Villosa Iris Research Articles

Clearance Rates of Villosa iris (Bivalvia: Unionidae) Fed Different Rations of the Alga Neochloris oleoabundans

We investigated effects of algal cell concentration and mussel size (shell length) on the clearance rate (CR) of the rainbow mussel, Villosa iris. Mussel were either batch-fed a single ration of algae for 24h, or were fed three different algal rations that were replenished every hour for 3 hours. Mean CR of V. iris batch fed a single ration (1.3 x 10 6 c/mL,

Toxicity of sediments potentially contaminated by coal mining and natural gas extraction to unionid mussels and commonly tested benthic invertebrates

Sediment toxicity tests were conducted to assess potential effects of contaminants associated with coal mining or natural gas extraction activities in the upper Tennessee River basin and eastern Cumberland River basin in the United States. Test species included two unionid mussels (rainbow mussel, Villosa iris, and wavy-rayed lampmussel, Lampsilis fasciola, 28-d exposures), and the commonly tested amphipod, Hyalella azteca (28-d exposure) and midge, Chironomus dilutus (10-d exposure). Sediments were collected from seven test sites with mussel communities classified as impacted and in proximity to coal mining or gas extraction activities, and from five reference sites with mussel communities classified as not impacted and no or limited coal mining or gas extraction activities. Additional samples were collected from six test sites potentially with high concentrations of polycyclic aromatic hydrocarbons (PAHs) and from a test site contaminated by a coal ash spill. Mean survival, length, or biomass of one or more test species was reduced in 10 of 14 test samples (71%) from impacted areas relative to the response of organisms in the five reference samples. A higher proportion of samples was classified as toxic to mussels (63% for rainbow mussels, 50% for wavy-rayed lampmussels) compared with amphipods (38%) or midge (38%). Concentrations of total recoverable metals and total PAHs in sediments did not exceed effects-based probable effect concentrations (PECs). However, the survival, length, or biomasses of the mussels were reduced significantly with increasing PEC quotients for metals and for total PAHs, or with increasing sum equilibrium-partitioning sediment benchmark toxic units for PAHs. The growth of the rainbow mussel also significantly decreased with increasing concentrations of a major anion (chloride) and major cations (calcium and magnesium) in sediment pore water. Results of the present study indicated that (1) the findings from laboratory tests were generally consistent with the field observations of impacts on mussel populations; (2) total recoverable metals, PAHs, or major ions, or all three in sediments might have contributed to the sediment toxicity; (3) the mussels were more sensitive to the contaminants in sediments than the commonly tested amphipod and midge; and (4) a sediment toxicity benchmark of 1.0 based on PECs may not be protective of mussels.

Toxicity of carbon nanotubes to freshwater aquatic invertebrates

Carbon nanotubes (CNTs) are hydrophobic in nature and thus tend to accumulate in sediments if released into aquatic environments. As part of our overall effort to examine the toxicity of carbon-based nanomaterials to sediment-dwelling invertebrates, we have evaluated the toxicity of different types of CNTs in 14-d water-only exposures to an amphipod (Hyalella azteca), a midge (Chironomus dilutus), an oligochaete (Lumbriculus variegatus), and a mussel (Villosa iris) in advance of conducting whole-sediment toxicity tests with CNTs. The results of these toxicity tests conducted with CNTs added to water showed that 1.00 g/L (dry wt) of commercial sources of CNTs significantly reduced the survival or growth of the invertebrates. Toxicity was influenced by the type and source of the CNTs, by whether the materials were precleaned by acid, by whether sonication was used to disperse the materials, and by species of the test organisms. Light and electron microscope imaging of the surviving test organisms showed the presence of CNTs in the gut as well as on the outer surface of the test organisms, although no evidence was observed to show penetration of CNTs through cell membranes. The present study demonstrated that both the metals solubilized from CNTs such as nickel and the "metal-free" CNTs contributed to the toxicity.

Acute effects of road salts and associated cyanide compounds on the early life stages of the unionid mussel Villosa iris

The toxicity of cyanide to the early life stages of freshwater mussels (order Unionida) has remained unexplored. Cyanide is known to be acutely toxic to other aquatic organisms. Cyanide-containing compounds, such as sodium ferrocyanide and ferric ferrocyanide, are commonly added to road deicing salts as anticaking agents. The purpose of the present study was to assess the acute toxicity of three cyanide compounds (sodium cyanide, sodium ferrocyanide, and ferric ferrocyanide), two road salts containing cyanide anticaking agents (Morton and Cargill brands), a brine deicing solution (Liquidow brand), and a reference salt (sodium chloride) on glochidia (larvae) and juveniles of the freshwater mussel Villosa iris. Sodium ferrocyanide and ferric ferrocyanide were not acutely toxic to glochidia and juvenile mussels at concentrations up to 1,000 mg/L and 100 mg/L, respectively. Lowest observed effect concentrations (LOECs) for these two chemicals ranged from 10 to >1,000 mg/L. Sodium cyanide was acutely toxic to juvenile mussels, with a 96-h median effective concentration (EC50) of 1.10 mg/L, although glochidia tolerated concentrations up to 10 mg/L. The EC50s for sodium chloride, Liquidow brine, Morton road salt, and Cargill road salt were not significantly different for tests within the same life stage and test duration (range, 1.66-4.92 g/L). These results indicate that cyanide-containing anticaking agents do not exacerbate the toxicity of road salts, but that the use of road salts and brine solutions for deicing or dust control on roads may warrant further investigation.

Population Characteristics of the MusselVillosa iris(Lea) (Rainbow Shell) in the Spring River Watershed, Arkansas

Abstract the goal of this study was to better understand population characteristics of Villosa iris (Lea) (Rainbow Shell) in the Spring River drainage in north-central Arkansas through documenting seasonal spatial patterns, movement behavior, population size, size-frequency distributions, sex ratios, and fecundity. We conducted monthly mark and recapture sampling between May and September 2007 (i.e., before, during, and after spawning) and documented the sex, size, fecundity, and spatial location of individual Rainbow Shell at 2 sites (SFSR1 and SR1). Population estimates were relatively high at both sites with 166 ± 32 (SE) and 381 ± 37 (SE) individuals at SFSR1 and SR1, respectively. Sex ratio was highly skewed toward males at SFSR1 with a ratio of 1.0:2.6, but only slightly skewed at SR1 with a ratio of 1.0:1.3. Mean fecundity was 27,849 ± 11,653 (SE) and 15,089 ± 11,710 (SE) glochidia at SFSR1 and SR1, respectively. Spatially, statistically more males were found upstream of non-gravid females during t...

Influence of dissolved organic carbon on toxicity of copper to a unionid mussel (Villosa iris) and a cladoceran (Ceriodaphnia dubia) in acute and chronic water exposures

Acute and chronic toxicity of copper (Cu) to a unionid mussel (Villosa iris) and a cladoceran (Ceriodaphnia dubia) were determined in water exposures at four concentrations of dissolved organic carbon (DOC; nominally 0.5, 2.5, 5, and 10 mg/L as carbon [C]). Test waters with DOC concentrations of 2.5 to 10 mg C/L were prepared by mixing a concentrate of natural organic matter (Suwannee River, GA, USA) in diluted well water (hardness 100 mg/L as CaCO(3) , pH 8.3, DOC 0.5 mg C/L). Acute median effect concentrations (EC50s) for dissolved Cu increased approximately fivefold (15-72 µg Cu/L) for mussel survival in 4-d exposures and increased about 11-fold (25-267 µg Cu/L) for cladoceran survival in 2-d exposures across DOC concentrations from 0.5 to 10 mg C/L. Similarly, chronic 20% effect concentrations (EC20s) for the mussel in 28-d exposures increased about fivefold (13-61 µg Cu/L for survival; 8.8-38 µg Cu/L for biomass), and the EC20s for the cladoceran in 7-d exposures increased approximately 17-fold (13-215 µg Cu/L) for survival or approximately fourfold (12-42 µg Cu/L) for reproduction across DOC concentrations from 0.5 to 10 mg C/L. The acute and chronic values for the mussel were less than or approximately equal to the values for the cladoceran. Predictions from the biotic ligand model (BLM) used to derive the U.S. Environmental Protection Agency's ambient water quality criteria (AWQC) for Cu explained more than 90% of the variation in the acute and chronic endpoints for the two species, with the exception of the EC20 for cladoceran reproduction (only 46% of variation explained). The BLM-normalized acute EC50s and chronic EC20s for the mussel and BLM-normalized chronic EC20s for the cladoceran in waters with DOC concentrations of 2.5 to 10 mg C/L were equal to or less than the final acute value and final chronic value in the BLM-based AWQC for Cu, respectively, indicating that the Cu AWQC might not adequately protect the mussel from acute and chronic exposure, and the cladoceran from chronic exposure.

Structural Community Changes in Freshwater Mussel Populations of Little Mahoning Creek, Pennsylvania

As part of a complete biotic survey for Little Mahoning Creek watershed, Western Pennsylvania Conservancy (WPC) used timed searches to survey for freshwater mussels along the entire mainstem of Little Mahoning Creek (56.8 km). The survey captured all historic sites sampled as early as 1905. The 15 sites revealed a high diversity of unionids (10 species) and several rare and endangered taxa, including Pleurobema sintoxia (Rafinesque, 1820), Villosa iris (I. Lea, 1829), and Alasmidonta marginata (Say, 1818). Present survey results indicate an established unionid community with several taxa increasing their distributions compared to historical surveys. Upstream dispersal was halted at the Savan Dam at river kilometer 36.69. No live or dead unionids were found at six sites upstream of the dam. Bray-Curtis similarity indices were calculated between present survey and historical survey accounts. Species composition in the present survey compares favorably (86.14%) with collections by Ortmann (1909) and Bogan and Davis (1992). Several locations have relatively high unionid diversity, despite being located in an area with anthropogenic perturbations.

A Survey of the Indigenous Microbiota (Bacteria) In Three Species of Mussels from the Clinch and Holston Rivers, Virginia

Freshwater mussel conservation efforts by many federal and state agencies have increased in recent years. This has led to a greater number of stream surveys, in which mussel die-offs involving high numbers of dead and moribund animals are being observed and reported with greater frequency. Typically, die-offs have been incidentally observed while research was being done for other purposes, therefore, accurate mortality data have been difficult to obtain. Specifically, seasonal die-offs were noted in localized areas of the Clinch and Holston Rivers, Virginia, and to lesser degrees, in neighboring rivers in this geographic region, including southeast Virginia. The observed mussel species affected were primarily the slabside pearlymussel (Lexingtonia dolabelloides) and to lesser extents, the pheasantshell (Actinonaias pectorosa), rainbow mussel (Villosa iris), and the endangered shiny pigtoe (Fusconaia cor). To determine if a bacterial pathogen might be involved in these recurring mussel die-offs, this study examined characteristics of the indigenous microbiota (bacteria) from healthy mussels from sites on the Clinch and Holston Rivers where die-offs were previously observed. These baseline data will allow for recognition of bacterial pathogens in future mussel die-offs. Means for total bacteria from soft tissues ranged from 1.77 × 105 to 3.55 × 106 cfu/g; whereas, the range in means from fluids was 2.92 × 104 to 8.60 × 105 cfu/mL. A diverse microbiota were recovered, including species that are common in freshwater aquatic environments. The most common bacterial groups recovered were motile Aeromonas spp. and nonfermenting bacteria. Flavobacterium columnare, a pathogen to cool- and warm-water fishes was recovered from one specimen, a Villosa iris from the Clinch River.

Chronic toxicity of copper and ammonia to juvenile freshwater mussels (unionidae)

The objectives of the present study were to develop methods for conducting chronic toxicity tests with juvenile mussels under flow-through conditions and to determine the chronic toxicity of copper and ammonia to juvenile mussels using these methods. In two feeding tests, two-month-old fatmucket (Lampsilis siliquoidea) and rainbow mussel (Villosa iris) were fed various live algae or nonviable algal mixture for 28 d. The algal mixture was the best food resulting in high survival (>or=90%) and growth. Multiple copper and ammonia toxicity tests were conducted for 28 d starting with two-month-old mussels. Six toxicity tests using the algal mixture were successfully completed with a control survival of 88 to 100%. Among copper tests with rainbow mussel, fatmucket, and oyster mussel (Epioblasma capsaeformis), chronic value ([ChV], geometric mean of the no-observed-effect concentration and the lowest-observed-effect concentration) ranged from 8.5 to 9.8 microg Cu/L for survival and from 4.6 to 8.5 microg Cu/L for growth. Among ammonia tests with rainbow mussel, fatmucket, and wavy-rayed lampmussel (L. fasciola), the ChV ranged from 0.37 to 1.2 mg total ammonia N/L for survival and from 0.37 to 0.67 mg N/L for growth. These ChVs were below the U.S. Environmental Protection Agency 1996 chronic water quality criterion (WQC) for copper (15 microg/L; hardness 170 mg/L) and 1999 WQC for total ammonia (1.26 mg N/L; pH 8.2 and 20 degrees C). Results indicate that toxicity tests with two-month-old mussels can be conducted for 28 d with >80% control survival; growth was frequently a more sensitive endpoint compared to survival; and the 1996 chronic WQC for copper and the 1999 chronic WQC for total ammonia might not be adequately protective of the mussel species tested. However, a recently revised 2007 chronic WQC for copper based on the biotic ligand model may be more protective in the water tested.

Adaptation of the antioxidant defence system in hydrothermal‐vent mussels (Bathymodiolus azoricus) transplanted between two Mid‐Atlantic Ridge sites

AbstractThe vent mussel Bathymodiolus azoricus is the dominant member of the Northern Mid‐Atlantic Ridge (MAR) hydrothermal megafauna, and lives in an environment characterized by temporal and spatial variations in the levels of heavy metals, methane and hydrogen sulphide, substances which are known to increase reactive oxygen species levels in the tissues of exposed organisms. To evaluate the effects of two contrasting hydrothermal environments on the antioxidant defence system of this vent mussel species, a 2‐week transplant experiment was carried out involving mussels collected from the relatively deep (2300 m), and chemical rich, Rainbow vent field. These were transplanted to the shallower (1700 m), and relatively less toxic, Lucky Strike vent field. To achieve this objective, levels of superoxide dismutase, catalase (CAT), total glutathione peroxidase (GPx), selenium‐dependent glutathione peroxidase and lipid peroxidation (LPO) were measured in the gills and mantle tissues of resident and transplant mussels before and after the transplant experiment. With the exception of CAT, the gills of the transplanted mussels had significantly higher antioxidant enzyme activity compared with the basal levels in the donor (Rainbow) and recipient (Lucky Strike) populations; whereas the antioxidant enzyme levels in the mantle tissues of the transplants reflected the baseline levels of activity in the native Lucky Strike mussels after 2 weeks. In contrast, LPO levels were significantly higher in both tissue types in the transplants than in either the source or the recipient populations, which suggested a response to hydrostatic pressure change (note, the transplant animals were brought to the surface for transportation between the two vent fields). The fact that the Rainbow mussels survived the transplant experience indicates that B. azoricus has a very robust constitution, which enables it to cope behaviourally, physiologically and genetically with the extreme conditions found in its naturally contaminated deep‐sea environment.

Anatomical descriptions and comparison of the reproductive tracts of Utterbackia imbecillis and Villosa iris (Bivalvia: Unionidae)

Summary The reproductive tracts of dioecious Villosa iris (Lea, 1829) and hermaphroditic Utterbackia imbecillis (Say, 1829) are described and compared in sections of viscera examined with light and transmission electron microscopy. In both species, gametes are transported via ciliated gonoducts to a collecting gonosinus, connected to a ciliated genital duct by a highly rugated and musculaturized gonopore. This gonopore may be sphinctural and important for retaining gametes in the gonosinus for timely release. The genital duct is separate from the kidney and leads to the suprabranchial chamber. Epithelia of the gonoducts and gonosinuses of U. imbecillis, but not V. iris, contain secretory cells whose granules stain positive with periodic acid/Schiff (PAS), indicating the presence of carbohydrates or glycoproteins. Examinations of reproductive tracts of other species revealed that those of Elliptio complanata (Lightfoot, 1786), Lexingtonia dolabelloides (Lea, 1840), Villosa vanuxemensis (Lea, 1838), and Lampsilis fasciola Rafinesque, 1820 are similar to those of V. iris and U. imbecillis, except that only the tracts of U. imbecillis contain PAS-positive secretory cells. The gonoducts and gonosinuses of all species examined had an abundance of cilia and microvilli. We hypothesize that the numerous microvilli in the reproductive tracts may indicate intra-luminal regulation of important ion and glucose concentrations, and that the PAS-positive secretions of U. imbecillis may temporarily inhibit selffertilization.

Determining a Suitable Substrate Size and Sampling Frequency for Rearing Juvenile Rainbow Mussels Villosa iris

AbstractThe effects of sampling frequency and substrate size on the overall size and survival of juvenile rainbow mussels Villosa iris were investigated in 4‐L round flow‐through tanks. All tanks contained either fine sediment (<50 μm), fine limestone sand (500–850 μm), or coarse limestone sand (1,000–2,500 μm) and were sampled every 2 weeks or once at the end of the 10‐week experiment. Tanks left unsampled for 10 weeks had 12.8% higher survival regardless of substrate treatment. Juveniles in unsampled tanks also had greater shell length than those in sampled tanks. Juveniles cultured in coarse sand had the best survival in the sampled tanks (36.4%), and juveniles reared in fine sand had the best survival in the unsampled tanks (51.9% at 10 weeks). Analyses of gut contents at 10 weeks revealed that juveniles were consuming large amounts of detritus and algal cells 5–10 μm in size, primarily Coelastrum, Chlorococcum, Chlorella, and Navicula spp. These results show that frequent disturbance of juveniles by sampling may impede physiological functions, resulting in stress and a decrease in overall survival and shell length. It also appears that fine limestone sand (500–800 μm in size) is the best substrate for juvenile culture purposes in similar rearing systems.

Chlorine toxicity to early life stages of freshwater mussels (Bivalvia: Unionidae)

Chlorine (Cl) is a highly toxic, widely used halogen disinfectant that is present in point-source pollution discharges from wastewater treatment plants and industrial facilities. The U.S. Environmental Protection Agency freshwater criteria for Cl are 19 microg total residual Cl (TRC)/L as a maximum 1-h average concentration and 11 microg TRC/L as a maximum 4-d average; however, toxicological data for unionids were not used in these calculations. To address this void in the data, we conducted acute tests with glochidia from several species and 21-d bioassays with three-month-old Epioblasma capsaeformis and three-, six-, and 12-month-old Villosa iris juveniles. The 24-h lethal concentration 50 values for glochidia were between 70 and 220 [Lg TRC/L, which are 2.5 to 37 times higher than those reported in other studies for cladocerans. Significant declines in growth and survivorship were observed in the 21-d test with E. capsaeformis at 20 microg TRC/L. Lowest-observed-adverse-effects concentrations in bioassays with juvenile V. iris were higher (30-60 microg TRC/L) but showed a significant trend of declining toxicity with increased age. Although endpoints were above water quality criteria, the long life spans of unionids and potential implications of chronic exposure to endangered juvenile mussels still warrant concern.

Use of Bivalve Metrics to Quantify Influences of Coal-related Activities in the Clinch River Watershed, Virginia

Previously, we reported that survivorship and growth of field-caged Asian clams (Corbicula fluminea [Muller]) were significantly reduced downstream of the wastewater effluent discharge of the Clinch River Plant (CRP), a coal-fired electric power-generating facility in Russell County, VA (USA). These findings warranted the present study, which investigated whether reduced survivorship and growth of transplanted C. fluminea were predictive of adverse effects on resident bivalves – most notably the Clinch River’s (CR’s) federally protected freshwater mussel fauna (Unionoidea). Thus, surveys of unionoid assemblages and C. fluminea population densities and age distributions were conducted to assess ecotoxicological effects on bivalve assemblages naturally occurring in the CR. Results of these surveys suggested that field bioassays with transplanted C. fluminea were predictive of in-stream C. fluminea densities and the presence/absence of indigenous unionoid assemblages. Relative to C. fluminea, additional field bioassays with a juvenile unionoid species (Villosa iris) native to the CR were less predictive of adverse effects on resident bivalves. Concurrence of transplant studies and in-stream surveys was evident at most study sites, particularly within 0.6 km downstream of the CRP effluent where resident bivalves were virtually non-existent relative to other stream sites having similar habitat conditions. Our findings indicate that in situ field bioassays with transplanted C. fluminea are valuable tools for predicting in stream occurrence and distribution of resident freshwater bivalves, and that field studies integrating multiple bivalve metrics may be useful for prioritizing source-reduction efforts in similar watersheds. Discrepancies observed for transplanted C. fluminea and V. iris have important implications to selection of bivalve species used in field bioassays and warrant further study.

CROSS-RESISTANCE OF LARGEMOUTH BASS TO GLOCHIDIA OF UNIONID MUSSELS

We tested whether host fish that acquired resistance to glochidia of one mussel species were cross-resistant to glochidia of other species. Largemouth bass (Micropterus salmoides) were primed with 4-5 successive infections of glochidia of Lampsilis reeveiana. The percentage of attached glochidia that survived and transformed to the juvenile stage (transformation success) was compared between primed fish and naïve controls. Transformation success of L. reeveiana, Lampsilis abrupta, Villosa iris, and Utterbackia imbecillis was significantly lower on primed fish (37.8%, 43.5%, 67.0%, and 13.2%, respectively) than on control fish (89.0%, 89.7%, 90.0%, and 22.2% respectively). Immunoblotting was used to analyze the binding of serum antibodies from primed fish with glochidia proteins. Antibodies bound to glochidia proteins of similar molecular weight from L. reeveiana and L. abrupta. Bound proteins of V. iris differed in molecular weight from those of the Lampsilis species. There was no binding to specific glochidia proteins of U. imbecillis or Strophitus undulatus. Our results indicate that host-acquired resistance can extend across mussel genera and subfamilies and might involve both specific and nonspecific mechanisms. Understanding the specificity of acquired resistance of hosts to glochidia could enhance understanding of the evolutionary and ecological relationships between mussels and their host fishes.

Diversity of the Unionidae in the Rocky River, Ohio

ABSTRACT We surveyed the freshwater mussels (Mollusca: Bivalvia: Unionidae) of the Rocky River, Ohio, USA, a river surrounded by suburban development. The survey produced 253 live unionid specimens and 572 empty shells. Most occurred in the west branch. Species living in the West Branch Rocky River included Anodontoides ferussacianus, Elliptio dilatata, Lampsilis cardium, Lampsilis radiata luteola, Lasmigona compressa, Lasmigona costata, Pyganodon grandis grandis, Strophitus undulatus undulatus, and Toxolasma parvus. Two additional species (Utterbackia imbecillis and Villosa iris iris) were represented as dead shells. Three species (Potamilis alatus, Quadrula quadrula and Leptodea fragilis) were found only near the mouth of the main stem of the river. No live mussels were found in the east branch. Although mussel diversity changed along the river, the presence of healthy mussel populations downstream of two expanding suburban areas suggests that these developments so far have minimally impacted populations.

Factors Affecting Survival and Growth of Juvenile Freshwater Mussels Cultured in Recirculating Aquaculture Systems

AbstractSeasonal differences in glochidial maturity, substrate, and diet were studied to determine how these factors affect the survival and growth of juvenile freshwater mussels. Comparisons were made between juveniles produced in the fall and spring of the year; cultured in sediment, sand, or without substrate; and fed either of two species of small (5–10‐μm) green algae. The survival and growth of endangered juveniles of oyster mussel Epioblasma capsaeformis were compared with those of a common, seemingly more robust species, the rainbow mussel Villosa iris. The growth of rainbow mussel juveniles was significantly greater than that of oyster mussel juveniles (P < 0.001). The survival and growth of oyster mussel juveniles were significantly greater when propagated in the spring, that is, when glochidia were mature and would normally be released, than in fall (P < 0.001). Survival and growth of juveniles of both species were significantly greater when they were cultured in a sediment substratum rather than sand or no substratum (P < 0.001). No differences (P > 0.05) were observed in survival and growth of juveniles fed algal species Neochloris oleoabundans or Nannochloropsis oculata. In the spring of the year, juvenile oyster mussels achieved a survival of 29.6% and mean length of 664 μm at 60 d of age, whereas at the same age rainbow mussel juveniles exhibited a survival of 25.1% and a mean length of 1,447 μm.

Potential effects of Asian clam (Corbicula fluminea) die-offs on native freshwater mussels (Unionidae) I: water-column ammonia levels and ammonia toxicity

The Asian clam (Corbicula fluminea) co-occurs with unionid mussels in many riverine ecosystems. Clam populations can reach high densities and may undergo rapid die-offs, particularly during the low flow and warm temperatures of summer drought. Our study objective was to determine whether ammonia produced by decaying clam tissues during die-offs could affect unionid mussels. We induced C. fluminea die-offs in artificial streams to simulate die-off effects in natural habitats, and measured total and unionized ammonia (NH3-N) and dissolved oxygen (DO) in the overlying water. When water flow was stopped, reductions in DO preceded the onset of mortality in streams having the highest density of clams (∼10,000 clams/m2). NH3-N concentrations in the overlying water increased in association with clam mortality and reached concentrations of up to 5.04 mg/L at 26 ± 2°C. Temperature significantly influenced the rate of DO reduction and NH3-N production in the systems, while resumption of water flow led to rapid dissipation of NH3-N from the water column. We also conducted laboratory experiments to determine median lethal concentrations (LC50s) of total ammonia and NH3-N for glochidia and juveniles of the unionid mussel Villosa iris, adults of the unionid Pyganodon grandis, and juveniles and adults of C. fluminea. The 96-h LC50s (24-h for V. iris glochidia) for NH3-N ranged from 0.11 mg/L for V. iris glochidia to 0.8 mg/L for adult C. fluminea, indicating that NH3-N levels produced by Asian clam die-offs have the potential to exceed acute effects levels for at least some species of unionid mussels.

Acute and chronic toxicity of mercury to early life stages of the rainbow mussel, Villosa iris (Bivalvia: Unionidae)

Mercury (Hg) contamination is receiving increased attention globally because of human health and environmental concerns. Few laboratory studies have examined the toxicity of Hg on early life stages of freshwater mussels, despite evidence that glochidia and juvenile life stages are more sensitive to contaminants than adults. Three bioassays (72-h acute glochidia, 96-h acute juvenile, and 21-d chronic juvenile toxicity tests) were conducted by exposing Villosa iris to mercuric chloride salt (HgCl2). Glochidia were more sensitive to acute exposure than were juvenile mussels, as 24-, 48-, and 72-h median lethal concentration values (LC50) for glochidia were >107, 39, and 14 microg Hg/L, respectively. The 24-, 48-, 72-, and 96-h values for juveniles were 162, 135, 114, and 99 microg Hg/L, respectively. In the chronic test, juveniles exposed to Hg treatments > or = 8 microg/L grew significantly less than did control organisms. The substantial difference in juvenile test endpoints emphasizes the importance of assessing chronic exposure and sublethal effects. Overall, our study supports the use of glochidia as a surrogate life stage for juveniles in acute toxicity tests. However, as glochidia may be used only in short-term tests, it is imperative that an integrated approach be taken when assessing risk to freshwater mussels, as their unique life history is atypical of standard test organisms. Therefore, we strongly advocate the use of both glochidia and juvenile life stages for risk assessment.

An Evaluation of Selective Feeding by Three Age‐Groups of the Rainbow Mussel Villosa iris

AbstractA tri‐algal diet was fed to three age‐groups of the rainbow mussel Villosa iris: ages 2–3 d, 50–53 d, and 3–6 years. Changes in the relative abundance of each algal species were determined in 5‐h feeding trials from feeding chambers and by gut content analyses. All age‐groups rejected Scenedesmus quadricauda and preferentially selected Nannochloropsis oculata and Selenastrum capricornutum, principally on the basis of size. Changes in the relative abundance of algae in feeding chambers did not differ significantly among age‐groups. Observed differences in the ingested quantities of the similar‐sized N. oculata and S. capricornutum were attributed to other particle‐related characteristics. Results indicate that the rainbow mussel can be fed similar‐sized algae at all ages in captive propagation facilities. When developing a suitable algal diet for rearing juvenile mussels, one probably need not investigate different species at each stage of development if the algae used are in the 2.8–8.5‐μm size range.