Effects of increased temperatures during air exposure on the morphology and physiology of Fucus virsoides (Fucales, Phaeophyceae)

The brown alga Fucus virsoides, an endangered species endemic to the Adriatic Sea, is subjected to increasingly changing ecological conditions in the intertidal zone, potentially driving its extinction. In this study, temperature fluctuations at one of the last remaining F. virsoides sites in the Istrian region (northern Adriatic) during a 1-year period were analysed and found to be only partially associated with water level changes linked to tidal dynamics, suggesting nontidal effects may strongly affect the emersion time and exposure of thalli to dry conditions, especially during spring. Additionally, the effects of increased temperature during air exposure on F. virsoides thalli were experimentally assessed under laboratory conditions. The results indicate that acute and repeated exposure to a high air temperature of 33°C can cause long-term damage to the thalli, whereas lower tested temperatures of 20, 25, and 29°C have little to no effect on the morphology or physiology of this algae. This study provides insights into how F. virsoides, a species adapted to the northernmost biogeographical region of the Mediterranean, copes with extreme temperature fluctuations during prolonged air exposure, as one of the environmental stressors that are expected to intensify under future climate scenarios.