Structure and diversity of zooplankton communities in four reservoirs with varying nutrient compositions in the Yangtze River Basin, China

A total of 147 zooplankton species were identified from four reservoirs. Protozoa and rotifers were the most abundant species recorded. The following fifteen species were common to all four reservoirs: six protozoan species, four rotifer species, three cladoceran species and two copepod species (accounting for 40.0%, 26.7%, 20.0%, and 13.3% of the species common to all of the reservoirs, respectively). Zooplankton diversity was significantly higher (p < 0.01) in the Jinshahe reservoir than in the remaining three reservoirs, with a Shannon-Wiener index (H) of 2.99 and a Simpson index (d) of 5.16. Zooplankton diversity in the Daoguanhe reservoir was the lowest of the four reservoirs (H = 1.80, d = 2.48); higher values were obtained for the Xujiahe (H = 2.08, d = 3.58) and Taoyuanhe (H = 2.07, d = 3.72) reservoirs. The Simpson indices of the Xujiahe and Taoyuanhe were significantly different from those of the Daoguanhe (all p < 0.05). Protozoan and rotiferan biomasses were significantly positively correlated with COD, TN and TP (p < 0.01) and significantly negatively correlated with DO (p < 0.01). The cladoceran and copepod densities were low and highly variable, and they were not significantly correlated with COD, DO, TN or TP. The dominant species density was significantly correlated with zooplankton density. Zooplankton abundance was significantly negatively correlated with phytoplankton abundance in the Jinshahe but positively correlated in the Daoguanhe (correlation coefficient r = 0.45); no significant correlations were observed in the remaining two reservoirs.