Using Bioenergetics to Evaluate Fish Consumption of the Spiny Waterflea in Lakes Michigan and Superior

Understanding trophic dynamics is essential in any ecological system.  In systems with numerous invasive species this necessity is increased due to the possible deleterious effects they induce. Lakes Michigan and Superior offer not only such features with zooplankton, but also dichotomous communities of native and non-native fishes. Even though many other invaders have been unable to proliferate in Lake Superior, the spiny waterflea (Bythotrephes longminanus) has been successful in establishment.  However, its role is dynamic throughout Great Lakes food webs as an important predator, competitor, and prey item.  Because top-down control of  Bythotrephes is varied, specific lake analysis is needed for characterizing effects on each system.  Our objective was to use bioenergetics modeling to estimate fish community consumption of Bythotrephes from nearshore to offshore in both lakes.  Results from comparing consumption to production estimates indicate that Lake Michigan fish consumption never exceeded production of Bythotrephes offshore with the highest consumption occurring nearshore, with the opposite being true in Lake Superior.  While numerous species consumed it in both lakes, Bythotrephes was a dominate prey item for Lake Superior cisco (Coregonus artedi) from September-November.  The role of fish consumption on Bythotrephes appears varied between lakes.