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Coastal exposure may affect the structure of littoral fish assemblages. To evaluate its effects, fish assemblages associated with shallow (0-3 m depth) rocky reefs were investigated by visual census at the Asinara Island National Park (northwestern Sardinia, Italy, Mediterranean Sea) during autumn 2003. Distribution patterns of ichthyofauna in sheltered and exposed rocky reefs were assessed over the spatial scales of locations (i.e. kilometres) and sites (i.e. hundreds of metres). Overall, 38 fish taxa belonging to 17 families were recorded, with Labridae, Sparidae and Serranidae being the families with the most species. Univariate analyses showed that the average density of Labridae and Serranidae was significantly greater at sheltered locations, while particulate organic matter feeders (i.e. Mugilidae) were more abundant at the exposed ones. Significant differences in species richness, total fish abundance and densities of Labridae and planktivorous fish were observed at the spatial scale of sites. Multivariate analyses revealed that whole fish assemblages differed more at the scale of locations than among sites. Planktivorous species contributed most to the dissimilarity between fish assemblages associated with exposed and sheltered stretches of coast. Direct and indirect effects of coastal exposure were hypothesized to explain the potential role of wave action in structuring fish assemblages associated with shallow rocky reefs. In particular, direct effects could affect the distribution patterns of fish, depending on their swimming ability, while indirect effects could include changes in the benthic cover (especially macroalgae) caused by wave action, which then had a repercussion on the fish. [ABSTRACT FROM AUTHOR]