Can the parthenogenetic marbled crayfish Marmorkrebs compete with other crayfish species in fights?

The parthenogenetic marbled crayfish, Marmorkrebs, has no known wild population, but has been introduced into natural ecosystems in two continents. Interactions with native crayfish, particularly through fighting, could affect the ecological impact of Marmorkrebs introductions. Marmorkrebs have been characterized anecdotally as having low levels of aggression, which could mitigate their potential to compete with native species. We isolated Marmorkrebs and Louisiana red swamp crayfish (Procambarus clarkii), then conducted size-matched intra and interspecific pairings. Marmorkrebs were as likely to win a fight as P. clarkii, although contests between P. clarkii and Marmorkrebs began significantly faster than contests between two Marmorkrebs. These results suggest that Marmorkrebs have the potential to compete with other species on the same level as P. clarkii, which is itself a highly successful introduced species around the world.     

Trophic niches of three sympatric invasive crayfish of EU concern

The spread of non-native species results in novel and often unexpected assemblages. Using stable isotopes, we disentangled the trophic relationships between three invasive crayfish species at two sites of a small thermal tributary of the Barát stream, Hungary. We studied Procambarus virginalis and Faxonius limosus living in sympatry in the upper section of this thermal tributary, and then an assemblage in a lower section also containing P. clarkii. The two species in the upper section largely shared trophic niches, although P. virginalis was more carnivorous than F. limosus, which fed more on detritus and aquatic plants. In the lower section, P. clarkii had a distinctive trophic niche, being more carnivorous than the other species and also preying on other crayfish and fish. The trophic niches of the other two species shifted slightly, being narrower and more overlapping in the presence of P. clarkii. It seems that the presence of P. clarkii affects the feeding habits and trophic niches of the other two crayfish. Our results also indicate that the species have somewhat distinctive feeding niches, which suggests that the ecosystem effects of these species are likely to be at least partially additive in the shared localities.

     

Crayfish invading Europe: the case study of Procambarus clarkii

The red swamp crayfish, Procambarus clarkii, native to northeastern Mexico and southcentral USA, is today the dominant macroinvertebrate in several European countries. While the first introduction of this species into Spain is well-documented, little is known about its pathways of invasion and the reason for its rapid spread in several European countries. Study of the biology of the species has revealed a number of properties that makes this crayfish a successful invader. Procambarus clarkii exhibits properties characteristic of an r-selected species, including early maturity at small body size, rapid growth rates, large numbers of offspring at a given parental size, and relatively short life spans. It is also plastic in its life cycle, able to disperse widely in the habitat and to tolerate environmental extremes. It displays generalist and opportunistic feeding habits, consuming macrophytes and preying on amphibians. Procambarus clarkii can also replace indigenous crayfish by a combination of mechanisms, including competitive exclusion and transmission of the fungus-like Aphanomyces astaci, responsible for the crayfish plague. Finally, this species shows a wide behavioral flexibility when coping with new types of predators. The results of these studies, combined with the increasing information available in the scientific literature on this and other crayfish species, will help us understand invasions in this taxon and make predictions about the identity of future crayfish invaders.     

Early assessment of the impact of alien species: differential consequences of an invasive crayfish on adult and larval amphibians

Aim Early assessment of the impact of invasive alien species is crucial to set up timely management, but often the impact is evident when it is too late for action. We evaluated relationships between the alien crayfish, Procambarus clarkii, the distribution of native amphibians, and the abundance of their larvae. We assessed whether considering measures of reproductive success provide a more prompt measure of impact than considering just species distribution. Location One hundred and twenty‐five wetlands in Northern Italy, in an area recently invaded by P. clarkii. Methods We surveyed wetlands to assess the presence of breeding activity of amphibians and the distribution of P. clarkii. We measured the abundance of amphibian larvae before metamorphosis through pipe sampling. We built models analysing the relationships between amphibian and crayfish distribution, while taking into account spatial autocorrelation and environmental features. Analyses were performed at both the species level (generalized linear models and spatial eigenvector mapping) and community level (constrained redundancy analysis). Results In terms of breeding site distribution, only two amphibians (Lissotriton vulgaris and Hyla intermedia) were negatively associated with P. clarkii, while the relationships between other the species and P. clarkii were positive or not significant. However, larval abundance for all amphibian species was negatively associated with the alien crayfish. Analyses performed at community and single species levels yielded consistent results. Main conclusions Procambarus clarkii impacts amphibians through different processes. Newts probably avoid invaded wetlands for breeding. Other species attempt breeding in wetlands with crayfish, but suffer very low success. Considering distribution data alone would not provide a correct picture of the impact of this alien species; measures of reproductive success may allow a more accurate assessment of the impact.     

The North American crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis> is the carrier of the oomycete <Emphasis Type="Italic">Aphanomyces astaci</Emphasis> 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.     

Invasive crayfish in Europe: the impact of Procambarus clarkii on the littoral community of a Mediterranean lake

1. Despite the growing number of non‐indigenous crayfish species introduced worldwide, little scientific attention has been given to their effects on the recipient communities. Here, we quantified the impact of adult red swamp crayfish (Procambarus clarkii) on key components of the littoral community of a mesotrophic lake in central Italy. We used two densities of crayfish plus a no‐crayfish control, and two complementary methods –in situ enclosures and a laboratory study. 2. Both experiments showed that P. clarkii strongly affects the community even at a low density (4 m⁻²), although a high crayfish density (8 m⁻²) showed a more pronounced impact in a shorter time. 3. In enclosures, P. clarkii quickly consumed the pond snail Haitia acuta, notwithstanding its anti‐predator behaviour, but not the mosquitofish Gambusia affinis. The biomass of the hydrophytes Nymphoides peltata and Potamogeton spp. was strongly reduced by crayfish grazing, coupled with their non‐consumptive plant clipping and uprooting, which were particularly intense in the case of Potamogeton crispus. In contrast, Utricularia australis was avoided by P. clarkii, even when other resources were exhausted. 4. The introduction of P. clarkii could reduce biodiversity and increase biotic homogenisation in a short time.     

Invasive species of crayfish use a broader range of predation-risk cues than native species

The responses of invasive and native species of crayfish to conspecific and heterospecific alarm odors were recorded in the laboratory. Individuals of the North American invasive Procambarus clarkii responded just as strongly to odors from crushed Austropotomobius pallipes as they did to crushed conspecifics. The North American invasive Orconectes limosus also responded as strongly to P. clarkii odor as to conspecific odor. The native Italian species A. pallipes responded more strongly to conspecific alarm than to heterospecific alarm from P. clarkii. The pattern of invasive species of crayfish using a broader range of danger signals than displaced native species appears to be robust.     

Feeding of the exotic Louisiana red swamp crayfish,Procambarus clarkii (Crustacea,Decapoda), in an African tropical lake: Lake Naivasha,Kenya

The Louisiana red swamp crayfish, Procambarus clarkii, has had a major impact on aquatic ecosystems in Europe and America where it has been introduced for human consumption. In Lake Naivasha, where it was introduced in 1970, it is suspected of causing the complete disappearance of native floating-leaved and submerged plants by 1982 and again by 1996; recovery of submerged plants occurred in between, concurrent with a decline in P. clarkii. Examination of the feeding of P. clarkii by microscopic analysis of gut contents collected from the lake confirmed information from both its native and exotic ranges; that it is an omnivore with green plants and insects the predominant items recognised. Feeding experiments confirmed this omnivory, with a preference from herbivory over carnivory. They further showed the importance of native plants as opposed to exotic water hyacinth Eichhornia crassipes. It is concluded that P. clarkii could well have accounted for the observed elimination of native plant species in Lake Naivasha; the cyclical nature of populations of submerged plant species and of P. clarkii in inverse proportion to each other lead us to hypothesise that P. clarkii is a `keystone' species in the lake ecosystem.     

Geographic expansion of the invasive red crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis> (Girard, 1852) (Crustacea: Decapoda) in Mexico

The red crayfish Procambarus clarkii, which is native to southcentral USA and northeastern Mexico, has been successfully introduced into several countries around the world. This study documents the geographic expansion of the exotic red crayfish in Mexico and discusses the consequence of a greater propagation of this species in Mexican inland waters. New state records of this crayfish in the Baja California peninsula and in the states of Durango and Sinaloa indicate its progressive dispersion. The propagation of P. clarkii in Mexico has been caused mainly by human introduction, but it is also facilitated because of the species’ tolerance to an ample range of environmental conditions. Because of the invasive capability of P. clarkii, we suspect that this exotic species is competing for habitat and food with native freshwater shrimp of the genus Macrobrachium in many sites of northern Mexico.     

Invasion of the shelter snatchers: behavioural plasticity in invasive red swamp crayfish,Procambarus clarkii

1. In many freshwater systems, competition for shelter plays an important role in determining the persistence of both native and alien species. The red swamp crayfish, Procambarus clarkii, is currently invading the native habitat of the signal crayfish, Pacifastacus leniusculus, in southern Oregon, and interspecific competition for shelter may be driving the species replacement in this region. 2. We designed a 2 × 3 factorial mesocosm experiment, with shelter density and species combination as factors, to investigate shelter occupancy and resource competition. Contrary to our predictions, the two crayfish species are equal competitors for shelter. Further, the invasive P. clarkii modified its shelter occupancy behaviour in the presence of the native P. leniusculus and has broader microhabitat preferences. 3. Specifically, we found that P. clarkii alters shelter occupancy and space use patterns when the two species occurred together, such that shelter use was identical between P. clarkii and P. leniusculus in mixed‐species treatments. In such treatments, both species increased their use of shelters when shelter density increased. When P. clarkii was alone, however, individuals did not alter shelter use as a function of shelter density, whereas P. leniusculus exhibited similar density‐dependent behaviour in both mixed‐ and single‐species treatments. 4. In a complementary field survey, we employed an ‘epicentre‐based’ design to sample two field sites. We observed patterns of microhabitat use and breadth for each species similar to those in our mesocosm experiment: the invasive P. clarkii was more abundant across different habitats and used a broader range of microhabitats than the native P. leniusculus. As such, we found that P. clarkii was more abundant across both field sites than the P. leniusculus, occupying microhabitats within and beyond the preferred range of P. leniusculus. Both field sites were affected by urban development and agriculture. 5. The use of microhabitats by both species was similar in the laboratory and the field. This study confirms that P. clarkii individuals can, and do, successfully occupy microhabitats preferred by P. leniusculus in the Willamette Valley. The results from our study may be relevant to other freshwater systems inhabited by P. clarkii and contribute to the understanding of ‘niche opportunity’, a concept which defines the environmental conditions that promote biological invasions.     

Population structure and dynamics of <Emphasis Type="Italic">Procambarus clarkii</Emphasis> (Girard, 1852) in a Mediterranean brackish wetland (Central Italy)

In 2006 an unusual find of Procambarus clarkii, today considered one of the most dangerous exotic crayfish, was made within the preserved brackish Mediterranean biotope “Palude di Torre Flavia” (Rome, Italy). Here the investigation on the population structure and dynamics of P. clarkii inhabiting this brackish wetland is presented in an attempt to describe the life history pattern in this type of habitat. The present study showed that this species has a lower growth rate and higher longevity than other studied European P. clarkii populations, and that it can damage brackish habitats and human livelihoods. The main results of this study chiefly concern the differences found between several life-history parameters of the studied population and those obtained in previous studies. These results showed the high ecological plasticity of P. clarkii, indicate the need to intervene before the species spreads further in brackish water, for the conservation of Mediterranean coastal habitats.     

Freshwater crayfish invasions in South Africa: past,present and potential future

Freshwater crayfish invasions have been studied around the world, but less so in Africa, a continent devoid of native freshwater crayfish. The present study reviews historical and current information on alien freshwater crayfish species introduced into South Africa and aims to indicate which areas are at risk from invasion. As is the case elsewhere, South Africans have shown a keen interest in both farming and keeping freshwater crayfish as pets, which has resulted in Cherax cainii, Cherax destructor, Cherax quadricarinatus and Procambarus clarkii being introduced to the country. There is evidence of successful establishment in the wild for C. quadricarinatus and P. clarkii in different parts of the country. Species distribution models suggest that the eastern part of the country and parts of the Eastern and Western Cape are at higher risk of invasion. At present, illegal translocations represent the most likely pathway of crayfish spread in South Africa. A continued risk of invasion by freshwater crayfish species in South Africa is highlighted, which reinforces the need for more research, as well as for strong mitigation measures, such as stronger policing of existing regulations, management or eradication where feasible and public education.     

Crayfish invasion facilitates dispersal of plants and invertebrates by gulls

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

To 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.     

The Decline of the Endangered Populations of the Native Freshwater Crayfish (Austropotamobius pallipes) in Southern Spain: It is Possible to Avoid Extinction?

The southeastern mountains of Spain represent the southernmost limit of the genus Austropotamobius and the species A. pallipes (Lereboullet). The taxonomic position of this isolated crayfish in southern Spain is not clear, being genetically close to A. italicus, but morphologically distinct. A severe decline occurred during the 1980s, especially due to expansion of the alien species Procambarus clarkii, a North American freshwater crayfish and a vector of the aphanomycosis disease. In order to design a strategy for native crayfish conservation, recent trends in native crayfish populations, influence of isolation and habitat variables on their survival and possibilities for their recovery through restocking were studied. A decline in populations was observed between 1991 and 2002 (from 26 to 14 populations), and a total extinction could be predicted within the next 13 years. Two well-defined periods of rapid extinction rates were detected, 1991–1994 (1.25 populations/year) and 1999–2002 (1.50 populations/year). Main causes of extinction for these two periods were invasion by P. clarkii and mortality by unknown causes, respectively. The isolation variables had some positive effects on survival of populations but these cannot offer a sufficient guarantee, since several cases of extinction can be affected by a large component of stochastic factors, including random catastrophes. On the other hand, survival trials and restocking experiments showed that it was possible to recover lost habitats, when P. clarkii was absent and environmental conditions were good. It is concluded that it is possible to avoid extinction of the native crayfish populations; however, the conservation strategies must be based on an urgent stocking/restocking program.     

Evaluation of the suitability of the parthenogenetic marbled crayfish for aquaculture: potential benefits versus conservation concerns

The parthenogenetic marbled crayfish, Procambarus virginalis, is currently being discussed as a promising new candidate for aquaculture that could supply people in developing countries with high-quality protein and income. The main advantage of marbled crayfish is parthenogenetic reproduction. Comparison of growth between marbled crayfish and red swamp crayfish, Procambarus clarkii, the leading species in crayfish aquaculture revealed inferior body size and considerably slower growth in marbled crayfish. Only a very small proportion of the production would meet the size requirement of the international market and could serve as a cash crop. Aquaculture for local markets in extensive outdoor systems is probably economically feasible in developing countries, but the highly invasive and competitive marbled crayfish could easily escape from such sites, invade natural ecosystems and impair the autochthonous fauna and flora. Culture in closed indoor systems would be a safe alternative but this cost-intensive approach is economically not profitable. Because of small body size and slow growth, conservation concerns, and economic reasons, the marbled crayfish is considered unsuitable for aquaculture. It should not be spread around the globe for aquaculture and sustainable fisheries as was earlier done with the congeneric Procambarus clarkii, resulting in devastating ecological effects in numerous countries.

     

Embryonic and larval defensive responses of agile frog (Rana dalmatina) to alien crayfish

Red swamp crayfish Procambarus clarkii, a widespread invasive alien crayfish, represents a serious threat for several freshwater species, including amphibians, which are declining at a global scale. As a shared coevolutionary history is the main factor determining the emergence of antipredator responses, Anuran tadpoles may not be able to cope effectively with this introduced predator. We performed two experiments to assess agile frog's (Rana dalmatina) defensive responses to both P. clarkii and native dragonfly larvae (Anax imperator). First, we conditioned embryos (collected from two ponds 30 km away from each other) with predators’ chemical cues to explore possible variation in hatching time caused by predation risk. In the second experiment, to evaluate how predators’ diet affects tadpole behavior, we conditioned tadpoles for a 5‐week period with cues from tadpole‐fed and gammarid‐fed predators and recorded behavioral and morphological responses. Embryos did not alter hatching time in the presence of any predator cue, while tadpoles from both populations strongly reduced activity and visibility when raised in the presence of tadpole‐fed dragonfly larvae. Morphological changes were less straightforward and were induced only in one population, for which broader tails and a slight increase in body size of tadpoles exposed to tadpole‐fed predators were observed. The lack of defensive responses in crayfish‐exposed tadpoles suggests that the spreading of this invasive species in agricultural lowlands of northern Italy may represent a further threat to their conservation.     

Predator–prey interactions of Procambarus clarkii with aquatic macroinvertebrates in single and multiple prey systems

Understanding the interspecific interactions of Procambarus clarkii with other aquatic macroinvertebrates will help to unveil the mechanisms and processes underlying biological invasiveness. The purpose of this study was to investigate predator–prey interactions of two ontogenic phases of P. clarkii with native and exotic species of aquatic macroinvertebrates at a single and multiple prey level. We performed laboratory experiments to determine the consumption and the behavioral responses of Chironomus riparius, Physa acuta and Corbicula fluminea to P. clarkii. The presence of P. clarkii significantly affected the abundance of C. riparius and P. acuta, but not of C. fluminea whether prey species were provided singly or simultaneously. The consumption of C. riparius by P. clarkii was higher than P. acuta for both crayfish sizes and situations (single/multiple prey systems) and C. fluminea was never consumed. Physa acuta was the only species that exhibited an anti-predator behavior to P. clarkii. Our results show that P. clarkii can have strong consumptive and trait effects on aquatic macroinvertebrate prey at a single and multiple prey level, resulting in differential impacts on different prey species. This study clarifies some aspects of the predator–prey interactions between P. clarkii and native as well as other exotic macroinvertebrate species that have invaded freshwater biocenosis worldwide.     

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.