Abi Kusuma, Darma2013-01-162013-01-162013-01-16sumarnihttp://repository.unri.ac.id:80/handle/123456789/1439Diatom is one of microalgae that are widely distributed throughout the aquatic environment. Diatom are very susceptible to any condition that occurs in the water. In the Sungai Mesjid water is occur many activity of human that environmental condition have an impact on ecosystem, especially marine diatom. This research was aimed to analyze distribution of planktonic diatom in the water of Muara Sungai Mesjid Kota Dumai. Data was obtained by using survey methods to make observations, measurements and sampling in the field. Identification of diatom samples was conducted at Integrated Laboratory of Marine Sciences, Faculty of Fisheries and Marine Science, University of Riau. The total number of planktonic diatom in the water Muara Sungai Mesjid were 12 species. The most total number of planktonic diatom found were Planktoniella sol and Chaetoceros debilis. Based on value of diversity index (H '), dominance (D), equability (E) and water quality parameters showed that condition of Sungai Mesjid is still balance. Water quality in the water of Sungai Mesjid is middle level of contamination.otherPlanktonic diatomDistributionMarinestudent Paper Post Degree