KEMELIMPAHAN FITOPLANKTON DI PERAIRAN ESTUARI PAYAU BONDAN CILACAP, JAWA TENGAH (The Abundance of Phytoplankton in the Brackish Estuary of Bondan, Cilacap, Central Java)

AbstrakKajian kemelimpahan fitoplankton di perairan estuari payau Bondan Cilacap telah dipelajari. Perairan Bondan merupakan perairan hutan bakau rusak dan dikoloni oleh semak dan liana bakau, padahal daun pohon bakau adalah sumber input nutrien utama untuk komunitas fitoplankton yang merupakan mata rantai pertama dalam jejaring makanan perairan hutan bakau. Pengambilan sampel fitoplankton dilakukan dengan pencuplikan menggunakan modifikasi van Dorn 5 L dan merupakan komposit 20 L air dengan ulangan 5 kali. Kualitas perairan yang diukur meliputi kecepatan arus dan angin, suhu air dan udara, kelembaban udara, jeluk perairan dan jeluk Secchi, intensitas cahaya, turbiditas, salinitas, pH, NH4+, NO3-, PO43-, dan SO42-. Hasil menunjukkan bahwa cacah spesies dominan adalah fungsional grup diatom, akan tetapi cacah individunya sedikit. Sebaliknya, cacah individu algae koloni melimpah tetapi cacah spesiesnya sedikit, dan terjadi peledakan Aphanocapsa pulchra, 188.260 individu per 100 L. Peledakan ini karena perairan didominasi air tawar dan kerusakan hutan bakau. Peledakan A. pulchra mengindikasikan kualitas perairan hutan bakau Bondan buruk. AbstractThe abundance of phytoplankton in the brackish estuary of Bondan Cilacap have been studied. Bondan waters are setting in the disturbed mangrove ecosystem, which colonized by mangrove shrubs and lianas, whereas, the mangrove leaves are the main source of nutrient input for the phytoplankton community as the first link in the mangrove aquatic food web. Phytoplankton were sampled using a 5 L modification of van Dorn and a composite of 20 L of water with 5 replications. The water qualities measured include surface current, wind speed, water and air temperatures, air humidity, Secchi depth and water depth, light intensity, turbidity, salinity, pH, NH4+, NO3-, PO43-, dan SO42-. The results showed that the number of the dominant species was diatoms, but the number of the individuals was small. In contrast, the individual number of algae colony was abundant but the species number were few, and Aphanocapsa pulchra was blooming, 188,260 individuals per 100 L. This bloom was due to the waters were dominated by freshwater and the disturbed mangrove trees. The blooming of population of A. pulchra indicated that bad waters quality.