Occurrence Of Crayfish Research Articles

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.

Lithology and disturbance drive cavefish and cave crayfish occurrence in the Ozark Highlands ecoregion

Diverse communities of groundwater-dwelling organisms (i.e., stygobionts) are important for human wellbeing; however, we lack an understanding of the factors driving their distributions, making it difficult to protect many at-risk species. Therefore, our study objective was to determine the landscape factors related to the occurrence of cavefishes and cave crayfishes in the Ozark Highlands ecoregion, USA. We sampled cavefishes and cave crayfishes at 61 sampling units using both visual and environmental DNA surveys. We then modeled occurrence probability in relation to lithology and human disturbance while accounting for imperfect detection. Our results indicated that occurrence probability of cave crayfishes was negatively associated with human disturbance, whereas there was a weak positive relationship between cavefish occurrence and disturbance. Both cavefishes and cave crayfishes were more likely to occur in limestone rather than dolostone lithology. Our results indicate structuring factors are related to the distribution of these taxa, but with human disturbance as a prevalent modifier of distributions for cave crayfishes. Limiting human alteration near karst features may be warranted to promote the persistence of some stygobionts. Moreover, our results indicate current sampling efforts are inadequate to detect cryptic species; therefore, expanding sampling may be needed to develop effective conservation actions.

Similar species, different fates: Abundance dynamics in spatially structured populations of common and threatened frogs

AbstractAimUnderstanding which factors determine the variation in population size across space and time is crucial to plan sound conservation interventions. Amphibians are often characterized by large demographic changes, therefore a better understanding of factors driving these changes could help mitigate their global crisis. We investigated drivers of abundance dynamics of two similar frog species to understand why they met different fates in the same study area.LocationNorthern Italy.MethodsIn seven different years between 2004 and 2020, we performed repeated counts of egg masses of two similar frog species, the agile frog (Rana dalmatina) and the Italian agile frog (Rana latastei), in 31 wetlands, and used Bayesian models to estimate the relationships between frog abundance and candidate drivers acting at the scale of (i) site: wetland surface, shading percentage and the presence of the invasive red swamp crayfish (Procambarus clarkii); (ii) landscape: forest cover around wetlands; (iii) climate: yearly precipitation and (iv) spatially structured population (SSP): clutch incidence of the focal species and crayfish incidence in the surrounding landscape.ResultsThe two species showed sharp differences in population size and trends: R. dalmatina was abundant and showed a stable trend throughout the entire study period; R. latastei showed low abundance in the first years and then almost disappeared. The abundance of R. dalmatina was positively related to forest cover, shading, wetland area and precipitation, while negatively related to the occurrence of invasive crayfish at both local and SSP level. R. latastei abundance increased with wetland area and precipitation, while models were not able to detect relationships with other factors.Main conclusionsThe high sensitivity to drought and demographic stochasticity could have contributed to the quasi‐extinction of R. latastei in the study area, highlighting that similar species can meet different fates even under the same environmental conditions.

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

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

Alien Crayfish Species in the Deep Subalpine Lake Maggiore (NW-Italy), with a Focus on the Biometry and Habitat Preferences of the Spiny-Cheek Crayfish

Invasive alien species are a major threat to biodiversity. Thus, it is fundamental to implement control strategies at the early stages of invasions. In the framework of the Italian-Swiss Alien Invasive Species in Lake Maggiore cooperative programme, we performed an extensive study on the occurrence and ecology of alien crayfish, one of the most significant invaders of freshwater habitats. From April 2017 to July 2018, we inspected seventy-five sites along the coastline to verify crayfish occurrence. We recorded, for the first time, the signal crayfish Pacifastacus leniusculus. Additionally, we found few individuals and remains of the red swamp crayfish Procambarus clarkii, and confirmed the presence of a consistent population of the spinycheek crayfish Orconectes limosus. Given the high number of O. limosus’ individuals found, it was possible to perform in-depth biometric and ecological analyses for this abundant species only. We observed no significant differences of biometric measures between males and females of O. limosus. We explore its habitat preferences with a generalized linear model, detecting a significant relationship between mean annual temperatures and the presence of shelters of this species. These results, together, have direct implications for planning rapid management response actions on alien crayfish in large and deep lakes.

English

Abstract Anthropogenic modifications to river-floodplain systems can decouple floodplains from mainstem inputs, alter flood pulse dynamics, and disrupt population dynamics and trophic web stability of aquatic biota. The Atchafalaya River Basin (ARB) receives an annual flood pulse from the Mississippi River that contributes to high crayfish abundance. Conversely, reduced crayfish abundance in the Barataria Basin (BB) is attributed to the system no longer receiving an annual flood pulse from the Mississippi River. Therefore, the purpose of this research was to determine if the absence of an annual flood pulse and reduced crayfish abundance influenced the diets of carnivorous fishes by examining stomach contents of fishes from both basins. Stomach contents were grouped as crayfish, fish, non-crayfish invertebrate, and herpetological. Although the percent occurrence of crayfish in fish stomachs differed between floodplain inundation and low-water periods in the ARB, crayfish were still the major diet constituent of ARB fishes during both periods. Non-crayfish invertebrate was the major diet constituent in BB fishes, with crayfish ranking as the second fewest diet constituent present. Our results demonstrate how flood pulse dynamics influence crayfish, and ultimately trophic webs, in large river-floodplain systems.

Network‐scale effects of invasive species on spatially‐structured amphibian populations

Understanding the factors affecting the dynamics of spatially‐structured populations (SSP) is a central topic of conservation and landscape ecology. Invasive alien species are increasingly important drivers of the dynamics of native species. However, the impacts of invasives are often assessed at the patch scale, while their effects on SSP dynamics are rarely considered. We used long‐term abundance data to test whether the impact of invasive crayfish on subpopulations can also affect the whole SSP dynamics, through their influence on source populations. From 2010 to 2018, we surveyed a network of 58 ponds and recorded the abundance of Italian agile frog clutches, the occurrence of an invasive crayfish, and environmental features. Using Bayesian hierarchical models, we assessed relationhips between frog abundance in ponds and a) environmental features; b) connectivity within the SSP; c) occurrence of invasive species at both the patch‐ and the SSP‐levels. If spatial relationships between ponds were overlooked, we did not detect effects of crayfish presence on frog abundance or trends. When we jointly considered habitat, subpopulation and SSP features, processes acting at all these levels affected frog abundance. At the subpopulation scale, frog abundance in a year was related to habitat features, but was unrelated to crayfish occurrence at that site during the previous year. However, when we considered the SSP level, we found a strong negative relationship between frog abundance in a given site and crayfish frequency in surrounding wetlands during the previous year. Hence, SSP‐level analyses can identify effects that would remain unnoticed when focussing on single patches. Invasive species can affect population dynamics even in not invaded patches, through the degradation of subpopulation networks. Patch‐scale assessments of the impact of invasive species can thus be insufficient: predicting the long‐term interplay between invasive and native populations requires landscape‐level approaches accounting for the complexity of spatial interactions.

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.

Environmental factors affecting the invasion success and morphological responses of a globally introduced crayfish in floodplain waterbodies

Floodplain ecosystems that are characterized by high habitat heterogeneity and hydrological connectivity are considered hotspots for freshwater biodiversity. However, these biodiversity-rich areas have been seriously threatened by biological invasions. The signal crayfish (Pacifastacus leniusculus) is listed as 100 of the world’s worst invasive species, and is a major threat to freshwater biodiversity and ecosystem functioning. Here, we examined environmental factors relating to the invasion success of signal crayfish and their morphological responses in floodplain waterbodies. Classification and regression tree analyses showed that most of the influential factors differed between tributary and lake populations. In floodplain tributaries, the occurrence of crayfish was positively related with water temperature and abundance of leaf cover, while crayfish abundance was highest where large-wood was abundant. In floodplain lakes, crayfish were absent at oxygen-poor sites, and abundant at sites with high connectivity to a main channel. These results indicate that conservation practitioners should consider different environmental factors in accordance with strategies for invasive species management (i.e., offensive or defensive management). Furthermore, we demonstrated morphological differences between tributary and lake populations, with tributary crayfish having wider chelae. These morphological differences might have resulted from the physical differences between the two types of waterbodies, facilitating the rapid invasion of signal crayfish to floodplain waterbodies. Our study showed that invasion-risk assessments should consider both environmental factors and morphological responses to new environments to understand invasion ecology and to form effective conservation plans and to prioritize management actions.

Causes and consequences of crayfish extinction: Stream connectivity, habitat changes, alien species and ecosystem services

Abstract Given the ongoing decline of many species, it is important to perform multifactorial analyses of conservation status and to assess the effects of species extinction on ecosystem services. In this study, we used long‐term surveys to assess the influence of habitat change, landscape alteration and invasive species on extinction risk of the native crayfish Austropotamobius pallipes. We reviewed the existing literature to assess which ecosystem services are threatened by local extinction of A. pallipes and replacement with alien crayfish. We sampled 196 streams and wetlands in northern Italy. Of these, 117 received multiple surveys over a 13‐year period (2004–2017), thus allowing accurate measurement of extinction rate. Thirty‐four percent of A. pallipes populations underwent extinction between 2004 and 2017. The occurrence of alien crayfish in the catchment basin and urban growth in the landscape surrounding streams were associated with A. pallipes extinction. The probability of persistence was significantly higher in populations close to stream springs and with physical barriers (especially waterfalls) separating them from basins with alien crayfish. Extinction of native crayfish alters community structure and impairs regulating services such as detrital breakdown and pest regulation. Replacement by alien crayfish (Procambarus clarkii and Faxonius limosus) also threatens supporting and regulating services by altering nutrient cycling, food webs, sediments and erosion. The implementation of management practices that control river connectivity using selective barriers is needed to prevent further local extinction of native species. Integrating information on extinction with knowledge of impacts on ecosystem services is essential in developing more effective conservation policies.

Fossil kōura (Paranephrops ?planifrons White 1842) (Crustacea: Decapoda: Parastacidae) from the Nukumaruan marginal-marine Hautotara Formation, southeastern Wairarapa

ABSTRACTHere we report an early Pleistocene occurrence of the New Zealand freshwater crayfish (kōura) Paranephrops White 1842 in the marginal-marine sediments of the Hautotara Formation, southeastern Wairarapa. The disarticulated parts are tentatively assigned to P. ?planifrons. This, to our knowledge, is the first fossil occurrence attributable to an extant species of Paranephrops, and only the second fossil occurrence of Paranephrops reported in the literature. This find provides a maximum constraint on the age of divergence of the two extant species of Paranephrops, and shows that post-glacial recovery of freshwater ecosystems in the North Island may have been rapid if the Northland refugium hypothesis for survival and dispersal of Paranephrops planifrons is accurate.

Clonal crayfish as biological model: a review on marbled crayfish

Since the mid-twentieth century, numerous vertebrates and invertebrates have been used as model organisms and become indispensable tools for exploring a broad range of biological and ecological processes. Crayfish seem to be adequate models which resulted in their involvement in research. In the two decades since its discovery, ongoing research has confirmed that the marbled crayfish (Procambarus virginalis Lyko, 2017) is an ideal taxon in this regard, especially due to its almost continuous asexual reproduction providing a source of genetically identical offspring. This review provides an overview of the occurrence, biology, ecology, ethology, and human exploitation of marbled crayfish with primary focus on its use as a laboratory model organism as well as potential risks to native biota in case of its introduction. Genetic uniformity, ease of culture, and a broad behaviour repertoire fosters the use of marbled crayfish in epigenetics and developmental biology, as well as physiological, ecotoxicological, and ethological research. Marbled crayfish could be further exploited for basic and applied fields of science such as evolutionary biology and clonal tumour evolution. However, due to its high invasive potential in freshwater environments security measures must be taken to prevent its escape into the wild.

Lake Hańcza – a new site for signal crayfish (Pacifastacus leniusculus Dana) occurrence in Poland

Abstract Crayfish catches were conducted using traps in Lake Hańcza, which is the deepest lake in Poland. Two crayfish populations were found to co-exist in the lake: spiny-cheek crayfish (Orconectes limosus Raf.) and signal crayfish (Pacifastacus leniusculus Dana), which is a new species for this lake. Signal crayfish dominated the samples at 98.5% of the specimens caught. The crayfish occurred at depths of 1-10 m. The mean total body length of the male and female signal crayfish (TL) was 99.5 ± 17.8 mm and 96.5 ± 11.7 mm, respectively, while the average body weight (BW) was 38.7 ± 24.9 g and 26.8 ± 9.5, respectively. Chelae were damaged in 4.5% of the individuals. Fishing efficiency (catch per unit effort – CPUE) was 0.96 crayfish trap−1 night−1. Selected characteristics of the population and of individual signal crayfish from Lake Hańcza were compared with those of the two closest neighboring populations of this species in lakes Mauda and Pobłędzie. The confirmed occurrence of the relatively large signal crayfish population in Lake Hańcza excludes this lake as a possible site for native noble crayfish (Astacus astacus L.) restoration.

Is it a hindrance for an invasive aquatic species to spread across scattered habitat patches?

Abstract1. Despite their importance for aquatic biodiversity, ponds are among the most vulnerable freshwater habitats. Owing to their isolation in terrestrial environments, ponds are expected to be relatively well protected from biological invasions, but this depends on many factors.2. The purpose of this study was to examine the influence of a range of variables (water quality, habitat, and landscape attributes) on the colonization of discrete ponds by a widespread aquatic invader, the red swamp crayfish Procambarus clarkii, which can disperse overland.3. Investigations were conducted in two networks of ponds, each located in close proximity to a large invaded marsh. The two marshes under study differed in the length of time since the crayfish were introduced.4. The proportions of colonized ponds and crayfish abundances were moderate in both networks, but higher in the network that had been invaded first. In both networks the distance to the marsh was the main predictor of pond colonization, considering similar energy costs to cross aquatic and terrestrial habitats for the recently invaded network, but assuming that dispersal was 25 times costlier across the terrestrial matrix than via streams for the earlier invaded network. Pond characteristics had no influence on crayfish occurrence in either network. Furthermore, predictions of pond invasion were lower for the recently invaded network.5. The importance of the distance to the marsh indicates that natural dispersal was the main process of pond colonization by crayfish. Findings also suggested that overland dispersal was rare and costly. By contrast, streams were probably significant in facilitating crayfish dispersal. Differences between the two networks might arise from an invasion process still in progress in the recently invaded network.6. From a management viewpoint, local actions are encouraged to prevent the spread of crayfish via streams. In addition, broader‐scale actions to mitigate other human disturbances would improve the outlook for pond biodiversity.

More invaders do not result in heavier impacts: The effects of non-native bullfrogs on native anurans are mitigated by high densities of non-native crayfish.

With accelerating species introductions in an era of globalization, co-occurring alien species have become increasingly common. Understanding the combined ecological impacts of multiple invaders is not only crucial for wildlife managers attempting to ameliorate biodiversity loss, but also provides key insights into invasion success and species coexistence mechanisms in natural ecosystems. Compared with much attentions given to single-invader impacts, little is known about the impacts of multiple co-occurring invaders. The American bullfrog (Lithobates catesbeianus=Rana catesbeiana) and the red swamp crayfish (Procambarus clarkii) are two aquatic invasive species in many different areas of the globe. They coexist with native anurans in a variety of permanent lentic waters, which provide an ideal model system to explore the combined effects of multiple invaders from different trophic levels on native species. Based on a global diet analysis covering 34 native and invasive bullfrog populations, and data from 10-year field surveys across 157 water bodies in the Zhoushan Archipelago, China, we observed a reduced impact of bullfrogs on native anurans at high crayfish densities when the two invaders co-occurred. The global diet analysis showed that crayfish occurrence reduced the number of native anuran prey consumed by bullfrogs in both native and invasive populations. After accounting for pseudoreplication of different observations among water bodies, islands, and survey time, model averaging analyses based on GLMMs showed a negative relationship between bullfrog density and native anuran densities for field observations of invasive bullfrogs alone and co-invaded observations with low crayfish density. However, this negative relationship disappeared when the two invaders co-occurred with high crayfish density. Structural equation modelling (SEM) analyses further validated that the impacts of bullfrogs on native frogs were mitigated by the negative interactions between crayfish and bullfrogs. Our results provide novel evidence of a density-dependent antagonistic effect of two sympatric invaders from different trophic levels on native species. This study highlights the importance of considering complex interactions among co-invaders and native species when prioritizing conservation and management actions and will facilitate the development of a more precise framework to predict invasion impacts.

Preliminary data on the distribution, morphology and genetics of white-clawed crayfish and on their ectosymbionts in Lunigiana (Tuscany, Italy)

The white-clawed crayfish is a complex of species (Austropotamobius pallipesplusA. italicus, Crustacea) pivotal to riverine environments. Regrettably, it is endangered in many European countries due to a recent massive decline. We carried out a fine-scale survey on white-clawed crayfish distribution, morphology and genetics in an under-investigated region of central Italy (Lunigiana, Tuscany) to improve local knowledge and aid conservation management of the species. The torrential fauna of Lunigiana is scarcely known and habitat alterations due to the anthropic exploitation of the territory represent a potential threat to its persistence. We investigated crayfish occurrence in eight streams of the Magra River Basin. We performed nocturnal and diurnal transects, took morphometric measurements, collected samples for genetic analysis and checked for the occurrence of ectosymbionts. Crayfish were disclosed in two streams (Civasola, Verdesina). Morphometric and phylogenetic analysis (mtDNA COI gene Bayesian tree reconstruction) concurrently identified both populations asAustropotamobius italicus carinthiacus. In the Verdesina stream, crayfish were heavily infested by branchiobdellidans (Annelida). Verdesina crayfish were also significantly smaller than those found in the Civasola stream, where branchiobdellidans were absent. Hence, we hypothesized that such difference in size might be related to the high density of ectosymbionts. In the light of habitat features and of data herein provided, we propose that both Civasola and Verdesina streams should be considered as “natural ark sites” forA. italicus, with the Magra River Basin representing a regional stronghold for the conservation of the species.

First record of the spiny-cheek crayfish (Orconectes limosus) in Slovenia – 300 km upstream from its known distribution in the Drava River

The spiny-cheek crayfish Orconectes limosus (Rafinesque, 1817) is one of the most problematic invasive crayfish species in Europe. Here we report the first occurrence of spiny-cheek crayfish in Slovenia, 300 km upstream from the previously known records in the mouth of Drava River in Croatia. The species was not expected to colonize this area for at least two decades. This new isolated population will significantly alter our predictions of the ongoing colonization of the Drava River basin in Austria, Slovenia and Croatia.

Expansion of the marbled crayfish in Slovakia: beginning of an invasion in the Danube catchment?

The marbled crayfish, <em>Procambarus fallax</em> f. <em>virginalis</em>, is a taxon widely available in the aquarium pet trade, which has been introduced to open waters in several European countries and in Madagascar. Recent studies confirmed this parthenogenetically reproducing crayfish as a high-risk invasive species, and vector of the crayfish plague pathogen, <em>Aphanomyces</em> <em>astaci</em>. It has been first discovered in Slovakia in 2010, but the status of the local population was not studied since then. Due to enlarged sampling area around the first report and one locality, where we presupposed the crayfish occurrence, we identified new marbled crayfish populations. Here, we report presence of three newly established marbled crayfish populations in Slovakia. Two populations are located critically close to the Váh River, a major tributary of the Danube River; one of them being directly connected to the Váh River <em>via</em> a side channel during occasional floods. The third established marbled crayfish population was found at the mouth of a thermal stream flowing into the Nitra River, a tributary of the Váh River. In this stream, crayfish coexist with other exotic fish and gastropod species of aquarium origin. We presume that the reported localities may serve as a source for further expansion of the marbled crayfish in the mid-part of the Danube catchment. Floods, active dispersal (including overland), passive dispersal by zoochory or anthropogenic translocations are among the major drivers facilitating the marbled crayfish colonization. We have not detected the crayfish plague pathogen in any of the studied populations. However, if spreading further, the marbled crayfish will encounter established populations of crayfish plague carriers in the Danube River, in which case they may acquire the pathogen by horizontal transmission and contribute to spread of this disease to indigenous European crayfish species.

Artificial water points for wildlife management facilitate the spread of red swamp crayfish (Procambarus clarkii)

The red swamp crayfish (Procambarus clarkii) has been widely introduced into aquatic systems all around the world, triggering multiple impacts. In Donana Natural Area, Abalario and the Biological Reserve of Donana, Spain (one of the most important biodiversity reserves in Europe), the red swamp crayfish was first introduced in 1974 and expanded its range quickly through marsh habitat, but distributed more slowly throughout scrubland ponds. Water persistence, salinity, and substrate can condition the presence of the species in the wild. Before the creation of the Natural Area and the Biological Reserve of Donana, farmers dug artificial water points in some scrubland ponds to provide water throughout the year for livestock. Once declared a protected area, managers assumed control of the maintenance of the park and opened new water points as a wildlife management tool. The aim of the study presented here was to determine the environmental conditions that favor the spread of crayfish in the temporal ponds of Donana and whether the occurrence of water points increases the spread of crayfish. For this purpose, we sampled crayfish using a sweep net in 60 randomly selected ponds in two different areas of Donana. Crayfish occurrence was significantly related to the presence of seasonal streams connecting the ponds with refuge areas and to the presence of artificial water points within the pond. The probability of occurrence of red swamp crayfish in a pond without seasonal streams was more than 5 times lower than that in a pond with seasonal streams. The probability of crayfish occurrence in ponds without artificial water points was 2.5 times lower than that in ponds with artificial water points. We review the advantages and disadvantages of water points as a management tool.

Factors inducing overland movement of invasive crayfish (Procambarus clarkii) in a ricefield habitat

The red swamp crayfish (Procambarus clarkii) is a widespread invader which can disperse overland. This study was conducted to determine which factors can induce overland dispersal. During 12 months, the numbers of P. clarkii out of water were monitored at an experimental rice research station. Data were obtained on preferential time period for overland dispersal; population structure on land and in water; direction of movement; and the relation between environmental variables and the occurrence of crayfish out of water. A main factor inducing overland dispersal was intentional drainage of the study area associated with rice cultivation. During post-drainage, crayfish dispersal overland was positively correlated with rainfall. Other variables significantly affecting the overland dispersal of crayfish were the relative humidity, air temperature and the period of the day. We found significant differences in the structure of the trappable population in the water and of the individuals out of the water, with a higher proportion of mature individuals dispersing overland. Because overland migrants were dominated by mature individuals, often with eggs or hatchlings attached to the abdomen, these may effectively colonize new areas.