Local zebra mussel presence within a benthic algal community has no impact upon nutrient levels, productivity and community composition.

Abstract

The invasion of zebra mussels (Dreissena polymorpha) into North America has caused an ecological transfer of primary productivity from the pelagic and limnetic to the littoral and benthic zones of affected freshwater ecosystems. Though increased light levels have been proposed as the mechanism for observed increases in benthic algal productivity and changes in nutrient levels, both local and lake-wide, may bear some responsibility for these benthic algal changes. We removed zebra mussels from mature cyanobacterial and diatom matrices above rocks off Grapevine Point in Douglas Lake, Northern Michigan, and placed these rocks, alongside controls with zebra mussels remaining, in a cleared zone. We then measured NH4, PO4, chlorophyll a and community compositional changes with an initial sampling, and a final sampling 10 days later, for both control and altered algal matrices. No significant changes were observed in nutrient concentrations, chlorophyll a concentrations, or community compositions within the benthic algal communities at either controlled or altered sites. Possible explanations include the limited spatial and temporal scale of the study, the influence of the surrounding lake environment, and potential complexity of observed broader ecological interactions at the local level.