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Abstract

In the Mediterranean Sea, one of the most important habitats, alongside dense seagrass
meadows found on sedimentary bottoms, is formed by canopy-forming brown algae of the
genus Cystoseira sensu lato on rocky shores. These long-living, slow-growing macroalgae
possess a complex, tree-like morphology and form dense, structurally intricate habitats, so
called marine forests. Cystoseira s.l. forests are known as biodiversity hotspots and areas
supporting high primary productivity, enhancing ecosystem complexity, and providing
essential habitats and food for numerous marine organisms. They also contribute
significantly to nutrient cycling, shoreline protection, and carbon sequestration. However,
due to a wide range of direct and indirect anthropogenic pressures, Cystoseira s.l. forests
are in decline across the Mediterranean. This dissertation focuses on Gongolaria barbata,
the most common Cystoseira s.l. species in the northern Adriatic Sea, where its forests
have undergone severe degradation.
The overarching aim was to advance knowledge of the species, refine cultivation
protocols, and explore restoration potential by identifying key ecological and
methodological limitations and testing potential solutions. Five interconnected studies
addressed key aspects of G. barbata ecology and restoration. The first study showed that
ex situ cultivation can be streamlined through UVC sterilization and shortened laboratory
phases, with early transfer to floating lantern net baskets, reducing costs while maintaining
seedling survival. The second study demonstrated that seedlings are highly temperaturesensitive,
with optimal growth at 15 °C and sharp declines above 20 °C, highlighting risks
from warming seas and thermal anomalies. The third study investigated algal extracts,
showing that certain formulations—such as those from the green microalga Desmodesmus
sp.—can enhance seedling growth and resilience when applied at appropriate
concentrations. The fourth study revealed that distinct G. barbata morphotypes represent
phenotypic plasticity rather than genetic divergence. Finally, the fifth study characterized
the G. barbata microbiome, uncovering body-part specificity and site-level variation, and
suggesting that microbiome-aware practices can improve restoration outcomes.
Together, these findings provide a comprehensive understanding of G. barbata ecology
and physiology, while offering practical guidance for restoration. They establish a scientific
and methodological foundation for the recovery of Cystoseira s.l. forests and contribute to
the development of an integrated, scalable, and climate-resilient framework for marine
habitat restoration in the Mediterranean Sea.