Austropotamobius Pallipes Research Articles

Ecotoxicological impact of Zequanox®, a novel biocide, on selected non-target Irish aquatic species

Effective, species-specific zebra mussel control is needed urgently for Ireland׳s freshwater bodies, which became infested with non-native zebra mussels in the 1990s. Zequanox®, a newly commercialized product for zebra and quagga mussel control, is composed of dead Pseudomonas fluorescens CL 145A cells. This paper describes ecotoxicology tests on three representative native Irish freshwater species: Anodonta (duck mussel), Chironomus plumosus (non-biting midge), and Austropotamobius pallipes (white-clawed crayfish). The species were exposed to Zequanox in a 72-h static renewal toxicity test at concentrations of 100–750mg active ingredient per liter (mga.i./L). Water quality parameters were measured every 12–24h before and after water and product renewal. After 72h, endpoints were reported as LC10, LC50, and LC100. The LC50 values derived were (1) Anodonta: ≥500mga.i./L (2) C. plumosus: 1075mga.i./L, and (3) A. pallipes: ≥750mga.i./L. These results demonstrate that Zequanox does not negatively affect these organisms at the concentration required for >80percent zebra mussel mortality (150mg a.i/L) and the maximum allowable treatment concentration in the United Sates (200mga.i./L). They also show the overall species-specificity of Zequanox, and support its use in commercial facilities and open waters.

The North American signal crayfish, with particular reference to its success as an invasive species in Great Britain

In the last 50 years, at least eight non-indigenous crayfish species (NICS) have been introduced into Great Britain for a variety of purposes including aquaculture, fish markets, restaurants and the aquarium trade, and incidental introductions (for example with consignments of fish and plants), and all have established viable wild populations except one. However, at present, only the North American signal crayfish [Pacifastacus leniusculus (Dana 1852)] is causing notable ecological problems, mainly due to its invasive capabilities, its impact on freshwater communities (including salmonid fish) through its feeding habits and its role as an ecosystem engineer, its interference with angling activities, and the fact that it can act as a vector of crayfish plague, to which Great Britain’s indigenous white-clawed crayfish is highly susceptible. The other four North American crayfish introduced into Great Britain are capable of similar negative impacts, but are nowhere near as widespread. It is estimated that the various activities set up to try and control and manage the signal crayfish and repair the damage caused by it cost Great Britain over £ 2 million per annum and are sure to increase as populations expand. Despite stringent legislation, the signal crayfish continues to be spread by illegal introductions as well as by natural expansion of range. The distribution and biology of signal crayfish and the reasons for its success in Great Britain are examined and discussed.

Ecotoxicological assessment of the impact of nitrate (NO3¯) on the European endangered white-clawed crayfish Austropotamobius italicus (Faxon)

Field studies and laboratory experiments were conducted to assess the impact of elevated nitrate (NO3¯) concentrations on the European endangered white-clawed crayfish Austropotamobius italicus (Faxon) in the Henares River Basin (Central Spain), within an area that is vulnerable to nitrate pollution. Two sampling surveys were carried out in the summer of 2009 and 2011 to collect freshwater crayfish at eight sampling sites along this vulnerable area. The invasive read-swamp crayfish Procambarus clarkii (Girard) was the only collected crayfish species. Nitrate toxicity experiments however showed that A. italicus is one of the most tolerant species to nitrate toxicity. Although the food consumption was the most sensitive endpoint to nitrate toxicity (followed by the escape response and mortality), the no-observed-effect concentration (NOEC) for this endpoint after 14 days of exposure to nitrate was as high as 100mg NO3¯N/l, with some crayfish being still alive after fourteen days of exposure to a nominal nitrate concentration of 800mg NO3−N/l. Besides, a safe concentration of nitrate for A. italicus, along with its respective 95% confidence limits, were estimated to be 68.5 (22.4–187) mg (NO3¯N/l. Overall we conclude that elevated nitrate concentrations would not be responsible for the absence of white-clawed crayfish in the Henares River Basin. Other environmental factors, particularly the presence of P. clarkii and its fungal pathogen, would be major causes.

Do culverts impact the movements of the endangered white-clawed crayfish?

Culverts can impact the migration and dispersal of aquatic animals and result in population fragmentation, increasing the risk of local extinction for endangered species such as the white-clawed crayfish Austropotamobius pallipes . This study used radio telemetry and passive integrated transponder (PIT) telemetry to determine whether existing and experimental covered culverts affect the upstream and downstream movements of adult white-clawed crayfish. Daily crayfish movement rates did not differ significantly between an unlit 363-m long culvert and open stream channel sections. Crayfish moved into dark, covered sections volitionally. However, limited upstream movement occurred at sudden transitions of bed height or smooth-concrete box culvert sections with fast flow, suggesting partial barrier effects. In the 20-m long experimental in-stream culvert, also dark, but with natural stream bed, 70% of radio-tagged crayfish released downstream entered the culvert, as did 60% of those released upstream. Overall 35% passed through, with similar numbers in each direction. We conclude that dark culverts up to several hundred metres do not inhibit dispersal of white-clawed crayfish, provided stream slope, bed type and water velocity are amenable for movement and refuge. Care is required to ensure that culverts are bioengineered to ensure that average water velocity is sufficiently low and local hydraulic variation high, the bed and/or sidewalls contain refuge structures, and there are no cross-channel steps in bed level. Smooth-bedded box culverts are unlikely to be suitable for white-clawed crayfish.

Aquatic macroinvertebrate responses to native and non-native predators

Key-words: antipredator behaviour, non-native, invasive, Austropotamobius pallipes, Pacifastacus leniusculus, alien, community ecology Non-native species can profoundly affect native ecosystems through trophic interactions with native species. Native prey may respond differently to non-native versus native predators since they lack prior experience. Here we investigate antipredator responses of two common freshwater macroinvertebrates, Gammarus pulex and Potamopyrgus jenkinsi, to olfactory cues from three predators; sympatric native fish (Gasterosteus aculeatus), sympatric native crayfish (Austropotamobius pallipes), and novel invasive crayfish (Pacifastacus leniusculus). G. pulex responded differently to fish and crayfish; showing enhanced locomotion in response to fish, but a preference for the dark over the light in response to the crayfish. P. jenkinsi showed increased vertical migration in response to all three predator cues relative to controls. These different responses to fish and crayfish are hypothesised to reflect the predators’ differing predation types; benthic for crayfish and pelagic for fish. However, we found no difference in response to native versus invasive crayfish, indicating that prey naivete is unlikely to drive the impacts of invasive crayfish. The Predator Recognition Continuum Hypothesis proposes that benefits of generalisable predator recognition outweigh costs when predators are diverse. Generalised responses of prey as observed here will be adaptive in the presence of an invader, and may reduce novel predators’ potential impacts. RESUME

Review of the state of knowledge of crayfish species in the Iberian Peninsula

Review of the state of knowledge of crayfish species in the Iberian Peninsula This paper reviews information relevant to managing the four crayfish species present in the Iberian Peninsula. The red swamp crayfish, Procambarus clarkii, signal crayfish, Pacifastacus leniusculus, and Yabbie, Cherax destructor, are classified as invasive alien species by Spanish legislation. The most significant negative impacts of these species in freshwater ecosystems are noted, and some management methods are proposed. In addition, scientific studies addressing the origin and taxonomy of the Iberian white-clawed crayfish, Austropotamobius italicus italicus, are discussed. The Iberian populations of A. i. italicus have been severely diminished since the onset of the expansion of the aphanomycosis disease in 1978. However, this trend began to undergo reversal a few years ago, and the populations of this species are now growing. Finally, current legislation concerning the fishing and conservation of crayfish species is explained and discussed.

Historical Ecology and Invasion Biology: Long-Term Distribution Changes of Introduced Freshwater Species

We used historical written accounts from Spain to describe the long-term dynamics in the distributions of tench (Tinca tinca), common carp (Cyprinus carpio), and white-clawed crayfish (Austropotamobius italicus) from the sixteenth century to the present. The results show the widespread, human-mediated expansion of the three species and support their introduced status, which has been controversial for tench and crayfish. The temporal patterns of spread of the three species differ dramatically. Although tench and crayfish expanded rapidly, carp spread mainly during the twentieth century, probably because of hydrologic alterations to Spanish streams. This prolonged time lag in the expansion of an introduced species calls for precaution when judging species invasiveness. Austropotamobius italicus is the focus of several conservation actions in Spain, a strategy that should be questioned in the view of the crayfish’s probable introduced status. This work provides an example of how historical ecology analyses may have implications for present-day environmental management.

AFLP-PCR and RAPD-PCR evidences of the transmission of the pathogen Aphanomyces astaci (Oomycetes) to wild populations of European crayfish from the invasive crayfish species, Procambarus clarkii

Aphanomyces astaci (Oomycetes) is responsible for the crayfish plague disease. This species is endemic of North America and five genotypes have been described using RAPD-PCR. The red swamp crayfish, Procambarus clarkii, is one of the most widely spread North American species and invasive in the world. However, no outbreaks on its specific genotype, i.e., genotype D, have ever been described in nature. We investigated three major series of crayfish plague outbreaks in indigenous crayfish populations of Austropotamobius pallipes, located in the areas of influence of P. clarkii. All samples collected tested positive for A. astaci using a rnDNA ITS-PCR test. We also performed an AFLP-PCR analysis on 19 isolates, and found that all isolates belong to genotype D. These isolates exhibited similar properties, i.e., adaptation to warm temperatures. We demonstrate, for the first time, the transmission of A. astaci genotype D to indigenous European populations of crayfish, and confirm that the properties of adaptation to warm water temperatures seem to be a specific character of genotype D. The results of this work emphasize once more the need of controlling invasive species and its trade, since they can carry harmful pathogens with specific adaptations or increased virulence in new environments.

Muddied waters: suspended sediment impacts on gill structure and aerobic scope in an endangered native and an invasive freshwater crayfish

Suspended sediment (SS) loadings in freshwater habitats have increased over the past century and SS is now a significant environmental stressor. Greater tolerance to environmental stressors has been proposed as a factor in the success of aquatic invasive species. Further, parasites may interact with environmental stressors to increase host susceptibility to loss of fitness and mortality. We compared the effects of SS exposure on the gill structure and aerobic scope of the endangered white-clawed crayfish (Austropotamobius pallipes), and the invasive signal crayfish (Pacifastacus leniusculus), and assessed impacts in relation to parasite burden. SS caused gill fouling and reduction in aerobic scope in both species, though A. pallipes was more susceptible than invasive P. leniusculus. The parasite Branchiobdella astaci, a crayfish worm that infests the gills, interacted with the sediment to affect gill structure whereas infection with the microsporidian parasite Thelohania contejeani had no effect on crayfish response to SS. Juvenile P. lenisuculus had a higher standard metabolic rate than A. pallipes, which may be linked to competitive advantages such as higher growth rate and behavioural dominance. Conservation of A. pallipes often involves relocation of threatened populations to isolated stillwaters; our findings suggest that SS levels should be assessed before relocation.

Reproductive performance in captivity of Austropotamobius pallipes in Abruzzi Region (central Italy)

Austropotamobius pallipes juveniles for restocking should originate from native breeders to preserve the genetic integrity of the populations. We compared the reproductive performance in captivity of A. pallipes populations of four drainage basins of the Abruzzi Region to assess their reproductive efficiency and improve their aquaculture. The broodstock were collected before the breeding season and reproduction took place in an experimental hatchery. The female carapace length ranged from 35.4 to 59.0 mm. Spawning occurred in 84% of females (range 69–93%) and the mean number of eggs per female was 89 (range 80–104). No significant differences were observed among the groups. Close to hatching, two groups maintained a high percentage of egg-bearing females (52%) and a high number of eggs, while the other groups lost most of their eggs. At the end of the cycle, the stage 2 juveniles obtained represented 19.5% of the initial egg number. The efficiency for stage 2 juvenile production ranged from 48.2 to 0.1%, and the mean number of stage 2 juveniles per female ranged from 42.2 to 1. These differences were not attributable to maternal size, but the characteristics of the brooks of origin might have influenced the reproductive performances of crayfish in the hatchery.

Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Populations of the Signal Crayfish Pacifastacus leniusculus in France: Evaluating the Threat to Native Crayfish

Aphanomyces astaci, the crayfish plague pathogen, first appeared in Europe in the mid-19th century and is still responsible for mass mortalities of native European crayfish. The spread of this parasite across the continent is especially facilitated by invasive North American crayfish species that serve as its reservoir. In France, multiple cases of native crayfish mortalities have been suggested to be connected with the presence of the signal crayfish Pacifastacus leniusculus, which is highly abundant in the country. It shares similar habitats as the native white-clawed crayfish Austropotamobius pallipes and, when infected, the signal crayfish might therefore easily transmit the pathogen to the native species. We investigated the prevalence of A. astaci in French signal crayfish populations to evaluate the danger they represent to local populations of native crayfish. Over 500 individuals of Pacifastacus leniusculus from 45 French populations were analysed, plus several additional individuals of other non-indigenous crayfish species Orconectes limosus, O. immunis and Procambarus clarkii. Altogether, 20% of analysed signal crayfish tested positive for Aphanomyces astaci, and the pathogen was detected in more than half of the studied populations. Local prevalence varied significantly, ranging from 0% up to 80%, but wide confidence intervals suggest that the number of populations infected by A. astaci may be even higher than our results show. Analysis of several individuals of other introduced species revealed infections among two of these, O. immunis and P. clarkii. Our results confirm that the widespread signal crayfish serves as a key reservoir of Aphanomyces astaci in France and therefore represents a serious danger to native crayfish species, especially the white-clawed crayfish. The prevalence in other non-indigenous crayfish should also be investigated as they likely contribute to pathogen transmission in the country.

Time‐series analysis of native and non‐native crayfish dynamics in the Thames River Basin (south‐eastern England)

ABSTRACT Monitoring is crucial for the conservation of endangered crayfish species as well as for managing and controlling invasive species. Yet, relatively few studies have assessed relationships between native white‐clawed crayfish Austropotamobius pallipes and non‐native signal Pacifastacus leniusculus, narrow‐clawed Astacus leptodactylus, virile Orconectes virilis and red‐swamp Procambarus clarkii crayfishes in freshwater environments at ecologically relevant spatial and temporal scales. Thus, the present study examines the distribution dynamics of native and non‐native crayfishes in the River Thames Basin District (16 133 km2, south‐eastern England) over four decades (1971–2010). To reveal geographical bioinvasion and decline patterns, data on occurrences (sampling site, date) of native white‐clawed and four non‐native crayfishes were used to create sequences of decade maps for each species. Cumulative numbers of occupied grid squares were used to construct ‘invasion/decline’ curves and rates. To quantify dynamic features, the frequencies of survey occurrence for each species were subjected to time‐series analysis, followed by cross‐correlation to determine relationships between crayfishes. White‐clawed crayfish was initially widespread, but gradually disappeared after the mid‐1970s, coinciding with the introduction and initial dispersal of signal crayfish. During 2001–2010 white‐clawed crayfish numbers declined steeply. Introduced in the mid‐1980s, narrow‐clawed crayfish spread within a few years, but is now restricted to the east of the basin, where virile and red‐swamp crayfishes were reported with low presence since their introductions in 2006. Dynamics of white‐clawed and signal crayfishes showed the opposing trends with a highly significant negative association. Geographical patterns indicate that non‐native crayfishes were introduced in multiple locations in the study area. Recovery of native crayfish seems unlikely, given the impacts of signal crayfish and the continuing arrival of new crayfish species. This paper demonstrates the utility of using broad temporal and spatial scales for revealing accurate insights on invasion and decline dynamics. Copyright © 2013 Crown copyright.

Distribution and biometry of native and alien crayfish in Trentino (Italian Alps)

To fill the existing gaps in the knowledge of the crayfish species distribution in Trentino region (North-East Italy), we surveyed fourteen lakes, six ponds and sixty-nine creeks and streams in 2010-2012. We recorded four populations of the invasive alien species Orconectes limosus in four lakes and twenty of the native Austropotamobius pallipes complex from four lakes, three ponds and thirteen creeks; three of these populations went extinct during the three years of our survey. Crayfish populations were monitored in spring, summer and early autumn, to assess the distribution, density and seasonal dynamics of the two species. Statistical analysis of morphometric data showed differences in body size and growth rates among sampling sites, possibly related to local environmental factors, with higher growth rates in males of both species; A. pallipes grew faster in creeks than in lakes. The extinction of twenty-two native populations of A. pallipes complex in the last century was likely due to habitat modifications, in particular to the loss of riparian habitat, in few cases to overfishing, and, more recently, to the spread of alien species and the related transmission of their parasite Aphanomyces astaci . Some populations of A. pallipes complex were infested with the parasite Thelohania sp ., and only one population with ectosymbiotic Branchiobdellida. In Trentino, small creeks with well developed riparian vegetation and good hydromorphological conditions, flowing through mountain slopes, can represent potential refuge and recruitment areas for of A. pallipes complex, without significant management intervention, although a sustainable management of piedmont water bodies would allow preserving or increasing the number and density of the relict populations.

Phylogeography of the white-clawed crayfish (Austropotamobius italicus) in Spain: inferences from microsatellite markers

The white-clawed crayfish (Austropotamobius italicus), a cornerstone of Spain's aquatic ecosystems, was once widely distributed throughout much of the country. Unfortunately, its populations have suffered very strong declines over the last 40years due to the spread of introduced species (red swamp and signal crayfishes), diseases, habitat loss and other anthropogenic impacts. The present work examines the genetic variation in 23 Spanish and four Italian populations of white-clawed crayfish via the analysis of microsatellite loci. The data show genetic variation in the Spanish populations to be affected by drastic and successive bottlenecks. Notwithstanding, the diversity of these Spanish populations in terms of observed heterozygosity is similar to or even higher than that recorded for other European populations studied using these same markers. North-central Spanish populations are clearly differentiated from the country's remaining populations; they should be considered distinct management units. Processes occurred in historical and recent times, such as genetic drift and translocations, contribute greatly to this genetic structure. These data provide useful information for conservation of this species, since the preservation of its population structure and genetic variability should be goals for management decisions.

Fluoride Bioaccumulation and Toxic Effects on the Survival and Behavior of the Endangered White-Clawed Crayfish Austropotamobius pallipes (Lereboullet)

Laboratory experiments were performed to examine the toxic effects of fluoride (F(-)) on the survival and behavior of white-clawed crayfish (Austropotamobius pallipes). Body fluoride contents (bioaccumulation) of test crayfish were also examined. No significant differences between male and female crayfish regarding mortality, escape (tail-flip) response, and fluoride bioaccumulation were detected. For mortality, 48-, 72-, 96-, 120-, 144-, 168-, and 192-h median lethal concentrations (LC50) were estimated to be 93.0, 55.3, 42.7, 36.5, 32.9, 30.6, and 28.9 mg F(-)/l, respectively. For the escape response, 48-, 72-, 96-, 120-, 144-, 168- and 192-h median effective concentrations (EC50) were estimated to be 18.4, 11.1, 8.6, 7.4, 6.7, 6.2 and 5.9 mg F(-)/l, respectively. Average food consumption in test crayfish tended to decrease with increasing water fluoride concentration with a 192-h lowest-observed effect concentration of 10.7 mg F(-)/l. These results indicate that the escape response was the most sensitive end point to fluoride toxicity followed by food consumption and mortality. Fluoride bioaccumulation in test crayfish increased with increasing water fluoride concentration and exposure time. The exoskeleton accumulated more fluoride than muscle. A comparison of the obtained results with previous data for other freshwater invertebrates shows that white-clawed crayfish are relatively tolerant to fluoride toxicity. We conclude that fluoride pollution in freshwater ecosystems should not be viewed as an important risk factor contributing to the catastrophic decrease of A. pallipes in many European countries. Our results indicate that fluoride bioaccumulation in A. pallipes might be used as a bioindicator of fluoride pollution in freshwater ecosystems where it is present.

Aphanomyces astaci in wild crayfish populations in Slovenia: first report of persistent infection in a stone crayfish Austropotamobius torrentium population

All 5 crayfish species inhabiting Slovenian freshwaters, of which 3 are indigenous crayfish species (ICS: Astacus astacus, Austropotamobius pallipes, and A. torrentium) and 2 are non-indigenous (NICS: Pacifastacus leniusculus and Cherax quadricarinatus), were inspected for the presence of Aphanomyces astaci, the causative agent of crayfish plague. Wild crayfish populations showing no clinical signs of infection were inspected using A. astaci-specific real-time PCR. In addition, a conventional PCR assay was employed and confirmative sequencing was performed. Out of 88 analyzed crayfish, 15/27 (55.6%) specimens of A. torrentium from Borovnišcˇ%%KERN_ERR%%ica Brook and 4/35 (11.4%) of P. leniusculus from the Mura River tested positive, showing low to moderate levels of infection (agent levels A1-A4 and A1-A3, respectively). Results revealed the presence of A. astaci not only in the resistant NICS but also in ICS, since the infected population of A. torrentium presumably had no contact with the NICS carrier and appeared to sustain A. astaci infection in the 2 sampling years. Although the A. astaci genotype has not yet been identified, a connection between the latent infection in ICS and a Group A strain of A. astaci, co-evolving with A. torrentium since its first introduction to Slovenia, is suggested as the most plausible conclusion. This is the first reported population of the genus Austropotamobius with persistent infection, in addition to the already known populations of the genus Astacus. Findings of the presumed co-evolution of A. astaci and ICS hosts open new perspectives, necessitating additional studies on the presence of A. astaci genotypes in the persistently infected ICS populations.

Self-limiting outbreak of crayfish plague in an Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy)

Crayfish plague, caused by the oomycete Aphanomyces astaci, is a serious disease of European freshwater crayfish and has eliminated entire populations in several European countries. In September 2011, mortality was observed among the Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy), and A. astaci DNA was detected by PCR in dead crayfish. A systematic survey was carried out to evaluate the spread and the effects of the plague in the river basin. The source of the outbreak remained unknown since North American crayfish species, which frequently act as subclinical carriers of the infection, were not detected in the area. The A. pallipes population disappeared from a river stretch of ~1 km, where A. astaci infection was detected in dead crayfish. However, apparently unaffected crayfish were still present upstream of that area as well as in a tributary that joined the brook in the apparently depopulated stretch. A. astaci infection was not detected in dead individuals collected in the upstream area and tributary. A follow-up visit conducted in the following season showed the presence of A. pallipes in the river stretch hit by the plague. In this outbreak, the spread of the infection could have been limited by a low density of the crayfish population and by the geographic conformation of the river basin, which includes a dense network of small tributaries, characterized by high flow velocity and low water temperature. In this particular setting, crayfish plague outbreaks can remain undetected. This underlines the importance of active monitoring programs aimed at the prompt recognition of both episodes of mortality and the presence of non-indigenous crayfish species.

Evaluating the combined threat of climate change and biological invasions on endangered species

Climate change and invasive species are two major biodiversity threats expected to provoke extinctions of many species in the future. This study evaluates the joint threat posed by climate change and two invasive species: the zebra mussel (Dreissena polymorpha) and the signal crayfish (Pacifastacus leniusculus), on the distribution of two endangered freshwater species: the depressed river mussel (Pseudanodonta complanata) and the white-clawed crayfish (Austropotamobius pallipes), at the scale of Europe. We expected the native species to experience a gradual contraction over time in their geographic range size, while the invasive species would maintain or increase their spread; therefore, their overlap would increase, further threatening the conservation of the native species. To test these three hypotheses, ensemble species distribution models (SDMs) were calibrated with current distributions and projected onto present and 2050 future climatic scenarios. In agreement with our expectations, the 2050 scenarios suggested D. polymorpha may strongly benefit from climate changes (increase of 15–20% in range size), while the depressed river mussel would experience a considerable loss (14–36%), the overlap between both mussels increasing up to 24%. Although both crayfishes were predicted to be negatively affected by climate changes, the contraction was more severe for the invasive P. leniusculus (up to 32% decrease in range size). Moreover, the overlap between both crayfishes decreased by 13–16%, which may reduce the pressure upon the native A. pallipes. This study illustrates how SDMs can assist in management of endangered species over large spatial and temporal scales by identifying current and future areas of shared bioclimatic suitability and potential refugia.

Effect of pH on growth and survival in the freshwater crayfishAustropotamobius pallipes

Conservation of endangered British crayfish (Austropotamobius pallipes) involves translocation to isolated waterbodies (Ark Sites) and reintroductions from hatchery stock. The species is restricted in the wild to relatively alkaline waterbodies. The optimum pH conditions that maximise growth and survival are unknown. This information would benefit the selection of Ark Sites and hatchery water chemistry. Here we measure growth and survival of juvenile A. pallipes in the laboratory using three pH levels from within the species' natural range. Survival at pH 8.6 was high (94%), whereas that at lower pH levels was low (pH 6.5, 25%; pH 7.1, 34%). Growth (moult increment and frequency) was also higher at pH 8.6. Survival was also lower for Thelohania contejeani-infected animals, with a trend towards higher mortality in infected individuals at lower pH. Electron microscopy revealed a lower cuticle thickness at pH 6.5 than higher pH which was associated with an apparent increase in the number of endocuticle layers. We therefore recommend that high pH (ca. 8.6) be used as a target for Ark Site selection and hatchery water chemistry in order to maximise survival and growth. (

Size-dependent impacts of the endangered white-clawed crayfish (Austropotamobius pallipes) (Lereboullet) on the littoral community

The demise of Britain’s only native crayfish (Austropotamobius pallipes (Lereboullet)) has prompted conservation-led translocations to safe isolated stillwaters (Ark sites). Many translocations represent introductions rather than re-stocking; hence it is important to ensure that there will not be a detrimental impact on communities already present. Current knowledge is insufficient to predict likely effects, although gut contents analyses suggest that A. pallipes is omnivorous and exhibits ontogenic diet shifts. A mesocosm study was conducted with the aim to first, determine community impacts of introducing A. pallipes on the benthic invertebrate community, and second investigate if impacts vary with crayfish life-stage. All crayfish life-stages strongly reduced shredder and grazer abundance, particularly thin-shelled Lymnaea snails. The small snail Physa fontinalis was preferentially consumed by juveniles, perhaps reflecting different prey-handling ability. Adults showed greater reliance on terrestrially derived detritus compared to juveniles. There were limited effects on other trophic levels, although by reducing shredders that process basal resources, crayfish impacts may be felt through the community in the long-term.