The invasive crayfish Procambarus clarkii is highly dispersed within lentic waters in northern and central Italy. It is a polytrophic predator, exerting a strong influence on animal communities, including amphibians, fish, gastropods, and insect larvae. The indigenous species Austropotamobius italicus, inhabiting lotic waters, behaves as a generalistbut not opportunistic -species. The object of this study was to compare the predatory pressure exercised by the two species on potential prey, i.e., anuran tadpoles, urodelan larvae, fish fry, larvae of insects, and gastropods. Three main conclusions were drawn: (1) both species are skilled predators, adopting a sit-and-wait strategy, (2) the two crayfish seemed to form a 'search image' of familiar prey, as the result of either visual or chemical perceptual changes, and (3) at least in the laboratory, P. clarkii readily switched to naive prey for it (tadpoles of Rana italica and larvae of Limnephilidae), unlike the less opportunistic A. italicus. These results furnish suggestions on the trophic preferences of the two crayfish species and provide a partial understanding of the effects that the invasive species have on the community dynamics.

In the laboratory, the motivation and/or ability to prey on anuran larvae (Bufo bufo, Rana kl. esculenta and R. italica) were compared between a native European (Austropotamobius pallipes) and an alien North American crayfish species (Procambarus clarkii). Both were skilled predators of tadpoles, adopting a sit-and-wait strategy. However, because P. clarkii displayed lower latency times in the presence of one of the three amphibians (Rana kl. esculenta) here tested, the hypothesis is raised that invasive crayfish are more opportunistic predators and possibly faster in switching to different prey than those species they are displacing. From a conservation perspective, these preliminary results further emphasise the importance of studies centred on the invasion-displacement dichotomy.Key-words : alien species, crayfish, predation, amphibian tadpoles, biodiversity conservation, Austropotamobius pallipes, Procambarus clarkii. PRÉDATION DE TÊTARDS PAR LES ÉCREVISSES : COMPARAISON ENTRE UNE ESPÈCE AUTOCHTONE (AUSTROPOTAMOBIUS PALLIPES) ET UNE ESPÈCE ÉTRANGÈRE (PROCAMBARUS CLARKII). RÉSUMÉLes auteurs ont testé en laboratoire la motivation et/ou la capacité de prédation sur les larves d'Anoures (Bufo bufo, Rana kl. esculenta et R. italica) entre une espèce native (Austropotamobius pallipes) et une espèce introduite (Procambarus clarkii) d'écrevisse. Les deux espèces se sont montrées comme d'habiles prédateurs de têtards, en adaptant une tactique d'immobilité et d'attente. Cependant on peut avancer l'hypothèse, en raison du fait que P. clarkii montre une période de latence plus courte en présence d'une des trois espèces d'amphibiens (Rana kl. esculenta) testées ici, que l'écrevisse introduite est un prédateur plus opportuniste et probablement plus rapide que l'espèce qu'elle est en train de remplacer. Du point de vue de la conservation, ces résultats préliminaires font ressortir l'importance des études sur la dichotomie invasion-déplacement.

Any initiative aimed at the management of a threatened species needs a good knowledge of its environmental requirements. Aims of this study were to individuate suitable areas for the reintroduction of crayfish species belonging to the Austropotamobius pallipes complex and to evaluate the causes of the local extinction in Tuscany (Italy) of some populations. Between May 2003 and September 2004, we collected ecological data from 19 streams of 4 catchments, 9 watercourses where crayfish were present (WI) and 10 where they were present in the recent past and absent now (WO), and we compared them. Multivariate analyses were performed using chemico-physical and biotic parameters to examine the relationships between their values and the presence of crayfish. The results did not allow us to find significant differences between the two categories of streams, suggesting their suitability for crayfish reintroduction. Key-words:Austropotamobius pallipes complex, Extended Biotic Index (IBE), Fluvial Functionality Index (IFF), biotic and abiotic parameters. Bull. Fr. Pêche Piscic. (2006) 380-381 : 1095-1114 -1096 -hydrographiques différents, qui abritent actuellement des écrevisses (WI) ou qui en sont dépourvus depuis peu (WO). Des analyses multivariées ont été réalisées en prenant en compte à la fois les paramètres physico-chimiques et biotiques afin d'examiner les relations entre ces données et la présence du complexe Austropotamobius pallipes. Les résultats ne montrent pas de différence significative entre les deux catégories de ruisseaux ce qui traduirait l'aptitude des sites WO à accueillir des écrevisses. CARACTÉRISATION ÉCOLOGIQUE DE RUISSEAUX TOSCANS (ITALIE) POUR LA GESTION DE L'ÉCREVISSE MENACÉE AUSTROPOTAMOBIUS PALLIPES

ABSTRACT1. As part of the Austropotamobius pallipes species complex, the crayfish Austropotamobius italicus is a species of community interest whose preservation requires the designation of Special Areas of Conservation (SACs) (Annex II, EU Habitats Directive). This study aimed at (1) assessing the conservation status of this threatened indigenous species by stock assessment in Central Italy and (2) identifying some aspects of its elective habitat.2. Surveys were conducted in nine streams harbouring A. italicus (streams WI) and in 10 streams where crayfish populations became extinct at least 5 years before the study (streams WO).3. The results confirmed that A. italicus is a K-selected species, with a relatively slow growth rate (males: 0.34; females: 0.37) and a long life expectancy (males: 8.2 years, females: 7.8 years). The extant populations are healthy, showing balanced sex-ratios and well structured age-class compositions. Mortality is mainly due to fishing, which is illegal in Tuscany.4. Principal Components Analyses showed that the streams WI and WO differ in the abundance of allochthonous plant detritus but not in the taxonomic composition of their macroinvertebrate communities. Age classes were found to be spatially segregated, juveniles mainly using cobbles as substrates and adults seemingly avoiding them.5. The loss of the pristine riverine landscape seems to have been responsible, together with illegal fishing, for the local extinction of the species. As a consequence, retaining, enhancing, and restoring the habitat and its complexity are required for the preservation of A. italicus.6. The designation of SACs might help in this endeavour if accompanied by programmes aimed at publicizing the need for conservation of this species. Unfortunately, crayfish-focused projects supported by LIFE in Italy since 1992 (4%) and the SACs involved (1.4%) have been relatively few, despite the poor conservation status of this species and its well recognized ecological role.

Abstract:The omnivorous habit and food selection in freshwater macroinvertebrates was investigated in the white-clawed crayfish, Austropotamobius pallipes, a threatened species. First, during an annual cycle we analysed gut contents for vascular plant detritus, moss, amorphous plant material, and animal remains, and evaluated their organic content. Second, we ran preference experiments in the laboratory, in which crayfish had to choose, in the first trial among three vegetal items, in the second trial among three animal prey, and in the third trial between the two preferred items of the previous two trials (i. e. moss and insect larvae). Third, we analysed whether the assimilation efficiencies of different food items affected crayfish food choice. Our results revealed that this species mostly acted as a detritus consumer, obtaining nutrition from the associated microbes, fungi, proto-and metazoans, but also showed herbivorous and carnivorous habits. However, at least when food resources were not limited, crayfish displayed distinct feeding preferences, often ruled by factors other than the nutritional quality and the assimilation efficiency of the selected food.