MARINE INVASIVE SPECIES AND FISHERIES IN LAGOONS OF THE NORTHERN ADRIATIC SEA

Marine-coastal invasive species and climate change are among the greatest threats to ecosystems worldwide, particularly in semi-enclosed basins like the northern Adriatic Sea and its lagoons. This thesis explores the ecological processes and the impacts of two invasive species: Mnemiopsis leidyi, the sea walnut, and Callinectes sapidus, the Atlantic blue crab on the artisanal fisheries and biodiversity of the Venice Lagoon. Using an interdisciplinary approach, which integrates ecological modelling, local ecological knowledge, field experiments, and statistical analysis. The study assesses the temporal and spatial dynamics of M. leidyi within the Venice Lagoon, connecting its proliferation to environmental variables like temperature and salinity. The impact of M. leidyi on lagoon fisheries was determined using landing data, interviews with local fishers, and fyke net sampling; findings reveal a significant decline in fishery landings coinciding with ctenophore blooms, underlining the species' detrimental impact on local fisheries, particularly through net obstruction. Moreover, it has been observed how blooms of the species are strictly linked with rising in water temperature. Thanks to laboratory experiments Temperature and salinity tolerances of M. leidyi in the invaded habitat were evaluated, informing predictions about its proliferation. Similarly, the study examines the Atlantic blue crab's distribution and seasonal dynamics in three lagoons located in the Po River Delta. Results highlighted the persistence of the species in all the period of investigation and evaluated the lagoons as possible nursery areas for C. sapidus. With that, experiments of its interaction with the native species, the mediterranean green crab Carcinus aestuarii, has been carried out. Experiments revolved around substrate preference of both species marking a possible interaction and competition between the two crab species and a preference of the blue crab towards sandier bottoms. Lastly morphological studies have been conducted on the blue crab exploring its sexual dimorphism helping with the implication of the blue crab for local ecology. The study highlights the dual role of invasive species as ecological threats and economic opportunities, advocating for innovative management strategies, such as leveraging invasive species as commercial resources. It also emphasizes the synergistic effects of climate change and invasive species on biodiversity, fisheries, and ecosystem services. In conclusion, this research provides critical insights into the mechanisms of biological invasions, their ecological impacts, and adaptive management measures to mitigate their effects, fostering resilience in coastal ecosystems against ongoing global changes.