Temporal and spatial variation of Phytoplankton/Zooplankton Mass Ratio in Southern Caspian Sea, Iranian Coasts

Anthropogenic and eutrophication pressure impaired functional structure of plankton community and phytoplankton/zooplankton biomass ratio (BPhyt/BZp). This paper studied dynamic of BPhyt/BZp ratio in different parts of southern Caspian Sea. The current study took effect during four seasons at 8 transects in 2009-2010. Results showed that not only abundance but also species composition had the great effect on BPhyt/BZp ratio. An increase of Cyanophyta abundance (low individual weight) decreased BPhyt:BZp ratio (4) in summer. While the ratio (11) was increased during winter which it was related to increasing of chain-forming species of Bacillariophyta. Although the BPhyt/BZp ratio was lowest in west part of southern Caspian Sea, however the ratio did not show significantly variation among different parts of the study area. In 2009-2010, the ratio was increased with 3 and 7 folds with comparison to the pervious studies in 1995 and 1996, respectively. In a conclusion, increase of BPhyt/BZp ratio, Shannon diversity index of phytoplankton and decreasing of Shannon diversity index of zooplankton indicate to insufficient consumption process (grazing) and energy transformation from phytoplankton to zooplankton.