Culturing freshwater pearl mussel Margaritifera margaritifera: a breakthrough in the conservation of an endangered species

• 1. The freshwater pearl mussel Margaritifera margaritifera L. is globally endangered and is threatened by commercial exploitation, pollution and habitat loss throughout its range. Captive breeding would be a valuable tool in enhancing the status of M. margaritifera in the UK.
• 2. We have developed a semi‐natural system for successfully infecting juvenile brown trout with glochidial M. margaritifera, and culturing juvenile mussels in experimental tanks where glochidial M. margaritifera can excyst from fish gills and settle into sediment.
• 3. Infected fish had less than 1% mortality. Levels of infection varied among fish. Two yearly cohorts of juvenile M. margaritifera were identified from samples of sediment taken from each experimental tank. Individuals range in size from 1.4 mm (2000 cohort) to >3 mm in length (1999 cohort).
• 4. The number of juvenile M. margaritifera present in the two experimental tanks are estimated to be between 3600 (tank A) and 0 (tank B) for the putative 1999 cohort and between 6000 (tank A) and 13 000 (tank B) for the putative 2000 cohort.
• 5. This pioneering method for large‐scale cultivation of juvenile M. margaritifera is intermediate between the release of infected fish into rivers and the intensive cultivation systems developed in continental Europe and the USA for other species of unionid. This is the first time that large numbers of M. margaritifera have been cultured and represents a significant breakthrough in the conservation of this globally endangered Red Data List species. The method is straightforward and is most cost‐effective when undertaken alongside established hatchery processes.

Copyright © 2006 John Wiley & Sons, Ltd.     

A protocol for stocking hatchery reared freshwater pearl mussel Margaritifera margaritifera

• 1. Freshwater pearl mussel (Margaritifera margaritifera L.) populations are under serious threat of extinction throughout their geographical range and only a few remnant populations are recruiting to adulthood. Consequently, M. margaritifera is classified as endangered on the International Union for Conservation of Nature Red List.
• 2. Several institutions across many countries have set up Ark sites at hatcheries to culture and rear young M. margaritifera from population remnants, with the intention of stocking these juveniles into rivers. The release location must fulfill the habitat requirements for the full life‐cycle of the species, so they can contribute to the next generation and thus the long‐term recovery of the species. However, little research or advice exists about how to decide if river environments are suitable for stocking.
• 3. A protocol is presented for determining whether a M. margaritifera population will benefit from stocking hatchery reared juveniles and how to identify suitable areas. Stocking locations are considered from catchment scale to microscale using water quality (reach), macrohabitat (site) and microhabitat, including physicochemical properties of the substratum (spots).
• 4. A case study of the River Esk in north‐east England, is incorporated to exemplify the myriad of considerations surrounding attempts to conserve M. margaritifera, and describes how implementation of the protocol can structure and assist stocking programmes. Copyright © 2010 John Wiley & Sons, Ltd.

     

Electrofishing as a new method to search for unknown populations of the endangered freshwater pearl mussel Margaritifera margaritifera

1. The freshwater pearl mussel Margaritifera margaritifera is threatened throughout its Holarctic range, but the occurrence of this species is insufficiently mapped. For the conservation of M. margaritifera, it is important to identify populations more comprehensively. 2. Traditionally mussels have been searched for visually using techniques such as diving and aquascope, both of which are potentially time‐consuming and demanding survey methods. 3. In this study, a new search method is presented. As glochidia of M. margaritifera are larval parasites on the gills of salmonid fish, electrofishing and non‐destructive examination of salmonids with the naked eye may reveal the presence of glochidia and therefore the occurrence of M. margaritifera in watercourses. This method was tested in both the field and laboratory in northern Finland. 4. In summer, when M. margaritifera glochidia were large, the status of salmonids being infected or uninfected by M. margaritifera was correctly identified with the naked eye with 62, 80, 88 and 93% accuracy in four streams sampled, 96% accuracy in the laboratory, and 100% accuracy in all cases when at least 20 glochidia per fish were present. Intensity of infection was also assessed successfully; a specifically tailored, qualitative abundance score correlated significantly with the real number of glochidia. However, during autumn with small glochidia freshly attached to fish, glochidia infection could be observed only under microscopic examination. 5. When the method was used in 40 previously incompletely surveyed tributaries, three M. margaritifera populations were found. The infection in salmonids was observed always with the naked eye, being subsequently confirmed microscopically. The existence of adult mussels in two of these rivers was also confirmed. 6. The results indicate that electrofishing and a relatively quick naked‐eye check of salmonids provides a new, non‐destructive, and potentially cost‐effective way to search for new, previously unrecorded M. margaritifera populations. Copyright © 2016 John Wiley & Sons, Ltd.     

Conservation status of two endangered freshwater mussel species in Bavaria,Germany: Habitat quality,threats, and implications for conservation management

1. The freshwater pearl mussel (Margaritifera margaritifera) and the thick‐shelled river mussel (Unio crassus) are relatively widespread across Europe, but are strongly declining and are now protected by the European Habitats Directive. In the course of this study, 20 pearl mussel and 14 thick‐shelled river mussel streams in Bavaria, Germany, were investigated.
2. The mussel populations were mapped to determine population size and age structure. For the assessment of habitat quality, host fish abundance and physicochemical parameters were investigated, e.g. substratum quality, water chemistry, redox potential, and turbidity. Furthermore, potential risks for the populations such as predation or river maintenance were also recorded and assessed.
3. The average population size and recruitment rates of M. margaritifera populations were lower than in U. crassus populations, with 3517 (2.2% juveniles) compared with 5566 (41.4% juveniles) individuals, respectively. On average, 22.3% of particles were smaller than 0.85 mm in diameter at M. margaritifera sites, whereas the mean proportion of fine particles at U. crassus sites was twice as high, at 41.3%. Other parameters such as redox potential or electric conductivity also indicated more favourable habitat conditions in M. margaritifera streams. Unio crassus seems to be less vulnerable to adverse substratum texture and increased nutrient levels than M. margaritifera.
4. The main threats for U. crassus were physical habitat destruction, predation by muskrat, or a lack of host fish, whereas M. margaritifera mainly suffered from siltation leading to a lack of oxygen supply to the interstitial zone, affecting recruitment. Consequently, conservation strategies need to be species‐specific and address stream‐specific reasons for decline. As a basis, accurate and comparable monitoring data are necessary, which implies the standardization of monitoring protocols.

     

A spatially explicit approach to prioritize protection areas for endangered freshwater mussels

1. In spite of their conservation importance, only a fraction of lakes and streams globally – including their catchments – are currently covered by conservation areas. To identify conservation gaps, assessing the spatial distribution of biodiversity in relation to conservation areas is a promising approach. A gap‐analysis approach was used to evaluate the protection status of the habitats of two endangered freshwater mussel species, Margaritifera margaritifera (Linnaeus, 1758) and Unio crassus (Philipsson, 1788), in the Federal State of Bavaria, Germany.
2. First, ecological niche models (ENMs) were developed for both mussel species based on presence‐only data in order to identify suitable habitats. Second, binary maps of suitable and unsuitable habitats for the species were used to compare different categories of currently protected areas in a gap analysis.
3. The ENMs for M. margaritifera revealed a spatially restricted distribution with good model performance, whereas the spatial distribution of U. crassus was wider and the model performance was weaker. For M. margaritifera, a higher percentage of suitable habitat is already under some sort of protection, whereas for U. crassus only half of the suitable habitats are under protection.
4. The results suggest that suitable habitats of both species are not sufficiently protected. More effective conservation of M. margaritifera and U. crassus requires separate management: increasing the respective protection categories of already protected habitats of M. margaritifera and incorporating an increased area of suitable habitats under legal protection for U. crassus.

     

Applying morphometrics to choose optimal captive brood stock for an endangered species: a case study using the freshwater pearl mussel,Margaritifera margaritifera (L.)

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Environmental DNA as a monitoring tool for the endangered freshwater pearl mussel (Margaritifera margaritifera L.): a substitute for classical monitoring approaches?

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Effects of aquatic weed removal on freshwater pearl mussels and juvenile salmonids in the River Spey,Scotland

• 1. Experiments were carried out in the River Spey, Scotland to determine the effects of aquatic weed (Ranunculus spp.) removal on populations of freshwater pearl mussels (Margaritifera margaritifera) and juvenile salmonids (Salmo salar, Salmo trutta) and their river‐bed habitats.
• 2. Physical removal of Ranunculus had no significant impact either on pearl mussels or on salmon and trout fry.
• 3. Regrowth of Ranunculus post‐removal was negligible for one year, indicating that hand‐removal may be an effective control measure.
• 4. Ranunculus roots appear to facilitate substantial depositions of fine sand that are detrimental both to pearl mussels and salmonid fry.
• 5. The rapid spread of invasive Ranunculus is a potential threat to the conservation status of M. margaritifera in the River Spey.

Copyright © 2007 John Wiley & Sons, Ltd.     

Dead or alive — Old empty shells do not prompt false-positive results in environmental DNA surveys targeting the freshwater pearl mussel (Margaritifera margaritifera L.)

1. Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA in monitoring programmes, various species-specific sampling or analytical issues remain to be resolved in order to minimize frequencies of false-positive and -negative results. For example, empty shells from freshwater pearl mussels (Margaritifera margaritifera) contain extractable DNA (chemical extraction from ground-up shells) suggesting a risk of false-positive samples at stream sites with extinct populations but with empty shell material remaining.
2. The aim of this study was to investigate whether empty and naturally degrading shells from M. margaritifera can cause false-positive eDNA signals in water samples.
3. Water samples were collected from outdoor stream channels (in Lemming, Denmark) with living freshwater pearl mussels or empty shell material (density ~10 individuals m⁻²) during a 3-week experimental period. Living freshwater pearl mussels were collected from Hemgravs stream in Sweden and transported to Denmark according to permissions granted by the Swedish and Danish authorities.
4. All water samples from stream channels containing empty shells were negative for eDNA indicating that eDNA traces in stream water are most likely to originate from living individuals located upstream of the sampling site. Water samples collected from stream channels containing living individuals of M. margaritifera were consistently positive for eDNA except for one sample (interpreted as a false negative).
5. The study shows that positive eDNA signals for freshwater pearl mussels most likely reflect the presence of living individuals. Consequently, we suggest that eDNA should be used to locate remaining population fragments of M. margaritifera in deep and turbulent streams, providing a platform for faster and more efficient decision making when launching investigative and mitigation initiatives.

     

Genetic structure of Irish freshwater pearl mussels (Margaritifera margaritifera and Margaritifera durrovensis): Validity of subspecies,roles of host fish,and conservation implications

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