Abstract
In Lake Iseo (Lombardia, Italy), the predominant species in the cyanobacterial taxa was Planktothrix rubescens. However, since 2014, the presence of an allochthonous Cyanobacteria, Tychonema bourrellyi, able to produce consistent biomasses and harmful toxins, was detected. The causes of this expansion are poorly understood. Many studies have linked the development of allochthonous Cyanobacteria populations with climate change. This study shows the spatio-temporal dynamics, the ecological requirements, and the interspecific relationship of P. rubescens and T. bourrellyi. Samples were collected monthly in 2016 at six different depths in the water column; 20 chemico-physical characteristics were measured; and Cyanobacteria density, morphology, and biovolume were evaluated. The results allowed a comparison of the spatial pattern of the two species, which showed a greater distribution at a depth of 10–20 m, and their seasonal dynamics. Both Cyanobacteria were present throughout the year, with the greatest abundance during the period from March to May. A temporal shift was observed in their development, linked to different capacities for overcoming winter and mixing periods. Principal Component Analysis, performed on 20 observations (4 months × 5 depths), highlighted the important role of the stability of the water column in determining T. bourrellyi settlement in Lake Iseo and the role of solar radiation in spring population development.
Highlights
Cyanobacteria are the most ancient phototrophs on the earth
The literature has reported that climate change is likely to stimulate the development of harmful Cyanobacteria (e.g., [6,7,8,9,10,11,12,13,14])
A proliferation of Cyanobacteria has been recorded in lacustrine phytoplanktonic communities, and studies have highlighted the possible role of climate change in promoting toxic blooms, and studies have highlighted the possible role of climate change in promoting toxic blooms, considerably different responses to temperature increase have been recorded among various considerably different responses to temperature increase have been recorded among various
Summary
As a result of their long evolutionary history (~2 by) [1,2], and due to their high ecological plasticity, Cyanobacteria are able to adapt to geochemical and climatic changes [3,4]. These organisms are capable of adapting to anthropogenic modifications of aquatic environments [5], such as enhanced nutrient loading or increasing temperatures. The literature has reported that climate change is likely to stimulate the development of harmful Cyanobacteria (e.g., [6,7,8,9,10,11,12,13,14]). Ecosystems are subjected to alterations that affect the biotic community, modifying the species composition with the invasion and the establishment of allochthonous populations of Cyanobacteria in freshwater ecosystems [4,15,16]
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