Segara Anakan is located in the southern part of Cilacap Regency. It consists of lagoon and riverine areas with mangrove forest. In these areas, the mixing of inland waters and marine waters is affected by climate and tidal range that influenced by a moon phase. Plankton can describe the effect of environmental changes. Based on that, the objectives of this research were to describe plankton species richness, abundance, and water quality during tides; and to analyze the relationship between them. The research used a survey method with purposive sampling technique. Sampling was done at five stations, four times during a dry season on spring tide (new and full moon phases) when maximum tidal range occurred. The parameters of water quality were temperature, current velocity, light penetration, pH, dissolved oxygen, free carbon dioxide, and salinity. The results showed that plankton species richness was the highest during the new moon at station three near Motean and dominated by marine Chrysophyta with a cosmopolitan species of Chaetoceros decipiens. The next were Cyanophyta, Chlorophyta, Euglenozoa, and Cnidaria. The plankton abundance was the highest during the new moon at station one near West Plawangan, which, again, dominated by marine Chrysophyta (C. decipiens). Water quality during maximum tidal range in new moon was better than that during the full moon in station 1. In general, the highest plankton abundance was related to the good water quality in station 1.

Lukman Adi Nugroho

Moh. Husein Sastranegara

Agatha Sih Piranti