Signal Crayfish Pacifastacus Leniusculus Research Articles

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.

Impacts of native and invasive crayfish on three native and one invasive freshwater mussel species

Abstract Freshwater mussels and crayfish provide important ecosystem functions and services. In both groups, global declines of native species are paralleled by invasions of non‐native species. Knowledge on differences in predation susceptibility of native and invasive freshwater mussels exposed to native and invasive crayfish is essential for understanding their ecological interactions and for conservation management. In this study, we compared the predation impact of the native European noble crayfish (Astacus astacus) and the invasive signal crayfish (Pacifastacus leniusculus) on three native (Anodonta anatina, Anodonta cygnea, and Unio pictorum) and one invasive (Sinanodonta woodiana) mussel species in controlled laboratory experiments. We repeated the same experiments with the same crayfish specimens to investigate a potential learning effect of crayfish and assessed the in situ impacts in a natural stream. Mussel predation and damage caused by P. leniusculus was significantly higher than by A. astacus. Irrespective of the crayfish species, susceptibility was greater in native mussel species compared to invasive S. woodiana. Predation and damage was greatest in the thick‐shelled U. pictorum, suggesting that other factors such as shell shape are more important in explaining susceptibility than shell thickness. A predation learning effect from previous co‐exposure was evident, being most pronounced for A. astacus. Even if our experimental findings could not be confirmed in the field, the experimental results suggest that crayfish may have a negative impact on mussels and this impact will likely increase with the ongoing spread of P. leniusculus replacing A. astacus populations in Europe. The co‐occurrence of invasive P. leniusculus with the invasive S. woodiana could potentially exacerbate declines of endangered native mussel populations.

Virome Analysis of Signal Crayfish (Pacifastacus leniusculus) along Its Invasion Range Reveals Diverse and Divergent RNA Viruses.

Crayfish are a keystone species of freshwater ecosystems and a successful invasive species. However, their pathogens, including viruses, remain understudied. The aim of this study was to analyze the virome of the invasive signal crayfish (Pacifastacus leniusculus) and to elucidate the potential differences in viral composition and abundance along its invasion range in the Korana River, Croatia. By the high-throughput sequencing of ribosomal RNA, depleted total RNA isolated from the crayfish hepatopancreas, and subsequent sequence data analysis, we identified novel and divergent RNA viruses, including signal crayfish-associated reo-like, hepe-like, toti-like, and picorna-like viruses, phylogenetically related to viruses previously associated with crustacean hosts. The patterns of reads abundance and calculated nucleotide diversities of the detected viral sequences varied along the invasion range. This could indicate the possible influence of different factors and processes on signal crayfish virome composition: e.g., the differences in signal crayfish population density, the non-random dispersal of host individuals from the core to the invasion fronts, and the transfer of viruses from the native co-occurring and phylogenetically related crayfish species. The study reveals a high, previously undiscovered diversity of divergent RNA viruses associated with signal crayfish, and sets foundations for understanding the potential risk of virus transmissions as a result of this invader’s dispersal.

Disturbance in invasion? Idiopathic necrotizing hepatopancreatitis in the signal crayfish Pacifastacus leniusculus (Dana, 1852) in Croatia.

As the most successful crayfish invader and possible vector for infectious agents, signal crayfish Pacifastacus leniusculus is among the major drivers of the native crayfish species decline in Europe. We describe histopathological manifestation and frequency of newly detected idiopathic necrotizing hepatopancreatitis along the invasion range of the signal crayfish in the Korana River in Croatia. Our results show extremely high prevalence of necrotizing hepatopancreatitis (97.3%), with 58.9% of individuals displaying mild and 31.5% moderate histopathological changes in the hepatopancreas, also reflected in the lower hepatosomatic index of analysed animals. Recorded histopathological changes were more frequent in the invasion core where population density is higher. Our preliminary screening of co-occurring native narrow-clawed crayfish Pontastacus leptodactylus showed lower incidence (33.3%) and only mild hepatopancreatic lesions, but potentially highlighted the susceptibility of native crayfish populations to this disease. Pilot analyses of dissolved trace and macro elements in water, sediment fractions and crayfish hepatopancreas do not highlight alarming or unusually high concentrations of analysed elements. Hepatopancreas microbiome analysis, using 16S rRNA gene amplicon sequencing, identified taxonomic groups that should be further investigated, along with impacts of the disease on health and viability of both invasive and native crayfish populations.

The Importance of Larval Stages for Considering Crab Microbiomes as a Paradigm for the Evolution of Terrestrialization.

The transition from an aquatic to a terrestrial lifestyle has evolved multiple times, and in numerous different phyla, in earth's history. In many crab species, this process is still underway (Bliss and Mantel, 1968), providing a unique opportunity to study the evolution of terrestrialization, as well as the role of associated microbiomes during this process (Cannicci et al., 2020). Recently, Cannicci et al. (2020) reported on the potential importance of microbiomes in the transition of crabs, formally wholly aquatic species, to life, fully or in part, in terrestrial environments. The authors argue that symbiotic bacteria, such as those of gill and gut microbiomes, may play a key role in easing this transition, by helping crabs to overcome physiological and morphological challenges associated with conquering the terrestrial environment, such as impaired respiration and osmotic regulation, and a new, often primary plant-based low nitrogen diet. Here we focus on the microbiomes of crab larvae and their potential role for the evolution of terrestrialization. Crabs that are transitioning to life on land fall into two broad categories: terrestrial species that spend their whole adult life (except for larval release) on land independent of tidal inundation or freshwater bodies, and semi-terrestrial species that spend their adult life on land but are dependent on tidal inundation or freshwater (Burggren and McMahon, 1988; Anger, 1995). Many marine organisms form symbiotic relationships with microorganisms to aid life in extreme environments (Sogin et al., 2020). In line with the hologenome theory, this suggests that host-microbe interactions play an important role in an organism's evolution, where the genes of both the host and its microbes co-evolve in the collective “holobiont” (Zilber-Rosenberg and Rosenberg, 2008), potentially allowing the colonization of formerly hostile environments (Bang et al., 2018). Microbial symbionts, as individual species or in mixed-species assemblages, are present in many crustaceans, such as the marine isopod Idotea balthica (diet-specific gut microbiomes, Mattila et al., 2014), the intertidal brachyuran crab Eriocheir sinensis (gill and gut microbiomes, Zhang et al., 2016), and the freshwater signal crayfish Pacifastacus leniusculus (intestinal bacteria, Hernandez-Perez et al., 2021). Given that microbial assemblages are often specific to certain organs of their hosts (Chomicki et al., 2020), symbioses have likely evolved in support of a specific function. The microbial assemblages associated with the guts of semi-terrestrial crabs have been proposed to aid in the adaptation of a low nitrogen, herbivorous diet during terrestrialization (Bui and Lee, 2015), like microbial assemblages of other aquatic invertebrates, e.g., isopods, where they enable the digestion of cellulose (Zimmer et al., 2002; O'Connor et al., 2014). The bacteria specifically associated with crab gills (Zhang et al., 2016, 2017) may facilitate ammonia excretion (Weihrauch et al., 2004), utilize gaseous CO2 (Morris, 2001), and buffer exposure to oxygen, which occurs at a concentration 30 times higher (Hsia et al., 2013) in the terrestrial compared to the marine environment where the host organism evolved. The microbiomes of both gut and gills could therefore provide terrestrial and semi-terrestrial crabs (here collectively called semi-/terrestrial) with means to cope with life in marine as well as in terrestrial environments. Whilst the presence of microbiomes and their role in buffering the stresses imposed on crabs by terrestrialization is beginning to be discussed (Bui and Lee, 2015; Cannicci et al., 2020), there are many unknowns. For example, the mode of bacterial acquisition, bacterial diversity, topological association, and the precise functions of their organ-specific microbial assemblages are still poorly understood, both for adult semi-/terrestrial crabs and their early life stages. Most semi-/terrestrial crab species, like their aquatic counterparts, have a biphasic life cycle including fully aquatic larvae, via which they transition to semi-/terrestrial juvenile/adult life (Anger, 1995; Hartnoll et al., 2014). Understanding microbial colonization of the larvae would likely provide critical insights into how these crabs have been able to move from water to land, and whether the bacteria themselves facilitate this transition.

Differences in the functional responses of four invasive and one native crayfish species suggest invader‐specific ecological impacts

AbstractInvasive non‐native species represent a leading threat to global freshwater biodiversity and non‐native crayfish species frequently cause extensive ecological damage. However, the extent to which their impact: (1) depends on invader identity and (2) differs from the natural state with native crayfish remains unclear. Comparison of the functional responses of invasive and native species represents a promising approach in this regard.Here, we explored whether four invasive crayfish species (calico crayfishFaxonius immunis, spiny‐cheek crayfishFaxonius limosus, signal crayfishPacifastacus leniusculus, and marbled crayfishProcambarus virginalis) in European freshwaters and the most widespread native species (noble crayfishAstacus astacus) overlap in function in their potential effects on key resources of benthic food webs. First, the impact on gammarids and zebra mussels was assessed by means of comparative functional response analysis using the functional response ratio as impact metric; second, the consumption of macrophytes (Charasp.) and detritus (leaf litter) was quantified and compared using feeding experiments.Both invader‐ and resource‐specific effects were observed. Invasive calico crayfish and signal crayfish exhibited the strongest per capita effects on gammarids and zebra mussels, respectively, with functional response ratios being 2‐fold higher than those of native noble crayfish. Marbled crayfish showed an intermediate effect on both prey species, whereas spiny‐cheek crayfish had lower impacts than noble crayfish. In the feeding experiment, calico crayfish consumed the highest amount of detritus, while the consumption of macrophytes did not differ among the five crayfish species.Our work demonstrates as‐yet unrecognised differences in functional responses among the four North American crayfish invaders and the European noble crayfish. The lack of congruence across the observed impacts suggests a mostly species‐specific pattern and stresses the importance of species and resource identity when considering the ecological impact of crayfish. An initial assessment of invader‐specific potential impacts positions calico crayfish and signal crayfish among the most impactful invaders.

Diet and trophic niche of the invasive signal crayfish in the first invaded Italian stream ecosystem

The occurrence of the signal crayfish Pacifastacus leniusculus in the Valla Stream was the first established population of this invasive species recorded in an Italian stream ecosystem. We evaluated the seasonality of diet and trophic niche of invasive signal crayfish in order to estimate the ecological role and effects on native communities of the stream ecosystem. We studied the differences in food source use between sexes, life stages and seasons using carbon and nitrogen stable isotope analyses. To supplement stable isotope analyses, we evaluated food source usage using traditional stomach content analysis. We tested the hypothesis that juveniles have a different diet, showing different trophic niches, compared to adults. Results indicated that signal crayfish adult and juvenile diets mainly rely on macroinvertebrates and periphyton in summer, shifting to mostly periphyton in autumn. Although the two age classes occupied an equivalent trophic niche, juveniles showed slightly different carbon isotope values, suggesting a somewhat ontogenetic shift consistent among seasons. No significant differences were found in adult and juvenile diets between summer and autumn seasons. Our findings suggest that signal crayfish juveniles and adults exhibited seasonal feeding habits, probably due to ecological behaviour rather than food resource availability, and that both are likely to impose similar effects on macroinvertebrate communities in this and similar stream ecosystems.

Patterns of infection in a native and an invasive crayfish across the UK

Invasive crayfish and the introduction of non-native diseases pose a significant risk for the conservation of endangered, white-clawed crayfish (Austropotamobius pallipes). Continued pollution of waterways is also of concern for native species and may be linked with crayfish disease dynamics. We explore whether crayfish species or environmental quality are predictors of infection presence and prevalence in native A. pallipes and invasive signal crayfish (Pacifastacus leniusculus). We use a seven-year dataset of histology records, and a field survey comparing the presence and prevalence of infectious agents in three isolated A. pallipes populations; three isolated P. leniusculus populations, and three populations where the two species had overlapped in the past. We note a lower diversity of parasites (Simpson’s Index) in P. leniusculus (‘Pacifastacus leniusculus Bacilliform Virus’ - PlBV) (n = 1 parasite) relative to native A. pallipes (n = 4 parasites), which host Thelohania contejeani, ‘Austropotamobius pallipes bacilliform virus’ (ApBV), Psorospermium haeckeli and Branchiobdella astaci, at the sites studied. The infectious group present in both species was an intranuclear bacilliform virus of the hepatopancreas. The prevalence of A. astaci in A. pallipes populations was higher in more polluted water bodies, which may reflect an effect of water quality, or may be due to increased chance of transmission from nearby P. leniusculus, a species commonly found in poor quality habitats.

English

Abstract Eroded swimmeret syndrome (ESS) was first described in 2014 from Swedish signal crayfish (Pacifastacus leniusculus (Dana)), and later also from Finland, with gross symptoms and disease agent candidates identified and described by 2015. The ESS was first discovered affecting alien signal crayfish in Fennoscandia. The ESS is caused by a multiple infection involving Aphanomyces astaci (Schikora) and Fusarium species complex (SC). The ESS symptoms include first melanised spots in swimmerets, then partial swimmeret erosion and finally loss of a swimmeret. There could be a total loss of all swimmerets in the most severe cases. Both females and males can be affected by the ESS. In females, the ESS lowers reproductive success while in males the ESS often causes erosion of the gonopods and thus possible partial failure in mating. The ESS is more frequent among mature females that have reproduced once compared to immature females or those that are mature but have not yet reproduced. The proportion of females with ESS has ranged from 10 to 50% among Lake Saimaa signal crayfish in Finland and in a wider survey from Sweden the range was from 0 to 38%. Among Lake Saimaa male signal crayfish, the ESS proportion has been less than 10%, while it was only 0.6% in the Swedish data. The ESS has also been observed among alien signal crayfish in Switzerland. There are recent observations of ESS affecting narrow-clawed crayfish, Pontastacus leptodactylus (Eschscholtz), in Croatia and Romania (i.e., among native European crayfish stocks). Here, we summarise current knowledge about the ESS and speculate on a few potentially crucial impacts of this syndrome.

The ‘Pritchard Trap’: A novel quantitative survey method for crayfish

Abstract As crayfish invasions continue to threaten native freshwater biota, a detailed understanding of crayfish distribution and population structure becomes imperative. Nonetheless, most current survey methods provide inadequate demographic data. The quantitative ‘Triple Drawdown’ (TDD) dewatering method has highlighted the importance of such data, yet practical constraints prevent its large‐scale application. Here, we introduce the ‘Pritchard Trap’, a novel passive sampling method that reliably generates quantitative crayfish population data while requiring substantially lower sampling effort than TDDs. This quadrat‐style sampler was extensively tested in headwater streams of North Yorkshire, England, along an invasion gradient for signal crayfish (Pacifastacus leniusculus) from well‐established sites to mixed populations of signal crayfish and native white‐clawed crayfish (Austropotamobius pallipes). The Pritchard Trap was trialled over several time intervals to determine the minimum required trap deployment time. TDDs at the same sites allowed for a robust evaluation of Pritchard Trap sampling accuracy in representing crayfish densities and population structure. The Pritchard Trap successfully sampled both invasive and native crayfish (8–42 mm carapace length). A minimum passive deployment time of 4 days was required. At low crayfish densities (0.5 individuals m−2), increased trapping effort was necessary to achieve accurate population density and size class distribution estimates. The Pritchard Trap required substantially less sampling effort (working hours) and resources than the TDD, whilst also posing less risk to non‐target species. The Pritchard Trap, for the first time, affords logistically simple, truly quantitative investigations of crayfish population demographics for headwater systems. It could be integrated into crayfish research and management, for example to explore density‐dependent ecological impacts of invasive crayfish and their management responses or to monitor populations and recruitment in native crayfish conservation initiatives.

Daily activity rhythms, chronotypes, and risk-taking behavior in the signal crayfish.

Consistent inter-individual differences in daily activity rhythms (i.e., chronotypes) can have ecological consequences in determining access to food resources and avoidance of predators. The most common measure to characterize chronotypes in animals as well as humans is the onset of activity (i.e., early or late chronotypes). However, daily activity rhythms may also differ in the relative amount of activity displayed at particular time periods. Moreover, chronotypes may also be linked to other consistent inter-individual differences in behavior (i.e., personality), such as the propensity to take risks. Here, we used the signal crayfish Pacifastacus leniusculus to test the presence of chronotypes and risk-taking personality traits and a potential behavioral syndrome between these traits. We first exposed crayfish to 5 days of light–darkness to measure daily activity rhythms and then we applied a visual predator-simulating stimulus in 2 different contexts (neutral and food). Our results showed consistent (i.e., across 5 days) inter-individual differences in the relative nocturnal activity displayed in the early and middle, but not in the late part of darkness hours. Moreover, while crayfish displayed inter-individual differences in risk-taking behavior, these were not found to be consistent across 2 contexts. Therefore, we were not able to formally test a behavioral syndrome between these 2 traits. In conclusion, our study provides the first evidence of chronotypes in the relative amount of activity displayed at particular time periods. This could be a valuable information for applied ecological aspects related to the signal crayfish, which is a major invasive species of freshwater ecosystems.

Detection of fish pathogen Saprolegnia parasitica in environmental DNA samples by droplet digital PCR

Oomycetes are fungal-like microorganisms parasitic towards a large number of plant and animal species. Genera from order Saprolegniales, such as Saprolegnia and Aphanomyces, cause devastating infections of freshwater animals. Saprolegnia parasitica is a widely distributed oomycete pathogen that causes saprolegniosis, a disease responsible for significant economic losses in aquaculture, as well as declines of natural populations of fish and other freshwater organisms. Despite its negative impact, no monitoring protocol for S. parasitica has been established to date. Thus, we aimed to develop a droplet digital PCR (ddPCR) assay for the detection and quantification of S. parasitica in environmental DNA samples. Saprolegnia parasitica-specific primers were designed to target internal transcribed spacer region 2 (ITS 2), based on the alignment of ITS sequences of S. parasitica and a range of Saprolegnia spp., as well as other oomycetes. The specificity of primers was tested using genomic DNA of S. parasitica (as positive control) and DNA of non–S. parasitica oomycete isolates, as well as trout/crayfish DNA (as negative control). The primers specifically amplified a segment of the ITS region of oomycete pathogen S. parasitica, while no amplification (i.e. no positive droplets) was obtained for closely related Saprolegnia spp. (e.g. Saprolegnia sp. 1 and S. ferax) and other more distantly related oomycetes. Next, the limit of detection (LOD) of the assay was established by using serial dilutions of the S. parasitica genomic DNA. The determined sensitivity of the assay was high: LOD was 15 fg of pathogen’s genomic DNA per µL of the reaction mixture. Assay performance was further assessed with environmental DNA samples isolated from water from the trout farms and natural environments, as well as (ii) biofilm from the host surface (swab samples). Water samples were collected from 21 different locations in Croatia, while swab samples were collected from S. parasitica host/carrier species: (i) skin and eggs of the rainbow trout (Oncorhynchus mykiss Walbaum, 1792) and brown trout (Salmo trutta Linnaeus, 1758), and (ii) cuticle of signal crayfish (Pacifastacus leniusculus Dana, 1852) and narrow clawed crayfish (Pontastacus leptodactylus Eschscholtz, 1823). Samples were classified into agent levels A0 to A6, depending of the number of S. parasitica ITS copies per ng of total DNA. Saprolegnia parasitica was detected in 76 % of water samples (16/21) and the range of pathogen’s ITS copies in positive samples was between 0.02 and 14 copies/ng of total DNA (agent levels A1 to A3). Regarding the swab samples, S. parasitica load was significantly higher in diseased trout than in those with healthy appearance: 9375 vs 3.28 S. parasitica copies/ng of total swab DNA (average agent level A6 vs. A2, respectively). Despite the fact that none of the sampled crayfish had signs of infection, the pathogen was detected in all tested cuticle swabs. Swabs of P. leniusculus, a known S. parasitica host, had significantly higher S. parasitica load than swabs of P. leptodactylus, S. parasitica carrier: 390 vs 83 S. parasitica copies/ng (agent level A5 vs. A4, respectively). In conclusion, our results demonstrate the applicability of the newly developed ddPCR assay in monitoring and early detection of S. parasitica in aquaculture facilities and natural freshwater environments. This would help in a better understanding of S. parasitica ecology and its effects on the host populations.

Modulation of endogenous antioxidants by zinc and copper in signal crayfish (Pacifastacus leniusculus)

Metal pollution is a long-standing concern and bioindicators are commonly used in ecotoxicological studies to monitor impacted wildlife populations for evidence of sublethal effects. Significant variation in the response of common biomarkers to metals is reported across taxa, thus necessitating careful characterization in model organisms. In this study, we describe the regulation of glutathione S-transferase (GST), glutathione (GSH), and metallothionein (MT) by zinc chloride (0.6, 0.9, 1.2, 2.4, 4.8, 9.6 μg g−1) and copper chloride (0.6, 0.9, 1.2 μg g−1) in signal crayfish (Pacifastacus leniusculus). Zinc chloride did not alter GST activity relative to controls in the hepatopancreas. Crayfish exposed to copper chloride exhibited decreased GST activity at the lowest dose tested (0.6 μg g−1) with no change observed at the higher doses. GSH did not change in response to either metal when sexes were grouped together. MT concentrations increased in response to zinc (2.4, 4.6, and 9.6 μg g−1 doses) and copper (0.6, 0.9, and 1.2 μg g−1 doses) in gill tissue. In tail tissue, MT increased at the 2.4 and 4.8 μg g−1 zinc chloride doses and all the concentrations of copper tested. Sex-specific differences in endogenous antioxidant expression were also analyzed with no clear patterns emerging. We concluded that these endpoints are sensitive to zinc and copper in signal crayfish, although careful interpretation is needed when applying them in field studies given the variation in responses, non-monotonic dose responses, and differences in biotic and abiotic factors that inevitably exist in different aquatic ecosystems.

Signal crayfish burrowing, bank retreat and sediment supply to rivers: A biophysical sediment budget

AbstractBurrowing into riverbanks by animals transfers sediment directly into river channels and has been hypothesised to accelerate bank erosion and promote mass failure. A field monitoring study on two UK rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes. Erosion pins were installed in 17 riverbanks across a gradient of crayfish burrow densities and monitored for 22 months. Bank retreat increased significantly with crayfish burrow density. At the bank scale (&lt;6 m river length), high crayfish burrow densities were associated with accelerated bank retreat of up to 253% and more than a doubling of the area of bank collapse compared with banks without burrows. Direct sediment supply by burrowing activity contributed 0.2% and 0.6% of total sediment at the reach (1.1 km) and local bank (&lt;6 m) scales. However, accelerated bank retreat caused by burrows contributed 12.2% and 29.8% of the total sediment supply at the reach and bank scales. Together, burrowing and the associated acceleration of retreat and collapse supplied an additional 25.4 t km−1 a−1 of floodplain sediments at one site, demonstrating the substantial impact that signal crayfish can have on fine sediment supply. For the first time, an empirical relation linking animal burrow characteristics to riverbank retreat is presented. The study adds to a small number of sediment budget studies that compare sediment fluxes driven by biotic and abiotic energy but is unique in isolating and measuring the substantial interactive effect of the acceleration of abiotic bank erosion facilitated by biotic activity. Biotic energy expended through burrowing represents an energy surcharge to the river system that can augment sediment erosion by geophysical mechanisms.

Risk of invasiveness of non-native aquatic species in the eastern Mediterranean region under current and projected climate conditions

Human-induced biological introductions pose a major threat to global biodiversity, and this is especially frequent in the eastern Mediterranean region, which is a globally important biodiversity hotspot area of high conservation value. To predict at which level introduced species in this region might become invasive under current and projected climate conditions, 232 non-native aquatic organisms were screened using the Aquatic Species Invasiveness Screening Kit. Based on receiver operative characteristic curve analysis, thresholds were identified to distinguish between low, medium and high risk species. The “top invasive” (very high risk) species identified were: brown bullhead Ameiurus nebulosus, blue crab Callinectes sapidus, gibel carp Carassius gibelio, Philippine catfish Clarias batrachus, Chinese mitten crab Eriocheir sinensis, bluespotted cornetfish Fistularia commersonii, silver carp Hypophthalmichthys molitrix, silver-cheeked toadfish Lagocephalus sceleratus, half-smooth golden pufferfish Lagocephalus spadiceus, Suez pufferfish Lagocephalus suezensis, signal crayfish Pacifastacus leniusculus, fathead minnow Pimephales promelas, channeled applesnail Pomacea canaliculata, red swamp crayfish Procambarus clarkii, devil firefish Pterois miles and European catfish Silurus glanis. The risk of being invasive of more than half of the screened species increased after taking global warming predictions into account, and several species considered to be globally invasive (cf. high risk) were classified as posing only a medium risk for the eastern Mediterranean region. Region-specific risk screenings, as implemented in this study, are therefore essential for setting priorities in preventative management for the conservation of key biodiversity hotspots and the optimal allocation of resources in view of full risk assessment for the species identified as (very) high risk.

Three crayfish species of different origin in a medium-sized river system: a new state of affairs

In view of contemporary changes in aquatic environments, determining the distribution of both native and emerging invasive crayfish species is increasingly important. In central Europe, the three invasive crayfish species of the signal crayfish Pacifastacus leniusculus (Dana, 1852), the spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817) and the red swamp crayfish Procambarus clarki (Girard, 1852) are of North American origin. The spiny-cheek crayfish was first brought to the southern Baltic basin at the end of nineteenth century, and its expansion ensued rapidly. At the same time, the indigenous species of the noble crayfish Astacus astacus (Linnaeus, 1758) began to disappear. The spread of the signal crayfish started in the second half of twentieth century; however, it has progressed strongly in recent years. Latest studies of fish fauna in the Drwęca River system, a tributary of the lower Vistula River, have simultaneously revealed new information on the occurrence of crayfish. The most widespread was spiny-cheek crayfish found at ten sites throughout the river basin. The second alien species, the signal crayfish, was noted in four locations in the upper part of the river system, but no mixed populations were noted. A particularly valuable result of the study was the discovery of an unknown site of noble crayfish in a small stream.

Vibrio areninigrae as a pathogenic bacterium in a crustacean

The occurrence of infectious diseases poses a significant threat to the aquaculture industry worldwide. Therefore, characterization of potentially harmful pathogens is one of the most important strategies to control disease outbreaks. In the present study, we investigated for the first time the pathogenicity of two Vibrio species, Vibrio metschnikovii, a foodborne pathogen that causes fatalities in humans, and Vibrio areninigrae, a bacteria isolated from black sand in Korea, using a crustacean model, the signal crayfish Pacifastacus leniusculus. Mortality challenges indicated that injection of V. metschnikovii (108 CFU/crayfish) has a mortality percentage of 22% in crayfish. In contrast, injection of P. leniusculus with 108 or 107 CFU of V. areninigrae resulted in 100% mortality within one and two days post-injection, respectively. V. areninigrae was successfully re-isolated from hepatopancreas of infected crayfish and caused 100% mortality when reinjected into new healthy crayfish. As a consequence of this infection, histopathological analysis revealed nodule formation in crayfish hepatopancreas, heart, and gills, as well as sloughed cells inside hepatopancreatic tubules and atrophy. Moreover, extracellular crude products (ECP’s) were obtained from V. areninigrae in order to investigate putative virulence factors. In vivo challenges with ECP’s caused >90% mortalities within the first 24 h. In vitro challenges with ECP’s of hemocytes induced cytotoxicity of hemocytes within the first hour of exposure. These findings represent the first report that V. areninigrae is a highly pathogenic bacterium that can cause disease in crustaceans. On the contrary, V. metschnikovii could not represent a threat for freshwater crayfish.

Prolonged phenanthrene exposure reduces cardiac function but fails to mount a significant oxidative stress response in the signal crayfish (Pacifastacus leniusculus)

Crustaceans are important ecosystem bio-indicators but their response to pollutants such as polyaromatic hydrocarbons (PAHs) remains understudied, particularly in freshwater habitats. Here we investigated the effect of phenanthrene (at 0.5, 1.0 and 1.5 mg L−1), a 3-ringed PAH associated with petroleum-based aquatic pollution on survival, in vivo and in situ cardiac performance, the oxidative stress response and the tissue burden in the signal crayfish (Pacifastacus leniusculus). Non-invasive sensors were used to monitor heart rate during exposure. Phenanthrene reduced maximum attainable heart rate in the latter half (days 8–15) of the exposure period but had no impact on routine heart rate. At the end of the 15-day exposure period, the electrical activity of the semi-isolated in situ crayfish heart was assessed and significant prolongation of the QT interval of the electrocardiogram was observed. Enzyme pathways associated with oxidative stress (superoxide dismutase and total oxyradical scavenging capacity) were also assessed after 15 days of phenanthrene exposure in gill, hepatopancreas and skeletal muscle; the results suggest limited induction of protective antioxidant pathways. Lastly, we report that 15 days exposure caused a dose-dependent increase in phenanthrene in hepatopancreas and heart tissues which was associated with reduced survivability. To our knowledge, this study is the first to provide such a thorough understanding of the impact of phenanthrene on a crustacean.

The effect of chronic exposure to chloridazon and its degradation product chloridazon-desphenyl on signal crayfish Pacifastacus leniusculus

The effects of chloridazon (Ch) and its metabolite chloridazon-desphenyl (Ch-D) at the environmentally relevant concentrations of 0.45 µg/L and 2.7 µg/L on signal crayfish Pacifastacus leniusculus were assessed in a 30-day exposure followed by a 15-day depuration period. Locomotion, biochemical haemolymph profile, oxidative and antioxidant parameters, and histopathology were evaluated. Crayfish exposed to Ch at 0.45 µg/L and 2.7 µg/L showed significantly (p < 0.01) higher CAT activity and GSH level in hepatopancreas and gill compared to controls. The concentration of Ch at 2.7 µg/L was associated with significantly (p < 0.01) higher levels of GLU, LACT, ALT, AST in haemolymph compared to controls. Chloridazon-desphenyl exposure at both tested concentrations caused significantly higher (p < 0.01) GLU, LACT, ALT, AST, NH3, and Ca in haemolymph; lipid peroxidation (TBARS) levels in hepatopancreas; and CAT activity and GSH level in hepatopancreas and gill. Alterations of structure including focal dilatation of tubules, increased number of fibrillar cells, and haemocyte infiltration in the interstitium were observed with 2.7 µg/L Ch and with both Ch-D exposures. Locomotion patterns did not vary significantly among groups. A 15-day recovery period was insufficient to restore normal physiological parameters in exposed groups. Chloridazon and its metabolite Ch-D exerts harmful effects on crayfish.

Selective fish passage: Restoring habitat connectivity without facilitating the spread of a non-native species

River managers are challenged to address two key threats to freshwater biodiversity. The first is the effects of habitat fragmentation by instream structures, such as dams and weirs, that disrupt migrations and impact species distributions. The second is the impact of non-native species on native species and ecological processes. However, mitigating anthropogenic habitat fragmentation through the installation of passage facilities can facilitate the invasion and spread of non-native species. This study compared the potential of two existing low-cost fish passage technologies designed for sloping weirs, a cylindrical bristle cluster (CBC) array and horizontally oriented studded tiles, to facilitate upstream movement of native European fish while preventing dispersal of non-native American signal crayfish (Pacifastacus leniusculus); thus providing a selective fish passage solution. Crayfish movement and passage was experimentally quantified at a Crump weir installed in a recirculating flume under two velocity regimes (low and high), without (control) and with the addition of either a CBC array or studded tiles. Results were compared to passage efficacy (PE) data for native fish species for both technologies (existing data). Most (84.4%) crayfish were active during the trials, exhibiting frequent up and downstream movements below the weir. During control conditions under the high velocity regime, high velocities (ca. 2.39 m s−1) prevented crayfish reaching the foot of the weir (PE: 0%). Under the low velocity regime, relatively low velocities (ca. 0.74 m s−1) at the weir crest prevented most crayfish from passing (PE: 10–16%). Crayfish movement speed and total distance moved were lower under the high than the low velocity regime. Neither fish pass technology improved crayfish maximum distance of ascent on the downstream weir face or PE under either velocity regime. Under comparable conditions to the high velocity regime tested here, previous studies have shown both technologies improve PE for native fish. Hence, both CBC arrays and studded tiles would likely function as suitable selective fish passes where the conservation objective is not to aid the spread of non-native crayfish. Additional passage inhibiting technologies will be required at sites where complete blockage of crayfish movement is required.