Mediterranean coastal lagoons are increasingly vulnerable to the impacts of climate change, including rising temperatures, altered precipitation regimes, and shifts in hydrological connectivity. These pressures are particularly pronounced in deltaic systems such as the Po River Delta, where the balance between freshwater input, marine intrusion, and anthropogenic activities—especially intensive shellfish farming—plays a critical role in shaping ecosystem structure and function. Phytoplankton communities, as the primary trophic resource for filter-feeding bivalves and sensitive indicators of environmental change, respond rapidly to fluctuations in salinity, light, and nutrient availability. In this study, we investigate the functional traits of phytoplankton—specifically size structure and photosynthetic efficiency (Fv/Fm)—as diagnostic tools to assess ecological responses to aquaculture pressure and climate-driven variability in the Sacca degli Scardovari lagoon, one of the most productive shellfish farming areas in Europe.
Our findings highlight how filter-feeding activity and climate-induced stressors interact to modulate phytoplankton biomass and community composition, with implications for carbon cycling, food web dynamics, and the resilience of transitional coastal ecosystems. By adopting a trait-based approach, this study contributes to a deeper understanding of the ecological functioning of Mediterranean lagoons under multiple stress regimes, offering insights relevant for sustainable aquaculture management and climate adaptation strategies in the Po Delta region.