Spatial Expansion and Ecological Correlates of Invasive Crayfish Procambarus clarkii and Pacifastacus leniusculus in Mediterranean Rivers of Catalonia (NE Iberian Peninsula)

Invasive freshwater crayfish are among the most impactful non-native taxa in European river systems, yet quantitative assessments of their spatial expansion and environmental drivers remain scarce in Mediterranean regions. We investigated the expansion dynamics and environmental drivers of two invasive North American crayfish, Procambarus clarkii and Pacifastacus leniusculus, in rivers of Catalonia (NE Iberian Peninsula). Using occurrence data from official biological monitoring programs and global repositories aggregated into 10 x 10 km grids, we quantified expansion rates and modeled current distributions against geomorphological and anthropogenic factors, including a composite Environmental Disturbance Score. Results indicate significant range expansions for both species, with P. clarkii spreading more rapidly (slope = 5.8) and extensively (>100 grids) than P. leniusculus (slope = 1.4). Generalized Linear Models (GLMs) identified anthropogenic pressure and altitude as the primary predictors for P. clarkii occurrence, confirming its high occupancy in degraded, lowland reaches. Conversely, P. leniusculus trended toward cooler, higher-altitude reaches with lower disturbance, though associations were statistically less pronounced. This spatial segregation highlights how longitudinal gradients and human-induced disturbances jointly structure crayfish invasions in Mediterranean river systems. The advance of P. leniusculus into headwaters may pose a critical threat to the last refugia of the native white-clawed crayfish (Austropotamobius pallipes) through the transmission of crayfish plague. Accordingly, we advocate for differentiated management strategies: impact mitigation in degraded lowland reaches and proactive prevention in high-quality headwater systems.