Gongolaria barbata plays a crucial role as a habitat-forming Fucales species in the Mediterranean Sea, thriving in shallow, sheltered coastal regions, where it exhibits optimal growth in a temperature range of 10 to 25 ◦C. In the northern Adriatic Sea, a semi-enclosed part of the Mediterranean,
there has been a remarkable increase in seawater temperatures in recent decades, often exceeding 28 ◦C in summer. These high temperatures pose a significant threat to the vulnerable early life stages of G. barbata. This study delves into the effects of four temperatures (15, 18, 24, and 28 ◦C) on the growth of G. barbata over its first 16 days, closely monitoring mortality, deformities, and overall survival. Our experiments reveal that higher temperatures can result in deformities and increased mortality of germlings. Notably, a temperature of 28 ◦C resulted in the death of all
germlings within the first week, whereas those exposed to 24 ◦C survived until the second week, albeit with significant deformities prior to death. In contrast, germlings cultivated at 15 and 18 ◦C exhibited normal development with minimal deformities. These results highlight the susceptibility of
the early life stages of G. barbata to temperature-induced stress and provide valuable insights into the potential consequences of rising seawater temperatures in the Mediterranean.
