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Aquatic macrophytes form a three dimensional complex structure in the littoral zones of lakes, with many physical, chemical and biological gradients and interactions. This special habitat harbours a unique microalgal assemblage called metaphyton, that differs both from the phytoplankton of the pelagial and from the benthic assemblages whose elements are tightly attached to the substrates. Since metaphytic assemblages significantly contribute to the diversity of lakes’ phytoplankton, it is crucial to understand and disentangle those mechanisms that ensure their development. Therefore, we focused on the question of how a single solid physical structure contribute to maintaining metaphytic assemblages. Using a laboratory experiment we studied the floristic and functional differences of microalgal assemblages in microcosms that simulated the conditions that an open water, a complex natural macrophyte stand ( Utricularia vulgaris L.), or an artificial substrate (cotton wool) provide for them. We inoculated the systems with a species rich (> 326 species) microalgal assemblage collected from a eutrophic oxbow lake, and studied the diversity, trait and functional group composition of the assemblages in a 24 day long experimental period. We found that both natural and artificial substrates ensured higher species richness than the open water environment. Functional richness in the open water environment was lower than in the aquaria containing natural macrophyte stand but higher than in which cotton wool was placed. This means that the artificial physical structure enhanced functional redundancy of the resident functional groups. Elongation measures of microalgal assemblages showed the highest variation in the microcosms that simulated the open water environment. Our results suggest that assembly of metaphytic algal communities is not a random process, instead a deterministic one driven by the niche characteristics of the complex three dimensional structure created by the stands of aquatic macrophytes.

Diverse macrovegetation can provide heterogeneous habitats for benthic diatoms. The removal of macrophytes as direct plant control, however, can be considered as a threat, which can even lead to remarkable microhabitat alterations. Lake Tisza (Hungary) has a high nature conservation value, but it is also an important recreation centre, which is why very delicate water management is necessary including vegetation thinning. Here, we studied the importance of microhabitat heterogeneity (emergent, submerged and floating macrophytes) in maintaining diverse periphytic diatom assemblages. We hypothesized that the substrate type has greater influencing role on the composition and diversity of diatoms than the lake heterogeneity related to basins. We also assumed that floating vegetation hosts the most different and least diverse diatom assemblages. Our results mostly proved these hypotheses. Heterogeneous assemblages were formed on the different substrates (support hypothesis), however, the basin level differences were also detected (reject hypothesis). Our results also highlighted, that macrophyte species with lesser morphological complexity hosted the least diverse periphytic assemblages (support hypothesis). However, many unique and red list taxa were found on floating plants (reject hypothesis). These findings emphasize the key role of microhabitat complexity in maintaining diverse and healthy functioning of microbial assemblages in a multi-purpose reservoir.

In phytoplankton ecology the shape of microalgae appears predominantly as a categorical variable. Using shape-realistic 3D models of 220 microalgae we proposed and calculated six shape metrics and tested how these relate to each other and to the size of the microalgae. We found that some of the metrics are more sensitive to elongation, while others are related to multicellularity. We found a linear relationship between shape measures and the greatest axial linear dimensions of the microalgae. Our findings suggest that there is an evolutionary trade-off between the shape and size of the microalgae. It is important to stress that we found that surface area to volume ratio of the microalgae are hyperbolic functions of the length and volume for each shape. In our study, we demonstrated that the proposed shape metrics serve as suitable quantitative traits, and help to understand better how simple shapes evolved to more complex outlines.

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.

Here, we studied the influence of changes of aquatic phases (standing and flowing phases) and human-induced habitat variability (natural and artificial) on the composition and diversity of benthic diatom assemblages in a small lowland stream in the Pannonian Ecoregion. Significant differences in composition were hypothesized between phases and habitats. Lower diversity was hypothesized in the flowing phase and in the artificial habitat. In addition, worser ecological status were assumed in the artificial habitat and in the standing phase than in the others. Our results only partially supported our hypotheses. While there was no significant difference in the composition of the assemblages between the natural and concreted habitats, the alteration in flow conditions resulted in a significant change. No significant differences in diversity were found between aquatic phases. In contrast, biodiversity was higher in the artificial habitat than in the natural one. While the anthropogenic impact, i.e., concreted streambed has no significant influence on diatom-based ecological status, values of diatom indices were significantly higher in the flowing phase. Our results highlight that extreme weather events play a major role in shaping diatom assemblages even during a short period, which should be taken into account in water management and nature conservation measures.

In contrast to pelagic and benthic realms of the aquatic ecosystems, studies on the metaphytic habitats remain underrepresented in the literature. However, this realm may have a potential impact on composition and diversity of the open water assemblages through metacommunity processes (source-sink dynamics, mass-effect) especially in small ponds with extended littoral zone. Using a limnocorral experiment we studied how metaphyton affects diversity and composition of open water phytoplankton in a small eutrophic pond in the vegetation period. The three habitats (metaphyton, isolated and non-isolated open water) showed considerable differences in their taxa and functional group composition. Abundance-based diversity measures did not reveal remarkable differences among the assemblages of the three habitats. However, taxonomic and functional richness of the metaphyton and the non-isolated part of the pelagial significantly exceeded that of the limnocorral. Incidence-based similarity index values also showed closer resemblance of the metaphyton and plankton samples compared to that of the limnocorral. In the case of several functional groups, their functional redundancy in the metaphyton exceeded that in the open water areas. These results suggest that the metaphyton provides a refuge for several euplanktic elements that survive in the littoral and occasionally enrich the phytoplankton of the open water areas, representing that a within–lake metacommunity processes shape the composition and functioning of the open water areas in standing waters.

In this study, we aim to investigate how the functional properties of microalgae help to delineate the major groups of aquatic habitats. Using functional trait-based and Reynolds’ functional group-based approaches similarities of the microalgal flora of all aquatic habitats occurring in Hungary were compared. The habitats covered the whole size spectrum of standing waters (10 -2 –10 8  m 2 ) and water currents (watershed: 10 2 –10 11  m 2 ), , limnological and chemical properties. Both functional trait-based and functional group-based habitat classifications overrode the hydromorphology-based typology, however, functional group-based clusters showed closer resemblance to limnological-hydromorphological types than clusters created by trait-based approaches both for qualitative and quantitative data. Most of the aquatic habitats that have similar limnological characteristics showed resemblance in the functional properties of their microflora. Rivers and river-related habitats were the most diverse functionally. These were followed by standing waters with extended macrophyte coverage. The small, unique habitats displayed the lowest functional richness. The occurrence of several functional groups in some extreme habitats implies two alternative explanations: first, the habitat template of the groups is wider than defined in the original description; second, detailed information on the autecology of species assigned to a functional group necessitates the creation of new groups specific for the unique habitats.

Tanulmányaink középpontjában a bevonatalkotó algaközösségek kolonizációja és az azt befolyásoló szélsőséges időjárási események hatása állt. A közösség taxonómiai-, jelleg- és jelleg alapú kombinált csoport összetételének, valamint az ezeken alapuló diverzitásmetrikáknak az időbeli változásait követtük nyomon (24. ábra).A kolonizációs vizsgálat alapjául egy terepi kísérlet szolgált, ezért lehetőségünk nyílt a kísérlet folyamán végbemenő, előre nem látható események közösségszerveződésre gyakorolt hatását is vizsgálni. A kísérleti időszak első felében viszonylag stabil időjárási- és vízjárási viszonyok uralkodtak. Ezzel szemben a későbbi időszakot szélsőséges időjárási események jellemezték (heves esőzés, majd egy hosszabb száraz periódus), melyek a vizsgált vízfolyás vízjárását is jelentősen befolyásolták (fluktuáció). Így mindhárom vizsgálat alapján a két időszak között jelentős különbségeket fedeztünk fel a fitobenton összetételében. A kísérlet folyamán lezajló folyamatokat és az elemzéseink által levont következtetéseket a 24. ábrában foglaltuk össze.

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. Cyanobacterial 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.