Invasive Crayfish Procambarus Clarkii Research Articles

Invisible invaders: range expansion of feral Neocaridina davidi offers new opportunities for generalist intracellular parasites

AbstractThe release of ornamental pets and associated pathogens outside their native range might directly or indirectly impact the recipient community. In temperate regions, e.g., central Europe, feral freshwater species of tropical and sub-tropical origins are mainly constrained to thermally polluted waters and thermal springs. However, species with high environmental plasticity and reproduction rates, such as the shrimp Neocaridina davidi, may adapt to colder water regimes over time. A widening thermal niche may eventually overcome thermal barriers, further expanding the range and enhancing transmission opportunities for host generalist parasites. This study assesses the observed (field observations) and theoretical (species distribution models) range expansion of N. davidi and associated parasites in Europe. We report three newly established N. davidi populations from thermally polluted waters in central Europe (Germany, Hungary, and Slovakia) and provide further evidence of its range expansion into colder environments. Species distribution models predict thermally suitable habitats in the Mediterranean and a foreseeable expansion into Western Europe and the Balkans by 2050. We confirm the presence of the microsporidian parasite Ecytonucleospora hepatopenaei in feral N. davidi populations across Europe and expand the list of microsporidians found in this host from two to four. Furthermore, we provide the first evidence of parasite spillover from/to the invasive crayfish Procambarus clarkii, suggesting that parasite exchange with native biota might be possible. Such possibility, coupled with an ongoing range expansion of N. davidi bolstered by human-mediated introductions and climate change, will likely exacerbate the impact on native biota.

First record of the semi-aquatic invasive plant Crassula helmsii in the Iberian Peninsula and its link to potential dispersal drivers

AbstractAquatic neophytes are among the most harmful invasive species worldwide. Here we report the finding of the semi-aquatic invasive plant Crassula helmsii, naturalized in a freshwater reservoir that provides water to the large city of A Coruña, NW Spain. To better understand the extent and potential environmental correlates of C. helmsii invasion, we recorded the presence and frequency of C. helmsii in its emerged and floating mat forms at twelve sampling sites along the reservoir margins, and characterized the soil characteristics, plant community and environmental factors. Crassula helmsii is dispersed by fragmentation of the stems, potentially aided through shredding by local fauna such as the invasive crayfish Procambarus clarkii. We hypothesize that this could be a case of an invasional meltdown, when multiple invasive species facilitate one another and have synergistic effects on native ecosystems. The emerged form of C. helmsii was found in ten out of twelve sites with a mean cover value of 9.8 ± 10.4% (mean ± SD). We found no correlation between frequency of the emerged form of C. helmsii and abundance of Procambarus clarkii, but frequency of the emerged form of C. helmsii increased with higher soil nitrogen and vascular plant richness. We outline emergency actions for management of C. helmsii at this stage of the invasion, focusing on containment and avoiding spread to nearby water bodies.

Oxygen consumption in relation to current velocity and morphology in the highly invasive crayfish Procambarus clarkii

The red swamp crayfish (Procambarus clarkii) is the most widely spread freshwater crayfish worldwide. Competing physiological traits can influence invasion success in any given environment by limiting the available scope for aerobically demanding activities. While high flows have been associated with reduced crayfish movement upstream, the effects of flow alteration on their metabolic demands have been largely overlooked. In this study, we estimated routine metabolic rate (RMR) at rest and oxygen consumption rates of crayfish under different current velocities in a flume respirometer, while maximum metabolic rate (MMR) was determined using the exhaustive chase protocol. We also measured some morphometric variables in males and females of crayfish. Oxygen uptake substantially increased with crayfish size and current velocity due to increased energy expenditure to overcome drag and hold a stationary position. Sexual dimorphism in morphological traits did not lead to sexual differences in oxygen uptake. Moreover, we found that individuals operated close to their maximum aerobic capacity at elevated current velocities (≥ 25 cm s−1). This suggested that the high flow-driven energetic demand may compromise the energy available for reproduction, growth and dispersal, thereby affecting overall fitness. These metabolic constraints could partly explain the failed invasions of invasive crayfish in fast-flowing waters.

Cardiac activity with acute exposure to sub-zero temperatures illustrates the survival mechanism of invasive crayfish

The ability to withstand climate and weather extremes can play a key role in survival and establishment of non-native species. We investigated the effect of acute exposure to sub-zero temperature on the heart rate and recovery capacity of invasive crayfish Faxonius limosus, Pacifastacus leniusculus, and Procambarus clarkii. The experiments used non-invasive sensors to assess cardiac activity relative to survival and recovery of crayfish during short (30 min) and prolonged (60 min) exposures to − 18 °C. All P. clarkii specimens survived freezing temperature and rewarming and recovered after the short exposure, and 25% recovered after prolonged exposure. All F. limosus and P. leniusculus died during the recovery period following both exposures. In all tested specimens a heartbeat was measurable several hours after conclusion of exposure, gradually declining in F. limosus and P. leniusculus. The P. clarkii heart rate decreased abruptly upon exposure to sub-zero temperature, and recovery to nearly the pre-exposure rate took longer than for F. limosus and P. leniusculus. Heartbeat decline slopes were as follows: P. clarkii, 80.2° ± 2.1°, > F. limosus, 74.9° ± 4.1°, > P. leniusculus, 70.3° ± 3.7°. During the cooling-warming cycle, F. limosus and P. leniusculus demonstrated more gradual heartbeat decline and more rapid recovery to original levels but ultimately did not survive, most likely due to energy depletion associated with heartbeat fluctuation while cooling. These findings may increase our understanding of the broader distribution of P. clarkii than expected according to its ecological optima and provide insight into the mechanisms of invasive crayfish adaptability.

More evidences for the nutritional quality and future exploitation of the invasive crayfish Procambarus clarkii (Girard, 1852) from the River Nile, Egypt

This study aimed to evaluate the nutritional quality with some food applications of the invasive Procambarus clarkii from the River Nile, Egypt. The moisture content was 75.75 ± 2.3% and crude protein on dry weight basis was estimated as 73.25 ± 4.1%. Essential amino acids were 0.529, 0.131, 0.181, 0.016 and 0.058 mg/g for isoleucine, leucine, lysine, methionine, and valine, respectively, whereas non-essential amino acids were 0.173 and 0.032 mg/g for tyrosine and cystine, respectively. A total of 15 fatty acids was detected [8 saturated fatty acids (SFAs) and 7 unsaturated fatty acids (USFA)], the major SFA was palmitic acid (C16:0; 26.63%), whereas the major USFA was oleic acid (C18:1n-9; 29.26%). Vitamins A, D, E, and K were 3181, 2, 175, and 1.7 mg/kg, respectively. Minerals were 937.7, 1639.1, 2171.6, and 0.01 mg/kg for Na, K, Mg, and I, respectively. Six heavy metals were monitored (mg/kg) 0.47, 0.32, 0.05, 81.31, 203.21, and 0.23 for Hg, Pb, Ca, Fe, Zn, and Ni, respectively. For food processing applications, the two products had acceptable levels for consumption in test panel responses. Moreover, P. clarkii should be considered for exploitation and recommended for further investigation as a potential raw material for the pharmaceutical industry and a new cheap animal protein source.

Phenotypic responses of invasive species to removals affect ecosystem functioning and restoration.

Reducing the abundances of invasive species by removals aims to minimize their ecological impacts and enable ecosystem recovery. Removal methods are usually selective, modifying phenotypic traits in the managed populations. However, there is little empirical evidence of how removal-driven changes in multiple phenotypic traits of surviving individuals of invasive species can affect ecosystem functioning and recovery. Overcoming this knowledge gap is highly relevant because individuals are the elemental units of ecological processes and so integrating individual-level responses into the management of biological invasions could improve their efficiency. Here we provide novel demonstration that removals by trapping, angling and biocontrol from lakes of the globally invasive crayfish Procambarus clarkii induced substantial changes in multiple phenotypic traits. A mesocosm experiment then revealed that these changes in phenotypic traits constrain recovery of basic ecosystem functions (decomposition of organic matter, benthic primary production) by acting in the opposite direction than the effects of reduced invader abundance. However, only minor ecological impacts of invader abundance and phenotypic traits variation remained a year after its complete eradication. Our study provides quantitative evidence to an original idea that removal-driven trait changes can dampen recovery of invaded ecosystems even when the abundance of invasive species is substantially reduced. We suggest that the phenotypic responses of invaders to the removal programme have strong effects on ecosystem recovery and should be considered within the management of biological invasions, particularly when complete eradication is not achievable.

Invasive crayfish does not influence spawning microhabitat selection of brown frogs.

Microhabitat selection is a key component of amphibian breeding biology and can be modulated in response to the features of breeding sites and the presence of predators. Despite invasive alien species being among the major threats to amphibians, there is limited information on the role of invasive species in shaping amphibians’ breeding microhabitat choice. The invasive red swamp crayfish (Procambarus clarkii) is a major predator of amphibians’ larvae, including those of the brown frogs Rana dalmatina and Rana latastei. Although qualitative information about the spawning site preferences and breeding microhabitat choice of brown frogs is available in the literature, only a few studies performed quantitative analyses, and the relationship between microhabitat choice and the presence of alien predators has not been investigated yet. The aims of this study were: (1) to characterize the microhabitats selected for clutch deposition by R. dalmatina and R. latastei and (2) to test if the position and the aggregation of egg clutches differ in sites invaded or not invaded by P. clarkii. During spring 2017, we surveyed multiple times 15 breeding sites of both brown frogs in Northern Italy; in each site we assessed the features of the microhabitat where each egg clutch was laid, considering its position (distance from the shore, depth of the water column) and the degree of aggregation of clutches. In each site we also assessed the presence/absence of the invasive crayfish and the relative abundance in the breeding period. We detected egg clutches in all sites; the crayfish occurred in eight ponds. Our results showed substantial differences between the spawning microhabitat features of the two brown frogs: Rana latastei clutches showed a higher degree of aggregation and were associated with deeper areas of the ponds , while Rana dalmatina deposited more spaced out clutches in areas of the ponds that were less deep. For both species, spawning microhabitat features were not significantly different between sites with and without P. clarkii. Although we did not detect behavioural responses to P. clarkii in the choice of spawning microhabitat , additional studies are required to assess whether these frogs modulate other behavioural traits (e.g. during larval development) in response to the invasive predator.

Salinity tolerance of the invasive red swamp crayfish Procambarus clarkii (Girard, 1852)

Introduction of alien species leading to unfavorable economic impacts and ecosystem collapse is a well-known threat. The aim was to define if high salinity may be a limiting factor for the survival and spread of the invasive crayfish Procambarus clarkii. Both sexes were exposed to increasing salt concentrations reaching 35.3‰ after 65 days to simulate the natural transition from freshwater into seawater. Higher mortality was recorded for salinity-treated females than for males. Condition indexes gave evidence of minor adverse effects, whereas altered values of oxidative stress biomarkers suggested a perturbation of redox state induced by the exposure conditions. The female survivors showed a strengthening of levels of oxidative stress biomarkers. A moderate oxidative pressure was recorded for gills in both sexes. Nevertheless, the non-indigenous red swamp crayfish has shown great resistance and adaptability to these simulated adverse environmental conditions. Survival of P. clarkii at high salinity may suggest that both sexes can be able to invade estuarine brackish water and lagoons initially exploited as ecological corridors, causing ecological imbalances in transitional ecosystems and in seawater. Moreover, this alien invasive species could be able to descend rivers up to the sea and vice versa to colonize new environments.

Long-lasting generalization triggered by a single trial event in the invasive crayfish Procambarus clarkii.

Behavioural flexibility allows adaptation to environmental changes, a situation that invasive species have often to face when colonizing new territories. Such flexibility arises from a set of cognitive mechanisms among which generalization plays a key role, as it allows the transfer of past solutions to solve similar new problems. By means of a habituation paradigm, we studied generalization in the invasive crayfish Procambarus clarkii Once crayfish had habituated their defensive response to a specific water jet, we tested whether habituation transferred to a new type of water jet. Although habituation did not generalize when the new stimulus was initially presented, it surprisingly emerged 15 and 45 days later. Hence, remarkably, in Pclarkii, a single presentation of a new event was sufficient to trigger a long-lasting form of learning generalization from previous similar stimuli, a cognitive ability that may concur in providing adaptive advantages to this invasive species.

The IAG gene in the invasive crayfish Procambarus clarkii – towards sex manipulations for biocontrol and aquaculture

The IAG gene in the invasive crayfish Procambarus clarkii – towards sex manipulations for biocontrol and aquaculture

First report of freshwater atyid shrimp, Caridina formosae (Decapoda: Caridea) as a host of ectosymbiotic branchiobdellidan, Holtodrilus truncatus (Annelida, Citellata)

In recent years, ornamental shrimps gained increasing popularity in the aquarium trade. Unfortunately, they are potential vectors of epibionts, which may be unintentionally introduced to aquaria with imported shrimps. This contribution presents the first report of the occurrence of Holtodrilus truncatus on aquarium freshwater shrimp Caridina formosae. A total of 120 shrimp imported from Taiwan as aquarium pets were examined for the presence of epibionts. Holtodrilus truncatus occurred in 23.3% of shrimps. A total of 29.6% of crustaceans showed signs of damages as a result of H. truncatus activity. The shrimp is not common in the ornamental trade and is not subject to selective breeding. Therefore C. formosae populations available on the market, if not wild-caught, are most likely very similar to those occurring in Taiwanese natural water bodies, where H. truncatus occurs in Neocaridina shrimp. Neocaridina spp. are a known host for this epibiont, and transmission between species might occur in nature as well as in the aquarium trade were densities of animals are often high. The ability of H. truncatus to infect also highly invasive crayfish Procambarus clarkii, might also pose concern for regions where this crustacean is widespread. The actual lack of preventive measures for shrimp epibionts as well as confirmed releases of ornamental crustaceans into new aquatic ecosystems may result in further spread of H. truncatus, a potential new threat to native crustaceans and other epibionts.

Thirty years of invasion: the distribution of the invasive crayfish Procambarus clarkii in Italy

The presence of the red swamp crayfish Procambarus clarkii in Italy is documented since 1989, but no comprehensive data are available on its spread through time at the national scale. New confirmed records for Procambarus clarkii are continuously arising in recent years across the country. By reviewing the scientific and grey literature, we obtained an up-to-date map of the species invasion in Italy. This information can help to monitor and understand the spread of this highly invasive crayfish and to implement more effective management measures.

Invasive crayfish (Procambarus clarkii, Girard, 1852) in a managed brackish wetland (Sardinia, Italy): Controlling factors and effects on sedimentary organic matter

The red swamp crayfish, Procambarus clarkii is among the most invasive aquatic species worldwide. Here we investigate the potential relationships between crayfish occurrence and a series of abiotic factors, as well as the effects of crayfish abundance on sedimentary organic matter (OM) quantity and degradation. A total of 329 sampling points was investigated in a managed protected brackish wetland (Southern Sardinia, Italy). A generalized additive model (GAM) was applied to investigate the influence of abiotic variables on the crayfish occurrence. We then assessed the potential effects of crayfish abundance on sedimentary OM quantity, biochemical composition and degradation rates. We report here that the occurrence of crayfish was mostly explained by the joint effects of water salinity, characteristics of soil's bank and bottom substrate composition. We report also that the presence of this crayfish, due to its bioturbation ability, is associated with a more homogeneous vertical distribution of OM along the sediment profile. Moreover, we revealed that the presence of P. clarkii is associated with OM contents and caloric contents that are significantly lower than those in crayfish-free sediments. These results suggest that the presence of P. clarkii determines not only a decrease in the quantity of food potentially available for the benthos, but also a decrease in its nutritional value. Moreover, we report also that the presence of P. clarkii is associated with a decrease in protein degradation rates and an increase in their turnover time, indicating that this species could have severe effects on the local C cycle.

Effects of the invasive crayfish Procambarus clarkii on growth and development of Pelophylax perezi tadpoles in field conditions

Introduced predatory aquatic invertebrates may contribute to the global decline of amphibians as their larval are extremely vulnerable to predators. The objective of this study was to examine the effects of the predatory invasive crayfish Procambarus clarkii on the growth and development of native Iberian green frog tadpoles, Pelophylax perezi, in field conditions. We hypothesized that P. clarkii might affect P. perezi development by (a) inducing a delay in its metamorphosis and (b) reducing survival and mass of metamorphs. The experiment was developed in two ponds (with and without P. clarkii’s presence) in the Natural Park of Aiguamolls de l’Empordà (NE of the Iberian Peninsula). For each pond, groups of 10 tadpoles were randomly assigned to 15 cylindrical field enclosures. These enclosures avoided direct contact (i.e. predation) between both species. Our results suggest that, in field conditions, the presence of P. clarkii accelerates metamorphosis of P. perezi tadpoles. The higher growth rate of P. perezi through shorter larval periods could be the result of behavioural plasticity in response to the strong pressure imposed by P. clarkii. This conclusion would be in accordance with the hypothesis that phenotypic plasticity plays an important role in the conservation of P. perezi in front of biological invasions.

The efficacy of a generalized antipredator defense against a novel predator depends on the source of induction in prey

Ecological naivete or the failure to recognize a novel enemy is often put forward as a cause of extirpation of biodiversity in newly invaded systems. We tested the efficacy of a generalized antipredator defense, namely reduced activity level, in the tadpoles of Rhacophorus arboreus to the threat of the invasive predator red swamp crayfish Procambarus clarkii in simplified laboratory environments. We first investigated the behavioral responses of the tadpoles in the presence of caged fed predators (native: dragonfly larvae and newts, and novel P. clarkii), and subsequently tested the vulnerability of predator-induced tadpoles to free-ranging predators. The tadpoles reduced activity level in the presence of the native predators but did not recognize the crayfish. Reducing activity level increased survival in the presence of native predators. This behavior was still effective in the presence of crayfish, but survivorship varied with the identity of the native predator from which the tadpoles received induction cues: tadpoles that were previously exposed to dragonfly larvae noticeably survived better than those previously induced by newts. Our findings suggest that naive prey may exploit information from native predators to better resist the threat of novel predators, but not all sources of induction confer the same benefit.

Differential vulnerability of two sympatric tadpoles to an invasive crayfish predator

Many amphibian population declines have been associated with the introduction of alien aquatic predators. Here, we explore the vulnerability of tadpoles of two sympatric Japanese species [Pelophylax nigromaculatus (PN) and Rhacophorus schlegelii (RS)] to the invasive crayfish Procambarus clarkii. We first examined the behavioral responses of the tadpoles to the cues of caged, fed crayfish predator in a controlled laboratory experiment, and subsequently tested their survival when together in the presence of free-ranging predator in outdoor mesocosms that simulated natural ponds. Only PN reduced activity level to the cues of the predator, but this apparent behavioral defense recorded in the laboratory did not result into higher survival in outdoor mesocosms. In mesocosms, PN exhibited higher biomass increment but experienced higher mortality in predator environments. The mechanism mediating mortality remains unclear though. These results indicate that sympatric prey may differentially respond and be disproportionally vulnerable to novel predators. Our study illustrates the possible contribution of a life-history trait influencing risk of predation in newly invaded systems.

Genetic diversity of the invasive crayfish Procambarus clarkii in France

Procambarus clarkii is a widespread invasive species and its biological traits have often been used to explain its successful colonization of new areas. However, studies on the genetic features of invasive populations are still scarce, and the use of molecular markers could bring new insights about biological invasions. After being introduced in Spain in 1973, P. clarkii was introduced in France (≈1976) and nowadays is widespread in its territory (61 departments) in wetlands which provide good conditions for a successful colonization. Here we ask whether the genetic diversity of invasive populations could help to understand the evolutionary history of its invasion. To investigate this issue, 227 individuals of P. clarkii from 27 French populations and 10 departments were collected, and a 553 bp COI fragment was amplified and sequenced using universal primers. For the analysis of genetic parameters, nucleotide diversity (π), and haplotype diversity (Hd), the populations were organized into four major groups. The nucleotide diversities (π) were 0.000154, 0.00119, 0.00118, and 0.00123 for group 1, 2, 3, and 4, respectively. The genetic diversity of French populations (Hd = 0.350; π = 0.00123) was lower than the native populations (Hd = 0.982; π = 0.00736). Nine haplotypes were found (H1–H9) in 230 sequences. Haplotype diversity (Hd) was 0.444, 0.239, 0.330, and 0.350 for groups 1, 2, 3, and 4, respectively. The haplotype network showed very similar haplotypes, differing by few mutational steps and showing some complex relationships. Three haplotypes related to the species’ native region were found (H1, H2, and H3). Each of these haplotypes was also related to biogeographical regions. The most frequent haplotype (H2) was widespread throughout 10 departments. The other six haplotypes (H4, H5, H6, H7, H8, and H9) were not found in the native region but, in some cases, shared some French populations. Translocation by humans is the most plausible explanation of the observed haplotype relationships. We suggest that genetic information should play a larger role in the development of policies to manage invasive species.

Habitat modification by invasive crayfish can facilitate its growth through enhanced food accessibility

BackgroundInvasive ecosystem engineers can facilitate their invasions by modifying the physical environment to improve their own performance, but this positive feedback process has rarely been tested empirically except in sessile organisms. The invasive crayfish Procambarus clarkii is an ecosystem engineer that destroys aquatic macrophytes, which provide a physical refuge for animal prey, and this destruction is likely to enhance vulnerability to predators. Using two series of mesocosm experiments, we tested the hypothesis that the invasive crayfish increases its feeding efficiency on animal prey by reducing submerged macrophytes, thus increasing its individual growth rate in a positive density-dependent manner.ResultsIn the first experiment, increasing crayfish density reduced both macrophytes and animal prey (dragonfly and chironomid larvae) and, importantly, increased the growth rate of individual crayfish, in accordance with our expectation. In the second experiment, we used artificial macrophytes to clarify whether the physical architecture of macrophytes itself protects animal prey and limits crayfish growth rate. Increasing the artificial macrophyte quantity not only increased the survival of animal prey, but also retarded the crayfish growth rate.ConclusionsWe conclude that macrophytes strengthen bottom-up control of crayfish, but this effect can be relaxed by increasing the density of crayfish via reduction in macrophytes. This positive feedback process may explain the crayfish outbreaks and regime shifts occasionally observed in invaded freshwater ecosystems.

Between‐lake variation in the trophic ecology of an invasive crayfish

Abstract The trophic ecology of invasive species has important implications for their impacts on recipient ecosystems, with omnivorous invaders potentially affecting native species and processes over multiple trophic levels. The trophic ecology of invaders might be affected by both their body size and the characteristics of their habitat due to variation in energy requirements and resource availability. Here, using stable‐isotope analysis, we investigated the trophic ecology of the invasive crayfish Procambarus clarkii in 15 populations in southwest France over a gradient of individual (crayfish body size), population (crayfish abundance) and ecosystem (lake size, productivity and predation pressure) characteristics. We predicted that population niche width, level of omnivory and trophic position of individuals would change with abiotic and biotic conditions, but that these relationships would vary with lake size. The trophic position of individual crayfish increased with body size in lakes with low productivity, but decreased with body size in more productive lakes. As crayfish abundance increased (and therefore potential intraspecific competition), individual trophic position and population niche width decreased. This was most apparent in smaller lakes, suggesting it related to an increase in encounter rates with conspecifics. Body size, population abundance, lake size and lake productivity influenced the trophic ecology of invasive crayfish, which can affect their interactions with native species. Our results demonstrated that the trophic ecology of invasive species can be variable across invaded landscapes, with implications for their ecological impacts on native communities. This emphasizes the importance of characterising the diet of invasive species across their non‐native range and environmental gradients to better predict and manage their impacts.

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.