Clam Farming Research Articles

Макрозообентос рыхлых грунтов под мидийно-устричной фермой (Чёрное море, район Севастополя)

В ходе съёмки 2015–2016 гг. проведено исследование видового состава, численности и биомассы макрозообентоса под мидийно-устричной фермой, расположенной в районе г. Севастополя. Материал собирали с помощью легководолазной техники ручным дночерпателем. Отмечено относительно низкое видовое разнообразие, обнаружено 56 видов макрозообентоса. Плотность макробентоса варьировала в пределах 500–975 экз.·м-2, биомасса — от 0,8 до 383,1 г·м-2. Зарегистрировано сообщество двустворчатого моллюска Lucinella divaricata (Linnaeus, 1758). Выявлены руководящие, характерные и редкие виды. Проведено сравнение с данными 1957 г. в районе Евпатория — Севастополь на сходных глубинах и грунтах. Обнаруженное сообщество отличается от регистрируемого ранее низкой плотностью особей и более высокой долей детритофагов, среди которых преобладают мелкие полихеты-грунтоеды.

DISTRIBUTION OF HEAVY METALS IN SURFACE WATER, SUSPENDED PARTICULATE MATTER, SEDIMENT AND CLAM (MERETRIX LYRATA) FROM DOWNSTREAM OF SAIGON-DONG NAI RIVER, VIETNAM

This study aimed to evaluate distribution of selected heavy metals (Cu, Zn, Pb, Cr and Cd) in clams Meretrixlyrata (clam), suspended particulate matter (SPM), water and sediment in the downstream area of Saigon – Dong Nai (SG-DN) River. During March to September 2015, the contamination of those metals at four sampling sites from fresh water to brackish water zone and Meretrix Lyrata clams, which were cultured at many clam farms at Can Thanh beach at Can Gio District, were monitored. The concentrations of metals in clam samples were also determined at a comparative sampling site at Tan Thanh beach (Tien Giang province). Generally, the order of metal concentrations in all environmental components along the SG-DN River was Zn>Cu>Cr>Pb>Cd while the metal concentrations in different environmental components at Can Thanh area were in different orders. According to the results, the increasing tendency of only Cu, Zn and Cd concentrations in SPM and sediment from river upstream to estuary were found. All trace metal concentrations in clam samples were higher than in water and smaller than in sediment and SPM at Can Thanh. Only Cr concentrations in medium and small clam samples had positive significant correlations with those in sediment and SPM (medium size only). In comparison with concentrations of trace metals in water, sediment, SPM and clams at Tan Thanh, those at Can Thanh were higher.

Assessment of household risk management strategies for coastal aquaculture: the case of clam farming in Thaibinh Province, Vietnam

Clam farmers have experienced different types of risks that have been further exacerbated by the rapid expansion of clam farming areas, increased growing densities, and increased market difficulties in recent years in the Thaibinh Province of Vietnam. Most farmers have been seriously affected by production risk, market risk, and financial risk, while a number of others have met with success in almost all of their clam-raising cycles. This study applied a differentiating comparative analysis method and multiple discriminant analysis method to discuss the differences in risk management strategies between and among clam farming households and the impacts of those differences on their success/failure rates. In general, the tactics are related to increase in farm size, the application of technical innovations, diversifying livelihood activities, and accessing secure financial sources all provided better conditions for clam growth, diminished losses, and led to speedier recovery from shocks. To support farmers in managing risks, several government interventions are needed: (1) better re-zoning of clam farming areas in parallel with an increase in the farm size of each household, (2) promoting sustainable linkages between the farmers and the formal financial market and output market, and (3) investing more funding into research and extension related to sustainable clam farming practices and to the improvement of farmers’ skills in cooperative works and management.

PAH (Polycyclic Aromatic Hydrocarbon) bioaccumulation and PAHs/shell weight index in Ruditapes philippinarum (Adams & Reeve, 1850) from the Vallona lagoon (northern Adriatic Sea, NE Italy)

The Vallona lagoon is a transitional area located in the Po River delta (NE, ITALY) traditionally exploited for Manila clam (Ruditapes philippinarum) farming. During 2007–2008, a pipeline was buried in the middle of the lagoon to connect an off-shore structure to facilities on land. PAH levels were monitored in Manila clams and sediments before, during and after the pipeline construction to assess the impact of the activities through the pattern of distribution of the PAH compounds.PAH bioaccumulation in clams displayed seasonal fluctuations with higher levels in autumnal and wintry surveys than in spring-summer. Principal component analysis applied to PAHs in clams highlighted a petrogenic input during ante operam period and a pyrolytic origin during the burying activities. On the contrary, sediment PAH concentrations resulted quite similar both among sites and periods. Biota-Sediment-Accumulation-Factor values also confirmed that sediments were not the major source of PAH pollution for clams in this study.The welfare of clams was examined through two physiological indices (condition index and survival in air) to check the effects of the activities on a commercial resource. Both physiological indices exhibited seasonal variations connected to natural endogenous and exogenous factors; however survival in air was the most sensitive index in highlighting the effects of the pipeline burying activities.Finally, to ensure that PAH bioavailability assessment was not affected by seasonal variation of soft tissues of molluscs, PAHs/shell weight index was applied. Higher levels of this index were observed before and during the burying activities, whilst, after that, values significantly lowered. Moreover, the normalization enabled us to highlight the PAH uptake from clams in some particular periods and to compare different populations in a long-term biomonitoring program with data obtained from different periods of the year.

Adaptive management for the sustainable exploitation of lagoon resources in remote islands: lessons from a massive El Niño-induced giant clam bleaching event in the Tuamotu atolls (French Polynesia)

SUMMARYSmall-scale mariculture of high-value species for trade in remote islands can offer valuable alternative livelihoods to local communities. The endangered giant clam speciesTridacna maximais naturally abundant in some atolls in French Polynesia (FP) and has been the focus of commercial mariculture activities since 2012. Shortly after spat collectors became operational in two atoll lagoons, FP rose to become one of the main exporters of giant clams for the aquarium trade. However, this activity has been threatened recently by a mass clam-bleaching event triggered by the 2015–2016 El Niño. This study reviews the roles that international (Convention on International Trade in Endangered Species of Wild Fauna and Flora) and national regulatory frameworks play in the development of this activity in a small island context, and how they can indirectly promote better science and monitoring in order to inform adaptive management strategies. The links between the nine main groups of stakeholders show the necessary adaptation measures required to mitigate climate-driven mortalities. While this case study remains specific to giant clam farming in FP, general lessons are provided that could help in mitigating economic impacts from climate-related events on other islands.

An economic analysis of hard clam (Meretrix meretrix) farmer polyculture with milkfish (Chanos chanos), silver sea bream (Rhabdosargus sarba), and shrimps at different hard clam stocking densities: a case study of Yunlin County, Taiwan

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 Land-Use Policy: The Case of Clam Farming in Thaibinh Province, Vietnam

Policy-making and enforcement remains centralized in Vietnam. Policies have been formulated with less scientific and public justification, thus being largely bureaucratic and infeasible, and in many cases, they have created plagues for people at the grass-roots levels. This article focuses on the implementation of policies related to intertidal land-use and supports for clam farming in the Thaibinh province as a case study to explore the impacts of policies on clam farming and farmers. During the period of 2011–2013, provincial policies on intertidal land allocation and technical and financial supports had boosted clam farming development in the province to a surprising extent. Rapid expansion of the clam farming area has created significant consequences for the farming sector, as well as farmer’s lives. However, for the same provincial policies, but with different enforcement, different farming outcomes for clam farmers in the three study communes have resulted. Where farmers had more of a voice and choice in bidding for the intertidal areas they preferred, they faced fewer problems. It is, thus, suggested that a more decentralized policy-making and enforcement are needed, in which more scientific assessment and farmer participation are required to not only make government policy more successful in supporting farmers and achieving their expected outcomes, but also to provide farmers with more room to make their own farming decisions from which farming and marketing risks could be mitigated.

Effects of Clam Aquaculture on Nektonic and Benthic Assemblages in Two Shallow-Water Estuaries

ABSTRACT 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...

Effects of Culture Area, Stocking Density, and Shrimp and Fish Polyculture on the Cost Efficiency of Hard Clam, Meretrix meretrix, Culture: A Case Study of Hard Clam Farms in Yunlin, Taiwan

AbstractUsing 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.

Screening for and Identification of an Anti‐clam Vibrio Marine Bacterium from an Aquaculture Pond in the Yellow Sea

AbstractThe identification and use of probiotic bacterial stains is a practical approach to protect clams grown in aquaculture farms from disease. The inhibition of the pathogenic bacterium Vibrio alginolyticus was used as a trait to select a candidate probiotic bacterial strain in this study. An ideal bacterial strain, SW‐1, was isolated from seawater from a clam farm. The selected isolate SW‐1 was identified based on its physiological, morphological, and biochemical characteristics and its 16S rDNA sequence. The experiments showed that strain SW‐1 had a high similarity to Pseudoalteromonas piscicida and could inhibit the growth of V. alginolyticus (V.‐MP‐1). SW‐1 also improved the survival of clams following challenge with the pathogenic V.‐MP‐1. The mortality of clams was 100% after infection with 108 CFU/mL of V. alginolyticus, whereas mortality was only 11% when clams were infected with 108 CFU/mL of V.‐MP1 while simultaneously exposed to the same concentration of Pseudoalteromonas SW‐1, indicating that Pseudoalteromonas SW‐1 could be used as a probiotic to protect farmed clams, and thus reduce the effects of antibiotics on aquatic environment.

Clam predator protection is effective and necessary for food production

Shellfish aquaculture is a widely practiced way of producing food for human consumption in coastal areas. When farming intertidal clams, farmers commonly protect young seedling clams from predatory losses by covering farmed plots with netting or screening. Recent discussion of the effectiveness of protective nets or screens and their environmental effects has raised questions concerning the utility of the practice. We provide data based on a review of more than 35 peer-reviewed articles, as well as our own research that demonstrates the efficacy of predator protection for clam farms in various habitats around the world. In addition, we evaluate the effects of screening on temperature, and comment on ancient practices of clam gardening as conducted in the Pacific Northwest.

곰소만 바지락(Ruditapes phillippinarum) 양식장 주변 퇴적물 내 유기물과 미량금속 분포특성

【Organic matter and trace metals were investigated in surface sediments of Gomso Bay, where there is dense Manila clam Ruditapes philippinarum farming activity, to evaluate contamination of sediments in intertidal shellfish farming area. We measured mean grain size (Mz), chemical oxygen demand (COD), ignition loss (IL), acid volatile sulfide (AVS), total organic carbon (TOC), and total nitrogen (TN), and trace metals (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb and Zn) in intertidal and sublittoral sediments. The intertidal sediments were mainly composed of coarser sediments (sand, silty sand, and sandy silt), with Mz values ranging from 2.61 to 4.79 O. Mz and the content of organic matter in sediments were lower in the intertidal zone than in the sublittoral zone. The mean metal concentrations in surface sediments decreased in the order Fe > Mn > Zn > Cr > Pb > Cu > As > Cd > Hg. The metal concentrations in surface sediments showed a significant positive correlation with Mz and organic matter content, indicating that metal concentrations in the surface sediments of Gomso Bay are controlled by Mz and organic matter. The concentrations of organic matter and trace metals in the study region were lower than or similar to those in other intertidal zones in western coast and much lower than those reported in other shellfish farming areas in Korea. Our results suggest that intertidal Manila clam farming sediments from Gomso Bay are not contaminated by organic matter and trace metals.】

Decision support system development for integrated management of European coastal lagoons

In this paper, a general framework for the development of Decision Support Systems (DSSs) for the management of coastal lagoons is presented. The proposed DSS structure integrates the information provided by several models accounting for different characteristics of lagoon ecosystems, including biogeochemical, hydrodynamic, ecological and socio-economic aspects. Outputs and indicators provided by the models are used to accomplish the decision task by the application of multicriteria analysis. Model uncertainty and robustness with respect to uncontrollable factors are addressed. Application of the proposed DSS structure to five lagoons located in the Mediterranean area is discussed, with special focus on the management of clam farming in the Sacca di Goro lagoon (Italy). Thanks to its flexibility, the proposed DSS structure is also applicable in decision problems arising in different fields.

First Report of Mud Shrimp Austinogebia wuhsienweni (Crustacea: Decapoda: Upogebiidae) from Korean Waters

Specimens of Austinogebia wuhsienweni (Yu, 1931) previously recorded from China to Japan were collected at a manila clam farm of 0.5 m depth in Hongseong, Yellow Sea. They were briefly described and illustrations included color photographs, since this was the first record of this rare species from Korean waters. Three species of Upogebiidae are known from Korean waters: Upogebia major (De Haan, 1839), U. issaeffi (Balss, 1913), and A. wuhsienweni (Yu, 1931). They are similar to each other, however, the presence of the ventral spines of the rostrum, a proximal knob on the lateral margin of the uropodal endopod, and a longitudinal carina on the inner surface of the palm of the male first pereiopod can easily distinguish the present species from the two species of Upogebia.

Cost Monitoring for Clam Raising Farmers in the Northern Area of Vietnam

Clam farming in the coastal provinces of Vietnam has notably developed since the last decade. It generated high income, improve socio-economic development for many local communities. However, many clam raising farms were facing difficulties of farm management, disease control, markets and systems of quality control. This research aimed to study about the real situation of cost monitoring in the clam raising farms in the Northern area of Vietnam and suggested some recommendation to promote the benefits for farmers. The paper is based on the semi-structure, standard questionnaires and PRA method to collect data from 112 clam raising farms in two coastal provinces (Nam

Natural Recovery and Planned Intervention in Coastal Wetlands: Venice Lagoon (Northern Adriatic Sea, Italy) as a Case Study

The goals of conservation and sustainable use of environmental ecosystems have increased the need for detailed knowledge of ecological evolution and responses to both anthropogenic pressures and recovery measures. The present study shows the effects of natural processes and planned intervention in terms of reducing nutrient inputs in a highly exploited coastal lagoon, describing its evolution over a 16-year period from the late 1980s (when eutrophication was at its peak) until 2003. Changes in nutrient and carbon concentrations in the top layer of sediments were investigated in parallel with macroalgal and seagrass biomass in the most anthropized basin of Venice Lagoon in four surveys conducted in accordance with the same protocols in 1987, 1993, 1998, and 2003. A pronounced reduction in trophic state (mainly total nitrogen, organic phosphorus, and organic carbon concentrations) and macroalgal biomass was recorded, together with the progressive expansion of seagrass meadows. General considerations are also made on the effects of Manila clam farming and the shift from illegal to managed clam farming.

Annual variations of biogenic element contents of manila clam (Ruditapes philippinarum) bottom-cultivated in Jiaozhou Bay, China

Manila clam (Ruditapes philippinarum) was monthly sampled from its benthic aquaculture area in Jiaozhou Bay from May 2009 to June 2010. The annual variations of major elemental composition, organic content, fatness and element ratio of Manila clam were examined. The element removal effect of clam farming in Jiaozhou Bay was analyzed based on natural mortality and clam harvest. The results indicated that the variation trend of carbon content in shell (Cshell) was similar to that in clam (Cclam). Such a variation was higher in summer and autumn than in other seasons, which ranged from 9.10 ± 0.13 to 10.38 ± 0.09 mmol g−1 and from 11.28 ± 0.29 to 12.36 ± 0.06 mmol g−1, respectively. Carbon content of flesh (Cflesh) showed an opposite variation trend to that of shell in most months, varying from 29.42 ± 0.05 to 33.64 ± 0.62 mmol g−1. Nitrogen content of shell (Nshell) and flesh (Nflesh) changed seasonally, which was relatively low in spring and summer. Nshell and Nflesh varied from 0.07 ± 0.009 to 0.14 ± 0.009 mmol g−1 and from 5.46 ± 0.12 to 7.39 ± 0.43 mmol g−1, respectively. Total nitrogen content of clam ranged from 0.50 ± 0.003 to 0.76 ± 0.10 mmol g−1 with a falling tend except for a high value in March 2010. Phosphorus content of clam (Nclam) fluctuated largely, while phosphorus content of shell (Pshell) was less varied than that of flesh (Pflesh). Pshell varied from 0.006 ± 0.001 to 0.016 ± 0.001 mmol g−1; while Pflesh fluctuated between 0.058 ± 0.017 and 0.293 ± 0.029 mmol g−1. Pclam ranged from 0.015 ± 0.002 to 0.041 ± 0.006 mmol g−1. Carbon and nitrogen content were slightly affected by shell length, width or height. Elemental contents were closely related to the reproduction cycle. The removal amounts of carbon, nitrogen and phosphorus from clam harvest and natural death in Jiaozhou Bay were 2.92×104t, 1420 t and 145 t, respectively. The nutrient removal may aid to reduce the concentrations of nitrogen and phosphorus, the main causes of eutrophication, and to maintain the ecosystem health of Jiaozhou Bay.

Distribution and morphological abnormalities of recent foraminifera in the Marano and Grado Lagoon (North Adriatic Sea, Italy)

The Marano and Grado Lagoon, is a northern Adriatic wetland system of relevant naturalistic and economic value, that is constantly under quality control in accordance with the current environmental directives. Benthic foraminifers community with its morphological abnormalities were investigated in the recent sediments (about 10 years old) of 21 stations collected in the framework of the “MIRACLE” Project which aimed at testing the coexistence of clam farming with high Hg contamination. Euryhaline foraminifers, well known in Mediterranean brackish-waters, mainly characterizes the total assemblage. A. tepida dominates in areas characterized by low salinity, high clay and Corg content, but also to anthropogenic pressure. E. gunteri and H. germanica are recorded in the western sector of the lagoon, which is more affected by salinity variations and agricultural activities. Slightly higher values of assemblage diversity appear in less restricted areas of the lagoon or, at least, where physical parameters such as temperature and salinity are less variable. The test abnormalities, carried out on total assemblage, shows that the FAI (Foraminiferal Abnormality Index) values always exceed 1% of the total assemblage, with clear decreasing gradients from inland to the sea (from N to S) and from W to E in the studied area.

Growth performance of the clam, Meretrix meretrix, breeding-selection populations cultured in different conditions

A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selection populationswere generated with the shell color pattern as an additional selection criterion and named as SP (purple stripes) population and SB (black dots) population. The third-generation SP and SB populations (08G3SP and 08G3SB, respectively) were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared. 08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms (p < 0.05), yet 08G3SB individuals were significantly smaller than 08G3SP individuals at the nursery pond (p < 0.05). Then, we examined the growth of the fourth-generation SP and SB populations (10G4SP and 10G4SB, respectively) at a commercial farm, and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams (p < 0.05) from May to September, when the water temperature was between 24.2-27.5A degrees C, while 10G4SB lost the growth advantage in the other months. These results indicated that SP and SB populations responded differently to environmental factors, so it is beneficial for the clam farmers to select a suitable population according to the culture environment. Furthermore, a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis. However, the heterosis was not shown in this study, whichmight result from the slight genetic divergence between SB and SP populations.

Seasonal Variation of Metals in Seawater, Sediment, and Manila Clam Ruditapes philippinarum from China

Concentrations of trace metals (Cu, Pb, Zn, Cd, Cr, Hg, and As) were determined for the first time in seawater, sediment, and Manila clam from Deer Island, Liaoning Province, China. The seawater, sediment, and clam samples were collected seasonally at three clam farming sites around Deer Island during 2010-2011. The average concentrations of Cu, Pb, Zn, Cd, Cr, Hg, and As in the seawater samples were 4.16, 0.72, 5.88, 0.45, 2.51, 0.03, and 1.02μg/l, respectively. The seasonal variations of trace metals in seawater showed a significant difference in the concentrations of Cu, Pb, Zn, Hg, and As among seasons. The average concentrations of Cu, Pb, Zn, Cd, Cr, Hg, and As in the sediment samples were 6.43, 13.80, 53.08, 1.10, 36.40, 0.05, and 4.78mg/kg dry weight, respectively. Trace metal concentrations in sediment seasonally varied significantly except for Cd and Hg. The average concentrations of Cu, Pb, Zn, Cd, Cr, Hg, and As in the clam samples were 11.28, 0.61, 92.50, 0.58, 3.98, 0.03, and 1.98mg/kg dry weight, respectively. Concentrations of Cu, Zn, Cd, Cr, and As in Manila clam showed marked seasonal fluctuations with significant difference. Cu and Zn were the metals with the highest mean biosediment accumulation factor values in Manila clam. Besides, significant correlations for the concentrations of Cu and Zn relative to their concentrations in sediment were also found. Such differences in regression analyzes may be explained by differential bioaccumulation of essential and xenobiotic metals. Concentrations of trace metals in Manila clam did not exceed the maximum established regulatory concentrations for human consumption. Moreover, the calculations revealed that the estimated daily intake values for the examined clam samples were below the internationally accepted dietary guidelines and the calculated hazard quotient values were well less than 1, thus strongly indicating that health risk associated with the intake studied metals through the consumption of Manila clam from Deer Island was absent.