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Cases of co-occurrence among freshwater decapods are few. In their European range, the crab Potamon fluviatile and the white-clawed crayfish Austropotamobius pallipes complex do not usually share the same stream section or pond even if they live in sympatry, suggesting a strong segregation of the two species. The coexistence was hypothesized during the Pleistocene era, but without evidence of recent contact between them. The co-occurrence of these two species (i.e., occupying a common area) is reported in a stream of the Central Italy, being the first case in Italy and in Europe. To assess this co-occurrence, in 2015 we investigated three transects (only crabs, only crayfish and both species), collecting biotic and abiotic data. The three transects were similar for canopy cover, substrate composition and density of potential shelters (but not for the abiotic parameters), and characterized by a good water quality and abundance of preys, being suitable for the two species. No agonistic behavioural patterns have been observed, leading to hypothesize that co-occurrence may be favoured by the slightly smaller size of crayfish and crabs in the shared area than the size of animals in the other transects or by the different microhabitats chosen by crayfish and crabs when sharing the same stream section. Other possible explanations are discussed here, but further studies are necessary to better understand the co-occurrence of these two native crustaceans. Moreover, urgent measures are demanded to guarantee the survival of these protected species hampered by several threats. [ABSTRACT FROM AUTHOR]

The protection of freshwater biodiversity has become a priority task for conservation practices, as freshwater ecosystems host high levels of cryptic diversity, while also record similarly high rates of extinction. The Italian white-clawed crayfish Austropotamobius italicus is an endemic freshwater crustacean, threatened by several anthropogenic impacts such as habitat fragmentation, pollution, invasion of exotics, and climate change. Previous phylogenetic studies conducted in Italy pointed out a complex phylogeographic framework for the species, with four different subspecies currently recognized. Conservation efforts, particularly when involving restocking and reintroduction, require a detailed knowledge of their population genetics. In this study we describe the genetic structure of A. italicus populations in northern Italy (Lombardy Alpine foothills and northern Apennines) by using the informative mitochondrial marker cytochrome c oxidase subunit I, in order to assess their current evolutionary diversity and past phylogeographic history from a conservation perspective. Our results contribute to the mapping of the contact area among A. i. carsicus and A. i. carinthiacus in the Orobie Larian Prealps. More interestingly, we highlight the existence of two deeply differentiated evolutionary lineages within A. i. carsicus, showing alternative phylogeographic patterns and past demographic trends. We propose to consider these two clades as distinct molecular operational taxonomic units for the conservation of this endangered crayfish. [ABSTRACT FROM AUTHOR]

Crayfish are regarded as useful indicators of environmental quality and freshwater biodiversity. However, reliable methods for monitoring their populations are needed so that this potential can be fully utilised. We report and discuss methodological aspects of the white-clawed crayfish (Austropotamobius pallipes complex) survey conducted in Piedmont, Italy, with the use of mark-recapture. The results suggest that the method can serve as a convenient tool for estimating the size of crayfish populations and inferring their temporal trends. The two populations investigated appeared closed except for wintertime and July. Consequently, the Robust Design, which is regarded as the most reliable mark-recapture approach, can be easily applied. The minimum effective sampling plan for monitoring purposes should comprise one primary period per year, conducted in the summer¿autumn season, and consisting of three capture sessions. If gaining insight into the ecology of the investigated species is the prime objective and sufficient resources are available, the optimal plan should include two primary periods (in spring and the summer¿ autumn season) of five capture sessions each. Capture sessions need to be separated by roughly 2-week intervals in order to avoid the strong, but short-term, negative effect of capturing crayfish on their recapture chances. As the model without heterogeneity in capture probabilities ensures better estimate precision we recommend that data collected for both sexes are analysed separately. Taking into consideration higher male catchabilities and sex ratio being invariably 1:1, it also seems beneficial to estimate only male numbers and double them to achieve total population sizes. [ABSTRACT FROM AUTHOR]