Do invasive dreissenid mussels influence spatial and temporal patterns of toxic Microcystis aeruginosa in a low-nutrient Michigan lake?
Invasive dreissenid mussels enable harmful Microcystis blooms in low-nutrient lakes not historically accustomed to high cyanobacteria densities. Here, we examined patterns in Microcystis and microcystin spatially across Little Traverse Lake, Michigan, and temporally over the course of the lake's bloom. Because Microcystis spends part of its life cycle in the sediment, we included benthic and surface densities in our study. We also looked at the spatial relationship between dreissenid biomass and Microcystis density using local and global statistics and found that the clear relationship previously demonstrated to exist between these 2 taxa on the lake scale does not seem to be maintained on a finer, site scale. Distributions of Microcystis (surface and benthic) and microcystin in the lake were largely random and we observed no link between dreissenid biomass and Microcystis density. This suggests that either these taxa are not related on the site scale, or that environmental factors have a greater influence on localized Microcystis distributions than the location of dreissenid beds. Finally, we observed highest densities of surface Microcystis during mid-summer and highest densities of benthic Microcystis in the fall. This is consistent with Microcystis's life history in many temperate lakes: densities increase to their highest levels in late summer and decline into autumn as temperatures drop and colonies sink to the sediment. As invasive dreissenids continue to spread, knowing how they will affect harmful algae will be vital to bloom mitigation.