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Due to life in extreme environments, cyanobacteria and algae from cave biofilms that form at the entrances or deep inside the cave around artificial lights are of increasing interest to many scientists. It is well-known that many phototrophic microorganisms are first to colonize exposed substrata and produce the organic matter on which other biofilm constituents relly. Many studies dealing with phototrophic microorganisms from biofilms focus on the diversity and community composition of cyanobacteria and algae, while quantitative assessments are rarely implemented. Biofilm sampling was conducted in Degurić and Vernjikica Cave located in Western and Eastern Serbia, respectively. Ecological parameters (temperature, relative humidity, light intensity) and distance from the entrance were measured. Additionally, chlorophyll content, as well as biofilm parameters (water content, organic and inorganic matter) were determined. The abundance of phototrophic microorganisms was assessed on microscope slides which contained 1 mg of biofilm that was dehydrated for a short period of time and homogenized prior to slide preparation, and then rehydratated. The biomass of recorded cyanobacterial and algal taxa was calculated by applying geometric approximations and standard mathematical formulas. In Degurić Cave, at the sampling site where the highest biomass was documented, the higher diversity, water content and chlorophyll values were also recorded, while in Vernjikica Cave a high content of organic matter was documented. According to the multivariate analyses performed, the biomass of simple trichal Cyanobacteria, Bacillariophyta, and Xanthophyta was positively correlated with the content of organic matter in biofilm and light intensity, while coccoid and heterocytous Cyanobacteria and Chlorophyta

Chara canescens is the only charophyte performing parthenogenetic reproduction. Although most recently found populations consist solely of parthenogenetically reproducing females, bisexual populations exist as well, making the species a unique example of the sympatric occurrence of both reproductive modes. In Serbia, C. canescens was found only once for certain, near Prokuplje in 2005. The purpose of the present study is to report a reliable new finding of C. canescens in Serbia, in a stable parthenogenetic female population. Sampling was conducted on 7 July 2018 from the Plava Banja pond near the city of Kikinda. Results of water analyses revealed high concentrations of almost all measured parameters, but especially high levels of salinity and alkalinity markers. Very high concentrations of sulphates and chlorides in the Plava Banja pond pointed to extreme ion anomalies. On the basis of the concentration of nutrients in it, the Plava Banja pond can be characterised as a eutrophic water body. Chara specimens collected from this pond were identified as C. canescens, and only females in the reproductive phase were detected. The environmental features of this habitat are typical in relation to preferences of the given species for light and salinity (ion concentration). This record is of great importance because C. canescens has been declared to be probably extinct in the wild in Serbia.

The summer phytoplankton community was studied across both vertical and temporal scales in relation to environmental factors in the shallow recreational Sava Lake. The sampling was conducted weekly at four depths from mid-July until mid-September 2014, in order to detect short-term changes within the assemblages. Besides physical and chemical parameters, meteorological data was also included in the investigation, as that year was characterized with extreme rainfall, which caused serious flooding in the region. The community succession was characterized by a reverse in the cyanobacteria (Codon M) and chlorococcal green algae (Coda F and J). Statistical analyses (RDA) indicated that changes in the community composition and successional pattern could have been due to the mixing regime variations in the reservoir, most likely induced by weather disturbances, especially high precipitation and wind events. These events did not permit massive cyanobacterial development, although they most likely caused resuspension of dissolved phosphorus from the sediment. When observing functional groups, three groups could be distinguished by their response to the above-mentioned parameters: the first prefers high temperature and insolation (Lm, Y, Lo, Xph, W2 and M), the second is correlated with precipitation and wind (Td, C, K, MP and X2), while the third group tolerates cloudiness (H1, F, N, X1, D, J and P).

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