ABSTRACT
Historically, Diporeia spp. were abundant and the dominant benthic consumer in offshore regions of the Great Lakes. Over the past several decades, however, Diporeia populations have declined, seemingly in response to Dreissena spp. introduction and expansion. As a result, consumption demand of food resources has likely undergone large changes. Bioenergetics models are commonly used to estimate consumption of aquatic organisms from observed growth patterns and environmental conditions. A Diporeia-specic bioenergetics model was parameterized from literature values of Diporeia growth, water temperature, energy density, and abundances in Lake Michigan. These data were used as input to derive model estimates of consumption. Specically, the model was used to investigate Diporeia consumption of particulate matter in Lake Michigan in 1995, 2005, and 2008, which covered a period of severe declines in Diporeia
and increased abundances of dreissenids. Comparisons of Diporeia consumption before and after their declines indicated that consumption rate decreased by 91%. In contrast, conservatively-estimated consumption rates for dreissenids in Lake Michigan were up to 24 times greater than Diporeia consumption rates during 2005, and by 2008, consumption rates of dreissenids in Lake Michigan were more than 330 times greater than consumption by Diporeia before their decline in 1995. We hypothesize that higher abundance and consumption by dreissenid mussels, relative to Diporeia, altered the function of the Lake Michigan ecosystem.
