Fucus virsoides in the Adriatic Sea: a glacial relict in the era of climate changes

On temperate and cold rocky coasts, Fucus species (Fucales, Phaeophyceae) form complex habitats in the intertidal zone that provide important ecosystem services. Fucus virsoides J. Agardh is a glacial relict endemic to the Adriatic and the only representative of the genus Fucus in the Mediterranean. It once formed extensive canopies widespread from northern Italy to southern Albania, but its populations have declined drastically in recent decades. This thesis aims to investigate long-term changes in the distribution of F. virsoides and to identify possible causes for its decline. To this end, a multidisciplinary approach was adopted that includes a critical analysis of historical datasets, environmental factors, ecophysiological laboratory experiments, field studies and modeling techniques. In the first chapter, we undertook a comprehensive assessment of the distribution and status of F. virsoides by analysing the historical and current occurrence since the 19th century. In addition, long-term analyses of key marine abiotic parameters were conducted to investigate possible causes of the species' decline. The mapping revealed a continuing decline with only about 20 fragmented populations left, possibly related to significant changes in the physical characteristics of the Adriatic,. In the second and third chapters, we conducted laboratory experiments to investigate the physiological effects of two potential stressors: nutrient changes, measured by O₂ evolution and PAM fluorimetry, and water stress, assessed through water relations parameters. The results showed the potential of the species to acclimatize to a wide range of nutrient conditions and the species’ tolerance to water stress. In the fourth chapter, restoration trials were carried out, combining laboratory and field studies. The results showed the optimal temperature for seedling growth at 15°C in selected culture media in the laboratory and the importance of site selection and herbivore control. In the fifth chapter, we modeled the occurrence of F. virsoides using environmental and anthropogenic data and assessed the changes in its future distribution under Representative Concentration Pathway (RCP) scenarios. According to the model, the increase in atmospheric temperatures due to climate change is the major factor affecting the occurrence of F. virsoides. The projections showed a future progressive decline in suitable habitats for the species, which could potentially lead to its disappearance under the most severe RCP scenario. Through a multidisciplinary approach, this study provides a thorough assessment of the overall status of F. virsoides and contributes to a deeper understanding of the factors driving its decline. The results emphasize the urgent need for immediate conservation measures to prevent the extinction of this key component of the Adriatic's natural heritage.