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International and national protection strategies and directives focus mainly on macroscopic organism and attempt to maintain their endangered habitats. However, microscopic communities are also threatened by decreasing biodiversity and many species including freshwater algae can disappear without even knowing they were present in the habitat. Defining rarity of microscopic taxa is not easy. The species’ rarity is based on detailed knowledge of distribution and abundance of species. But only limited information is available about rare algal species especially in a given ecoregion. Reducing the data gaps, here, we present altogether 20 phytoplankton taxa rare in Hungary: three species of Chlorophyceae, eight species of Trebouxiophyceae, two taxa of Euglenophyceae, one-one species of Cyanobacteria, Bacillariophyceae and Mediophyceae and three species of Xanthophyceae. One of them, the Cylindrotheca gracilis is on the Hungarian Red List. Physical and ecological characteristics of standing waters where these species were found as well as their former occurrence all over the world are also reviewed.

Some literature data suggest that one of the possible roles of the cyanotoxin cylindrospermopsin (CYN) is forcing other phytoplankton species in the environment to produce alkaline phosphatase, which enables the cyanobacterium to take up the enzymatically liberated phosphate. In this study, cultures of a planktonic green alga, Scenedesmus obtusus (Chlorophyta, Sphaeropleales), were treated with CYN producer Aphanizomenon (Cyanobacteria, Nostocales) crude extract (C+), with non-CYN producer Aphanizomenon crude extract (C−), and with non-CYN producer Aphanizomenon crude extract supplemented with CYN (C−+C). The results showed that C+ treatment induced both acidic and alkaline phosphatases of the studied cosmopolitan green alga, which otherwise was neither sensitive to the relatively high CYN concentration, nor to phosphate limitation. In cases of C− and C−+C treatments, these phenomena were not observed. Several studies suggest that additional compounds may support CYN action. The results presented here suggest in a more direct way that other components present in the cellular matrix of the producer organism itself are involved in the effects of CYN, activation of phosphatases (not only alkaline ones) among them. These other components are absent in C− crude extract or cannot actively contribute to the effects of exogenously added CYN.

Functional classification based on species traits brought a revolution in community ecology, and also boosted phytoplankton and in phytobenton (diatom) research. Several studies stressed the usefulness of phytoplankton functional groups in ecological status assessment, and there is also a strong emphasis to use combined traits in ecological assessments of diatom assemblages. The Combined Eco-Morphological Functional Groups (CEMFGs) help to reveal species-environmental correlations, which can be hidden, controlling traits separately. Nowadays, there are three types of functional guild classifications simultaneously used in the literature: (i) the original classification proposed by Passy (O); (ii) Passy’s classification complemented with a separated planktic guild (P); (iii) the refined guild classification by Rimet and Bouchez, also containing the planktic guild (RB). One of the most important criteria of the combined functional groups is the well-defined ecological frame of these combined groups; thus it is vital to harmonise the classification of the taxa into guild based combined eco-morphological functional groups (CEMFGs). In this study we tested the similarities and dissimilarities of the correlations between environmental factors and CEMFGs created in the (i)-(iii) classifications. Samples were collected in 138 sampling sites on lowland rivers and streams in the Hungarian Lowland Region. Strong correlations were anticipated between the functional groups and environmental factors due to the presence of common and/or abundant planktic taxa. Our results validated the necessity of a separated planktic guild in ecological assessments of diatom assemblages. Further relevant differences between the correlations of CEMFGs-P or CEMFGs-RB and abiotic factors were hypothesised in the case of those functional groups which contained reassigned taxa with high frequency and/or abundance. Our results confirmed this hypothesis. Furthermore, the present study also highlighted the relevance of well-defined trait classification. Abundant and/or frequent taxa, which are able to change their life forms, can modify significantly the relationship between the functional group containing them and environmental factors. In the future, both field and laboratory studies should focus on revealing the circumstances, which cause the mentioned changes in traits of diatoms.

Even though microscopic algae play pivotal role in the healthy functioning of freshwater ecosystems, recent water protection strategies rarely consider them and primarily focus on macroscopic organisms. Here, we studied the effect of protection level and utilization type of lowland standing waters on the composition and diversity of benthic diatom assemblages and on the diatom-based ecological status of waters. We hypothesized that (i) protected waters will sustain more diverse diatom assemblages and better ecological quality than not protected ones. We also hypothesized that (ii) the increase in number of utilization will affect negatively on biodiversity and on ecological quality. Clear taxonomic differences were revealed only in protected and not utilized waters while trait composition in protected waters was independent from the utilization type. Neither biodiversity nor ecological status of waters were influenced by protection level. The increase in number of utilization types, however, significantly decreased functional richness. Although high biodiversity of algae can effectively buffer the negative effects of climate change and anthropogenic impact, recent protection strategies are insufficient to support it.

International audience; Climate change is predicted to increase drought occurrence and severity in small continental watercourses. Here, we studied the structure and the functional diversity of benthic diatom assemblages in lowland intermittent and permanent watercourses of the Carpathian Basin. We assumed that the community structure of intermittent and permanent watercourses would be markedly different, and the functional diversity in both would be strongly influenced by autumn drought. We found that intermittent streams were primarily characterized by small-sized generalists and aerophilic taxa, while permanent watercourses were inhabited by large-sized planktic or fast moving groups. The functional richness was significantly lower in intermittent than in permanent streams. This decrease in the functional richness of benthic algal communities may negatively affect the functioning of lotic algal communities. We conclude that diatom assemblages in lowland intermittent watercourses are sensitive indicators of changes in ecosystem properties, and should be considered in appropriate evaluation and management of extreme climatic events on aquatic ecosystems.

International audience; Land-use imposes an important potential threat on the aquatic ecosystems of riverine habitats. In this study, DNA metabarcoding was used to assess the effect of land-use on diatom assemblages, with a special focus on cropland area as an integrative proxy for several direct-acting pressures. The so-called taxonomy-free approach was tested using exact sequence variants (ESVs) without pre-clustering and without assigning them to traditional taxonomy. Our hypothesis is that the taxonomy-free approach gives better interpretation of the effect of agricultural land use and it provides a more efficient index to indicate agricultural stress than the classical method with taxonomical clustering. Classical ordination techniques (PCA, NMDS) were performed to study the effects of cropland area proportion on diatom assemblages and a modified version of the Zelinka-Marvan equation for the index development. Results showed that (i) although ESVs provided better results when studying land-use effects on diatoms, taxonomic assignment after analysis was necessary to give ecological interpretations and that (ii) a better performing index could be developed by using the taxonomy-free approach. By using ESVs without taxonomic assignment, information on the ecology of sequences belonging to the same species and of unassigned sequences could be kept. New types of clustering methods are welcome in the future of biomonitoring where the delimitation of taxonomic units should be refined based on a higher emphasis on their ecology rather than on morphological or genetical criteria.

In general, reservoirs are multi-purpose objects and they often have to fulfil different tasks at the same time. The compliance with these different expectations is more manageable in reservoirs with well-separated heterogeneous basins than in homogenous ones. The Kiskore Reservoir is the second largest standing water in the Carpathian Basin. Its water level is artificially regulated which creates unique habitats with high nature conservation value. Furthermore, the Reservoir is also considered as an important recreation centre in the region. It consists of four basins with different protection degree and management strategy. Here, we tested whether spatial (usage-dependent) or seasonal (time-dependent) segregations characterized the benthic diatom composition in the Reservoir. We also tested the influence of different water usage of basins using diatom metrics and diversity indices. We hypothesized that spatial heterogeneity in diatom composition will be more pronounced than seasonal ones. We also supposed that composition and diversity of diatom assemblages as well as diatom based ecological status will clearly reflect to different management strategies in the basins, whereas we expected moderate ecological status and low diversity in basins with high level of human impact. Our first hypothesis was not confirmed by the results. While diatom composition was clearly heterogeneous in time, surprisingly no usage-dependent segregation was found. Furthermore, our second hypothesis was also only partially confirmed by the results. In early summer, diversity was significantly lower in basins with higher level of human impact, than in the other basins. In late summer, however, diversity was rather directly controlled by nutrients and light not by water usage. Moreover, diatom based ecological status positively correlated to the intensity of recreation activities and negatively to protection degree. Although these results were surprising at the first time, they clearly confirm that a balanced ecological-economical relation can be maintained with properly designed and performed strategies in artificial reservoirs. But protection strategies, because of their exclusive interest to habitat conservation of macroscopic not microscopic organisms, require careful revisions.

The economic role of certain types of cysts is unquestionable, since the production of several valuable biomolecules is connected to the resting stages of algae, including the red ketocarotenoid astaxanthin. It is relatively well known, how adverse environmental conditions induce cyst formation and astaxanthin accumulation. In the contrary, there is very limited information about stressors inhibiting these processes. An undesirable consequence of increasing drug use of the human and veterinary medicine is the appearance of the drugs both in natural and in mains water. Therefore, to study the effects of micro-contaminants, e.g. pharmaceuticals to non-target aquatic organisms is a recent issue both from ecological and economical point of view. In this study, the effects of three non-steroidal anti-inflammatory drugs (NSAIDs: diclofenac, diflunisal and mefenamic acid) on growth, cyst formation and astaxanthin accumulation of the flagellated green alga Haematococcus pluvialis were investigated. All three drugs inhibited growth, inhibition ranged from 29 to 81% on the basis of vegetative cell numbers on the 14th day of the experiments. Higher concentrations of the drugs led to higher proportion of cysts, which exceeded 60% of total cell number to the 14th day in diclofenac and diflunisal treatments. On the contrary, astaxanthin contents of treated cultures were lower with the increasing drug concentration, the pigment was undetectable in the presence of 0.075 and 0.05 mg ml−1 diclofenac. Results of carotenoid and chlorophyll content analysis suggest more specific processes behind the observed phenomena than membrane damage. Furthermore, the different phenomena or different extents of the same phenomena suggest that NSAIDs with diverse chemical structures may have different target points in physiological processes. Our results clearly show that NSAIDs could have much wider effective spectra than expected, long-term effects on microalgae might have unexpected ecological or economical consequences due to continuous exposure to these chemicals.

Cylindrospermopsin (CYN) is a toxic secondary metabolite produced by filamentous cyanobacteria which could work as an allelopathic substance, although its ecological role in cyanobacterial-algal assemblages is mostly unclear. The competition between the CYN-producing cyanobacterium Chrysosporum (Aphanizomenon) ovalisporum, and the benthic green alga Chlorococcum sp. was investigated in mixed cultures, and the effects of CYN-containing cyanobacterial crude extract on Chlorococcum sp. were tested by treatments with crude extracts containing total cell debris, and with cell debris free crude extracts, modelling the collapse of a cyanobacterial water bloom. The growth inhibition of Chlorococcum sp. increased with the increasing ratio of the cyanobacterium in mixed cultures (inhibition ranged from 26% to 87% compared to control). Interestingly, inhibition of the cyanobacterium growth also occurred in mixed cultures, and it was more pronounced than it was expected. The inhibitory effects of cyanobacterial crude extracts on Chlorococcum cultures were concentration-dependent. The presence of C. ovalisporum in mixed cultures did not cause significant differences in nutrient content compared to Chlorococcum control culture, so the growth inhibition of the green alga could be linked to the presence of CYN and/or other bioactive compounds.

Effects of zinc on growth, cell morphology, oxidative stress responses and zinc removal activity of two common phytoplankton species, Monoraphidium pusillum (Printz) Komarkova-Legnerova and Monoraphidium griffithii (Berkeley) Komarkova-Legnerova were investigated at a concentration range of 0.2–160 mg l−1 zinc. Cell densities and chlorophyll content decreased compared with controls in cultures of both species, effective concentrations causing 50 % growth inhibition within 72 h on the basis of cell numbers were 33.69 and 25.63 mg l−1 zinc for M. pusillum and M. griffithii, respectively. Changes in cell morphology and elevated lipid peroxidation levels appeared in zinc-treated cultures of both species, but only at higher (>10 mg l−1) zinc concentrations. The most effective zinc removal appeared at 20 and 10 mg l−1 zinc concentration for M. pusillum and M. griffithii, respectively. Removed zinc is mainly bound on the cell surface in the case of both species. This study provides new data for the zinc tolerance and zinc removal ability of the green algae M. pusillum and M. griffithii and shows that green algal species common in surface waters could have zinc tolerance and zinc-binding abilities, which makes them feasible in treatment of waters contaminated with 10–20 mg l−1 zinc.

In the last few years, halogenated hydrocarbons have been detected in the soil, in the aquatic environment, in organisms, and even in drinking water. The toxic effects of three chlorinated aliphatic hydrocarbons (trichloroethylene, tetrachloroethylene and tetrachloroethane) were studied in laboratory experiments (using the cyanobacterium Synecococcus elongatus PCC 6301 as test organism) and in field-like circumstances (natural phytoplankton assemblages enclosed in microcosms). The results of the laboratory experiments showed that all of the tested compounds significantly inhibited the growth of the cultures within the first 4 h. Enzymatic changes of the treated cultures suggested that oxidative stress occured—all of the three compounds caused an increase in the activity of peroxidases and superoxide dismutase, and also increased the levels of lipid peroxidation. Observed changes in microcosms were comparable with the results of the laboratory experiments: the number of individuals and chlorophyll contents decreased in the treated assemblages. The elevated levels of peroxidation on the second day in the assemblages treated with tetrachloroethane and tetrachloroetylene suggest that oxidative stress could occur in field conditions. One of the most important findings is the decrease in species number. Our results showed that cryptomonads, some green algae species and the cyanobacterium Limnothrix gradually disappeared from the treated beakers during the experiment.

Classifying benthic diatom taxa based on ecological and morphological features became increasingly important in recent years due to the demand of understanding the dynamics and functioning of diatom assemblages. The great potential in using these functional classifications in diatom ecology involves further refinement of current classification. In our experimental study, colonisation processes of diatom assemblages were studied in a typical small lowland stream, using both diatom guilds and cell size categories. We also tested newly proposed combined eco-morphological functional groups (ecological guilds combined with cell size categories) in the study of the colonisation process in benthic diatom assemblages. We hypothesised that (i) there is a decrease in the proportion of low profile guild, while an increase in that of high profile and motile guilds in time with the decreasing rate of physical disturbance; (ii) the presence of small size categories will be pronounced at the beginning of the colonisation processes, while proportion of larger size categories will be higher in the latter phases of colonisation; and (iii) the relationship between taxa and environmental factors are better reflected by the use of combined eco-morphological functional groups than by the sole analyses of rough guilds or cell size categories. The first hypothesis was not confirmed, and our second hypothesis was only partially confirmed by the results. We found that the relationship between environmental factors and guilds, as well as cell size categories was not appropriate to reveal the relationship between abiotic factors and taxa composition. In contrast we found that compositional changes in colonisation were appropriately reflected by the newly defined combined eco-morphological functional groups. In the combined eco-morphological functional groups, such kind of taxonomical and ecological features can be prevailed which are hidden in guilds or cell size categories separately. Thus these combined eco-morphological functional groups could help to come one step closer to develop a widely used ecological classification in diatom researches.

In recent years measurable concentrations of non-steroidal anti-inflammatory drugs (NSAIDs) have been shown in the aquatic environment as a result of increasing human consumption. Effects of five frequently used non-steroidal anti-inflammatory drugs (diclofenac, diflunisal, ibuprofen, mefenamic acid and piroxicam in 0.1 mg ml(-1) concentration) in batch cultures of cyanobacteria (Synechococcus elongatus, Microcystis aeruginosa, Cylindrospermopsis raciborskii), and eukaryotic algae (Desmodesmus communis, Haematococcus pluvialis, Cryptomonas ovata) were studied. Furthermore, the effects of the same concentrations of NSAIDs were investigated in natural algal assemblages in microcosms. According to the changes of chlorophyll-a content, unicellular cyanobacteria seemed to be more tolerant to NSAIDs than eukaryotic algae in laboratory experiments. Growth of eukaryotic algae was reduced by all drugs, the cryptomonad C. ovata was the most sensitive to NSAIDs, while the flagellated green alga H. pluvialis was more sensitive than the non-motile green alga D. communis. NSAID treatments had weaker impact in the natural assemblages dominated by cyanobacteria than in the ones dominated by eukaryotic algae, confirming the results of laboratory experiments. Diversity and number of functional groups did not change notably in cyanobacteria dominated assemblages, while they decreased significantly in eukaryotic algae dominated ones compared to controls. The results highlight that cyanobacteria (especially unicellular ones) are less sensitive to the studied, mostly hardly degradable NSAIDs, which suggest that their accumulation in water bodies may contribute to the expansion of cyanobacterial mass productions in appropriate environmental circumstances by pushing back eukaryotic algae. Thus, these contaminants require special attention during wastewater treatment and monitoring of surface waters.

The inhibitory effects of cyanobacterial compounds as possible explanation of the lack of stable Cyanobacteria–Cryptophyta coexistence in steady-state phytoplankton assemblages were studied. The possible interactions between two phytoplankton species, a toxic Microcystis aeruginosa (cyanobacteria) and a non-toxic Cryptomonas ovata (Cryptophyta) were investigated (i) in mixed cultures (containing C. ovata and M. aeruginosa cells); (ii) in M. aeruginosa crude extract-treated C. ovata cultures and (iii) in purified microcystin-LR (MC-LR) treated C. ovata cultures. The results of experiments proved that the presence of living M. aeruginosa cells have more inhibitory effects on C. ovata cultures than the crude extract of the M. aeruginosa cells; or the presence of the purified MC-LR. These results suggest that MCs does not play as important role in cyanobacteria–Cryptophyta interaction as it was presumed; hence more complex effects (allelopathy among them) can be significant in shallow lakes ecosystems.

In Hungary Navicula jakovljevicii was firstly recorded in biofilm of Elodea nuttallii in 2005 in an oxbow of the catchment area of the River Danube. Subsequently, in 2006, N. jakovljevicii was also found in the same oxbow on reed stems as well. In the following years it appeared in another oxbow, suggesting an expanding distribution in the tributaries of the Danube in Hungary. The Hungarian population can be characterised as having mixed morphological features in comparison with other known N. jakovljevicii populations of Europe. When the morphological study was expanded, a similar, but 'giant form' was detect ed in fossil material. We found similarities and a possible connection between N. jakovljevicii and Navicula lucida, a diatom taxon described from a Neogene deposit in the Carpathian Basin. Despite the morphological similarities in the shape, apices, striae pattern and raphe structure of these two species, there are significant differences in valve dimensions: the valves of N. lucida are larger and more heavily silicified than N. jakovljevicii.