Freshwater Mussels as Multifaceted Ecosystem Engineers: Insights into Their Ecological Importance, Bioindication, and Economic Contributions

Abstract

Freshwater mussels play a vital ecological role in aquatic ecosystems, serving as effective natural filters that enhance water quality by removing suspended particles and excess nutrients, thereby preventing eutrophication. Their filtration activity supports overall ecosystem stability and promotes biodiversity by providing habitat structure for various aquatic species. Additionally, mussels are valuable bioindicators of environmental health, reflecting water quality changes and accumulating pollutants, including pharmaceuticals and heavy metals, which can offer insights into pollution trends. Freshwater mussels offer considerable economic potential through sustainable aquaculture, particularly in pearl production and jewelry applications, while also contributing nutritionally in controlled and culturally appropriate contexts. Despite these benefits, freshwater mussels face significant threats, including habitat destruction, pollution, invasive species, and overexploitation. These pressures have resulted in drastic population declines and extinctions across various species. Effective conservation and management strategies are essential to protect freshwater mussels, focusing on habitat protection and restoration, ongoing research, and stakeholder engagement to ensure the sustainability of these crucial organisms. This review highlights the multifaceted ecological and economic values of freshwater mussels, the challenges they face, and the importance of comprehensive conservation efforts to maintain their populations and the health of aquatic ecosystems.

1. Introduction

Freshwater mussels are one of the most diverse and widely distributed groups of bivalves, inhabiting rivers, streams, lakes, and ponds across the globe. Their shells display vibrant colors, diverse shapes, and unique features like ridges, bumps, and spikes (Figure 1). Freshwater mussels have a unique parasitic life cycle involving a larval stage called glochidium, which is released by females into the water column and must attach to a host, typically a fish, to undergo metamorphosis into juveniles [1,2]. Glochidia exhibit diverse shapes—hookless types attach to gills, while hooked forms attach to skin or fins—and must find a host within days, with survival being influenced by species and temperature [3]. Some species produce larval threads that enhance their chances of contacting a host by suspending them in the water. While glochidia derive limited nutrition from their host and generally do not grow during encapsulation, mismatched attachment sites can hinder development [4]. Mussels are intriguing due to their complex life cycles carried out on riverbeds and are among the longest-living invertebrates, capable of surviving up to 100 years [5]. With over 900 species identified worldwide, they play critical roles in maintaining the health and functionality of freshwater ecosystems [6]. Mussels are often regarded as ecosystem engineers because they play a vital role in shaping and maintaining their habitats, thereby influencing the biodiversity and functioning of ecosystems. By forming dense beds or reefs, they create complex physical structures that provide shelter and substrate for a wide variety of organisms, including algae, invertebrates, and fish [7,8]. Mussels also enhance water quality through their filter-feeding behavior, removing suspended particles and nutrients, which can improve light penetration and promote aquatic plant growth [1]. Additionally, their excretions enrich the sediment with organic material, fostering microbial activity and nutrient cycling [9]. These activities collectively modify the physical, chemical, and biological conditions of their environment, demonstrating their significant impact as ecosystem engineers. Freshwater mussels are among nature’s most effective filtration systems. They not only stabilize aquatic ecosystems but also continuously enhance water quality. Each mussel can filter between 5 and 10 gallons of water daily, every day of the year [10]. With nearly 300 species, North America boasts the highest diversity of freshwater mussels in the world. However, over 70% of these species are in decline: 7% are extinct, 21% are classified as endangered, and another 40% are listed as threatened [11]. Historically, these organisms have also held significant economic value, particularly in the pearl and button industries [12].

They play a vital role in the food web, filtering water and transforming otherwise inaccessible nutrients into food for their predators, such as fish, crayfish, amphibians, reptiles, birds, and mammals [13]. Mussel shells also provide habitats for insects and plants, while empty shells become nesting sites for small fish-like darters [14]. Despite their importance, freshwater mussels are among the most endangered groups of animals globally [11]. Threats such as habitat degradation, water pollution, overexploitation, and the introduction of invasive species have led to drastic declines in their populations [15]. Understanding and appreciating both the ecological and economic contributions of freshwater mussels are essential for developing effective conservation strategies.

While freshwater mussels have historically been exploited for various purposes, including food, fashion (e.g., buttons and jewelry), and pearl production, it is critical to emphasize that such practices have often led to severe population declines and habitat degradation. In the current context of biodiversity conservation, the promotion of wild harvest for commercial use is neither ecologically sustainable nor ethically justifiable. Therefore, this manuscript does not advocate the extraction of mussels from natural ecosystems for economic purposes. Rather, it underscores the importance of sustainable aquaculture-based practices as the only permissible and responsible pathway for economic utilization. Freshwater mussel aquaculture, when properly managed, can support pearl production and rural livelihoods while also contributing to species conservation, water quality enhancement, and ecological restoration. It is essential that any economic use of mussels is guided by strict regulatory frameworks, ecological impact assessments, and conservation priorities, aligning with global best practices for the protection of freshwater biodiversity.

Building on previous ecological and conservation-focused reviews, this article systematically synthesizes and expands the current understanding of freshwater mussels by incorporating recent findings across multiple domains: ecotoxicology, ecosystem services, economic utilization, and conservation threats. This review also uniquely applies a PRISMA-based methodology, thereby ensuring a rigorous, transparent, and replicable synthesis of the literature. In doing so, it integrates emerging perspectives on mussels’ roles in pollution mitigation, bioaccumulation of pharmaceuticals and heavy metals, habitat enhancement, and socioeconomic contributions, areas which have been addressed in isolation but not yet comprehensively unified in a single review.

2. Materials and Methods

This review employs the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [16] methodology to ensure a comprehensive and systematic approach to the literature on the ecological and economic significance of freshwater mussels. The PRISMA method provides a framework for conducting transparent and replicable reviews, enhancing the reliability and validity of the findings.

2.1. Literature Search

A systematic search of the literature was conducted using multiple academic databases, including PubMed, Scopus, Google Scholar, and ResearchGate. The search was aimed at identifying studies that address the ecological functions and economic values of freshwater mussels, as well as the challenges they face. The following keywords and their combinations were used: “freshwater mussels”, “Unionida”, “Lasmigona”, “zebra mussel”, “Lamellidens”, “ecotoxicology”, “ecological functions”, “economic value”, “water filtration”, “bioindicators”, “bioaccumulation”, “nutrient cycling”, “habitat structuring”, “pearl industry”, “invasive species”, “overexploitation”, “environmental monitoring”, and “ecosystem services”.

2.2. Inclusion and Exclusion Criteria

Studies were included in the review if they met the following criteria: population: focused on freshwater mussels, including invasive species, mostly present in the order Unionida; interventions: investigated the ecological roles, economic contributions, or conservation challenges of freshwater mussels; outcomes: reported data on ecological functions (e.g., water filtration and nutrient cycling), economic values (e.g., pearl industry and environmental monitoring), and conservation issues (e.g., habitat degradation and pollution); study type: included primary research articles, reviews, meta-analyses, and case studies; and language: published in English.

Studies were excluded if they focused on marine mussels or other non-freshwater bivalves, did not provide empirical data, or where opinion pieces without scientific backing were published in languages other than English. The data were synthesized qualitatively, focusing on thematic analysis to identify key trends and gaps in the literature.

2.3. PRISMA Flow Diagram and Quality Assessment

A PRISMA flow diagram (Figure 2) was used to document the process of study selection. This included the number of studies identified through database searching, the number of studies screened, the number of studies excluded based on the inclusion and exclusion criteria, and the final number of studies included in the review.

The quality of the included studies was assessed using a modified version of the Newcastle–Ottawa Scale (NOS) for non-randomized studies. This assessment was used to evaluate the methodological rigor of the studies and the reliability of their findings.

3. Ecological Values of Freshwater Mussels

3.1. Water Filtration and Quality Improvement

Freshwater mussels are renowned for their impressive filtration capabilities. By filtering suspended particles, including algae, bacteria, and detritus, they play a crucial role in maintaining and improving water quality [17]. An individual mussel can filter several liters of water per day, cumulatively leading to significant reductions in turbidity and concentrations of potential pollutants in aquatic systems [18].

Different species of freshwater mussels have varying filtration rates, often correlated with their size. Larger mussels typically have a greater filtration capacity due to a larger gill surface area. Vaughn et al. [19] observed that species with larger body sizes and gill surface areas, such as Elliptio complanata, had higher filtration rates than smaller species.

The concentration of suspended particles in the water affects the filtration efficiency of mussels. High concentrations can lead to clogging of the gill structures, reducing the mussels’ ability to filter effectively [20]. Conversely, very low concentrations might not provide sufficient nutrition. Moderate water flow can enhance filtration efficiency by supplying mussels with a continuous flow of particulates. However, excessively high flow rates might impede the filtration process due to physical stress on the mussels or difficulty in maintaining their position [21].

This filtration process not only clarifies water but also facilitates the removal of excess nutrients, helping to prevent eutrophication and maintain the health of aquatic ecosystems [10]. By filtering the water, it provides oxygen for respiration and food in the form of algal cells, bacteria, and detrital particles, which are trapped on the gills and then transferred to the mouth. Through these filtration activities, suspended solids are significantly reduced, improving light penetration and oxygen levels in aquatic environments. By filtering bacteria, algae, and organic detritus, mussels reduce microbial loads and pathogens in aquatic systems [18]. Their ability to sequester contaminants, including bacteria and viruses, in their tissues further contributes to water purification [10]. In wastewater contexts, mussel-mediated filtration has been shown to improve effluent quality by lowering biochemical oxygen demand (BOD) and reducing coliform counts, offering a sustainable complement to conventional treatment methods [20,22]. This, in turn, benefits other aquatic organisms, such as fish and plants, while promoting overall ecosystem stability and resilience. Moreover, mussels can sequester contaminants in their tissues and shells, effectively acting as natural water purifiers and contributing to the overall resilience of freshwater habitats [23].

3.2. Bioindicator of Environment

Freshwater mussels act as bioindicators due to their sensitivity to changes in water quality and environmental conditions. Their presence and filtration activity can reflect the health of the aquatic environment, making them essential components in monitoring and conservation efforts [24]. Mussels can accumulate pollutants in their tissues at concentrations higher than those found in the surrounding water, effectively magnifying the presence of contaminants and making them easier to detect and quantify [25]. The long lifespan and stationary nature of mussels enable them to integrate pollution data over time and across specific locations. This provides valuable insights into the temporal and spatial distribution of pollutants, helping identify trends and sources of contamination [26]. Mussels are widely distributed across various freshwater systems, facilitating comparative studies across different geographic regions. This comparability enhances the ability to assess regional pollution levels and develop standardized monitoring protocols [27].

Numerous studies have demonstrated the effectiveness of freshwater mussels as indicator organisms of aquatic pollution. For example, a study conducted in the Mississippi River basin utilized freshwater mussels to assess the levels of trace metals, such as mercury, lead, and cadmium, in different water bodies [28]. The results revealed significant variations in metal concentrations across sites, reflecting the impact of local industrial activities and urban runoff on water quality.

In North America, researchers have used freshwater mussels to assess the presence of microplastics in freshwater systems. A study conducted in the Laurentian Great Lakes found significant amounts of microplastics in mussel tissues, highlighting the pervasive nature of plastic pollution in freshwater environments and the potential risks to aquatic organisms and food webs [29]. Mussels, particularly species like Unio crassus and Unio tumidus, serve as effective indicators for environmental monitoring, especially for microplastic contamination in aquatic ecosystems. As filter feeders, mussels ingest small particles, including microfibers, making them suitable for studying pollution (Figure 3). Research in the Tisza River, Hungary, showed that Unio tumidus has a higher accumulation capacity for fibers compared to Unio crassus, highlighting its potential as a reliable biomonitor for tracking fiber contamination in freshwater environments [30]. Moreover, Unio ravoisieri has been shown to accumulate trace metals (e.g., Cd and Pb) and organic pollutants at high concentrations, reflecting localized industrial contamination in North African freshwater systems [31]. Similarly, Unio gibbus exhibits strong correlations between tissue pollutant loads (e.g., PCBs and pesticides) and sediment contamination levels in European rivers, making it a reliable species for long-term monitoring [32].

Another study in Central Europe used the zebra mussel (Dreissena polymorpha), an opportunistic sentinel species, to monitor the presence of pharmaceutical residues, heavy metals, and pesticides in river and lake water [33,34,35]. The zebra mussel has been widely used in Europe and overseas for freshwater quality assessment and biomonitoring due to its ability to bioaccumulate various pollutants in its soft tissues. Initial studies in the 1970s focused on heavy metal contamination, identifying notable levels of metals such as Cd, Cu, Pb, and Zn in industrialized regions across Central Europe. Subsequent research expanded to Italy, Spain, and the United States, where zebra mussels were employed to monitor heavy metals, persistent organic pollutants (POPs), and radionuclides in water bodies such as the Great Lakes and Lake Maggiore [36,37,38,39]. These studies revealed alarming levels of pollutants, including DDT, PCBs, and mercury, highlighting zebra mussels’ utility in identifying contamination hotspots and tracking long-term pollution trends [40,41].

The ecological indicator utility of mussels extends beyond pollutant accumulation. Species like Potomida littoralis and Anodonta cygnea have been used to assess endocrine-disrupting compounds (EDCs) and microplastics, revealing species-specific differences in uptake efficiency [42,43]. For instance, Anodonta cygnea displays higher microplastic ingestion rates compared to Unio pictorum in the same habitat, suggesting that morphological or behavioral adaptations influence bioindicator performance [44].

In addition to passive biological monitoring (PBM), laboratory studies have utilized biochemical biomarkers in zebra mussels as early warning systems for pollutant exposure [33,45]. Enzymatic activities, including DT-diaphorase, NADPH–cytochrome c reductase, and EROD, have been investigated to assess the impacts of metals, PCBs, and other contaminants [46]. Changes in antioxidant enzyme levels, oxidative stress markers, and tissue damage indicators further underline the species’ effectiveness in evaluating the toxicity of emerging pollutants [47]. These methods, known for their sensitivity and efficiency, continue to play a crucial role in aquatic environmental monitoring programs worldwide.

Due to their sensitivity to environmental changes and ability to accumulate contaminants, freshwater mussels serve as effective biomonitoring agent for health of aquatic ecosystems [48]. Their presence, abundance, and physiological conditions provide valuable information on water quality and the impacts of pollution, aiding in environmental assessment and management efforts [49,50].

The use of mussels in biomonitoring programs contributes economically by enabling early detection of ecological disturbances, thereby preventing costly environmental degradation and facilitating informed decision making in water resource management [51].

The ecological services provided by freshwater mussels, such as water purification and habitat enhancement, translate into substantial socioeconomic benefits. Improved water quality reduces the costs associated with water treatment for human consumption and supports recreational activities like fishing and boating, which are important for local economies [52]. Furthermore, healthy mussel populations contribute to the sustainability of fisheries by supporting robust and diverse aquatic communities, thereby providing food resources and livelihoods for human populations dependent on freshwater systems [53].

3.3. Bioaccumulation of Pharmaceuticals and Personal Care Products (PPCPs)

PPCPs encompass a wide range of substances, including prescription and over-the-counter drugs, fragrances, and other chemicals used in personal care products. These substances enter freshwater systems through various routes, particularly from wastewater treatment plant (WWTP) effluents, which are often unable to completely remove these compounds [54,55]. Certain PPCPs exhibit distinct seasonal patterns that correlate with human activity and environmental conditions. Cotinine, a metabolite of nicotine, peaks in mid- to late summer, aligning with increased cigarette use in warmer months [56]. Similarly, diethyltoluamide (DEET), an insect repellent, is more prevalent in water bodies from late spring to late summer due to heightened insect activity [57]. These trends highlight the influence of both anthropogenic activities and natural environmental cycles on PPCP concentrations in freshwater systems.

Freshwater mussels, such as Lasmigona costata, serve as valuable environmental indicators of aquatic contamination due to their ability to accumulate pollutants over time. Studies have detected a wide range of PPCPs in mussel tissues, including stimulants, anti-inflammatory drugs, antibiotics, antidepressants, antihistamines, and even illicit drugs like cocaine and amphetamines [58]. This diversity reflects the various sources and uses of PPCPs, as well as the mussels’ exposure to contaminated water and sediments.

Research comparing caged and wild mussels in the Grand River, Ontario, found similar PPCP profiles, suggesting that mussels accumulate PPCPs from their environment relatively quickly, reaching equilibrium with their surroundings [58]. Despite the differences in collection years and locations, both caged and wild mussels upstream of the Kitchener WWTP exhibited comparable numbers of PPCPs detected and similar concentration profiles, indicating consistent exposure and bioaccumulation patterns.

Mussels often exhibit higher concentrations of PPCPs compared to other aquatic organisms, such as fish. For example, Metcalfe et al. [59] reported that concentrations of antidepressants were significantly higher in wild mussels than in fathead minnows (Pimephales promelas) caged at sites downstream of the Kitchener WWTP. This finding suggests that mussels have a greater potential for bioaccumulation, likely due to their filter-feeding habits and prolonged exposure to contaminants in their habitats.

Generally, a substance is considered bio accumulative if its BAF (bioaccumulation factor) is equal to or greater than 5000 or if its log K_ow (octanol–water partition coefficient) is greater than 5 [60]. Although most PPCPs are considered non-bioaccumulative, several, including amitriptyline, amlodipine, sertraline, and triclocarban, have been found to exceed a BAF of 5000 in freshwater mussels, with some having log K_ow values near or above 5 [58]. The bioaccumulation of PPCPs in mussels can have significant ecological implications. Mussels are integral to aquatic ecosystems.

3.4. Bio-Absorption of Metals

The research by Hossain et al. [61] discusses the use of freshwater mussel shells for metal removal, specifically using the shells of Lamellidens marginalis. This species is common in wetlands of Assam and West Bengal, India, and its shells are often discarded as waste after the soft tissue is consumed for its protein content. This study evaluated the potential of mussel shell dust (MSD), derived from the discarded shells of freshwater mussels (Lamellidens marginalis), as a biosorbent for removing heavy metals like cadmium, zinc, and lead from aqueous solutions. The shells were processed into granules, with smaller particles (≤200 µm) selected for their higher adsorption potential. Characterization using energy-dispersive X-ray spectroscopy (EDX) revealed a calcium carbonate (CaCO₃)-rich composition, and post-treatment EDX confirmed successful cadmium adsorption. Adsorption efficiency was influenced by several factors: it increased with pH, peaking at pH 6 before declining due to potential precipitation; higher initial metal ion concentrations enhanced adsorption capacity up to saturation at 800 mg/L; and increasing the biosorbent dose improved adsorption due to more available binding sites. Maximum adsorption was achieved within 60 min, indicating equilibrium [61].

Mechanistic insights from Fourier-transform infrared spectroscopy (FTIR) identified functional groups like hydroxyls and carbonyls as active in metal binding, while scanning electron microscopy (SEM) showed surface changes post-adsorption, suggesting metal precipitation [62]. The adsorption process was best described using the Langmuir isotherm model, indicating monolayer adsorption on a homogeneous surface, and kinetic analysis favored the pseudo-second-order model, highlighting chemisorption as the dominant mechanism. Comparative analysis showed that cadmium had the highest adsorption capacity (18.18 mg/g), followed by zinc (10.64 mg/g) and lead (8.06 mg/g) [61]. Overall, MSD demonstrated effective and eco-friendly heavy metal removal, leveraging its natural composition to minimize secondary pollution. This study supports the use of MSD as a sustainable, low-cost biosorbent in wastewater treatment and bioremediation of heavy metals in freshwater ecosystems, particularly in regions with abundant mussel shell waste (Figure 4).

3.5. Nutrient Cycling and Energy Transfer

Freshwater mussels serve as key ecosystem engineers, significantly contributing to nutrient cycling and energy transfer in freshwater ecosystems [19,63]. Through their filter-feeding activities, mussels extract particulate nutrients from the water, converting them into soft tissue, shell material, biodeposits (feces and pseudofeces), and dissolved nutrients [10,17]. These excreted nutrients are readily utilized by algae and heterotrophic bacteria, which subsequently cascade through aquatic food webs, enhancing biodiversity and improving water quality [13]. Mussels also alleviate nutrient limitations in water bodies by influencing algae composition; for example, in nitrogen-limited systems, they reduce nitrogen-fixing blue-green algae, promoting the growth of diatoms. Additionally, mussels link water column nutrients to sediments by depositing particulate matter, creating nutrient-rich hotspots around their beds that influence downstream ecosystems [9,64]. Nutrient storage in mussel tissues and shells provides long-term cycling benefits, as decomposition and shell dissolution gradually release stored nutrients back into the ecosystem.

Mussels also play a critical role in energy transfer by supporting aquatic and terrestrial food webs. Dense mussel beds act as biological hotspots, enriching benthic algae and macroinvertebrate communities, which, in turn, sustain higher trophic levels, such as fish [52,65]. Beyond aquatic systems, mussel-derived nutrients benefit terrestrial ecosystems by supporting terrestrial invertebrates like spiders, thereby linking aquatic and terrestrial food webs [65]. These processes contribute to the energy flow within the ecosystem and supports various trophic levels, including fish and invertebrate populations [66,67].

3.6. Habitat Structuring and Biodiversity Enhancement

Freshwater mussels significantly enhance habitat structuring and biodiversity by acting as ecosystem engineers. Their shells, whether living or dead, contribute to habitat complexity, creating microhabitats that offer shelter and breeding grounds for numerous aquatic species, including macroinvertebrates and small fish [7,8], and protection from predators, currents, and sediment stress. This structural diversity supports a wide range of organisms, including benthic macroinvertebrates and fish, fostering a biologically rich environment. The physical and functional roles of mussels, thus, make them critical components of benthic ecosystems.

The influence of mussels extends beyond physical habitat creation to nutrient cycling and productivity. Mussels excrete nitrogen and phosphorus while depositing biodeposits such as feces and pseudofeces, which enrich the surrounding environment [68]. These nutrient inputs stimulate algal and invertebrate growth, enhancing primary and secondary production. Hopper et al. [68] demonstrated that fish are attracted to mussel patches due to the habitat and trophic subsidies provided by mussel shells and biodeposits. This attraction increases spatiotemporal overlap between fish and mussels, strengthening ecosystem processes such as nutrient cycling and connecting benthic and pelagic food webs. Additionally, the burrowing activities of mussels aid in sediment mixing and oxygenation, further contributing to the ecological health and stability of aquatic habitats [69].

The effects of freshwater mussels on habitat structure and ecosystem function are strongly influenced by species composition. Native mussels such as Potomida littoralis and Unio delphinus contribute to habitat heterogeneity by modifying benthic substrates in ways that promote colonization by diverse macroinvertebrate communities [70,71]. These structural changes, along with the mussels’ filtration activity and biodeposition, enhance both biodiversity and functional diversity within freshwater systems. Additionally, native mussels engage in a range of ecological interactions, including mutualistic and commensal relationships with algae, invertebrates, and host fish species, contributing to nutrient cycling, energy flow, and habitat connectivity. While most native species are ecosystem facilitators, their effects can vary: some may exert competitive pressures on co-occurring benthic fauna under resource-limited conditions. Understanding this variability among native species is essential for ecosystem-based management and for maximizing the biodiversity-supporting roles of mussels in freshwater habitats. Overall, freshwater mussels play a pivotal role in enhancing ecosystem resilience and maintaining ecological processes [72].

4. Economic Values of Freshwater Mussels

4.1. Mussel Flesh as Food and Its Bioactivities

Freshwater mussels provide a superior source of proteins, essential amino acids, fatty acids, and both macro- and trace minerals for human nutrition compared to marine bivalves and other types of commercial meat. Mussel meat sells at rate of USD 4.5 to USD 8.5 per Kg depending upon the mussel species and variety. Lamellidens species have been identified as rich in proteins, containing essential dietary amino acids and taste-enhancing amino acids like glutamic acid, glycine, alanine, proline, and arginine. Their tissues are composed of medium- and long-chain saturated fatty acids, as well as monounsaturated and polyunsaturated fatty acids. Notably, they contain a high proportion of essential omega-3 (ω-3) and omega-6 (ω-6) fatty acids, with slight variations across species [73,74]. Mineral analysis indicates that Lamellidens species are a valuable source of both macro- and trace elements for human nutrition, supplying over 25% of the recommended dietary allowance (RDA) for certain minerals. They are particularly rich in calcium (Ca), iron (Fe), zinc (Zn), and copper (Cu), although magnesium (Mg) is comparatively lower. Lamellidens species are excellent sources of iron and copper, meeting more than 25% of the RDA per 100 g of raw tissue, while calcium and zinc contribute 16.78% and 10% of the RDA, respectively [75].

Mussel protein peptides exhibit diverse bioactivities depending on the receptors they interact with, including antioxidant, anti-inflammatory, anticancer, antimicrobial, antihypertensive, anticoagulant, antithrombotic, and antifatigue effects, along with ACE inhibition [76,77]. Mollusk-derived polysaccharides are highly effective in scavenging free radicals. Examples include the polysaccharide SVP from Patinopecten yessoensis scallops, which shows significant hydroxyl radical scavenging activity at concentrations of 6.5 mg/mL, and CFPS-2 from Corbicula fluminea, which acts dose dependently [78,79]. Additionally, polysaccharides from the Chinese surf clam (Mactra chinensis) demonstrate superoxide anion and hydroxyl radical scavenging capabilities, reaching 86.49% and 49.31% scavenging rates, respectively, at a concentration of 0.8 mg/mL [80,81].

Polysaccharides from mollusks influence immune responses. For instance, the polysaccharide HCLPS-1 from Hyriopsis cumingii clams enhances splenocyte proliferation and boosts delayed-type hypersensitivity reactions, underscoring its immune-stimulating potential [80,82]. Similarly, SCP-1 from Sinonovacula constricta can increase macrophage viability, promote phagocytosis, and elevate cytokine production, supporting its role as an immunostimulant [83].

Sulfated polysaccharides from mollusks display antiviral properties, particularly against HIV and HSV-1 [84,85]. A galactan sulfate from Meretrix petechialis effectively inhibits HIV syncytia formation, showing 56% fusion inhibition at 200 µg/mL, and scallop skirt glycosaminoglycan (SS-GAG) also exhibits substantial anti-HSV-1 effects [86,87]. Oyster polysaccharides (O-P) inhibit Hepatitis B Virus (HPV) by reducing DNA replication and antigen secretion [87], showing IC50 values of 294 µg/mL for HBsAg and 168 µg/mL for HBeAg [88].

Mussel polysaccharides, especially sulfated ones, demonstrate potent anticancer effects [80]. For instance, polysaccharides from Perna viridis and GAG-rich fractions from squid ink show anti-proliferative effects on various cancer cells and a reduction in tumor growth in vivo [89,90]. Non-sulfated polysaccharides, such as the glucan PE from Ruditapes philippinarum, show significant tumoricidal effects on human hepatoma cells and stimulate lymphocyte proliferation [91]. Sulfated mannan extracts from the mucilage of the mud snail Bullacta exarata showed strong inhibitory effects on the growth of B-16 melanoma cells, with an IC₅₀ of 31.1 μg/mL. Additionally, sulfation modification of mussel polysaccharides has been found to enhance their tumor cell inhibition activity [92,93].

Mollusk-derived glycosaminoglycans (GAGs), such as those from scallop skirts (SS-GAGs) and oysters, demonstrate strong antiatherogenic effects, primarily through vascular endothelial cell protection. SS-GAGs help safeguard endothelial cells against oxidative damage caused by oxidized low-density lipoproteins (ox-LDLs) and reactive oxygen species, crucial in atherosclerosis development [94]. This GAG not only reduces foam cell formation, which is key to plaque buildup in arteries, but also enhances antioxidant defenses by increasing glutathione peroxidase activity and nitric oxide (NO) production, supporting vascular health. Similarly, oyster-derived GAGs boost antioxidant activity, elevate NO secretion, and shield endothelial cells from oxidative stress, further reinforcing their potential as therapeutic agents to prevent or mitigate atherosclerosis [95,96].

Mollusks demonstrate a range of other bioactivities beyond the well-documented antioxidant, anti-inflammatory, and immunomodulatory effects. For example, squid cartilage chondroitin sulfate E (CS-E) displays neuroregulatory properties through interactions with specific proteins, including heparin cofactor II and growth factors, which support nerve health [85]. Mollusk polysaccharides, such as those from mussels and oysters, have hepatoprotective effects that mitigate acute liver damage by normalizing liver enzyme levels and reducing oxidative damage [97,98]. In addition, polysaccharides derived from abalone viscera and gonads improve gastrointestinal function by enhancing cholecystokinin (CCK) release through pathways involving CaM/CaMK, cAMP/PKA, and MAPK [99]. Bivalves also exhibit antibacterial activity, with polysaccharides from species like Mactra chinensis showing strong effects against Gram-positive bacteria, further emphasizing the therapeutic potential of molluscan bioactives in medicine [81,100].

4.2. Shell Powder and Its Derivatives

The shell composition of a marine bivalve (oyster) and freshwater bivalve (mussel) is almost similar. The shell constitutes approximately 60% of an oyster’s total weight [101]. Waste products from mussels have potential as safe and eco-friendly functional compounds. Utilizing these waste products as biocompatible antimicrobials could enhance human health and improve waste management practices [102,103]. Mussel and oyster shells are primarily composed of calcium carbonate (CaCO₃; around 95%), along with a small fraction of organic matrix proteins (about 0.1–5%), also known as skeleton or shell proteins [104]. Calcined mussel shell powder has garnered significant interest for its compatibility with living tissues and for its antimicrobial and biocidal activities and biocompatibility. Incorporating these natural antimicrobial agents into both processed and raw foods could provide a secure way to maintain the quality of food. The ability of oyster shells to fight off microorganisms mainly comes from the high pH levels of CaO, a key component in calcined oyster shells that raises the pH of its environment [76]. Calcium ions from CaO interact with cardiolipin (a primary component of the bacterial cell membrane), causing the cell wall to break down and the production of reactive oxygen species (ROS) and free radicals, which significantly impact the integrity of the cell. The antifungal properties of CaO are also linked to its high pH levels and the production of ROS [102]. In 2014, Choi and colleagues extended the shelf life of ham by incorporating calcined shell powder, which effectively prevented microbial growth [105]. Likewise, in 2015, Chen and collaborators developed an antimicrobial agent from the calcined shells of bivalves, hard clams, and sea urchins, successfully inhibiting foodborne pathogens including Staphylococcus aureus, Listeria monocytogenes, Salmonella typhimurium, Enterobacter aerogenes, and Proteus vulgaris [106].

In vitro studies conducted by Feng et al. revealed that matrix proteins aid in the formation and mineralization of osteoblasts [107]. Similar results were observed in in vivo studies. The researchers proposed that matrix proteins may regulate osteogenic growth through different mechanisms in vivo and in vitro (Figure 5). In vivo, after digestion, matrix proteins are transported to bone tissue, where they fulfill their function. Drawing from earlier research on mussel peptides, they speculated that matrix proteins primarily promote biomineralization through phosphorylation [108]. Some studies have indicated that low-molecular-weight proteins exhibit the strongest osteogenic activity. For instance, proteolytes from blue mussels and ark clams support osteogenic expression by modulating phosphorylation via the MAPK pathway [109,110]. In vitro findings suggested that trace amounts of matrix proteins can directly interact with osteoblasts, promoting their formation while inhibiting osteoclast activity. The researchers suggested that matrix proteins may function similarly to osteopontin, directly affecting osteoblasts and modulating cell tissues and the surrounding environment to encourage osteogenesis [107]. Various products in Indian Ayurvedic medicine (Traditional Medicine) are made from pearl and mussel shell powder, marketed under brand names like Motibhasma^®, Moti Pishti^®, and Mukta Pishti^®. These remedies are traditionally used to alleviate symptoms such as cough, cold, asthma, calcium deficiency, and digestive issues. The powder also exhibits anti-inflammatory properties, particularly benefiting the gastric mucosa.

4.3. Pearl and Jewelry Industry

Historically, freshwater mussels have been exploited for their pearls and shells, which have significant economic and cultural value. The nacre, or mother of pearl, produced by certain mussel species is highly prized for jewelry and decorative items (Figure 6 and Figure 7) [111].

In regions like North America and Asia, the collection and cultivation of freshwater pearls have supported local economies and traditional crafts for centuries [112]. Although the industry has declined due to overharvesting and competition from cultured pearls, it still represents an important economic aspect of freshwater mussel utilization [113]. The global pearl industry was valued at USD 11 billion in 2023 and is expected to grow to USD 23.46 billion by 2030. The increasing demand for freshwater pearls is driven by their diverse color range and versatility, making them a more affordable alternative to sea pearls. Freshwater pearls are particularly popular for everyday wear and are commonly used in fashion jewelry [114].

The utilization of freshwater mussels for food, pearls, or ornamental purposes must be strictly limited to sustainable aquaculture systems. Harvesting from wild populations is not only ecologically unsound but also contributes to biodiversity loss and population collapse, as observed in several regions globally. In contrast, aquaculture provides a controlled and renewable approach that minimizes environmental impact while supporting economic opportunities. Current best practices emphasize environmentally friendly rearing techniques, genetic conservation of native species, and closed-loop production systems to ensure ecological integrity. Therefore, any mussel-based industry, whether for nutrition, jewelry, or fashion, must be rooted in scientifically guided, conservation-compliant aquaculture models to prevent further endangerment of wild mussel populations.

5. Threats to Freshwater Mussel Populations and Conservation Strategies

5.1. Habitat Destruction and Pollution

Despite their ecological and economic importance, freshwater mussels face numerous threats that have led to widespread population declines and extinctions (Table 1). Recent studies indicate that close to one-third of the world’s freshwater mollusks are at risk of extinction, with gastropods facing higher threats than bivalves [115]. Human activities such as dam construction, dredging, and land development have significantly altered freshwater habitats, leading to the loss and fragmentation of suitable environments for mussels [116]. Changes in water flow, sedimentation patterns, and habitat connectivity adversely affect mussel survival, reproduction, and dispersal [117]. Habitat modification, particularly through damming and river fragmentation, is another significant threat to freshwater mussels. In the Nearctic region, where 36% of species are threatened, dam construction has been linked to severe population declines [118,119]. Dams alter sediment transport, water quality, and the availability of host fish, which are crucial for mussel reproduction. In North America, large dam projects have contributed to the decline of over 70% of native mussel species in some river basins [120,121]. The Indo-Burma region also faces similar challenges, with 17% of freshwater mollusks being threatened by habitat fragmentation [122]. The increasing global demand for hydropower exacerbates this issue, with thousands of new dams planned worldwide, further disrupting freshwater ecosystems (Table 1).

Pollution, particularly from agricultural runoff, industrial effluents, urban waste water, and sedimentation, is the most frequently reported threat, affecting 27% of assessed freshwater mollusk species globally [123]. Contaminants such as heavy metals, pesticides, and pharmaceuticals can impair mussel health and reproductive success, leading to population declines [28,124]. In the Afrotropics and Indomalaya, pollution is the primary cause of species decline, significantly impacting freshwater mussels, especially at juvenile stages, where exposure can lead to lethal and sublethal effects on survival and reproduction [115,125]. In Europe, 44% of freshwater mollusks are threatened, with pollution cited as a major driver. Similarly, in North America, over 200 unionid mussel species have been classified as extinct, possibly extinct, or critically endangered due to pollution and habitat degradation [115]. Emerging contaminants, such as pharmaceuticals, heavy metals, and microplastics, are increasingly detected in freshwater systems, raising concerns about their long-term impact on mussel health. Competition among individuals can lead mussels to increase water uptake through their gills. This results in congestion and the accumulation of harmful substances, including pollutants, in their tissues, potentially raising mortality rates [126,127]. Anthropogenic compounds and heavy metals can impact the defense mechanisms of bivalve mollusks and increase their susceptibility to diseases [128,129]. Moreover, environmental contaminants can exert direct toxic effects on tissues or cells. Mussels, in particular, have been shown to have weaker defense mechanisms against metal-induced oxidative stress and toxicity compared to oysters. Funes et al. [130] found that the activity of antioxidant enzymes in mussels is inadequate when compared to the Pacific oyster, C. gigas, indicating that mussels are less protected from oxidative stress related to metal pollution.

5.2. Climate Change, Overexploitation, and Invasive Species

Climate change is an emerging but increasingly significant threat to freshwater mussels. Rising temperatures, altered precipitation patterns, and an increased frequency of extreme weather events disrupt freshwater ecosystems. During the 20th century, the global mean air surface temperature increased by 0.3–0.6 °C, with Europe experiencing warming above the global average at 0.8 °C [131]. Climate models predict further increases of 1.5–4.5 °C by the end of the 21st century, with significant consequences for freshwater habitats. Studies suggest that climate change could impact 50% of global freshwater fish species, indirectly affecting mussel populations that rely on these fish for larval development [132]. In Scotland, where freshwater pearl mussels (Margaritifera margaritifera) are concentrated, increased storm events and flooding have been linked to significant population declines. Large floods, once rare, have become more frequent, washing away juvenile mussels and degrading riverbeds. In northwestern Scotland, 16 populations (27.5%) of M. margaritifera are expected to suffer significant losses due to a projected 0.5–1.0 m sea level rise over the next 100 years [133,134,135]. The timing of mussel reproduction is also affected by temperature fluctuations, with shifts in spawning periods potentially disrupting host fish–mussel interactions (Table 1).

Unsustainable harvesting for pearls, shells, and the pet trade has historically contributed to the depletion of mussel populations [136]. Although regulations have reduced some forms of exploitation, illegal collection and trade continue to pose threats in certain regions [137].

The introduction of invasive mussel species, such as zebra mussels (Dreissena polymorpha) and golden mussels (Limnoperna fortunei), significantly impact native mussel populations through ecological and trophic alterations, as evidenced in the research discussed (Table 1). Both species share traits that allow them to aggressively invade and transform aquatic ecosystems, often at the expense of native species [138].

Zebra mussels, originally from the Caspian and Black Seas, have profoundly impacted North American freshwater ecosystems since their introduction in 1988 [139]. Their rapid proliferation has been linked to habitat modification, the alteration of trophic interactions, and shifts in nutrient cycling, oxygen availability, and sedimentation rates. These changes directly and indirectly affect native mussel species by altering food availability and the physical and chemical conditions of their habitats [138,140]. Additionally, zebra mussels can outcompete native mussels for resources and physically attach to their shells, impairing their ability to feed, respire, and reproduce, often leading to mortality.

Similarly, golden mussels, native to Asia but now established in South America, exhibit high filtration rates (200–300 mL/h), which modify abiotic parameters such as water transparency and nutrient concentrations [141]. These changes mirror those caused by zebra mussels, including reduced seston and organic matter and increased ammonia, nitrate, and phosphate levels. Golden mussels also physically attach to native bivalves like Anodontites trapezeus, preventing them from opening their valves for essential functions [142]. Over time, this leads to the death of the host mussels.

The introduction of invasive mussels also indirectly impacts native mussel populations by restructuring food webs. Both invasive mussel species promote what has been termed “benthification”, where carbon and energy flows are redirected from pelagic (open water) pathways to benthic (bottom-dwelling) pathways [143,144]. This shift favors species associated with benthic habitats, including the invasive mussels themselves, while disadvantaging native pelagic and benthic species that are less adaptable to the new conditions. Invasive species can also introduce novel pathogens and alter ecological dynamics, further threatening native mussel communities [145]. Their invasive characteristics and ecosystem-level impacts underscore the need for management strategies to mitigate their effects on native biodiversity.

Emerging research indicates that bacterial, viral, and parasitic infections pose a growing threat to freshwater mussel populations. Mussels are vulnerable to a variety of pathogens, including Aeromonas hydrophila, Mycobacterium spp., and viral agents like iridoviruses, which have been linked to mass die-offs in both North America and Europe [146]. Parasitic trematodes and protozoans, such as Rhipidocotyle campanula and Ichthyophthirius multifiliis, can infest mussel tissues, impair filtration, reduce reproductive output, and cause systemic damage [147].

Environmental stressors like eutrophication and pollution (e.g., increased ammonia or heavy metal levels) compromise mussel immunity, increasing pathogen load and disease outbreaks [148,149]. For instance, oxidative stress caused by heavy metals can diminish antioxidant enzyme activities (e.g., SOD, CAT, and GPx), leaving mussels more susceptible to opportunistic infections [125]. Furthermore, thermal stress due to climate change may increase the virulence and transmission of aquatic pathogens, exacerbating mortality risks.

These disease threats, although historically under-reported, are increasingly recognized as major contributors to population declines, especially in ecosystems already degraded by anthropogenic pressures.

Table 1. Major threats outline to freshwater mussels across different regions worldwide.

Threat	Global Examples and Data	Source(s)
Pollution	- North America: Agricultural runoff and industrial discharges in interior basins have led to chronic chemical and nutrient pollution. In Missouri’s Big River, mussel density dropped by 70–75% in areas where sediment lead levels exceeded 128 mg/kg compared to less contaminated zones. - Europe: Urban and industrial effluents degrade water quality in several rivers, contributing to toxic conditions in mussel habitats. - Asia: Rapid industrialization introduces emerging contaminants (e.g., microplastics) into freshwater systems. - Pesticides like atrazine reduce mussel survival by 30–60% in lab studies.	[115,150,151,152,153]
Habitat modification and degradation	- North America: Extensive damming and river channelization (e.g., in interior basins) have reduced connectivity and altered sediment regimes. Over 60,000 large dams fragment rivers globally, contributing to declines. In the U.S., 75% of mussel species are extinct or imperiled in dammed rivers. - Europe: River engineering projects—such as modifications in the River Foyle (Northern Ireland)—and water abstraction have led to habitat fragmentation. - Asia: Large-scale water infrastructure development for irrigation and urban supply is rapidly transforming natural riverine habitats. - Global: Excess sediment smothers mussel beds, causing 50–90% declines in density in impacted streams.	[115,132,150,154,155,156]
Climate change	- Europe (Scotland): Predictions indicate a 1 °C increase by the 2020s and a 2 °C rise by the 2050s, leading to more frequent extreme flood events and thermal stress in small streams. - Globally: Shifts in hydrological regimes and increased thermal extremes are likely to disrupt mussel life cycles in temperate and tropical regions alike. Projected warming of 2–4 °C by 2100 could reduce suitable habitat for cold-water mussels by 50%. - North America: Extreme droughts in the southeastern U.S. caused 100% mortality of mussels in intermittent streams.	[132,151,157,158]
Invasive species	- Global: Invasive species contribute to 40% of freshwater mollusk extinctions. - Europe and North America: The spread of invasive bivalves such as zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) competes with native mussels. In the Great Lakes, zebra mussel invasions caused 90% declines in native unionid populations within 8 years. - Asia: Non-native species introductions associated with global trade (e.g., Asian clams, Corbicula fluminea) further alter community dynamics.	[150,151,159,160]
Overexploitation	- Europe (UK): Historical overharvesting for pearls and use as a food source has led to severe population declines in freshwater pearl mussels. - North America: Unsustainable collection practices in earlier decades contributed to the current imperilment of several unionid species. The U.S. pearl button industry harvested ~4000 t of mussel shells annually in the late 1900s, driving regional extinctions.	[115,132,161]
Declining host fish populations	- Europe (Scotland and elsewhere): Declines in Atlantic salmon and brown trout, which serve as obligatory hosts for mussel larvae (glochidia), result in reduced recruitment and compromised life cycles.	[132]
Emerging and novel pollutants	- Globally: New classes of contaminants—such as engineered nanomaterials and microplastics—are increasingly detected in rivers, complicating traditional pollution profiles and interacting with other stressors in both developed and developing regions.	[151]
Declining calcium availability	- Northern Europe: Observations indicate that reduced levels of bioavailable calcium may hinder shell formation and overall physiological health of mussels, potentially exacerbating vulnerability in already stressed systems.	[151]
Cumulative stressors	- Industrialized Regions: In areas with multiple simultaneous pressures (e.g., parts of North America and Europe), the interactive effects of pollution, habitat loss, climate change, and invasive species create compounded challenges, leading to steep declines in mussel populations.	[151]

Table 1. Major threats outline to freshwater mussels across different regions worldwide.

Threat	Global Examples and Data	Source(s)
Pollution	- North America: Agricultural runoff and industrial discharges in interior basins have led to chronic chemical and nutrient pollution. In Missouri’s Big River, mussel density dropped by 70–75% in areas where sediment lead levels exceeded 128 mg/kg compared to less contaminated zones. - Europe: Urban and industrial effluents degrade water quality in several rivers, contributing to toxic conditions in mussel habitats. - Asia: Rapid industrialization introduces emerging contaminants (e.g., microplastics) into freshwater systems. - Pesticides like atrazine reduce mussel survival by 30–60% in lab studies.	[115,150,151,152,153]
Habitat modification and degradation	- North America: Extensive damming and river channelization (e.g., in interior basins) have reduced connectivity and altered sediment regimes. Over 60,000 large dams fragment rivers globally, contributing to declines. In the U.S., 75% of mussel species are extinct or imperiled in dammed rivers. - Europe: River engineering projects—such as modifications in the River Foyle (Northern Ireland)—and water abstraction have led to habitat fragmentation. - Asia: Large-scale water infrastructure development for irrigation and urban supply is rapidly transforming natural riverine habitats. - Global: Excess sediment smothers mussel beds, causing 50–90% declines in density in impacted streams.	[115,132,150,154,155,156]
Climate change	- Europe (Scotland): Predictions indicate a 1 °C increase by the 2020s and a 2 °C rise by the 2050s, leading to more frequent extreme flood events and thermal stress in small streams. - Globally: Shifts in hydrological regimes and increased thermal extremes are likely to disrupt mussel life cycles in temperate and tropical regions alike. Projected warming of 2–4 °C by 2100 could reduce suitable habitat for cold-water mussels by 50%. - North America: Extreme droughts in the southeastern U.S. caused 100% mortality of mussels in intermittent streams.	[132,151,157,158]
Invasive species	- Global: Invasive species contribute to 40% of freshwater mollusk extinctions. - Europe and North America: The spread of invasive bivalves such as zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) competes with native mussels. In the Great Lakes, zebra mussel invasions caused 90% declines in native unionid populations within 8 years. - Asia: Non-native species introductions associated with global trade (e.g., Asian clams, Corbicula fluminea) further alter community dynamics.	[150,151,159,160]
Overexploitation	- Europe (UK): Historical overharvesting for pearls and use as a food source has led to severe population declines in freshwater pearl mussels. - North America: Unsustainable collection practices in earlier decades contributed to the current imperilment of several unionid species. The U.S. pearl button industry harvested ~4000 t of mussel shells annually in the late 1900s, driving regional extinctions.	[115,132,161]
Declining host fish populations	- Europe (Scotland and elsewhere): Declines in Atlantic salmon and brown trout, which serve as obligatory hosts for mussel larvae (glochidia), result in reduced recruitment and compromised life cycles.	[132]
Emerging and novel pollutants	- Globally: New classes of contaminants—such as engineered nanomaterials and microplastics—are increasingly detected in rivers, complicating traditional pollution profiles and interacting with other stressors in both developed and developing regions.	[151]
Declining calcium availability	- Northern Europe: Observations indicate that reduced levels of bioavailable calcium may hinder shell formation and overall physiological health of mussels, potentially exacerbating vulnerability in already stressed systems.	[151]
Cumulative stressors	- Industrialized Regions: In areas with multiple simultaneous pressures (e.g., parts of North America and Europe), the interactive effects of pollution, habitat loss, climate change, and invasive species create compounded challenges, leading to steep declines in mussel populations.	[151]

5.3. Current Protection Measures

Various conservation strategies have been implemented to safeguard freshwater mussels (

Table 2. Conservation efforts for freshwater mussels.

Conservation Measure	Current Major Research Directions and Protection Measures		Source(s)
Legal protection and policy	Description	Regional examples for protection measures	[115,132]
	National and international legal frameworks that restrict harmful activities, regulate exploitation, and establish conservation priorities.	In the UK, Margaritifera margaritifera is protected under the Wildlife and Countryside Act 1981, listed in the Bern Convention and EC Habitats Directive, and included in Biodiversity Action Plans. Global IUCN Red List assessments help guide conservation priorities in multiple regions.
Pollution control	Implementation of stricter regulations and improved management practices to reduce pollutant loads in freshwater systems.	North America and Europe have adopted tighter industrial discharge and urban wastewater standards. In parts of Asia, the adoption of best management practices in agriculture aims to reduce nutrient and pesticide runoff.	[132]
Habitat restoration and flow management	Restoration of natural hydrological regimes and physical habitats through dam removals, re-meandering rivers, and environmental flow programs that mimic natural conditions.	In North America and Europe, dam removal projects and river restoration initiatives have successfully re-established natural flow and sediment dynamics. Scandinavian and UK projects use environmental flow regimes to restore river connectivity.	[132,151,164]
Host fish conservation	Management practices aimed at restoring and supporting populations of key host fish species required for mussel larval development.	In the UK, targeted programs to restore Atlantic salmon and brown trout populations through habitat improvements and restocking efforts have supported mussel recruitment cycles.	[132]
Advanced monitoring and research	Utilization of modern tools such as environmental DNA (eDNA), remote sensing, and next-generation sequencing to monitor populations, understand genetic diversity, and inform conservation strategies.	In North America and Europe, non-invasive eDNA techniques are used to detect and monitor mussel populations. Research projects in Asia and Europe employ next-generation sequencing to delineate conservation units and assess population health.	[151,165]
Invasive species management	Strategies designed to monitor, control, and reduce the impacts of non-native species on native mussel populations.	In European rivers, management programs focus on monitoring invasive species such as Corbicula fluminea and implementing control measures to reduce competition and predation on native mussels.	[70,151,166]
Protected areas and conservation prioritization	Identification of key biodiversity hotspots and establishment of protected areas to safeguard critical habitats from ongoing threats.	IUCN and national assessments have led to the designation of priority conservation areas in Europe (e.g., where 44% of freshwater mollusks are threatened), and similar efforts in Africa and the Indo-Burma region help target limited conservation resources.	[115,122,150]
Global cooperation and public awareness	Collaborative efforts among scientists, managers, and policymakers to share best practices and develop coordinated strategies, complemented by increased public awareness campaigns.	International networks (e.g., IUCN SSC Mollusc Specialist Group) and regional conservation meetings have facilitated cooperation among stakeholders in North America, Europe, and Southeast Asia, leading to shared strategies and public outreach initiatives.	[152,162]

). Habitat restoration initiatives, such as riparian zone reforestation, contribute to riverbank stabilization and help regulate water temperatures. Improving water quality through enhanced wastewater treatment and stricter regulations on agricultural runoff is also crucial. Additionally, conservation breeding and translocation programs have been introduced for critically endangered species like Margaritifera margaritifera, with some success in captive propagation [162,163].

In certain regions, legal protections have been reinforced by designating critical habitats and implementing species recovery plans at national and international levels [162]. However, despite these efforts, several challenges hinder effective mussel conservation. A significant issue is the lack of comprehensive species assessments, leaving many freshwater mussel species understudied and their conservation status uncertain due to insufficient data. Moreover, habitat fragmentation caused by dams and water diversions disrupts mussel–host fish interactions, contributing to population declines. Pollution from industrial and agricultural activities continues to degrade water quality, further threatening mussel survival. Climate change poses an additional risk, with rising temperatures and altered hydrological conditions expected to negatively affect mussel habitats [151].

Furthermore, conservation initiatives often face limitations due to inadequate funding and a lack of public awareness. Unlike more charismatic endangered species, freshwater mussels receive less attention, resulting in lower prioritization in conservation programs.

5.4. Habitat Protection and Restoration

Protecting existing habitats and restoring degraded environments such as gravel pits created by sand mining can provide novel opportunities for supporting biodiversity, including freshwater mussels (Table 2), which often colonize these areas at high densities [167,168]. Efforts include improving water quality through pollution control measures, reestablishing natural flow regimes, and enhancing habitat connectivity [169]. Protecting riparian zones and mitigating the impacts of activities like sand mining through translocation of affected species and sustainable resource management are essential [170]. Employing advanced tools such as remote sensing can help monitor and guide restoration efforts effectively. Implementing and enforcing regulations that control pollution, manage water resources, and prevent illegal harvesting are critical components of mussel conservation [171]. International cooperation and policy frameworks can facilitate the protection of transboundary water systems and support sustainable management practices [172].

5.5. Research, Monitoring, and Stakeholder Engagement

Ongoing research into mussel biology, ecology, and responses to environmental changes is necessary to inform effective conservation actions [173]. The conservation of freshwater mussels is hindered by significant knowledge gaps, particularly in biodiversity-rich but understudied regions like Southeast Asia, Central America, and Africa [174,175]. Many species in these areas lack comprehensive conservation assessments, with a high proportion classified as data deficient on the IUCN Red List. Additionally, historical data on mussel populations are sparse, making it challenging to establish baselines for conservation efforts [150].

Emerging technologies, such as environmental DNA (eDNA) (meta)barcoding and underwater drones, offer promising avenues to improve the speed and accuracy of data collection [176]. Platforms like GenBank, MolluscaBase, GBIF, MUSSELp, and BOLD can facilitate the integration and dissemination of biodiversity data, but collaboration between these platforms is essential to ensure data consistency and accessibility. Monitoring programs that track population trends and habitat conditions enable the early detection of threats and the assessment of conservation efforts’ effectiveness [137]. Raising awareness about the importance of freshwater mussels and engaging stakeholders, including local communities, industries, and policymakers, are vital for fostering support for conservation initiatives [177]. Educational programs and community-based projects can promote stewardship and encourage sustainable practices that benefit both mussels and human populations [178].

6. Conclusions and Future Perspectives

Freshwater mussels are vital to maintaining the health, stability, and resilience of aquatic ecosystems. They serve as natural water purifiers, bioindicators of environmental quality, and key contributors to nutrient cycling and habitat structuring. Additionally, mussels hold significant economic value in sectors ranging from biomonitoring and ecotourism to the pearl and jewelry industries. However, mussel populations worldwide are facing severe declines, driven by habitat destruction, pollution, invasive species, and other anthropogenic pressures. With over 70% of species at risk, urgent conservation action is essential to protect these invaluable organisms and the ecosystems they support.

To avoid further endangerment of natural populations, any economic utilization of freshwater mussels must be strictly restricted to sustainable aquaculture systems. These systems offer a conservation-compatible alternative that can support livelihoods without compromising wild stocks. Incorporating ecological risk assessments, legal safeguards, and habitat-sensitive practices into aquaculture operations will be key to balancing economic development with species protection.

Moving forward, integrated conservation strategies should focus on habitat restoration, water quality improvement, and stricter regulation of pollutants, particularly PPCPs and heavy metals. Expanding research on mussel bioaccumulation capacities and resilience mechanisms may aid in developing targeted restoration and conservation efforts. Additionally, leveraging mussels as bioindicators could facilitate the development of comprehensive water quality monitoring programs, which are essential for maintaining the ecological health of freshwater systems.

Establishing mussel-friendly aquaculture practices and promoting public awareness of their ecological and socioeconomic importance could foster greater support for conservation initiatives. Enhancing genetic diversity through breeding programs, particularly for endangered species, can also contribute to long-term population resilience. By adopting these measures, society can work to preserve freshwater mussel populations, ensuring the sustainability of the vital ecosystem services they provide for generations to come.