The bad and the super-bad: prioritising the threat of six invasive alien to three imperilled native crayfishes

Multiple species invasions and limited resources for management require prioritisation of deleterious effects of invaders on imperilled native species. This study prioritises the threat of six non-indigenous crayfish species (NICS) to three indigenous crayfish species (ICS) in southwestern Germany, a European region with high diversity of crayfish species and freshwater habitats. Using multivariate statistical analyses and niche-based species distribution models, the (1) contemporary and potential range overlap, (2) habitat overlap, and (3) rate of spread of the nine species were assessed. Predicted and contemporary range overlap with ICS was consistently the highest for the alien signal crayfish. Environmental niches of ICS tended to be associated with cooler temperatures (except for white-clawed crayfish), lower Human Influence Index, and higher terrain slope than that of alien Orconectes and Procambarus species, but were mostly similar to that of signal crayfish. Habitat overlap was found to be the highest between signal crayfish and ICS. In contrast to Orconectes and Procambarus species, signal crayfish also invade headwaters, where the most ICS populations occur. Range expansion during the past 15 years was the highest for signal crayfish, followed by Orconectes species. Because of the great potential to invade as-yet isolated refuge areas and spread at a high rate, signal crayfish is of the highest concern for conservation of ICS and should be primarily targeted by prevention and control measures. However, it merely represents the ‘worst of the worst’, since all NICS of North American origin are natural reservoirs of crayfish plague, a fatal disease of ICS.     

Associations between stream habitat characteristics and native and alien crayfish occurrence

Human mediated introductions of non-indigenous crayfish species (NICS) are responsible for their rapid colonisation of European freshwaters. The introduction of North American crayfish is furthermore linked to the spread of crayfish plague and the decline of indigenous crayfish species (ICS). As the management of ICS and NICS have become necessary, a detailed knowledge on their distribution and ecological requirements is needed. We studied the current range of native noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium, as well as alien signal crayfish Pacifastacus leniusculus in Carinthia (Austria) and evaluated environmental and physical habitat features in streams with and without crayfish. Meanwhile, the loss of many ICS populations was recorded and alien P. leniusculus was found to be widespread in this region. Most of the habitat features of streams having crayfish differed significantly from sites lacking crayfish for at least one investigated native or alien species. Furthermore, multivariate and regression analyses showed specific differences in the habitat use of the investigated crayfish. Our results showed that the presence of alien P. leniusculus was associated with larger and smoother sloped lowland rivers, while the occurrence of the two native species was confined to smaller streams either at higher altitudes and with distinct physical habitat conditions (A. torrentium) or with moderate water temperatures (A. astacus). This study helps to identify potential refuge areas for the endangered native species and to predict the further spread of the most common non-native crayfish species in European streams.     

Uncertainty of using habitat fidelity in biomonitoring based on benthic diatoms - the Raška River case study

Epilithic diatoms are frequently recommended for river biomonitoring, while much less emphasis is placed on epiphytic communities. This study considers use of epiphytic and epilithic diatom communities from the Ra?ka River in biomonitoring. A total of 212 diatom taxa were recorded in both communities. Dominant diatoms were Achnanthidium minutissimum (Kützing) Czarnecki, A. affine (Grunow) Czarnecki, A. subatomus (Hustedt) Lange-Bertalot, Amphora pediculus (Kützing) Grunow, Diatoma vulgaris Bory, Gomphonema tergestinum (Grunow) Fricke, Cocconeis placentula var. lineata (Ehrenberg) Van Heurck, Melosira varians Agardh and Navicula tripunctata (Müller) Bory. Redundancy analysis (RDA) was used to detect the relationships between diatoms, some environmental factors and sampling sites. Diatoms of the epiphytic community showed a clearly grouping in relation to the sampling sites as compared with diatoms of the epilithic community. Species common to both communities showed a similar correlation with some environmental variables (BOD, pH, NH₄⁺, TP, NO₃^? and conductivity), with three exceptions (Diatoma vulgaris, Cymbella compacta, and Encyonema silesiacum). Pearson’s correlation coefficient showed correlation between selected environmental variables and diatom indices calculated using OMNIDIA 6.2 software (TDI, IPS, CEE, GENRE, TID, SID, SHE and IDSE/5). Diatoms of the epiphytic community are more clearly clustered in relation to the sampling sites as compared with diatoms of the epilithic community. According to our results there is still “place” in biomonitoring for epiphytic community. The present study highlights the necessity of sampling both epiphytic and epilithic communities because substrate specificity could play important role in biomonitoring.     

Disentangling the stream community impacts of <Emphasis Type="Italic">Didymosphenia geminata</Emphasis>: How are higher trophic levels affected?

Human activities frequently result in either intentional or unintentional introductions of species to new locations, and freshwater environments worldwide are particularly vulnerable to species invasions. An introduced freshwater diatom, Didymosphenia geminata, was first discovered in New Zealand in 2004 but there was limited research available to predict the drivers of D. geminata biomass and how biomass variability might influence higher trophic levels (e.g. invertebrates and fish). We examined the effect of D. geminata biomass on benthic invertebrates, invertebrate drift and fish communities in 20 rivers in New Zealand with variable hydrology, physical habitat and water chemistry. Variation in D. geminata biomass was best explained by a model that showed D. geminata biomass increased with time since the last flow event exceeding three times the median annual discharge and decreasing concentration of dissolved reactive phosphorus. Analyses of biotic responses showed that high D. geminata biomass did not affect either invertebrate or fish diversity but altered the structure of benthic communities, changed the composition of drifting invertebrate communities and reduced fish biomass by 90 %, particularly trout. A partial least squares path model was used to disentangle both direct and indirect effects of D. geminata on fish communities and showed D. geminata had a significant negative direct effect on fish communities. This is the first study to show how the potential effects of the introduced diatom D. geminata can impact fish communities and has shown that D. geminata impacts fish both directly and indirectly through changes in their invertebrate prey community.     

The endangered white-clawed crayfish <Emphasis Type="Italic">Austropotamobius pallipes</Emphasis> (Decapoda,Astacidae) east and west of the Maritime Alps: a result of human translocation?

The genetic variability among Italian populations of the white-clawed crayfish (Austropotamobius pallipes) was examined to determine their phylogeography and to assess their conservation status as a management unit. A fragment of the mitochondrial DNA COI gene of 107 specimens from ten populations was sequenced, and the phylogenetic relationships were established. Two out of three haplotypes sampled in two French populations from the Rhône basin were shared with Italian populations. Despite a moderate level of genetic variability within the Italian populations of A. pallipes, no genetic structure was revealed. It has been suggested that there have been translocation events throughout the Alpine barrier between the North-Western Italian basins and the Rhône basin. Genetic exchangeability of the French and Italian populations was demonstrated in this study, and a shift of conservation efforts towards the native, congeneric Austropotamobius italicus is recommended.     

Ecosystem of Caspian Sea threatened by pet-traded non-indigenous crayfish

Freshwater ecosystems are particularly vulnerable to biological invasions; the aquatic animal pet trade has been recognized as a significant pathway of introductions. Crayfish are considered a model group of traded organisms with a series of highly successful species already established in the wild, having the potential to negatively influence both indigenous crayfish species (ICS) as well as alter occupied ecosystems. Eastern Europe includes the entire native ranges of indigenous Astacus leptodactylus sensu lato and A. pachypus. This region has been largely overlooked and considered relatively safe from the adverse impacts of non-indigenous crayfish species (NICS). In this study, we evaluated the crayfish pet trade in the Lower Volga Region with special emphasis on Astrakhan, the biggest city of Russian Federation in the region located just in the delta of Volga River, thus being a potential gateway of introductions to the Caspian Sea and adjacent freshwaters. The local pet trade involves 12 NICS. Considering their origin, availability, probability of establishment, invasiveness and further aspects, Procambarus fallax f. virginalis, P. clarkii and Cherax destructor are considered potentially the most problematic, including transmission of diseases like crayfish plague caused by Aphanomyces astaci or white spot syndrome virus. Taking this information as a whole, the availability of NICS with a high probability of overlapping the entire range of European ICS means that attention is warranted. Further research is needed to corroborate the abilities of NICS and their associated diseases to withstand specific conditions of the Caspian Sea as well as the adjacent Black and Azov Seas, all possessing different degrees of elevated salinity.     

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

Free-drifting Antarctic icebergs can alter the phytoplankton in surrounding waters. In addition, diatom mats live attached to the submerged walls of the icebergs. In this study we describe a diverse diatom community associated with these mats and an atypical planktonic community in waters affected by icebergs. Samples were collected in the winter of 2008 and fall of 2009 from Antarctic icebergs and their adjacent waters, utilizing a remote operated vehicle and plankton nets, respectively, and subsequently analyzed using light and electron microscopy. Thalassioneis signyensis, dominant species growing on the icebergs’ flanks, provided substrate for other diatoms, mainly Synedropsis lata var. angustata, Synedropsis recta, Fragilaria cf. islandica var. adeliae, Attheya gaussii, Navicula cf. perminuta, Amphora sp. and Nitzschia spp. New morphological characteristics are given for S. lata var. angustata, S. recta and A. gaussii. We report also Biddulphia alternans and Coscinodiscus concinnus for the first time in Antarctic waters. Similar to sea ice algae, the term sympagic is used to describe the habitat of these diatom communities. A particular planktonic community is also found close to icebergs, including diatoms known to have a benthic, epiphytic, sympagic or freshwater habitat: Amphora sp., B. alternans, Cocconeis spp., Delphineis minutissima, Licmophora gracilis, Luticola cf. australomutica, Opephora sp., Pinnularia spp., Plagiogramma sp., Psammodictyon panduriforme var. minor, Pseudogomphonema kamtschaticum, Rhaphoneis amphiceros, S. recta and T. signyensis. Our results support the hypothesis that species associated with icebergs exchange freely with plankton, ice shelves and sea ice, suggesting that icebergs can act as physical agents to transport and distribute organisms in between these habitats.     

Comparison of trophic function between the globally invasive crayfishes <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> and <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Impacts of invasive species may manifest most strongly if these organisms are highly distinct functionally from the native species they often replace. Yet, should we expect functional differences between native and invasive species of generalist organisms like freshwater crayfish? Some existing evidence has pointed to native and invasive crayfish species as ecologically equivalent. We contribute to this literature by comparing the trophic niches of the globally invasive crayfishes Pacifastacus leniusculus and Procambarus clarkii, by applying carbon and nitrogen stable isotope analyses to replicated allopatric (alone) and sympatric (together) lake populations in western Washington State, USA, where P. clarkii has been recently introduced and P. leniusculus is presumed native. Our study corrected for potential inherent differences in lake food webs as a consequence of lake abiotic or biotic characteristics using random effects in linear mixed effects models. We found that although overall trophic niche size or area of these species was not significantly different, P. leniusculus was significantly higher in trophic position than P. clarkii when also accounting for the effects of body size, sex, and lakes as random effects. This pattern of increased trophic position of P. leniusculus over P. clarkii was conserved over time in one sympatric lake for which we had data over multiple years. Cumulatively, our findings point to trophic differences between the globally cosmopolitan crayfishes P. leniusculus and P. clarkii, particularly when accounting for the ways that ecosystem context can affect food web structure of communities and the trophic resources available to these consumers.     

Biodiversity influences invasion success of a facultative epiphytic seaweed in a marine forest

The biotic resistance hypothesis predicts that more diverse communities should have greater resistance to invasions than species-poor communities. However for facultative and obligate epiphytic invaders a high native species richness, abundance and community complexity might provide more resources for the invader to thrive to. We conducted surveys across space and time to test for the influence of native algal species abundance and richness on the abundance of the invasive facultative epiphytic filamentous alga Lophocladia lallemandii in a Mediterranean Cystoseira balearica seaweed forest. By removing different functional groups of algae, we also tested whether these relationships were dependent on the complexity and abundance of the native algal community. When invasion was first detected, Lophocladia abundance was positively related to species richness, but the correlation became negative after two years of invasion. Similarly, a negative relationship was also observed across sites. The removal experiment revealed that more complex native communities were more heavily invaded, where also a positive relationship was found between native algal richness and Lophocladia, independently of the native algal abundance. Our observational and experimental data show that, at early stages of invasion, species-rich seaweed forests are not more resistant to invasion than species-poor communities. Higher richness of native algal species may increase resource availability (i.e. substrate) for invader establishment, thus facilitating invasion. After the initial invasion stage, native species richness decreases with time since invasion, suggesting negative impacts of invasive species on native biodiversity.     

Life history traits determine the differential vulnerability of native and invasive apple snails (<Emphasis Type="Italic">Pomacea</Emphasis> spp.) to a shared juvenile-stage predator

The vulnerability of gastropods to their predators varies with life history traits such as morphology, body size, behavior, and growth rates as well as predator size. A recent study suggested that the invasive apple snail, Pomacea maculata, was considerably more vulnerable to crayfish predators than the native Florida apple snail, P. paludosa. The difference was hypothesized to be caused by the relatively small hatchling size of P. maculata. To test this hypothesis, we conducted a series of feeding assays designed to quantify maximum feeding rates and selective foraging of crayfish on apple snails. The rate at which crayfish killed individual P. maculata (i.e., kill rates) decreased with snail size, and kill rates on both species increased with crayfish size. Kill rates on juvenile P. maculata were higher than kill rates on size-matched hatchling P. paludosa, and crayfish fed selectively on P. maculata when offered mixed groups of size-matched snails. Further analyses revealed that hatchling P. paludosa possess shells 1.8× heavier than size-matched P. maculata suggesting differences in vulnerability to crayfish were consistent with interspecific differences in shell defenses. Differences in hatchling size and defensive traits in combination make crayfish kill rates on hatchling P. maculata approximately 15.4× faster than on hatchling P. paludosa, but the relative contribution of hatchling size to differences in apple snail vulnerability was >3× greater than the contribution of defensive traits.     

A comparison of epiphytic diatom communities on <Emphasis Type="Italic">Plocamium cartilagineum</Emphasis> (Plocamiales,Florideophyceae) from two Antarctic areas

Our understanding of diatoms, one of the most important Antarctic primary producers, is based mostly on investigations of plankton, sea-ice, and sediment samples. Herein, we contribute to the limited research devoted to benthic Antarctic diatoms by presenting a study on epiphytic diatom communities sampled in two remote Antarctic regions: Admiralty Bay (maritime Antarctica, Antarctic Peninsula) and Terra Nova Bay (Ross Sea). Recent studies have demonstrated that the most critical factor for the local epiphytic diatom communities was the nature of the substrate. In order to eliminate this factor so we could evaluate other potential controls, we sampled epiphytic diatoms from only one substrate that is common to both regions: the macroalgae Plocamium cartilagineum (L.) Dixon. Thalli of P. cartilagineum and their associated microalgal community was collected in January 2011 (Admiralty Bay) and 2012 (Terra Nova Bay) from a water depth of 5–25 m. Dehydrated macroalgal pieces were placed on stubs and sputter-coated, which allowed observation of diatoms attached to the substrate in their original position using scanning electron microscopy. A total of 72 taxa were observed, of which 31 taxa were common to both regions. Cell abundance and diatom growth form dominance were significantly different in Admiralty Bay and Terra Nova Bay samples. Total diatom abundance was higher in Admiralty Bay samples, dominated by adnate diatoms (Cocconeis spp.), but the number of taxa found as well as the values of ecological indices were higher for samples from the Ross Sea, where motile forms were dominant (Navicula spp.). Our results suggest that Antarctic shallow-water benthic habitats may present a high degree of microniche heterogeneity and highlight the need of fine-scale analyses in microbial studies. We also suggest grazers as a factor that contributes greatly to the observed differences.     

Non-indigenous signal crayfish <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> are now common in Danish streams: preliminary status for national distribution and protective actions

North American signal crayfish (Pacifastacus leniusculus) are invasive in Europe and pose a serious threat to indigenous European crayfish such as the noble crayfish (Astacus astacus). This is mainly because signal crayfish is the carrier of crayfish plague agent, Aphanomyces astaci, which freshwater crayfish from all other continents are highly susceptible to. Until recently, the distribution of signal crayfish in Danish streams has been considered local and restricted to a small geographical area. Here we present data demonstrating that signal crayfish are now widespread in Denmark, including the largest Danish river, River Gudenå. For one of the rivers where co-existing signal crayfish and indigenous noble crayfish were documented, sensitive molecular tests could not detect the crayfish plague agent Aphanomyces astaci in either species. Hence, it seems that not all signal crayfish are chronic carriers of the disease. For the remaining freshwater systems with the introduced signal crayfish, the infection status is presently unknown. Large areas of the freshwater systems in Denmark also remain unexplored with respect to presence/absence of signal crayfish and noble crayfish. Nevertheless, our preliminary data that covers about 14% of the Danish rivers, strongly suggests that signal crayfish should be considered as a common invader that poses an increased threat to the biota in Danish streams, in particular for the indigenous noble crayfish.     

First records of the non-indigenous signal crayfish (<Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis>) and its threat to noble crayfish (<Emphasis Type="Italic">Astacus astacus</Emphasis>) populations in Estonia

This study gives an overview of status and distribution of signal crayfish (Pacifastacus leniusculus), the first NICS in Estonia and its influence on native noble crayfish (Astacus astacus) populations. The first specimen of signal crayfish was caught during the monitoring of noble crayfish in North Estonia in 2008. The signal crayfish has since been found in three additional sites. Test fishing has indicated that the abundance of signal crayfish has been fluctuating between years and among localities. It has had strong negative impact on abundance of one noble crayfish population. The disconnected distribution of signal crayfish strongly suggests that these populations are the result of human-assisted introductions. Real-time PCR analyses proved that signal crayfish carry the causative agent of the crayfish plague, an oomycete Aphanomyces astaci, thus contributing to its spread. Mortalities in noble crayfish populations had been caused by A. astaci strains from A, B and E genotype group.     

An invasive plant provides refuge to native plant species in an intensely grazed ecosystem

Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.     

Evidence of multiple introductions and genetic admixture of the Asian brush-clawed shore crab <Emphasis Type="Italic">Hemigrapsus takanoi</Emphasis> (Decapoda: Brachyura: Varunidae) along the Northern European coast

The Asian brush-clawed shore crab Hemigrapsus takanoi is a non-indigenous species along the Northern European coast. Although the history of range expansion of European H. takanoi has been well-documented, little is known about the genetic compositions of either the introduced European populations or the native Asian ones. We therefore collected H. takanoi broadly from their native Asian sites and introduced European ranges, and genotyped them by sequencing the mitochondrial 16S RNA gene and by analyzing nuclear microsatellite loci. Our results revealed that the H. takanoi Bay of Seine (France) populations consisted of a genetic admixture between populations in Japan and those in the Yellow Sea region. These French populations should be carefully monitored in the future, since the genetic admixture of multiple source populations may accelerate range expansion in non-indigenous organisms. Our results also suggested that shipping lines from East Asia were more probable vectors than historical juvenile oyster transportations from Japan for the foundation of present European H. takanoi populations. Interestingly, gene flow between populations in Japan and those in the Yellow Sea region (i.e., domestic invasion) was not observed despite the higher potential for artificial translocations via shipping lines in the native Asian range compared with those from Asia to Europe. The lack of domestic invasions implied that intra-specific priority effects of the resident H. takanoi populations played an important role in preventing the successful colonization of artificially-transferred individuals.     

Living inside a sponge skeleton: the association of a sponge,a macroalga and a diatom

The relationships between sponges and macroalgae have been poorly investigated, especially in temperate waters. This work describes the consortium between the dictyoceratid sponge Dysidea pallescens and the red alga Acrochaetium spongicola permeating spongin fibres in the Mediterranean Sea; moreover, this is the first report of a diatom, Amphora pediculus, living also inside the spongin skeleton. The annual trend of the total algal biomass did not vary over time in relation to the temperature, irradiance and incorporation of foreign bodies. Our analyses, conducted by light and electron microscopy, suggest that both the macroalga and the diatom invade the skeleton of the sponge from the external environment, and that the benthic diatom, epiphyte of the macroalga, is passively carried inside the fibres through the growth of Acrochaetium spongicola. All the examined samples of D. pallescens showed that the macroalga permeated at least some fibres, while the presence of the diatom was occasional. The superficial layer of the sponge, thin and reticulate, likely allows the passage of the light and ensures the algal survival inside the sponge tissue. The high occurrence of the association with A. spongicola, together with the morphological adaptations of the sponge favouring the algal life, suggest that the relationship is mutualistic. The possible benefits for the involved partners are hypothesized. The taxonomy and ecology of endozoic Acrochaetiales are controversial due to the reduced size of thalli, the absence of peculiar diagnostic characters and unknown reproductive structures. Therefore, detailed studies on the relationships between the algae and their hosts will provide helpful information for the algal identification.     

Unique configuration of genes of silicon transporter in the freshwater pennate diatom <Emphasis Type="Italic">Synedra acus</Emphasis> subsp. <Emphasis Type="Italic">radians</Emphasis>

The existence of the cluster of duplicated sit silicon transporter genes in the chromosome of the diatom Synedra acus subsp. radians was shown for the first time. Earlier, the localization of sit genes in the same chromosome and cluster formation caused by gene duplication was shown only for the marine raphid pennate diatom P. tricornutum. Only non-clustered sit genes were found in the genomes of other diatoms. It is reasonable to assume that sit tandem (sit-td) and sit triplet (sit-tri) genes of S. acus subsp. radians occurred as a result of gene duplication followed by divergence of gene copies.     

Surface–sediment diatom assemblages of the urban ponds of St. Petersburg,Russia

The diatom assemblages of the surface sediments have been studied in 53 urban ponds and lakes of St. Petersburg for the first time. In total, 350 species and infraspecific taxa have been registered; the species of Achnanthidium, Cocconeis, Cyclostephanos, Cyclotella, Gomphonema, Lemnicola, Navicula, Nitzschia, and Stephanodiscus genera were the most common. The wide distribution of small centric planktonic taxa, Cyclostephanos dubius, C. invisitatus, Cyclotella pseudostelligera, Stephanodiscus hantzschii, and S. minutulus, is preconditioned by the depletion of dissolved silica, which is a result of the high phosphorus load. The high abundance of macrophytes in the shallowest sites favors the dominance of epiphytic Fragilaria, Staurosira, and Staurosirella taxa. Bottom-living diatoms in the shallow eutrophic and hypereutrophic urban ponds are light-limited; this is a result of either macrophytes or phytoplankton development. Alkaliphilous and alkalibiontic species prevail among the pH-indicative species, while eutraphentic and hypereutraphentic diatoms, as well as those thriving in a wide range of trophic conditions, dominate over other trophic groups. The β- and α-mesosaprobic species are the most common saprobity-indicative taxa.     

Predatory impacts of alien decapod Crustacea are predicted by functional responses and explained by differences in metabolic rate

Alien predators can have large impacts on prey. It is important that we understand, and ideally predict, these impacts. Here, we compare predatory impacts of size-matched decapod crustaceans—invasive alien Eriocheir sinensis and Pacifastacus leniusculus, and native European Austropotamobius pallipes—and use this case study to inform methods for impact prediction. We quantify functional responses (FRs) on three macroinvertebrate prey species, examine switching behaviour, and measure metabolic rates as a possible mechanistic explanation for differences in predation. FRs show a consistent pattern: attack coefficients and maximum feeding rates are ordered E. sinensis?≥?P. leniusculus?≥?A. pallipes for all prey species. Attack coefficients of E. sinensis are up to 6.7 times greater than those of size-matched crayfish and maximum feeding rates up to 3.0 times greater. FR parameters also differ between the invasive and native crayfish, but only up to 2.6 times. We find no evidence of switching behaviour in crayfish but suggestions of negative switching in E. sinensis. Differences in FR parameters are mirrored by differences in routine, but not standard, metabolic rate. Overall, our data predict strong predatory impacts of E. sinensis, even relative to alien P. leniusculus. Strong impacts of P. leniusculus relative to A. pallipes may be driven more by body size or abundance than per capita effect. FRs vary between prey types in line with existing knowledge of impacts, supporting the use of FRs in quantitative, prey-specific impact predictions. MRs could offer a general mechanistic explanation for differences in predatory behaviour and impacts.