Extended Data Fig. 4: Seagrass roots contained phenolic compounds.

Matrix-assisted laser desorption/ionization mass spectrometry image from a Mediterranean P. oceanica root cross-section collected off the Island of Elba, Italy. The ion image shows the presence of the phenolic compound, identified as caffeic acid (C₉H₈O₄, [M-H]^-, m/z 179.0354; Supplementary Fig. 7). Relative ion abundances are visualized from low (blue) to high (yellow).