Effects of extreme temperatures and recovery potential of Gongolaria barbata from a coastal lagoon in the northern Adriatic Sea: An ex situ approach.

BACKGROUND AND AIMS: Globally, rising seawater temperatures contribute to the regression of marine macroalgal forests. Along the Istrian coastline (northern Adriatic), an isolated population of Gongolaria barbata persists in a coastal lagoon, representing one of the last marine macroalgal forests in the region. Our objective was to examine the impact of extreme temperatures on morphology and physiology of G. barbata, and test its potential for recovery after simulating marine heatwave (MHW) conditions. METHODS: We explored the occurrence of marine heatwaves in southern Istria, adjacent to the study area, as well as extreme temperatures inside the area itself. Subsequently, we performed a thermotolerance experiment, consisting of a stress and recovery phase where we exposed G. barbata thalli to four extreme (28 °C, 30 °C, 32 °C, 34 °C) and one favourable (18 °C) temperature. We then monitored morphological and physiological responses. KEY RESULTS: Our findings indicate a significant rise in frequency, duration, and intensity of MHWs over decades on the southern Istrian coast. Experimental results show that G. barbata demonstrates both morphological and physiological recovery potential after exposure to temperatures as high as 32 °C. However, exposure to 34 °C led to thallus decay, with limited regeneration ability. CONCLUSIONS: Our results show that G. barbata has a remarkable resilience to long term exposure to extreme temperatures up to 32 °C and suggests that short term exposure to temperatures beyond this, as currently recorded inside the lagoon, do not notably affect the physiology or morphology of local G. barbata. With more MHWs expected in the future, such an adapted population may represent an important donor suitable for future restoration activities along the Istrian coast. These results emphasize the resilience of this unique population, but also warns of the vulnerability of marine macroalgal forests to rising seawater temperatures under rapidly changing climate conditions.

First Restoration Experiment for Endemic Fucus virsoides on the Western Istrian Coast-Is It Feasible?

Fucus virsoides is an endemic species of the Mediterranean limited to the Adriatic Sea. In recent decades, it has undergone a severe regression, which is well documented in the northern Adriatic. To develop a tool for mitigating this problem, we tested the feasibility of F. virsoides restoration and designed a very simple yet effective method for ex situ cultivation and planting. We also tested the effect of positioning in the upper vs. lower intertidal on the growth of F. virsoides. After planting, the algae reached fertility in nine months, which was followed by a period of stagnation and reduction in size due to grazing and fouling. There were some differences in growth of the algae according to positioning in the intertidal at different measurement times, but that had little impact on the overall success of the restoration experiment. This represents, to our knowledge, the first successful F. virsoides ex situ cultivation and restoration attempt.