Keve Tihamér Kiss

Structure and seasonal dynamics of the protozoan community (heterotrophic flagellates, ciliates, amoeboid protozoa) in the plankton of a large river (River Danube, Hungary).

Seasonal dynamics of all major protozoan groups were investigated in the plankton of the River Danube, upstream of Budapest (Hungary), by bi-weekly sampling over a 1-year long period. Sixty-one heterotrophic flagellate, 14 naked amoeba, 50 testate amoeba, 4 heliozoan and 83 ciliate morphospecies were identified. The estimated abundance ranges of major groups throughout the year were as follows: heterotrophic flagellates, 0.27-7.8 x 10(6)ind.l(-1); naked amoebae, max. 3300ind.l(-1); testaceans, max. 1600ind.l(-1); heliozoans, max. 8500ind.l(-1); ciliates, 132-34,000ind.l(-1). In terms of biovolume, heterotrophic flagellates dominated throughout the year (max. 0.58mm(3)l(-1)), and ciliates only exceeded their biovolume in summer (max. 0.76mm(3)l(-1)). Naked amoeba and heliozoan biovolume was about one, and testacean biovolume 1-3, orders of magnitude lower than that of ciliates. In winter, flagellates, mainly chrysomonads, had the highest biomass, whilst ciliates were dominated by peritrichs. In 2005 from April to July a long spring/summer peak occurred for all protozoan groups. Beside chrysomonads typical flagellates were choanoflagellates, bicosoecids and abundant microflagellates (large chrysomonads and Collodictyon). Most abundant ciliates were oligotrichs, while Phascolodon, Urotricha, Vorticella, haptorids, Suctoria, Climacostomum and Stokesia also contributed significantly to biovolume during rapid succession processes. In October and November a second high protozoan peak occurred, with flagellate dominance, and slightly different taxonomic composition.

Colonization processes of diatoms on artificial substrates in the River Danube near Budapest (Hungary)

Periphyton was collected from sand-blasted slides exposed in the main channel of River Danube at Gö (1669 rkm). Samples were taken from 21 May to 23 November in 1984. Three to four days after placing the substrates into the river the first traces of an observable coating appeared. The formation of the algal coating in the Danube presented certain periodical features. From time to time, an essential decrease in the number of individuals could be observed, which generally coincided with changes in the struc- ture of the community. This could be traced well, by grouping the algae according to morphological categories and following the temporal changes affecting these categories. The early phase of the colo- nization process is dominated by relatively large araphid and biraphid diatoms. In the second phase small bi- and monoraphid species are dominant. Finally, the medium size mono- and biraphid algae are dominating.

Effects of the water discharge on periphyton abundance and diversity in a large river (River Danube, Hungary)

This paper examines the relevance of intermediate disturbance theory in the context of in a large river the algal flora attaching to artificial substrata. It was observed that the theory is in good agreement with most of the communities analysed, however, with different frequency intervals compared to phytoplankton. Floods provided the most significant disturbances. As a rough generalization, we can say that in case of floods following each other in 8–14 days, respectively, the disturbance is of medium frequency. In case of 8 days, high frequency is more typical while in case of 14 days, low frequency is more characteristic. Owing to the fact that riverine periphytic algal organisms are attached in different ways and with differing efficiencies, the changes in the total mass occurring as a result of changes in water discharge lead to changes in diversity. The analysis of individual numbers can help in investigating the intensity of the disturbing effect on the algal communities. Negative correlation was found between water discharge and numbers of individuals, that is, the numbers of algae increase with low water discharge and decrease with high water level in the river. This second observation is valid only within a certain range of discharges (in this case up to 100 m3 s−1), which will be specific to particular rivers and individual reaches. Below the upper limit of the range, the increased water flows carry more nutrients to the organisms but with no severe wash-off effect. Beyond the upper limit (in this case in range 100–400 m3 s−1) the numbers of individuals is roughly in inverse proportion to the wash-off effect of the current, and the community is in equilibrium. In cases when discharge surpasses 400 m3 s−1 decrease in individual numbers is general. We suggest that in the environments similar to the study area, the periphyton of the artificial substrata (e.g., pontoons) undergo similar processes. In respect of the periphyton formed on the surface of the riverbeds in large rivers with considerable changes in water level, a more complex system can be supposed where part of the periphyton is periodically dried and flooded alternately.

Centric diatoms of large rivers and tributaries in Hungary: morphology and biogeographic distribution

Abstract Centric diatoms of 107 different Hungarian running waters were investigated. Among them the largest was the River Danube, from which more than one hundred plankton samples were analysed by scanning electron microscopy (SEM). Only one sample was analysed from creeks, which were the smallest running waters analysed in this study. There were also channels with slow currents flowing out of rivers or connecting different rivers. In total, 41 centric taxa belonging to 11 genera were found during this study. The average number of taxa found in a single watercourse was 7, the maximum 40 and the minimum 1. Cyclotella meneghiniana was the most frequently encountered species (present in 60% of sites). Twelve taxa were found in more than 20% of sites, 7 taxa between 5-10% and 6 taxa only in one site.

Algological and bacteriological investigations on reed periphyton in Lake Velencei, Hungary

In the shallow Lake Velencei (surface area 24.5 km2) reed communities (Scirpo-Phragmitetum) are of great significance due to extensive metabolic activity of algal-bacterial associations developing on their submerged surfaces. Samples for algological and bacteriological studies were taken in April 2000 and July 2001 at five sites of the lake and were analysed with traditional methods as well as with tools of molecular biology (16S rDNA sequencing). These investigations have shown that (i) The original mosaic structure of the lake disappeared; periphytic algae became spatially uniform both in terms of taxonomic composition and abundance. (ii) The biodiversity of the reed periphyton decreased. The dominance of the weed algal species Achnanthes minutissima Kütz. increased significantly. (iii) The most frequent bacteria were members of the genera Pseudomonas, Acinetobacter, Shewanella and Agrobacterium characterised by oxidative chemoorganotrophic heterotrophic- and Aeromonas and Bacillus species with fermentative metabolism. (iv) Among the studied bacterial strains both plant growth promoting bacteria, members of Pseudomonas fluorescens group, and potential plant pathogens (Agrobacterium, Aureobacterium, Curtobacterium) were present.

Phylogeny of six naviculoid diatoms based on 18S rDNA sequences

18S rDNA sequences of six Naviculaceae species [Amphora montana, Gomphonema parvulum, Eolimna minima (syn. Navicula minima), Eolimna subminuscula (syn. Navicula subminuscula), Navicula veneta and Phaeodactylum tricornutum] were determined in order to assess the monophyly of this important group of diatoms, to date not included in 18S rDNA databases, and also that of the recently described genus Eolimna. Phylogenetic trees were constructed using other known diatom 18S rDNA sequences, and best tree topologies obtained were tested against alternative trees for their reliability. The analyses do not reject the monophyly of Naviculaceae and strongly support the separation of the genus Eolimna from Navicula sensu lato. The two species of Eolimna, however, do not appear to be each others closest relatives among the species investigated: rather, E. subminuscula shows affinities to A. montana, and E. minima to P. tricornutum. A. montana, a species which it has been proposed should be transferred into a separate taxon from the other five species, was found to have grouped well within them in all analyses.

Ecological observations on Skeletonema potamos (Weber) Hasle in the River Danube, near Budapest (1991–92, daily investigations)

The small, chain-forming centric diatom Skeletonema potamos (Weber) Hasle is one of the most important species of phytoplankton in the River Danube in Hungary. In low water periods from May to October, its abundance is high, contributing 10–20% of total biomass (its fresh weight is 3–6 mg l−1). The first data about its occurrence in Hungary, in the southern Danube stretch, were published by Schmidt & Vörös (1981). The presence of S. potamos was noted in Danube samples taken at the end of fifties near Budapest (Kiss, 1986). This species became abundant in the Hungarian stretch of River Danube at the end of sixties simultaneously with eutrophication.The main factors influencing the quantities of S. potamos populations are floods and temperature. The nutrient supply of the river is very high, therefore it cannot be a limiting factor. The effect of floods is a complex one. Increase in current velocity is not insignificant. Transparency influenced by the suspended matter content is important. In low water periods when suspended matter content is low (10–20 mg l−1), 70–90% of water column belongs to the euphotic zone. For this reason, low water periods favour increases in phytoplankton density.On the basis of this study, we conclude that S. potamos is a warm stenothermic species, with high light demand. Changes in length of pervalvar axis, diameter, S\V ratio and cell number in chains is influenced by temperature, duration of daylight and rate of cell division.

Improvement of the ecological water qualification system of rivers based on the first results of the Hungarian phytobenthos surveillance monitoring

Results of an ecological quality ratio-based qualification system, developed on the basis of the analysis of 1,161 benthic diatom dataset of the Hungarian national database, are presented herein. Using Kohonen’s Self Organising Map technique, the 25 Hungarian physiographic river types were pooled into six larger distinct categories (diatom river groups). Diatom metrics were tested for their sensitivity to the targeted stressors (nutrients, COD hydromorphological alteration) in each group. The strongest relationships were found in the case of the IPS, SI and TI indices; therefore the average of these metrics (IPSITI) was proposed as a national multimetric index for Hungarian streams. Based on IPSITI values, the ratio of moderate to worse quality water was the highest in those groups containing small rivers. In the case of large, lowland and mid-altitude rivers with fine sediment, the good and moderate ecological status was more characteristic. Applicability of the IPSITI seems to be very useful in case of small- and medium-sized rivers. For these rivers, the index showed a significant relationship with nutrients and organic pollutants. In the case of very large rivers, the stressor–index relationships were not significant because of the insufficient number of samples and the small range of stressors.

Phytoplankton and zooplankton (Cladocera, Copepoda) relationship in the eutrophicated River Danube (Danubialia Hungarica, CXI)

The seasonal variation in primary production, individual numbers, and biomass of phyto- and zooplankton was studied in the River Danube in 1981. The secondary production of two dominant zooplankton species (Bosmina longirostris and Acanthocyclops robustus) was also estimated. In the growing season (April–Sept.) individual numbers dry weights and chlorophyll a contents of phytoplankton ranged between 30–90 × 106 individuals, l−1, 3–12 mg l−1, and 50–170 µg l−1, respectively. Species of Thalassiosiraceae (Bacillariophyta) dominated in the phytoplankton with a subdominance of Chlorococcales in summer. Individual numbers and dry weights of crustacean zooplankton ranged between 1400–6500 individuals m−3, and 1.2–12 mg m−3, respectively. The daily mean gross primary production was 970 mg C m−3 d−1, and the net production was 660 mg C m−3 d−1. Acanthocyclops robustus populations produced 0.2 mg C m−3 d−1 as an average, and Bosmina longirostris populations 0.07 mg C m−3 d−1. The ‘ecological efficiency’ between phytoplankton and crustacean zooplankton was 0.03%.

The occurrence and ecology of the centric diatom Cyclotella choctawhatcheeana Prasad in a Croatian estuary

The centric diatom Cyclotella choctawhatcheeana Prasad has been found for the first time in the Adriatic Sea. It develops dense populations in the highly stratified, oligotrophic, karstic estuary of the Zrmanja River (eastern Adriatic Sea, Croatia). Cyclotella choctawhacheeana contributed to the phytoplankton community in the estuary with high abundance of up to 2 x 10(6) cells L-1. Maximum abundance was found in the marine layer, below the halocline, at a salinity range between 13-28, but it was able to develop over a very wide salinity range. The maximum development appeared in the temperature range of 8-18 degrees C. It was present in 52% of samples throughout the year. The significant negative correlation with silica, nitrates and total inorganic nitrogen showed its preference for a marine, oligotrophic environment. We consider C. choctawhacheeana to be a significant constituent of the phytoplankton of the east Adriatic coast. It can be assumed that its succes is based on species wide tolerance to fluctuations of environmental factors.