Winter cyanobacterial blooms have become increasingly common in eutrophic lakes advocating a need for their monitoring and risk assessment. The present study evaluated the toxicity of a winter cyanobacterial bloom in a eutrophicated freshwater lake located in Western Poland. The bloom was dominated by potentially toxic species: Planktothrix agardhii, Limnothrix redekei, and Aphanizomenon gracile. The toxin analysis revealed the presence of demethylated forms of microcystin-RR and microcystin-LR in ranges of 24.6–28.7 and 6.6–7.6 µg/L, respectively. The toxicity of sampled water was further evaluated in platelet-rich plasma isolated from healthy human subjects using lipid peroxidation and lactate dehydrogenase assays. No significant adverse effects were observed. The present study demonstrates that toxicity of some winter cyanobacterial blooms in the temperate zone, like that in Lubosińskie Lake, may not exhibit significant health risks despite microcystin production.

Under conditions of global warming, organisms are expected to track their thermal preferences, invading new habitats at higher latitudes and altitudes and altering the structure of local communities. To fend off potential invaders, indigenous communities/populations will have to rapidly adapt to the increase in temperature. In this study, we tested if decades of artificial water heating changed the structure of communities and populations of theDaphnia longispinaspecies complex. We compared the species composition of contemporaryDaphniacommunities inhabiting five lakes heated by power plants and four non-heated control lakes. The heated lakes are ca. 3–4 °C warmer, as all lakes are expected to be by 2100 according to climate change forecasts. We also genotyped subfossil resting eggs to describe past shifts inDaphniacommunity structure that were induced by lake heating. Both approaches revealed a rapid replacement of indigenousD. longispinaandD. cucullataby invaderD. galeataimmediately after the onset of heating, followed by a gradual recovery of theD. cucullatapopulation. Our findings clearly indicate that, in response to global warming, community restructuring may occur faster than evolutionary adaptation. The eventual recolonisation byD. cucullataindicates that adaptation to novel conditions can be time-lagged, and suggests that the long-term consequences of ecosystem disturbance may differ from short-term observations.

Filamentous cyanobacteria are known to negatively affect the life history of planktonic herbivores through mechanical interference with filtering apparatus. Here, we hypothesise that not only the length but also thethickness of cyanobacterial filaments is an important factor shaping the life history of Daphnia. To test our hypothesis, we cultured Daphnia magna with non-toxin-producing strains of either Aphanizomenongracile orCylindrospermopsisraciborskii.The former possesses wide filaments, whereas the latter has thinner filaments. The strain of A. gracile has two morphological forms differing in filament widths. The exposure to the thicker A. gracile filaments caused a stronger body-length reduction in females at maturity and a greater decrease in offspring number than exposure to the thinner C. raciborskii filaments. The width of filaments, however, did not significantly affect the length of newborns. The analysis of mixed thick and thin A. gracile filament width distribution revealed that D. magna reduces the number of thinner filaments, while the proportion of thicker ones increases.Also, the effects of cyanobacterial exudates alone were examined to determine whether the changes in D.magna lifehistory were indeed caused directly by the physical presence of morphologically different filaments and not by confounding effects from metabolite exudation. This experiment demonstrated no negative effects of both A. gracile and C. raciborskiiexudates. To our knowledge, this is the first study that demonstrates that the thickness of a cyanobacterial filament might be an important factor in shaping D. magna's life history. At a given biomass, thicker filaments of A. gracile were more detrimental to D. magna than thinner ones of C. raciborskii. There was also a strong interaction between species of the cyanobacterium and filament biomass, where species with thicker filaments and at higher biomass had the strongest negative impact on D. magna life history.

Aphanizomenon gracile increases in width in the presence of Daphnia. A defence mechanism against grazing?