Integrated Metabolomic and Biological Profiling of Cymodocea nodosa: Tissue-Specific Chemical Diversity and Fouling-Relevant Activity

Seagrasses are important components of coastal ecosystems and represent a source of chemically diverse natural products with potentially relevant biological activities. This study aimed to characterize the biochemical and metabolomic profiles of leaves and rhizomes of the Mediterranean seagrass Cymodocea nodosa and to compare the biological activity of extracts from the two tissues across different marine organisms. Hydroalcoholic extracts were characterized by biochemical assays and untargeted liquid chromatography–high-resolution mass spectrometry, while biological responses were assessed using Aliivibrio fischeri, Phaeodactylum tricornutum, Dunaliella tertiolecta, Acartia tonsa, and the fouling serpulid Ficopomatus enigmaticus. Leaves and rhizomes differed in their biochemical characteristics but shared most putatively annotated metabolites, including phenolic acids, flavonoids, lipid-derived metabolites, and amino acid derivatives. Semi-quantitative analysis revealed tissue-associated differences in relative LC-HRMS signal intensities. Biological responses were species- and endpoint-dependent, with F. enigmaticus showing the highest sensitivity, particularly to the rhizome extract (EC50 = 48.8 mg/L), whereas the other organisms generally responded at higher concentrations. Overall, these findings highlight tissue-associated chemical and biological differences in C. nodosa extracts and identify rhizomes as particularly interesting for further investigation into the relationships between seagrass metabolites and fouling-related biological responses.