Small-scale crayfish distribution modelling of the invasive crayfish Procambarus clarkii in the Molentargius-Saline Regional Natural Park (Sardinia, Italy) in response to environmental variables

The crayfish, Procambarus clarkii, is among the worst invasive species capable of disperse overland, aiding the invasion of new environments. Because management options are limited once crayfish become established, there is a critical need to identify the suitable habitats for this invasive species. In this study, we forecast the potential distribution of crayfish based on environmental predictors in the Molentargius-Saline Regional Natural Park (Sardinia, Italy). Current known distribution was used to build correlative species distribution models (SDMs) and forecast distribution in the entire area. We considered, during the spring season, 5 quantitative environmental descriptors at the local scale (Depth, Water Temperature, Salinity, pH and Dissolved Oxygen). Single station data were used to generate synoptic distribution of environmental factors through the inverse distance weighted deterministic interpolation (IDW). The SDMs obtained through 2 different algorithms showed very good performance: GBM (General Boosted Models, ROC=0.847) and RF (Random Forest, ROC=0.996). For GBM the predicted distribution correlated most significantly with environmental variables (Salinity, Dissolved Oxygen and pH), while for RF all variables are homogeneously significant. Identified best models, performed by the Ensemble Modeling technique, showed that most of the areas outside the currently known distribution may offer potential habitats for P. clarkii. Greater probability to find the species presence were computed in correspondence of the Deflux Channel and ESF6B basin of the EcoSistema Filtro. However, for the Bellarosa Minore basin the forecast spread of the species is evident in all the tanks with large dense patches. Presented results deepen the knowledge about distribution patterns of P. clarkii in the Regional Natural Park. Moreover, the ongoing study gives a basic background for the future development of management strategies. This study was supported by the Fondazione di Sardegna for the project Impact of Invasive Alien Species on Sardinian ecosystems and by the Fondazione con il Sud for the project Nr. 2015-AMB-0065.