| Summary: | Global warming and eutrophication contribute to formation of HABs and distribution of alien cyanobacteria northward. The current study assessed how alien to Europe <i>Sphaerospermopsis aphanizomenoides</i> and <i>Chrysosporum bergii</i> will co-occur with dominant native <i>Planktothrix agardhii</i> and <i>Aphanizomenon gracile</i> species under changing conditions in temperate freshwaters. The experiments were carried out to examine the effect of nutrients and temperature on the growth rate of cyanobacteria, production of cyanotoxins, and interspecies competition. The highest growth rate was determined for <i>A. gracile</i> (0.43 day<sup>−1</sup>) and <i>S. aphanizomenoides</i> (0.40 day<sup>−1</sup>) strains at all the tested nutrient concentrations (IP and IN were significant factors). <i>S. aphanizomenoides</i> adapted to the wide range of nutrient concentrations and temperature due to high species ecological plasticity; however, <i>A. gracile</i> was able to suppress its dominance under changing conditions. Regularity between tested variables and STX concentration in <i>A. gracile</i> was not found, but IP concentration negatively correlated with the amount of dmMC-RR and other non-ribosomal peptides (NRPs) in <i>P. agardhii</i> strains. The relative concentration of NRPs in nontoxic <i>P. agardhii</i> strain was up to 3-fold higher than in MC-producing strain. Our study indicated that nutrients, temperature, and species had significant effects on interspecies competition. <i>A. gracile</i> had a negative effect on biomass of both alien species and <i>P. agardhii</i>.
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