The blue crab Callinectes sapidus, native to the western Atlantic, is one of the most successful marine invaders in the Mediterranean Sea, where transitional waters may function as key invasion landscapes. However, the ecological mechanisms shaping its local persistence in heterogeneous lagoon-channel-salt-pan systems remain poorly understood. We investigated the spatial distribution, population structure and reproductive evidence of C. sapidus in two coastal wetland systems of western Sicily, Italy: the Stagnone di Marsala lagoon and the Trapani salt-pan/channel complex. Monthly monitoring was conducted throughout 2025 using standardized baited traps combined with environmental measurements, enabling the assessment of habitat-specific abundance patterns, seasonal dynamics and population traits. C. sapidus was recorded at most monitored sites, with catches strongly structured by habitat type and environmental gradients. Abundance was highest in lagoon habitats, where spring-summer peaks were observed, whereas the channel showed lower but persistent year-round occurrence. Salt-pan habitats supported lower abundances but hosted larger individuals, suggesting habitat-specific filtering of population structure. A negative relationship between salinity and trap-level abundance indicated that hypersaline conditions may constrain densities, whereas sheltered lagoon sectors appear to provide favorable conditions for persistence. The population showed a consistent male bias, together with the co-occurrence of adults and juveniles. Reproductive activity was supported by ovigerous females across multiple months and egg developmental stages, primarily in lagoon sites, indicating an extended reproductive window.