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The marbled crayfish ( Procambarus fallax f. virginalis ) has become one of the potentially most dangerous non-indigenous crayfish species spreading in European countries and elsewhere. This taxon reproduces parthenogenetically and recently has been verified as a vector of the crayfish plague pathogen. Here, we report on two established populations of marbled crayfish in the Czech Republic. The marbled crayfish was observed during autumn 2015 in an urban pond connected by sewer piping with the Rokytka brook near its mouth to the Vltava River in Prague. Subsequently, three adult females, two of them having well-developed glair glands and oocytes, were captured in this pond during spring 2016, suggesting successful overwintering of the local population. Furthermore, four adult females were captured in an artificial pond at the Radovesická lignite spoil heap in the vicinity to the industrial conurbation of Bílina in summer 2016; one of them carried eggs. We tested these for the presence of the crayfish plague pathogen Aphanomyces astaci , with negative results. The introduction pathway for both populations is most likely a release from private aquaria, as these sites are popular for recreation activities. Our findings substantiate previous predictions that conurbations are likely to be the primary areas for marbled crayfish introductions.

There is a long history of crayfish introductions in Europe and numbers keep increasing. In Hungary, spiny-cheek crayfish Faxonius limosus , signal crayfish Pacifastacus leniusculus , red swamp crayfish Procambarus clarkii , marbled crayfish P . virginalis and Mexican dwarf crayfish Cambarellus patzcuarensis have become established. Here we report on monitoring at two localities with novel crayfish assemblages closely linked to releases associated with the pet trade. Florida crayfish Procambarus alleni were recorded from the Gombás brook near Vác living in syntopy with the established spiny-cheek crayfish. Dozens of Florida crayfish individuals including egg-carrying females have been detected. The short lifespan of this species and its documented presence including two overwintering in at least two years suggests possible establishment. However, the lack of juvenile records calls for further monitoring as long-term propagule pressure cannot be ruled out. We also identified a single marbled crayfish in the Danube floodplain at the end of the monitoring campaign. The second locality (Városliget thermal pond in Budapest) harbours an even more diverse crayfish assemblage. Here, we identified numerous red swamp and marbled crayfish in syntopy with dozens of monitored redclaws Cherax quadricarinatus and seven individuals of New Guinean Cherax species − C . holthuisi , C . snowden, as well as two scientifically undescribed species. These findings clearly indicate the attractiveness of urban and, especially, thermal waters for the release of even expensive aquatic pets and highlight the hitherto poorly known biodiversity of New Guinean crayfish species. Les introductions d'écrevisse en Europe est une longue histoire et leur nombre ne cesse d'augmenter. En Hongrie, l'écrevisse américaine Faxonius limosus , l'écrevisse signal Pacifastacus leniusculus , l'écrevisse rouge de Louisiane Procambarus clarkii , l'écrevisse marbrée P. virginalis et l'écrevisse naine mexicaine Cambarellus patzcuarensis se sont établies. Nous présentons ici un rapport sur la surveillance à long terme dans deux localités où des assemblages d'écrevisses nouvelles sont étroitement liés aux lâchers associés au commerce des animaux de compagnie. L'écrevisse bleue Procambarus alleni a été observée dans le ruisseau de Gombás, près de Vác, vivant en syntopie avec l'écrevisse américaine établie. Des dizaines d'individus d'écrevisses de Louisiane, y compris des femelles porteuses d'œufs, ont été détectées. La courte durée de vie de cette espèce et sa présence documentée, y compris deux hibernations en au moins deux ans, suggèrent une possible implantation. Toutefois, l'absence de données sur les juvéniles exige une surveillance plus poussée, car on ne peut exclure la possibilité d'une pression de propagation à long terme. Nous avons également identifié une seule écrevisse marbrée dans la plaine d'inondation du Danube È la fin de la mission de surveillance. La deuxième localité (l'étang thermal de Városliget à Budapest) abrite un assemblage d'écrevisses encore plus diversifié. Ici, nous avons identifié de nombreuses écrevisses rouges de Louisiane et marbrées en syntopie avec des dizaines de Cherax quadricarinatus et sept individus d'espèces de Cherax de Nouvelle-Guinée – C. holthuisi, C. snowden , ainsi que deux espèces non décrites scientifiquement. Ces résultats indiquent clairement l'attrait des eaux urbaines et, surtout, des eaux thermales pour le lâcher d'animaux aquatiques, même coûteux, et mettent en évidence la biodiversité jusqu'ici mal connue des espèces d'écrevisses de Nouvelle-Guinée.

The marbled crayfish, Procambarus fallax f. virginalis, is a taxon widely available in the aquarium pet trade, which has been introduced to open waters in several European countries and in Madagascar. Recent studies confirmed this parthenogenetically reproducing crayfish as a high-risk invasive species, and vector of the crayfish plague pathogen, Aphanomyces astaci. It has been first discovered in Slovakia in 2010, but the status of the local population was not studied since then. Due to enlarged sampling area around the first report and one locality, where we presupposed the crayfish occurrence, we identified new marbled crayfish populations. Here, we report presence of three newly established marbled crayfish populations in Slovakia. Two populations are located critically close to the Váh River, a major tributary of the Danube River; one of them being directly connected to the Váh River via a side channel during occasional floods. The third established marbled crayfish population was found at the mouth of a thermal stream flowing into the Nitra River, a tributary of the Váh River. In this stream, crayfish coexist with other exotic fish and gastropod species of aquarium origin. We presume that the reported localities may serve as a source for further expansion of the marbled crayfish in the mid-part of the Danube catchment. Floods, active dispersal (including overland), passive dispersal by zoochory or anthropogenic translocations are among the major drivers facilitating the marbled crayfish colonization. We have not detected the crayfish plague pathogen in any of the studied populations. However, if spreading further, the marbled crayfish will encounter established populations of crayfish plague carriers in the Danube River, in which case they may acquire the pathogen by horizontal transmission and contribute to spread of this disease to indigenous European crayfish species.

The spread of non-native species results in novel and often unexpected assemblages. Using stable isotopes, we disentangled the trophic relationships between three invasive crayfish species at two sites of a small thermal tributary of the Barát stream, Hungary. We studied Procambarus virginalis and Faxonius limosus living in sympatry in the upper section of this thermal tributary, and then an assemblage in a lower section also containing P. clarkii. The two species in the upper section largely shared trophic niches, although P. virginalis was more carnivorous than F. limosus, which fed more on detritus and aquatic plants. In the lower section, P. clarkii had a distinctive trophic niche, being more carnivorous than the other species and also preying on other crayfish and fish. The trophic niches of the other two species shifted slightly, being narrower and more overlapping in the presence of P. clarkii. It seems that the presence of P. clarkii affects the feeding habits and trophic niches of the other two crayfish. Our results also indicate that the species have somewhat distinctive feeding niches, which suggests that the ecosystem effects of these species are likely to be at least partially additive in the shared localities.

Introductions of non-native predators often reduce biodiversity and affect natural predator–prey relationships and may increase the abundance of potential disease vectors (e.g., mosquitoes) indirectly through competition or predation cascades. The Santa Monica Mountains (California, U.S.A.), situated in a global biodiversity hotspot, is an area of conservation concern due to climate change, urbanization, and the introduction of non-native species. We examined the effect of non-native crayfish (Procambarus clarkii) on an existing native predator, dragonfly nymphs (Aeshna sp.), and their mosquito larvae (Anopheles sp.) prey. We used laboratory experiments to compare the predation efficiency of both predators, separately and together, and field data on counts of dragonfly nymphs and mosquito larvae sampled from 13 local streams. We predicted a lower predation efficiency of crayfish compared with native dragonfly nymphs and a reduced predation efficiency of dragonfly nymphs in the presence of crayfish. Dragonfly nymphs were an order of magnitude more efficient predators than crayfish, and dragonfly nymph predation efficiency was reduced in the presence of crayfish. Field count data showed that populations of dragonfly nymphs and mosquito larvae were strongly correlated with crayfish presence in streams, such that sites with crayfish tended to have fewer dragonfly nymphs and more mosquito larvae. Under natural conditions, it is likely that crayfish reduce the abundance of dragonfly nymphs and their predation efficiency and thereby, directly and indirectly, lead to higher mosquito populations and a loss of ecosystem services related to disease vector control. La introducción de depredadores no nativos con frecuencia reduce la biodiversidad y afecta a las relaciones naturales entre presa y depredador, e incluso puede incrementar indirectamente la abundancia de vectores potenciales de enfermedades (p.ej.: mosquitos) por medio de la competencia o las cascadas de depredación. Las montañas de Santa Mónica (California, E.U.A.), situadas en un punto caliente de biodiversidad global, son un área de importancia para la conservación debido al cambio climático, la urbanización y la introducción de especies no nativas. Examinamos el efecto que tiene un cangrejo de río no nativo (Procambarus clarkii) sobre un depredador en existencia, las ninfas de libélula (Aeshna sp.), y sobre su presa: las larvas de mosquito (Anopheles sp.). Usamos experimentos de laboratorio para comparar la eficiencia de depredación de ambos depredadores, de manera separada y conjunta, y datos de campo sobre los conteos de ninfas de libélula y larvas de mosquito muestreadas en 13 riachuelos locales. Predijimos una eficiencia de depredación más baja de los cangrejos de río en comparación con las ninfas de libélula y una eficiencia de depredación reducida delas ninfasdelibélula en presencia de los cangrejos de río. Lasninfasde libélula fueron depredadores un orden de magnitud más eficientes que los cangrejos de río, y la eficiencia de depredación de las ninfas de libélula estuvo reducida en la presencia de cangrejos de río. Los datos de conteo de campo mostraron que las poblaciones de ninfas de libélula y de larvas de mosquito tuvieron una fuerte correlación con la presencia de cangrejos de río en los riachuelos, de tal manera que los sitios con cangrejos de río tendieron a tener menos ninfas de libélula y más larvas de mosquito. Bajo condiciones naturales, es probable que los cangrejos de río reduzcan la abundancia de ninfas de libélula y su eficiencia de depredación, lo que resulta directa e indirectamente en poblaciones mayores de mosquitos y una pérdida de los servicios ambientales relacionados con el control de los vectores de enfermedades. 引入外来捕食者常常会导致生物多样性丧失，影响自然界捕食者-猎物关系，还可能通过竞争或营养级联 效应间接增加潜、在疾病传播媒介_ 蚊子) 的数量。圣莫尼卡山脉(美国加利福尼亚州) 位于全球生物多样性热 点地区，因气候变化、城市化和外来物种的引入受到了保护关注。我们在这里分析了外来的小龙虾（克氏原螯 奸Procambarus clarkii) 对原有本地捕食者蜻艇若虫 (Aeshna sp.) 及其猎物蚊子幼虫 (Anopheles sp.) 的影晌。 我们通过实验室实验比较了这两种捕食者分别捕食和一起捕食的效率，以及当地13 条溪流中蜻蜓若虫和蚊子 幼虫的数量。我们预测小龙虾的捕食效率低于本地的蜻蜓若虫，而在有小龙虾存在的情况下，蜻艇若虫的捕食效 率会下降。结果表明蜻蜓若虫的捕食效率比小龙虾高一个数量级，且小龙虾存在时蜻蜓若虫的捕食效率的确会 下降。野外统计的数据显示，蜻蜓若虫和蚊子幼虫的种群数量与溪流中小龙虾的存在有很强的相关性有小龙虾 的位点一般蜻蜓若虫较少、蚊子幼虫较多。在自然条件下，小龙虾可能会引起蜻蜓若虫丰度下降，捕食效率降 低，从而直接和间接地导致蚊子种群数量增加，还导致与控制疾病传播媒介相关的生态系统服务功能丧失

Ornamental aquaculture and the related pet industry are known to be important sources of non-native species worldwide. In the temperate zone, thermal waterbodies are attractive places for irresponsible owners to release unwanted freshwater pets including decapod crustaceans. Several non-native ornamental species have been reported in the thermal locality of Miskolctapolca (a suburb of Miskolc, Hungary). So we surveyed this site in March 2019–November 2021 to update local occurrence records and detect potentially newly released species. A well-established population of Neocaridina denticulata and the occurrence of Caridina cf. babaulti had previously been noted. However, for the first time at this site, we found the shrimps Atyopsis moluccensis , Caridina gracilirostris and C . multidentata , as well as the crayfish Procambarus virginalis , P . clarkii , Cherax quadricarinatus , C . boesemani and C . snowden , and several formally undescribed Cherax species originating from New Guinea. Furthermore, in most species, gravid females carrying eggs were also noticed. Three shrimps, A . moluccensis , C. gracilirostris and C . multidentata, were recorded for the first time in European wild. Further monitoring of this locality and better education of the general public regarding the risks associated with the release of non-native species are strongly recommended.

Aim Exotic species invasion often leads to declines in local and regional biodiversity, particularly in freshwater ecosystems. This biodiversity loss is generally facilitated by human activities such as land cover change and hydrological alternation. Recent advances in stable isotope analysis (SIA) have been highlighted in many studies addressing fundamental issues in invasion ecology, especially in quantifying competition for resources between native and exotic species. However, how anthropogenic disturbance influences trophic relationships among invasive and native species remains poorly understood. Location Middle‐lower Yangtze River Region, China. Methods To investigate the effects of human disturbance on interspecific trophic interactions, this study compared isotopic niche space and overlap of the introduced red swamp crayfish (Procambarus clarkii) and the native oriental river shrimp (Macrobrachium nipponense) and freshwater snail (Bellamya aeruginosa) in natural and modified wetlands. Results Based on carbon and nitrogen SIA, we found ubiquitous niche shifts in macroinvertebrates with increased competition, which might lead to significant niche contraction in modified habitats at both community and population scales. Moreover, the isotopic niche width of the exotic crayfish was twice as larger as that of natives at both habitats, suggesting that the exotic P. clarkii had great competitive superiority over the native species. However, the effects of habitat modification on niche overlap were inconsistent. While the niche overlap between crayfish and shrimp was significantly higher in modified habitats than in natural open waters, niche overlap between crayfish and the snail was significantly reduced. Main conclusions Collectively, our findings highlight that the competitive outcomes of interspecific trophic interactions can be dependent on the prey availability and diversity, which embraces both the classic optimal foraging theory and competition theory to understand how environmental change, such as habitat alternation, affects the biological invasion processes.

Stable isotope analysis has been broadly used to study food webs, but often relies on inaccurate assumptions of trophic isotopic discriminations, which could lead to misinterpretation of obtained results. While many taxa exhibit similar trophic discrimination factors (TDFs), crayfish, exhibit omnivorous feeding strategies, yet TDFs are missing. In this study, we determined TDFs and tissue biokinetic parameters of the marbled crayfish Procambarus virginalis as a model species. Moreover, we compared commonly used TDFs and those determined from this study and applied them across species and ecosystems as a first attempt to compare the effect of species-specific TDFs in Bayesian trophic mixing models. Our results revealed differences between the TDFs of different tissues and biokinetic parameters of crayfish. Our result also revealed TDFs differences between crayfish relying mostly on plants versus those relying on an animal diet. We found differences of TDF suitability among species and ecosystems, highlighting the need for specific TDFs for different crayfish species. This study improves our understanding and the need for species-calibrated TDFs for robust statistical analysis of stable isotope data. Our approach is widely applicable across taxa and ecosystems to reduce the bias introduced by using unspecific TDFs in Bayesian mixing models.

Biological invasions by nonindigenous species can have negative effects on economies and ecosystems. To limit this impact, current research on biological invasions uses functional traits to facilitate a mechanistic understanding of theoretical and applied questions. Here we aimed to assess the role of functional traits in the progression of crayfish species through different stages of invasion and determine the traits associated with invasive success. A dataset of thirteen functional traits of 15 species currently occurring or available for sale in the Netherlands was evaluated. Six of these crayfish appeared invasive. Important traits distinguishing successful from unsuccessful invaders were a temperate climate in the native range, a medium to high egg count and producing more than one egg clutch per year. The most successful invaders had different functional trait combinations: Procambarus clarkii has a higher reproductive output, can migrate over longer distances and possesses a higher aggression level; Faxonius limosus is adapted to a colder climate, can reproduce parthenogetically and has broader environmental tolerances. Using a suit of functional traits to analyse invasive potential can help risk management and prevention. For example, based on our data Procambarus virginalis is predicted to become the next successful invasive crayfish in the Netherlands.

The pet trade with decapod crustaceans has been considered one of the main pathway of introduction of these animals worldwide. As the leading markets in this regards are the Czech Republic, Germany and the USA. Central Asia is not perceived as an important market with ornamental decapod crustaceans. Despite this assumption, we found at least 16 species of freshwater shrimp, crayfish and crab species pet-traded in the Republic of Kazakhstan, the largest country in this region. Considering computed risk assessment, the origin of particular species, their availability on the market, the probability of establishment and further aspects, we identified two crayfish Procambarus clarkii and Procambarus fallax f. virginalis being the seriously hazardous taxa with high potential to threaten native crayfish species as well as inhabited ecosystems. To prevent their introductions and to minimize the risks of mentioned species, similarly as in the case of European Union, we recommend the total ban of import, trade and keeping of these high-risk taxa within Central Asia. Le commerce des animaux de compagnie avec des crustacés décapodes a été considéré comme l'un des principaux moyens d'introduction de ces animaux dans le monde entier. Comme les principaux marchés à cet égard sont la République tchèque, l'Allemagne et les États-Unis, l'Asie centrale n'est pas perçue comme un marché important des crustacés décapodes ornementaux. Malgré cette hypothèse, nous avons trouvé au moins 16 espèces de crevettes, d'écrevisses et de crabes d'eau douce commercialisées dans la République du Kazakhstan, le plus grand pays de cette région. Compte tenu de l'évaluation des risques calculés, de l'origine d'espèces particulières, de leur disponibilité sur le marché, de la probabilité d'établissement et d'autres aspects, nous avons identifié deux écrevisses Procambarus clarkii et Procambarus fallax f. virginalis étant les taxons gravement dangereux avec un risque élevé de menacer les espèces d'écrevisses natives ainsi que les écosystèmes habités. Pour éviter leur introduction et minimiser les risques des espèces mentionnées, de même que dans le cas de l'Union européenne, nous recommandons l'interdiction totale d'importer, de commercialiser et de conserver ces taxons à haut risque en Asie centrale.