The costs of an invasion: How the blue crab impaired ecosystem services in the most productive lagoon of northwestern Adriatic

The introduction of non-native species can disrupt ecological processes and impair ecosystem services, particularly in intensively exploited systems such as coastal lagoons. The Atlantic blue crab (Callinectes sapidus) has recently expanded rapidly in the northern Adriatic, raising ecological and economic concerns. This study documents and evaluates its impact on provisioning services in the Sacca di Goro lagoon (Po Delta, Northern Italy), the most productive site for Manila clam in Europe. Net revenues from the emerging blue crab supply chain were also assessed by accounting for sales and disposal costs. Crab abundance showed no association with environmental variables. By contrast, a statistically significant negative relationship was detected with Manila clam production, which declined by 71.8 %, corresponding to annual losses of about €65 million. Small-scale fisheries also recorded reduced catches of native and commercially valuable species, with estimated losses of €0.18 million yr^-1. Revenues from the blue crab supply chain were positive in 2023 (+€0.41 million yr^-1) but turned negative in 2024 (-€0.71 million yr^-1) due to disposal costs and falling market prices. Thus, to date, not only are the revenues from blue crab sales negligible, but they are also outweighed by the high costs of disposal. This case shows how invasive species can simultaneously erode biodiversity and ecosystem services while failing to provide viable alternatives. It provides quantitative evidence of aquatic invasion costs and highlights the importance of integrating such assessments into ecosystem-based management and policy.