Resumen
The western Mediterranean Sea is one of the most affected areas by the introduction of alien seaweed. Penicillus capitatus Lam. and the recently introduced Halimeda incrassata (J.Ellis) J.V.Lamour are tropical algae that invade native algae assemblies in the shallow sandy beds of Mallorca (Balearic Islands, western Mediterranean) where they are already settled. The aim of this study was to evaluate the effect of a potential competition between the invasive P. capitatus and H. incrassata and the native Padina pavonica (L.) Thivy, by means of biomarkers. P. pavonica samples were collected in their habitat without invasive species and areas where P. capitatus and H. incrassata cohabitated. P. pavonica densities were measured in the three investigated areas. The coexistence of the invasive algae and P. pavonica was related to a significant decrease in the densities of native algae when compared to the area without the invaders. Antioxidant enzymes, catalase and superoxide dismutase, and the reduced glutathione and polyphenols levels were significantly increased in P. pavonica in the presence of both invasive algae. Malondialdehyde, a marker of oxidative damage, and the reactive oxygen species production tended to increase in the presence of the alien species, but without significant differences. The obtained results show that the presence of P. capitatus and H. incrassata altered the normal vegetative growth of P. pavonica and caused an antioxidant response that led to a context of stress, but without evidence of oxidative damage. In conclusion, the presence of the alien H. incrassata and P. capitatus can be considered a source of competitive stress for P. pavonica, although further research regarding the increased water temperature is required.