Unio Crassus Philipsson Research Articles

Age structure and growth patterns of the endangered freshwater mussel Unio crassus Philipsson, 1788 under different environmental conditions

Age structure and growth patterns of the endangered freshwater mussel Unio crassus Philipsson, 1788 under different environmental conditions

Accumulation of metal(loid)s in the digestive gland of the mussel Unio crassus Philipsson, 1788: A reliable detection of historical freshwater contamination

The possible influence of historical contamination of water/sediments on the metal(loid) bioaccumulation in the digestive gland of mussel Unio crassus Philipsson, 1788, from two differently contaminated sites at the Mrežnica River was studied in three seasons. The first data for this species on total/cytosolic concentrations of 27 (non)essential elements were obtained by HR ICP-MS. Higher bioaccumulation was observed at the historically contaminated site, with several nonessential elements (Bi, Cs, Pb, Sb, Tl, U) found in 5–6 times higher concentrations compared to the reference site. Although both total and cytosolic levels revealed the influence of water/sediment contamination, the latter showed association between bioaccumulation and exposure for larger number of studied elements. At the reference site, several elements (Ba, Ca, Cd, Cr, Mn, Sr) were also found in 2–10 times higher concentrations compared to contaminated one, but it was attributed to background levels characteristic for karst rivers (for Ca and Cd), and to coaccumulation due to chemical similarity (for Ba, Cr, Mn, Sr). The seasonal variability was also observed, with generally highest metal(loid) concentrations in mussel digestive glands found in autumn which was associated to mussels reproductive period. Our results confirmed that sediment-dwelling mussels, specifically U. crassus, represent a good bioindicators for detection of historical pollution due to their direct contact/exposure to contaminants stored in sediments, with concurrent consideration of physiological/chemical factors. Historical contamination potentially can have serious impact on freshwater environment even long time after its cessation, and, therefore, a careful continuous monitoring is recommended.

Parasites and their impact on thick-shelled river mussels Unio crassus from two populations in Luxembourg.

The thick-shelled river mussel Unio crassus Philipsson, 1788 is a species native to many European habitats, with declining populations. The impact of parasite communities on health status of this species is poorly understood. In this study, parasites of 30 U. crassus specimens from the Our and Sauer Rivers in Luxembourg were identified morphologically and, in some cases, using molecular genetic methods. The findings were correlated to selected parameters (total length, visceral weight, shell lesions, gonadal stage). The 2 populations did not differ in shell length, visceral weight, number of males and females, gonadal scoring, shell lesions, and the occurrence of glochidia. The prevalence and infestation intensities of detected Trichodina sp., Conchophthirus sp., and freshwater mite larvae did not differ between the 2 populations, whereas the prevalence and infestation intensities of mite eggs, nymphs, and adults were significantly higher in the Sauer River. Rhipidocotyle campanula and European bitterling Rhodeus amarus larvae were only present in the Sauer. Histopathology revealed the destruction of the gonads by R. campanula and tissue damage by the mites. The only significant correlation of the selected parameters was a positive correlation between R. amarus occurrence and total length as well as a negative correlation between R. amarus occurrence and gonadal stage. In the Sauer River, 2 mussels were found to be hermaphrodites.

Minimally Invasive DNA Sampling by Hemolymph Extraction Minimizes Risk to Freshwater Mussels: The Case of Endangered Unio crassus Philipsson, 1788 (Bivalvia: Unionidae)

Research on endangered species is important for species conservation. Some lines of conservation research require tissue or fluids so that molecular data can be obtained. Thus, there is an increasing demand for methods of DNA sampling in endangered species that minimize harm to live animals. This especially concerns such highly threatened and protected freshwater mussels as the thick-shelled river mussel Unio crassus. With two different field experiments in Germany under natural conditions, the short- and long-term survival of Unio crassus after hemolymph extraction from the foot tissue was evaluated. We detected no negative effects in individuals of over 40 mm shell length and older than five years. We also followed some individuals for up to three years after treatment and detected no harm to these individuals. DNA quality was high and proved fully suitable for single-gene sequencing (COI) and microsatellite analyses.

First description of freshwater mite Unionicola sauerensis sp. nov. infesting thick-shelled river mussel Unio crassus.

A sample of 30 thick-shelled river mussels Unio crassus Philipsson (Unionida: Unionidae) was collected from the River Sauer in Luxembourg to acquire data on parasitic infestations of the mussels. Among other parasites, different development stages of freshwater mites were collected from the gills and the mantle of the mussels and were documented with bright-field, stereo, and confocal laser scanning microscopy and microscopic X-ray computed tomography. The retrieved data allowed a morphological description of larvae and female adults of the mites and assigning them to the genus Unionicola Haldeman (Trombidiformes: Unionicolidae) and the subgenus Pentatax Thor. Additionally, adult stages and larvae were barcoded by sequencing a section of the mitochondrial COI and 18S rRNA genes. This resulted in 4 new, similar Unionicola lineages from the adult stages, which differ in at least 14.7% (uncorrected p distance) from those already published. Barcoding of larval DNA was not successful. The comparison with known European species of the genus Unionicola and analysis of the barcoding results allowed the proposal of a new species of the genus Unionicola. The species was named Unionicola sauerensis sp. nov. after the River Sauer in Luxembourg, where the infested mussels were collected.

Native and alien species of macrozoobenthos in rivers of the Belarusian part of the Dnieper River basin

The Dnieper River basin in Belarus was studied in 2016-2019. In total, 201 species and forms of macro-zoobenthos were found and 146 of them were identified to the species level. New habitats of several protected species (Unio crassus Philipsson, 1788, Anax imperator Leach, 1815, Ophiogomphus cecilia (Fourcroy, 1785) and Gomphus flavipes Char-pentier, 1825) and one alien species (Paramysis lacustris (Czerniavsky, 1882)) have been recorded in Belarus.

Influence of stream characteristics and population size on downstream transport of freshwater mollusk environmental DNA

Many freshwater mussel species are highly endangered. Knowledge of their occurrence and distribution is a crucial prerequisite for their conservation. The use of environmental DNA (eDNA) is a relatively new approach and an effective tool to detect the presence of target species in freshwater environments. This study aimed to establish a molecular identification tool for eDNA for the endangered thick-shelled river mussel Unio crassus Philipsson in Retzius, 1788 and to analyze the relationships between mussel abundance, stream discharge, sampling distance, and freshwater mollusk DNA signal (detectability and DNA quantity) by using binary logistic and linear regression modeling. We additionally correlated turbidity and mollusk DNA detectability. We developed a species-specific eDNA detection system in silico and tested the efficiency and species specificity on water samples collected downstream of extant populations of different sizes (100–42,000 individuals) in Bavaria, Germany. This system allowed detection of very small U. crassus populations over long distances (>3 km) and excluded amplification of DNA from other potentially co-occurring species. Signal strength was most strongly associated with population size and distance of sampling point from mussel population. Additionally, a negative correlation with stream turbidity was evident. This species-specific tool may help in screening of streams for target species that are otherwise difficult to monitor.

The Patterns and Puzzles of Genetic Diversity of Endangered Freshwater Mussel Unio crassus Philipsson, 1788 Populations from Vistula and Neman Drainages (Eastern Central Europe)

Mussels of the family Unionidae are important components of freshwater ecosystems. Alarmingly, the International Union for Conservation of Nature and Natural Resources Red List of Threatened Species identifies almost 200 unionid species as extinct, endangered, or threatened. Their decline is the result of human impact on freshwater habitats, and the decrease of host fish populations. The Thick Shelled River Mussel Unio crassus Philipsson, 1788 is one of the examples that has been reported to show a dramatic decline of populations. Hierarchical organization of riverine systems is supposed to reflect the genetic structure of populations inhabiting them. The main goal of this study was an assessment of the U. crassus genetic diversity in river ecosystems using hierarchical analysis. Different molecular markers, the nuclear ribosomal internal transcribed spacer ITS region, and mitochondrial DNA genes (cox1 and ndh1), were used to examine the distribution of U. crassus among-population genetic variation at multiple spatial scales (within rivers, among rivers within drainages, and between drainages of the Neman and Vistula rivers). We found high genetic structure between both drainages suggesting that in the case of the analyzed U. crassus populations we were dealing with at least two different genetic units. Only about 4% of the mtDNA variation was due to differences among populations within drainages. However, comparison of population differentiation within drainages for mtDNA also showed some genetic structure among populations within the Vistula drainage. Only one haplotype was shared among all Polish populations whereas the remainder were unique for each population despite the hydrological connection. Interestingly, some haplotypes were present in both drainages. In the case of U. crassus populations under study, the Mantel test revealed a relatively strong relationship between genetic and geographical distances. However, in detail, the pattern of genetic diversity seems to be much more complicated. Therefore, we suggest that the observed pattern of U. crassus genetic diversity distribution is shaped by both historical and current factors i.e. different routes of post glacial colonization and history of drainage systems, historical gene flow, and more recent habitat fragmentation due to anthropogenic factors.

Seasonal patterns in the developmental rate of glochidia in the endangered thick-shelled river mussel, Unio crassus Philipsson, 1788

Females of freshwater mussels spawn eggs which, after fertilization, are brooded until the developing larvae reach a stadium ready to infest a fish host in order to complete the obligate parasitic phase of their life. We investigated the duration of the brooding period in the endangered thick-shelled river mussel Unio crassus in two rivers in southern Poland and identified the stadia of glochidia development which could be used to assess current larval developmental stages. The eggs were fertilized in marsupia. The duration of the brooding period shortened significantly during the season, from 35 days in early spring to 9 days in summer. The break between consecutive broods was usually short but very variable: from almost no break to 17 days. 20% of brooding events inspected every other day were miscarried at different stadia of larval development. The recorded differences in brooding time may significantly influence the reproductive output of individuals and populations, depending on the thermal conditions, which may be affected by both anthropogenic impact and global climate change. The study offers a practical scheme for assessing female gravidity advancement in Unio crassus, which may be very informative for the future application of conservation measures in this endangered European species.

JUSTIFICATION FOR THE NECESSITY OF REGISTRATIONIN THE RED DATA BOOK OF UKRAINE THE UNIO CRASSUS PHILIPSSON, 1788 (MOLLUSCA, BIVALVIA, UNIONIDAE)

The article substantiates the necessity of registration in the Red Data Book of Ukraine the Unio crassus Philipsson, 1788 – a mollusk, which is an indicator of water purity and an important factor of self-purification of hydro-ecosystems. As a result of monitoring studies, 300 species of Unionidae-like biotopes within all river basins of Ukraine during the period 1993-2018 have been marked with a sharp reduction of the species distribution area. Mollusk has become quite rare in the basins of the Siverskyi Donets, Dniester, Dnieper, Southern Bug, Crimea rivers, and it has not been detected at all in the hydrocenoses of the Western Bug, although in the 40-60s of the last century it was considered to be a widespread species in these regions. Its occurrence in modern reservoirs of Ukraine is only 15 %. The most common Unio crassus in the Prypiat basin (41 % occurrence) U. crassus is a rheophilic species found only in rivers. Given the overall degradation of the country’s aquatic ecosystems, the tendency to reduce the occurrence of U. crassus may intensify, which is why it is important to undertake appropriate environmental measures in a timely manner aimed at preserving the malacofauna of water basins and streams of Ukraine. In due course, this species should be listed in the Red Data Book of Ukraine with the status of “vulnerable”.

NiSO4 spill inflicts varying mortality between four freshwater mussel species (including protected Unio crassus Philipsson, 1788) in a western Finnish river

Freshwater mussels are one of the most threatened taxonomic groups in the world, and many species are on the brink of local or global extinction. Human activities have altered mussel living conditions in a plethora of ways. One of the most destructive human-induced impacts on running waters is the catastrophic spill of harmful substances, which results in massive die-offs. Even though Finland is regarded as the world’s top country in terms of environmental regulation quality, riverine systems are not safe. In 2014, River Kokemäenjoki in western Finland experienced the worst NiSO4 spill in the country’s history, visibly affecting the mussel community – including protected Unio crassus – along the river. Because freshwater mussel toxicology is grossly understudied (particularly in Europe), any pollution –linked die-offs offer valuable opportunities to study the issue in natural environment. Here, we report the mussel investigations from 2014 and a follow-up study conducted in 2017 in order to assess the variation in species sensitivity on nickel pollution. In total, 104 sites were sampled, and over 20 000 mussels were identified and counted. Our results indicate that the most impacted species (i.e. that which experienced the highest spill-induced mortality) was Anodonta anatina (62%), followed by Unio pictorum (32%), U. crassus (24%) and Unio tumidus (9%). The underlying reason for the sensitivity of A. anatina is not resolved, hence more research is urgently needed. The low mortality among most of the species in 2017 highlights the temporal nature of the pollution impact and the recovery potential of the mussel community. However, the case is more complex with U. crassus population, which may be experiencing delayed impacts of the spill. Because nickel is one of the most commonly produced industrial metals in the world (hence the pollution incident risk is high) and River Kokemäenjoki hosts mussel community typical for European rivers, our results may benefit many researchers and stakeholders dealing with riverine environments.

Potential use of beaver Castor fiber L., 1758 dams by the thick-shelled river mussel Unio crassus Philipsson, 1788

ABSTRACTThe objective of this paper is to draw attention to a previously unrecognised habitat for Unio crassus Philipsson, 1788 (Bivalvia: Unionidae), namely beaver dam-and-pond complexes. The construction of beaver ponds will allow the colonisation of high energy streams by providing flow refuges during periods of high near-bed shear stress. The absence of freshwater mussels (Unionidae) in mountain streams may result from steep slopes, shear stress during floods, lack of food suspended in the water column (seston), and unfavourable conditions for the settlement and growth of juvenile mussels. Transportation of parasitic larvae on host fish is the main dispersal mechanism for the mussels. A possible constraint on the colonisation of beaver complexes by freshwater mussels is that beaver dams may hinder the upstream movement of their minnow hosts. In the surveyed beaver ponds, the first specimens of U. crassus were found in 2008. Single mussels were also found in subsequent years. It is uncertain whether the occurrence of U. crassus depends on the periodic support of the population from the main river, but the presence of beaver ponds is certain to have given it the opportunity of colonising new areas.

In vitro culture of glochidia of the threatened freshwater mussel Unio crassus Philipsson 1788 – the dilution problem

We applied in vitro techniques in culturing glochidia of the thick-shelled river mussel Unio crassus, seriously threatened European species. Glochidia were freshly isolated from a gravid female. The sterile phase of the cultures was terminated at different time points to assess the optimal length of this phase. We imitated the process of juvenile excision from a fish host by diluting the culture with water at regular time intervals. The metamorphosed juveniles that survived until the end of the experiment and started growing their shells were observed for 24–27 days from the start of the culture in samples diluted for the first time between days 13 and 17. Long-lasting cultures usually became infected and died, whereas in those that were terminated too early, glochidia were unable to develop further in clean water. The transfer of juveniles from an artificial medium to pure water should be done gradually, through a series of dilutions, so that the larvae have the opportunity to feed on the diluted medium after metamorphosis. Only individuals with an active foot capable of operating outside the shell were ready to inhabit water and forage on solid food from the external environment.

Glacial perturbations shaped the genetic population structure of the endangered thick-shelled river mussel (Unio crassus, Philipsson 1788) in Central and Northern Europe

The thick-shelled river mussel, Unio crassus Philipsson 1788, was formerly one of the most abundant and widely spread freshwater bivalves among the order of Unionida in Europe, but there is still a lack of information on its genetic diversity and spatial genetic structure. We characterised the genetic constitution of 18 U. crassus populations in Germany and Sweden originating from six major drainage systems using a set of nine microsatellite markers. U. crassus populations from Northern Germany and Sweden revealed similar genetic constitution with high genetic diversity, whereas populations from Southern Germany showed higher proportions of common ancestors and a stronger host-dependent diversification. The structured spatial genetic patterns suggest two glacial refugia and a strong north–south differentiation. The Elbe river basin was likely an important source for recolonisation northwards to Sweden, and populations from the low mountain range in the Danube–Rhine systems acted as a source for recolonisation southwards to the Alps after retreating glaciations. We identified three major conservation units for the analysed U. crassus populations which should be considered in future conservation efforts.

The populations of the freshwater pearl mussel, Margaritifera margaritifera (Linnaeus, 1758), and the thick shelled river mussel, Unio crassus Philipsson, 1788, in Latvia

The populations of two endangered species—the freshwater pearl mussel Margaritifera margaritifera and the thick shelled river mussel Unio crassus in Latvia were studied. The specimens were counted, measured, population density and age structure were calculated. The possible host fish presence was found.

Notes on the thick-shelled river mussel Unio crassus Philipsson, 1788 (Bivalvia: Unionidae) in Stradomka (southern Poland), a tributary of the Raba river

This contribution presents new data on the occurrence of the thick-shelled river mussel Unio crassus in the Stradomka river and its tributaries (S. Poland), not surveyed earlier. Live specimens and empty shells were found in 14 localities, mostly in the Stradomka river.

Effective growth cessation in adult Unio crassus Philipsson, 1788 (Bivalvia: Unionidae) from Germany

Information on the growth and age of the endangered freshwater mussel Unio crassus Philipsson, 1788 is crucial to correctly assess the conservation status of a particular population. This long-term study of individually marked specimens from four populations from central and southwest Germany revealed that zero growth and shrinkage of adult mussels from the upper 50% of their population’s length range were common phenomena. Therefore, overall shell length measurements or counting of growth lines on the shells of live adult mussels may grossly underestimate their age and should be regarded as unsuitable for determining the actual age structure of a population. Key wOrDs: growth cessation, age determination, long-term study, Unio crassus, Unionidae

Aquatic mollusc fauna of the Ohře River – an important site of Unio crassus Philipsson, 1788 (Bivalvia: Unionidae) in northwestern Bohemia

Aquatic mollusc fauna of the Ohře River – an important site of Unio crassus Philipsson, 1788 (Bivalvia: Unionidae) in northwestern Bohemia

The thick-shelled river mussel <i>Unio crassus</i> in Romincka Forest's rivers

The thick-shelled mussel Unio crassus Philipsson is a legally protected, endangered species. This paper reports on its previously unknown localities in Romincka Forest (NE. Poland). Out of the four largest rivers of the Forest, live individuals were found in the Bludzia and B3edzianka; only empty shells were found in the Jarka River, and neither live mussels nor shells were found in the ytkiejmska Struga. U. crassus avoids canalised river sections, while water quality does not seem to affect its distribution in the examined rivers.

Redescription of Unio tumidiformis Castro, 1885 (Bivalvia, Unionidae), an endemism from the south-western Iberian Peninsula

The possible occurrence of Unio crassus Philipsson, 1788 on the Iberian Peninsula has been a controversial issue since the nineteenth century. Several characters, including molecular, morphological and life cycle, show that the Iberian taxon is related to, but well differentiated from, the central European U. crassus. The valid name for this Iberian taxon is Unio tumidiformis Castro, 1885. Live populations are distributed throughout the Guadiana, Mira and Sado river basins. Unio tumidiformis can be distinguished from other Unio species by its regular oval shape, high relative height and width, strong wavy umbonal rugae, supra-cardinal tooth on the right valve, and lower glochidium height. From the potential fish hosts tested, only Squalius alburnoides (Steindachner, 1866) resulted in juvenile drop-off, suggesting some degree of specialization in the parasite–host relationship. The endemic nature, population status and habitat of U. tumidiformis make this species important from a conservation point of view.