LAUSR

Abstract Canopy-forming algal species, like those of the genus Cystoseira, are known to play an important role as ecosystems-engineers. Under key anthropogenic stressors (e.g. nutrient enrichment and urbanization), these species are replaced by persistent and smaller taxa, defined as turf-forming algae. The scope of this work was to search for shifts from canopy-forming to turf-forming taxa, changes in macrophytes spatial and seasonal diversity, and trends in macrophytes biodiversity on the infralittoral rocky bottom of the northern Adriatic Sea, during the period from 2006 to 2016. At many sampling sites a decline in the proportion of canopy-forming algae (Cystoseira spp. and Halopithys incurva) was observed until 2012, followed by a slight recovery in 2016. Moreover, the Shannon diversity index calculated for all upper-infralittoral macrophytes increased from 2006 to 2012, then decreased in the following two years, with a new increase from 2015. Despite the assessed fluctuations in the status of macroalgae, we can conclude that there are no visible signs (yet) of degradation of the benthic vegetation.