Mikroalga yang biasa menempel pada tumbuhan disebut mikroalga epifit. Mikroalga epifit hidup melekat pada permukaan rumput laut. Mikroalga menempel pada rumput laut disebabkan karena rumput laut dapat menjadi sumber zat hara ketika kadar zat hara di perairan rendah. Penelitian ini bertujuan untuk mengetahui jenis-jenis mikroalga yang menempel pada rumput laut di perairan Pulau Nunukan. Penelitian dilakukan pada tujuh lokasi berdasarkan persebaran rumput laut dengan melakukan identifikasi mikroalga epifit menggunakan mikroskop. Hasil penelitian didapatkan sebanyak 14 jenis mikroalga epifit yang berasosiasi pada rumput laut yaitu Cylotella sp., Pleurosigma sp., Tabellaria sp., Asterionella sp., Nitszchia sp., Licmophora sp., Coscinodiscus sp., Oocystis sp., Ceratium sp., Odontella sp, Cylindroctystis sp., Staurastrum sp., Tintinnopsis sp., dan Globigerina sp. Nilai kelimpahan dari tujuh stasiun berkisar antara 1.2933.203 sel/L. Nilai keanekaragaman berkisar 1,014-1,840. Nilai keseragaman berkisar 0,488-0,740 dan nilai dominansi yaitu berkisar 0,251-0,525.
Kata Kunci: Asosiasi, Komunitas, Mikroalga Epifit, Nunukan, Rumput Laut

The usual epiphytic microalgae attached to a plant called epifitic. Epiphytic microalgae live attached to the surface of the seaweed. Epiphytic icroalgae attached to seaweed is caused because seaweed can be a source of nutrients when the nutrient content in low water. The purpose of this research is to know the types of microalgae attached to seaweed in Nunukan Island waters. The study was conducted on seven locations based on seaweed distribution by identifying epiphytic microalgae using a microscope. The results of the study showed that 14 types of epiphytic microalgae associated with seaweed are Cylotella sp, Pleurosigma sp, Tabellaria sp., Asterionella sp, Nitszchia sp., Licmophora sp., Coscinodiscus sp., Oocystis sp., Ceratium sp., Odontella sp, Cylindroctystis sp., Staurastrum sp., Tintinnopsis sp and Globigerina sp. So we get the abundance value from seven stations ranging from 1.293-3.203 cell / L. And the value of diversity ranges from 1,014-1,840. The value of uniformity ranges from 0,488 0,740 and the value of dominance is around 0,251-0,525. Keywords: Association, Community, Epiphytic microalgae, Nunukan, Seaweed