The role of calcium concentration in the invasive capacity of Corbicula fluminea in crystalline basins.

The natural variation of environmental factors in freshwater basins determines their biodiversity. Among them, calcium is a key physiological compound for freshwater invertebrates. It is required for shell formation, muscle contraction, it mediates gene expression and allows counteracting acidosis during stress periods, among other functions. Although the distribution of different freshwater species has been suggested to be linked with the environmental calcium concentration, as yet, no research studies have confirmed this. Identifying whether environmental calcium concentrations might determine the invasion success of alien species would be critical in developing and implementing effective management strategies to control them. Here, a multidisciplinary approach integrating field surveys, analytical chemistry techniques, molecular biology analyses and a lab-scale experiment was taken to decipher whether the environmental calcium concentration might hamper the establishment of Corbicula fluminea in northwestern Iberian rivers. A Principal Component Analysis on water chemistry variables from 13 water bodies identified environmental calcium concentration, among others, as one key factor that best characterized the distribution area of C. fluminea. The calcium content in animals' bodies from two representative rivers was dependent on the environmental calcium concentration of freshwater basins; the lower the concentration, the lower the body's content. The expression of stress- and calcium homeostasis-related genes was higher in C. fluminea from low calcium concentration environments than in those from calcium-rich freshwater basins. Finally, under experimental conditions, lower water calcium concentrations decreased C. fluminea growth rates. The present data suggest, for the first time, that environmental calcium concentration may act as a determinant factor on the invasion success of C. fluminea in freshwater environments. Our results provide new clues for the identification of basins with increased risk of potential invasion by C. fluminea based on environmental calcium levels.

A 3D individual-based aquatic transport model for the assessment of the potential dispersal of planktonic larvae of an invasive bivalve.

The unwanted impacts of non-indigenous species have become one of the major ecological and economic threats to aquatic ecosystems worldwide. Assessing the potential dispersal and colonization of non-indigenous species is necessary to prevent or reduce deleterious effects that may lead to ecosystem degradation and a range of economic impacts. A three dimensional (3D) numerical model has been developed to evaluate the local dispersal of the planktonic larvae of an invasive bivalve, Asian clam (Corbicula fluminea), by passive hydraulic transport in Lake Tahoe, USA. The probability of dispersal of Asian clam larvae from the existing high density populations to novel habitats is determined by the magnitude and timing of strong wind events. The probability of colonization of new near-shore areas outside the existing beds is low, but sensitive to the larvae settling velocity ws. High larvae mortality was observed due to settling in unsuitable deep habitats. The impact of UV-radiation during the pelagic stages, on the Asian clam mortality was low. This work provides a quantification of the number of propagules that may be successfully transported as a result of natural processes and in function of population size. The knowledge and understanding of the relative contribution of different dispersal pathways, may directly inform decision-making and resource allocation associated with invasive species management.

The control of an invasive bivalve, Corbicula fluminea, using gas impermeable benthic barriers in a large natural lake.

Anoxia can restrict species establishment in aquatic systems and the artificial promotion of these conditions can provide an effective control strategy for invasive molluscs. Low abundances (2-20 m(-2)) of the nonnative bivalve, Asian clam (Corbicula fluminea), were first recorded in Lake Tahoe, CA-NV in 2002 and by 2010 nuisance-level population densities (>10,000 m(-2)) were observed. A non-chemical control method using gas impermeable benthic barriers to reduce dissolved oxygen (DO) concentrations available to C. fluminea was tested in this ultra-oligotrophic natural lake. In 2009, the impact of ethylene propylene diene monomer (EPDM) sheets (9 m(2), n = 6) on C. fluminea beds was tested on 1-7 day intervals over a 56 day period (August-September). At an average water temperature of 18 °C, DO concentrations under these small barriers were reduced to zero after 72 h resulting in 100 % C. fluminea mortality after 28 days. In 2010, a large EPDM barrier (1,950 m(2)) was applied to C. fluminea populations for 120 days (July-November). C. fluminea abundances were reduced over 98 % after barrier removal, and remained significantly reduced (>90 %) 1 year later. Non-target benthic macroinvertebrate abundances were also reduced, with variable taxon-specific recolonization rates. High C. fluminea abundance under anoxic conditions increased the release of ammonium and soluble reactive phosphorus from the sediment substrate; but levels of unionized ammonia were low at 0.004-0.005 mg L(-1). Prolonged exposure to anoxia using benthic barriers can provide an effective short term control strategy for C. fluminea.

Toxicity of pentachlorophenol to native aquatic species in the Yangtze River.

INTRODUCTION: While the literature is replete with studies of the toxic potency of pentachlorophenol (PCP), site-specific criteria for native aquatic species that can be used in ecological risk assessments has been lacking and application of toxicity information for non-native species is controversial. MATERIALS AND METHODS: In the present study, acute and chronic toxicities of PCP to six aquatic species native to the Yangtze River were determined. The HC5 and HC50 (hazardous concentration for 5% and 50% of species) were derived from dose-response curves for these native aquatic species and were then compared with those derived for non-native species. RESULTS: The acute toxicity values for the native species ranged from 8.8 × 10⁻² mg l⁻¹ (Plagiognathops microlepis) to 1.1 mg l⁻¹ (Soirodela polyrhiza), while chronic toxicity values based on no observed effect concentrations (NOECs) ranged from 0.01 mg l⁻¹ (Macrobrachium superbum) to 0.25 mg l⁻¹ (Soirodela polyrhiza). Native aquatic benthos was more sensitive to acute PCP exposure than non-native species. There was no significant difference in NOECs derived from native fish species and those based on non-native fish species. The median acute HC5 and HC50 derived from the toxicity data of native taxa were both less than those derived from non-native taxa. There was no significant difference between chronic HC5s derived from the two sets of taxa. However, the median chronic HC50 derived from native taxa was less than that derived from non-native taxa. CONCLUSION: The study upon which we report here provides site-specific toxicity information developed for native species which can be used for the protection of local aquatic life from a common contaminant, PCP.

A simple allometric diffusion-based biokinetic model to predict Cu(II) uptake across gills of freshwater clam Corbicula fluminea.

The purpose of this study was to link Fick's type mass transfer and biokinetics together with Michaelis-Menten kinetics to arrive at a simple predictive framework for quantifying biouptake mechanisms in gills of freshwater clam Corbicula fluminea exposed to Cu(II). A diffusion-based Cu(II) influx and permeability can be calculated using physiological and allometric-related parameters. Simulations indicate that Cu(II) bioconcentration factor of gills was 42. Estimated steady-state Cu(II) gill uptake influx and permeability were 0.097 nmol cm(-2) s(-1) and 0.48 cm s(-1), respectively. The proposed simple allometric diffusion-based biokinetic model meets the need for describing nonequilibrium aspects of biouptake mechanisms in bivalve gills.

Accumulation of trace elements and growth responses in Corbicula fluminea downstream of a coal-fired power plant.

Lentic organisms exposed to coal-fired power plant (CFPP) discharges can have elevated trace element concentrations in their tissues, but this relationship and its potential consequences are unclear for lotic organisms. To explore these patterns in a lotic environment, we transplanted Corbicula fluminea from a reference stream to a stream receiving CFPP discharge. We assessed trace element accumulation and glutathione concentration in clam tissue, shell growth, and condition index at five sites along a contamination gradient. Clams at the most upstream and contaminated site had the highest growth rate, condition index, glutathione concentrations, and concentrations of arsenic (7.85+/-0.25 microg/g [dry mass]), selenium (17.75+/-0.80 microg/g), and cadmium (7.28+/-0.34 microg/g). Mercury concentrations declined from 4.33+/-0.83 to 0.81+/-0.11 microg/g [dry mass] in clams transplanted into the selenium-rich environment nearest the power plant, but this effect was not as evident at less impacted, downstream sites. Even though dilution of trace elements within modest distances from the power plant reduced bioaccumulation potential in clams, long-term loading of trace elements to downstream depositional regions (e.g., slow moving, silty areas) is likely significant.

Sodium sulfate impacts feeding, specific dynamic action, and growth rate in the freshwater bivalve Corbicula fluminea.

Sodium sulfate is a ubiquitous salt that reaches toxic concentrations due to mining and other industrial activities, yet is currently unregulated at the Federal level in the United States. Previous studies have documented reduced growth of clams downstream of sulfate-dominated effluents, altered bioenergetics in filter-feeding invertebrates, and interactions between sulfate and other toxicants. Therefore, the purpose of this study was to determine if sodium sulfate affects the bioenergetics of the filter-feeding, freshwater bivalve, Corbicula fluminea, and the mechanism by which the effects are elicited. In addition to measuring effects on feeding, respiration and growth rates, I evaluated the relative sensitivity of a green algae consumed by clams to determine if top-down or bottom-up effects might be exhibited under field conditions. This study demonstrated that sodium sulfate had no effect on basal metabolic rates, but significantly reduced the feeding, post-feeding metabolic, and growth rates of C. fluminea. The proposed mechanism for these impacts is that filtering rates are reduced upon exposure, resulting in reduced food consumption and therefore, preventing increased metabolic rates normally associated with post-feeding specific dynamic action (SDA). In the field, these effects may cause changes in whole stream respiration rates and organic matter dynamics, as well as alter uptake rates of other food-associated contaminants like selenium, the toxicity of which is known to be antagonized by sulfate, in filter-feeding bivalves.

Assessment of diazinon toxicity in sediment and water of constructed wetlands using deployed Corbicula fluminea and laboratory testing.

Constructed wetlands for mitigation of nonpoint agricultural runoff have been assessed for their ability to decrease potential toxicity from associated contaminants. After a simulated runoff event, constructed wetlands positioned in series were used to measure the effects of the organophosphate insecticide diazinon. Water, sediment, and plant samples from five sites were analyzed for diazinon concentrations from 0.5 hours to 26 days; peak concentrations were measured in sediment after 0.5 hours (268.7 microg/kg) and in water and plant tissue after 3 hours (121.71 microg/L and 300.7 microg/kg, respectively). Cholinesterase activity and changes in shell growth were measured from Corbicula fluminea deployed at corresponding sites. Water collected after 9 hours from all wetland sites contained diazinon concentrations sufficient to cause toxicity to Ceriodaphnia dubia, but not to Pimephales promelas. C. dubia survival was decreased in water sampled through 7 days from the site nearest runoff introduction, whereas C. fluminea deployed at this same site experienced 100% mortality after 26 days. Clams from lower sites survived wetland conditions, but growth and ChE activity were significantly decreased lower than that of clams from a control site. C. dubia exposed to water from these sites continued to have decreased survival throughout the 26-day sampling. Sediment sampled from 48 hours through 14 days at the lowest wetland site decreased the laboratory survival of Chironomus dilutus, and sediment from upper sites elicited an effect only on day 26. Although wetland concentrations of aqueous diazinon were decreased lower than toxic thresholds after 26 days, decreased ChE activity in deployed clams provided evidence of residual diazinon effects to deployed organisms.

Land use influences and ecotoxicological ratings for upper clinch river tributaries in virginia.

The Clinch River system of southwestern Virginia and northeastern Tennessee is among the most biodiverse aquatic ecosystems of the United States, but its fauna are in decline. Unionidae (freshwater mussel) species are a major component of the Clinch's aquatic community, and their decline is well documented. Point-source discharges within the Clinch drainage are few, and primary stressors on the biota are believed to originate from non-point sources that are transported into the mainstem by tributaries. Currently, the relative influences of tributaries as stressors on aquatic biota are unclear. We studied 19 major tributaries of the free-flowing Upper Clinch River, developed an Ecotoxicological Rating (ETR) utilizing eight parameters, and assessed stream quality among land use categories using the ETR rating system. Biological, toxicological, habitat, and chemical variables were measured in each tributary, near its confluence with the Clinch. Geographic Information System software was used to quantify land use within each tributary watershed; all tributary watersheds are predominately forested, but agricultural, mining, and developed land uses (urban, transportation) are also present. ETRs indicated that the tributaries draining mining-influenced watersheds had greater potential impact on the mainstem than those draining agricultural or forested watersheds, because of poor benthic macroinvertebrate scores. ETRs ranged from 44 to 63, on a 100-point scale, for mining-influenced tributaries compared to agricultural (57-86) and forested tributaries (64-91). Mean ETRs for the mining-influenced tributaries (51) were significantly different than ETRs from agricultural and forested streams (75 and 80, respectively), and the presence of developed land uses had no significant relationship with ETRs.

[Effects of eutrophication on distribution and population density of Corbicula fluminea and Bellamya sp. in Chaohu Lake].

The investigation on the distribution an d population density of C. fluminea and Bellamya sp. in Chaohu Lake during September 2001 and September 2002 showed that in the west region of the lake where was seriously eutrophic, the density and biomass of C. fluminea were 5.1 ind. x m(-2) and 17.87 g x m(-2) in 2001, and 8.8 ind. x m(-2) and 47.29 g x m(-2) in 2002, while those of Bellamya sp. were 13.3 ind. x m(-2) and 45.45 g x m(-2) in 2001, and 3.8 ind. x m(-2) and 12.56 g x m(-2) in 2002, respectively. In the east region of the lake where was eutrophic, the density and biomass of C. fluminea were 23.8 ind. x m(-2) and 67.86 g x m(-2) in 2001, and 29.2 ind. x m(-2) and 96.18 g x m(-2) in 2002, while those of Bellamya sp. were 10.1 ind. x m(-2) and 32.00 g x m(-2) in 2001, and 9.4 ind. x m(-2) and 31.21 g x m(-2) in 2002, respectively. The density and biomass of C. fluminea and Bellamya sp. were declined with increasing eutrophication. In hypertrophic region, C. fluminea and Bellamya sp. were absent. The density and biomass of the two species were obviously higher in littoral than in pelagic region. The distribution type of C. fluminea was core-model, while that of Bellamya sp. was random. The correlation between the density and biomass of C. fluminea and Bellamya sp. and water depth was not significant (P > 0.05). The biomass of Bellamya sp. was negatively correlated with water TN (P < 0.01), NO3-N (P < 0.05), TP(P < 0.01) and PO4-P (P < 0.05), while that of C. fluminea only had a significantly negative correlation with PO4-P(P < 0.05). Compared with 1981, there was fewer C. fluminea in the lake nowadays. The effects of other environmental factors on the population distribution and growth of C. fluminea and Bellamya sp. were also discussed.