Signal Crayfish Pacifastacus Leniusculus Research Articles

Distribution of Non-Indigenous Crayfish Species in Estonia and Their Impacts on Noble Crayfish (Astacus astacus L.) Populations

Invasive non-indigenous crayfish species (NICS) are a major threat to the existence of native crayfish populations in European freshwater ecosystems. The discovery of signal crayfish Pacifastacus leniusculus, marbled crayfish Procambarus virginalis, and spiny-cheek crayfish Faxonius limosus in Estonia has increased the risk of extinction of Estonia’s only native crayfish species, the noble crayfish Astacus astacus. The aim of this study was to give an overview of the status, distribution, and impacts of P. leniusculus, F. limosus, and Procambarus virginalis on A. astacus populations and assess the effect of trapping on NICS abundance. Annual monitoring of crayfish has been carried out since 2008 as part of A. astacus conservation and the NICS eradication plan. In this study, we present data from nine sampling locations monitored from 2010 to 2022. The spread of NICS continues to increase beyond their distribution areas, and in two sampling locations P. leniusculus and A. astacus live in sympatry. Our results suggest that trapping has a limited effect on population abundance, as NICS have already caused the extinction of two A. astacus populations. However, intensive trapping should continue simultaneously with sensitive molecular techniques to monitor the spread of NICS.

River infrastructure and the spread of freshwater invasive species: Inferences from an experimentally‐parameterised individual‐based model

Abstract Invasive species and river infrastructure are major threats to freshwater biodiversity. These stressors are commonly considered in isolation, yet the construction and maintenance of river infrastructure can both enhance and limit the expansion of invasive species. Spatial and temporal limitations of laboratory and field studies, coupled with little consideration of population‐level responses (e.g. invasion rate), have limited understanding of the efficacy of infrastructure for long‐term, catchment‐scale containment of invasive species. This study utilised an individual‐based model (IBM) to investigate the ability of a partial riverine barrier to contain the spread of invasive species at large spatio‐temporal scales, using American signal crayfish Pacifastacus leniusculus as a model species. The base model (no barrier) accurately recreated longitudinal expansion rates of signal crayfish reported in existing literature. A virtual riverine barrier was added to the base model, with passage at the structure parameterised using existing literature and the results of an experiment that demonstrated no clear relationship between crayfish density and passage efficiency at a Crump weir. Model outputs indicated a weir downstream of the release point had no effect on longitudinal expansion of crayfish, whereas an upstream barrier slowed the invasion rate for 6.5 years after it was first encountered. After the invasion rate had recovered to pre‐barrier levels, the invasion front was 2.4 km further downstream than predicted in the absence of a barrier, representing a 1.73 year delay in longitudinal range expansion. Synthesis and applications. Despite substantial negative impacts on native biodiversity, river infrastructure can also delay the spread of freshwater invasive species, representing a trade‐off. This demonstrates the need to consider positive ecological consequences of river infrastructure when designing prioritisation techniques for barrier removal and mitigation (e.g. selective fish passage), and suggests that in some cases barriers may provide a useful integrated pest management tool.

Comparative ultrastructure of the antennae and sensory hairs in six species of crayfish.

Antennae in crayfish are essential for gaining information about the local topography and localising food, chemicals, conspecifics or predator. There are still gaps in the research on the morphology of antennae in decapods compared to other arthropods. Biometrical and ultrastructural methods were applied using light and cryo-scanning electron microscopies to study the morphology of antennae in six different crayfish species, including marbled crayfish Procambarus virginalis, Mexican dwarf crayfish Cambarellus patzcuarensis, red swamp crayfish Procambarus clarkii, signal crayfish Pacifastacus leniusculus, common yabby Cherax destructor, and spiny-cheek crayfish Faxonius limosus to find their potential morphological differences. Significant differences in the antenna length, length and width of each segment to carapace length ratios, and the number of segments were found in the six crayfish species. The ultrastructure revealed differences in the distribution of sensory hairs on the antenna and the morphology of the antennal surface. The different morphology of antennae might reflect adaptation to the conditions of their specific habitats. In addition, results showed that a combination of differences in the morphological features and biometrical measurements of antennae could be used for the distinguishment of different studied crayfish species.

Responses of signal crayfish Pacifastacus leniusculus to single short-term pulse exposure of pesticides at environmentally relevant concentrations

Although pesticides are often discharged into surface waters in pulses as opposed to a sustained release, the effect of episodic pollution events on freshwater crayfish is largely unknown. We monitored change in heart rate and distance moved to assess the response of signal crayfish Pacifastacus leniusculus to short-term exposure to environmentally relevant concentrations of metazachlor (MTZ), terbuthylazine (TER), and thiacloprid (TCL). Crayfish exposed to 20 µg/L of MTZ exhibited a significant increase in mean heart rate and distance moved. Increased heart rate was detected at 118 ± 74 s post-exposure to MTZ. There were no significant differences in mean heart rate and distance moved in crayfish exposed to 6 µg/L of TCL and 4 µg/L of TER. A significant correlation between heart rate and distance moved was found in all exposed groups. These results suggest that pulse exposure to MTZ impact crayfish physiology and behavior during short-term period. With pulse exposure to TCL and TER, crayfish not exhibiting a locomotor response may continue to be exposed to lower, but potentially harmful, levels of pollutants. Evidence of the impacts of pesticide pulse at environmentally relevant concentrations on crayfish is scarce. Further study is required to determine the ecological effects of such events on freshwater crayfish.

Exploring the eDNA dynamics of the host-pathogen pair Pacifastacus leniusculus (Decapoda) and Aphanomyces astaci (Saprolegniales) under experimental conditions

The oomycete Aphanomyces astaci causes crayfish plague, a disease threatening native European crayfish. It is carried and transmitted by American crayfish species, which are the original hosts of A. astaci. In recent years, environmental DNA (eDNA) methods have been successfully implemented to monitor the spread of both A. astaci and its hosts. However, still little is known about how population density and other environmental factors influence the detectability of this host-pathogen complex. In a mesocosm experiment, we tested the influence of crayfish density, temperature and food availability on the detectability of eDNA for A. astaci and its host, signal crayfish Pacifastacus leniusculus. We also compared eDNA results with crayfish population density measured by catch per unit effort (CPUE) from two lakes with varying crayfish density and A. astaci prevalence. The mesocosm experiment revealed that a limited set of controlled factors can substantially change the detectable amount of eDNA, even though the physical presence of the target organisms remains the same. In cold, clear water, eDNA quantities of both targets increased far more than in a linear fashion with increased crayfish density. However, the presence of food decreased the detectability of crayfish eDNA, presumably through increased microbial-induced eDNA degradation. For A. astaci, where eDNA typically represents living spores, food did not affect the detectability. However, high water temperature strongly reduced it. The increased complexity and variability of factors influencing eDNA concentration under natural conditions, compared to a controlled experimental environment, suggests that establishing a reliable relationship between eDNA quantities and crayfish density is difficult to achieve. This was also supported by field data, where we found minimal correspondence between eDNA quantity and CPUE data. A comparison between quantitative real-time PCR (qPCR) analysis and droplet-digital PCR (ddPCR) analysis revealed higher detection success of the targets in field samples when using qPCR. Overall, our results support eDNA as an effective tool for presence-absence monitoring, but it seems less suited for biomass quantification and population density estimates. Detection of A. astaci and P. leniusculus is not influenced uniformly by respective environmental factors. Consequently, we recommend a strategy of monitoring both targets, where the detection of one may point towards the presence of the other.

Climate change threatens unique genetic diversity within the Balkan biodiversity hotspot – The case of the endangered stone crayfish

The stone crayfish Austropotamobius torrentium is globally endangered due to anthropogenic pressure on its habitats, climate change and the invasive crayfish species, particularly the signal crayfish Pacifastacus leniusculus . Aiming to guide A. torrentium conservation within the hotspot of its genetic diversity in the western Balkan Peninsula, we combined population genetics and species distribution models (SDMs) to reveal the impact of climate change and the invasive P. leniusculus on A. torrentium diversity. Population genetic analyses based on newly developed microsatellites revealed moderate within-population genetic diversity and high differentiation among populations, reflecting isolated populations with limited gene flow. Alongside strong genetic structuring, we discovered high level of inbreeding coefficient indicating homozygote excess within the majority of populations. The SDMs results predicted substantial reductions of suitable habitats for A. torrentium by 2070; 80 % of its currently suitable habitat is predicted to be lost under high‐warming climate change scenario. Obtained results indicated that 44 % of populations with high and/or unique genetic diversity, including three highly divergent and geographically restricted evolutionary lineages, are located in the areas predicted to become unsuitable in the future, highlighting their vulnerability to extinction. Further, SDMs revealed considerable decrease of future habitat suitability for P. leniusculus , suggesting that climate change represents greater threat to A. torrentium . Our study highlights the importance of conserving remnant A. torrentium populations, among other, through assisted migration and population mixing that could help populations overcome the risks of inbreeding and maladaptation, and thus enabling A. torrentium to withstand the ongoing climate change. • Native freshwater crayfish decline is a global conservation concern. • The first study of Austropotamobius torrentium genetic diversity in its hotspot (Balkan Peninsula). • Climate change poses a higher risk to A. torrentium than invasive crayfish species. • Transboundary conservation actions needed for species long-term preservation. • . Conservation strategies should include assisted migration and population reinforcement.

Integrated biomarker response in signal crayfish Pacifastacus leniusculus exposed to diphenhydramine

Diphenhydramine (DPH) is a pharmaceutical with multiple modes of action, primarily designed as an antihistamine therapeutic drug. Among antihistamines, DPH is a significant contaminant in the environment, frequently detected in surface waters, sediments, and tissues of aquatic biota. In the present study, signal crayfish Pacifastacus leniusculus was used as a model organism because of their prominent ecological roles in freshwater ecosystems. The biochemical effects were investigated in crayfish exposed to the environmental (low: 2 μg L−1), ten times elevated (medium: 20 μg L−1), and the sublethal (high: 200 μg L−1) nominal concentrations of DPH in water for 96 h. Lipid peroxidation, antioxidant enzyme activities, and acetylcholinesterase activity were assessed as toxicological biomarkers in crayfish hepatopancreas, gills, and muscles. Low and medium DPH exposure caused imbalances only in glutathione-like enzyme activities. Integrated biomarker response showed the absolute DPH toxicity effects on all tested tissues under high exposure. This study identified that high, short-term DPH exposure induced oxidative stress in crayfish on multiple tissue levels, with the most considerable extent in muscles.

Long-term changes in the prevalence of the crayfish plague pathogen and its genotyping in invasive crayfish species in Czechia

The widespread presence of North American alien crayfish in Europe is a major driver of native crayfish population declines, mainly because they are chronic carriers of the oomycete Aphanomyces astaci responsible for crayfish plague. Screening for the crayfish plague pathogen in host populations has become a common practice across Europe, but sampling usually covers spatial but not temporal variation. Our study focuses on the current situation in Czechia, where screening for A. astaci was first conducted in the mid-2000s. We provide data about the distribution and prevalence of this pathogen at almost 50 sites with three host crayfish: the spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis. Among these sites were 20 localities that were resampled several years (usually more than a decade) after the original screening for A. astaci. We did not detect any A. astaci infection in two studied P. virginalis populations but documented several new hotspots of highly infected P. leniusculus in Czechia, and the first site with the coexistence of the latter with F. limosus. Our data suggest that despite some fluctuations, A. astaci prevalence in North American host populations generally does not tend to change significantly over time; we only observed two cases of a significant increase and one of a significant decrease. We no longer detected A. astaci in several originally weakly infected populations, but our data suggest it likely still persists in these areas and threatens native crayfish populations. At the single known site in the country where P. leniusculus and F. limosus coexist, we documented the presence of the same A. astaci genotype group in both crayfish species, likely due to interspecific transmission of the pathogen from the former host to the latter. However, genotyping of A. astaci in infected host individuals still supported the link between specific pathogen genotypes and crayfish hosts, suggesting that assessment of sources of mass mortalities from the pathogen genotyping is feasible in European regions where the mutual contact of different American crayfish species is uncommon.

Predation preference of signal crayfish (Pacifastacus leniusculus) on native and invasive bivalve species

AbstractPredatory, non‐native fauna can influence biodiversity and trophic dynamics in invaded ecosystems. Signal crayfish (Pacifastacus leniusculus) are a highly successful invader, which have altered freshwater benthic communities, including bivalve populations. Bivalves are a keystone freshwater group in global in decline, partly due to invasion by alien bivalve and crayfish species. However, little is known about the predatory impacts of invasive crayfish within co‐occurring native and invasive bivalve populations. Mesocosm predation choice experiments considered relative signal crayfish predation rates between paired native (Anodonta anatina and Unio tumidus) and invasive (Dreissena polymorpha, D. bugensis, and Corbicula fluminea) bivalves, and between paired invasive bivalves. All bivalves were actively predated, but there was no consistent difference in the biomass of invasive versus native bivalves consumed. However, the effects of consumption were consistently different; 18.2% of invasive bivalves were lethally predated, with 100% of surviving individuals remaining undamaged, whereas 1.1% of native bivalves were lethally predated, but 100% of surviving individuals received nonlethal damage in the form of shell chipping, which could reduce long‐term bivalve fitness in natural environments. In experiments considering paired invasive species, D. polymorpha was more resistant to predation when compared to other invasive taxa tested. The majority of field research considering aquatic invasions considers purely lethal predation effects inferred from invertebrate presence/absence. These experiments demonstrate the need to better understand both the processes and impacts of predation by invasive species, which may include substantial nonlethal effects on the fitness and life history of endangered taxa.

First Record of Microsporidia Infection in the Damselfly Ischnura elegans Larvae: Temperature and Predator Cue Effects on the Host’s Life History

Here, we report, for the first time, a microsporidian infection in laboratory-reared larvae of the damselfly Ischnura elegans. Infected larvae originated from field-collected adult females, which were caught in southern Poland in August 2020 (the second half of the flight season). Higher rearing temperatures and the presence of predator cues from the invasive alien signal crayfish (Pacifastacus leniusculus) increased the number of infected larvae. Infected larvae had distorted wing development, and all individuals died before emergence. Hence, microsporidian infection in I. elegans larvae impacted damselfly morphology and life history. We propose that warming temperature and stress caused by non-consumptive effects triggered by invasive alien predators are possible factors that produce negative fitness consequences following microsporidian infection in a key amphibious ectotherm.

Predicting invasive signal crayfish (Pacifastacus leniusculus) spread using a traditional survey and river network simulation

AbstractRivers are among the most vulnerable ecosystems to biological invasions. After introduction, predicting the timing and magnitude of population growth and range expansion is critical to decision making on where management tactics will be most efficient. Yet, management is often hindered by the lack of knowledge on species‐specific attributes and the spatially complex structure of river networks that influences connectivity between sites. We analysed the population structure and predicted the range expansion of signal crayfish (Pacifastacus leniusculus), an invasive species in North‐western Italy which was first recorded in the Valla Stream in 2009 and then spread to adjacent rivers including Erro Stream in 2020. A total of 1,284 individual P. leniusculus crayfish were collected in the Valla Stream. No significant difference was found in density or body condition along a downstream gradient for different sex and maturity classes. These empirical data were combined with the available scientific literature to obtain key life‐history information for P. leniusculus, including carrying capacity, downstream versus upstream dispersion and proliferation rate. We used the OCNet R package to simulate the Erro Stream network and applied a meta‐population model to predict the range expansion of this species over time. Results indicate P. leniusculus may completely invade the Erro Stream network in 30–40 years, depending on the proliferation rate and without additional introductions. These findings represent one of the first attempts to use optimal channel networks simulation in R to predict the meta‐population dynamics of aquatic invasive species, a potential key tool to prevent invasive species spread.

Ecosystem effects of invasive crayfish increase with crayfish density

Abstract The nature and extent of effects of increasing densities of non‐native species on stream ecosystems remain poorly understood. Non‐native crayfish are among the most invasive aquatic species and we hypothesised that, in temperate streams, the extent of trophic modification increases with non‐native crayfish density. Instream flow‐through mesocosms in the River Lune, north‐east England, were used over a 47‐day period in summer to measure density effects of invasive signal crayfish Pacifastacus leniusculus on different ecosystem components (benthic fish, macroinvertebrates, algal biomass, and leaf litter breakdown). Effects were measured through three density treatments (low, medium, and high; four, eight, or 12 crayfish with five bullhead Cottus perifretum per 1.5 m2) and two control (crayfish and fish absent; crayfish absent and benthic fish present) groups. Impacts of crayfish on macroinvertebrates (density, taxonomic composition), fish (growth, diet), algal standing stock, and decomposition rates increased with crayfish density. Direct effects of increased crayfish density were more important than indirect trophic cascade effects. Despite similar invertebrate abundance and richness across enclosures before introducing crayfish and bullhead, they differed significantly from controls at the end of the study, with >80% reduction in macroinvertebrate abundance recorded in the high‐density group. Stable isotope (δ15N, δ13C) analysis showed that the trophic niche of bullhead, but not signal crayfish, changed when the species were in sympatry. Bullhead in treatment enclosures occupied a lower trophic position in the food web than those from the control group. Bullhead in the high‐density group lost 4.2% of body mass over the study period, confirming the existence of resource competition. Leaf litter break down was 59.2% faster, and algal biomass was 91.4% lower in the treatment with the highest crayfish density compared to the control without study animals. This study indicates that signal crayfish, even at a low density, can strongly alter multiple ecosystem components in streams, and emphasises the need for minimising the spread of invasive crayfish within and between streams.

Effects of selenium treatment on endogenous antioxidant capacity in signal crayfish (Pacifastacus leniusculus)

Selenium is an essential element that plays a role in numerous physiological processes and is critical for the maintenance of a strong endogenous antioxidant system. Previous work by our research group reported that the organophosphate pesticide dimethoate decreased glutathione S-transferase activity (GST) in signal crayfish (Pacifastacus leniusculus) collected from the Boise River (Idaho, USA). The goals of this study were to examine whether: 1) sodium selenite modulated the endogenous antioxidants glutathione (GSH), metallothionein (MT), and glutathione S-transferase (GST), thus suggesting a mechanism of antioxidant activity, 2) dimethoate exposure (pro-oxidant stressor) decreased GST activity in a localized population of signal crayfish collected from the Snake River (Idaho, USA), and 3) investigate whether selenium cotreatment ameliorated the adverse effects of dimethoate on GST activity due to the antioxidant properties associated with selenium. Selenium and dimethoate treatments (and co-treatments) did not modulate GSH or MT concentrations at the doses tested in this study. Furthermore, neither selenium nor dimethoate was factors influencing GST activity, and no interaction was found between the treatments. While our results did not support our predictions, they are suggestive and future studies examining the protective role of selenium in pro-oxidant exposure in this species are warranted. Population-specific responses as well as seasonal variations in endogenous antioxidant expression should be considered in future experiments.

Combined per‐capita and abundance effects of an invasive species on native invertebrate diversity and a key ecosystem process

Abstract Invasive alien species (IAS) are leading to the homogenisation of taxonomic and functional biodiversity, with negative consequences for key ecosystem processes in fresh water. Invasive signal crayfish (Pacifastacus leniusculus) is expected to disrupt detritus‐based food webs by affecting leaf breakdown and/or by decreasing invertebrate density and diversity through predation. The combination of per‐capita and abundance effects of P. leniusculus in invaded ecosystems is still largely unknown. A four‐week field experiment was established in Rabaçal and Tuela Rivers (NE Portugal) to assess effects of P. leniusculus on invertebrate taxonomic and functional diversity and leaf litter breakdown following a gradient of invasion. We controlled the presence and absence of crayfish by placing the animals and leaf litter inside cages at six sites (three sites per river) according to the crayfish in situ abundance (absent, low, high). Cages were covered with coarse‐ or fine‐mesh net to allow or prevent invertebrates from accessing the leaves. Results showed that higher crayfish in situ abundance led to a decrease in abundance, richness and Shannon diversity of invertebrates and to changes in the communities’ structures. Higher crayfish abundance led also to a decrease in invertebrate functional redundancy and an increase in the percentage of invertebrate taxa with resistance forms. Leaf litter breakdown increased with crayfish presence and decreased at sites with higher crayfish abundance. Overall, signal crayfish changed the community structure of invertebrates, with potential severe long‐term effects on native communities and leaf litter breakdown. Given the widespread distribution of signal crayfish (and other crayfish species), their ecological impacts should be assessed carefully, especially in pristine freshwater ecosystems such as those described here.

Variations in host surfaces morphology and biology of ciliate epibionts explaining distribution pattern of epibionts in the invasive signal crayfish Pacifastacus leniusculus (Dana, 1852)

AbstractThe present paper reports the distribution of Epistylididae (Sessilida) epibiotic ciliates on the signal crayfish Pacifastacus leniusculus in relation to specialized structures of the host's exoskeleton for the first time. This species is known to maintain a relatively clean carapace, but it is sometimes overgrown by other organisms. Epibionts cover different parts of the signal crayfish body, mainly antennae, antennules, maxillipedes III and pereiopods with inner edges of chelae; however, some parts of the signal crayfish are not fouled. e.g. dorsal surfaces of the carapace and dorsal surfaces of chelae. Using scanning electron microscopy (SEM), topographies of different parts of the crayfish's exoskeleton were examined. Our investigations revealed that the epibiosis in the signal crayfish was determined by morphology of body surfaces. No epibionts were found on smooth surfaces with regular single setae (a known design that prevents fouling in aquatic environments). The dimpled surfaces with regular single micro‐papillae may be considered as a newly described example of self‐cleaning surfaces. Bio‐inspired surface patterning presents promising approaches to the design of novel functional surfaces that can prevent biofouling. The new self‐cleaning design may be used in further technological applications.

Personality, density and habitat drive the dispersal of invasive crayfish

There is increasing evidence that personality traits may drive dispersal patterns of animals, including invasive species. We investigated, using the widespread signal crayfish Pacifastacus leniusculus as a model invasive species, whether effects of personality traits on dispersal were independent of, or affected by, other factors including population density, habitat, crayfish size, sex and limb loss, along an invasion gradient. Behavioural traits (boldness, activity, exploration, willingness to climb) of 310 individually marked signal crayfish were measured at fully-established, newly-established and invasion front sites of two upland streams. After a period at liberty, recaptured crayfish were reassessed for behavioural traits (newly-established, invasion front). Dispersal distance and direction of crayfish movement, local population density, fine-scale habitat characteristics and crayfish size, sex and limb loss were also measured. Individual crayfish exhibited consistency in behavioural traits over time which formed a behavioural syndrome. Dispersal was both positively and negatively affected by personality traits, positively by local population density and negatively by refuge availability. No effect of size, sex and limb loss was recorded. Personality played a role in promoting dispersal but population density and local habitat complexity were also important determinants. Predicting biological invasion in animals is likely to require better integration of these processes.

Environmental DNA‐based methods detect the invasion front of an advancing signal crayfish population

AbstractAquatic invasive species, such as the signal crayfish (Pacifastacus leniusculus), present a major threat to freshwater ecosystems. However, these species can be challenging to detect in recently invaded habitats. Environmental DNA (eDNA)–based methods are highly sensitive and capable of detecting just a few copies of target DNA from non‐invasively collected samples. Therefore, they have considerable potential for broad‐scale use in mapping and monitoring the spread of invasive species. In this study, we aimed to increase our understanding of the current distribution of signal crayfish in a headwater stream system in the United Kingdom (tributaries of the River Wharfe, Addingham, Yorkshire). Environmental DNA sampling, assessment of water chemistry variables, and conventional crayfish hand‐searching were conducted across 19 study sites in five tributary streams. Using hand‐searching, we detected signal crayfish at 26% of the sites (5/19 study sites). However, using eDNA‐based methods, occupancy increased to 47% of study sites (9/19). Our sampling revealed previously unknown sites of crayfish occupancy, and using eDNA‐based methods, we were able to define the geographical extent of the invasion front in each headwater stream sampled. This study highlights that eDNA‐based methods are well‐suited for detecting newly established signal crayfish populations in recently invaded habitats, even when the invasive species is at low abundance and, therefore, might otherwise be under‐represented or undetected using conventional survey methods. Our study provides further evidence that headwater stream ecosystems are particularly vulnerable to signal crayfish invasion. However, their geomorphological features may make methods used to reduce or prevent invasive crayfish dispersal more effective than in other freshwater ecosystems.

Responses of Signal Crayfish Pacifastacus Leniusculus to Pulse Exposure of Pesticides at Environmentally Relevant Concentrations

Responses of Signal Crayfish Pacifastacus Leniusculus to Pulse Exposure of Pesticides at Environmentally Relevant Concentrations

Integrated Biomarker Response in Signal Crayfish Pacifastacus Leniusculus Exposed to Diphenhydramine

Integrated Biomarker Response in Signal Crayfish Pacifastacus Leniusculus Exposed to Diphenhydramine

Divergent temperature-specific metabolic and feeding rates of native and invasive crayfish

Temperature is one of the most important factors governing the activity of ectothermic species, and it plays an important but less studied role in the manifestation of invasive species impacts. In this study, we investigated temperature-specific feeding and metabolic rates of invasive and native crayfish, and evaluated how temperature regulates their ecological impacts at present and in future according to different climatic scenarios by bioenergetics modelling. We conducted a series of maximum food consumption experiments and measured the metabolic rates of cold-adapted native noble crayfish (Astacus astacus) and invasive signal crayfish (Pacifastacus leniusculus) originally from a warmer environment over a temperature gradient resembling natural temperatures in Finland. The maximum feeding rates and routine metabolic rates (RMR) of native noble crayfish were significantly higher at low temperatures (< 10 °C than the rates of invasive signal crayfish. The RMRs of the species crossed at 18 °C, and the RMRs of signal crayfish were higher at temperatures above 18 °C. These findings indicate that the invader’s thermal niche has remained stable, and the potential impacts per capita are lower at suboptimal cold temperatures than for the native species. Our bioenergetics modelling showed that the direct annual predation impact of noble and signal crayfish seem similar, although the seasonal dynamics of the predation differs considerably between species. Our results highlight that the temperature-specific metabolic and feeding rates of species need to be taken into account in the impact assessment instead of simple generalisations of the direction or magnitude of impacts.