31 December 2018

2018 was the second best year ever for Marmorkrebs research

It’s time for this blog’s longest running tradition! (Okay, the only tradition, if we’re honest.) It’s the eleventh annual look at trends in Marmorkrebs publishing!

As mentioned back in 2016, the graph above includes journal articles and book chapters. There were no book chapters this year, however. I feel compelled to add a second graph, plotting only the journal articles. The graph below is much more what this year felt like:

A barnstormer of a bumper crop of a year that was much busier than any before. But 2016 comes out on top because a single book dropped with a bunch of articles on Marmorkrebs. But several of those were reviews, and that they all came out in one volume meant it felt like one event instead of nine. Honestly, I think the activity in Marmorkrebs papers coming out in journals is a better indicator of the expansion of the field.

This year saw the biggest Marmorkrebs paper of all time published, at least as measured by its Altmetric score. Gutekunst and colleagues had two major findings in one paper:

  1. Announcing the sequencing of the Marmorkrebs genome, the first for a decapod crustacean.
  2. Documenting the spread of Marmorkrebs in Madagascar since their detection about a decade earlier.

What was strange, though, was that almost none of the news coverage (of which there was a lot) focused on either of those two things. Most focused on the fact that cloning crayfish were a thing, which we have known from 2003. Some focused on the invasive nature of Marmorkrebs, but tended to talk about their spread in Europe rather than Madagascar. Having the first decapod crustacean genome, which might have been the biggest long term result from this paper, was very underplayed.

Another trend was researchers started to adopt the name Procambarus virginalis, after the name was proposed three years ago. The initial 2015 proposal was a “naked name” (nomen nuden in taxonomic lingo) with none of the typical descriptive work to accompany the new Linnean name, and the community generally used Procambarus fallax forma virginalis in 2016 and 2017. But having a proper taxonomic paper published in 2017 seems to have turned the tide, and P. virginalis seems to now be the accepted name in the community.

With the trendline continuing to head up, and two papers with 2019 cover dates already out, the state of Marmorkrebs research is strong.

Related posts

2008 was the best year ever for Marmorkrebs research
2009 was tied for the best year ever in Marmorkrebs research
2010 was the best year ever for Marmorkrebs research
2011 was not the best year ever for Marmorkrebs research
2012 was an average year for Marmorkrebs research
2013 was the second best year ever for Marmorkrebs research
2014 was a good year for Marmorkrebs research
2015 was the best year ever for Marmorkrebs research
2016 was the best year ever for Marmorkrebs research
2017 was the second best year ever for Marmorkrebs research

29 December 2018

Fořt and colleagues, 2019

Fořt M, Hossain MS, Kouba A, Buřič M, Kozák P. 2019. Agonistic interactions and dominance establishment in three crayfish species non-native to Europe. Limnologica 74: 73-79. https://doi.org/10.1016/j.limno.2018.11.003


Ecosystems increasingly face concurrent invasions by multiple species, but knowledge about relationships among invasive species is under studied. We examined agonistic encounters among signal crayfish Pacifastacus leniusculus, marbled crayfish Procambarus virginalis, and the common yabby Cherax destructor, none native to Europe, to assess the influence of aggression on their success in a sympatric environment. In interspecific interactions, similar-sized signal crayfish were significantly more likely to initiate aggressive encounters and won significantly more fights against similar-sized opponents. The marbled crayfish was the least aggressive and least successful in agonistic interactions. The mean number of fights, fight duration, and number and duration of low and high intensity fights varied significantly between intra- and inter-specific interactions, tending to be more pronounced in conspecific encounters. We concluded that crayfish species differ in fighting strategies employed during intra- and inter-specific interactions. Of the species evaluated, the signal crayfish shows the highest potential to establish dominance. However, factors such as growth rate, reproductive potential, ecosystem variables, and temperature of habitat may alter the competitiveness of an invader.

Keywords: agonistic interaction • biological invasion • Cherax destructor • invasive species • Pacifastacus leniusculus • Procambarus virginalis

20 December 2018

Marenkov and colleagues, 2018b

Marenkov O, Lykholat T, Kurchenko V, Nesterenko O. 2018. Histology of marbled crayfish Procambarus virginalis (Lyko, 2017): annotated atlas. World News of Natural Sciences 21: 141-153. http://www.worldnewsnaturalsciences.com/article-in-press/2018-2/21-2018/


The educational publication contains microphotographs and description of histological preparations of the structure of marbled crayfish. The above materials may be used both for carrying out laboratory work on disciplines “Histology”, “Cytology”, “Cell Biology”, “Special Practice”, and for self-study of relevant educational topics. Designed for specialists in the field of hydrobiology and histology, students and graduate students of institutions of higher education who studying in the field of “091 Biology”, “207 Water bioresources and aquaculture” and “162 Biotechnology and bioengineering”. The publication contains the results of studies conducted by President’s of Ukraine grant for competitive projects Ф75/142 «The reproductive potential of invasive species of Dnieper region reservoirs and their impact on bioproductivity formation» (№ 0118U006319) of the State Fund for Fundamental Research.

Keywords: Marmorkrebs • histology • marbled crayfish • Procambarus virginalis • hemolymph • hepatopancreas

22 November 2018

Deidun and colleagues, 2018

Deidun A, Sciberras A, Formosa J, Zava B, Insacco G, Corsini-Foka M, Crandall KA. 2018. Invasion by non-indigenous freshwater decapods of Malta and Sicily, central Mediterranean Sea. Journal of Crustacean Biology 38(6): 748–753. http://dx.doi.org/10.1093/jcbiol/ruy076


Invasive species can cause significant changes in local and regional ecologies, especially in freshwater ecosystems. It is thus important to monitor and document the spread of non-indigenous species to such habitats as such information can be critical to preserving habitats and species. We document the spread of the red swamp crayfish Procambarus clarkii (Girard, 1852) (Cambaridae), a highly invasive non-indigenous species, in Malta and south Sicily. We also document the first records of other non-indigenous decapods important in the pet trade or in aquaculture, Procambarus virginalis Lyko, 2017 (Cambaridae), Pontastacus leptodactylus (Eschscholtz, 1823) (Astacidae), Cherax quadricarinatus von Martens, 1868 (Parastacidae), Pacifastacus leniusculus (Dana, 1852) (Astacidae), and Atyopsis moluccensis (De Haan, 1849 (Atyidae) from freshwater localities in the Maltese Archipelago and Cherax destructor Clark, 1936 (Parastacidae) from southeastern Sicily. The study provides recommendations on the adoption of control measures by the competent national authorities with respect to these non-indigenous species.

Keywords: None provided.

Vogt and colleagues, 2018

Vogt G, Lukhaup C, Williams BW, Pfeiffer M, Dorn NJ, Schulz R, Schrimpf A. 2018. Morphological characterization and genotyping of the marbled crayfish and new evidence on its origin. Zootaxa 4524(3): 329–350. https://doi.org/10.11646/zootaxa.4524.3.3


The obligately parthenogenetic marbled crayfish, Procambarus virginalis, is the first formally described asexual species of the Crustacea Decapoda. It is a triploid descendant of the sexually reproducing slough crayfish, Procambarus fallax. Here we describe the morphology of cultured and wild marbled crayfish of wide size ranges in detail and photodocument all taxonomically relevant characters. Some morphological traits and coloration showed considerable variation within populations despite the monoclonal nature of marbled crayfish. There were also significant differences between wild and laboratory populations with respect to body proportions, coloration and spination. Comparison with Procambarus fallax revealed no qualitative morphological characters that unambiguously identify the marbled crayfish. Analysis of the mitochondrial cytochrome c oxidase subunit I gene (COI) and nuclear microsatellites of marbled crayfish and Procambarus fallax from different sources indicated that the tri-allelic microsatellite PclG-02 is better suitable than COI to identify the marbled crayfish. A respective identification key is provided. The COI and  microsatellites of Procambarus fallax from different areas of Florida and southern Georgia suggest that the parents of the first marbled crayfish may have come from northern Union County, northern Florida.

Keywords: morphology, genotyping, evolution, marbled crayfish, Procambarus fallax

(Note: An open access preprint of this work is available. Vogt G, Dorn NJ, Pfeiffer M, Lukhaup C, Williams BW, Schulz R, Schrimpf A. 2018. In-depth investigation of the species problem and taxonomic status of marbled crayfish, the first asexual decapod crustacean. BioRxiv: 26 June 2018. https://doi.org/10.1101/356170)

06 November 2018

Marmorkrebs in silhouette

In case you need a representation of a marbled crayfish to pop into one of your figures, or any other kind of organism, try Phylopic. While I was tooling around there, I found this image of Marmorkrebs by Kamil S. Jaron:

Presumably, a couple of legs are being held under the body. And I wouldn’t trust this page for taxonomic information, as the authority given for Marmorkrebs is incorrect. Not sure how easy it is to fix that.

Update, 9 November 2018: It’s fixed on both counts! Woohoo!

New link for new image is here.

External links


09 October 2018

Gatzmann and colleagues, 2018

Gatzmann F, Falckenhayn C, Gutekunst J, Hanna K, Raddatz G, Carneiro VC, Lyko FJE. 2018. The methylome of the marbled crayfish links gene body methylation to stable expression of poorly accessible genes. Epigenetics & Chromatin 11(1): 57. https://doi.org/10.1186/s13072-018-0229-6


Background: The parthenogenetic marbled crayfish (Procambarus virginalis) is a novel species that has rapidly invaded and colonized various different habitats. Adaptation to different environments appears to be independent of the selection of genetic variants, but epigenetic programming of the marbled crayfish genome remains to be understood.

Results: Here, we provide a comprehensive analysis of DNA methylation in marbled crayfish. Whole-genome bisulfite sequencing of multiple replicates and different tissues revealed a methylation pattern that is characterized by gene body methylation of housekeeping genes. Interestingly, this pattern was largely tissue invariant, suggesting a function that is unrelated to cell fate specification. Indeed, integrative analysis of DNA methylation, chromatin accessibility and mRNA expression patterns revealed that gene body methylation correlated with limited chromatin accessibility and stable gene expression, while low-methylated genes often resided in chromatin with higher accessibility and showed increased expression variation. Interestingly, marbled crayfish also showed reduced gene body methylation and higher gene expression variability when compared with their noninvasive mother species, Procambarus fallax.

Conclusions Our results provide novel insights into invertebrate gene body methylation and its potential role in adaptive gene regulation.

Keywords: None provided.

05 October 2018

Anastácio and colleagues, 2019

Anastácio PM, Ribeiro F, Capinha C, Banha F, Gama M, Filipe AF, Rebelo R, Sousa R. 2019. Non-native freshwater fauna in Portugal: A review. Science of The Total Environment 650: 1923-1934. https://doi.org/10.1016/j.scitotenv.2018.09.251


We present the most updated list of non-native freshwater fauna established in Portugal, including the Azores and Madeira archipelagos. This list includes 67 species at national level but corresponds to 84 species records, of which 53 are in the mainland, 23 in the Azores and 8 in Madeira archipelagos. We also discuss the progression of the cumulative number of introductions since 1800 and identify the most probable vectors of introduction, main taxonomic groups and their regions of origin. Furthermore, we review the existing knowledge about ecological and economic impacts, invasion risk and potential distribution of invaders, under present and future climatic conditions, and the applied management actions, including the production of legislation. Along the 20th century the number of successful introductions increased at an approximate rate of two new species per decade until the beginning of 1970s. Since then, this rate increased to about 14 new species per decade. These introductions were mainly a result of fisheries, as contaminants or for ornamental purposes. Fish and mollusks are the taxonomic groups with more established species, representing more than half of the total. Most species (>70%) are native from other regions of Europe and North America. Studies about ecological or socioeconomic impacts are more common for fish, crustaceans and mollusks. Impacts for most amphibians, reptiles and mammals are not thoroughly studied. A few studies on the impacts and management actions of health-threatening mosquitoes are also available. The potential distribution in the Portuguese territory was modelled for 26 species. Only a minority of these models provides projections of distributions under scenarios of future climate change. A comparison of the Portuguese and EU legislation shows large discrepancies in the invasive species lists. Using the EU list and a ranking procedure for the national context, we identify freshwater species of high national concern for which actions are urgently needed.

Keywords: invasions • exotic species • Iberian Peninsula • risk assessment • inland waters • aquatic systems

25 September 2018

Göpel and Wirkner, 2018

Göpel T, Wirkner CS. 2018. Morphological description, character conceptualization and the reconstruction of ancestral states exemplified by the evolution of arthropod hearts. PLOS ONE 13(9): e0201702. https://doi.org/10.1371/journal.pone.0201702


Arthropods are the most species-rich taxon within Metazoa and have gone through major evolutionary changes with regard to body organization. Arthropod hearts and their associated vascular systems are thus morphologically highly disparate: while some arthropods exhibit very powerful hearts and complex vascular systems, other arthropods do not possess any kind of vascular system or heart at all. A comprehensive study investigating the structure of arthropods hearts has never been undertaken. In this study, we therefore investigate the hearts of 34 species from all major arthropod groups using various imaging techniques (confocal laser scanning microscopy, micro-computed tomography, histology) and describe them by addressing different aspects of heart morphology, e.g. the structure of the myocard or the composition of ostia. In a next step, we conceptualize 18 characters related to heart morphology and their respective character states and–using additional data from the literature–score a matrix for a total of 45 species from 38 supraspecific taxa. We map the characters onto prevailing phylogenetic hypotheses and perform parsimony-based ancestral state reconstruction to trace the evolutionary transformations undergone by arthropod hearts. An exploration of the character concepts (as explanatory hypotheses) reveals ontological peculiarities of character statements that clearly distinguish them in terms of ontological status from descriptive statements (i.e. descriptions of morphemes). The implications of these findings influence the interpretation of ground patterns as explanations. This first phylogenetic approach to heart morphology in the arthropod ground pattern reveals numerous new putative synapomorphies and leads to a reconsideration of the morphology of circulatory systems in early arthropods. Hypotheses on the evolution of hearts in (Pan-) Arthropoda are illustrated and discussed.

Keywords: None provided.

24 September 2018

Crayfish crimes 2

I mentioned a couple of weeks back that an American man had been convicted for selling and exporting crayfish as pets. Another case came to attention recently. An Australian man was convicted and fined AUD$8,550 for catching the world’s largest freshwater invertebrate, Astacopsis gouldii. The crayfish is threatened and protected by law.

I mention this because protecting invertebrates is hard, and law enforcement on this sort of issue is rare. It’s encouraging to see.

Related posts

Crayfish crimes

External links

Largest ever fine for poaching giant freshwater crayfish

21 September 2018

Linzmaier and colleagues, 2018

Linzmaier SM, Goebel LS, Ruland F, Jeschke JM. 2018. Behavioral differences in an over-invasion scenario: marbled vs. spiny-cheek crayfish. Ecosphere 9(9): e02385. https://doi.org/10.1002/ecs2.2385


New species often invade ecosystems already dominated by previous invaders. Ornamental freshwater crayfish, particularly parthenogenetic marbled crayfish (Procambarus virginalis), increasingly establish in European water bodies where they interact with resident native and non-native species. Behavioral traits and behavioral syndromes can influence the outcome of these species interactions. The behavior of non-native crayfish is often studied in notorious invaders but rarely in new and emerging species, although those provide the best opportunity for management. Activity, aggressiveness, and boldness have repeatedly been associated with invasion success and species displacement. Further, crayfish can adapt their behavior after they have established in the new range. We investigated whether marbled crayfish can displace the widely established spiny-cheek crayfish (Orconectes limosus). Specifically, we compared their behavioral traits and evaluated whether these traits differ, using marbled crayfish populations from aquaria and the field and spiny-cheek crayfish from the field.We staged agonistic encounters, measured activity levels, and recorded the response to a simulated threat of both species and both origins (field and aquarium) in laboratory trials. We found that in agonistic encounters, marbled crayfish were on average more aggressive than spiny-cheek crayfish, even against larger opponents. Aggressiveness and activity were positively correlated, which is indicative for an aggression syndrome. Marbled crayfish from the field were less active than those from aquaria, but there was no difference in aggressiveness. Marbled crayfish often froze in response to a simulated threat, whereas spiny-cheek crayfish reacted either offensively or defensively. These results from the laboratory illustrate potentially important behavioral mechanisms behind crayfish over-invasions and show behavioral plasticity in a species where all known individuals are genetically identical. To better understand the invasion process in nature, the species’ reproductive biology and interactions with other members of the community should be considered. We conclude that the recent success of marbled crayfish in establishing new populations could be influenced by their behavioral flexibility and their potential to competitively persist in the presence of established invasive crayfish.

Keywords: aggression • behavioral flexibility • behavioral syndromes • behavioral variability • biological invasions • freshwater crayfish • shelter use • threat response

19 September 2018

The Maltese crayfish: A dozen invaded European countries

It was Germany, then Italy, then the Netherlands, then Hungary, then Croatia, then Slovakia, then Romania, then Sweden, then the Ukraine, then the Czech Republic, then Estonia, and now Malta.

Malta makes it an even dozen European countries where Marmorkrebs have been found in outdoors, according to a paper in press from Deidun and colleagues. This is not a few stray individuals, either. Some sites (visited in 2016 and 2017) had hundreds of individuals. I will add the paper to the collection of abstract on the blog once the final paginated version is published.

I have updated the map of Marmorkrebs introductions accordingly.

My only consolation is that at some point, I’m going to run out of European countries to add to the list. Marmorkrebs will be in all of them.


Deidun A, Sciberras A, Formosa J, Zava B, Insacco G, Corsini-Foka M, Crandall KA. Invasion by non-indigenous freshwater decapods of Malta and Sicily, central Mediterranean Sea. Journal of Crustacean Biology: in press. http://dx.doi.org/10.1093/jcbiol/ruy076

External links

Alien crayfish invade Malta’s valleys and watercourses
Alien crayfish have invaded Malta’s valleys, study finds

13 September 2018

Cover cray

Nice cover accompanying this blog post. It’s covering the Marmorkrebs genome paper that came out back in February, but better late than never! The photo is aces in any case.

External links

Decoding the mutant, all-female, self-cloning crayfish

Crayfish crimes

Prosecutions for anything to do with the aquarium trade is rare, but last week, news reported Justin Doyle Pierce, an American was prosecuted for selling crayfish as pets, in violation of the Lacey Act)

Pierce sold over $19,000 worth of crayfish illegally, and for this, he got a $500 fine, 20 hours of community service, and a year on probation. By my quick scan of the act, he could have received jail time and thousands of dollars in fines.

Is this sort of enforcement acting as a deterrent? It’s not clear. When someone can make that much money, the fine is little more than a clap on the wrist. The real penalty may not be the fine or the service, but the criminal record. Pierce wrote:

(T)his will result in my disqualification of future employment in areas related to wildlife and conservation.

External links

Feds pinch Camden County man for illegal crayfish sales
Overview of the Lacey Act (16 U.S.C. SS 3371-3378)
Lacey Act cases

Hossain and colleagues, 2018

Hossain MS, Patoka J, Kouba A, Buřič M. 2018. Clonal crayfish as biological model: a review on marbled crayfish. Biologia 73(9): 841-855. https://doi.org/10.2478/s11756-018-0098-2


Since the mid-twentieth century, numerous vertebrates and invertebrates have been used as model organisms and become indispensable tools for exploring a broad range of biological and ecological processes. Crayfish seem to be adequate models which resulted in their involvement in research. In the two decades since its discovery, ongoing research has confirmed that the marbled crayfish (Procambarus virginalis Lyko, 2017) is an ideal taxon in this regard, especially due to its almost continuous asexual reproduction providing a source of genetically identical offspring. This review provides an overview of the occurrence, biology, ecology, ethology, and human exploitation of marbled crayfish with primary focus on its use as a laboratory model organism as well as potential risks to native biota in case of its introduction. Genetic uniformity, ease of culture, and a broad behaviour repertoire fosters the use of marbled crayfish in epigenetics and developmental biology, as well as physiological, ecotoxicological, and ethological research. Marbled crayfish could be further exploited for basic and applied fields of science such as evolutionary biology and clonal tumour evolution. However, due to its high invasive potential in freshwater environments security measures must be taken to prevent its escape into the wild.

Keywords: model species • epigenetics • developmental biology • Procambarus virginalis • biological invasion

01 September 2018

Naboka and colleagues, 2018

Naboka A, Marenkov O, Kovalchuk J, Shapovalenko Z, Nesterenko O, Dzhobolda B. 2018. Parameters of the histological adaptation of Marmorkrebs Procambarus virginalis (Lyko, 2017) (Decapoda, Cambaridae) to manganese, nickel and lead ions pollution. International Letters of Natural Sciences 70: 24-33. https://doi.org/10.18052/www.scipress.com/ILNS.70.24


Manganese, lead and nickel are heavy metals, which are the primary fresh water toxic contaminants being in the most dangerous class of chemicals. Heavy metals cause functional disorders in the tissues and organs of hydrobionts, affecting their linear and weight indices, reproductive system, digestive and extraction organs. In our experiment on marbled crayfish Procambarus virginalis (Lyko, 2017) we studied the long-term effects of various concentrations of heavy metal ions on the physiological state and histostructure of tissues and organs. According to the results of research, it was found that among the studied heavy metals nickel ions influenced the weight indexes and mortality of crustaceans the most negatively. The results of morphometric studies on marbled crayfish indicate no significant differences between the control group and experimental one, but heavy metals influenced the form of the hepatopancerase lobes and the size of the lumen of the gland. Research on adipocytes of the connective tissue showed a significant difference between the size of cells under the influence of heavy metals. Dimensions of adipocytes fluctuated over a wide range from 144 μm2 to 537 μm2. In control group the adipocyte area was 406.96 μm2. Experimental studies of hemolymph showed that, under the influence of lead ions, a significant 1.4 times increase was observed in the area of hemolymph cells; when manganese and nickel were added, moderate decrease was observed in cells. It was found that under the influence of nickel, the area of round hyalinocytes has reduced by 1.7 times.

Keywords: Procambarus virginalis • glandulocytes • hepatopancreas • hemolymph • manganese • nickel • lead • crustaceans

16 August 2018

Soes, 2016

Soes DM. 2016. Onderzoek voorkomen marmerkreeft in Middelburg. Rapportnummer 16‐250. Bureau Waardenburg, Culemborg. https://doi.org/10.13140/RG.2.2.10943.82081


De marmerkreeft is een in Nederland exotische rivierkreeft die valt onder de recent inwerking getreden Europese exotenverordening (EU 1143/2014). Van de marmerkreeft zijn uit Nederland tot op heden geen populaties bekend (Koese & Soes, 2011; D.M. Soes eigen informatie). Voor de marmerkreeft is het dan ook van belang nieuwe vestigingen snel te signaleren zodat eventueel maatregelen kunnen worden genomen die verdere verspreiding tegengaan of zelfs eliminatie mogelijk maken.

In 2014 en 2015 zijn in het westen van Middelburg (omgeving Hugo de Grootlaan) twee vondsten van mogelijke marmerkreeften gedaan. Eén waarneming betrof een dood exemplaar in een brandgang. Het tweede exemplaar werd levend aangetroffen in een tuinvijver. Verder is er nog een ongedateerde waarneming van een levende kreeft in dezelfde brandgang. Deze informatie was voor de NVWA aanleiding nader onderzoek uit te voeren.

In onderhavig rapportage wordt beschreven:
  1. de definitieve determinatie van de gevonden kreeften;
  2. een inventarisatie naar het eventueel voorkomen van de soort in de directe omgeving van de genoemde vondsten;
  3. de kansen op verspreiding indien zij in het westen van Middelburg daadwerkelijk zou voorkomen.
Keywords: None provided.

(English translation with Google Translate and some guesswork)

The marbled crayfish is a exotic crayfish in the Netherlands that falls under the recent the European Exotics Regulation (EU 1143/2014) came into effect. There are no populations known to date from the Netherlands (Koese & Soes, 2011; D.M. Soes, unpublished). It is therefore important for the early detection of marbled crayfish in new river branches quickly so that possible measures can be taken to prevent further dissemination or even enable elimination.

In 2014 and 2015 in the west of Middelburg (near Hugo de Grootlaan), two possible marbled crayfish were found. One observation was one dead individual in a firebreak. The second individual was found alive in a garden pond. There is also an undated observation of a living crayfish in the same firebreak. This information was further explained by the NVWA conduct research.

This report describes:
1. the definitive determination of the crayfish found;
2. an inventory of the possible occurrence of the species in the direct environment of the findings;
3. the chances of spreading if they are in the west of Middelburg.

14 August 2018

Marenkov and colleagues, 2018

Marenkov O, Prychepa M, Kovalchuk J. 2018. The influence of heavy metal ions on the viability and metabolic enzyme activity of the marbled crayfish Procambarus virginalis (Lyko, 2017). International Letters of Natural Sciences 70: 11-23. https://doi.org/10.18052/www.scipress.com/ILNS.70.11


The article shows the results of studies on the influence of heavy metal ions (manganese, nickel, lead) on the viability and metabolic enzyme activity of marbled crayfish Procambarus virginalis (Lyko, 2017) (Decapoda). Due to the fact that marbled crayfish got into the reservoirs of the Dnipropetrovsk region in 2015, it was necessary to study the possibilities of its adaptation to environmental factors of reservoirs for further prediction of its distribution or even acclimatization under conditions of toxicological contamination of the ponds of the steppe Prydniprovya. In the
experiment with marbled crayfish, chronic effects of various concentrations of heavy metal ions on the physiological state and enzyme activity were investigated. The obtained results showed that
among the investigated heavy metals nickel ions influenced the weight indexes and mortality of crustaceans the most negatively. According to the results of the research, significant changes were
noted in the individual biochemical parameters of marbled crayfish under the influence of manganese, lead and nickel ions. The most significant changes in the activity of lactate dehydrogenase were detected in muscle tissues affected by manganese and nickel ions. A significant decrease in the activity of succinate dehydrogenase in muscle of marbled crayfish was determined after the action of heavy metal ions. Investigation of changes in the activity of alkaline phosphatase under the influence of the ions of manganese, lead and nickel has its own characteristics, which indicates certain violations in the tissues of cell membranes. Changes in the activity of enzymes were also reflected in the overall protein content. In conclusion, changes in these parameters may indicate a rapid biochemical response of crustaceans to the toxic effects of heavy metals.

Keywords: manganese • nickel • lead • crustaceans • Procambarus virginalis • succinate • dehydrogenase • lactate dehydrogenase • alkaline phosphatase

04 August 2018

“Say my name, say my name”: The Guardian podcast

Marmorkrebs make an appearance in the Guardian's Science Weekly podcast as part of a discussion about naming species. If you're super directed, the marbled crayfish discussion with Tim Cockerill starts about 7 minutes in (07:20, to be exact).

This podcast raises a question for me, though. What is the preferred pronunciation of “slough”? As in Procambarus fallax, the slough crayfish? The podcast presenter, Graihagh Jackson, has it rhyme with “cow.” I’ve always pronounced with to rhyme with “you.” As this post notes, words ending in "-ough" have a bewildering number of sounds.

External links

Tricky taxonomy: the problems with naming new species

31 July 2018

The Great Lakes least wanted

The Michigan Sea Grant has spearheaded a “#CrayWeek” campaign for the second year in a row! Of course I’m participating.

One of the piece of information that Michigan Sea Grant tweeted out was that Marmorkrebs have found themselves on another invasive species watch list, this one for the Canadian / American Great Lakes and Saint Lawrence River.

On May 4, 2018, the Great Lakes St. Lawrence Governors & Premiers announced five additions to the list of “least wanted” aquatic invasive species. In 2013, the Governors and Premiers released the first list of 16 “least wanted” aquatic invasive species (AIS) that present a serious threat to the Great Lakes St. Lawrence Basin. Since then, the region’s eight states and two provinces have taken more than 40 actions to prohibit or restrict these high-risk species, including the Asian carp. The new “least wanted” AIS include:
  • Tench Tinca tinca
  • Marmorkreb (sic) (marbled crayfish) Procambarus fallax forma virginalis
  • New Zealand mud snail Potamopyrgus antipodarum
  • European frogbit Hydrocharis morsus-ranae
  • Yellow floating heart Nymphoides peltata
State and provincial AIS and fisheries experts, in conjunction with leading regional researchers, identified these five AIS as posing a high risk of invasion or spread within the region. The Governors and Premiers will take aggressive action and work with regional partners to prevent the spread of these aquatic invaders.

What’s not clear to me from this statment is what action has been, or might be, taken to try to curb the spread of any of these species. A recent paper I co-authored pointed out (Patoka et al. 2018), the track record of legislation on curbing the movement of aquarium pets is... not great.

External links

Great Lakes St. Lawrence Governors & Premiers Add Five “Least Wanted” AIS


Patoka J, Magalhães ALB, Kouba A, Faulkes Z, Jerikho R, Vitule JRS. 2018. Invasive aquatic pets: Failed policies increase risks of harmful invasions. Biodiversity and Conservation 27(11): 3037-3046. https://doi.org/10.1007/s10531-018-1581-3

26 July 2018

Le Page, 2018

Le Page M. 2018. Crayfish clone army on the loose. New Scientist 239(3185): 16. https://doi.org/10.1016/S0262-4079(18)31193-X


Without abstract. First paragraph:

Sometime before 1995, a container of freshwater crayfish from Florida got too hot or too cold en route to a pet shop in Germany. The shock disrupted the development of an egg being carried by one of the females, creating an army of clones that are invading rivers and lakes in continental Europe, Madagascar and Japan.

Keywords: None provided.

Notes: If you click to enlarge the cover of this issue, the cover includes “Clone crayfish” in the bottom left. This article was published online with the title, “Freak accident created a massive army of super-fertile clones.”

14 July 2018

Nischik and Krieger, 2018

Nischik ES, Krieger J. 2018. Evaluation of standard imaging techniques and volumetric preservation of nervous tissue in genetically identical offspring of the crayfish Procambarus fallax cf. virginalis (Marmorkrebs). PeerJ 6: e5181. https://doi.org/10.7717/peerj.5181


In the field of comparative neuroanatomy, a meaningful interspecific comparison demands quantitative data referring to method-specific artifacts. For evaluating the potential of state-of-the-art imaging techniques in arthropod neuroanatomy, micro-computed X-ray microscopy (μCT) and two different approaches using confocal laser-scanning microscopy (cLSM) were applied to obtain volumetric data of the brain and selected neuropils in Procambarus fallax forma virginalis (Crustacea, Malacostraca, Decapoda). The marbled crayfish P. fallax cf. virginalis features a parthogenetic reproduction generating genetically identical offspring from unfertilized eggs. Therefore, the studied organism provides ideal conditions for the comparative analysis of neuroanatomical imaging techniques and the effect of preceding sample preparations of nervous tissue. We found that wet scanning of whole animals conducted with μCT turned out to be the least disruptive method. However, in an additional experiment it was discovered that fixation in Bouin’s solution, required for μCT scans, resulted in an average tissue shrinkage of 24% compared to freshly dissected and unfixed brains. The complete sample preparation using fixation in half-strength Karnovsky’s solution of dissected brains led to an additional volume decrease of 12.5%, whereas the preparation using zinc-formaldehyde as fixative resulted in a shrinkage of 5% in comparison to the volumes obtained by μCT. By minimizing individual variability, at least for aquatic arthropods, this pioneer study aims for the inference of method-based conversion factors in the future, providing a valuable tool for reducing quantitative neuroanatomical data already published to a common denominator. However, volumetric deviations could be shown for all experimental protocols due to methodological noise and/or phenotypic plasticity among genetically identical individuals. MicroCT using undried tissue is an appropriate non-disruptive technique for allometry of arthropod brains since spatial organ relationships are conserved and tissue shrinkage is minimized. Collecting tissue-based shrinkage factors according to specific sample preparations might allow a better comparability of volumetric data from the literature, even if another technique was applied.

Keywords: μCT • confocal laser scanning microscopy • nervous system • volumetry • Marmorkrebs • phenotypic plasticity

10 July 2018

Conference hashtag #IAA22

I was unable to go to the International Association of Astacology meeting this year, but have been following along on Twitter, using the #IAA22 hashtag. Those following from home have been fortunate to have Maggie Watson sketchnoting many of the presentations, and I can’t resist sharing her Marmorkrebs notes here and here)!

If you go to a conference, tweet about it. More people want to attend than can attend.

07 July 2018

Velisek and colleagues, 2018

Velisek J, Stara A, Zuskova E, Kubec J, Buric M, Kouba A. 2018. Chronic toxicity of metolachlor OA on growth, ontogenetic development, antioxidant biomarkers and histopathology of early life stages of marbled crayfish. Science of The Total Environment 643: 1456-1463. https://doi.org/10.1016/j.scitotenv.2018.06.309


The metolachlor OA is a metabolite of herbicide metolachlor and s-metolachlor. The objective of the present study was to assess the effect metolachlor OA on early life stages of marbled crayfish (Procambarus virginalis). The early life stages of marbled crayfish were exposed for 45 days to three concentrations of metolachlor OA: 4.2 μg/L (environmentally relevant concentration, E1), 42 μg/L (E2) and 420 μg/L (E3) under laboratory conditions. The effects were assessed on the basis of mortality, growth, ontogenetic development, behaviour, oxidative stress, antioxidant biomarkers and histopathology. Metolachlor OA caused significantly lower growth, superoxide dismutase, catalase and glutathione s-transferase activity in all tested concentrations. Metolachlor OA in higher concentrations (42 and 420 μg/L) resulted in significantly delayed ontogenetic development, lower reduced glutathione level and lipid peroxidation. Metolachlor OA has not significant effect on behaviour (activity, total distance moved and walking speed). Histological examination revealed alteration of hepatopancreas and gills in crayfish exposed to two higher tested concentrations. Hepatopancreas reflected histomorphological structural changes of individual cell types. Changes of gills included focal hemocytic infiltration together with enlargement of intralamellar space packed with granular substance. In conclusion, chronic metolachlor OA exposure affected growth, ontogenetic development, and the antioxidant system and caused pathological changes in hepatopancreas and gills of early life stages of marbled crayfish.

Keywords: herbicide • metabolite • crayfish • mortality • behaviour • oxidative stress

03 July 2018

Vogt and colleagues, 2018

Vogt G, Dorn NJ, Pfeiffer M, Lukhaup C, Williams BW, Schulz R, Schrimpf A. 2018. In-depth investigation of the species problem and taxonomic status of marbled crayfish, the first asexual decapod crustacean. BioRxiv: 26 June 2018. https://doi.org/10.1101/356170 [Unreviewed pre-print]


The marbled crayfish is the only obligately parthenogenetic decapod crustacean and a novel research model and invasive animal on three continents. It is regarded either as a parthenogenetic form of slough crayfish Procambarus fallax or as a separate species named Procambarus virginalis. In order to investigate the species question of this unusual crayfish in detail we have identified the similarities and differences in morphology, life history, genetics, behaviour, ecology and biogeography between marbled crayfish and P. fallax. We have investigated specimens from natural habitats, laboratory colonies and museum collections and performed a meta-analysis of our data and published data. Our COI based molecular tree with 27 Cambaridae confirms closest relationship of marbled crayfish with P. fallax. Marbled crayfish and P. fallax are similar with respect to morphological characters, coloration and body proportions, but differ considerably with respect to body size, fertility and longevity. The mitochondrial genes of both crayfish are similar, but some nuclear genomic features are markedly different. Both crayfish are eurytopic and have two major annual recruitment periods, but marbled crayfish show different population structure and higher invasiveness. Marbled crayfish occur in boreal to tropical habitats of Europe, Madagascar and Japan, but P. fallax is confined to the subtropics and tropics of the southeastern USA. Laboratory experiments suggest reproductive isolation of both crayfish. The application of the Evolutionary Genetic Species Concept for asexuals to all available data supports raising marbled crayfish from "forma" to species rank. A determination key is provided to discriminate Procambarus virginalis, the first asexual decapod species, from its most likely parent species P. fallax.

Keywords: None provided.

22 June 2018

Vogt, 2018c

Vogt G. 2018. Glair glands and spawning in unmated crayfish: a comparison between gonochoristic slough crayfish and parthenogenetic marbled crayfish. Invertebrate Zoology 15(2): 215–220. https://doi.org/10.15298/invertzool.15.2.02, http://kmkjournals.com/journals/Inv_Zool/IZ_Index_Volumes/IZ_15/IZ_15_2_215_220_Vogt


In the period before spawning, freshwater crayfish females develop glair glands on the underside of the pleon. These glands produce the mucus for a gelatinous tentlike structure in which the eggs are fertilized and attached to the pleopods. Long-term observation of females of the sexually reproducing slough crayfish, Procambarus fallax, kept in captivity revealed that the glair glands developed in late winter and late summer of each year independently of the presence of males. In mated females, they secreted their contents shortly before spawning. In contrast, unmated females of slough crayfish did
neither empty their glair glands nor spawn. Their glands persisted for an unusually long period of time and disappeared only during the next moult. Apparently, slough crayfish females use information on sperm availability to either spawn or save the resources. Females of marbled crayfish, Procambarus virginalis, a parthenogenetic all-female descendant of slough crayfish, developed glair glands in approximately the same periods of the year but generally spawned despite of the lack of males. These findings suggest that in marbled crayfish glair secretion and spawning is decoupled from mating. Therefore, the species pair P. fallax and P. virginalis seems to be particularly suitable to investigate the regulation of spawning in freshwater crayfish.

Keywords: freshwater crayfish • glair gland • spawning • mating • Procambarus fallaxProcambarus virginalis

Zoo babies

Marbled crayfish are featured in this year’s Cincinnati Zoo’s Zoo Babies display! The Zoo’s website shows they are part of the display, but no more. I do complement their photographer for the particularly cute crayfish pic (above) on their site.

I reached out to the Zoo, and heard back from Mandy Pritchard, who is the “World of the Insect Team Leader” at the zoo. (Now there’s a great job title.) She was kind enough to send me a couple of pictures of the display:

There’s a very nice shirt available. Unfortunately, it’s doesn’t seem to be available in adult sizes.

Based on the description in the display, I think these are the sexual slough crayfish and not Marmorkrebs. But it’s fun to see crayfish on display nevertheless!

External links

Zoo Babies
The "Amazing" Marbled Crayfish - Youth Garments

19 June 2018

Herrmann and colleagues, 2018

Herrmann A, Schnabler A, Martens A. 2018. Phenology of overland dispersal in the invasive crayfish Faxonius immunis (Hagen) at the Upper Rhine River area. Knowledge and Management of Aquatic Ecosystems 419: 30. https://doi.org/10.1051/kmae/2018018


The non-indigenous crayfish Faxonius immunis (Hagen) is the dominant crayfish species at the Upper Rhine River system since his detection in 1993. As an invasive alien species, it is one of the biggest threats to aquatic biodiversity in the area. By dispersing over land, the species has a high potential to colonize small ponds created for threatened amphibians and dragonflies. Shortly after invasion, the fast growing population of F. immunis is changing the habitat drastically. In June 2016, our team started a local information campaign including citizen science project where the local people south of Karlsruhe, Baden-Wuerttemberg, Germany, could contact us when they spot a crayfish migrating over land to assess the activity of overland dispersal on a regional scale. Until January 2018, we got a total of 98 responses. Thirty-nine include suitable information including 33 records of overland dispersal of F. immunis. The species was recorded on land throughout the year, except February and July. Additionally, single observations of overland dispersal of other invasive crayfish species, naming Procambarus clarkii (Girard), Pacifastacus leniusculus (Dana), Procambarus virginalis (Lyko) and Faxonius limosus (Rafinesque), were recorded.

Keywords: amphibian conservation • citizen science • management • biological invasions • non-indigenous species

08 June 2018

If this is 2018, this must be Estonia

Estonia has now become the...

Wait a second, I’ve lost count.

  1. Germany.
  2. Italy.
  3. Netherlands.
  4. Hungary.
  5. Croatia.
  6. Slovakia.
  7. Romania.
  8. Sweden.
  9. Ukraine.
  10. Czech Republic.
  11. ...
Eleventh European country where Marmorkrebs have been found in outdoors. This is according to a press release from the Estonian Research Council. The crayfish were collected last year, not recognized as Marmorkrebs until the end of the year, and a repeat visit at the end of May confirmed a population was there.

I have updated the map of Marmorkrebs introductions accordingly.

External links

The marbled crayfish have established themselves in Narva power plant

30 May 2018

Scholz and colleagues, 2018

Scholz S, Richter S, Wirkner CS. 2018. Constant morphological patterns in the hemolymph vascular system of crayfish (Crustacea, Decapoda). Arthropod Structure & Development 47(3): 248-267. https://doi.org/10.1016/j.asd.2017.12.005


We present a study of the hemolymph vascular system of the marbled crayfish, Procambarus fallax f. virginalis, the only crayfish species known to be parthenogenetic. To identify potential evolutionary patterns, we compared data from a total of 48 specimens of P. fallax with 22 specimens of Orconectes limosus. Visualizations (2D and 3D) were carried out using a combination of classical and modern morphological techniques. Our data were compared to the existing literature. Like all Decapoda, both P. fallax and O. limosus have a hemolymph vascular system, consisting of a globular heart with seven off-branching arteries. We were able to visualize in detail the heart of crayfish for the first time, i.e., the heart muscle itself, with its loose bundles of myofibrils, as well as the valves and flaps of ostia and arteries. Furthermore, the branching patterns of the seven artery systems were analyzed. Anatomical structures identified to be consistent in all specimen of both species were combined, and a proposed schematic anatomy established of the hemolymph vascular system of crayfish.

Keywords: artery • circulatory system • evolutionary morphology • heart

Nentwig and colleagues, 2018

Nentwig W, Bacher S, Kumschick S, Pyšek P, Vilà M. 2018. More than “100 worst” alien species in Europe. Biological Invasions 20(6): 1611–1621. https://doi.org/10.1007/s10530-017-1651-6


“One hundred worst” lists of alien species of the greatest concern proved useful for raising awareness of the risks and impacts of biological invasions amongst the general public, politicians and stakeholders. All lists so far have been based on expert opinion and primarily aimed at representativeness of the taxonomic and habitat diversity rather than at quantifying the harm the alien species cause. We used the generic impact scoring system (GISS) to rank 486 alien species established in Europe from a wide range of taxonomic groups to identify those with the highest environmental and socioeconomic impact. GISS assigns 12 categories of impact, each quantified on a scale from 0 (no impact detectable) to 5 (the highest impact possible). We ranked species by their total sum of scores and by the number of the highest impact scores. We also compared the listing based on GISS with other expert-based lists of the “worst” invaders. We propose a list of 149 alien species, comprising 54 plants, 49 invertebrates, 40 vertebrates and 6 fungi. Among the highest ranking species are one bird (Branta canadensis), four mammals (Rattus norvegicus, Ondatra zibethicus, Cervus nippon, Muntiacus reevesi), one crayfish (Procambarus clarkii), one mite (Varroa destructor), and four plants (Acacia dealbata, Lantana camara, Pueraria lobata, Eichhornia crassipes). In contrast to other existing expert-based “worst” lists, the GISS-based list given here highlights some alien species with high impacts that are not represented on any other list. The GISS provides an objective and transparent method to aid prioritization of alien species for management according to their impacts, applicable across taxa and habitats. Our ranking can also be used for justifying inclusion on lists such as the alien species of Union concern of the European Commission, and to fulfil Aichi target 9.

Keywords: Aichi target 9 • environmental impacts • generic impact scoring system (GISS) • prioritization of alien species • risk assessment • socio-economic impacts

23 May 2018

Rymut, 2018

Rymut, JA. 2018.Determining the effects of nitric oxide on Procambarus fallax forma virginalis. Poster given at the International Crustacean Congress IX, Washington DC, USA, 22-25 May 2018. http://www.birenheide.com/ICC2018/program/singlesession.php3?sessid=P, poster P.33.


Ethanol (EtOH) effects inducible nitric oxide synthase (iNOS) activity by inhibiting the production of iNOS in cells. Acute doses increase the production of nitric oxide (NO) and endothelial NOS (eNOS). At higher dosages, ethanol impairs endothelial functions. NO has been found to suppress the feeding response in pond snails, Lymnaea stagnalis, induce synaptic depression in crayfish, and inhibit the swimming rhythm of Xeonpus laevis tadpoles. This in vivo study will be performed in order to determine if synaptic depression is caused by free radical NO and determine if overall movements are decreased in Procambarus forma fallax virginalis (P.f.f virginalis) in the presence of NO. It was hypothesized that there will be a depression in synaptic activity and less movement in crayfish exposed to free radical NO. A probe will be inserted near the cerebral ganglion to assess depression in synaptic inputs. Movement will be tested by placing crayfish into a partitioned tank and counting each movement across a partition as one movement. Movement will be tested on both an individual and group level to determine if group activity will be a variable factor. NO will be introduced through the usage of ethanol, an L-arginine supplement, and chlorhexidine​ in an approximate range of five to ten​ parts per million (​5 ​mg/L​ and 10 mg/L​).

Keywords: None provided.

Update, 30 May 2018: At the author’s request, here is the updated abstract from the poster as it was presented at the meeting (above).

Ethanol (Et-OH) effects inducible nitric oxide synthase (iNOS) activity by inhibiting the production of iNOS in cells. Acute doses increase the production of nitric oxide (NO) and endothelial NOS (eNOS). At higher dosages, ethanol impairs endothelial functions. NO has been found to suppress the feeding response in pond snails, Lymnaea stagnalis, induce synaptic depression in crayfish, and inhibit the swimming rhythm of Xenopus laevis tadpoles (Aonuma, et al. 2000). This in vivo study has been performed in order to determine if synaptic depression is caused by NO, and if overall movements are decreased in Procambarus forma fallax virginalis (P.f.f virginalis) and Procambarus blandingii, in the presence of NO. Movement was assessed in a labeled gridded tanks of water, denatured ethanol (3 ppm), L-arginine (Reagent grade, 1ppb) and chlorhexidine (99.95%, 1ppb). There was an evident trend over a time interval of 6 minutes ≤ t ≤ 8 minutes, where the control, ethanol and chlorhexidine all had a stark drop off in activity, whilst L-arginine had a stark increase. It is hypothesized that this could be due to a metabolic pathway of L-arginine is converted through nitric oxide synthase (NOS) to L-citrulline (Racke, et al. 2010); whereas ethanol has proven to inhibit iNOS, and due to the cytostatic characteristics of chlorhexidine, it can be assumed that the correlation of chlorhexidine to ethanol lies in this pathway as well. Synaptic depression is shown where L-arginine is present, over a time interval of 0 ms ≤ t ≤ 10ms (Aonuma et al. 2010); as found in the study, there is a correlation between L-arginine and chlorhexidine pre-wash, and it is hypothesized that this is from the terminal guanylyl group.

16 May 2018

Faulkes and colleagues, 2018

Faulkes Z, DeLeon H, Thomas J. 2018. Cloning crayfish cell culture. Poster presentation given at the International Crustacean Congress IX, 22-25 May 2018, Washington, DC, USA. http://www.birenheide.com/ICC2018/program/singlesession.php3?sessid=P, poster P.81.


The parthenogenetic marbled crayfish, Marmorkrebs, is an emerging model organism. For example, it is the only decapod crustacean with a sequenced genome, and several labs have used Marmorkrebs as a model for embryonic development. One difficulty in studying embryonic cells is that eggs contain a large amount of yolk, which can make imaging embryonic cells difficult. We successfully isolated and cultured cells from early stage Marmorkrebs embryos, and confirmed their identity using DNA sequencing. Cellular and molecular tools for use in crayfish are underdeveloped compared to other model organisms, and cultured embryonic cells could provide a new testbed for those techniques.

Keywords: None provided.

09 May 2018

Vogt, 2018b

Vogt G. 2018. Annotated bibliography of the parthenogenetic marbled crayfish Procambarus virginalis, a new research model, potent invader and popular pet. Zootaxa 4418(4): 301-352. https://doi.org/10.11646/zootaxa.4418.4.1


The marbled crayfish Procambarus virginalis is a new obligately parthenogenetic species that was detected in the mid-1990s in the German aquarium trade. Since then it has become a popular pet in many countries throughout the world and a valuable laboratory model for a broad range of biological disciplines. Releases have led to the establishment of wild
populations in several European countries, Madagascar and probably Japan, making marbled crayfish an interesting paradigm of evolutionarily young and ongoing bioinvasions. This article provides an annotated bibliography of the scientific and popular scientific literature on marbled crayfish from its detection until today. Each reference is assigned to a publication format and one or more biological categories. The content is shortly described and its significance for marbled crayfish research and general biology is assessed. Of the 239 references listed 140 (58.6%) deal primarily with laboratory experiments on the biology of marbled crayfish and the establishment and use of marbled crayfish as a research model, 74 (31.0%) with its biogeography, invasions and ecology and 25 (10.4%) with hobby aquarist issues and the pet trade.

Keywords: Crustacea • Decapoda • development • ecology • genetics • morphology • neurobiology • physiology • speciation • stem cell biology • toxicology

08 May 2018

Zeng and Yeo, 2018

Zeng Y, Yeo DCJ. 2018. Assessing the aggregated risk of invasive crayfish and climate change to freshwater crabs: A Southeast Asian case study. Biological Conservation 223: 58-67. https://doi.org/10.1016/j.biocon.2018.04.033


Primary freshwater crabs represent a culturally and ecologically significant component of freshwater habitats globally that has a high percentage of threatened species. Invasive species (especially non-indigenous crayfish) and climate change are not only important standalone threats, but are also expected to compound existing threats (e.g., habitat loss/modification, pollution) and challenge the long-term survival of these decapod crustaceans. This study illustrates the importance of considering these two emerging and growing threats in conservation or management strategies by quantifying (via species distribution models) the individual and aggregated risks of these threats in Southeast Asia, a region with the highest diversity of primary freshwater crabs and a high proportion of imperiled species. Results predicted that most species of crabs (82.1%) will co-occur (and hence interact) with invasive crayfish to a moderate to high degree, and most species (69.2%) will also experience a reduction in suitable climate conditions in the future. In terms of aggregated risk, the results also predict an increased overlap between invasive crayfish and native crabs for three out of the seven species analyzed (namely Procambarus virginalis, Cherax destructor and Orconectes rusticus). Findings from this study provide a quantitatively derived rationale for the development of adaptive regulations and conservation plans in the region to minimize the risk of invasive species in a cost-effective way, thereby enabling the protection of Southeast Asia's natural heritage and its vital ecosystem services.

Keywords: alien species • Cherax • environmental niche model • non-indigenous species • Procambarus • radiative forcing target levels • species distribution model