Reassessing Enigmatic Mussel Declines in the United States

Haag, Wendell R.

doi:10.31931/fmbc.v22i2.2019.43-60

Cited by 72 publications

(87 citation statements)

References 61 publications

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“…Overall, our results show that, while diverse, the virome of Clinch River pheasantshells contains only one virus, Clinch densovirus 1, showing a strong and consistent association with disease. Mass mortality events in freshwater mussels are unfortunately accelerating worldwide 12 . Studying other species of mussels in other geographic locations using both epidemiology and metagenomics could help reveal whether infection with viruses or other agents is a generalized characteristic of unionid mass mortality events.…”

Section: Discussionmentioning

confidence: 99%

“…Since the late 1970s, episodic mass mortality events have been documented in unionids throughout their range, including catastrophic mortality (> 90% population declines) in some cases 12 . Unlike the aforementioned gradual declines, many mass mortality events in freshwater mussels have not been directly attributed to any specific environmental changes or events 12 . Furthermore, mass mortality events often affect only a single species of mussel within a broad ecological community.…”

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confidence: 99%

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Mass mortality in freshwater mussels (Actinonaias pectorosa) in the Clinch River, USA, linked to a novel densovirus

Richard

Leis

Dunn

et al. 2020

Sci Rep

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freshwater mussels (order Unionida) are among the world's most biodiverse but imperiled taxa. Recent unionid mass mortality events around the world threaten ecosystem services such as water filtration, nutrient cycling, habitat stabilization, and food web enhancement, but causes have remained elusive. to examine potential infectious causes of these declines, we studied mussels in clinch River, Virginia and tennessee, USA, where the endemic and once-predominant pheasantshell (Actinonaias pectorosa) has suffered precipitous declines since approximately 2016. Using metagenomics, we identified 17 novel viruses in Clinch River pheasantshells. However, only one virus, a novel densovirus (Parvoviridae; Densovirinae), was epidemiologically linked to morbidity. Clinch densovirus 1 was 11.2 times more likely to be found in cases (moribund mussels) than controls (apparently healthy mussels from the same or matched sites), and cases had 2.7 (log 10) times higher viral loads than controls. Densoviruses cause lethal epidemic disease in invertebrates, including shrimp, cockroaches, crickets, moths, crayfish, and sea stars. Viral infection warrants consideration as a factor in unionid mass mortality events either as a direct cause, an indirect consequence of physiological compromise, or a factor interacting with other biological and ecological stressors to precipitate mortality. Freshwater mussels (order Unionida) are important members of freshwater biomes, providing ecosystem services such as water filtration, nutrient cycling and deposition, physical habitat stabilization, and food web enhancement 1. Mussels filter-feed on bacteria, suspended algae, detritus, phytoplankton and zooplankton 2 , removing suspended particulate matter from the water column and from interstitial spaces within the substrate. During periods of low summer discharge in small rivers, mussel assemblages are capable of circulating water as it flows over them, leading to multiple cycles of filtration 3 that can strongly influence ecosystem processes, even at moderate mussel densities 4. Unionids are also gaining attention for their ability to filter out chemical contaminants and water-borne pathogens 5-7. Unfortunately, the order Unionida contains an exceptional number of imperiled taxa. Among North America's 298 recognized unionid species 8 , > 70% are considered endangered, threatened, or vulnerable 9 , with 23 species having gone extinct from the Southeastern United States alone. Historically, habitat destruction (e.g., river impoundments), pollution, sedimentation, over-harvest for commercial use (most notably, pearl harvest and manufacture of shirt buttons from shells ca. 1850-1950) 10 , and competition from invasive species (e.g. the Asian clam Corbicula fluminea, zebra mussel Dreissena polymorpha, and quagga mussel D. bugensis) 11 have greatly reduced or extirpated many native mussel fauna. These threats have been present since the early twentieth century, mirroring trends in human development and land use 12 .

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Mass mortality in freshwater mussels (Actinonaias pectorosa) in the Clinch River, USA, linked to a novel densovirus

Richard

Leis

Dunn

et al. 2020

Sci Rep

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“…However, the extremely low abundance we observed may be a result of human factors that have further reduced mussel populations. Entire mussel assemblages have nearly disappeared from much of the Barren River system and from many other upland streams in the southeastern USA, but the reasons for these disappearances are unknown (Irwin 2018;Reed et al 2019;Haag 2019). The upper Barren River system is now isolated by Barren River Reservoir in Kentucky, which hinders mussel dispersal and gene flow.…”

Section: Discussionmentioning

confidence: 99%

A Survey of the Freshwater Mussels (Mollusca: Bivalvia: Unionida) of the Upper Barren River System, Tennessee

Dinkins

Womble

Ahlstedt³

2020

Freshwater Mollusk Biology and Conservation

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The freshwater mussel fauna of the Barren River system in Kentucky is well documented, but information on mussel occurrence in the Tennessee portion of the system was lacking. We conducted mussel surveys at 56 sites in 22 streams in the Barren River system in Tennessee. We found six species at 14 sites: Alasmidonta viridis (Slippershell), Fusconaia flava (Wabash Pigtoe), Lampsilis cardium (Plain Pocketbook), Lampsilis siliquoidea (Fatmucket), Pyganodon grandis (Giant Floater), and Villosa ortmanni (Kentucky Creekshell). Our records of V. ortmanni are the first reports of this species from Tennessee, and our records of L. siliquoidea considerably expand the known range of that species in the state. We found live or freshly dead V. ortmanni at five sites, and at least two sites supported relatively large populations with evidence of recent recruitment. These observations represent important information for the conservation of this imperiled species. Overall, mussel populations in the Barren River system of Tennessee were small and scattered, which may be due, in part, to the lower mussel abundance typical of headwater streams. However, the occurrence of widespread mussel declines in this region suggests that human factors may have further reduced mussel abundance.

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“…The spatial and temporal extent of unexplained mussel declines and die-offs is not well documented, and a comprehensive review of the topic is beyond the scope of this paper. A review of enigmatic declines is provided by Haag (2019). Sufficient historic and current evidence of mussel declines exists to justify a greater focus on the topic of health and disease.…”

Section: Perspective On Freshwater Mussel Mortality Eventsmentioning

confidence: 99%

“…However, these factors do not explain the declines and large-scale die-offs of mussels in otherwise healthy, unimpounded streams across a wide geographic region. The significant decline of mussels that occurred from the 1970s to 1990s has been described as ''enigmatic'' with characteristics suggesting a virulent and widespread factor specific to mussels (Haag and Williams 2014;Haag 2019).…”

Section: Introductionmentioning

confidence: 99%

The Status of Mussel Health Assessment and a Path Forward

Waller

Cope

2019

Freshwater Mollusk Biology and Conservation

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Declines of freshwater mussel (order Unionida) populations worldwide are attributed to habitat degradation, pollution, and invasive species, among other factors. However, these purported causes do not fully explain the enigmatic decline and large-scale die-offs of mussels that have occurred in apparently healthy streams across a wide geographic region. The roles of the microbiota and pathogens in mussel health have been understudied, and, as a result, few data exist to compare the microbiota of healthy mussels to that of stressed or dying mussels. Captive propagation and stocking programs have expanded across the globe without standard diagnostic protocols to assess health or potential diseases in hatchery-reared or wild stocks. Nonindigenous species, contaminants of emerging concern, and anthropogenic climate change could alter adversely the underlying processes that support mussel health, such as nutritional status and microbial composition, and these factors could increase the risk for outbreaks of opportunistic and emergent mussel disease. We propose a coordinated, collaborative, and multidisciplinary effort to advance methods for assessing freshwater mussel health. We identify research and resources needed to answer central questions surrounding mussel health, including identifying potential agents of disease, defining clinical signs of declining condition, refining stressspecific biomarkers for health assessment, and developing protocols specific for mussels.

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Reassessing Enigmatic Mussel Declines in the United States

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Cited by 72 publications

References 61 publications

Mass mortality in freshwater mussels (Actinonaias pectorosa) in the Clinch River, USA, linked to a novel densovirus

Mass mortality in freshwater mussels (Actinonaias pectorosa) in the Clinch River, USA, linked to a novel densovirus

A Survey of the Freshwater Mussels (Mollusca: Bivalvia: Unionida) of the Upper Barren River System, Tennessee

The Status of Mussel Health Assessment and a Path Forward

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