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Lower parasite pressure in invasive freshwater bivalves than in sympatric native Unionidae mussels in southern European lakes
AbstractThe Enemy Release Hypothesis (ERH) proposes that the success of bioinvasions is attributable to lower enemy pressure on invasive species compared to native ones, giving a competitive advantage for invaders. In line with the hypothesis, we previously observed in northern European bodies of fresh water that invasive bivalves were subject to lower parasite pressure than sympatric native mussels. Here, we investigated ERH in three southern European lakes, where the native mussels are rapidly declining and being replaced by non-native bivalves. In total, 679 bivalves (n of individuals per species per lake varying from 12 to 187) were collected during 2016–2018. Ten parasite taxa were found. The mean lake-specific number of parasite taxa in the native mussels (Anodonta exulcerata, A. cygnea, A. anatina and Unio elongatulus) was 2.6 times that in the invasive bivalves (Dreissena polymorpha, Corbicula fluminea and Sinanodonta woodiana). Similarly, the mean lake-specific sum of prevalences of infection by different parasite taxa in the native mussels was 3.4 times that in the invasive bivalves. Notable was the complete lack of parasites in C. fluminea. Thus, the results supported the Enemy Release Hypothesis and were in accordance with previous results from northern Europe, suggesting, on average, a lower parasite pressure in invasive bivalves than in sympatric native mussels. As parasites are usually harmful, this may contribute to the observed successful invasion of non-native freshwater bivalves in Europe.
Reintroduction of freshwater mussels (Bivalvia, Unionida) directly after channel dredging can serve as an effective measure in mitigation conservation
A roadmap for the conservation of freshwater mussels in Europe
AbstractEurope has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other groups remain largely off the public and scientific radar. Freshwater mussels (Bivalvia, Unionida) are an alarming example of this conservation bias and here we point out six conceptual areas that need immediate and long‐term attention: knowledge, threats, socioeconomics, conservation, governance and education. The proposed roadmap aims to advance research, policy and education by identifying the most pressing priorities for the short‐ and long‐term conservation of freshwater mussels across Europe.
Review of the globally invasive freshwater mussels in the genus Sinanodonta Modell, 1945
AbstractIn this review, we synthesize the current knowledge of the biology, ecology, and impact of Sinanodonta freshwater mussels (Bivalvia, Unionidae), native to East Asia, that have successfully invaded Europe, Central America, North Africa, and several Asian regions. The main introduction pathways of Sinanodonta were reconstructed based on DNA sequence data and distribution records. We show that invasive lineages of Sinanodonta belong to three species, namely, S. woodiana s. str. (“temperate invasive” lineage), S. pacifica (“tropical invasive” lineage), and S. lauta. Their generalist fish-dispersed larvae, short life span, high fecundity, use by humans for multiple purposes, and ability to establish populations in anthropogenically disturbed conditions were identified as crucial traits driving their invasions. Information on the consequences is scarcer, but Sinanodonta can impact native species through larval parasitism, host fish/food competition, and parasite transmission. In addition, ecosystem effects through their filtration—biodeposition—excretion activity and the occurrence of massive die-offs were detected. Ecosystem services and disservices have not yet been quantified, even at local scales, and management methods in the invasive range are understudied. A better understanding of Sinanodonta ecology, impacts, and management options is urgently needed to make informed decisions and set realistic and impactful restoration goals.
Species composition in assemblages of the family Unionidae Rafinesque, 1820 (Mollusca: Bivalvia) as an indicator of ecological changes in water bodies of Central Polissia, Ukraine
Though Ukraine is one of the countries with insufficient water supply, the northern region of central Polissia has a dense river network. The region’s major rivers – Teteriv, Sluch, Ubort, and Uzh – have undergone significant anthropogenic change. Water pollution has adversely affected their fauna, including the Unionidae (Mollusca: Bivalvia). This study has monitored these changes, and was conducted in two stages. A total of 78 sites with habitats typical for the Unionidae were examined; 45 in 1998–2013, of which 24 were resampled in 2019–2020, and a further 33 were sampled at the same time. Six native species generally characteristic of Ukraine (Unio pictorum Linnaeus, 1758, U. tumidus Philipson, 1788, U. crassus Philipsson, 1788, Anodonta anatina Linnaeus, 1758, A. cygnea Linnaeus, 1758, and Pseudanodonta complanata Rossmassler, 1835) were recorded. While nearly all sites examined in 1998–2013 held some unionids, by 2019–2020, they were recorded in only 62.5% out of the total number of sites in Sluch River basin, 80% in Teteriv River, 40% in Ubort River, and 62.5% in Uzh River. The species richness at sites where unionids were recorded had also declined. Pseudanodonta complanata, recorded in every surveyed basin in 1998–2013, was not observed at any of the sites examined in 2019–2020. In 23 out of the 24 re-examined sites, the extinction of one or more Unionidae species was recorded. It is evident that the role of these large mussels as ecosystem engineers is being compromised.
Off the conservation radar: the hidden story of Europe's tiny pea clams (Bivalvia: Sphaeriidae)
AbstractThis study highlights the conservation problems faced by the tiny freshwater bivalves of the family Sphaeriidae, also known as pea, pill, or fingernail clams (or mussels) in Europe. Despite their global distribution, assumed ecological importance, and potential uses, basic knowledge about their taxonomy, biology, and ecology is very limited and much lower than for the larger freshwater bivalve taxa. Immediate scientific priorities are required to fill knowledge gaps regarding their taxonomy, genetic diversity, distribution, reproductive cycle, ecosystem functions, and population trends. Such fundamental knowledge is necessary to identify specific threats and develop appropriate conservation actions. Deploying environmental DNA analysis at a large scale could be a valuable way to fill gaps in distribution and strengthen monitoring in areas where local taxonomic knowledge is lacking. Until taxon-specific management plans can be developed, we recommend that efforts concentrate on the general protection and restoration of wetland habitats, implementing pollution control measures, and managing invasive species. These actions should be complemented by community engagement through citizen science initiatives. Additionally, prioritising data collection to fill existing knowledge gaps and updating conservation statuses (Red Lists) based on comprehensive assessments will be crucial. Implementing these actions will provide a starting point for the broader protection of freshwater ecosystems, thus benefiting pea clams and other interconnected species within these habitats.
Integrative phylogenetic, phylogeographic and morphological characterisation of the Unio crassus species complex reveals cryptic diversity with important conservation implications
A global meta‐analysis of ecological functions and regulating ecosystem services of freshwater bivalves
AbstractFreshwater bivalves are globally distributed, diverse, and common in benthic communities. Many taxa, particularly in the most species‐rich order, Unionida, are declining due to anthropogenic stressors, while a small number of non‐native species have become increasingly abundant and widespread, commonly replacing native bivalve assemblages. To understand how these global changes may impact ecosystems and people, we conducted a meta‐analysis of existing literature quantifying the ecological functions (= supporting or intermediate ecosystem services) and regulating ecosystem services of freshwater bivalves (hereafter “ecosystem services”). Random effects meta‐analysis modeling across 447 case studies revealed a positive effect on human health, safety, or comfort of freshwater bivalve ecosystem services overall and specifically, via effects on native macrofauna, microorganisms, wastes, and pollutants, and the physico‐chemical condition or quantity of sediments. Generally, effects of native species and species within the orders Unionida and Venerida were more significant and positive than those of other freshwater bivalves. No significant overall effect was found for ecosystem services related to zooplankton, algae, invasive species, and the physico‐chemical condition of ambient water. Moreover, a significant bias toward publication of positive results existed for studies quantifying ecosystem services related to algae. These findings illustrate the global importance of the ecosystem services of freshwater bivalves and highlight the need for large‐scale conservation and restoration efforts for their species and populations globally, including those of common species. Our findings also question common assumptions of strong and ubiquitous effects of freshwater bivalves on algae and water condition, cautioning against extrapolating observations across systems.