The blue crab Callinectes sapidus, native to the western coasts of the Atlantic Ocean, has been introduced in Mediterranean waters where it is currently considered an invasive species. Here, we verified the occurrence of an established population of C. sapidus in the Torre Colimena basin, a Mediterranean habitat located in SE Italy, and provided a first assessment of its functional role in a Mediterranean coastal ecosystem. Crab traps were used to estimate the species abundance at a seasonal frequency; in addition, its trophic position was estimated in summer using nitrogen stable isotopes. Estimations were performed using both a generally adopted value of 3.4 % for the nitrogen trophic level fractionation factor D15N, and species-specific\ud estimations obtained from the literature. C. sapidus was sampled throughout the year, reaching peak abundances in summer. This result, taken together with the observed patterns of variation in the average body size and sex ratio of captured specimens, provided evidence of a fully established population in the Torre Colimena basin. The estimated trophic position of the crab was consistent with the literature information on western Atlantic populations,\ud and resulted, irrespective of the fractionation factor used, significantly provided novel information on the occurrence and potential functional impact of this non-indigenous species in Mediterranean coastal habitats, highlighting current knowledge lacunae and identifying future research lines on marine\ud alien species. than those characterizing an autochthonous brachyuran (Pachygrapsus marmoratus) and a fish predator (Sparus aurata). The present study provided novel information on the occurrence and potential functional impact of this non-indigenous species in Mediterranean coastal habitats, highlighting current knowledge lacunae and identifying future research lines on marine alien species

A quantitative study of the movement behaviour of the brackish isopod Lekanesphaera hookeri was performed. Isopods were collected in late spring 2007 from an Italian lagoon and held in the laboratory under temperature-controlled conditions. We used a real-time video acquisition system to measure in resource-free arenas the mean step length, total path length, average movement speed and movement complexity of individuals characterised by a 10-fold difference in body mass. The fractal dimension D was used as a tortuosity index to estimate the complexity of the movement trajectory. No significant size-related patterns were observed for the mean step length, total path length and average movement speed of the sphaeromatids. Conversely, fractal D values varied negatively with the body mass of specimens according to a power law. Our findings indicate that L. hookeri is characterised by a size-related shift in movement behaviour, occurring independently from the availability of resources in the surrounding environment. The implications of size-related changes in movement complexity are discussed in the context of current metabolic theories.

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