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Aquaculture ponds have garnered increasing attention for their potential roles in the global carbon cycle within the context of global warming. As a significant co-culture species in mariculture ponds, clams exert a notable impact on CO 2 flux across the water-air interface. However, the mechanism underlying this influence is as yet unclear. This study measured the CO 2 flux as well as the ecosystem carbon metabolism and environmental physiochemical parameters from four marine polyculture ponds, i.e., the pond containing swimming crabs and kuruma shrimp was referred to as CS, and the other three ponds containing three varying densities of razor clams additionally based on CS were noted as CSB 1 , CSB 2 , and CSB 3 in order of increasing clam density. All the bi-species and tri-species polyculture ponds acted as atmospheric CO 2 sinks during the farming season, with the peak in CSB 1 and the lowest in CSB 3. Net ecosystem production was a dominant regulator of CO 2 uptake, and sediment respiration significantly increased CO 2 production and then affected the CO 2 flux, contributing 16.7–20.0 % to the ecosystem respiration (ER). Water pH could function as a potentially reliable CO 2 flux predictor in the polyculture ponds, while Chl a was an internal driving factor. The polyculture of clams at low density may have exerted a "bottom-up" effect, accelerating nutrient cycling and thus stimulating the planktonic community, gross primary production (GPP), and ER, whereas a high stocking density of clams can have a "top-down" effect that would have the opposite ecological effects through increased predation pressure from clams. Although GPP and ER were simultaneously promoted or inhibited by clams at different stocking densities, the effect on GPP was always greater than that on ER, resulting in the CO 2 sink function that the polyculture ponds performed through the water-air interface being strengthened at low clam densities and weakened at high clam densities. Given the good predictive ability of water pH on CO 2 flux, monitoring and management of water pH could be an effective way to regulate the CO 2 sink function of mariculture ponds. • Net ecosystem production was a dominant regulator of CO 2 flux in polyculture ponds. • Sediment respiration contributed 16.7 %-20.0 % of the total ecosystem respiration. • The bottom-up effect by clams boosts CO 2 uptake, and the top-down effect reduces it. • Clams exert a greater effect on gross primary production than ecosystem respiration. • Water pH as a potential good factor to monitor and regulate CO 2 sink/source function. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We show how a simple species distribution model can be used for the rapid estimation of potential yield and for the identification of suitable sites for farming of Tapes philippinarum in two North Adriatic lagoons (Caleri and Marinetta-Vallona, Italy) in the face of limited data. We used a two-part species distribution model with sediment type, hydrodynamism, dissolved oxygen, and salinity as predictors of T. philippinarum potential yield. The first model component uses logistic regression to identify the areas in which clams occur, while the second component uses a weighted geometric mean of suitability values to estimate the potential annual yield (kg m year) for the sites where T. philippinarum is predicted to be present. We used site-specific yield data from Caleri and Marinetta-Vallona to estimate the weights of the geometric mean by constrained linear regression. We validated the two-part model on an independent set of yield data ( R = 0.82), and we then estimated the spatial distribution of potential yield in the two lagoons. The calibration and application of a simple species distribution model are useful tools for objectively identifying the most suitable sites for farming of T. philippinarum in North Adriatic lagoons. [ABSTRACT FROM AUTHOR]

We show how a simple species distribution model can be used for the rapid estimation of potential yield and for the identification of suitable sites for farming of Tapes philippinarum in two North Adriatic lagoons (Caleri and Marinetta-Vallona, Italy) in the face of limited data. We used a two-part species distribution model with sediment type, hydrodynamism, dissolved oxygen, and salinity as predictors of T. philippinarum potential yield. The first model component uses logistic regression to identify the areas in which clams occur, while the second component uses a weighted geometric mean of suitability values to estimate the potential annual yield (kg m −2 year −1) for the sites where T. philippinarum is predicted to be present. We used site-specific yield data from Caleri and Marinetta-Vallona to estimate the weights of the geometric mean by constrained linear regression. We validated the two-part model on an independent set of yield data ( Radj2 = 0.82), and we then estimated the spatial distribution of potential yield in the two lagoons. The calibration and application of a simple species distribution model are useful tools for objectively identifying the most suitable sites for farming of T. philippinarum in North Adriatic lagoons. [ABSTRACT FROM AUTHOR]

Abstract: Respiration and calcium carbonate (CaCO3) production by the farmed short-neck clam Ruditapes philippinarum were calculated to assess their importance as carbon dioxide (CO2) sink/source in a lagoon of the Po Delta River (Italy). Biomass and calcimass were established by monthly harvests during a 1-year period (2009). The ratio of CO2 released to CaCO3 precipitated was calculated as a function of the near-bottom temperature. From our estimates, R. philippinarum sequestered for shell formation, but the CO2 fluxes due to respiration and calcification resulted 22.7 and 5.56 , respectively. Clam farming seems therefore to be a significant additional source of CO2 to seawater. [Copyright &y& Elsevier]

Abstract: Ria Formosa lagoon in southern Portugal has an important population of seagrasses that includes Zostera noltii in the intertidal area. The area is classified as a Natural Park and supports a major economic activity – clam farming. This activity has a direct influence on Z. noltii populations by removal of seagrass beds and altering habitat. Geographic Information Systems and spatial analysis were used to produce the first distribution map of Z. noltii in the Ria Formosa and to analyse interactions between clam farming and the level of seagrass protection according to the Natural Park of Ria Formosa. Stakeholder analyses, using interviews, questionnaires and participant observation, were conducted to gain a better understanding of clam farming''s influence on seagrass populations. Seagrass covers 45% of the intertidal area while clam farming covers 14%. An additional 75% of the total area of Z. noltii can be potentially converted into clam cultures. The current management of clam farming is largely ineffective, representing a significant obstacle to seagrass conservation. [Copyright &y& Elsevier]

The clam fishing and aquaculture system in the Venice Lagoon still appears insufficiently resilient to buffer external and internal perturbations, such as productivity fluctuations, unregulated fishing, and market related dynamics, despite the efforts of regional and local authorities to achieve the sustainable development. According to the System Approach Framework (SAF), based on previous studies and stakeholder interactions, we developed a model integrating ecological, social, and economic (ESE) aspects. We chose the aspects necessary to represent the essential dynamics of major ecological, social, and economic clam farming system components to project the consequences of implementing alternative management policies and to address the ecological and social carrying capacity. Results of the simulations suggest that a properly managed farming system can sustain an acceptable income and support the local community, while reducing negative environmental impacts, social conflicts, and consumer health risks and improving system resilience. The results highlight the importance of an interdisciplinary, participatory, and adaptive approach in planning the management of this important renewable resource. [ABSTRACT FROM AUTHOR]

Abstract: The development of shellfish farming was analyzed with a coupled watershed and 3D biogeochemical model for the Sacca di Goro coastal lagoon (Northern Adriatic Sea, Italy). Sacca di Goro is the second site in Europe for the production of the Manila clam (Tapes philippinarum). Different scenarios were identified and analyzed, considering clam productivity under different environmental conditions, namely with and without macroalgal blooms. In addition, the influence of climatic variability – dry, average and wet years – was assessed. Model simulations indicated that macroalgal blooms have an important negative impact on clam productivity due to the risk of anoxia and subsequent clam mortality. Furthermore, simulation results evidenced that meteorological conditions also affect clam productivity, especially in a dry year due to a shortage of food supply. [Copyright &y& Elsevier]

Fluxes of dissolved oxygen and ammonium across the water sediment interface were measured in a control and in an experimental area farmed with the clam Tapes philippinarum. Young clams were seeded in March 2003 at mean (~500 ind m−2) and high (~1500 ind m−2) densities in a sandy area (2100 m2) of the Sacca di Goro Lagoon, Italy. Approximately every two months, until October 2003, intact sediment cores were collected and incubated in the light and in the dark and surface sediments (0–2 cm) were analysed for organic matter and nitrogen content. Clams farming induced pronounced changes in sediment characteristics and metabolism. Oxygen consumption and ammonium production at the high density area were, on average, 3 to 4 and 1.9 to 4.9 folds higher than those measured in the control field respectively; rates were positively correlated with clams biomass. Experimental fields resulted “Net and Total Heterotrophyc” in 3 out of 4 sampling dates and clams were the major factor shifting the benthic system towards this status. In only one occasion the appearance of the macroalgae Ulva spp. pushed the system rapidly towards hyperautotrophic conditions. Our results indicated that clams have the potential to drive benthic metabolism in farmed areas and to sustain macroalgal growth through regeneration of a limiting nutrient for seawater as inorganic N. [ABSTRACT FROM AUTHOR]

During the farming season of 2013 and 2014, carbon dioxide (CO 2) fluxes at the water-air interface were determined from two typical seawater polyculture systems. The mean CO 2 fluxes of 2013 and 2014 were − 0.316 ± 0.0674 μmol m−2 s−1 and -0.173 ± 0.242 μmol m−2 s−1 in the bi-species polyculture system of swimming crab (Portunus trituberculatus) with kuruma shrimp (Marsupenaeus japonicus) (PM) and 0.249 ± 0.251 μmol m−2 s−1 and 0.426 ± 0.151 μmol m−2 s−1 in the tri-species polyculture system of swimming crab with shrimp and short-necked clam (Ruditapes philippinarum) (PMR) (Negative flux values refer to CO 2 uptake and positive values refer to CO 2 emission). During the farming season, the CO 2 budgets in PM and PMR were − 113.1 g CO 2 m−2 and 154.0 g CO 2 m−2, respectively. Water pH seemed like a stable indicator for CO 2 flux and Chlorophyll a concentration was a key factor regulating the CO 2 flux. Subsequent decreasing in water pH and Chl a concentration was supposed to be the main contributor changing the carbon source/sink function from a CO 2 sink of PM to a CO 2 source of PMR. Under the condition of current study, pH of 8.26 could be considered to be the critical value between influxes and effluxes in seawater crab-shrimp and crab-shrimp-clam polyculture systems. • Among the first studies on CO 2 flux from two typical seawater aquaculture ponds in 2 consecutive years. • Water pH seemed like a stable indicator for CO 2 flux from mariculture system, Chl a was a key factor regulating CO 2 flux. • Polyculture system of crab with shrimp was a CO 2 sink while system of crab with shrimp and clam was a CO 2 source. • Subsequent decreasing in water pH and Chl a concentration after farming clam was supposed to be the main contributor. [ABSTRACT FROM AUTHOR]