## 4 Discussion
### Response at Population Level  
Among the dominant species present in the initially community and present during the experiments, mainly diatoms and single cyanobacterial species were distinguished, including numerous cosmopolitan taxa, e.g., _B. paxilifera_, _N. perminituta_, _N. ramossisima_, _T. fasciculata_, _M. nummuloides_, and _S. subsalsa_[83]. Irrespective of the degree of dominance in the initial community, cell size, or taxonomic group, individual taxa showed a variety of responses to the presence of the chemicals tested. The rate of uptake of selected ions across cell membranes and the internal detoxification mechanism were likely to be factors that significantly influenced the toxicity of the tested substances [84]. We distinguished three main types of response to the presence of potentially toxic chemicals. Some organisms responded with an increase in cell numbers relative to control samples. This was found to be a response characteristic of resistant species in which the chemical stimulates growth. Some taxa remained indifferent to the presence of the toxicant and showed no significant change in abundance. The last group was made up of sensitive taxa, which reacted by decreasing cell numbers under the influence of the test substances. Unfortunately, in the case of our tests, we are unable to determine whether the selected substances stimulated growth or reduced competition, which ultimately manifested itself in an increase in population size. An example of a particularly resistant species, which was stimulated by all the factors tested, was _N. perminituta_. Other resistant taxa that increased their abundance, contributing to the remodelling of the community structure were, e.g., _G. marina_ (copper chloride II), _Cylindotheca clostrium_, _Spirulina_ sp. (glyphosate), and _Merismopaedia_ sp. ([BMIM]Cl). Plants, including aquatic plants, have many defence mechanisms that enable them to survive under unfavourable conditions. As a result of oxidative stress caused by pollution, the activation of detoxification mechanisms and defensive antioxidant processes are observed, which enable microalgae cells to defend themselves, but these are taxon-specific responses [85]. Important regulatory factors in the adaptation strategies of algae to chemical stress are auxins and cytokins, whose production rates vary between species [86]. Taxa identified as indifferent to the tested chemicals in which these mechanisms were likely to have acted included: _C. pediculus_, _M. nummuloides_, and _N. gregaria_ in the case of copper (II) chloride. In contrast, glyphosate did not affect changes in abundance in, e.g., _Liconophora_ sp. and _T. fasciculata_. In the case of ionic liquid, no species described as indifferent were observed. A study by [PERSON] et al. [87] showed that multispecies algal communities with interspecies interactions respond differently to stress caused, for example, by the presence of chemicals. The authors determined the sensitivity of algae to the presence of copper ions by measuring the inhibition of the production of certain cellular enzymes and showed, among other things, that the EC\({}_{50}\) for _Microystis aeruginosa_ (Cyanobacteriota) in the community was significantly higher compared to monocultures of this species and that cell metabolism is also affected by interspecies interactions. Also, our previous studies indicate that taxa in communities have a higher resistance to the stressors tested than individual microalgal strains [45]. Microphyotbenthic communities usually consist of a large number of species,even at early stages of succession [88]; hence, it is to be expected that the response of taxa to the presence of toxic substances in communities will be different than in monocultures and further enhanced or weakened by competitive relationships. In our tests, we showed that high concentrations of Roundup\({}^{\text{\textregistered}}\) contributed to complete community conversion. Cyanobacteria were particularly resistant to this preparation.