Impacts of the invasive blue crab Callinectes sapidus on small-scale fisheries in a Mediterranean lagoon using fishery landing data.

Human activities have introduced numerous non-native species beyond their natural habitats, leading to their establishment in new regions. Among them, the Atlantic blue crab (Callinectes sapidus) has significantly impacted biodiversity and fisheries in the Mediterranean Sea. This study investigates the recent population increase of C. sapidus associated changes of small-scale fisheries in one Mediterranean lagoon, the Sacca di Goro lagoon within the Po River Delta. We analysed the influence of environmental factors and C. sapidus biomass on trends in landings of commercially important species, using multivariate analysis, including principal component analysis (PCA) and redundancy analysis (RDA), as well as variance partitioning, linear regression and change point analysis on fishery landings data. Our results suggest that the spread of C. sapidus coincides with a decline in several commercial species, such as the European flounder (Platichthys flesus), the big-scale sand smelt (Atherina boyeri), the European eel (Anguilla anguilla) and the Mediterranean green crab (Carcinus aestuarii), suggesting a strong ecological and economic impacts of the blue crab invasion. The main mechanisms by which C. sapidus could drive this trend likely involve predation and competition, although further investigation is needed for confirmation. Annually averaged environmental variables (i.e., water temperature, salinity, nitrate and chlorophyll-a concentrations) were not significant predictors of commercial species trends, suggesting that the changes in landings cannot be primarily attributed to environmental factors. This study is the first to provide a comprehensive analysis of the potential effects of C. sapidus on the relative abundance of key fisheries species in Mediterranean Sea, suggesting a potential link between the rapid increase in its abundance and observed fish landing trends. The results highlight the need for integrated management strategies, including promoting market opportunities for C. sapidus and consideration of ecosystem-based management to control its abundance such as the protection of native local predators.