Pengamatan pengaruh musim terhadap plankton di perairan Riau dan kepulauan sekitarnya dilakukan pada periode April - Mei 2002. Pengamatan difokuskan pada komunitas fitoplankton dan zooplankton di keduapuluhlima titik stasiun pengamatan yang dikelompokkan menjadi dua zona berdasarkan pada jarak stasiun pengamatan. Variasi kelimpahan plankton rata-rata antar kelompok lokasi adalah 50 - 90 % untuk fitoplankton. Struktur komunitas didominasi oleh kelimpahan diatom dengan marga dominan Chaetoceros, Dytilum, Nitzschia, Thalassionema, Thalassiothrix dan marga Ceratium dari kelompok Dinoflagellata. Struktur komunitas zooplankton didominasi oleh kelompok Copepoda (45 ? 90 %) dan lebih dari 90 % dari kelompok Polychaeta, Chaetognata, Bivalvia, Gastropoda dan Oikopleura. Dari hasil pengamatan ini diperoleh gambaran tentang adanya keterkaitan antara kondisi lingkungan perairan dan variasi kondisi plankton.

---

Seasonal influenzed on plankton of the waters around Riau islands. The observation was conducted during April - May 2002. This study was done in relation with observation on environment quality of the waters around Riau Islands. The parameter observed were focus on the plankton communities for tweentyfives points of stations which were grouped into two zone based on the distance of the each station. Plankton abundance varied with location groups from 50- 90 % respectively. Community structure was dominated by the group of diatoms such as Chaetoceros, Dytilum, Nitzschia, Thalassionema, Thalassiothrix and the genus Ceratium (the group of Dinoflagellata). Community structure of zooplankton was dominated by the group of Copepods (45 - 90 %) and Polychaeta, Chaetognata, Bivalvia, Gastropods and Oikopleura (more than 90 %). The results describe the relationship between the water environmental condition and variation of plankton condition.