## 3 Results  
### Phytoplankton Species Composition and Abundance, Obtained by Light Microscopy (LM)  
In total, 235 species from seven algal phyla (Cyanoprokaryota, Chlorophyta, Sreptophyta, Ochrophyta, Cryptopophyta, Pyrrhophyta and Euglenophyta) were identified using LM in the phytoplankton of the nine studied wetlands (Figure 2). Among them 68, or 29% of all taxa were cyanoprokaryotes from 30 genera of four orders: Chroococcales, Synechococcales, Oscillatoriales and Nostocales. In the studied samples we found different potential MC-producers from the genera _Anathece_, _Aphanothece_ and _Microcyts_ (Chroococcales), _Synechococcus_, _Jaaginema_ and _Pseudanabaena_ (Synechococcus), _Geitlerinema_, _Oscillatoria_, _Phormidium_ and _Planktothrix_ (Oscillatoriales), _Anabena_ s.str. and _Dolichospermum_ (Nostocales), which occurred separately or in different combinations. Some species from the nostocalean genera _Aphanizomenon_ s.l. (which recently belong to different genera _Aphanizomenon_ s.str., _Chrysosporum_, _Cuspidothrix_) and _Raphidiopsis_ (incl. former _Cylindrospermosis_)which may contain _mcy_ genes, were also identified in the studied wetlands. All observed species had different contribution to the phytoplankton biomass, with _Aphanizomenon_ s.l., _Dolicospermum_, and more rarely _Planktothrix_, recorded as dominants. The highest number of cyanoprokaryote species was recorded in Vaya (10), Izvornik 2 and Mandra West (8 in each), followed by Durankulak and Kriva Reka (7 in each), Poroy and Sinya Reka (5 in each), Mandra East (3), Krapets and Uzunegreen (1 in each). The relative contribution of these species to the phytoplankton composition in the studied sites ranged between 10 and 83% (Figure 3). Figure 3: Relative contribution of different taxonomic groups to the phytoplankton biodiversity according to the number of species, obtained by light microscopy, in the studied Bulgarian water bodies (August 2019). Legend: Mandra W—western part of the reservoir Mandra, Mandra E—eastern part of the reservoir Mandra; Cyano—Cyano@[EMAIL_ADDRESS]—Chlorophyta, Srepto—Streptophyta, Ochro—Ochroophyta, Crypto—Cryptophyta, Pyrrho—Pyrrhohpyta and Eugleno—Euglenophyta. Figure 2: General phytoplankton species composition in nine shallow Bulgarian wetlands sampled in August 2019. The number of identified taxa in each phylum is shown. Legend: Cyano—Cyano@Cyano@[EMAIL_ADDRESS]—Chiorophyta, Srepto—Streptophyta, Ochro—Ochroophyta (incl. classes Bacillariophyceaeae (diatoms)—28, Chrysophycae (gold algae)—4, Xanthophyceaeae (yellow-green algae)—5, Eustigmatophyceaeae \(-\)1, Crypto—Cryptophyta, Pyrrho—Pyrrhohpyta and Eugleno—Euglenophyta. Cyanoprokaryotes comprised from 11 to 99% of the total phytoplankton biomass, with highest relative contribution in the reservoir Sinyata Reka (99%) and lake Vaya (95%). Their lowest relative contribution was in the lake Durankulak (11%) and in the reservoir Krapets (20%) (Figure 4), where dominants were diatoms (_Cyclotella_) and green algae (_Elakatot thrix_), respectively. Considering the results from the PCR analysis, provided below, we will present in detail the LM data obtained for the genus _Microystis_. Based on the classical taxonomic criteria [27; 28; 29; 30; 31; 32; 33], we identified only two species: _M. aeruginosa_ ([PERSON]) [PERSON] and _M. Wesenbergii_ ([PERSON]) [PERSON] in Kondratieva 1964 (Figure 5; Table 2). In some samples we also found cells from disintegrated colonies and a few compact colonies with small cells (ca. 2 um in diameter) without gas vesicles, which could not be reliably identified using traditional morphological diagnostic features. The relative contribution (Table 2) of _Microystis_ was very low (<1% of the total phytoplankton biomass, except for the reservoir Mandra where it comprised <5% of the biomass). In the eastern part of this reservoir some small juvenile transitional colonies between both species with thin mucilage margin were also observed. In the reservoir Poroy and in the lake Durankulak _M.