This study provides a comprehensive analysis of the eco-physiological responses of the blue crab (Callinectes sapidus) to variations in salinity, shedding light on its adaptability and invasive success in aquatic environments. Gender-specific differences in osmoregulation and Electron Transport System (ETS) activity highlight the importance of considering sex-specific aspects when understanding the physiological responses of invasive species. Females exhibited increased ETS activity at lower salinities, potentially indicative of metabolic stress, while males displayed constant ETS activity across a range of salinities. Osmoregulatory capacity which depended on gender and salinity, was efficient within meso-polyhaline waters but decreased at higher salinities, particularly in males. These findings provide valuable understandings into how C. sapidus specimens in an invaded area responds to salinity changes, important for considerate its distribution through saline pathways during tidal cycle fluctuations. This study shows the importance of interdisciplinary research for effective management of invasive species and conservation of affected aquatic ecosystems.

The variability in trophic position and carbon isotopic signatures can provide information about their dietary flexibility and its ability to adapt to changing environmental conditions. The impact of the invasive blue crab Callinectes sapidus was assessed by estimating its trophic position and isotopic niche using stable isotopes (δ¹³C, δ¹⁵N, δ³⁴S) across different invaded Atlantic coastal areas. This study, the first of its kind in the eastern Atlantic range, reveals the crab's omnivorous behavior with a wide trophic position (TP = 2-4), consistent with findings from its native range. Significant spatial variability in trophic roles was observed between habitats, with salt marshes showing enriched δ¹³C and lower TP due to differences in primary producers like Spartina detritus and phytoplankton. Estuaries exhibited higher and broader δ¹⁵N and TP ranges, influenced by prey availability and anthropogenic nitrogen inputs, that implies a significant impact on marine benthic and pelagic animal communities. Seasonal changes in the Guadalquivir estuary, linked to overwintering and brooding migrations, showed sexual differences in isotopic signatures, with males more enriched in δ¹⁵N than females, indicating varied prey availability or metabolic differences. Overall, the Atlantic invaded range displayed broader and lower TP compared to the Mediterranean, underlining the blue crab's flexible and diverse trophic role across different habitats and trophic levels. The variability in trophic position and carbon isotopic signatures reflects the dietary flexibility of this invasive species and its potential effects on native fauna. These findings emphasize the need to consider trophic interactions in ecosystem management and conservation efforts.