Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.

Cyanobacteria of a picoplanktonic cell size (0.2 to 2.0 µm) are common organisms of both freshwater and marine ecosystems. However, due to their small size and relatively short study history, picoplanktonic cyanobacteria, in contrast to the microplanktonic cyanobacteria, still remains a poorly studied fraction of plankton. So far, only little information on picocyanobacteria toxicity has been reported, while the number of reports concerning their presence in ecosystems is increasing. Thus, the issue of picocyanobacteria toxicity needs more researchers’ attention and interest. In this report, we present information on the current knowledge concerning the picocyanobacteria toxicity, as well as their harmfulness and problems they can cause.

The cyanobacterial cytotoxin cylindrospermopsin (CYN) has become increasingly common in fresh waters worldwide. It was originally isolated from Cylindrospermopsis raciborskii in Australia; however, in European waters, its occurrence is associated with other cyanobacterial species belonging to the genera Aphanizomenon and Anabaena. Moreover, cylindrospermopsin-producing strains of widely distributed C. raciborskii have not yet been observed in European waters. The aims of this work were to assess the occurrence of CYN in lakes of western Poland and to identify the CYN producers. The ELISA tests, high-performance liquid chromatography (HPLC)-DAD, and HPLC-mass spectrometry (MS)/MS were conducted to assess the occurrence of CYN in 36 lakes. The cyrJ, cyrA, and pks genes were amplified to identify toxigenic genotypes of cyanobacteria that are capable of producing CYN. The toxicity and toxigenicity of the C. raciborskii and Aphanizomenon gracile strains isolated from the studied lakes were examined. Overall, CYN was detected in 13 lakes using HPLC-MS/MS, and its concentrations varied from trace levels to 3.0 μg L⁻¹. CYN was widely observed in lakes of western Poland during the whole summer under different environmental conditions. Mineral forms of nutrients and temperature were related to CYN production. The molecular studies confirmed the presence of toxigenic cyanobacterial populations in all of the samples where CYN was detected. The toxicity and toxigenicity analyses of isolated cyanobacteria strains revealed that A. gracile was the major producer of CYN.

Biological invasions have attracted particular attention since they often result in serious consequences for natural ecosystems. One planktonic invasive species is Cylindrospermopsis raciborskii, a cyanobacterium originally reported to occur exclusively in the tropics. Over the last few decades its range has extended to temperate regions and it occupies shallow highly eutrophic lakes previously dominated by other cyanobacteria. The purpose of this study was to examine the ecology of C. raciborskii during Planktothrix agardhii blooms in two shallow lakes in western Poland and to determine whether these species have different environmental preferences. Multiple linear regression showed that the biomass of P. agardhii was significantly negatively related to Secchi depth in Lake Bnińskie. In Lake Bytyńskie, P. agardhii was significantly positively related to concentrations of , chlorophyll a and total phosphorus and negatively related to Secchi depth, , and total nitrogen. Cylindrospermopsis raciborskii was significantly positively related only to concentrations of . There was a negative correlation between the biomass of P. agardhii and C. raciborskii perhaps showing different responses to environmental variables. Moreover, the biomass of P. agardhii was negatively correlated with Shannon–Wiener diversity of the phytoplankton assemblages. Our results support the concept that these cyanobacterial species have different environmental preferences and their niches differ from each other. These results suggest that light is an important driver of phytoplankton community structure resulting in shifts from a community dominated by P. agardhii in very turbid waters to more diverse communities perhaps including the invasive C. raciborskii in clearer waters.

Cylindrospermopsis raciborskii has recently attracted wide attention owing to its toxigenicity and its capacity for rapid invasion of new geographical regions. We studied the spatial distribution of C. raciborskii in western Poland and the environmental variables related to its occurrence near the border of its current temperate geographical range. We also identified the typical phytoplankton assemblages in which C. raciborskii occurs. Forty-six lakes were sampled once during the summers of 2008 and 2009. C. raciborskii was present in 43% of the samples and its biomass accounted for 0.1–13.9% of the total phytoplankton biomass found in the lakes. A General Linear Model (GLM) analysis and t-tests showed that the lakes in which C. raciborskii occurred were significantly shallower, more turbid and more eutrophic than the lakes from which it was absent. Redundancy Analysis (RDA) and GLM analyses showed that C. raciborskii biomass correlated positively with total nitrogen (TN), total phosphorus (TP) and conductivity. It correlated negatively with temperature, ammonium ( ) and orthophosphate ( ). According to Detrended Correspondence Analysis (DCA), C. raciborskii often co-occurred with Aphanizomenon ovalisporum, which is rarely observed in the studied region (common in subtropical regions, like C. raciborskii), rather than with the more common A. aphanizomenoides or the native A. gracile. Moreover, Planktothrix agardhii, the most common species in the studied region, was weakly associated with C. raciborskii. Overall, C. raciborskii was frequently present in the temperate lakes of western Poland, but it was most abundant in eutrophic lakes with high conductivity and high concentrations of TN and TP but low concentrations of and .