Long-term investigation of metal concentrations in brown algae Fucus vesiculosus from the Gulf of Riga, Baltic Sea The study was conducted in the coastal area of the Gulf of Riga at three stations (Ainaži, Saulkrasti, Mērsrags) from 1997 till 2010. Brown algae samples were collected at 3.0-m depth from a boat using scuba gear in August and September. The concentrations of metals (Cd, Pb, Cu, Ni, Zn) were determined by atomic absorption spectrophotometry method (model Spektra A 880), and of Hg by FIMS (Flow Injection Mercury System, Perkin Elmer). The aim of this investigation was to determine the concentration levels of metals (Hg, Cd, Pb, Cu, Ni, Zn) in the dominant species of macroalgae (Fucus vesiculosus) in the Gulf of Riga in different stations and years. Metal concentrations in F. vesiculosus varied between sampling years and stations, and significant differences in Hg, Pb and Ni concentrations between years were detected. In some years the concentrations of metals in F. vesiculosus were similar in all three stations. Brown algae F. vesiculosus can accumulate metals to concentrations thousand times higher than in marine water.

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The following heavy metal levels were found in plankton of the Gulf of Riga and of the open Baltic Sea: 0.89-10.20 mg Cu/kg; �0.89-106.96 mg Zn/kg; 2.31-199.9 mg Mn/kg 0.19-0.85 mg Cd/kg; and 0.35-9.35 mg Pb/kg wet weight. Heavy metal accumulation in the plankton was found to depend on species composition of the community and on deve• lopment stage of a species. Heavy metal contents in bottom sediments increase �ear densely populated coastal areas. Levels of lead, copper, and zinc depend on the season, increasing in spring in areas affected by river runoff. Maximum concentrations of the metals studied were found in 0.05-0.063 mm sediment fractions. Accumulation patterns of each metal exhibited their own respective peculia• rities.