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29 30Functional classification based on species traits brought a revolution in community ecology, 31and also boosted phytoplankton and in phytobenton (diatom) research. Several studies 32 stressed the usefulness of phytoplankton functional groups in ecological status assessment, 33and there is also a strong emphasis to use combined traits in ecological assessments of diatom 34 assemblages. The Combined Eco-Morphological Functional Groups (CEMFGs) help to reveal 35 species-environmental correlations, which can be hidden, controlling traits separately. between the correlations of CEMFGs-P or CEMFGs-RB and abiotic factors were 50 hypothesised in the case of those functional groups which contained reassigned taxa with high 51 frequency and/or abundance. Our results confirmed this hypothesis. Furthermore, the present 52 study also highlighted the relevance of well-defined trait classification. Abundant and/or 53 frequent taxa, which are able to change their life forms, can modify significantly the 54 relationship between the functional group containing them and environmental factors. In the 55 future, both field and laboratory studies should focus on revealing the circumstances, which 56 cause the mentioned changes in traits of diatoms. 57 58

Single trait analyses are used to select the most appropriate species characteristics for an effective indication of changes in multiple stressors, but they are robust to detect fine-scale functional changes in biofilms. The combination of single traits may appropriately reflect ecological properties of changing benthic assemblages. We studied colonisation processes of benthic algal assemblages focusing on the changes in trait composition using life-forms, type of attachments, cell size and mobility as single traits in a small lowland stream. We tested the descriptive power of single trait groups (STGs) and also combined trait groups (CTGs). We assumed, that STGs would be significantly affected by environmental factors, but compositional changes in biofilms would be described more easily by using CTGs rather than STGs. Our hypotheses were confirmed by the results. While some STGs correlated positively to environmental factors indicating disturbances, others correlated to environmental factors indicating the stable conditions. The fast settlement of large sized groups was also relevant determining the compositional changes in the studied benthic community. Despite the strong correlation between STGs and environmental variables, CTGs analyses revealed important functional relations in the ecosystem, since CTGs display more sophisticated functional features of the organisms, which may provide more realistic responses.

Freshwater ecosystems are threatened by the global change‐induced extreme climatic events worldwide. The unpredictable changes in water supply create strongly disturbed environments and ultimately result in diversity changes. Here, we studied the formation of benthic algal and cyanobacterial assemblages under intermediately disturbed (IDC) and highly disturbed conditions (HDC) in a small lowland intermittent stream. We addressed our hypotheses to the Intermediate Disturbance Theory supposing that intermediate frequencies or intensities of disturbances maximise diversity independently of its level. We expected a larger influence of extremes in water supply on functional than on taxonomic and phylogenetic diversity. Our results only partially proved our first hypothesis highlighting the (i) importance of short‐time but intense disturbing effect on biofilm formation and trait composition under IDC period and (ii) the instability within the assemblages caused by large and opposing influences during HDC. Although extreme weather events caused trait extremes (supporting second hypothesis), they did not result in a decrease in functional richness (rejecting the second hypothesis). These findings in accordance with the insurance hypothesis clearly stress that a system with high functional redundancy can keep its functionality even under drastic hydrological conditions and the accompanying loss of species.

Cyanobacteria are notorious bloom formers causing various water quality concerns, such as toxin production, extreme diurnal variation of oxygen, or pH, etc., therefore, their monitoring is essential to protect the ecological status of aquatic systems. Cyanobacterial cell counts and biovolumes are currently being used in water management and water quality alert systems. In this study, we investigated the accuracy of colonial biovolume and cell count estimation approaches used in the everyday practice. Using real like 3-dimensional images of cyanobacterial colonies, we demonstrated that their shape cannot be approximated by ellipsoids. We also showed that despite the significant relationship between overall colony volume and cell biovolumes because of the considerable scatter of cell count data the regressions give biased estimates for cyanobacterial cell counts. We proposed a novel approach to estimate cell counts in colonies that was based on the random close sphere packing method. This method provided good results only in those cases when overall colony volumes could be accurately measured. The visual investigation of colonies done by skilled experts has given precise but lower estimates for cell counts. Estimation results of several experts were surprisingly good which suggest that this capability can be improved, and estimation bias can be reduced to the level acceptable for water quality estimations.HighlightsCyanobacterial colony – cell biovolume relationships provide biased estimates for cellbiovolumes.Sphere packing approach provides good cellcount estimates if colony volumes are accurately measured.Considering cyanobacterial colonies as ellipsoids gives inaccurate volume estimates.Skilled experts slightly underestimate the cellcounts but dispersion of their estimates is low.

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