Lampsilis Siliquoidea Research Articles

Consequences of Dam Removal on Mussel Assemblages (Unionidae) in the Cuyahoga River

The primary objective of a new survey of the Cuyahoga River was to assess species richness and population abundance of various mussel species in the family Unionidae throughout the Middle Cuyahoga River and upper parts of the Lower Cuyahoga River. Historically, few records existed for this river between Lake Rockwell and the Cuyahoga Valley National Park, a region in which four dams have been removed in the past 12 years. Timed visual surveys were conducted during low flow conditions and by using tactile techniques in deeper water. Throughout the survey, only 37 live animals were located across the 18 Middle Cuyahoga River sites inspected, which included only Lampsilis siliquoidea, Pyganodon grandis and the state-endangered Ligumia nasuta. No live mussels were found between the Gorge and the Cuyahoga Valley National Park. That 434 shells and valves were collected, and all but two were classified as long dead, attests that mussels had been more abundant, and that at least nine of the ten species known to be present above Lake Rockwell had lived in the Middle Cuyahoga River. Remote sensing data and aerial photographs were used to characterize change in opening up the river, but benefits to water quality and stream flow subsequent to dam removal must be tempered with the apparent loss of an assemblage of mussels better adapted to lentic conditions.

Modulation of near-bed hydrodynamics by freshwater mussels in an experimental channel

Freshwater mussels are important ecosystem engineers, and recent studies have illustrated their many ecological contributions, but little is known about the interaction between mussels and their surrounding flow environment at the organism scale. In the present experimental campaign, we examine the hydraulic interactions between mussels and open-channel flow. We quantify how a mussel-covered bed alters bed roughness and near-bed turbulent flow, determine the filter behavior and capacity of live Lampsilis siliquoidea, and design a model mussel to simulate live mussel filtering to examine the impact of the biologically mediated activity of filter feeding on near-bed turbulent flow. In comparison to a gravel bed, a mussel-covered bed increased shear velocity by 28% and bed roughness by nearly 300%, and significantly reduced near-bed flow velocity. The filter velocity in L. siliquoidea varied within and between individuals, and ranged from 0.4 to 20 cm/s. The excurrent flow of the model mussel accurately simulated excurrent flow observed in live mussels and, when subjected to various boundary conditions, altered water velocity and turbulent kinetic energy downstream. The ability to describe and quantify these hydrodynamic interactions provides new insight into how mussels modulate near-bed flow and mixing processes, which can contribute to future conservation efforts.

Chronic toxicity of azoxystrobin to freshwater amphipods, midges, cladocerans, and mussels in water-only exposures.

Understanding the effects of fungicides on nontarget organisms at realistic concentrations and exposure durations is vital for determining potential impacts on aquatic ecosystems. Environmental concentrations of the fungicide azoxystrobin have been reported up to 4.6 μg/L in the United States and 30 μg/L in Europe. The objective of the present study was to evaluate the chronic toxicity of azoxystrobin in water-only exposures with an amphipod (Hyalella azteca; 42-d exposure), a midge (Chironomus dilutus; 50-d exposure), a cladoceran (Ceriodaphnia dubia; 7-d exposure), and a unionid mussel (Lampsilis siliquoidea; 28-d exposure) at environmentally relevant concentrations. The potential photo-enhanced toxicity of azoxystrobin accumulated by C. dubia and L. siliquoidea following chronic exposures to azoxystrobin was also evaluated. The 20% effect concentrations (EC20s) based on the most sensitive endpoint were 4.2 μg/L for H. azteca reproduction, 12 μg/L for C. dubia reproduction and C. dilutus emergence, and >28 μg/L for L. siliquoidea. Hyalella azteca was more sensitive to azoxystrobin compared with the other 3 species in the chronic exposures. No photo-enhanced toxicity was observed for either C. dubia or L. siliquoidea exposed to ultraviolet light in control water following azoxystrobin tests. The results of the present study indicate chronic effects of azoxystrobin on 3 of 4 invertebrates tested at environmentally relevant concentrations. The changes noted in biomass and reproduction have the potential to alter the rate of ecological processes driven by aquatic invertebrates. Environ Toxicol Chem 2017;36:2308-2315. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Effects of food resources on the fatty acid composition, growth and survival of freshwater mussels.

Increased nutrient and sediment loading in rivers have caused observable changes in algal community composition, and thereby, altered the quality and quantity of food resources available to native freshwater mussels. Our objective was to characterize the relationship between nutrient conditions and mussel food quality and examine the effects on fatty acid composition, growth and survival of juvenile mussels. Juvenile Lampsilis cardium and L. siliquoidea were deployed in cages for 28 d at four riverine and four lacustrine sites in the lower St. Croix River, Minnesota/Wisconsin, USA. Mussel foot tissue and food resources (four seston fractions and surficial sediment) were analyzed for quantitative fatty acid (FA) composition. Green algae were abundant in riverine sites, whereas cyanobacteria were most abundant in the lacustrine sites. Mussel survival was high (95%) for both species. Lampsilis cardium exhibited lower growth relative to L. siliquoidea (p <0.0001), but growth of L. cardium was not significantly different across sites (p = 0.13). In contrast, growth of L. siliquoidea was significantly greater at the most upstream riverine site compared to the lower three lacustrine sites (p = 0.002). In situ growth of Lampsilis siliquoidea was positively related to volatile solids (10 – 32 μm fraction), total phosphorus (<10 and 10 – 32 μm fractions), and select FA in the seston (docosapentaeonic acid, DPA, 22:5n3; 4,7,10,13,16-docosapentaenoic, 22:5n6; arachidonic acid, ARA, 20:4n6; and 24:0 in the <10 and 10 – 32 μm fractions). Our laboratory feeding experiment also indicated high accumulation ratios for 22:5n3, 22:5n6, and 20:4n6 in mussel tissue relative to supplied algal diet. In contrast, growth of L. siliquiodea was negatively related to nearly all FAs in the largest size fraction (i.e., >63 μm) of seston, including the bacterial FAs, and several of the FAs associated with sediments. Reduced mussel growth was observed in L. siliquoidea when the abundance of cyanobacteria exceeded 9% of the total phytoplankton biovolume. Areas dominated by cyanobacteria may not provide sufficient food quality to promote or sustain mussel growth.

Application of OEPA-Produced Biotic Indices and Physical Stream Measurements to Assess Freshwater Mussel (Unionidae) Habitat in the Upper Mahoning River, Ohio

Freshwater mussels continue to experience declines in population numbers in response to changing environments. Identifying aspects of the environment associated with the presence and abundance of mussels in small streams is challenging where past records are minimal. Thus, we sought to produce models of habitat favoring mussel species richness and abundance in the upper Mahoning River using data collected in 2 ways: (1) surveying sites deemed as suitable habitat via observation and (2) surveying existing Ohio Environmental Protection Agency (OEPA) sites used to evaluate water quality and aquatic life through biotic indices. Detailed physical measurements were added at each survey site. Surveys identified 963 freshwater mussels of 11 species. The more-forested Eagle Creek contained an abundant mussel assemblage compared to the rest of the Upper Mahoning River, yet this stream was still dominated by just 1 common species, Lampsilis siliquoidea (Fatmucket). Drainage area alone correlated with mussel richness and abundance, but a complex model of multiple characteristics provided equivalent predictive power to assess how variation in environmental components may enhance the likelihood of mussel presence. The OEPA composite qualitative habitat evaluation index, which encompasses substrate, instream cover, channel morphology, riparian zone, pool quality, and map gradient, also was indicative of greater mussel diversity.

Toxicity of Chromium (VI) to Two Mussels and an Amphipod in Water-Only Exposures With or Without a Co-stressor of Elevated Temperature, Zinc, or Nitrate.

The objectives of the present study were to develop methods for propagating western pearlshell (Margaritifera falcata) for laboratory toxicity testing and evaluate acute and chronic toxicity of chromium VI [Cr(VI)] to the pearlshell and a commonly tested mussel (fatmucket, Lampsilis siliquoidea at 20°C or in association with a co-stressor of elevated temperature (27°C), zinc (50µg Zn/L), or nitrate (35mg NO3/L). A commonly tested invertebrate (amphipod, Hyalella azteca) also was tested in chronic exposures. Newly transformed pearlshell (~1week old) were successfully cultured and tested in acute 96h Cr exposures (control survival 100%). However, the grow-out of juveniles in culture for chronic toxicity testing was less successful and chronic 28-day Cr toxicity tests started with 4month-old pearlshell failed due to low control survival (39-68%). Acute median effect concentration (EC50) for the pearlshell (919µg Cr/L) and fatmucket (456µg Cr/L) tested at 20°C without a co-stressor decreased by a factor of > 2 at elevated temperature but did not decrease at elevated Zn or elevated NO3. Chronic 28-day Cr tests were completed successfully with the fatmucket and amphipod (control survival 83-98%). Chronic maximum acceptable toxicant concentration (MATC) for fatmucket at 20°C (26µg Cr/L) decreased by a factor of 2 at elevated temperature or NO3 but did not decrease at elevated Zn. However, chronic MATC for amphipod at 20°C (13µg Cr/L) did not decrease at elevated temperature, Zn, or NO3. Acute EC50s for both mussels tested with or without a co-stressor were above the final acute value used to derive United States Environmental Protection Agency acute water quality criterion (WQC) for Cr(VI); however, chronic MATCs for fatmucket at elevated temperature or NO3 and chronic MATCs for the amphipod at 20°C with or without elevated Zn or NO3 were about equal to the chronic WQC. The results indicate that (1) the elevated temperature increased the acute Cr toxicity to both mussel species, (2) fatmucket was acutely more sensitive to Cr than the pearlshell, (3) elevated temperature or NO3 increased chronic Cr toxicity to fatmucket, and (4) acute WQC are protective of tested mussels with or without a co-stressor; however, the chronic WQC might not protect fatmucket at elevated temperature or NO3 and might not protect the amphipod at 20°C with or without elevated Zn or NO3.

The effects of pharmaceuticals on a unionid mussel (Lampsilis siliquoidea): An examination of acute and chronic endpoints of toxicity across life stages.

The toxicity and bioconcentration of 3 pharmaceuticals (amitriptyline, iopamidol, and sertraline) were examined using multiple life stages (larval, juvenile, and adult) of the unionid mussel Lampsilis siliquoidea. The endpoints examined varied with life stage but included survival, behavior (algal clearance rate, filtering frequency), and oxidative stress. Iopamidol was not toxic at concentrations up to 101 mg/L. Sertraline was the most toxic chemical (50% lethal concentrations [LC50] and effect concentrations [EC50] = 0.02-0.04 mg/L), but exposure did not induce oxidative stress. Glochidia and juveniles were more sensitive than adult mussels. Algal clearance rate in juvenile mussels was the most sensitive endpoint assessed, similar to or lower than the LC50 values for glochidia. However, the compounds examined were not toxic at concentrations detected in the environment. The relative bioconcentration factors were sertraline > amitriptyline > iopamidol. These results suggest that glochidia toxicity could be a screening tool for rapidly assessing the toxicity of chemicals of concern to freshwater mussels. Environ Toxicol Chem 2017;36:1572-1583. © 2016 SETAC.

Tetrahymena glochidiophila n. sp., a new species of Tetrahymena (Ciliophora) that causes mortality to glochidia larvae of freshwater mussels (Bivalvia).

A ciliate protozoan was discovered whose presence coincided with a rapid decrease in the viability (i.e. ability to close valves) of glochidia of the freshwater mussel Lampsilis siliquoidea. Microscopic examination showed it to be a histophagous tetrahymenine ciliate. Small subunit (SSU) rRNA and cytochrome c oxidase subunit 1 (cox1) barcode sequences from cultured cells showed that it belongs to the same new species isolated from water samples as a free-living ciliate. Phylogenetic analyses place this new ciliate in the same clade with the macrostome species Tetrahymena paravorax, and we propose the name T. glochidiophila n. sp. for this new species. The phylogeny provides further support for the hypothesis that histophagy was a life history trait of the ancestor of Tetrahymena.

Acute sensitivity of a broad range of freshwater mussels to chemicals with different modes of toxic action.

Freshwater mussels, one of the most imperiled groups of animals in the world, are generally underrepresented in toxicity databases used for the development of ambient water quality criteria and other environmental guidance values. Acute 96-h toxicity tests were conducted to evaluate the sensitivity of 5 species of juvenile mussels from 2 families and 4 tribes to 10 chemicals (ammonia, metals, major ions, and organic compounds) and to screen 10 additional chemicals (mainly organic compounds) with a commonly tested mussel species, fatmucket (Lampsilis siliquoidea). In the multi-species study, median effect concentrations (EC50s) among the 5 species differed by a factor of ≤2 for chloride, potassium, sulfate, and zinc; a factor of ≤5 for ammonia, chromium, copper, and nickel; and factors of 6 and 12 for metolachlor and alachlor, respectively, indicating that mussels representing different families or tribes had similar sensitivity to most of the tested chemicals, regardless of modes of action. There was a strong linear relationship between EC50s for fatmucket and the other 4 mussel species across the 10 chemicals (r2 = 0.97, slope close to 1.0), indicating that fatmucket was similar to other mussel species; thus, this commonly tested species can be a good surrogate for protecting other mussels in acute exposures. The sensitivity of juvenile fatmucket among different populations or cultured from larvae of wild adults and captive-cultured adults was also similar in acute exposures to copper or chloride, indicating captive-cultured adult mussels can reliably be used to reproduce juveniles for toxicity testing. In compiled databases for all freshwater species, 1 or more mussel species were among the 4 most sensitive species for alachlor, ammonia, chloride, potassium, sulfate, copper, nickel, and zinc; therefore, the development of water quality criteria and other environmental guidance values for these chemicals should reflect the sensitivity of mussels. In contrast, the EC50s of fatmucket tested in the single-species study were in the high percentiles (>75th) of species sensitivity distributions for 6 of 7 organic chemicals, indicating mussels might be relatively insensitive to organic chemicals in acute exposures. Environ Toxicol Chem 2017;36:786-796. Published 2016 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Effects of carbon dioxide on juveniles of the freshwater mussel (Lampsilis siliquoidea [Unionidae]).

Carbon dioxide (CO2 ) has shown promise as a tool to control movements of invasive Asian carp, but its effects on native freshwater biota have not been well studied. The authors evaluated lethal and sublethal responses of juvenile fatmucket (Lampsilis siliquoidea) mussels to CO2 at levels (43-269 mg/L, mean concentration) that bracket concentrations effective for deterring carp movement. The 28-d lethal concentration to 50% of the mussels was 87.0 mg/L (95% confidence interval [CI] 78.4-95.9) and at 16-d postexposure, 76.0 mg/L (95% CI 62.9-90.3). A proportional hazards regression model predicted that juveniles could not survive CO2 concentrations >160 mg/L for more than 2 wk or >100 mg/L CO2 for more than 30 d. Mean shell growth was significantly lower for mussels that survived CO2 treatments. Growth during the postexposure period did not differ among treatments, indicating recovery of the mussels. Also, CO2 caused shell pitting and erosion. Behavioral effects of CO2 included movement of mussels to the substrate surface and narcotization at the highest concentrations. Mussels in the 110 mg/L mean CO2 treatment had the most movements in the first 3 d of exposure. If CO2 is infused continuously as a fish deterrent, concentrations <76 mg/L are recommended to prevent juvenile mussel mortality and shell damage. Mussels may survive and recover from brief exposure to higher concentrations. Environ Toxicol Chem 2017;36:671-681. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

The response of two species of unionid mussels to extended exposure to elevated carbon dioxide

Changes in environmental conditions can act as stressors, with potential consequences for the health and fitness of organisms. Rising levels of carbon dioxide (CO2) is one potential environmental stressor that is occurring more frequently in the environment and can be a stressor for aquatic organisms. In this study, the physiological responses of two species of unionid mussel, Lampsilis siliquoidea and Amblema plicata, were assessed in response to exposure to two levels of elevated partial pressure of CO2 (pCO2) (~20,000 and ~55,000μatm) over a 28d period, followed by a subsequent 14d recovery period. Observations were consistent with responses associated with respiratory acidosis, as demonstrated by changes in hemolymph HCO3−, Ca2+, Cl−, and Na2+. Both species exposed to elevated pCO2 had elevated hemolymph HCO3– during the pCO2 treatment period compared to control mussels, but recovered once pCO2 was removed. Similarly, both species had elevated hemolymph Na+ during exposure to elevated pCO2, and this returned to control levels for A. plicata but remained elevated for L. siliquoidea once the pCO2 stimuli was removed. Changes in hemolymph Ca2+ and Cl− in response to elevated pCO2 were also observed, but these changes were species-specific. Additional physiological responses to elevated pCO2 (e.g., changes in hemolymph glucose and Mg2+) were consistent with a stress response in both species. This study demonstrates the importance of considering inter-specific differences in the response of organisms to stress, and also that responses to elevated pCO2 may be transient and can recover once the stress is removed.

Stress-induced variation in host susceptibility to parasitic freshwater mussel larvae

An increasing number of studies demonstrate the critical role of the host–parasite relationship for the persistence and distribution of freshwater mussels. Laboratory experiments are a powerful tool for quantifying the physiological compatibility between parasitic mussel larvae and fish hosts and are clearly applicable to species conservation. Recent findings, however, indicate potential need to control for biases caused by infection intensity and host stress responses. We tested glochidia metamorphosis success and host plasma cortisol response using Lampsilis siliquoidea glochidia on Lepomis macrochirus. The main aims were to (1) compare metamorphosis success in response to infection intensity (number of attached glochidia per fish) and (2) compare metamorphosis success between typical and reduced-stress approaches to the handling and infection of host fish. We found no effect of the glochidia bath density used to infect the fish (1000–4000–8000 glochidia l−1) or the resulting infection intensity on metamorphosis success, although host plasma cortisol was correlated with infection intensity at 24 h post infection. Small but statistically significant differences in metamorphosis success were observed between the typical and reduced-stress approaches. Overall, typical host compatibility testing methods appear to be robust to these variables, but more emphasis on standardizing laboratory protocols may provide more repeatable data.

Algal flux affects the clearance rates of recently metamorphosed freshwater mussels

Despite their role as ecosystem engineers, which is in large part a consequence of their suspension feeding activities, the early life history of unionid mussels is not well understood. We examined the suspension feeding rates (i.e., clearance rates, CR) of recently metamorphosed juvenile Lampsilis siliquoidea (1–4 week old), Lampsilis fasciola (1–3 week old), Villosa iris (2 week old), and Ligumia nasuta (1 week old) under ecologically relevant flux conditions in a recirculating racetrack flow chamber system. The range of velocities examined was determined experimentally using a permeameter containing riverbed material (63 μm to 6.5 cm diameter) in which juvenile mussels are thought to reside. The CR of the juvenile unionid species increased linearly with algal flux and the ranking of CR among species was V. iris > L. siliquoidea > L. nasuta > L. fasciola. CR also increased with the age (or size) of the mussel cohort but within a species CR increased non-linearly with shell length of the individual. These results provide new insight into the feeding abilities of recently metamorphosed juvenile mussels as well as potential threats to their growth and survival, which contributes to our understanding of their habitat requirements and may assist in the conservation of this imperiled taxon.

Measuring spatial variation in secondary production and food quality using a common consumer approach in Lake Erie.

Lake Erie is a large lake straddling the border of the USA and Canada that has become increasingly eutrophic in recent years. Eutrophication is particularly focused in the shallow western basin. The western basin of Lake Erie is hydrodynamically similar to a large estuary, with riverine inputs from the Detroit and Maumee Rivers mixing together and creating gradients in chemical and physical conditions. This study was driven by two questions: (1) How does secondary production and food quality for consumers vary across this large mixing zone? and (2) Are there correlations between cyanobacterial abundance and secondary production or food quality for consumers? Measuring spatial and temporal variation in secondary production and food quality is difficult for a variety of logistical reasons, so here a common consumer approach was used. In a common consumer approach, individuals of a single species are raised under similar conditions until placed in the field across environmental gradients of interest. After some period of exposure, the response of that common consumer is measured to provide an index of spatial variation in conditions. Here, a freshwater mussel (Lampsilis siliquoidea) was deployed at 32 locations that spanned habitat types and a gradient in cyanobacterial abundance in the western basin of Lake Erie to measure spatial variation in growth (an index of secondary production) and fatty acid (FA) content (an index of food quality). We found secondary production was highest within the Maumee river mouth and lowest in the open waters of the lake. Mussel tissues in the Maumee river mouth also included more eicosapentaenoic and docosapentaenoic fatty acids (EPA and DPA, respectively), but fewer bacterial FAs, suggesting more algae at the base of the food web in the Maumee river mouth compared to open lake sites. The satellite-derived estimate of cyanobacterial abundance was not correlated to secondary production, but was positively related to EPA and DPA content in the mussels, suggesting more of these important FAs in locations with more cyanobacteria. These results suggest that growth of secondary consumers and the availability of important fatty acids in the western basin are centered on the Maumee river mouth.

Assessing variability in chemical acute toxicity of unionid mussels: Influence of intra- and interlaboratory testing, life stage, and species.

The authors developed a toxicity database for unionid mussels to examine the extent of intra- and interlaboratory variability in acute toxicity tests with mussel larvae (glochidia) and juveniles; the extent of differential sensitivity of the 2 life stages; and the variation in sensitivity among commonly tested mussels (Lampsilis siliquoidea, Utterbackia imbecillis, and Villosa iris), commonly tested cladocerans (Daphnia magna and Ceriodaphnia dubia), and fish (Oncorhynchus mykiss, Pimephales promelas, and Lepomis macrochirus). The results of these analyses indicate that intralaboratory variability for median effect concentrations (EC50) averaged about 2-fold for both life stages, whereas interlaboratory variability averaged 3.6-fold for juvenile mussels and 6.3-fold for glochidia. The EC50s for juveniles and glochidia were within a factor of 2 of each other for 50% of paired records across chemicals, with juveniles more sensitive than glochidia by more than 2-fold for 33% of the comparisons made between life stages. There was a high concurrence of sensitivity of commonly tested L. siliquoidea, U. imbecillis, and V. iris to that of other mussels. However, this concurrence decreased as the taxonomic distance of the commonly tested cladocerans and fish to mussels increased. The compiled mussel database and determination of data variability will advance risk assessments by including more robust species sensitivity distributions, interspecies correlation estimates, and availability of taxon-specific empirically derived application factors for risk assessment.

Spatial Variation in Biofouling of a Unionid Mussel (Lampsilis siliquoidea) Across the Western Basin of Lake Erie

Abstract Invasion of North American waters by nonnative Dreissena polymorpha and D. rostriformis bugensis has resulted in declines of the Unionidae family of native North American mussels. Dreissenid mussels biofoul unionid mussels in large numbers and interfere with unionid movement, their acquisition of food, and the native mussels' ability to open and close their shells. Initial expectations for the Great Lakes included extirpation of unionids where they co-occurred with dreissenids, but recently adult and juvenile unionids have been found alive in several apparent refugia. These unionid populations may persist due to reduced dreissenid biofouling in these areas, and/or due to processes that remove biofoulers. For example locations inaccessible to dreissenid veligers may reduce biofouling and habitats with soft substrates may allow unionids to burrow and thus remove dreissenids. We deployed caged unionid mussels (Lampsilis siliquoidea) at 36 sites across the western basin of Lake Erie to assess spatial...

Assessing potential toxicity of chloride-affected groundwater discharging to an urban stream using juvenile freshwater mussels (Lampsilis siliquoidea)

Groundwater contaminants, such as chloride from road salt, pose a threat to aquatic ecosystems when and where they discharge to surface waters. Here we study the application of a laboratory toxicity bioassay to field-collected samples from contaminated groundwater discharging to an urban stream. The objectives were to assess the potential toxicity of the discharging groundwater, while also exploring the suitability of such standard tests to site groundwater. Juvenile freshwater mussels were chosen as a groundwater-appropriate (endobenthic) test organism. Groundwater was sampled from 6 sites at approximate depths of 0, 10, and 50cm below the sediment. Concentrations of chloride and several metals were above aquatic life guidelines in some samples. Exposure (96-h) to site groundwater resulted in survival of 90–100% and 80–100% for the 0-cm and deeper samples, respectively, indicating that groundwater may pose a toxicological threat to freshwater mussels. Several samples with high chloride had a survival rate of 80%, but generally there was poor correlation between survival and individual contaminants. Parallel juvenile mussel exposures using reconstituted water and NaCl predicted survival in the natural groundwater below 50% based on chloride concentrations. This indicates some protective ability of groundwater, possibly associated with water hardness. Finally, some technical issues with performing bioassays with groundwater were noted. First, aeration of previously anoxic groundwater samples caused marked changes in water quality (especially metal concentrations). Second, calcite crystals formed on the mussel shells in samples with elevated chloride and water hardness, though with no apparent negative effects.

Relative sensitivity of an amphipod Hyalella azteca, a midge Chironomus dilutus, and a unionid mussel Lampsilis siliquoidea to a toxic sediment.

The objective of the present study was to evaluate the relative sensitivity of test organisms in exposures to dilutions of a highly toxic sediment contaminated with metals and organic compounds. One dilution series was prepared using control sand (low total organic carbon [TOC; <0.1%, low binding capacity for contaminants]) and a second dilution series was prepared using control sediment from West Bearskin Lake, Minnesota, USA (high TOC [∼10% TOC, higher binding capacity for contaminants]). Test organisms included an amphipod (Hyalella azteca; 10-d and 28-d exposures), a midge (Chironomus dilutus; 20-d and 48-d exposures started with <1-h-old larvae, and 13-d and 48-d exposures started with 7-d-old larvae), and a unionid mussel (Lampsilis siliquoidea; 28-d exposures). Relative species sensitivity depended on the toxicity endpoint and the diluent. All 3 species were more sensitive in sand dilutions than in West Bearskin Lake sediment dilutions. The <1-h-old C. dilutus were more sensitive than 7-d-old C. dilutus, but replicate variability was high in exposures started with the younger midge larvae. Larval biomass and adult emergence endpoints of C. dilutus exhibited a similar sensitivity. Survival, weight, and biomass of H. azteca were more sensitive endpoints in 28-d exposures than in 10-d exposures. Weight and biomass of L. siliquoidea were sensitive endpoints in both sand and West Bearskin Lake sediment dilutions. Metals, ammonia, oil, and other organic contaminants may have contributed to the observed toxicity.

Aspidobothrean Parasites of Freshwater Mussels (Bivalvia: Unionidae) from the Saskatchewan–Nelson River Drainage in Manitoba, Canada and North Dakota, United States

ABSTRACT: A total of 1,021 freshwater mussels (Bivalvia: Unionidae) representing 12 species collected from 23 rivers between May 2002 and September 2006 in Manitoba, Saskatchewan, and North Dakota, U.S.A. were examined for aspidobothrean parasites. Nine of the 12 species were infected with aspidobothrean parasites. Anodontoides ferussacianus, Lasmigona complanata, Lasmigona compressa were uninfected. Aspidogaster conchicola was recovered from 77 individuals representing 6 of 12 mussel species. Prevalence as high as 100% was recorded for Amblema plicata and Potamilus alatus. The highest infection intensity was 254 observed in P. alatus. Cotylogaster occidentalis was recovered from 91 individuals representing 8 of 12 mussel species. Prevalence was typically lower by comparison with A. conchicola, although samples of single infected Fusconaia flava, Lampsilis siliquoidea, and Strophitus undulatus resulted in 100% prevalence in some localities. Cotylogaster occidentalis infection intensity was also much lower...

Intrinsic variability in shell and soft tissue growth of the freshwater mussel Lampsilis siliquoidea.

Freshwater mussels are ecologically and economically important members of many aquatic ecosystems, but are globally among the most imperiled taxa. Propagation techniques for mussels have been developed and used to boost declining and restore extirpated populations. Here we use a cohort of propagated mussels to estimate the intrinsic variability in size and growth rate of Lampsilis siliquoidea (a commonly propagated species). Understanding the magnitude and pattern of variation in data is critical to determining whether effects observed in nature or experimental treatments are likely to be important. The coefficient of variation (CV) of L. siliquoidea soft tissues (6.0%) was less than the CV of linear shell dimensions (25.1–66.9%). Size-weight relationships were best when mussel width (the maximum left-right dimension with both valves appressed) was used as a predictor, but 95% credible intervals on these predictions for soft tissues were ∼145 mg wide (about 50% of the mean soft tissue mass). Mussels in this study were treated identically, raised from a single cohort and yet variation in soft tissue mass at a particular size class (as determined by shell dimensions) was still high. High variability in mussel size is often acknowledged, but seldom discussed in the context of mussel conservation. High variability will influence the survival of stocked juvenile cohorts, may affect the ability to experimentally detect sublethal stressors and may lead to incongruities between the effects that mussels have on structure (via hard shells) and biogeochemical cycles (via soft tissue metabolism). Given their imperiled status and longevity, there is often reluctance to destructively sample unionid mussel soft tissues even in metabolic studies (e.g., studies of nutrient cycling). High intrinsic variability suggests that using shell dimensions (particularly shell length) as a response variable in studies of sublethal stressors or metabolic processes will make confident identifications of smaller effect sizes difficult.