Changes in Growth, Photosynthesis Performance, Pigments, and Toxin Contents of Bloom-Forming Cyanobacteria after Exposure to Macroalgal Allelochemicals.

Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (/) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll (Chl ) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, sp., , and sp. We found both negative and positive allelopathic effects of on tested cyanobacteria. The study clearly showed that the addition of the filtrate of significantly inhibited growth, decreased pigment content and / and ΦPSII values of and sp., and stimulated sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from caused a significant decrease in the MC-LR content in sp. cells. Moreover, it the phenol content in cells was increased. On the other hand, the cell-specific phenol content for sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of depends on the target species' identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.