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This paper reports on a detailed study of the influence of salinity on the biological activity of 1-alkyl-3-methylimidazolium chlorides on two green algae Oocystis submarina and Chlorella vulgaris, one diatom Cyclotella meneghiniana and one blue-green alga Geitlerinema amphibium. All these organisms inhabit the Baltic Sea, an environment naturally varying greatly in salinity. The toxicity effects of ILs towards cyanobacterial and algal organisms were tested in fresh water and in water of four different salinities-8, 16, 24 and 32 PSU-reflecting the whole range encountered in the Baltic Sea. Increasing the salinity was found to exert a significant influence on ionic liquid toxicity in all cases. The lower toxicity is probably due to the reduced permeability of ionic liquid cations through the algal cell walls. Higher chloride concentrations offer a good ion-pairing environment for imidazolium cations, which therefore compete with hydroxyl or silanol functional groups in cell-wall structures. The results of this work indicate that at higher salinities algal growth is inhibited to a significantly lesser extent. With the same IL concentration, the toxicity decreases by eight-ten times in the algae or about three times in the cyanobacterium in the 0-32 PSU salinity range.

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Picocyanobacteria are extremely important organisms in the world's oceans and freshwater ecosystems. They play an essential role in primary production and their domination in phytoplankton biomass is common in both oligotrophic and eutrophic waters. Their role is expected to become even more relevant with the effect of climate change. However, this group of photoautotrophic organisms still remains insufficiently recognized. Only a few works have focused in detail on the occurrence of massive blooms of picocyanobacteria, their toxicity and allelopathic activity. Filling the gap in our knowledge about the mechanisms involved in the proliferation of these organisms could provide a better understanding of aquatic environments. In this review, we gathered and described recent information about allelopathic activity of picocyanobacteria and occurrence of their massive blooms in many aquatic ecosystems. We also examined the relationships between climate change and representative picocyanobacterial genera from freshwater, brackish and marine ecosystems. This work emphasizes the importance of studying the smallest picoplanktonic fractions of cyanobacteria.Keywords: allelopathy; allelochemicals; climate change; cyanotoxins; picocyanobacteria; picoplankton; blooms; secondary metabolites Key Contribution: We have updated a review of the literature dealing with allelopathic activity of picocyanobacteria; their toxicity; occurrence of their massive blooms and the relationships between climate change and representative picocyanobacterial genera from aquatic ecosystems.