Over the past two decades, Diporeia in all of the Laurentian Great Lakes, except Superior, have declined dramatically. These declines have coincided with the expansion of invasive Dreissena polymorpha and D. bugensis, however the mechanisms underlying declines remain unclear. We used nucleic acid indices to index condition of Diporeia and conducted a series of experiments to evaluate the utility of nucleic acid indices as a metric of condition for Diporeia. In addition, during 2008–2009, we collected Diporeia from throughout the Great Lakes and Cayuga Lake (New York) and evaluated the spatial and temporal variation of nucleic acid indices using classification and regression tree (CART) analysis. Our experiments demonstrate that nucleic acid indices of Diporeia respond to temperature and periods of starvation. CART analysis revealed a high degree of spatial and temporal variation, showed marginal negative trends with extreme depths, and did not select Dreissena variables as influencing Diporeia nucleic acid indices.

Bioenergetics models are commonly used to estimate consumption of organisms from observed growth patterns and environmental conditions. We parameterized a Diporeia specific bioenergetics model from previous literature, and we used the model to investigate historical Diporeia consumption pre- and post- dreissenid establishment in Lake Michigan. We synthesized existing data pertaining to Diporeia growth, water temperature, energy density and abundance as input for model simulations previous studies. Comparisons of lake wide Diporeia consumption before and after declines indicate that consumption totals have dramatically decreased over the past two decades. In comparison, lake wide filtering rates of dreissenids far exceed both historic and present day Diporeia consumption rates.