Maya P. Stoyneva

Steady-state phytoplankton assemblages in shallow Bulgarian wetlands

The present paper reports the results on the occurrence and composition of steady state phytoplankton assemblages in the shallow water bodies of 18 Bulgarian natural wetlands. They all differ in their morphometry, hydrology and trophic state. Steady states were identified according to Sommer & Padisak (1993) when (i) 1, 2 or 3 species of algae contribute more than 80% of total biomass, (ii) their existence or coexistence persists for long enough (more than 1–2 weeks) and (iii) during that period the total biomass does not increase significantly. These situations were rare and were dominated by 7 stress-tolerant, colony-forming and ruderal disturbance-tolerant cyanoprokaryotes (Microcystis aeruginosa, Microcystis wesenbergii, Anabaena spiroides, Anabaenopsis arnoldii, Aphanizomenon flos-aquae, Aphanizomenon gracile and Cylindrospermopsis raciborskii). The equilibrium states had been registered only during hypertrophic conditions in three stressed and frequently disturbed shallow water bodies and were related to the summer – late summer season.

Shallows of the lower Danube as additional sources of potamoplankton

This paper presents studies on the algal flora of the Bulgarian Danube section during three summer periods (1980–1982) and during the four seasons of 1987/1988. The following variables were investigated: 1) species composition of the river phytoplankton and the phytobenthos; 2) frequency quotients of the species; 3) number of species at the investigated sites; 4) phytoplankton numbers and biomass; 5) floristic similarity between the sites. The data show the existence of a dynamic connection between phytoplankton and phytobenthos. The shallows in the midstream and river arms play an important role as potamoplankton sources during the periods of low waters. It is comparable with the role of the adjacent wetlands to which previously priority was given. This is especially so below 597th river kilometer.

Green algae in Lake Tanganyika: is morphological variation a response to seasonal changes?

In the framework of a planktological and ecological study in Lake Tanganyika, East Africa (CLIMLAKE, 2001–2005), variations of cell abundance and size were observed in a green alga, Eremosphaera tanganyikae, at two study sites, one in the north basin of the lake (off Kigoma, Tanzania) and the other in the south basin (off Mpulungu, Zambia). Whereas most green algae developed better in the rainy season and in the northern part of the lake, Eremosphaera developed better in the southern basin, in the dry season. It also exhibited large variations in cell abundance and cell size, with maxima in the middle of the dry season, which may be related to increased phosphorus availability. Moreover, increase in cell size (up to 80 μm in length), without notable change in S/V ratio, may provide the alga with resistance to grazing by copepods, which reach maximal abundance during the dry season.

Volatile compounds from some Black Sea red algae and their chemotaxonomic application

Abstract Volatile compounds from the Black Sea red algae Bangia fuscopurpurea, Gelidium latifolium, Callithamnion granulatum, Ceramium elegans, Laurencia papillosa and Laurencia coronopus were obtained by distillation-extraction and analysed by GC/MS. Different groups of compounds were identified: hydrocarbons, alkylated benzenes, alcohols, phenols, aldehydes, ketones, acids, esters, terpenes, nitrogen- and halogen-containing compounds. The results are compared with some recent data for the composition of the volatile compounds from four previously investigated Black Sea red algae, which are at different evolutionary stages. On the basis of their qualitative and semi-quantitative composition some chemotaxonomic conclusions are proposed. The eventual functions of some of the volatile compounds are briefly discussed.

Development of the phytoplankton of the shallow Srebarna Lake (north-eastern Bulgaria) across a trophic gradient

Results of an analysis of phytoplankton samples, collected between 1982 and 1995 from Srebarna Lake, a biosphere reserve, in north-eastern Bulgaria, are presented. The lake is polymictic, and strongly eutrophied. It has undergone an anthropogenically-forced succession. In 1994, a restoration of the lake was commenced when a canal connecting it to the Danube River was built.

green algae in the phytoplankton of the danube (bulgarian sector) species composition, distribution, cell numbers and biomass

Summary In the phytoplankton of River Danube (Bulgarian stretch) for period of eight years (1980–1988) 216 taxa of Euchlorophytina and 26 taxa of Zygnemophytina were found. The distribution of established taxa from the 2 subdivisions is: in summer − 142 and 8, in spring − 124 and 8, in autumn − 73 and 3, in winter − 63 and 0, respectively. The majority of the established taxa (55–76 per cent) are rarely distributed along the river flow. By their numbers and biomass the green algae (predominantly Chlorococcales) occupied an important place in the river phytoplankton and in some stations they dominate over diatoms. Average numbers of the planktonic green algae varied from 2.30 × 105 cells/l (in winter) to 37.70 × 105 cells/l (in summer) and average biomass from 0.05 mg/l in autumn and 0.06 mg/l in winter to 0.34 mg/l in summer (1987/88). For Zygnemophytina this average values are 0.01 × 105 cells/l (in spring, summer and autumn) and 0.003 mg/l. The number of taxa, cell numbers and biomass of the green algae decrease after big industrial and port towns and increase after shallows in river arms near islands and sand strips (in summer period).

Planktic green algae of Bulgarian coastal wetlands

The present paper reports on the contribution of green algae to the phytoplankton community structure in 13 euto hypertrophic Bulgarian coastal wetlands which were different in morphometry and salinity. The results obtained revealed the important role of green algae, which formed 43% of the total species composition, 18% of numbers and 21% of biomass and often had a dominant or subdominant role in phytoplankton community structure.

Siderocelis irregularis (Chlorophyta, Trebouxiophyceae) in Lake Tanganyika (Africa)*

Siderocelis irregularis Hindák, representing a genus Siderocelis (Naumann) Fott that is known from European temperate waters, was identified as a common phytoplankter in Lake Tanganyika. It was found aposymbiotic as well as ingested (possibly endosymbiotic) in lake heterotrophs, mainly Strombidium sp. and Vorticella spp. The morphology and ultrastructure of the species, studied with LM, SEM and TEM, are described with emphasis on the structure of the cell wall and the pyrenoid.

Мicroscopic investigations (LM, TEM and SEM) and identification of Chlorella isolate R-06/2 from extreme habitat in Bulgaria with a strong biological activity and resistance to environmental stress factors

An extremophilic Chlorella strain R-06/2, isolated from a geothermal spring (+42 °C) in the region of Rupite village (SW Bulgaria), was investigated for species identification. This was done by observation of the cell morphology, reproduction and ultrastructure by light microscopy, scanning electron microscopy and transmission electron microscopy, and by investigation of the cell-wall chemistry. The pyrenoid ultrastructure with a double-layered thylakoid traversing the matrix, the shape of the starch envelope, as well as the cell wall, composed of glucosamine and developed around young autospores, were the features that allowed us to classify the thermophilic strain Chlorella R-06/2 as Chlorella vulgaris Beijerinck 1890.

Comparison of ecological state/potential assessment of 19 Bulgarian water bodies based on macrophytes and phytoplankton (2011 2012)

Nowadays, one of the most striking challenges for Bulgarian limnologists comes from the attempts to implement the requirements of Water Framework Directive (WFD) for assessment of the ecological status of the water bodies. This work represents results from the monitoring of the reservoirs Aleksandur Stamboliyski, Antimovo, Batak, Burzina, Gorni Dubnik, Zhrebchevo, Iovkovtsi, Krapets, Mandra, Ognyanovo, Rabisha, Suedinenie, Tsonevo and the lakes Alepu, Atanasovsko Ezero, Dourankoulak, Pomoriysko Ezero, Shabla and Sreburna. The studies were conducted simultaneously in the summer months of 2011 and 2012 on the following parameters: algal taxonomic composition and abundance, presence/absence of algal blooms and blooms of potential toxic species, algal group index, reference index for macrophytes, water temperature, transparency, pH, conductivity, chlorophyll a, total phosphorus, total nitrogen, phosphate phosphorus, ammonium nitrogen, nitrate nitrogen and chemical oxygen demand. The ecological status was registered in the five WFD categories. The set of data, based on the detected species composition of 236 algal taxa and 33 species of macrophytes, allowed us to compare statistically the values of the used parameters and the water bodies according to their biodiversity and abiotic features. The obtained results are important for clarifying the official classification of the surface water bodies of Bulgaria according to State Order N4/14.09.2012 and for making proposals for its improvement. Comparisons of the finally attributed ecological status/potential, based on macrophytes and phytoplankton, showed some significant differences and were used as a basis for discussion of the parameters and their weighted values, used up-to-now for the assessment of Bulgarian water bodies.