A potential bottom-up cascade on the abundance of invasive Atlantic blue crab Callinectes sapidus in northwestern Adriatic lagoons

The introduction of the Atlantic blue crab (Callinectes sapidus) in the Mediterranean Sea dates back to the 1900s; however, the species has recently spread in the region resulting in negative impacts on the structure and functions of invaded ecosystems and local fisheries. This study investigated the covariation between spatiotemporal dynamics of the Atlantic blue crab fishery landings (catch-per-unit-area; CPUE) and environmental explanatory variables (i.e., salinity, water temperature, nitrate and chlorophyll-a used as a proxy of primary productivity) over a four-year period (2020–2023) in four key lagoonal ecosystems of the North Adriatic Sea. Our results showed that the marked increase in Atlantic blue crab CPUE in all studied lagoons since 2020 was strongly related with local primary productivity which likely supports a greater abundance of food resources for the suspension feeding Manila clam (Ruditapes philippinarum), a key prey for blue crabs and one of the most important fisheries in the region. Conversely, salinity and water temperature, two key parameters regulating blue crab biology, i.e., mating and subsequent larval spawning, did not significantly influence CPUE in the studied lagoons. These results suggest that primary production in the lagoons, which directly influences food availability (e.g., Manila clams) for the Atlantic blue crab, is the primary factor driving its apparent invasion success in the study area. Our results provide new insights into understanding the environmental factors that promote its invasion and spread, allowing for targeted control measures such as managed fisheries and water quality.