[ABSTRAKbrPenelitian mengenai struktur komunitas diatom epifit pada daun lamun di padang lamun perairan Muara Binuangeun, Banten telah dilakukan pada tanggal 30 April -- 3 Mei 2015. Penelitian bertujuan untuk mengetahui struktur komunitas Diatom epifitik pada daun lamun Thalassia hemprichii (Ehrenb. ex Solms) Asch. antara lain, komposisi genus, kepadatan, dominansi, keanekaragaman, dan kemerataan pada setiap stasiun di Muara Binuangeun, Kabupaten Lebak, Banten. Penentuan lokasi pengambilan sampel dilakukan secara purposive sampling. Hasil penelitian menunjukan bahwa komposisi Diatom epifitik yang diperoleh di lokasi penelitian sebanyak 12 genus dari 4 kelas. Kepadatan Diatom epifitik tiap stasiun berkisar antara 91800 – 420560 sel/ dm2. Nilai indeks dominansi berkisar antara 0,617—0,917 dan tergolong tinggi di setiap stasiun, hal tersebut disebabkan karena terdapat genus Navicula yang mendominasi disetiap stasiun. Nilai indeks keanekaragaman di setiap stasiun penelitian tergolong rendah (berkisar antara 0,25—0,86). Nilai indeks kemerataan berkisar antara 0,1—0,36 dengan stasiun 1 dan 4 tergolong tidak merata, sedangkan pada stasiun 2 dan 3 tergolong kurang merata. Rendahnya nilai indeks keanekaragaman dan kemerataan disebabkan karena adanya tekanan ekologis pada lokasi penelitian. Secara umum, struktur komunitas Diatom epifitik pada lokasi penelitian tergolong tidak stabil karena tingkat dominansi yang tinggi, keanekaragaman yang rendah, dan kemerataan yang tidak merata dan kurang merata.;Research on community structure of epiphyte Diatom on Thalassia hemprichii (Ehrenb. ex Solms) Asch. leaves at seagrass beds Muara Binuangeun Coastal, Kabupaten Lebak, Banten was conducted on 30 April -- 3 May 2015. The aim of this study was to determine community structure of epiphyte Diatom on Thalassia hemprichii (Ehrenb. ex Solms) Asch. leaves include genus composition, abundance, dominance, diversity, and evenness each stations at Muara Binuangeun, Kabupaten Lebak, Banten. Sampling location was determineted by purposive sampling method. Result shows that 4 classis 12 genera Diatom epiphytic composition was obtained . Diatom epiphytic abundance range in each station was 91800 – 420560 sel/ dm2. Dominance index score range was 0,617—0,917 and was classified as high at each stations because genus Navicula dominant in each stations. Diversity index score was classified as low (0,25—0,86) at each stations. Evenness index score range was 0,1—0,36 with station 1 and 4 classifed as highly unevenn and station 2 and 3 was classified as unevenly. Diversity and evenness index score was low because there were ecological pressures. In general, community structure of epiphyte Diatom in research location was unstable because dominance index was high, diversity index was low, and evenness index was highly uneven and unevenly., Research on community structure of epiphyte Diatom on Thalassia hemprichii (Ehrenb. ex Solms) Asch. leaves at seagrass beds Muara Binuangeun Coastal, Kabupaten Lebak, Banten was conducted on 30 April -- 3 May 2015. The aim of this study was to determine community structure of epiphyte Diatom on Thalassia hemprichii (Ehrenb. ex Solms) Asch. leaves include genus composition, abundance, dominance, diversity, and evenness each stations at Muara Binuangeun, Kabupaten Lebak, Banten. Sampling location was determineted by purposive sampling method. Result shows that 4 classis 12 genera Diatom epiphytic composition was obtained . Diatom epiphytic abundance range in each station was 91800 – 420560 sel/ dm2. Dominance index score range was 0,617—0,917 and was classified as high at each stations because genus Navicula dominant in each stations. Diversity index score was classified as low (0,25—0,86) at each stations. Evenness index score range was 0,1—0,36 with station 1 and 4 classifed as highly unevenn and station 2 and 3 was classified as unevenly. Diversity and evenness index score was low because there were ecological pressures. In general, community structure of epiphyte Diatom in research location was unstable because dominance index was high, diversity index was low, and evenness index was highly uneven and unevenly.]