Trophic Level Trends Across the Great Lakes Basin, From Nutrient Concentrations to Piscivores, and Implications for Predator/Prey Balance

In some of the Laurentian Great Lakes (i.e., Michigan, Huron), dramatic changes within trophic level biomass (piscovores, prey fish, zooplankton, benthic invertebrates, phytoplankton) have occurred in the past 5-10 years.  In this talk, we will determine the extent to which these changes are occurring across a broader basin-wide scale.  To that end, we have compiled long-term trends (1980s to present) spanning multiple trophic levels in all five Great Lakes- including nutrient loadings, chlorophyll, benthic invertebrates, zooplankton, prey fish, and piscivores.  We will seek to explain these trends from a broad, ecological perspective by discussing existing paradigms that are believed to govern food web dynamics in the Great Lakes.  For example, could benthification (increase in dreissenid mussel and round goby biomass) be reducing energy available to pelagic species? What is the relative importance of top-down (excessive consumption) vs. bottom-up (limited nutrients and phytoplankton) forces?   Viewing the time series trends of multiple trophic levels across multiple lakes should provide insight regarding the extent to which Great Lakes ecosystems are exhibiting balance or imbalance in predator/prey dynamics.