<p>Seaweeds, comprising green (Chlorophyta), brown (Phaeophyta), and red (Rhodophyta) algae, are recognized as valuable marine resources rich in bioactive phenolic compounds with nutraceutical potential. Despite growing interest in edible species, limited attention has been given to infesting seaweeds, which may represent an underexploited source of bioactives while addressing ecological challenges. In the present study, an innovative, structure-based data processing workflow was set up for the characterization of phenolic compounds in marine organisms and applied to eight edible and two infesting seaweed species from the major taxonomic groups by means of untargeted mass spectrometric data acquisition. The results reveal distinct phenolic profiles across seaweed taxa, with green algae exhibiting the highest abundances of phenol and phenolic acid sulfates, while brown algae were characterized by a predominance of phlorotannins. Sulfated phenolics outnumbered their non-sulfated counterparts, underscoring the importance of dedicated analytical workflows for marine-specific metabolites. Multivariate statistical analyses further distinguished seaweed classes based on phenolic content and compound classes, with infesting seaweeds demonstrating comparable phenolic profiles to their edible counterparts. This suggests the potential for valorizing infesting seaweeds as sustainable sources of bioactive compounds, aligning with Blue Economy principles. Our findings provide comprehensive insights into the chemical diversity of seaweed phenolics and highlight the unexplored potential of invasive species for nutraceutical applications, contributing to sustainable marine resource management and the development of functional foods.</p> Graphical Abstract <p></p>