26 June 2020

Link roundup for June 2020

Friend of the blogGünter Vogt has a write-up for non-specialists about Marmorkrebs at the Atlas of Science.

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Great Lakes Now has a story about the efforts to keep invasive species out of the Great Lakes. It starts with Marmorkrebs being banned in Michigan, saying that the new policy made headlines. Other crayfish are discussed more in the article, mostly Louisiana red swamp crayfish.

24 June 2020

Rusch and colleagues, 2020

NeoBiota volume 58 cover featuring crayfish image
Rusch JC, Mojžišová M, Strand DA, Svobodová J, Vrålstad T, Petrusek A. 2020. Simultaneous detection of native and invasive crayfish and Aphanomyces astaci from environmental DNA samples in a wide range of habitats in Central Europe. NeoBiota 58: 1-32. https://doi.org/10.3897/neobiota.58.49358


Crayfish of North American origin are amongst the most prominent high-impact invasive invertebrates in European freshwaters. They contribute to the decline of European native crayfish species by spreading the pathogen causing crayfish plague, the oomycete Aphanomyces astaci. In this study we validated the specificity of four quantitative PCR (qPCR) assays, either published or newly developed, usable for environmental DNA (eDNA) screening for widely distributed native and non-native crayfish present in Central Europe: Astacus astacus, Pacifastacus leniusculus, Faxonius limosus and Procambarus virginalis. We then conducted an eDNA monitoring survey of these crayfish as well as the crayfish plague pathogen in a wide variety of habitat types representative for Central and Western Europe. The specificity of qPCR assays was validated against an extensive collection of crayfish DNA isolates, containing most crayfish species documented from European waters. The three assays developed in this study were sufficiently species-specific, but the published assay for F. limosus displayed a weak cross-reaction with multiple other crayfish species of the family Cambaridae. In the field study, we infrequently detected eDNA of A. astaci together with the three non-native crayfish species under examination. We never detected eDNA from A. astaci together with native crayfish, but in a few locations eDNA from both native and non-native crayfish was captured, due either to passive transport of eDNA from upstream populations or co-existence in the absence of infected crayfish carriers of A. astaci. In the study, we evaluated a robust, easy-to-use and low-cost version of the eDNA sampling equipment, based mostly on items readily available in garden stores and hobby markets, for filtering relatively large (~5 l) water samples. It performed just as well as the far more expensive equipment industrially designed for eDNA water sampling, thus opening the possibility of collecting suitable eDNA samples to a wide range of stakeholders. Overall, our study confirms that eDNA-based screening for crayfish and their associated pathogen is a feasible alternative to traditional monitoring.

Keywords: crayfish plague • eDNA monitoring • eDNA sampling methods • quantitative PCR • TaqMan assay validation

Open access

01 June 2020

Bans on Marmorkrebs could hurt research

If you want to talk about a success story in invasive species management, you might want to talk about the province of Alberta, Canada. Alberta like to boast that it is rat free.

But I can let you in on a little secret. I’ve seen rats in Alberta many times, when I was a student at the University of Lethbridge. Last year, the university got a government grant to build a new rat facility.

So there was a disconnect between declaring “We don’t want this invasive species!” and actually having that species in research labs. The two situations are separable.

I am not sure if that separation will exist for Marmorkrebs, though.

This year, Saskatchewan and Michigan banned Marmorkrebs. Ontario and some other US states are thinking about it.  I have been thinking about what the bans might do for Marmorkrebs research. There are several issues.

First, researchers in those states and provinces might not be able to have Marmorkrebs at all. Some of the Marmorkrebs legislation does not appear to have exceptions for bona fide academic researchers.

For example, the Canadian province of Manitoba has a law against owning all crayfish species, not just Marmorkrebs. In the course of doing research, I once asked officials in Manitoba if a researcher might keep crayfish, and was told, “No.”

Second, if the laws work as intended, fewer people in general would have Marmorkrebs. It’s possible that some pet owners would stop keeping Marmorkrebs, even in jurisdictions where it is completely legal. Aquarium keepers might see “the writing on the wall” and decide not to keep Marmorkrebs any more, in case they become illegal.

This could affect researchers, too. When an animal is widely available in the pet trade, it’s easy for researchers to get them, either for a one-off study or to start a colony.

Crayfish researchers have a long history of asking for regulation of the movement and trade of crayfish. It has been hard to get those regulations, but it would be a shame if new laws were not nuanced enough to allow original research.

If there can be rats in labs in Alberta, we should be able to have crayfish in labs, too. After all, an escaped crayfish in a university building probably has a harder time getting far than an escaped rat would. 

External links

Extinction agenda: How border patrols enforce a uniquely rat-free Alberta

Poster from here.