| Summary: | Rocky reef fish assemblage structure in seven coastal islands of Southern Brazil was characterized by underwater visual census (20 m x 2 m transect method 40 m2), average depth of six meters, to obtain density (fish/40 m2) and biomass (grams/40 m2). Fish species were categorized according to their trophic category and geographical distribution. In total, 526 strip transects were performed, covering an area of 21,040 m2, totaling 19,377 individuals (means of 36.83 fish/40 m2 and 1,790.23 g/40 m2), distributed among 73 species from 34 families. Among these, 60% of the species occur in the western Atlantic, 20% are transatlantic and 9.60% occur only in the Brazilian Province. The species Stegastes fuscus was the most frequent and with highest density. Acanthurus chirurgus showed the highest biomass, followed by S. fuscus. Itacolomis Island presented the highest density, 48.18 fish/40 m2, followed by Veado Island with 43 fish/40 m2. Regarding biomass, Itacolomis Island and Pedra da Baleia were the most representative with mean values of 3,253 and 3,028 g/40 m2, respectively. Mobile invertebrate predator was the trophic category with the highest density, represented by 26% of species registered, also having the highest density (12.57 fish/40 m2). Mobile invertebrate showed the highest biomass (780.48 g/40 m2). Our results indicated that despite the similarity in taxonomic composition between islands, there are differences in density and biomass, highlighting singular assemblage structures, whether by environmental and/or anthropogenic factors, and dominated by few species, both in density and biomass.
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