The alien ctenophore Mnemiopsis leidyi which was transported from the Black Sea into Caspian Sea
at the end 1990s has been affecting the Caspian Sea
ecosystem. In this study, spatial and temporal distribution of M.leidyi, Salinity
and temperature were studied from July 2001to July 2002 in three transects (Lisar, Bandar Anzali and Sefidruod) in the Iranian coasts of the Caspian Sea. Each transect had four stations located at 5, 10, 20 and 50 m bottom depth contours. This study showed, Maximum water salinity had measured with value 12.1±0.32 ppt in surface layer at Lisar region. Minimum of water salinity have been with mean 11.4±0.8 ppt at Anzali area. The highest water temperature was been with mean 17.61±8.5 at Sefidruod region (surface layer). The lowest water temperature had measured with mean 10.93±0.46 at lisar region at 50 m depth. Decrease of water temperature had been slow from water surface to 20 m depth, after this depth, water temperature decreased sharply. Termocelain layer was main reason decrease. Ctenophore
abundance had decreased with water decrease. Temperature
and salinity have been factors important at fluctuation of ctenophore.