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Under‐ice photoautotrophs in lakes are generally considered to be limited by light rather than nutrients. Despite reduced light intensity under the ice, there is increasing evidence that suggests some lakes support high levels of photoautotrophs. We explored how snow cover (i.e., light) and nutrients (i.e., nitrogen and phosphorus) influence ice‐associated photoautotroph growth in a Minnesota, USA lake. Using a novel under‐ice approach, we deployed nutrient diffusing substrates (single or combined nutrient amendments) under two different light scenarios (snow covered, reduced light; snow removed, increased light) near the water‐ice interface to mimic a range of conditions ice‐associated photoautotrophs may be exposed to. Natural snow cover reduced light compared with snow removal, particularly early in the experiment before snow began to melt. When comparing photoautotroph chlorophyll a(Chl a) between snow treatments, we found a significant snow effect with higher concentrations in the snow removed treatment. We also found a significant nutrient effect, for all nutrient treatments, on Chl aconcentrations in both snow conditions. The effect of any nutrient treatment on Chl aconcentrations was similar. Our results suggest that ice‐associated photoautotrophs were able to grow in all snow conditions, but snow removal resulted in higher growth and nutrient availability also mediated responses. Thus, both light and nutrient conditions in the winter may strongly affect ice‐associated photoautotroph dynamics.

We conducted a survey of 50 thermally stratified lakes with similar nutrient concentrations and morphometries in Michigan to examine the direct and indirect effects of dreissenid mussels on the biomass and community composition of microzooplankton and macrozooplankton. Twenty‐five lakes were infested with dreissenid mussels (invaded), while 25 lakes were dreissenid free (uninvaded). In invaded lakes, phytoplankton biomass was 24% lower, and water clarity was 21% greater. Total microzooplankton biomass was 44% lower, with ciliate and rotifer biomass 39% and 45% lower, respectively, in invaded lakes. Total macrozooplankton biomass was 33% lower, largely driven by a 40% lower biomass of Daphnia spp. in invaded lakes. In contrast, dreissenid status had no significant influence on total copepod biomass, calanoid biomass, or cyclopoid biomass. Our microzooplankton results are similar to those of previous studies conducted in shallow, well‐mixed systems, although the magnitude of the dreissenid influence in our study was smaller, as might be expected in thermally stratified systems. On the other hand, ours is the first study to document lower biomass of Daphniaspp. and reduced rotifer diversity in invaded lakes. In contrast, we found no difference in macrozooplankton community structure. Dreissenids likely affected zooplankton directly through predation (microzooplankton) and indirectly through resource competition (micro‐ and macrozooplankton). Understanding how dreissenid mussels affect both microand macrozooplankton will help us to identify the potential mechanisms by which higher trophic levels (e.g., fish) are influenced by these invaders.