Regional monitoring of freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> in the County of Norrbotten,Sweden

A total of 16 freshwater pearl mussel Margaritifera margaritifera rivers out of 64 known freshwater pearl mussel rivers are included in the Administrative County of Norrbotten regional monitoring program. First surveys were done in 1994 and the results show that only three rivers have viable populations according to national criteria despite little visible human impact and that juvenile mussels (<50 mm in length) have been found in all rivers at every occasion. The results also indicate that there might be “missing years” for juvenile recruitment suggesting that freshwater pearl mussel populations at the extreme end of the species range might be dependent on “golden moments” in order to keep up viable populations. Deeper knowledge and better tools for determining viable populations might be necessary in order to make the right decisions on how to manage the rivers and the freshwater pearl mussel populations.     

Historical geography of pearl harvesting and current status of populations of freshwater pearl mussel Margaritifera margaritifera (L.) in the western part of Northern European Russia

This paper summarises data on the occurrence of freshwater pearl mussel Margaritifera margaritifera in the western part of Northern European Russia adjacent to White Sea, Barents Sea, Onega Lake and Ladoga Lake basins. Also, this article provides an overview of the literature-based data and archive materials on the history of pearl harvesting. We include a list of rivers of Northwestern Russia, where pearls were harvested during the period of the sixteenth to twentieth centuries. The pearl mussel populations at the present time exist in at least 24 water streams in Northwestern Russia. Many of these populations are in high abundance and are able to reproduce normally. Data on the status of populations are given in this paper. Data indicate that the pearl mussel population in Russia contains >143.5 million individuals, but this estimation is certainly undervalued. Timber floating (timber floating is the transport of timber on waterways), hydro-engineering construction, pollution of rivers by industrial wastes and introduction of alien species, as well as a reduction in host fish species numbers can all be cited as the main factors that transformed the ecosystems inhabited by pearl mussel of Northern Russia. In addition, methods used in the Russian Federation for decreasing the anthropogenic load on pearl mussel populations were considered.     

Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>) in northern Europe

Freshwater pearl mussels (Margaritifera margaritifera) are among the most critically threatened bivalve molluscs worldwide. An understanding of spatial patterns of genetic diversity is crucial for the development of integrative conservation strategies. We used microsatellites to study the genetic diversity and differentiation of 14 populations of M. margaritifera in central Sweden, an area which was described as a major secondary contact zone in postglacial colonisation for other species. Genetic diversity of Swedish pearl mussel populations was much greater than in central and southern Europe but similar to the genetic diversity observed in the northeastern portion of their European range. Genetic differentiation among populations was pronounced but to a large extent independent from present-day drainage systems. The complex patterns of genetic diversity and differentiation in pearl mussel seem to be strongly influenced by the species’ high degree of specialisation and extraordinary life history strategy which involves facultative hermaphrodism and an obligatory encystment stage on a host fish. Genetic drift effects and anthropogenic disturbances resulting in reduction of population size and loss of connectivity are less pronounced in northern pearl mussel populations compared to those in central and southern Europe.     

Overfishing in the Baltic Sea basin in Russia,its impact on the pearl mussel,and possibilities for the conservation of riverine ecosystems in conditions of high anthropogenic pressure

In recent studies nine populations of the freshwater pearl mussel have been described in the Baltic Sea basin in Russia. They are very scarce, although the condition of their habitats seems to be rather good. Overfishing of the host fish is a limiting factor for them. The number of salmon has decreased by at least 100 times over the past 200 years. Such a scale of decline tends to be hidden over time, and estimation of the normal conditions of the salmon–pearl mussel ecosystem becomes problematic. A significant increase in the number of salmon is necessary to prevent extinction of pearl mussels. Effective protected areas appear to be the only possibility for conservation of the pearl mussels and its host fish species.     

Preliminary results of the study of populations of the freshwater pearl mussel from streams of the Lopshenga River basin on Onega Peninsula in Arkhangelsk oblast

Streams of the Lopshenga River basin (Summer Coast of the White Sea) are studied. Sections of the Kamennyi and Zhemchuzhnyi streams with relatively high population densities of the freshwater pearl mussel, the populations of which can be attributed to those that are aging, but with a high abundance, are detected. It is noted that the ratio of morphological forms of the freshwater pearl mussel in the streams of the Lopshenga River basin is characteristic of more southern populations of this species.     

The impact of land use on the mussel Margaritifera margaritifera and its host fish Salmo trutta

Today, land use impacts a major proportion of all streams. Here, landscape features in corridors along streams and water chemical factors were analyzed in relation to recruitment of the threatened freshwater pearl mussel (Margaritifera margaritifera) and its host fish the brown trout (Salmo trutta). Mussel recruitment and trout density were negatively related to forest clear-cuts. Mussel recruitment was negatively related to water color and turbidity. Therefore, the threats to the mussel may be severe, as low mussel recruitment may be caused by direct effects on the juvenile mussels and indirect effects on the host fish. High proportions of lakes and ponds were found to be positive for recruitment and for trout, and deciduous forest was positively related to trout. The combination of investigations at different scales at the landscape level and at in-stream levels may be applicable to find threats to other threatened species. The results indicate that forestry activities may negatively affect recruitment of freshwater pearl mussels and its host fish. Reductions of forestry activities and the retaining of intact quantity and quality of the riparian zones next to streams, both for the mussel and its host fish may be important conservation measures to restore freshwater pearl mussel populations.     

The status of the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> in Scotland: extent of change since 1990s,threats and management implications

All known rivers in Scotland with recent records of freshwater pearl mussels Margaritifera margaritifera were surveyed in 2013–2015 using a standard methodology. Freshwater pearl mussel populations were classed as: (i) apparently extinct in 11 rivers, (ii) not successfully recruiting in 44 rivers, and (iii) evidence of recent successful recruitment in 71 rivers. On a regional basis, a high proportion of extant populations were located in North and West Scotland. In all regions extant populations were characterised by low pearl mussel densities, with 97 of 115 extant Scottish populations defined as ‘rare’ (0.1–0.9 mussels per 1 m ²) or ‘scarce’ (1.0–9.9 mussels per 1 m ²). Only 18 Scottish rivers now hold pearl mussel populations in densities that are considered to be ‘common’ (10–19.9 mussels per 1 m ²) or ‘abundant’ (>20 mussels per 1 m ²). Based on survey evidence, the number of apparently extinct pearl mussel populations in Scottish rivers is now 73. The decline is particularly pronounced in the West Highlands and Western Isles strongholds. The key threats are: (i) pearl fishing, (ii) low host fish densities, (iii) pollution/water quality, (iv) climate change and habitat loss, (v) hydrological management/river engineering and (vi) ‘other factors’, such as non-native invasive species. Over the last 100 years this endangered species has been lost from much of its former Holarctic range. Scotland’s extant M. margaritifera populations continue to be of international importance, but their continued decline since the first national survey in 1998 is of great concern.     

Threatened freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L. in NW Spain: low and very structured genetic variation in southern peripheral populations assessed using microsatellite markers

A genetic analysis of freshwater pearl mussel Margaritifera margaritifera populations from NW Spain, a peripheral area of its European distribution, was carried out using microsatellite markers. These populations were formerly reported as genetically differentiated on the basis of growth and longevity studies. Ten loci previously characterized in populations from central Europe were used to comparatively analyze the genetic variability at the southern edge of the species’ range. Iberian pearl mussel populations showed very low genetic variability and significant high genetic differentiation. Half of the total genetic diversity observed appeared to be distributed between populations, which suggested a highly structured adaptive potential in pearl mussel at the southern peripheral distribution of the species. Population distinctiveness was evidenced by assignment tests, which revealed a high accuracy of individual assignments to their population of origin. All data suggested low effective population size and major effects of genetic drift on population genetic structure. In order to avoid further loss of genetic variation in biologically distinctive populations from NW Spain, prioritization of genetic resources of this species is required for conservation and management.     

Strong genetic differentiation and low genetic diversity of the freshwater pearl mussel (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L.) in the southwestern European distribution range

Genetic diversity of European freshwater pearl mussel, Margaritifera margaritifera (L.), appears exceptional with highest genetic variability found in the northernmost European populations of Scandinavia and lower genetic variability in central and southern Europe. The objective of this study was to investigate genetic diversity and differentiation of 14 southernmost populations on the Iberian Peninsula which greatly differ in terms of life span and habitat conditions from the rest of central and northern European populations. The analyses of ten microsatellite loci revealed a pronounced level of genetic divergence and very low genetic diversity. These results match the expectations of geographically peripheral populations with respect to their genetic composition. The life history strategy, the narrow ecological niche of the species, and anthropogenic habitat modifications have most likely shaped the genetic pattern of Iberian pearl mussel populations. The peripheral position with less optimal habitat conditions may increase the extinction risk of these populations and thus effective conservation strategies for the Iberian M. margaritifera are needed. The successful conservation of the species at its southwestern margin requires inclusion of genetically different conservation units which may reveal local adaptation.     

Strategies for the conservation of endangered freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L.): a synthesis of Conservation Genetics and Ecology

Freshwater pearl mussels (Margartifera margaritifera L.) are among the most critically threatened freshwater bivalves worldwide. The pearl mussel simultaneously fulfils criteria of indicator, flagship, keystone and umbrella species and can thus be considered an ideal target species for the process conservation of aquatic ecosystem functioning. The development of conservation strategies for freshwater pearl mussels and for other bivalve species faces many challenges, including the selection of priority populations for conservation and strategic decisions on habitat restoration and/or captive breeding. This article summarises the current information about the species’ systematics and phylogeny, its distribution and status as well as about its life history strategy and genetic population structure. Based on this information, integrative conservation strategies for freshwater mollusc species which combine genetic and ecological information are discussed. Holistic conservation strategies for pearl mussels require the integration of Conservation Genetics and Conservation Ecology actions at various spatial scales, from the individual and population level to global biodiversity conservation strategies. The availability of high resolution genetic markers for the species and the knowledge of the critical stages in the life cycle, particularly of the most sensitive post-parasitic phase, are important prerequisites for conservation. Effective adaptive conservation management also requires an evaluation of previous actions and management decisions. As with other freshwater bivalves, an integrative conservation approach that identifies and sustains ecological processes and evolutionary lineages is urgently needed to protect and manage freshwater pearl mussel diversity. Such research is important for the conservation of free-living populations, as well as for artificial culturing and breeding techniques, which have recently been or which are currently being established for freshwater pearl mussels in several countries.     

The populations of the freshwater pearl mussel, <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> (Linnaeus, 1758), and the thick shelled river mussel, <Emphasis Type="Italic">Unio crassus</Emphasis> 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.     

Genetic diversity and differentiation of central European freshwater pearl mussel (Margaritifera margaritifera L.) populations: implications for conservation and management

Despite the fact that mollusc species play an important role in many aquatic ecosystems, little is known about their biodiversity and conservation genetics. Freshwater pearl mussel (Margaritifera margaritifera L.) populations are seriously declining all over Europe and a variety of conservation programs are being established to support the remaining endangered central European populations. In order to provide guidelines for conservation strategies and management programs, we investigated the genetic structure of 24 freshwater pearl mussel populations originating from five major central European drainages including Elbe, Danube, Rhine, Maas and Weser, representing the last and most important populations in this area. We present a nondestructive sampling method of haemolymph for DNA analyses, which is applicable for endangered bivalves. The analyses of nine microsatellite loci with different levels of polymorphism revealed a high degree of fragmented population structure and very different levels of genetic diversity within populations. These patterns can be explained by historical and demographic effects and have been enforced by anthropogenic activities. Even within drainages, distinct conservation units were detected, as revealed from high F(ST) values, private alleles and genetic distance measures. Populations sampled close to contact zones between main drainage systems showed lowest levels of correct assignment to present-day drainage systems. Populations with high priority for conservation should not only be selected by means of census population size and geographical distance to other populations. Instead, detailed genetic analyses are mandatory for revealing differentiation and diversity parameters, which should be combined with ecological criteria for sustainable conservation and recovery programs.     

Impacts of invasive crayfish (Pacifastacus leniusculus) on endangered freshwater pearl mussels (Margaritifera laevis and M. togakushiensis) in Japan

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

Variation in the <Emphasis Type="Italic">COI</Emphasis> gene of the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> from River Vuokkijoki

The freshwater pearl mussel Margaritifera margaritifera L. is one of the most endangered freshwater mussels in the world. Effective conservation of threatened species requires not only ecological, but also genetic information from the target species and populations. Since low genetic diversity can reduce the ability of a species to adapt to environmental changes, maintaining genetic diversity has been identified as one of the key elements in successful conservation programs. We examined genetic variation of the freshwater pearl mussel from the River Vuokkijoki, Karelia, Russia. We sequenced a fragment of the cytochrome c oxidase subunit I gene (COI) from 22 individuals and compared the data to 32 previously published COI sequences available in GenBank. We identified 10 different COI haplotypes in the sequenced samples, three of which had not been previously reported. Our results show that the River Vuokkijoki has high genetic diversity and suggest that the colonization of this northern freshwater pearl mussel population might have occurred from multiple and even distant refugia. Therefore, the freshwater pearl mussel population of the River Vuokkijoki is valuable for the conservation of the whole species.     

High levels of multiple paternity in a spermcast mating freshwater mussel

Multiple paternity is an important characteristic of the genetic mating system and common across a wide range of taxa. Multiple paternity can increase within‐population genotypic diversity, allowing selection to act on a wider spectre of genotypes, and potentially increasing effective population size. While the genetic mating system has been studied in many species with active mating behavior, little is known about multiple paternity in sessile species releasing gametes into the water. In freshwater mussels, males release sperm into the water, while eggs are retained and fertilized inside the female (spermcast mating). Mature parasitic glochidia are released into the water and attach to the gills of fish where they are encapsulated until settling in the bottom substrate. We used 15 microsatellite markers to detect multiple paternity in a wild population of the freshwater pearl mussel (Margaritifera margaritifera). We found multiple paternity in all clutches for which more than two offspring were genotyped, and numbers of sires were extremely high. Thirty‐two sires had contributed to the largest clutch (43 offspring sampled). This study provides the first evidence of multiple paternity in the freshwater pearl mussel, a species that has experienced dramatic declines across Europe. Previous studies on other species of freshwater mussels have detected much lower numbers of sires. Multiple paternity in freshwater pearl mussels may be central for maintaining genetic variability in small and fragmented populations and for their potential to recover after habitat restoration and may also be important in the evolutionary arms race with their fish host with a much shorter generation time.     

Ontogenetic morphometrics of individual freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> (L.)) reconstructed from geometric conchology and trigonometric sclerochronology

This study bridges two conchological approaches to model the growth characteristics of freshwater pearl mussel shell: size-at-age and sclerochronology. We demonstrate a simple numerical model that transfers sclerochronological data into realistic estimates of ontogenetic shell sizing. This model was constructed for a subset of shell growth data dealing with morphometrics and annual shell growth increments. Further, validation of the model was performed using a dataset that was withheld from the calibration. Both subsets of data showed significant correlations between the observed (measured by vernier callipers) and reconstructed size-at-age data, indicating a successful model. The practical applicability of the model was exemplified for the studied Finnish freshwater pearl mussel populations. In accordance with the previously set theory about the plasticity of life history traits of the species, the southern mussels showed higher growth rates than the northern mussels. Handling editor: K. Martens     

Population dynamics of glochidia of the freshwater pearl mussel Margaritifera margaritifera L., parasitizing on juvenile Salmonidae fishes in northern water reservoirs

This paper presents data on the population dynamics of glochidia of the freshwater pearl mussel Margaritifera margaritifera L. (1758) (a declining species of European fauna), parasitizing on juvenile Salmonidae fishes in rivers of northern Europe. It was found that the number of glochidia parasitizing on gills of juvenile salmon and trout in explored water reservoirs are stimulated by negative binomial distribution. Estimation of the distribution parameter allows us to obtain statistically valid data on the population number of pearl mussel and to judge the stable character of interactions in the host-parasite system (balance of host specimens that are resistant and nonresistant to infection).     

不同pH值对三角帆蚌珍珠质分泌的影响

运用多种组织化学方法和透射电镜技术,研究了５种ｐＨ水环境（ｐＨ５、６、７、８、９）对三角帆砷外套膜珍珠质分泌的影响机制,结果表明,在中性水环境中,贝体能积极地从外界水环境中吸收钙,并能旺盛地合成和分泌贝壳珍珠层及珍珠有机基质前体物质,持续的酸性水环境导致贝体的钙严重丢失,并引起珍珠质分泌细胞对有机基质前体物质的合成和分泌能力减弱,持续的碱性水环境虽能导致贝体对钙的积累,但珍珠质分泌细胞合成和分泌珍     

珍珠颜色和贝壳珍珠层颜色研究进展

颜色及其色度均一性是衡量珍珠价值的重要指标之一。珍珠颜色及贝壳珍珠层颜色的研究涉及多个学科领域,研究表明,珍珠的颜色与制片蚌外套膜对应的珍珠层颜色相一致,而蚌的珍珠层颜色主要由遗传因素决定。现有的研究资料对珍珠层颜色形成的机理虽然还不能给出一个系统、合理的诠释,但金属元素、卟啉、类胡萝卜素和物理结构等因素可能和珍珠层颜色形成密切相关,珍珠层中含有少量以蛋白质为主的有机基质,这些蛋白调控珍珠层的结构和颜色的形成,可能是解释珍珠层颜色形成机理的关键。本文对珍珠颜色和贝壳珍珠层颜色研究进展进行系统综述,探讨珍珠颜色的影响因素及相互关联,旨在为进一步研究珍珠和贝壳珍珠层颜色提供借鉴与思路。     

三角帆蚌五个野生群体线粒体DNA 16S rRNA遗传特性

对中国主要淡水湖泊(鄱阳湖、洞庭湖、太湖、洪泽湖及巢湖)三角帆蚌5个野生群体的线粒体DNA 16S rRNA基因片段进行了扩增和测序,得到473bp的碱基序列,没有发现插入/缺失突变的核苷酸位点。检测到了32个多态性核苷酸位点,共7种单倍型。鄱阳湖群体的222(C→G)和325(A→G)位点,太湖群体的233(A→G)位点,巢湖群体的40(A→G)、138(A→T)和294(C→T)位点,洪泽湖群体的241(A→C)位点的变异可以作为区分群体分子遗传标记位点。洞庭湖群体未发现特异位点。在5个群体间鄱阳湖群体多态性位点、核苷酸多态性、单倍型多态性和单倍型数量4个指标都最高,表明鄱阳湖群体具有最为丰富的遗传结构,遗传变异最大,可作为三角帆蚌选育的基础群体。