Invasion of freshwater systems by the Atlantic blue crab <i>Callinectes sapidus</i> Rathbun, 1896 – new insights from Italian regions

The Atlantic blue crab, Callinectes sapidus Rathbun 1896, is a highly invasive species in the Mediterranean Sea, posing significant ecological and socio-economic threats in marine and estuarine environments. This study investigates the occurrence and potential impacts of C. sapidus in Italian inland waters, specifically examining specimens collected from an irrigation canal in Pomposa on the Adriatic coast and from the Ombrone River, flowing into the Tyrrhenian Sea. Morphometric analysis revealed that males from Pomposa had a mean carapace width (CW) of 172.15 mm (±23.77 mm) and a mean weight of 282.10 g (±98.34 g), while females had a mean CW of 160.68 mm (±25.76 mm) and a mean weight of 173.26 g (±56.11 g). In contrast, males from the Ombrone River were significantly smaller, with a mean CW of 73.36 mm (±10.11 mm) and a mean weight of 25.33 g (±8.86 g). The sex ratio in Pomposa was heavily skewed towards males (3.26:1), suggesting a dominance of adult males in this freshwater habitat. A similar trend was observed in the Ombrone River, though based on a smaller sample size, with only 1 female among 10 specimens. The condition factor (K) was significantly higher for females (1.960) than for males (0.116), while growth coefficient (b) for males had a higher value (2.401) than that of females (1.788), indicating differing growth patterns. This study provides new ecological and biological data on C. sapidus in freshwater systems, underscoring the need for targeted monitoring and management to mitigate the spread and impact of this invasive species in Italian inland waters.