Alien Crayfish Research Articles

The importance of allochthonous litter input on the biomass of an alien crayfish in farm ponds

AbstractTo evaluate the effects of allochthonous litter input on the population density of invasive red swamp crayfish (Procambarus clarkii) in Japanese farm ponds, we analyzed gut contents, stable isotope ratios, and the correlation between crayfish biomass and environmental factors in the ponds. For our correlation analysis, we used Akaike's information criterion (AIC) corrected for small sample size (AICC) to select appropriate models within the generalized linear model. Allochthonous litter input was the most influential variable affecting crayfish biomass, followed by pond area. Gut content analysis demonstrated a positive correlation between the percentage of litter in the crayfish gut and the amount of litter input into the pond from which animals were collected. Crayfish δ13C became increasingly similar to litter δ13C as litter input into ponds increased. Nitrogen isotope signature analysis suggested that microorganisms attached to litter may contribute to crayfish diet. The above results obtained by three complementary approaches demonstrated an important influence of allochthonous litter input on crayfish biomass in farm ponds. We propose that the appropriate management of surrounding forests may be effective in controlling the abundance of exotic crayfish with minimized impacts on native communities.

Identification of exotic North American crayfish in Europe by DNA barcoding

Several alien crayfish of North American origin have become established in Europe in recent decades, but their identification is often confusing. Our aim was to verify the taxonomic status of their European populations by DNA barcoding. We sequenced the cytochrome c oxidase subunit I (COI) gene fragment of individuals representing all American crayfish known from European waters, and compared the results with reference sequences from North America. Our results confirm the morphological identification of Orconectes juvenilis from a population in eastern France, and of the marbled crayfish (Marmorkrebs),i.e., a parthenogenetic form of Procambarus fallax, from south-western Germany. Sequences of most individuals of presumed Procambarus acutus from the Netherlands were similar to American P .c f.acutus, but one was divergent, closer to a sequence of a reference individual of P .c f.zonangulus. However, divergences among three American P .c f.zonangulus samples were also high, comparable to interspecific variation within cambarid species complexes. The divergence between O. immunis from Europe and America also reached values corresponding to those observed among distinct Orconectes species. Genetic variation in the American range of these crayfish should therefore be further studied. Our study shows that DNA barcoding is useful for the rapid and accurate identification of exotic crayfish in Europe, and also provides insights into overall variation within these taxa.

The North American crayfish Procambarus clarkii is the carrier of the oomycete Aphanomyces astaci in Italy

Aphanomyces astaci (Saprolegniales, Oomycetes) is classified among the 100 world’s worst invasive species. This species is endemic to North America and has been introduced into Europe by imports of their hosts, the North American crayfish species. As a consequence, extensive mass mortalities involved several populations of the European crayfish. Here, we checked its occurrence in four Italian populations of Procambarus clarkii, the most widespread alien crayfish in Italy. Digital image analyses and image processing techniques were used to select micro-melanized areas in the subabdominal cuticle of 2–10 crayfish per population. All the selected areas tested positive for A. astaci ITS nrDNA specific primers; moreover, the obtained sequences clearly corresponded to A. astaci, thus revealing that P. clarkii is an active carrier of this oomycete in Italy. Decisions are to be urgently made to control the spread of both P. clarkii and A. astaci for the conservation of the indigenous crayfish biodiversity.

The Bait Industry as a Potential Vector for Alien Crayfish Introductions: Problem Recognition by Fisheries Agencies and a Missouri Evaluation

Abstract“Bait‐bucket introductions” related to the fishing bait industry are the suspected primary cause of alien (non‐indigenous) crayfish introductions that have damaged North American aquatic ecosystems. Our 2008 survey of U.S. and Canadian fisheries agencies revealed that 49% of respondents reported aquatic resource problems that were believed to have been caused by bait‐bucket introductions of alien crayfishes. Most respondents reported existing regulations designed to address those problems; however, only 4% prohibited the use of live crayfish bait. Our 2002–2007 examination of Missouri bait shops revealed sales of illegal and invasive alien crayfishes by bait shop proprietors who could not identify the species they were selling. Fisheries agencies should consider more effective bait regulations and education to prevent negative impacts to aquatic biodiversity, habitat, and fisheries that can result from alien crayfish introductions.

The new threat to Italian inland waters from the alien crayfish “gang”: the Australian Cherax destructor Clark, 1936

Biological invasions inflict damage to the ecology, economy, and human health, and pose serious threats to the native communities. Among the many invasive taxa, crayfish have attracted much attention by scientists and policy makers. Recently, an established population of an alien species of crayfish, new for Italy, was found in the Natural Preserve of “Laghi di Ninfa” (central Italy). Based on morphological and genetic evidence (molecular barcoding of COI and 16S rDNA), we classified it at subspecies level as the Parastacidae Cherax destructor destructor, native to Australia. Its introduction possibly occurred at the end of the 1980s but the species seems to be still confined in the preserve. The low temperature of the adjacent waters may be a barrier against its natural spreading but not against its intentional translocation into natural waters by man. Because of the invasive history of C. destructor, eradication of this population is urgent and still economically profitable.

Size-dependent impacts of invasive alien crayfish on a littoral marsh community

The invasive signal crayfish ( Pacifastacus leniusculus) may undergo ontogenetic diet shifts with increasing size, but the consequences of crayfish size–structure changes for aquatic food webs are little known. We evaluated size-dependent impacts of signal crayfish on a littoral marsh food web using in-situ enclosures in a northern Japanese marsh. During the 60-day experiment, large crayfish (<30 mm orbital carapace length) rapidly eliminated submerged macrophytes through mechanical destruction while the comparable impacts of small crayfish (>30 mm) appeared after more time had passed. Benthic algal biomass was reduced in the presence of large crayfish but was affected little by small crayfish, suggesting that large crayfish were significant bioturbators. On the other hand, total invertebrate biomass was reduced while total invertebrate density was enhanced in the presence of both crayfish size classes. Potential crayfish impacts on invertebrates are: (1) predation on large vulnerable taxa such as Trichoptera and predatory invertebrates, (2) mechanical destruction of macrophytes, thereby reducing microhabitats for invertebrates, (3) heightened emigration of invertebrates in response to bioturbation and/or (4) predation or competition release on small invertebrates as a result of crayfish reducing their predators/competitors. Invertebrate taxa richness was nearly halved in the presence of large crayfish, probably reflecting reductions of rare taxa. Overall, functional roles of signal crayfish as omnivores and ecosystem engineers remained similar during the ontogenetic stage but the magnitude and rate of crayfish impacts intensified with increasing crayfish size. Thus, removal of large invasive crayfish alone may reduce detrimental impacts on aquatic biodiversity.

The Invasive Crayfish Orconectes Limosus in Lake Varese: Estimating Abundance and Population Size Structure in the Context of Habitat and Methodological Constraints

Invasive alien species (IAS) potentially may alter all levels of the ecological organization of aquatic water bodies. Therefore, in the context of the EU Water Framework Directive, they represent a significant pressure that should be considered in the assessment of the ecological status of a water body and in the formation of restorative programs. A study was carried out to examine different sampling techniques and to assess the current population structure and the differences in spatial distribution of the alien crayfish Orconectes limosus at four sites in Lake Varese (Northern Italy). Three methods were used to assess the crayfish population: mark-recapture, catch per unit effort during night-time snorkelling and quadrat sampling. For the mark-recapture exercise the ventral somites of crayfish were marked using visible implant elastomer tags. A laboratory experiment was used to verify the effectiveness of elastomer tags for the species prior to their use in the field. Crayfish were more abundant at sites characterized by stone substrate than at sites dominated by macrophytes. Hydromorphological alteration of the shoreline (quantified using the newly developed lake habitat survey methodology) at one site appeared to promote the establishment of alien crayfish. Crayfish caught by snorkeling in open water led to an underestimation of the smallest size-classes compared with underwater quadrats. Underwater quadrats on stone substrates provide a quantitative estimation of abundance and size-structure allowing the comparisons of crayfish populations from different lakes. This method could be applied to assess the extent of pressure resulting from alien crayfish under the Water Framework Directive. Crayfish biomass was found to be 82.9% of other macroinvertebrates indicating their importance in the structure and functioning of the lake ecosystem. The presence of a second alien species of crayfish, Procambarus clarkii, was recorded for the first time in the lake.

Shifts in aquatic macroinvertebrate biodiversity associated with the presence and size of an alien crayfish

AbstractTo investigate the effects of Procambarus clarkii on macroinvertebrate diversity, we conducted a mesocosm experiment simulating small pools in rice field pads after the rice season. We hypothesized that crayfish predation would negatively impact macroinvertebrate diversity, and the magnitude of this impact should vary with the size of P. clarkii. We conducted a short‐term mesocosm experiment to determine macroinvertebrate diversity in the presence of three size classes and in the absence of crayfish, as well as the diet composition of crayfish from the three size classes. At the end of the experiments, the diet of crayfish was composed of the most available taxa (Culicidae, Chironomus, Tanytarsini and Orthocladinae). These results also show evidence that, in confined areas, crayfish are important predators of major rice pests such as rice Chironominae larvae. Macroinvertebrate diversity was negatively affected by crayfish presence, but the effect was inversely proportional to crayfish size. The highest diversity index was obtained in the absence of P. clarkii, and juvenile crayfish significantly reduced macroinvertebrate diversity. Thus, the impact of P. clarkii on aquatic macroinvertebrates is size dependent and may be relevant in small pools formed in rice field pads from early autumn to late winter. Overall, our findings suggest that the negative effects of P. clarkii on macroinvertebrate diversity may be particularly strong in local natural assemblages confined to puddles of water or small ponds in wetland areas.

Alien vs. endemic crayfish: roles of species identity in ecosystem functioning

In northern Japan, an alien crayfish species (signal crayfish; Pacifastacus leniusculus) is replacing Japan's only native crayfish species (Cambaroides japonicus) that is endemic to the country. We tested experimentally if these two crayfish species had similar roles in terms of ecosystem functioning in stream habitats. Experiments were performed to examine the impacts of alien and endemic crayfish on detritus-based food webs. During the experiment, neither crayfish species affected rates of breakdown of microbially conditioned oak leaves. In contrast, the amphipod Jesso-gammarus jesoensis, which dominated the non-crayfish invertebrate biomass, was significantly reduced in the presence of the two crayfish species. Thus, effects of crayfish on leaf breakdown were probably masked by the leaf processing activities of these large amphipods in the absence of crayfish. Overall, per-unit biomass impacts of Pacifastacus on leaf processing and invertebrate colonisation of leaves were comparable to those by Cambaroides. Laboratory experiments were performed to test whether rates of leaf processing of 10 riparian plant species, particulate organic matter (POM) production and nutrient excretion differed between crayfish species in the absence of other invertebrates. Although POM production rates did not differ between crayfish species, crayfish impacts on leaf processing differed depending on plant species reflecting differential leaf preference. Comparisons of individual nutrient excretion rates revealed that ammonia and phosphate excretion rates were higher in Cambaroides compared with Pacifastacus. Further, ammonia excretion rates were proportional to crayfish biomass in Cambaroides but not in Pacifastacus. Taken together, the two crayfish species had similar roles in stream food webs when biomass was similar. However, their roles as leaf processors and excretion rates of nutrients differed when there was a choice among different riparian species as sources of leaf litter. Species replacement between alien and endemic crayfish may therefore result in differential consequences for ecosystem processes.

Behavioral effects of invaders: alien crayfish and native sculpin in a California stream

Invasive crayfish have been shown to have negative impacts on a range of taxa, though the mechanisms for those effects have not always been evaluated. Signal crayfish (Pacifastacus leniusculus) in Sagehen Creek were associated with reduced growth rates and gut fullness of Paiute sculpin (Cottus beldingi) in earlier experiments. This paper assesses potential behavioral mechanisms of competition between the two species. I conducted experiments to determine crayfish effects on sculpin behavior and habitat use in a stream observation facility at the Sagehen Research Station, California, USA. Sculpin reduced their use of refuges and pools, shifted into higher-velocity microhabitats, and spent more time fleeing in the presence of crayfish. Crayfish used refuges, pools, and low-velocity habitats more than sculpin in either treatment. Both species were notably nocturnal, with most activity at dusk and night observations, although crayfish were more strongly so than sculpin. Detailed field surveys of lower Sagehen Creek found that potential refuges (unembedded rocks) were closely associated with total crayfish and sculpin numbers, suggesting that cover is at least sometimes limiting under natural conditions. By displacing sculpin from refuges and pools and increasing their activity rate, crayfish may increase the likelihood of predation on sculpin. Behavioral shifts in sculpin appear to be at least partly responsible for the reduced growth rates of sculpin in the presence of crayfish.

The Distribution of the White-Clawed Crayfish,&lt;i&gt;Austropotamobius pallipes&lt;/i&gt;, in Ireland

The Distribution of the White-Clawed Crayfish,&lt;i&gt;Austropotamobius pallipes&lt;/i&gt;, in Ireland

Origin and current distribution of the alien crayfish, Procambarus clarkii (Girard, 1852) in Japan

Origin and current distribution of the alien crayfish, Procambarus clarkii (Girard, 1852) in Japan

EXPLOITATION IS A PREREQUISITE FOR CONSERVATION OF ASTACUS ASTACUS

The noble crayfish, Astacus astacus, is highly valued from a recreational and economical point of view. In most noble crayfish areas, there are long traditions of crayfish catching. The noble crayfish is also included in national and international Red Lists as a vulnerable or threatened species. Intuitively, the first thought is that such a species should be protected from exploitation. However, in many cases the possibility for exploitation and local economic benefits may be important for the conservation of the species. For the noble crayfish this is especially true. The greatest threat against noble crayfish is the man-facilitated spread of plague-carrying alien crayfish species. If local people are allowed and encouraged to catch and make a benefit from noble crayfish, this is also the best protection against illegal stocking of alien crayfish. The possibility to exploit the crayfish is of major importance for the will to protect. Examples from Norway showing different ways of getting an economical and recreational outcome from the noble crayfish are presented.

Reproduction of the Alien Crayfish Species Pacifastacus Leniusculus in Lake Shikaribetsu, Hokkaido, Japan

The reproduction of the alien crayfish species Pacifastacus leniusculus inhabiting Lake Shikaribetsu, Hokkaido, Japan, was studied from August 2002 to August 2003. Spawning was for a short period after mating in mid October. The eggs developed to eyed stage in June the following year and hatched in mid July. After remaining with their mother for several weeks, the juveniles became independent between late July and August. The egg numbers attached to pleopods of this crayfish significantly increased with the female body size. The time of spawning in Lake Shikaribetsu was similar to that of this crayfish living in North America and Europe reported by previous studies, but the time of egg hatching was later in Lake Shikaribetsu compared with some populations in North America and Europe. A comparison of our results of the reproduction of P. leniusculus with that of the endangered Japanese endemic crayfish species Cambaroides japonicus reported by previous studies showed that P. leniusculus has a markedly higher reproductive ability than C. japonicus in terms of egg numbers.

ROUNDTABLE - SESSION 2 EXPLOITATION, CONSERVATION AND LEGISLATION

The link between socioeconomics and conservation and the role of legislation in conservation work was discussed in the group with participants from nine European countries. Interest and knowledge among the general public, stakeholders and managers is the key to successful conservation of native crayfish species. Exploitation and conservation do not necessarily exclude each other. A controlled fishery, where it can be sustained, may be an essential tool for conservation by increasing the general awareness and involving more people in the task of protecting the native crayfish species. This strategy is mainly possible for the noble crayfish in the northern part of its distribution, where strong traditions connected to crayfish also exist. A balance between utilisation and overexploitation has to be found and local guidelines for sustainable exploitation produced. Media, the Internet and educational material aimed at schools and stakeholders are excellent ways of reaching a wide audience with information. Universal objectives, rules and regulations at the European level are desirable and the noble crayfish and the stone crayfish should be included in Annex II of the Habitat Directive. Based on this framework detailed regulations are best worked out at the national level, considering the specific crayfish situation in the country. Information about the legislation, the purpose of the legislation and the consequences when not obeying it should be distributed. Stricter regulation of the trade with live alien crayfish is vital because of the associated risk of introducing new diseases and species.

UNDERSTANDING AND MANAGING BIODIVERSITY IN RELATION TO NATIVE CRAYFISH POPULATIONS IN EUROPE

The loss or diminution of European crayfish populations because of both habitat deterioration and competition with alien crayfish - also responsible for the dissemination of the crayfish plague - would reduce the biodiversity at the species level. The topic What is meant by biodiversity? in the context of native freshwater crayfish in Europe was discussed during the Kilkenny CRAYNET meeting in order to make the point about the varied meanings of biodiversity from genes and individuals to population levels.

Competition for Shelter of Preferred Sizes between the Native Crayfish Species Cambaroides Japonicus and the Alien Crayfish Species Pacifastacus Leniusculus in Japan in Relation to Prior Residence, Sex Difference, and Body Size

Abstract Intra- and inter-specific competition for shelter, in relation to prior residence, sex differences, and body-size effects, was studied in the laboratory to assess the potential impact of the alien crayfish species Pacifastacus leniusculus on the endangered Japanese endemic crayfish species Cambaroides japonicus. The resident was placed in an aquarium, which contained a single shelter of preferred size for both C. japonicus and P. leniusculus. After 24 h, the intruder was introduced into the aquarium. In the experiments using different sex pairs of crayfish of approximately equal size, male residents had a significant prior residence effect against female intruders in both crayfish species in the intraspecific contests. However, residents of P. leniusculus dominated C. japonicus regardless of the sex in interspecific contests. In experiments using male crayfish pairs of different sizes, larger individuals had more successful possessions of the shelter against smaller individuals regardless of cray...

Potential impacts of alien freshwater crayfish in South Africa

The habitat preferences and life history characteristics of four alien species of freshwater crayfish (Cherax tenuimanus, C. destructor, C. quadricarinatus and Procambarus clarkii) are reviewed. The potential impact of these species on South African freshwater ecosystems is assessed and the desirability of allowing their importation evaluated. On the basis of principles espoused in the European Inland Fisheries Advisory Council's Code of Practice on Aquatic Introductions, it is recommended that importation permits should not be granted for any of these species.

ROUNDTABLE SESSION 1B: CONTROL AND MANAGEMENT OF ALIEN CRAYFISH

Indigenous or native crayfish populations have long been the subject of management in many regions of Europe, largely in the form of sustainable harvest for the table. Since the arrival and subsequent proliferation of non-indigenous or alien crayfish species, the need to control or manage their spread has been identified as a priority by fisheries managers and conservationists. In practice the development of broad-based and sitespecific strategies for this purpose should take place alongside a programme of research into the feasibility of controlling or even eradicating nuisance populations. Practical experience has been gained from the deployment of crayfish harvesting methods, and other potential control measures have been utilised. Progress in this field is subject to the familiar constraints of limited funding and finite resources but the experience gained from such work represents an important pool of information from which conservation agencies and researchers can formulate knowledge-based management decisions.

CRAYFISH OCCURRENCE IN RELATION TO LAND-USE PROPERTIES: IMPLEMENTATION OF A GEOGRAPHIC INFORMATION SYSTEM (GIS)

On the basis of inventory data collected since 1994, the recent stocking situation for freshwater crayfish in three 10 by 10 km study sites in northeastern Germany (Uckermark) and northwestern Poland (Szczecin area, Koszalin area) is described. The native crayfish Astacus astacus (L.) was found in two of the three study sites (Uckermark, Koszalin area) with 1 and 7 stocks, respectively, while the American species Orconectes limosus (Raf.) was found in all three study areas, and in two of them (Uckermark, Szczecin area) was the dominant crayfish species. By means of spatial analysis on the basis of a geographic information system (GIS), influence of land-use properties and other human impact on crayfish distribution was estimated. A. astacus was found only in lakes with a proportion of arable land below 10% within a 50 m buffer around the shoreline. Proportion of forest around these lakes was above the average for all lakes. In contrast, O. limosus appeared indifferent to all factors related to land use. Average lake size was clearly different for the two species. A. astacus was found in smaller lakes without direct contact to settled areas, whereas O. limosus preferentially inhabited larger lakes, indicating the importance of human activities in respect of extinction of native crayfish stocks and propagation of alien crayfish species. GIS proved a suitable tool for the assessment of land-use effects and overall human impact on crayfish distribution on a landscape level.