EN
Allelopathy is a prevalent natural phenomenon in aquatic ecosystem. We reported the effects of the green macroalga Ulva intestinalis L. collected from estuaries of the Baltic Sea (Poland) on the growth and chlorophyll fluorescence of common filamentous cyanobacterium Nostoc sp. It was found that the addition of 50 µL mL–1 extracts obtained from U. intestinalis inhibited growth of cyanobacterium and after one week of exposition the reduction was 35% of initial amount of Nostoc sp. In addition, we demonstrated that on the seventh day of the exposition, the values of Fv/Fm of target cyanobacterium after addition of 100 µL mL–1 extracts obtained from U. intestinalis was reduced to 49%, compared to control treatment. These results showed for the first time the allelopathic activity of U. intestinalis on Baltic filamentous cyanobacteria Nostoc sp.