IL GAMBERO INVASIVO PROCAMBARUS CLARKII (GIRARD, 1852) NELLA LANCA DELLA RISERVA NATURALE INTEGRALE “BOSCO SIRO NEGRI”

The invasive crayfish Procambarus clarkii (Girard) in the pond of the Natural Reserve “Bosco Siro Negri”. The present paper summarizes the results of research activities performed from October 2005 to November 2007 in a pond bordering the “Bosco S. Negri” Natural Reserve. The aim of the work was to assess the ecological impact caused by the non-native red swamp crayfish (P. clarkii), probably of recent introduction in the study area. Crayfish samples were collected systematically (every 1-2 week) by ad hoc built traps in order to investigate structural parameters of the population (spatial distribution, abundance, size-class frequency, sex ratio). Impact on habitat structure was assessed in mesocosms replicated both in the study area and laboratory. A subsample of crayfishes was investigated for diet composition by stomach content analysis. Results of autoecological investigations on P. clarkii were integrated with a constant monitoring of the study area by collecting information on: water level, pH, oxygen concentration, water temperature, distribution of aquatic macrophytes and a qualitative assessment of the ecosystem biodiversity value (taxonomic identification of the major groups of invertebrate and vertebrates by visual census and crayfish trap by-catches). A subsample of P. clarkii specimens was selected for mycological investigations, with the aim of isolating the pathogen Aphanomyces astacii (Schikora), causal agent of the “crayfish plague”. The whole integrated data set revealed a severe impact of the red swamp crayfish in the study area. Mesocosm experiments foresaw a fast reduction of macrophytes coverage in the basin and the possible local extinction of native species such as Potamogeton natans (L.) characterised by a relatively lower production unable to contrast the herbivory pressure of P. clarkii. Ground truth observation totally confirmed experimental outputs. The last survey conducted in autumn 2007 reported a severe reduction in aquatic macrophyte coverage and the local extinction on P. natans. Other two macrophyes species present in autumn 2005, Potamogeton crispus (L.) and Myriophyllum spicatum (L.), were not recorded in 2007. This rapid habitat modification activity had indeed a strong repercussion on the structure of biocoenoses living in relation to the aquatic vegetation (from macroinvertebrate to fishes), whose richness effectively dropped from 8 taxa (2005) to 3 taxa (2007). Mycological investigation showed the absence of the pathogen A. astacii and the detection of a rich microfungal colinization that will be object of further studies. In conclusion this study confirmed the dangerousness of P. clarkii establishment into the wild, being this species able to exert strong impact on habitat, native communities, and ecosystem functioning.