Chlorophyll variability in a Coastal Ecosystem: Insights from Recent Decades and Future Projections

Climate change is transforming coastal ecosystems by altering key processes such as freshwater inputs, salinity, and stratification, which drive nutrient dynamics, primary productivity, and carbon cycling. This study explores the dynamics of chlorophyll concentration (as a proxy for local planktonic biomass) in the Gulf of Naples (GoN) within the Mediterranean Sea. Leveraging long-term monitoring data and machine learning, we identify the local drivers of chlorophyll concentrations as a combination of physical and biogeochemical conditions. Notably, salinity emerges as a key predictor of chlorophyll, emphasizing the critical role of freshwater inflows and mixed layer dynamics. We develop an empirical model to estimate salinity based on freshwater discharge and stratification, which proves robust even with simplified inputs. By combining these predictors with future climate projections (RCP4.5 and RCP8.5), we assess the potential impacts of changing precipitation and wind patterns on salinity and chlorophyll. Results suggest increasing salinity and declining chlorophyll concentrations, particularly in spring, while uncertainties persist for autumn trends. Crucially, changes occurring on land may have a greater impact than those at sea (e.g., temperature) on coastal ecosystems, particularly their microbiomes, which form the foundation of the main trophic webs. These findings highlight the importance of long-term monitoring and infrastructure development to enhance ecosystem management under future climate scenarios.