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1.
The toxicity of surface sediments collected from eight estuarine sites around the Irish coast was assessed in March 1997 using a whole sediment bioassay. Two molluscan species, Tapes semidecussatus (1 + age class) and Scrobicularia plana (unknown age) were exposed to test sediments for 21 days. Survival, morphometric, behavioural and histochemical measurements were taken during the 21 day bioassay. 100% mortality occurred in both species in sediments from one site in Dublin Bay within 18 days of initial exposure. 100% survival of T. semidecussatus was observed in all but four of the test sediments to which it was exposed during this study. The animal condition and wet tissue weight of T. semidecussatus decreased for all sediments during the bioassay. 95% survival of S. plana was observed after 21 days exposure to Youghal (reference) sediment. Condition and wet tissue weight of S. plana increased in all test sediments during the bioassay, however, there was significant variation in wet tissue weight of this species on day 25 of the bioassay in all test sediments. There was significant variation in the burrowing behaviour of S. plana during the bioassay. Lipofuscin accumulation was observed in the digestive diverticula of T. semidecussatus exposed to all test sediments with the exception of Youghal (reference). The potential for both species as bioassay organisms is discussed.  相似文献   
2.
Abstract. In this work we have developed a very simple stochastic mathematical model of Ulva spp. growth to quantitatively evaluate the economic costs of algal harvesting and the related benefits in terms of avoided'economic loss'of clam production due to an effective prevention of algal blooms and the consequent anoxic crises. Algal growth was simulated by means of a discrete time difference equation of Ulva biomass where the finite growth rate depends only upon water temperature. In order to explicitly include environmental variability, a seasonal autoregressive model calibrated on available data was used to simulate water temperature. Different harvesting scenarios were analysed in terms of the number of harvesting vessels employed and the threshold biomass of Ulva at which vessels start to operate. Costs of algal harvesting and disposal, as well as monetary damages resulting from the collapse of clam production as a consequence of algal blooms, were assessed by interviewing the managers of the Clam Fishermen's Union of Goro. A Monte Carlo approach was used to estimate the mean and total statistical distribution of costs and benefits of different harvesting strategies. Our analysis shows that the most cost-effective management policy is attained with 4–6 vessels operating at low algal density able to harvest as much Ulva as possible with intensive and short interventions at the beginning of the seasonal growth.  相似文献   
3.
Habitat Suitability (HS) models have been extensively used by conservation planners to estimate the spatial distribution of threatened species and of species of commercial interest. In this work we compare three HS models for the estimation of commercial yield potential and the identification of suitable sites for Tapes philippinarum rearing in the Sacca di Goro lagoon (Italy) on the basis of six environmental factors. The habitat suitability index (HSI) is based on expert opinion while the habitat suitability conditional (HSC) is calibrated on observational data. The habitat suitability mixed (HSM) model is a two-part model combining expert knowledge and regression analysis: the first component of the model uses logistic regression to identify the areas in which clams are likely to be present; the second part applies the same parameter-specific suitability functions of the HSI model only in the areas previously identified as productive by the logistic component.The HS models were validated on an independent data set and estimates of potential yield of the Goro lagoon were compared. The effectiveness of the three approaches is then discussed in terms of predicted yield and identification of suitable sites for farming.  相似文献   
4.
Variation of polycyclic aromatic hydrocarbons (PAHs) levels was assessed in Tapes philippinarum from the Lagoon of Venice. Clams were transplanted from a polluted area next to Porto Marghera to two rearing areas of the Southern Lagoon. Analyses of PAHs were made in sediments and clams by GC/MS at first sampling and after 30, 60 and 180 days. Principal component analysis was performed to elucidate bioaccumulation and depuration pattern and input sources. Biota-Sediment-Accumulation-Factor (BSAF) was applied to evaluate the PAHs input sources from sediment. Condition index was calculated to compare the seasonal variation of clam tissue to PAHs levels. To propose results not affected by seasonal changes in flesh weight of clams, the approach based on the calculation of PAHs/SW index was applied. From the results, it was concluded that PAHs/SW index is more recommendable to asses temporal variation of PAHs levels in Manila clams.  相似文献   
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Barbamarco Lagoon (area = 7 km2) is in the Po River Delta, adjoining the Northern Adriatic Sea, and supports a commercially valuable clam (Tapes philippinarum) fishery. This study investigated interactions of the lagoon with adjacent coastal waters and inland riverine inputs by modelling both the lagoon and the Northern Adriatic Sea, using a coupled three-dimensional (3D) hydrodynamic-ecological model (ELCOM-CAEDYM) adapted to include the clam population. The clam model accounted for carbon (C), nitrogen (N) and phosphorus (P) biomass in the benthos through parameterisations for filtration, excretion, egestion, respiration, mortality, and harvesting. Multiple clam size classes were included in a new population dynamics sub-model. Output from the coupled model was validated against hydrodynamic and water quality data from intensive field sampling and routine monitoring. Time scales of tidal flushing, primary production and clam grazing were investigated with the model to demonstrate that food supply to clam populations is dominated by phytoplankton inputs from the Northern Adriatic Sea. Effects of clam cultivation on nutrient concentrations and phytoplankton biomass in Barbamarco Lagoon were primarily localised, with strong tidal flushing minimising impacts of clam filtration on lagoon-wide nutrient concentrations at current clam stocking levels. Clam populations were found to alter the cycling of nutrients in the system, causing the lagoon to become a net sink for particulate organic matter and to export dissolved organic matter to the adjacent sea via tidal flushing. Ecosystem health and sensitivity of nutrient cycles to clam cultivation are important considerations for the long term sustainable management and potential expansion of the fishery.  相似文献   
7.
The aim of this investigation was to quantify the effects of tributyltin (TBT) on the immune reactivity of haemocytes from the cultivated clam Tapes philippinarum (Adams and Reeve, 1850) using a series of in vitro bioassays. It is known that TBT has adverse effects on cellular immune functions like mobility, phagocytosis and lysosomal enzyme activity. As defining TBT-sensitive immunologic biomarkers in sentinel organisms is important in the field of ecotoxicology, the authors propose three indexes, amoebocytic (A.I.), phagocytic (P.I.), and lysosomal activity (L.A.I.), as sensitive and useful biomarkers to assess environmental risks due to TBT contamination.  相似文献   
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9.
Barbamarco Lagoon is a small lagoon adjoining the Northern Adriatic Sea and is the site of a commercially valuable clam (Tapes philippinarum) fishery. A three-dimensional (3D) coupled hydrodynamic–ecological model was applied to the lagoon with the objective of assessing impacts on clam food supply, commercial harvests and water quality of different clam rearing strategies, lagoon morphologies and flow regimes. Harvest and net growth to seeding ratios, total harvest value, clearance efficiencies and clam satiety were used to quantify the commercial success of different management strategies, while bottom dissolved oxygen concentrations were used as an indicator of ecosystem health. Increasing exchange with the Northern Adriatic Sea or increasing freshwater inputs into the lagoon improved clam food supply and increased both harvest production and ecosystem health in model simulations of the system. Results indicated that the high spatial and temporal variability of clam production and water quality responses must be considered for a holistic assessment of the outcomes of strategies in the context of ecological and production carrying capacity.  相似文献   
10.
The concentration changes of 12 metals (As, Hg, Cd, Cr, Co, Cu, Pb, Mn, Ni, V, Zn, Fe, and Hg) in the soft tissues of Tapes philippinarum during growth were investigated. Clams were seeded in two contaminated areas of the Venice lagoon (San Giuliano and Fusina) and in an area of the Marano lagoon (Lignano Sabbiadoro) close to the clam-farm where the seed was produced. Metal trends were very different according to the considered element, the study site and the growth period.Arsenic was always higher in clam tissues than in surface sediments and suspended particles in all the three stations. Mercury, Cd and Cu were higher in the clams from Marano and Fusina but not in those from San Giuliano. Zinc and Co in clams exceeded the concentrations in the sediment and suspended particles only at Marano. The other elements (Cr, Pb, Mn, Ni, and Fe) were always higher in SPM and sediments. In general metal concentrations in clams were more highly correlated to concentrations in the suspended particles rather than in the surface sediments and in suspended clams rather than in bottom clams, nevertheless significant differences between stations and contaminants were found. Metal concentrations in clams were always lower than the European regulatory limits.  相似文献   
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