Cladophora is a native alga in the Great Lakes and can reach nuisance levels. Nuisance Cladophora can impede shoreline recreation and harbor bacterial reservoirs harmful to humans and wildlife. In the past, a strategy to reduce nuisance blooms of Cladophora was to limit the amount of external phosphorus (P) loading, which successfully managed algal blooms. Cladophora levels have recently returned to nuisance levels and there are indications that the invasion of two species of dreissenid mussels (Dreissena polymorpha and Dreissena rostriformis bugensis), may be facilitating the growth of Cladophora through altered resource availability including increased light penetrance, P levels, and habitat surface area (dreissenid shells). During the 2018 growing season, Cladophora and dreissenid biomass and supporting variables were measured monthly at 3, 6, 10, and 18 m depths along transects in Lakes Michigan, Huron, Erie, and Ontario. In addition, water quality parameters (temperature, light, and DO) and currents were monitored between sampling events at the 6 m site in each transect.
Results/Conclusions
Preliminary results suggest that temperature and light both facilitated Cladophora growth, with peak growth in July and August. As expected, the majority of maximum Cladophora dry weight occurred at shallower depths (3 and 6 m) throughout the growing season, coinciding with highest light availabilities. However, Cladophora growth was observed as deep as 18 m, suggesting that dreissenid induced increases in water clarity are expanding the area available for Cladophora growth. Continuing to monitor Cladophora growth, dreissenid mussel coverage, and abiotic variables can help us understand the ecological relationship between Cladophora and dreissenid mussels; guiding management practices to reduce future Cladophora nuisance events in the Great Lakes.