Past and present: changes in the Odonata fauna of small lowland watercourses.

Small lowland watercourses, strongly exposed to anthropogenic activities and climate change, have received negligible odonatological attention. This study provides a revised checklist of three typical lowland small watercourses (Kállai-fofolyás, Konyári-Kálló and Ölyvös) within the Pannonian Lowland and presents the changes in their diversity over the past decades. Results revealed a significant biodiversity loss, with a 31.6% decline in Odonata fauna over the last 53 years. The upper and middle sections degraded the most, where the habitats have dried out or become intermittent. However, a diverse Odonata assemblage (1,277 individuals of 27 species) was observed at the 14 sampling sites of the three watercourses, containing protected and sensitive species (Somatochloraflavomaculata, Orthetrumbrunneum, Aeshnaisoceles, Libellulafulva). However, the low abundance of larval and exuvial forms (59 individuals of 13 species) suggests that the majority of the observed adults were developed in other watercourses. While recolonisation from nearby habitats is still possible, a parallel degradation of adjecent waterbodies could lead to an irreversible biodiversity loss.

Possible mediation of Cladocera species by a researcher's chest wader.

Mediation of aquatic species has become an increasing problem for the last few decades. With the increasing commercial import, species' direct or indirect spread can gain more space. There are several ways for them to land in their new home and spread through the country. Most of the aquatic species are spread by waterways, boats, vehicles, or even with the help of humans. Cladocerans have a good dispersal ability, thanks to their small size, additionally they possess good adaptation, and mechanisms to develop resting eggs. Benthic or littoral species can be mediated much more easily due to their living space, and with the help of human activities (e.g., scientists, anglers and people working in water bodies) they have a higher chance to colonize new habitats. Our goal was to explore if Cladocera species might be mediated by a scientist chest wader, while sampling in similar-sized, close-to-each other lakes, with different utilization. Most of the species were found in abandoned fishing lakes, followed by oxbow lakes (protected), and ultimately in intensively fished lakes. NMDS showed that samples from lakes with the same utilization are similar to each other. Differently utilized lakes can have various Cladocera species, even though they are closely related to each other. Based on the results, scientists can mediate species on their chest wader from lake to lake and may deteriorate the results. We recommend a necessary chest wader cleaning after every sampling process, especially when samples are taken from differently utilized lakes.

Relative importance of climate and spatial processes in shaping species composition, functional structure and beta diversity of phytoplankton in a large river.

Although metacommunity dynamics of lentic phytoplankton are relatively well-documented, studies on the role of environmental and spatial processes in shaping phytoplankton communities of large rivers are still scarce. Here, we examined six phytoplankton data sets, which were collected in 1978-2017 from large river-scale segments (mean spatial extent 1117 km) in the Danube River. Our aim was to elucidate role of climatic, spatial and temporal predictors in variation of phytoplankton beta diversity using variance partitioning for compositions of species and functional groups sensu Reynolds. We hypothesised that phytoplankton beta diversity (measured as average distance to group centroid) would be positively related to both climatic heterogeneity and spatial extent used as a proxy for dispersal limitation. Additionally, we tested alternative dispersal models to evaluate different spatial processes structuring phytoplankton community. Our results revealed that spatial variables were more important than climatic factors in controlling both species and functional group composition. Climatic heterogeneity showed significant positive relationship with beta diversity. In contrast, there was no significant relationship between beta diversity and spatial extent, suggesting that spatial effect on beta-diversity was attenuated by anthropogenic disturbance. The better performance of non-directional model compared to model of water directionality suggested that spatial dynamics of phytoplankton metacommunity was in large part regulated by differences in the regional species pools. Spatial and temporal variables outperformed environmental (including climatic) factors in explaining phytoplankton metacommunity structure, indicating that phytoplankton exhibited strong biogeographical patterns. Thus, dispersal limitation interfered with species-sorting processes in determining phytoplankton community structure. In conclusion, our findings revealed that the development of a more reliable bioassessment program of the Danube River should be based on separation into basin regions.

Trait-based community assembly of epiphytic diatoms in saline astatic ponds: a test of the stress-dominance hypothesis.

The stress dominance hypothesis (SDH) postulates that strong environmental gradients drive trait convergence in communities over limiting similarity. Previous studies, conducted mostly with terrestrial plant communities, found controversial evidence for this prediction. We provide here the first test for SDH for epiphytic diatoms. We studied community assembly in diatom communities of astatic ponds. These water bodies serve as a good model system for testing SDH because they exhibit stress gradients of various environmental factors. Functional diversity of diatom communities was assessed based on four traits: (1) combined trait reflecting the trade-off between stress tolerance and competitive dominance, (2) cell size, (3) oxygen requirement and (4) N-uptake strategy. According to our results, salinity, pH and the width of the macrophyte belt appeared as significant predictors of the trait convergence/divergence patterns presumably acting through influencing the availability of carbon dioxide and turbidity. Lower trait diversity was found in turbid, more saline and more alkaline ponds and functional diversity was higher in transparent, less saline and less alkaline ponds. Overall, our results supported the stress dominance hypothesis. In habitats representing increased environmental stress, environmental filtering was the most important community assembly rule, while limiting similarity became dominant under more favourable conditions.

Unexpected consequences of bombing. Community level response of epiphytic diatoms to environmental stress in a saline bomb crater pond area.

The spatial response of epiphytic diatom communities to environmental stress was studied in a moderately saline wetland area located in the plain of Danube-Tisza Interfluve, Hungary. The area is characterised by World War II bomb crater ponds and can be regarded as an excellent ecological model system where the dispersion of species is slightly limited by distance. To study the effect of environmental variables on the communities, canonical correspondence analysis was applied. Salinity, pH, total suspended solids, total phosphorous and depth proved to be significant environmental drivers in this analysis. The ecological status of the ponds was assessed with Ziemann's halobity index, as the trophity-depending metric cannot be applied to these habitats (due to the naturally high phosphorus content). Ponds in "good" ecological status significantly differed from those appertaining to water quality category of "not-good" ecological status considering characteristic of natural astatic soda pans (e.g. salinity, pH, ammonium, total phosphorous concentration, nitrogen:phosphorous ratio and turbidity). The differences between epiphytic diatom communities inhabiting the ponds were detected using non-parametric multidimensional scaling. The samples formed three groups according to the types of ponds ("transparent", "transitional" and "turbid") based on the width of the macrophyte belt around them. Indicator species related to the ecological status of the ponds and diatom communities contributing to the separation of groups of ponds were identified. One of the indicator species differed from species already described. Light and scanning electron microscopy features and phylogenetic analyses based on three genes (18S and 28S rRNA genes, rbcL) proved that it was a new species of Nitzschia genus, closely related to Nitzschia frustulum and Nitzschia inconspicua. Therefore, description of a new species, Nitzschia reskoi Ács, Duleba, C.E.Wetzel & Ector is proposed. We concluded that the increasing abundance of Nitzschia reskoi was a signal of the degradation of the intermittent saline wetlands.

Alteration of cylindrospermopsin production in sulfate- or phosphate-starved cyanobacterium Aphanizomenon ovalisporum.

The effect of sulfate and phosphate deprivation on cell growth and cylindrospermopsin level was studied in Aphanizomenon ovalisporum ILC-164. Sulfate starvation induced a characteristic reduction of cylindrospermopsin pool size on the basis of cell number and unit of dry mass of culture. Phosphorous starvation of A. ovalisporum cultures induced a lesser reduction of cylindrospermopsin pool size. This divergence in the pool size of cylindrospermopsin may be the consequence of different growth rate. To show the metabolic changes concomitant with reduction of cylindrospermopsin pool size were obtained by measurement of ATP sulfurylase and alkaline phosphatase activity. The present study is the first concerning the cylindrospermopsin content under sulfate starvation and discusses it in relation to phosphorous starvation.

Microcystin-LR alters the growth, anthocyanin content and single-stranded DNase enzyme activities in Sinapis alba L seedlings.

Seedlings of the white mustard (Sinapis alba L.) are sensitive to the cell-free extracts of a toxigenic strain of Microcystis aeruginosa and to microcystin-LR. Fresh mass of plants, plant length, including hypocotyl and root length and lateral root formation is inhibited in microcystin-LR treated seedlings. The decrease of anthocyanin content is obtained in microcystin treated mustard cotyledons. The tissue necrosis of cotyledons is a characteristic consequence of microcystin treatment. Microcystin-LR induces an increase in single stranded deoxyribonucleases (ssDNases) activity of S. alba seedlings as shown by spectrophotometric assays and by ssDNase activity polyacrylamide gels. The significance of this phenomenon is discussed in relation to general stress responses in plants. We conclude that microcystin-LR affects the whole physiology and the growth of plants.

Capillary electrophoretic assay and purification of cylindrospermopsin, a cyanobacterial toxin from Aphanizomenon ovalisporum, by plant test (blue-green Sinapis test).

Toxic cyanobacteria are known to produce cyanotoxins, toxic secondary metabolites. In recent years the cylindrospermopsin (tricyclic guanidinyl hydroxymethyluracil)-producing organisms Aphanizomenon ovalisporum, Cylindrospermopsis raciborskii, and Umezakia natans have been inhabiting polluted fresh waters. Cylindrospermopsin, a potent hepatotoxic cyanotoxin, has been implicated in cases of human poisoning as well. This study describes the isolation and purification of cylindrospermopsin from A. ovalisporum with the help of a slightly modified Blue-Green Sinapis Test, a plant test suitable for determining the cyanotoxin content of chromatographic fractions besides plankton samples. The recent modification, using microtiter plates for the assay, improves the method and reduces the amount of sample needed for the assay. This approach proved that plant growth and metabolism, at least in the case of etiolated Sinapis alba seedlings, are inhibited by cylindrospermopsin. The establishment of capillary electrophoresis of cylindrospermopsin and consideration of the results reported here lead us to the expectation that capillary electrophoresis of cylindrospermopsin may be a powerful and useful analytical method for investigating cyanobacterial blooms for potential cylindrospermopsin content and toxicity. Confirmation of chemical identity of the purified compound is performed by UV spectrophotometry, NMR, and MALDI-TOF.