Dilkamural: A novel chemical weapon involved in the invasive capacity of the alga Rugulopteryx okamurae in the Strait of Gibraltar

The southwestern coasts of Europe (Strait of Gibraltar) are experiencing a severe invasion of the brown alga Rugulopteryx okamurae, original from the northwestern Pacific ocean. Currently there is no clue regarding to the reasons of such huge invasive potential, although the involvement of chemical defenses has recently been suggested. In this context, this study was aimed to investigate the presence and potential role of chemical defenses in the invasive success of R. okamurae. The chemical study of R. okamurae from the Strait of Gibraltar led to the isolation of six secondary metabolites, among which the compound dilkamural stands out because of its high concentration. Later, in a set of feeding deterrent assays, the generalist native herbivore Paracentrotus lividus showed higher consumption over the native alga Ulva sp. than over the non-native R. okamurae. This low consumption was tracked down to dilkamural, which displayed not only deterrent properties but also caused harmful and even lethal effects over the sea urchins. These results are consistent with the novel weapons hypothesis, since dilkamural was not described previously in the invaded area and has a defensive role against generalist herbivores in the new range, thus helping to explain the great expansion of R. okamurae in the Strait of Gibraltar.