Sándor Alex Nagy

Factors controlling the occurrence of Dinophyta species in Hungary

A total of 512 samples collected from 86 Hungarian water bodies were analyzed for Dinophyta species and compared to common limnological characteristics. Temperature and organic matter content were the most important factors controlling the occurrence of Dinophyta species. Total phosphorus and conductivity were of lesser importance. On average, seven to eight taxa of Dinophyta were recorded in individual samples at a temperature of 12–18u2009°C and a CODMn < than 5xa0mg l−1. Usually five to seven Dinophyta taxa were recorded at a temperature of 22–26u2009°C and CODMn > than 10xa0mg l−1. The most important genera were Peridiniopsis, Cleistoperidinium and Ceratium. A two-factor principal component model explained 72% of the total variance within the data set. The first principal component explained 75 and 85% of the total variance within the temperature and organic matter variables. A cluster analysis, using within-group linkages, resulted in five groups of organisms that differed primarily with respect to their distribution along a temperature gradient.

The effects of Microcystis aeruginosa (cyanobacterium) on Cryptomonas ovata (Cryptophyta) in laboratory cultures: why these organisms do not coexist in steady-state assemblages?

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.xa0aeruginosa 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.

An integrated system for creating and presenting complex computer-based documents

An experimental system is described for the design, development, and presentation of computer-based documents that combine pictures and text on a high-resolution raster color display. Such documents can be used, for example, for maintenance and repair tasks or computer-aided instruction.n Documents are directed graphs whose nodes we refer to as pages, in analogy to the pages of a paper book. A page includes a set of simultaneously displayed pictures, actions (procedures and processes) triggered when the page is accessed or when pickable picture elements on it are selected, and indexing information. Pages may be nested arbitrarily deeply in chapters that serve much the same organizing function as those of conventional books.n The system is comprised of separate programs for laying out and drawing pictures, for graphically specifying the contents of pages, chapters, and their interconnections, and for displaying the document for user interaction.n Examples are given from a prototype document for the maintenance and repair of computerized numerical control equipment. Emphasis was placed on designing actions for simple realtime animation (both by color table techniques and by transforming named primitives and manipulating their attributes), and for finding ones way around the document (displays include: a “timeline” of recently visited pages, immediate predecessor and successor pages, sibling pages and their interconnections, and those pages satisfying key-word retrieval requests).

Effects of non-steroidal anti-inflammatory drugs on cyanobacteria and algae in laboratory strains and in natural algal assemblages.

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 0.1xa0mgxa0ml(-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.xa0ovata was the most sensitive to NSAIDs, while the flagellated green alga H.xa0pluvialis 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.

Isolation of viable cell mass from frozen Microcystis viridis bloom containing microcystin-RR.

Cyanobacterial species commonly occur in the phytoplankton of freshwater lakes and sometimes develop as toxin-producing blooms. Microcystis is one of the most common genera of freshwater cyanobacteria and is often the dominating phytoplankton of eutrophic lakes all over the world. In eutrophic lakes, large amounts of Microcystis may overwinter in the sediment and re-inoculate the water column in spring. In most cases, the overwintering pelagic population—if it exists—is small, and its role in re-inoculation has not been clear yet. In December 2005, we found large amounts of Microcystis on the surface, frozen in the ice cover in a eutrophic pond (Pond Hármashegy, Hungary). We identified the Microcystis species and investigated the viability and the toxicity of the frozen cells. The dominant species in the bloom samples was Microcystis viridis. Viability tests showed that the colonies isolated from the ice cover were composed of living cells. The isolated strain was found toxic, we analyzed the microcystin composition in the frozen planktonic Microcystis mass; in the investigated samples microcystin-RR was the main cyanotoxin.

The relative importance of spatial and environmental processes in distribution of benthic chironomid larvae within a large and shallow lake

Although chironomids are popular model organisms in ecological research and indicators of bioassessment, the relative role of dispersal and environmental filtering in their community assembly is still poorly known, especially at fine spatial scales. In this study, we applied a metacommunity framework and used various statistical tools to examine the relative role of spatial and local environmental factors in distribution of benthic chironomid taxa and their assemblages in large and shallow Lake Balaton, Hungary. Contrary to present predictions on the metacommunity organisation of aquatic insects with winged terrestrial adults, we found that dispersal limitation can considerably affect distribution of chironomids even at lake scale. However, we also revealed the predominant influence of environmental filtering, and strong taxa–environment relationships were observed especially along sediment type, sediment organic matter content and macrophyte coverage gradients. We account that identified reference conditions and assemblages along with specified optima and tolerances of the abundant taxa can contribute to our understanding of chironomid ecology and be utilised in shallow lake bioassessment. Further, we propose that predictive models of species–environment relationships should better take into account pure spatial structuring of local communities and species-specific variability of spatial processes and environmental control even at small spatial scales.

Species diversity and abundance of plant-dwelling chironomids across hierarchical habitat and seasonal scales in the oxbow lakes of River Tisza, Hungary

In temperate regions, plant-dwelling chironomids can be considered as cyclic colonizers that inhabit seasonally ephemeral submerged and floating-leaved macrophytes. In this study, patterns of abundance and species richness of plant-dwelling chironomids were investigated within and among stands of three macrophyte species in oxbow lakes along the River Tisza (Hungary). Chironomids colonized macrophytes rapidly and most species occupied the habitat before it had completely developed in June. Assemblage structure and abundance of particular species varied considerably between plant species, oxbow lakes and summer months in a characteristic succession from June to August indicating the presence of dynamic selection mechanisms. Abundance of most species, except Endochironomus tendens, total chironomid abundance, within-sample and total species diversity were highest on the submerged plant Ceratophyllum demersum, and most species occurred at the beginning of the colonization succession, in June. The contribution of oxbow lakes (20.3%) and the month sampled (20.3%) to total chironomid diversity was higher than would be expected by chance alone and the contribution of within (19.7%) and between samples (13.5%) to total chironomid diversity was lower than would be expected by chance alone. We conclude that regional biodiversity conservation action plans should include multiple habitats. Moreover, the significant seasonal species turnover proved the need for seasonal sampling to assess accurately the total diversity of chironomids in the system.

Seasonal succession of phytoplankton in a small oligotrophic oxbow and some consideration to the PEG model

Most of the research on the structure and dynamics of phytoplankton in lacustrine environments was performed in larger lakes. In small lakes, especially oxbows in which there is a profusion of waterbodies, available information is scarce (REYNOLDS 1993). Phytoplankton seasonal succession is discussed by comparison with the world model for lakes, PEG (Plankton Ecology Group, SoMMER et al. 1986). This model consists of 24 sequential statements, which describe, step by step, the seasonal events, which occur in phytoplankton and zooplankton of an idealised standard lake (Lake Constance). These statements have been tested using data from 24 different lakes, none of which were oxbows. The objectives of this paper are to describe the phytoplankton structure and to discuss the main patterns of seasonal variations of the phytoplankton species of a Hungarian oxbow. The present article is the first concerning an oxbow phytoplankton community and discusses data in relation to the steps proposed by the PEG model

Phylogenetic evidence for a new species of Barbus in the Danube River basin.

Three species of small-sized rheophilic Barbus fishes are endemic to and widely distributed throughout the mountain regions in the Danube River basin. In Hungary, barbels referred to as B. petenyi occur in streams in the foothills of the Carpathians near the borders with Slovakia, Ukraine and Romania. However, up to now, no genetic investigations were carried out on rheophilic barbels in this region. This study aims to clarify the taxonomic identity and distribution of the rheophilic barbels in the Hungarian plain based on molecular and morphological analyses. Two mitochondrial genes (cytochrome b, ATPase 6/8) and one nuclear gene (beta-actin intron 2) were sequenced and several morphometric and meristic characters were recorded. Phylogenetic and morphological analyses revealed that there are four genetically distinct lineages among the rheophilic barbels in the Carpathian Basin. The results demonstrated that North-Hungarian Barbus populations belong to B. carpathicus and that B. petenyi presumably does not occur in Hungary. As expected, B. balcanicus was only recorded in samples from the Balkans analyzed for reference. A distinct species, new to science, was discovered to be present in Sebes-Körös River (Crişul Repede) in eastern Hungary and western Romania and is formally described here as B. biharicus Antal, László, Kotlík - sp. nov.

The scales of variability of stream fish assemblages at tributary confluences

Tributary confluences play an important role in the dispersal of organisms, and consequently, in shaping regional scale diversity in stream networks. Despite their importance in dispersal processes, little is known about how ecological assemblages are organized in these habitats. We studied the scales of variability of stream fish assemblages over three seasons using a hierarchical sampling design, which incorporated three tributaries, three sites at the mouth of each tributary and using four sampling units at each site. We found strong scale dependent variability in species richness, composition and relative abundance. Most of the variation was accounted for by the interactive effect of season, between stream and between site effects, while habitat structure of the sampling units had a relatively minor role. Species richness showed a continuous decrease from the mainstem river in most cases, while species composition and relative abundance changed less consistently along the longitudinal profile. Consequently, we found that not only the junctions presented a strong filter on the species pool, but some species were filtered out if they passed this critical habitat bottleneck. In addition, spatial position of the tributaries along the river also contributed to assemblage variability in the confluences. Overall, our results suggest high variability in fish assemblages across multiple scales at tributary confluences. Environmental management should take a more critical care on the filtering role of tributary confluences in species dispersal, for better understanding patterns and processes in the branches of dendritic stream networks.