Lake Superior is often described as the most pristine of the Laurentian Great Lakes, but in the past decade Dolichospermum blooms have been observed. Land use in the adjacent watershed has not changed appreciably during this time, but the lake is warming and climatological variables correspond with presence of blooms. Blooms occurred only in relatively warm years as measured by degree days. Furthermore, the two largest blooms, in 2012 and 2018, occurred during years of especially extreme rainfall, providing coincidental evidence that intense storms provide nutrients or living propagules to the blooms from the watershed. Nearshore lake water in the narrow zone where blooms appear shows some riverine influence compared to water further offshore even in the absence of blooms. Nevertheless, water chemistry associated with the largest bloom in 2018 more closely resembled nonbloom nearshore lake water than river water, suggesting that blooms develop or at least persist outside of distinct river plumes. Concentrations of P and N during peak bloom density greatly exceeded any nonbloom lake or river waters, indicating that a buildup of phytoplankton biomass perhaps by floating and drifting to shore also is a significant factor in bloom occurrence. One potentially toxic substance (Anabaenopeptin A) was observed but at low concentration. At peak phytoplankton concentration, high seston C : P indicated severe P limitation while low C : N pointed against N limitation. If these newly observed blooms are indeed driven by temperature and rainfall as this evidence suggests, blooms may continue. Cyanobacterial blooms (defined as "a massive accumulation of cyanobacterial biomass, formed through growth, migration, and physical-chemical forces"; Tromas et al. 2017) are a significant and increasingly prevalent global water quality problem (Paerl and Otten 2013; Ho et al. 2019). Blooms of cyanobacteria are most often associated with eutrophic or

The spiny cladoceran (Bythotrephes longimanus) is an invasive, predaceous zooplankter that is expanding from Great Lakes coastal waters into inland lakes within a northern latitudinal band. In a large, Boundary Water lake complex (largely within Voyageurs National Park), we use two comparisons, a 2-year spatial and a 12-year temporal, to quantify seasonal impacts on food webs and biomass, plus a preliminary calculation of secondary production decline. Bythotrephes alters the seasonal biomass pattern by severely depressing microcrustaceans during summer and early fall, when the predator is most abundant. Cladoceran and cyclopoid copepods suffer the most serious population declines, although the resistant cladoceran Holopedium is favored in spatial comparisons. Microcrustacean biomass is reduced 40-60 % and secondary production declines by about 67 %. The microcrustacean community shifts towards calanoid copepods. The decline in secondary production is due both to summer biomass loss and to the longer generation times of calanoid copepods (slower turnover). The Bythotrephes ''top-down'' perturbation appears to hold across small, intermediate, and largesized lakes (i.e. appears scale-independent), and is pronounced when Bythotrephes densities reach 20-40 individuals L -1 . Induction tests with small cladocerans (Bosmina) suggest that certain native prey populations do not sense the exotic predator and are ''blindsided''. Failure of prey to deploy defenses could explain the disproportionate community impacts in New World versus Old World lakes.

No abstract