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Biological invasions cause huge environmental and socio-economic losses worldwide. Among successful invaders, there are also several decapod crustacean species. In this study, we report the presence of an potentially invasive crab species that damages rice crops in Sumatra, Indonesia. This paddy-field crab Parathelphusa convexa De Man, 1879 is a freshwater species native to Java, which was introduced in Sumatra around 2000 via an uncertain pathway. The sampling was conducted from July to September 2021 in paddy fields in West Sumatra, where its well-established population was discovered. The crab negatively impacts rice plants and paddy fields in the region through grazing and burrowing behaviour. Since the species is too small to be attractive for human consumption and also, it is not popular for ornamental keeping due to indistinct colouration, it has no benefits for local communities and is considered unwanted. The continuous monitoring of the species with possible regulation or eradication activity in Sumatra is recommended. [ABSTRACT FROM AUTHOR]

In 2017, a new non-indigenous crayfish species was found established in Europe. The captured individuals were identified as an orange morph of the Mexican dwarf crayfish Cambarellus patzcuarensis Villalobos, 1943. Fifteen adults (including three ovigerous females) and 26 juveniles were collected in a thermal pond in Budapest, Hungary. Two additional adults were caught below the pond's outflow in the adjacent Danube River. To our knowledge, this is the first record of a C. 'patzcuarensis population outside North America, which is also true for the rest of dwarf crayfish (family Cambaridae, subfamily Cambarellinae). With this finding, indigenous crayfish species in Europe are now more than two-fold outnumbered by non-indigenous species. An analysis of the probability of establishment of C. patzcuarensis in continental Europe revealed that specific regions in the south of the continent are suitable areas for the establishment of the species. Moreover, as a confirmed carrier of the crayfish plague pathogen, this species should be treated with caution and eradicated if possible. [ABSTRACT FROM AUTHOR]

The pet trade has been responsible for many introductions of non-native species. Freshwater ornamental plants and animals originating from the pet trade are stocked to garden ponds. The present survey focused on awareness and responsible behaviour related to biological invasion risks of companies that designed, built, and stocked garden ponds., A representative number ( n = 124) of companies (commercial garden pond architects and builders) in the Czech Republic were surveyed regarding the offer of non-native, invasive and threatened native species. The survey was conducted over the entire warm period (from 1 May 2015 to 31 September 2015) while using personal visits, correspondence and interviews to list the species on offer., 'Traditional' ornamental species were offered by 39.1% of surveyed vendors, non-traditional 'marginal' species by 5.6%, common native species by 6.5% and threatened native species by 2.4%., The findings of this study support the hypothesis that 'garden pond' vendors offer non-native species with a risk of biological invasion; moreover, threatened native animals were also on sale. It is probable that a similar situation exists in other countries. It is important for the conservation of native aquatic biota to raise awareness of the need to reduce risk through responsible behaviour of those involved in the pet trade. It is also essential to prohibit stocking of potential invaders and to enforce the illegal capture and sale of native species. [ABSTRACT FROM AUTHOR]

The marbled craynsn ( Procambarus fallax f. virginalis) has become one of the potentially most dangerous nonindigenous 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. [ABSTRACT FROM AUTHOR]

Simple Summary: Biological invasions exert tremendous impacts on native biodiversity and ecosystem functioning. Invasive crayfish species are well known for their particularly vigorous impacts. Recent research indicated that locations with multiple invasive crayfish species are increasing, yet questions asking which species and under what circumstances will dominate have remained unanswered. Conducting a set of independent trials of single-species stocks (intraspecific interactions) and mixed stocks (interspecific interactions) of marbled crayfish in combination with other four crayfish species invasive to Europe we evaluated survival, growth, claw injury, and reproduction. In both single and mixed stocks, red swamp crayfish and common yabby grew faster than marbled crayfish, while marbled crayfish were superior to both spiny-cheek and signal crayfish in terms of growth. Except for the trial with signal crayfish, the faster-growing species consistently reached a higher survival rate. Thus, the success of the marbled crayfish is significantly driven by its relatively fast growth as well as early and frequent reproduction. Our results indicate how interactions between invasive populations can unfold in the future and underline the complex population dynamics between existing and emerging invasive species. Biological invasions are increasingly recognized ecological and economic threats to biodiversity and are projected to increase in the future. Introduced freshwater crayfish in particular are protruding invaders, exerting tremendous impacts on native biodiversity and ecosystem functioning, as exemplified by the North American spiny-cheek, signal and red swamp crayfish as well as the Australian common yabby. The marbled crayfish is among the most outstanding freshwater crayfish invaders due to its parthenogenetic reproduction combined with early maturation and high fecundity. As their introduced ranges expand, their sympatric populations become more frequent. The question of which species and under what circumstances will dominate in their introduced communities is of great interest to biodiversity conservation as it can offer valuable insights for understanding and prioritization of management efforts. In order to examine which of the aforementioned species may be more successful as an invader, we conducted a set of independent trials evaluating survival, growth, claw injury, and reproduction using single-species stocks (intraspecific interactions) and mixed stocks (interspecific interactions) of marbled crayfish vs. other crayfish invaders since the onset of exogenous feeding. In both single and mixed stocks, red swamp crayfish and yabby grew faster than marbled crayfish, while marbled crayfish were superior to both spiny-cheek and signal crayfish in terms of growth. With the exception of signal crayfish, the faster-growing species consistently reached a higher survival rate. The faster-growing species tended to negatively impair smaller counterparts by greater claw injury, delayed maturation, and reduced fecundity. Only marbled crayfish laid eggs as early as 14 weeks in this study, which is earlier than previously reported in the literature. Thus, the success of marbled crayfish among invasive crayfish is significantly driven by relatively fast growth as well as an early and frequent reproduction. These results shed light on how interactions between invasive populations can unfold when their expansion ranges overlap in the wild, thereby contributing to the knowledge base on the complex population dynamics between existing and emerging invasive species. [ABSTRACT FROM AUTHOR]