Abstract: A study was conducted from October 2010 to September 2011 to understand the rotifer community structure in the northern branch of the Yangtze River Estuary. A total of 19 species of rotifers were found. These species belong to 7 families and 17 genera. Brachionidae, Lecanidae and Gastropodidae were the most common families. Ascomorpha saltans and Polyarthra trigla were common species. A. saltans was the dominant species in spring, autumn and winter, whereas P. trigla was dominant in summer. The average density of rotifers for the whole year was 1.40±1.11 ind·L^-1. The monthly average density varied from 0.2 to 4.4 ind·L^-1, with the highest density values  occurring in autumn (2.25±1.7 ind·L^-1) and the lowest density values  in winter (0.93±0.69 ind·L^-1). The average density of rotifers was the lowest (1.00±0.67 ind·L^-1) at station 5 closer to the mouth of the river. Hierarchical clustering and MDS were applied to analyze the rotifer community structure, revealing two main groupings, one with data from January, February, March and September, and another with data from May, August and November. The CCA analysis showed that salinity was the main environmental factor affecting the rotifer community structure.

Key words: diversity, arbuscular mycorrhizal fungi (AMF), dominant species, species distribution, spore