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This well-illustrated book highlights freshwater mussels' fabulous diversity, amazing array of often bizarre ecological adaptations and their dire conservation plight. Summarizing and synthesizing historical and contemporary information as well as original research and analysis, the book describes the diverse array of mussel life history strategies and builds a cohesive narrative culminating in the development of explicit frameworks to explain pervasive patterns in mussel ecology. The fascinating and colorful role of mussels in human society is also described in detail, including the little-known pearl button industry of the early 1900s and the wild and often violent shell harvest of the 1990s. The final chapter details humans' efforts to save these fascinating animals and gives a prognosis for the future of the North American fauna. The book provides the first comprehensive review of mussel ecology and conservation for scientists, natural resource professionals, students and natural history enthusiasts.

Pearly mussels (Unionoidea) live in lakes, rivers, and streams around the world. These bivalves play important roles in freshwater ecosystems and were once both culturally and economically valuable as sources of food, pearls, and mother-of-pearl. Today, however, hundreds of species of these mussels are extinct or endangered. David L. Strayer provides a critical synthesis of the factors that control the distribution and abundance of pearly mussels. Using empirical analyses and models, he assesses the effects of dispersal, habitat quality, availability of fish hosts, adequate food, predators, and parasites. He also addresses conservation issues that apply to other inhabitants of fresh waters around the globe and other pressing issues in contemporary ecology.

A characteristic feature shared by all Margaritiferidae mussels consists in the presence of scars on the internal surface of their shells. These scars mark places of mantle attachment by specific epithelial cells. According to some authors, such parameters of mantle attachment scars as the density and degree of their manifestation can be used for the purposes of species identification. To this end, quality indicators (numerous or few, pronounced or poorly visible scars) are typically used; however, the use of quantitative criteria is preferable. This work was aimed at developing quantitative indicators of mantle attachment scars in the Margaritifera margaritifera freshwater pearl mussels for the populations of the Syuskyuyanyoki and Livoyoki rivers (Karelia). It is shown that the density and size of mantle attachment scars are approximately the same for all the investigated shell samples. These parameters display the absence of dependence on the age and size of molluscs. The regression coefficients for the linear dependence of the density or size of mantle attachment scars on the age or length of the shell show no significant difference from 0. For all the investigated molluscs, the density and size of mantle attachment scars are established to vary within the range of 0.37–1.16 scars/cm 2 (0.71 ± 0.03 scars/cm 2 on average) and 215–690 µm (417 ± 2 µm on average), respectively. According to a two-factor analysis of variance, the distribution of mantle attachment scars appears to be irregular across the shell surface. At the same time, a significant ( p < 0.001) increase in their density is observed in the posterior and ventral directions, as well as diagonally in the posterior ventral direction. Issues associated with the application of the investigated parameters for the purposes of mollusc species identification are discussed.

The invasive alien crayfish Pacifastacus leniusculus is considered harmful to freshwater pearl mussels Margaritifera laevis and M. togakushiensis. It also often colonises mussel habitats in Japan. In order to test the negative effects of alien crayfish on mussels, we evaluated the predation impact of signal crayfish on freshwater pearl mussels in vitro. We tested the relationship between the survival/injury rates of mussels and crayfish predation with respect to different sizes of mussels (four classes based on shell length: 10, 30, 50 and 70 mm). Crayfish selectively fed on the flesh of the 10-mm size class mussels after breaking their shells. The shell margins of mussels in all size classes were injured by crayfish. Results also showed that crayfish particularly injured the 50-mm size class of mussels. This observation could be attributed to this mussel size being the most suitable shell size (29.56-37.73 mm in carapace length) that the crayfish can effectively hold. This study shows that the presence of invasive crayfish reduces freshwater pearl mussel populations by damaging the shell margins and/or killing the mussels. This negative impact of invasive crayfish not only decreases the mussel population but could also limit mussel recruitment, growth and reproduction.

The knowledge of the routes of excretion of the toxins accumulated by molluscs is a key step in designing methods that accelerate depuration. In this work, the excretion route, in mussels and cockles, of the main diarrhetic shellfish poisoning (DSP) toxins in Europe (okadaic acid and dinophysistoxin-2) after natural intoxication were studied. During depuration, the amounts of free toxins and their derivatives were quantified in bivalves, faeces, and water. Most toxins (>98%) were excreted through faeces as acyl derivatives (most likely 7-O-acyl esters), independent of the ratio between these derivatives and free toxins in soft tissues. The small proportion of toxins excreted into water mostly constituted the free forms of the toxins. Both species shared the same route even though they contained very different proportions of free toxins in their soft tissues. No substantial changes in this general pattern were observed during the experiment. The esters of fatty acids with 16 carbon atoms were the most abundant in both soft tissues and faeces, but they were not the same in mussels and cockles. Most of the variability in ester proportions can be attributed to the species more than to their differential excretion (water or faeces) suggesting that there are not large differences in the depuration of the different esters.

Freshwater mussels are integral components of riverine ecosystems, influencing water quality, nutrient cycling, and habitat characteristics. Enigmatic freshwater mussel declines, often characterized by sudden mass mortality events, pose significant challenges to conservation efforts. The Clinch River, a freshwater biodiversity hotspot in Virginia and Tennessee, USA, has experienced several enigmatic mass mortality events since 2016. Studies have reported bacteria associated with moribund Pheasantshell (Actinonaias pectorosa) during mortality events in the Clinch River, specifically Yokenella regensburgei. Despite reports of bacterial infection, little is known about their role as pathogens. Through a multiyear case-control study, combining in-situ experiments, field surveys, histology, bacterial isolation, and high-throughput sequencing, we assessed the role of bacteria in Pheasantshell (Actinonais pectorosa) mortality at three sites in the Clinch River. Between May 2021 and December 2023, we collected 21 wild moribund free-living A. pectorosa and 68 hatchery-reared A. pectorosa maintained in silos at the same sites and investigated differences in pathology and microbiologye between groups. No silo mussels presented clinical signs of disease, or gross or microscopic lesions associated with pathological conditions leading to mortality. Our findings reveal a significant association between Yokenella regensburgei and severe multisystemic and multifocal infiltrative hemocytosis with necrosis, consistent with sepsis. Lesions associated with yokenellosis were of sufficient severity and physiological significance to explain mortality in infected hosts. Although our study does not explain the cause of these infections, it confirms that mussels at our study sites are ultimately dying with an infectious disease and that Y. regensburgei can be pathogenic in free-living mussels. Our results underscore the importance of considering bacterial diseases in wild mussel populations and emphasize the need for further research to elucidate the epidemiology and pathogenicity of Y. regensburgei. Overall, our study highlights the importance of integrated approaches combining pathology, microbiology, and epidemiology in freshwater mussel conservation efforts.

[This corrects the article DOI: 10.1371/journal.pone.0223525.].

Ecosystem services are the benefits that humans derive from ecosystems. Freshwater mussels perform many important functions in aquatic ecosystems, which can in turn be framed as the ecosystem services that they contribute to or provide. These include supporting services such as nutrient recycling and storage, structural habitat, substrate and food web modification, and use as environmental monitors; regulating services such as water purification (biofiltration); and provisioning and cultural services including use as a food source, as tools and jewelry, and for spiritual enhancement. Mussel-provided ecosystem services are declining because of large declines in mussel abundance. Mussel propagation could be used to restore populations of common mussel species and their ecosystem services. We need much more quantification of the economic, social, and ecological value and magnitude of ecosystem services provided by mussels, across species, habitats, and environmental conditions, and scaled up to whole watersheds. In addition, we need tools that will allow us to value mussel ecosystem services in a way that is understandable to both the public and to policy makers.