Benthic algal communities in the Laurentian Great Lakes (USA and Canada) have been strongly affected by the invasion of dreissenid mussels. Early (1990-1995) studies in Saginaw Bay, Lake Huron, demonstrated a shift from light to nutrient (phosphorus, P) limitation of benthic algae, and large changes in benthic algal community composition once zebra mussels (Dreissena polymorpha) became established. We conducted benthic algal sampling and a nutrient enrichment experiment at a historic sampling site to quantify benthic algae under current environmental conditions and to compare current results with historical data. Benthic algal P-demand was apparently saturated immediately post-invasion, but in subsequent years, algal growth on artificial substrata was consistently P-limited (p always <0.005), perhaps as a result of declining mussel abundance. Epilithic benthic algal community composition displayed large interannual changes, perhaps in response to mussel-induced alteration of light availability and natural changes in substratum characteristics at this site.
