Ekosistem mangrove, merupakan salah satu ekosistem yang berperan penting dalam menjaga keberlanjutan fungsi ekologi di kawasan pesisir. Berangkat dari hal tersebut penelitian ini bertujuan: 1) Mengidentifikasi jenis – jenis mangrove di Pulau Gili Rajeh; 2) Menganalisis Indeks Nilai Penting (INP) mangrove di Pulau Gili Rajeh; dan 3) Menganalisis struktur komunitas mangrove di Pulau Gili Rajeh Kabupaten Sumenep. Terdapat 4 stasiun dengan 3 titik di setiap stasiun yang digunakan. Analisa yang digunakan meliputi : 1) analisa deskriptif morfologi mangrove; 2) analisa INP (RDi, RCi, RFi); dan 3) analisa struktur komunitas (H’,E, D). Hasil penelitian menunjukkan: 1) terdapat 3 jenis mangrove di Pulau Gili Rajeh Kabupaten Sumenep yaitu Soneratia alba, Rhizophora apiculata, dan Rhizophora mucronata; 2) Jenis mangrove Rhizophora mucronata memiliki kontribusi terhadap lingkungan tergolong tinggi (INP = 204,97) di Pulau Gili Rajeh Kabupaten Sumenep; dan 3) Struktur komunitas mangrove di Pulau Gili Rajeh menunjukkan keanekaragaman rendah, penyebaran jumlah individu tiap spesies rendah (H’= 0,500 – 0,669); komunitas berada dalam kondisi labil, keseragaman sedang (E = 0,494 - 0,721); dan dominansi sedang (D = 0,627 - 0,718). Kata kunci : Struktur komunitas, Mangrove, indeks nilai penting, indeks keanekaragaman, indeks keseragaman, indeks dominansi.

Mangrove ecosystem, is one of the ecosystems which play an important role in ensuring the sustainability of ecological functions in coastal areas. Departing from the research aims: 1) Identify the type - the type of mangrove on the island of Gili Rajeh; 2) Analyze the Importance Value Index (INP) of mangroves on the island of Gili Rajeh; and 3) to analyze the community structure of mangrove on the island of Gili Rajeh Sumenep. There are 4 stations with 3 points in each of the station used. The analysis used include: 1) a descriptive analysis of morphological mangrove; 2) analysis of INP (RDI, RCI, RFI); and 3) analysis of the community structure (H ', E, D). The results showed: 1) there are three types of mangroves on the island of Gili Rajeh Sumenep is Soneratia alba, Rhizophora apiculata and Rhizophora mucronata; 2) Type of mangrove Rhizophora mucronata has a relatively high contribution to the environment (INP = 204,97) on the island of Gili Rajeh Sumenep; and 3) community structure of mangrove on the island of Gili Rajeh showed a low diversity, the spread of the low number of individuals of each species (H '= 0,500 to 0,669); communities are in unstable condition, uniformity being (E = 0,494 - 0,721); and dominance medium (D = 0,627 – 0,718). Keywords: Community structure, Mangrove, important value index, diversity index, uniformity index, dominance index.

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