Actinocyclus

Considerable fluctuations of the level and salinity of the Aral marine basin may be inferred from diatom data. Transgressive marine sediments typically abound in brackish-water species (87%), such as Thalassiosira, Actinocyclus, Cyclotella, Navicula, Diploneis [17], while freshwater diatoms (Fragilaria, Eunotia, Cymbella, and others) are present copiously in the regressive marine sediments. 

Species composition and biodiversity of the Aral phytoplankton have changed dramatically since the early 1970s [2, 26 and citations therein]. Before this period, the list of species numbered 375 with the domination of Bacillariophyta and Chlorophyta species [27], The most abundant species in the central parts of the sea was Actinocyclus ehrenhergii var. crassa [28]. In the 1970-1980s, not only did most brackish water species disappear from the Aral Sea, but also some marine species. In this period, the biodiversity of the phytoplankton community decreased from 306 to 250 species with the predominance of Bacillariophyta, Cyanophyta, and Chlorophyta [18,29]. In 1999-2002, the number of species dropped to 159 with the absolute dominance of Bacillariophyta (115 species) [26]. 

Tabularia fasciculata (Agardh) Williams et Round Hemidiscaceae Actinocyclus octonarius Ehrenberg... 

In the northern part of the Western basin, at 24.6 m water depth, the salinity was 92 ppt and the temperature 13.7 C. The centric diatom Actinocyclus octonarius dominated the assemblage. In total, we observed at that location 33 diatom algae species. The diversity was high (Dmg = 4.8, PIE = 0.73, H = 2). Dinophytes and euglenids were absent. 

Surirella fastuosa 30.9 Actinocyclus octonarius (3.6), Navicula phyllepta (3.6)... 

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