Abstract: Based on the data of four seasonal oceanographic censuses in East Chin a Sea (23°30′〖KG-*2〗-〖KG-*7〗33°00′ N, 118°30′〖KG-*2〗-〖KG-*7〗128°00 ′ E) in 1997〖KG-*2〗-〖KG-*7〗2000, the optimal water temperature and salinity and the ecological groups of Hydroidomedusae were stud ied by curve fitting, mathematical model forming, and geographic distribution an alyzing. The results showed that Hydroidomedusae could live in the waters with d ifferent temperature and salinity. 15 species of Hydroidomedusae had an optimal water temperature of <20 ℃, 8 species at 20 ℃〖KG-*2〗-〖KG-*7〗25 ℃, 12 spec ies at 22.5 ℃〖KG-*2〗-〖KG-*7〗25 ℃, and 17 species at ≥25 ℃. 32 species of Hydroidomedusae had an optimal salinity o f 32〖KG-*2〗-〖KG-*7〗34, 13 species at 34, 6 species at 30〖KG-*2〗-〖KG-*7〗3 2, and only 2 species at <30. Th e weak adaptability of most Hydroidomedusae species to the variation of water sa linity made them have low density and limited distribution in East China Sea. Sugiura chengshanense and Clytia hemisphaerica were of nearshore warm temperate water species, Cunina octonaria and other 12 species were of offshore warm temperate water species, 8 species represented by Ectopleura latitaeniata were of nearshore subtropical water species, 5 species represented by Aglaura hemistoma showed some oceanic tropical features, while 25 species represented by Liriope tetraphylla were of offshore subtropical species. Some Hydroidomedusae species could b e used as an important bio-indicator of water mass in East China Sea.

Key words: foliar water uptake, control experi-ment., stable isotope, reverse sap flow, heat ratio method