The seasonal fluctuation of Cyanophyta in the southern Caspian Sea

The objective of this study was to evaluate the seasonal fluctuation of density and biomass of cyanophyta in different water temperatures in the southern Caspian Sea in 1996 and 1999-2000. 432 samples of phytoplanktons were collected from 18 stations in coastal zone (depth less than 10 m). As a result, 11.1% (9 species from 81) and 15.6% (25 species from 160) of total phytoplanktons were cyanophyta in years 1996 and 1999-2000, respectively. The maximum density and biomass (1.65x106/m3 , 4.09 mg/m3) of Cyanophyta were found in the western region and in warm seasons (spring and summer). On the other hand, in cold seasons (autumn and winter), the maximum density and biomass (1.5x105fm3, 3.36 mg/m3) were found in the eastern part of the Caspian Sea. In years 1999-2000, the maximum biomass and density of Cyanophyta were found in eastern, central and western parts of the Caspian Sea in spring and summer, meanwhile in autumn and winter, they were found with maximum density and biomass in the eastern part. In all seasons, the minimum and maximum water temparture were measured in the western part and eastern part of the southern Caspian Sea, respectively. The results showed that the most density of cyanophyta were measured in summer that can be related to the increase of temperature and daylight. The non-parametric statiscal analysis indicated that there were no significant difference between biomass and density of cyanophyta in years 1996 and 1999-2000. As a conculsion, the population dynamic of cyanophyta were mostly affected by combination of enviromental factors than effect of a single factors sperately (such as temperature)