Tjut Sugandawaty Djohan
Laboratorium Ekologi Fakultas Biologi Universitas Gadjah Mada, Yogyakarta 55281
Email: tdjohan95@yahoo.com
The mangrove ecosystem of Segara Anakan is in the process of changing to the freshwater-wetland due to the heavy sedimentation. This change was responded by the plankton communities. In the 2002 during the rainy season, the salinity was 0 0/00, and the freshwater plankton from the river dominated this mangrove ecosystem. In contrast at the dry season, the salinities were between 20 – 32 0/00, and the estuarine plankton dominated the ecosystem. In the 2004 the Bondan area became shallower and was dredged. In responding to the changing ecosystem, the phyto and zooplankton study was carried out during the dry season of August 2005 at the fishing ground of Segara Anakan.
Results showed that there were blooms of phytoplankton. At the Bondan and Klaces waters, Chaetoceros dominated the communities with 206890 and 397273 individuals per 100 liter consecutively. However, at Cigatal Asterionella japonica with 69778 individuals per 100 liter dominated the community. The plankton bloom related to the intensive dredging of sediment at Bondan areas, which increased PO4 highly in the water of Bondan, Klaces, and Cigatal inconsecutively 4.95 ppm, 5.88, and 4.62 ppm. These communities were characterized by the present of 19 species of freshwater phytoplankton and 9 species of zooplankton. Even though the population of Chaetoceros was exploded, but the zooplankton community did not response to the phytoplankton increase. This indicated that the qualities of the mangrove ecosystem waters decreased, and the ecosystem was in the process of changing to freshwater-wetland ecosystem.
Key words: Brackish estuary, phytoplankton, zooplankton, Chaetoceros, Asterionella, PO