Knowl. Manag. Aquat. Ecosyst.
Number 419, 2018
Topical issue on Crayfish
Article Number 30
Number of page(s) 6
Published online 15 June 2018

© A. Herrmann et al., Published by EDP Sciences 2018

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License CC-BY-ND (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. If you remix, transform, or build upon the material, you may not distribute the modified material.

1 Introduction

Crayfish are known to be able to disperse moving over land (Braswell and Cooper, 1995), however, the potential and the annual phenology are based on accidental records only. Knowledge about the time period and factors influencing this behavior may support new management approaches. Banha and Anastácio (2014) studied the desiccation survival capacities of Pacifastacus leniusculus (Lyko) and Procambarus clarkii (Girard), as they are invasive at the Iberian Peninsula and disperse overland. Additionally, P. clarkii is known to show higher overland dispersal activity correlated to relative humidity (Ramalho and Anastácio, 2015). As invasive alien crayfish species (IACS) are known to be a threat to amphibians, overland dispersal can cause serious problems in conservation areas or breeding habitats for amphibians (Nyström, 1997; J Cruz et al., 2006; Cruz and Segurado, 2008). Omnivorous crayfish are key species in aquatic ecosystems, but IACS became a serious problem around the world, as invasive alien species turned out to be one of the biggest threats to biodiversity (Butchart et al., 2010; Lodge et al., 2012; Richardson et al., 2013). Managing them in an area means to combine as many different methods as there are known to minimize the further spread of the species (Gherardi et al., 2011).

The Upper Rhine River area is a hotspot to biodiversity in Central Europe (Ackermann and Sachteleben, 2012). Threatened amphibians as Triturus cristatus (Laurenti), Rana arvalis Nilsson and Hyla aborea (Linnaeus) are being supported by government and NGO-funded newly created ponds for nature conservation. The invasive, North American freshwater crayfish Faxonius immunis (Hagen) is colonizing these habitats by overland dispersal, forming new threat to amphibians. The species was known as Orconectes immunis (Hagen) until now. We follow the recent classification of crayfish by Crandall and De Grave (2017) and named it F. immunis (Hagen). The first population was detected in 1993 near the Baden Airpark (Gelmar et al., 2006). Since then, F. immunis spread north along the Rhine system through canals, ditches and streams and is still colonizing aquatic systems from the floodplain to the slope of the Black Forest (Chucholl, 2012). F. immunis grows high population densities in temporary and muddy ponds and can survive dry periods by building burrows (Tack, 1941; Bovbjerg, 1970; Martens, 2016). Juvenile F. immunis grow fast in their first year, needing a higher amount of protein in their diet than adult ones (Brown and Wetzel, 1993; Chucholl, 2012; Herrmann, 2017). The adults mainly feed on macrophytes and are decreasing hideouts for insects or aquatic vertebrates (Coler and Seroll, 1975). By moving overland, F. immunis invaded ponds and lakes which are not directly connected to streams and ditches of the River Rhine system. Understanding the ability to disperse overland could be a key to protect systems not yet colonized by this species and, especially, to give advice to those who are planning to create new artificial ponds for amphibian conservation. As the amount of IACS in Europe is rising, every information on overland dispersal can be crucial for the protection of other waters. Resulting in the lack of knowledge about factors influencing the behavior to disperse overland, a citizen science project has been started.

2 Material and methods

In collaboration with local administrations, forty-seven information boards (Fig. 1) were installed between June and August 2016. Along the River Rhine, a stretch of approximately 50 km was covered. The boards were placed from the city of Rheinstetten in the north and to the Baden-Airpark in the south next to areas where populations of F. immunis are known along pathways (Fig. 2).

The German text on the installed boards is translated in the following: “Crayfish wanted! The North American calico crayfish is spreading along the Upper Rhine River region. With the ability to move over land, it is colonizing several ponds and lakes. Therefore, the crayfish prefers easy routes, e.g. our streets or paths. To learn more about the spread of the calico crayfish, the Institute for Biology, University of Education Karlsruhe, asks for your help. Please contact us via email or telephone if you see crayfish moving over land. In addition, knowledge about earlier contact with crayfish migrating over land are of interest. Contact:, 017626754749 Thank you for your support!”

To support the project, articles in local newspapers were published shortly after installing the tables. The articles were published again later to keep them in focus.

The bigger part had taken reports on crayfish seen inside the water and emails with questions and suggestions about crayfish species in the area. Out of 98 emails sent to us 39 have been suitable for our study. Information sent to us was checked by evaluating the attached photos and comparing the described locality with our data base on the distribution of F. immunis. For further analysis, emails with (PIC: examples in supplementary material Fig. S1) and without (NPIC) attached photos were separated. The date of observation was taken from the EXIF data in the attached photos. All records apply to stray findings.

We compared these data with those from master theses and exam works reported quantitative short time data at three ponds in the city of Rheinstetten (48°58′17.04″ N; 8°17′44.394″ E), where the overland migration ability was evaluated. Data was provided from the periods of 23.04.2015 to 22.05.2015, 30.10.2015 to 31.05.2016 (Schnabler, 2016) and 23.02.2017 to 30.04.2017 (Marholtz, 2017), respectively.

thumbnail Fig. 1

Information board.

thumbnail Fig. 2

Map of the River Rhine system with reports of overland dispersal of crayfish recorded by citizen scientists.

3 Results

We got a total of 39 reports, 33 reports telling F. immunis seen migrating over land. One report had no exact date to note and five turned out to be other crayfish species. In total, 19 F. immunis could be identified by the photo sent to us (PIC), 14 emails had no attached photo while telling F. immunis would have been seen (NPIC). The data shows that this species can disperse overland throughout the whole year with peaks in spring and autumn (Fig. 3). Unpublished data from master theses and exam works reported quantitative short-time data, which follows the same implication (Fig. 4).

The reports of F. immunis migrating overland were from the area covered with information boards, and some additional from adjacent areas (Fig. 2). The furthest was more than 15 km far away from the nearest board, but the received picture was showing another crayfish species.

Four other IACS could be identified moving outside the water within the PIC-data: Faxonius limosus (Rafinesque), P. leniusculus (Dana), Procambarus virginalis (Lyko) and P. clarkii (Girard).

One dataset was not included in the analysis: In October 2016, within the village of Elchesheim-Illingen (48° 55′ 52.748″ N; 8° 12′ 38.541″ E), six individuals of F. immunis were collected by children on the road, just after excavated earth from a dredged ditch was placed at the edge of the village.

thumbnail Fig. 3

Total received data on F. immunis (Hagen) migrating overland (n=33) divided by years of record.

thumbnail Fig. 4

Data on overland migration of F. immunis (Hagen) (n=85) collected in unpublished master theses and exam works in the years 2015, 2016 (Schnabler, 2016, black) and 2017 (Marholtz, 2017, white), respectively.

4 Discussion

Citizen science studies grew more important in the past decade. They are well-established methods for ornithologists to collect data on migration seasons, habitat use or distribution as important ecological information in larger regions (Greenwood, 2007). Crall et al. (2010) could show that the highest amount of citizen science studies on invasive species aimed for presence or absence. These variables are easy to check and do not require much scientific knowledge. Collectively, citizen science studies show the potential to collect extensive data at low costs across large areas (Dickinson et al., 2010). For crayfish distribution, Perdikaris et al. (2017) have shown that citizen science data could provide useful data on presence and distribution of species. In our project, we wanted to collect data on the so far badly known phenology of overland dispersal as well as new data on distribution of F. immunis.

Our data clearly demonstrates that F. immunis is dispersing over land the entire year. The analysis from the PIC suggests that F. immunis has two seasons of higher activity in overland dispersal. The NPIC and the unpublished data from the master theses and exam works support this. The highest activity is between March and May, during the spawning season of this species. The other season of high activity is between September and November, when F. immunis is mating. So far, no activity is reported for December, February and July. We suppose that F. immunis leaves out extreme cold or dry periods of the year because the warmest month of the year at the Upper Rhine River area is July. The seasonality could therefore occur out of abiotic factors like dewy weather or rainfalls in combination with the right temperature, just as Ramalho and Anastácio (2015) have shown it for P. clarkii, which shows higher overland dispersal activity above 70% relative humidity and between a temperature range of 16.3–24.2 °C. As overland dispersal seems to depend on microclimate conditions, it could be supportive that the Upper Rhine River area shows the lowest amount of cold days in Germany (Heinemann, 2007). This should be investigated in a more focused study on the relative humidity and other meteorological effects. Another factor for seasonality could be the chance to colonize new habitats after mating or before spawning, because ovigerous females of F. immunis are taking the risk of moving over land, too (Schnabler, 2016, unpublished).

The knowledge about mechanisms in the dispersal of invasive crayfish, such as F. immunis, can lead to advanced management suggestions for the creation of new artificial ponds for amphibian conservation to minimize the spread of the species and their impact on the local ecosystem. Ponds should be protected by barriers like toad fences, where amphibians must be taken over it manually or with a permanent barrier, which is passable for amphibians but not for crayfish (Schnabler, 2016). Further and existing data on overland dispersal of F. immunis can also be used to identify main dispersal routes and areas of high activity, which lead to highly populated systems. Isolating these systems and closing the corridors can be a key method to minimalize the further spread of the species.

Resulting in his broad tolerance towards pollution and habitats (Holdich, 2002; Chucholl, 2012) and his invasive potential (Karatayev et al., 2009) linked to his strongly r-selected life history (Martens, 2016), we suggest that most existing ponds and lakes at the Upper Rhine River area could be colonized by F. immunis in the next 10 years. This prediction is supported by knowledge gained about P. clarkii in the southwest of the Iberian Peninsula (Cruz and Rebelo, 2007), where the crayfish also disperse overland frequently.

Supplementary Material

Figures Access here


We would like to thank all citizen scientists for participating in our study and providing us with data. We are indebted to S. Eisenbarth for providing the board material and for helping us installing it. We appreciate the help of R. Hertweck for organizing and installing boards in the southern areas. Further thank should go to the students C. Marholtz, S. Wentz and A. Wilberts for providing additional data on overland migration. The study would not have been possible without the help of the local administrations and newspapers. We appreciate the helpful suggestions and comments made by our two independent reviewers. This study is supported by the nature conservation foundation of Baden-Wuerttemberg with earmarked funds from lottery (ID: 73—8831.21/546 91-1744GL).


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Cite this article as: Herrmann A, Schnabler A, Martens A. 2018. Phenology of overland dispersal in the invasive crayfish Faxonius immunis (Hagen) at the Upper Rhine River area. Knowl. Manag. Aquat. Ecosyst., 419, 30.

All Figures

thumbnail Fig. 1

Information board.

In the text
thumbnail Fig. 2

Map of the River Rhine system with reports of overland dispersal of crayfish recorded by citizen scientists.

In the text
thumbnail Fig. 3

Total received data on F. immunis (Hagen) migrating overland (n=33) divided by years of record.

In the text
thumbnail Fig. 4

Data on overland migration of F. immunis (Hagen) (n=85) collected in unpublished master theses and exam works in the years 2015, 2016 (Schnabler, 2016, black) and 2017 (Marholtz, 2017, white), respectively.

In the text

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