Marine macroalgae are important primary producers and habitat engineers along arctic coastal rocky shorelines. The species inventory of approx. 160 macroalgal species is relatively small and there are only 19 Arctic endemic species. Few time series document the change of biodiversity in situ that is expected as a consequence of global warming. The island archipelagao Svalbard has been most extensively investigated. Several locations show an increased algal biodiversity at intertidal or shallow subtidal sites. The biomass of macroalgae increase considerably at some shallow water sites and in parallel the algal depth extension decrease. These changes are considered a consequence of warming inducing a sea-ice retreat in winter and meltwater increase in summer. The expected changes in the geographical distribution of species or the immigration of southern species have not yet been unequivocally documented.