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Paralytic shellfish toxins (PSTs) are notorious neurotoxins that threaten public health and food safety worldwide. Although PST monitoring programs have recently been established throughout China, the profiles and variation of PSTs in important commercial clams (e.g., Mactra veneriformis, Ruditapes philippinarum, and Meretrix meretrix) along the Jiangsu Province coastline remain largely unexplored. In this study, a validated hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC-MS/MS) method was used to examine PST profiles and levels in 540 clam samples from natural production areas along Jiangsu Province coastline during 2014–2016. Although the PST levels (≤6.38 μg saxitotoxin equivalents (eq)/kg) were consistently below European Union regulatory limits (≤800 μg saxitotoxin eq/kg) during this time period, saxitotoxin, decarbamoylsaxitotoxin, and gonyautoxins 1 and 4 were detected, and nearly 40% of the samples were saxitotoxin-positive. The PST levels also varied significantly by seasons, with peak values observed in May during 2014–2016. This is the first systematic report of PSTs in clams from Jiangsu Province, and additional research and protective measures are needed to ensure the safety of clams harvested in this area.

Bricelj, V.M.; Kraeuter, J.N., and Flimlin, G., 2017. Status and trends of hard clam, Mercenaria mercenaria, populations in a coastal lagoon ecosystem, Barnegat Bay–Little Egg Harbor, New Jersey. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay–Little Egg Harbor, New Jersey. This review examines the historical and current status of hard clam, Mercenaria mercenaria, populations in the Barnegat Bay–Little Egg Harbor (BB-LEH) Estuary using New Jersey State stock assessments and published studies and evaluates their potential for rehabilitation under present environmental conditions. This estuary has experienced increasing urbanization, population growth, bulkheading, and changes in watershed use. Clam populations have decreased markedly since the 1960s, and in LEH, substantial areas are now devoid of clams. Landings of wild-caught hard clams, and commercial and recreational clam licenses have all declined. There is no evidence that eutrophication an...

Condition Index (CI) was used to estimate the reproductive biology cycle of the hard clam Meretrix lyrata based on dry body weight and shell weight. High CI value was observed due to the increase in the body weight of the hard clam that corresponding to the maturity stage and early spawning. The CI value of M. lyrata from Buntal Village, Kuching, Sarawak showed three highest peaks during the 12-month study on May and October 2013 and March 2014. The lowest CI values were obtained in September and November 2013 and April 2014. Ammonia nitrogen was the only water parameter that significantly correlated to the CI values. The CI application is important to estimate the maturity of hard clam gonad to facilitate conservation activity through the hard clam harvesting out of the gonad maturation and spawning period.

Shellfishes can easily accumulate metals via water and sediment and which may pose a human health risk by consumption. This study assessed the distribution of metals, including Cd, Cr, Cu, Pb, Ni, Zn, and Hg, in soft tissues of hard clam (Meretrix lusoria), surrounding water body, and sediment in the southwest coast of Taiwan. Hard clams contained the relatively higher concentration of the essential element, such as Zn, Cu, and Ni, and the metal concentration from high to low was Zn > Cu > Ni > Cd > Cr > Pb > Hg. However, the metal concentrations found in hard clam all were lower than the Sanitation Standard for Aquatic Animal of Taiwan. Results of bioaccumulation factors indicated that hard clam shows the ability of metal accumulation from water was higher than that from sediment. Moreover, the metal concentrations in hard clam were negatively correlated with body size except for Hg, which could be presented by the significant power function. Generally, hard clams from the aquaculture pond located on the southwest coast of Taiwan would not be harmful to adult consumers, except for people that consume shellfish more than 100 g. Besides strengthening the management of seafood safety and aquaculture, adjusting the eating and purchasing habits of the consumer could be a practical and feasible way for decreasing health risks. These results can assist the government in determining seafood safety and its implementation in Taiwan.

Globally, coastal aquaculture is growing due to the large demand for marine products. Specific impacts caused by coastal aquaculture on the environment include the discharge of culture farm effluents, stress on ground water (the absence of recycling), nutrient pollution, and diseases of cultured animals. Three methods, integrated multitrophic aquaculture (IMTA), recirculating aquaculture system (RAS), and beneficial bacteria for aquaculture, have been developed to solve these problems. In this study, the advantages of IMTA and RAS were integrated to develop a novel multitrophic recirculating aquaculture system (MRAS) to adapt to the farm-scale culturing of milkfish (Chanos chanos). The photosynthetic bacteria Rhodovulum sulfidophilum was added to enhance the performance of the farm-scale milkfish MRAS. This setting could promote growth of beneficial bacteria, such as the nitrogen cycle-associated microbial community and the anoxygenic phototrophic Acidobacteria community. The ammonia level was reduced, and the total phosphorous level was stable in the water recycled in the MRAS. The cyanobacteria, algae, Vibrio, Escherichia, and other potential pathogenic bacteria communities were inhibited in the MRAS. This study provides an effective design of a water recycling aquaculture system. Milkfish, Asian tiger shrimp (Penaeus monodon), Asian hard clam (Meretrix lusoria), and seaweed (Gracilaria sp.) can be cultured and simultaneously produced in the system.

Microplastic pollution is a problem that is currently attracting the attention of various groups, from scientists to ordinary people. This type of pollution can have a negative impact on aquatic biota, especially organisms that have filter feeder behavior. Asiatic hard clam (Meretrix meretrix) is a filter feeder organism that has a considerable risk of being exposed to microplastics. This study aims to analyze the concentration of microplastics in Asiatic hard clam (M. meretrix) at Lemo Beach, Burau District, East Luwu Regency, South Sulawesi. Sampling was performed using purposive random sampling method. The number of samples of Asiatic hard clam was 118 which were divided into three groups of shell length, namely class A (2.75 - 3.40 cm), class B (3.41 - 4.21 cm), class C (4.22 - 5.24 cm). Observation of microplastic particles is carried out using a stereo microscope equipped with a camera (Miconos optical lab). The results of the frequency analysis of the presence of microplastics in the clam showed that class A was the class with the highest frequency, namely 95.67%. The observed microplastics were in the form of fibers, fragments, and films with a predominantly black and transparent color. The size of the observed microplastics ranged from 0.033-0.88 mm. The results of the microplastic concentration analysis showed that size class A had a greater concentration than class B and class C.

Concern over health risk from consumption of bivalves originating from Marudu Bay is escalating due to the rapid agricultural development surrounding the bay. This has motivated us to estimate the health risk index (HRI) of heavy metals from four commercially important and highly exploited bivalve species which are abundant in the bay. Samples (n = 30) of green mussel (Perna viridis), Asiatic hard clam (Meretrix meretrix), Pacific oyster (Crassosstrea gigas) and marsh clam (Polymesoda expans) were acquired from fishermen in Kg. Teritipan, Marudu Bay. These bivalves were analyzed for heavy metals content using the Inductively Couples Plasma-Optical Emission Spectroscopy (ICP-OES). The study found that the mean contents of Arsenic (As) and Manganese (Mn) in all analyzed bivalves exceeded the permissible limits as well as copper (Cu), lead (Pb) and zinc (Zn) in Pacific oyster, and Zn in marsh clam. It was also noticed that consumption of different bivalve species may bring about health risk from different metals as indicated by varied Total Hazard Index (THI) values. Consumption of the four bivalves was noticed to promote high health risk from As intoxication. Although metal pollution index (MPI) analysis revealed that the bivalves from the bay are currently not seriously impacted by heavy metal pollution, vigorous efforts should be taken to preserve the natural condition of the bay for years to come. There are several ways to minimize health issues from bivalve consumption which include keeping the bivalve natural habitat away from heavy metals pollution by strictly enforcing environmental laws and policies, establishing zones for bivalve fisheries, monitoring heavy metals concentration in bivalve on a regular basis and making depuration process a compulsory requirement in every seafood restaurant throughout the country.

This study uses a translog cost function model based on two different hard clam stocking densities to estimate the cost and price elasticity of input factors to evaluate whether the hard clam polycultures in Yunlin County, Taiwan, have economies of scale and economies of scope and to assess the substitutability between inputs. The study found that farmers with hard clam stocking densities higher than 1,500,000 individuals/ha (high-density farmers) generated more profit than farmers with stocking densities below 1,500,000 individuals/ha (low-density farmers), because they experienced lower average costs and higher production outputs. Moreover, the own price elasticity of labor input (−1.162) was more responsive to price changes for high-density farmers than for low-density farmers. That is, wage increases have a significant effect on reducing labor demand for high-density farmers. For these farmers, the Allen partial cross-price elasticities of the variable inputs labor-seed and labor-feed were 1.973 and 2.326, respectively. These positive elasticities indicate that labor-seed and labor-feed are substitutes. That is, increases in seed and feed prices could be compensated for by increasing labor inputs for high-density farmers. This study established the existence of constant overall scale economies and economies of scope for high- and low-density farmers. In addition, the study suggests that hard clam farmers with fish and shrimp polycultures consider cost complementarities and product-specific economies of scope at various levels of production. Low-density farmers are also advised to increase the milkfish population in their polycultures, whereas high-density farmers might increase silver sea bream and shrimp densities.

Aquaculture of the northern quahog (=hard clam) Mercenaria mercenaria (Linnaeus, 1758) is widespread in shallow waters of the United States from Cape Cod to the eastern Gulf of Mexico. Grow-out practices generally involve bottom planting and the use of predator exclusion mesh. Both the extent and scale of clam farms have increased in recent decades resulting in concerns regarding the impacts of these practices on estuarine fauna. Seasonal distribution, abundance, biomass, species richness, and community composition of nektonic, demersal, epibenthic, and infaunal organisms were examined in cultivated and uncultivated shallow-water habitats in Virginia and New Jersey. The results reveal that clam aquaculture, as practiced in both Virginia and New Jersey, has remarkably few quantifiable impacts on estuarine fauna. Seasonal variations were observed in the biota, but of the 39 population and community metrics tested, mean values associated with 26 did not differ between cultivated and uncultivated are...

Using the hard clam farms in Yunlin, Taiwan as examples, this study analyzes the effects of culture area, stocking density, and shrimp and fish polyculture on the cost efficiency (CE) of hard clam farming. A data envelopment analysis (DEA) is used to estimate the farms' technical efficiency (TE), allocative efficiency (AE), and CE values. The findings show that the mean TE, AE, and CE values of hard clam farms are 0.74, 0.57, and 0.43, respectively. The TE value is higher than the AE value, which indicates that cost inefficiency is mainly attributable to poor AE. Tobit regression results suggest that there are positive relationships between CE and both culture area and operator experience. Hard clam stocking density and age of the operators have negative effects on CE. Hard clam culture areas larger than 2 ha and a stocking density of 1.1–1.2 million hard clams per hectare have higher CEs than smaller culture areas and smaller or larger stocking densities. The use of sand shrimp, white shrimp, kuruma shrimp, and grass shrimp for polyculture and the use of milkfish and silver sea bream for polyculture are both associated with high CEs.

The aim of this study was to evaluate the antibacterial properties of oyster, hard clam, and sea urchin shell powders as a result of calcination. After subjection to calcination at 1050 °C for 2 h, and as identified by FTIR and XRD spectra, the structures of oyster, hard clam, and sea urchin shell powders were mainly transformed into calcium oxide, with slight amounts of calcium hydroxide. Metal content testing revealed no detectable harmful heavy metals, and showed rich content of trace elements including Ba, Sr, Mg, and Mn. To evaluate their antibacterial properties, activity against five foodborne microorganisms was assessed using the disk diffusion method, which indicated the presence of antibacterial activity in these products at a concentration of 1 %. These results indicate antibacterial potential for oyster, hard clam, and sea urchin shell powders after subjection to calcination.

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.

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006–2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km2) exceeded 1.5 kg m−2 in 2008. Small clams ( 40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams ( 5 mm SL in a short period of time.

The distribution and movement between habitats with growth of the hard clam Meretrix lusoria were examined by comparing the size–frequency distributions among 17 sites in the Shirakawa–Midorikawa Estuary of the Ariake Sea. This clam is a commercially important bivalve in Japan, and its annual catch is largest in the Ariake Sea. At the study sites, new recruits were abundant at river mouths, and density was strongly affected by the distance from coastal tidal rivers and streams. In contrast, adults were widely distributed on tidal flats, although density was low at many sites. At marine site Oda, the density of adults was higher than that of new recruits at all sites and higher than that of juveniles at most sites. These results indicate that this species moves from riverine sites to marine sites with growth. Moreover, the observed low density of adult clams may indicate overfishing. The active movement of M. lusoria across the fishing grounds complicates the sustainable resource management of this species. Therefore, further studies are needed for effective resource management of M. lusoria.

Asiatic hard clam (Meretrix meretrix) was one of molluscs (bivalve) with economical value. However, fishing activities were presumed to cause a decline in population. This condition was strengthened by the size of the clam which became smaller nowadays. The purpose of this study was to determine spatial distribution of M. meretrix, length distribution, and length-weight relationship. The study was conducted at 3 stations, consisted of Station I at Asahan River estuary which was located by mangrove forest, Station II at the sea and Station III at the waters near mainland of Batu Bara Regency. Estimation growth of M. meretrix was examined following FISAT II method. The density of M. meretrix was dominant at Station I which was low in salinity and high in organic matter. The class interval of 23-34 mm at station I dominated length distribution. Length-weight relationship was found to be very strong with determinant value approaching

Benthic communities in Long Island Sound (LIS) have experienced over 150 years of commercial shellfishing and excess nutrient loading (eutrophication) which causes hypoxia. We established an ecological baseline using a combination of live, dead, archaeological, and fossil material to investigate the impacts of these stressors on the molluscan community. We expected that ecological change would increase with eutrophication-hypoxia west towards New York City. Instead we found that taxonomic similarity, rank-order abundance, and drilling frequency are more strongly controlled by commercial fishing pressure than by decreasing dissolved oxygen. Commercial fisherman collecting quahog clams (Mercenaria mercenaria), physically disrupt surface-dwelling organisms and also kill large numbers of predatory gastropods, including the channeled whelk, Busycotypus canaliculatus, and the drilling moonsnails Neverita duplicata and Euspira heros, to protect hard clam stocks. As a result, areas dredged by commercial fishermen yield fewer shells with drill-holes and fewer surface-dwelling organisms than unfished sites. In spite of recent reductions in lobster fishing, crushing predation by crabs and lobsters on clams has been suppressed below baseline levels throughout LIS, even in the well oxygenated east. The absence of a clear relationship between eutrophication-hypoxia and ecological change questions the effectiveness of nitrogen reduction alone as a restoration strategy. LIS fossils revealed a relatively ancient loss of those mollusks associated with seagrass and oyster habitats (e.g., oysters, Crassostrea virginica; jingle shells, Anomia simplex; scallops, Argopecten irradiens; and the gastropod Bittiolum alternatum) that predates the accumulation of dead shells and underscores the need for older material to reveal the shifting baseline. The interactive nature of multiple stressors means that past overfishing may have dampened the response of communities in LIS to eutrophication or inhibited their capactiy to recover. The unexpected role of hypoxic areas protected from commercial fishing as refuges highlights the utility of no-take marine preserves in eutrophied estuaries worldwide.

Using data collected from 2007-2010, this study identifies price linkages and then forecasts vertical price transmission elasticities between markets (farm, wholesale, retail and export) in the value chain of hard clam (Meratrix lyrata) in Vietnam. After doing necessary tests to make sure that all price data are stationary, Seemingly Unrelated Regression (SUR) and Error Correction Model (ECM) are employed to examine short-time and long-time effects of hard clam price in one market on the other market in its value chain. The seemingly unrelated regression results show that hard clam prices seem not depend on seasons. Farm price of hard clam is transmitted completely to wholesale price while the price in retail market causes negative effect on farm price in the short run. Wholesale price of hard clam is transmitted to both prices in farm and retail markets. The export price of hard clam is estimated not to be affected in the short run by prices in other markets except retail price in domestic markets. Error correction models confirm the independence of hard clam price on annual seasons. The transmission elasticities of prices between the markets are also identified based on model estimation.

Samples of three hard clam Meretrix spp. (M. lusoria, M. petechialis, and Taiwanese Meretrix) were collected from 12 localities in Japan, China, Korea, and Taiwan between 2004 and 2013. PCR-RFLP analysis and nucleotide sequence analysis for the mtDNA COI region was performed on these samples. HincII and AseI restriction assay discriminated M. lusoria, M. petechialis, and Taiwanese Meretrix, corresponding to the relatively large nucleotide substitution (6.35–8.20 %). In Taiwan, M. lusoria was introduced from Japan in the 1920s; however, our results suggest that Taiwanese Meretrix is genetically differentiated from M. lusoria. As well, the exotic Taiwanese Meretrix was found from Nishinagisa on the north coast of Tokyo Bay, demonstrating the Taiwanese Meretrix now occurs with M. lusoria in its native habitat. Meretrix seedlings (Kumamoto origin) from a Taiwanese aquaculture facility has been released into Nishinagisa since 2008 suggesting the Taiwanese Meretrix is inadvertently mixed with the M. lusoria produced in the aquaculture facility. In contrast, all samples from Kisarazu, on the east coast of Tokyo Bay, were identified as M. lusoria despite there being mass releases of M. lusoria (Kumamoto origin) cultured in Taiwan since 2007. Quality control procedures are needed for future Meretrix spp. releases to prevent further spread of the Taiwanese Meretrix., 論文

Large mobile predators are hypothesized to fulfill integral roles in structuring marine foodwebs via predation, yet few investigations have actually examined the foraging behavior and impact of these species on benthic prey. Limited studies from the Cape Lookout system implicate large schooling cownose rays (Rhinoptera bonasus) in the devastation of patches of commercially harvested bay scallop via strong density-dependent foraging behavior during migrations through this estuary. However, despite the extensive Atlantic range of R. bonasus, the pervasiveness of their patch-depleting foraging behavior and thus impact on shellfisheries remains unknown outside of North Carolina waters. To further understand the potential impacts of cownose rays on benthic prey and the role of bivalve density in eliciting these impacts, we conducted exclusion and manipulation experiments at two sites in the northern Gulf of Mexico frequented by rays during spring migrations. Despite a correlation in ray abundance with haustorid amphipod (primary natural prey) density at our study sites, we were unable to detect any effect of rays on amphipod densities. In addition, through manipulation of predator access, we determined the main cause of mortality to manipulated patches of hard clams was predation by smaller predators such as Callinectes sapidus and not cownose rays. While cownose rays consume hard clam in other parts of their range, we suggest rays along northern Gulf of Mexico barrier islands may prefer foraging on smaller and thinner-shelled bivalves (e.g., Donax sp.), as well as more abundant amphipod crustaceans. We caution that these preferences may have reduced our ability to detect effects of rays on manipulated prey, and thus future impact experiments should strongly consider the local diet of these predators and explore novel techniques to estimate effects on small crustaceans. Further synchronized experimentation along basin-wide scales may elucidate the environmental factors that determine the severity of cownose ray foraging impacts across their range.

We identified the species of “kerang kapah” (hard clam) using the Gel Electrophoresis SDS Page, inorder to clarify the species of kerang kapah those found living along the East Coast of TarakanIsland. The study was conducted from July to December 2014. The kerang kapah were collectedfrom the several parts of East Coast Tarakan Island. Eight group samples of kerang kapah were used for Gel Electrophoresis SDS Page and scanned using the IMAGE software. Generally, thekerang kapah those found at the shouth part of East Coast of Tarakan Island have very similarmorphologies and shell colors, making species identification difficult. Four species of kerang kapahwere identified. Three species belong to Veneridae and one species belong to Corbiludae. Thespecies of Veneridae were Meretrix meretrix, Meretrix lyrata, and Meretrix sp. The species karangkapah belong to Corbiludae is Polymesoda erusa.Keywords: kerang kapah, meretrix, polymesoda, gel electrophoresis.

Mass production method on artificial seedling production of hard clam Meretrix petechialis was developed indoor culture system. Spawning of adult clam (SL 65.8 ± 8.4 mm) was induced using the combined method of air exposure and water temperature raising. The fertilized eggs were developed to D-shaped larvae after 17.7 hours at 27℃ and hatching rate was 6.1%. Shell length (SL) of D-shaped larvae was measured to be 131.4 ± 2.6 μm and thereafter the larvae grew to the settled spats with SL 190.2 ± 7.5 μm in 4 days. Estimated survival rate of settled spats was 48.1%. Spat collection on 130,000 spats with SL 0.19 ± 0.01 mm performed conducted by sand bottom circulation filtering method. Collected spats grew up to 3.1 ± 0.8 mm in 46 days, 6.6 ± 1.8 mm in 87 days, and 10.5 ± 0.9 mm in 114 days. The relative growth between SL and shell height (SH) was calculated to be SH = 0.8501SL + 0.0196 (R 2 = 0.9987) during the whole spat period. During spats rearing, they were suffered from one time of mass mortality at SL 3.1 mm, but 51,000 spats were finally survived with the rate of 39.2% at 114 days of spat rearing in indoor tank system.

The Florida cultured hard clam industry has drastically increased over the past thirty years but is built upon a single species. In order to increase economic stability and growth of the industry, the sunray venus clam, Macrocallista nimbosa , is now being evaluated as a potential new aquaculture species. Very little is known about the physiological characteristics of this species. It is important to investigate the sunray venus clam's physiology, to predict its susceptibility to environmental variations, pathogens or pollutions. The objective of this study was to characterize the hemocytes in adult sunray venus clams, using flow cytometry. The present work led to the discovery of severe immunodepression in M. nimbosa from Florida. Immunodepressed individuals accounted for about 17% of clams and displayed a drastic loss of circulating hemocytes (hemocytopenia) as well as no immune capacity. Immunodepression was thought as resulting from a recent infection. Although immunodepressed individuals were not dying, severe immunosuppression may constitute a serious threat to the ability of sunray venus clams to cope with environmental or pathogenic stresses. Due to its current evaluation as a potential new aquaculture species in Florida, further investigations are necessary to determine the etiological agent and the impact on sunray venus clam populations.

In Connecticut, cultivation of the northern quahog, or hard clam, Mercenaria mercenaria L., relies on hydraulic dredging. After harvesting, leased shellfish beds remain fallow for varying durations to facilitate natural reseeding and to allow small clams to reach harvestable size. The interval between dredging events, or harvest history, may influence benthic ecology and response of communities to further dredging. Two clam beds with different harvest histories, located near Milford, Connecticut, were studied from July through October 2012. These leased beds, fallowed for 3 and 8 years, respectively, were subdivided into two plots. One plot on each bed was commercially harvested in July while the other remained not dredged. Sediment sampling was conducted on alternate weeks using Smith MacIntyre grabs and sediment cores to compare ecology of benthic communities and chemistry of marine sediments on newly dredged and not dredged plots within leases. Main effects of lease (harvest history), dredging treatment (dredged versus not dredged plots), mean sediment phi size (ɸ), and season (sampling date) significantly affected benthic community structure. Newly settled bivalves, including early successional pioneer species, occurred in high abundance on 3-year beds. Diversity, evenness, and number of species were high on the 8-year beds, while abundance of individuals was low, more typical of later successional equilibrium communities. Differences among a subset of species on the 8-year beds were observed between dredged and not dredged plots while no community differences were observed between dredging treatments on 3-year beds. Significantly more individuals were observed on dredged versus not dredged plots on the 8-year beds only. Our results suggest that harvest frequency and/or sediment ɸ size may explain differences in benthic assemblages between leased areas with different dredging histories, while dredging had no measurable effect on sediment chemistry.

This study is the result of examining the growth and survival rate of larva and spat when supplied with Enriched live food by adding B12, chitosan, PSB, and polysaccharides to microalgae (Chaetoceros gracilis, Isochrysis galbana) to raise the survival rate of larva and spat during artificial clam seed production. Microalge (Chaetoceros gracilis, Isochrysis galbana) was strengthened for nutrition with B12 0.1 ppm, chitosan 0.2 ppm, PSB 3 ppm and polysaccharides 1 ppm and was daily supplied for 3 × 10 3 -15 × 10 3 Cells/mL and the growth and survival rates were measured. As the result of experiment, the growth of larva did not show much difference with PSB test section 199 ± 0.59 μm, B12 test section 198 ± 0.64 μm, and chitosan 197 ± 0.52 μm, survival rate was highest at PSB test section with 99.3%, followed by B12 test section 95.9%, and chitosan 94.5%. Growth of early spat was the highest for PSB test section at 2.74 ± 0.58 mm, followed by polysaccharides 2.67 ± 0.55 mm, B12 2.54 ± 0.48 mm, and chitosan 2.49 ± 0.51 mm, and the survival rate was the highest for PSB test group at 32.1%, followed by B12 test section 31.6%, chitosan 28.5%, and polysacharrides 21.4%. From such results, PSB is found to be very effective with low-quality improvement when breeding early spat of clams, and especially for floor-type early spat breeding, it had the effect of suppressing protozoan and germs so that detailed studies from various perspectives should be conducted with various chemicals in the future.

This study was performed to describe the effect of water temperature, salinity and density on the eggs development of the hard clam, Meretrix petechialis. Eggs of Meretrix petechialis were turned out to be demersal isolated eggs of in an average diameter after spawning. The hatching rate of D-shaped larvae by elapsed time after spawning was the highest in fertilization immediately after spawning and distinguished decrease from 1 hour of spawning. The optimum water temperature for development of D-shaped larvae from fertilization was ranged between to . However, D-shaped larvae was not developed at of water temperature. The required time from fertilization to D-shaped larvae were 37.3 hours in , 20.8 hours in , and 15.3 hours in . Biological minimum temperature for the egg development was estimated to be in average. The range of salinity for the development of eggs were 20.0-37.5 psu, optimum range was estimated to be 27.5-32.5 psu.

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.

The hard clam (Meretrix meretrix) is a popular edible shellfish in South and Southeast Asia, being heavily exploited by hand dredging in Marudu Bay, Malaysia. The current study was performed to evaluate the shell damages caused by this artisanal dredging gear. Samplings were conducted in triplicates at two sites using both hand dredging and hand collecting (control) sampling methods. The shell length and total weight, damage areas and breakage patterns of each clam were recorded. A questionnaire survey was conducted with local bivalve harvesters to gather information on the fishing pressure in Marudu Bay. Results revealed that the efficiency (fishing yield) of hand dredging gear was three times higher than hand collecting. However, hand dredging gear causes lethal shell damages to small hard clams (

A field experiment was conducted to compare the performance of different hard clam (Mercenaria mercenaria) strains in local clamming waters of New York state. Experimental clams included a Mercenaria mercenaria notata seed obtained from a Florida broodstock, and 2 New York seed strains obtained from local hatcheries, including a cultured M. mercenaria notata strain and a first-generation “wild-type” strain. Quahog parasite unknown (QPX) was acquired by the Florida clams in less than 2 mo of a July deployment of grow-out cages. Prior field studies comparing susceptibility of northern and southern hard clam strains observed QPX acquisition after clams had overwintered in the field, raising the question that higher susceptibility observed in southern seed clams could be a result of poor adaptation to winter water temperatures. Our results show that the southern strain acquired QPX after the clams had only been exposed to the warmest period of water temperatures for this field site (22.3°C on average...

The easternmost commercial population of hard clams, Mercenaria mercenaria, in Maine was discovered recently near the low intertidal in Goose Cove, in the town of Trenton (Hancock County). A fast- and slow-growing morph was identified that reaches commercial size (50.8 mm shell length) in 4 y and 5 y, respectively. Fast-growing individuals were selected as broodstock, and conditioned to spawn at the Downeast Institute. The fate and growth of cultured juveniles was followed for 5 mo beginning in July 2006 at 4 stocking densities (2,500-10,000 animals/1.1 m 2 floating, nylon window screen-lined tray; n ¼ 20) at a coldwater field nursery approximately 60 km east of Trenton, in the town of Beals, ME (Washington County). Survival was nearly 100%, and growth was density dependent, with animals attaining a final mean shell length ±95% confidence interval of 8.4 ± 0.13 mm and 7.6 ± 0.218 mm in the lowest and highest density treatments, respectively. In November 2006, cultured seed was separated into 2 sizes (large, 8.7 ± 0.2 mm; small, 5.1 ± 0.2 mm) and overwintered in window-screen bags (0.2 m 2 ) at densities ranging from 0.6-1.6 kg (large) and 0.5-1 kg (small), representing approximate densities ranging from 3,360-15,510 individuals per bag. Bags were placed on horizontal shelves within modified lobster traps (overwintering containers) that were added to a 35,000-L tank receiving ambient seawater for 177 days until May 2007. Seawater temperatures during this interval ranged from -1-10C. Survival rates exceeded 99%, and no negative effects resulting from stocking density were observed. Hatchery seed was transplanted in May 2007 to the lower intertidal at Goose Cove and a second intertidal location approximately 30 km east of Beals at Duck Brook Flat, in the town of Cutler, and the fate and growth of these juveniles was followed for 6-7 mo. Survival was independent of planting densities (330-1320 individuals/m 2 ), and predator netting did not enhance survival compared with controls without netting. Growth was seasonal, with the greatest incremental shell increases occurring between early July and late September. Growth rates varied between planting locations, with clams adding approximately 10 mm shell length at Goose Cove between May and December (initial shell length, 8.2 mm; final shell length, 17.9 mm) and approximately 5 mm shell length at Duck Brook Flat between June and November (initial shell length, 9.3 mm; final shell length, 14.3 mm). Hard clam farming in eastern Maine may help to diversify a wild shellfish industry that is currently in decline for most species except lobsters; however, additional efforts are needed to explore alternative grow-out sites and methods to enhance growth rates.

We hypothesized that the decline in hard clam Mercenaria mercenaria populations since the 1970s in many of the south shore bays of Long Island, New York, USA, was due to changes in reproduction caused by variations in phytoplankton available as a food resource. We measured in 2000 and 2001 the reproductive condition of female clams from 5 sites in south shore bays of Long Island and from 2 sites in New Jersey. Phytoplankton composition was measured as the concentration of total and size-fractionated chlorophyll a (chl a), particulate organic carbon (POC), and nitrogen (PON), and the abundance of the harmful picoplankter Aureococcus anophagefferens. Timing of peak hard clam reproduction was nearly identical across sites, and was the same as in archived sam- ples of clams collected in 1978 and 1979. Hard clam condition index differed between sites, with poorest condition being exhibited at the 3 Great South Bay (GSB) sites. There were also appreciable differences in relative reproductive output between locations, with clams again from the 3 GSB sites having the lowest estimated egg production. The central and eastern GSB had the highest levels of total chl a, POC, and PON, however, of any south shore bay, although this was mainly contributed by cells

Bivalve and microzooplankton community grazing on natural plankton assemblages were studied in 2 embayments of the Peconic Bay estuary (West Neck Bay, Long Island, New York) to determine the relative importance of each community on plankton mortality. Each embayment was characterized by a fringing salt marsh. The bivalve populations consisted of a re-stocked population of Mercenaria mercenaria (hard clam) and natural populations of Geukensia demissa (ribbed mussel) and Mya arenaria (soft-shell clam). Short-term (3 h) grazing experiments were conducted between May and October 2003 and 2004 using 59 l plastic buckets mounted on a floating platform at each study site. The total grazing pressure on phytoplankton by bivalves (i.e. percent bay volume cleared per day) was substantial, sometimes approaching or exceeding the daily flushing rate of the embay- ment, and was similar to microzooplankton grazing pressure. Experimental studies also showed that bivalves removed ciliates and copepod eggs of Acartia tonsa from the plankton. At times, bivalve- induced mortality was likely an important regulatory factor on the zooplankton. These findings demonstrate a complex trophic role for benthic suspension-feeders in shallow, coastal embayments. The effects of restoring shellfish populations will likely be beneficial to overall water quality by ameliorating some effects of eutrophication, but the resultant changes in pelagic food web structure are complex and will be difficult to predict.

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. Inte...

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.

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.

Wild stocks of hard clams from the genus Mercenaria historically supported commercial fisheries, but, as these stocks have been depleted, market demand has been filled by clams produced in aquaculture operations. Along the east coast of the USA, M. mercenaria is indigenous and used for aquaculture. Indigenous Gulf of Mexico (GOM) clam populations consist of M. campechiensis, a spe- cies less suited to aquaculture because of its short shelf life. Aquaculture operations have introduced M. mercenaria into GOM waters, resulting in altered Mercenaria species composition to the detri- ment of M. campechiensis. Where M. mercenaria have been introduced, the population now includes both M. mercenaria and M. campechiensis, and hybrids are common. This is particularly evident where commercial aquaculture is ongoing and introductions are, therefore, continuous. Where short- term introductions have occurred for research purposes, M. mercenaria is restricted to oyster reefs. At those sites, and at sites where no documented introductions of M. mercenaria have occurred, hybrids are rare and M. campechiensis dominate the more common sand/seagrass habitats. As the 2 species continue to interbreed, pure M. campechiensis will become rarer and hybrids more common, potentially resulting in reduced fitness of M. campechiensis from GOM waters. The trend towards hybrids may be ameliorated by an increased intensity of gonadal neoplasia in the hybrid clams. These results indicate that M. mercenaria introductions into the GOM, even on the relatively small scale of scientific research efforts, have a substantial and long-lasting influence on the genotype composition of hard clam populations in GOM waters.

A numerical bioenergetics simulation model 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 ...

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 (CI) 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 CI 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 CI and the gonadal index (GI). Results show that there is a significant difference between the CI of northern quahogs from conditional areas and quahogs from clos...

During the last several decades, the waters of mid Narragansett Bay, Rhode Island have increased in temperature and decreased in chlorophyll concentration, and it is possible that these changes affected the growth and success of a common benthic filter feeder, the hard clam, Mercenaria mercenaria. We determined recent hard clam growth rates through a sclerochronological analysis and compared them to the rich historical record of Narragansett Bay growth rates in order to understand how these opposing changes influenced hard clam growth. We found no significant differences in short-term growth between 1985 and 2000. Long-term juvenile growth showed a significant decrease between the 1960s and 1990s, while long-term adult (mature) growth showed a significant increase over this same time period. While it is not clear why the changes in juvenile and adult growth rates differ, it appears as though the decrease in chlorophyll concentration, together with a change in phytoplankton community composition, increasing water temperature, and an increase in predator abundance, may all have influenced hard clam growth between the 1960s and the 1990s.

In 2000, Florida's fast-growing hard clam aquaculture industry became eligible for federal agricultural crop insurance through the US Department of Agriculture, but the responsibility for identifying the cause of mortality remained with the grower. Here we describe the continuous water quality monitoring system used to monitor hard clam aquaculture areas in Florida and show examples of the data collected with the system. Systems recording temperature, salinity, dissolved oxygen, water depth, turbidity and chlorophyll at 30 min intervals were installed at 10 aquaculture lease areas along Florida's Gulf and Atlantic coasts. Six of these systems sent data in real-time to a public website, and all 10 systems provided data for web-accessible archives. The systems documented environmental conditions that could negatively impact clam survival and productivity and identified biologically relevant water quality differences among clam aquaculture areas. Both the real-time and archived data were used widely by clam growers and nursery managers to make management decisions and in filing crop loss insurance claims. While the systems were labor and time intensive, we recommend adjustments that could reduce costs and staff time requirements.

Increased numbers of benthic predators, especially crabs, have been proposed as a factor contributing to the decline of hard clams (Mercenaria mercenaria Linnaeus, 1758) in Great South Bay, NY. The long-term trend in benthic predators in this system was examined using observations on the distribution and abundance of predators that have been collected by the Town of Islip, NY as part of an annual survey of hard clam populations. The survey began in 1978 and extends to the present and provides concurrent observations of habitat (sediment type, and presence/absence of eelgrass), and hard clam size-frequency distribution and abundance. Predator type and abundance were reported from 1978 to 1981 and 1991 to 2003, which represents one of the most comprehensive benthic predator data sets currently available for any estuarine system. The annual averages of predator abundance in the survey area primarily show interannual fluctuations in abundance. Xanthid crabs (mud crabs, primarily Dispanopeus sayi Smith, 1869) were the numerically dominant predator in the system; blue crabs (Callinectes sapidus Rathbun, 1895) appeared in the late 1990s. Hard clam abundance has declined by 44% since the early 1990s. An Empirical Orthogonal Function (EOF) Analysis of the predator and hard clam data sets showed that fluctuations in predator abundance are: 1) mostly in phase over the survey region and 2) dominated by year-to-year fluctuations in abundance. The EOF results for the hard clams show that hard clam abundance fluctuations are: 1) in phase over the survey region and 2) dominated by a decreasing trend in abundance over the time series. The primary EOF modes essentially were uncoupled, which implies no strong predator- prey interactions between the predators and hard clams. By inference, increasing predator abundance does not appear to be a primary factor producing the long-term decline in hard clam populations. Predation pressure per recruit may still have increased because of declining hard clam population abundance and the concomitant decline in recruitment.

Along the mid-Atlantic coast of the United States in numerous areas where the water is shallow enough for light to reach the bottom, heavy spring-summer growth of drift seaweed (macroalgae) covers sessile benthic fauna for periods of days to weeks. Coverage for such prolonged periods can exert sublethal effects and eventually lead to death. This study examines the effects of seaweed coverage on body weight, relative abundance, and mortality in an economically important bivalve Mercenaria mercenaria Linnaeus (hard clam) within the Delaware Inland Bays, a shallow estuary representative of systems in which the species occurs and where mortality events have been observed in recent years. Mean body weights (dry weight) were compared between five groups of clams (80–90 mm shell length), taken from two paired sites (each of which had adjacent areas of heavy and light seaweed), and one seaweed-free site during September of 1999. Heavy seaweed density persisted into mid-to-late summer and the groups of cl...