Live Mussels Research Articles

Predicting dreissenid mussel abundance in nearshore waters using underwater imagery and deep learning

AbstractAccurate and cost‐effective dreissenid mussel abundance maps are vital to assess their ecological roles in aquatic systems. A deep neural network (DNN) modeling framework using semantic segmentation was developed to automatically assess the abundance distribution of two invasive mussel species: zebra and quagga. DNN models were trained on images captured in Lake Erie and Lake Ontario using an underwater color imaging technique. The accuracy of the method was assessed relative to manual laboratory counts of harvested mussels, their dry biomass, and percentage live coverage estimated from fixed‐size quadrats. Assessments performed on a test set collected from 2016 to 2018 show that DNN‐based mussel coverage predictions explain 79% of the variance in log biomass, and 71% for log abundance (N = 125). For reference, live coverage estimated by scuba divers was transformed and found to be a better predictor of biomass (93%) and abundance (91%) (N = 725), leaving room for improvement of our automated method. When identical images were presented to eight human analysts and the DNN, the agreement in live mussel coverage prediction was 85% (N = 189). Models generalize well to diverse underwater illuminations, camera orientations, and resolutions, but are adversely impacted by occluding vegetation and suspended sediment. DNN models are an efficient and accurate solution for mapping mussel abundances at a scale that was previously impossible. The method may be integrated with other studies to assess the mussels' impacts in a variety of aquatic ecosystems. Source code:https://github.com/AngusG/deep-learning-dreissenidand datahttps://doi.org/10.5683/SP3/MZEBOJfor reproducing our method are publicly available.

First person – Natalí Delorme and Leonardo Zamora

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Natalí Delorme and Leonardo Zamora are co-first authors on ‘ A new method to localise and quantify oxidative stress in live juvenile mussels’, published in BiO. They are both researchers in the laboratory of Serean Adams at the Cawthron Institute, Nelson, New Zealand. Natalí's research interests centre around ecophysiology of marine invertebrates, particularly on the organisms' stress response. Leonardo is investigating the biology of commercially, ecologically and culturally relevant marine invertebrates throughout their life cycle.

A new method to localise and quantify oxidative stress in live juvenile mussels.

ABSTRACTStress and survival of the juvenile New Zealand green-lipped mussel, Perna canaliculus, is a poorly understood bottleneck in the ecological and economic performance of a significant aquaculture crop. This species was therefore selected as a model organism for the development of a new method to quantify oxidative stress in whole individuals. An in vivo ROS-activated stain (CellROX™) was administered to anaesthetised, translucent juveniles that were subsequently formaldehyde fixed and then visualised using confocal microscopy. Subsequent application of image analysis to quantifying ROS-positive tissue areas was successfully used to detect stress differences in juvenile mussels exposed to varying levels of emersion. This integrated method can be used to localise and quantify ROS production in individual translucent bivalve life stages (larval and juvenile), while relative stability following fixation greatly expands potential practical field applications. This article has an associated First Person interview with the first and third authors of the paper.

Changes in extractive components in live Mytilus galloprovincialis mussels during ice storage

Changes in extractive components in live Mytilus galloprovincialis mussels during ice storage

Bivalves rapidly repair shells damaged by fatigue and bolster strength.

ABSTRACTHard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels’ success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage.

Epibiosis in sedimentary coastal environments: Effects of an introduced barnacle on a native mussel

AbstractIn the mobile sedimentary environment of San Antonio Bay (northern Patagonia), where hard substrate is scarce, the mussel Brachidontes rodriguezii dominates the intertidal zone, there being covered by the introduced epibiotic barnacle Balanus glandula. The aim of this study was to evaluate the distribution and the recruitment of B. glandula on different non‐living substrates (cobbles, biogenic debris) and on live‐mussel shells and to assess the effect of the epibiotic interaction on the condition index and the attachment strength of B. rodriguezii. Field samplings revealed that adult barnacles mainly fouled live mussels, with the main differences in biomass being between the high and mid‐intertidal. These differences in barnacle biomass between heights and substrates were greater in spring and autumn than in winter and summer. To assess the recruitment of barnacles, we performed a field experiment manipulating living and non‐living substrates. We found no differences in the density of barnacles recruitment; thus, the barnacle distribution on different substrates throughout the intertidal would vary solely according to the settling substrates available. The relationship between epibiosis and the condition index exhibited no pattern. Furthermore, the experimental manipulation of epibiosis (i.e., removing epibionts or adding epibionts mimics) did not affect the condition of the mussels. Finally, the attachment strength of mussels with epibionts was up to fivefold greater than that of clean mussels. In a system with high tidal hydrodynamic energy, epibiosis is thus seen to stimulate a greater byssal production in mussels for the prevention of detachment.

Drag and inertia coefficients of live and surrogate shellfish dropper lines under steady and oscillatory flow

Against the background of a drastically increased demand of marine proteins, off-bottom, bivalve aquaculture, provides significant potential for production growth when moved into more energetic marine waters. Hence, research, industry and politics are currently proposing the development of new offshore sites. The highly energetic conditions at these sites present a challenging environment for bivalve aquaculture. In this work, physical experiments of suspended bivalves provide new knowledge on the commonly used design parameters: the drag and inertia coefficients. Live bivalves and manufactured surrogate models at a 1:1 scale were tested in a towing tank as well as under waves. The drag coefficient of live blue mussels was determined to be Cd = 1.6 for Reynolds numbers between 2.3 × 104 and 1.4 × 105. The inertia coefficient obtained from the wave tests was Cm = 2.1 for Keulegan Carpenter numbers KC < 10. In a pursuit to better understand the differences between live mussels and surrogates in laboratory conditions, the analysis revealed that appropriate surrogates can be identified. A method to determine the characteristic diameter of mussel dropper lines is suggested. The results facilitate the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

Observations on recent mass mortality events of marine mussels in the Oosterschelde, the Netherlands

Two mass mortality events (MMEs) of marine mussels that took place in the Oosterschelde, the Netherlands—the first in 2015/2016 and the second in 2019—both severely affected mussel production. The current study presents our observations on the onset and course of both MMEs and discusses probable putative causes. The two MMEs displayed a distinct course of events. The first event started in November 2015 with high mortality rates on culture plots, which remained elevated until the autumn of 2016. Approximately 40–50% of mussels from all age classes were lost on culture plots and 100% were lost from wild seed beds. The second event started in April–May 2019 and continued until the end of July, with mortality ranging from 20 to 100%, again from all age classes. Culture areas other than the Oosterschelde and other shellfish species were not affected. Histological and bacteriological screening produced no evidence for common pathogens or pollution as a primary mortality factor and there is no indication of abnormal environmental conditions preceding or during the events. We hypothesize that a cumulation of stressors results in weakening of the mussels and in elevated mortality rates. In 2019, this cumulation of stressors could be high spawning activities (an unusual high concentration of mussel larvae was found in April) that resulted in very low condition from April to June, a Phaeocystis bloom in April to May that prevented a quick recovery, and the development of granulocytomas that were found in up to 60 to 70% of live mussels as a consequence of cumulative stress. Although no (single) putative causes could be identified, this study contributes to the knowledge on MMEs in mussels and fits in a wider and disturbing trend on mortality events in shellfish.

Geographical variation in the carbon, nitrogen, and phosphorus content of blue mussels, Mytilus edulis

Shellfish farming contributes to nutrient removal in coastal and estuarine systems, as bivalves incorporate nutrients into their tissues and shells, which is removed from the marine system on harvest. Fourteen locations around the UK were surveyed to explore geographic variation in carbon, nitrogen and phosphorus content of tissue and shell in blue mussels. Phosphorus in tissue had a significant negative relationship with mean annual seawater temperature for both rope and bottom cultured sites. Per tonne of live mussel, rope culture removed significantly more nitrogen (8.50 ± 0.59 kg) and phosphorus (0.95 ± 0.07 kg) than bottom cultured (5.00 ± 0.013 kg nitrogen and 0.43 ± 0.01 kg phosphorus). Bottom culture, however, provides significantly more C removal in shell (60.15 ± 0.77 kg) than in rope cultured (46.12 ± 1.69 kg). Further studies are required to examine the effect of growth rate, on the nitrogen and phosphorus remediation, and carbon stored in shell, of rope culture and bottom cultured mussel aquaculture.

Hyriid mussels (Unionoida) enhance benthic organic matter and meiofauna densities in a temperate Australian river

Abstract Studies in the Northern Hemisphere have shown that mussels play important roles as benthic‐pelagic couplers in freshwater systems, transferring filtered material, nutrients, and energy from the water column to sediments, through biodeposition and excretion. However, we know little of the functional roles of species of the Southern Hemisphere Hyriidae, the second most diverse family of the Unionoida. The aims of this study were to determine the biodeposition and excretion rates of nutrients and organic matter of the hyriid Alathyria jacksoni in an unregulated Australian river and test experimentally if the physical structure and biodeposition of A. jacksoni influenced sediment nutrients, organic matter, periphyton concentrations and meiofauna densities. In a lowland Australian river in late summer over 4 weeks, we measured biodeposition and excretion rates of A. jacksoni, and conducted a mesocosm experiment, during which we compared the effects of live mussels, dead mussel shells (shams), and controls without mussels on nutrients, organic matter, and meiofauna invertebrate densities in the sediment. Mean (± SE) mass of biodeposition was 70.85 ± 3.20 mg mussel−1 hr−1 and the relative rates of inorganic and organic biodeposition were 60.9 ± 3.1 and 9.9 ± 0.8 mg mussel−1 hr−1, respectively. Organic matter was significantly greater in the sediment of the mesocosms with live mussels than in that of the control mesocosms. There was also a trend of greater mean sediment chlorophyll‐a and total nitrogen concentrations in mussel treatments than in the controls. No significant difference was detected in sediment total phosphorous between mussel and control enclosures. The valves of live mussels had significantly higher amounts of organic material and chlorophyll‐a concentrations than the valves of sham mussels. There was a consistent trend of higher meiofauna densities collected in the benthos of the mussel enclosures than the control enclosures for total density and densities of Rotifera, Copepoda, Cladocera, Diptera, Oligocheata, Nematoda, and Ostracoda; this trend was near significant for total density; and significant for densities of Ostracoda, Rotifera, Cladocera, and Nematoda. Using our biodeposition and excretion rate estimates, and estimates of population size of A. jacksoni in the Lower Ovens River, we estimated that in a typical 1‐km reach in a month over summer, A. jacksoni would be biodepositing approximately 4.8 kg/day of organic matter (dry mass), 137 g N/day and 19 g P/day, and excreting 21 g N/day and 3.7 g P/day. Our findings are similar to those for Northern Hemisphere families of the Unionoida and serve to highlight the roles mussels play in processing of organic matter and cycling of nutrients in freshwater ecosystems.

Salt-Laden Winter Runoff and Freshwater Mussels; Assessing the Effect on Early Life Stages in the Laboratory and Wild Mussel Populations in Receiving Waters

The widespread use of road salt for winter road maintenance has led to an increase in the salinity of surface water in many seasonally cold areas. Freshwater mussels have a heightened sensitivity to salt, which is a concern, because many Canadian mussel species at risk have ranges limited to southern Ontario, Canada’s most road-dense region. This study examined the effect of winter road runoff on freshwater mussels. The impact of two bridges that span mussel habitat in the Thames River watershed (Ontario, Canada), the second most species-rich watershed for mussels in Canada, were studied. During a winter melt event, bridge runoff, as well as creek surface water surrounding the bridges were collected. Chloride concentrations in samples from bridge deck and tile drains varied (99–8250 mg/L). In general, survival of Lampsilis fasciola glochidia exposed to those samples reflected chloride levels (e.g. 84% at 99 mg/L; 0% at 8250 mg/L), although potassium (60 mg/L) may have at least contributed to toxicity in one sample. Serial dilution exposures with the two most toxic runoff samples revealed 48-h glochidia EC50s of 44% (McGregor Creek Tile Drain) and 26% (Baptiste Creek Deck Drain). During the melt event, the chloride concentrations in creek surface waters downstream of the bridges ranged from 69 to 179 mg Cl−/L; effects on glochidia (viability 77–91%) exposed to those waters was minimal. There were no live mussels surrounding one bridge (Baptiste Creek), likely due to poor habitat. At the other targeted bridge (McGregor Creek), fewer mussels were found close (< 100 m up- or downstream) to the bridge than further (> 200 m) away. However, other contributing factors, including agriculture, were present at both study areas.

Balance between biological and physical components in the impact of Mytilus edulis on associated organisms

An ecosystem engineer’s influence on associated organisms includes 2 components: physical and biological. The physical component is the spatial environment created by the ecosystem engineer, while the biological component is the physiological activity of the engineering species. However, little is known about the ratio between these components. We evaluated this ratio for Mytilus edulis L. by means of a field experiment in which communities of organisms that developed on bare ceramic plates (controls, C) were compared with those that formed on plates carrying patches of live mussels (L) or artificial patches made of mussel dummies (D). The experiment was performed using 2 different age-size groups of mussels and dummies (small-young and large-old). Live mussels had only a weak positive effect on species richness of the associated organisms, but the structure of the communities that formed on tests plates (L, D and C) differed significantly. The similarity of the communities of associated organisms between C and L was 1.5-3 times less than between C and D. Mussel size-age factor had no significant effect on community structure other than on the algal assemblage. The results of this experiment suggest that the influence of mussels on associated organisms cannot be reduced to only the effect of increasing complexity of the spatial environment. The influence of the biological component is significant and can exceed that of the physical component. Thus, in ecosystem engineering, non-living spatial structures cannot serve as an identical substitute for a population of living organisms.

Large-Scale Laboratory Experiments on Mussel Dropper Lines in Ocean Surface Waves

The rapid growth of marine aquaculture around the world accentuates issues of sustainability and environmental impacts of large-scale farming systems. One potential mitigation strategy is to relocate to more energetic offshore locations. However, research regarding the forces which waves and currents impose on aquaculture structures in such conditions is still scarce. The present study aimed at extending the knowledge related to live blue mussels (Mytilus edulis), cultivated on dropper lines, by unique, large-scale laboratory experiments in the Large Wave Flume of the Coastal Research Center in Hannover, Germany. Nine-months-old live dropper lines and a surrogate of 2.0 m length each are exposed to regular waves with wave heights between 0.2 and 1.0 m and periods between 1.5 and 8.0 s. Force time histories are recorded to investigate the inertia and drag characteristics of live mussel and surrogate dropper lines. The surrogate dropper line was developed from 3D scans of blue mussel dropper lines, using the surface descriptor Abbott–Firestone Curve as quality parameter. Pull-off tests of individual mussels are conducted that reveal maximum attachment strength ranges of 0.48 to 10.55 N for mussels that had medium 3.04 cm length, 1.60 cm height and 1.25 cm width. Mean drag coefficients of CD = 3.9 were found for live blue mussel lines and CD = 3.4 for the surrogate model, for conditions of Keulegan–Carpenter number (KC) 10 to 380, using regular wave tests.

Availability of Environmental Iron Influences the Performance of Biological Adhesives Produced by Blue Mussels.

Animals incorporate metals within the materials they manufacture, such as protective armor and teeth. Iron is an element used for adding strength and self-healing properties to load-bearing materials. Incorporation of iron is found beyond hard, brittle materials, even within the soft adhesive produced by marine mussels. Such findings suggest that the bioavailability of iron may have an influence on the properties of a biological material. Experiments were conducted using live mussels in which seawater iron levels were deficient, normal, or in excess of typical concentrations. The weakest adhesive strengths were produced in iron-deficient waters. Increasing seawater iron brought about more robust bonding. Changes in strengths correlated with varied adhesive morphology, color, and microstructural features, likely a result of variations in the degree of iron-induced protein cross-linking. This study provides the first whole animal scale data on how the manipulation of bioavailable iron influences the performance of a biological material. Changing ocean chemistries will alter the iron bioavailability when a decrease in pH shifts elemental speciation from particulate to dissolved, hindering the ability of filtering organisms to capture nutrients. These results show future implications of changing ocean chemistry as well as of the resulting abilities of marine organisms to construct essential materials.

Spatial and temporal variations of trace metal body burdens of live mussels Mytilus galloprovincialis and field validation of the Artificial Mussels in Australian inshore marine environment

The body burdens of eight trace metals: Cd, Pb, Cu, Zn, Cr, Se, Hg, and As, were measured in live mussels (LMs) Mytilus galloprovincialis at 14 coastal sites in Port Phillip Bay, Victoria, Australia in winter and summer between 2017 and 2018. The spatial and temporal variations of body burdens were evaluated. The results revealed significantly higher body burdens of Cd, Pb, Cu, Zn, Cr, and Hg in summer at the sites where the city centre and industries are located. Elevated levels of most trace metals including 3 toxic, non-essential metals (Cd, Pb, and Hg) were detected in LMs from the site of Geelong. The body burdens of Zn, Cr, Se, and As appeared higher at the sites from the Bellarine Peninsula and the mouth of Port Phillip Bay.Besides, the “Artificial Mussels” (AMs) were deployed at the same sites in summer for 28 d and retrieved when the LMs were collected. The accumulations of the eight metals were compared between AMs and LMs summer results. It indicated significant correlations for Pb, Cu, and Cr, lower correlations in Zn and Hg, and irregular correlations for Se and As. The AM results of Cd were below the detection limit of the analytical method. This study demonstrates that AMs are excellent replacement of LMs for the biomonitoring of multiple kinds of trace metals.

Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa

Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.

Common coypu predation on unionid mussels and terrestrial plants in an invaded Japanese river

The coypu (Myocastor coypus) is a semi-aquatic herbivorous rodent that has been suspected to prey on freshwater unionid mussels in Japan. Fecal DNA metabarcoding that targeted bivalves and terrestrial plants was performed to examine the diet of exotic coypu in the Kiso River, central Japan. Thirty-two fecal samples from four floodplain waterbodies were collected seasonally. In one of the waterbodies, live and dead mussels were investigated to examine the possible effects of coypu predation on mussel population structures. Common coypu predation on unionid mussels was confirmed in two waterbodies. Midden surveys showed that medium- to large-sized mussels tended to be consumed by coypu; possibly resulting in population structures with few large-sized individuals. Seasonal diet selection of terrestrial plants was also detected: two perennial plants were consumed throughout the year, whereas some perennial plants were consumed seasonally. The number of terrestrial plant species/taxa as primary food was higher in summer than in winter, which was attributed to the high consumption of annual plants in the summer. Future studies need to examine the exhaustive diet of coypu including other animals and plants, as well as its effects on freshwater ecosystems in invaded regions.

Temperature elevation and Vibrio cyclitrophicus infection reduce the diversity of haemolymph microbiome of the mussel Mytilus coruscus

Haemolymph microbiome was considered to be unique to healthy invertebrates and beneficial to the host against external pathogens, including disease resistance and maintenance of homeostasis. Here, we investigated the effects of elevated water temperature on infection of haemolymph microbiome of the hard-shelled mussel (Mytilus coruscus). Exposure to Vibrio. cyclitrophicus resulted in high mortality of mussels on day nine at 27 °C. The haemolymph was collected to determine the microbiota by 16 S rRNA gene sequencing. Exposure to waterborne V. cyclitrophicus increased the mortality of mussels that was associated with a reduction in the diversity of their microbial community. Principal coordinate analysis (PCoA) revealed that temperature was an essential factor in shaping microbial communities in mussel haemolymph. Vibrio exposure promoted the proliferation of opportunistic pathogens (e.g., Arcobacter and Francisella) at a lower temperature. A high abundance of Vibrio present in live and dead mussels, at 27 °C might contribute greatly to mortality, as indicated by linear discriminant analysis effect size (LEfSe). These data suggested that the dynamics of microbial community have unique biomarker species in mussel haemolymph that could be used as health indicators. An elevated temperature may reduce the ability of bacterial elimination function against infection in mussel haemolymph.

The distribution of Microcondylaea bonellii (Bivalvia: Unionidae) in Slovenia

The freshwater bivalve Microcondylaea bonellii is classified as Vulnerable according to the last IUCN Red List assessment and also listed in Annex V of the Habitats Directive. According to more than one hundred years old data, the species was present in Slovenia in a restricted section of the Vipava River and its tributary the Lijak Stream, which is also the species’ type location. We surveyed all previously known as well as new potential localities for M. bonellii. Live mussels were found only in the lower part of the Vipava River, but not in the Lijak Stream. Nevertheless, the population in Slovenia is isolated from other populations and restricted only to 16 km of the Vipava River. Unfortunately, key sections of the Vipava River have been subjected to habitat destruction in the past and are threatened by ongoing engineering works and developments. Thus the legislation should be taken into strict consideration immediately if we want to preserve this protected species and its habitat.

Pathobiology and first report of larval nematodes (Ascaridomorpha sp.) infecting freshwater mussels (Villosa nebulosa, Unionidae), including an inventory of nematode infections in freshwater and marine bivalves.

Little information is available on host-parasite relationships between bivalves and larval nematodes. Herein, we describe nematode larvae (likely stage 2) in the infraorder Ascaridomorpha infecting the foot, intestine, and mantle of a freshwater mussel (Alabama rainbow, Villosa nebulosa [Conrad, 1834]) and detail histopathological changes to infected tissues. A total of 43 live mussels from the South Fork of Terrapin Creek, Alabama, were collected between 2010 and 2014, with 14 sectioned for histopathology and 29 dissected. Of the 14 sectioned mussels, 5 appeared to be uninfected, and 7, 1, and 1 had histozoic infections observed in the foot and intestine, intestine only, and mantle edge and foot, respectively. Twenty-three of 29 (79%) of the mussels dissected were infected by live nematodes, and mean nematode abundance was 8.3 (CL = 5.23–13), with 2 mussels infected with >100 nematodes each. Thus, with a total of 32 of the 43 collected mussels observed with nematodes, overall infection prevalence was 74.4% (CL = 0.594–0.855). The 18S rDNA of this nematode was 99% similar to that of several ascaridids (species of Kathlaniidae Lane, 1914 and Quimperiidae Baylis, 1930) that mature in aquatic/semi-aquatic vertebrates; the recovered 18S phylogenetic tree indicated this nematode from V. nebulosa shares a recent common ancestor with Ichthyobronema hamulatum (Ascaridomorpha: Quimperiidae; GenBank Accession Number KY476351). Pathological changes to tissue associated with these infections comprised focal tissue damage, but a cellular response was not evident. The Alabama rainbow possibly represents an intermediate or paratenic host. Given these results, the nematode is likely not pathogenic under normal stream conditions; however, high intensity infections in the foot could inhibit pedal extension and retraction; which would have demonstrable health consequences to a freshwater mussel. Based on our review of the bivalve mollusc parasite literature, a collective biodiversity of 61 nematodes reportedly exhibit some degree of symbiosis (from commensal to parasitic) with 21 bivalves (28 nematode spp. from 17 marine bivalve spp.; 33 nematode spp. from 4 freshwater bivalve spp.); only four records exist of putatively parasitic nematodes from Unionida. The present study represents the first description of a nematode species that invades the tissues of a Unionidae species.