Historical and recent biomass and food web relations of Limnocalanus in Lake Huron

Reported population biomass of Limnocalanus macrurus in Lake Huron has been underestimated by several-fold owing to application of an inappropriate length-weight regression model. During August and September the underestimates can exceed three-fold, suggesting that secondary production of the species in the lake is greater than previously thought. Increased representation of the species in the plankton community in recent years is associated with a decrease in its trophic level deduced through nitrogen stable isotope analysis of specimens from opportunistic samples obtained in 1993, 1995, and 2009. Limnocalanus N-15 enrichment relative to primary herbivores appears to have decreased by 1.5%. over this time period. Similarly, Diaptomus N-15 enrichment relative to primary herbivores appeared to decrease by 1.1%. from 1993 to 2009. Our data offer at least two possible explanations for this shift. (I) Limnocalanus has adopted a more herbivorous diet in response to the ecological changes in Lake Huron or (2) hypolimnetic Diaptomus have adopted a more herbivorous diet and Limnocalanus is relying in part on Diaptomus as a food source. (C) 2013 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.