Effect of zebra mussel (Dreissena polymorpha) filtration on benthic algal composition in Douglas Lake, MI.

Abstract

The zebra mussel (Dreissena polymorpha) is a non-native species that has impacted lacustrine and riverine systems throughout much of the American East and Midwest. Due to its high fecundity and high rate of filtration feeding, Dreissena has succeeded in producing ecosystem-level changes in water clarity, substrate composition, nutrient load and primary productivity. Though the effects of Dreissena on productivity in the water column is well-characterized, the effect of mussel filtration on benthic production has been understudied. Previous studies have shown variable effects of new mussel colonization on the productivity and species composition of benthic algal communities. This study used a controlled plot in Douglas Lake, MI to test the effects of zebra mussel filtration on benthic production, community composition of algal mats, and near-bottom concentrations of NH4, PO4 and chlorophyll a. Results suggested that zebra mussels do not affect production or nutrient levels on a local (near-bottom) scale, though trends in cyanobacterial density were observed. Paucity of significant contrasts in this study may be the result of insufficient sample size and/or insufficient incubation time, therefore retesting of these hypotheses is recommended. Observed lack of local-scale effects of Dreissena filtration may indicate emergent effects of mussel colonization that only take place above certain density thresholds.