In order to verify the trophic transfer of mercury, the concentrations of total mercury (Hgtotal) were determined in the aggregated fauna from a sand reef region formed by polychaetes, Phragmatopoma lapidosa. In addition to the aggregated fauna, mussel (Perna perna), green algae (Ulva spp.), porcelain crab (Pachycheles sp) and gastropod (Thais haemastoma) and its posture, Hgtotal were also determined in the suspended particulate matter and in the superficial sediments from the region of the Lighthouse of St. Tomé Reef, Northern Rio de Janeiro State (22 04 52 S, 041 06 59 W). This oceanic area belongs to a transitional faunistic region, which presents a great biodiversity. Hgtotal in the biotic and abiotic samples were determined by a cold vapor atomic absorption spectrometry, coupled to a flow injection system, Perkin Elmer FIAS 400. In order to characterize the superficial water layer of the region, some physical and chemical water parameters (pH, Eh, salinity and temperature) were determined. At the moment of the water sampling, the concentrations of chlorophyll a (0.004 ug.L less 1) in the water column indicated that the trophic state was oligotrophic. The total suspended particulate matter showed a low mean of Hgtotal (156.78 more or less 0.61 ug.kg less 1). The gastropod soft tissues presented the highest Hgtotal (82.75 more or less 5.78 ug.kg less1) and were approximately fourfold higher than those found in its main food items, the mussel (19.13 more or less 0.58 ug.kg less 1). However, mercury concentrations in gastropod posture (7.36 more or less 0.71ug.kg less 1) were eleven times lower than those found in gastropod soft tissues. From these data, it suggests that there is trophic transfer of mercury between organisms studied.