultant increase in atmospheric CO2 during the past century has had a multitude of effects on this planet, including acidification of the world’s oceans. The oceans have absorbed nearly half of the anthropogenically produced CO2 during the past century (Sabine et al. 2004), altering its inorganic carbon chemistry and pH. Model simulations indicate that combustion of the world’s fossil fuel supply in the coming centuries could result in a fivefold increase in atmospheric CO2 levels to nearly 203 Pa (2000 ppm) and a decrease in surface ocean pH by 0.77 units (Caldeira and Wickett 2003). This decline in the pH of surface waters will concurrently reduce carbonate ion (CO 2{ 3 ) concentrations

We show that death by dissolution is an important size-dependent mortality factor for juvenile bivalves. Utilizing a new experimental design, we were able to replicate saturation states in sediments after values frequently encountered by Mercenaria mercenaria in coastal deposits (Varagonite 5 0.4 and 0.6). When 0.2-mm M. mercenaria were reared in sediments at Varagonite 5 0.4 and 0.6, significant daily losses of living individuals occurred (14.0% and 14.4% d21, respectively), relative to supersaturated-control sediments (3.9% d21). For 0.4mm M. mercenaria, significant mortality occurred under the most undersaturated conditions (Varagonite 5 0.4, mortality 5 9.6% d21), although mortality at Varagonite 5 0.6 was not significant (mortality 5 2.7% d21; controlsaturated mortality 5 0.2% d21). For the largest size-class investigated, 0.6 mm, we show significant mortality for clams under the most undersaturated sediments (Varagonite 5 0.4, 2.8% d21). To test if buffered sediments would increase survivorship of juvenile bivalves during periods of recruitment, we manually manipulated sediment saturation state by adding crushed Mya arenaria shell to a mud flat in West Bath, Maine, U.S.A. Although we increased the average sediment saturation state within retrieved cores from V 5 0.25 6 0.01 to only 0.53 6 0.06, numbers of live M. arenaria in buffered sediment increased almost three-fold in 2 weeks. Buffering muds against the metabolic acids that cause lowered saturation states may represent a potentially important management strategy to decrease dissolution mortality. Shallow-water deposits can be significantly undersaturated with respect to both calcite and aragonite and dissolution may occur in surface sediments where juvenile

Aquacultural Research Corporation (ARC) has operated a continuous mass algal culture facility for the nursery culture of the hard clam (Mercenaria mercenaria) for twenty years. Procedures have been developed for the mass culture of selected species of microalgae that are of proven nutritional value for rearing bivalve spat. Within the past three years a 60% increase in algal yield has been achieved by selection of small centric diatoms for mass culture and by empirical determination of optimum depths and seasonal dilution rates for the light limited 40 m3 continuous cultures. Cell densities of the diatoms Thalassiosira pseudonana (3H) and Skeletonema sp. have averaged over 109 cells/liter from March through November. The algal pond surface area necessary to support a hypothetical nursery with a monthly average clam biomass of 8 kg dry meat weight (ca 13 × lo6 clam seed) was calculated for latitude 41°N during the four seasons of the year. These calculations were based on 1982–1983 algal yields and an assumed food chain efficiency of 10%. The required minimum algal pond surface area ranged from 192 m2 in summer to 750 m2 in winter. The current ARC nursery operation is compared with this hypothetical model. Costs of nursery seed production and a proposed strategy for minimizing the seasonal algal areal requirements of a temperate zone bivalve nursery are discussed.

Economics dictates that the seed of the hard clam, Mercenaria mercenaria, be grown only to moderate sizes before field planting. Survival in the field nursery area is a function of multiple interactions with size specific predation playing the dominant role in survival of planted seed clams. This investigation compares field survival of five sizes of clam seed (4 to 14 mm) with two protective mesh sizes (6.25 mm and 12.5 mm openings) and poisoned bait treatments (malathion injected fish). Baffle treatments for two seed sizes are included to relate these studies to those previously published. Analysis indicates significant increases in survival with the use of poisoned bait and mesh size treatments for small seed sizes. No effect of poisoned bait was found for large seed sizes. Statistically significant interactions occur between seed size and mesh combinations. Comparisons are made with other data to indicate the significance of these interactions.

Diseases have been considered to be major factors in the failure of laboratory and commercial bivalve culture. Much of the work on disease has concentrated on the larval stages, but little information exists for the period from settlement to the age of about nine months. We noticed substantial mortalities of 2–10 mm shell height Mercenaria mercenaria which had been held all winter in the grow-out facility of our laboratory. In subsequent years we developed several methods for treating the clams to decrease the mortalities. Although presumptive tests indicated the presence of Vibrio bacteria we did not confirm the etiological agent and did not establish direct evidence that bacterial pathogens caused the observed mortalities. The most effective treatment tested for general purpose commercial usage was a two-hour bath of bleach at either 9 or 18 ppm.

Molluscan mariculture species of interest include four oysters, Crassostrea virginica, C. gigas, Ostrea edulis and O. lurida; four clam species, Mercenaria mercenaria, Tapes japonica, Spisula solidissima, and Mya arenaria; blue mussels Mytilus edulis, several abalone Haliotis spp., bay scallops Argopecten irradians and queen conch Strombus gigas. The American oyster C. virginica leads all molluscan species in landings and about 60% or 12.1 million kilograms of total national production in 1981 was a result of some form of culture. This includes state and private planters' efforts to increase harvest. West coast production of the Pacific oyster was 2.9 million kilograms resulting entirely from mariculture in 1981. The most intense oyster cultivation occurs in New England with production of European oysters, O. edulis, from hatchery produced seed and off bottom culture. Mariculture in some form accounted for about 4% of total national landings of 1.8 million kilograms for all species of clams in 1980. The hard clam, Mercenaria mercenaria, presently accounts for just about all clam commercial mariculture production. Blue mussel farming on both the east and west coasts are viable commercial ventures. Several molluscan mariculture programs have as their goal augmentation of natural stocks which have been reduced by loss of habitat and overfishing.

Reported diseases of juvenile clams (Mercenaria mercenaria) are reviewed. A summary of disease problems experienced by hard clam hatcheries and seed purchasers of juvenile clams during a ten-year period is presented. These include poor growth, poor seed quality and poor survival due to both chronic and acute mortalities. External fouling of juvenile cultured clams by bacteria, protozoans (including algae), molds, sponges, entoprocts, ectoprocts and others, are sometimes detected by microscopic examination of the external surface of the juvenile; however, the effects of external fouling and undetected diseases of the internal organs are not apparent on gross or microscopic examination of the entire juvenile clam. Histological studies are required to evaluate the health and presence of disease, including retrograde changes and atrophy of internal organs of the juvenile during culture. Suggestions for health evaluation of the cultured juvenile clam in order to increase productivity for hatcheries, and to assure quality control for clam seed purchasers, is presented.

Results from both previous and ongoing investigations on hard clam culture in South Carolina indicate a reasonable commercial potential for intensive clam culture on an industrial scale. To assess this potential and provide an appropriate economic feasibility analysis, the State of South Carolina, in cooperation with private industry and the U.S. Office of Sea Grant, has established a demonstration scale hard clam culture project near Charleston, S.C. The project operates on a two-stage grow-out protocol: raceways are used to provide initial grow-out (to 10 mm) and allow acclimation and disease monitoring for imported seed; final grow-out is accomplished in field units which provide protection from predators and substrate for support and orientation. Seed clams ranging in size from 300 μ to 10 mm are imported from commercial hatcheries, held in the raceway system for growth and observation and transferred to field units as they acclimate or attain minimum field planting size. Using this protocol, over 2.7 million seed are being planted in South Carolina estuaries over a 13-month period (October 1980-October 1981). Field units are stocked at three densities, 2,150, 4,300, and 6,450 m-2, using both intertidal and floating (raft) formats and a variety of substrates (crushed granite, chromium oxide slag, coarse sand, etc.). Units are sampled monthly to determine growth and survival, and these data are correlated with coincidental monitoring of various environmental parameters (temperature, salinity, particulate, dissolved, and total organic carbon, chlorophyll a, and turbidity). This paper reviews results to date and provides descriptive data concerning the raceway system, field units, and support equipment.

The quahog clam (Mercenaria sp.) is discussed as having potential for mariculture. The biology, and mariculture techniques are covered. Recommendations are made toward culture of the clam.

During the period from 1972–1975, northern (M. mercenaria) and southern (M. campechiensis) quahog clams, original parents from Maine to Louisiana, were reared, including F1 and F2 hybrids and backcrosses, to determine what crosses gave the best growth rate. Limited selection was done by crossing faster growing laboratory-reared clams, along with some progeny testing. During the four-year study, 46 crosses were reared through to termination size. Southern quahogs have a faster growth rate in this area than northerns and the best growth rates were the F1 hybrid between the two species that were backcrossed with the southern. The clams with the best growth rates reached minimum commercial size in 30–40% less time than in previous observations in the area. It is not known whether a strain can be produced with a certified fast growth rate that is genetically stable.

Clams (Mercenaria mercenaria) from the controlled environment system of the Delaware Mariculture Project and from the natural system of the Indian River Bay were selected for comparison of palatability and proximate composition. Sensory evaluations for appearance, texture, flavor and over-all acceptance were performed on steamed samples from both environmental treatments by eight trained taste panelists. No significant differences for these characteristics were found although there was a slight preference for the flavor of clams produced in the natural system. Analyses for protein, moisture, fat, and ash were made on the raw clams from both environmental treatments, and again there were no significant differences identified. From these data, it was concluded that the clams produced in the controlled environment process equalled the quality of those produced in natural systems.

The growth of hard shell clams (Mercenaria mercenaria Linne and Mercenaria campechiensis Gmelin) and their F1 cross in a controlled experimental environment was compared to growth in uncontrolled natural environments. The clams were spawned by Paul Chanley of Shelter Island Oyster Company, Inc., Greenport, New York. In the controlled environment of the artificial upwelling mariculture system on St. Croix, U.S. Virgin Islands, pollutants and predators were absent and fouling was minimal. Salinity was 34.75 to 34.95 ppt and water temperature varied between 22 and 30 C during the experiment. Natural environments in temperate, subtropical, and tropical waters were selected as sites for comparative studies: Southold on Southold Bay, New York; Wachapreague on Bradfords Bay, Virginia; Alligator Harbor on the northwest Gulf Coast of Florida; Kupeke Pond in Pukoo, Molokai, Hawaii; and Salt River Inlet, St. Croix. Clams from each population-M. mercenaria, M. campechiensis and their F1 cross-were planted at Southold, New York, and at both St. Croix sites. Only M. campechiensis and F1 clams were sent to Virginia and Florida, and F1 clams and M. mercenaria were sent to Hawaii. Increase in length, “wet” weight, and survival were measured at the different locations from April 1973 through May-June 1974. M. campechiensis and F1 clams reached market size (greater than 25.5 mm thick) in 6.5 to 13 months in the St. Croix artificial upwelling system. These clams did not reach market size in Southold, New York; Wachapreague, Virginia; or Salt River Inlet, St. Croix. The F1, clams in Molokai, Hawaii, and in Alligator Harbor, Florida, were close to market size when the experiment was terminated after 13 months. Survival and growth of M. mercenaria was poor in the artificial upwelling controlled environment, in Salt River Inlet, St. Croix, and in Molokai, Hawaii.

The major hindrances to field grow-out of juvenile hard clams (Mercenaria mercenaria) are wash by currents and predation. Previous data suggested that the effects of wind-driven and tidal currents could be ameliorated by baffles and to some extent by pens and gravel. In our experiments predation protection was provided by gravel, pens and crab traps. Analysis of variance (ANOVA) was performed on quantitative samples of juvenile hard clams (2 mm seed) taken quarterly from field plots established in October 1975. All possible combinations of gravel, current baffles, pens and crab traps were examined. The results are interpreted as showing the varying seasonal effects of current action (storms) and predation on these newly planted and growing seed. The protection afforded by the combination of gravel and baffles was statistically superior to any of the individual or combined effects of the four variables for the first 11 months. The method has the advantages of being simple and promises to be adaptable to infaunal species in wide variety of habitats with a minimum of modification.

Intensive hard clam (Mercenaria mercenaria) culture for the production of large seed and/or market size quahogs is being investigated as an alternative or supplemental clam fishery for South Carolina. A combination of cage culture and aggregate cover (crushed gravel) is being used in subtidal, intertidal, and floating configurations. Young seed clams (ȳ size = 3.4 mm) are planted at four densities (500, 1,000, 2,500, 5,000 m-2) in both production and experimental culture units at each of four locations along the South Carolina coast. Experimental units are divided into 0.1 m2 compartments to provide monthly replicate samples for each density. Coincidental water samples are taken monthly at each location for determinations of chlorophyll a, nitrate and nitrite nitrogen, orthophosphate, silicate, total organic carbon, particulate organic carbon, and dissolved organic carbon, as well as standard hydrographic parameters (temperature, salinity, turbidity). Results from preliminary bottom tray culture studies as well as ongoing cageaggregate culture are presented and discussed.

A program for genetical improvement of oysters and clams, with emphasis on better growth under different environmental conditions, will be started at Florida State University, funded by the Sea Grant Program. Growth rates are partly controlled by genetical factors, and selection for these, along with other desirable traits, will be attempted, through intra- and interspecific crossing. Hybridization is known to occur between three exotic species of our native oysters and there are indications that desirable traits from the exotic species, along with selection for better growth, could be established in our native species. The commercial advantages have been demonstrated in quahog clam (Mercenaria sp.) hybrids, with the faster growth of the southern parent and the good keeping qualities of the northern. Additional selection and hybridization attempts will be made to better the product.

The bivalve molluscs Crassostrea virginica and Mercenaria mercenaria require species of algal food for growth. Successful commercial culture of the hard clam and American oyster in a controlled environment depends on an ability to grow desirable species. Three methods are described for the selective culture of Thalassiosira pseudonana, a desirable bivalve food, in the presence of a contaminant species Phaeodactylum tricornutum, an undesirable food. The first method takes advantage of differences in cell wall characteristics between the two types of algae. Cultures of T. pseudonana contaminated with 34% and 60% P. tricornutum (by cell numbers) treated with ultrasonic waves yielded growing cultures of T. pseudonana which were free of P. tricornutum when 100% T. pseudonana were treated with ultrasonic waves they showed no growth and normal growth respectively. The second method involves manipulation of nutrient levels in a mixed culture of Thalassiosira pseudonana and Phaeodactylum tricornutum to eliminate one or other species from the culture. The third method utilizes a harvesting reseeding technique to maintain a relatively constant concentration of the slower growing species in a semi-continuous mixed species culture containing Carteria chuii and Thalassiosira pseudonana. The results are integrated into a two loop algal culturing process. One loop consists of a seed culture utilizing a small percentage of the influent water and a larger mass algae culture. The mass algae loop is continuosly inoculated with new seed from the seed loop in sufficient quantities so that desirable species out compete undesirable species. Water entering the seed loop is purified by an ultrasonic treatment process so that undesirable species may be eliminated from the seed cultures.

Since May 1972, the St. Croix Artificial Upwelling Project has utilized a constant flow of nutrient-rich water, pumped from 870 m depth in the sea into ponds (100 m2, one m deep) on the north shore of St. Crolx, to produce phytoplankton. This phytoplankton suspension was pumped continuously to filter-feeding shellfish. Initial technical feasibility experiments have demonstrated that Mercenaria campechiensis, a hybrid of M. mercenaria x M. campechiensis, Tapes japonica, Ostrea edulis, Crassostrea gigas, C. gigas Kumamoto variety, Argopecten irradians and Pinctada martensii grew rapidly in this system. Crassostrea virginica and M. mercenaria did not grow well. From October 1976 until October 1978, the St. Croix Artificial Upwelling Mariculture system was operated in pilot-plant fashion to determine yields and provide a basis for cost estimates of the system. Tapes japonica used in the pilot plant were produced in the hatchery of the Artificial Upwelling system in St. Croix. The phytoplankton protein production achieved in the pilot plant, including the down-time of the nutrient-limited pools for cleaning and reinoculation, was equivalent to 8.1 tons/ha/year from July 1977 until July 1978. During a 12-month period of pilot plant operation (October 1977-October 1978), 423 kg of Tapes japonica were produced, corresponding to 22% conversion efficiency of phytoplankton protein to shellfish meat protein and 42.3 tons of shellfish produced/year/ha of phytoplankton pond. An economic evaluation of the pilot plant results is underway.

Natural stress gradients can reduce predation intensity and increase prey abundances. Whether the harsh conditions of anthropogenic habitat degradation can similarly reduce predation intensity and structure community dynamics remains largely unexplored. Oxygen depletion in coastal waters (hypoxia) is a form of degradation that has recently emerged as one of the greatest threats to coastal ecosystems worldwide due to increased rates of eutrophication and climate change. I conducted field experiments and surveys to test whether relaxed predation could explain the paradoxically high abundance of clams that have sustained a fishery in a degraded estuary with chronic hypoxic conditions. Hypoxia reduced predation on all experimental species but enhanced the long-term survivorship of only sufficiently hypoxia-tolerant prey due to periodic extreme conditions. As a consequence, only the harvested quahog clam (Mercenaria mercenaria) thrived in hypoxic areas that were otherwise rendered dead zones with depauperate diversity and low abundances of other species. This suggests that enhanced populations of some key species may be part of a predictable nonlinear community response that sustains ecosystem services and masks overall downward trends of habitat degradation.

Hobbyist and researchers often use commercially available phytoplankton concentrates to maintain filter feeding organisms held in their ornamental or experimental tanks. This study investigated the nutritional value of 10 products available commercially for juvenile hard clams, Mercenaria mercenaria. Growth and mortality rates in clams fed these products were compared with those found in clams fed fresh cultures of the microalgae Isochrysis galbana, which is considered an industry standard for supporting growth of juvenile bivalves. Our results show a clear difference in feed nutritional value between non-living and living commercial diets, and among commercial diets advertised as containing live algae. Overall, results showed that juvenile hard clams fed fresh cultures of I. galbana displayed the best growth and lowest mortality rates, followed by those fed the commercial diet DT's Live Marine Phytoplankton. Growth and mortality rates in unfed controls were similar to those found in clams fed commercial non-living algae mixes or diets advertised as containing live algae (Phyto-Feast Live product). Results also showed that the nutritional value of fresh algae (I. galbana) cultures is lost rapidly when cultures are maintained at 4°C, suggesting that algae present in some commercial diets may lose their nutritional value during processing or refrigerated storage. The commercial blend, DT's Live Marine Phytoplankton, seems to represent a good substitute to lab grown algae for clams held in ornamental or experimental aquariums. Zoo Biol 0:1–13, 2006. © 2006 Wiley-Liss, Inc.

We evaluated marine aggregates as environmental reservoirs for a thraustochytrid pathogen, Quahog Parasite Unknown (QPX), of the northern quahog or hard clam, Mercenaria mercenaria. Positive results from in situ hybridization and denaturing gradient gel electrophoresis confirm the presence of QPX in marine aggregates collected from coastal embayments in Cape Cod, Massachusetts, where QPX outbreaks have occurred. In laboratory experiments, aggregates were observed and recorded by entering a quahogÂs pallial cavity, thereby delivering embedded particles from the water column to its benthic bivalve host. The occurrence of pathogen-laden aggregates in coastal areas experiencing repeated disease outbreaks suggests a means for the spread and survival of pathogens between epidemics and provides a specific target for environmental monitoring of those pathogens.

Patterns of larval dispersal influence the structure of marine biological communities, but many aspects of larval dispersal remain poorly understood. For example, much of our present understanding of larval dispersal is based on models that integrate aspects of physical oceanography and larval biology, but the predictions of those models are generally not tested because we lack the methodology for real-time larval tracking. In the present study, we used both modeled and measured data to track an introduced larval cohort essentially from fertilization to presumed settlement. Larvae of the hard clam Mercenaria were released into a labeled water parcel in the Banana River Lagoon, Florida, within 8.5 h of nursery production and then were tracked for the duration of their estimated 8-d pelagic life span. Comparisons of modeled versus measured larval distribution indicate that the fate of the larvae as predicted by a tracer model and by the concentration of coincidentally released sulfur hexafluoride (SF 6) did not agree with the fate of the larvae as predicted by the path of subsurface drifters and by a particle trajectory model. Thus, modeled predictions of larval dispersal must be interpreted with care. Additionally, one component of larval dispersal that was observed in the study but that was not accounted for in the model was the spread of larvae along the path of advection. That trail of larvae may have important consequences for patterns of recruitment and resultant community structure, but it is not considered in most treatments of larval dispersal.

Over 600 hard clams Mercenaria mercenaria from a wild population in Raritan Bay, New York, were examined histologically to assess the extent and intensity of quahog parasite X (QPX) disease in the fishery area. The overall rate of positive samples was 5.8%. A further 5.1% of clams had inflamed lesions suggestive of QPX infection but no QPX organisms were observed. In over half of the QPX-positive cases, infections of the viscera were involved. The significant proportion of visceral infections and the appearance of the pathogen in the gonads of clams are previously unreported presentations of QPX disease. Visceral infections are of concern for fisheries because they involve significantly larger numbers of parasites and higher biomass than mantle-only infections.

We studied the effects on invertebrate infauna and grain size of harvesting northern quahogs Mercenaria mercenaria with a short rake. The substrate was a mixture of medium-coarse sand (phi values, 0.847–1.159) that was covered by 0.5 m of water at low tide. Two experimental areas (I + II) in Raritan Bay, New Jersey, were subdivided into six 5.5-m × 5.5-m plots. We raked alternate plots, the unraked plots serving as controls. In area I, we raked the treatment plots once (in June 2000) and then sampled all plots for effects on invertebrates and grain size. The number of invertebrates in the five taxa we counted and the mean grain size did not differ significantly (P > 0.05) between treatment and control. In area II, we raked the treatment plots three times, one month apart (in July, August, and September 2000) and then sampled all plots. The results for invertebrates and grain size were similar to those for area I. This study suggests that short raking once or repeatedly during a harvesting season ...

We evaluate experimentally the effect of carbonate saturation state at the sediment-water interface (SWI) on survivorship of various size classes of the juvenile bivalve Mercenaria mercenaria. Populations of 0.2-mm, 0.3-mm, 1-mm, and 2-mm M. mercenaria were introduced to sediments realistically undersaturated (experimental, saturation state with respect to aragonite = Ώaragonite = IMP/K′sp = ~0.3) and saturated (control, Ώaragonite = ~1.5) with respect to aragonite in order to evaluate the impact of saturation state and dissolution on survivorship. Linear regression analysis was used to examine mortality within each treatment over time and show significant mortality for each size class in experimental-undersaturated treatments only (P < 0.05). Mortality rates in experimental undersaturated sediments were -11.8, -4.8, -1.9, and -1.1% d−1 for the 0.2-, 0.3-, 1.0-, and 2.0-mm bivalves, respectively. Analysis of covariance (ANCOVA) was used to examine differences in mortality between treatments over time and show significantly different mortality rates for the 0.2-, 0.3-, and 1-mm individuals (P < 0.05). Dissolution may represent a previously unrecognized yet significant source of mortality for "just-set" juvenile bivalves, particularly the very small individuals that have been largely ignored in recruitment studies to date. Dissolution-induced mortality may help explain the exponential losses of juvenile bivalves following their transition from the pelagic larval phase to the benthic juvenile phase.

Sediment toxicity assays were conducted with juvenile Mercenaria mercenaria to compare the results of laboratory assays and in situ deployments. Juvenile clams were deployed for one week at a variety of degraded and undegraded sites in Charleston Harbor, South Carolina, USA, during the summers of 1998, 1999, and 2000. Parallel laboratory assays were conducted with sediments collected from the deployment sites. Mortality and a sublethal endpoint, seed clam growth rate, were used to compare toxicity between reference and degraded sites. Growth rates of field-deployed clams tended to be higher than growth rates for laboratory assays, especially at the reference sites. Field studies indicated a higher potential for toxicity than did the laboratory studies at degraded sites. These studies suggest that laboratory assays may underestimate potential sediment toxicity at degraded sites. However, field growth rates may be affected by natural environmental factors (e.g., pH, dissolved oxygen, and salinity), so regression normalization techniques were used to distinguish the effects of these variables from those of contaminants.

In prior studies, we have argued that changes in sediment surface chemistry driven by biotic and physical disturbance affect recruitment decisions of infauna. Here, we provide additional data for oxygen concentrations and infaunal recruitment behavior and a time-dependent numerical model of oxygen concentration in disturbed sediments to further support our proposed linkage between disturbance, sediment chemistry, and recruitment decisions. We evaluated the recruitment responses of the polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to sediments that were undisturbed, disturbed, and allowed to recover for a specified period of time. We also obtained fine-scale measurements of oxygen concentration in surficial sediments and profiles in the upper sediment layer that new recruits explore. Undisturbed sediments were characterized by high oxygen levels and were readily accepted by recruiting organisms. Disturbance caused dramatic changes in surface and subsurface oxygen concentrations and was accompanied by nearly complete rejection of habitats by new recruits. Oxygen concentrations in cores that were disturbed and allowed to recover are consistent with the time scales of recovery as predicted by a transport-reaction numerical model. In addition, organism responses to recovering cores varied with oxygen concentration in the surface and subsurface sediments of these cores. The rapid recovery of cores suggests that diagenetic transport-reaction processes that determine pore-water composition drive the acceptability of sediments to new recruits.

Predators affect dynamics of prey populations not only by decreasing their survivorship, but also by changing other vital rates such as growth and reproduction. However, such nonlethal effects have rarely been examined experimentally in the field. In North Carolina estuaries, the hard clam Mercenaria mercenaria generally shows lower growth rates in habitats where predation rates are higher. Predator avoidance behavior of the clams (feeding inhibition) might be one of the factors responsible for this correlation. To examine possible effects of predators on clam growth, I first compared variation in clam growth rate among habitats with different predation pressure, and between predator-exclusion cages and uncaged controls. I then carried out a predator-enclosure experiment using the clam and the whelk Busycon carica, a major predator on adult clams. Among-habitat variation in survivorship, predation rate, and growth rate was generally small or not detected in winter, while large variation was found for adul...

Delayed fishing fleet restructuring complicates the assessment of efficiency gains from individual transferable quota (ITQ) fisheries management programs. This article presents a methodology to estimate harvest sector efficiency gains in lieu of incomplete fleet restructuring. The methodology is applied to assess the efficiency gains in the Mid-Atlantic surf clam and ocean quahog fishery ITQ program. While roughly 128 vessels harvested clams under the previous management regime, the analysis suggests that 21–25 vessels will remain under lTQs. The efficiency gains are estimated to be between $11.1 million and $12.8 million annually (1990 dollars). Copyright 1998, Oxford University Press.

Cadmium tansport in the plasma of Mytilus edulis L. displays attributes similar to those previously described for Mercenaria mercenaria (L.). The majority of Cr, Cu, Ni, and Zn is partitioned in the plasma rather than the hemocytes in both species, although differences in Fe and Mn are apparent. Mussels however contain twice the number of circulating hemocytes (2.1 ± 0.8% of whole blood weight; n = 75 vs 1.2 ± 0.3%; n = 70 for the quahog) and approximately three times more plasma protein than the quahog. Titration experiments using ion-specific electrode (ISE) measurements and equilibrium dialysis (ED) experiments indicate that both species have a low-affinity, high-capacity system for the internal transport of Cd. At low blood Cd concentrations (

This study assesses the viability of gametes produced by various age-classes of the northern quahog Mercenaria mercenaria (Linnaeus, 1758). Using weight of gonadal material, previous investigators concluded that reproductive senescence did not occur in older northern quahogs. However, the viability of the gonadal material in older clams was not determined in those studies. We established two replicates of eight age-groups (2–5, 6–10, . . ., 26–30, 31–34, and >34 years of age) and tested gamete viability. Age of clams had no significant effect on embryonic survival at 48 h. For all ages of parents, embryonic survival to day 2 was 20% with a range of 2. 1% to 32.8%. Within and among age-class groups, variability in survival levels was similar. Unfertilized egg size (mean ± SE) was 87.97 ± 0.25 um, and the size-frequency of eggs was normal. Individual unfertilized egg sizes (mean ± SE) ranged from 77.3 ± 1.07 to 100.5 + 1.19 μm. No linear relationship was evident between mean egg size and northern q...

The relationship between Cd and Cu distribution in sediment geochemical fractions and their bioavailability was studied. A fine-sandy textured estuarine sediment was treated with all combinations of 0, 2.5, and 5 mg/kg Cd and 0, 12, and 25 mg/kg Cu using the chloride salts of each metal. Grass shrimp (Palaemonetes pugio), blue mussel (Mytilus edulis), and hard clam (Mercenaria mercenaria) were exposed to the treated sediments in aquaria with 20 ppt artificial seawater for 14 d. Sediments were sequentially extracted before and after organism exposure to determine the exchangeable, easily reducible, organic-sulfide, moderately reducible, and acid extractable phases. Low mortalities were observed for all organism types and none were attributable to any of the treatments. The Cd and Cu concentrations in the easily reducible and organic-sulfide phases were found to be significantly related to the bio-availability of these metals. The most highly significant relationship was established between Cd in the easily reducible phase and body burden of Cd in the blue mussel. Notable interactions were found between Cd and Cu in some of the geochemical phases, body burdens, and respiration rates. Metal uptake, respiration, and interactions were highly dependent on the test species. A significant correlation was found between increased body burden and depressed respiration for Cd but not for Cu. Multiple regression models are used to describe these relationships. It appears that the interactive responses in the organisms are driven primarily by the sediment geochemical effects and mediated by individual organism processes. These results underscore the necessity of multicomponent (multielement) studies in assessing the fate and effects of toxic elements in the environment.

Sex ratios for 16 beds of northern quahogs Mercenaria mercenaria (N = 22–964 clams/site) from various habitats in the coastal waters of Georgia did not differ significantly from a 1:1 ratio, regardless of habitat. However, there was a trend toward a consistently higher percentage of males occurring farther up the intertidal zone. Northern quahogs collected during the peak of the reproductive period (spring) from the highest intertidal habitat in salt-marsh grass Spartina alternifora showed no apparent sexual development; however, 4–6 months after transplantation to the lower intertidal zone, gametes developed and the clams could be sexed. For pooled data from all sites (N = 2,637 northern quahogs), the sex ratio was equal for all ages (except for ages 1 and 23) and sizes (except for the 66–70-mm size-class). The sex ratio of the northern quahog population in Georgia was in equilibrium.

Fishery-related morphometric characteristics of the recently described gulf stone crab Menippe adina were measured, providing data applicable to managing the species. Because data used in managing crab stocks have traditionally been based on carapace width, we examined the relationship between propodus length (PL) and carapace width and compared it to similar data for the heavily exploited Florida stone crab M. mercenaria. Claws for M. adina reach harvestable size (70 mm PL, minimum legal size in Florida) when carapace widths are 82 mm for males and 92 mm for females. Menippe adina exhibits allometric growth, and the transition point (carapace width) at which differential growth occurs appears to be related to sexual maturity. Males and females exhibit similar relationships of propodus length to carapace width below the transition point. Above the transition point, males display a greater increase in propodus length per incremental increase in carapace width and enter the fishery at a smaller siz...

The assimilation efficiencies of nine elements were measured in planktonic bivalve mollusc larvae (oysters, Crassostrea virginica, and hard clams, Mercenaria mercenaria) fed uniformly radiolabeled phytoplankton cells (Zsochrysis galbana) in order to test whether the “liquid” digestion strategy observed in marine copepods operates in other planktonic hcrbivorcs with gut morphologies different from that of crustacean zooplankton. Of the elcmcnts studied (Ag, Am, C, Cd, Co, P, S, Se, and Zn), americium was assimilated the least by both the larval oysters (7.9%) and clams (2.6Oh), while selenium was assimilated with the highest efficiency by the larvae (oysters, 97%; clams, 1 OOO/o). Assimilation efficiencies were directly related to the fraction of each clement present in the cytoplasm of the ingested algae. Like copepods, bivalve larvae have short gut passage times and assimilate only the easily mobilized, cytoplasmic fraction of ingested phytoplankton cells. The cytoplasmic fraction of some elements (Se, Zn, and Cd) and ofprotein in

Marine sediments from 12 shallow water stations in Raritan Bay, New York were tested for the presence of Acanthamoeba. Eight stations were positive for one or more species of Acanthamoeba, A. castellanii, A. comandoni, A. hatchetti, A. lenticulata, A. polyphaga, A. rhysodes, and Acanthamoeba spp. Isolates that grew at 38–40° C were found at four stations (A. comandoni, A. lenticulata, and two unidentified strains). The two unknown strains were characterized on the basis of morphological features, isoenzyme profiles, and mouse pathogenicity tests. One of the two strains was determined to be a new species and is designated herein as Acanthamoeba stevensoni n. sp., ATCC 50388. Mature cysts were most similar to those of morphological Group II of Pussard & Pons (1977). Acanthamoeba stevensoni n. sp. was isolated from inshore coastal sediments where seawater ranged from 20–30%‰ (ppt.). The sediments supported commercially valuable populations of hard clams, Mercenaria mercenaria, that required depuration prior to sale because of contamination by sewage-associated bacteria.

Water currents were experimentally manipulated for 3 months in a shallow subtidal sandflat through a series of nine channels with diverging, parallel, or converging walls (7 m long, 1.2 m high). Three treatments were chosen to bracket the ambient flow rates; vertically averaged velocities were reduced by 40%, reduced by 2%, or increased by 65%. Within the center of each channel, six Mercenaria mercenaria [shell length, 36.9k2.2 mm (mean f1 SD)] were placed haphazardly in 0.25-m2 plots. Although water-col

The growth rate, age, size distribution, and commercial size-classes of northern quahogs Mercenaria mercenaria were determined at seven stations in Christmas Creek, Little Cumberland and Cumberland islands, Georgia. Experimental commercial harvesting was then allowed within the area, and afterward Christmas Creek was rechecked to determine the effects of harvesting on the clams. Northern quahogs in Christmas Creek reached commercial size (44.4 mm shell length) in 2–2.2 years. Mean age in the population was 16.1 years, and some individuals reached 36 years; 71% of the population was more than 10 years old. Shell lengths were as large as 105 mm and averaged 76.2 mm. Commercial harvest occurred sporadically from April to June 1986 and 1987. Four clammers harvested 70,015 clams from Christmas Creek during 56 person-days in 1986; two clammers harvested 66,400 clams during 44 person-days in 1987. Mean density of northern quahogs decreased by at least a factor of four at the four stations resampled. Mea...

This work reports on the effects of intertidal planting heights upon the growth and survival of the northern quahog, Mereenaria mercenaria (L.) and the Atlantic sod clam, Spisula solidissima (Dillwyn), in the castal waters of Georgia. Quahogs (N = 100 per cage) at 19.5 mm in shell length were planted in replicate cages (N = 3) placed at the spring (SLW), mean (MLW), one (+1), two (+2), and three (+3) hours above mean low water mark. Surf clams (N = 200 per cage) at 41.5 mm in shell length were placed in replicate cages (N = 3) deployed, as above, in all sites except +3. Quahogs grown at the SLW mark after 15 months were significantly larger than clams planted at other tidal heights. Quahogs planted at the MLW mark were significantly greater in shell length than those planted at the +3, +2, and +1 marks. Clams at the upper three sites were not significantly different in size. An inverse relationship between clam growth and intertidal planting height was evident among surf clams. Surf clams grown at the SLW mark for six months were signplificmtly larger than those at the MLW mark which were larger than those grown at the +1 above MLW mark. No significant differences in quahog survival were detected between intertidal planting sites. There was no significant difference in surf clam survival between SLW (77.5%) and MLW (61%) marks, but there was significantly lower survival at the +1 mark (15%) and no survival at the +2 mark.

The results of seasonality studies undertaken with prehistoric faunal materials from the Greenwich Cove site in coastal Rhode Island are presented. Growth patterns in shells of the hard clam or quahog (Mercenaria mercenaria) are used to reconstruct the time(s) of year this species was collected. A controlled study of seasonal growth provides a comparative baseline for this analysis. Seasonality of white-tailed deer (Odocoileus virginianus) hunting is interpreted through the examination of growth structures in preserved teeth. The seasonal availability of migratory species is also considered. Relatively year-round coastal settlement is proposed for the final centuries of the prehistoric period.

Sublethal test methods are being used with increasing frequency to measure sediment toxicity, but little is known about the relative sensitivity of these tests compared to the more commonly used acute tests. The present study was conducted to compare the sensitivity of several acute and sublethal methods and to investigate their correlations with sediment chemistry and benthic community condition. Six sublethal methods (amphipod: Leptocheirus plumulosus survival, growth, and reproduction; polychaete: Neanthes arenaceodentata survival and growth; benthic copepod: Amphiascus tenuiremis life cycle; seed clam: Mercenaria mercenaria growth; oyster: Crassostrea virginica lysosome destabilization; and sediment-water interface testing with mussel embryos, Mytilus galloprovincialis) and two acute methods (amphipod survival with Eohaustorius estuarius and L. plumulosus) were used to test split sediment samples from stations in California. The test with Amphiascus proved to be the most sensitive sublethal test and the most sensitive overall, identifying 90% of the stations as toxic. The Leptocheirus 10-d test was the most sensitive of the acute tests, identifying 60% of the stations as toxic. In general, the sublethal tests were not more sensitive to sediments than the acute tests, with the sublethal tests finding an average of 35% of the stations to be toxic while the acute found 44%. Of the sublethal tests, only the Amphiascus endpoints and Neanthes growth significantly (por= 0.05) correlated with sediment chemical concentrations. Poor correspondence occurred between the toxicity endpoints and the indicators of benthic community condition. Differences in test characteristics such as mode of exposure, species-specific contaminant sensitivity, changes in contaminant bioavailability, and influence of noncontaminant stressors on the benthos may have been responsible for variation in response among the tests and low correspondence with benthic community condition. The influence of these factors cannot be easily predicted, underscoring the need to use multiple toxicity methods, in combination with other lines of evidence, to provide an accurate and confident assessment of sediment toxicity.

Preset larval Mercenaria mercenaria were exposed to nominal concentrations of 1 (control) to 495 μg Cu/L in artificial seawater and monitored for mortality, activity, development, and metamorphosis in sealed 30-mm plastic petri plates containing 1.5 ml of artificial seawater or toxicant solution. The plastic petri plates sorbed only about 2.6 μg/L at any dose and allowed direct observation of larval clams under a light microscope for a period of two weeks; control survivorship was in excess of 60% at 400 h. The dose-response curve for mortality for clams exposed to copper and fed Isochrysis galbana was characterized by survival similar to or better than controls at doses of 5 and 14 μg Cu/L, while doses of 7 and ≥29 μg Cu/L exhibited mortality greater than controls. Values of lowest concentration at which 50% of the organisms died (LC50) were 62.4, 21.2, and 11.7 μg Cu/L, and the lowest observed adverse effect concentration values of 57, 29, and 29 μg Cu/L were determined at 48, 96, and 192 h, respectively. In contrast, activity, as judged by swimming, exhibited a typical exponentially decreasing response at these same concentrations. Experiments on the uptake of dissolved copper by I. galbana confirmed literature reports that these algae concentrate copper. Ingesting copper-containing algae was demonstrated to be a source of copper toxicity for larval clams.