Seasonal dynamics of phytoplankton assemblages across nutrient gradients in shallow hypertrophic Lake Manyas, Turkey

Species composition, abundance and size distribution (the average measure of the longest cell dimension and surface area to volume ratio) of phytoplankton in the shallow hypertrophic Lake Manyas, Turkey were studied between January 2003 and December 2004. A total of 165 species were recorded during the study. Diatoms and Cyanobacteria were the dominant taxa at most stations. Nitrate and phosphate values showed a decreasing gradient with the distance from Sigirci Inlet to Karadere Outlet. Bacillariophyta dominated the phytoplankton in spring, while Cyanobacteria prevailed in summer. Each summer, a peak of Euglenophyta was also observed at Sigirci Inlet. Nutrient gradients seemed to have a greater control over overall density than of species composition. The size distribution of the Cyanobacteria showed positive correlations with nutrient levels, while green algae and diatoms did not. There was a negative correlation between the average cell dimension of the phytoplankton cells and the surface area to volume ratio in general. The objective of this study was to determine the seasonal dynamics of species composition, abundance and size distribution of phytoplankton assemblages across nutrient gradients along a distance in the shallow hypertrophic Lake Manyas, Turkey.