Crayfish Pacifastacus Leniusculus Research Articles

Escape rooms: behavioural response of two invasive crayfish species under water decline scenarios

Climate change and invasive alien species pose a significant threat to biodiversity and the survival of native species. This study considered the impact of drought conditions on the escape behaviour through terrestrial dispersal ability of two invasive freshwater crayfish species, the red swamp crayfish (Procambarus clarkii) and signal crayfish (Pacifastacus leniusculus). Using an experimental design simulating drought conditions and Mediterranean summer temperatures, we tested the hypothesis that P. clarkii exhibits a greater tendency to terrestrial migration and a higher land-walking speed than the P. leniusculus. The results indicated that both species demonstrated strong escape behaviour, with P. clarkii showing escape success higher than P. leniusculus, and increasing with decreasing mean night temperature and crayfish weight. Although drought conditions did not trigger escape, invasive species showed increased resistance and the ability to move to more favourable environments, suggesting that drought is not an effective geographic barrier against the spread of these species. These results underline the importance of considering invasive species' ability to escape and climb as part of management and control strategies.

An i-type lysozyme from a crustacean, Pacifastacus leniusculus, functions as a clot-destabilising enzyme

Lysozymes are hydrolytic enzymes, and they are ubiquitous among all living organisms. They are mostly associated with antibacterial properties through their muramidase activity, while other properties such as iso-peptidase activity are also common. Invertebrate-type (i-type) lysozymes include the enzyme Destabilase, which is present in the salivary secretions of the medicinal leach Hirundo medicinalis. Destabilase has the ability to hydrolyse the ε-(γ-glutamyl)-lysine iso-peptide bonds formed by transglutaminase in fibrin of vertebrate blood, thereby destabilising blood clots.We have identified an i-type lysozyme from the hemocytes of the freshwater crayfish Pacifastacus leniusculus, which was found to be upregulated at the protein level in response to an injection of the β-1,3-glucan laminarin. Based on its sequence we predicted that this lysozyme would lack muramidase activity, and therefore we decided to determine its putative immune function. The P. leniusculus i-type lysozyme (Pl-ilys), is a protein with 159 amino acid residues, including a 29 residue signal peptide, with a predicted molecular weight of 16 kDa and a predicted pI of 5.6. It is expressed primarily in the hemocytes and to a lesser extent in the hematopoietic tissue. A recombinant mature Pl-ilys using an E. coli expression system was produced, and we could ascertain that this enzyme was deficient of muramidase activity. Moreover, no iso-peptidase activity could be detected against the substrate l-γ-glutamine-p-nitroanilide. Analysis of the conserved domains in Pl-ilys showed a putative destabilase domain, and thus we tested the clot dissolving activity of this enzyme. We could show that the purified P. leniusculus clotting protein which had been coagulated and clotted with transglutaminase was dissolved by the addition of Pl-ilys. Taken together our results indicate that Pl-ilys has a clot dissolving or destabilising activity in crustacean blood.

Prevalence of the crayfish plague pathogen in red swamp crayfish populations in western France: How serious is the risk for the native white-clawed crayfish?

The crayfish plague pathogen Aphanomyces astaci has been implicated in a number of mass mortalities and irreversible population declines of native crayfish across Europe. At present, the reservoirs of the pathogen in Europe are mainly populations of invasive North American crayfish species. In southwestern Europe, including France, a particularly widespread invader is the red swamp crayfish Procambarus clarkii. Recent distribution data confirm that P. clarkii is present in at least 75 French departments, i.e. more than 78% of those in metropolitan France. We analysed the prevalence and pathogen load of A. astaci in 42 populations of this species in western France (Nouvelle Aquitaine region), where the species is most densely distributed, particularly in a wide range of environments around the Gironde estuary. The pathogen was detected by two different quantitative PCR assays in more than three quarters of the populations studied (34 out of 42); 163 out of 480 analysed crayfish individuals tested positive for the presence of A. astaci. In most cases, individual infection levels were very low, detectable with quantitative PCR but not sufficient for pathogen genotyping. In seven P. clarkii individuals from four populations, however, we were able to assess A. astaci variation by microsatellite markers and sequencing of mitochondrial markers. All these host specimens carried A. astaci genotype group D, haplotype d1, which has caused the majority of crayfish plague outbreaks in neighbouring Spain. In contrast, the French outbreaks genotyped to date (including eight newly analysed in this study) were mostly caused by strains of genotype group B, specific to the signal crayfish Pacifastacus leniusculus. Haplotype d1 found in P. clarkii was involved in one of the newly characterised outbreaks. Our study confirms that P. clarkii is a potentially important reservoir of the crayfish plague pathogen in France, but not the main source of the pathogen in mass mortalities of A. pallipes, probably due to different ecological requirements of the different invasive host crayfish. However, as P. clarkii continues to spread, the threat posed by this species to native crayfish is likely to increase.

Microcystins in the benthic food-web of the Sacramento-San Joaquin Delta, California

Harmful cyanobacteria blooms are a growing threat in estuarine waters as upstream blooms are exported into coastal environments. Cyanobacteria can produce potent toxins, one of which—hepatotoxic microcystins (MCs)—can persist and accumulate within the food web. Filter-feeding invertebrates may biomagnify toxins up to 100× ambient concentrations. As such, bivalves can be used as an environmentally relevant and highly sensitive sentinel for MC monitoring. To date there has been little research on cyanotoxin bioaccumulation in estuaries. The Sacramento-San Joaquin Delta (Delta) aquatic food web has undergone a profound change in response to widespread colonization of aquatic invasive species such as Asian clams (Corbicula fluminea) in the freshwater portion of the Delta. These clams are prolific—blanketing areas of the Delta at densities up to 1000 clams/m2 and are directly implicated in the pelagic organism decline of threatened and endangered fishes. We hypothesized that Asian clams accumulate MCs which may act as an additional stressor to the food web and MCs would seasonally be in exceedance of public health advisory levels. MCs accumulation in Delta Asian clams and signal crayfish (Pacifastacus leniusculus) were studied over a two-year period. ELISA and LC-MS analytical methods were used to measure free and protein-bound MCs in clam and crayfish tissues. We describe an improved MC extraction method for use when analyzing these taxa by LC-MS. MCs were found to accumulate in Asian clams across all months and at all study sites, with seasonal maxima occurring during the summer. Although MC concentrations rarely exceeded public health advisory levels, the persistence of MCs year-round still poses a chronic risk to consumers. Crayfish at times also accumulated high concentrations of MCs. Our results highlight the utility of shellfish as sentinel organisms for monitoring in estuarine areas.

Environmental DNA can inform the trade‐off between proactive and reactive strategies for crayfish conservation

AbstractThe introduction of the signal crayfish Pacifastacus leniusculus to British rivers has led to ecological degradation and the decline of the native white‐clawed crayfish Austropotamobius pallipes. To manage and mitigate the impact of the signal crayfish, conservation agencies and government bodies employ multiple conservation strategies. These take the form of proactive native crayfish breeding and stocking programs and reactive invasive crayfish control programs. Here, we used eDNA to assess the populations of native and invasive crayfish species across 50 sites in 10 river catchments in Norfolk, United Kingdom (UK). The sites were chosen to enable assessment of the potential of eDNA to inform proactive and reactive crayfish conservation strategies. Three of the catchments sampled were selected to assess the success of recent A. pallipes reintroduction, whereas the remaining seven were selected to better understand the distribution of each species at the landscape scale. Combining results of eDNA‐based methods with net searches within an occupancy model enabled us to confidently determine the presence of P. leniusculus at eight sites, and A. pallipes at three sites, which was more than visual searches alone (five and two study sites, respectively). Neither eDNA nor net searches detected A. pallipes at sites where A. pallipes had been reintroduced. We recommend that practitioners using eDNA‐based surveys for management and conservation of crayfish should consider: (1) designing eDNA surveys with an emphasis on large spatial scales to comprehensively describe the distributions of native and invasive crayfish in a region of interest; (2) work with local conservation organizations and/or government bodies to inform the selection of study sites to generate results that are meaningful to real‐world conservation actions; and (3) use results from eDNA‐based crayfish surveys to target limited conservation resources to appropriate proactive and/or reactive conservation actions.

Human Consumption of Non-Native Species in a Circular Economy: Determination of Persistent Organic Pollutants in the Invasive Signal Crayfish from a Baltic Coastal River and Its Assessment for Consumption

A circular economy aims at decoupling value creation from waste generation and resource use. The signal crayfish Pacifastacus leniusculus is kept worldwide in aquaculture and after escaping into the wild, may further be used for human consumption rather than eradicated and used for purposes such as fertilizing fields. The level of contamination by two groups of persistent organic pollutants (POPs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), in non-native signal crayfish from a Baltic coastal river, was measured in two locations (under anthropogenic pressure and semi-natural pressure) to understand whether its consumption might be a threat to human health. Concentrations of indicators and total compounds of POPs in the edible parts of crayfish (muscular tissue of crayfish) with potential human health risks were determined. The levels of concentrations of POPs meet the requirements of Regulations (EU) No. 836/2011 and No. 1259/2011 for the consumption of crustaceans. Our results also indicate no significant public health risk caused by consumption of the signal crayfish (hazard quotients (HQ) < 1). The results show that the bioaccumulation of POPs depends on the species’ traits and environment.

Accounting for the power of nature: Using flume and field studies to compare the capacities of bio‐energy and fluvial energy to move surficial gravels

AbstractRiver channels, riparian and floodplain forms and dynamics are all influenced strongly by biological processes. However, the influence of macroinvertebrates on entrainment and transport of river sediments remains poorly understood. We use an energy‐based approach to explore the capacity of benthic animals to move surficial, gravel‐bed particles in field and laboratory settings and use the results to assess the relative significance of biological and physical benthic processes. Our results showed that in 11 British gravel‐bed rivers, the maximum energy content (i.e., calorific content) of macroinvertebrate communities generally matched the flow energy associated with median discharges and, at multiple sites, exceeded that of the 10‐year return interval flood. A series of laboratory experiments used to estimate the minimum energy expended by signal crayfish (Pacifastacus leniusculus) when performing geomorphic work established that crayfish move gravel particles at energy levels below that expected of the flow, complicating direct comparisons of the capacity for macroinvertebrates and fluvial flows to influence bed mobility. Our findings suggest that the influence of macroinvertebrate communities in either promoting or suppressing, the mobilisation of the bed may be large compared to equivalent values of fluvial energy. Based on these findings, we conclude that in the gravel‐bed rivers studied, the macroinvertebrate community's potential to perform geomorphic work matches or exceeds the stream power during most of the year. Although our study examined biological and fluvial energy systems separately, it is important to recognise that in nature, these systems are highly interactive. It follows that utilising the energy framework presented in this paper could lead to rapid advances in both fluvial biogeomorphology and river management and restoration.

Plastic Debris in the Stomach of the Invasive Signal Crayfish Pacifastacus leniusculus from a Baltic Coastal River

The signal crayfish Pacifastacus leniusculus is one of the most widespread non-indigenous crayfish in Europe and is of interest to aquaculture in many countries. Once they escape into the wild, they disperse and become a potential source of food exploited for consumption by local inhabitants. The ingestion of plastics by the invasive signal crayfish in the Wieprza River, a tributary to the Baltic Sea, was determined by the FTIR identification of plastic compounds found in stomachs. The occurrence of plastic debris in the stomachs of P. leniusculus is reported for the first time. Plastic particles with the size range between 70 and 450 µm were observed only among crayfish inhabiting the lower, urbanized part of the river (7.3% of specimens). The presence of PTFE (polytetrafluoroethylene), cellophane, PP (polypropylene), PE (polyethylene), PMMA (polymethyl methacrylate), and nylon was confirmed with the highest frequency of PTFE in the stomachs of crayfish. Fibres were the predominant type of microplastics in crayfish stomachs. The results indicated the size-selective uptake and ingestion of plastics depending on the traits of the species and environment.

Long-term decline of whitefish (Coregonus lavaretus) population in the boreal lake Pyhäjärvi, southwest Finland, relative to simultaneous abiotic and biotic changes

In recent decades many lake fish populations have faced complex pressures particularly due to climate warming and eutrophication. In Lake Pyhäjärvi, southwest Finland, profound changes have occurred in the commercial winter fisheries targeting the coregonids vendace, Coregonus albula, and whitefish, Coregonus lavaretus. The responses of vendace have been examined earlier, and here the detailed analyses are extended to the whitefish. In the 1970s and 1980s, the coregonid fishery was sustainable, but in 1991–1998, intense exploitation led to recruitment overfishing of vendace. Despite temporarily improved growth and recruitment of whitefish during vendace decline, whitefish population biomass declined throughout the study period, while perch (Perca fluviatilis), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernuus) increased and vendace and smelt (Osmerus eperlanus) maintained their abundance. As many other northern lakes, Pyhäjärvi seems to be changing from coregonid to perch dominance due to climate warming and eutrophication. Whitefish decline was associated with decreases in fecundity, winter survival of embryos, and larval density. The spawning stock was kept small by intensive fishery. The decline of the relative fecundity was likely due to food competition with vendace and especially the perch and roach populations that increased with eutrophication and more frequent hot summers. The winter survival of whitefish embryos decreased when the introduced signal crayfish (Pacifastacus leniusculus) increased. Despite decreasing fishing effort in the 2000s the larval numbers continued to decline. In the prevailing circumstances in Pyhäjärvi, whitefish will with high probability remain as a minor and still declining species of the fish assemblage.

Host-related traits influence the microbial diversity of the invasive signal crayfish Pacifastacus leniusculus

The microbiome influences a variety of host-environment interactions, and there is mounting evidence of its significant role in biological invasions. During invasion, shifts in microbial diversity and function can occur due to both changing characteristics of the novel environment and physiological condition of the host. The signal crayfish (Pacifastacus leniusculus) is one of the most successful crayfish invaders in Europe. During range expansion, its populations often exhibit differences in many traits along the invasion range, including sex-composition, size-structure and aggressiveness, but to date it was not studied whether crayfish traits can also drive changes in the host microbiome. Thus, we used 16S rRNA gene amplicon sequencing to examine the effects of host-related traits, namely total length (TL), body condition index (FCF), hepatosomatic index (HSI) and sex on the microbial diversity of the signal crayfish. We examined both external (exoskeletal) and internal (intestinal, hepatopancreatic, hemolymph) microbiomes of 110 signal crayfish individuals from four sites along its invasion range in the Korana River, Croatia. While sex did not exhibit a significant effect on the microbial diversity in any of the examined tissues, exoskeletal, intestinal and hemolymph microbial diversity significantly decreased with increasing crayfish size. Additionally, significant effects of signal crayfish condition (FCF, HSI) on microbial diversity were recorded in the hepatopancreas, a main energy storage organ in crayfish that supports reproduction and growth and also regulates immune response. Our findings provide a baseline for evaluating the contribution of microbiome to an invader's overall health, fitness and subsequent invasion success.

Estimating recreational trap‐fishing effort for crayfish from zig‐zag line transects, drone surveys and enforcement surveys

AbstractEstimates of recreational fishing effort and catch are needed to inform fisheries management, but such estimates can be challenging to obtain. We combined a zig‐zag line transect survey of buoys, a fisheries enforcement survey and a drone survey to estimate recreational effort in the open‐access trap fishery for signal crayfish (Pacifastacus leniusculus) in the sixth largest lake in Europe, Lake Vättern, Sweden. Using supporting variables such as size of nearby ports and bathymetry, our model‐assisted estimate of total effort was 6400 (±4300 CI) buoys during the three‐weekend season. Using the frequency of buoys to traps as a constant, the total number of crayfish traps was estimated to be 25,500 (±17,000 CI). The sampling design and methods presented are useful for ecologists and resource managers to design future multi‐source surveys of recreational trap fishing effort.

Toxicological effects of diclofenac on signal crayfish (Pacifastacus leniusculus) as related to weakly acidic and basic water pH

The widespread use and continuous discharge of pharmaceuticals to environmental waters can lead to potential toxicity to aquatic biota. Pharmaceuticals and their metabolites are often complex organic and environmentally persistent compounds that are bioactive at low doses. This study aimed to investigate the effects of diclofenac (DCF) on the antioxidant defence system and neurotoxicity biomarkers in signal crayfish (Pacifastacus leniusculus) under weakly acidic and basic conditions. Crayfish were exposed to 200 µg/L of DCF at pH 6 and 8 for 96 h and subsequently underwent the depuration phase for 96 h. Gills, hepatopancreas, and muscle were sampled after the exposure and depuration phases to assess the toxicological biomarker responses of DCF in crayfish by evaluating lipid peroxidation (LPO) levels, activities of antioxidant enzymes and acetylcholinesterase. After the exposure phase, the hemolymph DCF concentration was detected one order higher at pH 6 than at pH 8. The DCF was subsequently fully eliminated from the hemolymph during the depuration phase. Our results showed that DCF caused alteration in the activities of six of the seven tested biomarkers in at least one crayfish tissue. Although exposure to DCF caused imbalances in the detoxification system on multiple tissue levels, it was regenerated to a balanced state after the depuration phase. Integrated biomarker response (IBRv2) showed that the highest toxicological response to DCF exposure was elicited in the gills, whereas the hepatopancreas was the highest-responding tissue after the depuration phase. Exposure to DCF at pH 6 caused higher toxicological effects than at pH 8; however, crayfish antioxidant mechanisms recovered more quickly at pH 6 than at pH 8 after the depuration phase. Our results showed that water pH influenced the toxicological effects of DCF, an ionisable compound in crayfish.

Models based on chronological data correctly predict the spread of freshwater aliens, and reveal a strong influence of river access, anthropogenic activities and climate regimes

Alien species constitute one of the main threats to freshwater ecosystems, negatively impacting biodiversity, economy, biosecurity and ecosystem services. Predicting the arrival and spread of alien species is of paramount importance to prevent new introductions and control the expansion and establishment of already introduced species. We modelled the distribution of four freshwater invaders in Great Britain, using environmental and anthropogenic predictors, to help focus management actions. The species grouped different taxa including signal crayfish (Pacifastacus leniusculus), the marsh frog (Pelophylax ridibundus), the red-eared slider (Trachemys scripta) and the pike-perch (Sander lucioperca). The modelling approach accounted for methodological limitations and implemented two evaluations, a temporal evaluation using data corresponding to 70% of the oldest records to calibrate models and the remaining 30% for evaluation using various performance metrics (the common AUC, TSS and also null models) and an independent evaluation using the most recent range expansion of the species in the last six years. The distribution of the species was facilitated by multiple environmental and anthropogenic predictors. Road density was the second most important predictor of the occurrence of signal crayfish and red-eared slider preceded by the distance to ports and isothermality for each species respectively. Human population density was the most important predictor of marsh frog presence whereas pike-perch was mostly related to the proximity of boat ramps and precipitation regimes. Our distribution models were accurate and predicted the most recent range expansion of all of the species, highlighting their usefulness for preventing alien species spread and the value of using historical projections, usually available for non-native species, to calibrate and evaluate Species Distribution Models.

Predation risk by largemouth bass modulates feeding functional responses of native and non-native crayfish

Context-dependency is prevalent in nature, challenging our understanding and prediction of the potential ecological impacts of non-native species (NNS). The presence of a top predator, for example, can modify the foraging behaviour of an intermediate consumer, by means of non-consumptive effects. This raises the question of whether the fear of predation might modulate consumption rates of NNS, thus shaping the magnitude of ecological impacts. Here, we quantified the functional feeding responses of three non-native crayfish species – red swamp crayfish Procambarus clarkii, rusty crayfish Faxonius rusticus and virile crayfish Faxonius virilis – compared to the native analogue signal crayfish Pacifastacus leniusculus, considering the predation risk imposed by a top fish predator, the globally invasive largemouth bass Micropterus salmoides. We applied the comparative functional response (FR) approach using snails as prey and exposing crayfish to water containing predator and dietary chemical cues or not. All crayfish species presented a destabilising Type II FR, regardless of the presence of chemical cues. Predation risk resulted in significantly longer handling times or lower attack rates in non-native crayfish; however, no significant differences were observed in signal crayfish. We estimated per capita impacts for each species using the functional response ratio (FRR; attack rate divided by handling time). The FRR metric was lower for all crayfish species when exposed to predation risk. Rusty crayfish demonstrated the highest FRR in the absence of chemical cues, followed by signal crayfish, virile crayfish and red swamp crayfish. By contrast, the FRR of signal crayfish was nearly twice that of rusty crayfish and virile crayfish and ten times greater than red swamp crayfish when chemical cues were present. The latter result agrees with the well-recognised ecological impacts of signal crayfish throughout its globally-introduced range. This study demonstrates the importance of considering the non-consumptive effects of predators when quantifying the ecological impacts of intermediate non-native consumers on prey. The direction and magnitude of the modulating effects of predators have clear implications for our understanding of NNS impacts and the prioritisation of management actions.

The long-term dynamics of invasive signal crayfish forcing of fluvial sediment supply via riverbank burrowing

Animals are important drivers of sediment dynamics. Invasive signal crayfish (Pacifastacus leniusculus) have been shown to supply sediment to rivers by burrowing into riverbanks. Burrowing directly transfers excavated sediment into the river and also has an additional indirect affect by promoting riverbank failure. While previous research has isolated burrow densities at a point in time, rates of burrow construction and of burrow loss due to erosion are unknown, which introduces uncertainty into estimates of how much sediment burrows contribute to rivers. Here we report results from a 5-year study that evaluated the temporal dynamics of crayfish populations, rates of burrow loss due to erosion, and the mass of sediment directly supplied to rivers by burrow excavation. At ten reaches across five lowland streams in England, we estimated the mass of sediment displaced by 1861 new and previously constructed burrows. Both crayfish and burrow densities were variable over time, suggesting that burrows contribute temporally variable amounts of fine sediment to riverine systems. 42 % of observed burrows were constructed within the previous 365 days, and individual burrows lasted on average 461 days. Applying this to comparable historical data, an average of 2.0 t km−1 a−1 of sediment was excavated to construct burrows in the study reaches, which is eight times more than estimated in previous studies. Whilst total burrow densities in each year were not consistently correlated with contemporary crayfish densities, the mass of sediment excavated over the prior year was strongly correlated with contemporary crayfish densities. Current fine sediment management practices are largely aimed at controlling fine sediment delivery, predominately from agricultural activities, but biotic burrowing into riverbanks may represent an important and overlooked source of fine sediment supply. Incorporation of biotic processes in sediment dynamics would improve the accuracy of fluvial sediment budgets and enhance the knowledge base underpinning effective fine-sediment management practices.

Comparison of exoskeleton microbial communities of co-occurring native and invasive crayfish species

Host-associated microbial communities are an important determinant of individual fitness and have recently been highlighted as one of the factors influencing the success of invasive species. Invasive hosts introduce their microbes into the new environment, and then both the host and its associated microbes enter into a series of interactions with the native macroscopic and microscopic biota. As these processes are largely unexplored, we aimed to compare the exoskeletal microbial communities of co-occurring and phylogenetically related crayfish: the native narrow-clawed crayfish Pontastacus leptodactylus and the invasive signal crayfish Pacifastacus leniusculus from the recently invaded Korana River, Croatia. The results of high-throughput 16S rRNA sequencing showed that the exoskeletal microbiome of both species is very diverse, significantly influenced by the local environment and dominated by low abundance bacterial families from the phylum Proteobacteria. Furthermore, the exoskeletal microbiomes of the crayfish species differed significantly in the composition and abundance of Amplicon Sequence Variants (ASVs), suggesting that they are to some extent shaped by species-specific intrinsic factors, despite sharing a common habitat. However, over 95% of the bacterial genera associated with the exoskeleton were detected in the exoskeleton samples of both native and invasive crayfish. We paid particular attention to two known crayfish pathogens, Aphanomyces astaci and Saprolegnia parasitica, and find that both species carry low amounts of both pathogens. On the side, we find that a non-standard ddPCR protocol outperforms standard qPCR test for A. astaci under low concentration conditions. Taken together, our results indicate the possibility of bidirectional mixing and homogenisation of exoskeleton microbiome. As such, they can serve as a baseline in future detangling of the processes that act together to shape the microbiomes of co-occuring native and invasive congeners during biological invasions.

The signal crayfish Pacifastacus leniusculus (Dana, 1852) (Crustacea, Decapoda) is threatening the near future of Margaritifera margaritifera Linnaeus, 1758 (Bivalvia, Unionoida) in the Negro River (NW Zamora, Spain)

We studied the incidence of the signal crayfish on a population of Margaritifera margaritifera in the Negro River (Zamora, Spain) during the summers of 2019 to 2022. The incidence of predation was assessed as a mortality factor in relation to floods and the hydrology of the river. The crayfish were trapped in a small plot of high pearl mussels density monitored since 2002, and collected each summer since 2019, during which time their abundance increased (65 % in three years). Simultaneously, we counted the shells carried by the floods to the gravel riverbanks. The incidence of floods was stable between 2019 and 2022 (10.3 % to 19.4 % of mortality), while at the bottom of the river the mortality of pearl mussels increased due to predation from 2.7 % to 43.3 %. During the 2022 dry season, 29 pearl mussels that had recently died and whose shell edges were widely gnawed by crayfishes were collected from the plot. The shells appeared bitten only in the contour exposed above the gravel, ruling out the possibility that the marks could be the effect of the scavenging of dead specimens by the crayfish. Low intensity trapping barely affected the crayfish population, since the following year their abundance in the controlled section had recovered.

Niche dynamics along two centuries of multiple crayfish invasions.

The realised ecological niches of species may change in response to dynamic abiotic and biotic environments, particularly under fast global change. To fully understand the dynamics of niche features and their drivers, it is essential to have a long-term view of species distributions and the factors that may have influenced them. Here, we analysed the distribution and niche dynamics of the Italian crayfish (Austropotamobius fulcisianus) in the Iberian Peninsula over the past 200 years. The Italian crayfish was introduced to Spain in the 16th century, and spread due to multiple stocking events until the 1970s, when two North American crayfish (red swamp crayfish Procambarus clarkii, and signal crayfish Pacifastacus leniusculus) were introduced. Both North American species are carriers of a pathogen (Aphanomyces astaci, the causal agent of crayfish plague) lethal to the Italian crayfish. We hypothesised that the realised niche of the Italian crayfish, both in breadth and in position, has changed over time following changes in its range. The distribution of the Italian crayfish expanded from the mid-19th century until the mid-20th century, in association with an enlargement of its realised niched, mostly towards less abrupt and more coastal-influenced areas. After the introduction of the North American crayfishes, the collapse of the Italian crayfish involved a niche shift towards rough terrains in mountain areas. North American crayfish have eventually occupied most of the Italian crayfish's niche space, with the few no-coexistence areas being relegated to the most abrupt and high-elevation territories. Our historical approach allowed us to document and understand the highly dynamic distribution and niche of the Italian crayfish in the presence of invader counterparts, and to explore the environmental conditions under which their coexistence is minimised.

Finding of the American Signal Crayfish <i>Pacifastacus leniusculus</i> (Decapoda: Astacidae) in the Leningrad Region (Russia)

The American signal crayfish Pacifastacus leniusculus (Dana, 1852) was first found in the lake Zaprudnoye of the Saimaa Canal system between lake Saimaa (Finland) and Vyborgsky Bay (Russia). The Saimaa Canal belongs to a large lake-river network connecting the waters of the Gulf of Finland and Lake Ladoga. On this basis, a wide distribution of P. leniusculus is predicted in the water bodies of the Leningrad Region and the North-West of Russia as a whole. The captured part of the population was 9 individuals. The sex ratio in the population was significantly biased toward males: 8 ♂ и 1 ♀.

Investigating the Allometric Relationship for Total Mercury in Male and Female Signal Crayfish (Pacifastacus leniusculus) from Three Regions in the Columbia River Basin, USA.

The objective of this study was to evaluate the relationship between clawless body mass (CBM) and total mercury concentration (THg) in male and female crayfish captured from three different sites in the Columbia River Basin: the Spokane River, Boise River and Hangman Creek. It was found that the allometric relationships for THg in male and female crayfish did not differ from one another at any of the three locations (Spokane River: ANCOVA, F1,49 = 0.001, p = 0.63; Hangman Creek: ANCOVA, F1,73 = 0.007, p = 0.93; Boise River: ANCOVA, F1,38 = 0.02, p = 0.88. Furthermore, the slopes of the CBM and THg regression lines were not significantly different from one site to the next (ANCOVA, F2,166 = 1.5 p = 0.24), despite considerable differences in mean mass-adjusted THg across locations (Spokane River: 26.8 ± 2.6; Hangman Creek: 75.2 ± 2.1; Boise River: 99.0 ± 2.9). For signal crayfish (Pacifastacus leniusculus) from the Columbia River Basin, size and sex standardization can be accomplished with a single linear relationship.