Annual variations of zooplankton community structure in Shanghai downtown rivers

From November 2007 to October 2008, a monthly investigation was conducted to study the annual variations of zooplankton community structure and water environmental factors in the Wuchaogang River, Henggang River, Chaoyang River, and Caoyanghuanbang River of Shanghai downtown. A total of 63 species were identified, including 44 Rotifera (69%), 13 Cladocera (21%), and 6 Copepoda (10%). The dominant species were Rotaria rotatoria, R. neptunia, Brachionus calyciflorus, Keratella cochlearis, Asplanchna priodonta, Polyarthra dolichoptera, Daphnia magna, Moina irrasa, and Microcyclops leuckarti. In the four rivers, the zooplankton 's average abundance ranged from 726 to 2571 ind · L^-1, and the biomass ranged from 12. 04 to 44. 27 mg · L^-1. Both the zooplankton community density and the biomass were significantly positively correlated with dissolved oxygen (P < 0. 05), and the water body 's phosphate, nitrate, and nitrite contents had definite effects on the zooplankton abundance and biomass. Based on the analysis on the annual variations of zooplankton community structure in the four downtown rivers, no significant seasonal variations were found. Overall, the zooplankton community structure and density were in recovering, suggesting that a better aquatic ecosystem was being constructed in the four downtown rivers.