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

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

Genome survey sequencing of red swamp crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Red swamp crayfish, Procambarus clarkii, presently is an important aquatic commercial species in China. The crayfish is a hot area of research focus, and its genetic improvement is quite urgent for the crayfish aquaculture in China. However, the knowledge of its genomic landscape is limited. In this study, a survey of P. clarkii genome was investigated based on Illumina’s Solexa sequencing platform. Meanwhile, its genome size was estimated using flow cytometry. Interestingly, the genome size estimated is about 8.50 Gb by flow cytometry and 1.86 Gb with genome survey sequencing. Based on the assembled genome sequences, total of 136,962 genes and 152,268 exons were predicted, and the predicted genes ranged from 150 to 12,807 bp in length. The survey sequences could help accelerate the progress of gene discovery involved in genetic diversity and evolutionary analysis, even though it could not successfully applied for estimation of P. clarkii genome size.     

An invaded invader: high prevalence of entocytherid ostracods on the red swamp crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis> (Girard, 1852) in the Eastern Iberian Peninsula

The American red swamp crayfish Procambarus clarkii (Girard, 1852) was introduced in 1973 into the Iberian Peninsula for commercial purposes. As a result of both the expansion from the Iberian Peninsula and, probably, further introductions in other European countries, now it is widely distributed throughout much of Europe. The ecological impacts of this invading crayfish have received increasing attention, but nothing is known about its symbiotic entocytherid ostracods outside the American continent. The present survey has examined more than 200 crayfishes from 12 localities distributed over a wide area of Eastern Spain. Entocytherid ostracods were extracted from individual crayfishes and they were identified, counted, assigned to developmental instars and sexed. In all the study locations but one, we found at least one crayfish individual infected by entocytherid ostracods and the species determined was the same in all cases: Ankylocythere sinuosa (Rioja, 1942). The number of ostracods on individual P. clarkii varied notably in relation to crayfish size and also differed significantly among sampling sites. The crayfish size effects on ostracod densities might be related to the amount of resources and to the crayfish age and moulting frequency affecting ostracod distribution and population structure. In addition, the spatial variation in ostracod densities could also be related to site-specific habitat traits and the variability of crayfish population dynamics. Our study represents the first citation of an alien entocytherid species in Europe and demonstrates its wide distribution in the Iberian Peninsula. Further research is needed to know the potential effects of this ostracod species on the ecology of P. clarkii and of native species, with implications on the management of this aquatic invader.     

Effects of an introduced crayfish, Procambarus clarkii, on the distribution of south-western Iberian amphibians in their breeding habitats

The introduction of exotic species in aquatic habitats is one of the causes for the amphibian declines observed worldwide. In the 1970s, the red swamp crayfish Procambarus clarkii was introduced in the southwest Iberian Peninsula, where no native crayfish occur. In this study we assess the effect of P. clarkii presence in the breeding site distribution of each of the 13 southwest Iberian amphibians, while simultaneously accounting for the effects of potentially confounding habitat variables, as well as for the effects of the other large aquatic predators in the study area – predatory fish. Amphibian species richness was lower in places where P. clarkii was present than in places without P. clarkii , regardless of fish presence. After accounting for habitat variables and fish, crayfish presence was a negative predictor of the breeding probability for all urodeles ( Pleurodeles waltl , Salamandra salamandra , Triturus boscai and T. marmoratus ) and for two anurans ( Pelobates cultripes and Bufo bufo ). The majority of the species affected usually breed in temporary ponds without fish, but that may be colonized by the crayfish. The ongoing expansion of P. clarkii may eventually lead to a growing isolation of amphibian populations and ultimately to local extinctions and a permanent alteration of the amphibian communities in southwest Iberian Peninsula.     

Bivalve or gastropod? Using profitability estimates to predict prey choice by <Emphasis Type="Italic">P. clarkii</Emphasis>

Recently, a highly invasive alien species, the zebra mussel Dreissena polymorpha, has colonized Italian aquatic ecosystems that had been previously colonized by another highly invasive alien species—the North American crayfish Procambarus clarkii. This was the first time and world region where these two species met. To evaluate the relative importance of their interactions, we studied prey selection according to its length, as well as prey choice by P. clarkii preying on D. polymorpha in the presence and absence of alternative prey—the freshwater snail Physella acuta. We followed an optimability-based approach, by first estimating the most profitable length of each mollusc and then by conducting a prey choice experiment, on which both species were provided simultaneously to a crayfish with different size combinations. Prey selection was dependent on prey length, handling time and crayfish length for both molluscs. According to our profitability estimates, snails should be more profitable than mussels in the length range 7–10 mm, while for lengths over 11.0 mm, mussels should be more profitable. The results of the prey choice experiment indicated that D. polymorpha length, P. acuta length, and the difference in profitability between the offered individuals were all relevant for the choice of one species over the other by P. clarkii. However, the overall tendency was the choice of the smallest prey, regardless of species, and the estimates of prey profitability were not useful to predict prey choice. Our study shows that D. polymorpha represents a novel prey resource for P. clarkii, even in the presence of an alternative prey, and that zebra mussels may be a preferred prey, especially small-sized individuals (5–10 mm).     

Enhanced ecological indication based on combined planktic and benthic functional approaches in large river phytoplankton ecology

Environmental DNA (eDNA) is a powerful method for assessing the presence and distribution of invasive aquatic species. We used this tool to detect and monitor several invasive crayfishes Procambarus clarkii, Orconectes limosus and Pacifastacus leniusculus present in, or likely to invade, the ponds of the Brenne Regional Natural Park. A previous study showed that the eDNA method was not very efficient in detecting P. clarkii. In the present study, we explored new improvements in the detection of invasive crayfish. We designed specific primers for each crayfish species, and set up an experimental mesocosm approach to confirm the specificity of the primers and the sampling protocol. We analysed samples taken from ponds in 2014 and 2015. We compared two qPCR protocols involving either SybrGreen or TaqMan assays. Using these same primers, we were able to detect crayfish eDNA with both assays during the mesocosm experiment. However, crayfish from field samples could only be detected by performing qPCR with a SybrGreen assay. We successfully monitored the presence of three invasive species of crayfish using eDNA. This method is a powerful tool for establishing the presence or absence of invasive species in various freshwater environments.     

Positive selection of beautiful invaders: long-term persistence and bio-invasion risk of freshwater crayfish in the pet trade

After interest in keeping crayfish (Crustacea, Decapoda, Astacida) in home aquaria peaked in the mid-2000s, the aquarium trade has become a novel introduction pathway for non-native crayfish species in Germany. Here, we provide an update on the ornamental crayfish trade approximately one decade after the ‘crayfish hype’ to explore the long-term implications in terms of bio-invasion risk. Specifically, species’ availability in e-commerce and potential invasiveness were assessed and compared to previous studies. Morphological and ecological traits of the offered species were compiled and related to their long-term availability (covering 2005–2015). In July 2015, a total of 31 online shops offered 28 crayfish species, which represents a decline of 24 % in species diversity compared to the late 2000s. The estimated rate of import of new species has considerably flattened and approaches pre-hype values (<1 species year^?1). However, the risk associated with the offered species, as assessed by a risk screening tool, has not decreased compared to the late 2000s. Long-term availability in the trade was primarily determined by bright coloration, the ability to reproduce under warm aquarium conditions, and a preference for lentic habitats. Species featuring such traits are likely to persist in the aquarium trade and include four high-risk species, most notably invasive and crayfish plague-carrying red swamp crayfish (Procambarus clarkii) and Marmorkrebs (Procambarus fallax f. virginalis). Persistent propagule pressure from aquaria has substantially contributed to the establishment of both species in Germany, stressing the need for more effective pathway management.     

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

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

Historical,human, and environmental drivers of genetic diversity in the red swamp crayfish (Procambarus clarkii) invading the Iberian Peninsula

1. Patterns of genetic diversity in invasive populations can be modulated by a range of factors acting at different stages of the invasion process, including the genetic composition of the source population(s), the introduction history (e.g. propagule pressure), the environmental suitability of recipient areas, and the features of secondary introductions.
2. The North American red swamp crayfish, Procambarus clarkii, is one of the most widely introduced freshwater species worldwide. It was legally introduced into Spain twice, near the city of Badajoz in 1973 and in the Guadalquivir marshes in 1974. Thereafter the species rapidly colonised almost the entire Iberian Peninsula.
3. We used seven nuclear microsatellites to describe the genetic diversity and structure of 28 locations distributed across the Iberian Peninsula and to explain the expansion process of the red swamp crayfish. Additionally, we analysed the relationship between environmental suitability and genetic diversity of the studied locations.
4. The red swamp crayfish had a clear spatial genetic structure in the Iberian Peninsula, probably determined by the two independent introduction events in the 1970s, which produced two main clusters separated spatially, one of which was dominant in Portugal and the other in Spain.
5. The human-mediated dispersal process seemed to have involved invasion hubs, hosting highly genetically diverse areas and acting as sources for subsequent introductions. Genetic diversity also tended to be higher in more suitable environments across the Iberian Peninsula .
6. Our results showed that the complex and human-mediated expansion of the red swamp crayfish in the Iberian Peninsula has involved several long- and short-distance movements and that both ecological and anthropogenic factors have shaped the genetic diversity patterns resulting from this invasion process. Early detection of potential invasion hubs may help to halt multiple short-distance translocations and thus the rapid expansion of highly prolific invasive species over non-native areas.

     

Temporary pond ecosystem functioning shifts mediated by the exotic red swamp crayfish (<Emphasis Type="Italic">Procambarus clarkii</Emphasis>): a mesocosm study

Temporary ponds, acknowledged for their conservation value, are colonized by the invasive crayfish Procambarus clarkii. We have tested the consequences of this colonization for the ecosystem under two contrasted scenarios: one single individual arrival or three individuals arrival. We recreated the temporary pond ecosystem in 1 m² tanks to investigate the impact of the two crayfish densities. We studied the macrophyte community composition and abundance, chlorophyll a and total suspended solids concentrations, and the diversity and functional composition of micro-crustacean and macro-invertebrate communities. We observed a reduction of macrophyte biomass in experimental crayfish mesocosms in comparison with control tanks, nearly 80 and 40% less in 3 and 1 crayfish/m² tanks, respectively. The macrophyte community shifted, followed by a filamentous algae development, an increase of bare sediment and turbidity in crayfish tanks. The macro-invertebrate community suffered a richness loss of 28 and 22%, in 3 and 1 crayfish/m² tanks, respectively. Functionally, macro-invertebrate diversity reduction most strongly affected the grazer, detritivore and predator trophic groups. Microcrustaceans seemed not to be affected by the introduction of the crayfish. The introduction of the crayfish greatly altered the ecosystem structure and subsequently the ecosystem functioning.     

Factors determining active dispersal capacity of adult Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis> (Decapoda,Varunidae)

The Chinese mitten crab (Eriocheir sinensis) is an invasive crustacean with a widespread distribution, sometimes overlapping with the red swamp crayfish (Procambarus clarkii). E. sinensis performs long river migrations, often moving overland to cross obstacles, but the factors affecting its movement are not well known. We studied its movement speed in and out of water, the survival time out of water and also its interaction with the red swamp crayfish during dispersal. At 16°C the LT₅₀ (time to death of 50% of the individuals) was 70 h, with a mean weight loss of 20%, and at 24°C the LT₅₀ was 31 h, with a mean 22% weight loss. In and out of the water, these crabs moved with mean velocities of 0.074 and 0.016 m s^?1, respectively. P. clarkii did not affect the dispersion of E. sinensis. This crab was able to disperse under various environmental conditions and its speed was affected by density, temperature, relative humidity, carapace length, and condition of the individuals (Fulton index). Moreover, we found that this species has a great capacity to resist desiccation. These characteristics give them all the requirements to successfully invade and adapt to new areas.     

What drives <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> natural establishment outside plantations? The relative importance of climate,plantation and site characteristics

Eucalyptus globulus has great economic importance in the Iberian Peninsula and is now the most widespread tree species on the Portuguese mainland. We aimed to evaluate the establishment capacity of E. globulus from plantations into natural habitats and to understand its association with the climate, plantation characteristics and host site characteristics. We surveyed 50 E. globulus plantations across Portugal looking at the natural establishment (occurrence and density) of E. globulus in habitats adjacent to plantations. Eucalypts presence was only recorded in 8% of the plots. Site characteristics (such as habitat type, vegetation cover and disturbance) were the most important variables influencing the natural recruitment of E. globulus in comparison to climate or plantation variables. Forest and grassland were the most resistant habitats to eucalyptus invasion while highly disturbed areas can be considered hubs for eucalypt density. The high importance of site characteristics reflects that most of the variability in eucalypt establishment occurs at small spatial scales. Thus, monitoring and management efforts should focus on those sites with higher establishment probability (i.e. open areas) trying to promote native vegetation and reduce disturbance levels.     

Population dynamics of an epibiont Ostracoda on the invasive red swamp crayfish Procambarus clarkii in a western Mediterranean wetland

Recently, the American entocytherid ostracod Ankylocythere sinuosa was discovered for the first time in Europe to inhabit widely distributed populations of the invasive American crayfish Procambarus clarkii in the Iberian Peninsula. Based on this finding, the aim was to describe the population dynamics of exotic entocytherids for the first time beyond their original area, and to analyse the main variables modulating temporal demographic patterns. We monitored a population of A. sinuosa and its host, P. clarkii, in the Pego-Oliva wetland (Eastern Iberian Peninsula) monthly for 1 year. Crayfish entocytherid loads strongly related to crayfish weight, moult-related exoskeleton hardening stage and water temperature. The proportion of earliest juvenile entocytherid instars, an indicator of recent hatching periods, also related to water temperature and conductivity. According to our results, the most important factors affecting entocytherid dynamics are individual crayfish moulting events, which diminish ostracod load, together with water temperature and ionic concentration, both influencing the life cycle of the exotic epibiont ostracod A. sinuosa.     

Haplotype diversity of mt<Emphasis Type="Italic">COI</Emphasis> in the fall webworm <Emphasis Type="Italic">Hyphantria cunea</Emphasis> (Lepidoptera: Arctiidae) in introduced regions in China,Iran, Japan,Korea, and its homeland,the United States

Hyphantria cunea (Drury) has colonized many countries outside its native range of North America and has become a model species for studies of the colonization and subsequent adaptation of agricultural pests. Molecular genetic analyses can clarify the origin and subsequent adaptations to non-native habitats. Using the mitochondrial COI gene, we examined the genetic relationships between invasive populations (China, Iran, Japan, and Korea) and native populations (i.e., the United States). The Jilin (China) and Guilan (Iran) populations showed nine previously unknown haplotypes that differed from those found in the south–central United States, suggesting multiple colonization events and different regions of invasion. A dominant mtDNA haplotype in populations in the United States was shared by all of the populations investigated, suggesting that H. cunea with that haplotype have successfully colonized China, Iran, Japan, and Korea.     

Shelter-seeking behavior of crayfish, <Emphasis Type="Italic">Procambarus clarkii,</Emphasis> in elevated carbon dioxide

Carbon dioxide has been found to produce various negative consequences for a number of aquatic species and is projected to rise in the future for many aquatic ecosystems. Crayfish act as indicators of water quality and function as keystone species in aquatic food webs; however, there is a paucity of research on how crayfish may respond to elevated CO₂. This study quantified how shelter-seeking behavior in freshwater crayfish (e.g., family Cambaridae), a behavior critical for survival and fitness, may change following exposure to elevated pCO₂. Red Swamp crayfish (Procambarus clarkii, Girard, 1852) were exposed to one of three potential levels of dissolved CO₂ that could be found in freshwater basins currently or under future climate change conditions: Control (2 levels as the respective initial exposure. The treatment aquarium contained a shelter and was divided into three equal sections based on proximity to that shelter. Crayfish proximity to the shelter (defined by the tank sections) in the treatment aquarium was monitored every 5 s for a 2-min trial. Crayfish spent differing amounts of time in differing zones of the experiment and had different levels of activity, depending on their pCO₂ exposure; crayfish acclimated to High pCO₂ increased their time spent hiding and decreased their overall activity when compared to the Low pCO₂ and Control treatments. Augmented shelter-seeking behavior may affect crayfish social hierarchies, feeding, mating, and mortality, which could generate cascading effects on the ecology of many freshwater ecosystems.     

Geostatistical distribution modelling of two invasive crayfish across dendritic stream networks

Species distribution models combining environmental and spatial components are increasingly used to understand and forecast species invasions. However, modelling distributions of invasive species inhabiting stream networks requires due consideration of their dendritic spatial structure, which may strongly constrain dispersal and colonization pathways. Here we evaluate the application of novel geostatistical tools to species distribution modelling in dendritic networks, using as case study two invasive crayfish (Procambarus clarkii and Pacifastacus leniusculus) in a Mediterranean watershed. Specifically, we used logistic mixed models to relate the probability of occurrence of each crayfish to environmental variables, while specifying three spatial autocorrelation components in random errors. These components described spatial dependencies between sites as a function of (1) straight-line distances (Euclidean model) between sites, (2) hydrologic (along the waterlines) distances between flow-connected sites (tail-up model), and (3) hydrologic distances irrespective of flow connection (tail-down model). We found a positive effect of stream order on P. clarkii, indicating an association with the lower and mid reaches of larger streams, while P. leniusculus was affected by an interaction between stream order and elevation, indicating an association with larger streams at higher altitude. For both species, models including environmental and spatial components far outperformed the pure environmental models, with the tail-up and the Euclidean components being the most important for P. clarkii and P. leniusculus, respectively. Overall, our study highlighted the value of geostatistical tools to model the distribution of riverine and aquatic invasive species, and stress the need to specify spatial dependencies representing the dendritic network structure of stream ecosystems.     

Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community-wide study

Antipredator behaviour is an important fitness component in most animals. A co-evolutionary history between predator and prey is important for prey to respond adaptively to predation threats. When non-native predator species invade new areas, native prey may not recognise them or may lack effective antipredator defences. However, responses to novel predators can be facilitated by chemical cues from the predators’ diet. The red swamp crayfish Procambarus clarkii is a widespread invasive predator in the Southwest of the Iberian Peninsula, where it preys upon native anuran tadpoles. In a laboratory experiment we studied behavioural antipredator defences (alterations in activity level and spatial avoidance of predator) of nine anurans in response to P. clarkii chemical cues, and compared them with the defences towards a native predator, the larval dragonfly Aeshna sp. To investigate how chemical cues from consumed conspecifics shape the responses, we raised tadpoles with either a tadpole-fed or starved crayfish, or dragonfly larva, or in the absence of a predator. Five species significantly altered their behaviour in the presence of crayfish, and this was largely mediated by chemical cues from consumed conspecifics. In the presence of dragonflies, most species exhibited behavioural defences and often these did not require the presence of cues from predation events. Responding to cues from consumed conspecifics seems to be a critical factor in facilitating certain behavioural responses to novel exotic predators. This finding can be useful for predicting antipredator responses to invasive predators and help directing conservation efforts to the species at highest risk.     

Insect herbivory on native and exotic aquatic plants: phosphorus and nitrogen drive insect growth and nutrient release

The invasive clam Corbicula fluminea causes severe environmental and economic impacts in invaded sites and fouled water-dependent industries. The biological control of invasive species has potential as an effective, safe and low-cost tool. The potential of using direct (clam consumption) and indirect approaches (predator-avoidance behaviour) to control the pest was evaluated, aiming at establishing a proof-of-principle regarding the suitability of such strategies in confined settings (e.g. pipelines, channels, raw water tanks and other water-dependent facilities). Invertebrate (Procambarus clarkii) and vertebrate (Lepomis gibbosus, Luciobarbus bocagei) predators were examined for their control potential. In feeding experiments, barbels foraged upon C. fluminea but ingested very few clams, and clam consumption by crayfish was only observed in the smallest size class (<1 cm). Additional experiments linked these results to the protective role of the clam’s shell. In practical terms, the potential of the fish species as C. fluminea predators is limited, but crayfish can be important predators of small clams. In a second set of experiments, putative predator avoidance by clams was assessed in dual-choice aquaria. Refuge availability, predator diet and light conditions were taken into account. Clam avoidance was observed under particular conditions, but the amplitude of dislocation was limited.