Keberhasilan budidaya udang windu (penaeus monodon) di tambak sangat dipengaruhi oleh kualitas air, hama dan penyakit serta tingkat kesuburan perairan dan ketersediaan pakan alami, seperti plankton. penelitian ini bertujuan untuk menganalisis struktur komunitas plankton di tambak tradisional udang windu di pulau tibi, kabupaten bulungan. penelitian dilaksanakan pada bulan mei–september 2024. sampel plankton dikumpulkan sebanyak delapan kali (dua minggu sekali), menggunakan teknik pengambilan sampel komposit. identifikasi jenis, kelimpahan, serta indeks ekologi yang meliputi indeks keanekaragaman, indeks keseragaman, dan indeks dominansi. hasil menunjukkan bahwa fitoplankton didominasi kelas bacillariophyceae dan zygnemophyceae, sedangkan zooplankton didominasi kelas maxillopoda. kelimpahan fitoplankton berkisar 131–299 sel/l di petak 1 dan 177–345 sel/l di petak 2 (kategori oligotrofik). indeks keanekaragaman fitoplankton berkisar 0,88–1,51 (petak 1) dan 0,43–1,29 (petak 2), menunjukkan tingkat keanekaragaman rendah–sedang. indeks keseragaman berkisar 0,40–0,69 (petak 1) dan 0,18–0,55 (petak 2); indeks dominansi 0,24–0,50 (petak 1) dan 0,25–0,78 (petak 2). kelimpahan zooplankton 0–56 ind/l (petak 1) dan 0–47 ind/l (petak 2) (kategori oligotrofik). indeks keanekaragaman zooplankton berkisar 0,00–1,33; indeks keseragaman 0,00–1,00; dan indeks dominansi 0,00–1,00. struktur komunitas plankton menunjukkan kondisi perairan yang relatif subur dan masih mendukung kelangsungan budidaya udang windu secara tradisional. kata kunci : plankton, pulau tibi, tambak tradisional.

The success of tiger shrimp (penaeus mondon) aquaculture in ponds is highly influenced by water quality, the presence of pests and diseases, the fertility of the aquatic environment, and the availability of natural feed such as plankton. this study aims to analyze the plankton community structure in traditional tiger shrimp ponds on tibi island, bulungan regency. the research was conducted from may to september 2024. plankton samples were collected eight times (every two weeks) using a composite sampling technique. the study focused on species identification, abundance, and ecological indices including diversity index, evenness index, and dominance index. results showed that phytoplankton were dominated by the - classes bacillariophyceae and zygnemophyceae, while zooplankton were predominantly from the class maxillopoda. phytoplankton abundance ranged from 131-299 cells/l in plot 1 and 177-345 cells/l in plot 2, indicating oligotrophic conditions. the phytoplankton diversity index ranged from 0.88-1.51 (plot 1) and 0.43-1.29 (plot 2), reflecting low to moderate diversity levels. evenness index ranged from 0.40-0.69 (plot 1) and 0.18-0.55 (plot 2); dominance index ranged from 0.24-0.50 (plot 1) and 0.25-0.78 (plot 2). zooplankton abundance was recorded at 0-56 ind/l in plot 1 and 0-47 ind/l in plot 2 (also indicating oligotrophic conditions). zooplankton diversity index ranged from 0.00-1.33; evenness index from 0.00-1.00; and dominance index from 0.00-1.00. the overall plankton community structure suggests that the aquatic environment remains relatively fertile and continues to support traditional tiger shrimp aquaculture. keywords : plankton, tibi island, traditional ponds