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Review

Probable Extirpation of Anodonta vescoiana in Iraq: A Case Study of Unionid Displacement by Sinanodonta woodiana

by
Murtada Naser
1,2,*,
Amaal Yasser
1,2,
Juergen Geist
3,
Karel Douda
4 and
Franz Essl
2
1
School of Environment and Science, Griffith University, 170 Kessels Road, Nathan, QLD 4111, Australia
2
Division of BioInvasions, Global Change and Macroecology, Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria
3
Aquatic Systems Biology, Technical University of Munich, Mühlenweg 22, 85354 Freising, Germany
4
Department of Zoology and Fisheries, Czech University of Life Sciences Prague, Kamýcká 129, 165 00 Prague, Czech Republic
*
Author to whom correspondence should be addressed.
Diversity 2025, 17(6), 415; https://doi.org/10.3390/d17060415
Submission received: 27 May 2025 / Revised: 8 June 2025 / Accepted: 11 June 2025 / Published: 12 June 2025
(This article belongs to the Section Biodiversity Conservation)
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Abstract

:
Conservation of ecologically important freshwater mussels is high on the international agenda, but there is only limited knowledge about the status of rare unionid species in arid and semi-arid areas which are particularly vulnerable. One such example concerns Anodonta vescoiana which was recognized as one of the few endemic species of unionid mussels from Iraq and was restricted to the marshes of southern Mesopotamia and its connected river systems. The last confirmed report of A. vescoiana was in 2009 from the Al-Ezz River. We conducted extensive field surveys during the years 2021 and 2022 at approximately 20 freshwater sites, but we failed to observe any live or dead specimens, suggesting a probable extirpation or severe decline. In contrast, we documented the invasive Sinanodonta woodiana at numerous sites across the Tigris–Euphrates basin including the Al-Ezz River. This documentation of S. woodiana indicates successful establishment of the species and colonization of freshwater systems modified by anthropogenic practices, which include alterations of hydrological dynamics and ecological conditions. Here, we compile existing evidence of the global ecological impacts and development of S. woodiana invasion, while also highlighting Iraq as an important example of the displacement of native unionid mussel species by invasive alien unionids. We assessed the factors that contributed to the disappearance of A. vescoiana in Iraq including biological competition (with S. woodiana), salinity stress, habitat fragmentation, and pollution. The time window to act and prevent the further decline of rare unionid species in Iraq, as well as other arid and semi-arid areas which face similar threats, is short. Urgent actions include systematic monitoring to identify remnant populations, implementing biosecurity policies (for fisheries or habitats), and restoration (of habitats) to secure the long-term persistence of remaining unionid diversity.

1. Introduction

Freshwater unionid mussels are critical components of aquatic ecosystems, providing key ecological functions like water filtration [1], stabilization of substrate [2], and nitrogen and phosphorus cycling [3,4]. Unionids filter-feed and burrow which affects water quality, sediment structure, and supports complex benthic food webs [5,6], making them important providers of ecosystem services [7]. Globally, most unionid mussels are highly imperiled, and many are either rapidly declining or are at the brink of extinction [8].
Habitat destruction, pollution, flow modification, climate change and increasingly biological invasions are the biggest threats to freshwater fauna, including unionids [9,10,11]. Concerning biological invasions, the Chinese pond mussel, Sinanodonta woodiana (I. Lea, 1834), is one of the most invasive bivalve species in the world. It has its native range in East and Southeast Asia and has been introduced to many parts of the world (over 30 countries) primarily through aquaculture, the ornamental fish trade, fish stocking, but also from released specimens originating from the pet shop trade [12]. Its spread is facilitated by high fecundity, by using a wide range of generalist larval hosts, environmental tolerances, and its ability to colonize degraded or artificial habitats [13,14,15,16]. Its potential impacts on native unionid species and other taxa are concerning both due to the species’ continuing spread as well as its interactions with local species [11,17,18].
As S. woodiana becomes established, it frequently displaces native unionid species by monopolizing habitat space, exploiting a wide range of fish hosts, and altering benthic conditions. In many regions across Europe and North Africa, its proliferation has coincided with marked declines in native mussels, suggesting a consistent pattern of ecological displacement and biotic homogenization [13,18,19]. In contrast, native unionid species often need to be supported by captive breeding and other conservation tools [20].
In contrast to North America and Europe, there is little knowledge on the current status of endangered native unionids as well as on the distribution and potential impacts of invasive mussels in arid and semi-arid regions. One such example refers to the unionid mussel Anodonta vescoiana Bourguignat, 1856 which was historically reported in the southern Mesopotamian marshes and nearby river systems in Iraq. With a small range and reliance on stable, low-salinity freshwater environments, A. vescoiana was thought of as ecologically specialist and regionally endemic. However, in two species-habitat ecological surveys conducted in 2021 and 2022 and including the Al-Ezz River (the last known recorded locality) in 2009 [21], no living or dead individuals were observed, suggesting a probable extirpation or disappearance. By contrast, S. woodiana has been encountered in multiple disturbed aquatic ecosystems in southern Iraq throughout the same time.
This study explores the environmental drivers and ecological mechanisms that have likely contributed to the apparent loss of A. vescoiana and the concurrent spread of S. woodiana. By integrating global case studies with region-specific field observations and historical records, we present Iraq as a critical case study of unionid decline in arid and semi-arid regions. In doing so, we emphasize the need for coordinated conservation action, invasive species management, and restoration of freshwater habitat integrity in the Tigris–Euphrates basin and similar vulnerable regions.

2. Global Invasion Dynamics of Sinanodonta woodiana

Sinanodonta woodiana is one of the most widespread invasive unionid bivalves worldwide [11,19]. Native to East and Southeast Asia, it has rapidly expanded across Europe, the Middle East, North Africa, and parts of Central America. Its spread has been largely driven by human-mediated vectors, including carp aquaculture, the ornamental fish trade, and unintentional co-transport with host fish. Once introduced, its establishment is facilitated by its broad environmental tolerance, generalist host use, and high reproductive output [19]. Its glochidia larvae are more tolerant to warmer water where they survive longer than the larvae of native unionids [16], which, along with its flexible host fish use [14,22] and faster growth, all contribute to its competitive advantage over native unionids in many situations [18].
“Following its first European record in Romania in the 1980s [23]”, S. woodiana has since colonized diverse freshwater ecosystems across many European countries, and more recently Türkiye, Iran, and Iraq [24]. Its ability to thrive in degraded, artificial, or thermally impacted habitats gives it a marked advantage in anthropogenically altered environments.
For a comprehensive synthesis of its phylogeny, lineage-specific distributions, and global invasion chronology, see [19]. In this review, we focus on ecological impacts relevant to the Iraqi context, especially the species’ tendency to displace or competitively inhibit native species of freshwater mussels. This includes comparative examples from Europe where its spread has been associated with the decline of Anodonta and Unio species in thermally polluted or canalized waters [25,26,27].

3. Ecological Mechanisms of Displacement

The success of S. woodiana as a globally invasive species lies not only in its broad physiological tolerance and reproductive output but also in its ability to outcompete or suppress native unionid mussels through multiple, interacting mechanisms [11]. These mechanisms operate at individual, population, and ecosystem levels, contributing to the decline or apparent disappearance of sensitive native species, particularly in disturbed or stressed environments such as those found in southern Iraq [14,28,29].

3.1. Competition for Space and Resources

One of the most immediate forms of displacement involves physical space competition. S. woodiana often forms dense, monospecific aggregations in lentic or slow-flowing habitats, which can smother native unionids, alter sediment composition, and monopolize benthic surfaces. These aggregations reduce habitat heterogeneity, displace native mussels from optimal substrates, and limit their access to food particles suspended in the water column [24,30]. Another example of competition for resources is the mechanism of cross-resistance in which S. woodiana induces an increased level of acquired non-specific resistance in fish hosts, thereby subsequently reducing their suitability as hosts for the larvae of native unionids [17].

3.2. Broad Host Fish Range

In contrast to many native unionids, S. woodiana is a host-generalist. It can use a wide variety of both native and non-native fish to complete larval (glochidial) development [14]. This flexibility yields a distinct advantage in newly colonized regions, especially where host suitability for native mussels is decreasing. In Iraq, where freshwater fish diversity is facing strong pressures from pollution and habitat fragmentation, host-generalism is likely to bolster reproductive success for S. woodiana, while limiting recruitment success of endemics, such as A. vescoiana [13,31].

3.3. Rapid Growth and Early Maturity

S. woodiana has a rapid life history strategy, reaching sexual maturity in the first year of life and producing hundreds of thousands of glochidia at each spawning event. In contrast, native unionids have relatively slow growth, delayed maturity, and longer lifespans. Because of these differences in reproduction strategies, S. woodiana can quickly establish and expand populations [18,19,32].

3.4. Tolerance to Environmental Stressors

A crucial facet of the success of the invasive S. woodiana is its tolerance to environmental extremes (high temperature, low dissolved oxygen, nutrient enrichment, and moderate salinity) [33]. These environmental conditions are increasingly occurring in freshwater ecosystems in Iraq, and appear to be due to climate change, upstream water extraction, and pollution [34,35]. Due to its faster development and plasticity, S. woodiana is likely more tolerant concerning stable, oxygen-rich, and low-salinity habitats than A. vescoiana. The alterations of pristine environmental conditions favor S. woodiana while excluding native taxa. A recent study has also shown that the shell shape of S. woodiana makes it is less prone to predation by crayfish compared to several native mussel species [36].

3.5. Facilitation of Biotic Homogenization

As S. woodiana spreads across Iraq’s canals, rivers, and marshlands, it contributes to the homogenization of freshwater communities. The loss of functionally unique species like A. vescoiana and their replacement by generalist invaders reduces regional beta-diversity and diminishes ecosystem resilience. Such homogenization has been reported in multiple European contexts and now appears to be occurring in the Mesopotamian basin, further eroding its ecological distinctiveness [19,37].

3.6. Habitat Modification and Potential Disease Transmission

S. woodiana may also act as a habitat engineer, modifying local sediment properties, changing microbial communities, and influencing water chemistry, analogously to other large alien invertebrates [6,38] and lampreys [39]. These changes may create feedback loops that further favor its persistence. Additionally, although not yet documented in Iraq, S. woodiana has been hypothesized to carry parasites or pathogens that could affect native mussels or host fish species. In heavily managed and aquaculture-linked systems, such risks may be elevated [40].

4. Unionid Loss in Iraq: A Case Study

The decline of native unionid mussels in Iraq represents a severe case of biodiversity loss from environmental change and biological invasion. Heavily impacted is A. vescoiana, an endemic species that has been associated by previous field surveys with the southern Mesopotamian marshes and nearby freshwater environments, including the Al-Ezz River. Historical documents, museum specimens, and field surveys from the mid-20th century noted its presence at multiple sites across the lower Tigris–Euphrates basin, generally during sampling of stable backwater lakes, vegetated wetlands, or other slow-flowing waters.
The last confirmed record of A. vescoiana is from 2009 based on a preserved specimen collected from the Al-Ezz River [21] (Figure 1). Recently, we conducted a thorough survey of many freshwater environments including rivers, canals, marshes, and drainage ditches in southern Iraq between 2021 and 2022. Despite this effort, no live specimens or shells were found, suggesting a probable extirpation or severe population decline. The loss of the mussels coincides with dramatic ecological change, largely caused by anthropogenic hydrologic alteration. For example, construction of dams, irrigation channels, and water diversions across the Tigris–Euphrates system has altered natural hydrology, reducing flow volumes and altering sediment and nutrient dynamics essential for mussel habitats [41,42]. The drying of marshes and disruption of slow-flowing water bodies, where A. vescoiana historically thrived, has eliminated critical habitats. River fragmentation due to anthropogenic structures leads to decreased connectivity and habitat quality, adversely affecting freshwater biodiversity [43]. Also, research indicates that habitat fragmentation can reduce gene flow between populations, leading to decreased genetic diversity and increased vulnerability to environmental changes [44].
One of the most significant changes was the construction of the Al-Ezz waterway in the early 1990s, an artificial channel built to redirect water from the Tigris River to the Shatt al-Arab waterway. The channel was intended to improve irrigation and make conveyance more effective. The project had unanticipated and long-lasting ecological impacts. The Al-Ezz waterway became a major route for flow diversion and thus also contributed to the drainage of substantial areas of the central and southern marshes, particularly the Al-Hammar and Al-Chibayish marshes. The draining of the marshes, paired with the broader Marsh Drainage Campaign that commenced at the time under the former Iraqi regime, resulted in rapid deterioration of the quality of aquatic ecosystems in this area. Whilst artificial channels can sometimes also be habitats of unionids [45], there is no documented record of A. vescoiana from this specific waterway.
Hydrological disconnection, the drying-out of wetland habitats, and changes in sediment deposition and sediment stabilization negatively affected benthic organisms, specifically unionid mussels. A. vescoiana, like other unionids, requires stable substrate, stable water levels, and appropriate host fish for larval development, which were all changed because of habitat fragmentation, pollution from agricultural return flows into surface waters, and the increasing salinity in downstream ecosystems as freshwater inflow decreased and seawater intrusion increased.
Moreover, the ecological vacuum created by the degradation of native habitats may have facilitated the invasion of S. woodiana. This invasive mussel, first reported in Iraq in 2021, appears to have adapted well to the altered hydrological conditions, thriving in artificial and disturbed waterways such as canals and fishponds [18]. Its rapid spread across southern Iraq, particularly in regions once dominated by native mussels, raises the possibility that it has contributed to the competitive exclusion or direct displacement of A. vescoiana, consistent with patterns observed in other parts of the world (Table 1).
While strong spatial and temporal overlap between the establishment of S. woodiana and the decline of native unionid mussels is consistently observed across multiple regions, direct experimental confirmation of causality is limited. The impacts listed below should therefore be interpreted as probable associations, with biological displacement by S. woodiana acting alongside other stressors such as habitat degradation, pollution, and hydrological alteration.
This spatial overlap is illustrated in Figure 2, which shows historical records of A. vescoiana alongside recent and present-day occurrences of S. woodiana.
The loss of A. vescoiana in Iraq thus reflects a broader trend of species decline driven by the interplay of environmental degradation and biological invasion. It also serves as a critical case study in the importance of hydrological management, habitat restoration, and biosecurity policies to prevent further extirpations of native freshwater fauna in the region.
Also, climate change has become an important factor in the degradation of freshwater ecosystems in Iraq, and particularly in the water-stressed southern region. Rising temperatures have cause increased evaporation, especially during the long arid period of hot summer months, and can have severe consequences for freshwater mussels as recently reviewed [10]. Changes in precipitation, especially during the winter months when we see recharge, has resulted in lower and more unpredictable rainfall. These changes to the climate have altered the total volume of surface water and surface water flows, which has fundamentally changed the hydrology of important freshwater ecosystems including rivers, canals, and marshes [51]. In addition, changes to the rivers themselves [51] as well as those in land use need to be considered [52]. Climate-change impacts often result in combined changes of temperature regimes, flow regimes and fine sediment input which can act synergistically [53,54] and impact host fishes as well as mussels themselves.
Additional to the impacts related to climate change and climatic variability is the issue of transboundary water management, chiefly large dam construction and irrigation developments in upstream countries. For instance, the Turkish GAP project and damming of the Tigris and Euphrates Rivers have severely reduced the freshwater inflows into Iraq, resulting in long periods of low discharge and lowered water levels in the southern Mesopotamian plain [55,56]. Dams are known to homogenize abiotic habitat conditions and result in community shifts towards generalist species [57,58]. As a result, marshes and river ecosystems that once supported endemic unionids like A. vescoiana have been degraded by fragmentation in the southern Mesopotamian plain, becoming more shallow, isolated and physico-chemically altered.
Reduced freshwater inflow not only results in salinity intrusion but aggravates it, as is the case in southern Iraq, where tidal influence from the Persian Gulf combines with reduced river flow. Salinization modifies the chemical profile of freshwater habitats and in many instances leads to salinity levels that exceed the tolerance thresholds of many native aquatic species, including unionid mussels. This leads to an alteration in habitat suitability to the detriment of a variety of freshwater species that are not euryhaline or at least generalist invaders such as S. woodiana, which are suited for more unstable habitat conditions and are able to thrive under such conditions [51,59].
When taken together, these stressors of climatic and hydropolitical perturbation already have a tendency to find themselves in a co-dependent relationship, establishing conditions for the equivalent of a perfect storm for unionid decline, and allowing for the loss of resilience in ecosystems, reproductive catastrophes, and bioinvasions—i.e., A. vescoiana is causally related to what is happening more broadly in arid and semi-arid areas, where a combination of climate change, water control upstream, and ecological disturbance result in local extirpation of specialized freshwater taxa.
Along with changes in climate and hydrology, human activities significantly impact the ecological degradation in Iraq’s freshwater ecosystems. The development of irrigated agriculture along the Tigris and Euphrates has increased runoff of fertilizers, pesticides, and organic matter, which has increased nutrient loads and eutrophication of adjacent water bodies [60]. Similarly, untreated urban wastewater and industrial discharges from petrochemical and oil-production activities are directly discharged to rivers and canals, introducing numerous toxic constituents including heavy metals, petroleum hydrocarbons and suspended solids [61,62].
These pollutants can significantly affect the chemistry of the water, availability of oxygen, stability of benthic substrates, and create conditions that are unsuitable for sensitive unionid mussels, such as A. vescoiana, which require clean and well-oxygenated environments with stable chemistry to persist and reproduce. The larval stages (glochidia) of native mussels are relatively vulnerable to the dynamic nature of pH, oxygen, and contamination, which can adversely affect their ability to attach to host fish, and/or complete metamorphosis [63,64].
Conversely, these same habitats that are disturbed and degraded are often invaded by generalist invasive species such as S. woodiana. The presence of pollution, varying oxygen values, and increased nutrient values uniquely position S. woodiana to succeed in stressed environments. In addition, widespread invasive success of S. woodiana changes the composition of community structures by eliminating unionids [18,27]. Examples in Europe illustrate that healthy stream ecosystems with intact populations of native mussels have a greater resilience against biological invasions of non-native mussels where they can only establish at low densities [2,11].
This pollution-driven transition has illustrated the effects of multiple anthropogenic stressors and their synergistic effects such that habitat modification, pollutants, and biological invasions combine together to exacerbate the decline of endemic species [65,66]. In the absence of effective remediation strategies including wastewater treatment, pollution mitigation, or habitat restoration, these trends will continue and represent a long-term threat to Iraq’s freshwater biodiversity and ecosystem services.
At the same time, S. woodiana has colonized many disturbed freshwater habitats in southern Iraq, notably in artificial channels, drainage ditches, rivers, streams, wetlands and fishponds, largely impacted by pollution, hydrological alteration, and increasing salinity [35]. The species’ occurrence in these ecosystems demonstrates not only tolerance, but it may even thrive in these degraded environments, with a capacity to utilize the increased nutrients, unstable sediment, and poor water quality. These are much the same environmental conditions that are causing the decline or extirpation of native unionids, like A. vescoiana.
The recent detection of S. woodiana in regions where A. vescoiana was once historically abundant raises strong suspicions of ecological displacement. While direct causality is difficult to prove without long-term experimental data, the absence of A. vescoiana in recent surveys (2021–2022), despite targeted search efforts, and the concurrent establishment of S. woodiana, strongly indicate a pattern of competitive exclusion or habitat replacement. This scenario is consistent with findings from multiple case studies, where the spread of S. woodiana has been temporally and spatially associated with the decline of native unionids.
In Italy, S. woodiana was reported to form dense populations in areas where native Anodonta anatina (Linnaeus, 1758) once dominated, altering sediment characteristics and monopolizing space and host fish resources [25]. Similarly, in Bavaria, Germany, the expansion of S. woodiana in fish ponds, rivers, and reservoirs of Bavaria may affect the occurrence of Unio pictorum (Linnaeus, 1758), A. anatina, and A. cygnea (Linnaeus, 1758), suggesting low native mussel biomass [18]. In Montenegro, the authors of [46] documented competitive exclusion; reproductive interference with native unionids Unio pictorum, Unio tumidus Philipsson, 1788 in a shallow lake (Lake Šasko), where S. woodiana established large, tolerant populations that outcompeted native mussels under stressful conditions.
Together, these parallels provide compelling support for interpreting the Iraqi case as part of a broader pattern of invasion-driven biotic homogenization, where generalist, pollution-tolerant invaders like S. woodiana displace native mussels that are unable to adapt to anthropogenically modified environments. This trend poses a significant threat to the remaining freshwater biodiversity in Iraq, particularly in ecologically unique systems like the southern Mesopotamian marshes.

Verified Occurrence Records of Anodonta vescoiana

Verified museum occurrence records of Anodonta vescoiana from Iraq and the wider region are shown in Table 2.

5. Conservation Implications

The extinction of Anodonta vescoiana in Iraq underscores a broader conservation crisis for freshwater bivalves in the Tigris–Euphrates basin and across the Middle East which can be seen as a symptomatic case study for other arid and semi-arid areas facing similar challenges as well. Despite their critical ecological roles, unionid mussels remain unprotected under Iraq’s national environmental laws, and the management of invasive species is not yet incorporated into biodiversity or water resource policy frameworks. This regulatory gap has left native mussels especially vulnerable to compounded pressures from biological invasions, pollution, and habitat fragmentation.
To mitigate further biodiversity loss, there is an urgent need for nationwide monitoring programs that assess unionid diversity and population health, track the expansion of S. woodiana, and identify priority conservation sites. Whilst classical field monitoring of mussel populations remains essential in order to derive information on exact distribution patterns and population demography [67], eDNA methods may be an important additional tool for initial screening of potential distribution areas, especially if study regions are large [68]. These efforts must be supported by baseline ecological data and an identification of genetically important populations (e.g., [69]) which are currently limited or outdated for most freshwater taxa in Iraq. Such information can also serve as a basis for captive breeding efforts to prevent the extinction of particularly rare populations or species [21,70].
Equally critical is the restoration of marshland hydrology through re-establishing natural water flow regimes and reducing salinity intrusion. Improving water quality through effective wastewater treatment and agricultural runoff management will also enhance habitat suitability for any remaining native mussel populations or future reintroduction programs.
From a global perspective, the case of A. vescoiana demonstrates how the combination of rapid biological invasions and hydrological degradation can lead to the complete loss of endemic freshwater species within a few decades. Iraq’s experience should therefore serve as a cautionary model for countries in the Middle East, Central Asia, and beyond, especially those undergoing rapid water development or where invasive bivalves are emerging threats.
In the future, conservation efforts in Iraq would benefit from alignment with international biodiversity frameworks, such as the IUCN Red List of Threatened Species, the Convention on Biological Diversity (CBD), and Ramsar Convention obligations for wetland protection. Regional cooperation with neighboring countries and global conservation networks could provide essential technical, legal, and financial support to advance unionid protection and integrate aquatic invertebrates into Iraq’s national conservation agenda.

6. Conclusions

The apparent disappearance of Anodonta vescoiana in Iraqi freshwater ecosystems is indicative of a worldwide trend of native unionid declines, caused by invasive species, habitat change, and environmental degradation. The spread of S. woodiana, as well as increasing pollution, marsh drainage, and increased water extraction have led to conditions where sensitive endemic species can no longer survive. Based on global case studies and recent field data from Iraq, we demonstrate the role of S. woodiana as an ecological engineer, capable of replacing vulnerable native mussels in degraded habitats. These observations show the need to implement coordinated conservation approaches including the management of invasive species, active habitat restoration, and monitoring of biodiversity over long time scales. To maintain what little remains of our unionid diversity in Iraq and the wider Tigris–Euphrates basin, a coordinated regional approach is critical. Strengthening regional and international cooperation through transboundary conservation networks, particularly within the Middle East and neighboring regions, would help enhance biosecurity measures and improve the resilience of Iraq’s freshwater ecosystems. There only remains a limited time window for action to prevent the further losses of A. vescoiana and other rare freshwater mussel species from Iraq and other arid and semi-arid areas which deserve greater attention when it comes to mussel conservation.

Author Contributions

Conceptualization, M.N. and A.Y.; literature review and synthesis, M.N. and A.Y.; writing—original draft preparation, M.N. and A.Y.; writing—review and editing, J.G., K.D. and F.E. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

This research project is ethically compliant.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Anodonta vescoiana from the Al-Ezz River, Iraq, collected in 2009 by Abdul-Sahib & Abdul-Sahib, 2009. (Left) Preserved specimens stored in a jar in 2009, Marine Biology Department, Marine Science Centre, University of Basrah. (Top right) External view of a left valve showing the shell’s yellowish-brown coloration. (Bottom right) Prominent, elevated umbo with characteristic sculpture. This record represents one of the last documented occurrences of A. vescoiana in Iraq [21].
Figure 1. Anodonta vescoiana from the Al-Ezz River, Iraq, collected in 2009 by Abdul-Sahib & Abdul-Sahib, 2009. (Left) Preserved specimens stored in a jar in 2009, Marine Biology Department, Marine Science Centre, University of Basrah. (Top right) External view of a left valve showing the shell’s yellowish-brown coloration. (Bottom right) Prominent, elevated umbo with characteristic sculpture. This record represents one of the last documented occurrences of A. vescoiana in Iraq [21].
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Figure 2. Verified historical and recent distribution records of Anodonta vescoiana and Sinanodonta woodiana in southern Iraq. Red dots indicate verified occurrences of A. vescoiana: points 1 and 2 represent specimens from 1933 from the Museum of Comparative Zoology (Harvard), and point 3 corresponds to the last known observation in 2009 [21]. Blue dots represent field-verified occurrences of S. woodiana during surveys conducted between 2021 and 2022 [48]. Pink dots show S. woodiana specimens collected from the Al-Ezz River in February 2025 (this study). Purple dots represent field-verified occurrences of S. woodiana during surveys conducted March 2019 [49]. The yellow dot represents field-verified occurrences of S. woodiana during surveys conducted between December 2020 to February 2021 [50]. The map highlights the spatial overlap between historical A. vescoiana sites and current S. woodiana populations, supporting the hypothesis of ecological displacement.
Figure 2. Verified historical and recent distribution records of Anodonta vescoiana and Sinanodonta woodiana in southern Iraq. Red dots indicate verified occurrences of A. vescoiana: points 1 and 2 represent specimens from 1933 from the Museum of Comparative Zoology (Harvard), and point 3 corresponds to the last known observation in 2009 [21]. Blue dots represent field-verified occurrences of S. woodiana during surveys conducted between 2021 and 2022 [48]. Pink dots show S. woodiana specimens collected from the Al-Ezz River in February 2025 (this study). Purple dots represent field-verified occurrences of S. woodiana during surveys conducted March 2019 [49]. The yellow dot represents field-verified occurrences of S. woodiana during surveys conducted between December 2020 to February 2021 [50]. The map highlights the spatial overlap between historical A. vescoiana sites and current S. woodiana populations, supporting the hypothesis of ecological displacement.
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Table 1. Synthesis of probable ecological impacts associated with Sinanodonta woodiana in selected regions. Each case demonstrates a spatial and temporal association between native unionid decline and S. woodiana establishment. Causality is inferred based on observed patterns, but direct experimental evidence is generally limited.
Table 1. Synthesis of probable ecological impacts associated with Sinanodonta woodiana in selected regions. Each case demonstrates a spatial and temporal association between native unionid decline and S. woodiana establishment. Causality is inferred based on observed patterns, but direct experimental evidence is generally limited.
Region/CountryNative Unionids AffectedHabitat TypeMain Impact ObservedSource
IraqAnodonta vescoiana (endemic)Marshes, rivers, canals (degraded)Probable displacement; local extirpationThis study; [21]
ItalyA. anatinaCanals, agricultural reservoirsSpace dominance; sediment alteration[25]
MontenegroUnio pictorum, Unio tumidusSilt-clay substrate, slow flow, shallow lake (Lake Šasko)Competitive exclusion; reproductive interference[46]
PolandU. tumidus, U. pictorum, A. anatina, P. complanataNatural riverine ecosystems (Oder River, oxbow lakes)Recent co-occurrence; no confirmed replacement yet[47]
Germany (Bavaria)U. pictorum, A. anatina, A. cygneaFish ponds, rivers, reservoirsHigh S. woodiana biomass linked with low native mussel biomass in some plots[18]
Table 2. Verified museum occurrence records of Anodonta vescoiana from Iraq and the wider region. These records confirm the species’ historical distribution across the lower Tigris–Euphrates basin, prior to its apparent extirpation in the 21st century.
Table 2. Verified museum occurrence records of Anodonta vescoiana from Iraq and the wider region. These records confirm the species’ historical distribution across the lower Tigris–Euphrates basin, prior to its apparent extirpation in the 21st century.
Scientific NameCountryCoordinatesEvent DateStatusBasisInstitution/Source
Anodonta vescoiana Bourguignat, 1856Iraq33.3° N, 43.7° E1933PresentPreserved specimenMuseum of Comparative Zoology, Harvard
Anodonta vescoiana Bourguignat, 1856Iraq33.4° N, 43.6° ENot datedPresentPreserved specimenMuseum of Comparative Zoology, Harvard
Anodonta vescoiana Bourguignat, 1856IraqNot specified10 March 1980PresentPreserved specimenCollection Mollusca SMF, Frankfurt am Main, Germany
Anodonta vescoiana Bourguignat, 1856IraqNot specified1 August 1983PresentPreserved specimenCollection Mollusca SMF, Frankfurt am Main, Germany
Anodonta vescoiana Bourguignat, 1856Syrian Arab RepublicNot specifiedNot datedPresentPreserved specimenMuseu de Ciències Naturals de Barcelona
Anodonta vescoiana Bourguignat, 1856Iraq31.0833° N 46.1000° E
And
31.1167° N
47.2167° E		2009PresentField observation[21]
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Naser, M.; Yasser, A.; Geist, J.; Douda, K.; Essl, F. Probable Extirpation of Anodonta vescoiana in Iraq: A Case Study of Unionid Displacement by Sinanodonta woodiana. Diversity 2025, 17, 415. https://doi.org/10.3390/d17060415

AMA Style

Naser M, Yasser A, Geist J, Douda K, Essl F. Probable Extirpation of Anodonta vescoiana in Iraq: A Case Study of Unionid Displacement by Sinanodonta woodiana. Diversity. 2025; 17(6):415. https://doi.org/10.3390/d17060415

Chicago/Turabian Style

Naser, Murtada, Amaal Yasser, Juergen Geist, Karel Douda, and Franz Essl. 2025. "Probable Extirpation of Anodonta vescoiana in Iraq: A Case Study of Unionid Displacement by Sinanodonta woodiana" Diversity 17, no. 6: 415. https://doi.org/10.3390/d17060415

APA Style

Naser, M., Yasser, A., Geist, J., Douda, K., & Essl, F. (2025). Probable Extirpation of Anodonta vescoiana in Iraq: A Case Study of Unionid Displacement by Sinanodonta woodiana. Diversity, 17(6), 415. https://doi.org/10.3390/d17060415

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