Abstract: Based on the investigations at the Yangtze River Estuary and its adjacent waters (121°15′E-122°41′E, 30°00′N-31°30′N) in August of 1998 and 1999, the distribution characteristics of medusa and their affecting factors were studied. A total of 21 medusa species including 15 of Hydromedusae, 4 of Siphonophore, and 2 of Ctenophore were identified, which could be classified into three ecological groups, i.e., low salinity neritic group, low salinity estuarine group, and oceanic warm water group. The first group distributed widely, the second group was more prevalent in lower salinity estuary, and the third one only appeared in higher salinity offshore area. The dominant species were Nemopsis bachei, Pleurobrachia globosa, Clytia folleata, Muggiaea atlantica, Lensia subtiloides, and Diphyes chamissonis. With the increase of salinity from the Yangtze River Estuary to the offshore, the abundance of medusa increased gradually, being the highest in western Zhoushan Fishing Ground where the waters from the Yangtze River and open sea were mixed together. Water mass had significant effects on the distribution of medusa. The more severe the open seawater invaded,the higher the abundance of medusa was. In contrast, when the whole area was under the control of diluted water from Yangtze River, the abundance of medusa was lower.

Key words: Fungal-feeding nematode, Fungi, Nematode-fungi interaction, N-mineralization