Abstract
In recent years, cyanobacterial invasions have increased in European temperate lakes. Climate warming is highlighted as a key driver of the distribution and establishment of alien cyanobacteria, and water bodies in poor ecological status, characterized by meso-eutrophic conditions, are underlined as a suitable habitat for invasion. The establishment of newly arrived species is directly related to fluctuating physicochemical factors such as temperature, and nutrient concentrations, especially phosphorus and nitrogen, or biotic factors such as competition. Cyanobacterial invasions can have profound ecological impacts, such as displacing native species, causing the biodiversity loss of local communities, and modifying the ecosystem’s cyanotoxins profile. This study presents the occurrence of four alien bloom-forming potentially toxic cyanobacteria - Chrysosporum bergii, Cuspidothrix isstaschenkoi, Raphidiopsis raciborskii and Sphaerospermopsis aphanizomenoides - in the northern parts of their current range in temperate Europe and provides insights into their ecology. Special attention was paid to the lakes of Lithuania (Simnas, Jieznas and Gineitiškės), which is the northernmost location of distribution zone for some alien cyanobacteria and provides as a dispersion route to Norther Europe via the continental area. We i) described dynamics of indigenous cyanobacteria community invaded by alien cyanobacteria; ii) assessed concentrations of cyanotoxins in field and culture samples, and suggested toxin producers; and iii) detailed the correlation between the biomass of alien cyanobacteria and environmental conditions. These species were found in three human-affected shallow hyper-eutrophic lakes during warm period of the year; however, their biomass was low. We assume that present temperatures do not limit the occurrence of these alien species but are insufficient for their successful proliferation. In addition, we provided the first evidence of anatoxin-a production by isolated strains of C. issatschenkoi in Lithuania. Alien cyanobacteria were detected at an early stage of their development, however, a rise in global temperatures and the spread of strains with toxigenic potential could lead to increased proliferation and further northward expansion of these alien species.