Does the introduced signal crayfish occupy an equivalent trophic niche to the lost native noble crayfish in boreal lakes?

The introduced North-American signal crayfish (Pacifastacus leniusculus) has become widespread throughout Europe where it has often replaced the native noble crayfish (Astacus astacus). The impact of this replacement on ecosystem processes in boreal lakes is still largely unknown. We compared the trophic niches of these two crayfish species in 16 small to medium sized boreal lakes in southern Finland; eight lakes with noble crayfish and eight lakes where the native crayfish populations had been lost and replaced by signal crayfish. We analysed carbon and nitrogen stable isotopes from samples of the crayfish and their putative food sources, and used stable isotope models to compare trophic niche widths of the two species of crayfish and to quantify the food sources used by them. At species level the signal crayfish exhibited a substantially larger trophic niche than that of the noble crayfish, but within-lake populations of the species did not differ in their niche widths. The isotopic niches of the two species strongly overlapped, and while the estimated proportions of food resources (profundal and littoral macroinvertebrates, terrestrial leaf detritus and macrophytes) used by crayfish varied considerably among individual populations, they did not differ consistently between the species. Our results suggest that, contrary to often expressed concerns, replacement of lost noble crayfish populations by the signal crayfish may not greatly alter the littoral food web structure in boreal lakes.     

Non-indigenous signal crayfish <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> are now common in Danish streams: preliminary status for national distribution and protective actions

North American signal crayfish (Pacifastacus leniusculus) are invasive in Europe and pose a serious threat to indigenous European crayfish such as the noble crayfish (Astacus astacus). This is mainly because signal crayfish is the carrier of crayfish plague agent, Aphanomyces astaci, which freshwater crayfish from all other continents are highly susceptible to. Until recently, the distribution of signal crayfish in Danish streams has been considered local and restricted to a small geographical area. Here we present data demonstrating that signal crayfish are now widespread in Denmark, including the largest Danish river, River Gudenå. For one of the rivers where co-existing signal crayfish and indigenous noble crayfish were documented, sensitive molecular tests could not detect the crayfish plague agent Aphanomyces astaci in either species. Hence, it seems that not all signal crayfish are chronic carriers of the disease. For the remaining freshwater systems with the introduced signal crayfish, the infection status is presently unknown. Large areas of the freshwater systems in Denmark also remain unexplored with respect to presence/absence of signal crayfish and noble crayfish. Nevertheless, our preliminary data that covers about 14% of the Danish rivers, strongly suggests that signal crayfish should be considered as a common invader that poses an increased threat to the biota in Danish streams, in particular for the indigenous noble crayfish.     

Microsatellite markers reveal clear geographic structuring among threatened noble crayfish (Astacus astacus) populations in Northern and Central Europe

Noble crayfish (Astacus astacus L.), the most highly valued freshwater crayfish in Europe, is threatened due to a long-term population decline caused mainly by the spread of crayfish plague. Reintroduction of the noble crayfish into restored waters is a common practice but the geographic and genetic origin of stocking material has rarely been considered, partially because previous genetic studies have been hampered by lack of nuclear gene markers with known inheritance. This study represents the first large scale population genetic survey of the noble crayfish (633 adults from 18 locations) based on 10 newly developed microsatellite markers. We focused primarily on the Baltic Sea area (Estonia, Finland and Sweden) where the largest proportion of the remaining populations exists. To allow comparisons, samples from the Black Sea catchment (the Danube drainage) were also included. Two highly differentiated population groups were identified corresponding to the Baltic Sea and the Black Sea catchments, respectively. The Baltic Sea catchment populations had significantly lower genetic variation and private allele numbers than the Black Sea catchment populations. Within the Baltic Sea area, a clear genetic structure was revealed with population samples corresponding well to their geographic origin, suggesting little impact of long-distance translocations. The clear genetic structure strongly suggests that the choice of stocking material for re-introductions and supplemental releases needs to be based on empirical genetic knowledge.     

Plasticity in fecundity highlights the females’ importance in the spiny-cheek crayfish invasion mechanism

Invasion is one of the most consequential phenomena affecting the distribution of native species. Few in number of species, European crayfish are losing the competition with introduced North American crayfish. The spiny-cheek crayfish, Orconectes limosus, is an outstanding example, successfully competing against the native narrow-clawed crayfish, Astacus leptodactylus. For four years, we collected data regarding crayfish occurrences, their relative abundance, and the structure of populations in the ongoing colonisation process of O. limosus in the lower Danube. The mature females of both invasive and indigenous crayfish species were analysed with respect to biometry and production of oocytes in relation to the dynamics of invasion. The interspecific comparisons showed no significant differences regarding body size, with an average of approximately 102 mm total length and 31 g wet weight for both species. However, the fecundity of the indigenous species was found to be constant throughout the investigated area, whereas the number of eggs produced by the invasive females was significantly increased at the active front of the invasion. The maximum number of ovarian eggs found was 887 and 1156 in the indigenous species and the invasive species, respectively. We propose the scenario that the invasive species, which carries the deadly crayfish plague, creates an ecological advantage by reducing the populations of indigenous crayfish. Subsequently, the invasive females opportunistically use the available resources to enhance their fecundity, resulting in the acute growth of populations. However, the long-term competitiveness and colonisation success of O. limosus still remain in question.     

Associations between stream habitat characteristics and native and alien crayfish occurrence

Human mediated introductions of non-indigenous crayfish species (NICS) are responsible for their rapid colonisation of European freshwaters. The introduction of North American crayfish is furthermore linked to the spread of crayfish plague and the decline of indigenous crayfish species (ICS). As the management of ICS and NICS have become necessary, a detailed knowledge on their distribution and ecological requirements is needed. We studied the current range of native noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium, as well as alien signal crayfish Pacifastacus leniusculus in Carinthia (Austria) and evaluated environmental and physical habitat features in streams with and without crayfish. Meanwhile, the loss of many ICS populations was recorded and alien P. leniusculus was found to be widespread in this region. Most of the habitat features of streams having crayfish differed significantly from sites lacking crayfish for at least one investigated native or alien species. Furthermore, multivariate and regression analyses showed specific differences in the habitat use of the investigated crayfish. Our results showed that the presence of alien P. leniusculus was associated with larger and smoother sloped lowland rivers, while the occurrence of the two native species was confined to smaller streams either at higher altitudes and with distinct physical habitat conditions (A. torrentium) or with moderate water temperatures (A. astacus). This study helps to identify potential refuge areas for the endangered native species and to predict the further spread of the most common non-native crayfish species in European streams.     

The introduced signal crayfish and native noble crayfish have different effects on sublittoral macroinvertebrate assemblages in boreal lakes

相似文献   

Post-mating spermatophore storage strategies in two species of crayfish: implications for broodstock management

Female crayfish stores male gametes after mating until the beginning of egg laying and fertilization. The aim of the present study was to investigate the duration of post-mating spermatophore storage as well as the timing and temperature of spawning in two crayfish species of economic importance, namely the signal crayfish Pacifastacus leniusculus and the noble crayfish Astacus astacus. Results showed that the average duration of the post-mating spermatophore storage is significantly (P<0.05) longer in the noble crayfish (34.6±1.7 days, range: 19 to 60 days) than the signal crayfish (3.9±0.5 days, range: 1 to 18 days). The highest percentages of the post-mating spermatophore storage duration in the signal crayfish (46.5%) and the noble crayfish (44.5%) were 1 and 31 to 40 days, respectively. While there is an overlap in the timings of mating and egg laying in the signal crayfish, these two reproductive processes were not observed at the same days in the noble crayfish and there was at least 2 weeks interval between last mating and first egg laying individuals. Average mating and egg laying temperatures were significantly (P<0.05) higher in the signal crayfish than the noble crayfish. The average temperatures for mating in both species were significantly (P<0.05) higher than the temperatures that they utilized for egg laying. In conclusion, female noble crayfish stores post-mating spermatophores a longer duration compared with the signal crayfish. Also, the signal crayfish mates and lays egg in temperatures that are higher than the noble crayfish. Spawning season is shorter in the signal crayfish compared with the noble crayfish. The results of present study provide information contributing to the crayfish broodstock management in aquaculture.     

Absence of the crayfish plague pathogen (Aphanomyces astaci) facilitates coexistence of European and American crayfish in central Europe

1. Most European crayfish species are strongly threatened, mainly as a result of the introduced pathogen, Aphanomyces astaci, transmitted by invasive North American crayfish. Long‐term coexistence of American and European crayfish species is therefore regarded as almost impossible, even though some coexisting populations have been observed. 2. In this study, crayfish were collected from presently coexisting populations of the introduced spiny‐cheek crayfish (Orconectes limosus) and the native noble crayfish (Astacus astacus) from nine standing waters in central Europe. Our aim was to resolve whether the coexistence resulted from reduced virulence in local strains of A. astaci, increased immunity in the native crayfish or an absence of the pathogen in these populations. We used highly sensitive A. astaci‐specific real‐time PCR to evaluate the crayfish latent carrier status, combined with transmission experiments to further validate the molecular results. 3. From the total of 523 crayfish tested (490 spiny‐cheek crayfish, 33 noble crayfish), none positive for A. astaci was detected. Transmission experiments confirmed these results: No abnormal mortality or behavioural changes were seen in noble crayfish kept together with American crayfish from the coexisting populations. If we assume a very low prevalence of A. astaci of 10% in a carrier population, there is a 98% probability of disease being absent in five of the nine coexisting populations tested. Hence, a consistent absence, or an extremely low prevalence, of A. astaci seems to allow the coexistence of European and American crayfish in these central European populations. 4. The results are important for native crayfish conservation and management and demonstrate that disease transmission risk may vary substantially between the different populations of spiny‐cheek crayfish in central Europe.     

The distribution and the abundance of hydrophytes along the Danube River in Serbia

The Danube River runs through Serbia with flow 588 km long. Different hydrological, geological and ecological conditions occuring along the Danube in Serbia enables its division into four sections: The upper region, Đerdap I accumulation, Đerdap II accumulation, and the lower region. Each section is characterized by unique plant species diversity, frequency of occurrence and distribution pattern. The species diversity ranged from low in the upper reach, to high or very high in the impoundments and decreased in the lower reach. This paper provides a basis for a detailed study on the influence of large power plant impoundments over the aquatic vegetation of rivers.     

First records of the non-indigenous signal crayfish (<Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis>) and its threat to noble crayfish (<Emphasis Type="Italic">Astacus astacus</Emphasis>) populations in Estonia

This study gives an overview of status and distribution of signal crayfish (Pacifastacus leniusculus), the first NICS in Estonia and its influence on native noble crayfish (Astacus astacus) populations. The first specimen of signal crayfish was caught during the monitoring of noble crayfish in North Estonia in 2008. The signal crayfish has since been found in three additional sites. Test fishing has indicated that the abundance of signal crayfish has been fluctuating between years and among localities. It has had strong negative impact on abundance of one noble crayfish population. The disconnected distribution of signal crayfish strongly suggests that these populations are the result of human-assisted introductions. Real-time PCR analyses proved that signal crayfish carry the causative agent of the crayfish plague, an oomycete Aphanomyces astaci, thus contributing to its spread. Mortalities in noble crayfish populations had been caused by A. astaci strains from A, B and E genotype group.     

Genetic characterization of Western European noble crayfish populations (<Emphasis Type="Italic">Astacus astacus</Emphasis>) for advanced conservation management strategies

One central goal of conservation biology is to conserve the genetic diversity of species in order to protect their adaptive potential. The main objective of this study was to identify management units (MUs) for the threatened noble crayfish (Astacus astacus) in Western Europe by utilizing sequence and microsatellite analysis to determine populations in need of focused conservation programs. With the analysis of noble crayfish from 31 sampling sites from Belgium, France, The Netherlands and Germany, and further comparison of this data with a European-wide dataset, we propose four distinct MUs: the French Meuse (MU 1), the French Rhine (MU 2), the Belgian Scheldt and Meuse (MU 3) as well as populations from the French Seine (MU 4). This knowledge enables advanced A. astacus conservation management practises in these catchments by distinguishing between outbreeding and inbreeding populations and by preserving the maximum genetic diversity. When required, a high genetic diversity can be conserved by strengthen existing populations via stocking with populations that either bear the most common haplotype or population-specific private haplotypes in order to maintain recent and regional adaptions. Above all, stocking with populations that exhibit haplotypes from outside Western Europe should be avoided in these catchments. This study supports the preservation of the genetic diversity of noble crayfish in Western Europe and provides thus a proposition for advanced conservation management.     

Invasive crayfish and crayfish plague on the move: first detection of the plague agent Aphanomyces astaci in the Romanian Danube

Native European crayfish, such as Astacus leptodactylus, are threatened, among other factors, by the crayfish plague agent Aphanomyces astaci, dispersed by invasive North American crayfish. Two of these invaders, Pacifastacus leniusculus and Orconectes limosus, have extended their distribution in the River Danube catchment; the latter was detected for the first time in Romania in 2008. We monitored, at monthly intervals for over 2 yr, occurrence of native A. leptodactylus and invasive O. limosus at 6 sites on the Romanian Danube and checked for the invasive species in 4 of its tributaries. Between January 2009 and March 2011, the relative abundances of O. limosus steadily increased with time, while the native A. leptodactylus dramatically decreased in abundance. O. limosus expanded downstream at a rate of ca. 15 km yr-1; in August 2011, it was already present in the upper 105 km of the Romanian Danube. An agent-specific real-time PCR analyses demonstrated the presence of A. astaci DNA in at least 32% of the analysed invasive (n = 71) and 41% of the native (n = 49) crayfish coexisting in the Danube. Furthermore, A. astaci was also detected in A. leptodactylus captured about 70 km downstream of the O. limosus invasion front (at the time of sampling). Assuming a steady rate of expansion, O. limosus may invade the sensitive Danube delta area in the mid-2060s, even without long-distance dispersal. The crayfish plague agent, however, may reach the delta substantially earlier, through dispersal downstream among populations of native crayfish.     

Threat of non-native crayfish introductions into Turkey: global lessons

Introductions of crayfish species from their home range to new environments have been carried out in many parts of the world. The most important introduced crayfish species are Procambarus clarkii, Pacifastacus leniusculus, Cherax destructor, C. quadricarinatus, Orconectes limosus, O. rusticus and Astacus leptodactylus. The environmental impact of crayfish introductions can be positive, negative or neutral. However, native crayfish populations in Europe have been negatively affected by introductions of non-indigenous crayfish species from America. Negative effects of non-native crayfish introductions included displacement of native crayfish species, transfer of disease (crayfish plague), consumption of fish eggs, reduction of fish stocks, consumption of large amounts of macrophytes, indirect and direct effects on other invertebrates and upsetting production in rice fields. As a result of non-native crayfish introductions, the natural harvest and crayfish industry in Europe have been severely affected. Large quantities of Turkish A. leptodactylus were harvested (approximately 7,000 tonnes annually) and exported to Europe before the crayfish plague was observed in these populations. The total harvest of A. leptodactylus in Turkey reduced dramatically to 320 in 1991 after the plague. Therefore, although Turkey currently has no known non-native crayfish species, there is a threat of non-native crayfish introduction in order to increase crayfish productions and subsequent harvest. The North American spiny-cheek crayfish, O. limosus, has been spreading quickly down the River Danube and could soon reach neighboring countries including Turkey. The North American signal crayfish, P. leniusculus is known from Greece and could be a threat to native stocks if it is introduced into Turkey for aquaculture. Additional threats may come from the release of other North American species, which are widely available through the aquarium trade. We conclude that the spread of non-native crayfish introductions throughout Turkey will increase local problems, because introductions of non-native crayfish in many parts of the world have been known to have caused important reductions in population density and numbers of native crayfish species. Furthermore, freshwater ecosystems may be altered by such introductions and the economic viability of native crayfish species fisheries could be severely reduced in Turkey.     

Phylogeography of noble crayfish (Astacus astacus) reveals multiple refugia

相似文献   

Phylogeographic analysis reveals northerly refugia for the riverine amphibian Triturus dobrogicus (Caudata: Salamandridae)

We investigated the recent evolutionary history of the Danube crested newt, Triturus dobrogicus through reconstructions of: (1) the number and position of refugia at the last glacial maximum, (2) the role of major central European rivers in pattern of post‐glacial dispersal, and (3) the present‐day distribution pattern. We analysed sequences of mitochondrial DNA (ND2, 1065 bp) and six microsatellite loci in 363 T. dobrogicus individuals from 58 populations covering the range of the species. Our analyses suggested that T. dobrogicus survived the last glacial maximum in two separate refugia positioned in northwestern Pannonia and in Southern Pannonia from where its range expanded along the Danube and Tisza Rivers. Our findings also confirmed that rivers played an important role in shaping the evolutionary history of amphibian species in Central Europe. We compared the T. dobrogicus range with another lowland amphibian, the fire‐bellied toad Bombina bombina, using species distribution modelling. In line with these models, the isolated mountains inside Pannonia are occupied not by B. bombina, but by its mountain‐dwelling sister‐species B. variegata. However, in contrast to the model, crested newts (including T. dobrogicus) are absent from these mountains. We attribute this biogeographical discrepancy to the positioning of the species’ refugia at the last glacial maximum.     

Habitat use and population biology of the Danube Clouded Yellow butterfly Colias myrmidone (Lepidoptera: Pieridae) in Romania

The Danube Clouded Yellow (Colias myrmidone) is one of the most endangered butterflies in Europe. Its distribution range shrank dramatically in the last few decades due to the extinction of populations in Western and Central Europe. Ecological studies were commenced when populations were already at the verge of extinction, thus our knowledge on the population ecology and habitat use of this butterfly is very limited. Here we report the results of a study on habitat preferences, egg distribution and demography of C. myrmidone in Romania, perhaps the last remaining stronghold of the species in Central Europe. We found that Danube Clouded Yellow adults occurred mainly in mesophilous grasslands created by forest clearing and then maintained by low intensity grazing allowing bushes and forest-edge vegetation to develop and host Chamaecytisus species to grow. Butterflies highly preferred lightly grazed pastures over hay meadows and abandoned grasslands, their density was positively related to host plant density. Egg-laying females preferred habitat patches with relatively high cover of the host plant and tall vegetation. Both apparent survival rate and encounter probability were lower for females than males, and parameter estimations also had much higher errors for females. These indicate that much higher sampling effort is needed to estimate and monitor population parameters for females than for males. Our results provide guidelines for the habitat management and population monitoring of Colias myrmidone, thus may significantly contribute to its successful conservation.     

Diatoms prefer strangers: non-indigenous crayfish host completely different epizoic algal diatom communities from sympatric native species

Despite their wide distribution and ecological importance, almost no information is available about the role of freshwater crayfish as basibiont for epizoic algae. Moreover, studies on epizoic freshwater diatoms have been largely neglected. In this study, we examined the occurrence of diatoms on two sympatric species, the native white-clawed crayfish Austropotamobius pallipes and the non-indigenous signal crayfish Pacifastacus leniusculus, coexisting in the same stream in NW Italy. We detected that signal crayfish showed a far more productive epizoic algal community than white-clawed crayfish. Microscopical analysis confirmed that non-indigenous crayfish hosted rich and diversified diatom communities while virtually no diatom was found on the native. After analyzing different hypotheses, we suggested that this significant difference can be the result of diverse crayfish behavioral habits. Because of the lack of studies investigating epibiontic diatoms on freshwater crayfish, we performed a detailed characterization on the epizoic flora, including comparisons with natural epilithic communities. The exponential diffusion of non-indigenous freshwater crayfish is a subject of greatest interest. Increasing our knowledge on their role as basibionts is definitely necessary to better understand their ecological role, also considering their influence on primary producer community and their role as vectors of algal species of concern, such as Didymosphenia geminata.     

Boldness as a consistent personality trait in the noble crayfish, <Emphasis Type="Italic">Astacus astacus</Emphasis>

Consistent individual differences in behavioural responses to perceived predation risk may have extensive ecological and evolutionary implications. We studied the repeatability of boldness across time and its relation to resource holding potential in the noble crayfish, Astacus astacus L., using predator-naïve immature individuals. We followed individual’s shelter use both with and without exposure to the chemical and physical cues of predators, and with and without the presence of a conspecific. In addition, we examined if armament, i.e. relative chelae size, would be correlated with individual differences in behaviour. Individuals showed repeatable behaviours across time and context. Individuals that occupied the shelter in competitive dyadic tests also spent more time in the shelter during individual control observations, suggesting that boldness is a personality trait that does not necessarily relate positively to high resource holding potential in the noble crayfish. The relative size of chelae did not correlate with any of the measured behavioural variables. Our results suggest that boldness can be considered as individually consistent and ecologically important personality trait in the noble crayfish.     

Isolation and characterization of first microsatellite markers for the noble crayfish, <Emphasis Type="Italic">Astacus astacus</Emphasis>

Noble crayfish (Astacus astacus) is listed as vulnerable by the IUCN Red List of Threatened Species in Europe. However, very little is known about genetic diversity and structuring of noble crayfish populations, mainly because of the lack of informative genetic markers. We describe the isolation and characterization of the first microsatellite markers for this species, which were obtained by screening 4,000 recombinant clones. Eight loci revealed polymorphisms in a panel of 172 individuals from seven populations in Northern Europe. Number of alleles per locus ranged from two to 10 (average 4.4) and heterozygosity levels among populations varied from 0 to 0.80 for H _o and from 0 to 0.72 for H _e.     

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.