In Lake Iseo (Lombardia, Italy), the predominant species in the cyanobacterial taxa\nwas Planktothrix rubescens. However, since 2014, the presence of an allochthonous Cyanobacteria,\nTychonema bourrellyi, able to produce consistent biomasses and harmful toxins, was detected.\nThe causes of this expansion are poorly understood. Many studies have linked the development of\nallochthonous Cyanobacteria populations with climate change. This study shows the spatio-temporal\ndynamics, the ecological requirements, and the interspecific relationship of P. rubescens and\nT. bourrellyi. Samples were collected monthly in 2016 at six different depths in the water column;\n20 chemico-physical characteristics were measured; and Cyanobacteria density, morphology,\nand biovolume were evaluated. The results allowed a comparison of the spatial pattern of the\ntwo species, which showed a greater distribution at a depth of 10ââ?¬â??20 m, and their seasonal dynamics.\nBoth Cyanobacteria were present throughout the year, with the greatest abundance during the\nperiod from March to May. A temporal shift was observed in their development, linked to different\ncapacities for overcoming winter and mixing periods. Principal Component Analysis, performed on\n20 observations (4 months Ã?â?? 5 depths), highlighted the important role of the stability of the water\ncolumn in determining T. bourrellyi settlement in Lake Iseo and the role of solar radiation in spring\npopulation development.
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