Two papers in Animal Conservation

Posted by Karl Filipsson | Papers

Two papers from NRRV were recently published in the journal Animal Conservation. The first paper presents a field study on how sedimentation affects brown trout (Salmo trutta) fry emergence in relation to freshwater pearl mussel (Margaritifera margaritifera) recruitment. The second paper presents a combined field and laboratory study on passage solutions for upstream-migrating eels (Anguilla anguilla).


Sedimentation affects emergence rate of host fish fry in unionoid mussel streams

Martin Österling


In the abstract, the author writes:

Freshwater pearl mussel, Margaritifera margaritifera

“Free-living, sympatric sedentary life stages of hosts and parasites are often adapted to similar environmental conditions. When the environment where these life stages occur is disturbed, both species can decline, causing strong negative effects on the parasitic species. For the highly threatened unionoid mussels with their larval parasitic life stage on fish, habitat degradation may simultaneously affect the conditions for the sedentary host fish eggs and the juvenile mussels in the sediment. This study provides novel information on the effect of sedimentation on the emergence rate of yolk sac fry, and its relation to mussel recruitment in two drainage basins, and is exemplified by the brown trout Salmo trutta, host fish for the threatened freshwater pearl mussel Margaritifera margaritifera. The results imply that turbidity and sedimentation can reduce the survival of trout eggs and yolk sac fry emergence rate regardless of trout strain and drainage basin. The results further suggest that low yolk sac fry emergence rates reduce the potential for mussel infestation and recruitment. The results indicate a year round negative effect of sedimentation, having strong and combined direct and indirect effects on juvenile mussel recruitment. Conservation measures that reduce anthropogenic sediment transportation into streams are a key factor for the conservation of mussels and their host fish.”

Access the paper here, or contact the author.


Climbing the ladder: an evaluation of three different anguillid eel climbing substrata and placement of upstream passage solutions at migration barriers

Johan Watz, Anders Nilsson, Erik Degerman, Carl Tamario and Olle Calles


European eel, Anguilla anguilla. Photo: Jörgen Wiklund

In the abstract, the authors write:

“Conservation programmes for endangered, long-lived and migratory species often have to target multiple life stages. The bottlenecks associated with the survival of juvenile anguillid eels migrating into inland waters, the survival and growth of the freshwater life stage, as well as the recruitment and survival of silver eels, migrating back to the ocean to spawn, must be resolved. In this study, we focus on the efficiency of passage solutions for upstream-migrating juveniles. Such solutions can consist of inclined ramps lined with wetted climbing substrata. We evaluated different commonly used substrata in a controlled experiment, recorded eel behaviour at the entrance of the ramp with infrared videography and validated the experimental results at a hydropower dam, where we also investigated the effects of ramp placement on performance. In the experiment on eel substratum selection, 40% of the eels passed in lanes with studded substratum, whereas only 21 and 5% passed using open weave and bristle substrata respectively. Video analysis revealed that the studded substratum attracted more approaches and initiated climbs than the other substrata, but once a climb had been initiated, passage success rates did not differ between substrata. Eels using the studded substratum climbed 26% faster than those using the bristle substratum and almost four times as fast as those climbing in the open weave. The superior performance of the studded substratum was supported by data from the field validation. Moreover, ramps positioned by the bank with low water velocities caught the most eels, but proximity to the dam had no effect on performance. To strengthen the European eel population, more juveniles need to reach their freshwater feeding grounds. A critical step to achieve this increase is to equip upstream passage solutions with suitable substrata and to optimize ramp placement at migration obstacles.”

Access the paper here, or contact any of the authors.

Two PhD positions (1: vegetation ecology, 2: ecosystem function/host-parasite interactions) are now open for applicants at Karlstad University. Both positions are full time for five years within the River Ecology and Management (NRRV) research group and include 80 % research and 20 % department duties (mainly teaching).

The applications for both positions close on 31 January 2019.


PhD position in vegetation ecology

River Klarälven, Värmland

The project will study which factors control diaspore dispersal and plant community composition along boreal streams, which in turn may have cascading effects on functional plant diversity and ecosystem functioning. The specific research questions to be addressed will be decided in consultation with the candidate. Areas of particular interest are (1) the effects of local and landscape-scale factors for plant species composition and diversity and cascading effects on ecosystem functioning and (2) studies of factors promoting or constraining plant dispersal along streams.

Read more and apply for the position here!


Ecosystem function/host-parasite interactions

The position will focus on either the role of mussels for ecosystem function or host-parasite interactions. Areas of interest are (1) the role of mussels for stream ecosystem function and (2) host-parasite interactions between mussels and their host fish. The specific research questions to be addressed will be decided in consultation with the candidate.

Read more and apply for the position here!

A thick shelled river mussel (Unio crassus).

Lea SchneiderAnders Nilsson, and Martin Österling from Karlstad University, and Johan Höjesjö from University of Gothenburg, recently published the scientific article “Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish in Aquatic Conservation. In the article the authors present a study on thick shelled river mussels (Unio crassus) and their interaction with potential host fishes originating from the same or a different river than the individual mussels. In the abstract they write:

“1. Parasite–host interactions can involve strong reciprocal selection pressure, and may lead to locally adapted specializations. The highly threatened unionoid mussels are temporary parasites on fish, but local adaptation has not yet been investigated for many species.

2. Patterns of local adaptation of one of Europe’s most threatened unionoids, the thick-shelled river mussel (Unio crassus) were investigated. Eurasian minnows (Phoxinus phoxinus) from two rivers (separate drainage areas) were cross-infested in the laboratory with sympatric and allopatric mussel larvae, while bullheads (Cottus gobio), inhabiting only one of the rivers, were infested with sympatric or allopatric mussel larvae. Larval encystment, juvenile mussel excystment and survival were measured.

3. For one river, but not the other, juvenile excystment from P. phoxinus was highest when infested with sympatric mussels. The opposite pattern was found for C. gobio in this river, where juvenile excystment and post-parasitic juvenile survival from allopatric C. gobio were highest. The results thus cannot confirm local adaptation of U. crassus to P. phoxinus in the study rivers, as excystment was not consistently higher in all sympatric mussel–host combinations, whereas there were potential maladaptive signs of U. crassus in relation to C. gobio. There was no loss of encysted larvae 3 days after infestation until juvenile excystment. Most juveniles were excysted between 17 and 29 days after infestation, and the numbers of excysted juveniles increased with fish size.

4. The results have implications for parasite–host ecology and conservation management with regard to unionoid propagation and re-introduction. This includes the need to (1) test suitability and adaptation patterns between U. crassus and multiple host fish species, (2) evaluate the suitability of certain unionoids and host fish strains after more than 3 days, and (3) determine whether large fish produce more juvenile mussels than smaller fish.”

Access the paper here: “Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish“, or email any of the authors.


According to tradition, Lea Schneider (center) last week nailed her thesis to the wall, at the entrance to Karlstad University. On the photo are also Martin Österling (supervisor) and Reine Lundin (dean).

On February 24, Lea Schneider, will defend her PhD-thesis “Conservation ecology of the thick-shelled river mussel Unio crassus – the importance of parasite-host interactions”. In the abstract Lea Schneider writes: “Unionoid mussels are globally threatened and their conservation requires species-specific knowledge on their ecology and parasite-host interaction. Unio crassus is one of Europe’s most threatened unionoid species and has a temporary obligate parasitic life stage (glochidia) on fish. A lack of suitable hosts is probably a major limitation for mussel recruitment, but host species composition, suitability and availability in time and space have yet to be fully explored. This thesis examines different aspects of the host fish species, including their composition, suitability and ecological importance, in relation to U. crassus, using both field and laboratory studies. The effects of mussel and host density on mussel reproductive potential were considered, as were aspects of evolutionary adaptations between mussels and fish and how climate change may affect their interaction.

The results show that U. crassus is a host generalist, parasitizing a variety of fish species. Host suitability and density, which varied among fish species and rivers, affected the level of glochidia encapsulation, hence mussel reproductive potential, more so than the density of mussels taking part in reproduction. Ecologically important hosts included both highly suitable primary hosts, and less suitable hosts that were highly abundant. Whether or not U. crassus has specific adaptations to its hosts to enhance juvenile transformation remains unclear. No distinct pattern of local adaptation was found, nor was there an effect of host fish presence on the timing of glochidia release by adult mussels. Instead, temperature played a major role, with results suggesting that changes in spring water temperature regimes can cause temporal and spatial mismatches in the mussel-host interaction. This thesis indicates that investigations of local mussel-host interactions help in identifying mechanisms important for unionoid conservation management and prioritization.”

The defense will take place on February 24 at 10:15 in room 1B309 (Sjöströmsalen) at Karlstad University. The frame of the thesis is available online here.

For the defense, Caryn Vaughn (University of Oklahoma, USA) is the opponent, and Leonard Sandin (Swedish University of Agriculture), Niklas Janz (Stockholm University, Sweden), and Annie Jonsson (University of Skövde, Sweden) constitute the grading committee (betygskommitté).

In the afternoon (from 13:30 onwards) the day before the defense (Feb 23), seminars related to the thesis will be given in Room 5F416 at Karlstad University. Here Caryn Vaughn will present on “Consumer aggregations act as hotspots of ecosystem function and services in rivers”, Niklas Janz on “What is host range?”, and Leonard Sandin on “Evaluation of ecological restoration in Swedish streams – some results from the EKOLIV project”. 

Everyone is welcome to attend both the PhD-defense and the seminars.