DECADAL REGRESSION OF SEAGRASSES IN THE GULF OF TRIESTE INDUCED BY ENVIRONMENTAL ALTERATIONS AND SEA WARMING

Seagrass meadows play an essential role as habitat builders, providing food, shelter and nursery grounds for many species and a vast array of goods and services for humanity. In recent decades, however, their populations have suffered from multiple impacts that have led to a widespread decline. The northern Adriatic Sea is no exception: in recent years, and especially since 2014, a steady decline in seagrass populations has been observed. In this study, we investigated the factors affecting seagrasses in the Gulf of Trieste and made a comprehensive assessment of their distribution, also in comparison with the past. To assess whether the fluctuations of seagrasses between 2014 and 2018 could be related to changes in environmental conditions, we analyzed the spatiotemporal patterns of environmental variables and applied generalized additive models considering two main periods: 2009-2013 and 2014-2018. Results showed that Cymodocea nodosa is the dominant seagrass species and is still abundant along the northern coast of the Gulf, while in Slovenia and close to Trieste it has experienced a 30% and 89% decline, respectively, in the last five years. Analysis of the physicochemical variables highlighted an increase in seawater temperature throughout the Gulf and a change in nutrient load, especially in Slovenia where it decreased considerably. Models achieved high-performance scores and showed that PAR, nutrients, temperature, and sediment type were the major predictors of seagrass presence. The probability of finding seagrasses gradually increased with PAR and nutrients and decreased with temperature. Other local factors, however, probably contributed to reducing the plants’ resilience to disturbance. Appropriate protection and restoration measures are essential to reduce the loss of these valuable species. Our results will be useful to establish a baseline for future monitoring activities and to develop integrated spatial planning strategies.