Canopy algae of the genus Cystoseira are considered important habitat formers providing shade and shelter for a diversified assemblage of animals and plants. Some evidence suggested that these algae are highly sensitive to anthropogenic disturbances and their presence could be used as an `ecological quality' indicator. In this paper we tested the hypothesis that structure of assemblages understoried by these algae is dependent on Cystoseira species. To achieve this aim the composition of benthic assemblages under the canopy of three Cystoseira species was estimated at Sinis-Mal di Ventre MPA (western Mediterranean), where at some sites these algae occur on the same upper-infralittoral platforms. At one site 2 areas have been sampled and in each area 5 replicates were taken per Cystoseira species. The percent coverage of benthic species was estimating in the field using a 20X20 cm multiple-scale quadrats. A multivariate analysis was performed to highlight differences in taxa composition. Results have evidenced significant variations in assemblages depending on Cystoseira species (ANOSIM R=0.585 p=0.1%). These results suggest that the three Cystoseira species co-occurring on the same platforms do structure different habitats supporting diversified species assemblages. Hence, given the high variability on small spatial scale of habitats it is necessary to perform well designed experiments to correctly interpret results collected during monitoring program
