rThe emergent demand for carrageenan by Chilean and global industries caused increasing extraction pressures on natural populations of ‘red luga’, Gigartina skottsbergii, displacing fishing effort from 41°S to the southernmost region of Chile (54-56 °S). Despite the knowledge generated in the biology of G. skottsbergii, unknown the flora associated with G. skottsbergii, therefore we don ́t know, the real impacts of: global warming, ocean acidification, extractive fishery, among others, in benthic community associated with G. skottsbergii. In this work we evaluate seasonal composition of macroalgae associated with two populations of G. skottsbergii in the Strait of Magellan. The study sites corresponded to Santa María (Tierra del Fuego Island) and Santa Ana (Brunswick peninsula). We identified a total of 31 species (21 Rhodophyta, 7 Ochrophyta and 3 Chlorophyta). The species richness average of the macroalgae, per quadrant, in Santa Ana have a significant increase during summer, with the greatest richness in autumn (p<0.05), meanwhile, Santa María did not show significant differences between the different seasons (p>0.05). The multivariate analysis showed significant differences in the assemblage composition of macroalgae between the two localities at each season (p<0.05). This work is the first report of the seasonal dynamics of assemblages of subtidal macroalgae in the Strait of Magellan.