Environmental alterations and sea warming drive seagrass meadow decline in urbanized coastal areas of the northern Adriatic Sea

Seagrass meadows are important habitat builders, providing food, shelter, and nursery grounds for many species, alongside essential goods and ecosystem services for humanity. However, in the last decades, seagrass meadows have been subjected to numerous pressures, leading to their widespread decline. The northern Adriatic Sea is no exception, with seagrass regression observed notably between 2014 and 2018. This study aims to identify the drivers of the recent seagrass decline in the Gulf of Trieste through a spatial and temporal assessment of seagrass distribution. To assess the relationship between seagrass dynamics and environmental changes, spatiotemporal patterns of environmental variables were analyzed, and generalized additive models were applied for two different time periods: 2009–2013 and 2014–2018. Historical data on seagrass distribution was also collected and compared with the current distribution. Our findings indicate that Cymodocea nodosa remains the dominant species on the northern coast of the Gulf, with a decrease of 30 % in Slovenian waters and up to 89 % near Trieste (Italy) during 2014–2018. Analysis of physicochemical variables revealed an increase in seawater temperature across the Gulf and a change in nutrient load, particularly in Slovenia, where it decreased significantly. Models achieved high-performance scores, identifying photosynthetically active radiation, nutrients, temperature, and sediment type as key determinants of seagrass occurrence. Nonetheless, additional local-scale factors likely contributed to lower seagrass’ resilience to disturbances. These findings stress the need to develop integrated spatial planning strategies and provide a crucial baseline for future seagrass monitoring and restoration activities.