The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana, Croatia)

Shallow aquatic ecosystem Lake Vrana, with special attention to phytoplankton was studied over one year period. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. Regular annual development was observed not as seasonal changes of species compositions but as species contribution to the total abundance. Assemblage was dominated by Cosmarium tenue Arch. and Synedra sp.. Winter, same as vernal assemblage was clearly dominated by Cosmarium tenue. The assemblage was determined by the high contribution of Synedra sp. during the summer and autumn. Nutrient availability as external control and competition between species were assessed as forces which drive species diversity and changes in predominance.