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Abstract. Pratiwi NTM, Imran Z, Ayu IP, Iswantari A, Wulandari DY. 2020. The phosphorus load and the variation of the trophic states of Cirata Reservoir (West Java, Indonesia) from 1988 to 2017. Biodiversitas 21: 4176-4183. Cirata Reservoir was constructed in 1987 between Saguling and Jatiluhur Reservoirs; these are the three man-made cascading lakes in West Java, Indonesia. Cirata Reservoir has been used for floating cage aquaculture activities. The high organic content from the remains of the fish pellets raised the phosphorus (P) load, resulting in the eutrophication of the reservoirs. This research was aimed to assess the P load and the variation of the trophic states of the reservoir from year 1988 to 2017. The trophic states and the nutrients’ conditions of the water were determined using Myxophycean Index. Four groups of phytoplankton were found in the reservoir during observation: Cyanophyceae, Chlorophyceae, Bacillariophyceae, and Dinophyceae. In addition, one group was found in a smaller number of observations: Eugolenophyceae. Although the community structure of the phytoplankton has changed, the Cyanophyceae was always dominant in response against the condition of nutrients, especially P. The P load is closely related to the number of floating cages in the reservoir. This evidence showed that Cirata Reservoir tended to be relatively eutrophic. In general, despite that the P load tended to fluctuate, the trophic states of Cirata Reservoir remained dynamic in relatively high conditions; showed by the oligo-mesotrophic state during its first year of operation, then increased to eutrophic and hypertrophic by the next decade. Although the P load tended to decrease, it remains in the eutrophic condition in the recent time.

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Zooplankton play a significant role in ecosystem as secondary producer. Climate change will potentially affect the abundance and global composition of zooplankton. This research aimed to study the geographical variation of zooplankton abundance relative to anthropogenic pressure. The research was conducted in April 2014 in area with presumably distinct anthropogenic level by its relative distance to the mainland of Jakarta. Samples were collected at Pramuka Island, Karang Beras Island, Kotok Island, and Sepa Island where subsequently lying to the nearest until furthest distance from mainland. Zooplankton samples were collected by towing the plankton net for 10 minutes for each site for three replicates. Abundance was obtained from Pramuka Island was 266698,214 ind/L, Karang Beras Island was 597363,1 ind/L, Kotok Island was 526447,8 ind/L and Sepa Island was 438225,3 ind/L. Overall, the closer to mainland, the richer nutrient and the more abundant zooplankton was conceived in the waters. Surprisingly, in Pramuka Island, the nearest island to mainland among other sites, had the lowest abundance of zooplankton although nutrient level was the richest among others.