Abstract
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 Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (Fv/Fm) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and Fv/Fm and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon 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 U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis 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.
Highlights
Macroalgal allelopathy is considered to be a special strategy to deter or eliminate competitors and predators coexisting in a shared ecosystem [1]
We found positive allelopathic effects of U. intestinalis on another toxic cyanobacterium Aphanizomenon sp
The present study investigated the allelopathic effects of aqueous extract and cell-free filtrate from the Baltic green macroalgae U. intestinalis on the growth and the physiology of three bloom-forming cyanobacteria: Aphanizomenon sp., N. spumigena, and Nostoc sp
Summary
Macroalgal allelopathy is considered to be a special strategy to deter or eliminate competitors and predators coexisting in a shared ecosystem [1]. The secondary metabolites produced and secreted into the environment by donor organisms have been called allelopathic compounds [2]. Macroalgal allelopathy depends on the production and secretion of active allelopathic compounds and their efficient dispersal to target organisms that were affected by these compounds [3]. These compounds can affect other plants, and cyanobacteria, protists, zooplankton, bivalves, crustaceans, and fish by limiting their reproduction and causing high mortality [4,5]. Allelopathic compounds can affect the growth and photosynthesis of coexisting cyanobacteria and microalgae (e.g., [6,7,8,9]).
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