Abstract

The algal assemblages of the northern Adriatic Sea have been studied intensively, but few quantitative data on their spatial and temporal dynamics are available. The intertidal assemblages of two coasts on the Gulf of Trieste were studied for a year, and the patterns of spatio-temporal variability were examined at several scales in space and time. Patterns for the whole assemblage and individual species were analysed by multivariate and univariate analyses. The assemblages of the two shores were relatively poor in species and characterised by different compositions. A moderate temporal variation was found, mostly related to differences between the periods winter-spring and summer-autumn. Patterns for individual species were mainly characterised by differences between the two shores (Polysiphonia opaca), interactions among shores and sampling dates (Fucus virsoides, Ulva compressa, Gelidium pusillum, Lophosiphonia obscura) and differences on the spatial scale of tens of metres (Ceramium species in aggregate, Cladophora albida, Ectocarpus siliculosus, Ulva laetevirens). The dissimilarity between the assemblages of the two shores was the emergent pattern, and differences in the texture and composition of the rocky substratum (marl and limestone, respectively) are considered perhaps the main causes of these differences. Future studies in this region should give more attention to this factor.