ABSTRAK
Penelitian mengenai analisis struktur komunitas fitoplankton di Perairan Selat Lembeh dan Wori, Sulawesi Utara pada Tahun 2015 telah dilakukan. Sebanyak 20 sampel diambil dari 11 stasiun perairan Selat Lembeh dan 8 stasiun perairan Wori. Hasil identifikasi dan pencacahan sampel diperoleh 26 marga fitoplankton, 20 marga diatom, 5 marga marga dinoflagellata, dan 1 marga Cyanophyceae. Kelimpahan fitoplankton perairan Selat Lembeh lebih tinggi dibandingkan kelimpahan fitoplankton perairan Wori. Kelimpahan fitoplankton di perairan Selat Lembeh mencapai 624.400 sel/m3. Marga fitoplankton mendominansi perairan Selat Lembeh adalah Trichodesmium dan Chaetoceros, sedangkan di perairan Wori adalah Trichodesmium. Marga dinoflagellata yang dominan di Perairan Selat Lembeh dan Wori adalah Prorocentrum. Keanekaragaman fitoplankton di perairan Selat Lembeh lebih tinggi dibandingkan dengan perairan Wori. Kekayaan dan kemerataan fitoplankton di kedua wilayah perairan tergolong rendah dan tidak merata. Indeks Nilai Penting INP menunjukkan Trichodesmium sebagai marga yang paling mendominansi di kedua lokasi.

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ABSTRACT
The research on community structure of phytoplankton in the waters of Lembeh Strait and Wori was conducted on 2015. Twenty sample was taken from 11 stations at Lembeh Strait and 8 stations at Wori. There were found 26 phytoplankton genera consist of 20 Diatoms genera, 5 Dinoflagellates genera, and 1 Cyanophyceae genera. The abundance of Lembeh Strait were higher than Wori. The phytoplankton abundance of Lembeh Strait reached 624.400 cells m3. Phytoplankton genera that dominate at Lembeh Strait were Trichodesmium and Chaetoceros, meanwhile at Wori was Trichodesmium. Dinoflagellate genera that dominate on both location was Prorocentrum. The diversity index at Lembeh Strait were higher than Wori. The richness and evenness index on both location were categorized as low and not even. The important score index shows that Trichodesmium was the most dominate genera on both location.